[Characteristics of soil enzyme stoichiometry along an altitude gradient on Qinghai-Tibet Pla-teau alpine meadow, China]. / é’è—é«˜åŽŸé«˜å¯’è‰ç”¸ä¸åŒæµ·æ‹”åœŸå£¤é ¶åŒ–å­¦è®¡é‡ç‰¹å¾.

Soil enzymes play critical roles in material cycle and energy flow of ecosystems. Understanding soil enzyme activities is of great significance for exploring ecosystem functions. In this study, we investigated soil enzyme activities, stoichiometry and their driving factors at six different altitudes (4300-5100 m) on Qinghai-Tibet Plateau alpine meadow using Biolog microplate analysis. The results showed that ß-1,4-glucosidase (ßG) closely related to C cycle, ß-1,4-N-acetylglucosaminidase (NAG) and L-leucine aminopeptidase (LAP) closely related to N cycle and the activity of acid phosphatase (AP), which was closely related to P cycle, all exhibited unimodal trends with increasing altitude, with the order of 4800 m＞4950 m＞4400 m＞4650 m＞5100 m＞4300 m. Soil N:P enzyme activity ratio showed the same trend as soil enzyme activity, and reached the highest value at 4950 m, however, soil C:N and C:P enzyme activities ratios increased along the altitude. Pearson correlation analysis showed that SOC, TN and soil water content were significantly positively correlated with the activities of four types of enzymes. Mean annual precipitation was significantly negatively associated with the activities of NAG and AP. Mean annual precipitation, mean annual temperature, Shannon diversity, vegetation richness, vegetation coverage and TN affected ratios of soil C:P and N:P enzymes. Soil C:N activity ratio correlated with mean annual temperature, mean annual precipitation, vegetation richness, vegetation coverage, SOC and TN. In summary, soil enzyme activities and stoichiometry had remarkable difference along the altitude gradient on Qinghai-Tibet Plateau alpine meadow, with certain N limitation in high altitude areas. Soil water content, TN, SOC, mean annual precipitation and mean annual temperature were key factors driving such differences.

[Influence of long-term enclosure and free grazing on soil microbial community structure and carbon metabolic diversity of alpine meadow.] / é•¿æœŸå›´å°å’Œè‡ªç”±æ”¾ç‰§å¯¹é«˜å¯’è‰ç”¸åœŸå£¤å¾®ç”Ÿç‰©ç¾¤è½ç»“æž„åŠç¢³æºä»£è°¢å¤šæ ·æ€§çš„å½±å“.

Soil microbial community structure and functional diversity have great implications for the maintenance of the function and stability of grassland ecosystem. We studied the variation of soil microbial community structure, community diversity of carbon metabolism and their driving factors between the long-term enclosure and the free grazing grasslands in Qinghai-Tibet Plateau by using phospholipid fatty acid and Biolog techniques. The results showed that: 1) there were significant differences in soil microbial community structure and the utilization of carbon source between the long-term enclosed and free grazed grasslands. 2) Long-term enclosure significantly increased the content of total PLFA, bacteria, fungi and actinomycetes. 3) Soil carbon metabolic activity, diversity and richness in free-grazing grassland was significantly higher than the enclosed grassland, but evenness showed an opposite pattern. 4) Compared with the free grazed grassland, long-term enclosure significantly increased the utilization of polymers, carbohydrates, carboxylic acids, and amines by soil microorganisms. 5) Results from the redundancy analysis showed that vegetation coverage significantly affected soil microbial community structure and carbon metabolism. The soil microbial content, carbon metabolism diversity and richness in the long-term enclosed grassland were higher than those of the free grazing grassland, indicating that long-term enclosure was more conducive to improve the diversity and carbon metabolism of soil microbial community.

[Temperature sensitivity of soil organic carbon mineralization and ß-glucosidase enzymekinetics in the northern temperate forests at different altitudes, China].

Soil samples, which were collected from three typical forests, i.e., Betula ermanii forest, coniferous mixed broad-leaved forest, and Pinus koraiensis forest, at different altitudes along the southern slope of Laotuding Mountain of Changbai Mountain range in Liaoning Province of China, were incubated over a temperature gradient in laboratory. Soil organic carbon mineralization rates (Cmin), soil ß-1,4-glucosidase (ßG) kinetics and their temperature sensitivity (Q10) were measured. The results showed that both altitude and temperature had significant effects on Cmin · Cmin increased with temperature and was highest in the B. ermanii forest. The temperature sensitivity of Cmin [Q10(Cmin)] ranked in order of B. ermanii forest > P. koraiensis forest > coniferous mixed broad-leaved forest, but did not differ significantly among the three forests. Both the maximum activity (Vmax) and the Michaelis constant (Km) of the ßG responded positively to temperature for all the forests. The temperature sensitivity of Vmax [Q10(Vmax)] ranged from 1.78 to 1.90, and the temperature sensitivity of Km [Q10(Km)] ranged from 1.79 to 2.00. The Q10(Vmax)/Q10(Km) ratios were significantly greater in the B. ermanii soil than in the other two forest soils, suggesting that the ßG kinetics-dependent impacts of the global warming or temperature increase on the decomposition of soil organic carbon were temperature sensitive for the forests at the higher altitudes.

[Impacts of land-use types on soil C mineralization and temperature sensitivity of forests in Qianyanzhou, Jiangxi Province, China].

Decomposition of soil organic matter plays an important role in the regulation of carbon (C) cycles at ecosystem or regional scales, and is closely related to temperature, moisture, and land-use types. The influences of soil temperature, moisture, and land-use types on soil C mineralization in Citrus reticulata and Pinus elliottii forests were investigated at the Qianyanzhou Ecological Experiment Station, Chinese Academy of Sciences, by conducting incubation experiments at 5-level temperatures (5, 10, 15, 20 and 25 degrees C) and 3-level moistures (30%, 60% and 90% saturated soil moisture, SSM). The results showed that soil temperature, moisture, and land-use types had significant effects on soil C mineralization and they had significant interaction effects. Soil C mineralization was positively correlated with incubation temperature in the two forests, and the maximum of soil C mineralization was in the 60% SSM treatment. The accumulation of soil C mineralization was higher in the C. reticulata forest than in the P. elliottii forest under the same temperature and moisture conditions. The temperature sensitivity (Q10) of soil C mineralization was influenced by land-use type and soil moisture. Q10 increased with the increasing soil moisture in both C. reticulata and P. elliottii forests at incubation 7 and 42 d. Q10 in the C. reticulata forest was higher than in the P. elliottii forest in the same moisture level, and the deviation increased with the increasing soil moisture. The model including temperature and moisture could depict the response of soil C mineralization to temperature and moisture. Temperature and moisture together explained 79.9% -91.9% of the variation in soil C mineralization.

Convergent responses of nitrogen and phosphorus resorption to nitrogen inputs in a semiarid grassland.

Human activities have significantly altered nitrogen (N) availability in most terrestrial ecosystems, with consequences for community composition and ecosystem functioning. Although studies of how changes in N availability affect biodiversity and community composition are relatively common, much less remains known about the effects of N inputs on the coupled biogeochemical cycling of N and phosphorus (P), and still fewer data exist regarding how increased N inputs affect the internal cycling of these two elements in plants. Nutrient resorption is an important driver of plant nutrient economies and of the quality of litter plants produce. Accordingly, resorption patterns have marked ecological implications for plant population and community fitness, as well as for ecosystem nutrient cycling. In a semiarid grassland in northern China, we studied the effects of a wide range of N inputs on foliar nutrient resorption of two dominant grasses, Leymus chinensis and Stipa grandis. After 4 years of treatments, N and P availability in soil and N and P concentrations in green and senesced grass leaves increased with increasing rates of N addition. Foliar N and P resorption significantly decreased along the N addition gradient, implying a resorption-mediated, positive plant-soil feedback induced by N inputs. Furthermore, N : P resorption ratios were negatively correlated with the rates of N addition, indicating the sensitivity of plant N and P stoichiometry to N inputs. Taken together, the results demonstrate that N additions accelerate ecosystem uptake and turnover of both N and P in the temperate steppe and that N and P cycles are coupled in dynamic ways. The convergence of N and P resorption in response to N inputs emphasizes the importance of nutrient resorption as a pathway by which plants and ecosystems adjust in the face of increasing N availability.

Biogenic VOCs emission inventory development of temperate grassland vegetation in Xilin River basin, Inner Mongolia, China.

Given the key role of biogenic volatile organic compounds (VOCs) to tropospheric chemistry and regional air quality, it is important to generate accurate VOCs emission inventories. However, only a less fraction of plant species, in temperate grassland of Inner Mongolia, has been characterized by quantitative measurements. A taxonomic methodology, which assigns VOCs measurements to unmeasured species, is an applicable and inexpensive alternation for extensive VOCs emission survey, although data are needed for additional plant families and genera to further validate the taxonomic approach in grassland vegetation. In this experiment, VOCs emission rates of 178 plant species were measured with a portable photoionization detector (PID). The results showed the most of genera and some families have consistent feature of their VOCs emission, especially for isoprene, and provide the basic premise of taxonomic methodology to develop VOCs emission inventories for temperate grassland. Then, the taxonomic methodology was introduced into assigning emission rate to other 96 species, which no measured emission rates available here. A systematical emission inventory of temperate grassland vegetation in Inner Mongolia was provided and further evidence that taxonomy relationship can serve as a useful guide for generalizing the emissions behavior of many, but not all, plant families and genera to grassland vegetation.