Decreased carbon limitation of litter respiration in a mortality-affected piñon-juniper woodland

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) water and sucrose applications increase temperature sensitivity of respiration; (3) the mortality-affected site will show a reduction in C limitation in the litter; (4) the mortality-affected site will show an enhancement of C limitation in the mineral soil. Litter respiration at both sites responded to increased water availability, yet surprisingly, mineral soil respiration was not limited by water. Temperature sensitivity was enhanced by some of the sucrose and water treatments. Consistent with hypothesis 3, C limitation of litter respiration was lower at the recent mortality site compared to the intact canopy site. Results following applications to the mineral soil suggest the presence of abiotic effects of increasing water availability, precluding our ability to measure labile C limitation in soil. Widespread piñon mortality may decrease labile C limitation of litter respiration, at least during the first growing season following mortality.