Effects Of Silicon, Nitrogen And Phosphorus Addition On Plant Community Structure And Productivity Of Alpine Meadow On Qinghai-tibetan Plateau, China

A two-year artificial Si, N, P fertilizer addition experimental study was undertaken from2012to2013in the alpine meadow on Qinghai-Tibetan Plateau, China. The plant community structure and ecological stoichiometry content characteristics such as aboveground productivity and C, N, P element changes of six community representative species leaves under different Si, N, P addition levels were explored. The main results were as follows:(1)The study indicated that the aboveground productivity of plants added with Si, N, P fertilizer significantly increased, so did the fertilization treatment in the second year than the first year. Adding a low concentration of Si did not affect plant productivity, however, high concentrations of Si added alone, N added alone, and N added together with Si (NSi) all significantly increased the aboveground productivity; the differences between N and N mixed with Si treatments under the same N concentration were not significant in2012, while in2013, the aboveground productivity of plants under NSi treatments was significantly higher than those applied with the same concentration of N, what’s more, the aboveground productivity increased with N concentration increase as was described in the alpine meadow in N fertilizer; P treatments and P mixed with Si (PSi) treatments significantly increased the aboveground production, the differences between P and PSi treatments with the same concentration of P were not significant, in addition, plant productivity increased with the increasing P concentration.(2) In2012, Si, N, P fertilizer addition didn’t have any significant impact on the species richness; In2013, there were no significant differences of species richness between Si, P and PSi treatments, N added alone or added with Si significantly reduced species richness, but the species richness under NSi addition was higher than that under the same concentration of N addition alone. There was a significant negative correlation between aboveground productivity and species richness.(3) Si, N, NSi, P, PSi addition had no significant effect on soil organic matter and total N content; high concentrations of Si alone, Si mixed with N or P can increase the content of soil nitrate N or total P and available P content; N and NSi addition both improved the content of soil nitrate and ammonium N significantly; P and PSi addition both improved the soil total P and available P content; for Si element, the high concentration of Si alone, Si mixed with N or P can improve nitrate N, total P and available P content of soil and promote the absorption of the six representative species of soil N and P, thus increased the N and P content of plant leaves.(4) Si, N, NSi, P, PSi addition had no significant effects on the organic C content of six species; Si, N, NSi and PSi addition improved the leaf total N content of the other five species except O. ochrocephala; Si, NSi, P and PSi addition improved the leaf total P content of the six species, while adding N to the plants had no significant effect on leaf total P content; except O. ochrocephala, the leaf N content of the other five species increased significantly when plants were added with PSi. All the above results suggested that adding the appropriate silicon fertilizer in the process of adding nitrogen phosphorus fertilizer can increase the content of nitrogen and phosphorus in plant leaves.(5) Values of the N:P varied in the range of7.3-11.2in treatments without Si,N,P addition, indicating that the plant growth was limited by N to a large extent in the alpine meadow. Values of the N:P reduced and were less than16with P,PSi addition in six species, indicating that P,PSi addition induced N deficiency in six species. Values of the N:P increased and were greater than16with N,NSi addition in five species except O. ochrocephala, which indicated that N addition induced P deficiency in these five species. Values of the N:P reduced and were less than16with P,PSi addition in six species, indicating that P,PSi addition induced N deficiency in six species.In summary, leaf N, P content of the alpine meadow grassland plant in Qinghai-Tibet were low, plants were affected by N, P significantly, Si, N, P addition significantly increased the aboveground productivity but decreased the plant species richness, but when the N concentration were the same, NSi addition had a high species richness than that plants applied with N alone under the same N concentrations, suggesting that in the alpine meadow adding the right amount of Si together with N, not only can improve the productivity of plants in the region, but also can alleviate the contradiction between the nitrogen and the reduced species richness. There was a significant negative correlation between productivity and species richness; the leaf total P content of six species increased with the increasing amount of P, what’s more Si can improve the whole leaf P content, but different species reacted differently to the adding N, the leaf total N content of the other five species increased with the increasing amount of N, Si can improve the whole leaf N content. Findings in this study highlight the importance for fertilization and management of alpine meadow.