Plant derived carbon (C) compounds mainly enter soils as either aboveground litter inputs or as belowground root derived inputs. Primarily research has focused on aboveground inputs but recently this focus has shifted to the belowground, particularly towards root exudates. Root exudates are composed of low molecular weight C compounds which are passively or actively exuded from plant roots. Additionally the composition of root exudates is likely to alter in response to global change. Such a change in the composition of root exudates has been linked to changes in microbial community structure but whether this also impacts the function of these communities remains unknown. Here under laboratory conditions, we amended soils sourced from three habitats (deciduous forests, coniferous forests, and meadows) with one of eight cocktails (i.e. glucose, glycine, oxalic acid, glucose + glycine, glucose + oxalic acid, glycine + oxalic acid, glucose + glycine + oxalic acid, and water) meant to simulate root exudates. These soils were amended for 90 days at a rate comparable to that found under field conditions. After 90 days we assessed microbial community function using an abbreviated catabolic response profile which allowed us to determine the mineralization of glucose, glycine, and oxalic acid by these soils.
Results/Conclusions
Prior to amending the soils with simulated root exudates, we found that habitat was a determinant of microbial community function and after the 90 day experiment it remained a dominant control. Unexpectedly, the amendments of root exudates exerted no influence on microbial community function. This indicates that microbial community function may be resistant to changes in the composition of root exudates in general and low molecular weight C compounds specifically. Potentially, this may be because such compounds are broadly utilized by the microbial community and unlike more chemically recalcitrant plant inputs do not invoke a functional change. Ultimately this suggests that changes in the composition of root exudates under global change scenarios may not alter the function of soil microbial communities.
