An increasing body of literature provides evidence of a positive relationship between biodiversity and ecosystem functioning (BEF), however, there are far fewer studies of this relationship that examine belowground processes. In two experimental plantations (temperate and sub-boreal), we investigated the relationship between tree diversity, and understory diversity, and belowground processes, as well as soil carbon and nitrogen status (fine root productivity, fine root decomposition, soil C and N concentrations in the surface mineral soil).Fine root productivity (< 2mm) in the temperate plantation was measured by one year ingrowth cores. Decomposition was measured by mass loss of a common substrate (cellulose) in the temperate plantation, while in the second sub-boreal plantation, decomposition was evaluated by mass loss of fine roots (of the entire community, including understory). Total soil C and N, as well as fractions (labile and more stable) were measured in the surface 15 cm of the mineral soil in each case.
Results/Conclusions
In young temperate plantations (4 yrs : monocultures and mixtures of 2, 4 species), fine root productivity was not higher with increasing species richness (SR), however species identity effects on productivity were noted (higher root productivity of conifer versus deciduous species). Decomposition of a common substrate (cellulose) tended to increase with SR. In older sub-boreal plantations (27 yr) with monocultures and mixed species, decomposition of fine roots was not related to overstory diversity, nor to understory SR, but rather to the presence of certain understory species groups, such as ferns and certain forest herbs. The effect on fine root decomposition is likely due to species-specific effects inducing a favorable soil environment (such as higher leaf and root litter quality, higher soil moisture). In general, total soil C and N (and fractions) were unaffected by SR of either the overstory or the understory. Both experiments then point towards a stronger species identity effects of dominant species, rather than an SR effect, on belowground processes in relatively young plantation ecosystems.