Carbon and nitrogen allocation in leaf, fine root, soil, and microbial biomass in invasive Prosopis juliflora and native Acacia nilotica in semi-arid forests of the Aravalli hills

Abstract

Semi-arid forests of the Aravalli hills are rich in tree diversity, but plant invasions during the last several decades, especially by Prosopis juliflora (Sw.) DC. have affected the vegetation structure and biogeochemical cycles of these forests. We compared carbon (C), and nitrogen (N) concentrations in the fine root, leaf, and soil physicochemical properties under the invasive tree species, P. juliflora, and native, Acacia nilotica (L.) Willd. ex Delile, to evaluate the effect of invasive tree species on total soil C, N concentrations, and C:N ratios. We also analyzed the soil samples for soil organic C (SOC), total N (TN), soil microbial biomass C (MBC), and soil microbial biomass N (MBN) and stocks. Soil physical and chemical properties under the invasive P. juliflora and native A. nilotica trees varied significantly (p < 0.05). The C and N concentrations in the fine root, leaf, soil SOC, TN and MBC, and MBN concentrations were significantly (p < 0.05) higher in P. juliflora than A. nilotica while C:N ratio, and bulk density, exhibited the opposite trends. The C concentrations followed the order fine root > leaf > soil > microbial biomass while for N concentration and C:N ratios, it was leaf > fine root > soil > microbial biomass. The invasive P. juliflora had a lower C:N ratio in leaf, fine root, and soil than the native A. nilotica. The average rhizosphere soil, fine root, and leaf C concentration for P. juliflora were 36.72 ± 0.84 g kg−1, 547.84 ± 18.56 g kg−1, and 534.77 ± 5.12 g kg−1, respectively and were 1.42, 1.16 and 1.04 times higher than for A. nilotica. Similarly, P. juliflora average rhizosphere soil, fine root, and leaf N concentrations were 4.37 ± 0.11 g kg−1, 19.96 ± 0.94 g kg−1, and 23.18 ± 0.84 g kg−1, respectively, and 2.0, 1.27, and 1.85 times, respectively, higher than for A. nilotica. Further, the MBC:SOC or MBN:TN ratios were higher in native A. nilotica, likely indicating higher efficiency of microbes in soil C decomposition. Together, our results indicate that invasive P. juliflora altered the ecosystem processes and increased the soil and microbial C, and N stocks compared to native A. nilotica in the semi-arid forests of the Aravalli hills.