Mowing, Fertilization And Watering On The Growth Of Elymus Nutans Grass Compensation In Alpine Meadow

Grazing is one of the primary modes in the utilization of grassland. With the increasing number of grazing livestock and population, it appears different degrees of degradation in alpine meadow. As effective ways of artificial intervention to alleviate the grassland degradation, fertilization and watering could supplement the nutrients of soil, increase the water content, promote the compensatory growth of plants and improve the quality of grassland. Plant compensatory growth affected by both clipping intensity and resource availability is the basis of plant tolerances to the clipping and grazing. At present, controlled experiments attracts more and more attention and becomes a hot in Ecology study. Therefore, a field manipulative experiment, which included clipping (stubbled 1 cm,3 cm and unclipped), watering (watered, unwatered) and fertilizing (fertilized. unfertilized) treatments was conducted in Haibei Research Station to study the changes of species diversity and the importance value of dominant species in community and compensatory growth response of Elymus natans from 2007 to 2008 year. In addition, we measured compensatory height (CH), the specific leaf area (SLA), net photosynthesis rate (NPR) and relative growth rate (RGR) of defoliated plants in order to discuss the compensatory mechanism of the species. At the same time, we analyzed the relationship between environmental factors and the important values of dominant species by Canonical Correspondence Analysis (CCA). The main results showed as follow:1. In the first year of treatments, the species diversity index which contains species richness. Shannon-Wiener index and Simpson index, almost showed the same tendency. In the second year. Simpson indexes were no remarkable difference in these three clipping groups. Shannon-Wiener index and species richness in the clipping treatment was significantly lower than the control group. Regression analysis showed that the species diversity and clipping intensity had a significant negative correlation. These results indicate that species diversity presents declined trendency with the clipping intensity increased and stubbling 1-3 cm already heavy, which is not conducive to biodiversity protection.2. Species with high important value (â…£) have a controlling influence on the community structure and environment. After two years of treatment, our results show that some differences emerged among 20 major speciesâ…£in community in different treatment. Clipping makes E. nutans, Stipa aliena, Kobresia humilis, and Poa sp. important values decreased and its competitive is weakened.3. E. nutans has certain density compensation mechanism, but the undercompensation in plant height resulting from the CH was restrained by clipping. Meanwhile, the increase of RGR and SLA also indicated E. nutans has some ability of overcompensation. But overcompensation depends on the net profits of acceleration and alleviation.4. Fertilization has obvious promoting effects on RGR, SLA and NPR, and these effects are more remarked after clipped. These results show that additional fertilizing could enhance plant compensation ability, and promote its tolerance for defoliation; at same time, their ability to absorb nutrients has increased after defoliation. Our study demonstrated that "antagonistic" interactions between fertilization and clipping alleviate the negative effects of defoliation, and partially confirmed the simplified limiting resource model (LRM)5. Water effect, as an important factor during plant growth, was not significant in the different treatments in our study. That may confirmed that water is not a limit factor for compensatory growth, and its effect has influence to local species by chance, relates to rainfall.6. Responses of plant species important value to soil resources are related to plant life forms. Respondence to changes of ammonium nitrogen (NA) and total phosphorus (Pt) in grasses is more obvious than that in non-grass plants; Broadleaf weeds significantly respond to changes of available phosphorus (Pe). Available phosphorus and nitrogen are important resources for the composition of species in alpine K. meadow. Meanwhile, CCA analysis showed that the contribution of different nutrients on the E. nutans compensation is different, in addition, ammonia nitrogen and total phosphorus are the major limiting resource factors on E. nutans compensation.In short, clipping intensity and recourses availability play an important role on E. nutans compensatory growth, community structure and species diversity. To specific plants, these effects of clipping intensity and limiting resources are more important than others on plant compensatory. E. nutans is a primary choice in objective species on forging artificial grassland, and the establishment of artificial grassland is to obtain high and stable yield. By controlling the clipping intensity and the supplement of soil nutrients content, we could keep the compensation ability of E. nutans artificial grass meadow, which has a great significance to the protection of the natural grassland ecosystem in that it reduces the grazing pressure of the natural grassland and alleviates the contradictions between grass supply and farm animals.