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Serious soil degradation due to human intervention in subtropical China has resulted in a series of ecological problems. Soil fauna is an important part of forest soil ecosystems and plays a vital role in the maintenance of soil quality and can sensitively reflect the soil disturbances caused by human activities. This study assessed the long-term effects of reforestation on the soil fauna community and underground food web. Soil fauna was sampled from plots in a 30-year reforestation positioning test site. Six reforestation models (the pure Schima superba (Ss) forest, pure Liquidambar formosana (Lf) forest, pure Pinus massoniana (Pm) forest, mixed forest of Lf & Ss, mixed forest of Pm & Ss, and the mixed forest of Lf & Pm) were chosen in Taihe County, southern China. The results found that the mixed vegetation restoration of Lf & Pm significantly improved the soil fauna abundance and biomass when compared with other reforestation models in the degraded red soil region. Acari and Collembola accounted for 65.8% and 23.3%, respectively, of the total soil fauna abundance in the region. The mixed forest of Lf & Pm had a positive effect on the abundance of secondary decomposers and micro predators in Acari. Moreover, a significant increase in the abundance of Collembola was found in the Lf & Pm stand type. The stand type with the highest soil faunal population also had a higher soil fauna biomass. Therefore, reforestation in a degraded red soil area had positive effects on the soil fauna community. [ABSTRACT FROM AUTHOR]

Root nutrients are required for the growth and development of roots and shoots, which are closely related to soil quality and fruit productivity. In this study, trees of contrasting stand ages, including young, middle-aged, and old trees, were selected in field sites with common management practices in the navel orange (Citrus sinensis) orchards of Southern China. The fine root N decreased with soil depth and the fine root P was higher of old trees (1.82 g kg-1) than young (1.57 g.kg-1) and middle-aged trees (1.37 g. kg-1). Soil organic C, total N, and P generally increased with plant age in the rhizosphere and bulk soils, while reverse trend was found for sucrase and urease activities. Interestingly, acid phosphatase activity was much higher at a lower depth (202 and 82 g.kg-1 OC d-1 for rhizosphere and bulk soils, respectively) than at an upper depth (46 and 43 g.kg-1 OC d-1 for rhizosphere and bulk soils, respectively). In conclusion, root and soil nutrients generally increased with plant growth. Fine root N decreased while fine root P remained unchanged with soil depth due to the content and rhizosphere effect of index at different soil layers related to N and P, respectively. [ABSTRACT FROM AUTHOR]