Nitrogen‐transforming microorganisms potentially facilitate the invasion of Moso bamboo (<i>Phyllostachys edulis</i>) into evergreen broadleaf forests

Abstract Moso bamboo ( Phyllostachys edulis ) invasions into broadleaf forests can cause serious ecological problems, such as reducing biodiversity and disrupting community succession. An elevated soil NH 4 + /NO 3 − ratio has been identified as a potential mechanism that facilitates Moso bamboo invasion. However, it remains unclear whether and how this change is the result of the modification of soil nitrogen‐transforming microorganisms by bamboo. Here, we collected soil from evergreen broadleaf forests that were either uninvaded or heavily invaded by Moso bamboo. We then compared the effects of soil origin on: (1) the growth of two common broadleaf tree species, Castanopsis fissa and Schima superba ; (2) the soil nitrogen content and nitrogen transformation rates; and (3) the key microbial functional genes involved in nitrogen fixation, nitrification and denitrification. The plant sizes and relative growth rates of the study trees were significantly lower when they were grown in soil from the bamboo‐invaded forest than when they were grown in the uninvaded forest, with values reduced by approximately half. Compared with uninvaded soil, bamboo‐invaded soil presented a significantly greater denitrification rate, NH 4 + ‐N content and NH 4 + /NO 3 − ratio. Further correlation analyses suggested that the increased diversity of denitrifying genes and altered community compositions of denitrifying microbes might be the drivers of the elevated NH 4 + /NO 3 − ratio, which consequently led to the reduced growth of broadleaf trees. Our study offers the first comprehensive synthesis of the positive feedback mechanisms of Moso bamboo invasion, with a focus on the instrumental role of nitrogen transformation processes. Read the free Plain Language Summary for this article on the Journal blog.