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Forest management in drained forested peatlands can negatively affect water quality due to the increase in exports of organic matter and nutrients. Therefore, new methods to alleviate this impact are needed. In laboratory conditions, biochar has been shown to be a strong sorbent of organic and inorganic nutrients due to its high surface area and ion‐exchange capacity. However, evidence of the adsorption capacity in field conditions is lacking. Here, we studied the water purification performance of two different biochar feedstocks (wood‐ and garden residue‐based) in a 10‐day laboratory experiment where we incubated biochar with runoff water collected from drainage ditches in clear‐cut peatland forests. We measured changes in pH and concentrations of inorganic phosphorus (PO4), total dissolved nitrogen (TDN), and dissolved organic carbon (DOC). The biochar with the best adsorbent capacity in the laboratory experiment was then tested in field conditions in a replicated catchment‐scale experiment, where both clear‐cutting and ditch cleaning were performed. We determined the nutrient concentration of water at the inlet and outlet of biochar filters placed in outflow ditches of four catchments. We found that under laboratory conditions wood‐based biochar efficiently adsorbed TDN and DOC, however, it released PO4. Furthermore, we found that the biochar filters reduced TDN and DOC concentration in field conditions. However, the percentage decrease in concentration was dependent on the initial concentrations of nutrients in the water and could be considered low. Moreover, we found that the biochar in the filters increased in TN content over the course of the experiment. This suggests that a wood‐based biochar filter has the potential to be a water protection tool for reducing the export of nutrients from catchments with high nutrient concentration. And that the biochar from the ditches could be applied back to the regenerating forest catchment as a potential soil amendment, closing the nutrient cycle. [ABSTRACT FROM AUTHOR]

Biochar and manure can be used for sustainable land management. However, little is known about how soil amendments might affect surface and belowground microbial processes and subsequent wood decomposition. In a split‐split‐split plot design, we amended soil with two rates of manure (whole plot; 0 and 9 Mg ha−1) and biochar (split plot; 0 and 10 Mg ha−1). Wood stakes of three species (hybrid poplar, triploid Populus tomentosa Carr.; aspen, Populus tremuloides Michx.; and pine, Pinus taeda L.) were placed in two positions (horizontally on the soil surface, and inserted vertically in the mineral soil), which served as a substrate for fungal growth. In 3 years, the decomposition rate (density loss), moisture content, and fungal community (via high‐throughput sequencing methods) of stakes were evaluated. Results indicated that biochar and/or manure increased the wood stake decomposition rates, moisture content, and operational taxonomic unit abundance. However, the richness and diversity of fungi were dependent on wood stake position (surface > mineral), species (pine > the two Populus), and sample dates. This study highlights that soil amendment with biochar and/or manure can alter the fungal community, which in turn can enhance an important soil process (i.e., decomposition). [ABSTRACT FROM AUTHOR]

It is well established that application of biochar to soils can promote soil fertility, which ultimately may enhance plant growth. While many mechanisms have been proposed to explain this, one specific mechanism, the "microbial refugia hypothesis," suggests that biochar may provide physical protection for soil microbe from soil microfauna that otherwise exert top‐down control on microbial biomass and activity. We tested the microbial refugia hypothesis by incubating two boreal soils with and without biochar derived from a wood mixture of boreal tree species (Picea abies and Pinus sylvestris), and with and without soil nematodes. We measured phospholipid fatty acids (PLFA) as a relative measure of microbial biomass, and several variables indicative of microbial activity, including extractable nutrient concentrations (NH4+, NO3−, and PO4−), heterotrophic N2‐fixation, and soil respiration. Contrary to our expectations, we found that biochar by itself did not stimulate microbial biomass or activity. Furthermore, we found that nematode addition to soil stimulated rather than depressed the biomass of several bacterial PLFA groups. Finally, interactive effects between the nematode treatment and biochar never worked in a way that supported the microbial refugia hypothesis. Our findings suggest that a typical boreal biochar applied to boreal soils may not have the same stimulatory effect on microbial biomass and activity that has been shown in some other ecosystems, and that enhanced plant growth in response to biochar addition sometimes observed in boreal environments is likely due to other mechanisms, such as direct nutrient supply from biochar or amelioration of soil pH. [ABSTRACT FROM AUTHOR]

Biochar soil amendment may provide the forestry sector with a formidable tool to simultaneously sequester carbon (C) in the soil and aboveground by enhancing plant productivity, yet several key uncertainties remain. Crucially, empirical evidence of long‐term effects of biochar management on vegetation and on greenhouse gas emissions in forest ecosystems is scarce. Using a large field experiment in a young managed boreal forest in northern Sweden, we investigated the effects of biochar (applied either on the soil surface or mixed in the soil 8–9 years prior to this study) on supply rates of soil nutrients, on survival and growth of planted Pinus sylvestris, on community composition of the understory vegetation, and on forest floor fluxes of N2O, CH4, and CO2. We found that biochar promoted P. sylvestris survival only when biochar was applied on the soil surface. Conversely, biochar enhanced P. sylvestris growth overall, resulting in a 19% increase in C stored in biomass. Biochar also altered the composition of the understory vegetation, especially when mixed into the soil, and promoted a more resource‐conservative community (i.e., with more ericaceous shrubs and less graminoids and forbs). Meanwhile, supply rates of the main soil nutrients were largely unaffected by biochar. Finally, we found that biochar did not alter overall N2O and CO2 emissions and CH4 uptake from the forest floor. Our findings show that biochar amendment increased the net C input to the system, since, besides directly increasing soil C stocks, biochar enhanced biomass growth without increasing soil C losses. Therefore, our study suggests that biochar could potentially be used for emissions abatement in intensively managed boreal forests. [ABSTRACT FROM AUTHOR]

Biochar has the potential to mitigate the impacts of climate change and soil degradation by simultaneously sequestering C in soil and improving soil quality. However, the mechanism of biochar's effect on soil microbial communities remains unclear. Therefore, we conducted a global meta‐analysis, where we collected 2,110 paired observations from 107 published papers and used structural equation modeling (SEM) to analyze the effects of biochar on microbial community structure and function. Our result indicated that arbuscular mycorrhizal fungal abundance, microbial biomass C, and functional richness increased with biochar addition regardless of loads, time since application, and experiment types. Results from mixed linear model analysis suggested that soil respiration and actinomycetes (ACT) abundance decreased with biochar application. With the increase of soil pH, the effect of biochar on fungal abundance and C metabolic ability was lessened. Higher biochar pH associated with higher pyrolysis temperatures reduced the abundance of bacteria, fungi, ACT, and soil microbes feeding on miscellaneous C from Biolog Eco‐plate experiments. SEM that examined the effect of biochar properties, load, and soil properties on microbial community indicated that fungal abundance was the dominant factor affecting the response of the bacterial abundance to biochar. The response of bacterial abundance to biochar addition was soil dependent, whereas fungi abundance was mostly related to biochar load and pyrolysis temperature. Based on soil conditions, controlling biochar load and production conditions would be a direct way to regulate the effect of biochar application on soil microbial function and increase the capacity to sequester C. [ABSTRACT FROM AUTHOR]

Biochar management has been proposed as a possible tool to mitigate anthropogenic CO2 emissions, and thus far its impacts in forested environments remain poorly understood. We conducted a large-scale, replicated field experiment using 0.05-ha plots in the boreal region in northern Sweden to evaluate how soil and vegetation properties and processes responded to biochar application and the disturbance associated with burying biochar in the soil. We employed a randomized block design, where biochar and soil mixing treatments were established in factorial combination (i.e., control, soil mixing only, biochar only, and biochar and soil mixing; n = 6 plots of each). After two growing seasons, we found that biochar application enhanced net soil N mineralization rates and soil [ABSTRACT FROM AUTHOR]

[Display omitted] • Biochar decreased Acidobacteria abundance while increasing Gemmatimonadetes. • Biochar increased the genetic richness and diversity of soil microbes. • Experiment types played a role in shaping microbial response to biochar addition. • Biochar and soil properties were related to the changes of phyla abundance. • Selecting key biochar properties can improve soil microbial functions. Biochar has gained global attention due to its potential for climate change mitigation and soil quality improvement. Yet, the consequences of biochar additions for soil microbes -the major biotic drivers of soil function- remain unknown across global environmental gradients. We aimed to explore the responses of soil bacterial communities to biochar addition, and further investigate how biochar and soil properties impact these responses. We conducted a global meta -analysis and found that, in general, biochar has a limited impact on the proportion of major bacterial phyla, with only Acidobacteria and Gemmatimonadetes being largely impacted: the relative abundance of Acidobacteria decreased by 14.6%, while that of Gemmatimonadetes increased by 19.8%. Also, the experimental type played a role in shaping the response of microbial community to biochar application. In addition, biochar significantly promoted the diversity of soil bacteria, i.e., genetic richness and diversity. These changes were significantly associated with biochar load, C/N ratio, pyrolysis temperature, biochar pH, as well as soil C/N ratio and pH. We further found that the impacts of biochar on functional diversity, i.e., C substrate richness consumed by soil microbes increased with the biochar load, which might relate to increased genetic richness. Our work suggests that selecting key biochar properties can improve soil quality, microbial function, and climate change mitigation while maintaining the positive impacts of biochar on soil microbial diversity. Further research is needed to link the response of soil microbial composition at the genus level to biochar addition, with microbial functions. [ABSTRACT FROM AUTHOR]