High-resolution induced polarization imaging of biogeochemical carbon turnover hotspots in a peatland

Biogeochemical hotspots are defined as areas where biogeochemical processes occur with anomalously high reaction rates relative to their surroundings. Due to their importance in carbon and nutrient cycling, the characterization of hotspots is critical for predicting carbon budgets accurately in the context of climate change. However, biogeochemical hotspots are difficult to identify in the environment, as methods for in situ measurements often directly affect the sensitive redox-chemical conditions. Here, we present imaging results of a geophysical survey using the non-invasive induced polarization (IP) method to identify biogeochemical hotspots of carbon turnover in a minerotrophic wetland. To interpret the field-scale IP signatures, geochemical analyses were performed on freeze-core samples obtained in areas characterized by anomalously high and low IP responses. Our results reveal large variations in the electrical response, with the highest IP phase values (> 18 mrad) corresponding to high concentrations of phosphates (> 4000 µM), an indicator of carbon turnover. Furthermore, we found a strong relationship between the electrical properties resolved in IP images and the dissolved organic carbon. Moreover, analysis of the freeze core reveals negligible concentrations of iron sulfides. The extensive geochemical and geophysical data presented in our study demonstrate that IP images can track small-scale changes in the biogeochemical activity in peat and can be used to identify hotspots.

Root architecture and hydrologic fluctuations explain spatiotemporal soil aggregation patterns

<p>Soil aggregation is a dynamic state involving numerous biophysical interactions that cannot be deduced from snapshots of soil aggregate sizes nor the state of bulk soil organic carbon (SOC) alone. Hydrophysical and  biogeochemical functions of soil aggregation are directly linked with dynamic nature of soil aggregation. At the local scale, aggregates are formed and around particulate organic debris and they evolve as undifferentiated biogeochemical hotspots. The rate of evolution varies with the life-stage of each hotspot (the remaining reserve of C and nutrients within the hotspot) as well as the physical environmental conditions (wetness and temperature). Thus, the macroscopic patterns of hotspot (aggregate) distributions reflect the interplay between the spatial/temporal patterns of C inputs and fluctuations of physical environmental conditions. Here, we show a modeling analysis of how these aggregation patterns vary across ranges of climatic and vegetation (root architecture) conditions. We utilize a model that considers the dynamic lifecycle of ensembles of multigenerational aggregates originating from polydisperse C inputs.</p>

Patterns of Denitrification and Methanogenesis Rates from Vernal Pools in a Temperate Forest Driven by Seasonal, Microbial Functional Gene Abundances, and Soil Chemistry

Due to their relatively small sizes, temperate forest vernal pools are less studied than other wetlands, despite being potential biogeochemical hotspots in landscapes. We investigated spatial and temporal factors driving N2O and CH4 emission rates from vernal pools in a temperate forest. We determined higher N2O (3.66 ± 0.53 × 10−6, μg N2O/m2/h) and CH4 (2.10 ± 0.7 × 10−3, μg N2O/m2/h) rates in spring relative to fall (~50% and 77% lower for N2O and CH4 rates, respectively) and winter (~70% and 94% lower for N2O and CH4 rates, respectively). Soil organic matter, nitrate content and bacterial 16S rDNA, nirS, and norB gene abundances emerged as significant drivers of N2O rates, whereas, soil pH, organic matter content and mcrA abundance were significant drivers of CH4 rates. Denitrification gene abundances were negatively correlated with N2O rates, whereas mcrA abundance correlated positively with CH4 rates. Results suggest that CH4 rates may be directly coupled to methanogen abundance, whereas N2O rates may be directly impacted by a variety of abiotic variables and indirectly coupled to the abundance of potential denitrifier assemblages. Overall, additional studies examining these dynamics over extended periods are needed to provide more insights into their control.

Hydration status and diurnal trophic interactions shape microbial community function in desert biocrusts

Biological soil crusts (biocrusts) are self-organised thin assemblies of microbes, lichens, and mosses that are ubiquitous in arid regions and serve as important ecological and biogeochemical hotspots. Biocrust ecological function is intricately shaped by strong gradients of water, light, oxygen, and dynamics in the abundance and spatial organisation of the microbial community within a few millimetres of the soil surface. We report a mechanistic model that links the biophysical and chemical processes that shape the functioning of biocrust representative microbial communities that interact trophically and respond dynamically to cycles of hydration, light, and temperature. The model captures key features of carbon and nitrogen cycling within biocrusts, such as microbial activity and distribution (during early stages of biocrust establishment) under diurnal cycles and the associated dynamics of biogeochemical fluxes at different hydration conditions. The study offers new insights into the highly dynamic and localised processes performed by microbial communities within thin desert biocrusts.

Hydration Status and Diurnal Trophic Interactions Shape Microbial Community Function in Desert Biocrusts

Biological soil crusts (biocrusts) are self-organised thin assemblies of microbes, lichens and mosses ubiquitous in arid regions serving as important ecological and biogeochemical hotspots. Biocrust ecological function is intricately shaped by strong gradients of water, light, oxygen and dynamics in abundance and spatial organisation of the microbial community within a few millimetres of the soil surface. We report a mechanistic model that links biophysical and chemical processes that shape the functioning of biocrust representative microbial community that interacts trophically and responds dynamically to cycles of hydration, light, and temperature. The model captures key features of observed microbial activity and distribution (during early stages of biocrust establishment) and associated dynamics of biogeochemical fluxes. The study offers new insights into the highly dynamic and localised processes that shape biocrust functioning and elude quantification based on averaged representation of such delicate and globally important ecological assembly.