Microbial Biomass C Research Articles

Nitrogen addition increases topsoil carbon stock in an alpine meadow of the Qinghai-Tibet Plateau

Soil carbon (C) sequestration plays a critical role in mitigating climate change. Nitrogen (N) deposition greatly affects soil C dynamics by altering C input and output. However, how soil C stocks respond to various forms of N input is not well clear. This study aimed to explore the impact of N addition on soil C stock and to elucidate the underlying mechanisms in an alpine meadow on the eastern Qinghai-Tibet Plateau. The field experiment involved three N application rates and three N forms, using a non-N treatment as a control. After six years of N addition, the total C (TC) stocks in the topsoil (0–15 cm) were markedly increased by an average of 12.1 %, with a mean annual rate of 20.1 ‰, and no difference was found between the N forms. Irrespective of rate or form, N addition significantly increased the topsoil microbial biomass C (MBC) content, which was positively correlated with mineral-associated and particulate organic C content and was identified as the most important factor that affecting the topsoil TC. Meanwhile, N addition significantly increased the aboveground biomass in the years with moderate precipitation and relatively high temperature, which leads to higher C input into soils. Owing to decreased pH and/or activities of β-1,4-glucosidase (βG) and cellobiohydrolase (CBH) in the topsoil, organic matter decomposition was most likely inhibited by N addition, and this inhibiting effect varied under different N forms. Additionally, TC content in the topsoil and subsoil (15–30 cm) exhibited parabolic and positive linear relationship with the topsoil dissolved organic C (DOC) content, respectively, indicating that DOC leaching might be an important influencing factor for soil C accumulation. These findings improve our understanding of how N enrichment affects C cycles in alpine grassland ecosystems and suggest that soil C sequestration in alpine meadows probably increases with N deposition.

Linking soil organic carbon dynamics to microbial community and enzyme activities in degraded soil remediation by reductive soil disinfestation

Reductive soil disinfestation (RSD) is a widely practiced strategy for remediating soil degradation that seriously threatens crop production and sustainable agriculture. However, the soil organic carbon (SOC) dynamics and its underlying mechanisms induced by RSD remain unknown. To clarify this problem, a field experiment explored the SOC dynamics under degraded soils (C3) remediated with CK (untreated) and RSD (combination of added maize straw (C4), water flooding, and plastic mulch). The relationships of SOC dynamics with microbial community composition and activities of C-related hydrolase were also disentangled using structural equation model (SEM) and variation partitioning analysis (VPA). Results indicated that the SOC concentration under CK treatment decreased by 0.96 g C kg−1 compared with that in the initial soil, while the SOC concentration under RSD treatment increased by 1.26 g C kg−1 because of old SOC loss (0.56 g C kg−1) and new SOC formation (1.82 g C kg−1). Compared to the CK, the RSD increased the soil dissolved organic C (DOC), but decreased the microbial biomass C (MBC) and abundances of bacteria and fungi. The soil microbial community shifted from Proteobacteria and Actinobacteria to Firmicutes and Ascomycota after RSD treatment, and the activities of C-related hydrolase were also enhanced, such as β-glucosidase, cellobiohydrolase, β-xylosidase, and invertase. The SEM and VPA suggested that the new SOC formation and the reduced old SOC loss under RSD treatment were collaboratively driven by soil properties (i.e., redox potential, DOC, and MBC), microbial taxa (i.e., Arthobacter, Symbiobacterium) and hydrolase activities (i.e., BG and CBH). Meanwhile, the RSD doubled the yield of subsequent tomato by mitigating soil degradation (i.e., salinization and Fusarium oxysporum) and increasing the SOC concentration. In summary, RSD, as a remediation strategy for soil degradation, can increase SOC concentration by modifying microbial community and C-related hydrolase activities.

Effect of forest chronosequence on ecological stoichiometry and nitrogen and phosphorus stocks in Alnus nepalensis forest stands, central Himalaya

AbstractIn the mid and high elevations of the central Himalaya, Nepalese alder (Alnus nepalensis D. Don) occurs in areas affected by landslides/landslips and is a nitrogen‐fixing species; it quickly improves soil physical and chemical properties and facilitates the restoration of degraded forests. In the present study, we evaluated the effect of A. nepalensis forest chronosequence on the carbon (C), nitrogen (N), and phosphorus (P) concentrations, N and P stocks, and stoichiometry in the soil, including microbial biomass C (MBC), microbial biomass N (MBN) and microbial biomass P (MBP), and in the plant components. Six naturally occurring forest stands were identified in a chronosequence of A. nepalensis (age 3–270 years old) forest stands, namely alder‐early regenerating (AER), alder‐late regenerating (ALR), alder young‐mixed (AYM), alder mature‐oak (Quercus leucotrichophora) mixed (AMOM), alder mature‐rhododendron (Rhododendron arboreum) mixed (AMR), and alder old‐oak (Q. leucotrichophora) mixed (AOOM) forests. The biomass of tree components was estimated using species‐specific allometric equations developed by previous workers for the region. Soil total N and total P stocks of each species were determined by the N and P concentrations and bulk density. Structural equation modeling (SEM) was performed to quantify the contribution of N and P pools to ecosystem nitrogen and phosphorus stocks. The results of this study revealed that the stoichiometry (C:N, N:P, and C:P ratios) of tree components (i.e., leaves, leaf litter, twig), soil and microbial biomass varied widely, and the presence of nitrogen‐fixing A. nepalensis in different succession stages significantly improved the soil and microbial biomass stoichiometry. Total vegetation (tree, herbs, shrubs, and litter) biomass N stock ranged from 346.77 to 4662.06 kg N ha−1, and soil N stock varied from 816.48 to 7334.24 kg N ha−1. Total ecosystem N and P stocks ranged from 1163.26 to 11,996.31 kg N ha−1 and 76.10 to 799.28 kg P ha−1, respectively, and positively increased with A. nepalensis total biomass. The soil P stock accounted for 63.49% to 74.80% of the total P stocks of the forest ecosystems. Overall, our findings suggest that A. nepalensis forest chronosequence enhanced the N and P stocks, and introducing this species in degraded forests appears to be an option for enhancing forest conservation and rehabilitation actions in the central Himalaya.

Changes in soil microbial biomass and organic C pools improve the sustainability of perennial grass and legume system under organic nutrient management.

The perennial grass-legume cropping system benefits soil because of its high biomass turnover, cover cropping nature, and different foraging behaviors. We investigated the response of soil organic carbon (SOC) pools and their stock to organic and inorganic nutrient management in the Guinea grass and legume (cowpea-Egyptian clover) cropping system. Depth-wise soil samples were collected after harvesting the Egyptian clover. Based on the ease of oxidation with chromic acid, different pools of SOC oxidizable using the Walkley-Black C method, very labile, labile, less labile, non-labile; and dissolved organic C (DOC), microbial biomass C (MBC), and total organic C (TOC) in soils were analyzed for computing several indices of SOC. After 10 years of crop cycles, FYM and NPKF nutrient management recorded greater DOC, MBC, SOC stocks, and C sequestration than the NPK. Stocks of all SOC pools and carbon management index (CMI) decreased with soil depth. A significant improvement in CMI, stratification ratio, sensitivity indices, and sustainable yield index was observed under FYM and NPKF. This grass-legume intercropping system maintained a positive carbon balance sequestered at about 0.8Mg C ha-1 after 10 years without any external input. Approximately 44-51% of the applied carbon through manure was stabilized with SOC under this cropping system. The DOC, MBC, and SOC in passive pools were identified for predicting dry fodder yield. This study concludes that the application of organics in the perennial grass-legume inter cropping system can maintain long-term sustainability, enhance the C sequestration, and offset the carbon footprint of the farm enterprises.

Linking between soil properties, bacterial communities, enzyme activities, and soil organic carbon mineralization under ecological restoration in an alpine degraded grassland.

Soil organic carbon (SOC) mineralization is affected by ecological restoration and plays an important role in the soil C cycle. However, the mechanism of ecological restoration on SOC mineralization remains unclear. Here, we collected soils from the degraded grassland that have undergone 14 years of ecological restoration by planting shrubs with Salix cupularis alone (SA) and, planting shrubs with Salix cupularis plus planting mixed grasses (SG), with the extremely degraded grassland underwent natural restoration as control (CK). We aimed to investigate the effect of ecological restoration on SOC mineralization at different soil depths, and to address the relative importance of biotic and abiotic drivers of SOC mineralization. Our results documented the statistically significant impacts of restoration mode and its interaction with soil depth on SOC mineralization. Compared with CK, the SA and SG increased the cumulative SOC mineralization but decreased C mineralization efficiency at the 0-20 and 20-40 cm soil depths. Random Forest analyses showed that soil depth, microbial biomass C (MBC), hot-water extractable organic C (HWEOC), and bacterial community composition were important indicators that predicted SOC mineralization. Structural equal modeling indicated that MBC, SOC, and C-cycling enzymes had positive effects on SOC mineralization. Bacterial community composition regulated SOC mineralization via controlling microbial biomass production and C-cycling enzyme activities. Overall, our study provides insights into soil biotic and abiotic factors in association with SOC mineralization, and contributes to understanding the effect and mechanism of ecological restoration on SOC mineralization in a degraded grassland in an alpine region.

Recovering of soil organic matter and associated C and N pools on regenerated forest ecosystems at different tree species influence on post-fire and reclaimed mine sites

Understanding the processes in soils after disturbances could be helpful in better designing restoration practices. The labile fraction of soil organic carbon (LSOC) plays a vital role in recovering soil properties and quality. This study compared labile C and N fractions, including microbial biomass C (MBC), cold-water-soluble C (WSC), water-soluble N (WSN), hot-water-extractable C (HWC), hot-water-extractable N (HWN), particulate organic carbon (POC), and particulate organic nitrogen (PON) in post-mining, post-fire, and undisturbed soils under different tree cover (Scots pine, common birch, and black alder). Nearly 30 years after the disturbance, post-mining soils were characterized by lower soil organic carbon (SOC) and total nitrogen (TN) as well as their labile fractions compared to those of post-fire and undisturbed soils. Disturbed soils had less stable SOC than undisturbed soils. Compared to the post-fire site, the higher proportion of WSC in SOC in post-mining soils suggests higher SOC turnover and leaching potential during primary succession compared to secondary succession. The post-fire soils had a similar SOC stock to undisturbed soils but differed in the C and N labile fractions stock. Post-fire soils were characterized by higher POC stocks due to charcoal admixture and lower WSN, HWC, and HWN fractions than undisturbed soils. The studied tree species differently affected the recovery of SOM properties after disturbances. Post-mining soils under alder had higher SOC, TN, and labile fractions (except MBC) than soils under birch and pine cover. However, this was not true for the post-fire site, where only WSN was higher under the alder. The soils under birch stands had the highest MBC stocks across all sites. The soils under pine had less stable SOM than those under birch and alder, which may accelerate podzolization processes. Results indicate a longer time for the recovery of C and N pools during primary succession than in secondary succession on sandy soils. Alder, as phytomelioration species that increases the C and N pools in post-fire sites, has limited usefulness.

Carbon and nitrogen allocation in leaf, fine root, soil, and microbial biomass in invasive Prosopis juliflora and native Acacia nilotica in semi-arid forests of the Aravalli hills

Semi-arid forests of the Aravalli hills are rich in tree diversity, but plant invasions during the last several decades, especially by Prosopis juliflora (Sw.) DC. have affected the vegetation structure and biogeochemical cycles of these forests. We compared carbon (C), and nitrogen (N) concentrations in the fine root, leaf, and soil physicochemical properties under the invasive tree species, P. juliflora, and native, Acacia nilotica (L.) Willd. ex Delile, to evaluate the effect of invasive tree species on total soil C, N concentrations, and C:N ratios. We also analyzed the soil samples for soil organic C (SOC), total N (TN), soil microbial biomass C (MBC), and soil microbial biomass N (MBN) and stocks. Soil physical and chemical properties under the invasive P. juliflora and native A. nilotica trees varied significantly (p < 0.05). The C and N concentrations in the fine root, leaf, soil SOC, TN and MBC, and MBN concentrations were significantly (p < 0.05) higher in P. juliflora than A. nilotica while C:N ratio, and bulk density, exhibited the opposite trends. The C concentrations followed the order fine root > leaf > soil > microbial biomass while for N concentration and C:N ratios, it was leaf > fine root > soil > microbial biomass. The invasive P. juliflora had a lower C:N ratio in leaf, fine root, and soil than the native A. nilotica. The average rhizosphere soil, fine root, and leaf C concentration for P. juliflora were 36.72 ± 0.84 g kg−1, 547.84 ± 18.56 g kg−1, and 534.77 ± 5.12 g kg−1, respectively and were 1.42, 1.16 and 1.04 times higher than for A. nilotica. Similarly, P. juliflora average rhizosphere soil, fine root, and leaf N concentrations were 4.37 ± 0.11 g kg−1, 19.96 ± 0.94 g kg−1, and 23.18 ± 0.84 g kg−1, respectively, and 2.0, 1.27, and 1.85 times, respectively, higher than for A. nilotica. Further, the MBC:SOC or MBN:TN ratios were higher in native A. nilotica, likely indicating higher efficiency of microbes in soil C decomposition. Together, our results indicate that invasive P. juliflora altered the ecosystem processes and increased the soil and microbial C, and N stocks compared to native A. nilotica in the semi-arid forests of the Aravalli hills.

Pine Chip and Poultry Litter Derived Biochars Affect C and N Dynamics in Two Georgia, USA, Ultisols

Some biochars produced by pyrolysis of biomass have the potential to sequester C and enhance nutrient supplies in agricultural soils. A 28-day lab incubation was used to assess the potential effects of biochars derived from pine chips (PC) or poultry litter (PL) applied at five application rates (0, 22.5, 45.0, 67.5, and 90 Mg ha−1 equivalent). Biochars were applied to two acidic Ultisols, a Cecil sandy loam and a Tifton loamy sand, found in Georgia, USA. Cumulative basal soil respiration was measured over the 28-day incubation. Other soil properties measured before and after incubation were soil pH, total soil organic carbon (SOC), total soil N, soluble organic C (OC), soil mineral nitrogen (NH4+-N and NO3−-N), and microbial biomass C (MBC). Before incubation, addition of both PC and PL biochars increased soil pH, total SOC, and C:N ratio in both soils. Addition of the PL biochar increased total soil N, soluble OC, and NO3−-N in both soils, MBC in Tifton soil, and NH4+-N in Cecil soil. Addition of the PC biochar decreased NO3−-N in Cecil soil but increased it in Tifton soil. After the 28-day incubation, averaged across soils, pH increased in the 22.5 Mg ha−1 PC and 22.5 and 67.5 Mg ha−1 PL treatments, total SOC declined in the 45 and 67.5 Mg ha−1 PC treatments, and the C:N increased in soil controls and decreased in the 67.5 Mg ha−1 PC treatment. In Cecil soil, the MBC declined in PL treatments except at 90 Mg ha−1, and NH4+-N declined in the 90 Mg ha−1 PC treatments. In Tifton soil, MBC increased in the 45 Mg ha−1 PL treatment, and NH4+-N increased in all but the 22.5 Mg ha−1 PL treatments. Total N and NO3−-N did not change with incubation. Basal respiration was not affected by biochar, thought it was generally greater in Cecil than Tifton soil. Net SOC loss and the initial increase in soluble OC and MBC indicated potential C priming from adding both biochars. Increased NH4+-N with time in Tifton PL treatments indicated potential N priming. In Cecil soil, the PC biochar may have immobilized NH4+-N, but PL biochar likely supplied it. In Tifton soil, PC biochar appeared to be generally inert, but PL biochar supplied soluble OC and NH4+-N, although it might have inhibited nitrification.

How the Birch effect differs in mechanisms and magnitudes due to soil texture

Global climate change is predicted to intensify temperature and precipitation extremes, exposing soils to frequent and/or intense alternate wetting and drying regimes. Rewetting a dry soil causes a burst of CO2 known as the “Birch effect”. This spike in respiration can be attributed to: (i) release of cellular solutes (metabolites) accumulated during drought due to rapid increase in water potential upon re-wetting; (ii) sudden death of certain microbes serving as carbon (C) sources for surviving microbes, leading to microbial community shifts; and (iii) release of physically protected C due to aggregate breakdown upon repeated drying-wetting. The relative importance of these mechanisms may change in different soil textures, but very few studies examine all three processes. In this study, we evaluated the effects of repeated drying and wetting cycles (transient state moisture conditions) on the Birch effect and elucidated the mechanisms that contributed to this effect in different textured soils. Soils of three distinct textures (sandy, loamy, and clayey) were incubated for 140 days under five alternate cycles of drying (10% WHC) and wetting (100% WHC) conditions. Control soils were held at 55% WHC for the same duration. Microbial biomass C (MBC), extractable organic C (EOC), metabolites, microbial community structure, and changes in aggregate associated C were determined at each time point. Sandy soil had the lowest respiration rate followed by loamy and clayey soils, and cumulative CO2 loss was higher under transient moisture state compared to steady state. In sandy and clayey soils, changes in bacterial abundance controlled the Birch effect, while in loamy soil, the release of aggregate protected C majorly controlled the Birch effect.

Alteration of the organic wheat rhizobiome and enzyme activities by reduced tillage and diversified crop rotation

The acreage of organic agriculture continues to grow world-wide. Growing organic crops relies on soil tillage for weed control, and organic soil inputs for nutrient supply, because chemical inputs are not permitted. Organic inputs build soil organic C, a key determinant of soil quality, but tillage-induced C losses through erosion and decomposition reduce soil organic C. Crop rotations also supply nutrients and break pest cycles. In 2014 (normal rainfall) and 2015 (below-normal rainfall), we investigated whether reduced tillage (low tillage vs high tillage), and diversification of a 2-year forage pea green manure (GM)-wheat rotation to a 4-year rotation (simplified rotation vs diversified rotation) altered the soil microbiome and enzyme activities in the rhizosphere of organic wheat in a trial that had been established in 2010. Planctomycetes and Gemmatimonadetes were more abundant under high tillage than low tillage in both rotations. The Shannon index of α-diversity was greater in the diversified rotation than the simplified rotation under high tillage. Microbial biomass C (MBC) was greater in the diversified rotation than the simplified rotation in 2014. The relative abundances of Gemmatimonadetes, Proteobacteria and Tharmarchaeota were greater in the diversified rotation than the simplified rotation under high tillage. Low tillage increased the activity of acid phosphomonoesterase (P cycling), and in 2014, the activity of this enzyme was greater in the diversified rotation than the simplified rotation. The growing season precipitation shaped the soil microbiome (α- and β-diversity) the most: the drier-than-normal 2015 had less microbial biomass C (MBC), Actinobacteria, Bacteroidetes, Proteobacteria and enzyme activities than the normal 2014, but vice-versa for α-diversity, AD3, Armatimonadetes and Chloroflexi. Therefore, although the growing season affected these soil microbial properties more than tillage or crop rotation, both low tillage and crop diversification altered the soil microbial community composition and increased the soil P cycling potential

Depth-dependent response of particulate and mineral-associated organic carbon to long-term throughfall reduction in a subtropical natural forest

Climate change has altered the precipitation patterns and prolonged the drought season in subtropical areas, which affects forest productivity and soil carbon (C) cycling. However, the response of different soil organic C (SOC) fractions to the reduction in precipitation and the potential mechanisms remain poorly understood in subtropical forests. In this study, we examined the effects of long-term (9 years) throughfall reduction on SOC fractions, including particulate organic C (POC) and mineral-associated organic C (MAOC), dissolved organic C (DOC), microbial biomass C (MBC), mycorrhizal fungal biomass, and fine-root biomass of two soil layers (0–10 cm and 40–60 cm) in a subtropical Castanopsis carlesii forest. The results showed that throughfall reduction had a significant effect on soil C cycling in the topsoil but not in the subsoil. Throughfall reduction significantly decreased soil POC but increased soil MAOC in the topsoil. Meanwhile, soil MBC, DOC, fine-root biomass, and mycorrhizal fungal biomass were reduced with throughfall reduction. Regression and partial least squares path modeling analyses revealed that soil POC was positively correlated with fine-root biomass, necromass, and mycorrhizal fungal biomass, whereas negative relationships were observed for topsoil MAOC. The results from this study implied that fine roots play an important role in the contrasting responses of POC and MAOC to throughfall reduction in the topsoil. Such information is essential for understanding the roles of plant roots and mycorrhizal fungi in the soil C cycle in subtropical forests under drought conditions.

Deciphering biochar compost co-application impact on microbial communities mediating carbon and nitrogen transformation across different stages of corn development

Under current climatic conditions, developing eco-friendly and climate-smart fertilizers has become increasingly important.The co-application of biochar and compost on agricultural soils has received considerable attention recently.Unfortunately, little is known about its effects on specific microbial taxa involved in carbon and nitrogen transformation in the soil.Herein, we report the efficacy of applying biochar-based amendments on soil physicochemical indices, enzymatic activity, functional genes, bacterial community, and their network patterns in corn rhizosphere at seedling (SS), flowering (FS), and maturity (MS) stages.The applied treatments were: compost alone (COM), biochar alone (BIOC), composted biochar (CMB), fortified compost (CMWB), and the control (no fertilizer (CNTRL).The non-metric multidimensional scaling (NMDS) indicated total nitrogen (TN), pH, NO3−-N, urease, protease, and microbial biomass C (MBC) as the dominant environmental factors driving soil bacteria in this study.The dominant N mediating genes belonged to nitrate reductase (narG) and nitronate monooxygenase (amo), while beta-galactosidase, catalase, and alpha-amylase were the dominant genes observed relating to C cycling.Interestingly, the abundance of these genes was higher in COM, CMWB, and CMB compared with the CNTRL and BIOC treatments.The bacteria network properties of CWMB and CMB indicated robust niche overlap associated with high cross-feeding between bacterial communities compared to other treatments.Path and stepwise regression analyses revealed norank_Reyranellaceae and Sphingopyxis in CMWB as the major bacterial genera and the major predictive indices mediating soil organic C (SOC), NH4+-N, NO3−-N, and TN transformation.Overall, biochar with compost amendments improved soil nutrient conditions, regulated the composition of the bacterial community, and benefited C/N cycling in the soil ecosystem.

Effects of on- and off-year management practices on the soil organic C fractions and microbial community in a Moso bamboo (Phyllostachys edulis) forest in subtropical China.

On- and off-year management practices are usually adopted in Moso bamboo (Phyllostachys edulis) forests to achieve higher productivity. However, little is known about the effects of these management practices on soil C sequestration and microbial community structure. In the present study, soil nutrient content, organic C fractions, and bacterial and fungal communities were comparatively investigated in on- and off-year bamboo stands. The results showed that soil organic C (SOC), alkali-hydrolyzable N (AN), and available P (AP) in the on-year were significantly lower (p ≤ 0.05) than those in the off-year. Among the different soil organic C fractions, easily oxidizable organic C (EOC), microbial biomass C (MBC), Ca-bound SOC (Ca-SOC), and Fe/Al-bound SOC (Fe/Al-SOC) also had significantly higher contents in the off-year than in the on-year, with MBC and EOC decreasing by 56.3% and 24.5%, respectively, indicating that both active and passive soil organic C pools increased in the off-year. However, the alpha diversities of both soil bacteria and fungi were significantly lower in the off-year soils than in the on-year soils. The bacterial taxa Actinobacteria, Planctomycetes, WPS-2, Acidothermus, Candidatus_Solibacter, Burkholderia-Caballeronia-Paraburkholderia, and Candidatus_Xiphinematobacter were increased in off-year soils relative to on-year soils. Meanwhile, fungal taxa Ascomycota, Mortierella, Hypocrea, Cryptococcus, Clitopilus, and Ceratocystis were significantly increased in on-year soils. Soil pH, SOC, AP, MBC, EOC, and Ca-SOC were significantly correlated with bacterial and fungal communities, with soil pH being the most important driving factor for the shift in bacterial and fungal communities. Our findings showed that the studied bamboo forest possessed an inherent restorative ability in the off-year, which can reverse the soil nutrient and C depletion in the on-years and ensure soil fertility in the long term.

Alteration of the soil microbiome and enzyme activities by forage-applied manure from cattle fed the methane inhibitor 3-nitrooxypropanol supplement

The microbial fermentation of plant feed by ruminants produces enteric methane (CH4), a potent greenhouse gas. Supplementing ruminant diets with an experimental methane inhibitor, 3-nitrooxypropanol (3-NOP), has been shown to decrease enteric CH4 production, but the effect of manure from these cattle on the soil microbiome has not been studied. In 2017 and 2018, we examined the effects of stockpiled manure and composted manure from cattle fed 3-NOP supplement alone or in combination with monensin (an ionophore) on soil permanganate-oxidizable C, microbial biomass C (MBC), the composition and diversity of prokaryotic and fungal communities, and the activities of β-glucosidase (C cycling), N-acetyl-β-glucosaminidase (C and N cycling), acid and alkaline phosphomonoesterases (P cycling), and arylsuphatase (S cycling) in a forage cropping system. Stockpiled or composted manure from cattle fed 3-NOP increased MBC in 2017, fungal α-diversity in 2018 and the relative abundance of Actinobacteriota, but it decreased the relative abundances of Acidobacteriota and Basidiomycota, relative to stockpiled or composted manure from cattle that were not fed 3-NOP. In 2017, relative to the conventional stockpiled manure, 3-NOP in stockpiled manure increased the activities of N-acetyl-β-glucosaminidase and acid phosphomonoesterase, but these effects were not observed for composted manure. Monensin, when used in combination with 3-NOP, did not affect any of the soil parameters measured in this study. The core microbiome found in 90 % of the soil samples included the bacterial and fungal genera Vicinamibacteraceae and Solicoccozyma, respectively. Therefore, 3-NOP manure or compost altered the composition of the soil microbiome, and the 3-NOP in stockpiled manure increased the potential activities of enzymes involved in C-and-N and P cycling in the first year of the study, and fungal α-diversity in the second year, but no negative or persistent effects of 3-NOP on enzyme activities were observed.

Soil Labile Organic Carbon Fractions and Carbon Management Index in Response to Different Fertilization under Organic Maize Farming System

Organic farming has been known to improve soil quality by enhancing soil organic carbon (SOC) contents. The labile organic carbon (LOC) pools and carbon management index (CMI) are commonly used as very sensitive indicators of changes in SOC and assessment of soil quality. This study was conducted to investigate the effect of organic farming practices on soil quality by LOC fractions and CMI analysis in a 6-year field experiment. Four treatments were included: compost (COM), green manure (GM), inorganic fertilizer (NPK), and no fertilization (NF). This study was designed to explore changes in SOC concentrations, soil labile organic C fractions (microbial biomass C (MBC), water and hot water-extractable C (WEC, HWEC), particulate organic C (POC), light fraction organic C (LFOC) and permanganate oxidizable C (POXC)) and CMI within the bulk soil under organic corn cultivation condition. Organic fertilization significantly increased SOC concentrations and stocks by 10 - 55% compared to NPK and NF, especially, compost treatment. All labile carbon fractions were higher in COM and GM compared to NPK and NP, except MBC content. Among the LOC fractions, POC showed the highest proportion (32 - 87%) on total SOC. The CMI varied from 0.87 to 2.77, organic fertilized treatments increased by 1.7 - 3.2 times over NPK. These results showed that POC and POXC could be used as a rapid and informative indicator to assess soil quality and SOC changes. Hence, organic farming management could therefore contribute to improved nutrient cycling services and higher soil quality.Effect of different fertilization on labile organic C fractions; water extractable C (WEC), hot-water extractable C (HWEC), microbial biomass C (MBC), permanganate oxidizable C (POXC), particulate organic C (POC) and light fraction organic C (LFOC) in soil.

High stand density promotes soil organic carbon sequestration in Robinia pseudoacacia plantations in the hilly and gully region of the Loess Plateau in China

Planting density has an effect on the accumulation and stabilization of soil organic carbon (SOC) in plantations. However, the mechanism by which SOC dynamics and sequestration respond to stand density is not well understood in Robinia pseudoacacia plantations. Here, we analyzed R. pseudoacacia plantations in the loess hilly-gully region of northern Shaanxi Province, China with three stand densities: 750 trees ha−1 (low-density), 1125 trees ha−1 (medium-density) and 1550 trees ha−1 (high-density). We determined the effects of stand density on SOC, SOC fractions, microbial carbon (C) use efficiency (CUE), and microbial C metabolism function. In particular, soil microbial metabolism function was investigated with the Biolog-ECO microplate. Carbohydrates and amino acids were the main available C sources for soil microbes in R. pseudoacacia plantations. Microbial biomass C (MBC), mineral-associated organic C (MOC), and dissolved organic C (DOC) content were the highest in high-density plantations, whereas easily oxidizable C (EOC) content, the MBC/SOC ratio, the DOC/SOC ratio, and the EOC/SOC ratio were the lowest in high-density plantations. Compared with low- and medium-density plantations, the average SOC content in high-density plantations increased by 61% and 52%, respectively. Across all stands, the MOC/SOC ratio ranged from 32% to 65%, whereas labile C accounted for only a minor portion of SOC (20 ± 8%). A substantially higher CUE and lower microbial metabolic activity were found in high-density plantations. Pearson correlation analysis showed that SOC content was significantly positively correlated with above-ground litter biomass and CUE but was significantly negatively correlated with microbial metabolic activity and liable C/SOC ratios. Mantel tests showed that soil nitrogen (N) level and the microbial biomass C/N ratio were the main factors affecting SOC quantity and stability changes. These results suggested that R. pseudoacacia plantations under high density increased SOC sequestration by increasing C input via aboveground litter and decreased C loss by improving microbial CUE and suppressing microbial metabolic activity. Thus, increasing stand density may be an effective tool for improving SOC sequestration in R. pseudoacacia plantations.

Effects of Precious Tree Introduction into Moso Bamboo Forests on Soil Carbon and Nitrogen Pools

Forest type conversion is an important factor affecting soil carbon (C) and nitrogen (N) pools. Planting precious trees in moso bamboo forest is an important measure taken to establish a mixed forest due to the vulnerable ecological functioning of moso bamboo forest. However, the ways in which soil C and N pools in moso bamboo forest are affected by precious tree introduction are still unclear. A pure moso bamboo forest (BF), a bamboo forest interplanted with Phoebe chekiangensis (BPC), and a bamboo forest interplanted with Taxus wallichiana var. mairei (BTW) were selected. Soil organic C (SOC), total N, microbial biomass C (MBC), microbial biomass N (MBN), water-soluble organic C (WSOC), water-soluble organic N (WSON), and litter C and N concentrations were determined. Our results showed that the concentrations of SOC and N in BF were significantly lower than those in BPC and BTW. The total SOC and N concentrations decreased with increasing soil depth, and they were significantly higher at 0–20 cm than those at 20–40 cm and 40–60 cm. The biomasses of litters and their concentrations of C and N were increased after planting precious trees in moso bamboo forest, and they were significantly lower in BF than in BPC and BTW. In addition, precious tree introduction also improved the concentrations of soil MBC, MBN, WSOC, and WSON. To conclude, planting precious trees in moso bamboo forest significantly increased SOC and N concentrations at soil depths of 0–60 cm.

Relative contributions of fungi and bacteria to litter decomposition under low and high soil moisture in an Australian grassland

Fungi and bacteria differ in their sensitivity to soil moisture, but their activity and contributions to soil carbon (C) cycling under different soil moisture conditions remain unclear. We manipulated soil fungi and bacteria with the fungicide captan and bactericide bronopol, respectively, and examined their effect on C dynamics at low and high moisture levels (40 and 80 % water holding capacity) in a grassland soil over a 21-day incubation period in the laboratory. 13C-labeled ryegrass was added with and without biocide treatments to separate ryegrass from soil-derived C in respiration, dissolved organic C (DOC) and soil C. We also measured activities of four C-degrading enzymes. Soil total- and ryegrass-respiration rates and microbial biomass C (MBC) decreased, while ryegrass-derived C in DOC and soil increased with decreased soil moisture, suggesting reduced microbial activity with decreased soil moisture. Initially, ryegrass respiration rates were suppressed by both biocides and both soil moisture levels. However, at low soil moisture, ryegrass respiration no longer was suppressed by bronopol after eight days of incubation, but remained suppressed with captan, suggesting that with low moisture fungi played a more important role in decomposing ryegrass litter than bacteria. On the other hand, at high soil moisture, biocide effects on ryegrass respiration mostly disappeared after eight days, suggesting that more labile components of ryegrass litter were no longer present, and that the surviving microorganisms adapted similarly to decomposing the more recalcitrant litter. Bacteria preferred to decompose labile substrates early on during the incubation, and fungi played a greater role in decomposing more recalcitrant ryegrass left over in soil at the end of the incubation. At low moisture with captan, a reduction in oxidative enzyme production contributed to the increase in the hydrolytic:oxidative enzyme ratio, further indicating the importance of fungi for decomposing more recalcitrant substances under low moisture conditions.

Effects of enhanced-efficiency nitrogen fertilizers on CH4 and CO2 emissions in a global perspective

It is widely recommended that enhanced efficiency nitrogen fertilizers (EENFs; urease inhibitors, nitrification inhibitors, urease and nitrification inhibitors combined, coated controlled-release urea) be applied to croplands to improve N use efficiency and crop yield via regulating N transformations. However, EENFs may inevitably affect soil C dynamics for the coupled relationship between soil carbon (C) and N biogeochemical cycles. Yet, a comprehensive assessment of the effects of EENFs on soil C dynamics is lacking. Here, we conducted a global meta-analysis using 67 publications to assess the overall effects of EENFs on soil CH 4 production, CO 2 emission, organic C (SOC) content, dissolved organic C (DOC) content, microbial biomass C (MBC) content under different environmental and management conditions (climate conditions, soil properties and fertilizer management practices). Our results showed that on average, compared to conventional N fertilizer, EENFs with the same amount of N fertilizer have a non-significant impact on CH 4 emission, which further depended on environmental and management conditions. Best scenarios for CH 4 reduction included: paddy field (25.8%), urease inhibitor (26.9%) and medium N application rate (150–300 kgN ha −1 ; 23.6%), mainly due to the decreased stimulation of NH 4 + on CH 4 production; acid soil (33.7%), which was attributed to the enhanced methanotrophic communities' activities. The positive effect was also amplified by the increased mean annual precipitation and soil clay content that facilitated CH 4 production. Contrarily, EENFs significantly reduced CO 2 emission by 9.3%. The greater reduction was observed for the conditions producing more CO 2 after fertilization, i.e. field experiment, alkaline soils, low soil inorganic N content and high N application rate (≥300 kgN ha −1 ). Nitrification inhibitors and coated N fertilizer were the best available options as they can reduce inorganic C dissolution in calcareous soil and SOC mineralization, respectively. Besides, EENFs application did not significantly alter SOC, DOC and MBC contents. Our findings highlighted the role of EENFs played in decreasing soil C emission in agroecosystems. • Global use of EENFs did not significantly affect SOC, DOC, MBC contents. • EENFs succeed in reducing CO 2 emission (9.3%) rather than CH 4 emission. • EENFs provide a viable solution for decreasing soil C emissions in global agroecosystems.

Biodynamic compost effects on soil parameters in a 27-year long-term field experiment

BackgroundSoil samples were taken after 27 years from a long-term field experiment to study the effects of composted pure cattle farmyard manure (FYM) and two FYM treatments with biodynamic preparations on soil chemical and microbiological properties.MethodsSoil organic carbon (SOC), total nitrogen, basal respiration, fungal ergosterol, microbial biomass C (MBC) and nitrogen (MBN) were analyzed in a 6-field crop rotation system, conducted as a randomized block design with six replicates. The multi-substrate-induced respiration (multi-SIR) approach was used to assess microbial functional diversity by the respiratory response of 17 low molecular weight organic substances.ResultsAll composted FYM treatments revealed generally positive effects on SOC, total N, basal respiration, MBC, and MBN in contrast to control without FYM. Only fungal ergosterol was not increased by FYM application. After 27 experimental years, discriminant function analysis of multi-SIR data not only revealed significant general effects of biodynamic preparations, but was also able to differentiate between the sole application of the Achillea millefolium preparation and the standard application of all 6 biodynamic compost preparations.ConclusionsThe Achillea preparation was specifically able to improve the N status of the microbial community as indicated by the higher catabolic use of D-glucosamine as well as the amino acids γ-aminobutyric acid, L-cysteine, and L-leucine. The reason for different effects of the sole Achillea preparation and all 6 preparations cannot be explained by the current study.Graphical