Effects of nitrogen, phosphorus and potassium additions on functional diversity of soil microorganisms in Podocarpus macrophyllus

The purpose of the study was to characterize the response, as well as the regularitity of soil microorganisms in Podocarpus macrophyllus to different levels of nitrogen (N), phosphorus (P), and potassium (K). Using two-year old P. macrophyllus seedlings as the test species, the researchers controlled the gradients of N, P and K nutrient levels using the L9 orthogonal test in the potted soil. The dilution plate coating method and Biolog-ECO microplate method were used to explore the effects of different soil nutrient levels on the amount and community diversity of P. macrophyllus soil microorganisms and their utilization characteristics of six carbon sources. The results were as follows: (1) The number of soil bacteria (P<0.05) and actinomycetes (P<0.001) decreased while the number of fungi (P<0.001) and nitrogen-fixing bacteria (P<0.01) increased significantly when different levels of N were added. Additionally, the Pielou index (P<0.001) of the soil microbial community decreased, and the Simpson index (P<0.05) and McIntosh index (P<0.001) increased with increasing N addition. This reduced the intensity of utilization of six carbon sources by soil microorganisms, especially the intensity of utilization of difficult carbon sources such as amines (P<0.001), carboxylic acids (P<0.001), polymers (P<0.001) and other compounds (P<0.001). (2) The increase in P addition significantly reduced the Shannon index of soil microbial community (P<0.05). (3) The increase in K addition significantly reduced the Shannon index (P<0.05) and Pielou index (P<0.05) of the soil microbial community and the intensity of utilization of two easily available carbon sources, carbohydrates (P<0.001) and amino acids (P<0.01), by the microbial community. In conclusion, N addition and K addition are the main factors affecting the functional diversity of soil microbial communities of P. macrophyllus. Attention should be paid to the cultivation of P. macrophyllus by applying fertilizer in small amounts and multiple times, reducing the addition of N and K, and appropriately increasing the addition of P to promote the growth of P. macrophyllus and its sustainable cultivation.