Functional Diversity of the Soil Culturable Microbial Community in Eucalyptus Plantations of Different Ages in Guangxi, South China

We selected five different ages of eucalyptus plantation sites to understand the culturable microbial functional diversity and the ecological functions of the soil from the eucalyptus plantations in Guangxi. We investigated the carbon source metabolic activity and diversity features of surface soil microbes using the Biolog EcoPlate method (Biolog Inc., Hayward, CA, USA), along with the microbial functional diversity and physicochemical properties of the soil. The results suggest that the carbon source utilization capacity of the soil microbes at various forest ages manifested as 3-year-old > 5-year-old > 2-year-old > 1-year-old > 8-year-old. The abundance, Shannon-Weiner, Pielou, Simpson, and McIntosh diversity indices of the soil microbes initially increased and then decreased with further increase in forest age, with the highest levels in 3- and 5-year-old forests. As per the heatmap analysis, the 3-year-old forest could metabolize the most carbon source species, while the 1- and 8-year-old forests could metabolize the least. Carbohydrates were the most frequently metabolized carbon source. The principal component analysis (PCA) shows that PC1 and PC2 extracted from the 31 factors have 52.42% and 13.39% of the variable variance, respectively. Carbohydrates contributed most to PCA, followed by amino acids and carboxylic acids, and phenolic acids and amines, the least. Canonical correspondence analysis shows that total carbon, alkali-hydrolyzable nitrogen, total nitrogen, total potassium, and pH negatively correlate with soil microbial functional diversity, whereas total and available phosphorus positively correlate with it. To sum up, the soil microbial community structure of eucalyptus plantations at various ages reflects the soil environmental conditions and nutrient availability, which is of great significance in the efficient management and high-quality operation of their plantations in Guangxi.