B4WarmED forest warming experiment: shifts in nematode community influence plant cover and composition

Background/Question/Methods

Global temperature rise and deforestation are key forces driving plant community shifts, such as range shifts of temperate forest species into boreal forests. As range shifts of plant communities are slow to observe, ecotones - boundaries between two ecosystems - are target areas for providing early evidence of ecological responses to warming. The role of soil fauna is however poorly explored in ecotones, although positive and negative effects of soil fauna on plant species can influence plant community structure and hence can provide insights into the mechanisms of range shifts. We studied nematode communities encompassing key trophic groups of soil food webs in response to experimentally increased temperature (ambient, +1.8°C, +3.6°C) in soils of closed canopy and open (recently harvested) forest stands in the temperate-boreal forest ecotone of Minnesota, USA at two experimental sites: Cloquet and Ely and calculated various established nematode indices. Additionally, we estimated species-specific coverage of herbaceous and shrub species from the same experimental plots and examined if changes in nematode community are significantly associated with plant community productivity and structure.

Results/Conclusions

Individual trophic groups did not differ among temperature treatments, but the ratio between microbial-feeding and plant-feeding nematodes increased significantly with temperature rise in both undisturbed (closed canopy) and harvested (open) areas. Such a change could contribute to better plant performance if predation pressure on microbes led to higher nutrient availability. We found that the increase in this ratio was positively related to the total coverage of herbaceous and shrub plant species, a proxy for plant community productivity. Further, multivariate analyses revealed that temperature rise consistently shaped understory herbaceous and shrub plant communities in both closed canopy and recently cleared areas. Our findings suggest that shifts in nematode community structure in response to temperature rise and forest harvest may alter plant performance and community structure in ecotone regions. Notably, these results were consistent across the two distinct experimental sites. We thus conclude that future studies should consider changes in both aboveground and belowground communities as well as potential interactions between those to improve understanding of plant community shifts, including their range shifts, in ecotone regions in response to global change.