Soil organic carbon (SOC), as the largest terrestrial carbon pool, plays an important role in global carbon (C) cycling, which may be significantly impacted by global changes such as nitrogen (N) ...fertilization, elevated carbon dioxide (CO2), warming, and increased precipitation. Yet, our ability to accurately detect and predict the impact of these global changes on SOC dynamics is still limited. Investigating SOC responses to global changes separately for mineral-associated organic carbon (MAOC) and the particulate organic carbon (POC) can aid in the understanding of overall SOC responses, because these are formed, protected, and lost through different pathways. To this end, we performed a systematic meta-analysis of the response of SOC, MAOC, and POC to global changes. POC was particularly responsive, confirming that it is a better diagnostic indicator of soil C changes in the short-term, compared to bulk SOC and MAOC. The effects of elevated CO2 and warming were subtle and evident only in the POC fraction (+5.11% and − 10.05%, respectively), while increased precipitation had no effects at all. Nitrogen fertilization, which comprised the majority of the dataset, increased SOC (+5.64%), MAOC (+4.49%), and POC (+13.17%). Effect size consistently varied with soil depth and experiment length, highlighting the importance of long-term experiments that sample the full soil profile in global change SOC studies. In addition, SOC pool responses to warming were modified by degree of warming, differently for air and soil warming manipulations. Overall, we suggest that MAOC and POC respond differently to global changes and moderators because of the different formation and loss processes that control these pools. Coupled with additional plant and microbial measurements, studying the individual responses of POC and MAOC improves understanding of the underlying dynamics of SOC responses to global change. This will help inform the role of SOC in mitigating the climate crisis.
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•Used meta-analysis to investigate soil carbon fractions responses to global change.•All soil organic carbon fractions increase under nitrogen fertilization.•Particulate organic carbon decreases with atmospheric warming.•Particulate organic carbon increases with elevated carbon dioxide.•Soil depth and experiment length were consistently important moderators.
Nitrogen (N) deposition influences both above- and below-ground communities and influences ecosystem functioning. However it is not clear about direct or indirect interactions among plants, soils and ...microbes in response to nitrogen deposition. In this study, the responses of soil bacterial diversity to N enrichment were investigated at surface (0–10 cm) and sub-surface (10–20 cm) soils in a temperate steppe ecosystem. N addition (>120 kg N ha−1 yr−1) resulted in a significant shift in bacterial community composition and a decrease in bacterial OTU richness in surface soil, but the effect on the sub-surface layer was far less pronounced, even at the highest addition rate (240 kg N ha−1 yr−1). Bacterial OTU richness was significantly correlated with soil and plant characteristics. Hierarchical structural equation modeling showed that soil ammonium availability was responsible for the shift in bacterial richness, whereas the change in bacterial community composition was due to alterations in soil pH and plant composition. These results indicated that N fertilization directly affected soil bacterial richness but indirectly affected bacterial communities through soil acidification and plant community change, indicating distinct controls on soil bacterial diversity and community composition. Our results also suggest that N availability could be a good predictor for the loss of soil bacterial diversity under atmospheric nitrogen deposition.
•N deposition impacts soil bacterial community in grassland.•Different controls on soil bacterial diversity and community composition.•An integrated mechanism of plant–soil–microbe interactions.
•Impacts of N-induced soil acidification on SOC stock are assessed.•N fertilization synchronously causes soil acidification and SOC accrual.•Soil acidification increases SOC content by decreasing its ...decomposition.•Soil acidification is a linkage between N fertilization and SOC accumulation.
Significant increase in soil organic carbon (SOC) has been found in Chinese croplands. Current literature largely attributes this to the increased organic C inputs from manure, crop straw and root. However, using a meta-analysis of 185 long-term trials and 6669 spatial data pairs across China, we show here that soil acidification is an additional significant cause for the SOC accumulation. Results from long-term experiments showed that soil acidification due to excessive N fertilization coincided with, and significantly (p < 0.01) contributed to, the observed SOC accrual. Spatially, the amount of SOC increase caused by soil acidification decreased with increasing initial content. In addition, the soil’s basal respiration rate (SBRR), microbial metabolic quotient (MMQ) and the percentage of dissolved organic carbon (DOC) relative to total SOC decreased significantly (p < 0.01) with soil pH decline. This indicates that soil acidification depresses the decomposition of organic matter, both by decreasing microbial activity and by increasing protection of SOC by mineral phases. Thus, N-induced soil acidification promotes the SOC accumulation in Chinese croplands, by increasing its stability. In contrast to the current view emphasizing the importance of organic C inputs, our meta-analysis reveals an alternative mechanism connecting N-fertilization and the resulting SOC accumulation in agricultural ecosystems. More research is needed to further clarify its operating processes, relative importance, and agro-environmental consequences.
Plastic film mulch (PFM) is a double-edged-sword agricultural technology, which greatly improves global agricultural production but can also cause severe plastic pollution of the environment. Here, ...we characterized and quantified the amount of macro- and micro-plastics accumulated after 32 years of continuous plastic mulch film use in an agricultural field. An interactive field trial was established in 1987, where the effect of plastic mulching and N fertilization on maize yield was investigated. We assessed the abundance and type of macroplastics (>5 mm) at 0–20 cm soil depth and microplastic (<5 mm) at 0–100 cm depth. In the PFM plot, we found about 10 times more macroplastic particles in the fertilized plots than in the non-fertilized plots (6796 vs 653 pieces/m2), and the amount of film microplastics was about twice as abundant in the fertilized plots than in the non-fertilized plots (3.7 × 106 vs 2.2 × 106 particles/kg soil). These differences can be explained by entanglement of plastics with plant roots and stems, which made it more difficult to remove plastic film after harvest. Macroplastics consisted mainly of films, while microplastics consisted of films, fibers, and granules, with the films being identified as polyethylene originating from the plastic mulch films. Plastic mulch films contributed 33%–56% to the total microplastics in 0–100 cm depth. The total number of microplastics in the topsoil (0–10 cm) ranged as 7183–10,586 particles/kg, with an average of 8885 particles/kg. In the deep subsoil (80–100 cm) the plastic concentration ranged as 2268–3529 particles/kg, with an average of 2899 particles/kg. Long-term use of plastic mulch films caused considerable pollution of not only surface, but also subsurface soil. Migration of plastic to deeper soil layers makes removal and remediation more difficult, implying that the plastic pollution legacy will remain in soil for centuries.
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•N fertilization aggravated the abundance of macroplastic and film microplastic.•Microplastics consisted of films, fibers, and granules in long film-mulched soil.•Film microplastic was identified as originating from the plastic mulch films.•Plastic film-derived microplastics can readily migrate down the soil profile.•Plastic films contributed 33%–56% to total microplastics for 0–100 cm profile.
Conservation agriculture practices, such as reduced tillage, cover crops and fertilization, are often associated with greater microbial biomass and activity that are linked to improvements in soil ...quality. This study characterized the impact of long term (31 years) tillage (till and no-till), cover crops (Hairy vetch- Vicia villosa and winter wheat- Triticum aestivum, and a no cover control), and N-rates (0, 34, 67 and 101 kg N ha−1) on soil microbial community structure, activity and resultant soil quality calculated using the soil management assessment framework (SMAF) scoring index under continuous cotton (Gossypium hirsutum) production on a Lexington silt loam in West Tennessee.
No-till treatments were characterized by a significantly greater (P < 0.05) abundance of Gram positive bacteria, actinomycetes and mycorrhizae fungi fatty acid methyl ester (FAME) biomarkers compared to till. Saprophytic fungal FAME biomarkers were significantly less abundant (P < 0.05) under no-till treatments resulting in a lower fungi to bacteria (F:B) ratio. Key enzymes associated with C, N & P cycling (β-glucosidase, β-glucosaminidase, and phosphodiesterase) had significantly higher rates under no-till relative to till, corresponding to significantly greater (P < 0.05) soil C and N, extractable nutrients (P, K and Ca) and yields. Mycorrhizae fungi biomarkers significantly decreased (P < 0.05) with increasing N-rate and was significantly less (P < 0.05) under the vetch cover crop compared to wheat and no cover. Treatments under vetch also had significantly higher β-glucosaminidase and basal microbial respiration rates compared to wheat and no cover.
Consequently, the total organic carbon (TOC) and β-glucosidase SMAF quality scores were significantly greater under no-till compared to till and under the vetch compared to wheat and no cover treatments, resulting in a significantly greater overall soil quality index (SQI).
Our results demonstrate that long-term no-till and use of cover crops under a low biomass monoculture crop production system like cotton results in significant shifts in the microbial community structure, activity, and conditions that favor C, N and P cycling compared to those under conventional tillage practices. These practices also led to increased yields and improved soil quality with no-till having 13% greater yields than till and treatments under vetch having 5% increase in soil quality compared to no cover and wheat.
•Significant microbial community shifts due to no-till, cover crops and N-fertilization.•Greater gram positive bacteria, mycorrhizae and actinomycetes under no-till.•Vetch cover and N-fertilization decrease mycorrhizae abundance.•Carbon, nitrogen and phosphorous cycling enzymes greater under no-till.•Greater total carbon, nitrogen and yield under no-till with cover crop treatments.
Nitrogen (N) fertilization affects the rate of soil organic carbon (SOC) decomposition by regulating extracellular enzyme activities (EEA). Extracellular enzymes have not been represented in global ...biogeochemical models. Understanding the relationships among EEA and SOC, soil N (TN), and soil microbial biomass carbon (MBC) under N fertilization would enable modeling of the influence of EEA on SOC decomposition. Based on 65 published studies, we synthesized the activities of α-1,4-glucosidase (AG), β-1,4-glucosidase (BG), β-d-cellobiosidase (CBH), β-1,4-xylosidase (BX), β-1,4-N-acetyl-glucosaminidase (NAG), leucine amino peptidase (LAP), urease (UREA), acid phosphatase (AP), phenol oxidase (PHO), and peroxidase (PEO) in response to N fertilization. The proxy variables for hydrolytic C acquisition enzymes (C-acq), N acquisition (N-acq), and oxidative decomposition (OX) were calculated as the sum of AG, BG, CBH and BX; AG and LAP; PHO and PEO, respectively. The relationships between response ratios (RRs) of EEA and SOC, TN, or MBC were explored when they were reported simultaneously. Results showed that N fertilization significantly increased CBH, C-acq, AP, BX, BG, AG, and UREA activities by 6.4, 9.1, 10.6, 11.0, 11.2, 12.0, and 18.6%, but decreased PEO, OX and PHO by 6.1, 7.9 and 11.1%, respectively. N fertilization enhanced SOC and TN by 7.6% and 15.3%, respectively, but inhibited MBC by 9.5%. Significant positive correlations were found only between the RRs of C-acq and MBC, suggesting that changes in combined hydrolase activities might act as a proxy for MBC under N fertilization. In contrast with other variables, the RRs of AP, MBC, and TN showed unidirectional trends under different edaphic, environmental, and physiological conditions. Our results provide the first comprehensive set of evidence of how hydrolase and oxidase activities respond to N fertilization in various ecosystems. Future large-scale model projections could incorporate the observed relationship between hydrolases and microbial biomass as a proxy for C acquisition under global N enrichment scenarios in different ecosystems.
•A meta-analysis was conducted based on 65 published nitrogen fertilization experiments.•Nitrogen fertilization stimulated hydrolases associate with C and P but depressed oxidases..•Nitrogen fertilization has no significant effect on hydrolases associated with N.•A significantly positive relationship was found between response ratios of hydrolases associate with C and microbial biomass.•Future model projections could consider the above relationship for different ecosystems.
Straw incorporation serves as an effective strategy to enhance soil fertility and soil microbial biomass carbon (SMBC), which in turn improves maize yield and agricultural sustainability. However, ...our understanding of nitrogen (N) fertilization and straw incorporation into soil microenvironment is still evolving. This study explored the impact of six N fertilization rates (N0, N100, N150, N200, N250, and N300) with and without straw incorporation on soil fertility, SMBC, enzyme activities, and maize yield.BACKGROUNDStraw incorporation serves as an effective strategy to enhance soil fertility and soil microbial biomass carbon (SMBC), which in turn improves maize yield and agricultural sustainability. However, our understanding of nitrogen (N) fertilization and straw incorporation into soil microenvironment is still evolving. This study explored the impact of six N fertilization rates (N0, N100, N150, N200, N250, and N300) with and without straw incorporation on soil fertility, SMBC, enzyme activities, and maize yield.Results showed that both straw management and N fertilization significantly affected soil organic carbon (SOC), total N, SMBC, soil enzyme activities, and maize yield. Specifically, the N250 treatment combined with straw incorporation significantly increased SOC, total N, and SMBC compared to lower fertilization rates. Additionally, enzyme activities such as urease, cellulase, sucrose, catalase, and acid phosphatase reached their peak during the V6 growth stage in the N200 treatment under for both straw management conditions. Compared to N250 and N300 treatments of traditional planting, the N200 treatment with residue incorporation significantly increased yield by 8.30 and 4.22%, respectively. All measured parameters, except for cellulase activity, were significantly higher in spring than in the autumn across both study years, with notable increases observed in 2021.RESULTSResults showed that both straw management and N fertilization significantly affected soil organic carbon (SOC), total N, SMBC, soil enzyme activities, and maize yield. Specifically, the N250 treatment combined with straw incorporation significantly increased SOC, total N, and SMBC compared to lower fertilization rates. Additionally, enzyme activities such as urease, cellulase, sucrose, catalase, and acid phosphatase reached their peak during the V6 growth stage in the N200 treatment under for both straw management conditions. Compared to N250 and N300 treatments of traditional planting, the N200 treatment with residue incorporation significantly increased yield by 8.30 and 4.22%, respectively. All measured parameters, except for cellulase activity, were significantly higher in spring than in the autumn across both study years, with notable increases observed in 2021.These findings suggest that optimal levels of SOC, soil total N (STN), and SMBC, along with increased soil enzyme activities, is crucial for sustaining soil fertility and enhancing maize grain yield under straw incorporation and N200 treatments.CONCLUSIONSThese findings suggest that optimal levels of SOC, soil total N (STN), and SMBC, along with increased soil enzyme activities, is crucial for sustaining soil fertility and enhancing maize grain yield under straw incorporation and N200 treatments.
Nitrogen fertilization (NF) is one of the common practices to increase crop production worldwide over the past several decades. Nevertheless, unreasonable NF results in massive greenhouse gas (GHG) ...emissions, leading to climate change and global warming. Many studies have already reported the impact of NF on crop yield, global warming potential (GWP) and greenhouse gas intensity (GHGI), but the studies were limited to only some parameters. In this study, a total of 174 studies from 16 countries were collected and then a regression analysis was conducted to obtain the appropriate N fertilization rates that enhance crop yield while reducing GWP and GHGI. After that, a meta-analysis was performed to evaluate the effects of NF on crop yield, GHGI, GWP and GHG emissions and identify NF management strategies that benefit crop yield and maintain GWP. The results showed that the suitable N fertilization rate was 180, 150, 130 and 200 kg ha−1 for wheat, maize, rice and vegetables or industrial crops, respectively. Overall, NF resulted in positive effect size in crop yield (0.56) and negative effect size in GHGI (−0.14) compared to NNF. GWP showed positive effect size (0.37) due to an increase in N2O emissions (0.91) relative to NNF, which is higher than the increase of CH4 emissions (0.01) and CO2 emissions (0.22). It was recommended that split and banded application of urea or urea plus manure is employed for cereals (especially wheat) in the arid and semi-arid regions with medium-textured and neutral or alkaline soil.
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•174 peer-reviewed publications were used to conduct a global meta-analysis.•Crop yield, GWP and GHGI increased curvilinearly with increased N fertilization rate.•NF could improve crop yield and reduce GHGI in arid and semi-arid regions.•Split and banded application of urea is employed for cereals to control GWP.
Dissimilatory nitrate reduction to ammonium (DNRA) and diazotrophic N2 fixation contribute to nitrogen (N) supply in rice paddies, whereas denitrification contributes to N loss. Continuous N ...fertilization in rice paddies is known to increase denitrification and reduce N2 fixation, however little is known about its effect on DNRA and the NO3− partitioning between DNRA and denitrification. Here, we investigated the rates of DNRA, denitrification and N2 fixation, and their relevant microbial gene abundances, in long-term high and low N fertilized rice paddies using a 15NO3− tracer, an acetylene reduction assay and quantitative PCR analysis, in laboratory incubation studies. We observed that DNRA exceeded denitrification by a factor of eight in low N fertilized rice paddies, while DNRA was almost half of the denitrification rate in high N fertilized rice paddies. The nrfA gene abundance, related to DNRA, was significantly higher in the low N fertilized rice paddies and was positively correlated with DNRA rates. However, no clear difference in denitrifying gene (narG, nirK and nosZ) abundances was observed between the N fertilization regimes. The proportion of total NO3− reduced by DNRA had a significantly positive correlation with the soil organic carbon-to-NO3- ratio and negative correlation with the soil NO3− concentration. N2 fixation added ten times more N in the low N input than in the high N input paddies. Our findings highlight the self-regulated microbial N cycling in low N input paddy systems which maintain long-term paddy soil N nutrition.
•N2 fixation added ten times more N to low N input than to high N input rice paddies.•DNRA retained the majority of nitrate in long-term low N input rice paddies.•Denitrification dominated nitrate reduction in long-term high N input rice paddies.•High SOC:NO3− ratio favours NO3− partitioning to DNRA in NO3− limited paddy soils.
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