Search

Biochars are porous charcoal‐like materials that can enhance soil health and plant growth, but their use has not been adequately evaluated in woody cropping systems. To fill this knowledge gap, we investigated the effects of two slow pyrolysis pine biochars on plant performance, soil physicochemical properties, extracellular enzyme activities, and root‐associated fungal community composition in an experimental Christmas tree plantation over 3 yr. Both biochars stimulated the activities of five extracellular enzyme activities between 67 and 446%, but appeared to reduce N availability. Structural equation modelling identified increased soil moisture as a potential mechanism of biochar's effects on all measured enzyme activities, whereas increased dissolved organic C was a possible mechanism of biochar's effect on N and P targeting enzymes. This finding suggests that biochar‐induced increases to dissolved organic C have a specific effect on nutrient targeting enzymes. Biochar was found to negatively impact tree growth and survival, but impacts varied between tree species and biochar type. High‐throughput sequencing showed that biochar decreased the diversity of root‐associated fungal communities, with the ectendomycorrhizal species Wilcoxina mikolaebecoming hyper‐dominant on balsam fir in response to one of the biochars. Changes to root‐associated fungal communities may have been partially responsible for negative effects on conifer performance. Although our study identified negative effects of biochar on plant performance and fungal diversity, we also found widespread changes to soil chemistry and microbial function that might be leveraged in systems with more acidic soils or different crops to increase plant performance. Biochar application increased soil extracellular enzyme activities up to fivefold.Dissolved organic C and soil moisture were increased by biochar.Decreases to N availability suggest biochar induced N immobilization.Biochar led to less diverse root fungal communities and dominance by Wilcoxina.The growth and/or survival of two conifer trees was decreased by biochar.

Background: Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowground fungal communities is largely unknown. We sought to test if (i) fungal community spatial structure matched aboveground forest structure; (ii) fungal functional guilds exhibited differential associations to aboveground trees, snags, and deadwood; and (iii) that large-diameter trees and snags have a larger influence on fungal community richness than smaller-diameter trees. We used MiSeq sequencing of fungal communities collected from soils in a spatially intensive survey in a portion of Cedar Breaks National Monument, Utah, USA. We used random forest models to explore the spatial structure of fungal communities as they relate to explicitly mapped trees and deadwood distributed across 1.15 ha of a 15.32-ha mapped subalpine forest. Results: We found 6,177 fungal amplicon sequence variants across 117 sequenced samples. Tree diameter, deadwood presence, and tree species identity explained more than twice as much variation (38.7% vs. 10.4%) for ectomycorrhizal composition and diversity than for the total or saprotrophic fungal communities. Species identity and distance to the nearest large-diameter tree (≥ 40.2 cm) were better predictors of fungal richness than were the identity and distance to the nearest tree. Soil nutrients, topography, and tree species differentially influenced the composition and diversity of each fungal guild. Locally rare tree species had an outsized influence on fungal community richness. Conclusions: These results highlight that fungal guilds are differentially associated with the location, size, and species of aboveground trees. Large-diameter trees are implicated as drivers of belowground fungal diversity, particularly for ectomycorrhizal fungi.

Understanding the chemical composition of our planet's crust was one of the biggest questions of the 20th century. More than 100 years later, we are still far from understanding the global patterns in the bioavailability and spatial coupling of elements in topsoils worldwide, despite their importance for the productivity and functioning of terrestrial ecosystems. Here, we measured the bioavailability and coupling of thirteen macro‐ and micronutrients and phytotoxic elements in topsoils (3–8 cm) from a range of terrestrial ecosystems across all continents (∼10,000 observations) and in response to global change manipulations (∼5,000 observations). For this, we incubated between 1 and 4 pairs of anionic and cationic exchange membranes per site for a mean period of 53 days. The most bioavailable elements (Ca, Mg, and K) were also amongst the most abundant in the crust. Patterns of bioavailability were biome‐dependent and controlled by soil properties such as pH, organic matter content and texture, plant cover, and climate. However, global change simulations resulted in important alterations in the bioavailability of elements. Elements were highly coupled, and coupling was predictable by the atomic properties of elements, particularly mass, mass to charge ratio, and second ionization energy. Deviations from the predictable coupling‐atomic mass relationship were attributed to global change and agriculture. Our work illustrates the tight links between the bioavailability and coupling of topsoil elements and environmental context, human activities, and atomic properties of elements, thus deeply enhancing our integrated understanding of the biogeochemical connections that underlie the productivity and functioning of terrestrial ecosystems in a changing world. Globally, the most bioavailable elements (Ca, Mg, and K) are amongst the most abundant in the crust, but N is more abundant than predictedBioavailability was controlled by soil pH, organic matter content, texture, plant cover, and climate, and altered by global changeElements were highly spatially correlated (coupled), and coupling was predictable by the atomic properties of elements, particularly mass Globally, the most bioavailable elements (Ca, Mg, and K) are amongst the most abundant in the crust, but N is more abundant than predicted Bioavailability was controlled by soil pH, organic matter content, texture, plant cover, and climate, and altered by global change Elements were highly spatially correlated (coupled), and coupling was predictable by the atomic properties of elements, particularly mass

Pyrogenic carbon (PyC) is hypothesized to play an important role in the carbon (C) cycle due to its resistance to decomposition; however, much uncertainty still exists regarding the stocks of PyC that persist on‐site after the initial erosion in postfire forests. Therefore, understanding how fire characteristics influence PyC stocks is vital, particularly in the context of California forests for which an increase of high‐severity fires is predicted over the next decades. We measured forest C and persistent PyC stocks in areas burned by low‐to‐moderate and high‐severity fire, as well as in adjacent unburned areas in a California mixed‐conifer forest, 2 to 3 years after wildfire. We measured C and PyC stocks in the following compartments: standing trees, downed wood, forest floor, and mineral soil (0–5 cm), and we identified PyC using the weak nitric acid digestion method. We found that the total stock of PyC did not differ among fire severity classes (overall mean 248 ± 30 g C m−2); however, fire severity influenced the distribution of PyC in the individual compartments. Areas burned by high‐severity fire had 2.5 times more PyC stocked in the coarse woody debris (p< 0.05), 3.3 times more PyC stocked in standing trees (p< 0.05), and a lower PyC stock in the forest floor (−22%, p< 0.05) compared to low‐to‐moderate fire severity areas. These results have important implications for the permanence time of PyC, which is putatively higher in standing trees and coarse woody debris compared to the forest floor, where it is susceptible to rapid losses through erosion. PyC stock in standing trees and coarse woody debris increased with fire severity, whereas the forest floor PyC stock decreased with fire severityThe forest floor of unburned areas had a larger PyC stock, but lower PyC concentration, relative to burned areasOnly a small fraction (between 10% and 15%) of the C in visually blackened biomass was chemically stable Charcoal (i.e., pyrogenic carbon) is an important form of carbon present in forest soil subject to fire events that is characterized by a high resistance to decomposition and thus may remain in soil for hundreds of years before it is transformed into carbon dioxide (an important green house gas). However, charcoal production is so far not considered when assessing the impact of forest fires on green house gas production. It is possible that due to this neglection the impact of forest fires on the carbon cycle is currently overestimated. Here we quantified charcoal production during forest fires in a forest burned by fires of different severity. We found that fire severity does not alter the amount of charcoal created, whereas it influences the distribution in the forest compartments (forest floor versus trees). Our results have important implications for the residence time of charcoal in the terrestrial ecosystems, because charcoal is expected to stay longer in standing trees and coarse woody debris compared to the forest floor, where it is susceptible to rapid losses through erosion.