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The interactions between plants and soil microorganisms are fundamental for ecosystem functioning. However, it remains unclear if seasonality of plant growth impacts plant-microbial interactions, such as by inducing shifts in the microbial community composition, their biomass, or changes in the microbial uptake of plant-derived carbon. Here, we investigate the stability of microbial biomass of different functional groups and their net assimilation of plant-derived carbon over an entire growing season. Using a C3-C4 vegetation change experiment, and taking advantage of natural abundances of13C, we measured the plant-derived carbon in lipid biomarkers of soil microorganisms in rhizosphere and non-rhizosphere soil. We found that temporal and spatial stability was higher in bacterial than in fungal biomass, while the high temporal stability of all bacterial groups even increased in close proximity to roots. Moreover, differences in the association to plants, i.e., symbionts vs. free-living microorganisms, tend to determine the stability in the uptake of plant-derived carbon. Our results indicate, the inputs of plant-derived carbon over the growing season did not result in a shift in the microbial community composition, but instead, functional groups that are not in obligate symbiosis with plants showed a varying use of soil- and plant-derived carbon.

Recently, a new annotation tool “FungalTraits” was created based on the previous FUNGuild and FunFun databases, which has attracted high attention in the scientific community. These databases were widely used to gain more information from fungal sequencing datasets by assigning fungal functional traits. More than 1500 publications so far employed FUNGuild and the aim of this study is to compare this successful database with the recent FungalTraits database. Quality and quantity of the assignment by FUNGuild and FungalTraits to a fungal internal transcribed spacer (ITS)–based amplicon sequencing dataset on amplicon sequence variants (ASVs) were addressed. Sequencing dataset was derived from leaves and needles of 12 temperate broadleaved and coniferous tree species. We found that FungalTraits assigned more functional traits than FUNGuild, and especially the coverage of saprotrophs, plant pathogens, and endophytes was higher while lichenized fungi revealed similar findings. Moreover, ASVs derived from leaves and needles of each tree species were better assigned to all available fungal traits as well as to saprotrophs by FungalTraits compared to FUNGuild in particular for broadleaved tree species. Assigned ASV richness as well as fungal functional community composition was higher and more diverse after analyses with FungalTraits compared to FUNGuild. Moreover, datasets of both databases showed similar effect of environmental factors for saprotrophs but for endophytes, unidentical patterns of significant corresponding factors were obtained. As a conclusion, FungalTraits is superior to FUNGuild in assigning a higher quantity and quality of ASVs as well as a higher frequency of significant correlations with environmental factors.

Currently, lichen surveys are generally based on the examination of fruiting bodies. Lichens in the mycelial stage, in spores, or awaiting conditions for fruiting body formation are usually overlooked, even though they are important for maintaining biodiversity and ecosystem functions. This study aimed to explore the lichenized fungal community composition and richness associated with leaves and needles of 12 temperate tree species using Illumina MiSeq-based amplicon sequencing of the internal transcribed spacer (ITS) 2 region. Picea abies harbored the highest richness and number of lichenized fungal species. We found that the lichenized fungus Physcia adscendens dominated the leaves and needles of the most temperate tree species. Eleven lichenized fungal species detected in this study were recorded for the first time on leaves and needles. In addition, we identified Athallia cerinella, Fellhanera bouteillei, and Melanohalea exasperata that are on the German national red lists. Lichenized fungal richness was higher in conifer compared to broadleaf trees. Overall, tree species (within coniferous trees) and tree types (broadleaved vs. coniferous trees) harbored significantly different lichenized fungal community compositions pointing out the importance of host species. Diversity and community composition patterns of lichenized fungi were correlated mainly with tree species. Our study demonstrates that the diversity of foliicolous lichens associated with leaves and needles of 12 temperate tree species can be appropriately analyzed and functionally assigned using the ITS-based high-throughput sequencing. We highlighted the importance of conifers for maintaining the biodiversity of foliicolous lichens. Based on the discovery of many red list lichens, our methodological approach and results are important contributions to subsequent actions in the bio-conversation approaches.

Future climate scenarios indicate increasing drought intensity that threatens ecosystem functioning. However, the behavior of ecosystems during intense drought, such as the 2018 drought in Northern Europe, and their respective response following rewetting is not fully understood. We investigated the effect of drought on four different vegetation types in a temperate climate by analyzing dissolved organic matter (DOM) concentration and composition present in soil leachate, and compared it to two accompanying years. DOM is known to play an important role in ecosystem recovery and holds information on matter flows between plants, soil microorganisms and soil organic matter. Knowledge about DOM opens the possibility to better disentangle the role of plants and microorganisms in ecosystem recovery. We found that the average annual DOM concentration significantly decreased during the 2018 drought year compared to the normal year. This suggests a stimulation of DOM release under normal conditions, which include a summer drought followed by a rewetting period. The rewetting period, which holds high DOM concentrations, was suppressed under more intense drought. Our detailed molecular analysis of DOM using ultrahigh resolution mass spectrometry showed that DOM present at the beginning of the rewetting period resembles plant matter, whereas in later phases the DOM molecular composition was modified by microorganisms. We observed this pattern in all four vegetation types analyzed, although vegetation types differed in DOM concentration and composition. Our results suggest that plant matter drives ecosystem recovery and that increasing drought intensity may lower the potential for ecosystem recovery.

Despite the abundance of observations of foliar pathogens, our knowledge is severely lacking regarding how the potential fungal pathobiome is structured and which processes determine community assembly. In this study, we addressed these questions by analysing the potential fungal pathobiome associated with the senescing leaves and needles of 12 temperate tree species. We compared fungal plant pathogen load in the senescing leaves/needles and demonstrated that healthy-looking leaves/needles are inhabited by diverse and distinct fungal plant pathogens. We detected 400 fungal plant pathogenic ASVs belonging to 130 genera. The fungal plant pathogenic generalist, Mycosphaerella, was found to be the potential most significant contributor to foliar disease in seedlings. The analyses of assembly process and co-occurrence network showed that the fungal plant pathogenic communities in different tree types are mainly determined by stochastic processes. However, the homogenising dispersal highly contributes in broadleaf trees, whereas ecological drift plays an important role in coniferious trees. The deterministic assembly processes (dominated by variable selection) contributed more in broadleaf trees as compared to coniferous trees. We found that pH and P level significantly corresponded with fungal plant pathogenic community compositions in both tree types. Our study provides the first insight and mechanistic understanding into the community assembly, networks, and complete taxonomy of the foliar fungal pathobiome in senescing leaves and needles.

Drought is an ever-increasing threat; its negative effects on ecosystems and their functioning directly impact our food security. It is therefore critical to understand the mechanisms that affect drought resilience of ecosystems. Many ecosystem functions depend on plant-soil interactions and are mediated by dissolved organic molecules, which are then recorded in the dissolved organic carbon (DOC) that leaches from plants and soils. In particular, DOC properties during and after rewetting can reveal if and how ecosystems are affected by drought. We therefore investigated the concentration of DOC in four different plant communities on sandy soils in Germany over three years that differed in drought intensity, including the extreme 2018 drought. We also analysed the molecular composition of DOC using ultrahigh-resolution mass spectrometry to identify the carbon sources during the rewetting period. A linear mixed effect model revealed that drought intensity significantly affected DOC concentration. DOC concentration in soil leachate was slightly increased following medium drought intensity, but was significantly reduced following high drought intensity. This suggests that medium intensity drought may stimulate DOC release, however, high intensity drought reduces DOC release. Molecular composition analysis of the DOC present during the rewetting period revealed an initial release of plant-derived carbon followed by an increase in soil organic matter-like compounds. Our findings indicate that the initial release of plant-derived carbon into soil leachate might be crucial for the ability of ecosystems to quickly recover from drought. High intensity drought may interrupt plant functioning to the point of preventing the accumulation and subsequent release of plant-derived carbon during drought, and therefore hamper ecosystem recovery. This suggests the presence of tipping points with respect to the ability of ecosystems to recover from drought. As such, monitoring DOC concentrations could lead to better assessements of the drought resilience of ecosystems.