Browsing by Subject "leaf area index"

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    Divergent trends of ecosystem-scale photosynthetic efficiency between arid and humid lands across the globe
    (Wiley, 2022-09) Wei, Fangli; Wang, Shuai; Fu, Bojie; Wang, Lanhui; Zhang, Wenmin; Wang, Lixin; Pan, Ning; Fansholt, Rasmus; Earth and Environmental Sciences, School of Science
    Aim Widespread greening and an increasing global terrestrial carbon sink over recent decades have been reported. However, the spatio-temporal relationships between vegetation greenness and productivity and the factors influencing this relationship remain unclear. We define a new metric of ecosystem-scale photosynthetic efficiency (EPE) to analyse its spatio-temporal pattern and investigate how potential drivers regulate the greenness–productivity relationship. Location Global. Time period From 2001 to 2016. Major taxa studied Global terrestrial ecosystems. Methods This study used global datasets of leaf area index (LAI) and solar-induced fluorescence (SIF) as proxies of vegetation greenness and ecosystem productivity, respectively, to propose a new metric of SIF/LAI, representing ecosystem-scale photosynthetic efficiency (EPE). We identified the spatial pattern and dynamics of EPE and examined factors influencing EPE. Results The results showed a weaker increase in productivity compared with the global greening rate from 2001 to 2016, suggesting a decline in EPE at the global scale. This decline in EPE indicates a disproportionate increase in terrestrial productivity against the widespread greening. When stratified into areas following an aridity gradient, we found that EPE overall showed upward trends in arid and semi-arid areas, and downward trends in dry sub-humid and humid regions. The EPE was controlled primarily by soil moisture, which promoted or constrained the EPE in xeric and mesic ecosystems, respectively. Moreover, the increase in short vegetation cover and atmospheric water demand contributed positively or negatively to EPE changes in xeric and mesic ecosystems, respectively. Main conclusions Our study shows that greening of the Earth is associated with decreasing EPE, revealing that current rates of carbon sequestration do not increase proportionally to greening of the Earth and highlighting that soil moisture is a key controller of EPE. These results help to reduce the uncertainties in future climate change impacts on vegetation dynamics, thus having implications for sustainable ecosystem management and climate change mitigation.
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    Quantifying the Controls on Evapotranspiration Partitioning in the Highest Alpine Meadow Ecosystem
    (AGU, 2020-04) Cui, Jiangpeng; Tian, Lide; Wei, Zhongwang; Huntingford, Chris; Wang, Pei; Cui, Zhongyin; Ma, Ning; Wang, Lixin; Earth Sciences, School of Science
    Quantifying the transpiration fraction of evapotranspiration (T/ET) is crucial for understanding plant functionality in ecosystem water cycles, land‐atmosphere interactions, and the global water budget. However, the controls and mechanisms underlying the temporal change of T/ET remain poorly understood in arid and semiarid areas, especially for remote regions with sparse observations such as the Tibetan Plateau (TP). In this study, we used combined high‐frequency laser spectroscopy and chamber methods to constrain estimates of T/ET for an alpine meadow ecosystem in the central TP. The three isotopic end members in ET (δET), soil evaporation (δE), and plant transpiration (δT) were directly determined by three newly customized chambers. Results showed that the seasonal variations of δET, δE, and δT were strongly affected by the precipitation isotope (R2 = 0.53). The δ18O‐based T/ET agreed with that of δ2H. Isotope‐based T/ET ranged from 0.15 to 0.73 during the periods of observation, with an average of 0.43. This mean result was supported by T/ET derived from a two‐source model and eddy covariance observations. Our overarching finding is that at the seasonal timescale, surface soil water content (θ) dominated the change of T/ET, with leaf area index playing only a secondary role. Our study confirms the critical impact of soil water on the temporal change of T/ET in water‐limited regions such as the TP. This knowledge sheds light on diverse land‐surface processes, global hydrological cycles, and their modeling.