Understanding the stability of soil organic matter (SOM) is central to predicting soil carbon persistence and informing sustainable land management. We combined thermal, chemical, and biological approaches to evaluate SOM stability in 108 soils spanning diverse ecozones in Canada, New Zealand, Scotland, and the Subarctic. Thermal stability was measured using Rock–Eval (RE) pyrolysis, chemical composition was characterized with X-ray absorption near-edge structure (XANES) spectroscopy, and biological stability was assessed through 98-day C mineralization assays. Across soils, thermal stability (T50) was strongly and negatively correlated with mineralized C, indicating that stronger bond structures reduce biodegradability. Importantly, our results demonstrate that T50 not only reflects SOM quality but also serves as a proxy for the extent of organo-mineral associations that contribute to stabilization. The Hydrogen Index (HI) showed a positive relationship with mineralized C, confirming its role as a reliable indicator of labile SOM. XANES results further revealed that alkyl-C and the alkyl/O-alkyl-C ratio were positively related to thermal stability, whereas ketones and aromatic groups correlated negatively with T50, suggesting they are labile byproducts of microbial decomposition or contributions from lignin and tannins, rather than highly recalcitrant aromatic compounds typically associated with stable SOM. Together, these findings highlight that SOM persistence is shaped by both intrinsic chemical composition and extrinsic mineral protection. Rock–Eval pyrolysis and XANES spectroscopy thus provide complementary insights into SOM stability and, when combined with biological assays, offer generalizable tools for evaluating soil carbon resilience across ecosystems.

Abstract Mycotoxins, such as deoxynivalenol (DON) produced by Fusarium, are harmful fungal secondary metabolic products that cause economic losses and health risks to humans and livestock. Measures to control and prevent feed contamination with DON are necessary to ensure the safety of livestock. These include strategies based on preventing fungal contamination of feed or limiting contaminants in feed through mycotoxin adsorption and degradation. Soil is a valuable source of diverse microbial communities, potentially harboring DON-degrading bacteria that can be developed into feed additives to mitigate DON. This study aimed to identify microbial consortia from diverse soil samples, that could degrade DON. Soil from central (Lacombe; LA) and southern (Lethbridge; LE) Alberta were used as microbial inoculant. These soils were suspected to host Fusarium spp. which could produce DON in cereal crops growing upon them. The LE samples were further categorized into soil amended with manure (LE-MA) or non-manure (LE-UF). Prior to the study, soil pH and moisture content were measured. After soil collection, field-moist samples were mixed with DON-contaminated wheat (10% wt/wt; d 0) and each soil type was divided into triplicate pots and placed in a controlled environment for 32 d. On d 0, 7, 14 and 32, subsamples were collected from pots, serially diluted in a limited medium containing DON (10 µg/mL) as the only carbon source, and incubated for 2 wk (30°C). The degradation of DON in bacterial cultures was calculated using ELISA. The LA soil was slightly acidic (pH 6.4) compared with LE-MA (7.3) and LE-UF (pH 7.0), while moisture content was greater in LA (18.4%) than LE-MA (14.7%) and LE-UF (13.5%) soils. DON-degrading activity was only detected in LA soil samples and was greatest after 7 d of incubation (21%). We are currently isolating individual bacteria from LA soil for identification and are characterizing the soil microbiota using 16S rRNA sequencing. Overall, this study showed that soil contained bacteria capable of degrading DON, however variation existed depending on soil source.

Mycotoxins, such as deoxynivalenol (DON) produced by Fusarium, are harmful fungal secondary metabolic products that cause economic losses and health risks to humans and livestock. Measures to control and prevent feed contamination with DON are necessary to ensure the safety of livestock. These include strategies based on preventing fungal contamination of feed or limiting contaminants in feed through mycotoxin adsorption and degradation. Soil is a valuable source of diverse microbial communities, potentially harboring DON-degrading bacteria that can be developed into feed additives to mitigate DON. This study aimed to identify microbial consortia from diverse soil samples, that could degrade DON. Soil from central (Lacombe; LA) and southern (Lethbridge; LE) Alberta were used as microbial inoculant. These soils were suspected to host Fusarium spp. which could produce DON in cereal crops growing upon them. The LE samples were further categorized into soil amended with manure (LE-MA) or non-manure (LE-UF). Prior to the study, soil pH and moisture content were measured. After soil collection, field-moist samples were mixed with DON-contaminated wheat (10% wt/wt; d 0) and each soil type was divided into triplicate pots and placed in a controlled environment for 32 d. On d 0, 7, 14 and 32, subsamples were collected from pots, serially diluted in a limited medium containing DON (10 µg/mL) as the only carbon source, and incubated for 2 wk (30°C). The degradation of DON in bacterial cultures was calculated using ELISA. The LA soil was slightly acidic (pH 6.4) compared with LE-MA (7.3) and LE-UF (pH 7.0), while moisture content was greater in LA (18.4%) than LE-MA (14.7%) and LE-UF (13.5%) soils. DON-degrading activity was only detected in LA soil samples and was greatest after 7 d of incubation (21%). We are currently isolating individual bacteria from LA soil for identification and are characterizing the soil microbiota using 16S rRNA sequencing. Overall, this study showed that soil contained bacteria capable of degrading DON, however variation existed depending on soil source.

Context: Intercropping is used to improve crop productivity and sustainability. However, total and partial yields of intercrops vary widely due to both intercropping system and environment. Understanding the factors controlling this variability would be of value for crop producers deciding whether and how to adopt intercropping. Objective: Our objective was to determine the dominant factors controlling total and partial yields of pulse-oilseed intercrops in a semiarid region. Method: We conducted a field study for three years in southern Alberta under both dryland and irrigated conditions with lentil (Lens culinaris) and pea (Pisum sativum) intercropped with canola (Brassica napus) or mustard (Sinapis alba). Oilseed plant density and N fertility was varied and competition for soil and fertilizer N was measured using 15N. Results: Crop productivity expressed using the Land Equivalent Ratio (LER) ranged from 0.98 to 1.75, similar to the range reported in the literature. High LER occurred when monocrop oilseed yields were strongly limited by N and increased when the oilseed crop was more competitive for fertilizer and soil N. In 2018, canola was about 4to 6-fold more competitive for fertilizer N than pea or lentil and LER was high when N was limiting. In 2019 and 2020, mustard was about 3-fold more competitive than lentil but no more competitive than pea and LER was only higher when mustard was intercropped with lentil and N was limiting. Modifying oilseed plant density primarily impacted partial yields, not LER. Application of N fertilizer at 50 kg ha-1 reduced LER by 12%, whether applied at seeding or at five weeks. Over-yielding in this study was largely controlled by complementary N use, with variation in total and partial yields largely accounted for by the deficit in N supply for the oilseed crop, relative crop competiveness for soil N, and plant density. Implications: The primary benefit of intercropping pulse and oilseed crops is sustained crop productivity with reduced N fertilizer inputs or under variable N sufficiency. Reliable prediction of total and partial yields should be feasible and allow crop producers to evaluate whether and how to incorporate intercrops into crop rotations. Studies on intercrops of legumes with non-legumes should include an N-sufficient non-legume control and benefit from the use of 15N to measure competition for soil N.

Identifying the primary regulators of plant litter decay in agricultural soils is important for understanding ecosystem function now and for managing post-harvest litter in a warmer world. We conducted a litter decay study at 11 sites in Canada and New Zealand with diverse soils and climates. We incorporated C-13-labelled barley litter into the surface 10 cm of soil and monitored amount remaining over 8-10 years; at five sites litter was also applied to the soil surface to simulate no-tillage. Our objectives were to evaluate litter decay as influenced by soil type, tillage practice, and environmental conditions, and quantify the most important factors controlling C retention in soil. Loss of C via decomposition occurred quickly - more than half was lost within 1 year and only about 5-12% remained at the end of the experiment. A double exponential decay model, based on temperature and developed from the first 5 years of the study, accurately described litter decay, but only after re-tuning using measurements from the full experimental period. Including precipitation in the model further improved its fit. Soil properties exerted minimal discernible influence on the amount of litter C remaining, implying that properties such as the amount and surface area of clay minerals, were less important than climate in limiting litter decay or enhancing retention of C in soil. Comparison of litter application treatments showed that no-till slowed decay of plant litter, but only for a short time (similar to 1 yr) and only in environments with a mean annual precipitation of <1000 mm. These findings have implications for the role of soils in climate mitigation. If only 10% of added plant litter C remains in soil beyond a few years, regardless of climate, residue placement, or soil type, then rates of soil gain are limited without substantive increases in residue inputs.

Soil organic carbon (SOC) is closely tied to soil health. However, additional biological indicators may also provide insight about C dynamics and microbial activity. We used SOC and the other C indicators (potential C mineralization, permanganate oxidizable C, water extractable organic C, and beta-glucosidase enzyme activity) from the North American Project to Evaluate Soil Health Measurements to examine the continental-scale drivers of these indicators, the relationships among indicators, and the effects of soil health practices on indicator values. All indicators had greater values at cooler temperatures, and most were greater with increased precipitation and clay content. The indicators were strongly correlated with each other at the site-level, with the strongest relationship between SOC and permanganate oxidizable C. The indicator values responded positively to decreased tillage, inclusion of cover crops, application of organic nutrients, and retention of crop residue, but not the number of harvested crops in a rotation. The effect of decreased tillage on the C indicators was generally greater at sites with higher precipitation. The magnitude and direction of the response to soil health practices was consistent across indicators within a site but measuring at least two indicators would provide additional confi-dence of the effects of management, especially for tillage. All C indicators responded to management, an essential criterion for evaluating soil health. Balancing the cost, sensitivity, interpretability, and availability at commercial labs, a 24-hr potential C mineralization assay could deliver the most benefit to measure in conjunction with SOC.

Global environmental change can substantively alter soil carbon storage and dynamics in agroecosystems. However, investigations of soil organic matter (OM) composition associated with various environmental factors are still limited, and this hinders the understanding of soil carbon biogeochemistry in agricultural settings. Soil samples were collected at two times (time 0 and 8 or 10 years) from 10 agricultural sites across Canada and New Zealand with varying soil properties (i.e., soil texture, pH) and climates (MAT, mean annual temperature; MAP, mean annual precipitation). The soils were analyzed for organic carbon, nitrogen and soil OM composition using molecular-level techniques that included targeted compound-specific and solid-state 13C nuclear magnetic resonance analyses. Soil carbon contents were similar over time and were not correlated with environmental factors. Molecular-level characterization of soils found that the preservation and degradation of specific soil OM components differed. Simple sugars and microbial-derived compounds (i.e., fungi-derived ergosterol and microbial-derived lipids) persist less with time in soils compared to other OM components. However, the increased cutin- and suberin-derived compounds at most sites and similar alkyl carbon contents with time suggested that cutin- and suberin-derived compounds were longer-lived compared to other soil OM compounds. Correlation analyses indicated that temporal differences in fungal-derived ergosterol were positively correlated with silt content (r = 0.78). An inverse correlation was observed between lignin degradation and silt content (r = -0.75). Cutin- and suberin-derived compounds were negatively correlated with MAT (r = -0.69); when the analysis was restricted to only Canadian sites, cutin- and suberin-derived compounds and their degradation were correlated with MAP and MAT (climate variables). Further, partial correlation analysis revealed that the correlations between soil texture and the temporal shifts in soil OM composition were indirectly regulated by MAP but not MAT. Overall, distinct environmental constraints were observed for specific OM components in agroecosystems, suggesting that the preservation mechanisms are not uniform across a wide range of soils under different climates and soil properties.

Canada's interest in agricultural lands has changed with time from a desire of crop yields at Confederation through to discussions in the Senate on adaptation and resilience in 2018. Long-term research experiments (LTRs) have been present and utilized by federal and university researchers to provide answers throughout. Here we highlight the importance of LTRs by identifying the historical context of LTRs and soil health research in Canada. We then briefly describe the history and key results from select LTRs and illustrate the wealth of information collected from the North American Project to Evaluate Soil Health Measurements cross-country point-in-time soil sampling from these LTRs. We discuss the LTRs, and the knowledge gained from them, with the hope that by showing the distinctive narratives associated with each of these study sites, researchers will be inspired to use them to address their research questions and make sound predictions to facilitate the adaptation of Canadian agroecosystems to climate challenges. Through identifying the value generated by these unique LTRs, we hope that the importance of these sites will inspire not only their continued maintenance but also the next generation of LTRs.

Farmers, scientists, and other soil health stakeholders require interpretable indicators of soil hydraulic function. Determining which indicators to use has been difficult because of measurement disconformity, spatial and temporal variability, recently established treatments, and the effect of site characteristics on management practice differences. The North American Project to Evaluate Soil Health Measurements includes 124 sites uniformly sampled across a range of soil health management practices in North America in 2019. We compare and recommend indicators of hydraulic function that best characterize soil health. We assessed the relationship of each indicator to a suite of soil inherent properties and climate variables, the response of each indicator to soil health management practices, the effect that soil inherent properties (clay content, sand content, and pH) and climatic variables (10-yr mean annual precipitation and temperature) had on response to management practices, and the relationship among the responses of the indicators to soil health management practices. Field capacity measured on intact cores (theta(FC_INTACT)) was the best measure of soil hydraulic function, because it responded to management, represents a direct measure of soil hydraulic function, is proximal to stakeholder values, and its response to management was not significantly influenced by inherent and climatic variables. Other suitable indicators are bulk density, soil organic carbon (SOC), and aggregate stability, which are not direct measures of soil hydraulic function but do respond to management and may be practical in situations in which measuring theta(FC_INTACT) is not. This study informs selection of soil health indicators to measure soil hydraulic function.

Currently accepted pedotransfer functions show negligible effect of management-induced changes to soil organic carbon (SOC) on plant available water holding capacity (theta(AWHC)), while some studies show the ability to substantially increase theta(AWHC) through management. The Soil Health Institute's North America Project to Evaluate Soil Health Measurements measured water content at field capacity using intact soil cores across 124 long-term research sites that contained increases in SOC as a result of management treatments such as reduced tillage and cover cropping. Pedotransfer functions were created for volumetric water content at field capacity (theta(FC)) and permanent wilting point (theta(PWP)). New pedotransfer functions had predictions of theta(AWHC) that were similarly accurate compared with Saxton and Rawls when tested on samples from the National Soil Characterization database. Further, the new pedotransfer functions showed substantial effects of soil calcareousness and SOC on theta(AWHC). For an increase in SOC of 10 g kg(-1) (1%) in noncalcareous soils, an average increase in theta(AWHC) of 3.0 mm 100 mm(-1) soil (0.03 m(3) m(-3)) on average across all soil texture classes was found. This SOC related increase in theta(AWHC) is about double previous estimates. Calcareous soils had an increase in theta(AWHC) of 1.2 mm 100 mm(-1) soil associated with a 10 g kg(-1) increase in SOC, across all soil texture classes. New equations can aid in quantifying benefits of soil management practices that increase SOC and can be used to model the effect of changes in management on drought resilience.

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity.

Aggregate stability is a commonly used indicator of soil health because improvements in aggregate stability are related to reduced erodibility and improved soil-water dynamics. During the past 80 to 90 years, numerous methods have been developed to assess aggregate stability. Limited comparisons among the methods have resulted in varied magnitudes of response to soil health management practices and varied influences of inherent soil properties and climate. It is not clear whether selection of a specific method creates any advantage to the investigator. This study assessed four commonly used methods of measuring aggregate stability using data collected as part of the North American Project to Evaluate Soil Health Measurements. The methods included water stable aggregates using the Cornell Rainfall Simulator (WSACASH), wet sieved water stable aggregates (WSAARS), slaking captured and adapted from SLAKES smart-phone image recognition software (STAB10), and the mean weight diameter of water stable aggregates (MWD). Influence of climate and inherent soil prop-erties at the continental scale were analyzed in addition to method responses to rotation diversity, cash crop count, residue management, organic nutrient amendments, cover crops, and tillage. The four methods were moderately correlated with each other. All methods were sensitive to differences in climate and inherent soil properties between sites, although to different degrees. None measured significant effects from rotation diversity or crop count, but all methods detected significant increases in aggregate stability resulting from reduced tillage. Significant increases or positive trends were observed for all methods in relation to cover cropping, increased residue retention, and organic amendments, except for STAB10, which expressed a slightly negative response to organic amendments. Considering these results, no single method was clearly superior and all four are viable options for measuring aggregate stability. Therefore, secondary considerations (e.g., cost, method availability, increased sensitivity to a specific management practice, or minimal within-treatment variability) driven by the needs of the investigator, should determine the most suitable method.

Variable results have been reported on the effects of crop residue loads on soil microbial properties. We investigated changes in soil bacterial composition, beta-glucosidase enzyme activity and nutrient bioavailability in response to wheat residue loading. The treatments included three levels of above-ground wheat residues (removed, retained or supplemented), with or without fertilizer N. Bacteroidetes, Firmicutes and Verrucomicrobia (the first two are copiotrophs) were less abundant where residues were removed than where residues were retained or supplemented. but the reverse was true for Actinobacteria, Cyunobacteria, Chloroflexi and Nitrospirue (all oligotrophs, although some Actinobacteria can be copiotrophic). Actinobacteria were also less abundant where fertilizer N was applied, and the abundances of their genera (including Arthrobacter and Mycobacterium) increased where residues were removed, confirming that they were oligotrophic in this study. beta-diversity showed similar differences in the bacterial community structures because of residue management, but alpha-diversity was not affected by residue management or N fertilizer. beta-glucosidase enzyme activities increased as C inputs increased with residue manipulation and N fertilizer. The enzyme activities increased with increasing residue loading in the 0-15 cm soil depth. but decreased with soil depth. Soil K supply increased with increasing residue loading, but nitrate-N supply was highest with residue retention. These results demonstrate remarkable resilience of soil microbial functioning under a wide range of crop residue inputs, without adverse effects on enzyme activity attributable to inorganic N fertilizer. The increasing beta-glucosidase activity with increasing residue loading probably explains why crop residue return does not always increase soil C stocks.

Soil temperature affects the rate of C-cycle processes by influencing the activities of microbial communities but little is known about whether the effects on these communities are consistent in different soils. We studied bacterial and fungal communities in six different soils, originating from two different Canadian climatic regions and incubated for three years at a common field site under ambient or warming (ca. +4.6 ?C for 653 d of warming) conditions. Similar to early responses (reported after 295 d of warming), soil respiration is consistently higher (up to 2.8-fold) for 653 d of warming. However, soil origin-related differences in the community structure of bacteria were smaller at the end of the experiment, suggesting that environmental factors and management practices are important in shaping the structure of communities, but that this is a cumulative effect over time. In contrast, warming-induced shifts were greater and consistent across soils after longer period of soil warming. These shifts coincided with significant increases in the relative proportions of some potentially copiotrophic bacteria (e.g., Thermoleophilia, Alphaproteobacteria, and Bacilli). Fungal responses to warming, determined at the end of incubation, were largely soil-specific. The relative proportions of some fungi (e.g., Nectriaceae) increased with warming while several other taxa (e.g., Mortierellaceae and Lasiosphaeriaceae) showed significant reductions with warming. Unlike community structure, differences in the DNA content, microbial biomass carbon (MBC), and abundance of bacteria or fungi between the control and warmed soils were minor. This might be related to depletion of readily available substrates because measurements were made a year after the annual addition of litter. Our observation that community shifts became more pronounced over time suggests that these differences may have been realized through physiological temperature optima and through resulting shifts in resource availability.

Understanding the mechanisms controlling the formation and persistence of soil organic matter (SOM) is important for managing soil health and sustainable food production. The formation of SOM and the degree to which it is protected from decomposition are important for determining the long-term persistence of SOM. We used soils collected in a C-13-labelled litter decomposition study established at agricultural sites in Canada to understand the formation and persistence of newly-formed SOM. The ten agricultural sites spanned a wide range of soil carbon contents, texture, and climatic conditions. We fractionated the soil to isolate water extractable organic matter (WEOM), free light POM (fPOM), sand-sized and occluded particulate organic matter (oPOM), and silt and clay sized particles, referred to as mineral-associated organic matter (MAOM). Quantitative isotope tracing was used to determine the litter-derived C in all fractions. We performed these analyses early (six months after incubation) and later (five years after incubation) in the decomposition process to evaluate factors that control the formation and persistence of POM and MAOM. After six months litter-derived C was found in all fractions, but after five years it had declined in all fractions except the MAOM. Formation of MAOM was related to high mean annual precipitation and low sand content, whereas occluded POM formation was related to high soil C content. Persistence of MAOM and POM during the incubation were associated with low soil temperature and high soil C content. There was no consistent indication that formation of MAOM occurred from the decomposition of POM, suggesting that MAOM and POM are formed by two separate pathways. This has important implications for SOC models, which assume that plant-derived C passes through a sequence of pools, becoming more stable along the way.

Mycorrhizal fungi transfer nutrients to plants in exchange for photosynthates. Plants allocate up to 20% of their carbon to mycorrhizal structures, mycelium and fruit bodies of their fungal partners. Individuals of mycorrhizal fungi may encompass hundreds of square metres of soil and defragmented litter, linking multiple plant individuals of different species and size (Figure 1). Using a free‐air 13CO2 enrichment (web‐FACE) technique in a mature forest, interspecific transfer accounted for 40% of fine root carbon after 5 years of back and forth transfer between trees. In this issue of Molecular Ecology, Rog, Rosenstock, Körner, and Klein (2020) show that closely related trees shared relatively more mycorrhizal fungi than distantly related trees in the same experimental site, which correlated to increased carbon sharing.

The soil microbial community regulates decomposition of plant litter, but little is known about how the composition of the community responds to litter quality. To evaluate this, we applied C-13-labelled oat [Avena saliva] leaf or stem litter to soil at a rate of 5 mg C g(-1) soil and incubated it at 20 degrees C for 170 days. We measured total C mineralized and litter-derived C remaining in soil over the incubation. Quantitative real-time PCR and Illumina MiSeq sequencing of marker genes were used to characterize shifts in abundance and composition of bacteria and fungi. We found no difference in litter-derived C remaining in the amended soils during the incubation; but more C (similar to 23%) was mineralized from soil amended with leaf litter than those amended with stems, suggesting that leaf litter enhanced decomposition of the native soil organic matter. Leaf and stem litter supported the growth of bacteria and fungi throughout the incubation, but fungal growth and the fungal to bacterial ratio were more pronounced with the addition of stem litter. These changes in relative abundance as well as more pronounced shifts in fungal community structure in stem vs. leaf litter amended soils highlights the importance of fungi in degrading relatively resistant fractions of the lignin-enriched stem litter. Unlike the control soil (no litter added), the modularity (i.e., communities with some degree of independence) of co-occurrence in microbial networks increased, and this coincided litter-induced enrichment of specific taxa and with reduced alpha diversity. Leaf addition enriched a few bacterial (e.g., Bacilli) and many fungal (e.g., Nectriaceae, Didymellaceae, and Stachybotryaceae) taxa, whereas stem addition caused enrichment of fungi (e.g., Trichocomaceae and Chaetomiaceae) that are known to degrade resistant plant material. The findings of this study show that litter composition has a stronger influence on the composition of fungal than bacterial communities. Our results also suggest that some key fungal taxa have greater advantage in degrading relatively resistant plant material thereby supporting the growth of other bacterial and fungal taxa through release of simple, more degradable, compounds.

Mycorrhizal fungi transfer nutrients to plants in exchange for photosynthates. Plants allocate up to 20% of their carbon to mycorrhizal structures, mycelium and fruit bodies of their fungal partners. Individuals of mycorrhizal fungi may encompass hundreds of square metres of soil and defragmented litter, linking multiple plant individuals of different species and size (Figure 1). Using a free-air(13)CO(2)enrichment (web-FACE) technique in a mature forest, interspecific transfer accounted for 40% of fine root carbon after 5 years of back and forth transfer between trees. In this issue of Molecular Ecology, Rog, Rosenstock, Korner, and Klein (2020) show that closely related trees shared relatively more mycorrhizal fungi than distantly related trees in the same experimental site, which correlated to increased carbon sharing.

Climate change may profoundly influence soil organic carbon (SOC) dynamics through effects on soil temperature and water, but the mechanisms and magnitude of those effects remain uncertain. We measured the response of residue-C and native SOC in six soils with diverse texture subjected to artificial heating after transplanting to a common field site. The soils, three from each of two climatic zones in Canada, were amended with C-13 labelled oat (Avena sativa) residue to distinguish turnover of recently-applied C and native SOC. The soils were either kept at ambient temperature or heated to 5 degrees C above ambient and CO2 emission was monitored over two growing seasons. Temperature was the primary factor regulating soil respiration across all six soils; water content did not have any additional explanatory effect, probably because the study site conditions were generally wet and thus decomposition was not limited by water. Soil aggregation and loss of residue-C (68% after 295 days) were not affected by warming. Compared to residue-C, native-SOC was more sensitive to loss by warming. The effect of physical aggregate protection against loss of SOC under warming was not evident. Bacterial community structure (16S rRNA gene sequencing) showed that there was a strong and persistent legacy effect on microbial communities. These differences among soils were far greater than those between heating and ambient treatments despite transplanting to a common location. Our results show that decomposition of residue-C and SOC were strongly governed by soil temperature rather than water content, even among transplanted soils with different textures and bacterial communities.

We planted continuous wheat, with and without nitrogen fertilizer, onto a preceding long-term (44 yr) experiment with contrasting cropping systems, and measured soil organic carbon (SOC) after 6 yr. Changes in SOC were driven mostly by cumulative plant C inputs, as influenced by yield response to added nitrogen.