Belowground biomass decomposition is driven by chemical composition in subtropical pastures and native rangelands

Abstract

Abstract Litter decomposition, particularly from belowground pools, is a key process controlling the flow of nutrients and the sustainability of native and cultivated grazinglands. This study evaluated in situ belowground decomposition of saw‐palmetto (Serenoa repens [W. Bartram] Small) and bahiagrass (Paspalum notatum Flügge; BG), which corresponded to the predominant plant species in native and cultivated pastures in the southeastern United States. Belowground biomass decomposition (180 d) was estimated using the litterbag technique during the summer and winter. Season showed no effect on belowground decomposition. Decomposition followed a double exponential model (P ≤ .01) and was greater for BG than for native rangeland (NR) (−0.0008 and −0.0001 g g−1 d−1, respectively; P = .0035), resulting in less remaining material at the end of incubation for BG (74% compared with 93% for NR; P ≤ .002). Greater decomposition in BG occurred due to more favorable chemical composition than NR, namely greater initial N concentration (17 and 8 g kg−1 organic matter for BG and NR, respectively) and lower initial C/N ratio (29 and 65 for BG and NR, respectively), lignin/N ratio (13 and 54 for BG and NR, respectively), and C/P ratio (407 and 1,327 for BG and NR, respectively). Despite the differences in initial C/N ratios, remaining N was similar between BG and NR at end of incubation (96 and 84%, respectively; P = .3711). Land use intensification in grazinglands, in particular conversion of native rangelands to cultivated pastures, can have major impacts on belowground decomposition and on the biogeochemical cycle of nutrients in these ecosystems.