Authors:

Chao Li , Chunwang Xiao , Bertrand Guenet , Mingxu Li , Li Xu , Nianpeng He 

Abstract：

It remains unclear how soil microbes respond to labile organic carbon (LOC) inputs and how temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is affected by LOC inputs in a short-term. In this study, 13C-labeled glucose was added to a pristine grassland soil at four temperatures (10, 15, 20, and 25 °C), and the immediate utilization of LOC and native SOM by microbes was measured minutely in a short-term. We found that the LOC addition stimulated the native SOM decomposition, and elevated temperature enhanced the intensity of microbial response to LOC addition. The ratio between microbial respiration derived from LOC and native SOM increased with higher temperature, and more LOC for respiration. Additionally, LOC addition increased the Q10 of SOM decomposition, and the Q10 of LOC decomposition is higher than that of native SOM. Overall, these findings emphasize the important role of temperature and LOC inputs in soil C cycles.

Keywords:

Temperature

LOC addition

Microbial respiration

Authors:

Jun Pan , Nianpeng He , Yuan Liu , Li Xu , Mingxu Li , Chao Li

Abstract：

Temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is an essential parameter that reflects the feedback relationship between climate warming and atmospheric CO2 concentration and plays a key role in accurately estimating changes in soil carbon pools and their feedback to climate change. Setting the incubation temperature range (ITR) scenario is essential to accurately estimate the temperature sensitivity of SOM decomposition; however, this has been widely ignored. To address this issue, we conducted a systematic incubation experiment using 54 soils covering the most typical ecosystems in China and nine ITR scenarios. The results showed that ITR scenarios had a significant effect on Q10 in different ecosystems and soil types. Combining the results of fitting mean annual temperature (MAT) to the Q10 of different ITR and the interpretation rate of factors (including climate, soil, and microbial community composition) to the Q10 of different ITR, the results indicate that the growing season average temperature range (GSA) scenario had better performance than the other ITR scenarios and should be the optimum ITR scenario. Furthermore, the variation of main influence factors of Q10 across different ecosystems should be accounted for to accurately predict the feedback between soil C cycle and climate change. Overall, our findings highlight the importance of the ITR for the estimates of Q10 using widespread experimental data, providing a reference for subsequent experiments accurately measure Q10, as well as compare and compile global data to better predict the feedback between the global carbon cycle and climate change.

Keywords:

Soil organic matter

Decomposition

Temperature sensitivity

Incubation

Temperature range

Authors:

Xiali Mao , Jinyang Zheng , Wu Yu , Xiaowei Guo , Kang Xu , Ruiying Zhao , Liujun Xiao , Mingming Wang , Yefeng Jiang , Shuai Zhang , Lun Luo , Jinfeng Chang , Zhou Shi , Zhongkui Luo

Abstract：

Through soil profile, both chemical composition of soil organic carbon (SOC) and edaphic physiochemical properties present a vertical gradient, likely resulting in depth-specific SOC dynamics in response to climate change (e.g., global warming). We assessed temperature sensitivity of SOC decomposition (Q10) by incubating (128 days) soils sampled across five sequential layer depths (i.e., 0–10, 10–20, 20–30, 30–50, and 50–100 cm) at ten sites along a ~2500 m elevational transect (from ~2100 m to ~4600 m) covering various vegetation types (from evergreen broadleaved forest to alpine meadow) in southeast Tibet, China. The Q10 of SOC decomposition was significantly affected by both soil depth and elevation. However, depth-induced variation of Q10 was much smaller than that induced by the elevation gradient. Across the ten sites and five soil depths, chemical composition of SOC and its physiochemical protection against decomposition contributed >80% to the explained variance of Q10 values. Path analysis suggested that climate indirectly affected Q10 via its regulation on chemical composition of SOC and their physiochemical stabilization. The results from a carbon model constrained by the collected data further revealed that fast, slow and passive SOC pools exhibited significant difference in their Q10, resulted from different involvement of chemical composition and physicochemical protection in their decomposition. Our findings demonstrate similar temperature sensitivity of SOC decomposition across soil depths, but spatially heterogeneous temperature sensitivity due to climate-induced variability of both chemical recalcitrance of SOC and its physiochemical protection against decomposition.

Keywords:

Carbon models

Climate change

Carbon compounds

Deep soil

Warming

Authors:

Yanghui He, Xuhui Zhou, Zhen Jia, Lingyan Zhou, Hongyang Chen, Ruiqiang Liu, Zhenggang Du, Guiyao Zhou, Junjiong Shao, Junxia Ding, Kelong Chen, Iain P. Hartley

Abstract：

Multiple lines of existing evidence suggest that increasing CO2 emission from soils in response to rising temperature could accelerate global warming. However, in experimental studies, the initial positive response of soil heterotrophic respiration (RH) to warming often weakens over time (referred to apparent thermal acclimation). If the decreased RH is driven by thermal adaptation of soil microbial community, the potential for soil carbon (C) losses would be reduced substantially. In the meanwhile, the response could equally be caused by substrate depletion, and would then reflect the gradual loss of soil C. To address uncertainties regarding the causes of apparent thermal acclimation, we carried out sterilization and inoculation experiments using the soil samples from an alpine meadow with 6 years of warming and nitrogen (N) addition. We demonstrate that substrate depletion, rather than microbial adaptation, determined the response of RH to long-term warming. Furthermore, N addition appeared to alleviate the apparent acclimation of RH to warming. Our study provides strong empirical support for substrate availability being the cause of the apparent acclimation of soil microbial respiration to temperature. Thus, these mechanistic insights could facilitate efforts of biogeochemical modeling to accurately project soil C stocks in the future climate.

Keywords:

Authors:

Xiaoliang Ma, Shengjing Jiang, Zhiqi Zhang, Hao Wang, Chao Song, Jin-Sheng He

Abstract：

1. Accurate measurements of soil respiration (Rs ) are critical for understanding how soil carbon will respond to environmental changes. However, a commonly used method for Rs measurements, the collar deployment method, may introduce artefacts that cause bias in Rs measurements. Our objective was to quantify the effect of long-term collar deployment on Rs and to unravel potential causes due to changes in the soil environment.
2. A field experiment (2017–2019) including short-term (2–3 days before the measurement) and long-term collar deployment (lasting three consecutive growing seasons) was conducted to assess the methodological effect on Rs in an alpine grassland of the northeastern Tibetan Plateau. Soil incubation was used to further explore the mechanisms underlying the effects of collar deployment.
3. The effect of long-term collar deployment on Rs varied over time. In the first one and a half growing seasons, no significant difference in Rs was noted under shortand long-term collar deployment. This may be attributed to the negative effects of lower root biomass inside long-term collars and the positive effects of higher temperature and pulse input of dead roots following collar deployment. Under the long-term collar, Rs decreased rapidly in the middle of the second growing season and remained low until the end of the experiment, resulting in an 18.2% decrease relative to short-term collar deployment in the third growing season. Higher soil bulk density and lower root and microbial biomass inside long-term collars may explain the decrease in Rs and temperature sensitivity (Q10). Soil incubation experiments revealed that the soil organic carbon (SOC) decomposition rate and Q10 were significantly reduced after long-term collar deployment.
4. Long-term collars led to substantial underestimates of Rs after more than 2 years. Our findings suggest that such potential artefacts should be considered when interpreting Rs data based on long-term collar deployment. Long-term collars should be relocated every 1–2 years to avoid artefacts if feasible. Alternatively, periodic measurements using short-term collars are recommended to quantify the magnitude of collar artefacts.

Keywords:

alpine grassland, carbon cycle, chamber collar, soil respiration, temperature sensitivity

Authors:

Chao Li , Chunwang Xiao , Mingxu Li , Li Xu , Nianpeng He 

Abstract：

Continuous and pulsed inputs of labile organic carbon (LOC) into soil are common. However, because soil microbial responses to LOC input are rapid, the relative contributions of respiration derived from LOC to total microbial respiration and their influencing factors remain elusive. Furthermore, although numerous studies have explored the priming effect (PE) of soil organic matter (SOM) mineralization induced by LOC addition, few studies have focused on its short-term effects. There are some indications that the response of soil microbes to LOC input depends on the microbial demand of nutrients, especially C and N. Therefore, variations in soil C and N characteristics may further influence microbial response processes to LOC inputs and the decomposition of LOC and SOM, but a comprehensive understanding of this is lacking. To address this gap, 13C-labeled glucose was added to six temperate grassland soils with different C/N ratios (9.98–12.0), which were collected from areas with different grazing exclusion durations and at different soil depths. The microbial respiration was measured at 9-min intervals across a 105-h period. We found that soil microbes responded rapidly to LOC input, and microbial biomass controlled by soil organic C (SOC) and C/N was the most important factor directly influencing the intensity of the microbial response to LOC input. Grazing and deeper soil layers decreased the respiration derived from LOC and their relative contribution to total respiration, mainly attributed to variations in soil C/N and fungal/bacterial ratio (Fu/Ba). LOC addition stimulated SOM decomposition in all soils and increased respiration of SOM by 11.3–92.4 mg C/g SOC, equivalent to 18.7–266.1 % priming. Grazing and increased soil depth resulted in a greater PE and soil C loss, with soil C/N and SOC content being the most important regulators. Overall, this study revealed the important influence of LOC on soil C fluxes and highlighted the important role of SOM quality and quantity in regulating grassland soil C cycling.

Keywords:

C/N ratio

SOM quantity

Priming effect

Grazing exclusion

Soil depth

Soil C balance

作者：

劉源豪 , 熊德成 , 吳晨 , 王云 , 林德寶 , 黃錦學

摘要：

為研究外源葡萄糖輸入量對土壤CO₂排放動態過程的影響及機理，以中亞熱帶常綠闊葉林土壤為研究對象，在培養溫度為恒溫20 ℃，土壤田間持水量60%的條件下，輸入不同濃度的葡萄糖(碳含量分別為0、50、150、450 μg·g^-1，分別標記為CK、C₁、C₂、C₃處理)進行室內培養試驗，測定不同濃度葡萄糖輸入下不同時間的土壤CO₂排放。結果表明:C₂、C₃處理的土壤CO₂排放速率和土壤CO₂累積排放量均顯著升高(P<0.05)；C₂、C₃處理28 h后，土壤CO₂排放速率隨培養時間的延長顯著升高(P<0.01)，土壤CO₂累積排放量隨培養時間的延長顯著升高(P<0.01)；當培養時間超過65 h后，開放科學標識碼 (OSID碼)C₁處理的土壤CO₂排放速率隨培養時間的延長有顯著降低的趨勢(P<0.01)，C₃處理的土壤C/N、DOC變化量較CK顯著增大(P<0.05)，土壤CO₂排放速率與C/N、DOC含量呈顯著正相關關系(P<0.05)。不同濃度葡萄糖輸入對土壤CO2排放的影響存在異質性，在中亞熱帶常綠闊葉林土壤中，根系分泌物葡萄糖的輸入增加可能會改變土壤C、N含量，提高CO₂排放量，從而進一步加速土壤碳損失。

關鍵詞:

碳輸入；葡萄糖； CO₂排放速率； CO₂累積排放量； 表層土壤； 常綠闊葉林

Authors:

Jinyang Zheng, Xiali Mao , Kees Jan van Groenigen , Shuai Zhang , Mingming Wang , Xiaowei Guo, Wu Yu , Lun Luo , Jinfeng Chang , Zhou Shi , Zhongkui Luo

Abstract：

Soil microbes drive soil organic carbon (SOC) mineralization. Because microbial groups differ in metabolic efficiency and respond differently to temperature variation, it is reasonable to expect a close association of SOC mineralization and its temperature sensitivity (Q10 which is defined as the factor of the change of soil carbon mineralization induced by 10 °C temperature increase) with microbial community diversity and composition. However, these relations have rarely been tested. Here, we conducted an incubation experiment to assess the temperature responses of microbial α diversity and the relative abundance of microbial r- and K-strategists in soils from a wide range of ecosystems across a climate gradient in the southeast Tibet. The results indicated that the instantaneous α diversity and the relative abundance of r- and K-strategists are significantly (P < 0.05) influenced by temperature, but these microbial variables are poor predictors of SOC mineralization measured at the same time. Rather, microbial community diversity and the relative abundance of r- and K-strategists of fresh soils showed consistent and significant (P < 0.05) effects on both SOC mineralization and Q10 at different incubation stages. Importantly, path analysis indicated that microbial α diversity and r- and K-strategists exerts no independent effects on SOC mineralization and Q10 when variation in climate, SOC chemistry, physical protection, and edaphic properties are accounted for. Together, our results suggest that while soil microbial community diversity and composition are a strong proxy of SOC quality and availability, they are not a fundamental determinant of SOC mineralization and Q10.

Keywords:

Bacteria

Carbon fractions

Fungi

Microbial diversity

r/K strategists

Soil organic carbon

Temperature sensitivity (Q10)

Soil profile

Authors:

Jun Pan , Yuan Liu , Nianpeng He , Chao Li , Mingxu Li , Li Xu , Osbert Jianxin Sun

Abstract：

As one of the most important drivers of global climate change, land use change (LUC) has markedly altered the regional and global carbon (C) cycles. However, the geographic variations and the key drivers in the effects of LUC on temperature sensitivity (Q10) of soil microbial respiration (Rs) are still not fully elucidated, hence impeding the spatially explicit predictions of soil C cycling under climate change. Here, we used a paired-plot approach with data for 19 locations distributed from the tropical to temperate zones in eastern China, and compared the temperature responses of Rs between forest and cropland soil. Results showed that the latitudinal patterns of Q10 in forest soils were better explained by climatic variables; whereas in cropland, soil Q10 trended higher with increasing latitude, with climatic factors, pH, clay, and soil organic C (SOC) jointly modulating the spatial variations in Q10. Overall, the values of Q10 tended to converge with latitude between forests and croplands, with change in Q10 from forest to cropland, ΔQ10, significantly decreasing from the tropical region (9.23 ± 3.58 %) to the subtropical (0.58 ± 1.93 %) and temperate (−0.97 ± 1.11 %) regions. Moreover, the spatial variations of ΔQ10 were significantly affected by climatic factors, ΔpH, Δmicrobial biomass C (ΔMBC), and their interactions. Our findings highlight the potential impacts of LUC-related biogeographic variations in the temperature response of Rs, and emphasize the importance of incorporating the land-use effects on the temperature sensitivity of soil microbial respiration into terrestrial C cycle models to improve predictions of carbon-climate feedbacks in the future.

Keywords:

Carbon；Global warming；Land use change；SOM；Geographical variation；Temperature sensitivity；ORGANIC-MATTER DECOMPOSITION；LAND-USE CONVERSION；CARBON DECOMPOSITION；CLIMATE-CHANGE；CO2 EMISSIONS；Q(10) VALUES；INCUBATION；PH；MINERALIZATION；AVAILABILITY

Authors:

Yalong Kang , Linjun Shen , Canfeng Li , Yong Huang , Liding Chen

Abstract：

Vegetation degradation caused by intense human disturbances poses a significant challenge to the preservation and improvement of ecosystem functions and services in the karst region of southwest China. Soil microorganisms are major regulators of ecosystem multifunctionality (EMF). Currently, there is a dearth of knowledge regarding the effects of vegetation degradation on soil microbial communities and their corresponding multiple ecosystem functions in karst regions. In this study, we selected the vegetation degradation sequences of second natural forest (NF), agroforestry (AS) and cropland (CL) to investigate the diversity of bacterial, fungal and protistan communities, and their hierarchical co-occurrence network, and EMF to explore the relationships between them. Compared to the NF, the carbon cycling index, nitrogen cycling index, soil water regulation power, and the EMF were significantly decreased by 8.2%–50.6%, 48.7%–86.8%, 19.8%–24.5%, and 31.4%– 69.5% in the AS and CL, respectively. The development of EMF can be explained by the fungal, protistan and microbial hierarchical β-diversity, as well as the complexity (e.g. degree) of microbial hierarchical interactions during the process of vegetation degradation. Notably, correlations between the abundances of sensitive amplicon sequence variants (sASVs) for different karst vegetation types and EMF varied in distinct network modules, being positive in module 1 and negative in module 2. Moreover, the relative abundance of keystone taxa in fungal and protistan communities provided greater contributions to EMF than the bacterial communities. Additionally, random forest modeling showed that carbon and nitrogen sources, and soil water content, and trace elements (e.g. exchangeable magnesium, iron, manganese, and zinc) were identified as key driving factors of the EMF. Collectively, our findings demonstrate that vegetation degradation obviously alters soil microbial diversities and hierarchical interactions, emphasizing their key role in maintaining ecosystem functions and health in karst regions.

Article info:

Keywords:

Karst

Vegetation degradation

Microbial diversity

Microbial multitrophic network

Core phylotypes

Ecosystem multifunctionality

Authors:

Ruiqiang Liu , Xuhui Zhou , Yanghui He , Zhenggang Du , Hongyang Chen , Yuling Fu , Liqi Guo , Guiyao Zhou , Lingyan Zhou , Jie Li , Hua Chai , Changjiang Huang , Manuel Delgado-Baquerizo

Abstract：

Ecological succession and restoration rapidly promote multiple dimensions of ecosystem functions and mitigate global climate change. However, the factors governing the limited capacity to sequester soil organic carbon (SOC) in old forests are poorly understood. Ecological theory predicts that plants and microorganisms jointly evolve into a more mutualistic relationship to accelerate detritus decomposition and nutrient regeneration in old than young forests, likely explaining the changes in C sinks across forest succession or rewilding. To test this hypothesis, we conducted a field experiment of root-mycorrhizal exclusion in successional subtropical forests to investigate plant-decomposer interactions and their effects on SOC sequestration. Our results showed that SOC accrual rate at the 0–10 cm soil layer was 1.26 mg g−1 yr−1 in early-successional arbuscular mycorrhizal (AM) forests, which was higher than that in the late-successional ectomycorrhizal (EcM) forests with non-significant change. A transition from early-successional AM to late-successional EcM forests increase fungal diversity, especially EcM fungi. In the late-successional forests, the presence of ectomycorrhizal hyphae promotes SOC decomposition and nutrient cycle by increasing soil nitrogen and phosphorus degrading enzyme activity as well as saprotrophic microbial richness. Across early- to late-successional forests, mycorrhizal priming effects on SOC decomposition explain a slow-down in the capacity of older forests to sequester soil C. Our findings suggest that a transition from AM to EcM forests supporting greater C decomposition can halt the capacity of forests to provide nature-based global climate change solutions.

Authors:

Yuan Liu, Amit Kumar, Lisa K. Tiemann, Jie Li, Jingjing Chang, Li Xu & Nianpeng He

Abstract:

Purpose

The purpose of this study was to investigate how changes in substrate availability (stimulating root exudate input) affect the temperature response (Q10) of soil organic carbon (SOC) mineralization across different soil profiles to increase our ability to predict the response of soil organic matter dynamics to climate change.

Materials and methods

We sampled the topsoil and subsoil of two typical mineral soil profiles and one buried soil profile. Soils were incubated at 10–25 °C at 0.75 °C intervals, SOC mineralization rates were continuously measured with and without glucose addition, and Q10 was calculated.

Results and discussion

Our results showed that Q10 decreased with increasing depth in typical mineral soils, but decreased before increasing with depth in buried soil. As expected, substrate addition significantly increased Q10 across soil depths; however, the magnitude of this increase (ΔQ10) differed with soil depth and type. Unexpectedly, in typical mineral soils, ΔQ10 was higher in topsoil than in subsoils, and vice versa for buried soil. ΔQ10 was negatively correlated with initial soil substrate availability (CAI) and positively correlated with soil inorganic N.

Conclusions

Overall, our results suggested that increased substrate availability under climate change scenarios (i.e., increased root exudates with elevated CO2 concentrations) could further strengthen the temperature response of SOC mineralization, especially in soils with high inorganic N content or regions with high N deposition rates.

Authors:

Mengyang You , Diankun Guo , Hongai Shi , Peng He , Martin Burger , Lu Jun Li

Abstract:

Soil organic carbon (SOC) mineralization which relates to SOC stability and sequestration, predicating the SOC stocks under climate change, is affected by land use and exogenous carbon addition. However, how SOC chemical composition and soil enzymes regulate SOC mineralization of grassland and forest soils receiving exogenous C addition is still not well understood.

Forest and grassland soils were incubated without or with two levels of ¹³C-enriched glucose, simulating labile C inputs, at 15 and 25 ℃ for 28 days. The priming effect, temperature sensitivity (Q₁₀), enzyme activities and chemical composition of SOC were determined.

Increasing labile C addition and higher temperature accelerated native SOC mineralization in forest and grassland soil. Changes of enzyme C:N and N:P ratio contributed to the differences in CO₂ production in forest and grassland soil. In grassland soil, the relationship between soil-derived CO₂ production and relative peak areas of SOC at 1420 cm⁻¹ by Fourier-Transform infrared spectroscopy was significant. The temperature sensitivity of the native SOC mineralization in the forest soil amended with 0.8 g glucose-C kg⁻¹ dry soil application was greater than that with 0.4 g glucose-C kg⁻¹ dry soil application, but in the grassland soil, the Q₁₀ of glucose derived CO₂ emission was lower after the higher glucose application.

Soil enzyme nutrient ratios and chemical composition of SOC together play an important role in regulating the mineralization of SOC and the Q₁₀ value of external C addition mineralization in forest and grassland soil.

Authors:

Xuhui Zhou , Zhiqiang Feng , Yixian Yao , Ruiqiang Liu , Junjiong Shao , Shuxian Jia , Yining Gao , Kui Xue , Hongyang Chen , Yuling Fu , Yanghui He

Abstract:

The combination of biochar and nitrogen (N) addition has been proposed as a potential strategy to sustain crop productivity and mitigate climate change by increasing soil fertility, sequestering carbon (C), and reducing soil greenhouse gas emissions. However, our current knowledge about how biochar and N additions interactively alter mineralization of native soil organic C (SOC), which is referred to priming effects (PEs), is largely limited.To address this uncertainty, C3 biochar (pyrolyzing rice straw at 300, 550, and 800 ?C) and its combination with N fertilizer (urea) were incubated in a C4-derived soils at 25 ?C. All these 3 types of biochar with different addition rates caused positive priming of native soil organic matter decomposition (up to +58.4%). The maximum negative priming effects (up to − 25.4%) occurred in soil treated with 1% of N-bound biochar pyrolyzed at 300 ?C. In addition, a negative correlation was found between the priming intensity and soil inorganic N content across all treatments. The decrease in biochar-induced PEs was related with a shift in microbial community composition and reduction in microbial biomass determined by chloroform-fumigation. Such a reduction, however, was not confirmed by PLFA analysis. These findings advance our understanding on the microbial mechanisms mediating net soil C balance with the adequate biochar use for blending traditional mineral fertilizers.

Authors:

Mengyu Liu , Yao Yu , Ying Liu , Sha Xue b, Darrell W.S. Tang , Xiaomei Yang

Abstract:

astic pollution in agricultural soils due to polyethylene plastic film mulch used, biodegradable film is being studied as a promising alternative material for sustainable agriculture. However, the impact of biodegradable and polyethylene microplastics on soil carbon remains unclear. The field experiment was conducted with Poly (butyleneadipate-co-terephthalate) debris (PBAT-D, 0.5–2 cm), low-density polyethylene debris (LDPE-D, 0.5–2 cm) and microplastic (LDPE-Mi, 500–1000 μm) contaminated soil (0% (control), 0.05%, 0.1%, 0.2%, 0.5%, 1% and 2% w:w) planted with soybean, to explore potential impacts on soil respiration (Rs), soil organic carbon (SOC) and carbon fractions (microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidizable carbon (EOC), particulate organic carbon (POC), mineral-associated organic carbon (MAOC)), and C-enzymes (β-glucosidase, β-xylosidase, cellobiohydrolase). Results showed that PBAT-D, LDPE-D and LDPE-Mi significantly inhibited Rs compared with the control during the flowering and harvesting stages (p < 0.05). SOC significantly increased in the PBAT-D treatments at both stages, and in the LDPE-Mi treatments at the harvesting stage, but decreased in the LDPE-D treatments at the flowering stage. In the PBAT-D treatments, POC increased but DOC and MAOC decreased at both stages. In the LDPE-D treatments, MBC, DOC and EOC significantly decreased but POC increased at both stages. In the LDPE-Mi treatments, MBC and DOC significantly decreased at the harvesting stage, while EOC and MAOC decreased but POC increased at the flowering stage. For C-enzymes, no significant inhibition was observed at the flowering stage, but they were significantly inhibited in all treatments at the harvesting stage. It is concluded that PBAT-D facilitates soil carbon sequestration, which may potentially alter the soil carbon pool and carbon emissions. The key significance of this study is to explore the overall effects of different forms of plastic pollution on soil carbon dynamics, and to inform future efforts to control plastic pollution in farmlands.

Authors:

Shenliang Zhao , Hua Chai , Yuan Liu , Xiaochun Wang , Chaolian Jiao , Cheng Liu a , Li Xu d, Jie Li , Nianpeng He

Abstract:

How and what soil fauna influence the soil organic matter (SOM) decomposition rate (Rs) and its temperature sensitivity (Q10) have been largely ignored, although this is a crucial matter, especially under the scenario of global change. In this study, a novel approach was adopted with a continuous changing-temperature incubation (daytime, from 7 °C to 22 °C; nighttime, from 22 °C to 7 °C) with rapid and continuous measurement, to examine the effect of soil macrofauna (specifically, earthworms) on Rs and Q10 with three densities (no addition, low density, and high density). According to the results, the earthworms accelerated Rs. Furthermore, Rs with earthworm addition had a symmetrical pattern during daytime and nighttime cycles, which is contrary to traditional soil incubation, with only soil microbe as asymmetrical. More importantly, earthworm addition increased Q10 markedly, ranging from 48% to 67%. Overall, the findings highlight the pivotal role of earthworms as soil macrofauna that regulating soil carbon release, and their effects should be integrated into process-based ecological models in future.

Authors:

Jinyang Zheng , Kees Jan van Groenigen d, Iain P. Hartley , Ran Xue , Mingming Wang , Shuai Zhang , Ting Sun , Wu Yu, Bin Ma, Yu Luo , Zhou Shi , Zhongkui Luo

Abstract:

Authors:

Ming Gao,Wei Hu,Meng Li,Mingming Guo,Yongsheng Yang

Abstract:

Land-use change directly impacts soil basal respiration (Br), soil microbial attributes, and soil organic matter (SOM) composition. However, the role of soil microbial attributes and SOM composition in influencing soil Br under land-use changes remains largely undetermined. We examined how interactions between soil physicochemical properties, SOM chemical structure, and microbial attributes regulate soil Br across three land-use types, cropland, forest, and grassland, in the Mollisol and Arenosol of Horqin Sandy Land. The results showed that soil Br, phospholipid fatty acid content, and the relative peak areas of aliphatic and aromatic compounds were significantly lower in cropland than in forest and grassland. Additionally, the Arenosol exhibited poorer soil properties compared to the Mollisol (p < 0.05). Soil Br in the Mollisol (3.60–5.56 mgCO2-C kg−1 h−1) was significantly higher than in the Arenosol (0.86–2.60 mgCO2-C kg−1 h−1, p < 0.05). G+/G− ratios and bacteria were identified as the main predictors of Br in the Mollisol and Arenosol, respectively. The structural equation model revealed that microbial attributes are the primary drivers of Br, influencing it indirectly through changes in SOM composition. Our findings are instrumental in understanding the role of microbial attributes in carbon turnover during land-use changes.

Authors:
Huiling Wang, Hang Jing , Huizhen Ma , Guoliang Wang

Abstract:

The mechanisms by which belowground plant deposits influence soil organic carbon dynamics under increasing nitrogen (N) deposition remain unclear. In this study, ingrowth cores with different mesh sizes (1?µm, 45?µm and 1?mm) were used to investigate the effects of mycelium and fine root deposits on soil dissolved organic matter (DOM) and CO₂ emissions under N addition. Results indicated that mycelium did not significantly alter DOM composition or microbial community, whereas several labile (including amino sugars and carbohydrates) and recalcitrant DOM (including lignin and tannin) were enriched in the fine root and coarse root treatments, respectively. The fungal community shifted towards a K-strategy in the presence of mycelium and roots compared to the control treatment (1?µm). N addition increased the abundance of recalcitrant DOM molecules, particular in fine root treatments. Root deposit inputs increased DOM transformation and the complexity of the DOM-microbe network. The associations between microbes and labile carbon were enhanced in the mycelium and fine root treatments. The relationships between oligotrophic Basidiomycota and recalcitrant carbon were strengthened in the coarse root treatment. CO2 emissions in mycelium treatments were inhibited by N addition, primarily due to a decrease in mycorrhizal colonization. Root deposit inputs and DOM-microbe interactions dominated the CO₂ emissions in the forest soil under N addition. Our findings confirm the essential role of fine root deposits, in regulating soil CO₂ emissions by influencing DOM characteristics under N deposition.

Authors:

Zhiyun Zhou, Ni Zhang, Yijun Wang & Kelong Chen

Abstract:

Background and aims

Freeze–thaw cycles (FTC) can affect the rates of soil organic carbon (SOC) mineralization and carbon (C) and nitrogen (N) cycling in soils. However, little is known about whether this effect changes with litter inputs, especially for alpine grassland ecosystems.

Methods

Using soil and Litter from Tibetan Plateau alpine meadows, we conducted a 15-day indoor experiment under two FTC regimes (-15 to 15℃ and -10 to 10℃), constant 10℃, and litter addition.

Results

The results showed that the SOC mineralization rates under the I ± 10 and I ± 10L treatments were significantly lower than those of the control by 7.85% and 6.20%, respectively, while the C mineralization rates under the I ± 15L treatment were significantly higher than that of the control by 20.78%. The temperature sensitivity (Q10) was significantly higher under I ± 10 than under I ± 15. The C mineralization rates under the control + L treatment were 42.76% higher than those of the control and induced a significant priming effect (PE), which was significantly lower in the I ± 10L treatment compared to the control + L. Structural equation modeling suggested that FTC indirectly affected C mineralization via changes in ammonium nitrogen (NH4+-N) and microbial biomass carbon (MBC), whereas litter addition directly altered MBC to promote C release.

Conclusion

Our findings suggest that the I ± 10L treatment can reduce the rates of soil C mineralization and PE in alpine swamp meadows. However, the control + L treatment significantly enhances the availability of organic carbon for microbial decomposition, thereby accelerating C release. Therefore, the impact of the reduction in freeze–thaw events under climate warming must be re-evaluated within broader environmental and ecological contexts.