Distance-dependent varieties of microbial community structure and metabolic functions in the rhizosphere of Sedum alfredii Hance during phytoextraction of a cadmium-contaminated soil

Abstract

The recovery of microbial community and activities is crucial to the remediation of contaminated soils. Distance-dependent variations of microbial community composition and metabolic characteristics in the rhizospheric soil of hyperaccumulator during phytoextraction are poorly understood. A 12-month phytoextraction experiment with Sedum alfredii in a Cd-contaminated soil was conducted. A pre-stratified rhizobox was used for separating sub-layer rhizospheric (0-2, 2-4, 4-6, 6-8, 8-10 mm from the root mat)/bulk soils. Soil microbial structure and function were analyzed by phospholipid fatty acid (PLFA) and MicroResp™ methods. The concentrations of total and specified PLFA biomarkers and the utilization rates for the 14 substrates (organic carbon) in the 0-2-mm sub-layer rhizospheric soil were significantly increased, as well as decreased with the increase in the distance from the root mat. Microbial structure measured by the ratios of different groups of PLFAs such as fungal/bacterial, monounsaturated/saturated, ratios of Gram-positive to Gram-negative (GP/GN) bacterial, and cyclopropyl/monoenoic precursors and 19:0 cyclo/18:1ω7c were significantly changed in the 0-2-mm soil. The PLFA contents and substrate utilization rates were negatively correlated with pH and total, acid-soluble, and reducible fractions of Cd, while positively correlated with labile carbon. The dynamics of microbial community were likely due to root exudates and Cd uptake by S. alfredii. This study revealed the stimulations and gradient changes of rhizosphere microbial community through phytoextraction, as reduced Cd concentration, pH, and increased labile carbons are due to the microbial community responses.

The Effects of Different Lead Pollution Levels on Soil Microbial Quantities and Metabolic Function with/without Salix integra Thunb. Planting

“…However, the trends were complex when compared with unplanted soil. These were consistent with previous studies' indications that microbial biomass clearly increased in rhizospheric soils compared to bulk soil [16,[62][63][64]. Similarly, T. caerulescens growth increased microbial respiration rates in the Zn-and Cd-contaminated soil [23].…”

“…The difference between bulk soil and unplanted soil seen with S. integra planting not only had direct effects on rhizospheric soil, but also had indirect effects on bulk soil. As in the earlier studies, the effects of the rhizosphere should not be limited to specific volumes [62,67]. For instance, the rhizosphere effects of Sedum alfredii on the microbial community structure and metabolic function were not limited to the root surface, notwithstanding that the effect decreased as the distances increased [62].…”

“…As in the earlier studies, the effects of the rhizosphere should not be limited to specific volumes [62,67]. For instance, the rhizosphere effects of Sedum alfredii on the microbial community structure and metabolic function were not limited to the root surface, notwithstanding that the effect decreased as the distances increased [62]. Similarly, the interactive effects of pioneer plants and harsh soil environmental conditions remodel the specific bacterial communities, both in rhizosphere and bulk soil, in mine tailings [19].…”

“…These findings could be partly explained by the reduction of metal concentration in the rhizospheric soil due to plant uptake. Yang et al [62] reported that phytoextraction by Sedum alfredii significantly reduced the available and total Cd of 0-2 and 2-4 mm soils. In addition, there were more root exudates in the rhizosphere environment, which may lead to higher microbial populations and stimulate the growth of specific bacterial and fungal populations [15][16][17].…”

Indigenous Bacteria Have High Potential for Promoting Salix integra Thunb. Remediation of Lead-Contaminated Soil by Adjusting Soil Properties

“…A high-throughput sequencing approach was therefore used to measure rhizospheric bacterial community that may influence the accumulation of heavy metal in S. integra. Planting S. integra decreased the total Pb concentration both in rhizosphere and bulk soil in the low Pb treatment, which could be explained by the effects of root activity not being limited to the root surface, though the effect declined when the distances increase (Yang et al, 2017). Furthermore, our previous study also showed that microbial quantity and metabolism were promoted both in the rhizosphere and bulk soil in the low Pb treatment (Niu et al, 2019).…”