Endophytic and epiphytic phyllosphere fungi of Camellia japonica: seasonal and leaf age-dependent variations

Seasonal and leaf age-dependent variations in the endophytic and epiphytic phyllosphere fungal assemblages of Camellia japonica were examined and compared. Live leaves of C. japonica were collected in four seasons (May, Aug, Nov, Feb), and fungi were isolated from healthy-looking leaves of 0, 1, 2 and 3 y old. The infection rate and total number of endophytic fungi increased May-Feb, and species richness of endophytes increased as leaves aged. In contrast the infection rate of epiphytic fungi was 100% for all leaf ages at every sampling date. The total number of epiphytic fungi isolated was greatest in May and lowest in Aug. The species richness of epiphytes did not differ significantly by season or leaf age. Eight fungal species were recorded as major phyllosphere fungi of C. japonica. Seasonal variations were detected for the frequencies of Colletotrichum gloeosporioides, C. acutatum, and epiphytes Pestalotiopsis sp.1, Aureobasidium pullulans, Phoma sp.1 and Ramichloridium sp., whereas the frequency of the endophyte Geniculosporium sp.1 varied with leaf age. The frequency of the epiphyte Cladosporium cladosporioides varied with both season and leaf age.     

Community structures of N2‐fixing bacteria associated with the phyllosphere of a Holm oak forest and their response to drought

Biological nitrogen (N) fixation is a key pathway in terrestrial ecosystems and is therefore critical for understanding the responses of ecosystems to global environmental changes. The free‐living diazotrophic community is distributed along the canopy‐to‐soil profile, but the ecological significance of epiphyllic N₂ fixers, despite their functional relevance, on plant foliar surfaces remains very poorly understood compared with the N₂‐fixing community in forest litter and soils. We assessed the community structure of N₂ fixers and overall bacteria by genetic fingerprinting (t‐RFLP) to explore the seasonal successional patterns of the microbial community in the natural phyllosphere of a Holm oak (Quercus ilex) forest submitted to 12‐year field experiment of rain exclusion mimicking the conditions of drought projected for the coming decades. Leaves of Holm oak were analysed in different seasons over a period of 1.5 years. The bacterial community of the phyllosphere did not correspond to the surrounding soil biome in the same area. These analyses provided field evidence for the presence of free‐living diazotrophs associated with the tissues of leaves of Holm oak, the dominant tree species of many Mediterranean forests. The results also revealed that the community composition is affected seasonally and inter‐annually by the environment, and that the composition shifts in response to climate change. Drought treatment increased the richness of the epiphyllic microbial community, especially during the summer. These changes were associated with higher C:N ratios of leaves observed in response to drought in semiarid areas. This epiphyllic microbiota that can potentially fix N₂ extends the capacity of plants to adapt to the environment.     

Seasonal and leaf age-dependent changes in occurrence of phyllosphere fungi of giant dogwood

To examine the relative importance of leaf age and season on the occurrence of phyllosphere fungi, temporal patterns of epiphytic and endophytic phyllosphere fungi of giant dogwood (Swida controversa) were studied with reference to leaf emergence at first occurrence and in the middle of the growing season. A total of 15 and 44 species were isolated from the surface and interior of leaves, respectively. On the leaf surface, detection rate of fungi was consistently 100% and their frequencies increased during the growing season, whereas in the leaf interior, detection rate of fungi and their frequencies were low at leaf emergence and gradually increased during the growing season. Six epiphytic and two endophytic fungi were observed frequently. A white sterile mycelium was frequent only on the surface of newly emerged leaves in the first-order shoot in May. The other 7 species increased during the growing season. The frequencies of Phomopsis sp., Pestalotiopsis sp. 1, and Trichoderma viride were higher on the leaves of first-order shoots than those of higher-order shoots that emerged between July and September, suggesting the possible effects of leaf age on their occurrence. On the other hand, the frequencies of Colletotrichum gloeosporioides, Clonostachys rosea, Cladosporium cladosporioides, and Phoma sp. 1 were not different between the first- and higher-order shoots, suggesting the negligible effect of leaf age. The influence of phenological patterns of leaf emergence of deciduous trees on the diversity and composition of assemblages of phyllosphere fungi is discussed.     

Exploring Biodiversity in the Bacterial Community of the Mediterranean Phyllosphere and its Relationship with Airborne Bacteria

We studied the structure and diversity of the phyllosphere bacterial community of a Mediterranean ecosystem, in summer, the most stressful season in this environment. To this aim, we selected nine dominant perennial species, namely Arbutus unedo, Cistus incanus, Lavandula stoechas, Myrtus communis, Phillyrea latifolia, Pistacia lentiscus, Quercus coccifera (woody), Calamintha nepeta, and Melissa officinalis (herbaceous). We also examined the extent to which airborne bacteria resemble the epiphytic ones. Genotype composition of the leaf and airborne bacteria was analysed by using denaturing gradient gel electrophoresis profiling of a 16S rDNA gene fragment; 75 bands were cloned and sequenced corresponding to 28 taxa. Of these, two were found both in the air and the phyllosphere, eight only in the air, and the remaining 18 only in the phyllosphere. Only four taxa were found on leaves of all nine plant species. Cluster analysis showed highest similarity for the five evergreen sclerophyllous species. Aromatic plants were not grouped all together: the representatives of Lamiaceae, bearing both glandular and non-glandular trichomes, formed a separate group, whereas the aromatic and evergreen sclerophyllous M. communis was grouped with the other species of the same habit. The epiphytic communities that were the richest in bacterial taxa were those of C. nepeta and M. officinalis (Lamiaceae). Our results highlight the remarkable presence of lactic acid bacteria in the phyllosphere under the harsh conditions of the Mediterranean summer, the profound dissimilarity in the structure of bacterial communities in phyllosphere and air, and the remarkable differences of leaf microbial communities on neighbouring plants subjected to similar microbial inocula; they also point to the importance of the leaf glandular trichome in determining colonization patterns.     

Leaf shedding and weather in tropical dry-seasonal forest shape the phenology of fungi – Lessons from two years of monthly surveys in southwestern Panama

In the present study, conducted in a secondary dry-seasonal forest in the pacific lowlands of southwestern Panama over 2 years, fungal diversity is linked to plant phenology, litter, and climatic data. Agaricales fungi showed maximum species richness at the beginning of rainy seasons, probably due to the important litter accumulation during the dry season and the increase in humidity favoring fungal growth. Species richness declined during the wet season possibly due to torrential rains, moulds, and decreasing availability of nutrients. Occurrence of foliar pathogenic microfungi correlated negatively with flushing of new leaves at the beginning of the rainy season. Their incidence increased during the wet season and remained high during the dry season. Synchronization of leaf shedding in most tree species significantly reduced the yearly incidence of foliar pathogenic fungi causing an annual turn-over of fungal pathogens that probably contributes to maintain a high diversity of plant pathogenic species.     

Quantitative and qualitative seasonal changes in the microbial community from the phyllosphere of sugar beet (Beta vulgaris)

Bacteria, yeasts and filamentous fungi colonizing immature, mature and senescing primary leaves of field grown Beta vulgaris (sugar beet) were analysed over a complete growing season. Greatest microbial numbers were detected on senescing primary leaves and these numbers increased over most of the season. The number of colonizers detected on mature leaves was found to be stable over most of the study.Filamentous fungi and yeasts were identified to the genus level and the communities found to have greatest diversity during the summer months. There was no consistent pattern of diversity according to leaf type. Two genera of filamentous fungi, Cladosporium and Alternaria and two yeast genera, Cryptococcus and Sporobolomyces were the most numerous fungal populations isolated. Only 8 filamentous fungi and 3 yeast genera were commonly isolated on PDA (potato dextrose agar).Bacterial strains (1236) were isolated on Tryptic Soy Broth (TSB) agar and identified to species, or in some cases sub-species level, by analysis of their fatty acid methyl ester (FAME) profiles. Isolated bacteria were grouped into 78 named and 37 unnamed species clusters. Greatest number of bacterial species were isolated from young plants and leaves, sampled during the autumn months. Bacterial community diversity was lowest in mid-summer and winter months. Pseudomonas was the most commonly isolated genus and Erwinia herbicola the most common species. P. aureofaciens was the only species isolated from soil that was also isolated from the phyllosphere of B. vulgaris throughout the season.     

健康与患病刺梨植株可培养叶际真菌菌群差异比较

本研究比较了健康与患叶斑病刺梨植株叶际真菌群落特征差异,以期探索病原菌的潜在来源,为人工构建具拮抗功能群落和刺梨叶斑病的生物防控提供参考。通过可培养方法对不同健康状况的刺梨叶际真菌进行分离培养,结合形态学和分子系统学对菌株进行综合鉴定;利用FUNGuild平台对真菌进行功能注释;结合根际、根部真菌作拆分网络分析探索病原菌的潜在来源。本研究结果表明：1）刺梨叶际真菌具有丰富的多样性。从刺梨叶际8个样品中共分离到真菌266株,其隶属于3门、6纲、13目、30科、46属中的61个种。其中,健康植株叶际内生真菌（LHE）包括8属10种27株,附生真菌（LHS）包括33属37种77株。患病叶际内生真菌（LDE）分离到7属10种38株;附生真菌（LDS）分离到31属35种124株。2）不同样品的真菌优势属和特有类群有差异。不同健康状况下叶际附生真菌的优势属均为拟盘多毛孢属Pestalotiopsis,但二者的相对多度存在差异,LHS为11.49%,LDS为32.26%;内生真菌优势属二者均为链格孢属Alternaria,但相对多度各异,LHE为33.33%,LDE为63.16%。其中,LHE特有类群为盘长孢状刺盘孢 Colletotrichum gloeosporioides和果生刺盘孢Colletotrichum fructicola等8种;LDE特有类群为茄链格孢 Alternaria solani和Didymella sinensis 等8种;LHS特有类群是草酸青霉Penicillium oxalicum和Peniophora crassitunicata等21种;LDS特有类群是尖孢镰刀菌Fusarium oxysporum、赭绿青霉Penicillium ochrochloron和易脆毛霉Mucor fragilis等19种。3）不同样品叶际真菌功能不同。经FUNGuild解析表明,LHS、LHE和LDE的叶际真菌功能群主要以腐生型为主,LDS则主要以植物病原菌群为主。本研究结果初步揭示刺梨植株健康与患叶斑病叶际间真菌多样性、群落组成及营养功能群存在差异,植株健康状况与其真菌群落特征密切相关;叶斑病病原菌主要源于刺梨叶际的附生微生物群。     

Links between soil microbial communities and plant traits in a species‐rich grassland under long‐term climate change

Climate change can influence soil microorganisms directly by altering their growth and activity but also indirectly via effects on the vegetation, which modifies the availability of resources. Direct impacts of climate change on soil microorganisms can occur rapidly, whereas indirect effects mediated by shifts in plant community composition are not immediately apparent and likely to increase over time. We used molecular fingerprinting of bacterial and fungal communities in the soil to investigate the effects of 17 years of temperature and rainfall manipulations in a species‐rich grassland near Buxton, UK. We compared shifts in microbial community structure to changes in plant species composition and key plant traits across 78 microsites within plots subjected to winter heating, rainfall supplementation, or summer drought. We observed marked shifts in soil fungal and bacterial community structure in response to chronic summer drought. Importantly, although dominant microbial taxa were largely unaffected by drought, there were substantial changes in the abundances of subordinate fungal and bacterial taxa. In contrast to short‐term studies that report high resistance of soil fungi to drought, we observed substantial losses of fungal taxa in the summer drought treatments. There was moderate concordance between soil microbial communities and plant species composition within microsites. Vector fitting of community‐weighted mean plant traits to ordinations of soil bacterial and fungal communities showed that shifts in soil microbial community structure were related to plant traits representing the quality of resources available to soil microorganisms: the construction cost of leaf material, foliar carbon‐to‐nitrogen ratios, and leaf dry matter content. Thus, our study provides evidence that climate change could affect soil microbial communities indirectly via changes in plant inputs and highlights the importance of considering long‐term climate change effects, especially in nutrient‐poor systems with slow‐growing vegetation.     

Mycorrhizal fungal abundance is affected by long-term climatic manipulations in the field

Climate change treatments – winter warming, summer drought and increased summer precipitation – have been imposed on an upland grassland continuously for 7 years. The vegetation was surveyed yearly. In the seventh year, soil samples were collected on four occasions through the growing season in order to assess mycorrhizal fungal abundance. Mycorrhizal fungal colonisation of roots and extraradical mycorrhizal hyphal (EMH) density in the soil were both affected by the climatic manipulations, especially by summer drought. Both winter warming and summer drought increased the proportion of root length colonised (RLC) and decreased the density of external mycorrhizal hyphal. Much of the response of mycorrhizal fungi to climate change could be attributed to climate‐induced changes in the vegetation, especially plant species relative abundance. However, it is possible that some of the mycorrhizal response to the climatic manipulations was direct – for example, the response of the EMH density to the drought treatment. Future work should address the likely change in mycorrhizal functioning under warmer and drier conditions.     

Microbial community composition but not diversity changes along succession in arctic sand dunes

The generality of increasing diversity of fungi and bacteria across arctic sand dune succession was tested. Microbial communities were examined by high‐throughput sequencing of 16S rRNA genes (bacteria) and internal transcribed spacer (ITS) regions (fungi). We studied four microbial compartments (inside leaf, inside root, rhizosphere and bulk soil) and characterized microbes associated with a single plant species (Deschampsia flexuosa) across two sand dune successional stages (early and late). Bacterial richness increased across succession in bulk soil and leaf endosphere. In contrast, soil fungal richness remained constant while root endosphere fungal richness increased across succession. There was, however, no significant difference in Shannon diversity indices between early and late successional stage in any compartment. There was a significant difference in the composition of microbial communities between early and late successional stage in all compartments, although the major microbial OTUs were shared between early and late successional stage. Co‐occurrence network analysis revealed successional stage‐specific microbial groups. There were more co‐occurring modules in early successional stage than in late stage. Altogether, these results emphasize that succession strongly affects distribution of microbial species, but not microbial diversity in arctic sand dune ecosystem and that fungi and bacteria may not follow the same successional trajectories.     

Fungal community composition in neotropical rain forests: the influence of tree diversity and precipitation

Plant diversity is considered one factor structuring soil fungal communities because the diversity of compounds in leaf litter might determine the extent of resource heterogeneity for decomposer communities. Lowland tropical rain forests have the highest plant diversity per area of any biome. Since fungi are responsible for much of the decomposition occurring in forest soils, understanding the factors that structure fungi in tropical forests may provide valuable insight for predicting changes in global carbon and nitrogen fluxes. To test the role of plant diversity in shaping fungal community structure and function, soil (0-20?cm) and leaf litter (O horizons) were collected from six established 1-ha forest census plots across a natural plant diversity gradient on the Isthmus of Panama. We used 454 pyrosequencing and phospholipid fatty acid analysis to evaluate correlations between microbial community composition, precipitation, soil nutrients, and plant richness. In soil, the number of fungal taxa increased significantly with increasing mean annual precipitation, but not with plant richness. There were no correlations between fungal communities in leaf litter and plant diversity or precipitation, and fungal communities were found to be compositionally distinct between soil and leaf litter. To directly test for effects of plant species richness on fungal diversity and function, we experimentally re-created litter diversity gradients in litter bags with 1, 25, and 50 species of litter. After 6?months, we found a significant effect of litter diversity on decomposition rate between one and 25 species of leaf litter. However, fungal richness did not track plant species richness. Although studies in a broader range of sites is required, these results suggest that precipitation may be a more important factor than plant diversity or soil nutrient status in structuring tropical forest soil fungal communities.     

Effect of drought and season on arbuscular mycorrhizal fungi in a subtropical secondary forest

Arbuscular mycorrhizal (AM) fungi in both soil and roots were examined in May (summer) and December (winter) under a 4-y drought experiment in a Chinese subtropical secondary forest. Drought significantly decreased AM fungal extra-radical hyphal density, spore density, and root colonization rate in both seasons. These AM parameters were significantly higher in summer than in winter in the control treatment, but only AM fungal extra-radical hyphal density exhibited the same seasonal trend in the drought treatment. In total, 45 AM fungal operational taxonomic units (OTUs) were obtained at a 97% sequence similarity level using Illumina sequencing of 18S rDNA. Drought and season had no significant effects on AM fungal OTU richness in soil and roots. AM fungal community composition in soil and roots was significantly affected by season but not by drought. This finding enhances our understanding of the response of AM fungi to global climate change in subtropical forest ecosystems.     

Fungal endophyte communities in two tropical forests of southern India: diversity and host affiliation

Fifteen tree species from a tropical dry thorn forest and fifteen tree species from a tropical dry deciduous forest in the Mudumalai Wildlife Sanctuary, Nilgiri Biosphere Reserve, southern India, were surveyed for their foliar endophyte communities during the dry and wet seasons. Surface sterilized leaf segments of uniform dimension were plated on nutrient agar and culturable endophytes growing from the segments were identified. Endophyte diversity was greater in the dry thorn forest than in the dry deciduous forest in the dry season. Although the isolation frequency of culturable endophytes increased for both forests during the wet season, the assemblages were represented not by any unique fungal species but by the commonly occurring ones. Furthermore, although individual leaves were densely colonized by endophytes, only a few species of endophytes colonized the whole leaves; and, only a few fungal species dominated the foliar endophytic communities and were common for both forests during both dry and wet seasons. Thus, even under wet conditions that favour dispersal and infection by fungi, the endophyte diversity increased only marginally, an indication that certain tropical forests are not hyperdiverse with reference to fungal endophytes. This should be considered when using culturable endophyte diversity as a surrogate for estimating global fungal diversity.     

Plant diversity does not buffer drought effects on early‐stage litter mass loss rates and microbial properties

Human activities are decreasing biodiversity and changing the climate worldwide. Both global change drivers have been shown to affect ecosystem functioning, but they may also act in concert in a non‐additive way. We studied early‐stage litter mass loss rates and soil microbial properties (basal respiration and microbial biomass) during the summer season in response to plant species richness and summer drought in a large grassland biodiversity experiment, the Jena Experiment, Germany. In line with our expectations, decreasing plant diversity and summer drought decreased litter mass loss rates and soil microbial properties. In contrast to our hypotheses, however, this was only true for mass loss of standard litter (wheat straw) used in all plots, and not for plant community‐specific litter mass loss. We found no interactive effects between global change drivers, that is, drought reduced litter mass loss rates and soil microbial properties irrespective of plant diversity. High mass loss rates of plant community‐specific litter and low responsiveness to drought relative to the standard litter indicate that soil microbial communities were adapted to decomposing community‐specific plant litter material including lower susceptibility to dry conditions during summer months. Moreover, higher microbial enzymatic diversity at high plant diversity may have caused elevated mass loss of standard litter. Our results indicate that plant diversity loss and summer drought independently impede soil processes. However, soil decomposer communities may be highly adapted to decomposing plant community‐specific litter material, even in situations of environmental stress. Results of standard litter mass loss moreover suggest that decomposer communities under diverse plant communities are able to cope with a greater variety of plant inputs possibly making them less responsive to biotic changes.     

Response of the Soil Microbial Community to Changes in Precipitation in a Semiarid Ecosystem

Microbial communities regulate many belowground carbon cycling processes; thus, the impact of climate change on the structure and function of soil microbial communities could, in turn, impact the release or storage of carbon in soils. Here we used a large-scale precipitation manipulation (+18%, −50%, or ambient) in a piñon-juniper woodland (Pinus edulis-Juniperus monosperma) to investigate how changes in precipitation amounts altered soil microbial communities as well as what role seasonal variation in rainfall and plant composition played in the microbial community response. Seasonal variability in precipitation had a larger role in determining the composition of soil microbial communities in 2008 than the direct effect of the experimental precipitation treatments. Bacterial and fungal communities in the dry, relatively moisture-limited premonsoon season were compositionally distinct from communities in the monsoon season, when soil moisture levels and periodicity varied more widely across treatments. Fungal abundance in the drought plots during the dry premonsoon season was particularly low and was 4.7 times greater upon soil wet-up in the monsoon season, suggesting that soil fungi were water limited in the driest plots, which may result in a decrease in fungal degradation of carbon substrates. Additionally, we found that both bacterial and fungal communities beneath piñon pine and juniper were distinct, suggesting that microbial functions beneath these trees are different. We conclude that predicting the response of microbial communities to climate change is highly dependent on seasonal dynamics, background climatic variability, and the composition of the associated aboveground community.     

青杨雌雄株叶际微生物群落多样性和结构的差异

【目的】本论文探究了青杨雌雄株的叶际微生物的群落结构差异及其主要环境影响因素。【方法】以河北小五台山的天然青杨林为研究对象,采用基于16S rRNA/ITS1基因的MiSeq高通量测序技术,分析了青杨雌雄株叶际细菌和真菌的群落结构,并耦合分析其与叶片理化性质的相关性。【结果】测序结果表明细菌和真菌的多样性指数ACE、Chao1、Shannon、Simpson在雌雄株间都无显著性差异(P>0.05)。Metastats组间群落显著性差异分析表明,在门水平,青杨雌雄株叶际细菌和真菌都无显著差异。而在属水平,青杨雌雄株的叶际细菌Amnibacterium和Spingomonas及真菌Aureobasidium、Elmerina、Exobasidium、Endoconidioma、Monilinia和Rhodotorula的相对丰度在雌雄株叶际有显著差异(P<0.05)。基于OTUs的菌群分析表明,青杨雌株和雄株的叶际环境上都有其各自的特有菌群,如雌株的特有真菌Pringsheimia(0.15%)和细菌Chitinophaga(0.04%)。RDA冗余分析表明,叶片含水量与青杨叶际真菌的群落结构有显著相关性(P<0.05),而未发现青杨细菌群落结构与测定的叶片理化性质有显著相关。【结论】青杨雌雄株叶际微生物在属水平有显著分异的菌属,且可能受叶片理化性质影响,该结果为揭示雌雄异株植物的叶际微生物差异有重要借鉴意义。     

Summer drought decreases soil fungal diversity and associated phenol oxidase activity in upland Calluna heathland soil

Natural moisture limitation during summer drought can constitute a stress for microbial communities in soil. Given globally predicted increases in drought frequency, there is an urgent need for a greater understanding of the effects of drought events on soil microbial processes. Using a long-term field-scale drought manipulation experiment at Clocaenog, Wales, UK, we analysed fungal community dynamics, using internal transcribed spacer-denaturing gradient gel electrophoresis (DGGE), over a 1-year period in the 6th year of drought manipulation. Ambient seasonality was found to be the dominant factor driving variation in fungal community dynamics. The summer drought manipulation resulted in a significant decline in the abundance of dominant fungal species, both independently of, and in interaction with, this seasonal variation. Furthermore, soil moisture was significantly correlated with the changes in fungal diversity over the drought manipulation period. While the relationship between species diversity and functional diversity remains equivocal, phenol oxidase activity was decreased by the summer drought conditions and there was a significant correlation with the decline of DGGE band richness among the most dominant fungal species during the drought season. Climatically driven events such as droughts may have significant implications for fungal community diversity and therefore, have the potential to interfere with crucial ecosystem processes, such as organic matter decomposition.     

Shifts in microbial biomass and the bacteria: fungi ratio occur under field conditions within 3 h after rainfall

Increases in the frequency of soil drying and extreme precipitation projected by climate models may have important consequences for soil microbial community composition. However, the microbial response may occur over short time scales not captured by traditional sampling methods. Following a 2-year rainfall exclusion experiment in a pine forest ecosystem, we used phospholipid fatty acid profiling to measure the hourly, daily, and weekly-scale response of soil microbial biomass and the bacteria/fungi ratio to a precipitation event. We compared this response to the rewetting of un-manipulated plots. Within 3 h of watering, we detected increases in fungal and bacterial biomass of 125% and 66%, respectively, in un-manipulated plots, but only small increases in biomass within drought plots. We detected a decrease in the bacteria/fungi ratio in un-manipulated plots and an increase in this ratio in the drought plots. This surprising result was likely caused by root mortality (resulting from the previous 2-year rain exclusion) and an increase in ammonium pools in the drought plots, both of which could have suppressed fungal growth. Whereas past research suggests that soil microbes are resistant to drying–rewetting stress and to changes in annual precipitation patterns, here we show that microbes are sensitive to soil drying, but highly resilient, recovering within hours or days of a rain event. We propose that more emphasis be placed on hourly-scale field measurements of soil microbial community structure in future climate change studies.     

Differential sensitivity of total and active soil microbial communities to drought and forest management

Climate change will affect semiarid ecosystems through severe droughts that increase the competition for resources in plant and microbial communities. In these habitats, adaptations to climate change may consist of thinning—that reduces competition for resources through a decrease in tree density and the promotion of plant survival. We deciphered the functional and phylogenetic responses of the microbial community to 60 years of drought induced by rainfall exclusion and how forest management affects its resistance to drought, in a semiarid forest ecosystem dominated by Pinus halepensis Mill. A multiOMIC approach was applied to reveal novel, community‐based strategies in the face of climate change. The diversity and the composition of the total and active soil microbiome were evaluated by 16S rRNA gene (bacteria) and ITS (fungal) sequencing, and by metaproteomics. The microbial biomass was analyzed by phospholipid fatty acids (PLFAs), and the microbially mediated ecosystem multifunctionality was studied by the integration of soil enzyme activities related to the cycles of C, N, and P. The microbial biomass and ecosystem multifunctionality decreased in drought‐plots, as a consequence of the lower soil moisture and poorer plant development, but this decrease was more notable in unthinned plots. The structure and diversity of the total bacterial community was unaffected by drought at phylum and order level, but did so at genus level, and was influenced by seasonality. However, the total fungal community and the active microbial community were more sensitive to drought and were related to ecosystem multifunctionality. Thinning in plots without drought increased the active diversity while the total diversity was not affected. Thinning promoted the resistance of ecosystem multifunctionality to drought through changes in the active microbial community. The integration of total and active microbiome analyses avoids misinterpretations of the links between the soil microbial community and climate change.     

Drought consistently alters the composition of soil fungal and bacterial communities in grasslands from two continents

The effects of short‐term drought on soil microbial communities remain largely unexplored, particularly at large scales and under field conditions. We used seven experimental sites from two continents (North America and Australia) to evaluate the impacts of imposed extreme drought on the abundance, community composition, richness, and function of soil bacterial and fungal communities. The sites encompassed different grassland ecosystems spanning a wide range of climatic and soil properties. Drought significantly altered the community composition of soil bacteria and, to a lesser extent, fungi in grasslands from two continents. The magnitude of the fungal community change was directly proportional to the precipitation gradient. This greater fungal sensitivity to drought at more mesic sites contrasts with the generally observed pattern of greater drought sensitivity of plant communities in more arid grasslands, suggesting that plant and microbial communities may respond differently along precipitation gradients. Actinobateria, and Chloroflexi, bacterial phyla typically dominant in dry environments, increased their relative abundance in response to drought, whereas Glomeromycetes, a fungal class regarded as widely symbiotic, decreased in relative abundance. The response of Chlamydiae and Tenericutes, two phyla of mostly pathogenic species, decreased and increased along the precipitation gradient, respectively. Soil enzyme activity consistently increased under drought, a response that was attributed to drought‐induced changes in microbial community structure rather than to changes in abundance and diversity. Our results provide evidence that drought has a widespread effect on the assembly of microbial communities, one of the major drivers of soil function in terrestrial ecosystems. Such responses may have important implications for the provision of key ecosystem services, including nutrient cycling, and may result in the weakening of plant–microbial interactions and a greater incidence of certain soil‐borne diseases.