Hyposensitive canopy conductance renders ecosystems vulnerable to extreme droughts

Increased drought intensity with rising atmospheric demand for water (hereafter VPD) increases the risk of tree mortality worldwide. Ecosystem-scale water-use strategy (WUS), quantified here by canopy stomatal sensitivity to VPD (S), is increasingly recognized as a factor in drought-related ecosystem dysfunction. However, the links between S and ecosystem adaptation to and stability following droughts are poorly established. We examined how S regulates carbon sequestration, identifying ecosystems potentially susceptible to drought-induced mortality based on data from the global flux network, remote-sensing products, and plant functional-traits archive. We found that S is higher where ecosystem water availability is low in arid regions, reflecting conservative WUS (i.e., hypersensitivity), but ecosystems of all regions converge on permissive WUS (i.e., hyposensitivity) under ample water supply. During extreme droughts, hyposensitive and hypersensitive ecosystems achieved similar net ecosystem productivity employing considerably different structural-functional strategies. However, hyposensitive ecosystems, risking their hydraulic system with permissive WUS, did not recover from extreme droughts as quickly. Models predicting current performance and future distributions of vegetation types should account for the greater vulnerability of hyposensitive ecosystems to intensifying atmospheric and soil drought.

Duke Scholars

Author Ram Oren Environmental Sciences and Policy