Soil respiration responses to variation in temperature and moisture availability under woody plants and grasses
Abstract
Woody plant encroachment into grasslands, such as in the southwestern US, is thought to have altered regional carbon fluxes due to the differences in structure and function between grasses and woody plants. It is unknown how climate change predictions for such areas, particularly warmer temperatures and fewer but larger precipitation events, might further acerbate our ability to estimate flux dynamics. Soil respiration, a key flux affecting ecosystem carbon balance, has been increasingly studied, but the exact effects of temperature and precipitation changes on flux rates have not been fully determined, particularly their interactive effects. The goal of this study was to compare soil respiration responses to different temperatures in soils under native southwestern mesquites and grasses undergoing a precipitation pulse, whilst removing other confounding factors, such as soil history, through the controlled environments within Biosphere 2. Mesquites and grasses were transplanted into ground basalt within two environments maintained at a 4°C temperature difference, the projected temperature increase from climate change. Post-transplant soil samples were incubated between 10 and 40°C to determine the temperature sensitivities of soils from each microhabitat within a month of this transplant. A single-peak, best-fit model for grass soils suggested a weak temperature sensitivity, while mesquite soils showed little to no sensitivity. Additionally, all plants underwent a drought treatment prior to the precipitation event, and soil respiration rates were tracked over several days using the collar technique. This portion of the study allowed for an estimation of the sensitivity of soil respiration to precipitation pulses under a variety of antecedent moisture conditions. Initial results illustrate that soils under mesquites tend to respire significantly more than soil under grasses or in bare soils over the course of a precipitation event. Together, these results suggest that autotrophic respiration drives soil respiration as soils develop. Over the course of soil evolution, changes in temperature sensitivity are expected as organic material and the microbial community develop. The continuation of this study over a nine-month period for a wider range of precipitation event sizes could provide important findings for soil respiration and climate change models.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B41E0243P
- Keywords:
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- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0465 BIOGEOSCIENCES / Microbiology: ecology;
- physiology and genomics;
- 0486 BIOGEOSCIENCES / Soils/pedology;
- 1632 GLOBAL CHANGE / Land cover change