Ageratina adenophora invasions are associated with microbially mediated differences in biogeochemical cycles

Authors: ZHAO, MENGXIN - Chinese Academy Of Agricultural Sciences; LU, XIAOFEI - Chinese Academy Of Agricultural Sciences; ZHAO, HAIXIA - Weifang Vocational College; YANG, YUNFENG - Tsinghua University; Hale, Lauren; LIU, WANXUE - Chinese Academy Of Agricultural Sciences; GUO, JIANYING - Chinese Academy Of Agricultural Sciences; LI, QIAO - Chinese Academy Of Agricultural Sciences; ZHOU, JIZHONG - University Of Oklahoma; WAN, FANGHAO - Chinese Academy Of Agricultural Sciences

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2019
Publication Date: 8/10/2019
Citation: Zhao, M., Lu, X., Zhao, H., Yang, Y., Hale, L.E., Liu, W., Guo, J., Li, Q., Zhou, J., Wan, F. 2019. Ageratina adenophora invasions are associated with microbially mediated differences in biogeochemical cycles. Science of the Total Environment. 677:47-56. https://doi.org/10.1016/j.scitotenv.2019.04.330.
DOI: https://doi.org/10.1016/j.scitotenv.2019.04.330

Interpretive Summary: Exotic plant invasions have considerable economic and ecological impacts on agricultural and natural systems. Native and introduced soil microbial communities may facilitate plant invasion, but mechanistic understanding of these interactions, particularly in natural ecosystems, is limited. Invasive plant species, Ageratina adenophora, grows rapidly in high soil nitrogen (N) conditions. Soils with A. adenophora in monoculture had unique properties relating to soil N, compared to those under mixed plant species and without A. adenophora. Soil nitrogen (N) content, relative abundances of microbial functional genes involved in N cycling, and N cycling process rates all increased under A. adenophora. This finding reveals that a potential mechanism of its invasion may be supporting a self-reinforcing environment via altered microbial community composition and functions. These insights are essential to control the spread of invasive plants.

Technical Abstract: Invasive plant species may alter soil nutrient availability to facilitate growth and competitiveness. However, roles and functional mechanisms of plant-associated microbes that mediate soil biogeochemical cycles remain elusive. Here, the effect of an invasive plant, Ageratina adenophora, on soil microorganisms and functional processes in a region of China was assessed. The results indicated that soil nitrogen contents were over 4.32 mg/kg higher (p < 0.05) in both rhizosphere soils and bulk soils dominated by A. adenophora as compared with soils dominated by native plants. Concurrently, soil microbial-mediated functional processes, i.e. nitrogen fixation rate, nitrification rate and ammonification rate, also were significantly (p < 0.05) higher in either rhizosphere or bulk soils of invasive A. adenophora. Higher relative abundances of soil microbial genes involved in N cycling processes were measured in A. adenophora soils using a functional gene microarray. Specifically, nifH genes, required for nitrogen fixation, significantly correlated with ammonia contents (r=0.35-0.37, p < 0.05) and the nitrogen fixation rate (r=0.44, p < 0.05). Relative abundances of labile carbon decomposition genes were higher in invasive A. adenophora soils, implying a potential higher availability of carbon. These results suggest that the soil surrounding the invasive plant A. adenophora is a self-reinforcing environment. The plant litter and rhizosphere environment of the invasive may influence soil microbial communities, promoting self-supporting soil processes. Alternatively, the regions invaded by A. adenophora may have already had properties that facilitated these beneficial microbial community traits, allowing easier invasion by exotics. Both scenarios offer important insights for the mitigation of plant invasion and provide an ecosystem-level understanding of the invasive mechanisms utilized by alien plants.