[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.

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.