Soil biogeochemical cycling
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    Wei Zhang, Rick Muir, Nicholas Dickinson
    Soil Ecology Letters, 2024, 6(1): 230187.

    ● Nutrient constraints in low-fertility soil were modified by different species combinations.

    ● Grass-clover assemblages benefited both species in terms of nutrient procurement.

    ● Interplay of competition and facilitation is demonstrated.

    ● An invasive weed removed essential nutrients from the grazing cycle.

    To investigate the interplay of competition and facilitation between plants in low-fertility pasture grasslands of New Zealand, we compared nutrient uptake and acquisition of key nutrients of three species from different functional groups. Combinations of Pilosella officinarum (mouse-eared hawkweed, an invasive weed), Trifolium repens (white clover, a nitrogen fixer) and Dactylis glomerata (cocksfoot, a pasture grass) were planted into a soil with low-to-deficient concentrations of key nutrients. Highest yields were achieved by the grass growing alone but, when the clover and grass had grown together, there were complementary benefits in terms of procurement of a wide range of nutrients from soil despite lower root biomass. The invasive weed negated these benefits, and soil nutrients were exploited less efficiently when Pilosella had grown alone or in a mixture with the other species. Competition from the weed removed the benefits of grass-legume coexistence. These findings are interpreted to suggest that requirements for legumes to be the main source of nitrogen in pasture grasslands may be compromised unless competitive weeds are controlled to avoid disrupted procurement of key nutrients. It is likely these constraints to nutrient procurement would similarly impact conservation grasslands.

    Zhenhui Jiang, Xin Wang, Ting Liu, Xiaojuan Feng
    Soil Ecology Letters, 2024, 6(1): 230189.

    ● No consistent variation was found in soil respiration Q10 under various O2 conditions.

    ● Substrate C quality had a strong effect on Q10 in oxic soils.

    ● N limitation had a large impact on Q10 in soils under O2 limitation.

    Current studies on the temperature sensitivity (Q10) of soil organic matter (SOM) decomposition mainly focus on aerobic conditions. However, variations and determinants of Q10 in oxygen (O2)-deprived soils remain unclear. Here we incubated three grassland soils under oxic, suboxic, and anoxic conditions subjected to varying temperatures to compare variations in Q10 in relation to changing substrates. No consistent variation was found in Q10 under various O2 conditions. Further analysis of edaphic properties demonstrated that substrate carbon quality showed a strong influence on Q10 in oxic soils, whereas nitrogen limitation played a more important role in suboxic and anoxic soils. These results suggest that substrate carbon quality and nitrogen limitation may play roles of varying importance in determining the temperature sensitivity of SOM decomposition under various O2 conditions.

    Yaping Zhao, Yuqing Zhao, Shuohong Zhang, Yulin Xu, Xinhui Han, Gaihe Yang, Chengjie Ren
    Soil Ecology Letters, 2024, 6(1): 230188.

    ● Afforestation effectively improved soil microbial communities and significantly increased soil nitrogen mineralization rate ( R m).

    ● Soil microorganisms drive R m by regulating soil N-cycling genes.

    ● Soil nitrification genes had a major effect on soil R m than denitrification genes after afforestation.

    Assessing the function of forest ecosystems requires an understanding of the mechanism of soil nitrogen mineralization. However, it remains unclear how soil N-cycling genes drive soil nitrogen mineralization during afforestation. In this study, we collected soil samples from a chrono-sequence of 14, 20, 30, and 45 years of Robinia pseudoacacia L. (RP14, RP20, RP30, and RP45) with a sloped farmland (FL) as a control. Through metagenomic sequencing analysis, we found significant changes in the diversity and composition of soil microbial communities involved in N-cycling along the afforestation time series, with afforestation effectively increasing the diversity (both alpha and beta diversity) of soil microbial communities. We conducted indoor culture experiments and analyzed correlations, which revealed a significant increase in both soil nitrification rate (Rn) and soil nitrogen mineralization rate (Rm) with increasing stand age. Furthermore, we found a strong correlation between soil Rm and soil microbial diversity (both alpha and beta diversity) and with the abundance of soil N-cycling genes. Partial least squares path modeling (PLS-PM) analysis showed that nitrification genes (narH,narY,nxrB, narG,narZ,nxrA, hao, pmoC-amoC) and denitrification genes (norB, nosZ, nirK) had a greater direct effect on soil Rm compared to their effect on soil microbial communities. Our results reveal the relationships between soil nitrogen mineralization rate and soil microbial communities and between the mineralization rate and functional genes involved in N-cycling, in the context of Robinia pseudoacacia L. restoration on the Loess Plateau. This study enriches the understanding of the effects of microorganisms on soil nitrogen mineralization rate during afforestation and provides a new theoretical basis for evaluating soil nitrogen mineralization mechanisms during forest succession.

    Michael N. Weintraub
    Soil Ecology Letters, 2023, 5(4): 230183.
    Shi Yao, Yongrong Bian, Xin Jiang, Yang Song
    Soil Ecology Letters, 2023, 5(4): 230179.

    ● Characterization of mollisol soil DOM by untargeted metabolomics is possible.

    ● The polarity of the extractants determines the polarity of the extracted DOM.

    ● Land use patterns affect the biological functions and co-network interaction of DOM.

    Mollisol soil is a major contributor to food production. Clarification of the molecular characteristics of dissolved organic matter (DOM) will contribute to the overall understanding and management of mollisol soil. However, the complexity of DOM poses a challenge to understanding its molecular characteristics. In this study, we investigated the molecular characteristics of DOM (< 1000 Da) in mollisol soils with different soil use patterns (forestland and dryland) based on untargeted metabolomics. Here, we confirmed the feasibility of untargeted metabolomics for the molecular characterization of DOM in mollisol soils. DOM in forestland is mainly derived from plant metabolites, and DOM can perform more biological functions. However, DOM in dryland has complex composition and has powerful co-occurrence network interactions due to human activities. Water has better extraction efficiency for polar DOM, while organic reagents can efficiently extract lipid-like DOM, but the polarity of the extractant has less influence on the DOM than the soil physicochemical properties. Meanwhile, 14-dihydroxyzeatin screened based on metabolomics can be used as a potential indicator for corn land. Therefore, untargeted metabolomics can be an effective method to characterize the DOM molecules of mollisol soil, which provides new insights for management of mollisol soil and sustainable agricultural development.

    Tao Lu, Nuohan Xu, Chaotang Lei, Qi Zhang, Zhenyan Zhang, Liwei Sun, Feng He, Ning-Yi Zhou, Josep Peñuelas, Yong-Guan Zhu, Haifeng Qian
    Soil Ecology Letters, 2023, 5(4): 230172.

    ● 6102 high-quality sequencing results of soil bacterial samples were re-analyzed.

    ● The type of land use was the principal driver of bacterial richness and diversity.

    ● SOC content is positively correlated with key bacteria and total nitrogen content.

    Soil organic carbon (SOC) is the largest pool of carbon in terrestrial ecosystems and plays a crucial role in regulating atmospheric CO2 concentrations. Identifying the essential relationship between soil bacterial communities and SOC concentration is complicated because of many factors, one of which is geography. We systematically re-analyzed 6102 high-quality bacterial samples in China to delineate the bacterial biogeographic distribution of bacterial communities and identify key species associated with SOC concentration at the continental scale. The type of land use was the principal driver of bacterial richness and diversity, and we used machine learning to calculate its influence on microbial composition and their co-occurrence relationship with SOC concentration. Cultivated land was much more complex than forest, grassland, wetland and wasteland, with high SOC concentrations tending to enrich bacteria such as Rubrobacter, Terrimonas and Sphingomona. SOC concentration was positively correlated with the amounts of soil total nitrogen and key bacteria Xanthobacteraceae, Streptomyces and Acidobacteria but was negatively correlated with soil pH, total phosphorus and Micrococcaceae. Our study combined the SOC pool with bacteria and indicated that specific bacteria may be key factors affecting SOC concentration, forcing us to think about microbial communities associated with climate change in a new way.

    Junhui Yin, Huaihai Chen, Pengpeng Duan, Kun Zhu, Naihui Li, Yan Ma, Yumeng Xu, Jingheng Guo, Rui Liu, Qing Chen
    Soil Ecology Letters, 2023, 5(4): 230178.

    ● Soil pH was a key driver of N2O emission and sources in acidic soils.

    ● N2O emission was significantly positively associated with the ratio of ITS to 16S.

    ● N2O was significantly correlated with bacterial and fungal community composition.

    ● Fungi contributed to N2O in highly acidic tea plantations and vegetable fields.

    Acidic soil is a main source of global nitrous oxide (N2O) emissions. However, the mechanism behind the high N2O emissions from acidic soils remains a knowledge gap. The objective of this microcosm incubation study was to pin-point the microbial mechanisms involved in N2O production processes in acidic soils. For that purpose, the isotopic signatures and microbial community structure and composition of four soil samples were examined. The results showed that highly acid soils (pH = 3.51) emitted 89 times more N2O than alkaline soils (pH = 7.95) under the same nitrogen (N) inputs. Fungal denitrification caused high N2O emissions in acidic soils. ITS to 16S abundance ratio was positively correlated with cumulative N2O emissions from the tested soils. The highly acid soils (pH < 4.5) showed greater fungal nirK gene abundance and lower abundance of AOA-amoA, AOB-amoA, nirK, nosZ I and nosZ II genes. The unclassified Aspergillaceae fungi (63.65%) dominated the highly acidic soils and was the most strongly correlated genus with N2O emissions. These findings highlight that soil microbial community structures, denitrifying fungi in particular, shaped by low pH (pH < 4.5) lead to high N2O emissions from acidic soils.

    Xuebing Zhang, Guangting Pei, Tianyu Zhang, Xianlei Fan, Ziping Liu, Edith Bai
    Soil Ecology Letters, 2023, 5(4): 230176.

    ● Soil erosion decreased soil microbial CUE and increased microbial uptake of carbon.

    ● Soil erosion decreased microbial CUE by decreasing substrate C, N and MBC and increasing soil pH.

    ● Soil microbes had to increase their uptake rate to cope with the loss of substrates with increasing erosion rate.

    ● Soil microbial respiration increased with increasing degree of erosion.

    ● Soil microbial growth rate remained relative stable under different degrees of soil erosion.

    ● Microbial CUE in soil surface was less responsive to erosion than that in deeper soil.

    Soil microbial carbon use efficiency (CUE) is an important synthetic parameter of microbial community metabolism and is commonly used to quantify the partitioning of carbon (C) between microbial growth and respiration. However, it remains unclear how microbial CUE responds to different degrees of soil erosion in mollisol cropland. Therefore, we investigated the responses of soil erosion on microbial CUE, growth and respiration to different soil erosion rates in a mollisol cropland in northeast China based on a substrate independent method (18O-H2O labeling). Soils were sampled at four positions along a down-slope transect: summit, shoulder, back and foot. We found microbial CUE decreased significantly with increasing soil erosion rate in 5−20 cm soil, but did not change in 0−5 cm. The decrease of microbial CUE in subsoil was because microbes increased C uptake and allocated higher uptake C to microbial basal respiration with increasing soil erosion rate. Microbial respiration increased significantly with soil erosion rate, probably due to the more disturbance and unbalanced stoichiometry. Furthermore, soil microbes in surface soil were able to maintain their growth rates with increasing degree of erosion. Altogether, our results indicated that soil erosion could decrease microbial CUE by affecting soil physical and chemical properties, resulting in more decomposition of soil organic matter and more soil respiration, which had negative feedbacks to soil C sequestration and climate changes in cropland soil.

    Fang-Jie Zhao
    Soil Ecology Letters, 2023, 5(3): 220170.
    Yingdong Huo, Guoqing Hu, Xu Han, Hui Wang, Yuping Zhuge
    Soil Ecology Letters, 2023, 5(4): 220168.

    ● In low-salinity soil, straw-returning did not change necromass contribution to SOC.

    ● In medium-salinity soil, straw-returning reduced necromass contribution to SOC.

    ● Straw-returning reduced POC contribution to SOC in low-salinity soil.

    ● Straw-returning increased POC contribution to SOC in medium-salinity soil.

    ● Salinity affects the contribution of microbial-derived and plant-derived C to SOC.

    Salinization affects microbial-mediated soil organic carbon (SOC) dynamics. However, the mechanisms of SOC accumulation under agricultural management practices in salt-affected soils remain unclear. We investigated the relative contribution of microbial-derived and plant-derived C to SOC accumulation in coastal salt-affected soils under straw-returning, by determining microbial necromass biomarkers (amino sugars) and particulate organic C (POC). Results showed that, straw-returning increased necromass accumulation in low-salinity soil but did not change its contribution to SOC. In medium-salinity soil, straw-returning did not increase necromass accumulation but decreased its contribution to SOC. In low- and medium-salinity soils, the contribution of POC to SOC showed the opposite direction to that of the necromass. These results suggest that under straw-returning, the relative contribution of microbial-derived C to SOC decreased with increasing salinity, whereas the reverse was true for plant-derived C. Our results highlighted that straw-returning reduces the contribution of microbial anabolism to SOC accumulation in salt-affected soils with increasing salinity.

    Zhaoan Sun, Tianxiang Hao, Biao Zhu
    Soil Ecology Letters, 2023, 5(4): 220169.

    ● We studied the effect of nitrogen and biochar on CO2 emission from SOC and SIC.

    ● Nitrogen increased SIC-derived CO2 by 41% but decreased SOC-derived CO2 by 20%.

    ● Biochar reduced total soil-derived CO2 by neutralizing nitrogen-induced acidity.

    ● We proposed a method for 3- or 4-source partitioning CO2 emission from calcareous soils.

    Biochar addition generally increases the alkalinity regeneration to resist soil acidification driven by nitrogen (N) fertilization. Calcareous soils contain soil organic carbon (SOC) and inorganic C (SIC). Owing to technical limitations in three-source partitioning CO2, how biochar addition affects SOC- and SIC-derived CO2 emission has not been clarified yet. Therefore, we conducted a 70-day incubation experiment of ammonium-N and maize-straw-derived biochar additions to investigate the N plus biochar impacts on SOC- and SIC-derived CO2 emission. Over the 70-day incubation, we found that the N-only addition increased the SIC-derived CO2 emission by approximately 41% compared with the control, but decreased the SOC-derived CO2 emission by approximately 20%. This suggests that the distinct responses of SIC- and SOC-derived CO2 emission to N-only addition come from N-induced acidification and preferential substrate (N) utilization of soil microorganisms, respectively. Compared with N-only addition, N plus biochar addition decreased the SIC-derived CO2 emission by 17%−20% during the first 20 days of incubation, but increased it by 54% during the next 50 days. This result suggested that biochar addition reduced the SIC-derived CO2 emission likely due to the alkalization capacity of biochar exceeding the acidification capacity of ammonium-N in the short term, but it may increase the SIC-derived CO2 emission induced by the weak acidity produced from biochar mineralization in the long term. This study is helpful to improve the quantification of CO2 emission from calcareous soils.

    Erika Valente de Medeiros, Érica de Oliveira Silva, Gustavo Pereira Duda, Mario Andrade Lira Junior, Uemeson José dos Santos, Claude Hammecker, Diogo Paes da Costa, Fabio Fernando Araujo, Arthur Prudêncio de Araujo Pereira, Lucas William Mendes, Ademir Sergio Ferreira Araujo
    Soil Ecology Letters, 2023, 5(3): 220159.

    ● The enzymatic stoichiometry varied between land-use in both soil depth.

    ● The values of C- and N-acquiring enzymes were higher at 0−5 cm depth.

    ● Soils under different land-use types in the Brazilian semiarid are P-limited.

    This study hypothesized that different land-use affect the microbial enzymatic stoichiometry and C-, N-, and P-acquisition in Brazilian semiarid soils. Thus, the enzymes β-glucosidase (C-acquiring enzyme), urease (N-acquiring enzyme), and acid phosphatase (P-acquiring enzyme) were assessed in soil samples collected at 0−5 and 5−10 cm depth from a tropical dry forest, a protected area with Angico, a protected area with Ipê, scrub area, and an agricultural area with maize. The values of C-, N-, and P-acquiring enzymes were used to calculate the enzymatic C:N, C:P, and N:P ratios. The values of C:P and N:P ratios were higher at 0−5 cm depth, while no significant variation, between soil depth, was observed for C:N ratio. The values of C- and N-acquiring enzymes were higher at 0−5 cm in tropical dry forest areas and Angico forest, respectively. In all land use types, the values of vectors L and A were higher than 1° and 45°, respectively. This study showed that both land-use and soil depth influence the enzymatic stoichiometry, showing higher values of C- and N-acquiring enzymes in native and protected forests at soil surface.

    Shinichi Watanabe, Makoto Shibata, Yoshiko Kosugi, Lion Marryanna, Keitaro Fukushima, Arief Hartono, Shinya Funakawa
    Soil Ecology Letters, 2023, 5(3): 220167.

    ● Some O horizons showed higher nitrification rate than mineral horizons.

    ● Both total N and pH were positively correlated with nitrification rate in O horizon.

    ● Nutrient richness in litters supported active nitrification in O horizon.

    ● Nitrification rate in O horizon increased along with a pH threshold of 5.5–6.0.

    High nitrate leaching has been observed from the O horizons of some tropical forests; however, the drivers of high nitrate production (active nitrification) in these O horizons have not yet been identified. This study investigated the drivers of active nitrification in the O horizon of tropical forest soils by focusing on two of the most widely recognized controlling factors of nitrification, total N, and pH. We collected mineral and O horizons from eight tropical forests in Cameroon, Indonesia, and Malaysia and measured gross nitrification rates. Some O horizons showed significantly higher gross nitrification rates than mineral horizons, indicating that these O horizons have a high potential for nitrification. Gross nitrification rates in the O horizons were positively correlated with both total N and pH, and the chemical properties (e.g., total content of N, P, and base cations) were intercorrelated. These correlations suggested that the underlying driver of nitrification in the O horizon was nutrient richness in the litter. Results also indicated a threshold of gross nitrification rates around pH values of 5.5–6.0. We elucidate that active nitrification and subsequent high nitrate leaching from the O horizon could be driven by nutrient-rich litter, possibly derived from soil fertility and tree species.

    Ruibo Sun, Daozhong Wang, Zhibin Guo, Keke Hua, Xisheng Guo, Yan Chen, Binbin Liu, Haiyan Chu
    Soil Ecology Letters, 2023, 5(3): 220165.

    ● The abundance of N-cycling genes differently responded to NPK application.

    ● Chemical NPK application greatly altered the N-cycling microbial community structure.

    ● Soil acidification was the main driver for the variation in the N-cycling microbial community.

    ● Manure addition was beneficial for stabilizing the N-cycling microbial community.

    Straw and manure are widely applied to agricultural systems, and greatly shape soil N-cycling microflora. However, we still lack a comprehensive understanding of how these organic materials structure soil N-cycling microbial communities. In this study, metagenomic analysis was performed to investigate the compositional variation in N-cycling microbial communities in a 30-year long-term experiment under five fertilization regimes: no fertilization (Control), chemical fertilization only (NPK), and NPK with wheat straw (NPK + HS), pig manure (NPK + PM), and cow manure (NPK + CM). Long-term NPK application differentially changed N-cycling gene abundance and greatly altered N-cycling microbial community structure. NPK + HS resulted in a similar pattern to NPK in terms of gene abundance and community structure. However, NPK + PM and NPK + CM significantly increased most genes and resulted in a community similar to that of the Control. Further analysis revealed that serious soil acidification caused by long-term NPK fertilization was a major factor for the variation in N-cycling microbial communities. The addition of alkaline manure, rather than wheat straw, stabilized the N-cycling microbial community structure presumably by alleviating soil acidification. These results revealed the strong impact of soil acidification on microbial N-cycling communities and illustrated the possibility of resolving nitrogen-related environmental problems by manipulating pH in acidified agricultural soils.

    Xiao Liu, Xia Xu, Tian Ma, Shiwei Zhou, Xiaoli Bi, Hongbo He, Xudong Zhang, Weihuan Li
    Soil Ecology Letters, 2023, 5(2): 220140.

    ● SOC stocks and MCP capacity and efficacy decreased under medium and heavy pollution.

    ● The decrease in MCP capacity was tightly related to the decline in SOC storage.

    ● The lower MCP efficacy implied worse SOC stability under the heavier level.

    Heavy metal pollution can lead to a great loss of soil organic carbon (SOC). However, the microbial mechanisms that link heavy metal pollution to SOC remain poorly understood. Here, we investigated five apple-orchard soils at different distances from a Pb-Zn smelter. After assessing the heavy metal pollution level based on Grade II of the national soil environmental quality standard (China), we found SOC stocks and microbial carbon pump (MCP) capacity (i.e., microbial residue carbon) under medium and heavy pollution levels were significantly lower than those under safe, cordon and light pollution levels. The structural equation model showed causality in the SOC variations linked to pollution level through MCP capacity, which could contribute 77.8% of the variance in SOC storage. This verified MCP capacity can serve as a key parameter for evaluation of SOC storage under heavy metal pollution. Soil MCP efficacy, i.e., the proportion of microbial residue carbon to SOC, also decreased under medium and heavy pollution. This suggested that, with a heavier pollution level, there was a higher rate of reduction of microbial residue carbon in soil than the rate of reduction of SOC. As MCP efficacy can be a useful assessment of SOC stability, the significantly positive relationship between MCP efficacy and clay content in correlation analysis implied that lower MCP efficacy was correlated with SOC stability under the heavier pollution level. Our study provides valuable insights to identify the mechanisms of microbially mediated C transformation processes that are influenced by heavy metal pollution in agroecosystems.

    Panpan Jiao, Lei Yang, Xiaodong Nie, Zhongwu Li, Lin Liu, Peng Zheng
    Soil Ecology Letters, 2023, 5(2): 220147.

    ● The bacterial and fungal diversity decreased greater in 5%−36% DRW than 5%−25% DRW.

    ● Fungal network was complicated after 1-cycle DRW, but that for bacteria occurred until 4-cycle DRW.

    ● Stronger DRW treatment enhanced the pulse amplitude of respiration in soil.

    Altered drying-rewetting (DRW) procedures due to climate change may influence soil microbial properties and microbially-mediated carbon cycling in arid and semi-arid regions. However, the effects of DRW of different intensities on the microbial properties and respiration are not well understood. Thus, the responsive patterns of microbial communities and carbon mineralization in agriculture soil on the Chinese Loess Plateau to DRW treatments with different wetting intensities (5%−25% and 5%−36%) and frequency (1-cycle to 4-cycle) were investigated. Continuous moisture levels of 5%, 25% and 36% were used as control. Results revealed that the reduction of bacterial diversity and richness were greater for 5%−36% than 5%−25% treatment, while diversity of fungi was similar for different wetting intensities. Bacterial communities became clustered by wetting intensity rather than cycle number, however fungal community was unaffected by DRW. The complexity of bacterial co-occurrence network increased because of higher nodes, edges, average degree, diameter and average cluster coefficient after 4-cycles, and the interaction was more complex after 1-cycle for fungi. Rewetting caused a pulse-like increase of respiration rate, and the pulse amplitude was greater for DRW with high rewetting intensity and decreased with the increase of cycle number. The cumulative CO2 emission for DRW treatments was lower than that for the continuous moisture conditions. The net reduction of carbon release for 5%−36% treatment was 1.18 times higher than that for 5%−25% treatment. Our study provides experimental evidence of the positive potential of DRW processes for maintaining soil carbon stock in an agriculture system on the Loess Plateau.

    Stavros D. Veresoglou, Junjiang Chen, Xuheng Du, Qi Fu, QingLiu Geng, Chenyan Huang, Xilin Huang, Nan Hu, Yiming Hun, Guolin C. Li, Zhiman Lin, Zhiyu Ma, Yuyi Ou, Shuo Qi, Haitian Qin, Yingbo Qiu, Xibin Sun, Ye Tao, YiLing Tian, Jie Wang, Lingxiao Wu, Ziwei Wu, Siqi Xie, Ao Yang, Dan Yang, Chen Zeng, Ying Zeng, RuJie Zhang
    Soil Ecology Letters, 2023, 5(1): 137-141.

    ● On average conventional tillage outperformed no tillage.

    ● Across fertilized trials, however, no tillage performed best.

    ● Aridity increases yield benefits of no tillage over conventional tillage.

    ● Fertile settings favor conventional tillage over no tillage.

    Reduced tillage practices present a tool that could sustainably intensify agriculture. The existing literature, however, lacks a consensus on how and when reduced tillage practices should get implemented. We reanalyzed here an extensive dataset comparing how regular tillage practices (i.e., conventional tillage) impacted yield of eight crops compared to stopping tillage altogether (i.e., no-tillage practice). We observed that aridity and fertilization favored no tillage over conventional tillage whereas conventional tillage performed better under high fertility settings. We further show that the responses are consistent across the crops. Our reanalysis complements the original and fills a gap in the literature questioning the conditions under which reducing tillage presents a viable alternative to common tillage practices.

    Zhaoan Sun, Fanqiao Meng, Biao Zhu
    Soil Ecology Letters, 2023, 5(1): 6-20.

    ● This study reviewed the contribution of carbonates to soil CO2 emissions.

    ● The contribution was on average 27% in calcareous soils.

    ● The contribution was affected by both biotic and abiotic factors.

    ● We proposed a new method of distinguishing three CO2 sources from calcareous soils.

    In calcareous soils, recent studies have shown that soil-derived CO2 originates from both soil organic carbon (SOC) decomposition and soil inorganic carbon (SIC) dissolution, a fact often ignored in earlier studies. This may lead to overestimation of the CO2 emissions from SOC decomposition. In calcareous soils, there is a chemical balance between precipitation and dissolution of CaCO3-CO2- HCO3, which is affected by soil environmental factors (moisture, temperature, pH and depth), root growth (rhizosphere effect) and agricultural measures (organic materials input, nitrogen fertilization and straw removal). In this paper, we first introduced the contribution of SIC dissolution to CO2 emissions from calcareous soils and their driving factors. Second, we reviewed the methods to distinguish two CO2 sources released from calcareous soils and quantify the 13C fractionation coefficient between SIC and SIC-derived CO2 and between SOC and SOC-derived CO2, and to partition three CO2 sources released from soils with plants and organic materials input. Finally, we proposed methods for accurately distinguishing three CO2 sources released from calcareous soils. This review helps to improve the accuracy of soil C balance assessment in calcareous soils, and also proposes the direction of further investigations on SIC-derived CO2 emissions responses to abiotic factors and agricultural measures.

    Muhammad Azeem, Sajjad Raza, Gang Li, Pete Smith, Yong-Guan Zhu
    Soil Ecology Letters, 2022, 4(4): 293-306.

    ● Soil acidification caused severe losses of soil inorganic carbon stock worldwide.

    ● SIC losses could be mitigated via alkalinity regeneration approaches.

    ● Rock/mineral powder can supply substantial basic cations to soil to reduce acidification.

    ● Microorgnisms could be utilized to enhance weathering of rock/mineral powder.

    ● Biochar and bone biochar could reduce SIC losses via alkalinity regeneration.

    Soil inorganic carbon (SIC) accounts for about half of the C reserves worldwide and is considered more stable than soil organic carbon (SOC). However, soil acidification, driven mainly by nitrogen (N) fertilization can accelerate SIC losses, possibly leading to complete loss under continuous and intensive N fertilization. Carbonate-free soils are less fertile, productive, and more prone to erosion. Therefore, minimizing carbonate losses is essential for soil health and climate change mitigation. Rock/mineral residues or powder have been suggested as a cheaper source of amendments to increase soil alkalinity. However, slow mineral dissolution limits its efficient utilization. Soil microorganisms play a vital role in the weathering of rocks and their inoculation with mineral residues can enhance dissolution rates. Biochar is an alternative material for soil amendments, in particular, bone biochar (BBC) contains higher Ca and Mg that can induce even higher alkalinity. This review covers i) the contribution and mechanism of rock residues in alkalinity generation, ii) the role of biochar or BBC to soil alkalinity, and iii) the role of microbial inoculation for accelerating alkalinity generation through enhanced mineral dissolution. We conclude that using rock residues/BBC combined with microbial agents could mitigate soil acidification and SIC losses and also improve agricultural circularity.

    Qiufang Zhang, Wenkuan Qin, Jiguang Feng, Biao Zhu
    Soil Ecology Letters, 2022, 4(4): 307-318.

    ● This study reviewed the effect of warming on microbial carbon use efficiency (CUE).

    ● Different measurement method is one of the key reasons for the variation of CUE.

    ● The warming effect on CUE is complicated by changes in biotic and abiotic factors.

    ● Future research on CUE should focus on new methods, multi-factor experiments, etc.

    Microbial carbon use efficiency (CUE) is an important factor driving soil carbon (C) dynamics. However, microbial CUE could positively, negatively, or neutrally respond to increased temperature, which limits our prediction of soil C storage under future climate warming. Experimental warming affects plant production and microbial communities, which thus can have a significant impact on biogeochemical cycles of terrestrial ecosystems. Here, we reviewed the present research status of methods measuring microbial CUE and the response of microbial CUE to the changes of biotic and abiotic factors induced by warming. Overall, current measurement methods mainly include metabolic flux analysis, calorespirometry, stoichiometric model, 13C and 18O labeling. Differences in added substrate types can lead to an overestimation or underestimation on microbial CUE, particularly when using the 13C labeling method. In addition, changes in the dominant microbial community under warming may also affect CUE. However, there is still uncertainty in CUE characteristics of different microorganisms. Microbial CUE is generally decreased under warming conditions as microbes are subjected to water stress or soil labile organic matter is much more depleted compared to ambient conditions. In contrast, considering that warming increases soil nutrient availability, warming may enhance microbial CUE by alleviating nutrient limitations for microbes. In conclusion, the response of microbial CUE to warming is more complex than expected. The microbial growth and physiological adaptation to environmental stress under warming is one of the main reasons for the inconsistence in microbial CUE response. Finally, we propose five aspects where further research could improve the understanding of microbial CUE in a warmer world, including using new technologies, establishing multi-factor interactive experiments, building a network of experimental research platform for warming, and strengthening studies on response of CUE to warming at different soil depths and on different temporal scales.

    Lin Mei, Yihong Yue, Yong Qin, Xueping Chen, Fushun Wang
    Soil Ecology Letters, 2022, 4(4): 399-408.

    • A calibration models for the rapid determination of TOC and TN contents using FTIRS.

    • Ÿ A rapid analytical method for quantitatively calculating TOC and TN.

    Ÿ• A general model for TOC and TN quantitative analysis in reservoir sediments in the southwest China.

    This study aims to quantitatively assess the total organic carbon (TOC) and total nitrogen (TN) content of reservoir sediments in southwest China using Fourier transform infrared spectroscopy (FTIRS). FTIRS measurements were performed on 187 sediment samples from four reservoirs to develop calibration models that relate FTIR spectral information with conventional property concentrations using partial least squares regression (PLSR). Robust calibration models were established for TOC and TN content. The external validation of these models yielded a significant correlation between FTIR-inferred and conventionally measured concentrations of R2 = 0.88 for TOC, R2 = 0.90 for TN. This method can be performed with a small sample size and is non-destructive throughout the simple measurement process. The TOC and TN content in the sediment can be determined with high effectiveness without being overly expensive, making it an advantageous method when measuring a large number of samples.

    Pengshuai Shao, Tian Li, Kaikai Dong, Hongjun Yang, Jingkuan Sun
    Soil Ecology Letters, 2022, 4(4): 328-336.

    • SIC was higher at a low salinity of<6‰, and declined with increased salinity.

    • SOC and microbial residues exponentially decreased during increasing salinity.

    • Microbial residues and SOC was tightly related to the variations in SIC.

    • Microbial residues act as the proxy converting SIC to SOC in saline lands.

    Soil inorganic carbon (SIC), including mainly carbonate, is a key component of terrestrial soil C pool. Autotrophic microorganisms can assimilate carbonate as the main or unique C source, how microorganisms convert SIC to soil organic carbon (SOC) remains unclear. A systematic field survey (n = 94) was performed to evaluate the shift in soil C components (i.e., SIC, SOC, and microbial residues) along a natural salinity gradient (ranging from 0.5‰ to 19‰), and further to explore how microbial necromass as an indicator converting SIC into SOC in the Yellow River delta. We observed that SIC levels linearly decreased with increasing salinity, ranging from ~12 g kg−1 (salinity<6‰) to ~10 g kg−1 (salinity >6‰). Additionally, the concentrations of SOC and microbial residues exponentially decreased from salinity<6‰ to salinity >6‰, with the decline of 39% and 70%, respectively. Microbial residues and SOC was tightly related to the variations in SIC. The structural equation model showed the causality on explanation of SOC variations with SIC through microbial residues, which can contribute 89% of the variance in SOC storage combined with SIC. Taken together, these two statistical analyses can support that microbial residues can serve as an indicator of SIC transition to SOC. This study highlights the regulation of microbial residues in SIC cycling, enhancing the role of SIC playing in C biogeochemical cycles and enriching organic C reservoirs in coastal saline soils.

    Zhijie Li, Rüdiger Reichel, Zimin Li, Kaijun Yang, Li Zhang, Bo Tan, Rui Yin, Kerui Zhao, Zhenfeng Xu
    Soil Ecology Letters, 2022, 4(4): 376-382.

    • Snow absence increased soil N availabilities within soil aggregates.

    • Snow absence did not change net N mineralization rate within soil aggregates.

    • Soil enzyme activities affected by snow were different within soil aggregates.

    Winter climate change has great potential to affect the functioning of terrestrial ecosystems. In particular, increased soil frost associated with reduced insulating snow cover may impact the soil nitrogen (N) dynamics in cold ecosystems, but little is known about the variability of these effects among the soil aggregates. A snow manipulation experiment was conducted to investigate the effects of snow absence on N cycling within soil aggregates in a spruce forest on the eastern Tibetan Plateau of China. The extractable soil available N (ammonium and nitrate), net N mineralization rate, and N cycling-related enzyme activities (urease, nitrate reductase, and nitrite reductase) were measured in large macroaggregate (>2 mm), small macroaggregate (0.25–2 mm), and microaggregate (<0.25 mm) during the early thawing period in the years of 2016 and 2017. Snow absence increased soil N availabilities and nitrite reductase activity in microaggregate, but did not affect net N mineralization rate, urease or nitrate reductase activities in any of the aggregate fractions. Regardless of snow manipulations, both soil inorganic N and nitrate reductase were higher in small macroaggregate than in the other two fractions. The effect of aggregate size and sampling year was significant on soil mineral N, net N mineralization rate, and nitrite reductase activity. Our results indicated that snow cover change exerts the largest impact on soil N cycling within microaggregate, and its effect is dependent on winter conditions (e.g., snow cover and temperature). Such findings have important implications for soil N cycling in snow-covered subalpine forests experiencing pronounced winter climate change.

    Geng Sun, Mei Sun, Zunchang Luo, Chao Li, Xiaoping Xiao, Xiaojing Li, Junjie Zhong, Hua Wang, San’an Nie
    Soil Ecology Letters, 2022, 4(3): 254-263.

    1. Anammox responded to different fertilization practices.

    2. Organic residues treated soils contributed lower (4.07–4.95%) N loss than solely chemical fertilizer (9.13%) in terms of anammox.

    3. Incorporation of organic residues increased the abundance of anammox bacteria but decreased the activity.

    4. The anammox activity was not related to functional gene abundance and soil physicochemical properties.

    The return of crop residue and green manure into agricultural soil is known to be important agricultural management strategies, yet how they affect the anammox process remains poorly characterized. A field experiment containing four treatments: chemical fertilizer (F), F plus rice straw (FS), FS plus green manure (FSM), FSM with integrated management (FSMM), was performed to examine the effects of incorporation of rice straw and green manure residues on anammox. The results showed that the anammox activities in FS and FSM treatments (0.65 and 0.80 nmol N g−1 soil h−1, respectively) were significantly lower than those in F and FSMM treatments (1.60 and 1.28 nmol N g−1 soil h−1, respectively). Anammox contributed 4.07%-4.95% of total N loss in soil incorporated with residues, lower than soil treated with chemical fertilizer only (9.13%), the remaining being due to denitrification. However, the abundance of the hzsB gene (the hydrazine synthase β-subunit gene) in FS and FSM treatments (1.13 × 106 and 1.18 × 106 copies g−1 soil) were significantly higher than soil using chemical fertilizer only (7.49 × 105 copies g−1 soil) while showed no significant difference with FSMM treatment (8.81 × 105 copies g−1 soil). Illumina sequencing indicated that Brocadia was the dominant anammox genus, following by Scalindua and Kuenenia. Anammox bacterial diversity was altered after 4-year incorporation of rice straw and green manure, as shown by α-diversity indices. We concluded that rice straw and green manure incorporated with mineral fertilizer reduce N removal from paddy soil in terms of anammox in spite of stimulating anammox bacterial growth.

    Rishikesh Singh, Tanu Kumari, Pramit Verma, Bhupinder Pal Singh, Akhilesh Singh Raghubanshi
    Soil Ecology Letters, 2022, 4(3): 187-212.

    • Resource-conservation practices are emerging for attaining sustainability in agriculture.

    • The research is now progressing towards combined application of emergent agronomic practices.

    • Role of agro-climatic zones is imperative in developing compatible agronomic packages.

    • Compatible agriculture packages may help in buffering the yield penalty occurred one system.

    • Compatible agriculture packages would be the need for attaining true sustainability in agriculture.

    Besides contributing majorly in the growth of a country, agriculture is one of the severely affected sectors at present. Several modifications and adaptations are being made in agricultural practices to cope-up with the declining soil fertility and changing climate scenarios across the world. However, the development and adoption of a single agricultural practice may not help in the holistic mitigation of the impacts of climate change and may result in economic vulnerability to farmers. Therefore, it is high time to develop and recommend a group of agricultural practices i.e. package-based agriculture system having some compatibility for one another in the long term. In this article, a viewpoint has been given on some emergent agronomic practices adopted in the tropical agro-ecosystems which have potential to be developed as compatible agricultural package in combination. Moreover, we also emphasized on exploring some key indicators/environmental factors to assess the compatibility of different agronomic practices. For identifying the research transition from single to combined agricultural practices, a bibliometric analysis was performed by using conservation agriculture (CA), the system of rice intensification (SRI), organic agriculture and soil (biochar) amendment as the major agronomic practices being used for improving agro-ecological services such as improving nutrient cycling, soil fertility and crop productivity as well as climate change mitigation. The results revealed that scientific communities are now paying attention to exploring the role of combined agricultural practices for agro-ecological balance and climate change adaptation. Moreover, the limitations of the adoption of agronomic packages under different agro-climatic zones have also been highlighted. The recommendations of the study would further help the environmental decision-makers to develop potential measures for climate change mitigation without compromising the agro-ecological balance.

    Xingran Huang, Lili Zheng, Pingping Guo, Zhigang Yi
    Soil Ecology Letters, 2021, 3(1): 63-72.

    • Effects of N addition on MT fluxes from forest floor were first investigated.

    • N addition inhibited MT emissions from forest floors, while increased for litter.

    • MT emissions from the PF floor was significantly higher than those from the BF floor.

    Monoterpenes (MTs) play crucial roles not only in atmospheric chemistry and global climate change but also in soil processes and soil ecology. Elevated nitrogen (N) deposition can influence soil microbial community and litter decomposition, and consequently alters MT fluxes from forest floors and litter. Yet, the responses of soil and litter MT to increased N deposition remain poorly understood and the influences of N addition are sometimes contradictory. In the present study, static chambers were placed in masson pine forest (PF) and in monsoon evergreen broad-leaf forest (BF) at Dinghushan, subtropical China. The preconcentrator-GC–MS was used to analyze the effect of N addition on MT fluxes from the forest floors and litter. The results showed that under control treatment (without N addition), the total MT emission rates were 279.90±137.17 and 102.70±45.36 pmol m2 s1 in the PF and BF floors, respectively, with α-pinene being the largest MT species in the PF and limonene in the BF. α-pinene and β-pinene emission rates decreased significantly in both forest floors after N addition, whereas a diverse trend was found for limonene and camphene in the PF floor. Furthermore, some MT fluxes showed significant negative correlations with soil respiration and soil temperature. Litter was important in MT fluxes from forest floors and its emission rates were enhanced by N addition. Moreover, different MT response to elevated N was found between the forest floor and litter. This study indicated that the elevated N deposition in the future would inhibit the MT emissions from the subtropical forest floor.