How grasses stabilize soil organic carbon in aggregates of semi-arid ecologically restored land: Evidence from 13C natural abundance

Abstract

Land restoration with grasses is suitable for boosting soil organic carbon (SOC) and biomass productivity. For developing better restoration policies to preserve or increase SOC stock and ecosystem function, a deeper knowledge on the impact of various grasses on SOC dynamics in restored land is required. Here, long-term SOC sequestration was assessed by investigating aggregate-associated carbon (C) and ¹³C natural abundance following land restoration with Cenchrus ciliaris, Panicum maximum, Chrysopogon fulvus, Heteropogon contortus, Sehima nervosum, and Vetiveria zizanioides grasses in semi-arid India. Among the grasses, C. ciliaris, H. contortus, and S. nervosum improved the proportion of large macroaggregates from 5 to 21 % at the surface and from 1.7 to 12.3 % in the subsurface layer, while the proportion of microaggregates declined significantly (P < 0.05). The higher δ¹³C values of small macroaggregates (SM) indicated greater C stabilization within the microaggregates under all grasses. The SM could protect ∼22–33 % and 8–15 % of total SOC in land restored with C. ciliaris, H. contortus, and S. nervosum at the surface and the subsurface soil, respectively. However, the roots of C. ciliaris, H. contortus, and S. nervosum contributed to ∼12.66–13.75 % and 2.22–11.24 % of SOC in those layers, respectively. The direction of C transfer was from macroaggregates to microaggregates in soils under C. cilirais, S. nervosum, and H. contortus. This C flow direction could explain greater SOC stabilization than other grasses. The greater amount of aggregate-protected C under these grasses was linked to their greater root biomass, density, and decay rate. In contrast, C transfer from microaggregates to macroaggregates under P. maximum, C. fulvus, and V. zizanioides could result in poor C stabilization. Thus, C. ciliaris, H. contortus, and S. nervosum could be potential options for SOC sequestration in semi-arid ecosystems.