Temperature sensitivity of carbon decomposition in soil aggregates along a climatic gradient

Abstract

Global warming affects the carbon (C) pools in terrestrial ecosystems, accelerating biological processes that feed back into the phenomenon of climate change. Globally, grassland ecosystems accumulate large quantities of organic C into soils and are considered a corner stone for global warming mitigation. The aim of this study was to evaluate the temperature sensitivity of C decomposition in different soil aggregate fractions in grassland ecosystems across a north-south latitudinal gradient in Chile. Soil samples were collected from Mediterranean semi-arid (MSA; 32°31, to 34°19, south latitude), temperate semi-oceanic (TSO; 35°36, to 36°27, south latitude), temperate oceanic (TO; 40°36, to 43°03, south latitude) and subpolar semi-oceanic (SPSO; 43°57, to 47°40, south latitude) climate zones, and water-stable macroaggregates (250-2,000 µm) and free microaggregates (50-250 µm) were isolated. Two experiments were performed using short-term incubations (14 days). First, absolute soil respiration and specific soil respiration from isolated aggregates were assessed at 20 °C, and second, the isolated aggregates were incubated at different temperature levels (20-30 oC for MSA and TSO; 10-20 oC for TO and SPSO) to quantify the energy of activation (Ea) and temperature sensitivity (Q10). In general, the results do not provide evidence of differences between soil aggregate fractions in any of the evaluated parameters, but the soils differed across the latitudinal gradient. High absolute respiration rates and specific respiration, which were related to high grassland productivity, were observed in soils from TO and SPSO zones. The Q10 values demonstrated a strong positive correlation with annual precipitation, so C decomposition in soils from zones with high precipitation exhibits increased temperature sensitivity.