Evapotranspiration Efficiency Research Articles

Benefits of a robotic chamber system for determining evapotranspiration in an erosion-affected, heterogeneous cropland

Abstract. In the light of the ongoing global climate crisis and the related increases in extreme hydrological events, it is crucial to assess ecosystem resilience and – in agricultural systems – to ensure sustainable management and food security. For this purpose, a comprehensive understanding of ecosystem water cycle budgets and spatiotemporal dynamics is indispensable. Evapotranspiration (ET) plays a pivotal role in returning up to 90 % of incoming precipitation back to the atmosphere. Here, we studied the impacts of soil types and management on an agroecosystem's seasonal cumulative ET (ETsum) and agronomic water use efficiency (WUEagro, the dry matter per unit of water used by the crop). To do so, a plot experiment with winter rye (17 September 2020 to 30 June 2021) was conducted in an eroded cropland which is located in the hilly and dry ground moraine landscape of the Uckermark region in northeastern Germany. Along the experimental plot (110 m × 16 m), two closed chambers were mounted on a robotic gantry crane system (FluxCrane as part of the AgroFlux platform) and used to determine ET. Three soil types representing the full soil erosion gradient related to the hummocky ground moraine landscape (extremely eroded: Calcaric Regosol; strongly eroded: Nudiargic Luvisol; non-eroded: Calcic Luvisol) and additional topsoil dilution (topsoil removal and subsoil admixture) were investigated (randomized block design, three replicates per treatment). Five different modeling approaches were used and compared in the light of their potential for reliable ETsum over the entire crop cultivation period and to reproduce short-term (e.g., diurnal) water flux dynamics. While machine-learning approaches such as support vector machines (SVMs) and artificial neural networks (with Bayesian regularization; ANN_BR) generally performed well during calibration, SVMs also provided a satisfactory prediction of measured ET during validation (k-fold cross-validation, k=5). We found significant differences in dry biomass (DM) and small trends in ETsum between soil types, resulting in different WUEagro. The extremely eroded Calcaric Regosol showed an up to 46 % lower ETsum and up to 54 % lower WUEagro compared to the non-eroded Calcic Luvisol. The key period contributing to 70 % of ETsum spanned the beginning of stem elongation in April to the harvest in June. However, differences in the ETsum between soil types and topsoil dilution resulted predominantly from small differences between the treatments throughout the cultivation rather than only during this short period of time.

Impacts of altitudinal ecohydrological dynamic changes on water balance under warming climate in a watershed of the Qilian Mountains, China

In alpine areas of northwest China, one of the major concerns is the rapid warming and stimulated vegetation growth consume more water and reduce available water for downstream oasis development. Investigating the response of these ecohydrological dynamics to climate change is thus crucial, but is also challenging because of tremendous variability of vegetation, hydrology, and climate in elevation and complex interactions between them. Here, we performed numerical simulations in a mountainous watershed covering a range of contrasting climatic conditions and vegetation characteristics representative of the Qilian Mountains, China. The simulations were run with a dynamic global vegetation model LPJ-WHyMe to quantify spatiotemporal changes of vegetation (e.g., species and net primary production (NPP)) and hydrological components (e.g., runoff and evapotranspiration (ET)) in recent decades (1982–2018). The simulated results were compared with those derived from MODIS and observations. Results show that the favorable climate condition for vegetation growth appears around the freezing altitude (3000–3250 m asl) where the NPP, ET, and water use efficiency (WUE = NPP/ET) exhibit a ‘humped’ peak value while runoff increases with precipitation towards higher altitudes. The warming and moistening climate and elevated CO2 since 1982 have favored vegetation growth, leading to uphill migration of the treeline and the ‘humped’ peak to higher elevation (3250–4000 m asl). The climate warming and stimulated vegetation growth consumed 83 % of the increased precipitation (34.6 mm) in the whole catchment. The greatly increased ET and thus decreased runoff were found at high elevation (above 4000 m asl) due to the reduced freezing days (up to 43 days) in the warming climate. Meanwhile, the substantially elevated WUE and moistening climate can balance the increased ET in the vegetation occupation areas below 4000 m asl, leading to increased runoff. The results indicate that despite a little increase of runoff in the recent decades, stimulated vegetation growth and climate warming could reduce water resources availability in the mountains if climate warming continues and/or climate wetting ceases in future.

An independent framework-based evapotranspiration model (IFEM) for dual-source: From field to regional scale

The triangle/trapezoid framework model (TFM) is a widely used approach for mapping regional evapotranspiration (ET) based on thermal infrared remote sensing imagery. However, the homogeneity assumption for meteorological forcing and surface properties involved in TFM contradicts the characteristics of heterogeneous regions, leading to high uncertainty at regional scale, especially under energy-limited or strong advection conditions. Therefore, this study examined the linear relationship between soil moisture availability (ΛSM), evapotranspiration efficiency (ΛET) and radiation surface temperature (Trad), and developed an Independent Framework-based dual-source ET Model (IFEM) for heterogeneous regions. By fixing two key meteorological forcing variables, air temperature (Ta) and vapor pressure deficit (VPD), and three surface characteristic parameters, aerodynamic resistance (ra), albedo (α) and the ratio of soil heat flux to net radiation (Γ), the IFEM constructs a uniform fractional vegetation cover (fc)- Trad space. In this uniform fc-Trad space, isolines of ΛSM and ΛET are aligned with those of Trad, and an independent trapezoid framework is constructed for each pixel of RS images. It avoids the systematic bias caused by the distorted trapezoid space involved in traditional TFMs. The proposed model was applied in a hydrologically semi-enclosed irrigation area, the Hetao Irrigation District, with Landsat and MODIS datasets from 2016 to 2020 to evaluate its performance at the field and region scales. Firstly, the IFEM was capable of retrieving latent heat with a mean absolute error (MAE) of 34.43 W m−2 and a mean absolute percentage error (MAPE) of 8.68%, compared with the measurements from flux towers. Secondly, the IFEM reasonably separated the soil (MAPE = 21.33%) and canopy (MAPE = 14.33%) components from ET, compared with the soil evaporation observed by micro-lysimeters and the plant transpiration calculated by sap velocity upscaling technology. Thirdly, the IFEM showed high accuracy in estimating annual total ET with a percentage error range within ±3.0%, compared against the regional water balance calculations. Overall, the IFEM demonstrated high robustness and accuracy for field-scale and regional-scale applications, validating its potential as a reliable method for mapping regional ET in heterogeneous regions.

Response of Evapotranspiration (ET) to Climate Factors and Crop Planting Structures in the Shiyang River Basin, Northwestern China

Evapotranspiration (ET) is an essential part of energy flow between the surface of the earth and the atmosphere, simultaneously involving the water, carbon, and energy cycles. It is mainly determined by climate, land use, and land cover changes. Additionally, there is still a need for quantitative characterization of the impacts of climate factors and human activities on ET and regional water resource efficiency in arid and semiarid regions. Based on Landsat-8 remote sensing imagery and land use data, the crop planting structures in the Liangzhou District of the middle reaches of the Shiyang River Basin were identified using a multiband and multi-temporal approach in this study. Subsequently, the ET of major cash crops was inverted using the three-temperature model. This research quantitatively describes the responses of wheat and corn to the climate and human activities over a two-year period. Furthermore, the impact of crop planting structures and climatic factors on ET was elucidated. The results indicate that a combination of multi-temporal green and shortwave infrared 1 bands is the optimal spectral combination to extract the planting structures. Compared to 2019, the wheat area decreased by 23.27% in 2020, while the corn area increased by 5.96%. Both crops exhibited significant spatial heterogeneity in ET during the growing season. The typical daily range of ET for wheat was 0.4–7.2 mm/day, and for corn, it was 1.5–4.0 mm/day. Among the climatic factors, temperature showed the highest correlation with ET (R = 0.80, p ≤ 0.05). Our research findings provide valuable insights for the fine identification of crop planting structures and a better understanding of the response of ET to climatic factors and planting structures.

Potential Impacts of Climate Change Using Long-Term Historical Climate Data on Evapotranspiration (ET) and Groundwater Contribution to Wheat and Cotton Crop

Assessing the potential impacts of climate change on crop evapotranspiration (ET), groundwater contribution (GWC) towards meeting ET and yield is crucial in allocating water resources particularly in the areas where shallow water-table depths (WTDs) are expanding on larger area. The impact of climate change on crop ET and yield has been evaluated in the past by indirect methods using simulation models. However, those models are lacking the function of GWC which is one of the most important parameters while determining ET at different water-table depths (WTDs) and its impact on yield. Direct methods (without simulation models) using long term historical weather data (observed data) provide more accurate results of climate change impact on ET, GWC towards meeting ET and yield at different WTDs. In this study, long-term historical weather data for the last 34 years (1987-2020) and data obtained through lysimeteric studies were analyzed to examine the trends of climatic parameters, their relationship and impact on wheat and cotton ET, GWC to ET, yield and water use efficiency (WUE). These studies were carried out during 1986-1987 and 2017-2021 periods at 1.50 m, 2.25 m, and 2.75 m WTDs in Sultanpur soil series (silt loam textured) and Miani soil series (silty clay loam textured). The mean daily temperature has increased 0.45 oC and rainfall 75.5 mm/year over a period from 1987 to 2020 which is witnessing the climate change. Wheat ET is increased, GWC contribution to ET is decreased and, yield and WUE is highest during the cropping periods of 2017-2021 as compared to 1986-1987. Climate change has decreased cotton ET and GWC towards meeting ET. It has also reduced the wheat and cotton cropping cycles by 8 days and 21 days, respectively. Higher magnitude of rainfall (during July-September) in 2019 and 2020 resulted in reducing cotton average yield of 2017-2020 compared to 1987. The study demonstrates that irrigation allocation should be increased for wheat and decreased for cotton particularly in the shallow water-table areas under Sultanpur soil type where water-table remains at 1.50 m – 2.25 m depths. Moreover, cotton crop should be cultivated by the 1st week of April, so that highest yield of cotton could be harvested before onset of monsoon.

Biostimulants for Sustainable Management of Sport Turfgrass.

Research on the efficacy of innovative, ecofriendly biostimulants in sport turf management is scarce, with less information available from open-field experiments, and even less pertaining to thatch control-related problems. The objective was to investigate the open-field effectiveness of a commercial product, EM-1, and two newly developed products, ExpA and ExpB, in improving both rhizosphere and turfgrass, Agrostis stoloniferous L., characteristics on a golf green. ExpA and ExpB, identical in microbial composition, were equally effective in significantly increasing chlorophyll synthesis and visual turf quality, as well as in resistance to tearing out, compared to the untreated control 56 days after treatment (DAT). EM-1 showed intermediate trends between the control and novel biostimulants. The inclusion of humic acids and mycorrhizal fungi to the microbial composition in ExpB significantly improved some rhizosphere properties 56 DAT relative to the control. Results on ExpB evidenced a significant decrease in the thatch layer thickness and fresh leaf weight, associated with a significant increase in the humus thickness, organic matter decomposition and evapotranspiration efficiency. An increased dry leaf biomass was also shown. ExpA and EM-1 showed either marginal or intermediate improvements relative to the control. ExpB represents a promising alternative to alleviate negative environmental impacts associated with turf maintenance-related activities.

The Simulation and Subseasonal Forecasting of Hydrological Variables: Insights from a Simple Water Balance Model

Abstract Past work has shown that a land surface model’s (LSM) implicit (not explicitly coded) relationships between soil moisture and both evapotranspiration (ET) and runoff largely determine the LSM’s hydrological behavior. Here we estimate the relationships that appear to be operating in the real world and compare them to those of the LSM component of a state-of-the-art Earth system model (ESM). The two sets of relationships are determined by calibrating them within a simple water balance model (WBM): once using stream gauge observations from small, unregulated rivers over the eastern half of the United States, and once using the runoffs generated by the LSM as part of a state-of-the-art atmospheric reanalysis. Hydrological simulations and subseasonal hydrological forecasts performed with the two calibrated versions of the WBM provide two key results. First, the version calibrated to the LSM-generated runoffs does successfully reproduce, to first order, the hydrological behavior of the full LSM within its ESM environment. Second, of the two WBM versions, the one calibrated to the observations reproduces more accurately a broad collection of fully independent streamflow observations as well as a similarly broad collection of in situ soil moisture measurements. Taken together, the two results suggest that the observations-calibrated ET and runoff efficiency functions do successfully represent, at least to some degree, soil moisture controls over hydrological variability in nature and can serve as potentially useful targets for further LSM development. Significance Statement For all their complexity, and for all the work that underlies their development, the land surface model components of Earth system models may be suboptimal in fundamental yet unstudied ways. Here we estimate how the joint control of soil moisture over evapotranspiration and runoff processes in nature differs from that built implicitly into a state-of-the-art land model. Validation exercises demonstrate how this difference appears to lead to reduced accuracy in the land model’s simulation and forecasting of such hydrological variables as streamflow and soil moisture. Our results indicate that the relationships estimated for nature could serve as a potentially valuable target for further land model development.

The Influence of Natural and Anthropogenic Forcing on Water and Energy Balance and on Photosynthesis

Land surface processes are rarely studied in Detection and Attribution Model Inter-comparison Project (DAMIP) experiments on climate change. We analyzed a CMIP6 DAMIP historical experiment by using multi-linear regression (MLRM) and analysis of variance methods. We focused on energy and water budgets, including gross primary productivity (GPP). In MLRM, we estimated each forcing’s contribution and identified the role of natural forcing, which is usually ignored. Contributions of the forcing factors varied by region, and high-ranked variables such as net radiation could receive multiple influences. Greenhouse gases (GHG) accelerated energy and water cycles over the global land surface, including evapotranspiration, runoff, GPP, and water-use efficiency. Aerosol (AER) forcing displayed the opposite characteristics, and natural forcing accounted for short-term changes. A long-term analysis of total soil moisture and water budget indicated that as the AER increases, the available water on the global land increases continuously. In the recent past, an increase in net radiation (i.e., a lowered AER) reduced surface moisture and hastened surface water cycle (GHG effect). The results imply that aerosol emission and its counterbalance to GHG are essential to most land surface processes. The exception to this is GPP, which was overdominated by GHG effects.

Investigating the Rainforest Canopy Phenology Variation and Productivity Responses to Drought by Using Digital Camera Images

Among the natural disturbances, drought may cause significant change in forest ecosystems by shifting phenology and productivity. Digital cameras have been used in phenological observations for their high accuracy and the colour index values (digital-number of red, green and blue) derived from long-term continuous digital camera imagery are useful as proxies for investigating a forest canopy’s response to drought. Here, we examine the interaction between colour indices (the strength of red (Sred), the strength of green (Sgreen), green excess index (GEI)), productivity (gross primary productivity (GPP)) and drought (standardised precipitation evapotranspiration index (SPEI)) and climatic factors. We use forest canopy images derived from a digital camera and flux tower-based productivity from 2010 to 2016 to show the rainforest’s responses to drought in phenology and productivity. The SPEI indicated the occurrence of drought condition in 2014. The lowest values of the SPEI (-0.403 mmday-1), and total precipitation (1062 mmyr-1), and the highest values of average air temperature (21.3 C)”, need to be changed like that “the highest values of average air temperature (21.3°C)”, to put Degree symbol between the 21.3 and C, potential evapotranspiration (3.31 mmday-1) and rain use efficiency (2.26 gCL-1) were found in 2014. Leaf color variation period (CVP) become longer with an advance in foliage green-up after drought. The peak GEI values were found at the end of the CVPs. The GPP and the Sgreen had positive and the Sred had negative relationship with drought index. The GPP dropped during the drought and bounced back after the drought due to a longer leaf CVP. The Sgreen and GEI were significantly (p<0.05) related to GPP during the drought. During the CVP of the drought, the Sgreen and GEI were significantly correlated (p<0.05) with total P, PET and average Ta, meanwhile, there was only a significant relationship (p<0.05) between the GPP with PET and avg Ta. Among the variables, the GPP was more significant (p < 0.001) with avg Ta. There was also a relationship between the colour indices and GPP with climatic factors on a yearly time series. Our results indicate an understanding of the phenology and productivity response of rainforests to drought, which might be useful for ecologists when predicting the effects of future climatic change on rainforest phenology and productivity.

Emerging satellite observations for diurnal cycling of ecosystem processes.

Diurnal cycling of plant carbon uptake and water use, and their responses to water and heat stresses, provide direct insight into assessing ecosystem productivity, agricultural production and management practices, carbon and water cycles, and feedbacks to the climate. Temperature, light, atmospheric water demand, soil moisture and leaf water potential vary over the course of the day, leading to diurnal variations in stomatal conductance, photosynthesis and transpiration. Earth observations from polar-orbiting satellites are incapable of studying these diurnal variations. Here, we review the emerging satellite observations that have the potential for studying how plant functioning and ecosystem processes vary over the course of the diurnal cycle. The recently launched ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) and Orbiting Carbon Observatory-3 (OCO-3) provide land surface temperature, evapotranspiration (ET), gross primary production (GPP) and solar-induced chlorophyll fluorescence data at different times of day. New generation operational geostationary satellites such as Himawari-8 and the GOES-R series can provide continuous, high-frequency data of land surface temperature, solar radiation, GPP and ET. Future satellite missions such as GeoCarb, TEMPO and Sentinel-4 are also planned to have diurnal sampling capability of solar-induced chlorophyll fluorescence. We explore the unprecedented opportunities for characterizing and understanding how GPP, ET and water use efficiency vary over the course of the day in response to temperature and water stresses, and management practices. We also envision that these emerging observations will revolutionize studies of plant functioning and ecosystem processes in the context of climate change and that these observations and findings can inform agricultural and forest management and lead to improvements in Earth system models and climate projections.

Impacts of heterogeneous CO2 on water and carbon fluxes across the global land surface

ABSTRACT Over the recent decades, the increase of atmospheric carbon dioxide (CO2) concentration has caused large effects on the earth system. However, few studies have paid attention to the effects of heterogeneity of CO2 on the biosphere and the hydrosphere. Using a coupled diagnostic biophysical model (PML-V2) and comparing three heterogeneous CO2 datasets (GOSAT, CMIP6 and CarbonTracker) against a baseline homogeneous data (ESRL), this study investigated the effects of heterogeneous CO2 on gross primary production (GPP), actual evapotranspiration (ET) and water use efficiency (WUE) across the global. The results show that among the three heterogeneity CO2, CarbonTracker produced the highest CO2 concentration and showed the largest difference in ET (−6% to 2%), GPP (−2% to 5%) and WUE (4% to 11%) compared to those from the baseline. The most effects of the CO2 heterogeneity occurred in summer. Russia was identified as a vulnerable region with prominent decrease in GPP and an increase in ET due to CO2 heterogeneity. An obvious increase in GPP and a decrease in ET appeared in the Amazon rainforest, the Congo rainforest, and eastern Asia. On global scale, the effects of the CO2 heterogeneity on ET/GPP/WUE were not significant.

Water Saving Strategies in Mediterranean Areas

Mediterranean climate is associated with summer water scarcity and, consequently, with a general susceptibility to erosion, degradation, and desertification. Thin soils, with low water storage capacity, develop in slopes where all main factors for erosion can at its worst. The need for wise irrigation is crucial for human activities. Plant adaptation includes stomatal closure as a strategy to reduce water use improving plant survival, while reducing photosynthesis and control of leaf temperature. Other strategies at leaf level include reducing radiation interception and increasing sensible heat diffusion, for instance by developing small leaf size, high leaf reflectance and adapted positions towards sunlight. Another order of survival strategies to cope with summer water scarcity concerns the increase of water uptake at root level and hydraulic lift or water redistribution. Finally, irrigation efficiency and evapotranspiration efficiency also should be optimised. Several experiments were performed on olive orchards under the harsh summer conditions of South East Portugal. The results were consistent in several aspects related to water uptake: colonization of the inter-row space, qualitative and quantitative importance of hydraulic redistribution and water balance estimates from soil water content versus plant water use measured by a micrometeorological technique. In orchards under deficit irrigation, analysed in same study, water use was also quantified and parameters of stress coefficients functions were critically analysed.

Effects of Rice Husk Compost on Some Soil Properties, Water Use Efficiency and Tomato (Solanum lycopersicum L.) Yield under Greenhouse and Field Conditions

ABSTRACT The effect of rice husk compost (RHC) on some soil properties, evapotranspiration (ETa), yield (Y) and water use efficiency (WUE) of tomato (Solanum lycopersicum L.) plant under the field and greenhouse conditions was investigated. In the experiments carried out at the experimental field and the greenhouse of Agricultural Faculty in Ondokuz Mayıs University, Samsun, Turkey. The RHC was applied to surface soil (0–20 cm) at 0%, 3%, 6% and 9% (0 – 6 – 12 – 18 Mg ha−1) doses with three replications according to the randomized plots experimental design. RHC application generally improved the soil quality parameters according to the control treatment during the experiment carried out with growing tomato plant in the field and greenhouse conditions. RHC treatments increased electrical conductivity, field capacity and permanent wilting point, available water content with increasing soil organic matter content, reduced soil pH and bulk density (Db) over the control treatment. Db values of the soils in the field and greenhouse decreased according to the control treatment with 3% > 6% > 9% doses of RHC. Field capacity, permanent wilting point and available water capacity (AWC) values of the soils generally increased according to the control with 9% > 6% > 3% doses of RHC application. While 92-day ETa values in field ranged from 426 mm in control to 314 mm in 9% RHC application, 112-day ETa values in greenhouse ranged from 547 mm in control to 375 mm in 3% RHC application. According to the control treatment, the highest reduction in ETa values was 26.3% with 9% RHC in the field and 31.5% with 3% RHC application in the greenhouse. Soil organic matter values of the soils had significant correlations with Db (−0.868**), AWC (0.667*), yield (0.593*) and WUE (0.722**) in the greenhouse conditions and with Db (−0.628**), AWC (0.427*), yield (0.468*) in the field conditions. While there were negative relationships between WUE and ETa in field (−0.818**) and greenhouse (−0.365) conditions, the positive relationships between yield and WUE were determined in field (0.280) and greenhouse (0.887**). When comparing the control treatments, RHC applications in field and greenhouse conditions helped to water saving as 118 mm (1181 ton ha−1) and 216 mm (2160 ton ha−1), respectively. According to the results, the applications of 6% RHC in field and 9% RHC in greenhouse conditions were suggested to reduce ETa values, and to improve the soil quality parameters, WUE and tomato yield.

WATER STRESS ON DIFFERENT GROWING STAGES FOR QUINOA (Chenopodium quinoa willd) AND ITS INFLEUNCE ON WATER REQUIRIMENTS AND YIELD

A factorial experiment was conducted within split-split plot design with three replicates. Four genotypes seeds (Regalona, Q-37, KVL-SR2, and Q21) were planted in the sub plots while six water treatments distributed in the main plots. They were ordinary river irrigation (S0), stress at emergence (S1), branching (S2), at ear formation (S3), at flowering (S4), and at maturity (S5). Irrigation water was applied in the normal irrigation when 50-60% of the available water was depleted and one irrigation was omitted from the water stress treatments. Reference and actual evapotranspiration, pan evaporation, yield, crop coefficient, and water use efficiency were calculated. Mean irrigation requirement for the four genotypes based on irrigation scheduling was 230.8 mm, decreased by 14 and 17% under stress conditions of the drought tolerant stages. Grain yield ranged between 3.1 and 5 Mg ha-1 for water stress treatments compared to 5.6 and 4.2 mg. ha-1 for normal irrigation treatments. Genotype Q21 gave the highest yield and differed significantly from others. Field water use efficiency ranged between 1.6 to 1.1 kg m-3 and crop water use efficiency 1.38 to 2.22 kg m-3. KVL-SR2 and Q21 showed the highest efficiency (1.87 kg m-3). Results indicated that the stage of ear formation and flowering are the most tolerant to water stress. On the other hand, the branching, and maturity were critical stages with high reduction in yield under stress conditions.

Floating Azolla Cover Influences Evapotranspiration from Flooded Water Surfaces

Floating vegetation is a common sight in flooded environments and plays a key role in regulating the global water balance, particularly through evapotranspiration (ET). Azolla is a dominant floating fern in lowland paddy fields, and its biological characteristics contribute mainly to nitrogen (N) fertilization. Here, to determine the potential of the rapidly growing Azolla as an alternative N source and its role in water conservation in flooded paddy ecosystems, we investigated its productivity and the resulting reduction in ET in two separate pot experiments. Azolla cover significantly decreased ET losses under high and low flooding depths compared with open water surfaces and green polyester covered mats (analogous to plant cover). Additionally, Azolla showed significantly higher biomass productivity, carbon assimilation, and N accumulation in presence of phosphorous (P) than in its absence under both high and low flooding depths. Overall, our results indicate that the efficiency of Azolla as an N alternative in agricultural ecosystems can be realized in presence of P, regardless of the flooding water depth. Additionally, we predict a relative reduction in the ET efficiency of Azolla in rice paddies. Field studies are, however, necessary to confirm these findings.

The role of phosphorus in growing tomatoes in near water-saturated soil

High-yielding, waterlogged cultivations with considerable nitrogen input are widely practiced in Kyushu Island, Japan. Our objective was to determine the role of available phosphorus in relation to nitrogen and soil microorganisms on tomato growth in such systems. Tomato seedlings were grown in a pasteurized soil with ample KNO3 in addition to different amounts of sodium or potassium phosphates to assess effects of phosphorus on growth enhancement and water-use efficiency in the seedlings grown with copious soil water (>－0.7 kPa). Both monobasic and dibasic phosphates applied at 40 mM to near-saturated soil markedly promoted seedling growth when fertilized with 120 mM KNO3 or NH4Cl, but not in the soil without nitrogen. The final concentration of NO3－ near the soil surface was maximized in the nitrated soil with no added PO43－ but declined significantly when fertilized with any phosphates except Na2HPO4. No significant accumulation of NO3－ was detected in the water-saturated bottom soils regardless of soil fertilization with any plant minerals. Increased seedling growth was accompanied by lower dry root/shoot ratios and marked increases in evapotranspiration efficiency. Such positive effects of PO43－ were greater with NO3－ than NH4＋ but diminished with increased concentrations of Na＋ up to 160 mM. Nonetheless, growth promotions by ample NO3－ with PO43－ were nearly negated in the non-pasteurized soil. Apparently, the activities of indigenous soil microbes were more significant than soil nitrogen and phosphorus in limiting the growth potential of tomato plants in near-saturated soils.

Biochar e esterco bovino aumentam a eficiência no uso de água da alface

O biochar vem sendo recomendado para melhorar propriedades físicas, químicas e biológicas do solo e a produtividade das culturas. Assim, o objetivo do presente trabalho foi avaliar os efeitos da aplicação de biochar e esterco bovino na produtividade, evapotranspiração (ET) e eficiência no uso de água (EUA) da alface. Um experimento em casa de vegetação foi realizado utilizando-se dois tipos de biochar e esterco bovino, no delineamento experimental inteiramente casualizado, com três repetições. Os tratamentos foram quatro tipos de adubação: esterco+biochar de borra de café (E+BBC); esterco+biochar de casca de café (E+BCC); biochar de borra de café (BBC) e biochar de casca de café (BCC). Foram avaliadas a biomassa fresca (BF), o número de folhas (NF), a ET e a EUA da alface. Verificou-se que o tratamento E+BBC proporcionou maior BF. Não se verificou efeito dos tratamentos no NF da alface. Maiores perdas de água (ET) foram observadas nos tratamentos que tinham biochar de borra de café (BBC e E+BBC). Os tratamentos com esterco, independentemente do tipo de biochar, foram os que apresentaram as maiores EUA. Recomenda-se o uso de biochar mais esterco bovino para reduzir a ET e aumentar a produtividade e EUA da alface.

Community carbon and water exchange responses to warming and precipitation enhancement in sandy grassland along a restoration gradient.

Temperature increasing and precipitation alteration are predicted to occur in arid and semiarid lands; however, the response mechanism of carbon and water exchange at community level is still unclear in semiarid sandy land. We investigated the responses of carbon and water exchanges to warming and precipitation enhancement along a sand dune restoration gradient: mobile sand dunes (MD), semifixed sand dunes (SFD), and fixed sand dunes (FD). The average net ecosystem productivity (NEP) and evapotranspiration (ET) between May and August increased by 98% and 59%, respectively, from MD to SFD, while they had no significant differences between FD and the other two habitats. Warming inhibited ecosystem NEP, ET, and water use efficiency (WUE) by 69%, 49% (p < .001), and 80%, respectively, in SFD, while it nearly had no significant effects in MD and FD. However, precipitation addition by 30% nearly had no significant effects on community NEP, ET, and WUE, except for warming treatment in FD. In general, precipitation addition of 30% may still not be enough to prevent drought stress for growth of plants, due to with low water holding capacity and high evaporation rates in sandy land. Temperature increase magnified drought stress as it increased evapotranspiration rates especially in summer. In addition, community NEP, ET, and WUE were usually influenced by interactions between habitats and temperature, as well as the interactions among habitats, temperature, and precipitation. Species differences in each habitat along the restoration gradient may alter climate sensitivity of sandy land. These results will support in understanding and the prediction of the impacts of warming and precipitation change in semiarid sandy grassland.

Drought-induced change in yield capacity of ten wheat cultivars in relation to their vegetative characteristics at heading stage.

Ten wheat (Triticum aestivum L.) cultivars were tested in a semi-field experiment for drought response in terms of their flag leaf vigor, whole shoot growth and ultimate yield capacity. At booting stage, 25% of field capacity was held for 3weeks, then the plants were normally irrigated. Based on split plot analysis of the pooled data, the order in which the source of variation could affect the estimated traits was watering level, then cultivar and finally the combination of both. At p ≤ 0.05, significant positive linear correlation was recorded between the drought-induced change in grain total carbohydrate content and leaf total carbohydrate content, between biological yield and each of water use efficiency for biomass and evapotranspiration efficiency as well as between economic yield and each of leaf catalase activity, water use efficiency for grain and hundred kernel mass. On contrary, significant negative correlation was recorded between the drought-induced change in shoot evapotranspiration rate and each of leaf proline content and shoot water content. Based on the drought-induced change in the estimated vegetative and yield traits, cluster analysis could sequester the concerned cultivars into drought-tolerant, moderate and sensitive ones; with Sids 13 being the most drought-tolerant cultivar as well as Shandaweel 1 and Giza 168 as the most drought-sensitive ones.

Observing the Whole-Canopy Short-Term Dynamic Response to Natural Step Changes in Incident Light: Characteristics of Tropical and Temperate Forests

We examine the physical and biological responses of forest canopies to step changes in light caused by passing low cumulus clouds that intermittently block the direct solar beam. Using data obtained at a tropical rainforest and at a midlatitude deciduous forest, we estimate the course of sensible heat flux, net ecosystem exchange, evapotranspiration, and water-use efficiency in response to the rapid changes in the incident radiative flux. To describe these fluxes during the interval over which the effects of stomatal time delays can be most influential, eddy fluxes are estimated over minute or shorter intervals by invoking a conditional-sampling procedure based on forming a Reynolds-average ensemble. The most important differences between the two forests’ physical responses are in the thermal balances and heat-flux time response constants. During the initial period after the light transition the only mean variables that show appreciable changes are the blackbody and air temperatures, the other scalars being little affected. We find that a distinct transient thermal internal boundary layer appears ≈ 20 m thick above the temperate deciduous forest and ≈ 45 m thick above the tropical rainforest. At each forest, the effective thickness of the inferred thermal outer-canopy ‘big leaf’ is about 1 mm. Twenty minutes after the abrupt change in incident light, ensemble eddy-flux estimates approach those found using conventional time averaging, confirming the validity of the ensemble approach. Previously unrecognized transient maxima in net ecosystem exchange and evapotranspiration are evident 5–10 min following the shadow-to-light transition, longer than the average light interval between shadows observed on partly-cloudy days in each case. Short-term variations in sensible heat flux, net ecosystem exchange, and evapotranspiration approximate an exponential adjustment, implying that first-order time-dependent single-leaf models are adequate to describe whole-canopy processes in these cases, providing an experimental method for determining whole-canopy bulk stomatal time constants. During the sunlit interval (direct and diffuse radiative fluxes combined) net ecosystem exchange is enhanced, while under cloud shadow (only diffuse radiative flux) water-use efficiency increases. This light and shadow alternation provides a mechanism describing the observed enhanced net ecosystem exchange and water-use efficiency under certain types of partly-cloudy sky. We apply empirical flux-response curves to an idealized case of radiative flux varying in a regular on–off light and shadow pattern. For this case, an analytical solution for mean net ecosystem exchange flux as a function of diffuse-radiation fraction yields results that strongly resemble previous findings based on conventional time-averaged fluxes. Our analysis and modelling indicates that a well-known correlation between diffuse radiative flux and enhanced net ecosystem exchange and water-use efficiency on cloudy days is in many cases not causal, but rather to be a consequence of time averaging over light-and-shadow intervals. By linking processes associated with photosynthesis in fluctuating light at the leaf scale to the canopy scale, our efforts facilitate the scaling-up of leaf responses to the ecosystem scale.