Abstract
Abstract. Microbial respiration depends on microclimatic variables and carbon (C) substrate availability, all of which are altered when ecosystems experience major disturbance. Widespread tree mortality, currently affecting piñon–juniper ecosystems in southwestern North America, may affect C substrate availability in several ways, for example, via litterfall pulses and loss of root exudation. To determine piñon mortality effects on C and water limitation of microbial respiration, we applied field amendments (sucrose and water) to two piñon–juniper sites in central New Mexico, USA: one with a recent (< 1 yr), experimentally induced mortality event and a nearby site with live canopy. We monitored the respiration response to water and sucrose applications to the litter surface and to the underlying mineral soil surface, testing the following hypotheses: (1) soil respiration in a piñon–juniper woodland is water- and labile C-limited in both the litter layer and mineral soil; (2) piñon mortality reduces the C limitation of litter respiration; and (3) piñon mortality enhances the C limitation of mineral soil respiration. Litter respiration at both sites responded to increased water availability, yet surprisingly, mineral soil respiration was not limited by water. Consistent with hypothesis 2, C limitation of litter respiration was lower at the recent mortality site compared to the intact canopy site. Applications to the mineral soil showed evidence of reduction in CO2 flux on the girdled site and a non-significant increase on the control. We speculate that the reduction may have been driven by water-induced carbonate dissolution, which serves as a sink for CO2 and would reduce the net flux. Widespread piñon mortality may decrease labile C limitation of litter respiration, at least during the first growing season following mortality.
Highlights
Earth System SciencesArid and semi-arid ecosystem processes are dynamic over time, pulsing in response to rainfall events (Reynolds et al., 2004; Schwinning and Sala, 2004)
Consistent with our hypotheses, respiration responded to both water and sucrose additions and results were similar for the repeated experiments conducted at the reference site (Fig. 1)
The low k following treatments to the mineral soil indicated that the sucrose effect was longer-lasting compared to the litter treatment response (Fig. 3b)
Summary
Arid and semi-arid ecosystem processes are dynamic over time, pulsing in response to rainfall events (Reynolds et al., 2004; Schwinning and Sala, 2004). The response of soil respiration to small (< 5 mm) rain events is fueled by heterotrophs utilizing soil organic carbon (C), rather than autotrophs, because such events often cannot be accessed by vegetation; ,SsmoallildraEinaevretnhts lead to net C loss from these systems (Huxman et al, 2004; Carbone et al., 2011). Predicting future climate effects on soil C requires a better understanding of controls over, or limitations to, arid and semi-arid respiration. Increases in soil moisture enhance substrate availability for microorganisms, which typically increases respiration rates and enhances temperature
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