Sounds of Soil: A New World of Interactions under Our Feet?

Soils are biodiversity-dense and constantly carry chemical flows of information, with our mental image of soil being dark and quiet. But what if soil biota tap sound, or more generally, vibrations as a source of information? Vibrations are produced by soil biota, and there is accumulating evidence that such vibrations, including sound, may also be perceived. We here argue for potential advantages of sound/vibration detection, which likely revolve around detection of potential danger, e.g., predators. Substantial methodological retooling will be necessary to capture this form of information, since sound-related equipment is not standard in soils labs, and in fact this topic is very much at the fringes of the classical soil research at present. Sound, if firmly established as a mode of information exchange in soil, could be useful in an ‘acoustics-based’ precision agriculture as a means of assessing aspects of soil biodiversity, and the topic of sound pollution could move into focus for soil biota and processes

A general stochastic model shows that plant-soil feedbacks can buffer plant species from extinction risks in unpredictable environments

Theory and experiments have demonstrated that negative plant-soil feedback (PSF) promotes coexistence between plant species. Plants and soils, however, face the challenge of an increasingly unpredictable environment due to multiple global change factors. Environmental stochasticity induces fluctuations that increase the variability and unpredictability of population dynamics, plant associations in the community and thus properties such as overall productivity. In this paper, we formulate a stochastic version of a classic PSF deterministic model, which describes the outcome of plant species competition in the presence of soil feedback. Especially when the soil feedback is negative, the deterministic expectation is that pulse perturbations to the system (e.g. a drought episode) cause plants and soil to move away from their equilibrium and then return to it. Environmental stochasticity alters this expectation: the system can either settle into a fluctuation regime around the deterministic expectation, or plant species may go extinct. Probability of extinction predictably increases with environmental stochasticity but the more negative the PSF, the more it can counteract the increase in extinction probability caused by increased environmental stochasticity. We stress that in nature the actual impact of PSF will depend on the interactions that link different types of soil organisms to plant species. We conclude that theory shows that plant communities with strong negative PSF are best placed to withstand the risk posed by increased environmental stochasticity but also that we still need more experimental evidence to validate theory and develop applications

Legacy effect of microplastics on plant–soil feedbacks

Microplastics affect plants and soil biota and the processes they drive. However, the legacy effect of microplastics on plant–soil feedbacks is still unknown. To address this, we used soil conditioned from a previous experiment, where Daucus carota grew with 12 different microplastic types (conditioning phase). Here, we extracted soil inoculum from those 12 soils and grew during 4 weeks a native D. carota and a range-expanding plant species Calamagrostis epigejos in soils amended with this inoculum (feedback phase). At harvest, plant biomass and root morphological traits were measured. Films led to positive feedback on shoot mass (higher mass with inoculum from soil conditioned with microplastics than with inoculum from control soil). Films may decrease soil water content in the conditioning phase, potentially reducing the abundance of harmful soil biota, which, with films also promoting mutualist abundance, microbial activity and carbon mineralization, would positively affect plant growth in the feedback phase. Foams and fragments caused positive feedback on shoot mass likely via positive effects on soil aeration in the conditioning phase, which could have increased mutualistic biota and soil enzymatic activity, promoting plant growth. By contrast, fibers caused negative feedback on root mass as this microplastic may have increased soil water content in the conditioning phase, promoting the abundance of soil pathogens with negative consequences for root mass. Microplastics had a legacy effect on root traits: D. carota had thicker roots probably for promoting mycorrhizal associations, while C. epigejos had reduced root diameter probably for diminishing pathogenic infection. Microplastic legacy on soil can be positive or negative depending on the plant species identity and may affect plant biomass primarily via root traits. This legacy may contribute to the competitive success of range-expanding species via positive effects on root mass (foams) and on shoot mass (PET films). Overall, microplastics depending on their shape and polymer type, affect plant–soil feedbacks

Controls on the production, incorporation and decomposition of glomalin - a novel fungal soil protein important to soil carbon

OAK B263 Glomalin is an operationally defined soil protein, produced by arbuscular mycorrhizal fungi (AMF), with importance in soil carbon sequestration through its relationship with soil aggregation. The goal of the project was to further explore the natural history of glomalin and to address several questions regarding basic behavior of this compound in soil (production, incorporation, decomposition). We have obtained a significant amount of novel information on the arbuscular mycorrhizal fungal soil protein, concerning factors controlling its production to mechanisms of incorporation and decomposition. These findings have resulted in 10 publications in peer-reviewed journals, with several more submitted or in preparation, and 16 contributed presentations at meetings. I have sought collaborative opportunities whenever they fit within the research proposed to enhance our productivity. Additionally, although not part of the original proposed work, we have made a significant effort to elucidate the molecular biology of glomalin (in response to Program Officer suggestions). In addition to peer-reviewed publications there have also been a number of invited presentations, including a keynote address delivered by the PI at the International Conference on Mycorrhizae (ICOM4) in Montreal, summer 2003. Two Master's students have been trained (and graduated), and a postdoctoral associate has been mentored, as well as numerous undergraduate researchers at UM. In this report I summarize the major findings of the project in the areas of glomalin production control (host factors, elevated CO2), incorporation, and decomposition. Section D is newly added and describes recent progress in molecular biology. Briefly, we found that glomalin production is influenced by the host, as shown by host species effects and responses to elevated CO2. We have recently made a significant breakthrough in understanding how glomalin may become deposited into soil; apparently the dominant pathway is via hyphal turnover rather than by secretion (as previously assumed). In terms of decomposition, we have learned that glomalin is surprisingly stable (data from soil incubation experiments and from carbon dating) and has a residence time far greater than the AMF hyphae (on the order of decades, putting at least some glomalin fractions in the slow soil C pool). Finally, our exploratory work on molecular biology of glomalin has yielded some promising preliminary data (including an immunoreactive band that was used to obtain N-terminal amino acid sequence). While the gene has not yet been identified, this strongly suggests that glomalin is a unique compound; - a significant step from an operational definition (based on soil extraction conditions) to biochemical characterization

Microplastic transport in soil by earthworms

Despite great general benefits derived from plastic use, accumulation of plastic material in ecosystems, and especially microplastic, is becoming an increasing environmental concern. Microplastic has been extensively studied in aquatic environments, with very few studies focusing on soils. We here tested the idea that microplastic particles (polyethylene beads) could be transported from the soil surface down the soil profile via earthworms. We used Lumbricus terrestris L., an anecic earthworm species, in a factorial greenhouse experiment with four different microplastic sizes. Presence of earthworms greatly increased the presence of microplastic particles at depth (we examined 3 soil layers, each 3.5 cm deep), with smaller PE microbeads having been transported downward to a greater extent. Our study clearly shows that earthworms can be significant transport agents of microplastics in soils, incorporating this material into soil, likely via casts, burrows (affecting soil hydraulics), egestion and adherence to the earthworm exterior. This movement has potential consequences for exposure of other soil biota to microplastics, for the residence times of microplastic at greater depth, and for the possible eventual arrival of microplastics in the groundwater

Classifying human influences on terrestrial ecosystems

Human activity is affecting every ecosystem on Earth, with terrestrial biodiversity decreasing rapidly. Human influences materialize in the form of numerous, jointly acting factors, yet the experimental study of such joint impacts is not well developed. We identify the absence of a systematic ordering system of factors according to their properties (traits) as an impediment to progress and offer an a priori trait-based factor classification to illustrate this point, starting at the coarsest level with the physical, biological or chemical nature of factors. Such factor classifications can serve in communication of science, but also can be used as heuristic tools to develop questions and formulate new hypotheses, or as predictors of effects, which we explore here. We hope that classifications such as the one proposed here can help shift the spotlight on the multitude of anthropogenic changes affecting ecosystems, and that such classifications can be used to help unravel joint impacts of a great number of factors

Litter Decomposition Is Not Affected by Perfluorobutane Sulfonate (PFBS) in Experimental Soil Microcosms

Perfluorobutane sulfonate (PFBS) has been found in increasing concentrations in the environment. However, its effect on litter decomposition in soils is still unclear. Therefore, the effect of PFBS on the decomposition of various litter types was tested, as well as on selected aspects of soil quality. Soil samples were treated with different concentrations of PFBS (0, 1, and 10 µg g–1) and five organic litter materials were used with various C:N ratios. A soil microcosm experiment was performed at 20 °C for 6 weeks. Litter decomposition, soil respiration, enzyme activities, soil pH, water-stable aggregates (WSA), and soil total C and N contents were measured. PFBS treatments were observed to have negligible effects on litter decomposition as well as on other soil properties. This means that in the concentration range examined, this substance has no observable effects on the key soil parameters examined. The present result was inconsistent with the findings of a previous study with similar experimental microcosms but different soils. This study suggests that the effects of PFBS may be less pronounced in the tested soil, but it cannot be concluded that PFBS is harmless in soil ecosystems. A wider range of soil types and PFBS levels should be tested in future studies