Simulating adaptive grazing management on soil organic carbon in the Southeast U.S.A. using MEMS 2.

Grazing lands play a significant role in global carbon (C) dynamics, holding substantial soil organic carbon (SOC) stocks. However, historical mismanagement (e.g., overgrazing and land-use change) has led to substantial SOC losses. Regenerative practices, such as adaptive multi-paddock (AMP) grazing, offer a promising avenue to improve soil health and help combat climate change by increasing SOC accrual, both in its particulate (POC) and mineral-associated (MAOC) organic C components. Because adaptive grazing patterns emerge from the combination of different levers such as frequency, intensity, and timing of grazing, studying AMP grazing management in experimental trials and representing it in models remains challenging. Existing ecosystem models lack the capacity to predict how different adaptive grazing levers affect SOC storage and its distribution between POC and MAOC and along the soil profile accurately. Therefore, they cannot adequately assist decision-makers in effectively optimizing adaptive practices based on SOC outcomes. Here, we address this critical gap by developing version 2.34 of the MEMS 2 model. This version advances the previous by incorporating perennial grass growth and grazing submodules to simulate grass green-up and dormancy, reserve organ dynamics, the influence of standing dead plant mass on new plant growth, grass and supplemental feed consumption by animals, and their feces and urine input to soil. Using data from grazing experiments in the southeastern United States and experimental SOC data from two conventional and three AMP grazing sites in Mississippi, we tested the capacity of MEMS 2.34 to simulate grass forage production, total SOC, POC, and MAOC dynamics to 1-m depth. Further, we manipulated grazing management levers, i.e., timing, intensity, and frequency, to do a sensitivity analysis of their effects on SOC dynamics in the long term. Our findings indicate that the model can represent bahiagrass forage production (BIAS = 9.51 g C m-2, RRMSE = 0.27, RMSE = 65.57 g C m-2, R2 = 0.72) and accurately captured the dynamics of SOC fractions across sites and depths (0-15 cm: RRMSE = 0.05; 15-100 cm: RRMSE = 1.08-2.07), aligning with patterns observed in the measured data. The model best captured SOC and MAOC stocks across AMP sites in the 0-15 cm layer, while POC was best predicted at-depth. Otherwise, the model tended to overestimate SOC and MAOC below 15 cm, and POC in the topsoil. Our simulations indicate that grazing frequency and intensity were key levers for enhancing SOC stocks compared to the current management baseline, with decreasing grazing intensity yielding the highest SOC after 50 years (63.7-65.9 Mg C ha-1). By enhancing our understanding of the effects of adaptive grazing management on SOC pools in the southeastern U.S., MEMS 2.34 offers a valuable tool for researchers, producers, and policymakers to make AMP grazing management decisions based on potential SOC outcomes.

Ruminating on soil carbon: Applying current understanding to inform grazing management.

Among options for atmospheric CO2 removal, sequestering soil organic carbon (SOC) via improved grazing management is a rare opportunity because it is scalable across millions of globally grazed acres, low cost, and has high technical potential. Decades of scientific research on grazing and SOC has failed to form a cohesive understanding of how grazing management affects SOC stocks and their distribution between particulate (POM) and mineral-associated organic matter (MAOM)-characterized by different formation and stabilization pathways-across different climatic contexts. As we increasingly look to grazing management for SOC sequestration on grazinglands to bolster our climate change mitigation efforts, we need a clear and collective understanding of grazing management's impact on pathways of SOC change to inform on-the-ground management decisions. We set out to review the effects of grazing management on SOC through a unified plant ecophysiology and soil biogeochemistry conceptual framework, where elements such as productivity, input quality, soil mineral capacity, and climate variables such as aridity co-govern SOC accumulation and distribution into POM and MAOM. To maximize applicability to grazingland managers, we discuss how common management levers that drive overall grazing pattern, including timing, intensity, duration, and frequency can be used to optimize mechanistic pathways of SOC sequestration. We discuss important research needs and measurement challenges, and highlight how our conceptual framework can inform more robust research with greater applicability for maximizing the use of grazing management to sequester SOC.

Distinct, direct and climate-mediated environmental controls on global particulate and mineral-associated organic carbon storage.

Identifying controls on soil organic carbon (SOC) storage, and where SOC is most vulnerable to loss, are essential to managing soils for both climate change mitigation and global food security. However, we currently lack a comprehensive understanding of the global drivers of SOC storage, especially with regards to particulate (POC) and mineral-associated organic carbon (MAOC). To better understand hierarchical controls on POC and MAOC, we applied path analyses to SOC fractions, climate (i.e., mean annual temperature [MAT] and mean annual precipitation minus potential evapotranspiration [MAP-PET]), carbon (C) input (i.e., net primary production [NPP]), and soil property data synthesized from 72 published studies, along with data we generated from the National Ecological Observatory Network soil pits (n = 901 total observations). To assess the utility of investigating POC and MAOC separately in understanding SOC storage controls, we then compared these results with another path analysis predicting bulk SOC storage. We found that POC storage is negatively related to MAT and soil pH, while MAOC storage is positively related to NPP and MAP-PET, but negatively related to soil % sand. Our path analysis predicting bulk SOC revealed similar trends but explained less variation in C storage than our POC and MAOC analyses. Given that temperature and pH impose constraints on microbial decomposition, this indicates that POC is primarily controlled by SOC loss processes. In contrast, strong relationships with variables related to plant productivity constraints, moisture, and mineral surface availability for sorption indicate that MAOC is primarily controlled by climate-driven variations in C inputs to the soil, as well as C stabilization mechanisms. Altogether, these results demonstrate that global POC and MAOC storage are controlled by separate environmental variables, further justifying the need to quantify and model these C fractions separately to assess and forecast the responses of SOC storage to global change.

Microbially mediated mechanisms underlie soil carbon accrual by conservation agriculture under decade-long warming.

Increasing soil organic carbon (SOC) in croplands by switching from conventional to conservation management may be hampered by stimulated microbial decomposition under warming. Here, we test the interactive effects of agricultural management and warming on SOC persistence and underlying microbial mechanisms in a decade-long controlled experiment on a wheat-maize cropping system. Warming increased SOC content and accelerated fungal community temporal turnover under conservation agriculture (no tillage, chopped crop residue), but not under conventional agriculture (annual tillage, crop residue removed). Microbial carbon use efficiency (CUE) and growth increased linearly over time, with stronger positive warming effects after 5 years under conservation agriculture. According to structural equation models, these increases arose from greater carbon inputs from the crops, which indirectly controlled microbial CUE via changes in fungal communities. As a result, fungal necromass increased from 28 to 53%, emerging as the strongest predictor of SOC content. Collectively, our results demonstrate how management and climatic factors can interact to alter microbial community composition, physiology and functions and, in turn, SOC formation and accrual in croplands.

Simulating soil C dynamics under intensive agricultural systems and climate change scenarios in the Matopiba region, Brazil.

The recent agricultural expansion in the Matopiba region, Brazil's new agricultural frontier, has raised questions about the risk of increasing soil organic carbon (SOC) loss as large areas of native vegetation (NV; i.e., Cerrado biome) have been replaced by large-scale mechanized agriculture. Although sustainable managements, such as integrated crop-livestock (ICL) systems, are considered strategic to counterbalance the SOC loss associated with land-use change (LUC) while keeping food production, little is known about their long-term effects on SOC stocks in the Matopiba region. To this end, we used the DayCent model to simulate the effects of converting the management commonly used in this region, i.e., soybean-cotton rotation under no-tillage (NT), into ICL systems with distinct levels of intensification (e.g., crop rotations: soybean-pasture and soybean-pasture-cotton; soil and crop management: grass irrigation, scarification/harrowing, and length of grass cultivation) on long term SOC dynamics. Additionally, data from two projected climate scenarios: SSP2-4.5 [greenhouse gases emissions (GHG) will not change markedly over time and global temperature will increase by 2.0 °C by 2060] and SSP5-8.5 (marked changes in GHG emissions are expected to occur resulting in an increase of 2.4 and 4.4 °C in global temperature in the middle and at the end of the century) were included in our simulations to evaluate climate change effects on SOC dynamics in this region. Based on a 50-yr-time frame simulation, we observed that SOC stocks under ICL systems were, on average, 23% and 47% higher than in the NV (36.9 Mg ha-1) and soybean-cotton rotation under NT (30.9 Mg ha-1), respectively. Growing grasses interlaid with crops was crucial to increase SOC stocks even when disruptive soil practices were followed. Although the irrigation of grass resulted in an early increase of SOC stocks and a higher pasture stoking rate, it did not increase SOC stocks in the long term compared to non-irrigated treatments. The SSP2-4.5 and SSP5-8.5 climate scenarios had little effects on SOC dynamics in the simulated ICL systems. However, additional SOC loss (∼0.065 Mg ha-1 yr-1) is predicted to occur if the current management is not improved. These findings can help guide management decisions for the Matopiba region, Brazil, to alleviate the anthropogenic pressure associated with agriculture development. More broadly, they confirm that crop-livestock integration in croplands is a successful strategy to regenerate SOC.

Restoring particulate and mineral-associated organic carbon through regenerative agriculture.

Sustainability of agricultural production and mitigation of global warming rely on the regeneration of soil organic carbon (SOC), in particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) forms. We conducted a global systematic meta-analysis of the effects of regenerative management practices on SOC, POC, and MAOC in cropland, finding: 1) no-till (NT) and cropping system intensification increase SOC (11.3% and 12.4%, respectively), MAOC (8.5% and 7.1%, respectively), and POC (19.7% and 33.3%, respectively) in topsoil (0 to 20 cm), but not in subsoil (>20 cm); 2) experimental duration, tillage frequency, the intensification type, and rotation diversity moderate the effects of regenerative management; and 3) NT synergized with integrated crop-livestock (ICL) systems to greatly increase POC (38.1%) and cropping intensification synergized with ICL systems to greatly increase MAOC (33.1 to 53.6%). This analysis shows that regenerative agriculture is a key strategy to reduce the soil C deficit inherent to agriculture to promote both soil health and long-term C stabilization.

Grassland soil carbon sequestration: Current understanding, challenges, and solutions.

Grasslands store approximately one third of the global terrestrial carbon stocks and can act as an important soil carbon sink. Recent studies show that plant diversity increases soil organic carbon (SOC) storage by elevating carbon inputs to belowground biomass and promoting microbial necromass contribution to SOC storage. Climate change affects grassland SOC storage by modifying the processes of plant carbon inputs and microbial catabolism and anabolism. Improved grazing management and biodiversity restoration can provide low-cost and/or high-carbon-gain options for natural climate solutions in global grasslands. The achievable SOC sequestration potential in global grasslands is 2.3 to 7.3 billion tons of carbon dioxide equivalents per year (CO2e year-1) for biodiversity restoration, 148 to 699 megatons of CO2e year-1 for improved grazing management, and 147 megatons of CO2e year-1 for sown legumes in pasturelands.

Persistent soil carbon enhanced in Mollisols by well-managed grasslands but not annual grain or dairy forage cropping systems.

Intensive crop production on grassland-derived Mollisols has liberated massive amounts of carbon (C) to the atmosphere. Whether minimizing soil disturbance, diversifying crop rotations, or re-establishing perennial grasslands and integrating livestock can slow or reverse this trend remains highly uncertain. We investigated how these management practices affected soil organic carbon (SOC) accrual and distribution between particulate (POM) and mineral-associated (MAOM) organic matter in a 29-y-old field experiment in the North Central United States and assessed how soil microbial traits were related to these changes. Compared to conventional continuous maize monocropping with annual tillage, systems with reduced tillage, diversified crop rotations with cover crops and legumes, or manure addition did not increase total SOC storage or MAOM-C, whereas perennial pastures managed with rotational grazing accumulated more SOC and MAOM-C (18 to 29% higher) than all annual cropping systems after 29 y of management. These results align with a meta-analysis of data from published studies comparing the efficacy of soil health management practices in annual cropping systems on Mollisols worldwide. Incorporating legumes and manure into annual cropping systems enhanced POM-C, microbial biomass, and microbial C-use efficiency but did not significantly increase microbial necromass accumulation, MAOM-C, or total SOC storage. Diverse, rotationally grazed pasture management has the potential to increase persistent soil C on Mollisols, highlighting the key role of well-managed grasslands in climate-smart agriculture.

Soil organic carbon response to global environmental change depends on its distribution between mineral-associated and particulate organic matter: A meta-analysis.

Soil organic carbon (SOC), as the largest terrestrial carbon pool, plays an important role in global carbon (C) cycling, which may be significantly impacted by global changes such as nitrogen (N) fertilization, elevated carbon dioxide (CO2), warming, and increased precipitation. Yet, our ability to accurately detect and predict the impact of these global changes on SOC dynamics is still limited. Investigating SOC responses to global changes separately for mineral-associated organic carbon (MAOC) and the particulate organic carbon (POC) can aid in the understanding of overall SOC responses, because these are formed, protected, and lost through different pathways. To this end, we performed a systematic meta-analysis of the response of SOC, MAOC, and POC to global changes. POC was particularly responsive, confirming that it is a better diagnostic indicator of soil C changes in the short-term, compared to bulk SOC and MAOC. The effects of elevated CO2 and warming were subtle and evident only in the POC fraction (+5.11% and - 10.05%, respectively), while increased precipitation had no effects at all. Nitrogen fertilization, which comprised the majority of the dataset, increased SOC (+5.64%), MAOC (+4.49%), and POC (+13.17%). Effect size consistently varied with soil depth and experiment length, highlighting the importance of long-term experiments that sample the full soil profile in global change SOC studies. In addition, SOC pool responses to warming were modified by degree of warming, differently for air and soil warming manipulations. Overall, we suggest that MAOC and POC respond differently to global changes and moderators because of the different formation and loss processes that control these pools. Coupled with additional plant and microbial measurements, studying the individual responses of POC and MAOC improves understanding of the underlying dynamics of SOC responses to global change. This will help inform the role of SOC in mitigating the climate crisis.

Adaptive multi-paddock grazing enhances soil carbon and nitrogen stocks and stabilization through mineral association in southeastern U.S. grazing lands.

Grassland soils are a large reservoir of soil carbon (C) at risk of loss due to overgrazing in conventional grazing systems. By promoting regenerative grazing management practices that aim to increase soil C storage and soil health, grasslands have the potential to help alleviate rising atmospheric CO2 as well as sustain grass productivity across a vast area of land. Previous research has shown that rotational grazing, specifically adaptive multi-paddock (AMP) grazing that utilizes short-duration rotational grazing at high stocking densities, can increase soil C stocks in grassland ecosystems, but the extent and mechanisms are unknown. We conducted a large-scale on-farm study on five "across the fence" pairs of AMP and conventional grazing (CG) grasslands covering a spectrum of southeast United States grazing lands. We quantified soil C and nitrogen (N) stocks, their isotopic and Fourier-transform infrared spectroscopy signatures as well as their distribution among soil organic matter (SOM) physical fractions characterized by contrasting mechanisms of formation and persistence in soils. Our findings show that the AMP grazing sites had on average 13% (i.e., 9 Mg C ha-1) more soil C and 9% (i.e., 1 Mg N ha-1) more soil N compared to the CG sites over a 1 m depth. Additionally, the stocks' difference was mostly in the mineral-associated organic matter fraction in the A-horizon, suggesting long-term persistence of soil C in AMP grazing farms. The higher N stocks and lower 15N abundance of AMP soils also point to higher N retention in these systems. These findings provide evidence that AMP grazing is a management strategy to sequester C in the soil and retain N in the system, thus contributing to climate change mitigation.

Elevated temperature increases the accumulation of microbial necromass nitrogen in soil via increasing microbial turnover.

Microbial-derived nitrogen (N) is now recognized as an important source of soil organic N. However, the mechanisms that govern the production of microbial necromass N, its turnover, and stabilization in soil remain poorly understood. To assess the effects of elevated temperature on bacterial and fungal necromass N production, turnover, and stabilization, we incubated 15 N-labeled bacterial and fungal necromass under optimum moisture conditions at 10°C, 15°C, and 25°C. We developed a new 15 N tracing model to calculate the production and mineralization rates of necromass N. Our results showed that bacterial and fungal necromass N had similar mineralization rates, despite their contrasting chemistry. Most bacterial and fungal necromass 15 N was recovered in the mineral-associated organic matter fraction through microbial anabolism, suggesting that mineral association plays an important role in stabilizing necromass N in soil, independently of necromass chemistry. Elevated temperature significantly increased the accumulation of necromass N in soil, due to the relatively higher microbial turnover and production of necromass N with increasing temperature than the increases in microbial necromass N mineralization. In conclusion, we found elevated temperature may increase the contribution of microbial necromass N to mineral-stabilized soil organic N.

Conceptualizing soil organic matter into particulate and mineral-associated forms to address global change in the 21st century.

Managing soil organic matter (SOM) stocks to address global change challenges requires well-substantiated knowledge of SOM behavior that can be clearly communicated between scientists, management practitioners, and policy makers. However, SOM is incredibly complex and requires separation into multiple components with contrasting behavior in order to study and predict its dynamics. Numerous diverse SOM separation schemes are currently used, making cross-study comparisons difficult and hindering broad-scale generalizations. Here, we recommend separating SOM into particulate (POM) and mineral-associated (MAOM) forms, two SOM components that are fundamentally different in terms of their formation, persistence, and functioning. We provide evidence of their highly contrasting physical and chemical properties, mean residence times in soil, and responses to land use change, plant litter inputs, warming, CO2 enrichment, and N fertilization. Conceptualizing SOM into POM versus MAOM is a feasible, well-supported, and useful framework that will allow scientists to move beyond studies of bulk SOM, but also use a consistent separation scheme across studies. Ultimately, we propose the POM versus MAOM framework as the best way forward to understand and predict broad-scale SOM dynamics in the context of global change challenges and provide necessary recommendations to managers and policy makers.

Belowground biota responses to maize biochar addition to the soil of a Mediterranean vineyard.

Biochar is a high carbon material resulting from biomass pyrolysis that, when applied to croplands, can increase soil carbon and soil water retention. Both effects are of critical importance in semi-arid regions, where carbon decline and desertification are the main drivers of soil degradation. Since most environmental services provided by soil are mediated by belowground biota, effects of biochar on soil microbial and invertebrate communities must be evaluated under field conditions before its agricultural application can be recommended. We tested maize biochar for its mid-term effect on soil microbes and micro-arthropods of a Mediterranean vineyard. We applied biochar to three field plots with neutral sandy loam soils at a dose of 5 Mg ha-1. During two years, we monitored the abundance of functional groups of soil micro-arthropods and estimated the biomass of soil microbial groups. We also analyzed the δ13C value of microbial PLFA biomarkers to determine biochar-C utilization by each microbial group taking advantage of the δ13C natural abundance differences between the applied biochar and the soil. Biochar addition significantly reduced soil microbial biomass but did not alter the functional microbial diversity nor the abundance or biodiversity of soil micro-arthropods. The contribution of biochar-C to the diet of most microbial groups was very low through the monitoring period. However, two gram-negative bacterial groups increased their biochar-derived carbon uptake under extreme soil dryness, which suggests that biochar-C might help soil microbes to overcome the food shortage caused by drought. The decrease in microbial biomass observed in our experiment and the concomitant decrease of SOM mineralization could contribute to the carbon sequestration potential of Mediterranean soils after biochar addition.

Anti-stiction coating for mechanically tunable photonic crystal devices.

A method to avoid the stiction failure in nano-electro-opto-mechanical systems has been demonstrated by coating the system with an anti-stiction layer of Al2O3 grown by atomic layer deposition techniques. The device based on a double-membrane photonic crystal cavity can be reversibly operated from the pull-in back to its release status. This enables to electrically switch the wavelength of a mode over ~50 nm with a potential modulation frequency above 2 MHz. These results pave the way to reliable nano-mechanical sensors and optical switches.

Temperature enhances the affinity of soil alkaline phosphatase to Cd.

Both elevated temperature and heavy metal contamination can have profound effects on microbial function and soil biogeochemical cycling. However, the interactive effects of heavy metal toxicity and temperature on microbial activity have been poorly understood. The aim of this study was to quantify the effect of temperature and cadmium (Cd) toxicity on alkaline phosphatase (ALP) produced by microbes to acquire phosphorus. To determine whether these effects were dependent on soil properties, we utilized 11 soil types from cropland throughout China. We measured ALP activities and kinetics across a temperature (17, 27, 37, and 47 °C) and Cd concentration gradient (0, 0.6, 5, 25, 50, 100, 200, 300, and 500 mg kg-1). We found that the half saturation constant (Km) and the velocity constant (k) of ALP increased nonlinearly with temperature across all soil types. However, the maximum reaction velocity (Vmax) increased linearly with temperature. Regardless of soil type and temperature, Cd had a non-competitive inhibitory mechanism. Soil pH, TOC, and clay content were the major factors controlling the affinity of ALP for Cd (Ki). The ecology dose (ED50) for Vmax and k, and Ki were negatively related to temperature, indicating that the toxicity of Cd on ALP is temperature-dependent. Additionally, higher temperatures led to more inhibition of Cd on ALP activity in alkaline soils than that in acidic and neutral soils. Our results suggest that global warming might accelerate the deficiency of available phosphorus in Cd contaminated soils due to higher inhibition of Cd on ALP activity, particularly in alkaline soils.