[Carbon and nitrogen stable isotopes technology in the researches on alpine meadow ecosystem in Qinghai-Tibet Plateau: Progress and prospect]. / ç¢³æ°®ç¨³å®šåŒä½ç´ æŠ€æœ¯åœ¨é’è—é«˜åŽŸé«˜å¯’è‰ç”¸ç”Ÿæ€ç³»ç»Ÿç ”ç©¶ä¸­çš„åº”ç”¨: 进展与展望.

Carbon and nitrogen stable isotopic technique has been widely used in research of glassland ecosystems. Here, we summarized studies using carbon and nitrogen stable isotopes in the alpine meadow ecosystem on the Qinghai-Tibet Plateau. Firstly, we reviewed the environmental factors which influenced carbon and nitrogen isotope composition (δ13C and δ15N) of plants and soils in alpine meadow, such as altitude, moisture, fertilization, grassland degradation, and temperature. The values of plant δ13C were positively correlated with altitude, and negatively correlated with atmospheric pressure, grassland degradation and temperature. The relationship between plant δ13C and precipitation was non-linear. The values of soil δ13C were positively correlated with altitude and grassland degradation. The values of plant δ15N were positively correlated with soil moisture and fertilization, and negatively correlated with grassland degradation. Secondly, we reviewed the current application and progresses of 13C and 15N in the identification of plant photosynthetic type, water use, nutrient transport along food chain and carbon and nitrogen cycle in the alpine meadow. Finally, we prospected the 13C and 15N isotopes application in researches on soil organic carbon and soil respiration in the alpine meadow, transitions of vegetation type, and climate change, soil N2O trace, exploration of vegetation degradation, identification of the origin of Tibetan medicine and animal food, etc. 13C and 15N isotopes could be widely used and play important roles in researches on the alpine ecosystems.

[Changes of soil enzyme activities and nutrients across different succession stages of grazing alpine Kobresia grassland.] / æ”¾ç‰§é«˜å¯’åµ©è‰è‰åœ°ä¸åŒæ¼”æ›¿é˜¶æ®µåœŸå£¤é ¶æ´»æ€§åŠå »åˆ†æ¼”å˜ç‰¹å¾.

The variation of soil enzyme activity and relevance with soil nutrients was examined in multistable grazing alpine Kobresia grassland, including Gramineae-Kobresia humilis community, K. humilis community, K. pygmaea community at thickened stage, K. pygmaea community at cracked stage and forb-black soil type secondary bare land. The results showed that the vegetation coverage and aboveground biomass successively decreased with degenerative succession. The belowground biomass was the highest in the K. pygmaea community at thickened and cracked stages. The activities of soil sucrase, urease, cellulase, alkaline phosphatase and aryl sulfatase were higher at the surface soil layer (0-10 cm) than those at the subsurface soil layer (10-20 cm), while the pattern of chitinase activity was contrary. The activities of cellulase, alkaline phosphatase and aryl sulfatase were the highest in the Gramineae-K. humilis community and the lowest at the forb-black soil type secondary bare land, and they slightly increased during the thickened stage of K. pygmaea community. Chitinase activity was relatively high at the middle three stages, while urease and sucrase activity had an obvious increase in the forb-black soil type secondary bare land. Soil moisture, ammonium, alkali-hydrolyzable nitrogen, total nitrogen, total carbon and organic carbon successively decreased with degenerative succession, whereas the concentrations of nitrate and available phosphorus increased at the latter two succession stages. The activities of the other enzymes, except for chitinase, were significantly positively correlated with the soil available phosphorus, ammonium, alkali-hydrolyzed nitrogen, total carbon, and organic carbon, and negatively correlated with soil pH. The activities of cellulose, alkaline phosphatase and aryl sulfatase were significantly positively correlated with soil moisture and total nitrogen. The main factors affecting soil enzyme activity were available phosphorus and ammonium. Soil enzymes showed different evolutionary trends influenced by grazing degradation succession in the alpine grassland, with a synergistic effect with soil nut-rients. Moreover, severely degraded extreme environments may stimulate soil enzyme activities related to nitrogen and carbon transformation.

[Effect of degradation succession process on the temperature sensitivity of ecosystem respiration in alpine Potentilla fruticosa scrub meadow].

Grazing is one of the main artificial driving forces for the degradation succession process of alpine meadow. In order to quantitatively study the temperature sensitivity of alpine meadow ecosystem respiration in different degradation stages, we conducted the research in Haibei Alpine Meadow Ecosystem Research Station, CAS from July 2003 to July 2004. The static chamber-chromatography methodology was used to observe the seasonal changes of alpine scrub ecosystem respiration flux during different degradation stages. The results showed that: (1) The seasonal changes of ecosystem respiration flux in different degradation stages of alpine shrub presented a unimodal curve. The maximum appeared in August and the minimum appeared during the period from October to next April. The degradation succession process significantly decreased the ecosystem respiratory CO2 release rate. The respiratory rate ranges of alpine Potentilla fruticosa scrub (GG), Kobresia capillifolia meadow (GC) and bare land (GL) were 34.21-1 168.23, 2.30-1 112.38 and 20.40-509.72 mg (m2 x h)(-1), respectively. The average respiration rate of GG was 1.29 and 2.56 times of that of GC and GL, respectively; (2) Temperature was the main factor that affected the ecosystem respiration rate, and contributed 25% - 79% of the variation of the ecosystem respiration. The degradation succession process significantly changed the correlation between ecosystem respiration rate and temperature. The correlation (R2) between ecosystem respiration rate and each temperature indicator (T(s), T(d) and T(a)) was reduced by 47.23%, 46.95% and 55.28%, respectively when the ground vegetation disappeared and the scrub was degraded into secondary bare land; (3) The difference of Q10 between warm and cool seasons was significant (P < 0.05), and the value of cold season was larger than that of warm season. Degradation succession process apparently changed the temperature sensitivity of ecosystem respiration. The Q10 values of GG, GC and GL were 2.38, 2.91 and 1.62, respectively. Q10 of GC was increased by 22.26% and that of GL was decreased by 31.93% compared with that of GG.

Different inter-annual responses to availability and form of nitrogen explain species coexistence in an alpine meadow community after release from grazing.

Plant species and functional groups in nitrogen (N) limited communities may coexist through strong eco-physiological niche differentiation, leading to idiosyncratic responses to multiple nutrition and disturbance regimes. Very little is known about how such responses depend on the availability of N in different chemical forms. Here we hypothesize that idiosyncratic year-to-year responses of plant functional groups to availability and form of nitrogen explain species coexistence in an alpine meadow community after release from grazing. We conducted a 6 year N addition experiment in an alpine meadow on the Tibetan Plateau released from grazing by livestock. The experimental design featured three N forms (ammonium, nitrate, and ammonium nitrate), crossed with three levels of N supply rates (0.375, 1.500 and 7.500 g N m-2  yr-1 ), with unfertilized treatments without and with light grazing as controls. All treatments showed increasing productivity and decreasing species richness after cessation of grazing and these responses were stronger at higher N rates. Although N forms did not affect aboveground biomass at community level, different functional groups did show different responses to N chemical form and supply rate and these responses varied from year to year. In support of our hypothesis, these idiosyncratic responses seemed to enable a substantial diversity and biomass of sedges, forbs, and legumes to still coexist with the increasingly productive grasses in the absence of grazing, at least at low and intermediate N availability regimes. This study provides direct field-based evidence in support of the hypothesis that idiosyncratic and annually varying responses to both N quantity and quality may be a key driver of community structure and species coexistence. This finding has important implications for the diversity and functioning of other ecosystems with spatial and temporal variation in available N quantity and quality as related to changing atmospheric N deposition, land-use, and climate-induced soil warming.

[Soil quality assessment of alpine meadow in Haibei State of Qinghai Province].

Taking the typical alpine meadows Potentilla froticosa shrub meadow, Kobresia humilis meadow, and K. pygmaea meadow in the Haibei State of Qinghai Province as the research objects, a comprehensive assessment of soil quality was conducted by principal component analysis (PCA), with seven indices of soil microbial activities and ten indices of soil chemical properties. The soil quality of the alpine meadow could be characterized by three principal components (PC). In the first component (PC1), 13 indices had high factorial loads; in the second component (PC2), 3 indices had high factorial loads; in the third component (PC3), only one index, total phosphors, had high factorial load. In combining with Norm values, eleven indices including microbial biomass carbon (MBC), urease, alkaline phosphatase, protease, organic matter, total N, available N, available P, available K, bulk density, and CEC were selected to establish minimum data set (MDS) for the comprehensive assessment of soil quality of alpine meadow in Haibei. The PCA and corresponding weight coefficient analysis showed that the soil quality (0-10 cm and 10-20 cm layers) of the three kind meadows was in the order of K. humilis meadow > P. froticosa shrub meadow > K. pygmaea meadow, and P. froticosa shrub meadow > K. pygmaea meadow > K. humilis meadow, respectively.

[Changes in plant communities and soil microbial physiological groups of artificial grasslands established for different years in headwater region of Yangtze River and Yellow River].

An investigation was made on the plant communities of artificial grasslands established for different years in headwater region of Yangtze River and Yellow River, and the related soil physical and chemical properties and soil microbial physiological groups were analyzed. With the increase of establishment years, most of plant communities on the grasslands showed a "V" type change trend in their quantities, i.e., high-low-high, but the forbs biomass had a "A" type change trend and the sedge biomass increased gradually. Soil nutrients presented a "V" type but soil bulk density presented a "A" type change trend, while soil pH presented a decreasing trend. Most of soil microbial physiological groups and microbial biomass carbon showed a "V" type change trend, phosphorus-dissolving bacteria showed a "A" type change trend, denitrifying bacteria decreased gradually, while cellulose-decomposing bacteria showed an increasing trend. The numbers of soil microbes had a close relationship with tested soil factors, and the soil microbial physiological groups were directly or indirectly affected by the soil factors. All the results indicated that the establishment of artificial grassland and the positive succession of vegetation could effectively improve soil physical and chemical properties, which benefit for the beneficial microbes to settle down and propagation, while proliferation of the non-beneficial microbes was inhibited.

Growing season ecosystem respirations and associated component fluxes in two alpine meadows on the Tibetan Plateau.

From 30 June to 24 September in 2003 ecosystem respiration (Re) in two alpine meadows on the Tibetan Plateau were measured using static chamber- and gas chromatography- (GC) based techniques. Simultaneously, plant removal treatments were set to partition Re into plant autotrophic respiration (Ra) and microbial heterotrophic respiration (Rh). Results indicated that Re had clear diurnal and seasonal variation patterns in both of the meadows. The seasonal variability of Re at both meadow sites was caused mainly by changes in Ra, rather than Rh. Moreover, at the Kobresia humilis meadow site (K_site), Ra and Rh accounted for 54% and 46% of Re, respectively. While at the Potentilla fruticosa scrub meadow (P_site), the counterparts accounted for 61% and 39%, respectively. T test showed that there was significant difference in Re rates between the two meadows (t = 2.387, P = 0.022). However, no significant difference was found in Rh rates, whereas a significant difference was observed in Ra rates between the two meadows. Thus, the difference in Re rate between the two meadows was mainly attributed to plant autotrophic respirations. During the growing season, the two meadows showed relatively low Q10 values, suggesting that Re, especially Rh was not sensitive to temperature variation in the growing season. Additionally, Re and Rh at the K_site, as well as Rh at the P_site was negatively correlated with soil moisture, indicating that soil moisture would also play an important role in respirations.

[Comparison of eddy covariance and static chamber/gas chromatogram methods in measuring ecosystem respiration].

Based on the measurement of carbon flux by the methods of eddy covariance and static chamber/gas chromatogram, a comparison was made between the two methods in evaluating ecosystem respiration over winter wheat (Triticum aestivum)--summer maize (Zea mays) double cropland and Kobresia humilis alpine meadow. The results showed that under the conditions of obtained data having good quality, nighttime ecosystem respiration from eddy covariance measurement was significantly agreed with that from static chamber/gas chromatogram measurement, with the correlation coefficients ranging from 0.95 to 0.98, and the daytime ecosystem respiration from these two measurements also had a good consistency though the static chamber/gas chromatogram measurement often produced higher values. The daily mean value of ecosystem respiration was significantly different between these two measurements, but the seasonal pattern was similar. For winter wheat-summer maize double cropland, the difference of mean air temperature inside and outside the chamber was 1.8 degrees C, and the daily mean value of ecosystem respiration across the whole study period was 30.3% lower in eddy covariance measurement than in static chamber/gas chromatogram measurement; while for alpine meadow, the difference of the mean air temperature was 1.9 degrees C, and the daily mean value of ecosystem respiration was 31.4% lower in eddy covariance measurement than in static chamber/gas chromatogram measurement. The variance between the daily mean values of ecosystem respiration obtained from the two measurements was higher in growing season than in dormant season.

[Characteristics of artificial grassland plant communities with different establishment duration and their relationships with soil properties in the source region of three rivers in China].

This paper studied the biomass, species composition, and diversity index of artificial grassland plant communities with different establishment duration in the source region of the Three Rivers, and examined the relationships of soil physical and chemical properties with the changes of the plant community biomass and species diversity. The results showed that the species composition, functional group composition, and quantitative characters of the plant communities varied greatly. Soil moisture content increased with increasing species diversity, while soil bulk density was in adverse. Soil microbial biomass carbon significantly positively correlated with soil moisture and organic matter contents, but negatively correlated with soil bulk density. Soil organic carbon content had a "V" type change, which was consistent with the change pattern of soil moisture content, and decreased with increasing soil bulk density. Plant community biomass had significant positive correlations with the contents of soil nutrients and moisture, and the increase of the above- and below-ground biomass of plant communities promoted the increase of soil nutrient contents.

[Study on actinomycetes population of alpine meadow soil in Qinghai].

Soil samples were collected from six kinds of soil in Haibei alpine meadow ecosystem during 2001 - 2002. More than 300 strains of actinomycete were isolated by five agar media. On the basis of morphological characteristics and some chemotaxonomic properties, the isolated strains were classified into different genera, such as Micromonospora, Nocardia, Saccharopolyspora, Promicromonospora, Streptomyces, and the Streptomyces strains were classified into seven groups. The result indicated that the biodiversity of actinomycetes in different soils and the actinomycetes abundance of different kinds showed significant differences. The activities of some enzymes produced by mesophilic and psychrophilic actinomycetes also discussed in this paper. It is found that many strains of streptomyces not only have some enzyme activities such as starch decomposition, nitrate deoxidization, gelatin utilization etc., but also have some inhibiting activities for fungi and bacteria offered to test, whereas the rare actinomyces showed low positive rate of enzyme activities and inhibiting activities for fungi and bacteria.