Effects of nitrogen addition on the growth and asexual reproduction characteristics of Deyeuxia purpurea

Under the background of global change, to explore the mechanism of wetland vegetation response to nitrogen deposition, we selected Deyeuxia purpurea which is one of the dominant plants of Sanjiang Plain Wetland as the research object, through controlled experiments to study the effects of nitrogen addition level and nitrogen addition time on its functional traits, asexual reproduction and biomass allocation. In this controlled experiment, five nitrogen addition levels were set, CK0 g/(m²·a), N12 g/(m²·a), N2 4 g/(m²·a), N36 g/(m²·a)and N48 g/(m²·a), and the experimental period was 2 years. The research results indicated that nitrogen addition time, nitrogen addition level and their interaction had extremely significant impacts on plant height, base diameter, and number of branches of D. purpurea (p<0.01). Nitrogen addition increased the number of branches, decreased the leaf length, and significantly reduced the plant height and base diameter of D. purpurea in the first year (p<0.01), while showed opposite trends in the second year. Nitrogen addition time and levels had significant effects on the number of dormant buds and sprouting buds at the tillering nodes of D. purpurea (p<0.01), and their interaction had extremely significant effects on the number of established individuals, the number of elongating rhizome branches, and the number of sprouting buds of rhizomes (p<0.01). Nitrogen addition increased the number of established individuals, the number of sprouting buds at tillering nodes, and the number of dormant buds, but decreased the length and number of elongating rhizome branches. Total biomass, above-ground biomass, and below-ground biomass of D. purpurea gradually increased with the increase of nitrogen addition concentration, and the results of the second year were significantly higher than those of the first year (p<0.01). The allocation proportion of root and leaf biomass gradually increased, while the allocation proportion of stem biomass decreased. Our study demonstrated that the addition of nitrogen increased the number of branches, tillering buds, sprouting buds of rhizomes, and the number of established individuals of D. purpurea, decreased the leaf length, the number and length of elongating rhizome branches, and promoted the biomass accumulation. At nitrogen addition levels of 6 g/(m²·a) and 8 g/(m²·a), and with an additional period of two years, it effectively regulated the growth and asexual reproduction of D. purpurea. The results showed that D. purpurea through an ‘intensive’ growth strategy to expand its population number under the the nitrogen addition background.