[Response Characteristics of Soil Microbial Community Under Long-term Film Mulching].

Film mulching is an important practice to increase the yield and income in agricultural production. Soil samples were collected from four farmland sites with different mulching years to reveal the effect of long-term plastic mulching on characteristics of soil microbial community structure. In order to explore the long-term effect of soil microbial community change and its effect on the microbial ecological environment, high-throughput sequencing technology was used to analyze the changes in soil bacterial and fungal community structure. The results showed that long-term film mulching had no significant effect on soil bacterial diversity but decreased fungal diversity. Long-term film mulching decreased the abundance of Acidobacteriota and Mortierellomycetes and increased the abundance of Actinobacteriota. Long-term film mulching enriched the beneficial microbial communities such as Bacillus, Nocardioidaceae, Aspergillus, and Hypocreales in soil. However, long-term film mulching indued a simple and fragile soil fungal co-occurrence network pattern. The unidentified Sordariales under Ascomycota was the only key species in the fungal co-occurrence network, which resulted in potential risks to the ecological environment of the farmland soil. This study provided a theoretical basis for further understanding the effects of long-term film mulching on the ecological and environmental effects of microorganisms in farmland.

[Effects of Plastic Mulch Film on Soil Nutrients and Ecological Enzyme Stoichiometry in Farmland].

Ecological enzyme stoichiometry can be used to evaluate the limit of soil microbial energy and nutrient resources. To illustrate the effects of plastic mulch film on soil ecological enzyme stoichiometry in farmland, this study collected soil with different amounts of mulching film residual and used the fluorescence analysis to determine the activities of key enzymes for the carbon, nitrogen, and phosphorus cycle processes including ß-1,4-glycosidase (BG), ß-1,4-N-acetyl amino glycosidase (NAG), and phosphatase (ACP) activity. This study investigated the effects of plastic mulch film on soil nutrient cycling and supply in farmland. The results showed that in the soil with chemical fertilizer, plastic film mulching decreased soil Olsen-P and NO3--N contents to 48%-62% and 16%-24% of those in the soil without plastic film mulching, respectively. In the soil with the combined application of organic-chemical fertilizers, plastic film mulching increased Olsen-P and NO3--N contents by 144%-203% and 1.9-5.1 times, respectively. In the organic-chemical fertilization soils, plastic film mulching decreased SOC:TN in soils by 6.6%-25.8%, whereas it increased SOC:TP and TN:TP significantly. MBC, MBN, and MBP contents in the soil with plastic film mulching were significantly lower than that in non-plastic film mulching farmland, and there were no significant differences in MBC:MBN and MBC:MBP between soil with and without plastic film mulching. The MBN:MBP was reduced by 36.6% and 23.8% in S1 and S2, and 5.4 and 1.3 times in S3 and S4 by plastic film mulching, respectively. The change pattern of NAG:ACP in soil was similar to that of the corresponding elements ratio in microbial biomass. In the soil from plastic film mulching, the ratio of BG:NAG was 1.3-15 times higher in organic-chemical fertilization soils than that with only chemical fertilizer. In conclusion, plastic film mulching reduced the availability of soil nutrients, and organic-chemical fertilization alleviated the limitation of soil nutrients to a certain extent. This study deepened the understanding of the response of soil microorganisms to nutrient cycling after plastic film mulching. It provides a theoretical basis for optimizing the farmland management in the use of plastic film.

Patterns and Drivers of Soil Respiration under Long-Term Citrus reticulate in Southern China.

Soil respiration (Rs) is a major source of carbon emission in terrestrial ecosystems. Despite the fact that the influence of land use practice on Rs has been widely studied, the patterns and drivers on Rs of Citrus reticulata cultivation, a worldwide land use practice are unclear. In this current study, we investigated the influence of long-term cultivation of Citrus reticulata (CO) and of CO intercropped with soybean (CB) on soil nutrients, water availability, and Rs in southern China. Results indicated that after 21 years of cultivation, CO and CB significantly increased total soil carbon (TC), total soil nitrogen (TN), and soil organic matter (OM) at 0-20 cm and 20-40 cm, both at upslope and downslope compared with bare soil (CK). However, soil moisture (SM), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) decreased under CB. In addition, no significant variation was found in soil pH between CK, CO, and CB. Across incubation time (56 days), Rs decreased exponentially with incubation time and CB showed the highest Rs rate irrespective of soil depth or topography. Linear regression further showed TC and TN as the two major factors influencing Rs upslope, while DOC was the dominant factor in regulating Rs downslope. These findings demonstrated that long-term cultivation of citrus significantly changed soil nutrients, water availability, and Rs rate.

[Effects of forest type on soil organic matter, microbial biomass, and enzyme activities].

Taking the typical forest types Pinus elliottii var. elliotttii, Araucaria cunninghamii, and Agathis australis in southern Queensland of Australia as test objects, an investigation was made on the soil soluble organic carbon (SOC) and nitrogen (SON), microbial biomass C (MBC) and N (MBN), and enzyme activities, aimed to understand the effects of forest type on soil quality. In the three forests, soil SOC content was 552-1154 mg kg(-1), soil SON content was 20.11-57.32 mg kg(-1), soil MBC was 42-149 mg kg(-1), soil MBN was 7-35 mg kg(-1), soil chitinase (CAS) activity was 2.96-7.63 microg g(-1) h(-1), soil leucine aminopeptidase (LAP) activity was 0.18-0.46 microg g(-1) d(-1), soil acid phosphatase (ACP) activity was 16.5-29.6 microg g(-1) h(-1), soil alkaline phosphatase (AKP) activity was 0.79-3.42 microg g(-1) h(-1), and soil beta-glucosidase (BG) activity was 3.71-9.93 microg g(-1) h(-1). There was a significant correlation between soil MBC and MBN. Soil SOC content and soil CAS and LAP activities decreased in the order of P. elliottii > A. cunninghamii > A. australis, soil SON content decreased in the order of A. cunninghamii > A. australis > P. elliottii and was significantly higher in A. cunninghamii than in P. elliottii forest (P < 0.05), soil MBC and MBN and AKP activity decreased in the order of A. australis > P. elliottii > A. cunninghamii, and soil ACP and BG activities decreased in the order of P. elliottii > A. australis > A. cunninghamii. Among the test soil biochemical factors, soil MBC, MBN, SON, and LAP had greater effects on the soil quality under the test forest types.