| Summary: | Soil microorganisms fundamentally regulate biochemical processes of soil organic matter decomposition in terrestrial ecosystems. In this study, we examined seasonal and yearly variations in soil microbial attributes (i.e., total phospholipid fatty acids (PLFAs), bacteria (B) and fungi (F), actinobacteria (ACT), microbial respiration (MR)) and potential controls at two soil depths under conversion from the cropland and uncultivated land to afforested lands (woodland and shrubland) of different years (2015, 2017) in the Danjiangkou Reservoir of subtropical China. The total PLFA (2.29–11.24 ug g−1), B (1.66–6.73 ug g−1) and F (0.32–1.44 ug g−1) biomass did not significantly vary with seasons of 2015, but they were significantly higher in summer (3.73–13.97, 1.49–7.36, 0.47–2.31 ug g−1, respectively) than in winter (1.30–9.73, 0.61–5.79, 0.23–1.49 ug g−1, respectively) of 2017 due to the larger fluctuation in soil moisture between winter and summer of 2017. In contrast, the lower MR (0.58–2.56 mg CO2−1 g soil−1h) in summer compared to winter (0.77–3.77 mg CO2−1 g soil−1h) was observed in 2015 primarily due to higher soil moisture in winter, but the higher MR (0.77–4.42 mg CO2−1 g soil−1h) was detected in summer than that in winter (0.43–2.89 mg CO2−1 g soil−1h) of 2017, which was closely related to lower soil moisture together with larger PLFA biomass in summer. The MR significantly changed with seasons in afforested lands, but it did not significantly vary with seasons in cropland and uncultivated land. Conversely, the MR/total PLFAs ratios significantly changed with seasons in cropland and uncultivated land, but it did not significantly vary with seasons in afforested lands. Collectively, our results revealed the different temporal pattern of soil microbial community composition under afforestation, thereby providing very useful information for governments to better manage and protect agricultural land use in future global change scenarios.
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