Soil carbon and associated bacterial community shifts driven by fine root traits along a chronosequence of Moso bamboo (Phyllostachys edulis) plantations in subtropical China

Abstract

Moso bamboo (Phyllostachys edulis) is widely considered to be effective in capturing and sequestering atmospheric C, but the long-term effects of extensive management strategies on soil organic carbon (SOC), bacterial communities, fine root (FR, ø ≤ 2 mm) traits, and their inherent connection remain unclear. In this study, we simultaneously measured the SOC content of the bulk and rhizosphere soil fractions, the aggregate stability, the chemical composition of SOC (solid-state ¹³C nuclear magnetic resonance [NMR]), the bacterial community structure in the rhizosphere, and the FR morphological traits including biomass, specific root length (SRL), and root length density (RLD) along a chronosequence (stand age of 19, 37, and 64 years) of extensively managed Moso bamboo plantations and in an adjacent secondary forest as a control. The organic C content in both the rhizosphere and bulk soil increased rapidly with plantation age in the 0-20- and 20-40-cm soil layers, accompanied by an increase in the aggregate stability. FR traits including biomass, SRL, and RLD also increased continuously in response to soil C:N:P stoichiometry. All of these traits were significantly correlated with SOC, occluded particulate organic C (oPOC), and mineral-associated organic C (MOC), suggesting that FR traits could drive the soil C sequestration with the plantation age. Further analysis indicated that the microbial biomass C (MBC) content, MBC/total organic carbon (TOC) ratio, and bacterial abundance decreased with the plantation age, and the shift from soil oligotrophy to copiotrophy bacteria were mainly driven by changes in FR traits and SOC properties. Such a reassembly of bacterial communities combined with an increase in root biomass is favorable for the accumulation of stable C functional groups (alkyl C or aromatic C). Our findings indicate that extensive management regimes of Moso bamboo plantations could promote long-term soil C sequestration especially in the rhizosphere by promoting the formation of soil aggregates and organic-mineral complexes and by shifting bacterial community composition, and that these changes can be inferred through changes in the FR traits.

Keywords: Bacterial community structure; Extensive management; Root morphology; Soil C sequestration.