Vegetation Water Use Research Articles

Responses of Water Use Efficiency to climate change in evapotranspiration and transpiration ecosystems

Climate change intensifies the fluctuation of arid/semi-arid evaporation and rearranges vegetation distribution patterns. Therefore, popular studies were proceeded, such as the responses of ecosystem’s water use efficiency(EWUE) and vegetation water use efficiency(VWUE) to precipitation and temperature fluctuations, which are essential to understand the relationship between carbon and water in ecosystems. Herein, this study defines two types of EWUE (GPP/ET; ET: evapotranspiration) and VWUE(GPP/T; T: transpiration to response to climate change, through which the spatial and temporal were revealed. We found that the decreasing rate of VWUE is greater than EWUE in winter (December). The interannual fluctuation(2000–2014 year) VWUE showed a decreasing trend (slope = -0.001). However, the EWUE showed an increasing trend (slope = 0.0014). There is a significant spatial pattern of differences between the stability of EWUE and VWUE. Precipitation negatively affects WUE (EWUE:79.4 %; VWUE:63.6 %), and temperature significantly affects WUE (EWUE:87.9 %; VWUE:87.7 %). The negative contribution of temperature and precipitation to VWUE is 81.73 % and 53.60 %, and the positive contribution is 12.27 % and 46.40 %, respectively. The negative contribution of temperature and precipitation to EWUE is 87.87 % and 66.55 %, and the positive contribution is 12.13 % and 33.45 %, respectively. The negative contribution rate indicates that climate factors have a promoting effect on WUE. The greater the negative contribution rate, the more pronounced the promoting effect. Through sensitivity and contribution rate methods analysis, the results of the two methods are consistent: precipitation attenuates WUE and temperature promotes WUE. This study enhanced our understanding of the climate response of ecosystems and vegetation canopy of carbon water fluxes.

Spatial-temporal variation of vegetation water use efficiency and its relationship with climate factors over the Qinghai-Tibet Plateau, China

Water use efficiency (WUE) is an effective index to study the coupling of land carbon and water cycle. The Qinghai-Tibet Plateau is the most important ecological security barrier in China. Understanding the characteristics and mechanism of WUE is important for the carbon cycle and water resources rational utilization in the plateau. Based on MODIS data of gross primary productivity (GPP) and evapotranspiration (ET), we analyzed the spatial-temporal variations of WUE over the Qinghai-Tibet Plateau and the effects of climate factors. The results showed that WUE in the Qinghai-Tibet Plateau had an upward trend under the combined action of GPP and ET during 2001-2020. The southeast and northeast of the Plateau had the highest WUE value, while the central part had the lowest WUE value. WUE of grassland, marsh and alpine vegetation showed an increasing trend, while that of shrub land, broadleaved forest and coniferous forest showed a decreasing trend. There was a significant positive correlation between WUE and annual air temperature, and the sensitivity increased with the increases of air temperature. The relationship between WUE and annual precipitation was non-linear. When precipitation was less than 700 mm, the sensitivity of WUE to precipitation decreased with the increases of precipitation. When precipitation was more than 700 mm, the sensitivity of precipitation increased with the increases of precipitation. However, WUE was negatively correlated with precipitation in more than 75% of regions, and was affected by precipitation in a larger area. In the future, warm and humid climate would lead to a decrease in WUE.

Remote sensing of water use efficiency in Southwest China's karst area.

As the largest contiguous karst area in China, the southwestern karst area is a typical ecologically fragile area affecting local vegetation dynamics. Ecosystem water use efficiency (WUE) is an important factor reflecting the ability of vegetation to produce organic matter with a limited water supply. Therefore, determining the WUE variation trends in this ecologically fragile region is important. In this paper, we used MODIS remote sensing datasets, meteorological data, and land cover data to analyze the spatiotemporal changes in vegetation water use efficiency in the southwestern karst region from 2001 to 2017. We also further quantitatively analyzed the effects of climate change and human activities on the spatial and temporal patterns of vegetation WUE in the study area. The main conclusions were as follows. (1) From 2001 to 2017, in terms of temporal characteristics, the interannual variation in WUE fluctuated greatly, ranging from 1.33 to 1.51g C kg-1 H2O, with a multiyear average of 1.43g C kg-1 H2O and an average rate of change of - 0.0046g C kg-1 H2O year-1. In terms of spatial characteristics, areas with a higher WUE were concentrated in central Sichuan and northeastern Yunnan. (2) The annual average WUE of each vegetation type decreased in the following order: evergreen coniferous forest > evergreen broad-leaved forest > mixed forest > deciduous broad-leaved forest > cultivated land > deciduous coniferous forest > grassland > cultivated land and natural vegetation > shrub forest. (3) The vegetation WUE of 70.66% in this area was positively correlated with temperature. Additionally, 79.68% of the vegetation WUE was negatively correlated with precipitation. The relative contribution rates of climate change and human activities to the change trend in WUE were 15% and 85%, respectively. Compared with WUE results in other studies, the WUE of different karst landform areas obtained in this study was quite different, indicating that the geological and landform features of the karst area are complex. Our study provides scientific support for local vegetation restoration and protection policies and promotes the understanding of the principle of the carbon-water cycle in karst areas.

Deficit irrigation effects on five pomegranate cultivars water use efficiency and biochemical parameters

The purpose of this study was to compare the effects of two irrigation levels [100 percent of field capacity (FC) (control)] and 30 percent FC (deficit irrigation) on vegetative growth, biochemical status, and water use efficiency of five pomegranate cultivars (Wonderful, Manfalouty, Acco, Assuity and 116) over two seasons in 2019 and 2020. The results showed that deficit irrigation reduced the dry weight of the shoots and roots, as well as the chlorophyll content of the leaves, in all the pomegranate cultivars. Meanwhile, under stress, proline content, total soluble sugars, total phenols, and peroxidase activity all increased significantly. The Manfalouty cultivar had the highest shoot and root dry weights, as well as the highest water use efficiency, proline content, and total phenols. Furthermore, when compared to other cultivars, the Wonderful cultivar had the highest chlorophyll content during both seasons. In comparison to the other cultivars studied, the Wonderful cultivar showed the limited or no significant increase in peroxidase activity. This could be due to a genotype’s variable peroxidase activity potential in pomegranate cultivars under water stress. The obtained results may indicate that Manfalouty and Wonderful cultivars are more tolerant of deficit irrigation than the other cultivars studied.

Effect of afforestation on soil water dynamics and water uptake under different rainfall types on the Loess hillslope

Knowledge on water uptake is crucial for understanding water transport processes of the soil–vegetation-atmosphere continuum and plant survival strategy in the Loess Plateau. Even though vegetation water sources have been widely explored using hydrogen and oxygen isotopes, the quantification of vegetation water sources after returning farmland to forestland/grassland under different rainfall types, especially extreme rainstorm event, still remains challenging due to difficulties in field monitoring. This study collected precipitation, soil water from 0 to 100 cm soil layer and xylem/stem water and measured their hydrogen (δD) and oxygen (δ18O) isotope compositions in Robinia pseudoacacia forestland (PL), natural forestland (NF) and natural grassland (NG) under four typical rainfall events. The results indicated that among three vegetation types, soil water content was lowest in PL during each rainfall event. In addition, the sensitivity of water-use strategies to precipitation was affected by rainfall types, dry/wet periods and vegetation types. When antecedent soil water was deficit, vegetation water use was more sensitive to precipitation, and the primary water sources after rainfall transferred from deep soil to upper soil. However, when the antecedent soil water was sufficient, water uptake after rainfall tended to be more homogeneous in different soil layers. Among three vegetation types, Robinia pseudoacacia was more sensitive to precipitation. During the extreme rainstorm event II, in PL, the primary water source shifted from the 80–100 cm soil water before rainfall (88.7%) to the 0–10 cm soil water at 1 day after rainfall (64.3%) and the 0–20 cm soil water at 7 day after rainfall (82.8%). Thus, Robinia pseudoacacia can adapt to the environment by switching water-use strategy. The finding can provide a guidance for vegetation rehabilitation in the Loess Plateau.

Browsing herbivores improve the state and functioning of savannas: A model assessment of alternative land-use strategies.

Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle‐dominated land use to one dominated by comparatively specialized browsers and usually native herbivores. However, the consequences for ecosystem properties and processes remain largely unclear. We used the ecohydrological, spatially explicit model EcoHyD to assess the impacts of two contrasting, herbivore land‐use strategies on a Namibian savanna: grazer‐ versus browser‐dominated herbivore communities. We varied the densities of grazers and browsers and determined the resulting composition and diversity of the plant community, total vegetation cover, soil moisture, and water use by plants. Our results showed that plant types that are less palatable to herbivores were best adapted to grazing or browsing animals in all simulated densities. Also, plant types that had a competitive advantage under limited water availability were among the dominant ones irrespective of land‐use scenario. Overall, the results were in line with our expectations: under high grazer densities, we found heavy bush encroachment and the loss of the perennial grass matrix. Importantly, regardless of the density of browsers, grass cover and plant functional diversity were significantly higher in browsing scenarios. Browsing herbivores increased grass cover, and the higher total cover in turn improved water uptake by plants overall. We concluded that, in contrast to grazing‐dominated land‐use strategies, land‐use strategies dominated by browsing herbivores, even at high herbivore densities, sustain diverse vegetation communities with high cover of perennial grasses, resulting in lower erosion risk and bolstering ecosystem services.

Seasonal hydrological traits in Salix psammophila and its responses to soil moisture and meteorological factors in desert areas

Drought is a key factor limiting vegetation water use and growth. More frequent and extreme drought events are increasing around the world, which may affect plant physiological reactions and vegetation restoration activities. The present study explored the seasonal trends of sap flow in Salix psammiphlia (Sf) by continuously collecting data on abiotic factors (net radiation [Rn], atmospheric relative humidity [Rh], atmospheric temperature [T], saturated vapor pressure difference [VPD], wind speed at 2 m height [U2], soil water storage [SWS], soil temperature [ST]) and transpiration rate (Ts) in the Mu Us Desert. According to the results, Sf exhibited considerable seasonal trends accompanied by a unimodal pattern during the growing season, and with a bimodal pattern during the dormant season. Notably, the ratio of nocturnal sap flow to whole daily sap flow could increase by up to 100% (from October to December and March to May). Multivariate stepwise regression and structural equation modeling results suggested that different factors drive the seasonal trends. During the growing season, Rn, VPD, and U2 controlled Ts directly (R2 = 0.80). While Ts was directly controlled by Rh, T, U2, SWS2 (20–100 cm) and ST_50 during the dormant season (R2 = 0.43). Topsoil freezing in winter may led to water stress in S. psammiphlia, and then appeared the bimodal pattern. The plants survived freezing drought water stress by using the soil moisture stored in the deep soil layer (50–100 cm) and reducing Ts, or even temporarily stopping transpiration. According to this data, the threshold of S. psammophila in the region was estimated to be 480–540 clusters/ha2. These findings could guide ecosystem restoration activities and facilitate sustainable development in dry and degraded regions.

云南省植被水分利用效率时空变化及影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 云南省植被水分利用效率时空变化及影响因素 DOI: 10.5846/stxb202011253023 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41871198） Spatiotemporal variation and influencing factors of vegetation water use efficiency in Yunnan Province Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:对云南省植被水分利用效率（WUE）的时空特征及影响因素进行研究可以更加全面的了解全球气候变化在区域上的响应。基于MODIS数据定量估算了2000-2014年云南省植被水分利用效率，利用趋势分析法和相关分析来对其时空格局和影响因素进行研究。研究结果表明：（1）云南省植被WUE整体呈现显著上升的趋势，增速为0.0078 gC mm-1 m-2 a-1，年内表现为"M"型的变化趋势。2009-2013年的干旱对该地区植被WUE产生了滞后的正效应。不同土地利用类型下的植被WUE从高到低依次为森林，灌木地，草地和耕地。（2）在空间分布上植被WUE呈现西部高于东部的分布特征；在时间尺度上呈现北增南减的趋势。云贵高原与青藏高原的连接区域--丽江市的植被WUE最高，整体上大于2.5 gC mm-1 m-2。澜沧江上游的三江并流区植被WUE随着山脉的走势呈现条状变化分布，不仅是植被WUE的低值集中区，同时也是植被WUE增加10%以上的集中区，另外滇东北和滇东南也是植被WUE的低值区。总的来看，除丽江以外，其他WUE高值区从2000-2014年呈下降的趋势，WUE低值区呈上升的趋势。（3）随着海拔的上升，植被WUE呈先上升后下降的变化趋势，并且海拔越高植被WUE增加越明显，变化率为0.01%。在低海拔区植被蒸散量（ET）和总初级生产力（GPP）都较高，随着海拔的上升ET骤降，GPP波动下降，直至海拔3000 m左右植被WUE达到峰值。高于海拔3000 m后，GPP直线下降，ET波动变化，直至海拔5000 m左右植被WUE几乎为0。（4）相较于降水因子，植被WUE受气温影响更大，特别是在三江并流区，其他地区则受非气候因素影响较大。在全球气候变化的背景下，这些发现展现了全球碳水循环变化在区域上的响应；云南省作为中国低纬高原的主体，研究也可为全球低纬高原区域生态建设提供参考。 Abstract:The study of the spatiotemporal characteristics and influencing factors of vegetation water use efficiency (WUE) in Yunnan Province could provide a more comprehensively understanding of the regional response to global climate change. In this study, MODIS data were used to quantitatively estimate the water use efficiency in Yunnan Province from 2000 to 2014, and trend analysis and correlation analysis were used to investigate the spatiotemporal patterns and influencing factors. The results showed that:(1) the overall WUE in Yunnan Province indicated a significant upward trend, with a growth rate of 0.0078 gC mm-1 m-2 a-1, and exhibited an "M" shape trend during the year. The drought events that occurred during 2009-2013 had a lagged positive effect on the vegetation WUE in this area. The vegetation WUEs of different land use types, in descending order, were forest, shrubland, grassland and the cultivated land. (2) The spatial distribution of WUE was higher in the west than in the east with a tendency of increasing in the north and decreasing in the south. The highest WUE was found in Lijiang, the region connecting the Yunnan-Guizhou Plateau and the Qinghai-Tibet Plateau, where the WUE was greater than 2.5 gC mm-1 m-2 overall. The vegetation WUE in the Three Parallel Rivers of upper Lancang River showed a striped distribution with the trend of the mountains, and was a concentration of low vegetation values. But it was also a focus where the WUE increased by more than 10%. In addition, northeastern and southeastern Yunnan were also areas with low WUE. Overall, except for Lijiang, there was a decreasing trend of high WUE and an increasing trend of low WUE from 2000 to 2014. (3) With the rise of altitude, WUE showed a tendency to increase first and then decrease, and the increase of WUE was more obvious in the higher altitude, with a change rate of 0.01%. Both evapotranspiration (ET) and Gross Primary Productivity (GPP) were prominent at low altitude, and with the rise of altitude ET plummets and GPP fluctuates and decreases until the peak of WUE was reached 3000 m. Above about 3000 m, the GPP dropped linearly and the ET fluctuated until the WUE was almost zero at about 5000 m. (4) Compared with precipitation, WUE was more obviously influenced by temperature, especially in the Three Parallel Rivers, while other regions were more significantly influenced by non-climatic factors. In the context of global climate change, the findings demonstrated the regional response to changes in the global carbon and water cycle; as the main body of low-latitude plateau in China, this study also could provide a reference for the ecological construction in low-latitude plateau regions around the world. 参考文献 相似文献 引证文献

The seasonal response of vegetation water use efficiency to temperature and precipitation in the Loess Plateau, China

Water use efficiency (WUE), which integrates ecosystem carbon and water cycles, is an important index for evaluating ecosystem sensitivity to climate change. Based on MODIS remote sensing data and meteorological data, this paper quantitatively studied the variation in seasonal vegetation WUE in the Loess Plateau over the period 2001–2019. Temperature and precipitation threshold effects on seasonal WUE of different vegetation types were also discovered using regression and partial correlation analysis methods. The results showed that seasonal WUE decreased with time in each season studied, with the rate of decrease of WUE in summer being the most significant of the three seasons studied. The following was the order of change in vegetation WUE values over time in different seasons: summer > autumn > spring. WUE of different vegetation types showed seasonal differences as well as varying responses to temperature and precipitation. The WUE of shrubland and grassland both tended to decrease over the study period from spring to autumn, with grassland WUE decreasing the most. When compared to grassland and shrubland, the negative relationship between forest WUE and the temperature was highest in spring and summer. The proportion of the area of vegetation where WUE was negatively correlated with temperature and precipitation in the three seasons, was largest in summer. In the relationship between seasonal WUE and either temperature or precipitation, there was a threshold effect. In spring, summer, and autumn, the optimum precipitation thresholds were 50–80 mm, 280–370 mm, and 65–125 mm, respectively, and the corresponding optimum temperature thresholds were > 14 °C, 15–19 °C, and 6–13 °C, respectively.

The role of groundwater in the spatio-temporal variations of vegetation water use efficiency in the Ordos Plateau, China

Groundwater influences the water and carbon cycle by supplying moisture to plants in the semi-arid and arid zones. However, little is known about the response of ecosystem water use efficiency (WUE) to climate change in different groundwater depth (GD) sections. Recent research has shown that plant photosynthesis and growth are closely related to GD via field experiments but the wider recognition of GD effect on regional-scale ecosystems has not been yet established. In this study, we test whether the GD has an impact on ecosystem WUE and its variability to climate change at the regional scale. Based on the observed data of nearly 3000 wells, meteorological data (precipitation and pan evaporation), and the 0.01°-resolution remote sensing datasets including gross primary production (GPP), evapotranspiration (ET), and normalized difference vegetation index (NDVI), we explored the spatio-temporal variations of WUE and its composites (i.e., GPP and ET), and their characteristics depending on GD under different aridity conditions and biomes across the Ordos Plateau, a semi-arid to arid area in northern China. Results show that WUE increases with decreasing GD due to water availability in the semi-arid lands where WUE variability is mainly regulated by biological processes (i.e., GPP), while WUE is insensitive to the changes in GD across the arid zone where the physical processes (i.e., ET) control WUE change. However, when drought happens the groundwater-independent vegetation in the arid zone can also utilize groundwater, characterized by lower reductions of GPP with the decrease in GD. A dense vegetation condition (i.e., large NDVI) is more vulnerable to climatic disturbance over the semi-arid zone because it tends to decrease GPP and WUE, especially in the large GD regions. These findings have important implications for reasonable land use and groundwater management over the semi-arid and arid regions.

Applying a projection pursuit model for evaluation of ecological quality in Jiangxi Province, China

Monitoring and evaluating ecological quality and changes are crucial for policy formulation to guide ecosystem management and socioeconomic sustainable development. However, evaluation of ecological quality is still very challenging due to difficulties in determination of its associated indicators and weights. This paper proposes supporting, providing and regulating ecosystems services-based indicators to describe ecological quality, and applies a Projection Pursuit Model to eliminate redundant indicators and objectively determine weights for an ecological quality index (EQI) on a regional scale. Taking Jiangxi Province, China, as a demonstration area, the data for indicator measures were retrieved from satellite remote sensing and ecosystem modelling with a spatial resolution of 1 km for the three years 2005, 2010 and 2015. The results suggest that Normalized Difference Vegetation Index (NDVI) and water use efficiency (WUE) should be weighed higher and leaf area index (LAI) and Bowen ratio should be weighed lowest in the calculation of an EQI for Jiangxi Province. For 2015, the regional EQI was calculated to be 55.32 on a scale from 0 as the worst to 100 as the best, with higher values ascribed to the hills and mountains and the lower values existing near urban areas. The EQI increased from 52.26 in 2005 to 55.32 in 2015 with an increased area of good-and-above grade from 25.47% to 36.8% for the whole province. The changes in EQI could be attributed to a warmer and wetter climate trend playing a positive dominant effect, while urbanization and afforestation have negative and positive effects, respectively. This study demonstrates that it is feasible to evaluate ecological quality based on a comprehensive set of indicators and PPM-based weight determination, which could be further applied in regular ecological quality monitoring and evaluation on the regional, or even the national scale.

Estimating ecosystem maximum light use efficiency based on the water use efficiency principle

Light use efficiency (LUE) defines the vegetation efficiency of converting radiative energy into biochemical energy through photosynthesis. Estimating the maximum LUE (ε max) is critical yet challenging for quantifying gross primary production (GPP) using LUE-based models. This study describes an analytical method for estimating ε max based on water use efficiency (WUE) as determined by plant water use and carbon gain. Unlike other complex parameterization schemes, this WUE-based method is simple and requires four variables relatively easy to acquire. The WUE-based ε max estimates compare favorably well with values based on traditional curve fitting method and that reported in the literature, and clearly distinguished ε max between C3 (1.48 ± 0.33 ) and C4 (2.63 ± 0.21 ) dominated ecosystems. The range in ε max estimates was narrow across different years and sites within a biome. The WUE-based ε max estimate is theoretically constrained by vegetation water use and can be directly incorporated into LUE models for GPP estimation across ecosystems.

Evaluating the long‐term ecohydrological suitability of restoration efforts in a typical watershed of the Loess Plateau

AbstractThe vegetation growth of the Loess Plateau is often restricted by water, which seriously threatens the water sustainability of regional ecosystem. In order to clarify the relationship between supply and demand of vegetation water use after Grain for Green Project, this study selected Malian River Basin as the research area and calculated the vegetation water use and water demand using the eco‐hydrological model. The results showed that the annual water demand of the basin was 570 mm, while the average annual water supply was only 294 mm, accounting only for 52.0% of the demand. From 2000 to 2018, the temporal and spatial matching degree of water supply and demand in the Malian River Basin were 0.63 and 0.65, respectively. On the whole, the water resources in Malian River Basin can basically support the growth of vegetation, but in some areas are not sustainable. Water resources in the southern region can only barely maintain the normal growth of vegetation under the current conditions, so it is not recommended to carry out new plantation in this area. The evaluation of matching degree in the northern from January to April is poor, so it is necessary to appropriately reduce the planting area of economic crops and replace it with planting herbaceous plants with small water consumption in Spring. Compared with the current conditions, under the future climate scenarios of ssp126 and ssp585, the Malian River Basin will show a trend of warming and humidification. The temporal matching degree of water supply and demand also significantly improved to 0.83 and 0.92, indicating that even if the planting structure did not change significantly, water supply would gradually meet the needs of vegetation. The study results can provide the basis for formulating more scientific and reasonable vegetation restoration policies.

Drought and intensified agriculture enhanced vegetation growth in the central Pearl River Basin of China

Plant-water relation is one of the key focus of Ecohydrology, and it usually presents specific characteristics varying with climate, species and soils based on field studies. The large-scale plant-water relations in the Pearl River Basin were previously analysed and the hotspot for water and vegetation changes was identified in the cropland-dominated region. Here, we focused in this region and analysed how intensive agriculture could have modified or been affected by water resources in response to droughts. Pearson correlation analysis showed that the monthly vegetation change was more likely subject to energy availability while the annual change was mainly affected by precipitation and water storage. This cropland area experienced fairly frequent mild droughts, and the trend of a drought index SPEI showed a clear difference from that in the non-agricultural areas, particularly in growing seasons. Further examination showed that SPEI, vegetation parameters and agricultural data had strong positive relationships; vegetation parameters and water use varied significantly and positively with the planting structure and intensification of agricultural activities like fertilization and irrigation (r > 0.6, p < 0.05). A positive influence of droughts on crop production was detected, i.e. the mild droughts can promote productivity probably through firstly enhanced photosynthesis induced by enhanced solar exposure and secondly increased supplementary water supply by irrigation under drought. This study strengthens our understanding of the agriculture-water interactions in the humid subtropical region and has implications for agricultural water management and drought impact mitigations.

Low and contrasting impacts of vegetation CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fertilization on global terrestrial runoff over 1982–2010: accounting for aboveground and belowground vegetation–CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; effects

Abstract. Elevation in atmospheric carbon dioxide concentration (eCO2) affects vegetation water use, with consequent impacts on terrestrial runoff (Q). However, the sign and magnitude of the eCO2 effect on Q are still contentious. This is partly due to eCO2-induced changes in vegetation water use having opposing responses at the leaf scale (i.e., water-saving effect caused by partially stomatal closure) and the canopy scale (i.e., water-consuming induced by foliage cover increase), leading to highly debated conclusions among existing studies. In addition, none of the existing studies explicitly account for eCO2-induced changes to plant rooting depth that is overwhelmingly found in experimental observations. Here we develop an analytical ecohydrological framework that includes the effects of eCO2 on plant leaf, canopy density, and rooting characteristics to attribute changes in Q and to detect the eCO2 signal on Q via vegetation feedbacks over 1982–2010. Globally, we detect a very small decrease of Q induced by eCO2 during 1982–2010 (−1.7 %). Locally, we find a small positive trend (p &lt; 0.01) in the Q–eCO2 response along a resource availability (β) gradient. Specifically, the Q–eCO2 response is found to be negative (i.e., eCO2 reduces Q) in low-β regions (typically dry and/or cold) and gradually changes to a small positive response (i.e., eCO2 increases Q) in high-β areas (typically warm and humid). Our findings suggest a minor role of eCO2 on changes in global Q over 1982–2010, yet we highlight that a negative Q–eCO2 response in semiarid and arid regions may further reduce the limited water resource there.

Biochar and vermicompost improve growth and physiological traits of eggplant (Solanum melongena L.) under deficit irrigation

BackgroundDrought is one of the most important environmental stresses that can adversely influence soil properties, plant growth, and productivity of agricultural crops including eggplant as an important vegetable crop. In recent years, the use of agricultural wastes has been reported as a beneficial and sustainable measure in soil water retention and fertility enhancement. In this study, the effect of date palm and pistachio biochar, vermicompost and a combination of biochar and vermicompost was evaluated on eggplant growth, yield and water use efficiency under deficit irrigation.Materials and methodsThe experiment was done in a split-split plot based on randomized complete block design with three replications and under open field conditions. The main plot was deficit irrigation in three levels of 100, 75 and 50% of plant water requirement (PWR), and the sub-plots were vermicompost in two levels of 0, 1500 g m−2, and biochar in three levels of 0, 500 g m−2 of the pistachio biochar and 500 g m−2 of the date palm biochar.ResultsThe results showed that soil amendment with vermicompost and pistachio biochar and 100% PWR showed the best plant growth and performance. The early crop yield was highest under pistachio biochar and 50% PWR, while the total plant yield was highest under combined application of vermicompost and pistachio biochar at 100% PWR. The plant water use efficiency was maximum under mixed application of vermicompost and pistachio biochar at 50% PWR. Application of both pistachio biochar and vermicompost at 100% PWR resulted in the highest leaf concentrations of nitrogen, phosphorus, potassium, iron and manganese. The highest levels of physiologically important stress metabolites, including malondialdehyde, guaiacol peroxidase, superoxide dismutase and catalase enzymes were found in treatments without amendments or only with vermicompost and 50% PWR.ConclusionThe results indicate that under normal and particularly water deficit conditions, vermicompost and biochar increased eggplant vegetative growth, yield and water use efficiency.

Stomatal conductance limited the CO2 response of grassland in the last century

BackgroundThe anthropogenic increase of atmospheric CO2 concentration (ca) is impacting carbon (C), water, and nitrogen (N) cycles in grassland and other terrestrial biomes. Plant canopy stomatal conductance is a key player in these coupled cycles: it is a physiological control of vegetation water use efficiency (the ratio of C gain by photosynthesis to water loss by transpiration), and it responds to photosynthetic activity, which is influenced by vegetation N status. It is unknown if the ca-increase and climate change over the last century have already affected canopy stomatal conductance and its links with C and N processes in grassland.ResultsHere, we assessed two independent proxies of (growing season-integrating canopy-scale) stomatal conductance changes over the last century: trends of δ18O in cellulose (δ18Ocellulose) in archived herbage from a wide range of grassland communities on the Park Grass Experiment at Rothamsted (U.K.) and changes of the ratio of yields to the CO2 concentration gradient between the atmosphere and the leaf internal gas space (ca – ci). The two proxies correlated closely (R2 = 0.70), in agreement with the hypothesis. In addition, the sensitivity of δ18Ocellulose changes to estimated stomatal conductance changes agreed broadly with published sensitivities across a range of contemporary field and controlled environment studies, further supporting the utility of δ18Ocellulose changes for historical reconstruction of stomatal conductance changes at Park Grass. Trends of δ18Ocellulose differed strongly between plots and indicated much greater reductions of stomatal conductance in grass-rich than dicot-rich communities. Reductions of stomatal conductance were connected with reductions of yield trends, nitrogen acquisition, and nitrogen nutrition index. Although all plots were nitrogen-limited or phosphorus- and nitrogen-co-limited to different degrees, long-term reductions of stomatal conductance were largely independent of fertilizer regimes and soil pH, except for nitrogen fertilizer supply which promoted the abundance of grasses.ConclusionsOur data indicate that some types of temperate grassland may have attained saturation of C sink activity more than one century ago. Increasing N fertilizer supply may not be an effective climate change mitigation strategy in many grasslands, as it promotes the expansion of grasses at the disadvantage of the more CO2 responsive forbs and N-fixing legumes.

Grain Yield, Heat use Efficiency and Water use Efficiency of Diverse Wheat (Tritcum aetivum L.) Varieties under Different Sowing Environments in North-Western India

Background: Wheat is an important food crop of world. This crop has the wider adaptability due to its genetic makeup. The sowing environment and varieties interaction plays important role to enhance its productivity and optimum utilization of the resources. As this crop has wider adaptability so we planned our experiment to study the grain yield, heat use and water use efficiency of diverse wheat varieties which have been recommended in different wheat growing zones, sown at different environment in North-western India, to increase the varietal spectrum.Methods: The field experiment was conducted in 2017-18 and 2018-19 at the research farm of the Punjab Agricultural University, Ludhiana, India. The experiment was conducted with four sowing dates (November 5, November 25, December 15 and January 5) in main plot and six wheat varieties (HS 562, HD 2967, HD 3086, HI 1544, MACS 6222 and WR 544) in sub-plot of split plot design with three replications. Result: The wheat crop sown on November 5 recorded the highest emergence count, plant height, heat use efficiency, normalized difference vegetative index, yield attributes, grain yield and water use efficiency than later sowing dates. Among the wheat varieties, HS 562 recommended for northern hill zone recorded heat use efficiency, helio-thermal use efficiency, at Leaf value, effective tillers, grains per earhead, grain yield and water use efficiency similar to HD 3086 recommended for North-western zone. The varieties recommended for other zones like HI 1544, MACS 6222 and WR 544 could not perform similar to the HD 3086.

Environmental Drivers of Water Use for Caatinga Woody Plant Species: Combining Remote Sensing Phenology and Sap Flow Measurements

We investigated the water use of Caatinga vegetation, the largest seasonally dry forest in South America. We identified and analysed the environmental phenological drivers in woody species and their relationship with transpiration. To monitor the phenological evolution, we used remote sensing indices at different spatial and temporal scales: normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), and green chromatic coordinate (GCC). To represent the phenology, we used the GCC extracted from in-situ automated digital camera images; indices calculated based on sensors included NDVI, SAVI and GCC from Sentinel-2A and B satellites images, and NDVI products MYD13Q1 and MOD13Q1 from a moderate-resolution imaging spectroradiometer (MODIS). Environmental drivers included continuously monitored rainfall, air temperature, soil moisture, net radiation, and vapour pressure deficit. To monitor soil water status and vegetation water use, we installed soil moisture sensors along three soil profiles and sap flow sensors for five plant species. Our study demonstrated that the near-surface GCC data played an important role in permitting individual monitoring of species, whereas the species’ sap flow data correlated better with NDVI, SAVI, and GCC than with species’ near-surface GCC. The wood density appeared to affect the transpiration cessation times in the dry season, given that species with the lowest wood density reach negligible values of transpiration earlier in the season than those with high woody density. Our results show that soil water availability was the main limiting factor for transpiration during more than 80% of the year, and that both the phenological response and water use are directly related to water availability when relative saturation of the soil profile fell below 0.25.

Plant Hydraulic Stress Strategy Improves Model Predictions of the Response of Gross Primary Productivity to Drought Across China

AbstractThe response of the terrestrial carbon cycle to droughts, which have recently increased in incidence and severity, is a hot topic in research, but the role played by vegetation water use strategies remains unclear. Both the soil moisture stress (SMS) and plant hydraulic stress (PHS) strategies are used in land surface models, but their performance in simulating the terrestrial carbon cycle and its response to droughts in various climatic zones remains uncertain. In this study, we used Community Land Model Version 5 to simulate gross primary productivity (GPP) across four different climatic subregions of China during 2000–2015 to investigate the roles played by PHS and SMS in the response of GPP to dry events and dry or rainy years in various climate zones. Simulated GPP with the two strategies were overestimated by 2.0–2.3% for the entire China compared to Moderate Resolution Imaging Spectroradiometer (MODIS) data. GPP simulated using PHS configuration fit eddy covariance and MODIS data better than that obtained using SMS across China, except for the Qinghai‐Tibet Plateau. PHS increased simulated GPP by 0.10–0.63 g C m−2 day−1 during dry events across different climatic regions because of root hydraulic lift but decreased GPP by 0.37–0.45 g C m−2 day−1 during growing season in the humid southeastern region because of high atmospheric vapor pressure deficit and root hydraulic descent. Simulations forced by data collected locally in China performed better than those forced by CRUNCEP7 global data at the site but worse at the regional scale, in particular for the Qinghai‐Tibet Plateau.