The phoD-Harboring Microorganism Communities and Networks in Karst and Non-Karst Forests in Southwest China

Abstract

Phosphorous (P) limitation is common not only in tropical rainforest and savanna ecosystems, but also in karst forest ecosystems. Soil phoD-harboring microorganisms are essential in soil P cycles, but very little information is available about them in karst ecosystems. A total of 36 soil samples were collected from two types of forest ecosystems (karst and non-karst) over two seasons (rainy and dry), and the diversity and community structure of soil phoD-harboring microorganisms were measured. The contents of available P (AP), soil total P (TP), microbial biomass P (MBP) and the activity of alkaline phosphatase (ALP) in karst forest soils were higher than those in non-karst forest soils, whereas the contents of CaCl2-P, citrate-P, enzyme-P and the activity of acid phosphatase (ACP) were the opposite. Soil AP content was significantly higher in the rainy season than in the dry season, whereas ALP activity was the opposite. The community structure of phoD-harboring microorganisms was more influenced by forest-type than season. The network connectivity was higher in non-karst forests than in karst forests. Two dominant orders, Burkholderiales and Rhizobiales, were the keystone taxa in these networks in two forests, and their relative abundances were higher in non-karst forests than in karst forests. The microorganic diversity indices (e.g., Shannon–Wiener, Evenness, Richness, and Chao1) were substantially higher in karst than in non-karst forests. These indices were positively correlated with the contents of SOC and TN in the two forests; meanwhile, richness and evenness indices were positively correlated with citrate-P, HCl-P, and TP in non-karst forests. Structural equation modelling results showed that the relative abundance of phoD-harboring microorganisms was mainly influenced by pH and AP, with direct affection of soil AP, pH, and ALP activity, and indirect affection of ALP activity through affecting AP. These findings highlight that the P cycle is mainly regulated by the diversity of phoD-harboring microorganisms in karst forest ecosystems, whereas it is mainly regulated by dominant taxa in non-karst forest ecosystems. In future, regulating the interaction networks and keystone taxa of phoD-harboring microorganisms may be critical to alleviating P limitations in karst forest ecosystems.