Fertilization managements mitigate microbial carbon and nitrogen limitations while preserving soil organic carbon in croplands compared to grasslands: A meta-analysis.

Global warming can differentially alter ecosystem carbon, nitrogen, and phosphorus dynamics, regulating the balance between soil substrate supply and microbial metabolic demand. However, empirical research on how warming influences microbial resource limitation along the soil profile remains limited, particularly in tropical–subtropical regions. Here, we investigated vertical variations (0–60 cm soil layers) in microbial resource limitation and their corresponding responses to warming in subtropical forests in southern China, using a soil warming experiment with heating cables (+4 °C) and enzymatic stoichiometry. Alleviated carbon limitation but aggravated nutrient (nitrogen and phosphorus) limitation for microbial metabolism was observed along soil profiles, regardless of warming treatment. Among different soil depths, warming mitigated microbial carbon limitation conditions and exacerbated microbial nutrient limitation conditions in a 0–10 cm surface layer, but had no significant effect below the 20 cm soil depth. Moreover, vertical variations in microbial nitrogen limitation were primarily regulated by soil moisture and the fungal–bacterial ratio regardless of warming treatment. In contrast, vertical changes in microbial carbon and phosphorus limitation were driven by soil moisture and the fungal–bacterial ratio under ambient conditions, but by the soil carbon–phosphorus ratio and the fungal–bacterial ratio after warming. For surface soil, warming effects on microbial carbon, nitrogen, and phosphorus limitation were mainly explained by microbial biomass stoichiometry and the fungal–bacterial ratio. Overall, warming had diverse effects on microbial resource limitation along the entire soil profile. These findings provide important insights for accurately predicting biogeochemical cycles under global warming scenarios.

Soil copper (Cu) pollution is a serious environmental risk in the Panax notoginseng planting area. However, the effect of Cu on soil microbial metabolism and nutrient cycling in this area remains unknown. Therefore, Biolog ECO-plate and enzyme stoichiometry methods were utilized in this study to investigate the impact of exogenous Cu (control: 0 mg·kg-1; Cu100: 100 mg·kg-1; Cu400: 400 mg·kg-1; and Cu600: 600 mg·kg-1) on the metabolic function of soil microbial and nutrient limitation in the P. notoginseng soil. The results indicated that Cu100 significantly increased soil organic carbon (SOC), total phosphorus (TP), soil C:N, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) 9.89%, 15.65%, 17.91%, 61.87%, and 90.56% higher than the control, respectively. Moreover, the carbon source utilization ratio of carbohydrates, amino acids, and amphiphilic compounds of Cu100 also increased by 7.16%, 25.47%, and 84.68%, respectively, compared with the control. The activities of β-1,4-glucosidase, cellobiohyrolase, leucine amino peptidase, β-1,4-N-acetylglucosaminidase, and phosphatase significantly decreased with increasing Cu concentration. Soil enzyme stoichiometry showed that all treatments were limited by nitrogen (vector angle < 45°; 19.045-22.081). Cu600 led to the lowest carbon limitation (1.798) and highest carbon use efficiency (CUE:0.267). The PLS-SEM model also showed that MBC, MBN, MBP, and microbial diversity positively affected carbon and nitrogen limitation (0.654 and 0.424). Soil carbon, nitrogen, phosphorus, stoichiometric ratio, MBC, MBN, and MBP positively affected CUE (0.527 and 0.589). The microbial diversity index significantly negatively affected CUE (-1.490). Multiple linear stepwise regression analyses showed that CUE was mainly influenced by MBC, AP, C:P, and LAP. Thus, P. notoginseng soil can benefit soil microbial carbon and nitrogen limitations at low Cu concentrations. Clarifying the metabolic activity and nutritional status of microorganisms under Cu stress can provide some theoretical basis for realizing China's comprehensive and effective management and control policies for environmental risks from metals by 2035.

Excessive nitrogen fertilizer application is the main driving force threatening soil health and reducing multiple soil functions. The enhanced-efficiency nitrogen fertilizers （EENFs）, such as urease inhibitors （NBPT）, nitrification inhibitors （DCD）, and coated controlled-release urea （RCN）, have been proven to be effective measures for reducing nitrogen fertilizer application. However, the effects of EENFs on soil quality （SQI）, microbial metabolic characteristics, and soil ecosystem multifunctionality （EMF） and their internal relationships are still unclear. Therefore, based on the field positioning experiment started in 2019 by Pengyang Experimental Station of Guyuan City, Ningxia Hui Autonomous Region, we studied the effects of different fertilization strategies （no nitrogen fertilizer （N0）, mineral nitrogen fertilizer （N200）, DCD, NBPT, and RCN） on SQI, soil enzyme stoichiometry, and EMF under white plastic film mulching. The results revealed that： ① Compared with that under N0, N200 and EENFs increased soil total nitrogen （TN）, microbial biomass carbon （MBC）, and microbial biomass nitrogen （MBN） contents. Compared to the SQI of N0 and N200, that of NBPT and DCD significantly increased by 59.97%-104.78% and 43.28%-83.42%, respectively, while RCN showed no significant change. ②EENFs can alleviate microbial carbon and nitrogen limitations better than N200 and increase soil EMF by 21.97% -51.53%. ③ The MBC, MBN, available nitrogen （AN）, available phosphorus （AP）, and water content （SWC） of soil factors were the common main factors affecting microbial C limitation, N limitation, and soil EMF. Moreover, the improvement in soil quality and alleviating microbial C and N limitation were conducive to improving soil EMF. Overall, the NBPT and DCD application under white plastic film mulching can achieve a win-win situation of soil health and EMF in the short term, which can provide references for optimizing local fertilization management measures.

Soil microbial necromass carbon (MNC) is an important component of soil organic carbon (SOC) in croplands. Microbial communities contribute over 50% of the SOC in croplands through continuous turnover and the formation of necromass, which is characterized by its large scale and strong persistence. Agricultural production systems are widely influenced by human activities. There is still a lack of understanding regarding key issues such as the dynamics of MNC and SOC under management practices and their global distribution potential. In this study, we combined meta-analysis with machine learning methods, revealed the impact patterns of cropland management on soil MNC components and SOC. The results showed that the MNC storage reached the highest value of 5.93 Mg C ha&amp;#8315;&amp;#185; under the practice of mineral fertilizer combined with manure. The fungal necromass carbon storage in cropland soils is much higher than that of bacterial necromass carbon, which dominates the changes in microbially-derived organic carbon storage. Assessment results of global potential distribution patterns of MNC and SOC storage under management practices based on machine learning indicate that conservation tillage has the highest global carbon storage potential, reaching up to 2.58 Mg C ha&amp;#8315;&amp;#185; yr&amp;#8315;&amp;#185; and 3.55 Mg C ha&amp;#8315;&amp;#185; yr&amp;#8315;&amp;#185;. This study emphasizes the impact and importance of soil microorganisms in croplands as a driving force on SOC storage, accurately quantifies their response to management practices, and comprehensively evaluates the application potential of different management practices on a global scale, enhancing our understanding of the relationship patterns between MNC and SOC in agricultural systems.

Mapping the high-precision spatiotemporal dynamics of soil organic carbon (SOC) in croplands is crucial for enhancing soil fertility and carbon sequestration and ensuring food security. We conducted field surveys and collected 1121 soil samples from cropland in Changzhi, northern China, in 2010 and 2020. Random Forest (RF) models combined with 19 environmental covariates were used to map the topsoil (0–20 cm) SOC in 2010 and 2020, and uncertainty maps were used to calculate the dynamic changes in cropland SOC between 2010 and 2020. Finally, RF and Structural Equation Modeling (SEM) were employed to explore the effects of climate, vegetation, topography, soil properties, and agricultural management on SOC variation in croplands. Compared to the prediction model using only natural variables (RF_C), the model incorporating agricultural management (RF_A) significantly improved the simulation accuracy of SOC. The coefficient of determination (R2) increased from 0.77 to 0.85, while the Root Mean Square Error (RMSE) decreased from 1.74 to 1.53 g kg−1, and the Mean Absolute Error (MAE) was reduced from 1.10 to 0.94 g kg−1. The uncertainty in our predictions was low, with an average value of only 0.39–0.66 g kg−1. From 2010 to 2020, SOC in the Changzhi croplands exhibited an overall increasing trend, with an average increase of 1.57 g kg−1. Climate change, agricultural management, and soil properties strongly influence SOC variation. Mean annual precipitation (MAP), drainage condition (DC), and net primary productivity (NPP) were the primary drivers of SOC variability. Our findings highlight the effectiveness of agricultural management for predicting SOC in croplands. Overall, the study confirms that improved agricultural management has great potential to increase soil carbon stocks, which may contribute to sustainable agricultural development.

Responses of soil microbial resource limitation to multiple fertilization strategies

Assessments of the global carbon (C) cycle typically rely on simplified models which consider large areas as homogeneous in terms of the response of soils to land use or consider very broad land classes. For example, “cropland” is typically modelled as an aggregation of distinct practices and individual crops over large regions. Here, we use the process-based Rothamsted soil Carbon Model (RothC model), which has a history of being successfully applied at a global scale, to calculate attainable SOC stocks and C mineralization rates for each of c. 17,000 regions (combination of soil type and texture, climate type, initial land use and country) in the World, under near-past climate conditions. We considered 28 individual crops and, for each, multiple production practices, plus 16 forest types and 1 grassland class (total of 80 classes). We find that conversion to cropland can result in SOC increases, particularly when the soil remains covered with crop residues (an average gain of 12 t C/ha) or using irrigation (4 t C/ha), which are mutually reinforcing effects. Attainable SOC stocks vary significantly depending on the land use class, particularly for cropland. Common aggregations in global modelling of a single agricultural class would be inaccurate representations of these results. Attainable SOC stocks obtained here were compared to long-term experiment data and are well aligned with the literature. Our results provide a regional and detailed understanding of C sequestration that will also enable better greenhouse gas reporting at national level as alternatives to IPCC tier 2 defaults.

Mulching measures can regulate soil properties; however, little is known about the effects metabolic limitations on farmland during the key growth stages of broomcorn millet in multiple regions of the Loess Plateau. We conducted field experiments to compare three techniques: flat planting with no mulching (TP), ridge–furrow mulching system (RF), and plastic film mulching (PFM). Soil extracellular enzymatic stoichiometry and physicochemical properties of three growth periods (jointing, flowering, and maturity) of proso millet (Panicum miliaceum L.) were measured to investigate microbial metabolic limitations and the relationship with soil moisture, temperature, and nutrients in the three regions of the Loess Plateau (Guyuan city, Huining County, and Yulin city). The results show that compared with TP, both PFM and RF techniques increased soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (), and nitrate nitrogen () during the jointing period, but the levels decreased during the flowering period, and the activities of C‐, N‐, P‐acquiring enzymes were 29.02%, 33.68%, and 19.46% higher when using PFM, and 13.78%, 6.81%, and 6.52% higher when using RF. Meanwhile, RF treatment significantly increased the carbon metabolism limitation during the jointing, flowering, and maturity periods of proso millet in the three regions, and also improved the nitrogen metabolism limitation during the jointing and flowering periods of proso millet in the Huining and Yulin regions. Linear regression analysis showed that pH, SOC, and contents significantly affected carbon limitation, and nitrogen limitation was gradually alleviated with increases in SOC, TN, and contents in proso millet farmland soils. Partial least squares path modeling showed that soil moisture and nutrients differed significantly among the regions, and soil temperature positively regulated the soil nutrients. Mulching significantly improved the carbon limitation owing to increased soil temperature and moisture. These results provide important ideas for nutrient cycling and microbial metabolism of broomcorn millet farmland soil under mulching measures on the Loess Plateau.

Cover crops (CC) offer numerous benefits to agroecosystems, particularly in the realm of soil organic carbon (SOC) accrual and loss mitigation. However, uncertainties persist regarding the extent to which CCs, in co‐occurrence with environmental factors, influence SOC responses and associated C pools. We therefore performed a weighted meta‐analysis on the effects of CCs on the mineral‐associated organic carbon (MAOC), the particulate organic carbon (POC) and the microbial biomass carbon (MBC) pool compared to no CC cultivation in arable cropland. Our study summarized global research of comparable management, with a focus on climatic zones representative of Europe, such as arid, temperate and boreal climates. In this meta‐analysis, we included 71 independent studies from 61 articles published between 1990 and June 2023 in several scientific and grey literature databases. Sensitivity analysis was conducted and did not identify any significant publication bias. The results revealed that CCs had an overall statistically significant positive effect on SOC pools, increasing MAOC by 4.8% (95% CI: 0.6%–9.4%, n = 16), POC by 23.2% (95% CI: 13.9%–34.4%, n = 39) and MBC by 20.2% (95% CI: 11.7%–30.7%, n = 30) in the top soil, compared to no CC cultivation. Thereby, CCs feed into the stable as well as the more labile C pools. The effect of CCs on MAOC was dependent on soil clay content and initial SOC concentration, whereas POC was influenced by moderators such as CC peak biomass and experiment duration. For MBC, for example, clay content, crop rotation duration and tillage depth were identified as important drivers. Based on our results on the effects of CCs on SOC pools and significant moderators, we identified several research needs. A pressing need for additional experiments exploring the effects of CCs on SOC pools was found, with a particular focus on MAOC and POC. Further, we emphasize the necessity for conducting European studies spanning the north–south gradient. In conclusion, our results show that CC cultivation is a key strategy to promote C accrual in different SOC pools. Additionally, this meta‐analysis provides new insights into the state of knowledge regarding SOC pool changes influenced by CCs, offering quantitative summary results and shedding light on the sources of heterogeneity affecting these findings.

Mapping soil organic carbon and total nitrogen in croplands of the Corn Belt of Northeast China based on geographically weighted regression kriging model

Regulation of growth, sucrose storage and ion content in sugarcane cells, measured with suspension cells in continuous culture grown under nitrogen, phosphorus or carbon limitation

Understanding the characteristics and driving factors of soil carbon, nitrogen, phosphorus, and enzyme stoichiometry during land use/cover change is of great significance for assessing microbial nutrient restriction and sustainable land development during the process. China, the world’s largest tea producer, is witnessing a significant expansion of tea plantations into previously forested areas. We performed field sampling in three forest types with the area partially converted to tea plantations in Wuyishan National Park. We examined the changes in soil carbon (TC), nitrogen (TN), phosphorus (TP), and three kinds of extracellular enzyme activities, β-glucosidase (BG), β-n-acetylglucosidase (NAG), and acid phosphatase (ACP). By analyzing the enzyme stoichiometric ratio, vector length (VL), and vector angle (VA), the relative nutrient limitations of soil microorganisms were explored. The results showed that soil TC and TN decreased significantly (p &lt; 0.05), TP increased significantly, and soil carbon (C):nitrogen (N), carbon (C):phosphorus (P), and nitrogen (N):phosphorus (P) ratios decreased significantly after the conversion of forest land to tea plantation. Soil BG, NAG, and ACP contents decreased significantly (p &lt; 0.05). There were no significant differences in enzyme carbon:nitrogen ratios (EC/N), enzyme carbon:phosphorus ratios (EC/P), enzyme nitrogen:phosphorus ratios (EN/P), VL, or VA (p &gt; 0.05). Through the analysis of soil enzyme stoichiometry, it was found that forest soil was generally limited by P, which was, to some extent, relieved after the conversion to tea plantation. Redundancy analysis showed that TC, TN, and the C:N ratio were the main factors influencing enzyme activity and stoichiometry. These results indicated that land use/cover change had significant effects on soil nutrient status, enzyme activity, and stoichiometry. Soil enzyme activity is very sensitive to the changes in soil nutrients and can reflect the restriction of soil nutrients more accurately.

Ecoenzymatic stoichiometry reveals stronger microbial carbon and nitrogen limitation in biochar amendment soils: A meta-analysis

Straw return with fertilizer improves soil CO2 emissions by mitigating microbial nitrogen limitation during the winter wheat season

A quantitative review of the effects of residue removing on soil organic carbon in croplands