Differential rhizosphere soil nutrient use strategy of invasive and native shrub species in oak, pine, and oak-pine mixed forest ecosystems of the Himalaya

Abstract

Vegetation types contribute differently to the soil nutrient status; however, this study aims to investigate the rhizosphere soil nutrient use strategy of invasive (Ageratina adenophora) and native (Berberis asiatica and Rubus ellipticus) shrub species under varied soil nutrient regimes. The rhizosphere soil samples of A. adenophora, B. asiatica, and R. ellipticus were collected from the upper (0–10 cm) and lower (10–20 cm) soil depths in oak, pine, and oak-pine mixed forest stands. Bulk soil was collected as control in the selected forest stands. Linear Mixed Model (LMM) and analysis of variance demonstrated that most soil properties were significantly (p < 0.05) higher in the rhizosphere soil of A. adenophora than in that of B. asiatica and R. ellipticus. Specifically, soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), nitrogen (MBN), and dehydrogenase enzyme activity (DHA) were higher in the rhizosphere of invasive A. adenophora than in that of native B. asiatica and R. ellipticus in oak forest. In contrast, the rhizosphere soil of native shrubs retained higher TN, Available phosphorus, and DHA than the invasive A. adenophora in the pine forest stand. Redundancy analysis (RDA) demonstrated that the shrub species and forest stands accounted for 22.6% and 10% variance in the rhizosphere soil properties, respectively. Among the forest stands, the rhizosphere soil traits of A. adenophora were higher than the rhizosphere of native species in oak forests suggesting that nutrient-rich soil ecosystems and favourable microclimatic conditions are suited for the growth and survival of invasive species. Conversely, pine forests, which are adapted to resource co-limitation and higher temperatures may suppress the proliferation of A. adenophora, obligating A. adenophora to alter its nutrient use strategies from nutrient acquisition in oak to nutrient conservation in pine forests. Thus, our findings suggest that mixed forests (oak and pine) should be conserved to enhance the species richness.