Nitrogen Application Timing and Levels Affect the Fate and Budget of Fertilizer Nitrogen in the Apple-Soil System.

This study aimed to determine the effects of the nitrogen (N) application period and level on the fate of fertilizer N and the contribution of N absorption and translocation to apple organ N. Two N application periods (labeled by the 15N tracer technique in spring and summer, represented by SP and SU, respectively) and three N levels (N0, MN, and HN) were used to determine the physiological indexes and aboveground, root, and soil 15N content of 4-year-old dwarf ('Red Fuji'/M9T337) and arborized ('Red Fuji'/Malus hupehensis Rehd.) apple trees. The results showed that HN led to shoot overgrowth, which was not conducive to the growth of the apple root system (root length, root tips, root surface area, and root volume) or the improvement of root activity. The contribution of soil N to apple organ N accounted for more than 50%, and the contribution of N application in summer to fruit N was higher than that in spring. Under HN treatment, the proportion of soil N absorbed by trees decreased, while that of fertilizer N increased; however, the highest proportion was still less than 50%, so apple trees were highly dependent on soil N. Under MN treatment, fertilizer N residue was similar to soil N consumption, and soil N fertility maintained a basic balance. Under HN treatment, fertilizer N residue was significantly higher than soil N consumption, indicating that excessive N application increased fertilizer N residue in the soil. Overall, the 15N utilization rate of arborized trees (17.33-22.38%) was higher than that of dwarf trees (12.89-16.91%). A total of 12.89-22.38% of fertilizer 15N was absorbed by trees, 30.37-35.41% of fertilizer 15N remained in the soil, and 44.65-54.46% of fertilizer 15N was lost. The 15N utilization rate and 15N residual rate of summer N application were higher than those of spring N application, and the 15N loss rate was lower than that of spring N application. High microbial biomass N (MBN) may be one of the reasons for the high N utilization rate and the low loss rate of N application in summer.

The effects of litter input and increased precipitation on soil microbial communities in a temperate grassland.

Global warming has contributed to shifts in precipitation patterns and increased plant productivity, resulting in a significant increase in litter input into the soils. The enhanced litter input, combined with higher levels of precipitation, may potentially affect soil microbial communities. This study aims to investigate the effects of litter input and increased precipitation on soil microbial biomass, community structure, and diversity in a temperate meadow steppe in northeastern China. Different levels of litter input (0%, +30%, +60%) and increased precipitation (0%, +15%, +30%) were applied over a three-year period (2015-2017). The results showed that litter input significantly increased the biomass of bacteria and fungi without altering their diversity, as well as the ratio of bacterial to fungal biomass. Increased precipitation did not have a notable effect on the biomass and diversity of bacteria and fungi, but it did increase the fungal-to-bacterial biomass ratio. However, when litter input and increased precipitation interacted, bacterial diversity significantly increased while the fungal-to-bacterial biomass ratio remained unchanged. These findings indicate that the projected increases in litter and precipitation would have a substantial impact on soil microbial communities. In energy-and water-limited temperate grasslands, the additional litter inputs and increased precipitation contribute to enhanced nutrient and water availability, which in turn promotes microbial growth and leads to shifts in community structure and diversity.

Effects of water stress on nutrients and enzyme activity in rhizosphere soils of greenhouse grape.

In grape cultivation, incorrect water regulation will lead to significant water wastage, which in turn will change soil structure and disrupt soil nutrient cycling processes. This study aimed to investigate the effects of different water regulation treatments [by setting moderate water stress (W1), mild water stress (W2), and adequate water availability (CK)] on soil physical-chemical properties and enzyme activity in greenhouse grape during the growing season. The result showed that the W2 treatment had a negative impact on the build-up of dissolved organic carbon (DOC), nitrate nitrogen (NO3-N), and available phosphorus (AP). Throughout the reproductive period, the W1 and W2 treatments decreased the soil's microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents, and MBC was more vulnerable to water stress. During the growth period, the trends of urease, catalase, and sucrase activities in different soil depth were ranked as 10-20 cm > 0-10 cm > 20-40 cm. The urease activity in 0-10 cm soil was suppressed by both W1 and W2 treatments, while the invertase activity in various soil layers under W1 treatment differed substantially. The W1 treatment also reduced the catalase activity in the 20-40 cm soil layer in the grape growth season. These findings suggested that W2 treatment can conserve water and enhance microbial ecology of greenhouse grape soils. Therefore, W2 treatment was the most effective water regulation measure for local greenhouse grape cultivation.

A metatranscriptomics strategy for efficient characterization of the microbiome in human tissues with low microbial biomass.

The high background of host RNA poses a major challenge to metatranscriptome analysis of human samples. Hence, metatranscriptomics has been mainly applied to microbe-rich samples, while its application in human tissues with low ratio of microbial to host cells has yet to be explored. Since there is no computational workflow specifically designed for the taxonomic and functional analysis of this type of samples, we propose an effective metatranscriptomics strategy to accurately characterize the microbiome in human tissues with a low ratio of microbial to host content. We experimentally generated synthetic samples with well-characterized bacterial and host cell compositions, and mimicking human samples with high and low microbial loads. These synthetic samples were used for optimizing and establishing the workflow in a controlled setting. Our results show that the integration of the taxonomic analysis of optimized Kraken 2/Bracken with the functional analysis of HUMAnN 3 in samples with low microbial content, enables the accurate identification of a large number of microbial species with a low false-positive rate, while improving the detection of microbial functions. The effectiveness of our metatranscriptomics workflow was demonstrated in synthetic samples, simulated datasets, and most importantly, human gastric tissue specimens, thus providing a proof of concept for its applicability on mucosal tissues of the gastrointestinal tract. The use of an accurate and reliable metatranscriptomics approach for human tissues with low microbial content will expand our understanding of the functional activity of the mucosal microbiome, uncovering critical interactions between the microbiome and the host in health and disease.

Plant-soil interactions alter nitrogen and phosphorus dynamics in an advancing subarctic treeline.

Treelines advance due to climate warming. The impacts of this vegetation shift on plant-soil nutrient cycling are still uncertain, yet highly relevant as nutrient availability stimulates tree growth. Here, we investigated nitrogen (N) and phosphorus (P) in plant and soil pools along two tundra-forest transects on Kola Peninsula, Russia, with a documented elevation shift of birch-dominated treeline by 70 m during the last 50 years. Results show that although total N and P stocks in the soil-plant system did not change with elevation, their distribution was significantly altered. With the transition from high-elevation tundra to low-elevation forest, P stocks in stones decreased, possibly reflecting enhanced weathering. In contrast, N and P stocks in plant biomass approximately tripled and available P and N in the soil increased fivefold toward the forest. This was paralleled by decreasing carbon (C)-to-nutrient ratios in foliage and litter, smaller C:N:P ratios in microbial biomass, and lower enzymatic activities related to N and P acquisition in forest soils. An incubation experiment further demonstrated manifold higher N and P net mineralization rates in litter and soil in forest compared to tundra, likely due to smaller C:N:P ratios in decomposing organic matter. Overall, our results show that forest expansion increases the mobilization of available nutrients through enhanced weathering and positive plant-soil feedback, with nutrient-rich forest litter releasing greater amounts of N and P upon decomposition. While the low N and P availability in tundra may retard treeline advances, its improvement toward the forest likely promotes tree growth and forest development.

[Effects of Straw Returning and Biochar Addition on Greenhouse Gas Emissions from High Nitrate Nitrogen Soil After Flooding in Rice-vegetable Rotation System in Tropical China].

In rice-vegetable rotation systems in tropical areas, a large amount of nitrate nitrogen accumulates after fertilization in the melon and vegetable season, which leads to the leaching of nitrate nitrogen and a large amount of N2O emission after the seasonal flooding of rice, which leads to nitrogen loss and intensification of the greenhouse effect. How to improve the utilization rate of nitrate nitrogen and reduce N2O emissions has become an urgent problem to be solved. Six treatments were set up [200 mg·kg-1 KNO3 (CK); 200 mg·kg-1 KNO3 + 2% biochar addition (B); 200 mg·kg-1 KNO3+1% peanut straw addition (P); 200 mg·kg-1 KNO3 + 2% biochar + 1% peanut straw addition (P+B); 200 mg·kg-1 KNO3 + 1% rice straw addition (R); 200 mg·kg-1 KNO3 + 2% biochar+1% rice straw addition (R+B)] and cultured at 25℃ for 114 d to explore the effects of organic material addition on greenhouse gas emissions and nitrogen use after flooding in high nitrate nitrogen soil. The results showed that compared with that in CK, adding straw or combining straw with biochar significantly increased soil pH (P<0.05). The B and P treatments significantly increased the cumulative N2O emissions by 41.6% and 28.5% (P<0.05), and the P+B, R, and R+B treatments significantly decreased the cumulative N2O emissions by 14.1%, 24.7%, and 36.7% (P<0.05), respectively. The addition of straw increased the net warming potential of greenhouse gases (NGWP). The addition of coir biochar significantly reduced the effect of straw on NGWP (P<0.05). The combined application of straw and biochar decreased NGWP, and P+B significantly decreased NGWP, but that with R+B was not significant (P>0.05). Adding straw or biochar significantly increased soil microbial biomass carbon (MBC) (P<0.05), and that of P+B was the highest (502.26 mg·kg-1). The combined application of straw and biochar increased soil microbial biomass nitrogen (MBN), and that of P+B was the highest. The N2O emission flux was negatively correlated with pH (P<0.01) and positively correlated with NH4+-N and NO3--N (P<0.01). The cumulative emission of N2O was negatively correlated with MBN (P<0.05). There was a significant negative correlation between NO3--N and MBN (P<0.01), indicating that the reduction in NO3--N was likely to be held by microorganisms, and the increase in the microbial hold of NO3--N also reduced N2O emission. In conclusion, the combined application of peanut straw and coconut shell biochar could significantly inhibit N2O emission and increase soil MBC and MBN, which is a reasonable measure to make full use of nitrogen fertilizer, reduce nitrogen loss, and slow down N2O emission after the season of Hainan vegetables.

Response of maize yield and nitrogen recovery efficiency to nitrogen fertilizer application in field with various soil fertility.

Appropriate nitrogen (N) management system is essential for effective crop productivity and minimizing agricultural pollution. However, the underlying mechanistic understanding of how N fertilizer regulates crop yield via soil properties in soils with different fertilities remains unresolved. Here, we used a field experiment that spanned 3 cropping seasons to evaluate the grain yield (GY), aboveground biomass and N recovery efficiency (NRE) after treatment with five N fertilizer application rates (N0, N75, N112, N150, and N187) in soils with three levels of fertility. Our results indicated that the highest GY across low, moderate, and high fertility soils were 1.5 t hm-2 (N150), 4.9 t hm-2 (N187), and 5.4 t hm-2 (N112), respectively. The highest aboveground biomass and NRE were observed at N150 for all three levels of soil fertility, while only the N uptake by aboveground biomass of low and high fertility soils decreased at N187, confirming that excessive N fertilization results in a further decline in crop N uptake. The relationship between GY, NRE and N fertilizer application rates fit the unary quadratic polynomial model. To achieve a balance between grain production and environmental benefits in N fertilizer, appropriate N fertilizer rates were determined to be 97.5 kg hm-2, 140 kg hm-2 and 131 kg hm-2 for low, moderate and high fertility soils, respectively. Structural equation modeling suggested that GY was significant correlated with soil microbial biomass carbon (SMBC) and N directly in low fertility field, with SMBC directly in moderate fertility field, and via SOC and NO3 -N in high fertility field. Therefore, a soil-based management strategy for N fertilizers could enhance food security while reducing agricultural N fertilizer inputs to mitigate environmental impacts.

Effects of stand ages on soil enzyme activities in Chinese fir plantations and natural secondary forests.

Forest type and stand age are important biological factors affecting soil enzyme activities. However, the changes in soil enzyme activities across stand ages and underlying mechanisms under the two forest restoration strate-gies of plantations and natural secondary forests remain elusive. In this study, we investigated the variations of four soil enzyme activities including cello-biohydrolase (CBH), ß-1,4-glucosidase (ßG), acid phosphatase (AP) and ß-1,4-N-acetylglucosaminidase (NAG), which were closely associated with soil carbon, nitrogen, and phosphorus cycling, across Cunninghamia lanceolata plantations and natural secondary forests (5, 8, 21, 27 and 40 years old). The results showed that soil enzyme activities showed different patterns across different forest types. The acti-vities of AP, ßG and CBH in the C. lanceolata plantations were significantly higher than those in the natural secon-dary forests, and there was no significant difference in the NAG activity. In the plantations, AP activity showed a decreasing tendency with the increasing stand ages, with the AP activity in the 5-year-old plantations significantly higher than other stand ages by more than 62.3%. The activities of NAG and CBH decreased first and then increased, and ßG enzyme activity fluctuated with the increasing stand age. In the natural secondary forests, NAG enzyme activity fluctuated with the increasing stand age, with that in the 8-year-old and 27-year-old stand ages being significantly higher than the other stand ages by more than 14.9%. ßG and CBH enzyme activities increased first and then decreased, and no significant difference was observed in the AP activity. Results of the stepwise regression analyses showed that soil predictors explained more than 34% of the variation in the best-fitting models predicting soil enzyme activities in the C. lanceolata plantations and natural secondary forests. In conclusion, there would be a risk of soil fertility degradation C. lanceolata plantations with the increasing stand age, while natural secondary forests were more conducive to maintaining soil fertility.

Unveiling hidden interactions: Microorganisms, enzymes, and mangroves at different stages of succession in the Shankou Mangrove Nature Reserve, China.

Understanding the interactions between microorganisms, soil extracellular enzymes, and mangroves is crucial for conserving and restoring mangrove ecosystems. However, the unique environments associated with mangroves have resulted in a lack of pertinent data regarding the interactions between these components. Root, stem, leaf, and soil samples were collected at three distinct stages of mangrove succession. Stoichiometry was employed to analyze the carbon, nitrogen, and phosphorus contents of these samples and to quantify extracellular enzyme activities, microbial biomass, and various physicochemical factors in the soil. The results showed that the trends of C, N, and P in the mangrove plants were consistent. Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP) were the highest in the Kandelia obovate community. Catalase (CAT) and ß-D-G showed the highest content in K. obovate and Bruguiera gymnorrhiza, whereas cellulase showed the opposite trend. Urease was least abundant in the K. obovate community, whereas neutral protease (NPR) and acid phosphatase (ACP) were most abundant. The overall soil environment in mangroves exhibited a state of N limitation, with varying degrees of limitation observed across different succession stages. The demand for P became more intense in the later stages of succession, particularly in the K. obovate and B. gymnorrhiza communities. In conjunction with correlation analysis, it indicated that the input of mangrove plant litter had a significant regulatory influence on the C, N, and P contents in the soil. There was a significant positive correlation between MBC, MBN, and MBP, indicating synergistic effects of C, N, and P on soil microorganisms. Therefore, evaluating the nutrient ratios and sufficiency of mangroves allowed us to comprehensively understand the present environmental conditions. This study aims to develop sustainable management strategies for the conservation and restoration of mangroves.

Decreased snow depth inhibits litter decomposition via changes in litter microbial biomass and enzyme activity.

Decreased snow depth resulting from global warming has the potential to significantly impact biogeochemical cycles in cold forests. However, the specific mechanisms of how snow reduction affects litter decomposition and the underlying microbial processes remain unclear, this knowledge gap limits our ability to precisely predict ecological processes within cold forest ecosystems under climate change. Hence, a field experiment was conducted in a subalpine forest in southwestern China, involving a gradient of snow reduction levels (control, 50 %, 100 %) to investigate the effects of decreased snow on litter decomposition, as well as microbial biomass and activity, specifically focused on two common species: red birch (Betula albosinensis) and masters larch (Larix mastersiana). After one year of incubation, the decomposition rate (k-value) of the two types of litter ranged from 0.12 to 0.24 across three snow treatments. A significant lower litter mass loss, microbial biomass and enzyme activity were observed under decreased snow depth in winter. Furthermore, a hysteresis inhibitory effect of snow reduction on hydrolase activity was observed in the following growing season. Additionally, the high initial quality (lower C/N ratio) of red birch litter facilitated the colonization by a greater quantity of microorganisms, making it more susceptible to snow reduction compared to the low-quality masters larch litter. Structural equation models indicated that decreased snow depth hindered litter decomposition by altering the biological characterization of litter (e.g., microbial biomass and enzyme activity) and environmental variables (e.g., mean temperature and moisture content). The findings suggest that the potential decline in snow depth could inhibit litter decomposition by reducing microbial biomass and activity, implying that the future climate change may alter the material cycling processes in subalpine forest ecosystems.

The contribution of microbial necromass to soil organic carbon and influencing factors along a variation of habitats in alpine ecosystems.

A growing consensus is reached that microbes contributes to regulating the formation and accumulation of soil organic carbon (SOC). Nevertheless, less is known about the role of soil microbes (necromass, biomass) in SOC accumulation in different habitat conditions in alpine ecosystems. To address this knowledge gap, the composition and distribution of amino sugars (ASs) and phospholipid fatty acids (PLFAs) as biomarkers of microbial necromass and biomass were investigated in forest, meadow and wetland soil profile (0-40 cm) of Mount Segrila, Tibet, China, as well the contribution of bacterial and fungal necromass to SOC. The results revealed that microbial necromass carbon contributed 45.15 %, 72.51 % and 78.08 % on average to SOC in 0-40 cm forest, meadow and wetland soils, respectively, and decreased with microbial biomass. Fungal necromass contributed more to SOC in these habitats than bacterial necromass. Microbial necromass increased with microbial biomass and both of them decreased with soil depth in all habitats. The necromass accumulation coefficient was significantly correlated with microbial necromass and biomass, affected by habitat and soil moisture. Structural equation model indicated that soil abiotic factors indirectly mediated the accumulation of SOC through microbial necromass and biomass. This study revealed that different habitats and soil depths control considerably soil physicochemical properties and microbial community, finally influencing SOC accumulation in alpine ecosystems, which emphasized the influence of abiotic factors on microbial necromass and biomass for SOC accumulation in alpine ecosystems.

Nitrogen deposition suppresses soil respiration by reducing global belowground activity.

Soil respiration (Rs) indicates below-ground biological activities. Previous studies have suggested that higher nitrogen (N) deposition due to human activities exerts an increasingly negative effect on Rs. However, the mechanisms underlying this negative effect remain highly uncertain on a global scale. Using a global dataset of 262 N addition experiments, here we show the overall N addition effects on Rs changed from positive to negative with increasing N addition rate and duration. By constructing a structural equation model (SEM) that explained 41 % variation in the responses of Rs to N addition, we revealed that Rs under increasing N addition was simultaneously associated with decreases in soil pH, root biomass and microbial biomass, with the strongest influence by root biomass. Decreasing soil pH had cascading effects on root and microbial biomass, while N-addition-induced root biomass reduction further manifested a decrease in microbial biomass. Across global variations in the environment, lower background soil pH amplified the negative impacts of N addition on root and microbial biomass, which consequently exhilarated the negative impact of high N on Rs. Our results highlight that predicting the response of belowground biological activities to global changes is complex with the essence of integrative understanding for the multivariate pathways through soil physical properties, plants and microorganisms.

Imprint of clay mineralogy, sesquioxides, and crop residue addition for evaluation of soil organic carbon stability and associated microbial activity in dominant soil orders of Indian subcontinent.

The full behaviour of natural clay minerals in soil organic carbon (SOC) stabilization in the presence of oxides and external C inputs is yet unknown. Thus, an incubation experiment was conducted in a sand-clay mixture with different soil clay fractions (SCFs) obtained from Alfisol, Inceptisol, Mollisol, and Vertisol in the presence of wheat residues to compare their C stabilization capacity. The C mineralization rates were higher in 1:1 type dominated SCFs (Alfisol and Inceptisol) compared to 2:1 interstratified mineral dominated SCFs (Vertisol). Wheat residues as C source altered SCFs' abilities to stabilize SOC at only moderate dosages of application (3-12 g kg-1). C mineralization and microbial biomass carbon (MBC) fell by 40% and 30%, respectively, as the amount of clay increased from 7.5 to 40%. However, removing sesquioxides from the SCFs boosted C mineralization and MBC by 22% and 16-32%, respectively, which matched with higher enzymatic activities in the sand-clay mixture. The increased C stabilization capacity of Vertisol-SCF may be attributed to its greater specific surface area (SSA) (506 m2 g-1) and cation exchange capacity (CEC) [meq/100 g]. Regression analysis revealed that SSA, CEC, and enzymatic activity explained approximately 86% of total variations in C mineralization. This study highlighted the critical role of 2:1 expanding clay minerals and sesquioxides in greater stabilization of external C input compared to its 1:1 counterpart. It also implied that the role of mineralogy or texture and sesquioxides levels in different soils (Vertisol, Mollisol, Inceptisol, Alfisol) should be prioritized while adding crop residues to reduce C footprint and enhance sequestration.

Soybean inclusion reduces soil organic matter mineralization despite increasing its temperature sensitivity.

Legume-based cropping increased the diversity of residues and rhizodeposition input into the soil, thus affecting soil organic matter (SOM) stabilization. Despite this, a comprehensive understanding of the mechanisms governing SOM mineralization and its temperature sensitivity across bulk soil and aggregate scales concerning legume inclusion remains incomplete. Here, a 6-year field experiment was conducted to investigate the effects of three cropping systems (i.e., winter wheat/summer maize, winter wheat/summer maize-soybean, and nature fallow) on SOM mineralization, its temperature sensitivity, and the main drivers in both topsoil (0-20 cm) and subsoil (20-40 cm). Soybean inclusion decreased the SOM mineralization by 17%-24%, while concurrently increasing the majority of soil biochemical properties, such as carbon (C) acquisition enzyme activities (5%-22%) and microbial biomass C (5%-9%), within the topsoil regardless of temperature. This is attributed to the increased substrate availability (e.g., dissolved organic C) facilitating microbial utilization, thus devoting less energy to mining nutrients under diversified cropping. In addition, SOM mineralization was lower within macroaggregates (∼12%), largely driven by substrate availability irrespective of aggregate sizes. In contrast, diversified cropping amplified the Q10 of SOM mineralization in mesoaggregates (+6%) and microaggregates (+5%) rather than in macroaggregates. This underscores the pivotal role of mesoaggregates and microaggregates in dominating the Q10 of SOM mineralization under soybean-based cropping. In conclusion, legume-based cropping diminishes soil organic matter mineralization despite increasing its temperature sensitivity, which proposes a potential strategy for C-neutral agriculture and climate warming mitigation.

Understanding the Relations between Soil Biochemical Properties and N2O Emissions in a Long-Term Integrated Crop-Livestock System.

Edaphoclimatic conditions influence nitrous oxide (N2O) emissions from agricultural systems where soil biochemical properties play a key role. This study addressed cumulative N2O emissions and their relations with soil biochemical properties in a long-term experiment (26 years) with integrated crop-livestock farming systems fertilized with two P and K rates. The farming systems consisted of continuous crops fertilized with half of the recommended P and K rates (CCF1), continuous crops at the recommended P and K rates (CCF2), an integrated crop-livestock system with half of the recommended P and K rates (ICLF1), and an integrated crop-livestock at the recommended P and K rates (ICLF2). The ICLF2 may have promoted the greatest entry of carbon into the soil and positively influenced the soil's biochemical properties. Total carbon (TC) was highest in ICLF2 in both growing seasons. The particulate and mineral-associated fractions in 2016 and 2017, respectively, and the microbial biomass fraction in the two growing seasons were also very high. Acid phosphatase and arylsulfatase in ICLF1 and ICLF2 were highest in 2016. The soil properties correlated with cumulative N2O emissions were TC, total nitrogen (TN), particulate nitrogen (PN), available nitrogen (AN), mineral-associated organic carbon (MAC), and microbial biomass carbon (MBC). The results indicated that ICLF2 induces an accumulation of more stable organic matter (OM) fractions that are unavailable to the microbiota in the short term and result in lower N2O emissions.

Microbiological attributes as indicators of soil quality in coffee growing systems in Southwest Bahia, Brazil.

Microorganisms are important indicators of soil quality due to their sensitivity to changes, reflecting the impacts caused by different land uses. The objective of this study was to evaluate the microbiological and physical-chemical attributes of the soil in areas cultivated with coffee under three different management systems (shaded coffee and full sun coffee with two spacings), as well as in adjacent areas under pasture and native forest, in Bahia, Brazil. The microbiological and physicochemical indicators evaluated were basal soil respiration (MBR), soil total organic carbon (TOC), microbial biomass carbon (MBC), metabolic quotient (qCO2), microbial quotient (qMic), enzyme activities (urease, acid phosphatase and fluorescein diacetate hydrolysis (FDA)). Physical and chemical indicators (particle size, texture, pH, P, K+, Ca2+, Mg2+, Al3+, and sum of bases) were also evaluated. Biological and chemical attributes were much more discriminative of study areas in the dry season. Microbial quotient (qMic) and metabolic quotient (qCO2) in the dry season showed that pasture is the most degraded land use. Conversely, nature forest and coffee with Grevillea were similar and were the best ones. In general, soil quality indicators were more sensitive to discriminate pasture and native forest from coffee systems, which, in turn, were not well discriminated among themselves.

Soil nitrogen availability drives the response of soil microbial biomass to warming.

Although soil microbial biomass responses to experimental warming have been extensively studied, the mechanisms through which elevated temperatures influence soil microbial biomass remain unclear. In this study, we performed a global meta-analysis to quantify the global pattern of soil microbial biomass in response to warming. Our findings suggest that global warming effect is not apparent when all the data are pooled together, while warming does increase microbial biomass under specific conditions (Δ°C ≥ 2 °C). This constructive influence is particularly accentuated under certain circumstances, including high precipitation levels (>800 mm), short treatment durations (<1 year), and within agricultural ecosystems. More importantly, our findings suggest that the impact of global warming on soil microbial biomass is largely mediated by changes in soil nitrogen availability. These findings underscore the pivotal role of nitrogen availability in modulating the response of soil microbial biomass to warming, while also emphasizing the intricate influence between multiple factors such as temperature, duration, and precipitation in shaping the patterns of warming effects.

Di-(2-ethylhexyl) phthalate (DEHP) contamination suppressed soil microbial biomass carbon and mitigated CO2 emissions against the background of alfalfa from different soils.

Plastic mulching and organic amendments are prevalent agricultural practices worldwide. Plastic mulching has long been suspected as a significant source of DEHP contamination in terrestrial ecosystems. However, effects of DEHP contamination on greenhouse gas emissions and microbial biomass carbon (MBC) remain unclear. Here, a microcosm experiment was set up to assess the impact of DEHP exposure on MBC and carbon dioxide (CO2) emission in two different soils (acidic and alkaline) with the inclusion of alfalfa straw. The treatment includes: (i) control with no amendment (T1); (ii) alfalfa straw addition (20 g kg-1) (T2); (iii) DEHP (10 mg kg-1) + alfalfa straw (T3); and (iv) DEHP (100 mg kg-1) + alfalfa straw (T4). Against the background of alfalfa inclusion, DEHP exposure led to a potential reduction in cumulative CO2 emissions by 16.35 % and 6.91 % in alkaline soil and 12.27 % and 13.65 % in acidic soil for T3 and T4, respectively. The addition of DEHP triggered CO2 emissions and manifested a detrimental negative priming effect in both soil types. In both soils, average CO2 emission fluxes were highest for the T2 treatment. The MBC fluctuated at around 80 mg kg-1 for the control group, alfalfa straw alone (T2) treatment considerably enhanced MBC contents, whereas DEHP contamination in T3 and T4 treatments suppressed the stimulatory effect of alfalfa on MBC in both alkaline and acidic soils. Furthermore, a positive relationship was observed between soil CO2 emissions and MBC in both soils. Overall, these findings highlight the toxic impact of DEHP on MBC and its role in mitigating CO2 emissions in diverse soils. DEHP exposure counters the CO2 emissions induced by alfalfa straw. In addition, the inhibitory effect of DEHP on CO2 fluxes in alkaline soil is less pronounced than in acidic soil. Therefore, further cutting-edge research is crucial since DEHP contamination poses serious ecological threats to agroecosystems.

Effect of composite organic amendment on Cd(II) ions stabilization and microbial activity under various ammonium sulfate levels.

To attenuate the risk of Cadmium(Cd) contamination and the deterioration of soil quality caused by excessive nitrogen fertilizer application in greenhouse, a composite organic amendment (spend mushroom substrate and its biochar) was prepared to remedy Cd(II) ions contaminated soil (0.6 mg/kg) under different N fertilizer levels. The results showed that in the absence of a composite organic amendment, the soil pH decreased by 0.15 when the N level increased from 0.1 to 0.8 g N⋅kg-1. However, the pH increased by 0.86-0.91, the exchangeable Cd(II) ions content decreased by 26.0%-26.7%, the microbial biomass increased by 34.34%-164.46%, and the number of copies of the AOB gene increased by 13-20 times with the application of composite organic amendment and the increase of N level. Both Pearson correlation analysis and Mantel test demonstrated the reduction in Cd(II) ions availability, the restoration of soil properties and the increase in microbial biomass all contributed to the composite organic amendment, which is of importance for soil remediation under excessive N fertilizer.

Blue carbon sink capacity of mangroves determined by leaves and their associated microbiome.

Mangroves play a globally significant role in carbon capture and storage, known as blue carbon ecosystems. Yet, there are fundamental biogeochemical processes of mangrove blue carbon formation that are inadequately understood, such as the mechanisms by which mangrove afforestation regulates the microbial-driven transfer of carbon from leaf to below-ground blue carbon pool. In this study, we addressed this knowledge gap by investigating: (1) the mangrove leaf characteristics using state-of-the-art FT-ICR-MS; (2) the microbial biomass and their transformation patterns of assimilated plant-carbon; and (3) the degradation potentials of plant-derived carbon in soils of an introduced (Sonneratia apetala) and a native mangrove (Kandelia obovata). We found that biogeochemical cycling took entirely different pathways for S. apetala and K. obovata. Blue carbon accumulation and the proportion of plant-carbon for native mangroves were high, with microbes (dominated by K-strategists) allocating the assimilated-carbon to starch and sucrose metabolism. Conversely, microbes with S. apetala adopted an r-strategy and increased protein- and nucleotide-biosynthetic potentials. These divergent biogeochemical pathways were related to leaf characteristics, with S. apetala leaves characterized by lower molecular-weight, C:N ratio, and lignin content than K. obovata. Moreover, anaerobic-degradation potentials for lignin were high in old-aged soils, but the overall degradation potentials of plant carbon were age-independent, explaining that S. apetala age had no significant influences on the contribution of plant-carbon to blue carbon. We propose that for introduced mangroves, newly fallen leaves release nutrient-rich organic matter that favors growth of r-strategists, which rapidly consume carbon to fuel growth, increasing the proportion of microbial-carbon to blue carbon. In contrast, lignin-rich native mangrove leaves shape K-strategist-dominated microbial communities, which grow slowly and store assimilated-carbon in cells, ultimately promoting the contribution of plant-carbon to the remarkable accumulation of blue carbon. Our study provides new insights into the molecular mechanisms of microbial community responses during reforestation in mangrove ecosystems.