[Effects of labile carbon addition on organic carbon mineralization and microbial growth strategies in subtropical forest soils.] / å¤–æºç¢³è¾“å ¥å¯¹ä¸­äºšçƒ­å¸¦æ£®æž—æ·±å±‚åœŸå£¤ç¢³çŸ¿åŒ–å’Œå¾®ç”Ÿç‰©å†³ç­–ç¾¤è½çš„å½±å“.

Deep soil is a major organic carbon pool in terrestrial ecosystems. Labile carbon inputs can stimulate soil organic carbon (SOC) mineralization, causing priming effect, which in turn affects soil carbon emission. However, the mechanism of the priming effect in deep soil is still unclear. Therefore, to know how deep soil responds to labile carbon addition is essential for better understanding of deep soil carbon dynamics. In this study, we incubated three profiled soils (0-10 cm, 10-30 cm, 30-60 cm) from a subtropical forest with 13C-labeled glucose addition to analyze the priming effects and their relationship with the shift of microbial communities (r-K strategies). The results showed that glucose addition increased SOC mineralization in all soil layers, causing positive priming effects. But glucose addition significantly decreased the specific growth rates of microorgani-sms for all soils, indicating a relative decrease of r-strategists and a relative increase of K-strategists in the microbial community. Thus, we inferred that the positive priming effect was possibly attributed to the increased contribution of K-strategists. The priming effect in deep soil (156%) was significantly higher than that in surface soil (45%). Meanwhile, the ratio of dissolved organic carbon (DOC) and dissolved nitrogen (DN) after glucose addition was significantly higher in deep soil (76.03) than that in surface soil (13.00). These results suggested that there existed a stronger nitrogen limitation in deep soil. The microorganisms in deep soil tended to decompose recalcitrant SOC to acquire nitrogen, which then caused a greater priming effect. Overall, deep soil was more vulne-rable to labile carbon addition due to its carbon and nitrogen limitations, and hence was likely more sensitive to climate change in the future.

[Effects of altitude on soil microbial community in Quercus liaotungensis forest].

Taking the Quercus liaotungensis forest soil in Dongling Mountain of Beijing as the object, and by using chloroform fumigation-extraction and phospholipid fatty acid (PLFA) analysis methods, this paper studied the variation characteristics of soil microbial community along an altitudinal gradient in the tree growth season. With increasing altitude, the soil microbial biomass carbon and nitrogen and the quantities of various soil microbial groups in the forest had definite differences but not significant. The ratio of soil bacteria to fungi increased, but the ratio of G(+)- to G- bacteria decreased. The soil microbial biomass carbon and nitrogen and the quantities of soil bacteria, fungi, and G(+)- and G- bacteria had significant positive correlations with the contents of soil moisture, organic carbon, and total nitrogen, and the quantity of soil fungi was positively correlated with soil carbon/nitrogen ratio. The variations of the soil microbial community structure (bacteria/fungi and G(+)-/G- bacteria) were mainly affected by soil temperature and moisture content, which meant that the soil microbial community structure was sensitive to the environmental conditions. Along with the global warming, the proportions of soil fungi and G+ bacteria in the Q. liaotungensis forests in warm temperate zone would have an increase.

[Soil microbial properties under different vegetation types in Loess hilly region].

By using fumigation-extract (FE) method and Biolog Ecoplate, this paper investigated the microbial biomass and diversity in 0-20 cm soil layer under five vegetation types, including artificial woodland, shrubland, cropland, abandoned farmland, and natural grassland, in Dingxi of Gansu Province. In the meanwhile, the relationships between soil microbes and soil nutrients were studied by path analysis, and the five typical vegetation types were evaluated from the aspect of soil microbes. Relative to cropland, "grain for green" project played a key role in improving soil microbial resources. Microbial biomass carbon was the highest in ridge grassland, abandoned farmland, and pine woodland, followed by in Caragana korshinskii land, Medicago sativa land, restored land, and roadside land, and in wheat field and potato field. Microbial biomass nitrogen was the highest in ridge land, abandoned farmland, Pinus tabulaeformis woodland, Caragana korshinskii land, and Medicago sativa land, followed by in restored land and roadside land, and in wheat field and potato field. Caragana korshinskii land and Medicago sativa land, due to the existence of N-fixing rhizobium, had the highest ratio of soil microbial biomass nitrogen to soil total nitrogen. Owing to the continual biomass loss and rare feedback, cropland had the lowest quantity and activity of soil microbes. Through planting trees, shrubs and grasses or through fallowing, soil microbial biomass and activity were recovered, and the effect was increased with time. In 20-year old Caragana korshinskii land, the quantity and activity of soil microbes were similar to those in 50-year old Pinus tabulaeformis woodland, and the microbial community catabolic activity and soil nutrient use efficiency were higher. Considering the features of soil microbes under test vegetation types, Caragana korshinskii would be a good choice for local vegetation restoration.

[Influence of soil moisture, nitrogen and phosphorus contents on Bauhinia faberi seedlings growth characteristics in arid valley of Minjiang River].

To study the influence of resources thresholds on plant growth is a major theme in restoration ecology. Based on the simulation of the natural thresholds of soil moisture, nitrogen (N), and phosphorus (P) under drought condition in the arid valley of Mingjiang River, a full factorial experiment was designed to study the dynamics of Bauhinia faberi seedlings survival rate, growth, biomass production, and resources use efficiency across one growth season. High soil moisture (40% field water capacity), high soil P (24 mg P x kg(-1)), and low N (100 mg N x kg(-1)) increased the seedlings survival rate, and promoted the seedlings growth, biomass production, and water use efficiency. There was a significant coupling effect between soil N and P, but the interactions between soil moisture and soil N and P were not obvious. High N (240 mg N x kg(-1)) restrained the seedlings growth markedly, while high P mitigated the negative effects of high N via increasing root area, root length, and root mass to promote the seedlings N and P uptake. The N and P use efficiency across one growth season kept steady, and had significant positive correlation with root/shoot mass ratio. The combination of high soil moisture, low N, and high P promoted the seedlings growth effectively, while that of low soil moisture, low P, and high N inhibited the seedlings growth markedly.