Abstract
Copper contamination on China's arable land could pose severe economic, ecological and healthy consequences in the coming decades. As the drivers in maintaining ecosystem functioning, the responses of soil microorganisms to long-term copper contamination in different soil ecosystems are still debated. This study investigated the impacts of copper gradients on soil bacterial communities in two agricultural fields with contrasting soil properties. Our results revealed consistent reduction in soil microbial biomass carbon (SMBC) with increasing copper levels in both soils, coupled by significant declines in bacterial abundance in most cases. Despite of contrasting bacterial community structures between the two soils, the bacterial diversity in the copper-contaminated soils showed considerably decreasing patterns when copper levels elevated. High-throughput sequencing revealed copper selection for major bacterial guilds, in particular, Actinobacteria showed tolerance, while Acidobacteria and Chloroflexi were highly sensitive to copper. The thresholds that bacterial communities changed sharply were 800 and 200 added copper mg kg−1 in the fluvo-aquic soil and red soil, respectively, which were similar to the toxicity thresholds (EC50 values) characterized by SMBC. Structural equation model (SEM) analysis ascertained that the shifts of bacterial community composition and diversity were closely related with the changes of SMBC in both soils. Our results provide field-based evidence that copper contamination exhibits consistently negative impacts on soil bacterial communities, and the shifts of bacterial communities could have largely determined the variations of the microbial biomass.
Highlights
Soils represent the largest sink for copper released into the environment by anthropogenic activities, such as sewage irrigation, mining activities, municipal waste disposal, and intensive use of pesticides and herbicides (Smith, 2009; Zhuang et al, 2009)
SIMILAR RESPONSES OF THE BACTERIAL COMMUNITIES IN TWO CONTRASTING SOILS TO THE COPPER CONTAMINATION the long-term effects of copper contamination on microbial communities have been investigated in some studies (Macdonald et al, 2008; Singh et al, 2014), the responses of microbial community composition and function to copper contaminations differed across various sites and no firm conclusions had been drawn
Our results showed that the relative abundances of Gemmatimonadetes, Proteobacteria, Bacteroidetes, and Verrucomicrobia were higher in the neutral/alkaline fluvoaquic soil, which were in agreement with previous studies that www.frontiersin.org these groups were favored under high pH (7∼8) conditions (He et al, 2012; Fierer et al, 2013; Marcina et al, 2013)
Summary
Soils represent the largest sink for copper released into the environment by anthropogenic activities, such as sewage irrigation, mining activities, municipal waste disposal, and intensive use of pesticides and herbicides (Smith, 2009; Zhuang et al, 2009). High copper concentrations have been found in paddy soils (109–1313 mg kg−1) near mining sites (Zhuang et al, 2009), and vineyard soils increasing from background levels of 10 mg kg−1 to approximately 250 mg kg−1 with intensive use of copper-based fungicides (Pietrzak and McPhail, 2004). Excessive inputs of it into soil ecosystems could persist for a long time after their introduction and cause negative and toxic effects on the inhabitant microorganisms, and thereby affect the critical functioning they mediate (Giller et al, 2009). Understanding responses of soil microbial assemblages to copper contamination is essential to counteract its negative effect on ecosystem functions and services
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