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CO2, nitrogen deposition and a discontinuous climate response drive water use efficiency in global forests

2021; Nature Portfolio; Volume: 12; Issue: 1 Linguagem: Inglês

10.1038/s41467-021-25365-1

2041-1723

Mark A. Adams, Thomas N. Buckley, Dan Binkley, Mathias Neumann, Tarryn L. Turnbull,

Climate variability and models

Reduced stomatal conductance is a common plant response to rising atmospheric CO2 and increases water use efficiency (W). At the leaf-scale, W depends on water and nitrogen availability in addition to atmospheric CO2. In hydroclimate models W is a key driver of rainfall, droughts, and streamflow extremes. We used global climate data to derive Aridity Indices (AI) for forests over the period 1965-2015 and synthesised those with data for nitrogen deposition and W derived from stable isotopes in tree rings. AI and atmospheric CO2 account for most of the variance in W of trees across the globe, while cumulative nitrogen deposition has a significant effect only in regions without strong legacies of atmospheric pollution. The relation of aridity and W displays a clear discontinuity. W and AI are strongly related below a threshold value of AI ≈ 1 but are not related where AI > 1. Tree ring data emphasise that effective demarcation of water-limited from non-water-limited behaviour of stomata is critical to improving hydrological models that operate at regional to global scales.