Soil moisture, temperature, and carbon substrate influences on soil respiration in a piñon-juniper woodland
Abstract
Arid and semi-arid ecosystems may be more vulnerable to climate change than mesic systems, having potentially large consequences for ecosystem carbon balance of the US southwest. Specifically, piñon-juniper woodlands cover much of the land area in the SW US, and they have experienced widespread piñon mortality in the past ten years. The impact of this mortality on carbon cycling in these ecosystems has yet to be fully examined. Of particular current interest is how soil temperature, soil moisture, and substrate availability interact to influence short-term variability of soil respiration rates. In this study, we examined the dependence of soil respiration on recent piñon photosynthate, temperature, and moisture in a piñon-juniper woodland in central New Mexico. We utilized phloem-girdling to study the importance of recently-fixed photosynthate as substrate for respiration, and we treated the stable carbon isotope ratio of soil respiration as indicative of different substrate sources contributing to soil respiration. Due to the presence of C3, C4, and CAM photosynthetic pathways in the ecosystem, we were able to infer changing contribution of different sources to soil respiration. We found that soil-respired δ13C depended on both soil moisture and lagged precipitation, although in dissimilar manners, suggesting different mechanisms are triggered by rainfall events compared to elevated soil moisture. C3-source respiration responded quickly to precipitation events. Over a ten-day period following girdling of piñon trees, soil-respired δ13C did not significantly change compared to a reference plot. There were also distinct differences in carbon isotope signatures and temporal patterns of such signatures of soil respiration collected in open spaces compared to underneath piñon canopies, emphasizing the importance of considering spatial variability when sampling soil-respired CO2 in patchy ecosystems. Overall, we found little evidence that soil respiration in this ecosystem depended strongly on recently-fixed photosynthate from piñon trees, and instead seemed to be largely regulated by precipitation events and soil moisture levels.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B23H0483B
- Keywords:
-
- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0454 BIOGEOSCIENCES / Isotopic composition and chemistry