Soil respiration across a disturbance gradient in sclerophyllous ecosystems in Central Chile

Abstract

Sclerophyllous shrubs and forests are predominant in semiarid Central Chile and have a long history of degradation by fire, cultivation, firewood extraction and grazing. The aim of this study was to compare the amount and environmental drivers of soil respiration across a disturbance gradient in sclerophyllous ecosystems in the National Reserve Robleria del Cobre de Loncha in Central Chile. In a north-facing toe slope, four disturbance conditions were identified: slightly (D1) and moderately disturbed (D2) sclerophyllous forest, (D3) strongly disturbed thorn scrub and (D4) most disturbed A. caven savanna. Twelve 25 x25-m plots (625 m2) were distributed equally across D1, D2, D3 and D4. Soil respiration (Rs), soil temperature (Ts), volumetric water content (0v) and exchangeable nitrogen (Ns) were measured at six dates in each plot between August 2009 and May 2010. Additionally, Ts and 0v were continuously recorded from July 2010 to August 2012 (30-minute intervals) in one plot per disturbance condition (i.e., 4 out of 12 plots). The values of Rs increased linearly with 0v with similar slopes but different intercepts, which increased as the disturbance receded. Once soil water content was taken into account, Rs increased with Ts with the same slope but with a disturbance-dependent intercept. Additionally, the response of Rs to Ts was more pronounced as 0v increased. The values of Ns were uncorrelated with Rs. The annual values of Rs were 4.4-fold greater in D1 (1,735 g C m-2 yr-1) compared with D4 (392g C m-2 yr-1). Disturbance presumably decreased Rs by reducing the litter layer, soil organic matter, root biomass and soil water content, particularly in the hot-dry season. Under a predicted climate change scenario of a 40% decrease in rainfall and 4 [grados]C increase in air temperature by the year 2100, we found that annual Rs would be reduced on average by 28% compared with the current climate, with that reduction being more pronounced under more disturbed conditions, suggesting that less disturbed conditions would be more resistant to climate change, thus further justifying the restoration of these damaged ecosystems.