Synergy and trade-off between carbon sequestration and soil water balance: impact of revegetation choices

Abstract

Revegetation is an effective measure for preventing land degradation and for mitigating climate change by reducing carbon dioxide in the atmosphere. However, vegetation cover is also generally considered to be a cause of a dried soil layer in drylands. The trade-off between soil water storage and soil carbon sequestration along a precipitation gradient in dryland ecosystems is well known, but the contributions of revegetation measures on the variations in the trade-off between carbon sequestration and soil water resource maintenance in soil profiles are often ignored. In this study, the trade-off and synergy between soil moisture content (SMC) maintenance and soil organic carbon (SOC) improvement in soil profiles on a semiarid hillslope are investigated in the context of revegetation choices. Three revegetation choices were selected for the comparative analysis: (a) afforestation using single tree species (Robinia pseudoacacia); (b) mixed tree species (R. pseudoacacia and Hippophae rhamnoides Linn); and (c) a mosaic of single tree bands (R. pseudoacacia, Armeniaca vulgaris, and H. rhamnoides Linn). Our results reveal a shift of synergy to trade-off at a depth of around 10–30 cm and a weakened trade-off between the middle (30–40 cm) and deep soil layers. For afforestation using a single tree species, there is a trade-off between SOC improvement and SMC promotion, as indicated by a negative correlation between the relative benefit of SOC and the relative benefit of SMC. For revegetation using mixed tree species and a mosaic of tree bands, positive correlations appeared. We draw two conclusions from these results: first, a shift in the trade-off and synergy between SMC maintenance and SOC improvement exists in soil profiles after revegetation on this semiarid hillslope; second, revegetation choices matter when reconciling the trade-off between SMC maintenance and SOC improvement. Revegetation with a single tree species (R. pseudoacacia) is not a good choice. When discussing the trade-off between carbon sequestration and soil water resource conservation in water-limited regions, more attention should be paid to site-level mechanisms and revegetation choices.