| With the rapid population increasing, fossil fuel burning and agricultural fertilizer application will cause the increase of atmospheric nitrogen deposition, and it will have a significant impact on the ecosystem structure and function. N and P addition have profound impacts on ecosystem functioning in grasslands. The function of ecosystem is directly related to the plant traits, so the plant traits and its stoichiometric characteristics can be used to illustrate the effects of nutrient addition on ecosystem function. In this study, we discuss the effects of nutrient additions on plant functional traits, in Hulun Buir grassland. In this study, we compared the leaf trait difference of Leymus chinensis (LC), Stipa baicalensis (SB), Potentilla tanacetifolia (PT) and Thermopsis lanceolata (TL). We assessed the role of N type and rate in controlling specific leaf area (SLA), leaf dry matter content (LDMC), stem:leaf ratio (SL), leaf chlorophyll (SPAD), leaf nitrogen concentration (LNC), leaf phosphorus concentration (LPC) and stoichiometry. In addition, the responses of different plant organs to phosphorus enrichment undergoing contrasting N background were clarified. In the mean time, we investigated the leaf biomass, stem biomass, stem:leaf ratio and stoichiometry of P. tanacetifolia following P addition and N addition in a meadow steppe in Northeast China. These studies will improve our understanding to the mechanisms leading ecological effect of N and P addition in ecosystem management and nutrient physiology. The key findings are as following.LDMC, SL and LPC of L. chinensis, S. baicalensis, P. tanacetifolia and T. lanceolata were significantly different, of which L. chinensis with higher LDMC, SL and SPAD; The leaf nutrient concentration of P. tanacetifolia and T. lanceolata was higher, these results suggest that grass mainly through changing the leaf traits to increase their ability to compete for light, comparing with grass species (i.e., legumes and forbs) that ensuring its own growth mainly by increasing the concentration of nutrients.Nitrogen addition had a significant effect on SLA, LDMC, SPAD of L. chinensis. With nitrogen addition rate increasing, SLA of L.chinensis increased and LDMC decreased. As N addition, the ability of photosynthesis improved greatly because of SPAD increased. Different types and rates of nitrogen had no significant effect on SL. LNC was increased with nitrogen addition rate, so that the N:P ratios increased and C:N decreased. However, N input had little effect on LPC in L. chinensis.The aboveground biomass of P. tanacetifolia increased with the increasing phosphorus under the conditions of N addition, but there was no significant change in biomass when only phosphorus was added. Furthermore, P addition with the absence of N addition increased linearly P concentrations in leaf, stem, and seed, declined significantly leaf and seed N:P ratio. Moreover, for the treatment only with N but no P addition, we found N addition significantly increased leaf N:P ratio, seed P concentration and N:P ratio changed remarkably. However, as the P addition rates became higher, the effects of N fertilization are weakened and eventually disappeared. Our results indicate that nitrogen and phosphorus cycling in different plant organs was diverse. These maybe had implications that N deposition affects the response of plants to phosphorus. |
