Soil respiration responses to precipitation pulse-dynamics in a piñon-juniper ecosystem

Arid ecosystem CO₂ efflux is significantly impacted by the response of individual ecosystem constituents to precipitation events. Woodland ecosystems of Southwestern USA have experienced severe variability in precipitation over the last decade, and such variability is expected to increase in association with climate change. Our objective is to understand the impacts of precipitation variation on CO₂ efflux in piñon-juniper woodlands. At a field site located at the Sevilleta LTER in central New Mexico, we used automated soil respiration chambers along with widely distributed spot measurements located between (interspace) and under the crowns of piñon (Pinus edulis) and juniper (Juniperus monosperma) trees and followed the response of CO₂ flux to seasonal changes in precipitation. The automated chambers collect 20 points per day for each chamber, while a LICOR 6200 is used to measure the distributed collars. Here we compare respiration data from August 2006 to the present with micro-meteorological data from the site. This data forms the basis for comparison to CO₂ flux responses to ecosystem scale manipulations of water availability (increases and decreases) that will be imposed on these plots during the spring of 2007. CO₂ flux magnitudes and duration for most pulse sizes were significantly higher for piñon cover than for interspaces. Soil respiration under piñon crowns is always higher than interspaces, and rates under juniper are intermediate between piñon and interspace respiration. Interspaces have a higher response to very small pulse events than piñon or juniper, but pre-pulse respiration values are larger under piñon and juniper than interspaces. Daytime soil respiration during winter months rarely peaks above 1.0 μmol/m²/s, while summer months rarely fall below 1.0 μmol/m²/s. Understanding soil respiration responses aid in predicting the effects of climate change on carbon budgets of the expansive ecosystem.