Rhizospheric processes are more biogeochemically active between plant and soil systems and appear to be more responsive to environmental change than bulk soil processes. A better understanding of rhizosphere carbon (C) and nitrogen (N) interactions under elevated carbon dioxide (CO₂) is essential for accurately predicting long-term C fixation in terrestrial ecosystems under future climate change. The responses of rhizospheric processes to elevated CO₂ vary across mono-species studies, yet our understanding of the responses of multiple co-occurring species is still limited.

Prof. CHENG Xiaoli from Wuhan Botanical Garden, cooperated with New Zealand AgResearch Grasslands conducted a field study using the New Zealand free-air CO₂ enrichment (FACE) experiment to evaluate rhizospheric C and N dynamics in a low-fertility species (Agrostiscapillaris) and a high-fertility species (Loliumperenne) under 13 years of elevated CO₂ and at ambient levels.

Study demonstrated that the responses of the two species to elevated CO₂ differed in terms of growth, with a positive response for L. perenne and a negative response for A. capillaris. Despite contrasting responses of plant growth, elevated CO₂ significantly increased the total C and N (TC and TN, respectively), net N mineralization and nitrification rates in the rhizospheres across species. However, the rhizospheric microbial biomass C (MBC) was significantly enhanced for L. perenne but reduced for A. capillarisunder elevated CO₂. Elevated CO₂ did not affect rhizospheric NO₃^--N concentrations for either species, while it significantly increased the rhizospheric NH₄⁺-N concentration for A. capillaris.  

Together, the increased TC as well as the decreased MBC suggested rhizosphere in A. capillaris may be more favorable to long term C sequestration under elevated CO₂. The increased NH₄⁺-N concentration may stimulate the growth of A. capillaris under elevated CO₂ in the near future, which will have significant implication for the change in species composition.  

The findings in this study are useful for parameterizing terrestrial biogeochemical models with mixed-species ecosystems, which can be used to analyze the effects of possible future climate change. 

This research was financially supported by the National Natural Science Foundation of China and the “Strategic Priority Research Program-Climate Change: Carbon Budget and Relevant Issues” of the Chinese Academy of Sciences.  

Results have been published in Agriculture, Ecosystems and Environment “Rhizospheric carbon-nitrogen interactions in a mixed-species pasture after 13 years of elevated CO₂” .