The relationship between soil bacteria and metal nutrient availability for uptake of apple trees in Chinese orchards

Abstract

Soil bacteria are widely recognized for their roles in nutrient cycling, such as for nitrogen and phosphorus, and for promoting soil health. However, the relationship between soil bacteria and the availability of calcium, magnesium, iron, manganese, copper and zinc under different climatic conditions in orchard systems remains poorly understood. Here, we explored the relationship between soil bacteria and metal nutrient availability and uptake by apple trees based on 36 soil samples from three climate zones that span the major apple-producing areas in China. The results indicated that six phyla (e.g., Acidobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes, Nitrospirae, and Proteobacteria) in the soil bacterial communities were positively related to the metal nutrients availability, especially to calcium (16 OTUs) and magnesium (19 OTUs). At the class level, Alphaproteobacteria improved the availability of calcium, magnesium, iron, manganese and copper, while Actinobacteria improved the availability of zinc and altered absorption by the roots and the contents in leaves. We found that the underground bacterial community diversity was determined by climatic conditions and soil properties, which altered the effect of bacteria on soil metal nutrients availability, and led to differences of nutritional content in the aboveground plant portions. Therefore, soil bacteria played a central role in this process for sustainable development in apple orchard systems.