The Relationship between pH and Bacterial Communities in a Single Karst Ecosystem and Its Implication for Soil Acidification.

Yuan Yun,Xing Xiang,Baiying Man,Annette S Engel,Jianping Zhou,Hongmei Wang,Yong Duan,Xuan Qiu

doi:10.3389/fmicb.2016.01955

Abstract

Enhanced monsoon duration and soil acidification from acid rain are expected to impact the distribution of microbial communities in surface and subsurface environments, although these impacts are poorly understood for most systems. In central China, soluble carbonate bedrock forms extensive karst landscapes. Current predictions are that the amount of monsoonal precipitation and acid rainfall in central China will increase, which is expected to lead to changes in the pH balance of karst ecosystems. To evaluate the role of pH, total organic carbon, and other geochemical parameters (e.g., Ca2+, Mg2+, NH4+, NOx, SO42-) in shaping bacterial communities within a single karst system in central China, samples were collected from the thin surface soils overlying Heshang Cave, cave sediments, and weathered cave passage rocks from the entrance, twilight, and dark zones, as well as from epikarstic drip waters inside the cave. Illumina sequencing of 16S rRNA genes and multivariate statistical analyses revealed that each tested community was distinct and the community variability was significantly correlated with pH, total organic carbon, and potassium concentrations. Specifically, surface soils were dominated by Acidobacteria, Verrucomicrobia and Planctomycetes, and diversity significantly decreased with acidic pH values. Nitrospirae, Gemmatimonadetes, Firmicutes, and Chloroflexi were unique to cave sediments, while Actinobacteria and Proteobacteria dominated weathered rocks and drip waters, respectively. The results reveal important implications regarding the effects of acidification on bacterial communities in karst areas, and on the control of pH in shaping bacterial communities throughout a karst system. Increased water flux into and through karst habitats due to monsoonal precipitation may result in deeper penetration of acidic solutions into karst and shift the bacterial communities inside the cave in the future.

Highlights

The 540,000 km2 karst region in eight provinces of central China (102–111◦ E, 23–32◦ N) is the key zone of east Asia karst areas, which is one of the three largest karst areas in the world (Fan et al, 2011)
Soil pH is widely accepted as a critical factor impacting the compositions of soil bacterial communities (Fierer and Jackson, 2006; Nicol et al, 2008; Baker et al, 2009; Davis et al, 2009; Jenkins et al, 2009; Jones et al, 2009; Lauber et al, 2009; Chu et al, 2010; Shen et al, 2013; Liu et al, 2014)
Karst soils and other habitats associated with a single karst system are poorly represented in studies focused on bacterial community diversity and structure

Summary

Introduction

The 540,000 km karst region in eight provinces of central China (including Yunnan, Sichuan, Chongqing, Guizhou, Hunan, Hubei, Guangdong, and Guangxi provinces) (102–111◦ E, 23–32◦ N) is the key zone of east Asia karst areas, which is one of the three largest karst areas in the world (Fan et al, 2011). The central China karst is experiencing severe acid rain recently due to anthropogenic activities and increased precipitation from enhanced monsoon pH, TOC Shape Bacterial Communities durations (Figure 1A). Widespread ecological and agricultural consequences are expected to include soil acidification (Larssen et al, 2006; Duan et al, 2011; Xu et al, 2015). There is limited understanding of karst soil bacterial communities in central China. It is expected that as precipitation increases in central China, especially acid rainfall, soil pH will decrease and subsequently affect microbial communities (Pu et al, 2011). Soil acidification in other parts of China has already been linked to lower microbial abundances in soils (Wu et al, 2006; Xu et al, 2015), as well as diminished microbial diversity (Zhalnina et al, 2015)

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Results

Conclusion