The long-term effects of reforestation on soil microbial biomass carbon in sub-tropic severe red soil degradation areas

Soil microbial biomass carbon (MBC) and soil microbial entropy (MBC/TOC: ratio of MBC to total organic carbon) are frequently used as indicators to assess soil quality, belowground processes and their responses to elevated CO2 in climate change studies. Using these two indicators, this study investigated the effect of three different reforestation types (coniferous, broadleaved, and mixture of conifer and broadleaved) on soil recovery following the plantations in 1991 in a severely degraded red soil area of the sub-tropic regions of China. Our results indicate that different reforestation types had significant effect on the MBC concentration in the 0–20 cm of soil depth after the 20-year soil recovery (p < 0.05). The MBC improved the most in the broadleaved forest (148.5 mg kg−1), followed by the mixture of conifer-broadleaved (127.7 mg kg−1) and the coniferous plantation (100.4 mg kg−1), as compared to the control (62.0 mg kg−1) where the sites are naturally covered with grasses. This result suggests that the importance of selecting reforestation types in restoring the severely-degraded ecosystems. In spite of the MBC increase following the 20-year rehabilitation, MBC remains at low levels, suggesting that restoration is a long-term, slow recovery process when soils are severely degraded. However, there were no significant differences in soil microbial entropy among three reforestation types, indicating that soil microbial entropy is not a sensitive indicator to reforestation types in severely-degraded areas as previously thought. We discussed our results in the context of forest carbon, climate change and restoration.

► We studied soil microbial biomass carbon and entropy for soil quality.
► Three types of plantations are compared after the 20-year reforestation.
► Broadleaved plantation is the best for improving soils.
► Soil recovery process is slow once soils are severely degraded.