Decline in Topsoil Microbial Quotient, Fungal Abundance and C Utilization Efficiency of Rice Paddies under Heavy Metal Pollution across South China

Abstract

Agricultural soils have been increasingly subject to heavy metal pollution worldwide. However, the impacts on soil microbial community structure and activity of field soils have been not yet well characterized. Topsoil samples were collected from heavy metal polluted (PS) and their background (BGS) fields of rice paddies in four sites across South China in 2009. Changes with metal pollution relative to the BGS in the size and community structure of soil microorganisms were examined with multiple microbiological assays of biomass carbon (MBC) and nitrogen (MBN) measurement, plate counting of culturable colonies and phospholipids fatty acids (PLFAs) analysis along with denaturing gradient gel electrophoresis (DGGE) profile of 16S rRNA and 18S rRNA gene and real-time PCR assay. In addition, a 7-day lab incubation under constantly 25°C was conducted to further track the changes in metabolic activity. While the decrease under metal pollution in MBC and MBN, as well as in culturable population size, total PLFA contents and DGGE band numbers of bacteria were not significantly and consistently seen, a significant reduction was indeed observed under metal pollution in microbial quotient, in culturable fungal population size and in ratio of fungal to bacterial PLFAs consistently across the sites by an extent ranging from 6% to 74%. Moreover, a consistently significant increase in metabolic quotient was observed by up to 68% under pollution across the sites. These observations supported a shift of microbial community with decline in its abundance, decrease in fungal proportion and thus in C utilization efficiency under pollution in the soils. In addition, ratios of microbial quotient, of fungal to bacterial and qCO2 are proved better indicative of heavy metal impacts on microbial community structure and activity. The potential effects of these changes on C cycling and CO2 production in the polluted rice paddies deserve further field studies.

Enhanced rice production but greatly reduced carbon emission following biochar amendment in a metal-polluted rice paddy

“…As shown in the work by Cui et al (2013), biochar amendment reduced Cd and Pb bioavailability while increased microbial abundance and biochemical activity. This is also consistent with our previous finding in a microbial study by Liu et al (2012a) that metal pollution increased soil basal respiration, and in a field soil respiration measurement that soil CO 2 evolution was increased in the metal-polluted rice soil over the unpolluted one . All these findings point to a recovery of soil microbial abundance and their functioning when metal mobility was depressed with biochar.…”

“…Smolders et al (2001) described suppressed activity of nitrification, driven by soil ammonia-oxidizing archaea and bacteria, under metal pollution both in spiked soil samples and in long-term polluted fields. Liu et al (2012a) reported a consistent decline in microbial biomass and fungal to bacterial ratio but an increase in the metabolic quotient in metal-polluted rice paddies across sites from South China. Using similar soils, Liu et al (2014) characterized changes in community structure and activities of ammonia oxidizers and denitrifier with heavy metal contamination in rice paddies.…”

“…Reduction in microbial abundance and diversity had been often reported, either in short-term lab spiked incubation (Gao et al 2010;Harris-Hellal et al 2009;Khan et al 2010) or under long-term exposure to toxic metals in fields Wakelin et al 2010). Heavy metal contamination in soil could affect the rates of microbial-mediated biogeochemical processes (Liu et al 2012a(Liu et al , 2014, resulting in changes in GHG production and emission. Smolders et al (2001) described suppressed activity of nitrification, driven by soil ammonia-oxidizing archaea and bacteria, under metal pollution both in spiked soil samples and in long-term polluted fields.…”

Changes in soil microbial community functionality and structure in a metal-polluted site: The effect of digestate and fly ash applications

“…A similar response was found in fungal communities from paddy soil after heavy metal exposure (Chen et al, 2013). An unchanged bacterial abundance was also observed by Liu et al (2012), who reported no differences in bacterial abundance in two different sites subjected to metal pollution. One explanation for these divergent results could be that, compared with fungi, bacteria can likely be well adapted to chronic toxicity or stress in contaminated soils due to their wide substrate utilization profile and high metabolic activity.…”

Response of rhizosphere microbial community structure and diversity to heavy metal co-pollution in arable soil

“…In tested conditions, pollutants (phenanthrene and arsenic) did not have a major effect on community abundance or taxonomic composition but rather had an impact on metabolic and functional bacterial properties (Cebron et al 2014). Liu et al (2012) revealed a consistent change in soil microbial community under heavy metal pollution of rice paddy across South China. These changes could be characterized by a decline in abundance of Fig.…”