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.