Abstract
Soil carbon (C) sequestration and stabilization are determined by not only the C input to the soil but also the decomposition rate of soil organic matter (SOM), which is mainly mediated by soil microbes. Afforestation, an effective practice to restore forests from degraded or bare lands, may alter soil microbial properties, and thus soil C and nitrogen (N) dynamics. The aim of this study was to investigate the impacts of different afforestation strategies on soil microbial compositions and activities after afforestation for half a century. Soil samples were collected from two afforested sites (i.e., a restored secondary forest (RSF) and a managed Eucalyptus forest (MEP)) and two reference sites (i.e., a nearby undisturbed forest (UF), representing the climax vegetation and a bare land (BL), representing the original state before restoration) in south China. We quantified the soil microbial biomass, microbial community compositions, and activities of nine extracellular enzymes at different soil depths and in different seasons. Results showed that the soil microbial biomass, all the main soil microbial groups, and the activities of all extracellular enzymes were significantly increased after afforestation compared to the BL sites, while the ratios of fungi/bacteria (F/B), specific enzyme activities, and the ecoenzymatic stoichiometry were significantly decreased regardless of the season and soil depth. Between the two afforested sites, these microbial properties were generally higher in the RSF than MEP. However, the microbial properties in the RSF were still lower than those in the UF, although the differences varied with different seasons, soil depths, and microbial groups or enzymes. Our findings demonstrated that afforestation might significantly improve microbial properties. Afforestation is more effective in mixed-species plantation than in the monoculture Eucalyptus plantation but needs a much longer time to approach an equivalent level to the primary forests.
Highlights
Soil degradation due to deforestation creates a series of issues, such as ecosystem carbon (C) losses, low productivity, and decreases in biodiversity [1,2]
We addressed the following three questions in this study: (1) How were microbial properties changed after afforestation over the half-century? (2) Did the changes of microbial properties vary with different restoration strategies? (3) Could the microbial properties at the restored secondary forest recover equivalence to the nearby undisturbed forest? The findings of this study would be useful in selecting adequate tree species and assisting in the better restoration of degraded lands in the future
Compared to the UF, the two seasons’ and two soil depths’ average values of soil water content in restored secondary forest (RSF), managed Eucalyptus (Eucalyptus exserta) plantation (MEP), and bare land (BL) declined by 9.81%, 53.87%, and
Summary
Soil degradation due to deforestation creates a series of issues, such as ecosystem carbon (C) losses, low productivity, and decreases in biodiversity [1,2]. Numerous studies have demonstrated that C stocks in plant biomass and soil can rapidly increase with afforestation [8,9] and recover to an equivalent level to the nearby undisturbed forests within a few decades [10]— in tropical regions, where the consistent warm temperature and ample rainfall favor rapid plant growth [7]. Studies regarding the influence of afforestation on soil C and nutrient pools have been conducted extensively in recent years; how the microbial properties will change with afforestation are still not well understood [17,18], which may have important implications for ecosystem function and stability in these restored forests
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