Elsevier

CATENA

Volume 201, June 2021, 105224
CATENA

Tree species composition and nutrient availability affect soil microbial diversity and composition across forest types in subtropical China

https://doi.org/10.1016/j.catena.2021.105224Get rights and content

Highlights

  • Soil microbial diversity increased following the conversion of native forests.

  • The composition of soil bacteria and fungi differed with forest type and soil layer.

  • Tree species composition influences microbial diversity.

  • The availability of soil nutrients affects soil microbial composition.

Abstract

Soil microorganisms represent a significant component of terrestrial biodiversity and play a critical role in myriad ecological processes. The conversion of native forests to tree plantations is a major contributor to biodiversity loss on a global scale; however, our understanding of the influences of forest type conversion on soil microbial diversity and community composition remains unclear. Here we sampled twelve spatially interspersed stands of native mixed broadleaf forests, broadleaf-dominated (50–70% broadleaf trees), bamboo-dominated (20–40% broadleaf trees), and pure bamboo forests in subtropical China, to examine the effects of forest type conversion on soil bacterial and fungal diversity and composition. We found that the tree species richness, stand basal area, and soil carbon to nitrogen ratio decreased, while the total soil phosphorus increased from the native broadleaf forests to pure bamboo forests. Bacterial and fungal operational taxonomic units (OTUs) across the three soil depths increased significantly from 760 and 243 in native broadleaf to 795 and 336 in pure bamboo forests, respectively. However, neither bacterial nor fungal richness differed significantly among forest types at the phylum level. Across forest types, both bacterial and fungal OTU richness increased with the bamboo proportion and decreased with the soil carbon and nitrogen ratio. The fungal OTU richness also increased with the soil phosphorus content; however, neither bacterial nor fungal richness was affected by the tree species richness or stand basal area. Both bacterial and fungal community compositions changed with forest type and soil depth, with their compositional overlap from native broadleaf forests decreasing consistently with the bamboo proportion and soil phosphorus. Overall, our results provide insights into the importance of overstory tree composition and the availability of soil nutrients in affecting soil microbial diversity and composition, while providing management guidance for the inclusion of soil microbial diversity in forest conservation and management.

Introduction

Soil microorganisms comprise a major proportion of terrestrial biodiversity and are essential to many ecological processes, including primary production, nutrient cycling, and the decomposition of organic matter (Bardgett and van der Putten, 2014, Chen et al., 2019). Global forests, particularly those in China, continue to change and suffer the loss of tree species diversity due to the conversion of natural forests to fast-growing tree plantations to meet increasing anthropogenic demands for timber and other wood products (Chen et al., 2020, Newbold et al., 2015). Despite the importance of soil microbial communities for ecosystem functionality (Chen et al., 2019, Li et al., 2019), the effects of forest type conversion on soil microbial diversity and composition remain poorly understood.

Under similar climates and localized site conditions, the conversion of forest types may affect soil microbial communities through changes in tree species composition and diversity. Tree species influence soil microbial communities through their litter, mycorrhizal fungal associates, and exudates (Prescott and Grayston, 2013). The identities of tree species have been observed to influence the diversity of soil bacteria and fungi (Liu et al., 2018, Xiao et al., 2019) and community composition (Guo et al., 2016). Meanwhile, microbial diversity is expected to increase with tree species diversity, due to the strong links between the identities of tree species and soil microorganisms (Wardle et al., 2004), and the dominant effects of trees in forest ecosystems (Grime, 1998). In species-rich forests, enhanced aboveground and belowground litter productivity (Ma and Chen, 2018, Zheng et al., 2019) and litter diversity can increase the quantity and variety of available food resources, as well as expand niches for soil microorganisms (Hooper et al., 2000, Lange et al., 2015, Xiao et al., 2020). However, microbial alpha diversity is not always positively associated with tree species richness (Cai et al., 2018, Rodrigues et al., 2013, Xu et al., 2015). Moreover, fungi may benefit more from tree species richness than bacteria (Rousk et al., 2010).

Changes in the soil environment induced by forest type conversion can also impact microbial diversity and composition (Meng et al., 2020). The soil environment is a strong determinant for microbial diversity and composition (Nakayama et al., 2019, Prescott and Grayston, 2013). For example, soil microorganisms can benefit from mineral fertilization (Geisseler and Scow, 2014), whereas the excessive addition of nitrogen increases soil acidity and adversely affects soil microbial communities (Zhang et al., 2018). Microbial diversity and composition may vary both within individual soil profiles and across a wide range of ecosystem types (Eilers et al., 2012). Furthermore, soil residing bacteria and fungi may respond differently to the soil environment. For instance, bacteria are more sensitive to soil C:N ratios than are fungi (Guo et al., 2019). Since soil nutrients are limited in terrestrial ecosystems (Yuan and Chen, 2012) for which plants and soil microorganisms compete (Kuzyakov and Xu, 2013), we anticipated that the addition of soil nutrients would promote soil microbial diversity and influence the composition of soil microbes.

We examined soil microbial diversity and composition across forest types and soil depths in subtropical China. Specifically, we address two overarching questions: (i) How are the diversity and composition of bacteria and fungi altered across a wide range of forest types? (ii) How are changes in the diversity and composition of soil bacteria and fungi correlated with those of vegetation and the soil environment induced by forest type conversion?

Section snippets

Study area

This study was conducted in the TianBaoYan Nature Reserve (25°50′51″ to 26°01′20″ N and 117°28′03″ to 117°35′28″E), which is a transition zone that lies between the middle and lower reaches of the Daiyun Mountains, located in Yongan County, Fujian Province, China. The study area is characterized by a subtropical marine monsoon climate, with a mean annual temperature of 15 °C, annual precipitation of 2039 mm, and an annual mean relative humidity of 80%. The study plots ranged in elevation from

Results

Tree species richness was highest in the broadleaf dominated forests, followed by native broadleaf and bamboo dominated forests, and lowest in the pure bamboo forests (Table 1). Both the mean tree height and stand basal area were the highest in broadleaf dominated and bamboo dominated forests, followed by the native broadleaf forests, with the lowest in the pure bamboo forests. The mean tree D.B.H. and stand density did not differ significantly between forest types (P > 0.05, Table 1). The soil

Discussion

Our study revealed evidence for the impacts of forest type conversions on soil bacterial and fungal diversity, and the composition in subtropical forests. We found that the soil fungi:bacteria ratio, as well as the bacterial and fungal diversity of all three sampled soil depths increased following the conversion of native broadleaf forests to managed mixed and pure bamboo forests. Both bacterial and fungal community compositions were significantly altered following forest type conversion. We

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We thank Tiangui Yang, Yegui Wu, Jialiang Chen, and Chun Feng for assisting with fieldwork and laboratory analysis, and Neil Hillis, Eric Searle, Chen Chen and two anonymous reviewers for their constructive comments. Funding from the Special Fund for Basic Scientific Research of International Centre for Bamboo and Rattan (2018YFD0600103) and the National Natural Science Foundation of China [31971548] supported this research.

Data availability:

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