|其他摘要||Ili is a vital grassland pasturing area in Xinjiang, China. It is of great importance to investigate the ecological characteristics as well as the biomass of typical grasslands in the Kunes River Basin, the upper stream of Ili River. As affected by the uplift of Tianshan Mountains and the westerly circulation, obvious spatial heterogeneities of grassland ecosystem structure and pattern were detected in the area. By analyzing the spatial distribution of various nutrient elements’ concentrations in grassland soils along the elevation, this study revealed the spatial heterogeneities, the mechanism of pattern evolvements and the responses of spatial patterns of the different forms of nutrients to the elevation changes in grassland soils. This study also discussed the classifications of the soil organic carbon (SOC) in different grassland types, the vertical distribution patterns of various SOC forms (active organic carbon, slow organic carbon and passive organic carbon) in different grassland types as well as the spatial distribution of the nutrient contents of plant community in different grassland types. The results clarified the ecological and biogeochemical features of grasslands in terms of soil nutrients and plant nutrients, which could help to understand the evolvement rules and living matters' cycle characteristics of grassland ecosystems in Xinjiang. The study could provide the theoretical basis for vegetation restorations of damaged ecosystems and support for further protecting grassland and ecosystems.
Based on field survey and laboratory analysis of samples collected from the sampling sites in the study area, the main conclusions are as follow:
1. The pH, concentrations of available nitrogen (AN), available phosphorus (AP), available potassium (AK) and organic matter (OM) in surface soils of each sampling site decreased as the soil depth increased, while concentrations of other soil elements showed fluctuation with insignificant change. On the spatial pattern, concentrations of soil AN, AP, AK, OM and iron (Fe) increased from west to east along the Kunes River. There was significantly positive correlation between altitudinal gradient and each of the other soil indexes. As the altitudinal gradient increases, concentrations between soil total N (TN) and total P (TP) increase first and then decrease with the increase of altitude, and their concentrations were highest in the middle part of the mountain. Concentrations of soil total K (TK) decreased with the increase of altitude. Soil selenium (Se) contents also increased first and then decreased with the increase of altitude, whereas Se contents in aboveground and root of plant decreased first and then increased with the increase of altitude, which showed an opposite tendency on comparison with soil selenium contents. Soil selenium content is enough for plant growth and the Se content in plants are moderate.
2. There were great differences in concentrations of soil organic carbon fractions among the soils from different grassland types. The concentration of soil active organic carbon ranged from 0.070 to 1.553 g.kg-1 with a mean value of 0.557 g.kg-1 under various grassland types. Soil active organic carbon contents increased first and then decreased with the increase of soil depth in desert steppes, while contents of soil slow carbon consistently decreased with the increase of soil depth; concentrations of both soil active and slow organic carbon increased first and then decreased with the increase of soil depth in semi-desert steppes; in mountain meadow steppes and alpine meadows, concentrations of both soil active and slow organic carbon showed a decreasing tendency with the increase of soil depth; inertia organic carbon increased first and then decreased with the increase of soil depth in desert steppe and semi-desert steppe soils; concentrations of soil inertia organic carbon decreased with the increase of soil depth in mountain meadows, mountain meadow steppes and alpine meadows. In general, concentrations of soil active organic carbon, slow organic carbon as well as inertia organic carbon concentrations followed a same order: mountain meadow >alpine meadow >mountain meadow steppe >desert steppe and semi-desert steppe. Soil active organic carbon decreased with the increase of soil depth in both types of grassland desert steppe and semi-desert steppe. This indicates that grassland soil organic carbon stability in the study area is good and beneficial for the soil organic carbon fixed storage for a long time.
3. Under community scale, R/S of various grassland types ranged from 0.3~8.6 with a mean value of 2.9. According to the ratio of R/S, it is able to estimate the underground biomass, carbon allocation and fixation of grasses in the research area. These results showed that higher grassland biodiversity index in this area have more stable system structure, which is more suitable for grazing. The grazing intensity from semi-desert grassland and desert grassland can be reduced and the grazing should be shifted to the mountain zone, which is better for grassland protection and management.
4. C contents in underground parts were lower than that in aboveground parts from the temperate steppe community. The average values of total C in plant leaves and roots were 346.1 g.kg-1 and 341.8 g.kg-1, respectively. The average values of N and P in plant leaves were 13.6 g.kg-1 and 1.7 g.kg-1, respectively. For the underground part, the average values of N and P were 9.5 g.kg-1 and 1.4 g.kg-1, respectively. By comparison with the mean N and P contents of leaves in China, N contents in the study area were lower, while the P contents were consistent with national level. In the future, we should pay more attention to the study of N nutrient. The average aboveground parts and root’s chemometrics of N/P were 7.5 and 7.1, respectively. N is a limiting factor and it should be taken into consideration for the appropriate supply nitrogen.
5. There were significant correlations among nutrients concentrations in different parts of the grassland plants. Plant C concentrations in aboveground were significantly positively correlated to plant N and K concentrations (p<0.01). Plant N was negatively correlated to C/N ratio, but significantly positively to other nutrient indexes both in the aboveground and underground parts (p<0.01). Plant P contents in aboveground parts were significantly positively correlated to plant K contents in aboveground parts and plant P contents in the underground parts (p<0.01), but significantly negatively to plant C/N ratio and N/P ratio in aboveground parts (p<0.01).|