[Influencing mechanism of stand age to the accumulation of microbial residue carbon in the Pinus masso-niana plantations]. / 林龄对马尾松人工林微生物残体碳积累的影响机制.

Clarifying the accumulation pattern of soil microbial residue carbon and its contribution to soil organic carbon (SOC) across stand age is helpful to understand the mechanism underlying soil carbon cycling. In this study, we analyzed the differences of amino sugar content, physicochemical properties and microbial composition in surface soil (0-10 cm) in young (6 a), middle-aged (13 a), near-mature (29 a), mature (38 a) and over-mature (57 a) Pinus massoniana plantations of subtropical China, quantified the microbial residue carbon content and its contribution to SOC, and discussed the mechanism. The results showed that SOC, total nitrogen, amorphous iron oxide and leucine aminopeptidase contents in the middle-aged plantation were significantly lower than those in the mature plantation. Soil pH and fungal/bacteria in young plantation were significantly higher than those in other age groups. Across the stand age gradient, the ranges of microbial, fungal and bacterial residue carbon were 7.52-14.63, 4.03-8.00 and 3.48-6.63 g·kg-1, respectively. The contents of all the residue carbon were significantly higher in the mature plantation than that of the middle-aged plantation, which were positively affected by soil total nitrogen content. The contribution of microbial, fungal, and bacterial residue carbon to SOC was 59.7%-72.3%, 33.4%-45.6%, and 24.3%-30.8%, respectively. The contribution of fungal residue carbon to SOC in young plantation was significantly higher than that in other age groups, and the contribution of bacterial residue carbon to SOC in middle-aged plantation was significantly higher than that in young and near-mature plantations, both of which were affected by soil inorganic nitrogen. Fungal residue carbon content was 1.2-1.7 times as that of bacterial residue carbon content, and dominated for the accumulation of microbial residue carbon. Results of the partial least squares model showed that stand age, soil environmental factors (such as leucine aminopeptidase, amorphous iron oxide, pH, and total nitrogen), bacterial residue carbon, fungal residue carbon and the contribution of bacterial residue carbon to SOC had total effects on the contribution of fungal residue carbon to SOC (-0.37, -1.16, 0.90, 1.09, and 0.83, respectively). In conclusion, stand age promoted the accumulation of microbial residue carbon but did not increase its contribution to SOC.

Living grass mulching improves soil enzyme activities through enhanced available nutrients in citrus orchards in subtropical China.

Living grass mulching (LGM) is an important orchard floor management that has been applied worldwide. Although LGM can effectively enhance soil nutrient availability and fertility, its effects on microbial-mediated soil nutrient cycling and main drivers are unclear. Meanwhile, the variation of enzyme activities and soil nutrient availability with LGM duration have been rarely studied. This study aims to explore the effects of mulching age and soil layer on enzyme activities and soil nutrients in citrus orchards. In this study, three LGM (Vicia villosa) treatments were applied, i.e., mulching for eight years, mulching for four years, and no mulching (clean tillage). Their effects on the enzyme activities and soil nutrients were analyzed in different soil layers of citrus orchards in subtropical China, i.e., 0-10, 10-20, and 20-40 cm. Compared to clean tillage, mulching for four years had fewer effects on enzyme activities and soil nutrients. In contrast, mulching for eight years significantly increased available nitrogen (N), phosphorus (P) nutrients, ß-glucosidase, and cellobiohydrolase activities in the soil layer of 0-20 cm. In the soil layer of 0-40 cm, microbial biomass carbon (C), N, P, N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase activities also increased (P < 0.05). Mulching for eight years significantly promoted C, N, and P-cycling enzyme activities and total enzyme activities by 2.45-6.07, 9.29-54.42, 4.42-7.11, and 5.32-14.91 times, respectively. Redundancy analysis shows that mulching treatments for eight and four years had soil layer-dependent positive effects on soil enzyme activities. Microbial C and P showed the most significant positive correlation with enzyme activities, followed by moisture content, organic C, and available N (P < 0.05). Available nutrients contributed almost 70% to affect enzyme activities significantly and were the main drivers of the enzyme activity variation. In summary, LGM could improve soil enzyme activities by increasing available nutrients. The promotion effect was more significant under mulching for eight years. Therefore, extending mulching age and improving nutrient availability are effective development strategies for sustainable soil management in orchard systems. Our study can provide valuable guidelines for the design and implementation of more sustainable management practices in citrus orchards.

Ecosystem service value effects of the Three Gorges Reservoir Area land use transformation under the perspective of "production-living-ecological" space.

In the context of rapid socio-economic development, eliciting "production-living-ecological" space (PLES) changes with corresponding ecosystem service benefits is critical for national land optimization and regional sustainability. Based on land use data obtained via remote sensing of 1980, 2000, 2018, and from a PLES perspective, we applied geo-information Tupu to depict land use transformations in the Three Gorges Reservoir Area (TGRA) from 1980 to 2018. The ecological/environmental effects of land use transformation were also explored based on the contribution value of ecosystem service. The results showed that both industrial production space and living space had increased from 1980 to 2018, while agricultural production space and ecological space displayed a decreasing trend. From the perspective of Tupu transformation, land use transformation pattern was relatively stable from 1980 to 2000, with the untransformed Tupu unit being dominant. However, with the complex land use transformation from 2000 to 2018, mutual transformation of agricultural production space and forest and grassland ecological space became dominant. Urbanization and industrialization were the main factors contributing to the decreased agricultural production space and ecological space. The ecosystem service value of TGRA initially decreased, then increased temporally, with greater change in the east than in the west. In the study period, ecological protection and restoration projects had positive effects on ecosystem service values, while rapid socio-economic development negatively impacted agricultural production space and ecological space. Combined with second ploughing, socio-economic development negatively impacted ecosystem ser-vice values.

Occurrence of Minerals in Coal and Its Geological Controlling Factors-Significance in Evaluation of Coal Washability.

The precombustion washing and washability of coal are increasingly gaining attention as a clean coal technology in China. In this study, the raw coal was collected from different coal seams in the south of Qinshui Coalfield, and flotation experiments were carried out in the laboratory after simple crushing. X-ray diffraction was used for qualitative analysis of the minerals in coal, and mineral morphology and disseminated particle size were measured with the help of an optical microscope. The samples were characterized to determine the original mineral content, combination type, occurrence characteristics, and dissemination type in coals of different lithotypes to establish a relationship with the coal-forming environment and to evaluate coal selectivity from a geological perspective. The results were obtained from the float-sink experiment by which the coal washability of different lithotypes is evaluated, combined with the information resulting from investigating the change law of the mineral occurrence and dissemination characteristics of the raw coal and the clean coal before and after the flotation experiment. The content of minerals with the particle size larger than 200 µm accounts for 35-50% of the easy-to-wash coal. The particles were mostly concentrated in the 50-100 µm size range in moderate difficulty washability coal, and the mineral occurrence forms are diverse. The disseminated particle size distribution of 10-20 µm in the refractory washability coal is between 35 and 45%, and the massive and fracture filling minerals are rarely found in the coal. The proportion of minerals smaller than 2 µm in the extremely difficult washability coal is more than 60%, and cell filling, dispersed, and banding forms are plentiful in this type of coal. The removal rates of ash and sulfur obtained through elution match well with the mineral form and distribution characteristics. The reason for the difference was the influence of the coal-forming environment on the occurrence of minerals in coal, which led to the removal of minerals in the coal washing procedure. The process is controlled by the occurrence and dissemination characteristics of minerals.