Responses of Lowland, Upland and Aerobic Rice Genotypes to Water Limitation During Different Phases
Vijayaraghavareddy, Preethi ; Xinyou, Yin ; Struik, Paul C. ; Makarla, Udayakumar ; Sreeman, Sheshshayee - \ 2020
Rice Science 27 (2020)4. - ISSN 1672-6308 - p. 345 - 354.
Aerobic - Oryza sativa - Phenology - Upland - Water limitation - yield
Rice yield reduction due to water limitation depends on its severity and duration and on the phenological stage of its occurrence. We exposed three contrasting rice genotypes, IR64, UPLRi7 and Apo (adapted to lowland, upland and aerobic conditions, respectively), to three water regimes (puddle, 100% and 60% field capacity) in pots during the vegetative (GSI), flowering (GSII) and grain filling (GSIII) stages. Stress at all the three stages significantly reduced yield especially in lowland genotype IR64. Effect of water limitation was more severe at GSII than at the other two stages. Stress at GSI stage reduced both source activity (leaf area and photosynthetic rate) and sink capacity (tiller number or panicle number per pot). When stress was imposed at GSII, spikelet fertility was most affected in all the three genotypes. In both GSII and GSIII, although leaf area was constant in all the three water regimes, estimated relative whole-plant photosynthesis was strongly associated with yield reduction. Reduced photosynthesis due to stress at any given stage was found to have direct impact on yield. Compared to the other genotypes, Apo had deeper roots and maintained a better water relation, thus, higher carbon gain and spikelet viability, and ultimately, higher biomass and productivity under water-limited conditions. Therefore, screening for these stage-dependent adaptive mechanisms is crucial in breeding for sustained rice production under water limitation.
Late-spring frost risk between 1959 and 2017 decreased in North America but increased in Europe and Asia
Zohner, Constantin M. ; Mo, Lidong ; Renner, Susanne S. ; Svenning, Jens Christian ; Vitasse, Yann ; Benito, Blas M. ; Ordonez, Alejandro ; Baumgarten, Frederik ; Bastin, Jean François ; Sebald, Veronica ; Reich, Peter B. ; Liang, Jingjing ; Nabuurs, Gert Jan ; De-Migueln, Sergio ; Alberti, Giorgio ; Antón-Fernández, Clara ; Balazy, Radomir ; Brändli, Urs Beat ; Chen, Han Y.H. ; Chisholm, Chelsea ; Cienciala, Emil ; Dayanandan, Selvadurai ; Fayle, Tom M. ; Frizzera, Lorenzo ; Gianelle, Damiano ; Jagodzinski, Andrzej M. ; Jaroszewicz, Bogdan ; Jucker, Tommaso ; Kepfer-Rojas, Sebastian ; Khan, Mohammed Latif ; Kim, Hyun Seok ; Korjus, Henn ; Johannsen, Vivian Kvist ; Laarmann, Diana ; Langn, Mait ; Zawila-Niedzwiecki, Tomasz ; Niklaus, Pascal A. ; Paquette, Alain ; Pretzsch, Hans ; Saikia, Purabi ; Schall, Peter ; Seben, Vladimír ; Svoboda, Miroslav ; Tikhonova, Elena ; Viana, Helder ; Zhang, Chunyu ; Zhao, Xiuhai ; Crowther, Thomas W. - \ 2020
Proceedings of the National Academy of Sciences of the United States of America 117 (2020)22. - ISSN 0027-8424
Climate change - Freezing damage - Late frost - Phenology - Spring leaf-out
Late-spring frosts (LSFs) affect the performance of plants and animals across the world's temperate and boreal zones, but despite their ecological and economic impact on agriculture and forestry, the geographic distribution and evolutionary impact of these frost events are poorly understood. Here, we analyze LSFs between 1959 and 2017 and the resistance strategies of Northern Hemisphere woody species to infer trees' adaptations for minimizing frost damage to their leaves and to forecast forest vulnerability under the ongoing changes in frost frequencies. Trait values on leaf-out and leaf-freezing resistance come from up to 1,500 temperate and boreal woody species cultivated in common gardens. We find that areas in which LSFs are common, such as eastern North America, harbor tree species with cautious (late-leafing) leaf-out strategies. Areas in which LSFs used to be unlikely, such as broad-leaved forests and shrublands in Europe and Asia, instead harbor opportunistic tree species (quickly reacting to warming air temperatures). LSFs in the latter regions are currently increasing, and given species' innate resistance strategies, we estimate that ∼35% of the European and ∼26% of the Asian temperate forest area, but only ∼10% of the North American, will experience increasing late-frost damage in the future. Our findings reveal region-specific changes in the spring-frost risk that can inform decision-making in land management, forestry, agriculture, and insurance policy.
Editorial of special issue “drones for biodiversity conservation and ecological monitoring”
Díaz-Delgado, Ricardo ; Mücher, Sander - \ 2019
Drones 3 (2019)2. - ISSN 2504-446X - p. 1 - 4.
Biodiversity - Biological conservation - Drone mapping - Ecological monitoring - Phenology - UAVs
Unmanned Aerial Vehicles (UAV) have already become an affordable and cost-efficient tool to quickly map a targeted area for many emerging applications in the arena of Ecological Monitoring and Biodiversity Conservation. Managers, owners, companies and scientists are using professional drones equipped with high-resolution visible, multispectral or thermal cameras to assess the state of ecosystems, the effect of disturbances, or the dynamics and changes of biological communities inter alia. It is now a defining time to assess the use of drones for these types of applications over natural areas and protected areas. UAV missions are increasing but most of them are just testing its applicability. It is time now to move to frequent revisiting missions, aiding in the retrieval of important biophysical parameters in ecosystems or mapping species distributions. This Special Issue is aimed at collecting UAV applications contributing to a better understanding of biodiversity and ecosystem status, threats, changes and trends. Submissions were welcomed from purely scientific missions to operational management missions, evidencing the enhancement of knowledge in: Essential biodiversity variables and ecosystem services mapping; ecological integrity parameters mapping; long-term ecological monitoring based on UAVs; mapping of alien species spread and distribution; upscaling ecological variables from drone to satellite images: methods and approaches; rapid risk and disturbance assessment using drones, ecosystem structure and processes assessment by using UAVs, mapping threats, vulnerability and conservation issues of biological communities and species; mapping of phenological and temporal trends and habitat mapping; monitoring and reporting of conservation status.
No evidence of flowering synchronization upon floral volatiles for a short lived annual plant species: Revisiting an appealing hypothesis
Fricke, Ute ; Lucas-Barbosa, Dani ; Douma, Jacob C. - \ 2019
BMC Ecology 19 (2019)1. - ISSN 1472-6785
Flowering onset - Flowering synchronization - Phenology - Plant-plant communication
Background: Self-incompatible plants require simultaneous flowering mates for crosspollination and reproduction. Though the presence of flowering conspecifics and pollination agents are important for reproductive success, so far no cues that signal the flowering state of potential mates have been identified. Here, we empirically tested the hypothesis that plant floral volatiles induce flowering synchrony among self-incompatible conspecifics by acceleration of flowering and flower opening rate of non-flowering conspecifics. We exposed Brassica rapa Maarssen, a self-incompatible, in rather dense patches growing annual, to (1) flowering or non-flowering conspecifics or to (2) floral volatiles of conspecifics by isolating plants in separate containers with a directional airflow. In the latter, odors emitted by non-flowering conspecifics were used as control. Results: Date of first bud, duration of first flower bud, date of first flower, maximum number of open flowers and flower opening rate were not affected by the presence of conspecific flowering neighbors nor by floral volatiles directly. Conclusions: This study presents a compelling approach to empirically test the role of flower synchronization by floral volatiles and challenges the premises that are underlying this hypothesis. We argue that the life history of the plant as well as its interaction with pollinators and insect herbivores, as well as the distance over which volatiles may serve as synchronization cue, set constraints on the fitness benefits of synchronized flowering which needs to be taken into account when testing the role of floral volatiles in synchronized flowering.
The complex interactions between flowering behavior and fiber quality in hemp
Salentijn, Elma M.J. ; Petit, Jordi ; Trindade, Luisa M. - \ 2019
Frontiers in Plant Science 10 (2019). - ISSN 1664-462X
Cannabis sativa - Fiber development - Flowering-time - Hemp - Phenology - Sex determination - Short-day plant
Hemp, Cannabis sativa L., is a sustainable multipurpose fiber crop with high nutrient and water use efficiency and with biomass of excellent quality for textile fibers and construction materials. The yield and quality of hemp biomass are largely determined by the genetic background of the hemp cultivar but are also strongly affected by environmental factors, such as temperature and photoperiod. Hemp is a facultative short-day plant, characterized by a strong adaptation to photoperiod and a great influence of environmental factors on important agronomic traits such as “flowering-time” and “sex determination.” This sensitivity of hemp can cause a considerable degree of heterogeneity, leading to unforeseen yield reductions. Fiber quality for instance is influenced by the developmental stage of hemp at harvest. Also, male and female plants differ in stature and produce fibers with different properties and quality. Next to these causes, there is evidence for specific genotypic variation in fiber quality among hemp accessions. Before improved hemp cultivars can be developed, with specific flowering-times and fiber qualities, and adapted to different geographical regions, a better understanding of the molecular mechanisms controlling important phenological traits such as “flowering-time” and “sex determination” in relation to fiber quality in hemp is required. It is well known that genetic factors play a major role in the outcome of both phenological traits, but the major molecular factors involved in this mechanism are not characterized in hemp. Genome sequences and transcriptome data are available but their analysis mainly focused on the cannabinoid pathway for medical purposes. Herein, we review the current knowledge of phenotypic and genetic data available for “flowering-time,” “sex determination,” and “fiber quality” in short-day and dioecious crops, respectively, and compare them with the situation in hemp. A picture emerges for several controlling key genes, for which natural genetic variation may lead to desired flowering behavior, including examples of pleiotropic effects on yield quality and on carbon partitioning. Finally, we discuss the prospects for using this knowledge for the molecular breeding of this sustainable crop via a candidate gene approach.
Improving WOFOST model to simulate winter wheat phenology in Europe : Evaluation and effects on yield
Ceglar, A. ; Wijngaart, R. van der; Wit, A. de; Lecerf, R. ; Boogaard, H. ; Seguini, L. ; Berg, M. van den; Toreti, A. ; Zampieri, M. ; Fumagalli, D. ; Baruth, B. - \ 2019
Agricultural Systems 168 (2019). - ISSN 0308-521X - p. 168 - 180.
Calibration - Crop yield forecasting - Europe - Phenology - Triticum aestivum - WOFOST
This study describes and evaluates improvements to the MARS crop yield forecasting system (MCYFS) for winter soft wheat (Triticum aestivum) in Europe, based on the WOFOST crop simulation model, by introducing autumn sowing dates, realistic soil moisture initialization, adding vernalization requirements and photoperiodicity, and phenology calibration. Dataset of phenological observations complemented with regional cropping calendars across Europe is used. The calibration of thermal requirements for anthesis and maturity is done by pooling all available observations within European agro-environmental zones and minimizing an objective function that combines the differences between observed and simulated anthesis, maturity and harvest dates. Calibrated phenology results in substantial improvement in simulated dates of anthesis with respect to the original MCYFS simulations. The combined improvements to the system result in a physically more plausible spatial distribution of crop model indicators across Europe. Crop yield indicators point to better agreement with recorded national winter wheat yields with respect to the original MCYFS simulations, most pronounced in central, eastern and southern Europe. However, model skill remains low in large parts of western Europe, which may possibly be attributed to the impacts of wet conditions.
Checking the consistency of volunteered phenological observations while analysing their synchrony
Mehdipoor, Hamed ; Zurita-Milla, Raul ; Augustijn, Ellen-Wien ; Vliet, Arnold J.H. van - \ 2018
ISPRS International Journal of Geo-Information 7 (2018)12. - ISSN 2220-9964
Citizen science - Climate change - Constraint satisfaction - Data quality - Geocomputation - Phenology - Synchrony - Volunteered geographical information
The increasing availability of volunteered geographic information (VGI) enables novel studies in many scientific domains. However, inconsistent VGI can negatively affect these studies. This paper describes a workflow that checks the consistency of Volunteered Phenological Observations (VPOs) while considering the synchrony of observations (i.e., the temporal dispersion of a phenological event). The geographic coordinates, day of the year (DOY) of the observed event, and the accumulation of daily temperature until that DOY were used to: (1) spatially group VPOs by connecting observations that are near to each other, (2) define consistency constraints, (3) check the consistency of VPOs by evaluating the defined constraints, and (4) optimize the constraints by analysing the effect of inconsistent VPOs on the synchrony models derived from the observations. This workflow was tested using VPOs collected in the Netherlands during the period 2003–2015. We found that the average percentage of inconsistent observations was low to moderate (ranging from 1% for wood anemone and pedunculate oak to 15% for cow parsley species). This indicates that volunteers provide reliable phenological information. We also found a significant correlation between the standard deviation of DOY of the observed events and the accumulation of daily temperature (with correlation coefficients ranging from 0.78 for lesser celandine, and 0.60 for pedunculate oak). This confirmed that colder days in late winter and early spring lead to synchronous flowering and leafing onsets. Our results highlighted the potential of synchrony information and geographical context for checking the consistency of phenological VGI. Other domains using VGI can adapt this geocomputational workflow to check the consistency of their data, and hence the robustness of their analyses.
LiDAR derived topography and forest stand characteristics largely explain the spatial variability observed in MODIS land surface phenology
Misra, Gourav ; Buras, Allan ; Heurich, Marco ; Asam, Sarah ; Menzel, Annette - \ 2018
Remote Sensing of Environment 218 (2018). - ISSN 0034-4257 - p. 231 - 244.
Bavarian Forest National Park - Forest stand characteristics - Land cover - LiDAR - Modelling - Mountains - NDVI - Phenology - Spatial variability
In the past, studies have successfully identified climatic controls on the temporal variability of the land surface phenology (LSP). Yet we lack a deeper understanding of the spatial variability observed in LSP within a land cover type and the factors that control it. Here we make use of a high resolution LiDAR based dataset to study the effect of subpixel forest stand characteristics on the spatial variability of LSP metrics based on MODIS NDVI. Multiple linear regression techniques (MLR) were applied on forest stand information and topography derived from LiDAR as well as land cover information (i.e. CORINE and proprietary habitat maps for the year 2012) to predict average LSP metrics of the mountainous Bavarian Forest National Park, Germany. Six different LSP metrics, i.e. start of season (SOS), end of season (EOS), length of season (LOS), NDVI integrated over the growing season (NDVIsum), maximum NDVI value (NDVImax) and day of maximum NDVI (maxDOY) were modelled in this study. It was found that irrespective of the land cover, the mean SOS, LOS and NDVIsum were largely driven by elevation. However, inclusion of detailed forest stand information improved the models considerably. The EOS however was more complex to model, and the subpixel percentage of broadleaf forests and the slope of the terrain were found to be more strongly linked to EOS. The explained variance of the NDVImax improved from 0.45 to 0.71 when additionally considering land cover information, which further improved to 0.84 when including LiDAR based subpixelforest stand characteristics. Since completely homogenous pixels are rare in nature, our results suggest that incorporation of subpixel forest stand information along with land cover type leads to an improved performance of topography based LSP models. The novelty of this study lies in the use of topography, land cover and subpixel vegetation characteristics derived from LiDAR in a stepwise manner with increasing level of complexity, which demonstrates the importance of forest stand information on LSP at the pixel level.
Lessons from the first generation of marine ecological forecast products
Payne, Mark R. ; Hobday, Alistair J. ; MacKenzie, Brian R. ; Tommasi, Desiree ; Dempsey, Danielle P. ; Fassler, Sascha ; Haynie, Alan C. ; Ji, Rubao ; Liu, Gang ; Lynch, Patrick D. ; Matei, Daniela ; Miesner, Anna K. ; Mills, Katherine E. ; Strand, Kjersti O. ; Villarino, Ernesto - \ 2017
Frontiers in Marine Science 4 (2017)SEP. - ISSN 2296-7745
Ecological forecasting - Ecological prediction - Marine ecological forecasting - Phenology - Recruitment - Seasonal-to-decadal-forecasting - Spatial distribution
Recent years have seen a rapid expansion in the ability of earth system models to describe and predict the physical state of the ocean. Skilful forecasts ranging from seasonal (3 months) to decadal (5-10 years) time scales are now a reality. With the advance of these forecasts of ocean physics, the first generation of marine ecological forecasts has started to emerge. Such forecasts are potentially of great value in the management of living marine resources and for all of those who are dependent on the ocean for both nutrition and their livelihood; however, this is still a field in its infancy. We review the state of the art in this emerging field and identify the lessons that can be learnt and carried forward from these pioneering efforts. The majority of this first wave of products are forecasts of spatial distributions, possibly reflecting the inherent suitability of this response variable to the task of forecasting. Promising developments are also seen in forecasting fish-stock recruitment where, despite well-recognized challenges in understanding and predicting this response, new process knowledge and model approaches that could form a basis for forecasting are becoming available. Forecasts of phenology and coral-bleaching events are also being applied to monitoring and industry decisions. Moving marine ecological forecasting forward will require striking a balance between what is feasible and what is useful. We propose here a set of criteria to quickly identify "low-hanging fruit" that can potentially be predicted; however, ensuring the usefulness of forecast products also requires close collaboration with actively engaged end-users. Realizing the full potential of marine ecological forecasting will require bridging the gaps between marine ecology and climatology on the one-hand, and between science and end-users on the other. Nevertheless, the successes seen thus far and the potential to develop further products suggest that the field of marine ecological forecasting can be expected to flourish in the coming years.
Long-term patterns in fish phenology in the western Dutch Wadden Sea in relation to climate change
Walraven, Lodewijk Van; Dapper, Rob ; Nauw, Janine J. ; Tulp, Ingrid ; Witte, Johannes IJ. ; Veer, Henk W. van der - \ 2017
Journal of Sea Research 127 (2017). - ISSN 1385-1101 - p. 173 - 181.
Long-term changes - Phenology - Fish fauna - Wadden Sea - Temperature
Long-term patterns in fish phenology in the western Dutch Wadden Sea were studied using a 53 year (1960–2013) high resolution time series of daily kom-fyke catches in spring and autumn. Trends in first appearance, last occurrence and peak abundance were analysed for the most common species in relation to mode of life (pelagic, demersal, benthopelagic) and biogeographic guild (northern or southern distribution). Climate change in the western Wadden Sea involved an increase in water temperature from 1980 onwards. The main pattern in first day of occurrence, peak occurrence and last day of occurrence was similar: a positive trend over time and a correlation with spring and summer water temperature. This is counterintuitive; with increasing temperature, an advanced immigration of fish species would be expected. An explanation might be that water temperatures have increased offshore as well and hence fish remain longer there, delaying their immigration to the Wadden Sea. The main trend towards later date of peak occurrence and last day of occurrence was in line with our expectations: a forward shift in immigration into the Wadden Sea implies also that peak abundance is delayed. As a consequence of the increased water temperature, autumn water temperature remains favourable longer than before. For most of the species present, the Wadden Sea is not near the edge of their distributional range. The most striking phenological shifts occurred in those individual species for which the Wadden Sea is near the southern or northern edge of their distribution.
Ridge and furrow systems with film cover increase maize yields and mitigate climate risks of cold and drought stress in continental climates
Dong, Wanlin ; Zhang, Lizhen ; Duan, Yu ; Sun, Li ; Zhao, Peiyi ; Werf, Wopke van der; Evers, Jochem B. ; Wang, Qi ; Wang, Ruonan ; Sun, Zhigang - \ 2017
Field Crops Research 207 (2017). - ISSN 0378-4290 - p. 71 - 78.
Climate change - Growth - Instantaneous growth rate - Phenology - Yield components
Ridge-furrow tillage and plastic film cover are widely applied in China to mitigate climate risks, e.g. cool temperature and low rainfall. This study aimed to quantify the effects of ridge-furrow tillage and film cover on maize growth and yield in an environment with frequent seasonal drought and cold spells. Field experiments were carried out in 2013 and 2014 in Jilin and Inner Mongolia, northeast China. Maize yield without film cover increased 15% by ridging, and further increases of 9% or 16% were achieved by applying 58% or 100% film cover, respectively. Maize growth rate was significantly enhanced by both partial and full film cover, but not significantly increased by ridging alone. The time reached to the maximum growth rate was significantly advanced. The growing duration of maize was significantly shortened by film cover while ridging did not affect. The increase of maize yield by ridge and film cover was associated with significant increases in kernel number per ear, kernel weight and harvest index. Harvest index of maize increased with 11% by ridge-furrow tillage and with a further 15–17% by film cover. We conclude that maize with ridge and film cover increases crop yield by enhancing crop growth and development and could also reduce risks of crop failure due to drought or cold spells. The results could help optimize maize management in arid continental regions where yields are constrained by drought and a short growing season due to low temperature.
Using a phenological network to assess weather influences on first appearance of butterflies in the Netherlands
Kolk, Henk Jan Van Der; Wallis de Vries, Michiel ; Vliet, Arnold J.H. Van - \ 2016
Ecological Indicators 69 (2016). - ISSN 1470-160X - p. 205 - 212.
Anthocharis cardamines - Butterflies - Climate change - Monitoring network - Phenology - Plant-host interaction
Phenological responses of butterflies to temperature have been demonstrated in several European countries by using data from standardized butterfly monitoring schemes. Recently, phenological networks have enabled volunteers to record phenological observations at project websites. In this study, the quality of the first appearance data of butterflies from the Dutch phenological network 'De Natuurkalender' was examined and these data were then used to analyze trends in butterfly appearance between 2001 and 2013, the effects of climatic factors on appearance of butterflies as well as the phenological interaction of one butterfly species, Anthocharis cardamines, and its two major host plants. Although phenological networks are relatively unstructured, this study shows that data from De Natuurkalender were highly comparable to more standardized data collected by the Dutch Butterfly Monitoring Scheme. No trend in first appearance of any butterfly species was found during the time period 2001-2013. The first appearance dates of most butterflies showed, however, a clear relationship with spring temperature. Higher temperatures, especially in March and April, advanced the first appearance of butterflies. Therefore, with climatic warming in the future, earlier appearance of butterflies is expected. Although climate warming is a potential threat for phenological mismatches between different trophic levels, this study shows a similar temperature response of A. cardamines and its main host plants in the Netherlands. However, as only few phenological interactions between species are examined, further research including rarer monophagous butterfly species and their host plants is needed.
Comparing hemp (Cannabis sativa L.) cultivars for dual-purpose production under contrasting environments
Tang, Kailei ; Struik, P.C. ; Yin, X. ; Thouminot, C. ; Bjelková, M. ; Stramkale, V. ; Amaducci, S. - \ 2016
Industrial Crops and Products 87 (2016). - ISSN 0926-6690 - p. 33 - 44.
Cultivar - Fibre - Hemp (Cannabis sativa L.) - Modelling - Phenology - Seed
Interest in hemp as a multi-purpose crop is growing worldwide and for the first time in 2015 it was cultivated in Europe on more than 20.000 ha as a dual-purpose crop, for the seeds and for the fibre. In the present study, fibre and seed productivity of 14 commercial cultivars were tested in four contrasting European environments (Latvia, the Czech Republic, France, Italy). At full flowering, the stem yield ranged from 3.7 Mg ha-1 to 22.7 Mg ha-1, the bast fibre content ranged from 21% to 43%, and the bast fibre yield ranged from 1.3 Mg ha-1 to 7.4 Mg ha-1. When harvesting was postponed from full flowering until seed maturity, the stem yield of monoecious cultivars significantly increased but in dioecious cultivars it decreased at all tested sites, except for Italy. Only the early cultivars Fedora 17 and Markant produced seed in the most northern location Latvia. The seed yield ranged from 0.3 Mg ha-1 to 2.4 Mg ha-1 in Italy, France and the Czech Republic. The cultivar effect on stem and seed yield was mainly determined by the genetic variation in time of flowering. Stem yield at full flowering was strictly related to the duration of the vegetative phase while seed yield was lowest in the late flowering cultivar. The late cultivar CS is suitable for stem and fibre production as it had the highest stem yield at full flowering in all locations. Both Fedora 17 and Futura 75 are candidate cultivars for dual-purpose production in Italy, France and the Czech Republic, with Fedora 17 being more suitable for seed production and Futura 75 for fibre production.The application of modelling to design production strategies for dual-purpose hemp is promising. However, accurate parameterisation is needed based on large data sets and diverse genetic background.
Matching the phenology of Net Ecosystem Exchange and vegetation indices estimated with MODIS and FLUXNET in-situ observations
Balzarolo, M. ; Vicca, S. ; Nguy-Robertson, A.L. ; Bonal, D. ; Elbers, J.A. ; Fu, Y.H. ; Grünwald, T. ; Horemans, J.A. ; Papale, D. ; Peñuelas, J. ; Suyker, A. ; Veroustraete, F. - \ 2016
Remote Sensing of Environment 174 (2016). - ISSN 0034-4257 - p. 290 - 300.
Net Ecosystem Exchange (NEE) - Phenology - Plant functional types (PFT's) - Start of growing season (SGS) - Start of net carbon uptake (SGS) - Vegetation indices (VI's)
Shifts in ecosystem phenology play an important role in the definition of inter-annual variability of net ecosystem carbon uptake. A good estimate at the global scale of ecosystem phenology, mainly that of photosynthesis or gross primary productivity (GPP), may be provided by vegetation indices derived from MODIS satellite image data.However, the relationship between the start date of a growing (or greening) season (SGS) when derived from different vegetation indices (VI's), and the starting day of carbon uptake is not well elucidated. Additionally, the validation of existing phenology data with in-situ measurements is largely missing. We have investigated the possibility to use different VI's to predict the starting day of the growing season for 28 FLUXNET sites as well as MODIS data. This analysis included main plant functional types (PFT's).Of all VI's taken into account in this paper, the NDVI (Normalized Difference Vegetation Index) shows the highest correlation coefficient for the relationship between the starting day of the growing season as observed with MODIS and in-situ observations. However, MODIS observations elicit a 20-21 days earlier SGS date compared to in-situ observations. The prediction for the NEE start of the growing season diverges when using different VI's, and seems to depend on the amplitude for carbon and VI and on PFT. The optimal VI for estimation of a SGS date was PFT-specific - for example the WRDVI for cropland, but the MODIS NDVI performed best when applied as an estimator for Net Ecosystem Exchange and when considering all PFT's pooled.