Identification and screening for key factors of soil quality under the conversion of low-yield Camellia oleifera forest

Camellia oleifera, as a “money spinner” for poverty alleviation in southern China, has an important effect on local economy. In recent years, due to the surging demand for grain and oil reserves in China, it is urgent to reform the low-yield and low-efficiency old forest. However, the influence of the transformation process on soil quality and fungal community is still unclear. On the forest land replanted after clear cutting, the composition of litter and rhizosphere sediment has been changed, showing an impact on soil properties. By comparing the soil before and after the transformation, the key factors regulating the soil nutrients in the stand were clarified, which had important guiding significance for the transformation of the low-yield C. oleifera forest.

This study collected soil samples from the old C. oleifera forest, young C. oleifera, Pinus massoniana forest and Cunninghamia lanceolata forest. We then determined 13 indexes including soil chemical properties, enzyme activity indexes and the community diversity of fungi. The minimum data set was selected and revised by the principal component analysis (PCA) and discriminant (MDA) analysis. The evaluation index system of soil quality in this area was established, and comprehensively evaluated.

There were significant differences in pH, soil organic carbon (SOC), total potassium (K), magnesium (Mg), iron (Fe), manganese (Mn) and nitrate nitrogen (NO₃) in the soil after transformation. The activities of acid phosphatase (AP), N-acetylglucosaminidase (NAG) and β-glucosidase (BG) in the replanted P. massoniana forest were higher than others. Finally, it was demonstrated that the minimum data set of soil fertility evaluation indexes of C. oleifera in this area was significantly affected by nitrate, K, available K, NAG, total nitrogen (N), pH, SOC, total phosphorus (P), and fungal Shannon indexes. Moreover, SOI was improved by stand transformation.

Acidic soil environment is conducive to the growth of C. oleifera. Besides N, P, K and Mg, the trace mineral contents of Fe and Mn should be paid attention to in C. oleifera forests. Besides, as C. oleifera is a mycorrhizal-dependent woody oil plant, the use of fungal fertilizer can be considered when applying bacterial fertilizers. This study provides guidance for future soil management and precise fertilization in this area.