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A strategic selection of tree species will shift the type and quality of litter input, and subsequently magnitude and composition of the soil organic carbon (SOC) through soil microbial community. We conducted a manipulative experiment in randomized block design with leaf litter inputs of four native subtropical tree species in a Pinus massoniana plantation in southern China and found that the chemical composition of SOC did not differ significantly among treatments until after 28 months of the experiment. Contrasting leaf litter inputs had significant impacts on the amounts of total microbial, Gram-positive bacterial, and actinomycic PLFAs, but not on the amounts of total bacterial, Gram-negative bacterial, and fungal PLFAs. There were significant differences in alkyl/O-alkyl C in soils among the leaf litter input treatments, but no apparent differences in the proportions of chemical compositions (alkyl, O-alkyl, aromatic, and carbonyl C) in SOC. Soil alkyl/O-alkyl C was significantly related to the amounts of total microbial, and Gram-positive bacterial PLFAs, but not to the chemical compositions of leaf litter. Our findings suggest that changes in forest leaf litter inputs could result in changes in chemical stability of SOC through the altered microbial community composition.

A field experiment was conducted on fluvo-aquic soil in the North China Plain to study the effects of nitrogen application rate on soil nitrogen contents and enzyme activities in rhizosphere and non-rhizosphere of summer maize. The results showed that the soil enzyme activities under different nitrogen application rates showed similar seasonal patterns. In comparison to no nitrogen ferti-lizer treatment, all nitrogen application treatments significantly increased NO 3 - -N content in rhizosphere soil and the activities of β-N-acetylglucosaminidase, β-glucosidase, β-xylosidase and Cellobiohyrolase. During the whole summer maize growing season, the NO 4 -N content in non-rhizosphere soil was significantly higher than that in rhizosphere soil. The NH + -N content in non-rhizosphere soil was also significantly higher than that in rhizosphere soil at filling stage but significantly lower at seedling and maturity stages. Furthermore, soil enzyme activities in rhizosphere soil were significantly higher than those in non-rhizosphere soil. Effect of nitrogen application on soil organic carbon content was not significant. Soil total nitrogen content increased significantly when the nitrogen application rate was 0-180 kg·hm 3 - . Generally, a proper rate of nitrogen fertilizer application could significantly increase soil enzyme activities and total nitrogen content, and then improve soil biochemistry properties.4 + -N content in non-rhizosphere soil was also significantly higher than that in rhizosphere soil at filling stage but significantly lower at seedling and maturity stages. Furthermore, soil enzyme activities in rhizosphere soil were significantly higher than those in non-rhizosphere soil. Effect of nitrogen application on soil organic carbon content was not significant. Soil total nitrogen content increased significantly when the nitrogen application rate was 0-180 kg·hm -2 but decreased significantly when the rate was higher than 180 kg·hm -2 . Generally, a proper rate of nitrogen fertilizer application could significantly increase soil enzyme activities and total nitrogen content, and then improve soil biochemistry properties.

Soil aggregate stability and microbial diversity play important roles in nutrient recycling in soil-crop systems. This study investigated the impacts of different soil tillage systems on soil aggregation and soil microbial diversity based on a 15-year long-term experiment on loess soil in Henan Province of China. Treatments included reduced tillage (RT), no-tillage (NT), sub-soiling with mulch (SM), wheat-peanut two crops (TC), and conventional tillage (CT). Soil aggregates were separated by wet sieving method, and soil microbial (bacterial, archaeal and fungal) diversity was examined by using the techniques of denaturing gradient gel electrophoresis (PCR-DGGE) analysis. The results showed that water-stable macroaggregates concent (R0.25) and the mean mass diameter (MWD) in the surface soil significantly increased under NT, SM and TC, R0.25 increased by 21.5%, 29.5% and 69.2%, and MWD increased by 18.0%, 12.2% and 50.4%, respectively, as compared with CT. Tillage practices caused changes in bacterial, archaeal and fungal community compositions. With NT, SM and TC, the bacterial, archaeal and fungal Shannon indices increased by 0.3%, 0.3%, and 0.6%, and 20.2%, 40.5%, and 49.1%, and 23.7%, 19.5%, and 25.8%, respectively, as compared with CT. Both bacterial and archaeal Shannon indices were significantly correlated with the indices of R0.25 and MWD, while the fungal Shannon index was not significantly correlated with these two indices. In conclusion, conservation tillage, including NT and SM, and crop rotation, including TC, improved soil aggregation and soil microbial diversity.

This paper studied the change of soil physical and chemical properties under eleven vegetation restoration patterns (1 kind of secondary forest, 2 kinds of pure coniferous plantations, 5 kinds of evergreen broad-leaved plantations, 2 kinds of conifer and broad-leaved mixed plantations, and 1 kind of shrub) typical in Daqingshan of Guangxi. Obvious differences were observed in the soil physical and chemical properties under different vegetation restoration patterns. The soil physical properties were better in secondary forest but poorer in pure conifer plantations. Conifer and broad-leaved mixed plantations had lower soil bulk density, and their soil total porosity and water-holding capacity were higher than those in pure plantations. There were no significant differences in the soil porosity among the 5 evergreen broad-leaved plantations. Except that of soil total K, the contents of soil nutrients in secondary forest were higher than those in plantations, and the soil C/N ratio and pH value were relatively lower. Comparing with shrub, the 9 plantations had an obvious change in their soil nutrient contents, e. g. , the increase of soil total N and available K. The 2 pure coniferous plantations had lower soil nutrient contents, but after mixed planted with evergreen broad-leaved trees, their soil nutrient contents increased markedly, and the soil C/N ratio decreased.

By using plot investigation and sampling analysis methods, the understory vegetation and soil properties of Pinus massoniana plantations with different stand density in subtropical area were studied in Daqingshan, Guangxi Province. In the P. massoniana plantations after 14-year natural growth, the understory species diversity index of shrub layer increased with the increase of stand density from 1050 trees x hm(-2) to 1800 trees x hm(-2), but decreased when the stand density further increased to 2250 trees x hm(-2). Herb species diversity index was not sensitive to the stand density change. With increasing stand density, shrub biomass had the same variation trend as that of shrub species diversity index, while herb biomass decreased with increasing stand density. Significant differences (P < 0.05) were observed in the soil (0-20 cm) physical and chemical properties between the plantations with different stand density. The soil nutrient contents except those of total P and available K and P had the same variation trend with that of the understory species diversity index of shrub layer. Soil available K and P contents fluctuated with stand density, whereas soil total P content was higher when the stand density was 2100 trees x hm(-2). In the plantations with moderate stand density (1800 trees x hm(-2)) , soil water-holding capacity and soil porosity were higher, and soil bulk density was lower.

With spatial autocorrelation analysis, this paper studied the temporal and spatial variations of soil organic carbon (SOC) storage in Henan Province during the period from the 1st national soil survey (1958) to the 2nd national soil survey (1985). The results showed that spatial auto-correlation indices could better describe the spatiotemporal variation of the SOC storage between the two soil surveys. The total SOC storage was 54.93 x 10(8) t in 1958 and 69.65 x 10(8) t in 1985, with an annual increase of 1%, and the SOC density had a trend of higher in southeast and west Henan, followed by north and central Henan, and east Henan. The SOC storage per unit area decreased more quickly in southeast Henan, with the maximum of 1.57% per year, while increased greater in east Henan, with an average rate of 5.27% per year. The spatiotemporal variation of SOC storage had a close correlation with the original SOC content, i. e., the higher the original SOC content, the more greatly the SOC storage decreased.