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Effects of Global Risks — Nitrogen Additions on Growth and Competitive Relations among Invasive and Native Congeneric Species — Bidens frondosa

Pan Y., Tang S., Wei C., Li X.

Polish Journal of Ecology

2016

Vol. 64, nr 4

443--452

Human activity has greatly increased the amount of biologically available nitrogen entering the natural environment. Addition of N can affect growth of and competitive interactions between native and invasive plants, thus increasing or decreasing the risk of invasion by alien species. Bidens frondosa is an invasive weed native to North America that recently has begun to spread in China. The influence of soil nutrient content on B. frondosa invasion has not yet been reported. In a common garden experiment, we compared the growth and competitive effects between B. frondosa and its co-occurring native congeners — B. tripartita and B. biternata — under three N levels (0 g m-2, 1 g m-2, 5 g m-2) to assess whether increased levels of N modifies risk of B. frondosa invasion. Our results showed that while N additions increased both the growth and competitive advantage of B. frondosa as compared with that of the native congener species, results are particularly pronounced under high N levels. While growth responses to N addition varied little among invasive populations under high N levels, the competitive effect of B. frondosa did vary among populations and was significantly greater than that of the congeners. Anthropogenic N additions are likely to increase risks of B. frondosa invasions. Thus, management efforts should focus on the reduction of N input to ecosystems to mitigate invasions by B. frondosa.

Interactive effects of nitrogen and water addition on competitive hierarchies between early- and late-successional plant species

Jiang L., Lan Z., Liu G., Kardol P.

Polish Journal of Ecology

2014

Vol. 62, nr 4

665--678

Increased nitrogen (N) and water availability, resulting from global changes or ecosystem management, were predicted to promote plant productivity and change community composition through shifts in competition hierarchies. So far, however, it still remains unclear how competitive interactions respond to N and water additions, which will be important to understand how plant community composition changes. To test plant competition ability in different successional stages under N and water addition treatments, a pot experiment under field conditions was performed. Six dominant plant species, three early-successional species, Artemisia lavandulaefolia, Artemisia capillaris, and Pennisetum centrasiaticum versus three late-successional species, Stipa krylovii, Leymus chinensis, and Artemisia frigida, were grown in monocultures and in two-species mixtures under factorial combinations of N and water addition treatments. We found that (1) there were interactive effects of N addition, water addition and interspecific competition on plant biomass; (2) For a given species, competitive abilities were correlated with biomass difference of neighboring species; (3) N and water additions interactively increased competition intensity and shifted species competitive hierarchies; (4) Late- successional species had stronger competitive abilities in the N addition treatment, whereas early-successional species had stronger competitive abilities after water addition or N + water addition. Our results show that N and water additions increased the intensity and impact of interspecific competition on plant growth, which has great implications for community structures. Since interspecific differences in competitive abilities were not well explained by species biomass, species identity, such as plant functional traits, should be included to predict the impact of increased N and water availability on plant communities and ecosystem functions.