Comparison Of Nitrogen Utilization By Alpine Plants And The Influence Of Pasture Degradation On Soil And Root Carbon/carbohydrate In Alpine Meadow

The alpine meadow of the Qinghai-Tibetan plateau is the main grassland area for animal husbandry in China. In addition, it constitutes an important barrier, enhancing ecological security and is the home for people of multi-ethnic origins. It is also an important carbon sink in this region, playing an important role in regulating the balance of carbon sources and carbon store. However, the structure of the alpine meadow ecosystem is highly influenced by climate change and human activities, while showing different degrees of degradation. Planting artificial grassland was one of the more important measures taken to restore severely degraded grassland, but due to improper management and utilization artificial grassland showed deteriorated after 3-5 years. Our goal of this study was to comprehend the adaptability of different alpine meadow plants to the process of degradation and the ecological restorative effect of degraded artificial grassland on "black soil land" grassland. First study, seven different alpine meadow plant species (Kobresia humilis、Carex scabrirostris、 Carex enervis、Elymus nutans、Festuca sinensis、Stipa purpurea and Ajania tenuifolia)were selected in order to examine their adaptability to nitrogen through 15N isotopic tracer method; Second study was conducted at three different land types, including:degraded artificial grassland, "black soil land" grassland and natural grassland. The plant community and soil characteristics analyzed were:species diversity, soil carbon, nitrogen, amino sugar and neutral sugar content in the different types of grassland. The main results of this study were the following:1. With the increase of nitrogen levels, the efficiency use of nitrate and the rate of its absorption by alpine meadow plants decreased. The efficiency use of the stem leaf of Elymusnutans (140.49 g/g) was the highest among the seven examined plants. The efficiency of Kobresiahumilis roots (290.69 g/g) was the highest among the seven plants.2. The average number of species in the degraded artificial grassland, "black soil land" and natural grassland was 29,32 and 35, respectively. The Shannon-Wiener index, Simpson dominant concentration index and Pielou evenness index of different types of grassland communities all showed a similar trend; natural grassland> "black soil land">degraded artificial grassland. The Sorensen and Jaccard index showed that community similarity of degraded artificial grassland and "black soil land "was the highest, the community similarity of "black soil land" and natural grassland was intermediate, and the community similarity of degraded artificial grassland and natural grassland was the smallest.3. The content of soil organic carbon, total nitrogen, soluble organic carbon, nitrogen and microbial biomass carbon, nitrogen and inorganic nitrogen had shown no significant difference between degraded artificial grassland and "black soil land". The soluble organic carbon and nitrogen contents of natural grassland were significantly higher than those found in degraded artificial grassland and "black soil land"(P< 0.05).4. The total soil neutral sugars in natural grassland were significantly higher than in degraded artificial grassland and "black soil land"(P< 0.05).There was no significant difference between degraded artificial grassland and "black soil land" in this respect. The glucose content accounted for 16.38-25.34% among the total soil neutral monosaccharide. But the ribose content accounted for only 0.81-3.17% of the total soil neutral monosaccharide. The soil neutral monosaccharide in degraded artificial grassland and natural grassland was mainly derived from plants, and that of "black soil land" was mainly derived from microorganisms, according to the (galactose and mannose)/(arabinose+xylose) ratio.5. Total soil amino sugars content showed no significant difference between degraded artificial grassland and "black soil land". Soil amino glucose content was the highest among the four kinds of soil amino sugar, accounting for 59.03% of the total soil amino sugar. The second highest was galactosamine, accounting for 31.57%.Amino mannose and muramic acid content were lower than the first two, accounting for 3.55% and 5.84% of the total soil amino sugar, respectively. The degraded artificial grassland changed the microbial community composition of "black soil land" to some extent, according to the glucosamine and muramic acid content ratio.The conclusion is that:The adaptability of Ajania tenuifolia Elymus nutans and Kobresia humilis to low nitrogen environment were better than other selected plants. The degraded artificial grassland improved plant community structure of the "black soil land" according to that the forbs’cover percentage at the degraded artificial grassland was about10% less compare to that of the "black soil land". The main factors which influenced the neutral sugar content of the alpine meadow soil included soil organic carbon, total nitrogen and soluble organic nitrogen. The main factors which influenced the amino sugar content of the alpine meadow soil included soil organic carbon, total nitrogen and ammonium nitrogen. But it did not improve soil quality.This may lead to secondary happen of the "black soil land".