Altered limitations to soil CO2 efflux following a tree mortality event in a semi-arid woodland
Abstract
Recent mass tree mortality events occurring throughout western North America during the past decade will potentially increase COtextsubscript{2} loss from affected forests and woodlands. A major portion of C lost to the atmosphere is soil COtextsubscript{2} efflux (SE). SE, a combination of root and microbial respiration, is likely affected by mass mortality through key limiting variables: water, C substrate, and nitrogen (N) availability. The loss of active roots may lead to increases in soil water and N availability; the fall of dead litter may enhance labile C supply. These limitations may not act independently of each other; trade-offs may exist between C and water limitation and between C and N limitation. This "sliding scale" model of limitations can help us understand how disturbance might affect C cycle mechanisms. We used field amendments to directly test the effects of piñon mortality on limitations to SE in a piñon-juniper woodland in central New Mexico, USA. In September 2009, piñons were girdled and sprayed with herbicide to induce a mass mortality event and a nearby area was retained as a reference site. Limitation of SE to water, labile C, and N was experimentally tested three years later by monitoring the response of SE to water, sucrose and ammonium sulfate solution applications to both the mineral soil and litter surface. SE was limited by water, C, and N in the mineral soil at both the mortality and reference sites (two-way ANOVA; P<0.001 for all comparisons). In addition, we found that SE increased more in response to both water and N at the mortality-affected site than at the reference site. In contrast, SE responded less to C additions at the mortality-affected site than at the unaltered site. Treatments to the litter surface revealed greater water limitation of SE at the mortality site but no differences in C or N limitation. We propose that the increase in litterfall C at the mortality site drove the increased response of SE to water additions. In the mineral soil, N limitation was induced as soil-available N was used by microbes to metabolize the additional litterfall C. We conclude that the SE response following mortality is more dependent on soil water and N availability than from non-mortality-affected areas. Thus, SE in the years after mortality may follow increases in water and N availability.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.B34A..02B
- Keywords:
-
- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0469 BIOGEOSCIENCES / Nitrogen cycling