Soil Organic Matter Decomposition Research Articles

Impact of Climate on Soil Organic Matter Composition in Soils of Tropical Volcanic Regions Revealed by EGA-MS and Py-GC/MS.

Soil organic matter (SOM) crucially influences the global carbon cycle, yet its molecular composition and determinants are understudied, especially for tropical volcanic regions. We investigated how SOM compounds change in response to climate, vegetation, soil horizon, and soil properties and the relationship between SOM composition and microbial decomposability in Tanzanian and Indonesian volcanic regions. We collected topsoil (0-15 cm) and subsoil (20-40 cm) horizons (n = 22; pH: 4.6-7.6; SOC: 10-152 g kg-1) with undisturbed vegetation and wide mean annual temperature and moisture ranges (14-26 °C; 800-3300 mm) across four elevational transects (340-2210 m asl.). Evolved gas analysis-mass spectrometry (EGA-MS) documented a simultaneous release of SOM compounds and clay mineral dehydroxylation. Subsequently applying double-shot pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) at 200 and 550 °C, we detailed the molecular composition of topsoil and subsoil SOM. A minor portion (2.7 ± 1.9%) of compounds desorbed at 200 °C, limiting its efficacy for investigating overall SOM characteristics. Pyrolyzed SOM closely aligns with the intermediate decomposable SOM pool, with most pyrolysates (550 °C) originating from this pool. Pyrolysates composition suggests tropical SOM is mainly microbial-derived and subsoil contains more degraded compounds. Higher litter inputs and attenuated SOM decomposition due to cooler temperatures and lower soil pH (<5.5) produce less-degraded SOM at higher elevations. Redundancy analyses revealed the crucial role of active Al/Fe (oxalate-extractable Al/Fe), abundant in low-temperature/high-moisture conditions, in stabilizing these less-degraded components. Our findings provide new insights into SOM molecular composition and its determinants, critical for understanding the carbon cycle in tropical ecosystems.

Shifts in controls and abundance of particulate and mineral-associated organic matter fractions among subfield yield stability zones

Abstract. Spatiotemporal yield heterogeneity presents a significant challenge to agricultural sustainability efforts and can strain the economic viability of farming operations. Increasing soil organic matter (SOM) has been associated with increased crop productivity, as well as the mitigation of yield variability across time and space. Observations at the regional scale have indicated decreases in yield variability with increasing SOM. However, the mechanisms by which this variability is reduced remain poorly understood, especially at the farm scale. To better understand the relationship between SOM and yield heterogeneity, we examined its distribution between particulate organic matter (POM) and mineral-associated organic matter (MAOM) at the subfield scale within nine farms located in the central United States. We expected that the highest SOM concentrations would be found in stable, high-yielding zones and that the SOM pool in these areas would have a higher proportion of POM relative to other areas in the field. In contrast to our predictions, we found that unstable yield areas had significantly higher SOM than stable yield areas and that there was no significant difference in the relative contribution of POM to total SOM across different yield stability zones. Our results further indicate that MAOM abundance was primarily explained by interactions between crop productivity and edaphic properties such as texture, which varied amongst stability zones. However, we were unable to link POM abundance to soil properties or cropping system characteristics. Instead, we posit that POM dynamics in these systems may be controlled by differences in decomposition patterns between stable and unstable yield zones. Our results show that, at the subfield scale, increasing SOM may not directly confer increased yield stability. Instead, in fields with high spatiotemporal yield heterogeneity, SOM stocks may be determined by interactive effects of topography, weather, and soil characteristics on crop productivity and SOM decomposition. These findings suggest that POM has the potential to be a useful indicator of yield stability, with higher POM stocks in unstable zones, and highlights the need to consider these factors during soil sampling campaigns, especially when attempting to quantify farm-scale soil C stocks.

The effects of elevated CO2 and temperature on soil organic carbon and total nitrogen contents and mineralization in the 0 to 50 cm paddy soil layer were masked by different land use history

Global warming can accelerate soil organic matter (SOM) decomposition resulting in faster carbon loss and positive climate-C feedback. Previous studies on response of SOM decomposition to climate change mainly focus on plow soil layer. However, the effects of elevated CO2 and soil warming on soil organic carbon (SOC) and total nitrogen (TN) contents and mineralization are rarely studied in subsoil layer. In this study, soil samples were collected from the 0–50-cm paddy soil layer of the Tsukuba free-air CO2 enrichment experimental site with elevated CO2 (+200 ppm) and soil warming (+2 °C), Japan, after 5-year rice growth season. The amounts of SOC, TN, δ13C, and δ15N were analyzed. A 4-week anaerobic incubation experiment was conducted to measure C decomposition and N mineralization potentials. Due to the intrinsic variation in SOC and TN contents in soil layers and fields, the effects of elevated CO2 and soil warming on C decomposition and N mineralization potentials could not be determined here. However, the effect of elevated CO2 on δ13C was only found in 0‒10-cm soil layer. In the 0–50-cm soil profiles, significant correlations were observed among SOC and TN, δ13C and δ15N, decomposed C and mineralized N, and δ13C in decomposed C. The variables associated with soil C and N pools, and dynamics showed large spatial heterogeneity within paddy field, due to variation in the original land use history. Therefore, great caution should be exercised when evaluating the effects of elevated CO2 and temperature on SOM decomposition and sequestration in paddy soil profiles.

Soil Ecological Stoichiometric Characteristics and Influencing Factors of Degraded Alpine Grassland in Northwest Sichuan

Alpine grasslands are important ecosystems providing a variety of ecosystem services. However, alpine grassland degradation poses significant threats impacting soil health, stabilization and soil ecosystem function. This study aims to investigate the soil ecological stoichiometric characteristics and influencing factors in alpine grasslands, to find the primary contributing factors in soil degradation process. Soil samples were collected from alpine grassland areas with varying degrees of degradation, including non-, lightly, moderately and severely degraded (ND, LD, MD, SD). Soil characteristics including soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), available nitrogen (AN), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) were measured. The results revealed that soil TN, N:P ratios and C:P ratios were below the average level of China’s soil, while C:N ratio were above the average. With increasing aggravation of grassland degradation, SOC, TP, AN, MBN and MBC significantly decreased. Correlation were observed between SOC and C:N ratios as well as C:P ratios in alpine grassland with different degradation degrees (P &lt; 0.05). The C:N ratios in degraded grasslands were lower than those in ND grasslands but higher than the average level of China’s soil. Additionally, the N:P and C:P ratios of LD and MD were significantly higher than those of ND, but lower than the China’s soil average level. In conclusion, soil degradation in alpine grasslands is associated with lower TN contents, higher C:N ratios, and lower N:P ratios, which can impact soil organic matter decomposition and act as plant growth restriction factor. This study provides comprehensive insights into the ecological stoichiometry of alpine grasslands, understanding these factors is essential for the sustainable management of alpine grasslands and restoration strategies for the ecosystem services.

Input of high-quality litter reduces soil carbon losses due to priming in a subtropical pine forest

To date, it is unclear how differences in litter quality affect soil organic matter (SOM) decomposition through a phenomenon called 'priming effects' (PEs), especially for low-fertility forest soils under field conditions. Here, the effects of low- and high-quality leaf litter on PE and microbial metabolism of litter-derived carbon (C) were explored in a low-fertility pine (Pinus massoniana) plantation. A 185-day in situ incubation experiment was carried out by adding two 13C-labeled leaf litters to the pine soil—a low-quality (high lignin: nitrogen ratio) litter sourced from pine and a broadleaved species Schima superba produced high-quality (low lignin: nitrogen ratio) litter. To determine the key microbial groups contributing to PEs, the abundance of 13C-labeled litter enrichment in soil phospholipid fatty acids (13C-PLFAs) was quantified. We found that high-quality litter decomposed more rapidly than low-quality litter, with both litter-derived CO2 efflux reaching a plateaued level during the experimental period. Low-quality litter induced net positive PEs, while high-quality litter induced net negative PEs during the litter decomposition processes. The 13C-PLFAs results showed that bacterial groups governed the negative PEs induced by high-quality litter, whereas fungal communities targeted the positive PEs induced by low-quality litter. Random forest model and variation partitioning analysis demonstrated that the direction and magnitude of PEs were driven by litter-induced changes in key microbial groups rather than the structure of the microbial community. Our results demonstrate that microorganisms preferentially utilized litter-derived C in high-quality litter treatment and SOM in low-quality litter treatment, respectively. In contrast to low-quality litter, adding high-quality litter promoted the microbial metabolism of litter-derived C, reducing SOM decomposition (strong negative PEs). Taken together, this study provides isotope-based suggestions for the improvement of degraded pine forests—introducing tree species that produce high-quality litter may benefit soil C sequestration by reducing soil C losses due to PE in nutrient-poor pine forests.

Optimal enzyme allocation leads to the constrained enzyme hypothesis: the Soil Enzyme Steady Allocation Model (SESAM; v3.1)

Abstract. Describing the coupling of nitrogen (N), phosphorus (P), and carbon (C) cycles of land ecosystems requires understanding microbial element use efficiencies of soil organic matter (SOM) decomposition. These efficiencies are studied by the Soil Enzyme Steady Allocation Model (SESAM) at the decadal scale. The model assumes that the soil microbial communities and their element use efficiencies develop towards an optimum where the growth of the entire community is maximized. Specifically, SESAM approximated this growth optimization by allocating resources to several SOM-degrading enzymes proportional to the revenue of these enzymes, called the Relative approach. However, a rigorous mathematical treatment of this approximation has been lacking so far. Therefore, in this study we derive explicit formulas of enzyme allocation that maximize the total return from enzymatic processing, called the Optimal approach. Further, we derive another heuristic approach that prescribes the change of allocation without the need of deriving a formulation for the optimal allocation, called the Derivative approach. When comparing predictions across these approaches, we found that the Relative approach was a special case of the Optimal approach valid at sufficiently high microbial biomass. However, at low microbial biomass, it overestimated allocation to the enzymes having lower revenues compared to the Optimal approach. The Derivative-based allocation closely tracked the Optimal allocation. These findings increase our confidence in conclusions drawn from SESAM studies. Moreover, the new developments extend the range of conditions at which valid conclusions can be drawn. Further, based on these findings we formulated the constrained enzyme hypothesis. This hypothesis provides a complementary explanation why some substrates in soil are preserved over decades, although they are often decomposed within a few years in incubation experiments. This study shows how optimality considerations lead to simplified models, new insights, and new hypotheses. This is another step in deriving a simple representation of an adaptive microbial community, which is required for coupled stoichiometric C–N–P dynamic models that are aimed to study decadal processes beyond the ecosystem scale.

Warming reduces soil CO2 emissions but enhances soil N2O emissions: A long-term soil transplantation experiment

Climate warming can accelerate soil organic matter decomposition and stimulate soil CO2 and N2O emissions. However, long-term climate warming and land-use changes in relatively high-latitude regions on soil CO2 and N2O emissions remain largely unexplored, posing challenges to climate change research. Therefore, we conducted a long-term soil transplant experiment (8 years) across three relatively high-latitude northeastern regions in China to study the impacts of climate warming and land-use changes (from cropland to grassland) on soil CO2 and N2O emissions. As the temperature increased by 3 °C and 5 °C, the soil CO2 emissions from cropland were reduced by 59.07% and 56.87%, respectively, and those from grassland were reduced by 17.11% and 10.62%, respectively. The experiment duration, soil C storage, soil microbial abundance and soil moisture may be the main factors that explain why warming did not stimulate soil CO2 emissions. Soil N2O emissions increased by 76.57% in cropland and 263.81% in grassland as the temperature increased by 5 °C. Higher soil CO2 and N2O emissions were observed in grassland compared to cropland. Warming promoted aboveground plant biomass and indirectly promoted soil N2O emissions, particularly in grassland. The effects of long-term warming on soil CO2 and N2O emissions exhibited contrasting patterns, with CO2 emissions in relatively high-latitude and cold regions showing sensitivity to climate warming. When taking strategies to enhance soil C sequestration, consideration should be given to whether these strategies will be offset by stimulating soil N2O emissions, which is crucial for mitigating global warming. Overall, the impacts of long-term natural field warming and land-use changes on soil CO2 and N2O emissions and associated controls provide new insights for mitigating climate change.

Interaction between ectomycorrhizal and ericoid mycorrhizal plants decelerates stable soil organic matter decomposition

Boreal forests are N-limited ecosystems storing globally significant amounts of carbon (C) belowground as soil organic matter (SOM). The significant role of mycorrhizal fungi, both ericoid (ERM) and ectomycorrhizal (ECM) in decomposition and building up SOM has been proposed, but it is still largely unknown how these two types of mycorrhiza interact in terms of SOM changes. Here we try to elucidate the combined effect of these mycorrhizal types on the SOM decomposition and accumulation in a pot study with ECM-pine (Pinus sylvestris L.) and ERM-heather (Calluna vulgaris L.). Experimental design included plants growing alone or in a mixture, and a non-planted control. In contrast to the mixture, heather growing alone exerted higher biomass, higher uptake of N from stable SOM pool, slightly higher microbial biomass C and fungal biomass. Moreover, heather soil had the highest dissolved organic carbon and nitrogen. On the contrary, mixed cultures showed lower growth of heather and stable SOM decomposition. Our results suggest that interaction between ERM and ECM plants may lead to stable SOM accumulation in boreal forest soils.

Nutrient supplementation changes chemical composition of soil organic matter density fractions in desert steppe soil in northern China

The influence of reactive nitrogen (N) and phosphorus (P) supplementation on ecosystem dynamics of soil organic matter (SOM) shows extensive variations. The underlying mechanisms of regulation of the chemical composition and dynamics of different SOM density fractions (DFs) in aggregates in a desert steppe by N and P supplementation are unclear. Here, the chemical composition and organic carbon (C) and N dynamics of various SOM DFs under N and P addition were assessed. Surface soil samples taken at 0–10 cm depth were obtained from 4-year (2017–2021) experiments under four conditions, namely N treatment, P treatment, combined N and P treatment (NP), and no nutrient supplementation (CK), in a desert steppe located in northern China. Nutrient supplementation significantly increased (P < 0.05) SOM content by 8.89–35.4%; however, the total N content remained constant. N addition mainly increased SOM content in the macroaggregates (>0.25 mm), while P enhanced SOM in microaggregates (0.25–0.053 mm) and silt-clay (<0.053 mm). The fine particulate organic matter (fPOM) proportion was increased significantly (P < 0.05) by 18.4% and 16.4% in macro- and microaggregates under N addition, respectively; P addition mainly enhanced mineral-associated SOM (mSOM) proportion in aggregates. N supplementation remarkably enhanced (P < 0.05) fPOM’s organic C content by 27.3% and 32.0%, and N content by 40.9% and 145.7% in macro- and microaggregates, respectively. Single N and P addition promoted the enrichment of labile and resistant organic components in light fraction (LF), respectively. N promoted the enrichment of stable organic components in the mSOM of microaggregates. Nutrient inputs drive mSOM formation through the interaction of carboxyl-C and mineral surface. Based on a stronger δ13C and δ15N signal, N addition enhanced SOM decomposition in aggregates. Nutrient supplementation promoted SOM accumulation through the formation of more stable old C in POM and silt-clay. Our findings suggest that SOM accumulation in desert steppe probably increases following nutrient addition, but the mechanism is different through which N or P enrichment affects soil dynamics and chemical composition of SOM DFs in desert steppe.

Unperforated film-covered planting contributes to improved film recovery rates and foxtail millet grain yields in sandy soils

Plastic film mulching improves the soil water content and temperature and, thus, contributes to enhanced grain yield in arid and semi-arid areas, such as Northwest China. However, in traditional film-covering methods, plastic films are difficult to recycle, causing environmental issues. Therefore, developing cultivation methods with enhanced film recovery rates is important for sustainable agricultural development. Here, we evaluated how the planting method affected the soil temperature, water content, film recovery rate, and grain yield by applying the following three planting patterns to the traditional crop, foxtail millet, in 2021–2022: no plastic film mulching (NP), plastic film mulching (MP), and planting on the film edge (PFE); in the latter, holes were not punched in the film and crops were planted approximately 5 cm from the film edge. The results for 2021 showed that the biomass ranged from 27.69 g to 33.76 g per plant, and the biomass was increased by 21.9% and 3.2% in PFE compared with NP and MP, respectively. However, in 2022, the biomass increased in PFE by 52.5% and 17.7% compared with NP and MP, respectively. In 2021, the highest grain yield was observed in PFE (2480 kg/hm2), followed by MP (2470 kg/hm2) and NP (2343 kg/hm2); in 2022, a significantly higher grain yield was observed in PFE than that in MP and NP. Although the soil temperature increased in PFE, it was not as high as in MP. The relatively higher soil temperature increased the root growth process, stimulated the production of root exudates (acetic acid and citric acid), and increased the soil enzyme (sucrase and urease) activity. Increases in organic acids and soil enzymes assisted in the decomposition of soil organic matter and induced relatively higher levels of available nutrients, such as nitrogen and phosphorus, and the higher root reuse rates contributed to higher grain yields. In addition, fewer holes were punched in the film of the PFE model, which improved film recovery, and the recovery rate of PFE was higher than that of MP. These results indicate that the proposed unperforated film-covered planting pattern is suitable for millet production in sandy soil.

Manganese and soil organic carbon stability on a Hawaiian grassland rainfall gradient

Manganese (Mn) is a possibly critical yet poorly understood element controlling soil carbon (C) stocks. In temperate forests, Mn availability correlates strongly with organic C decay, but we know little about its role in soil organic matter decomposition in most terrestrial environments. In this study, we evaluate Mn in grassland C dynamics along a rainfall gradient in Hawaii. We measured Mn, organic matter, and microbial enzyme activities along the rainfall gradient to evaluate relationships among Mn oxidation state, chemical/biological reactivity, and soil C turnover. Neither Mn abundance nor its oxidation state are strong predictors of organic C instability along the grassland gradient. We also used an incubation experiment to investigate how dissolved organic C and CO2 release from the grassland soil respond to increased Mn bioavailability. We found that Mn availability did not correlate with soil C instability; Mn additions corresponded with lower dissolved organic C and CO2 fluxes from soils than did additions of deionized water. Mn availability may not predict soil C stability as well as previously thought.

Effect of temperature, water availability, and soil properties on soil CO2 efflux in beech-fir forests along the Carpathian Mts

Carpathian Mountain beech-fir forests are exposed to severe pressures related to climate change. Alterations in soil respiration, the main source of CO2 emissions from forest ecosystems into the atmosphere, could potentially impact the future carbon balance of these ecosystems. We performed soil CO2 efflux measurements along the whole Carpathian arc on eight selected locations during two separate campaigns in 2022 and 2023. The correlations between soil CO2 efflux and various climatic, micrometeorological, and soil conditions were evaluated as well as the impact of canopy gaps at each site.Soil CO2 efflux varied between the two campaigns primarily due to fluctuations in soil water content, while differences among the sites were more influenced by soil carbon and nitrogen content. The presence of a canopy gap did not consistently affect soil CO2 efflux; in some sites, it was lower in the gap than under a closed canopy, while in others, the opposite trend was observed. In conclusion, soil CO2 efflux measured at eight sites was closely associated with soil properties rather than with climate or micrometeorological parameters. Therefore, the potential influence of climate on the input of new organic matter through forest productivity and species composition will play a significant role in the decomposition and storage of soil organic matter.

Modelled forest ecosystem carbon–nitrogen dynamics with integrated mycorrhizal processes under elevated CO2

Abstract. Almost 95 % of all terrestrial plant species form symbioses with mycorrhizal fungi that mediate plant–soil interactions: mycorrhizae facilitate plant nitrogen (N) acquisition and are, therefore, vital for plant growth, but they also build a pathway for plant-assimilated carbon (C) into the rhizosphere. Therefore, mycorrhizae likely play an important role in shaping the response of ecosystems to environmental changes such as rising atmospheric carbon dioxide (CO2) concentrations, which can increase plant N demand and the transfer of plant C assimilation to the soil. While the importance of mycorrhizal fungi is widely recognised, they are rarely represented in current terrestrial biosphere models (TBMs) explicitly. Here, we present a novel, dynamic plant–mycorrhiza–soil model as part of the QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system) TBM. This new model is based on mycorrhizal functional types that either actively mine soil organic matter (SOM) for N or enhance soil microbial activity through increased transfer of labile C into the rhizosphere, thereby (passively) priming SOM decomposition. Using the Duke Free-Air CO2 Enrichment (FACE) experiment, we show that mycorrhizal fungi can have important effects on projected SOM turnover and plant nutrition under ambient as well as elevated-CO2 treatments. Specifically, we find that including enhanced active mining of SOM for N in the model allows one to more closely match the observations with respect to observed decadal responses of plant growth, plant N acquisition and soil C dynamics to elevated CO2, whereas a simple enhancement of SOM turnover by increased below-ground C transfer of mycorrhizae is unable to replicate the observed responses. We provide an extensive parameter uncertainty study to investigate the robustness of our findings with respect to model parameters that cannot readily be constrained by observations. Our study points to the importance of implementing mycorrhizal functionalities in TBMs as well as to further observational needs to better constrain mycorrhizal models and to close the existing major knowledge gaps in actual mycorrhizal functioning.

Moisture and temperature effects on the radiocarbon signature of respired carbon dioxide to assess stability of soil carbon in the Tibetan Plateau

Abstract. Microbial release of CO2 from soils to the atmosphere reflects how environmental conditions affect the stability of soil organic matter (SOM), especially in massive organic-rich ecosystems like the peatlands and grasslands of the Qinghai–Tibetan Plateau (QTP). Radiocarbon (14C) is an important tracer of the global carbon cycle and can be used to understand SOM dynamics through the estimation of time lags between carbon fixation and respiration, often assessed with metrics such as age and transit time. In this study, we incubated peatland and grassland soils at four temperature (5, 10, 15 and 20 °C) and two water-filled pore space (WFPS) levels (60 % and 95 %) and measured the 14C signature of bulk soil and heterotrophic respired CO2. We compared the relation between the Δ14C of the bulk soil and the Δ14CO2 of respired carbon as a function of temperature and WFPS for the two soils. To better interpret our results, we used a mathematical model to analyse how the calculated number of pools, decomposition rates of carbon (k), transfer (α) and partitioning (γ) coefficients affect the Δ14C bulk and Δ14CO2 relation, with their respective mean age and mean transit time. From our incubations, we found that 14C values in bulk and CO2 from peatland were significantly more depleted (old) than from grassland soil. Our results showed that changes in temperature did not affect the Δ14C values of heterotrophic respired CO2 in either soil. However, changes in WFPS had a small effect on the 14CO2 in grassland soils and a significant influence in peatland soils, where higher WFPS levels led to more depleted Δ14CO2. In our models, the correspondence between Δ14C, age and transit time highly depended on the internal dynamics of the soil (k, α, γ and number of pools) as well as on model structure. We observed large differences between slow and fast cycling systems, where low values of decomposition rates modified the Δ14C values in a non-linear pattern due to the incorporation of modern carbon (14C bomb) in the soil. We concluded that the stability of carbon in the peatland and grassland soils of the QTP depends strongly on the direction of change in moisture and how it affects the rates of SOM decomposition, while temperature regulates the number of fluxes. Current land cover modification (desiccation) in Zoigê peatlands and climate change occurring on the QTP might largely increase CO2 fluxes along with the release of old carbon to the atmosphere potentially shifting carbon sinks into sources.

Long-term fertilization differentially increased the CAZyme encoding genes responsible for soil organic matter decomposition under winter wheat on the Loess Plateau of China

Long-term fertilization greatly affects soil organic matter (SOM) decomposition in cropping systems, but less information was related to carbohydrate active enzyme (CAZyme) encoding genes in decomposing the components that derived from plant and microbial biomass. Using high-throughput metagenomic sequencing, the responses of CAZyme encoding genes to 35-yr fertilization were assessed in a winter wheat field on the Loess Plateau of China. Four treatments were included as chemical nitrogen fertilizer (N), manure (M), chemical nitrogen plus manure (NM), and control with no fertilization (CK). The results showed that the abundances of genes encoding auxiliary activities and glycosyl transferases were greater in N, and those encoding carbohydrate esterases and glycoside hydrolases were higher in NM than in other treatments. The abundance of genes encoding glycosyl hydrolases was lower in M than in other treatments. Compared to CK, long-term fertilization increased the abundances of CAZyme encoding genes in decomposing the SOM that derived from plant and bacteria biomass, but did not affect those in decomposing fungi-derived component. The Actinobacteria and Proteobacteria were the main phyla contributing to plant- and microbe-derived SOM decomposition. Mantel test indicated that the abundance of CAZyme encoding genes for plant-derived SOM decomposition was mainly affected by the content of microbial biomass nitrogen, while that for bacteria-derived SOM decomposition was associated with soil carbon and nitrogen fractions. Overall, long-term fertilization improved the CAZyme encoding genes in decomposing SOM especially derived from plant and bacteria biomass. These findings help to better understand the decomposition potential of SOM in cropping systems.

Long-term tropospheric ozone pollution disrupts plant-microbe-soil interactions in the agroecosystem.

Tropospheric ozone (O3 ) threatens agroecosystems, yet its long-term effects on intricate plant-microbe-soil interactions remain overlooked. This study employed two soybean genotypes of contrasting O3 -sensitivity grown in field plots exposed elevated O3 (eO3 ) and evaluated cause-effect relationships with their associated soil microbiomes and soil quality. Results revealed long-term eO3 effects on belowground soil microbiomes and soil health surpass damage visible on plants. Elevated O3 significantly disrupted belowground bacteria-fungi interactions, reduced fungal diversity, and altered fungal community assembly by impacting soybean physiological properties. Particularly, eO3 impacts on plant performance were significantly associated with arbuscular mycorrhizal fungi, undermining their contribution to plants, whereas eO3 increased fungal saprotroph proliferation, accelerating soil organic matter decomposition and soil carbon pool depletion. Free-living diazotrophs exhibited remarkable acclimation under eO3 , improving plant performance by enhancing nitrogen fixation. However, overarching detrimental consequences of eO3 negated this benefit. Overall, this study demonstrated long-term eO3 profoundly governed negative impacts on plant-soil-microbiota interactions, pointing to a potential crisis for agroecosystems. These findings highlight urgent needs to develop adaptive strategies to navigate future eO3 scenarios.

ЭФФЕКТИВНОСТЬ ИСПОЛЬЗОВАНИЯ ОКУЧИВАЮЩИХ РАБОЧИХ ОРГАНОВ С МУЛЬЧИРУЮЩИМ РЕАКТИВНЫМ УСТРОЙСТВОМ В ГРЕБНЕВОЙ ТЕХНОЛОГИИ ВОЗДЕЛЫВАНИЯ КАРТОФЕЛЯ

An analysis of machines and equipment for hilling potato plantings is given, the timing of technological hilling operations is considered, starting from the pre-emergence period until the tops are closed in ridges and rows. The geometric shapes of the bed during the process of hilling potatoes are considered in the form of drawings according to the phases of development and height of the plants. To implement the task, a Hiller with a device for mulching the surface of the ridge is proposed, which allows you to keep the tuberous nest from overheating in hot weather, destroy germinating weeds and retain moisture in the ridge, it is proposed to be used to implement the task. This is a hiller with flaps, behind the body of which grinding devices are installed in the form of rotating disks with blade fingers mounted on an axis. A rod with a spring for copying the surface of the ridge by the mulching device is installed at an angle in the flaps of the hiller body with a pitch equal to twice the diameter of the fingers of the chopping device. It is noted that the use of the proposed hilling device makes it possible to perform interrow cultivation in one pass, combine the operation of destroying the pruned soil layer and crushing it, destroying weeds and mulching the surface of the ridge. The results of a study of the use of an experimental hiller in practice show that in the created fine-lumpy ridge layer from the soil, it is saturated with air oxygen, which accelerates the anaerobic and aerobic processes occurring in it, contributing to the accelerated decomposition and mineralization of soil organic matter. A comparison of the performance indicators of serial and experimental hillers has been carried out. It has been established that the experimental hiller allows the cultivator to operate at increased speeds of up to 2.6 m/s and to create a cover of the ridge with a mulching layer of soil of 3–4 cm, with the size of lumps on the surface layer of the ridge of 1–1.5 cm, to destroy weed seedlings in comb up to 95%. During the research, it was found that the effectiveness of the introduction of an experimental hiller will increase potato yields by 5-7%.

Soil nitrogen availability mediates the positive effects of intercropping on soil organic carbon at global scales

Intercropping is an effective cultivation practice to develop sustainable agroecosystems and increase soil organic carbon (SOC) and nitrogen (N) with rich crop diversity. With increased duration, the changes in soil N availability might affect microbial and plant growth and consequently regulate the intercropping effects on SOC sequestration. However, the response of intercropping effects on SOC components to soil N availability has been poorly explored. In this study, we constructed a global database with 939 paired data (intercropping vs. monoculture) from 60 publications. We found that intercropping increased SOC (by 7.94%), microbial biomass carbon (MBC, by 23.73%), particulate organic carbon (POC, by 23.27%), and dissolved organic carbon (DOC, by 16.46%) compared to monoculture. The intercropping effects (percentage change, %) on SOC content strongly depends on soil N availability (soil C: N) and the interactions with duration and crop types. In N-limited soils (soil C: N > 15), intercropping increased SOC and POC contents by 14% and 31%, respectively, which were 2–3 times higher than those in N-rich soils (soil C: N < 15). It implies higher intercropping effects in more N-limited soils. In addition, intercropping increased MBC:SOC by 63% in N-limited but not in N-rich soils, indicating greater contributions of microbial-derived C to SOC storage in N-limited but not in N-rich soils. This might be attributed to that the stimulated microbial decomposition of soil organic matter counterbalanced the microbial-derived C accumulation in N-rich soils. Taken together, these results indicate that soil N availability regulates the intercropping effects on SOC content and the contributions of microbial-derived C to SOC storage. Overall, these findings highlight the importance of soil N availability on SOC content with intercropping, implying that intercropping is a suitable agricultural approach especially in N-limited soils and nutrient management should be carefully considered in long-term intercropping experiments.

Effects and regulation Mechanisms of Phosphorus Fertilizer on Soil Carbon Cycle

This paper reviews the effects and regulation mechanisms of phosphorus fertilizer on soil carbon cycle, which is an important process for soil fertility, productivity, and climate change and introduces the background, significance, main pathways, mechanisms, influencing factors, research progress and challenges. The paper shows that phosphorus fertilizer can affect soil carbon cycle through various pathways, such as affecting plant productivity and carbon allocation, soil organic matter decomposition and mineralization, soil microbial community and function, and soil aggregate formation and stability. The paper also shows that the effects of phosphorus fertilizer on soil carbon cycle are influenced by many factors, such as the type, amount, application method and time of phosphorus fertilizer, and the soil type, climate condition, vegetation type and management measures. The paper concludes that the effects of phosphorus fertilizer on soil carbon cycle are both positive and negative, direct and indirect, short-term and long-term, local and global, forming a complex impact network. The paper suggests that more research is needed to clarify the mechanisms, interactions and feedbacks of the effects of phosphorus fertilizer on soil carbon cycle, and to develop effective models and indicators to evaluate and predict the effects of phosphorus fertilizer on soil carbon cycle. The paper also suggests that rational application of phosphorus fertilizer and scientific management of soil carbon cycle are important for improving crop phosphorus use efficiency, reducing excessive application of phosphorus fertilizer, protecting water resources and soil quality, and mitigating climate change.

Emergent temperature sensitivity of soil organic carbon driven by mineral associations

Soil organic matter decomposition and its interactions with climate depend on whether the organic matter is associated with soil minerals. However, data limitations have hindered global-scale analyses of mineral-associated and particulate soil organic carbon pools and their benchmarking in Earth system models used to estimate carbon cycle–climate feedbacks. Here we analyse observationally derived global estimates of soil carbon pools to quantify their relative proportions and compute their climatological temperature sensitivities as the decline in carbon with increasing temperature. We find that the climatological temperature sensitivity of particulate carbon is on average 28% higher than that of mineral-associated carbon, and up to 53% higher in cool climates. Moreover, the distribution of carbon between these underlying soil carbon pools drives the emergent climatological temperature sensitivity of bulk soil carbon stocks. However, global models vary widely in their predictions of soil carbon pool distributions. We show that the global proportion of model pools that are conceptually similar to mineral-protected carbon ranges from 16 to 85% across Earth system models from the Coupled Model Intercomparison Project Phase 6 and offline land models, with implications for bulk soil carbon ages and ecosystem responsiveness. To improve projections of carbon cycle–climate feedbacks, it is imperative to assess underlying soil carbon pools to accurately predict the distribution and vulnerability of soil carbon.