Multiple scales of spatial heterogeneity control soil respiration responses to precipitation across a dryland rainfall gradient

Soil respiration (Rs) is a major pathway for carbon release to the atmosphere. We explored variability in dryland Rs response to rainfall pulses at multiple levels of spatial heterogeneity: 1) along a hyper-arid to arid rainfall gradient, 2) across soil surfaces that differ in stability and composition, and 3) among different geomorphic and vegetation patch types. We measured in situ Rs responses for 48 h following simulated rainfall pulses in the Namib Desert. Working across the rainfall gradient, we compared Rs responses on two soil surfaces. Each soil surface had two vegetation/geomorphic patch types that differed in organic matter sources and transport processes, with one characterized by depositional inputs and one characterized by erosional losses. Soil respiration was highly responsive to rainfall pulses, although soil surfaces and patch types often exerted more control on Rs than did rainfall pulses. Rainfall generally had proportionally greater influence on Rs with higher annual rainfall. Greater Rs occurred on stable than unstable soil surfaces and in depositional than erosional patch types. Large differences in Rs among rainfall zones, soil surfaces, and patch types point to the need to carefully consider multiple scales of spatial heterogeneity when interpreting dryland biogeochemical fluxes.