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Water use efficiency (WUE), the amount of assimilated carbon per amount of transpired water is central to assess how trees and forests respond to the ongoing climate changes and, particularly, to increasing drought severity. We concurrently evaluated leaf- and ecosystem-scale intrinsic WUE (WUE i) of a Mediterranean evergreen oak (Quercus ilex) forest in southern France using stable carbon isotopic discrimination, leaf gas exchange and eddy covariance fluxes. Nine years of continuous daily eddy fluxes were converted into 7-day composite chronicle of WUE i and then into δ13C input to check, is there a link between eddy and bulk leaf δ13C? The relationship between ecosystem-scale WUE i and water limitation, assessed by the predawn tree potential (ψ pd), followed a trapezoidal curve with a plateau value of 158.0 ± 4.0 µmol CO 2 mol-1 H 2 O. WUE i began to decline from -2.4 MPa with gas exchange ceasing at -4.4 MPa. WUE i measured at leaf scale followed a bi-linear relationship with ψ pd that peaked at ψ pd = -3.15 MPa, reaching 120.5 ± 16.4 µmol CO 2 mol-1 H 2 O. Current year leaf δ13C is linearly related to the averaged δ13C input over the leaf expansion period. In 1-year old leaves, adjustment in bulk δ13C was dependent on the degree of water limitation. Whole-isotopic mass balance at tree or ecosystem scales continue to be a major challenge because large gaps remain in understanding all the processes that influence δ13C of fluxes and C pools. [ABSTRACT FROM AUTHOR]

Water use efficiency (WUE) is a key physiological trait in studying plant carbon and water relations. However, the determinants of WUE across a large geographical scale are not always clear, limiting our capacity to predict WUE in response to future global climate change. We propose that tree WUE is influenced by calcium (Ca) availability and precipitation. In addition, although it is well-known that transpiration is the major driving force for passive nutrient uptake, the linkage between these two processes has not been well-established. Because Ca uptake is an apoplastic and passive process that purely relies on transpiration, and there is no translocation once assimilated, we further developed a theoretical model to quantify the relationship between tree Ca accumulation and WUE using soil-to-plant calcium ratio (S Ca/ B Ca) and tree WUE derived from δ13C. We tested our theoretical model and predicted relationships using three common tree species across their native habitats in Northern China, spanning 2300 km and a controlled greenhouse experiment with soil Ca concentrations manipulated. We found that tree WUE was negatively related to precipitation of the growing season (GSP) and positively with soil Ca. A multiple regression model and a path analysis suggested a higher contribution of soil Ca to WUE than GSP. As predicted by our theoretical model, we found a positive relationship between WUE and S Ca/ B Ca across their distribution ranges in all three tree species and in the controlled experiment for one selected species. This relationship suggests a tight coupling between water and Ca uptake and the potential use of S Ca/ B Ca to indicate WUE. A negative relationship between S Ca/ B Ca and GSP also suggests a possible decrease in tree Ca accumulation efficiency in a drier future in Northern China. [ABSTRACT FROM AUTHOR]

Summary: The least‐cost economic theory of photosynthesis shows that water and nitrogen are mutually substitutable resources to achieve a given carbon gain. However, vegetation in the Sahel has to cope with the dual challenge imposed by drought and nutrient‐poor soils.We addressed how variation in leaf nitrogen per area (Narea) modulates leaf oxygen and carbon isotopic composition (δ18O, δ13C), as proxies of stomatal conductance and water‐use efficiency, across 34 Sahelian woody species.Dryland species exhibited diverging leaf δ18O and δ13C values, indicating large interspecific variation in time‐integrated stomatal conductance and water‐use efficiency. Structural equation modeling revealed that leaf Narea is a pivotal trait linked to multiple water‐use traits. Leaf Narea was positively linked to both δ18O and δ13C, suggesting higher carboxylation capacity and tighter stomatal regulation of transpiration in N‐rich species, which allows them to achieve higher water‐use efficiency and more conservative water use.These adaptations represent a key physiological advantage of N‐rich species, such as legumes, that could contribute to their dominance across many dryland regions. This is the first report of a robust mechanistic link between leaf Narea and δ18O in dryland vegetation that is consistent with core principles of plant physiology. [ABSTRACT FROM AUTHOR]

Understanding the variations in plant traits across elevations may provide valuable insights into the species structure and function of forests and their responses to climate change. To explore the patterns of trait variation across elevations, we analysed 14 leaf and stem traits associated with resource acquisition and stress tolerance in Schima superba Gardner & Champion, Castanopsis chinensis (Sprengel) Hance, and Pinus massoniana Lambert trees at two elevations in a subtropical forest in southern China. Wood density increased, whereas crown width, leaf water potential at 0700 hours (ΨL-0700), and leaf δ18O decreased in high-elevation plants. Vessel diameter, daily maximum sap flux density, leaf δ13C, and leaf C and N concentrations per unit mass were comparable across elevations. We found species-specific variations in specific leaf area, midday leaf water potential, and leaf P concentration across elevations. Decreasing crown width with increasing elevation was associated with decreasing leaf δ18O and ΨL-0700, suggesting that higher stomatal conductance may moderate the loss of carbon assimilation. We elucidated the adaptive strategies of plants in response to environmental change, and showed that physiological traits varied in coordination with structural traits. Future studies incorporating multi-dimensional trait analyses can improve our understanding of the responses of forest ecosystems to climate change and global warming. [ABSTRACT FROM AUTHOR]

Climate change will increase uncertainty in restoration outcomes due to greater water stress and other abiotic filters that limit plant survival. Drought‐related plant functional traits can help species withstand filters in a semi‐arid environment. Our objective was to provide guidance for selecting species to improve restoration success in a changing climate.We planted 12 native species in ambient rainfall and under 60% rain‐out shelters in an invaded coastal grassland in central California. We measured survival and size annually for 4 years and quantified plant community and trait composition in the third and fourth years. We measured growth rate, specific leaf area (SLA), leaf C:N, leaf lobedness and leaf δ13C of all planted species and dominant extant species, and evaluated the effect of treatments, traits and phylogenetics on mortality risk using Cox proportional hazards.Native perennial species cover was greater, whereas thatch depth and per cent cover of shrubs and non‐native annual grasses were lower, on drought plots. Drought plots had lower community‐weighted leaf C:N and higher leaf lobedness.Planted species with resource conservative traits, such as higher leaf lobedness and lower growth rate, had lower mortality risk. Increased plasticity of morphological traits (SLA and lobedness) was associated with decreased mortality risk, whereas increased plasticity of physiological traits (leaf C:N and δ13C) and risk was positively correlated. Trait plasticity explained a greater degree of plant mortality risk compared to absolute trait values.Plants that were more phylogenetically related to the surrounding plant community had lower mortality risk. Traits of planted species that were important for determining plant mortality in this coastal grassland may be conserved, which was supported by a phylogenetic signal (Blomberg's K = 0.380, Pagel's λ = 0.830) in leaf C:N.Synthesis and applications. Our results suggest that leaf traits and phylogenetics could serve as plant selection criteria for reducing plant mortality risk during drought, thereby improving restoration outcomes. Because some traits have a phylogenetic signal that explains drought survival, restoration practitioners could expand the use of trait‐based selection for closely related species when restoring other arid‐ and semi‐arid ecosystems. ​ [ABSTRACT FROM AUTHOR]

Drought-induced events of massive tree mortality appear to be increasing worldwide. Species-specific vulnerability to drought mortality may alter patterns of species diversity and affect future forest composition. We have explored the consequences of the extreme drought of 2005, which caused high sapling mortality (approx. 50 %) among 10-year-old saplings of two coexisting pine species in the Mediterranean mountains of Sierra Nevada (Spain): boreo-alpine Pinus sylvestris and Mediterranean P. nigra. Sapling height growth, leaf δ 13C and δ 18O, and foliar nitrogen concentration in the four most recent leaf cohorts were measured in dead and surviving saplings. The foliar isotopic composition of dead saplings (which reflects time-integrated leaf gas-exchange until mortality) displayed sharp increases in both δ 13C and δ 18O during the extreme drought of 2005, suggesting an important role of stomatal conductance (g s) reduction and diffusional limitations to photosynthesis in mortality. While P. nigra showed decreased growth in 2005 compared to the previous wetter year, P. sylvestris maintained similar growth levels in both years. Decreased growth, coupled with a sharper increase in foliar δ 18O during extreme drought in dead saplings, indicate a more conservative water use strategy for P. nigra. The different physiological behavior of the two pine species in response to drought (further supported by data from surviving saplings) may have influenced 2005 mortality rates, which contributed to 2.4-fold greater survival for P. nigra over the lifespan of the saplings. This species-specific vulnerability to extreme drought could lead to changes in dominance and distribution of pine species in Mediterranean mountain forests. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ground cover rice production system increase grain yield by 18% at regional scales. [•] Success of GCRPS is depending on suitable water management avoiding excess water. [•] GCRPS is an invaluable technique in regions where temperature and water limited. [ABSTRACT FROM AUTHOR]

Global change factors affect plant carbon uptake in concert. In order to investigate the response directions and potential interactive effects, and to understand the underlying mechanisms, multifactor experiments are needed. The focus of this study was on the photosynthetic response to elevated CO2 [CO2; free air CO2 enrichment (FACE)], drought (D; water-excluding curtains), and night-time warming (T; infrared-reflective curtains) in a temperate heath. A/Ci curves were measured, allowing analysis of light-saturated net photosynthesis (Pn), light- and CO2-saturated net photosynthesis (Pmax), stomatal conductance (gs), the maximal rate of Rubisco carboxylation (Vcmax), and the maximal rate of ribulose bisphosphate (RuBP) regeneration (Jmax) along with leaf δ13C, and carbon and nitrogen concentration on a monthly basis in the grass Deschampsia flexuosa. Seasonal drought reduced Pn via gs, but severe (experimental) drought decreased Pn via a reduction in photosynthetic capacity (Pmax, Jmax, and Vcmax). The effects were completely reversed by rewetting and stimulated Pn via photosynthetic capacity stimulation. Warming increased early and late season Pn via higher Pmax and Jmax. Elevated CO2 did not decrease gs, but stimulated Pn via increased Ci. The T×CO2 synergistically increased plant carbon uptake via photosynthetic capacity up-regulation in early season and by better access to water after rewetting. The effects of the combination of drought and elevated CO2 depended on soil water availability, with additive effects when the soil water content was low and D×CO2 synergistic stimulation of Pn after rewetting. The photosynthetic responses appeared to be highly influenced by growth pattern. The grass has opportunistic water consumption, and a biphasic growth pattern allowing for leaf dieback at low soil water availability followed by rapid re-growth of active leaves when rewetted and possibly a large resource allocation capability mediated by the rhizome. This growth characteristic allowed for the photosynthetic capacity up-regulations that mediated the T×CO2 and D×CO2 synergistic effects on photosynthesis. These are clearly advantageous characteristics when exposed to climate changes. In conclusion, after 1 year of experimentation, the limitations by low soil water availability and stimulation in early and late season by warming clearly structure and interact with the photosynthetic response to elevated CO2 in this grassland species. [ABSTRACT FROM PUBLISHER]

Recent advances in optical designs and electronic circuits have allowed the transition from passive to active proximal sensors. Instead of relying on the reflectance of natural sunlight, the active sensors measure the reflectance of modulated light from the crop and so they can operate under all lighting conditions. This study compared the potential of active and passive canopy sensors for predicting biomass production in 25–32 randomly selected positions of a Merlot vineyard. Both sensors provided estimates of the normalized difference vegetation index (NDVI) from a nadir view of the canopy at veraison that were good predictors of pruning weight. Although the red NDVI of the passive sensors explained more of the variation in biomass ( R2 = 0.82), its relationship to pruning weight was nonlinear and was best described by a quadratic regression (NDVI = 0.55 + 0.50 wt−0.21 wt2). The theoretically greater linearity of the amber NDVI-biomass relationship could not be verified under conditions of high biomass. The linear correlation to stable isotope content in leaves (13C and 15N) provided evidence that canopy reflectance detected plant stresses as a result of water shortage and limited fertilizer N uptake. Thus, the canopy reflectance data provided by these mobile sensors can be used to improve site-specific management practices of vineyards. [ABSTRACT FROM AUTHOR]

• Water use strategies of three economic tree species were investigated. • Peach, walnut, and apple trees have different water use strategies. • Walnut trees have greater ecological plasticity by absorbing more deep soil water. • Peach and apple trees have higher water use efficiencies than walnut trees. Economic tree species growing in the semi-arid Loess Plateau of China are important for maintaining sound economic viability and protecting the fragile hydro-ecological environment. However, their water use strategies and ecological adaptation to dryland environments remain poorly understood. In this study, we measured variations in soil water content, root distribution, water isotopic signature for hydrogen (δ2H) and oxygen (δ18O) in xylem and soil water of peach (Prunus persica), walnut (Juglans regia L.), and apple (Malus pumila) trees, as well as carbon isotopic signature (δ13C) in their leaves during two consecutive growing seasons—2018 (normal year) and 2019 (wet year). The results showed all species consumed less deep soil water in 2019 than in 2018 due to the increased precipitation. Peach trees used more shallow soil water compared to walnut and apple trees that used more deep soil water during high water-demanding periods. Walnut trees depended more on deep soil water throughout the growing season, contributing 46.2% in 2018, compared to 26.0% for peach trees and 24.0% for apple trees. Moreover, walnut trees had lower deep soil water and leaf δ13C than peach and apple trees. The findings suggest differences in phenology periods of the three rainfed economic tree species to affect the water source used. The three tree species differed in their water use strategies: walnut trees had ecological plasticity for reducing water stress by absorbing deep soil water, and peach and apple trees had higher water use efficiencies. This study has significance for evaluating water use characteristics and drought stress responses of economic trees in water-limited environments. [ABSTRACT FROM AUTHOR]

• Leaf δ15N was mainly affected by soil ectomycorrhizal fungi. • Biogeographic patterns for soil fungal guilds in forests of China. • Biogeographic patterns for leaf δ15N and δ13C in forests of China. • The linkage between leaf δ15N, δ13C and soil fungi of forests. Leaf δ15N and δ13C are important functional traits in biogeographic studies of forest ecosystems. However, little is known about their relationships with soil fungal biodiversity, ectomycorrhizal and plant pathogenic abundance at large scales. In this study, leaf and soil samples were collected from 33 forest reserves along a large range across China to explore the associations between leaf δ15N and δ13C and soil fungal biodiversity, ectomycorrhizal and plant pathogenic relative abundance, using molecular and stable isotope techniques. Leaf δ15N was significantly positively correlated with the soil fungal Shannon index, significantly negatively correlated with the relative abundance of plant pathogens, and significantly positively correlated with the relative abundance of ectomycorrhizas. Leaf δ13C was significantly positively correlated with the relative abundance of ectomycorrhizas and significantly inverted unimodal correlated with the relative abundance of plant pathogens. Soil–plant–microbial interactions may contribute to variations in leaf δ15N, δ13C, and soil fungal communities among different types of forest ecosystems. Temperature and precipitation were the main factors that affected large-scale latitudinal and longitudinal biogeographic patterns. Leaf δ15N was mainly affected by the relative abundance of ectomycorrhizal fungi and leaf δ13C was affected by the mean annual temperature and mean annual precipitation. Leaf δ15N and δ13C may be indicators that reflect soil fungal communities in forest ecosystems. [ABSTRACT FROM AUTHOR]

• Mountain ecosystems of Central Asia are a biodiversity hotspot under climatic risk. • Lagochilus species are key medicinal herbaceous plants native to Central Asia. • Lagochilus climate sensitivity was assessed by population structure and carbon 13. • Lagochilus populations regeneration and carbon 13 were highly sensitive to drought. • Conservation of Lagochilus should become a priority in drying Central Asia. The high-mountain ecosystems of Central Asia are a biodiversity hotspot with unique plant communities and many endemic species. Intense human pressure and global warming have caused habitat destruction in these areas and a parallel increase in the number of endangered species. Lagochilus species are key medicinal herbaceous plants native to Central Asia, many of which have been recently added to the endangered of species in Uzbekistan. To assess the climate sensitivity of Lagochilus species, we (1) located populations of six species in their native sites across Uzbekistan, and assessed their health by partitioning to ontogenetic stages along five consecutive years; (2) collected plant materials from these species, as well as from old herbarium samples (1918–1964); and (3) analyzed the carbon-13 composition in those samples, as an indicator for drouht stress. Over the course of five years (2014–2018) of continuous monitoring, fluctuations in annual precipitation in the region indicated a decrease by ∼20 %, and the fraction of young plants in each population decreased from 20–50% to 0–5 %, depending on the species. Comparing the carbon-13 composition in current and historical leaf samples showed an increase of 1.5–3.5‰ associated with a decrease in precipitation of 2–30 %, depending on the site and species. Our results show the high sensitivity of Lagochilus populations' regeneration to drying, among six species and in sites across Uzbekistan. On a multi-decadal temporal scale, the dramatic changes in carbon-13 indicate that the response to precipitation reduction is related with drought stress. Considering the expectation for drier and hotter climate in Uzbekistan in the coming decades, conservation of Lagochilus populations should become a priority in Central Asia. [ABSTRACT FROM AUTHOR]