Landscape‐scale plant water content and carbon flux behavior following moisture pulses: from dryland to mesic environments

Abstract

Rain pulses followed by interstorm drying periods are the fundamental units of water input into ecosystems on subweekly time scales. It is essential to understand landscape-scale vegetation responses on these unit time scales as they may describe sensitivity of landscape water, carbon, and energy cycles to shifts in rainfall intensity and frequency, even if the average seasonal precipitation remains unchanged. Because pulse investigations are primarily carried out in drylands, little is known about the characteristics and extent of ecosystem plant pulse responses across the broader range of climates and biomes. Using satellite-based plant water content (from vegetation optical depth) and plant carbon uptake observations from eddy covariance towers across the continental United States climate gradient (dry to humid), we characterize large-scale plant carbon and water uptake responses to rain pulses during spring and summer months. We find that while all ecosystems in the study region show discernable plant water content and carbon flux responses to rain pulses, drier ecosystems exhibit more frequent and longer duration responses. Unlike mesic environments, drylands show significantly different responses under varying antecedent soil moisture and pulse magnitude conditions; the largest water and carbon uptakes follow large pulses on initially wet soils. We detect soil moisture thresholds primarily in drylands, which can partly explain dryland vegetation's different responses under dry and wet conditions. We conclude that vegetation responds to individual pulses of water availability across all climates and therefore a range of ecosystems are sensitive to rainfall distributions beyond simple seasonal precipitation totals.