Nutrient supply at the local tree level in mixed forests of sessile oak and beech

Abstract

In mixed-species forests, tree species composition can affect nutrient return through litter fall. This in turn is expected to have an effect on soil available nutrients, which could influence the nutrient status at the local tree level. Using ion-exchange resins, we estimated resin available soil nutrients at two depths beneath target trees of sessile oak and beech in the Belgian Ardennes. First we tested whether resin available nutrients were related to tree nutrition, using foliar nutrient concentrations as a proxy. In a second step, we tested whether local litter fall, through total nutrient return or litter species composition, affected resin available nutrients. In a final stage, we tested the impacts of local stand composition, as an integrated proxy of above- and belowground processes, and compared them to those of litter composition. With the exception of P for oak, nutrient supply was only poorly related to foliar nutrient concentrations for both target species. The effects of litter fall on nutrient supply were driven by litter species composition and not by total nutrient inputs. Litter composition and local stand composition effects were in close agreement. Our results show that nutrient supply to target trees in mixed-species stands is affected by local neighbourhoods, yet to a limited extent. Direct translation of resin available nutrients into foliar concentrations is probably hampered by complex capture patterns.