Rewetting a dry soil can result in two response patterns of bacterial growth and respiration. In type 1, bacterial growth starts to increase linearly immediately upon rewetting and respiration rates ...are highest immediately upon rewetting. In type 2, bacterial growth starts to increase exponentially after a lag period with a secondary increase in respiration occurring at the start of the exponential increase in growth. We previously observed that the type 1 response occurred after rewetting 4-day dried soil and type 2 for 1-year dried soil. Here we studied in detail how the duration of drought related to the two types of responses of bacterial growth and respiration to rewetting. Soil was air dried for different time periods from 4 days up to 48 weeks. Upon rewetting, bacterial growth and respiration was measured repeatedly at 17 °C during one week. Drought periods of ≤2 weeks resulted in a type 1 response whereas drought periods of ≥4 weeks resulted in a type 2 response. The lag period increased with drought duration and reached a maximum of ca. 18 h. The bacterial growth response was also affected by incubation of moist soil before drying–rewetting. The lag period increased with duration of moist soil incubation before the 4-day drying–rewetting event and reached also a maximum of ca. 18 h. The exponential growth increase in the type 2 response coincided with a secondary increase in respiration, which increased in magnitude with increasing drought duration. Cumulative respiration increased with drought duration and was ca. 4 times higher after 48 weeks of drought compared to 4 days. Thus, prolonged drought affected the response type of bacterial growth and respiration to rewetting, and also increased lag period, the magnitude of the secondary increase in respiration and total C release. The effect of drought was, however, modified by the lenght of the incubation period of moist soil before drought, suggesting that soil conditions before a drying–rewetting event need consideration when evaluating microbial responses.
Bacterial growth upon rewetting soils dried for 4 days up to 48 weeks. The lag period before bacterial growth increased with duration of drought. Display omitted
•Soils were dried from 4 days up to 48 weeks before rewetting.•Bacterial growth and respiration were measured during one week upon rewetting.•Longer drought induced, and increased duration of a lag period before growth.•The cumulative respiration after rewetting increased with duration of drought.•Incubation of moist soil before drying–rewetting also induced a lag period.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Fluctuations in soil moisture create drying-rewetting events affecting the activity of microorganisms. Microbial responses to drying-rewetting are mostly studied in soils that are air-dried before ...rewetting. Upon rewetting, two patterns of bacterial growth have been observed. In the Type 1 pattern, bacterial growth rates increase immediately in a linear fashion. In the Type 2 pattern, bacterial growth rates increase exponentially after a lag period. However, soils are often only partially dried. Partial drying (higher remaining moisture content before rewetting) may be considered a less harsh treatment compared with air-drying. We hypothesized that a soil with a Type 2 response upon rewetting air-dried soil would transform into a Type 1 response if dried partially before rewetting. Two soils were dried to a gradient of different moisture content. Respiration and bacterial growth rates were then measured before and during 48 h after rewetting to 50% of water holding capacity (WHC). Initial moisture content determined growth and respiration in a sigmoidal fashion, with lowest activity in air-dried soil and maximum above ca. 30% WHC. Partial drying resulted in shorter lag periods, shorter recovery times and lower maximum bacterial growth rates after rewetting. The respiration after rewetting was lower when soil was partially dried and higher when soils were air-dried. The threshold moisture content where transition from a Type 2 to a Type 1 response occurred was about 14% WHC, while >30% WHC resulted in no rewetting effect. We combine our result with other recent reports to propose a framework of response patterns after drying-rewetting, where the harshness of drying determines the response pattern of bacteria upon rewetting dried soils.
•Soils were dried to different moisture content before rewetting.•Bacterial growth and respiration were measured before and during 48 h post-rewet.•Shorter lag periods and recovery time of growth when moisture pre-rewet was higher.•Cumulative respiration was lower when soil moisture pre-rewet was higher.•Harshness of drying determines bacterial growth patterns upon rewetting.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
ABSTRACT
There is increasing evidence that microbial volatile organic compounds (mVOCs) play an important role in interactions between microbes in soils. In this minireview, we zoom in on the ...possible role of mVOCs in the suppression of plant-pathogenic soil fungi. In particular, we have screened the literature to see what the actual evidence is that mVOCs in soil atmospheres can contribute to pathogen suppression. Furthermore, we discuss biotic and abiotic factors that influence the production of suppressive mVOCs in soils. Since microbes producing mVOCs in soils are part of microbial communities, community ecological aspects such as diversity and assembly play an important role in the composition of produced mVOC blends. These aspects have not received much attention so far. In addition, the fluctuating abiotic conditions in soils, such as changing moisture contents, influence mVOC production and activity. The biotic and abiotic complexity of the soil environment hampers the extrapolation of the production and suppressing activity of mVOCs by microbial isolates on artificial growth media. Yet, several pathogen suppressive mVOCs produced by pure cultures do also occur in soil atmospheres. Therefore, an integration of lab and field studies on the production of mVOCs is needed to understand and predict the composition and dynamics of mVOCs in soil atmospheres. This knowledge, together with the knowledge of the chemistry and physical behaviour of mVOCs in soils, forms the basis for the development of sustainable management strategies to enhance the natural control of soil-borne pathogens with mVOCs. Possibilities for the mVOC-based control of soil-borne pathogens are discussed.
The authors review literature reporting on pathogen suppressive activities of volatiles (mVOCs) produced in soils by microbial communities and indicate management strategies to enhance mVOC-mediated disease control.
Climate change alters frequencies and intensities of soil drying-rewetting and freezing-thawing cycles. These fluctuations affect soil water availability, a crucial driver of soil microbial activity. ...While these fluctuations are leaving imprints on soil microbiome structures, the question remains if the legacy of one type of weather fluctuation (e.g., drying-rewetting) affects the community response to the other (e.g., freezing-thawing). As both phenomenons give similar water availability fluctuations, we hypothesized that freezing-thawing and drying-rewetting cycles have similar effects on the soil microbiome. We tested this hypothesis by establishing targeted microcosm experiments. We created a legacy by exposing soil samples to a freezing-thawing or drying-rewetting cycle (phase 1), followed by an additional drying-rewetting or freezing-thawing cycle (phase 2). We measured soil respiration and analyzed soil microbiome structures. Across experiments, larger CO
pulses and changes in microbiome structures were observed after rewetting than thawing. Drying-rewetting legacy affected the microbiome and CO
emissions upon the following freezing-thawing cycle. Conversely, freezing-thawing legacy did not affect the microbial response to the drying-rewetting cycle. Our results suggest that drying-rewetting cycles have stronger effects on soil microbial communities and CO
production than freezing-thawing cycles and that this pattern is mediated by sustained changes in soil microbiome structures.
Full text
Available for:
NUK, SBMB, SBNM, UL, UM, UPUK
Two patterns of bacterial growth response upon drying and rewetting (DRW) of soils have previously been identified. Bacterial growth can either start increasing immediately after rewetting in a ...linear fashion (“type 1” response) or start increasing exponentially after a lag period (“type 2” response). The effect of repeated DRW cycles was studied in three soils with different response patterns after a single DRW cycle (“type 1”, “type 2” with a short lag period and “type 2” with a long lag period). The soils were exposed to seven DRW cycles, and respiration and bacterial growth were monitored after 1, 2, 3, 5, and 7 cycles. Exposure to repeated DRW shifted the bacterial growth response from a “type 2” to a “type 1” pattern, resulting in an accelerated growth recovery to a pre-disturbance growth rate. Bacterial growth in soils that initially had a “type 1” response also tended to recover faster after each subsequent DRW cycle. The respiration patterns after DRW also indicated the same transition from a “type 2” to a “type 1” pattern. Our results show that exposure to repeated DRW cycles will shape the bacterial response to future DRW cycles, which might be mediated by a shift in species composition, a physiological adjustment, evolutionary changes, or a combination of the three.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
It is increasingly acknowledged that climate change is influencing terrestrial ecosystems by increased drought and rainfall intensities. Soil microbes are key drivers of many processes in terrestrial ...systems and rely on water in soil pores to fulfill their life cycles and functions. However, little is known on how drought and rainfall fluctuations, which affect the composition and structure of microbial communities, persist once original moisture conditions have been restored. Here, we study how simulated short-term drying and re-wetting events shape the community composition of soil fungi and prokaryotes. In a mesocosm experiment, soil was exposed to an extreme drought, then re-wetted to optimal moisture (50% WHC, water holding capacity) or to saturation level (100% WHC). Composition, community structure and diversity of microbes were measured by sequencing ITS and 16S rRNA gene amplicons 3 weeks after original moisture content had been restored. Drying and extreme re-wetting decreased richness of microbial communities, but not evenness. Abundance changes were observed in only 8% of prokaryote OTUs, and 25% of fungal OTUs, whereas all other OTUs did not differ between drying and re-wetting treatments. Two specific legacy response groups (LRGs) were observed for both prokaryotes and fungi. OTUs belonging to the first LRG decreased in relative abundance in soil with a history of drought, whereas OTUs that increased in soil with a history of drought formed a second LRG. These microbial responses were spread among different phyla. Drought appeared to be more important for the microbial community composition than the following extreme re-wetting. 16S profiles were correlated with both inorganic N concentration and basal respiration and ITS profiles correlated with fungal biomass. We conclude that a drying and/or an extreme re-wetting history can persist in soil microbial communities via specific response groups composed of members with broad phylogenetic origins, with possible functional consequences on soil processes and plant species. As a large fraction of OTUs responding to drying and re-wetting belonged to the rare biosphere, our results suggest that low abundant microbial species are potentially important for ecosystem responses to extreme weather events.
In many parts of the world, agricultural ecosystems are increasingly exposed to severe drought, and rainfall events due to climate changes. This coincides with a higher vulnerability of crops to ...soil-borne diseases, which is mostly ascribed to decreased resistance to pathogen attacks. However, loss of the natural capacity of soil microbes to suppress soil-borne plant pathogens may also contribute to increased disease outbreaks. In this perspectives paper, we will discuss the effect of extreme weather events on pathogen-antagonist interactions during drought and rainfall events and upon recovery. We will focus on diseases caused by root-infecting fungi and oomycetes. In addition, we will explore factors that affect restoration of the balance between pathogens and other soil microbes. Finally, we will indicate potential future avenues to improve the resistance and/or recovery of natural biocontrol during, and after water stresses. As such, our perspective paper will highlight a knowledge gap that needs to be bridged to adapt agricultural ecosystems to changing climate scenarios.
Climate change is expected to increase future abiotic stresses on ecosystems through extreme weather events leading to more extreme drought and rainfall incidences Jentsch A, et al. (2007) Front Ecol ...Environ 5(7):365–374. These fluctuations in precipitation may affect soil biota, soil processes Evans ST, Wallenstein MD (2012) Biogeochemistry 109:101–116, and the proportion of exotics in invaded plant communities Jiménez MA, et al. (2011) Ecol Lett 14:1277–1235. However, little is known about legacy effects in soil on the performance of exotics and natives in invaded plant communities. Here we report that drought and rainfall effects on soil processes and biota affect the performance of exotics and natives in plant communities. We performed two mesocosm experiments. In the first experiment, soil without plants was exposed to drought and/or rainfall, which affected soil N availability. Then the initial soil moisture conditions were restored, and a mixed community of co-occurring natives and exotics was planted and exposed to drought during growth. A single stress before or during growth decreased the biomass of natives, but did not affect exotics. A second drought stress during plant growth resetted the exotic advantage, whereas native biomass was not further reduced. In the second experiment, soil inoculation revealed that drought and/or rainfall influenced soil biotic legacies, which promoted exotics but suppressed natives. Our results demonstrate that extreme weather events can cause legacy effects in soil biota, promoting exotics and suppressing natives in invaded plant communities, depending on the type, frequency, and timing of extreme events.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The physiological performance of organisms depends on their environmental context, resulting in performance–response curves along environmental gradients. Parasite performance–response curves are ...generally expected to be broader than those of their hosts due to shorter generation times and hence faster adaptation. However, certain environmental conditions may limit parasite performance more than that of the host, thereby providing an environmental refuge from disease. Thermal disease refuges have been extensively studied in response to climate warming, but other environmental factors may also provide environmental disease refuges which, in turn, respond to global change. Here, we (1) showcase laboratory and natural examples of refuges from parasites along various environmental gradients, and (2) provide hypotheses on how global environmental change may affect these refuges. We strive to synthesize knowledge on potential environmental disease refuges along different environmental gradients including salinity and nutrients, in both natural and food‐production systems. Although scaling up from single host–parasite relationships along one environmental gradient to their interaction outcome in the full complexity of natural environments remains difficult, integrating host and parasite performance–response can serve to formulate testable hypotheses about the variability in parasitism outcomes and the occurrence of environmental disease refuges under current and future environmental conditions.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Invasive exotic plant species effects on soil biota and processes in their new range can promote or counteract invasions via changed plant–soil feedback interactions to themselves or to native plant ...species. Recent meta-analyses reveale that soil influenced by native and exotic plant species is affecting growth and performance of natives more strongly than exotics. However, the question is how uniform these responses are across contrasting life forms. Here, we test the hypothesis that life form matters for effects on soil and plant–soil feedback. In a meta-analysis we show that exotics enhanced C cycling, numbers of meso-invertebrates and nematodes, while having variable effects on other soil biota and processes. Plant effects on soil biota and processes were not dependent on life form, but patterns in feedback effects of natives and exotics were dependent on life form. Native grasses and forbs caused changes in soil that subsequently negatively affected their biomass, whereas native trees caused changes in soil that subsequently positively affected their biomass. Most exotics had neutral feedback effects, although exotic forbs had positive feedback effects. Effects of exotics on natives differed among plant life forms. Native trees were inhibited in soils conditioned by exotics, whereas native grasses were positively influenced in soil conditioned by exotics. We conclude that plant life form matters when comparing plant–soil feedback effects both within and between natives and exotics. We propose that impact analyses of exotic plant species on the performance of native plant species can be improved by comparing responses within plant life form.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
PDF
