Study On Nutrient Use And Stoichiometry Of Dominant Plants In Desert Steppe

Grassland ecosystem mainly is N and water limited, specially Stipa breviflora desert steppe located in the arid region. Grazing change the nutrients in the habitat conditions, and cause the competition to take advantage of limited nutrient conditions between species. Plant constantly adjust their own nutrient use efficiency and Stoichiometry in order to adapt to the environment, the adaptive strategy is to determine the important mechanism of the species competition ability and the ability to adapt, at the same time, it is important to maintain the community biomass. With dominant plants in Stipa breviflora desert steppe as the research object, and discusses nutrient use and stoichiometric features of dominant plants caused by N element, water and grazing species competition and adaptive response in Stipa breviflora desert steppe, and helps to reveal The change of nutrient utilization strategy of dominant plants in Stipa breviflora desert steppe under the the human interference background, and provide theoretical support for ecological system dynamic to predict the future.Four experiments were respectively set up. i.e. nitrogen addition (ND), water addition (WD), nitrogen and water addition (NWD) and control (CK) with five repeats in a free grazed paddock and a grazing enclosed paddock in Stipa breviflora desert steppe, Inner Mongolia. The other experimental site is grazing from2002. and was designed with random blocks completely. The experimental treatments were denoted control (CK), light grazing (LG), moderate grazing (MG), and heavy grazing (HG), composed of4stocking rate levels (0,0.91.1.82. and2.71sheep hm half year), and respectively. Each stocking rate level included three replications. The experimental livestock was two years old Mongolian wether with fuzz.Through2consecutive years (that were2011and2012) of field surveys, indoor testing and data analysis on Stipa breviflora desert steppe, this paper did researches about Stipa breviflora desert steppe community characteristics and stoichiometry nutrient utilization in aspect of different N and water addition, and species competitions. The main results are as follows:1N and water were added to improve the community characteristics indicators to favor the recovery of degraded grassland. In terms of rehabilitation of degraded grassland. N and water has a coupling effect. While being added together they have significant impact, compared to the impact of being added alone. N availability and moisture conditions are major growth limiting factors of breviflora desert steppe vegetation.2Species competition caused by long-term grazing leads to changes of the anatomical structure of plants. Some changes in the anatomy of the species let them to adapt to the barren habitats.3Species competition results in breviflora total N (TN) content decrease, increasing the total organic carbon content (TOC), for a disadvantage in the community. When compared to A. cleistogenes. A.frigida occupies a dominant position in the community, because of its ability to tune elements content.4The interaction of N and water on Stipa breviflora and Cleistogenes songorica nutrient usage efficiency is still not affected. Species competition caused by grazing have relatively small influence on tall grasses like Stipa breviflora,but relatively large influence on grasses like Cleistogenes songorica and Artemisia frigida.5N and water addition and their interactions were significantly reduced the NUE of Stipa breviflora and Cleistogenes songorica, and both of them are rich in NUE. With increase of the species competition caused by grazing, the NUE of Stipa breviflora and Cleistogenes songorica first increased and then decreased. As competitive pressures increase, there is possibiliy that Stipa breviflora would be expelled by Cleistogenes songorica and Artemisia frigida.6With the increase of species competition caused by grazing, the three main structures of plant anatomy in stipa breviflora desert steppe kept of increased the C:N or C:P, and at the same time reduced the N:P to faster growth to adapt the competitive enviroment. Stipa breviflora the large individual have greater flexibility than Cleistogenes songorica the small one to habitat the enviromental changes in nutrient. Therefore, from the perspective of adapt ability, Stipa breviflora have greater advantages. However, if the competitive pressures continue to increase, Stipa breviflora were more vulnerable to the constraints of N elements, and expelled by Cleistogenes songorica and Artemisia frigida.