Effect of primary mild stresses on resilience and resistance of the nitrate reducer community to a subsequent severe stress

Abstract

The factors regulating soil microbial stability (e.g. resistance and resilience) are poorly understood, even though microorganisms are essential for ecosystem functioning. In this study, we tested whether a functional microbial community subjected to different primary mild stresses was equally resistant or resilient to a subsequent severe stress. The nitrate reducers were selected as model community and analysed in terms of nitrate reduction rates and genetic structure by narG PCR-restriction fragment length polymorphism fingerprinting. Heat, copper and atrazine were used as primary stresses and mercury at a high concentration as a severe stress. None of the primary stresses had any significant impact on the nitrate reducer community. Although primary stress with heat, copper or atrazine had no effect on the resilience of the nitrate reducer activity to mercury stress, pre-exposure to copper, another heavy metal, resulted in increased resilience. In contrast, the resistance of both structure and activity of the nitrate reducer community to severe mercury stress was not affected by any of the primary stresses tested. Our experiment suggests that the hypothetical effect of an initial stress on the response of a microbial community to an additional stress is complex and may depend on the relatedness of the two consecutive stresses and the development of positive cotolerance.

Responses of activities, abundances and community structures of soil denitrifiers to short-term mercury stress

“…The inhibiting effect of heavy metals to soil DEA had been reported proviously (Holtan-Hartwig et al, 2002;Magalhães et al, 2007;Ruyters et al, 2010). The significantly higher soil EDA in the Hg25 and Hg50 treatments was in accord with the result of Philippot et al (2008), who found that Hg (100 mg Hg/kg) resulted in a three to fourfold increase of soil DEA within 2 weeks compared with CK (without Hg addition). The stimulation of Hg on soil DEA could attribute to the increased organic matter due to the lysis of microorganisms under the toxicity of Hg (Philippot et al, 2008).…”

“…Liu et al (2010) found mercury inhibited the activities and changed the community compositions of soil ammonia oxidizers. Philippot et al (2008) found Hg (100 mg Hg/kg soil) obviously increased the soil denitrification enzyme activity (DEA) at day 45 and changed the community structure of soil narG (periplasmic nitrate reductase gene) at day 120 during the soil incubation. Nevertheless, the relationship between soil DEA and soil denitrifiers and the responses of other functional genes involved in denitrification under Hg stress were less available.…”

Functional Redundancy and Ecosystem Function — The Soil Microbiota as a Case Study

“…If ecological resilience is considered as a function in the same way as Biodiversity in Ecosystems -Linking Structure and Function invasion resistance and stability, then it too can be progressively eroded. While research on this topic has been sparse and has not directly manipulated diversity, evidence of this phenomenon exists [74][75][76][77][78]. For example, mercury-contaminated, heat-shocked soils responded much more slowly to substrate additions than the transiently tylosin-contaminated or control soils [79].…”

Initial Copper Stress Strengthens the Resistance of Soil Microorganisms to a Subsequent Copper Stress

“…In addition, it is important to understand how repeated stresses influence microbial community. The influence of initial stress on resistance and resilience of soil microbial community to a subsequent stress was less studied and is still being debated [18]. Compared with the uncontaminated soils, soil microorganisms in the heavy metal-contaminated soils were more affected by a subsequent heat or salt stress due to the less energy of stressed system to cope with additional stress [19].…”