LAUSR

Restoration of agricultural riparian buffers with trees (agroforestry) provides an elegant solution to enhance carbon storage while also augmenting local biodiversity. Yet the scope and role of riparian plant community diversity in key soil dynamics remain unresolved. Operationalizing riparian age [young (<10 years) and mature (>30 years) since establishment] and forest stand type [coniferous and deciduous dominant] to capture the potential extent of plant diversity, we measured plant functional trait diversity (FD) and community weighted mean trait values (CWM), microbial composition, abiotic soil conditions and rates of soil CO2 efflux (mg CO2 -C m-2 h-1 ). We used piecewise structural equation modelling (SEM) to further refine the role of biotic indices (leaf, root and microbial characteristics), and abiotic factors (soil physio-chemical metrics) on soil C cycling processes in riparian systems. We found significantly lower rates of CO2 efflux (F = 8.47; p<0.01) over one growing season and higher total soil C (F = 3.46; p = 0.03) in mature buffers as compared with young buffers. Using SEM, we describe influences on soil C content (marginal r2 = 61) and soil CO2 efflux (marginal r2 = 53). Within young buffers, soil C content was significantly predicted by fungal:bacterial ratio and root length density, whereas in mature buffers, tree leaf characteristics were associated with soil C content. Soil CO2 efflux was predicted by soil moisture, soil carbon content, and herbaceous root characteristics. Evidently, leaf and root functional traits in combination with broad soil parameters significantly describe soil C dynamics in the field however, significant pathways are not the same throughout the lifecycle of a riparian forest. This article is protected by copyright. All rights reserved.