Land-use and climate effects on soil respiration quantified with a landscape sensor network

Thursday, 18 December 2014
Steven Crum and Darrel Jenerette, University of California Riverside, Riverside, CA, United States
Land-use change alters the magnitudes and variability of soil respiration (Rs). However, the importance of ecosystem and landscape drivers of Rs remain poorly understood from an empirical and mechanistic standpoint and likely vary across climate gradients. To address this knowledge gap we asked, what regulates the spatial and temporal variation of Rs across a human dominated region? From a landscape perspective, climate and land-use are hypothesized to be key drivers of Rs. From a soil physiological perspective, variability in temperature, moisture, and substrate availability regulate Rs. According to an inverse metabolic activity hypothesis, systems with higher metabolic activity will have less temporal variability in Rs than those with lower rates. Alternatively, soil substrate availability may drive sensitivity of Rs to water inputs. To quantify variability in Rs and test hypotheses of its regulation we deployed an Rs sensor network beginning in November 2013 with nodes distributed across three land-use types ─ lawn, agriculture, and wildland ─ at three sub-regions spanning a coastal to inland to desert climate gradient (total 9 sites, 3 land-uses x 3 sub-regions). At each node we are measuring soil Rs using the flux gradient approach, which includes soil state CO2 sensors, temperature, and moisture measured at three depths and at five minute intervals.

We analyzed the data for the winter sampling period, which is southern California's rainy season. The mean of Rs was lowest at the coastal and highest in the desert sub-regions for both lawn (3.99 and 4.7 μmol CO2 m-2 s-1) and wildland (0.23 and 0.49 μmol CO2 m-2 s-1)  land-uses. Rs was the highest in the inland sub-region for agricultural land-uses (4.1 μmol CO2 m-2 s-1). Lawn and wildland land-uses had increasing coefficient of variation in Rs across the coastal to desert climate gradient, while agriculture had decreasing variation. Sites that had higher mean fluxes and soil organic matter, a proxy for substrate availability, also had higher variability, supporting the hypothesis on substrate regulation of Rs sensitivity to water inputs. As urban centers spread in the arid and semi-arid Southwest, the likely consequences of land-use change will be increased magnitude and variance in Rs as the result of increased soil nutrient and water inputs.