Soil prokaryotic community structure and co-occurrence patterns on the fragmented Chinese Loess Plateau: Effects of topographic units of a soil eroding catena

doi:10.1016/j.catena.2020.105035

CATENA

Volume 198, March 2021, 105035

https://doi.org/10.1016/j.catena.2020.105035 Get rights and content

Highlights

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Reassembly of the soil environmental characteristics along the soil-eroding catena altered prokaryotic communities.
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Less extensive prokaryotic interactions and lower community stability potential in the depositional zone.
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The higher SOC increased copiotrophic group abundance in the depositional zone.

Abstract

Soil prokaryotes composition and diversity are the key to uncovering the mechanisms that drive variations in soil biogeochemical processes. Soil erosion is a primary factor that affects the spatial distribution of the soil prokaryotic community, but how soil prokaryotes in soil-eroding catena respond to environmental factors related to topography remains largely unclear. In this study, topsoils were sampled from three typical erosion geomorphic units (autonomous, transitional and depositional zones) in 2018 to identify the soil prokaryotic community and interactions among the species on the Chinese Loess Plateau. The alpha-diversity was greater but the beta-diversity was lower in the autonomous and transitional zones than in the depositional zone. Gammaproteobacteria and Bacteroidetes were 73% and 68% lower in the autonomous and transitional zones than in the depositional zone. In addition, Deltaproteobacteria, Acidobacteria, Firmicutes, Actinobacteria, Chloroflexi, Gemmatimonadetes and Nitrospirae were significantly higher in the autonomous and transitional zones. A less clustered network and fewer co-occurrences within the prokaryotic community and functional groups of processes were found in the depositional zone than in the autonomous and transitional zones. The alpha-diversity index was significantly negatively correlated with clay particles, soil water content, soil organic carbon (SOC), and ratio of SOC and nitrogen (C/N) but positively correlated with total nitrogen (TN). The higher relative abundances of copiotrophic groups (including Gammaproteobacteria, Bacteroidetes, etc.) in the depositional zone was mainly due to the increased SOC caused by the deposition of SOC-rich clay. Reassembly of the soil physico-chemistry characteristics among the topographic units significantly altered the soil prokaryotic community along the soil-eroding catena.

Introduction

Soil prokaryotes are important for functioning of terrestrial ecosystems by influencing carbon storage and nutrient recycling (Allison and Goulden, 2017, de Carvalho et al., 2016, Takriti et al., 2018). While soil prokaryotes are sensitive indicators of changes in environmental properties (Griffiths and Philippot, 2013), previous studies showed that soil prokaryotes are cosmopolitan and that their patterns are mainly driven by environmental factors. For example, several studies highlighted that particle size (Sessitsch et al., 2001), organic carbon (SOC) (Goldfarb et al., 2011), cation exchange capacity (Mapelli et al., 2018), and nutrient availability (Fierer et al., 2007) significantly influenced soil prokaryotes community structure and interactions among species. Therefore, systematically investigate the effects of physico-chemical factors on soil prokaryotes community structure and interactions among species are essential are needed to understand activity of microbial processes and microbial ecology.

A soil-eroding catena, which has been systematically studied by Lei et al. (2000), is a chain that is mainly characterized by the transport and output of erosion materials with an energy link and an interrelated, orderly evolving erosive form. In fact, the effect of the topography on soil-eroding catena is apparent (Hook and Burke, 2000, Seibert et al., 2007), with redistribution of the water, nutrient elements (carbon, nitrogen etc.) and soil particles along topographic units (Khomo et al., 2013, Hu and Kuhn, 2014). To date, the influences of soil-eroding catena on physiochemical properties at different topographies has been extensively studied (Khomo et al., 2013, Sun et al., 2014, Sun et al., 2015, Wang et al., 2017b). Several studies have suggested the topography controls the reception and (re)distribution of radiation, water and sediments over the land surface, influencing soil erosion (Seibert et al., 2007, Gabarron-Galeote et al., 2013, Sun et al., 2014). Some studies showed eroding slopes and depositional plots differentiate soil microbial diversity (Xiao et al., 2017), communities structure (Du et al., 2020, Sun et al., 2018), and microbial activity, such as metabolic coefficient (Mohammadi et al., 2017), greenhouse gas emission (Sun et al., 2018, Wiaux et al., 2014) and enzyme activities (Sun et al. 2018). Nevertheless, very few studies have taken the effects of topographic units (topographically defined as autonomous, transitional and depositional zones, Fig. 1) on soil-eroding catena into consideration when addressing the potential variation of the soil prokaryotic community composition and their co-occurrence patterns.

The Chinese Loess Plateau (6.4 × 10⁵ km²) is a semi-arid region and is considered to be one of the most severely eroded areas (mean soil loss rate: 2860 t km⁻² year⁻¹); the Chinese Loess Plateau is characterized by an extremely complex soil-eroding catena (Wang et al., 2017b). Inevitably varied soil-eroding catena are found on the Loess Plateau, which are the result of changing erosion processes with different of hydrodynamic conditions. The southern gully region of the Loess Plateau has three typical topographic units, including autonomous, transitional and depositional zones. The effects of complex topography on soil physiochemical characteristics, such as SOC, nitrogen (TN) and soil water content distribution, on the Loess Plateau have been well documented (Sun et al., 2015, Yang et al., 2017, Wang et al., 2018). Systematic investigations of the soil prokaryotic properties are beneficial to deepen the comprehending of the effects of spatial differentiation on soil erosion and, in particular, to explore this effect on a complex topography under a whole soil-eroding catena. However, such studies on the fragmented southern Loess Plateau are still limited. We hypothesized that the topography of the soil-eroding catena would affect the soil prokaryotic community structure, interactions and functions due to the different clay, water and SOC content. Therefore, this study aimed to explore (1) the changes in the soil prokaryotic community, interactions and functions; (2) the altered keystone species; and (3) the factors influencing the changes in the prokaryotic properties among the topographic units of a whole soil-eroding catena.

Section snippets

Study site

The study area is located in the Wangdonggou watershed, Shaanxi Province, China (Fig. 1). Soil is loam, clay content is 22%, annual mean precipitation is 568 mm, air temperature is 9.1 °C, frost-free period is 194 days, and potential evapotranspiration is 967 mm (Huang et al., 2003). The topography of the watershed is complex, including autonomous, transitional and depositional zones, with the gully density at 2.78 km km⁻² (Wang et al., 2017b). Variations in topographic units and changes in

Soil properties

The soil properties markedly differed across the three topographic units (Table 1). SOC, soil water content, clay (<0.002) and C/N were significantly higher but TN and Olsen-P were significantly lower in the depositional zone than the autonomous and transitional zones (Table 1). Compared with that in the autonomous zone (7.80 g kg⁻¹), the SOC was increased by 55% in the depositional zone but decreased by 12% in the transitional zone. Olsen-P was 12% and 32% lower and TN was 22% and 29% lower in

Soil-eroding catena induced differences in soil properties among topographic units

A continuous increasing trend of clay content, soil water content and SOC and a decreasing trend of TN and Olsen-P values occurred from the autonomous zone to the depositional zone (Table 1). The clay content in the depositional zone was pronouncedly lower than that in the autonomous and transitional zones, similar result has been observed in previous studies who found finer soil textures at downslope positions (Khomo et al., 2011, Bojko and Kabala, 2016). This may be the result of the

Conclusion

This study analysed the effects of topographic units on the structure of microbial community composition and co-occurrence patterns under a whole soil-eroding catena on the fragmented Chinese Loess Plateau. Alpha-diversity was greater, beta-diversity was lower, in the autonomous and transitional zones than in the depositional zone. Less clustered networks and fewer co-occurrences within the soil prokaryotic community and functional groups of processes in the depositional zone indicated that the

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.

Acknowledgements

National Key Research and Development Program of China (2016YFD0800105) and the China Postdoctoral Science Foundation (2018M643755) were funded this study. The contributions of Xin Gao and Sheng Gao in sample collection are gratefully acknowledged.

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