Microbial Biomass Nitrogen Content Research Articles

Effects of seasonal precipitation regimes on microbial biomass and extracellular enzyme activity during shrub foliar litter decomposition in a subtropical forest

Elucidating the mechanisms underlying microbial biomass and extracellular enzyme activity responses to the seasonal precipitation regime during foliar litter decomposition is highly important for understanding the material cycle of forest ecosystems in the context of global climate change; however, the specific underlying mechanisms remain unclear. Hence, a precipitation manipulation experiment involving a control (CK) and treatments with decreased precipitation in the dry season and extremely increased precipitation in the wet season (IE) and decreased precipitation in the dry season and proportionally increased precipitation in the wet season (IP) was conducted in a subtropical evergreen broad-leaved forest in China from October 2020 to October 2021. The moisture, microbial biomass, and extracellular enzyme activities of foliar litter from two dominant shrub species, Phyllostachys violascens and Alangium chinense, were measured at six stages during the dry and wet seasons. The results showed that (1) both IE and IP significantly decreased the microbial biomass carbon and microbial biomass nitrogen content and the activities of β-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, acid phosphatase and cellulase in the dry season, while the opposite effects were observed in the wet season. (2) Compared with those of IE, the effects of IP on foliar litter microbial biomass and extracellular enzyme activity were more significant. (3) The results from the partial least squares model indicated that extracellular enzyme activity during foliar litter decomposition was strongly controlled by the foliar litter water content, microbial biomass nitrogen, the ratio of total carbon to total phosphorus, foliar litter total carbon, and foliar litter total nitrogen. These results provide an important theoretical basis for elucidating the microbial mechanisms driving litter decomposition in a subtropical forest under global climate change scenarios.

Long-term fertilization differentially increased the CAZyme encoding genes responsible for soil organic matter decomposition under winter wheat on the Loess Plateau of China

Long-term fertilization greatly affects soil organic matter (SOM) decomposition in cropping systems, but less information was related to carbohydrate active enzyme (CAZyme) encoding genes in decomposing the components that derived from plant and microbial biomass. Using high-throughput metagenomic sequencing, the responses of CAZyme encoding genes to 35-yr fertilization were assessed in a winter wheat field on the Loess Plateau of China. Four treatments were included as chemical nitrogen fertilizer (N), manure (M), chemical nitrogen plus manure (NM), and control with no fertilization (CK). The results showed that the abundances of genes encoding auxiliary activities and glycosyl transferases were greater in N, and those encoding carbohydrate esterases and glycoside hydrolases were higher in NM than in other treatments. The abundance of genes encoding glycosyl hydrolases was lower in M than in other treatments. Compared to CK, long-term fertilization increased the abundances of CAZyme encoding genes in decomposing the SOM that derived from plant and bacteria biomass, but did not affect those in decomposing fungi-derived component. The Actinobacteria and Proteobacteria were the main phyla contributing to plant- and microbe-derived SOM decomposition. Mantel test indicated that the abundance of CAZyme encoding genes for plant-derived SOM decomposition was mainly affected by the content of microbial biomass nitrogen, while that for bacteria-derived SOM decomposition was associated with soil carbon and nitrogen fractions. Overall, long-term fertilization improved the CAZyme encoding genes in decomposing SOM especially derived from plant and bacteria biomass. These findings help to better understand the decomposition potential of SOM in cropping systems.

Effects of Different Forest Types on Stoichiometric Characteristics of Carbon, Nitrogen, and Phosphorus in Tropical Soils, China

The stoichiometric characteristics of carbon (C), nitrogen (N), and phosphorus (P) in soil can directly reflect the level of soil fertility. In this study, a secondary forest, two kinds of plantation forests (Dacrycarpus imbricatus and Pinus caribaea Morelet), and a primary forest in tropical areas were selected for soil sample collection and analysis. We found that the soil [leucine aminopeptidase (LAP) + β-N-acetylglucosidase (NAG)]/acid phosphatase (APho) value was less than 1, indicating that there was P limitation. In addition, we also found that compared with primary forest, the β-glucosidase (BG) activity and (LAP + NAG) activity of the secondary forest were lower, and the microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents were higher. The contents of total nitrogen (TN) and MBN in the Dacrycarpus imbricatus forest soil were significantly higher than those in the primary forest, but the activity of (LAP + NAG) was lower. The structural equation model showed that the factors that significantly affected the total nutrients were the available nutrients (0.396**) and the enzyme activities (0.600**). For the long-term requirements of sustainable development, ecological adjustment and soil nutrient optimization of plantations should be carried out scientifically.

Contribution of ammonia-oxidizing archaea and bacteria to nitrogen transformation in a soil fertilized with urea and organic amendments

The contribution of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) is crucial for nitrogen transformation. The effects of four organic amendments (OAs) plus urea on soil nitrogen transformation and the contribution of the ammonia-oxidizing microbial community were investigated using an incubation experiment. The OAs plus urea treatments included pig manure plus urea (PM + U), wheat straw plus urea (WS + U), compost plus urea (CP + U) and improved-compost plus urea (IC + U), while no OAs and urea amended control was noted as CK. The abundance and composition of AOA and AOB were determined using high through-put sequencing. Compared with CK, the OA plus urea treatments significantly enhanced the amount of total mineralized nitrogen released during the incubation process. After incubation, the highest mineralized nitrogen and net nitrogen mineralization was under the PM + U treatment and the lowest was in the WS + U treatment. In conclusion, among all OA plus urea treatments, the microbial biomass nitrogen content was the highest in WS + U treatment and dissolved organic nitrogen content was the highest with the PM + U treatment. Additionally, the abundance of AOB was inhibited in comparison to that of AOA; however, AOB contributed more to nitrification than AOA. Soil NO3−-N and dissolved organic nitrogen were the principal components influencing the distribution of AOA and AOB. The result illustrated that the OAs plus urea, especially PM plus urea promoted mineralization to produce more dissolved organic nitrogen and NH4+-N, thus accelerating the growth of AOB to strengthen nitrification in soil.

Microbial traits dictate soil necromass accumulation coefficient: A global synthesis

AbstractAimThe accumulation of microbial necromass carbon has gained increasing attention due to its slow decomposition. However, it remains unclear what induces the accumulation of microbial necromass carbon via reiterated community turnover on large spatial scales. This study explores the characteristics of soil necromass carbon accumulation in terrestrial ecosystems.LocationGlobal.Time PeriodContemporary (1999–2022).Major Taxa StudiedSoil microorganisms.MethodsA dataset was compiled using 993 observations from 82 peer‐reviewed papers on the effects of coefficients of microbial necromass accumulation (hereafter NAC) in equilibrium. Linear mixed‐effect models and structural equation models were used to ascertain the controlling factors of the NAC.ResultsThe average NAC was higher in croplands (28.2) and forests (26.8) than in grasslands (21.1). Edaphic factors seemingly affected the NAC, which was lower in soils with high pH and clay content on a global scale. Biotic factors, particularly those related to living microorganism abundance and microbial biomass nitrogen content, were the pivotal drivers of NAC and accounted for approximately 43.6% of its geographic variability. More organic carbon was likely to be preserved in soil with a higher NAC, regardless of ecosystem type.ConclusionsNovel findings regarding the overriding controls for the living microorganism abundance and microbial biomass nitrogen that drive the NAC highlight an urgent need for viable strategies to manipulate microbial attributes for enhancing carbon sequestration.

Responses of soil N-cycle enzyme activities to vegetation degradation in a wet meadow on the Qinghai-Tibet Plateau

Soil enzymes play a vital role in the functioning of wetland ecosystems, driving energy flow and material cycling processes. Gahai wet meadow, one of the important components of alpine wetlands on the Qinghai-Tibet Plateau, has suffered serious degradation in the last 30 years due to climate change and human activities. We studied the spatial and temporal heterogeneity of soil nitrogen content and nitrogen (N)-cycle enzyme activities (i.e., urease, protease, nitrate reductase and nitrite reductase) in four degraded wet meadows in the Gahai wetlands. Our results suggested that with increasing wet meadow degradation, there was a significant decrease in soil water content, total nitrogen, ammonium nitrogen, microbial biomass nitrogen content, protease activities, and nitrite reductase activities; Conversely, soil temperature, nitrate nitrogen content, urease activities, and nitrate reductase activities increased significantly. Soil urease, protease, and nitrite reductase activities significantly decreased with increasing soil depth;The highest activity levels of the three N-cycle enzymes were observed in July and August. The linear mixed modeling results indicated that there were significant effects of degradation level and soil depth and their interactions on soil nitrate reductase and nitrite reductase activities (p < 0.01), while soil depth had significant effects only on soil urease and protease activities (p < 0.01). Redundancy analyses showed that soil ammonium and nitrate nitrogen were the main drivers of changes in soil N-cycle enzyme activity during the degradation of wet meadows. In summary, our study sheds light on the processes of soil enzyme activity in an alpine wetland ecosystem and provides valuable information for understanding the N cycling in these complex systems.

Responses of Soil CO2 Emission and Tree Productivity to Nitrogen and Phosphorus Additions in a Nitrogen-Rich Subtropical Chinese Fir Plantation

Nitrogen (N) and phosphorus (P) nutrients have been regularly applied to improve productivity in intensively managed and short-rotation forest plantations in subtropical China. Under the constraint of the national policy of “carbon neutrality”, it is necessary to determine the rational fertilization options by considering both forest productivity and soil CO2 emissions. Past worldwide studies have shown varied responses of forest soil heterotrophic respiration and CO2 emissions to N and P additions. This study designed six treatments with N additions (high level: 15 g N/m2, HN), P (low: 5 g P/m2, LP; high: 15 g P/m2, HP), and their interactions (HNLP and HNHP) to explore the effects of N and P additions on soil CO2 emissions in a P-limited and N-rich Chinese fir plantation (Cunninghamia lanceolata), and we identified the underlying controls using the structural equation model (SEM). The results indicated that LP, HNLP, and HNHP treatments significantly increased soil CO2 emissions in the first four months after treatment and the effects leveled since then. The balance between N and P inputs affected the responses of soil CO2 emissions to P additions. A low P addition significantly increased tree productivity, but the promoting effect gradually declined and was no longer significant after 3 years. Other treatments did not significantly affect tree productivity. The SEM analysis revealed that the promoting effects of P additions on CO2 emission were mainly due to their effects on increasing soil water-soluble organic carbon content and reducing microbial biomass nitrogen content. Considering both soil respiration and tree productivity, this study suggested that LP treatment can effectively balance the N and P nutrients and, in the meantime, maintain relatively low greenhouse gas emissions; thus a low P application level is suggested for N-rich Chinese fir plantations.

Impacts of Grazing Disturbance on Soil Nitrogen Component Contents and Storages in a Leymus chinensis Meadow Steppe

Long-term grazing leads to soil degradation in Inner Mongolia grassland. Based on the Hulunbeier meadow steppe, the variation characteristics of soil nitrogen content and storage in soil layers between 0–40 cm, under six different grazing intensities, and the response of vegetation and other physical and chemical properties of soil to grazing were studied. The main results were as follows: (1) Moderate grazing increased soil total nitrogen (TN), soluble total nitrogen (STN) and microbial biomass nitrogen (MBN) contents, while heavy grazing decreased MBN content. In the year with more rain, heavy grazing increased nitrate nitrogen (NO3−-N) content and storage, while less rain increased ammonium nitrogen (NH4+-N) content. (2) The proportion of 0–40 cm nitrogen components showed an upward trend in the year with more rain, and the opposite in the years with less rainfall with the increase of grazing intensity. Soil soluble organic nitrogen (SON) and NO3−-N storages decreased and MBN storage increased in rainy years. (3) Soil nitrogen component contents and storages were correlated with plant growth status, soil moisture (SM) and soil bulk density (SBD), and were significantly negatively correlated with soil temperature (ST) and pH (p < 0.05). The content and storage of soil nitrogen were affected by grazing, soil, vegetation, meteorological and other environmental factors. Moderate grazing was more conducive to the improvement of soil nitrogen storage capacity and the healthy development of grassland.

Is degradable plastic film alternative? Insights from crop productivity enhancement and soil environment improvement

Currently, it is unclear whether degradable film mulching is a feasible viable alternative to non-degradable film mulching for improving crop productivity and soil environmental conditions. In the present study, a three-year-long field experiment was conducted to evaluate the effects of three alternative degradable films and a traditional plastic film (PF) on soil properties and peanut growth performance. Results showed that degradable films enhanced peanut yields by 6.0–14.3% compared to no mulching (CK), while reduced the peanut yield compared to PF. The results of the structural decomposition model analysis attributed the positive correlations between peanut yields and soil temperature, soil organic carbon, soil alkali-hydrolyzable nitrogen, soil microbial biomass carbon (MBC), and soil microbial biomass nitrogen (MBN). The degradable films decreased soil temperature, soil organic matter, soil alkali-hydrolyzable nitrogen content, MBC and MBN content by 0.12–11.8%, 1.40–10.9%, 1.90–9.91%, 2.31–13.2% and 12.7–34.2% compared to PF, respectively, despite they performed better effects on soil environment than CK. Moreover, the degradation rates of the three degradable films ranged from 7.38% to 91.3%. The aliphatic polyester polylactic acid-based film was found to be the best alternative because of improvement of soil environment and crop yield as well as superior degradation properties.

Effects of exogenous organic matter addition on agricultural soil microbial communities and relevant enzyme activities in southern China

Soil microbial community composition plays a key role in the decomposition of organic matter, while the quality of exogenous organic matter (EOM: rice straw, roots and pig manure) can influence soil chemical and biological properties. However, the evidences of the effect of combination of crop residues and pig manure on the changes in soil microbial community and enzymes activities are scarce. A greenhouse pot experiment was conducted to investigate the potential effect of EOM by analyzing soil properties, enzyme activities and microbial communities. The experiment consisted of eight treatments: CK (control), S (1% (w/w) rice straw), R (1% (w/w) rice root), SR (1% (w/w) rice straw + 1% (w/w) rice root), and added 1% (w/w) pig manure to CK, S, R and SR, respectively. Results showed that the straw treatment significantly increased the microbial biomass (carbon and nitrogen) and total carbon and nitrogen contents, cellulase and β-1,4-glucosidase activities, bacteria (i.e., gram-positive bacteria and gram-negative bacteria) PLFAs contents relative to CK regardless of whether pig manure was added. Moreover, the interaction between crop residues (e.g., straw and roots) and pig manure significantly influenced the contents of microbial biomass nitrogen and microbial biomass phosphorus, and the ratio of gram-positive bacteria to gram-negative bacteria. Redundance analysis confirmed that pH, nitrate nitrogen, ammonium nitrogen and dissolve organic carbon contents were significantly associated with soil microbial community under crop residues without pig manure addition. Furthermore, the experiment results showed that pig manure application not only provided more abundant nutrients (C, N and P) but also induced higher microbial and enzymatic activity compared with no pig manure addition. Our findings suggest that the combination of above-ground straw and pig manure is a better option for improving the functions of soil ecosystem.

青海云杉林凋落物分解早期微生物生物量时空动态变化

PDF HTML阅读 XML下载 导出引用 引用提醒 青海云杉林凋落物分解早期微生物生物量时空动态变化 DOI: 10.5846/stxb202203220711 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31901130）；中国地质调查局地质调查项目（DD20208065） Temporal and spatial changes of microbial biomass in litter decomposition early process in Qinghai spruce (Picea crassifolia) forests Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:凋落物分解过程中的微生物生物量动态对于深入了解森林生态系统凋落物分解机理具有重要意义。为了解高寒山地森林典型树种凋落物分解过程中的微生物生物量动态特征，采用凋落物袋野外原位分解法，研究了海拔2850 m、2950 m、3050 m、3150 m和3250 m树冠中心（CC）与树冠边缘（CE）青海云杉（Picea crassifolia）叶凋落物分解过程中凋落物和土壤中的微生物生物量碳（MBC）、微生物生物量氮（MBN）和微生物生物量磷（MBP）时空动态变化。时间尺度上，不同海拔CC与CE凋落物中的MBC、MBN和MBP在生长季节初期上升，生长季节后期下降；但土壤中的MBC、MBN和MBP却在生长季节初期下降，生长季节后期上升。然而，3050 m海拔CE和3250 m海拔土壤中的MBP含量呈"先下降-后上升-再下降"的倒"N"型变化格局。空间尺度上，凋落物中的MBC和MBN含量高于土壤中的，但MBP出现相反情况；CE处的MBC、MBN和MBP含量均显著（P<0.05）高于CC；总体而言，MBC、MBN和MBP含量以中海拔显著最高（P<0.05），其次为低海拔，高海拔显著最低（P<0.05）。这些结果为清晰地认识高寒山地森林凋落物分解过程及机理，以及进一步理解陆地生态系统结构和功能奠定了基础。 Abstract:Microorganism plays an important role in litter decomposition, and the change of microbial biomass is of ecological significance in understanding the mechanism of litter decomposition in the forest ecosystem. In order to understand the dynamic characteristics of microbial biomass during litter decomposition process in the Qinghai spruce forest, Qilian Mountains, we collected leaf litter samples at the crown center (CC) and crown edge (CE) by decomposition litterbags in different times (the early growing season and the late growing season) and altitudes (i.e., 2850 m, 2950 m, 3050 m, 3150 m and 3250 m). The temporal and spatial changes of microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) in litter and soil were analyzed. Temporally, the MBC, MBN and MBP increased in the early growing season and decreased in the late growing season. On the contrary, the MBC, MBN and MBP in soil decreased in early growing season and increased in late growing season. However, the content of MBP in soil at CE of 3050 m altitude and 3250 m altitude showed an inverted "N" shaped pattern, that is, "decrease-rise-decrease". Spatially, the contents of MBC and MBN in litter were higher than those in soil at all plots, but MBP was the opposite. The contents of MBC, MBN and MBP at the CE were significantly (P<0.05) higher than those at the CC. In general, the contents of MBC, MBN and MBP were the highest at medium altitude (P<0.05), followed by low altitude, and then the lowest at high altitude (P<0.05). The results would lay foundation to understand the process and mechanism of litter decomposition in the alpine mountain forest ecosystem, and further understand the structure and function of the ecosystem. 参考文献 相似文献 引证文献

Influence of vegetation types on soil physical and chemical properties, microbial biomass and stoichiometry in the central Himalaya

Soil physical and chemical properties and microbial biomass dynamics are significantly related to vegetation types. However, how different vegetation types influence the soil and microbial dynamics remains poorly understood. The aim of the present study is to assess the influence of vegetation types on soil physical properties (bulk density (BD), porosity, moisture, texture, and water holding capacity), chemical properties (soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), soil pH and electrical conductivity (EC), and SOC, TN and TP stocks), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and stocks as well as soil and microbial biomass C: N: P stoichiometry within three soil depth (0–10 cm, 10–30 cm and 30–60 cm) in central Himalaya. Five vegetation types, namely oak (Quercus leucotrichophora A. Camus) forest, Chir-pine (Pinus roxburghii Sarg.) forest, deodar (Cedrus deodara (Roxb.) G.Don) forest, Sal (Shorea robusta (Roth) forest) and one was abandoned agricultural land was selected for the present study. Principal component analysis (PCA) and correlation analyses were performed to evaluate the relationship among physical, chemical, and microbial characteristics and stoichiometry. ANOVA revealed significant differences in soil physical and chemical properties, microbial biomass, and stoichiometry due to vegetation types (P < 0.001), soil depths (P < 0.001), and vegetation types × soil depth interaction (P < 0.001). The results showed that the SOC, TN, TP, MBC, MBN, and MBP contents decreased with soil depths. MBC, MBN, and MBP contents were significantly and positively related to SOC, TN, and TP contents. Oak and deodar forests had the highest, SOC, TN, TP, MBC, MBN, and MBP contents, compared with other vegetation types. Sal forest soil (0–10 cm) had the highest SOC: TN, and SOC: TP ratios. Different vegetation types have different soil properties and stoichiometry, implying their different soil C, N, and P stocks. Thus our findings can help in developing a promising guideline for sustainable management strategies and soil management in long run.

Effects of biochar addition on nitrous oxide emission during soil freeze-thaw cycles.

Biochar applied to soil can reduce nitrous oxide (N2O) emissions produced by freeze-thaw processes. Nonetheless, how biochar modification affects N2O emissions during freeze-thaw cycles is not completely clear. In our research, during freeze-thaw cycles, microcosm experiments were conducted to investigate the effects of maize straw biochar (MB) or rice straw biochar (RB) addition on soil N2O emissions under different water conditions. The N2O emissions peaked at the initial stage of thawing in all the soils, and the total N2O emissions were considerably greater in the flooded soils than in the nonflooded soils. Compared with the soils without biochar addition, RB and MB amendments inhibited N2O emissions by 69 and 67%, respectively. Moreover, after biochar addition, the abundance of AOB amoA genes decreased by 9-13%. Biochar addition significantly decreased the content of microbial biomass nitrogen (MBN) in flooded soil during thawing, which was significantly correlated with N2O emissions and nitrification and denitrification communities. The PLS-PM further revealed that biochar can inhibit the production and emission of soil N2O by reducing soil MBN during soil thawing. In addition, soil moisture directly significantly affects N2O emissions and indirectly affects N2O emissions through its influence on soil physicochemical properties. Our results revealed the important function of biochar in decreasing the emission of N2O in flooded soil during freeze-thaw cycles.

Effect of prescribed burning on the small-scale spatial heterogeneity of soil microbial biomass in Pinus koraiensis and Quercus mongolica forests of China

Prescribed burning can alter soil microbial activity and spatially redistribute soil nutrient elements. However, no systematic, in-depth studies have investigated the impact of prescribed burning on the spatial patterns of soil microbial biomass in temperate forest ecosystems in Northeast China. The present study investigated the impacts of prescribed burning on the small-scale spatial heterogeneity of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in the upper (0–10 cm) and lower (10–20 cm) soil layers in Pinus koraiensis and Quercus mongolica forests and explored the factors that influence spatial variations of these variables after prescribed burning. Our results showed that, MBC declined by approximately 30% in the 10–20 cm soil layer in the Q. mongolica forest, where there were no significant effects on the soil MBC and MBN contents of the P. koraiensis forest (p > 0.05) after prescribed burning. Compared to the MBC of the Q. mongolica forest before the prescribed burn, MBC spatial dependence in the upper and lower soil layers was approximately 7% and 2% higher, respectively. After the prescribed burn, MBN spatial dependence in the upper and lower soil layers in the P. koraiensis forest was approximately 1% and 13% lower, respectively, than that before the burn, and the MBC spatial variability in the 0–10 cm soil layer in the two forest types was explained by the soil moisture content (SMC), whereas the MBN spatial variability in the 0–10 cm soil layer in the two forests was explained by the soil pH and nitrate nitrogen (NO3–-N), respectively. In the lower soil layer (10–20 cm) of the Q. mongolica forest, elevation and ammonium nitrogen (NH4+-N) were the main factors affecting the spatial variability of MBC and MBN, respectively. In the 10–20 cm soil layer of the P. koraiensis forest, NO3–-N and slope were the main factors affecting the spatial variability of MBC and MBN, respectively, after the burn. The spatial distributions of MBC and MBN in the two forests were largely structured with higher spatial autocorrelation (relative structural variance C/[C0 + C] > 0.75). However, the factors influencing the spatial variability of MBC and MBN in the two forest types were not consistent between the upper and lower soil layers with prescribed burning. These findings have important implications for developing sustainable management and conservation policies for forest ecosystems.

Forage mixed planting can effectively improve soil enzyme activity and microbial community structure and diversity in agro-pastoral interlacing arid zone

Aiming at the problems of serious soil desertification and continuous reduction of effective soil nutrients in the agricultural and animal husbandry interlaced arid area in Inner Mongolia, this study used Aohan alfalfa, old awn wheat, and fodder oats at the Siziwang Banner, Ulanchabu City, Inner Mongolia Autonomous Region. There were a total of five treatments, namely, single seeding alfalfa, single seeding old awn wheat, single seeding fodder oats, alfalfa and old awn wheat mixed sowing, and control. The results showed that the urease activity and microbial biomass nitrogen content of mixed planting were higher than other treatments. With the advancement of the growth period, the bacteria α-diversity index showed an upward trend; β-diversity analysis showed that planting method was the main factor affecting bacteria diversity and sampling time was the main factor affecting fungi diversity. In summary, mixed planting treatment was more helpful to improve soil enzyme activity, microbial biomass, and enrich soil microbial diversity, which was of great significance to maintain the balance of soil ecosystem. It is hoped that this study will contribute to the theoretical basis and practical experiences for efficient utilization of microbial resources in the field of soil improvement.

Bioorganic and silicon amendments alleviate early defoliation of pear trees by improving the soil nutrient bioavailability, microbial activity, and reshaping the soil microbiome network

Pear trees with severe early defoliation usually suffer from weakened aboveground growth and a serious decrease of fruit quality and yield. Soil fertility and its microbial community and functional activity are significant factors impacting plant growth and yield, which also might be the very factors that influence the early defoliation of pear trees. To address the problems caused by chemical fertilizers, bioorganic fertilizer (BIO) and silicon amendment (SOA) are increasingly used as amendments to improve soil microbial activity and increase soil nutrient availability. However, how effective BIO and SOA are at improving the health of soils and reducing early defoliation remains unclear. Here, we conducted a 4-year field experiment (2016–2019) in a 25-year-old ‘Cuiguan’ pear orchard in Jianning county, Fujian province, comparing local custom fertilization (CK), local custom fertilization supplemented with SOA (CK-SOA), BIO, and BIO supplemented with SOA (BIO-SOA). At the end of the 4-year study we found that BIO and BIO-SOA treatments resulted in reduced leaf nitrogen content and increased leaf potassium (K), calcium (Ca), silicon (Si), and manganese (Mn) content. BIO and BIO-SOA treatments also resulted in a 50% reduction of the early deciduous rate and a 47% increase in pear yield. Compared with CK treated soil, BIO and BIO-SOA treated soils had higher nitrate nitrogen content (NO3−-N), available Si, Fe, Mn, and Zn content, and significantly improved microbial biomass nitrogen content (MBN), geometric mean enzyme activity (GMEA) and ecosystem multifunctionality (EMF). Network analysis revealed that BIO and BIO-SOA treatments had significantly altered the bacterial and fungal community composition in the orchard soil. Redundancy analysis (RDA) and the Mantel test indicated that soil available K, exchangeable Ca and Mg, and available Si, Fe, Mn and Zn content were the main factors influencing bacterial and fungal communities. The increased nutrient availability (e.g., NO3−-N and microelement contents), MBN, GMEA and EMF had negative effects on the early defoliation rate. Random Forest model identified soil available Si content, microbial biomass nitrogen content, EMF, and GMEA as the main predictors of early defoliation rate. Overall, this study demonstrates that application of BIO or BIO mixed with SOA can alleviate the early defoliation rate of pear trees by increasing the availability of microelements, microbial functional activity, and changing the soil microbial community composition.

Effects of nitrogen addition on soil microbial biomass and enzyme activities of Pinus massoniana-Quercus variabilis mixed plantations in the Three Gorges Reservoir Area

We examined the effects of nitrogen addition (0, 30, 60, and 90 kg N·hm-2·a-1) to soil microbial biomass, enzyme activities, and nutrient contents of the Pinus massoniana-Quercus variabilis mixed plantations in the Three Gorges Reservoir Area, with the aim to provide a theoretical basis for predicting soil carbon dynamics under the background of continuously increasing atmospheric nitrogen deposition in this area. The results showed that nitrogen addition at all levels led to a significant increase of the contents of organic carbon, total nitrogen, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP) in the forest soil, while a decrease of soil pH-value, and no significant effect on the total phosphorus content. Nitrogen addition increased the activities of β-1-4 glucosidase (BG), cellobiose hydrolase (CB), acid phosphatase (AP), N-acetylglucosaminosidase (NAG) and peroxidase (POD), while inhibited that of polyphenol oxidase (PPO). There was a significant seasonal variation in soil oxidase activities, in which the peroxidase activity was higher in May and August, and the polyphenol oxidase activity was the highest in August. Soil enzyme activities were significantly correlated with soil moisture and the contents of soil nutrients, MBC, MBN, and MBP. The variation of soil enzyme activities was caused by the comprehensive effects of multiple factors. The redundancy analysis (RDA) showed that the contents of total soil nitrogen and MBC were the main environmental factors driving soil enzyme activities. The continuous increase of atmosphere nitrogen deposition would lead to soil acidification and promote the turnover of soil organic carbon and nutrient cycling in the Pinus massoniana-Quercus variabilis mixed plantations of the study area.

Effect of Plastic Mulching on Soil Carbon and Nitrogen Cycling-Related Bacterial Community Structure and Function in a Dryland Spring Maize Field

Plastic mulching, given its positive effects on temperature and water retention, has been widely used to solve water shortages and nutrient scarcity in rainfed agricultural soils. This practice affects the physical and chemical processes of soil, including carbon and nitrogen cycling. However, research into microbe-mediated carbon and nitrogen cycling in soil with plastic mulching is still limited. In this study, the structures and functions of the soil bacterial community in non-mulched spring maize, plastic-mulched spring maize, and bareland fallow in a dryland field on the Loess Plateau in China were analyzed to explore the responses of microbe-mediated carbon and nitrogen cycling to plastic mulching. Results showed that the richness of soil bacteria was the highest in bareland fallow. Plastic mulching increased the diversity and richness of soil bacteria to a certain extent (p &gt; 0.05), and significantly increased the content of microbial biomass nitrogen (MBN) (p &lt; 0.05). Plastic mulching enhanced the total abundances of carbon and nitrogen cycling-related microbes, exhibiting a significant increase in the abundances of Cellvibrio, Bacillus, Methylobacterium and Nitrospira (p &lt; 0.05). Predicted functional analysis revealed 299 metabolic pathways related to carbon and nitrogen cycling, including methane metabolism, carbon fixation in photosynthetic organisms, and nitrogen metabolism. The number of gene families assigned to carbon and nitrogen cycling-related metabolic pathways was higher in plastic mulched than that in non-mulched spring maize. This study demonstrated that plastic mulching enhances the capacity of carbon and nitrogen cycling, revealing its potential in mediating greenhouse gas emissions in the dryland spring maize fields on the Loess Plateau.

Fertility and biochemical activity in sodic soils 17 years after reclamation with flue gas desulfurization gypsum

Previous studies have mainly focused on changes in soil physical and chemical properties to evaluate the reclamation of sodic soils using flue gas desulfurization (FGD) gypsum. However, information on the effects of this reclamation method on microbial-based indicators of soil quality is limited, particularly after many years of FGD gypsum application. This study aimed to investigate the long-term effects of FGD gypsum on soil organic carbon (SOC), nutrients, microbial biomass and enzyme activity. Data were collected from soils of three exchangeable sodium percentage (ESP) classes (i.e., low-, middle- and high-ESP classes of 6.1–20, 20–30 and 30–78.4%, respectively) 17 years after FGD gypsum treatment in Inner Mongolia, China. Averaged across the three ESP classes, FGD gypsum application increased the SOC contents at the 0–20 and 20–40-cm soil depths by 18 and 35%, respectively, and increased available potassium at the 0–20-cm soil depth by 51% compared with the no-gypsum controls. The microbial biomass carbon and microbial biomass nitrogen contents at the 20–40-cm soil depth increased by 69 and 194%, respectively, under FGD gypsum. Except in the high-ESP class, urease activities in the 0–40 cm soil profile were significantly higher in the FGD gypsum treatments than in the controls. A significant increase in alkaline phosphatase activity was concentrated in the 20–40 cm soil layer; few classes showed significant increases in catalase and invertase activities in the 0–20 cm soil layer. Pearson correlation analysis showed that increases in soil fertility and biological activity could be attributed to reductions in electrical conductivity, pH and ESP caused by FGD gypsum application. These results confirm that FGD gypsum application is a viable strategy for reclaiming sodic soils due to its positive effects on soil fertility and biochemistry and that it may contribute to soil ecosystem sustainability.

Unimodal response of N2O flux to changing rainfall amount and frequency in a wet meadow in the Tibetan Plateau

The rainfall amount and the frequency of extreme rainfall events have been predicted to increase in the Qinghai-Tibetan Plateau during the growing season. These changes will likely affect ecosystem processes, including those that control nitrogen (N) cycling and storage; however, the direction of the changes remains unclear. In this study, we experimentally altered the amount and frequency of precipitation events during the growing season (May through October) at an alpine wetland in the Qinghai-Tibetan Plateau. The treatments included ambient rain (CK) plus 25 mm of extra water for each irrigation event but with different irrigation frequency, i.e., weekly (DF1), biweekly (DF2), every three weeks (DF3) and every four weeks (DF4). During the growing season, the N2O flux showed a large seasonal variation. Compared with the treatment of natural rainfall events, the increase in the rainfall amount promoted the N2O emission flux. As the frequency of rainfall events increased, the aboveground biomass increased significantly from 85.82 g·m−2 to 245.79 g·m−2, and the accumulated N2O emissions first increased and then decreased; we observed the peak of the N2O flux at the DF2 rainfall frequency. We also found the significant linear relationships between soil N2O flux, nitrate nitrogen, and microbial biomass nitrogen content. Furthermore, among the soil microbial factors, higher rainfall frequency (DF1) significantly reduced the relative abundance of the original dominant species (Alphaproteobacteria) in the studied wetland soil. Our results indicate that alpine wetlands are highly sensitive to increased precipitation variability and high frequencies of extreme rainfall events could significantly reduce N2O emission. Future precipitation patterns could weaken the contribution rate of wetland N2O emission to the global warming.