Numerous studies have reported that an elevated temperature increases plant growth and biomass accumulation and forest net primary productivity (NPP). Nutrient availability, mainly N, is the primary limiting factor for plant growth and productivity in boreal forest ecosystems, and thus, any continued enhancement of forest NPP will require either increase in the availability of resources or physiological adjustments that allow increased uptake of these resources. However, the potential mechanisms by which the sustained growth responses of plants to experimental warming may be maintained are poorly understood.

Recently, Prof. LIU Qing’ team from Chengdu Institute of Biology of CAS performed an experiment in which in situ exudates were collected from Picea asperata seedlings that were transplanted in disturbed soils under experimental warming and varying N availability. They found that the trees exposed to an elevated temperature increased their exudation rates in the unfertilized plots, which was coupled with stimulated microbial activity and accelerated N transformations in the unfertilized soils.

 In contrast, the trees exposed to both experimental warming and N fertilization did not show increased exudation rates or soil enzyme activity, indicating that the stimulatory effects of experimental warming on root exudation depend on soil fertility.Collectively, the results provide preliminary evidence that an increase in the release of root exudates into the soil may be an important physiological adjustment by which the sustained growth responses of plants to experimental warming may be maintained via enhanced soil microbial activity and soil N transformation.

Given the perceived importance of root exudates on SOM decomposition and nutrient cycling, this call for incorporating the underlying mechanisms by which plant root-microbe interactions influence soil processes in climate-carbon cycle models to determine reliable estimates of long-term C storage in forests.

The study entitled “Enhanced root exudation stimulates soil nitrogen transformations in a subalpine coniferous forest under experimental warming” has been published online in Global Change Biology.