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The majority of the Earth's terrestrial carbon is stored in the soil. If anthropogenic warming stimulates the loss of this carbon to the atmosphere, it could drive further planetary warming. Despite evidence that warming enhances carbon fluxes to and from the soil, the net global balance between these responses remains uncertain. Here we present a comprehensive analysis of warming-induced changes in soil carbon stocks by assembling data from 49 field experiments located across North America, Europe and Asia. We find that the effects of warming are contingent on the size of the initial soil carbon stock, with considerable losses occurring in high-latitude areas. By extrapolating this empirical relationship to the global scale, we provide estimates of soil carbon sensitivity to warming that may help to constrain Earth system model projections. Our empirical relationship suggests that global soil carbon stocks in the upper soil horizons will fall by 30 ± 30 petagrams of carbon to 203 ± 161 petagrams of carbon under one degree of warming, depending on the rate at which the effects of warming are realized. Under the conservative assumption that the response of soil carbon to warming occurs within a year, a business-as-usual climate scenario would drive the loss of 55 ± 50 petagrams of carbon from the upper soil horizons by 2050. This value is around 12-17 per cent of the expected anthropogenic emissions over this period. Despite the considerable uncertainty in our estimates, the direction of the global soil carbon response is consistent across all scenarios. This provides strong empirical support for the idea that rising temperatures will stimulate the net loss of soil carbon to the atmosphere, driving a positive land carbon-climate feedback that could accelerate climate change.

No-till agriculture represents a relatively widely adopted management system that aims to reduce soil erosion, decrease input costs, and sustain long-term crop productivity. However, its impacts on crop yields are variable, and an improved understanding of the factors limiting productivity is needed to support evidence-based management decisions. We conducted a global meta-analysis to evaluate the influence of various crop and environmental variables on no-till relative to conventional tillage yields using data obtained from peer-reviewed publications (678 studies with 6005 paired observations, representing 50 crops and 63 countries). Side-by-side yield comparisons were restricted to studies comparing conventional tillage to no-till practices in the absence of other cropping system modifications. Crop category was the most important factor influencing the overall yield response to no-till followed by aridity index, residue management, no-till duration, and N rate. No-till yields matched conventional tillage yields for oilseed, cotton, and legume crop categories. Among cereals, the negative impacts of no-till were smallest for wheat (−2.6%) and largest for rice (−7.5%) and maize (−7.6%). No-till performed best under rainfed conditions in dry climates, with yields often being equal to or higher than conventional tillage practices. Yields in the first 1–2 years following no-till implementation declined for all crops except oilseeds and cotton, but matched conventional tillage yields after 3–10 years except for maize and wheat in humid climates. Overall, no-till yields were reduced by 12% without N fertilizer addition and 4% with inorganic N addition. Our study highlights factors contributing to and/or decreasing no-till yield gaps and suggests that improved targeting and adaptation, possibly including additional system modifications, are necessary to optimize no-till performance and contribute to food production goals. In addition, our results provide a basis for conducting trade-off analyses to support the development of no-till crop management and international development strategies based on available scientific evidence.

Winter cover crops represent a land cover change that may sequester carbon in the soil and improve agricultural sustainability. Their adoption may also change the Earth's radiative balance and result in biophysical feedbacks to climate through alterations in albedo and latent heat fluxes. Understanding the mechanisms underlying these alterations to the radiative balance is important for making reliable future climate projections. However, data on cover crop biophysics are limited, requiring models to rely on data from summer plants for parameterization, likely biasing predictions. To address this gap, we measured the albedo and stomatal conductance of two summer crops and three winter crops on farms in the High Plains region of Texas. We also established a winter cover crop field experiment with two cover crops and fallow fields to estimate the change in albedo and latent heat flux that results from a switch to winter cover cropping. We found that albedo was significantly higher in winter‐like conditions than in summer‐like conditions due to an increase in plant albedo and a reduction in leaf area index. The albedo of winter cover crops was higher than the soil albedo, resulting in an increase in top‐of‐atmosphere reflected radiation of 7%–14% when converting from fallow fields to winter cover cropped fields. There was an additional cooling effect through doubling of the estimated latent heat flux caused by the presence of cover crops. The combined changes in albedo and latent heat resulted in a change in the surface energy balance that is associated with an overall cooling effect of winter cover crops on surface atmospheric temperatures. While this effect is likely to be region‐specific, these results strongly indicate that winter cover crops alter the surface albedo and latent heat flux of agricultural fields and provide a direct cooling effect in the High Plains region of Texas. [ABSTRACT FROM AUTHOR]

A global meta-analysis of conservation agriculture principles indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed. Does conservation agriculture work? Advocates of conservation agriculture, which integrates ecological management (namely zero tillage, permanent soil cover and crop rotation) with modern agricultural production techniques, see it as a means of sustainably increasing global food supply. So far it has proved difficult to establish conclusively whether crop yields are maintained by conservation agriculture and whether it can be applied effectively in widely differing farming contexts. In this meta-analysis of more than 5,000 observations from 610 studies, Cameron Pittelkow and colleagues show that farming using a combination of conservation agriculture techniques can yield as much or more than conventional farming under certain conditions. The use of 'no-till' alone, the central concept of conservation agriculture, negatively impacts yields. But used with the other two conservation agriculture techniques of residue retention and crop rotation, no-till can increase rainfed crop productivity in dry climates, suggesting it may become an important climate-change adaptation strategy. One of the primary challenges of our time is to feed a growing and more demanding world population with reduced external inputs and minimal environmental impacts, all under more variable and extreme climate conditions in the future.sup.1,2,3,4. Conservation agriculture represents a set of three crop management principles that has received strong international support to help address this challenge.sup.5,6, with recent conservation agriculture efforts focusing on smallholder farming systems in sub-Saharan Africa and South Asia.sup.7. However, conservation agriculture is highly debated, with respect to both its effects on crop yields.sup.8,9,10 and its applicability in different farming contexts.sup.7,11,12,13. Here we conduct a global meta-analysis using 5,463 paired yield observations from 610 studies to compare no-till, the original and central concept of conservation agriculture, with conventional tillage practices across 48 crops and 63 countries. Overall, our results show that no-till reduces yields, yet this response is variable and under certain conditions no-till can produce equivalent or greater yields than conventional tillage. Importantly, when no-till is combined with the other two conservation agriculture principles of residue retention and crop rotation, its negative impacts are minimized. Moreover, no-till in combination with the other two principles significantly increases rainfed crop productivity in dry climates, suggesting that it may become an important climate-change adaptation strategy for ever-drier regions of the world. However, any expansion of conservation agriculture should be done with caution in these areas, as implementation of the other two principles is often challenging in resource-poor and vulnerable smallholder farming systems, thereby increasing the likelihood of yield losses rather than gains. Although farming systems are multifunctional, and environmental and socio-economic factors need to be considered.sup.14,15,16, our analysis indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed., Author(s): Cameron M. Pittelkow [sup.1] [sup.8] , Xinqiang Liang [sup.2] , Bruce A. Linquist [sup.1] , Kees Jan van Groenigen [sup.3] , Juhwan Lee [sup.4] , Mark E. Lundy [sup.1] [...]

The long-tailed shrew, Sorex dispar, is an eastern North American forest-talus specialist. The species has been the subject of detailed taxonomic study over the past decades, with considerable disagreement over the taxonomy and nomenclature assigned to the various forms (species, subspecies) across its geographic range. Morphological differences among the different subspecies of S. dispar currently recognized have been noted. However, there is still variation to document and contextualize over the species full geographic range, with consequent conservation implications. Here, we present craniometric analyses that support the differentiation of the proposed Canadian endemic subspecies of the long-tailed shrew, S. d. gaspensis. This subspecies differs in skull shape: S. d. gaspensis has a significantly larger braincase (P<0.05) than the other 2 recognized subspecies of S. dispar, but is significantly smaller in other craniodental characters. While S. dispar, encompassing S. d. kirklandi and S. d. gaspensis, in Canada is currently designated Not at Risk, we show that S. d. gaspensis is a morphologically distinct Canadian endemic that occupies rare habitat in a limited range. Modern conservation practice advocates the preservation of the evolutionary potential of taxa, particularly peripheral populations in the species' range. Hence, on this basis, we caution against status assessments or management plans that would discount the distinct cranial morphology exhibited by S. d. gaspensis. [ABSTRACT FROM AUTHOR]

The carbon stored in soil exceeds that of plant biomass and atmospheric carbon and its stability can impact global climate. Growth of decomposer microorganisms mediates both the accrual and loss of soil carbon. Growth is sensitive to temperature and given the vast biological diversity of soil microorganisms, the response of decomposer growth rates to warming may be strongly idiosyncratic, varying among taxa, making ecosystem predictions difficult. Here, we show that 15 years of warming by transplanting plant–soil mesocosms down in elevation, strongly reduced the growth rates of soil microorganisms, measured in the field using undisturbed soil. The magnitude of the response to warming varied among microbial taxa. However, the direction of the response—reduced growth—was universal and warming explained twofold more variation than did the sum of taxonomic identity and its interaction with warming. For this ecosystem, most of the growth responses to warming could be explained without taxon‐specific information, suggesting that in some cases microbial responses measured in aggregate may be adequate for climate modeling. Long‐term experimental warming also reduced soil carbon content, likely a consequence of a warming‐induced increase in decomposition, as warming‐induced changes in plant productivity were negligible. The loss of soil carbon and decreased microbial biomass with warming may explain the reduced growth of the microbial community, more than the direct effects of temperature on growth. These findings show that direct and indirect effects of long‐term warming can reduce growth rates of soil microbes, which may have important feedbacks to global warming. [ABSTRACT FROM AUTHOR]