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Autotrophic and heterotrophic contributions to short‐term soil CO 2 efflux following simulated summer precipitation pulses in a Mediterranean dehesa
Author(s) -
Casals Pere,
LopezSangil Luis,
Carrara Arnaud,
Gimeno Cristina,
Nogués Salvador
Publication year - 2011
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2010gb003973
Subject(s) - environmental science , heterotroph , topsoil , autotroph , soil respiration , soil water , litter , soil carbon , mineralization (soil science) , environmental chemistry , mediterranean climate , soil organic matter , plant litter , cycling , soil science , chemistry , agronomy , ecosystem , ecology , biology , history , archaeology , genetics , bacteria
Autotrophic and heterotrophic components of soil CO 2 efflux may have differential responses to environmental factors, so estimating the relative contribution of each component during summer precipitation pulses is essential to predict C balance in soils experiencing regular drought conditions. As even small summer rains induced high instantaneous soil respiration rates in Mediterranean wooded grasslands, we hypothesized that standing dead mass, surface litter, and topsoil layer could play a dominant role in the initial flush of CO 2 produced immediately after soil rewetting; in contrast, soil CO 2 effluxes during drought periods should be mostly derived from tree root activity. In a grazed dehesa, we simulated four summer rain events and measured soil CO 2 efflux discontinuously, estimating its δ 13 C through a Keeling plot nonsteady state static chamber approach. In addition, we estimated litter contribution to soil CO 2 efflux and extracted soil available C fractions (K 2 SO 4 ‐extracted C and chloroform‐fumigated extracted C). The δ 13 C‐CO 2 from in‐tube incubated excised tree roots and rewetted root‐free soil was −25.0‰ (±0.2) and −28.4‰ (±0.2), respectively. Assuming those values as end‐members' sources, the autotrophic component of soil CO 2 efflux was dominant during the severe drought, whereas the heterotrophic contribution dominated from the very beginning of precipitation pulses. As standing dead mass and fresh litter contribution was low (<25%) in the first day and negligible after, we concluded that CO 2 efflux after rewetting was mostly derived from microbial mineralization of available soil organic C fractions.