Metataxonomic Analysis of Bacteria Entrapped in a Stalactite’s Core and Their Possible Environmental Origins

Much is known about microbes originally identified in caves, but little is known about the entrapment of microbes (bacteria) in stalactites and their possible environmental origins. This study presents data regarding the significant environmental distribution of prokaryotic bacterial taxa of a Greek stalactite core. We investigated the involvement of those bacteria communities in stalactites using a metataxonomic analysis approach of partial 16S rRNA genes. The metataxonomic analysis of stalactite core material revealed an exceptionally broad ecological spectrum of bacteria classified as members of Proteobacteria, Actinobacteria, Firmicutes, Verrucomicrobia, and other unclassified bacteria. We concluded that (i) the bacterial transport process is possible through water movement from the upper ground cave environment, forming cave speleothems such as stalactites, (ii) bacterial genera such as Polaromonas, Thioprofundum, and phylum Verrucomicrobia trapped inside the stalactite support the paleoecology, paleomicrobiology, and paleoclimate variations, (iii) the entrapment of certain bacteria taxa associated with water, soil, animals, and plants such as Micrococcales, Propionibacteriales, Acidimicrobiales, Pseudonocardiales, and α-, β-, and γ-Proteobacteria.

Studying the Activity of Leaf-Litter Fauna: A Small World to Discover

Hundreds of thousands of little creatures live in soils. Some eat live plants, live animals, or both. Others, called decomposers, consume dead plants, and the waste of other living beings (their feces and their dead bodies), and transform them into food for plants. The health of soils depends largely on the presence of decomposers, and thus it is necessary to study how these creatures may be affected by climate change. To this end, we built a new type of traps to catch live soil animals, which we called cul-de-sac and basket traps. Here, we show how these traps are better for studying animal activity (how much they move in the soil) compared to the most used devices to date, pitfall traps. Comparatively, our traps capture more active animals and prevent predators from killing prey inside, which will improve the accuracy of future studies all over the world.

The Isotopic Signature of the “Arthropod Rain” in a Temperate Forest: Wingless Are From Crowns, Winged Are From Soil

Invertebrate phyto-, sapro-, and microbophages, as well as predators and parasitoids, densely populate tree crowns. Eventually, all crown inhabitants fall from the trees and become a food source for litter-dwelling predators, scavengers, and saprophages. However, the functional significance of the arthropod rain, i.e., the flux of invertebrates falling from the crowns, remains unexplored. We collected arthropod rain in a temperate mixed forest throughout the growing season. The δ13С and δ15N values of the arthropods (730 samples in total) were compared to a large reference dataset of the isotopic composition of soil animals from temperate forests. The most numerous taxa in the arthropod rain were collembolans and mites. The most diverse orders were Diptera (18 families) and Coleoptera (29 families), which formed the major portion of the winged specimens. The total ranges of δ13С and δ15N values of individual animals forming arthropod rain reached 14‰ and 26‰, respectively. Nevertheless, invertebrates forming arthropod rain were on average depleted in 13C and 15N by 1.6‰ and 2.7‰, respectively, compared to the soil-dwelling animals. This difference can be used to detect the contribution of the arthropod rain to detrital food webs. Low average δ13С and δ15N values of the arthropod rain were primarily driven by the presence of microphytophages, represented mainly by Collembola and Psocoptera, and macrophytophages, mainly aphids, caterpillars, and heteropterans. Furthermore, wingless arthropods were depleted in heavy isotopes relative to winged specimens. Among wingless invertebrates, predators and parasitoids differed significantly in δ15N values from phytophages and microbi/saprophages. In contrast, there was no consistent difference in δ values between saprophages and predators among winged insects, all of them being similar in the isotopic composition to soil-dwelling invertebrates. This result suggests that winged insects in the arthropod rain represented a random assemblage of specimens originating in different biotopes, but most were tightly linked to soil food webs. Overall, our data suggest that invertebrates falling from the crown space and flying arthropods originating from the soil are an important channel connecting food webs in tree crowns and in the soil.

The Impact of Root-Derived Resources on Forest Soil Invertebrates Depends on Body Size and Trophic Position

Forest soil food webs have been assumed to be fueled substantially by root-derived resources. However, until today the flux of root-derived resources into soil animals has been investigated virtually exclusively using isotope labeling experiments, whereas studies on the consequences of disrupting the flux of root-derived resources into the soil animal food web are scarce. We here investigated the importance of root-derived resources for a wide range of soil animals by interrupting the resource flux into the soil of different forest types in Central Europe using a trenching experiment. We recorded the abundance of soil animal taxa varying in body size (micro-, meso-, and macrofauna) 1 and 3 years after root trenching, and quantified changes in biomass, species composition, and trophic shift using stable isotopes and NLFA analysis. Among the microfauna groups studied (trophic groups of Nematoda) only the abundance of plant feeding nematodes showed a trend in being decreased by -58% due to root trenching. Major soil mesofauna groups, including Collembola and Oribatida, suffered to a similar extent from root trenching with their abundance and biomass being reduced by about 30–40%. The soil macrofauna groups studied (Diplopoda, Isopoda, Chilopoda, Araneae, Coleoptera) generally were only little affected by root trenching suggesting that they rely less on root-derived resources than micro- and in particular mesofauna. Notably, the community structure of micro-, meso-, and macrofauna was not affected by root trenching. Further, we observed trophic shifts only in 2 out of 10 investigated species with the shifts generally being only minor. The results indicate that soil animal communities are markedly resilient to deprivation of root-derived resources suggesting that links to root-derived resources are non-specific. However, this resilience appears to vary with body size, with mesofauna including both decomposers as well as predators being more sensitive to the deprivation of root-derived resources than microfauna (except for root feeders) and macrofauna. Overall, this suggests that body size constrains the channeling of energy through soil food webs, with root-derived resources in temperate forests being channeled predominantly via soil taxa of intermediate size, i.e., mesofauna.

Detritivore conversion of litter into faeces accelerates organic matter turnover

Litter-feeding soil animals are notoriously neglected in conceptual and mechanistic biogeochemical models. Yet, they may be a dominant factor in decomposition by converting large amounts of plant litter into faeces. Here, we assess how the chemical and physical changes occurring when litter is converted into faeces alter their fate during further decomposition with an experimental test including 36 combinations of phylogenetically distant detritivores and leaf litter of contrasting physicochemical characteristics. We show that, across litter and detritivore species, litter conversion into detritivore faeces enhanced organic matter lability and thereby accelerated carbon cycling. Notably, the positive conversion effect on faeces quality and decomposition increased with decreasing quality and decomposition of intact litter. This general pattern was consistent across detritivores as different as snails and woodlice, and reduced differences in quality and decomposition amongst litter species. Our data show that litter conversion into detritivore faeces has far-reaching consequences for the understanding and modelling of the terrestrial carbon cycle.