Aims Nutrient deficiency is one of the important factors that cause grassland ecosystem degradation. Nutrient addition was regarded as an effective method to restore the degraded grassland. Legumes, an important component of grassland ecosystems, would be significantly affected nutrient addition. This study aims to clarify the effects of nutrient addition on the functional traits of legumes.
Methods We carried out a nutrient addition experiment in Onqin Daga Sandy Land, in which different amount of chicken manure (CMA, L0-L6 were 0, 500, 1 000, 1 500, 2 000, 2 500 and 3 000 kg·hm-2·a-1) was used as the nutrients. Then we explored the effects of nutrient addition on Melilotus officinalis, a typical legume plant.
Important findings The results showed that the leaf nitrogen (N), phosphorus (P), potassium (K) content, maximum photosynthetic rate (Pnmax), water use efficiency (WUE), specific leaf area (SLA) and plant height (H) of M. officinalis were significantly affected by CMA. Leaf N, P and K content of M. officinalis increased linearly with the increase of CMA. When CMA amount arrived at 3 000 kg·hm-2·a-1 (L6), the leaf N, P, and K content of M. officinalis increased by 15%, 67% and 25% respectively compared with L0. CMA also influenced H, SLA, Pnmax and WUE of M. officinalis, and the responses of these functional traits to CMA was hump shaped. When CMA amount was lower than 1 500 kg·hm-2·a-1 (L3), H, SLA, Pnmax and WUE of M. officinalis in August increased significantly by 51%, 18%, 12% and 38% respectively; when CMA amount was higher than 1 500 kg·hm-2·a-1 they all decreased significantly. There was no significant difference in the values of H, SLA, Pnmax and WUE between L6 and L0. CMA in an appropriate amount could improve the photosynthetic capacity and water use capacity of legumes growing in grassland, and then promote their growth, ultimately improve the maintenance of their population.