Search

Highlights • Delaying sowing promoted forage maize, Sudan grass used water from deep layers at jointing, flowering and maturity. • Delaying sowing promoted foxtail millet and Japanese millet absorbed deep water at flowering and maturity. • Plant water use in a semi-arid environment is controlled by both environment and growth stage. Abstract Plant water use strategies are crucial for fodder production in semi-arid environments, with implications for food supply, livestock products and social sustainability in a global warming environment. This study aimed to determine the effect of phenology and sowing date on water use in four annual forage crops on the Loess Plateau of China. Hydrogen and oxygen isotope ratios (δD and δ18O) measured soil water in different layers (0–1.2 m), xylem water at jointing, flowering and maturity, and rainwater. The IsoSource model was used to calculate the relative contribution of soil water to plant water use in the shallow (0–0.1 m), middle (0.1–0.6 m) and deep (0.6–1.2 m) layers. As the forage crops grew, more water was absorbed from deeper layers. Delaying sowing up to four weeks could promote forage maize (Zea mays), Sudan grass (Sorghum sudanense Stapf.) used water from deep layers at all measured growth stages (jointing, flowering, and maturity). Foxtail millet (Setaria italica) and Japanese millet (Echinochloa crus-galli var. frumentacea) absorbed deep water at flowering and maturity. Further, maize, Sudan grass, and foxtail millet used more water at flowering while Japanese millet used more at maturity. The distinct water use patterns of the four crops at different growth stages and sowing dates showed that plant water use in a semi-arid environment is controlled by both environment and growth stage. Delaying sowing might be an efficient way of coping with water stress caused by unpredictable rainfall by using water from deeper layers to reduce the risk of yield losses. Our results provide a reference for agricultural water management under global warming and sustainability in rainfed farming systems. [ABSTRACT FROM AUTHOR]

Highlights • Calibrating parameters is necessary for dynamic vegetation model in local scale. • Potential forest areas will decrease, while potential steppe areas will increase. • Existing land use pattern should be adjusted to adapt to climate change. • Shrubs have larger area and higher habitat suitability than forests. • Results could guide decision makers in developing effective revegetation plans. Abstract Global concern about the restoration of vegetation ecosystems has recently increased. Potential natural vegetation (PNV) and climate adaptation concepts should be integrated into revegetation programs to achieve sustainable ecosystems. The Yanhe Basin in the Loess Plateau of China (7687 km2) has been subjected to intense human activity for centuries. It was selected as the study area because vegetation degradation and restoration are occurring there. The objectives of this study were to (1) evaluate whether the current vegetation pattern is appropriate, and (2) provide a restoration plan for future revegetation programs based on PNV and habitat suitability patterns simulated by the dynamic vegetation model LPJ-GUESS. Current work focused on the parameter calibration and high-resolution climate data of the model over the study area. The comparisons of model performances in the PNV pattern and productivity indicated that parameter calibration was necessary for the model application. PNV of the Yanhe Basin may shift by 21.37–29.67% from 1981–2010 to 2071–2100, mainly in the southern part. Forests may decrease and steppes may increase as the climate becomes drier in the future. Comparisons between an existing land use map and the current PNV pattern indicated that only 40.8% of the forestland was coincident with the current PNV pattern, whereas grassland was a more suitable vegetation type for the rest of the terrain. In contrast, 83.1% of the grassland aligned with the current PNV pattern. Therefore, 16.9% remains to be forested. Current forestland and grassland patterns should be adjusted to cope with future climate change. Broadleaf summer-green shrubs covered a larger area and had higher habitat suitability than forests; they might be the most suitable woody plants for revegetation of the Yanhe Basin. The applied research approach could be extended to other regions undergoing similar revegetation programs and help promote sustainable vegetation management. [ABSTRACT FROM AUTHOR]

• The uWUE method was cross–compared with three traditional methods. • Daily T partitioned by the uWUE method well agreed with the SW model. • G c had more significant seasonal variations than G s. • The Jarvis model parameterized with G c performed better than those with G s. • The uWUE method can exclude influences of nonstomatal conductances. Canopy conductance (G c) largely regulates carbon/water cycling and land–atmosphere interactions, but quantifying G c using eddy flux data is limited by the difficulty of partitioning plant transpiration (T) and surface evaporation (E). We introduced an underlying water use efficiency (uWUE) method to partition evapotranspiration (ET) in an oasis maize ecosystem, and cross–compared with the Shuttleworth and Wallace (SW) model, the lysimeter and isotope measurements. We then estimated surface conductance (G s) by ET and G c by T partitioned using the uWUE method, followed by a performance evaluation on the Jarvis model parameterized with both G s and G c. The results showed that T/ET estimated by the uWUE method was close to the isotope method in the peak growing season of 2012, it showed similar seasonal variations with the lysimeter/eddy covariance method and the SW model throughout this growing season. Daily T partitioned by the uWUE method was in good agreement with the SW model from 2012 to 2015 (r2 = 0.91). Additionally, G c had more significant seasonal variations than G s. The Jarvis model parameterized with G c exhibited superior performance than those with G s. Our study suggests that the uWUE method can exclude influences of nonstomatal conductances, and will have great potential to provide more reasonable parameterization for simulation of plant stomata. [ABSTRACT FROM AUTHOR]

• The PHM captures the observed Ψ l , sap-flow and ecosystem ET. • Hydraulic sensitivities generally reduce as the water stresses intensify. • Ecosystem water flux and mortality risk are not always coupled. • Hydraulic traits control the stress resistance of desert riparian ecosystems. • Different water stresses have coupled impact on ET and mortality risk. Plant response to soil and atmospheric water stresses is the dominant control of Dryland ecosystem functions, affecting water resources, ecosystem stability and biodiversity. The link between water stresses and plant water status is regulated by plant hydraulics, of which the corresponding impact on plant water use and the susceptibility of Dryland ecosystems remains under-explored. We used a plant hydraulic model to describe hydraulic states and water flux of two species (Populus euphratica and Tamarix ramosissima) in desert riparian ecosystems. We optimized hydraulic parameters and tested the model using observed physiological states and ecosystem water flux. The optimized model was used to evaluate plant hydraulic sensitivity, tree mortality risk, and evapotranspiration under a wide range of water stress scenarios. The model captures the observed leaf water potential, sap-flow and ecosystem evapotranspiration. Our scenario analysis demonstrates that hydraulic sensitivities generally reduce as the water stresses intensify. The results highlight a strong coupled impact of the co-occurrence of soil and atmospheric water stresses on restricting ecosystem water flux and intensifying mortality risk. The assessment of multiple aspects of eco-physiological functions and the stress scenario analysis of desert riparian ecosystems will contribute to a better prediction of ecosystem functions and facilitate resource management under future climate. [ABSTRACT FROM AUTHOR]