Time lags between crown and basal sap flows in tropical lianas and co-occurring trees
Chen, Ya Jun ; Bongers, Frans ; Tomlinson, Kyle ; Fan, Ze Xin ; Lin, Hua ; Zhang, Shu Bin ; Zheng, Yu Long ; Li, Yang Ping ; Cao, Kun Fang ; Zhang, Jiao Lin - \ 2016
Tree Physiology 36 (2016)6. - ISSN 0829-318X - p. 736 - 747.
frequency domain reflectometry - hydraulic capacitance - transpiration - volumetric water content - water relations, water storage
Water storage in the stems of woody plants contributes to their responses to short-term water shortages. To estimate the contribution of water storage to the daily water budget of trees, time lags of sap flow between different positions of trunk are used as a proxy of stem water storage. In lianas, another large group of woody species, it has rarely been studied whether stored water functions in their daily water use, despite their increasing roles in the carbon and water dynamics of tropical forests caused by their increasing abundance. We hypothesized that lianas would exhibit large time lags due to their extremely long stems, wide vessels and large volume of parenchyma in the stem. We examined time lags in sap flow, diel changes of stem volumetric water content (VWC) and biophysical properties of sapwood of 19 lianas and 26 co-occurring trees from 27 species in 4 forests (karst, tropical seasonal, flood plain and savanna) during a wet season. The plants varied in height/length from 60 m. The results showed that lianas had significantly higher saturated water content (SWC) and much lower wood density than trees. Seven of 19 liana individuals had no time lags; in contrast, only 3 of 26 tree individuals had no time lags. In general, lianas had shorter time lags than trees in our data set, but this difference was not significant for our most conservative analyses. Across trees and lianas, time lag duration increased with diurnal maximum changeable VWC but was independent of the body size, path length, wood density and SWC. The results suggest that in most lianas, internal stem water storage contributes little to daily water budget, while trees may rely more on stored water in the stem.
HNT Gerbera vraagt om meer inzicht in luchtstromen en vochtafvoer in de kas : Telers zelf actief in onderzoek en ontwikkeling
Rodenburg, J. ; Weel, P.A. van - \ 2015
Onder Glas 12 (2015)4. - p. 42 - 43.
glastuinbouw - snijbloemen - teeltsystemen - teelt onder bescherming - luchtstroming - ontvochtiging - vergelijkend onderzoek - proeven - transpiratie - greenhouse horticulture - cut flowers - cropping systems - protected cultivation - air flow - dehumidification - comparative research - trials - transpiration
Volgens innovatiemakelaar Stefan Persoon verdient het gerberavak een compliment. Als geen ander zijn de telers zelf actief in onderzoek en ontwikkeling. En met de resultaten komen ze aantoonbaar verder. “We hebben samen inderdaad veel bereikt”, meent ook Mathieu van Holstein, directeur van Holstein Flowers. “Op het gebied van belichting, verduistering en natuurlijk Het Nieuwe Telen. We weten nu bijvoorbeeld dat we energiezuiniger kunnen telen met behoud van kwaliteit.”
Selecting crop models for decision making in wheat insurance
Castaneda Vera, A. ; Leffelaar, P.A. ; Alvaro-Fuentes, J. ; Cantero-Martinez, C. ; Minguez, M.I. - \ 2015
European Journal of Agronomy 68 (2015). - ISSN 1161-0301 - p. 97 - 116.
use efficiency - management-practices - farming systems - field-capacity - soil - yield - evaporation - photosynthesis - transpiration - irrigation
In crop insurance, the accuracy with which the insurer quantifies the actual risk is highly dependent on the availability on actual yield data. Crop models might be valuable tools to generate data on expected yields for risk assessment when no historical records are available. However, selecting a crop model for a specific objective, location and implementation scale is a difficult task. A look inside the different crop and soil modules to understand how outputs are obtained might facilitate model choice. The objectives of this paper were (i) to assess the usefulness of crop models to be used within a crop insurance analysis and design and (ii) to select the most suitable crop model for drought risk assessment in semi-arid regions in Spain. For that purpose first, a pre-selection of crop models simulating wheat yield under rainfed growing conditions at the field scale was made, and second, four selected models (Aquacrop, CERES-Wheat, CropSyst and WOFOST) were compared in terms of modelling approaches, process descriptions and model outputs. Outputs of the four models for the simulation of winter wheat growth are comparable when water is not limiting, but differences are larger when simulating yields under rainfed conditions. These differences in rainfed yields are mainly related to the dissimilar simulated soil water availability and the assumed linkages with dry matter formation. We concluded that for the simulation of winter wheat growth at field scale in such semi-arid conditions, CERES-Wheat and CropSyst are preferred. WOFOST is a satisfactory compromise between data availability and complexity when detail data on soil is limited. Aquacrop integrates physiological processes in some representative parameters, thus diminishing the number of input parameters, what is seen as an advantage when observed data is scarce. However, the high sensitivity of this model to low water availability limits its use in the region considered. Contrary to the use of ensembles of crop models, we endorse that efforts be concentrated on selecting or rebuilding a model that includes approaches that better describe the agronomic conditions of the regions in which they will be applied. The use of such complex methodologies as crop models is associated with numerous sources of uncertainty, although these models are the best tools available to get insight in these complex agronomic systems.
Atmospheric turbulence over crops : confronting theories with observations
Boer, A. van de - \ 2015
Wageningen University. Promotor(en): Bert Holtslag, co-promotor(en): Arnold Moene; A. Graf. - Wageningen : Wageningen University - ISBN 9789462572416 - 143
turbulentie - meteorologie - atmosfeer - gewassen - watergebruiksrendement - transpiratie - modellen - eddy-covariantie - turbulente stroming - turbulence - meteorology - atmosphere - crops - water use efficiency - transpiration - models - eddy covariance - turbulent flow
Atmospheric turbulence plays a key role in hydrological and carbon cycles, and in weather and climate. Understanding and forecasting turbulence is thereby relevant for human life and environment.
We deal with some major challenges for studying atmospheric turbulence over crops. Land-atmosphere interactions are specifically complex because of surface heterogeneity. Also, boundary-layer entrainment complicates measuring and studying surface fluxes. Furthermore, the absence of high-frequency observations and of measurements of underlying soil and vegetation processes impedes studying land-atmosphere interactions.
We show the applicability of analytical footprint models over a heterogeneous land surface, and the validity of Monin-Obukhov similarity theory for a strongly-convective boundary-layer. Moreover, we present improvements on a scheme that can be used to estimate the amount of atmospheric turbulence from single-level weather data. We furthermore suggest to improve the partitioning theory that is used to distinguish soil processes from plant processes in eddy-covariance flux observations.
Minimal heating and cooling in a modern rose greenhouse
Beveren, P.J.M. van; Bontsema, J. ; Straten, G. van; Henten, E. van - \ 2015
Applied Energy 137 (2015). - ISSN 0306-2619 - p. 97 - 109.
horizon optimal-control - closed greenhouse - temperature control - energy analysis - climate - crop - management - transpiration
In a modern greenhouse there are a number of alternative systems that can be deployed to control the climate, and the choice what to use and when is not easy for the grower. A novel management system is proposed, consisting of an energy input minimizing module, and a module to realise the determined input with the available equipment. The current paper describes the energy minimization part. A dynamic optimization tool based on optimal control theory was used to obtain time trajectories of the energy flux that minimizes total external energy input over the year, while maintaining greenhouse air temperature and humidity between grower defined bounds. By giving the grower the lead in defining the bounds, the method stays as closely as possible to the grower’s daily practice and experience, and no crop production models and market prices are needed. The underlying dynamic model of temperature and humidity, based on known physical principles and parameters, compared very well with unique, year round high frequent data from a commercial rose greenhouse. A relatively simple crop transpiration model was validated separately, with very good results. It was shown that over twelve selected days, distributed over the entire year, the energy saving potential as compared to the actual grower’s practice is substantial. This potential was related to the definition of lower and upper bounds, less natural ventilation at colder days, and more natural ventilation and less heating at warmer days. The prominent role of the bounds was clearly demonstrated. Relaxing the temperature and humidity bounds decreases the energy input to the greenhouse. While this is obvious, the quantification of the effect as demonstrated here is of great interest to growers, and is essential for the development of the second part of the system.
Tulpscheutjes in weefselkweek blijken zwaar ondervoed
Klerk, G.J.M. de; Bos, H. ; Pramanik, D. - \ 2014
BloembollenVisie (2014)305. - ISSN 1571-5558 - p. 18 - 19.
weefselkweek - tulpen - voedingsstoffentransport - transpiratie - plantenfysiologie - opname (uptake) - tissue culture - tulips - nutrient transport - transpiration - plant physiology - uptake
Voor tulp is weefselkweekvermeerdering cruciaal. Nieuwe cultivars kunnen met weefselkweek veel sneller op de markt gebracht worden dan de huidige 20-25 jaar. Bovendien zijn bollen uit de weefselkweek vitaler en robuuster. Commerciële weefselkweekvermeerdering is ondanks veel onderzoek niet van de grond gekomen. Nieuw onderzoek werpt een ander licht op dit probleem. Ondervoeding blijkt de bottlenek; ondervoeding niet omdat er te weinig voeding wordt toegediend maar omdat de plantjes te weinig naar de groeizones kunnen transporteren.
Temperature is especially important for meristem and fruit : sensitivity different plant organs to changes in temperature
Heuvelink, E. ; Gelder, A. de; Kierkels, T. - \ 2014
In Greenhouses : the international magazine for greenhouse growers 3 (2014)1. - ISSN 2215-0633 - p. 34 - 35.
kassen - teelt onder bescherming - temperatuur - vruchtgroenten - fotosynthese - transpiratie - koeling - glastuinbouw - semi-gesloten kassen - groenten - greenhouses - protected cultivation - temperature - fruit vegetables - photosynthesis - transpiration - chilling - greenhouse horticulture - semi-closed greenhouses - vegetables
Temperature influences plant processes. But the different organs – root, stem, leaf, flower, fruit – all react differently. This is something to take into account with new cultivation systems such as (semi) closed greenhouses, where an essential aspect is cooling.
Substrate water status and evapotranspiration irrigation schedulingin heterogenous container nursery crops
Incrocci, L. ; Marzialetti, P. ; Incrocci, G. ; Vita, A. Di; Balendonck, J. ; Bibbiani, C. ; Spagnol, S. ; Pardossi, A. - \ 2014
Agricultural Water Management 131 (2014). - ISSN 0378-3774 - p. 30 - 40.
viburnum-odoratissimum - woody ornamentals - plant - transpiration - requirements - management - climate - systems - growth - model
A study was conducted to determine the effects of implementing different irrigation scheduling meth-ods on heterogeneous container hardy ornamental nursery stocks. Four ornamental shrub specieswere grown in the same irrigation sector during the summer of four consecutive years (2007–2010):Forsythia × intermedia, Photinia × fraseri, Prunus laurocerasus L. and Viburnum tinus L. Automated dripirrigation based on either substrate water status (SW) or calculated crop evapotranspiration (ET; MODEL)was compared with “typical” timer-controlled irrigation (TIMER). In TIMER treatment, containers wereirrigated based on grower management. In SW treatment, irrigation was controlled either by a water-filled tensiometer (2007) or by a dielectric soil moisture sensor (2008–2010) placed in one pot with aPrunus plant, the species with intermediate water need as found in preliminary work. In MODEL treat-ment, irrigation was controlled on the basis of the species with the greatest ET. Crop ET was calculatedmultiplying reference ET (ET0) by a species-specific crop coefficient (KC), which in turn was estimated fromplant height. In all treatments, pre-irrigation substrate water deficit was lower than the plant availablewater in the container. Compared with TIMER treatment, SW and MODEL irrigation scheduling reducedconsiderably both water use (-21% to -40%) and nutrient emission (-39% to -74%) with no significanteffect on plant growth and quality. Water saving resulted from a reduction of irrigation frequency andleaching fraction (water leached/water applied). Wireless sensor network technology and near/remotemonitoring techniques can facilitate the application of plant-driven irrigation scheduling in commercialnurseries, where generally hundreds of plant taxa are cultivated in many independent irrigation sectors.
Zonder transport staat alles stil, ook in weefselkweek : oplossing ligt in bevordering verdamping
Klerk, G.J.M. de; Kierkels, T. ; Heuvelink, E. - \ 2013
Onder Glas 10 (2013)9. - p. 18 - 19.
glastuinbouw - plantenvermeerdering - weefselkweek - kweektechnieken - in vitro kweek - transpiratie - tca - plantenontwikkeling - greenhouse horticulture - propagation - tissue culture - culture techniques - in vitro culture - transpiration - tca - plant development
Nuchter beschouwd is het opmerkelijk dat planten in staat zijn in kweekbuizen te groeien. Het is daarom niet verwonderlijk dat zich regelmatig problemen voordoen. De oplossing daarvan is van groot belang voor de praktijk. Dat maakt snelle vermeerdering door weefselkweek voor veel meer gewassen toegankelijk.
A coupled agronomic-economic model to consider allocation of brackish irrigation water
Gal, A. Ben; Weikard, H.P. ; Shah, S.H.H. ; Zee, S.E.A.T.M. van der - \ 2013
Water Resources Research 49 (2013)5. - ISSN 0043-1397 - p. 2861 - 2871.
agrohydrologie - irrigatie - verzilting - semi-aride klimaat - gewasproductie - modellen - agrohydrology - irrigation - salinization - semiarid climate - crop production - models - river-basin - salinity - transpiration - agriculture - stress - state
 In arid and semiarid regions, irrigation water is scarce and often contains high concentrations of salts. To reduce negative effects on crop yields, the irrigated amounts must include water for leaching and therefore exceed evapotranspiration. The leachate (drainage) water returns to water sources such as rivers or groundwater aquifers and increases their level of salinity and the leaching requirement for irrigation water of any sequential user. We develop a conceptual sequential (upstream-downstream) model of irrigation that predicts crop yields and water consumption and tracks the water flow and level of salinity along a river dependent on irrigation management decisions. The model incorporates an agro-physical model of plant response to environmental conditions including feedbacks. For a system with limited water resources, the model examines the impacts of water scarcity, salinity and technically inefficient application on yields for specific crop, soil, and climate conditions. Moving beyond the formulation of a conceptual frame, we apply the model to the irrigation of Capsicum annum on Arava Sandy Loam soil. We show for this case how water application could be distributed between upstream and downstream plots or farms. We identify those situations where it is beneficial to trade water from upstream to downstream farms (assuming that the upstream farm holds the water rights). We find that water trade will improve efficiency except when loss levels are low. We compute the marginal value of water, i.e., the price water would command on a market, for different levels of water scarcity, salinity and levels of water loss
Simultaneous assimilation of satellite and eddy covariance data for improving terrestrial water and carbon simulations at a semi-arid woodland site in Botswana
Kato, T. ; Knorr, W. ; Scholtze, M. ; Veenendaal, E.M. ; Kaminski, T. ; Kattge, J. ; Gobron, N. - \ 2013
Biogeosciences 10 (2013). - ISSN 1726-4170 - p. 789 - 802.
land-surface model - isba-a-gs - atmospheric co2 - soil-moisture - exchange - photosynthesis - transpiration - uncertainties - variability - biosphere
Terrestrial productivity in semi-arid woodlands is strongly susceptible to changes in precipitation, and semi-arid woodlands constitute an important element of the global water and carbon cycles. Here, we use the Carbon Cycle Data Assimilation System (CCDAS) to investigate the key parameters controlling ecological and hydrological activities for a semi-arid savanna woodland site in Maun, Botswana. Twenty-four eco-hydrological process parameters of a terrestrial ecosystem model are optimized against two data streams separately and simultaneously: daily averaged latent heat flux (LHF) derived from eddy covariance measurements, and decadal fraction of absorbed photosynthetically active radiation (FAPAR) derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Assimilation of both data streams LHF and FAPAR for the years 2000 and 2001 leads to improved agreement between measured and simulated quantities not only for LHF and FAPAR, but also for photosynthetic CO2 uptake. The mean uncertainty reduction (relative to the prior) over all parameters is 14.9% for the simultaneous assimilation of LHF and FAPAR, 8.5% for assimilating LHF only, and 6.1% for assimilating FAPAR only. The set of parameters with the highest uncertainty reduction is similar between assimilating only FAPAR or only LHF. The highest uncertainty reduction for all three cases is found for a parameter quantifying maximum plant-available soil moisture. This indicates that not only LHF but also satellite-derived FAPAR data can be used to constrain and indirectly observe hydrological quantities.
Modelling of soil salinity and halophyte crop production
Vermue, E. ; Metselaar, K. ; Zee, S.E.A.T.M. van der - \ 2013
Environmental and Experimental Botany 92 (2013). - ISSN 0098-8472 - p. 186 - 196.
gewasproductie - bodemfactoren - zoute gronden - halofyten - bodemwater - verzilting - modellen - crop production - edaphic factors - saline soils - halophytes - soil water - salinization - models - salt tolerance - root water - growth - plants - irrigation - stress - extraction - simulation - wheat - transpiration
In crop modelling the soil, plant and atmosphere system is regarded as a continuum with regard to root water uptake and transpiration. Crop production, often assumed to be linearly related with transpiration, depends on several factors, including water and nutrient availability and salinity. The effect of crop production factors on crop production is frequently incorporated in crop models using empirical reduction functions, which summarize very complex processes. Crop modelling has mainly focused on conventional crops and specific plant types such as halophytes have received limited attention. Crop modelling of halophytes can be approached as a hierarchy of production situations, starting at the situation with most optimal conditions and progressively introducing limiting factors. We analyze crop production situations in terms of water- and salt limited production and in terms of combined stresses. We show that experimental data as such may not be the bottleneck, but that data need to be adequately processed, to provide the basis for a first analysis. Halophytic crops offer a production perspective in saline areas, but in other areas long-term use of low quality irrigation water for halophyte production can result in serious soil quality problems. An overview is given of potential problems concerning the use of (saline) irrigation water, leading to the conclusion that soil quality changes due to poor quality water should be considered in determining the areas selected for halophyte growing.
Pressure Heads and Simulated Water Uptake Patterns for a Severely Stressed Bean Crop
Durigon, A. ; Santos, M.A. dos; Lier, Q.D. van; Metselaar, K. - \ 2012
Vadose Zone Journal 11 (2012)3. - ISSN 1539-1663
root hydraulic conductivity - flux potential approach - polymer tensiometers - soil-water - wilting point - transpiration - evaporation - model - architecture
In modeling, actual crop transpiration as a function of soil hydraulic conditions is usually estimated from a water content or pressure head dependent reduction function. We compared the performance of the empirical pressure head based reduction function of Feddes (FRF) and a more physically based reduction function using matric flux potential as the main parameter (DRF), both available in the SWAP ecohydrological model. Model performance was evaluated by comparison of SWAP predictions and observed water contents and pressure head values in a field experiment with a common bean (Phaseolus vulgaris L.) crop. For >50 d, no rain occurred and the soil reached very dry conditions with pressure heads in the range -100 to -150 m. The SWAP-DRF-predicted pressure head and water content values were less sensitive to root length density distribution than those predicted by SWAP-FRF. Varying wilting pressure head did not improve predictive performance. Root water uptake distribution with time and depth simulated by SWAP showed very different patterns depending on the reduction function used. Root water uptake estimated by SWAP-FRF showed smooth transitions with time and between layers, whereas SWAP-DRF, highly sensitive to hydraulic conditions, generally predicted uptake to be concentrated at a few depths. The order of magnitude of the pressure head difference between root xylem and root surface based on SWAP-DRF-predicted uptake rates, root length density, and reported values of root conductance was the same as the order of magnitude of the limiting root water pressure head, implying the necessity to include root hydraulic resistance in the DRF.
Water, watergift, verdamping (bij chrysant)
Voogt, Wim - \ 2012
chrysanthemums - ornamental crops - cropping systems - irrigation - water requirements - transpiration - water uptake - emission - lysimeters - instruments
Postharvest water relations in cut rose cultivars with contrasting sensivity to high relative air humidity during growth
Fanourakis, D. ; Carvalho, S.M.P. ; Almeida, D.P.F. ; Kooten, O. van; Doorn, T. van der; Heuvelink, E. - \ 2012
Postharvest Biology and Technology 64 (2012)1. - ISSN 0925-5214 - p. 64 - 73.
xylem hydraulic conductivity - stomatal response - lighting period - vase life - stems - cavitation - flowers - trees - transpiration - dimensions
A constant high relative air humidity (RH) during cultivation can strongly reduce the vase life in some cut rose cultivars. We studied three contrasting cultivars in their tolerance to high RH in order to analyse in detail the water relations during postharvest and better understand this genotypic variation. Plants were grown at moderate (60%) and high (95%) RH, and cut flowers were placed in water immediately after cutting. Flowers of cv. Pink Prophyta grown at high RH did not open throughout vase life, while flower opening of cvs. Frisco and Dream was not affected by preharvest RH. Cultivation at high RH resulted in about 80% shorter vase life in Pink Prophyta, whereas in Dream and Frisco the negative effect was considerably smaller (15 and 9% shorter vase life, respectively). The shorter vase life and reduced flower opening of cut roses grown at high RH was due to a higher rate of transpiration both in the light and dark periods. It was found that the leaves of Pink Prophyta grown at high RH could partly close their stomata upon lowering of the water potential or when flower stalks were fed with abscisic acid, but stomata remained far more open than in leaves grown at moderate RH. The RH during cultivation did not affect stem hydraulic conductivity and its recovery after air emboli induction. Preventing vascular occlusion largely alleviated the high-cultivation-RH effect on vase life and flower opening, showing that the effect of high-cultivation-RH becomes only important if water uptake is limited.
Analyzing transient closed chamber effects on canopy gas exchange for optimizing flux calculation timing
Langensiepen, M. ; Kupisch, M. ; Wijk, M.T. van; Ewert, F. - \ 2012
Agricultural and Forest Meteorology 164 (2012). - ISSN 0168-1923 - p. 61 - 70.
portable chamber - h2o fluxes - sap flow - co2 - evapotranspiration - transpiration - trees - crop - temperature - forest
Transient type canopy chambers are still the only currently available practical solution for rapid screening of gas-exchange in agricultural fields. The technique has been criticized for its effect on canopy microclimate during measurement which affects the transport regime and regulation of plant gas-exchange. Field studies in which the technique has been compared against independent methods are still fragmentary. The aims of this study were to quantify the changes of the physical environment during chamber placement, to determine optimum flux measuring windows, to compare three flux-calculation procedures, and to test the performance of the method against independent measurements of sap-flow. Two wheat experiments were conducted for these purposes under German temperate climate conditions. Leaf transpiration and sap-flow remained relatively constant during the first 120 s after chamber deployment, but changed considerably afterwards. Canopy H2O fluxes could thus be inferred from concentration measurement series during this interval. A saturation function, previously not mentioned in the literature, was compared against the commonly used constant and quadratic regression methods and identified as the most suitable method for calculating vapor fluxes. The study reconfirmed that small proportional changes of CO2 concentrations during the calculation interval facilitate the application of the frequently applied quadratic regression method for calculating CO2 fluxes. Sap-flow, leaf and canopy gas-exchange were severely perturbed after chamber removal. Revisiting times of same sample locations need to be planned accordingly. The study confirms that the transient chamber technique can be applied for determining canopy gas-exchange, provided that characteristic time intervals within concentration measuring series are determined and their non-linearity tested to establish appropriate flux calculation procedures.
Estimation of leaf area for large scale phenotyping and modeling of rose genotypes
Gao, M. ; Heijden, G.W.A.M. van der; Vos, J. ; Eveleens, B.A. ; Marcelis, L.F.M. - \ 2012
Scientia Horticulturae 138 (2012). - ISSN 0304-4238 - p. 227 - 234.
co2 enrichment popface - capsicum-annuum-l - linear measurements - cell expansion - sweet-pepper - elevated co2 - transpiration - environments - temperature - cucumber
Leaf area is a major parameter in many physiological and plant modeling studies. When we want to use physiological models in plant breeding, we need to measure the leaf area for a large number of genotypes. This requires a fast and non-destructive method. In this study, we investigated whether for cut roses a statistical model of simple measurements of length and width of leaves, together with other information like relative rank and number of leaflets per leaf can provide an unbiased estimate of leaf area across many genotypes and environments. Harvestable shoots of 20 genotypes of cut roses (Rosa hybrida L.) were collected from 4 different commercially operated glasshouses in the Netherlands. Regression analysis of square root of leaf area source versus leaf length, leaf width, and leaflet number revealed several models that showed a high correlation for individual rose leaves. However, the factors genotype and environment were significant (P <0.001) indicating that there is no simple unbiased model across all genotypes and environments. Models ignoring genotypic information showed a 10% over- or underestimation of individual leaf area in at least 4 out of 20 genotypes. When genotype information was included in the model, good estimates of leaf area (R2 = 0.917, RMSE = 0.592, CV% = 6.7 and AIC = 8907) were obtained based on measurements of leaf width and leaflet number per leaf, so ignoring leaf length. This does require that the model should be calibrated for each specific genotype. For Dutch climate conditions, it was not necessary to calibrate the model per greenhouse environment, although there were considerable differences in leaf size between greenhouses. If the model was validated for total shoot leaf area, instead of individual leaves, similar results were obtained, but with higher accuracy
Leaf gas exchange in the frankincense tree (Boswellia papyrifera) of African dry woodlands
Mengistu, T. ; Sterck, F.J. ; Fetene, M. ; Tadesse, W. ; Bongers, F. - \ 2011
Tree Physiology 31 (2011)7. - ISSN 0829-318X - p. 740 - 750.
vapor-pressure deficit - water relations - stomatal conductance - forest tree - seasonal-changes - photosynthesis - traits - transpiration - australia - ethiopia
A conceptual model was tested for explaining environmental and physiological effects on leaf gas exchange in the deciduous dry tropical woodland tree Boswellia papyrifera (Del.) Hochst. For this species we aimed at (i) understanding diurnal patterns in leaf gas exchange, (ii) exploring cause–effect relationships among external environment, internal physiology and leaf gas exchange, and (iii) exploring site differences in leaf gas exchange in response to environmental variables. Diurnal courses in gas exchange, underlying physiological traits and environmental variables were measured for 90 trees on consecutive days at two contrasting areas, one at high and the other at low altitude. Assimilation was highest in the morning and slightly decreased during the day. In contrast, transpiration increased from early morning to midday, mainly in response to an increasing vapor pressure deficit (VPD) and gradual stomatal closure. The leaf water potential varied relatively little and did not influence gas exchange during the measurement period. Our results suggest that the same cause–effect relationships function at contrasting areas. However, leaves at the higher altitude had higher photosynthetic capacity, reflecting acclimation to higher light levels. Trees at both areas nevertheless achieved similar leaf assimilation rates since assimilation was down-regulated by stomatal closure due to the higher VPD at the higher altitude, while it became more light limited at the lower altitude. Gas exchange was thus limited by a high VPD or low light levels during the wet season, despite the ability of the species to acclimate to different conditions
Comparison of the root water uptake term of four simulation models
Willigen, P. de; Dam, J.C. van; Javaux, M. ; Heinen, M. - \ 2011
Wageningen : Alterra (Alterra-report 2206) - 65
bodem-plant relaties - bodemwater - transpiratie - modellen - soil plant relationships - soil water - transpiration - models
Water uptake by plant roots is an important component of the soil water balance. In this report we studied four water uptake models, of different complexity, that were all embedded in a greater model dealing with transport of water in (an unsaturated) soil. Though also some attention was paid to performance of the routines by themselves, the focus was directed to their functioning as a part of the greater models. We examined the results of two scenarios of potential transpiration and precipitation, comprising a period of 16 days. As could be expected the models yielded different results, but the differences in actual transpiration are modest due to feedback mechanisms.
On-line monitoring van transpiratie en fotosynthese: de praktijk
Bontsema, J. ; Hemming, J. ; Janssen, H.J.J. ; Meinen, E. ; Rispens, S. ; Steenhuizen, J.W. ; Visser, P.H.B. de - \ 2011
Wageningen : Wageningen UR Glastuinbouw (Rapporten GTB 1091) - 65
gasuitwisseling - fotosynthese - transpiratie - glastuinbouw - kasgewassen - gewasmonitoring - on-line - gegevensverwerking - gas exchange - photosynthesis - transpiration - greenhouse horticulture - greenhouse crops - crop monitoring - on line - data processing
WUR Glastuinbouw heeft monitoren ontwikkeld voor de on-line bepaling van de verdamping en fotosynthese. Deze monitoren zijn uitgetest bij diverse vruchtgroentetelers en slatelers. In het onderzoek is ook een nieuwe transpiratiemonitor ontwikkeld, op basis van een statische energie- en vochtbalans