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

[摘要] Microbial respiration depends on microclimatic variables and carbon (C)substrate availability, all of which are altered when ecosystems experiencemajor disturbance. Widespread tree mortality, currently affectingpiñon–juniper ecosystems in southwestern North America, may affect Csubstrate availability in several ways, for example, via litterfall pulsesand loss of root exudation. To determine piñon mortality effects on C andwater 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 mortalityevent and a nearby site with live canopy. We monitored the respirationresponse to water and sucrose applications to the litter surface and to theunderlying mineral soil surface, testing the following hypotheses: (1) soilrespiration in a piñon–juniper woodland is water- and labile C-limited inboth the litter layer and mineral soil; (2) piñon mortality reduces the Climitation of litter respiration; and (3) piñon mortality enhances the Climitation of mineral soil respiration. Litter respiration at both sitesresponded to increased water availability, yet surprisingly, mineral soilrespiration was not limited by water. Consistent with hypothesis 2, Climitation of litter respiration was lower at the recent mortality sitecompared to the intact canopy site. Applications to the mineral soil showedevidence of reduction in CO₂ flux on the girdled site and anon-significant increase on the control. We speculate that the reduction mayhave been driven by water-induced carbonate dissolution, which serves as a sinkfor CO₂ and would reduce the net flux. Widespread piñon mortalitymay decrease labile C limitation of litter respiration, at least during thefirst growing season following mortality.

[学科分类] 地球化学与岩石