Nitrogen and litter addition decreased sexual reproduction and increased clonal propagation in grasslands.

The trade-offs between sexual reproduction and clonal propagation are of great significance in terms of ecology and evolution for clonal plants, and they vary with environmental change. Nitrogen (N) deposition can increase litter accumulation in grassland and promote litter decomposition and consequently increase nutrient availability. However, the response of plant reproduction to N and litter addition in grasslands remains unclear. We examined the combined effects of N addition and litter manipulation (i.e. initial litter, removal, addition) on sexual reproduction and clonal propagation of a perennial clonal grass, Leymus chinensis, at the population (total number) and individual (number per ramet) levels in an 11-year field experiment. Nitrogen addition and litter additionally decreased spike and seed number at the population level, and N addition reduced those at the individual level. Nitrogen addition and litter interactively affected bud number at the two levels, and N addition decreased bud number in the litter removal treatments and increased that in the litter addition treatments. The increased soil available N, rather than light and soil water content, explained the change in sexual reproduction and clonal propagation. The positive effects of litter addition on bud number in the treatments with N addition, suggested that the N deposition increased litter accumulation could intensify clonal propagation of perennial grasses and increase their dominance in grasslands. Grassland management that reduces litter accumulation, such as grazing and mowing, can therefore, help alleviate the negative effects of N deposition on plant diversity through decreasing clonal propagation of the dominant species.