Hydrological drought and wildfire in the humid tropics
Taufik, Muh - \ 2017
Wageningen University. Promotor(en): R. Uijlenhoet, co-promotor(en): Henny van Lanen. - Wageningen : Wageningen University - ISBN 9789463436359 - 99
wildfires - drought - humid tropics - wetlands - hydrology - prediction - water management - natuurbranden - droogte - humide tropen - wetlands - hydrologie - voorspelling - waterbeheer
Drought is a recurrent hazard, which has happened throughout human history, and it is anticipated to become more severe in multiple regions across the world. Drought occurs in all climate regimes from humid to dry and from hot to cold. Drought is often viewed through its impact on environment and society, including wildfire, which is the topic of this study. The nature of such impacts differs remarkably from region to region. Although drought does not directly cause wildfire, it provides favorable conditions for wildfire ignition and spread. When drought coincides with strong El Niño events in the humid tropics, e.g. Southeast Asia, the impacts worsen through uncontrolled forest fires affecting the global carbon cycle. These include reduction of the carbon stock, intensifying the haze hazard, and other severe socio-economic impacts in Southeast Asia, including areas far away from the burnt area, e.g. Singapore because of fires in Sumatra.
There still remains a serious lack of scientific understanding about the fundamental role of drought in fire-generating processes. Most research, so far, suggests that climate controls wildfire occurrence in the humid tropics. However, this climate-centered approach, which is reflected in contemporary drought-fire related indices, overlooks soil and hydrological processes beneath the surface across the humid tropics. There is also uncertainty about the relative roles of climate variability and human activities in influencing the nature and distribution of drought-related wildfires. Hence, the general objective of this PhD research is to examine how characterization of hydrological drought under natural and human-modified conditions can improve understanding of wildfires in general in the humid tropics.
Chapter 2 discusses the contribution of humans to an increase of hydrological drought severity in the tropical peatland of Southeast Asia. Climate variability induces drought in the region, however, human activities (human-modified drought) may increase its severity. Analyzing long time series of simulated historical groundwater levels from selected regions in Southeast Asia, which were validated against some years with observations, revealed that human interference (through canalization and land-use change) has amplified drought severity. The drought amplification due to human interference was at least double that of climate-induced drought. The amplification is even higher when peatland is converted into acacia plantation. Further, research findings suggest that even if the Paris Agreement target is met, drought risk of peatlands remains high unless sustainable water management receives top priority in the region.
Chapter 3 deals with how an existing, well-known drought-fire related index, i.e. the Keetch-Byram Drought Index (KBDI), is modified to improve applicability in the humid climate environment of Southeast Asia. The improvement includes: (i) adjustment of the drought factor to the local climate, and (ii) addition of the water table depth as a dynamic factor to fine-tune the drought index. The results indicate that the modified Keetch-Byram Drought Index (mKBDI) performed well in predicting fire hazard. Furthermore, the research identified a critical water table depth, which represents maximum fire hazard (0.85 m for the wetland forest of South Sumatra). Below this value hazard does not increase anymore. The mKBDI could be more widely applied, if pedotransfer functions would be developed that link easily-obtainable soil properties to the parameters of the water table factor.
Chapter 4 shows that wetland transformation (i.e. through canalization and land-use change) not only affects hydrological drought (Chapter 2), but also influences fire behaviour. In Southeast Asia, expansion of agricultural cropland and forest plantations has changed the landscape of wetlands. The findings showed that the transformation into acacia plantation has amplified the fire hazard from 4% (under natural conditions) to 17%. An even higher amplification (40% fire hazard) is expected under poor water management, that is, uncontrolled drainage. The findings derived from this observation-based modeling experiment suggest that improved water management (controlled drainage with higher dry season surface water levels) can minimize fire susceptibility.
Chapter 5 explains the importance of hydrology for fire hazard studies. Borneo is selected to investigate the added value of including hydrological variables in fire hazard prediction approaches. More than 300 statistical models were tested, and the results showed that models that include hydrological variables better predict area burnt than those solely based on climate indicators/indices. Further, modelling evidence shows amplifying wildfires and greater area burnt in response to El Niño Southern Oscillation (ENSO) strength, when hydrology is considered. These results highlight the importance of considering hydrological drought for wildfire prediction. I recommend that hydrology should be considered in future studies of the impact of projected ENSO strength, including effects on tropical ecosystems and biodiversity conservation.
The contributions of this thesis research to science are summarized and synthesized in Chapter 6. First, the research identified that fire hazard studies would benefit from adding hydrology, which is reflected in the improved model performance when hydrological variables are integrated. Next, the research revealed that humans play a substantial role in modifying groundwater drought characteristics, hence amplifying the fire hazard in Southeast Asia. Further, the chapter identified several relevant research findings, including the model choice, which should consider the simplicity and the applicability of the model. Another finding demonstrated that controlling canal water level through canal blocking is a practical water management tool to restore degraded wetland. This restored wetland would benefit some endemic species. However, the restored wetland still faces high drought severity. Hence they remain more fire-prone until the un-impacted hydrology condition is achieved. Finally, this research suggest that currently widely-used drought indices (such as FWI) require improvements in their model structure, which means integration of hydrological variables to increase their applicability for fire hazard studies in the humid tropics.
The role of strigolactones and the fungal microbiome in rice during drought adaptation
Andreo Jimenez, Beatriz - \ 2017
Wageningen University. Promotor(en): H.J. Bouwmeester, co-promotor(en): C. Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789463437028 - 205
drought resistance - drought - abiotic injuries - rice - oryza sativa - plant-microbe interactions - nutrient uptake - defence mechanisms - hormones - fungi - genes - droogteresistentie - droogte - abiotische beschadigingen - rijst - oryza sativa - plant-microbe interacties - voedingsstoffenopname (planten) - verdedigingsmechanismen - hormonen - schimmels - genen
Rice is the most important food crop in the world, feeding over half the world’s population. However, rice water use efficiency, defined by units of yield produced per unit of water used, is the lowest of all crops. The aim of this thesis was to study the effect of plant hormones and the root microbiome on drought tolerance in rice. The new plant hormone, strigolactone, was shown to be upregulated under drought and to regulate drought tolerance in interaction with the drought-hormone abscisic acid. Using a large collection of rice genotypes grown in the field, we showed that the composition of the root associated fungal microbiome is determined by the rice genotype and can contribute to drought tolerance.
Understanding the productivity of cassava in West Africa
Ezui, Kodjovi Senam - \ 2017
Wageningen University. Promotor(en): Ken Giller, co-promotor(en): Linus Franke; A. Mando. - Wageningen : Wageningen University - ISBN 9789463430470 - 183
manihot esculenta - cassava - crop production - rainfed agriculture - drought - crop yield - water use efficiency - radiation use efficiency - fertilizers - togo - ghana - west africa - manihot esculenta - cassave - gewasproductie - regenafhankelijke landbouw - droogte - gewasopbrengst - watergebruiksrendement - stralingsbenuttigingsefficiëntie - kunstmeststoffen - togo - ghana - west-afrika
Drought stress and sub-optimal soil fertility management are major constraints to crop production in general and to cassava (Manihot esculenta Crantz) in particular in the rain-fed cropping systems in West Africa. Cassava is an important source of calories for millions of smallholder households in sub-Sahara Africa. The prime aim of this research was to understand cassava productivity in order to contribute to improving yields, food security and farm incomes in rain-fed cassava production systems in West Africa. A long-term goal was to contribute to a decision support tool for site-specific crop and nutrient management recommendations. Firstly, we studied farmers’ perception of cassava production constraints, assessed drivers of diversity among households and analysed the suitability of farmers’ resource endowment groups to the intensification of cassava production. The results indicate that farmers perceived erratic rainfall and poor soil fertility to be prime constraints to cassava production. The agricultural potential of the area and the proximity to regional markets were major drivers for the adoption of crop intensification options including the use of mineral and organic fertilizers. While the use of mineral and organic fertilizers was common in the Maritime zone that had a low agricultural potential, storage roots yields were below the national average of 2.2 Mg dry matter per hectare, and average incomes of 0.62, 0.46 and 0.46 US$ per capita per day for the high, medium and low farmer resource groups (REGs – HRE, MRE and LRE, respectively) were below the poverty line requirement of 1.25 US$. In the high agricultural potential Plateaux zone, HRE and MRE households passed this poverty line by earning 2.58 and 2.59 US$ per capita per day, respectively, unlike the LRE households with 0.89 US$ per capita per day. Secondly, we investigated the effects of mineral fertilizer on nutrient uptake, nutrient physiological use efficiency and storage roots yields of cassava since soil fertility was a major issue across the zones. We used an approach based on the model for the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS). This model was successfully adapted for cassava and it appropriately assessed the response of cassava to N, P and K applications, especially in years with good rainfall. Under high drought stress, the model overestimated cassava yields. Thirdly, we investigated the impact of balanced nutrition on nutrient use efficiency, yield and return on investment compared to blanket fertilizer use as commonly practiced in cassava production systems in Southern Togo, and in Southern and Northern Ghana. The balanced nutrition approach of the QUEFTS model aimed to maximize simultaneously nutrient use efficiency of N, P and K in accordance with the plant’s needs. Larger nutrient use efficiencies of 20.5 to 23.9 kg storage root dry matter (DM) per kilo crop nutrient equivalent (1kCNE of a nutrient is the quantity of that nutrient that has the same effect on yield as 1 kg of N under balanced nutrition conditions) were achieved at balanced nutrition at harvest index (HI) of 0.50 compared to 20.0 to 20.5 kg storage root DM per kilo CNE for the blanket rates recommended by national research services for cassava production. Lower benefit:cost ratios of 2.4±0.9 were obtained for the blanket fertilizer rates versus 3.8±1.1 for the balanced fertilizer rates. Our study revealed that potassium (K) was a major yield limiting factor for cassava production, especially on the Ferralsols in Southern Togo. Hence, we fourthly studied the effect of K and its interaction with nitrogen (N), phosphorus (P), and the timing of harvest on the productivity of cassava in relation to the effects of K on radiation use efficiency (RUE), light interception, water use efficiency (WUE) and water transpiration. The results suggest that K plays a leading role in RUE and WUE, while N is the leading nutrient for light interception and water transpiration. Potassium effects on RUE and WUE depended on the availability of N and harvest time. Values of RUE and WUE declined with harvest at 4, 8 and 11 months after planting. Thus, enhanced K management with sufficient supply of N during the early stage of development of cassava is needed to maximize RUE and WUE, and consequently attain larger storage root yields. Given that erratic rainfall was another major constraint to cassava production according to the results of the farm survey, and due to the inability of QUEFTS modelling to assess drought effects on cassava yield successfully, another modelling approach based on light interception and utilization (LINTUL) was used. We quantified drought impacts on yields and explored strategies to improve yields through evaluation of planting dates in Southern Togo. The evaluation of the model indicated good agreement between simulated and observed leaf area index (Normalised Root Mean Square Error - NRMSE - 17% of the average observed LAI), storage roots yields (NRMSE 5.8% of the average observed yield) and total biomass yield (NRMSE 5.8% of the average observed). Simulated yield losses due to drought ranged from 9-60% of the water-limited yields. The evaluation of planting dates from mid-January to mid-July indicated that the best planting window is around mid-February. Higher amount of cropping season rainfall was also achieved with early planting. These results contradict current practices of starting planting around mid-March to mid-April. However, the results indicate the possibility to increase cassava yields with early planting, which led to less yield losses due to drought. By contrast, late planting around June-July gave larger potential yields, and suggested these periods to be the best planting window for cassava under irrigated conditions in Southern Togo. This shows that appropriate water control and planting periods can contribute to attaining larger yields in Southern Togo. Further improvement of the LINTUL model is required towards using it to assess water-limited yield, which can be used as boundary constraint in QUEFTS to derive site-specific fertilizer requirements for enhanced cassava yield and returns on investments in West Africa.
Evaluation of Socio-Economic Factors that Determine Adoption of Climate Compatible Freshwater Supply Measures at Farm Level : a Case Study in the Southwest Netherlands
Veraart, Jeroen A. ; Duinen, Rianne van; Vreke, Jan - \ 2017
Water Resources Management 31 (2017)2. - ISSN 0920-4741 - p. 587 - 608.
Adaptation - Adoption - Agriculture - Climate - Freshwater supply - Knowledge - water supply - fresh water - climate adaptation - drought - watervoorziening - zoet water - landbouw - klimaatadaptatie - droogte
The availability of freshwater resources in soil and groundwater bodies in the southwestern part of The Netherlands is expected to decrease during the agricultural growing season because of an expected increase of freshwater demands and a changing climate. This expected shortage of fresh water might negatively affect agricultural production. To cope with this problem, three pilots were initiated aimed at increasing freshwater supply at farm-level. The objective of this paper is to evaluate the socio-economic factors that determine the wider use of the measures investigated in these pilots. Therefore, the results of a feasibility study and a survey about drought risks were compared. The survey indicates that respondents do not make distinction between a dry and extremely dry year in their estimation of the return period. The results of a feasibility study illustrate that confidence and the level of common understanding regarding the reliability of these innovative measures has increased amongst project participants since 2012. The survey respondents were less optimistic about the wider implementation of the investigated technologies. A reliable freshwater supply and supportive legislation are the most decisive socio-economic factors for a future investment in additional freshwater supply for farmers in this region. Both studies illustrate that the impact of additional freshwater supply on farm economics strongly depends on farm type and crop cultivation plan. These insights may support the wider use of these innovations and may help to improve agro-hydrological models.
African elephant in a cleft stick : choosing between starving or dying from thirst in arid savanna
Wato, Yussuf - \ 2016
Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Ignas Heitkonig; Frank van Langevelde. - Wageningen : Wageningen University - ISBN 9789463430005 - 126
loxodonta africana - starvation - thirst - savannas - arid zones - animal ecology - mortality - drought - loxodonta africana - uithongering - dorst - savannen - aride klimaatzones - dierecologie - mortaliteit - droogte
Elephant population studies have become important especially because of the long standing perception that high elephant densities have negative impact on vegetation and other wildlife species. Thus, in areas of high elephant density, managers attempt to re-distribute them or keep their numbers low through provision of water, translocation or culling. These approaches are thought to keep the population within the limits that can be sustained by the ecosystem, termed “the ecological carrying capacity”, a management option hinged on equilibrium theory. Equilibrium systems are considered stable, with resources and the animals that depend on them being at balance with each other. This stability is rarely the case in tropical savannas where the rule appears to be “a flux of nature” rather than “a balance of nature”.
Tropical savannas, where over half of the African elephant live, are prone to constant environmental fluctuations, especially prolonged droughts, and hence there is a growing understanding that populations of wildlife species and their communities are rarely at equilibrium. Therefore, it is critical to understand how the constant environmental flux in this system affects wildlife populations and the implication for their management. In this thesis, the central focus is to investigate the role of drought occurrences on elephant population dynamics in tropical savannas. To address this question, it is important to have a good understanding of the historical changes of elephant population in relation to drought events and the ecology of elephant in semi-arid savannas - their distribution and density, their movements and behaviour. For the historical data, I analysed the best existing long-term data in Africa of wild elephant population that has been consistently monitored for over 40 years where life histories of over 3000 wild individual elephant are known, at Amboseli National Park in Kenya. In addition, I also analysed geo-referenced elephant mortality data collected daily for 10 years from Tsavo Conservation Area. Further, I analysed 2 years data from 8 GPS collared African elephant to investigate their movement response to seasonal water and forage distribution in Tsavo Ecosystem.
First, I investigated the temporal effects of drought duration (number of consecutive dry months) and intensity (amount of rainfall) on elephant population structure in Amboseli National Park, Kenya. The result corroborates findings from past studies that calves (<2years) are more susceptible to drought caused mortality and the risk of dying decreased with age. A new finding in this study reveals that the effect of drought induced mortality for the adult elephant is sex and age dependent, with males older than 25 years being less likely to die as compared to females of the same age. This new result is because of the resolution of analysis in this study which focused on the length and severity of drought as opposed to past studies that restricted their analysis to seasonal and inter-annual differences in rainfall pattern. As they grow older and sexually mature, the foraging range of male elephant increase and they begin to take more risks and disperse to unfamiliar habitats to seek for quality forage and mates. Generally, foraging strategies between sexes in many species are more pronounced during periods of food scarcity, and the driving force in the differences appears to be driven by energy need requirements, reproductive status of an individual, body sizes and the social context, all of which differ between sexes.
In the next study, I investigated the spatial pattern of elephant mortality in relation to drought occurrences in Tsavo National Park using MaxEnt. The results shows that elephant carcasses were aggregated and elephant mortality was negatively correlated with four months cumulative precipitation prior to death, forage availability and distance to water, while local elephant density showed a positive correlation. This finding rules out dehydration as the cause of elephant mortality in Tsavo as the river where the carcasses were aggregated is perennial. Furthermore, forage availability was low close to water sources and did not show a significant difference close to or further away from the river despite high elephant density around the river. Hence, these elephant mortalities may have occurred as a result of starvation.
I went further to focus on two main limiting resources for elephants, namely forage and water, and their effect on elephant-habitat utilization in semi-arid savannas. I first investigated how water source distribution affect elephants’ seasonal movement patterns. Results indicate that male elephant moved maximally 20 km away from the nearest water source in the dry season while the female elephant foraged to a maximum of about 10 km and only moved further than this distances in the wet season. The strong directionality of elephant movement from a distance of 15km towards water sources (rho > 0.5) as they re-visited their watering source in the dry season suggest that elephant have information on location of the water sources.
Next, I investigated the factors that determine selection of a foraging site for elephant with a focus on forage nutrients or biomass. Because of their large body size, it is thought that elephant can survive on a less nutritious but high biomass of forage. The results from this study shows that elephant selected foraging site based on forage biomass in dry seasons, whereas they selected areas with higher nutrients in the wet season. Moreover, females selected sites with a higher forage biomass as compared to males. This result may be explained by the difference in social organisation and foraging strategies between the sexes. In the previous studies on human-elephant conflict, for instance, male elephant raided crops more than the mixed herd, perhaps to seek for high quality forage.
Together, the four studies in this thesis strongly suggest that elephant starve to death in prolonged drought contrary to the past studies that reported that adult elephant are less affected by drought. Even though prolonged droughts usually result in higher elephant mortalities, the resilience of semi-arid savannas may perhaps be as a result of these deaths that release the system from high browsing pressure and give it a window to regenerate. If that is the case, then drought induced elephant mortality may be a better way to regulate elephant numbers than culling. This finding strongly suggests that semi-arid savannas may in fact be a non-equilibrium system sustained by growth and crashes of herbivore populations. Maintaining the system as natural as possible may therefore keep elephant populations in savannas sustained for posterity. The modern day park managers have daunting challenges such as mass elephant deaths in drought, increased human-wildlife conflicts or changes in wildlife use of the landscape which may all be symptoms of wrong management interventions taken in the past or negative impacts of anthropogenic activities that have tipped the natural functioning of a non-equilibrium system. Therefore, park managers should undergo regular trainings on new conservation techniques and they should apply evidence-based science to make informed long term decision.
De Wageningen Lowland Runoff Simulator (WALRUS): een snel neerslag-afvoermodel speciaal voor laaglandstroomgebieden
Brauer, C.C. ; Torfs, P.J.J.F. ; Teuling, A.J. ; Uijlenhoet, R. - \ 2016
Stromingen : vakblad voor hydrologen 22 (2016)1. - ISSN 1382-6069 - p. 7 - 18.
neerslag - hydrologie van stroomgebieden - modellen - afvoerwater - laaglandgebieden - stroomgebieden - grondwater - oppervlaktewater - kwel - reservoirs - droogte - risicoanalyse - precipitation - catchment hydrology - models - effluents - lowland areas - watersheds - groundwater - surface water - seepage - reservoirs - drought - risk analysis
De Wageningen Lowland Runoff Simulator (WALRUS) is een nieuw neerslag-afvoermodel dat het gat moet vullen tussen complexe, ruimtelijk gedistribueerde modellen die vaak gebruikt worden in laaglandstroomgebieden en simpele, ruimtelijk geïntegreerde, parametrische modellen die voornamelijk zijn ontwikkeld voor hellende stroomgebieden. WALRUS houdt expliciet rekening met hydrologische processen die belangrijk zijn in laaglandgebieden, in het bijzonder (1) de koppeling tussen grondwater en onverzadigde zone, (2) vochttoestandafhankelijke stroomroutes, (3) grondwater-oppervlaktewaterterugkoppeling en (4) kwel, wegzijging en het inlaten of wegpompen van oppervlaktewater. WALRUS bestaat uit een gekoppeld reservoir voor grondwater en onverzadigde zone, een reservoir voor snelle stroomroutes en een oppervlaktewaterreservoir. Het is geschikt voor operationele toepassingen omdat het efficiënt rekent en numeriek stabiel is. In de vrij toegankelijke modelcode zijn standaardrelaties geïmplementeerd, zodat er slechts vier parameters overblijven die gekalibreerd hoeven te worden. Het model is geschikt voor het operationeel simuleren van hoogwater en droogte ten behoeve van risico-analyses en scenario-analyses, voor het ontwerpen van infrastructuur en voor het aanvullen van ontbrekende gegevens in afvoermeetreeksen
Exploring the genetics underlying the responses to consecutive combinations of biotic stresses and drought in Arabidopsis thaliana
Huang, Pingping - \ 2016
Wageningen University. Promotor(en): Maarten Koornneef, co-promotor(en): Mark Aarts. - Wageningen : Wageningen University - ISBN 9789462578593 - 291
arabidopsis thaliana - genetic models - stress - stress response - drought - botrytis - pieris (lepidoptera) - genetics - gene expression - arabidopsis thaliana - genetische modellen - stress - stressreactie - droogte - botrytis - pieris (lepidoptera) - genetica - genexpressie
Plants growing in natural environments are exposed to a broad range of biotic (pathogen attack, insect herbivory, etc.) and abiotic factors (drought, extreme temperatures, UV radiation, salinity, etc.) that are known to cause stress symptoms in many species (Pareek et al., 2010; Robert-Seilaniantz et al., 2010). Biotic and abiotic stress-inducing determinants often adversely impact plant growth and development, frequently leading to severe annual yield losses in agricultural production (Pierik et al., 2013; Pieterse et al., 2012; Stam et al., 2014). In the research endeavors described in this thesis, Arabidopsis thaliana was used as a model organism to study plant responses to different sequential combinations of biotic factors (infection with Botrytis or herbivory by Pieris) and drought. The main objective was to identify genes that contribute to tolerance to the aforementioned sequential stress combinations. Genome-wide association (GWA) mapping and RNA sequencing (RNA-seq) approaches were used to identify combinatorial stress responsive genes. A number of candidate genes to combinatorial stress responses were identified by GWA analysis and RNA-seq. The physiological function of some candidate genes in different stress conditions were characterized using T-DNA insertion mutants and gene expression study. However, the physiological function of many allelic variants in stress conditions remain to be discovered. The study highlights the importance of an array of genes, crucial to the underlying defense processes, as targets for breeding by allele mining, ultimately aimed at improvement of crop tolerance to frequent combinations of stress factors.
Plantsensoren geschikt gemaakt voor toepassing op tuinbouwbedrijf : de pratende plant rukt op
Steppe, K. ; Heuvelink, E. ; Kierkels, T. - \ 2015
Onder Glas 12 (2015)11. - p. 20 - 21.
tuinbouw - glastuinbouw - sensors - fotosynthese - droogte - gewassen, groeifasen - stengels - waterbalans - koolstof - suikers - gewasmonitoring - horticulture - greenhouse horticulture - sensors - photosynthesis - drought - crop growth stage - stems - water balance - carbon - sugars - crop monitoring
De ontwikkeling van geavanceerde sensoren zorgt ervoor dat er steeds meer aan de plant te meten valt. Dat leidt tot nieuwe inzichten in het functioneren, die op termijn kunnen worden vertaald in aanbevelingen voor teeltmaatregelen. Een meer directe spin-off is dat de plantsensoren geschikt worden gemaakt voor toepassing op het tuinbouwbedrijf. Als middel om snel stress te detecteren, nog voor je het met het blote oog ziet.
Fine scale ecohydrological processes in northern peatlands and their relevance for the carbon cycle
Nijp, J.J. - \ 2015
Wageningen University. Promotor(en): Frank Berendse; Sjoerd van der Zee, co-promotor(en): Juul Limpens; Klaas Metselaar. - Wageningen : Wageningen University - ISBN 9789462575837 - 202
ecohydrologie - veengebieden - koolstofcyclus - koolstof - klimaat - neerslag - droogte - bodem - ecohydrology - peatlands - carbon cycle - carbon - climate - precipitation - drought - soil
Ky’osimba Onaanya: understanding productivity of East African Highland banana
Taulya, G. - \ 2015
Wageningen University. Promotor(en): Ken Giller, co-promotor(en): Peter Leffelaar; P.J.A. van Asten. - Wageningen : Wageningen University - ISBN 9789462575615 - 167
bananen - musa - droogte - voedingsstoffenbeschikbaarheid - kalium - stikstof - kunstmeststoffen - afrika - uganda - gewasgroeimodellen - beslissingsmodellen - drogestofverdeling - groeianalyse - licht - fenotypische variatie - bananas - musa - drought - nutrient availability - potassium - nitrogen - fertilizers - africa - uganda - crop growth models - decision models - dry matter distribution - growth analysis - light - phenotypic variation
Over 30 million people in East Africa depend on East African highland bananas for food and income. The bananas are grown with limited additions of nutrients and no irrigation, despite widespread poor soil fertility and regular dry seasons. This thesis describes the effect of increasing rainfall and application of potassium and nitrogen fertilizers on banana growth and yields. In areas that receive less than 1100 mm of rainfall per year, additional rainfall increases yields by 65%. Application of potassium increases yields by 88%, while nitrogen is not required. A framework for computing banana growth and yield in response to the amount of water stored in the soil is described. Where the soil water storage capacity is low, mulching increases yields by 10% but it has no effect in areas where the soil water storage is high. This framework is envisaged to guide improvements in banana management and productivity in East Africa.
Using natural variation to unravel the dynamic regulation of plant performance in diverse environments
Molenaar, J.A. - \ 2015
Wageningen University. Promotor(en): Harro Bouwmeester; Joost Keurentjes, co-promotor(en): Dick Vreugdenhil. - Wageningen : Wageningen University - ISBN 9789462573444 - 186
planten - genomen - loci voor kwantitatief kenmerk - warmtestress - genetische kartering - groei - droogte - plantengenetica - plantenfysiologie - plants - genomes - quantitative trait loci - heat stress - genetic mapping - growth - drought - plant genetics - plant physiology
All plants are able to respond to changes in their environment by adjusting their morphology and metabolism, but large differences are observed in the effectiveness of these responses in the light of plant fitness. Between and within species large differences are observed in plant responses to drought, heat and other abiotic stresses. This natural variation is partly due to variation in the genetic composition of individuals. Within-species variation can be used to identify and study genes involved in the genetic regulation of plant performance.
Growth of the world population will, in the coming years, lead to an increased demand for food, feed and other natural products. In addition, extreme weather conditions with, amongst others, more and prolonged periods of drought and heat are expected to occur due to climate change. Therefore breeders are challenged to produce stress tolerant cultivars with improved yield under sub-optimal conditions. Knowledge about the mechanisms and genes that underlie tolerance to drought, heat and other abiotic stresses will ease this challenge.
The aim of this thesis was to identify and study the role of genes that are underlying natural variation in plant performance under drought, salt and heat stress. To reach this goal a genome wide association (GWA) mapping approach was taken in the model species Arabidopsis thaliana. A population of 350 natural accessions of Arabidopsis, genotyped with 215k SNPs, was grown under control and several stress conditions and plant performance was evaluated by phenotyping one or several plant traits per environment. Genes located in the genomic regions that were significantly associated with plant performance, were studied in more detail.
Plant performance was first evaluated upon osmotic stress (Chapter 2). This treatment resulted not only in a reduced plant size, but also caused the colour of the rosette leaves to change from green to purple-red due to anthocyanin accumulation. The latter was visually quantified and subsequent GWA mapping revealed that a large part of the variation in anthocyanin accumulation could be explained by a small genomic region on chromosome 1. The analysis of re-sequence data allowed us to associate the second most frequent allele of MYB90 with higher anthocyanin accumulation and to identify the causal SNP. Interestingly MYB75, a close relative of MYB90, was not identified by GWA mapping, although causal sequence variation of this gene for anthocyanin accumulation was identified in the Cvi x Ler and Ler x Eri-1 RIL populations. Re-sequence data revealed that one allele of MYB75 was dominating the population and that the MYB75 alleles of Cvi and Ler were both rare, explaining the lack of association at this locus in GWA mapping. For MYB90, two alleles were present in a substantial part of the population, suggesting balancing selection between them.
Next, the natural population was exposed to short-term heat stress during flowering (Chapter 3). This short-term stress has a large impact on seed set, while it hardly affects the vegetative tissues. Natural variation for tolerance against the effect of heat on seed set was evaluated by measuring the length of all siliques along the inflorescence in both heat-treated and control plants. Because the flower that opened during the treatment was tagged, we could analyse the heat response for several developmental stages separately. GWA mapping revealed that the heat response before and after anthesis involved different genes. For the heat response before anthesis strong evidence was gained that FLC, a flowering time regulator and QUL2, a gene suggested to play a role in vascular tissue development, were causal for two strong associations.
Furthermore, the impact of moderate drought on plant performance was evaluated in the plant phenotyping platform PHENOPSIS. Homogeneous drought was assured by tight regulation of climate cell conditions and the robotic weighing and watering of the pots twice a day. Because plant growth is a dynamic trait it was monitored over time by top-view imaging under both moderate drought and control conditions (Chapter 4 and 5). To characterise growth it was modelled with an exponential function. GWA mapping of temporal growth data resulted in the detection of time-dependent QTLs whereas mapping of model parameters resulted in another set of QTLs related to the entire growth period. Most of these QTLs would not have been identified if plant size had only been determined on a single day. For the QTLs detected under control conditions eight candidate genes with a growth-related mutant or overexpression phenotype were identified (Chapter 4). Genes in the support window of the drought-QTLs were prioritized based on previously reported gene expression data (Chapter 5). Additional validation experiments are needed to confirm causality of the candidate genes.
Next, to search for genes that determine plant size across many environments, biomass accumulation in the natural population was determined in 25 different environments (Chapter 6). Joint analysis of these data by multi-environment GWA mapping resulted in the detection of 106 strongly associated SNPs with significant effects in 7 to 16 environments. Several genes involved in starch metabolism, leaf size control and flowering time determination were located in close proximity of the associated SNPs. Two genes, RPM1 and ACD6, were located in close proximity of SNPs with significant GxE effects. For both genes, alleles have been identified that increase resistance to bacterial infection, but that reduce biomass accumulation. The sign of the allelic effect is therefore dependent on the environmental conditions. Whole genome predictions revealed that most of the GxE interactions observed at the phenotypic level were not the consequence of strong associations with strong QxE effects, but of moderate and weak associations with weak QxE effects.
Finally, in Chapter 7 I discuss the usefulness of GWA mapping in the identification of genes underlying natural variation in plant performance under drought, heat stress and a number of other environments. Strong associations were observed for both environment-specific as well as common plant performance regulators. Some choices in phenotyping and experimental design were crucial for our success, like evaluation of plant performance over time and simplification of the quantification of the phenotype. It is suggested that follow-up work should focus on the functional characterization of the causal genes, because such analyses would be helpful to identify pathways in which the causal genes are involved and to understand why sequence variation results in changes at the phenotype level. Although translation of the findings to applications in crops is challenging, this thesis contributes to the understanding of the genetic regulation of stress response and therefore will likely contribute to the development of stress tolerant and stable yielding crops.
Bepaling van economische effecten van droogte voor de landbouwland; Baten van maatregelen om effecten te verminderen
Reinhard, A.J. ; Polman, N.B.P. ; Helming, J.F.M. ; Michels, R. - \ 2015
Den Haag : LEI Wageningen UR (LEI report 2015-012 ) - 42
economische analyse - kosten-batenanalyse - droogte - klimaatverandering - agrarische economie - landbouw - economic analysis - cost benefit analysis - drought - climatic change - agricultural economics - agriculture
Om de kosten en de baten te bepalen van maatregelen, die de gevolgen van droogte door klimaatverandering verminderen, zijn in opdracht van het deelprogramma Zoetwater (DPZW) van het deltaprogramma maatschappelijke kosten-batenanalyses (MKBA) uitgevoerd (onder andere Stratelligence, 2014). Op basis van deze analyses is uit de kansrijke maatregelen een voorkeursstrategie geselecteerd. De landbouw is een grote gebruiker van water, vandaar dat de kosten en baten van maatregelen voor deze sector een belangrijk deel van de MKBA zijn. Een goede bepaling van de baten voor de landbouw is daarom essentieel voor betrouwbare MKBA-resultaten. In dit rapport werken we de baten uit van maatregelen om de effecten van droogte tegen te gaan. Dezelfde aanpak kan worden gebruikt voor andere weersextremen (zoals extreme neerslag).
Goede grond voor een duurzaam watersysteem : verdere verkenningen in de relatie tussen agrarisch bodembeheer, bodemkwaliteit en waterhuishouding
Schipper, P.N.M. ; Groenendijk, P. ; Eekeren, N.J.M. van; Zanen, M. ; Rozemeijer, J. ; Jansen, G. ; Swart, B. - \ 2015
Amersfoort : Stichting Toegepast Onderzoek Waterbeheer (Rapport / STOWA 2015-19) - ISBN 9789057736889 - 72
landbouwgronden - bodemwater - drainage - bodemkwaliteit - droogte - nutriëntenuitspoeling - inventarisaties - modellen - gelderse vallei - agricultural soils - soil water - soil quality - drought - nutrient leaching - inventories - models
Een optimale bodemkwaliteit draagt bij aan de wateropgaven en een betere opbrengst van landbouwgewassen. In de praktijk zijn veel landbouwbodems in meer of mindere mate verdicht, zijn de condities voor bodemleven niet gunstig, is het organisch stofgehalte niet optimaal en de beworteling beperkt. De laatste jaren zijn daarom projecten opgezet waarin waterbeheerders en agrariërs samenwerken om bodem verbeterende maatregelen in de praktijk uit te voeren. Het is echter geheel niet bekend wat de effecten van zulke maatregelen zijn op de kwantiteit en kwaliteit van het water op lokaal (perceel) niveau en op het regionale watersysteem. Op perceelniveau zijn nu twee verschillende bodemtypen die beiden veel voorkomen in de Gelderse Vallei geschematiseerd en doorgerekend met het modelinstrumentarium SWAP-WOFOST-ANIMO voor verschillende gewassen en verschillende hydrologische omstandigheden.
Waterwijzer Landbouw, fase 2. Modellering van het bodem-water-plantsysteem met het gekoppelde instrumentarium SWAP-WOFOST
Kroes, J.G. ; Bartholomeus, R. ; Dam, J.C. van; Hack-ten Broeke, M.J.D. ; Supit, I. ; Hendriks, R.F.A. ; Wit, A.J.W. de; Bolt, F.J.E. van der; Walvoort, D.J.J. ; Hoving, I.E. ; Bakel, J. van - \ 2015
Amersfoort : Stowa (Rapport / STOWA 2015-16) - ISBN 9789057736766 - 121
landbouw - grondwaterstand - droogte - klimaatverandering - ecohydrologie - plant-water relaties - modellen - agriculture - groundwater level - drought - climatic change - ecohydrology - plant water relations - models
Voor het bepalen van de effecten van de ingrepen in de waterhuishouding op landbouwopbrengsten zijn in Nederland al geruime tijd drie methodes in gebruik: de HELPtabellen, de TCGB-tabellen en AGRICOM. In bijna elke berekening wordt gebruik gemaakt van een van deze methodes. Landbouw, waterbeheerders en waterleidingbedrijven dringen al langere tijd aan op een herziening van deze methodes, onder meer omdat ze gebaseerd zijn op verouderde meteorologische gegevens en ze niet klimaatrobuust zijn.
Warmer klimaat slecht voor veen in Friesland
Osinga, T. ; Terwisscha Van Scheltinga, W. ; Medenblik, J. ; Jansen, P.C. ; Kwakernaak, C. - \ 2015
H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 47 (2015)2. - ISSN 0166-8439 - p. 74 - 75.
veenweiden - bodemdaling - peilbeheer - drainage - grondwaterstand - klimaatverandering - droogte - pompstations - friesland - peat grasslands - subsidence - water level management - groundwater level - climatic change - drought - pumping stations
Enkele jaren geleden is voor het westelijk veenweidegebied aangetoond dat een warmer klimaat leidt tot snellere afbraak van veenbodems. Nu zijn er ook gegevens over de Friese veenweiden. Als het echt opwarmt is in Friesland halverwege deze eeuw op veel plekken het veen praktisch verdwenen.
Eikensterfte: een serieus en complex probleem
Oosterbaan, A. ; Bobbink, R. ; Decuyper, M. - \ 2015
Vakblad Natuur Bos Landschap (2015)113. - ISSN 1572-7610 - p. 10 - 14.
quercus - bodem-plant relaties - bodemchemie - verzuring - droogte - bomen - groeiplaatsen - soil plant relationships - soil chemistry - acidification - drought - trees - sites
Steeds meer beheerders zien met lede ogen aan hoe de eiken in hun bossen langzaam maar zeker afsterven. Over de precieze oorzaak is nog niet zo heel veel bekend. Wel maakt onderzoek duidelijk dat er meerdere oorzaken zijn die elkaar lijken te versterken. Droogte en aantasting door insecten zijn zeker een deel van het probleem, maar ook de snelle uitspoeling van basische kationen zijn waarschijnlijk een heel belangrijke factor
Pilot SWAP berekening droogteschade : vergelijking droogteschadeberekening volgens SWAP met de TCGB-tabel voor de waterwinning Vierlingsbeek
Massop, H.T.L. ; Kroes, J.G. ; Vroon, H.R.J. ; Mulder, H.M. - \ 2014
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2600) - 65
grondwaterwinning - grondwaterstand - oogstverliezen - droogte - modellen - noord-limburg - groundwater extraction - groundwater level - yield losses - drought - models
Sinds de jaren tachtig gebruikt de Advies Commissie Schade Grondwater (ACSG) zogenaamde TCGB tabellen om opbrengstdepressies als gevolg van drinkwaterwinning te berekenen. In deze studie wordt de mogelijkheid verkend van een modernisering van de methodiek door daarvoor het model SWAP in te zetten. Oude en nieuwe methodiek zijn toegepast in de pilot Vierlingsbeek. Resultaten zijn vergeleken en daarbij bleek dat, voor deze pilot, de nieuwe methodiek zowel hogere als lagere droogteschades kan berekenen dan de TCGB-tabel aangeeft. De droogteschades als gevolg van de winning vallen voor dit gebied lager uit. De conclusies uit deze pilotstudie kunnen in andere gebieden anders uitvallen omdat er mogelijk andere randvoorwaarden gelden. De nieuwe methodiek is dynamischer en biedt meer mogelijkheden voor aansluiting bij realistischere randvoorwaarden.
Onderzoek naar de relatie van eikensterfte met droogte en bodemchemie
Oosterbaan, A. ; Bobbink, R. ; Decuyper, M. - \ 2014
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2575) - 29
quercus - bodem-plant relaties - bodemchemie - verzuring - droogte - bomen - groeiplaatsen - soil plant relationships - soil chemistry - acidification - drought - trees - sites
In verband met verhevigde eikensterfte is onderzocht of er verband is tussen de eikensterfte en droogte en/of bodemchemie. Hiervoor is op tien locaties in een opstand met veel sterfte en een opstand met weinig sterfte de jaarringbreedte van de laatste 50 jaar vergeleken met weersgegevens van de dichtstbijzijnde weerstations, de hoeveelheid fijne wortels op 0-25 cm en 25-50 cm diepte bepaald en aan de hand van grondmonsters de bodemchemie gekarakteriseerd. Uit dit onderzoek is gebleken dat er een duidelijk verband is tussen de van tijd tot tijd optredende sterke groeivermindering van eiken en droogteperioden. Niet alle sterke groeiverminderingen zijn hiermee te verklaren. Er zijn aanwijzingen dat het aantal vorstdagen in de lente ook een rol speelt. In opstanden met veel sterfte zitten gemiddeld bovenin het bodemprofiel meer wortels en onderin minder dan in opstanden met weinig sterfte. In opstanden met veel sterfte heeft de bodem in de meeste gevallen lagere gehaltes aan uitwisselbaar Ca en/of K en/of Mg (dus een lagere buffercapaciteit). Het gehele proces van primaire oorzaken en secundaire factoren, die verantwoordelijk zijn voor de sterfte, is nog niet helder. Hiervoor is een breder en fundamenteler onderzoek noodzakelijk. Voor het beheer van eikenbossen worden voorlopige adviezen gegeven.
Assessing water stress of desert vegetation using remote sensing : the case of the Tamarugo forest in the Atacama Desert (Northern Chile)
Chávez Oyanadel, R.O. - \ 2014
Wageningen University. Promotor(en): Martin Herold, co-promotor(en): Jan Clevers; E. Acevedo. - Wageningen : Wageningen University - ISBN 9789462570795 - 175
waterstress - woestijnen - vegetatie - remote sensing - bossen - waterbeheer - ecosystemen - droogte - adaptatie - chili - water stress - deserts - vegetation - remote sensing - forests - water management - ecosystems - drought - adaptation - chile
Water stress assessment of natural vegetation plays a key role in water management of desert ecosystems. It allows scientists and managers to relate water extraction rates to changes in vegetation water condition, and consequently to define safe water extraction rates for maintaining a healthy ecosystem. Previous research has shown that optical remote sensing constitutes a powerful tool for assessing vegetation water stress due to its capability of quantitatively estimating important parameters of vegetation such as leaf area index (LAI), green canopy fraction (GCF), and canopy water content (CWC). However, the estimation of these parameters using remote sensing can be challenging in the case of desert vegetation. Desert plants have to cope with high solar irradiation and limited water. In order to maintain an adequate water balance and to avoid photoinhibition, desert plants have evolved different adaptations. A common one is heliotropism or ‘solar tracking’, an ability of many desert species to move their leaves to avoid facing direct high solar irradiation levels during the day and season. This adaptation (paraheliotropism) can have an important effect on the canopy spectral reflectance measured by satellites as well as on vegetation indices such as the normalized difference vegetation index (NDVI). In this thesis, I propose a remote sensing based approach to assess water stress of desert vegetation, exemplified in the case of the Tamarugo (Prosopis tamarugo Phil) tree in the Atacama Desert (Northern Chile), a ‘solar tracker’ species, which is threatened by groundwater overexploitation.
In the first chapter of this thesis (general introduction), I explained the motivation of the PhD project and elaborated four research questions, which are later discussed in chapters 2, 3, 4, and 5. The thesis concluded with chapter 6, where I provide a synthesis of the main results, general conclusions and a final reflection and outlook.
In the second chapter, I studied the effects of water stress on Tamarugo plants under laboratory conditions and modelled the light-canopy interaction using the Soil-Leaf-Canopy radiative transfer model. I described for the first time pulvinar movement of Tamarugo and quantified its effects on canopy spectral reflectance with and without stress. I showed that different spectral indices have potential to assess water stress of Tamarugo by means of LAI and CWC. In the third chapter, I measured the effects of pulvinar movements on canopy reflectance for Tamarugos under field conditions and used high spatial resolution images to assess water stress at the tree level. I developed an automated process to first identify single trees and delineate their crowns, and secondly, to estimate LAI and GCF using spectral vegetation indices. These indices (NDVI and chlorophyll red-edge index) were negatively correlated to diurnal values of solar irradiation as a consequence of leaf pulvinar movements. For this reason, higher values of both vegetation indices are expected to occur in the morning and in winter (low solar radiation) than at midday or summer.
In the fourth chapter I studied the effects of diurnal pulvinar movements on NDVI time series from the MODIS-Terra satellite (acquired in the morning) and the MODIS-Aqua satellite (acquired at midday) for the period 2003-2012 and the seasonal effects of pulvinar movements on NDVI time series of Landsat images for the period 1998-2012 for Tamarugo areas with and without water stress. NDVI values measured by MODIS-Terra (morning) were higher than the NDVI values measured by MODIS-Aqua (afternoon) and the difference between the two, the ΔNDVImo-mi, showed good potential as water stress indicator. In a similar way, I observed a strong seasonal effect on the Landsat NDVI signal, attributed to pulvinar movements, and the difference between winter and summer, the ΔNDVIW-S, also showed good potential for detecting and quantifying water stress. The ΔNDVImo-mi, the ΔNDVIW-S and the NDVI itself measured systematically in winter time (NDVIW) were negatively correlated with in situ groundwater depth measurements.
In chapter five I used a dense NDVI time series of Landsat images for the period 1989-2013, combined with high spatial resolution satellite imagery and hydrogeological records, to provide a quantitative assessment of the water status of Tamarugo vegetation after 50 years of increasing groundwater extraction. The results showed that the NDVIW and ΔNDVIW-S of the Tamarugo vegetation declined 19% and 51%, respectively, as groundwater depleted (3 meters on average) for the period 1989-2013. Both variables were negatively correlated to groundwater depth both temporally and spatially. About 730.000 Tamarugo trees remained in the study area by 2011, from which 5.2% showed a GCF<0.25 which is associated to severe water stress. Based on this spatio-temporal analysis, I suggest that the survival of Tamarugo trees is limited to a maximum groundwater depth of 20 meters.
The main conclusions of this PhD thesis are summarized as follows:Heliotropism or leaf ‘solar tracking’, a common adaptation among desert plants, has an important impact on canopy spectral reflectance. As shown in the case of the Tamarugo trees, widely used vegetation indices such as the NDVI were negatively correlated to solar irradiation (the stimulus for leaf solar tracking), showing a distinct diurnal and seasonal cycle.An early symptom of water stress in paraheliotropic plants (leaves facing away the sun) is the decline of the amplitude of the diurnal and seasonal NDVI cycles. Thus, remote sensing estimations of this amplitude (e.g. the NDVI difference between winter and summer or the difference between midday and morning) can be used to detect and map early water stress of paraheliotropic vegetation.At the tree level, very high spatial resolution images combined with object based image analysis and in-situ data provided accurate estimations of the water status of small desert vegetation features, such as isolated trees. For monitoring purposes, careful consideration of the time during the day and the season at which the images are taken needs to be taken to avoid misleading interpretations.Time series analysis of historical satellite images combined with very high spatial resolution images and hydrogeological records can provide a quantitative spatio-temporal assessment of the effects of long-term groundwater extraction on desert vegetation.
Hydrological drought : characterisation and representation in large-scale models
Huijgevoort, M.H.J. van - \ 2014
Wageningen University. Promotor(en): Remko Uijlenhoet, co-promotor(en): Henny van Lanen. - Wageningen : Wageningen University - ISBN 9789461739414 - 124
hydrologie van stroomgebieden - droogte - klimaatverandering - wateropslag - scenario-analyse - modellen - europa - vs - catchment hydrology - drought - climatic change - water storage - scenario analysis - models - europe - usa
De verwachting is dat door klimaatverandering de intensiteit van droogte zal toenemen in verschillende gebieden op de wereld. Uitkomsten van vijf hydrologische modellen in combinate met drie klimaatmodellen voor het A2 emissie scenario zijn gebruikt om effecten van klimaatverandering op hydrologische droogte te analyseren voor verschillende stroomgebieden. Droogtes en lage afvoeren (maandelijkse 20ste percentiel waarden, Q20) zijn geïdentificeerd uit de uitkomsten van de hydrologische modellen voor een historische periode (1971–2000) en een periode in de toekomst (2071–2100). De gesimuleerde lage afvoeren voor de historische periode zijn vergeleken met geobserveerde lage afvoeren van de verschillende stroomgebieden. De modelcombinaties (combinatie van een klimaatmodel en een hydrologisch model), die de beste resultaten gaven, zijn gebruikt voor verdere analyse. In koude klimaten werd een verschuiving in het hydrologische regime (de piek van sneeuwsmelt zal eerder optreden) waargenomen en een verhoging van de lage afvoeren tussen de historische periode en de periode in de toekomst. Voor aride klimaten gaven de modelcombinaties aan dat omstandigheden nog droger zullen worden in de toekomst. Voor vochtige klimaten werden zowel drogere als nattere situaties verwacht op basis van de modelcombinaties