Soil Extracellular Enzyme Activities Research Articles

Soil degradation regulates the effects of litter decomposition on soil microbial nutrient limitation: Evidence from soil enzymatic activity and stoichiometry.

Soil microorganisms could obtain energy and nutrients during litter decomposition with the help of soil extracellular enzymes. The litter types were among the most critical factors that affect soil extracellular enzyme activities. However, how litter types modulate the soil extracellular enzyme activity with grassland gradation is unclear. Here, we conducted a 240-day experiment of two different types of litter decomposition on soil extracellular enzyme activity and stoichiometry in different degraded grasslands. We found that C-acquiring enzyme activity and the enzyme stoichiometry of C/N were higher in Chloris virgata litter than in Leymus chinensis litter at lightly degraded level and C-acquiring enzyme activity in C. virgata was 16.96% higher than in L. chinensis. P-acquiring enzyme activity had the same trend with litter types in moderately and highly degraded levels and it was 20.71% and 30.89% higher in C. virgata than that in L. chinensis, respectively. The change of the enzyme stoichiometry with litter types was only showed in the enzyme stoichiometry of C/N at lightly degraded level, suggesting that litter types only affected the microbial C limitation in lightly degraded grassland. Almost all soil extracellular enzyme activities and extracellular enzyme stoichiometry, except the enzyme stoichiometry of N/P, decreased with grassland degraded level increasing. All vector angles were less than 45° suggesting that soil microorganisms were limited by N rather than by P during the decomposition process. Enzyme vector analysis revealed that soil microbial communities were co-limited by C and N during litter decomposition. Moreover, based on Random Forest (explaining more than 80%), we found that soil total nitrogen, total carbon, total phosphorus, dissolved organic C, pH and EC were important factors affecting soil enzyme activities by degradation levels. Our results emphasized that degradation levels could modulate the influences of litter types on soil extracellular enzyme activity. Our study enhanced our understanding in resource requirements for microbial communities to litter resources in degraded grassland and helped us to provide new ideas for improving degraded grassland ecosystems.

不同优势树种菌根类型差异对土壤胞外酶活性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同优势树种菌根类型差异对土壤胞外酶活性的影响 DOI: 10.5846/stxb202201040021 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（31270489，31700555）；江苏省高等学校自然科学研究项目（20KJA220002） Effects of different mycorrhizal types in dominant tree species on soil extracellular enzyme activity Author: Affiliation: Fund Project: The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan) 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:土壤酶作为微生物代谢指标，在森林生态系统土壤碳和养分循环过程中发挥着重要作用，是土壤质量的重要指标。针对不同优势树种的内生菌根（AM）和外生菌根（ECM）所占比例差异，设置4种菌根类型比例梯度（即林分中ECM树种所占比例为<25%、25%-50%、50%-75%、>75%），分析4种林分中土壤水解酶[β-葡糖苷酶（BG）、β-N-乙酰氨基葡萄糖苷酶（NAG）、亮氨酸氨基肽酶（LAP）、酸性磷酸酶（AP）]和过氧化物酶（PER）活性差异，运用方差分析和多重比较分析方法，探究水解酶和氧化酶沿菌根类型梯度的变化规律及原因。结果表明：①lnBG和ln （NAG+LAP）与lnAP的回归斜率小于1，且AP远大于BG和NAG+LAP，这表明森林土壤微生物受磷（P）限制更严重，随着林分中ECM优势树种的增加，微生物受碳（C）和P限制的状况得到缓解；②土壤有机碳（SOC）随着ECM树种占比的增加而增加，ECM森林比AM森林表现出更高的全氮（TN）和全磷（TP）含量；③随着林分中ECM树种占比的增加，BG、AP和NAG+LAP呈逐渐显著增加的趋势（P<0.05）；但氧化酶活性差异不显著；④土壤水解酶活性与铵态氮、硝铵比、TN、TP、SOC有显著相关关系，氧化酶活性只与土壤水分（SM）含量呈现显著相关性。研究支持资源分配理论，验证了土壤胞外酶活性随AM和ECM菌根比例变化而呈现梯度变化，证实了菌根--养分经济模型的适用性，研究结果可加强对不同菌根梯度林分土壤理化性质和酶活性的可预测性，有助于生物地球化学循环模型的补充与完善。 Abstract:Soil enzyme is a crucial indicator of microbial metabolic activity and soil quality monitoring, playing an important role in the soil carbon and nutrient cycle. Global change could alter tree species composition, leading the transfer of dominant mycorrhizal at the individual or ecosystem level. In order to investigate the effect of mycorrhizal types on soil extracellular enzyme activity, four stands with percentage of different mycorrhizal type (the percentage of ECM trees was <25%, 25%-50%, 50%-75% and >75%, respectively) were set up in pure Cunninghamia lanceolata stand, pure Quercus acutissima stand, and the two species mixed forest. We measured the soil hydrolase activities[β-glucosidase (BG), β-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), acid phosphatase (AP)], and soil peroxidase (PER) activity and analyzed the pattern of hydrolase and oxidase activities along the gradient of mycorrhizal types using one-way ANOVA and multiple comparisons. The results showed that:① the regression slope of the ratio of lnBG to ln(NAG+LAP) and to lnAP were less than 1, indicating that AP activity was much higher than that of BG and NAG+LAP. This indicated that forest soil microorganisms were more severely restricted by phosphorus (P). The increase of ECM-associated tree species relieved the limitation of C and P for microorganisms. ② Soil organic carbon (SOC) increased as the proportion of ECM-associated tree species increased. While ECM-dominated forests had higher total soil nitrogen (TN) and total soil phosphorus (TP) contents than AM-dominated forests. ③ With the increase in the proportion of ECM-associated tree species in the forest, activities of BG, AP, and NAG+LAP showed a gradual increase trend (P<0.05)except for soil oxidase activity. ④ Soil hydrolase activity exhibited a significant correlation with ammonium nitrogen, nitrate-ammonium ratio, TN, TP, and SOC, while the oxidase activity only exhibited a significant correlation with the content of soil moisture (SM). These results support the theory of resource allocation, verify that the activity of soil extracellular enzymes changes gradually with the percent of AM-associated and ECM-associated tree species, and confirm the applicability of the mycorrhizal-associated nutrient economy pattern. The results also strengthen the predictability of the soil physical and chemical properties as well enzyme activities in the forest with different percentages of AM-associated and ECM-associated tree species, and thus contributing to the improvement of biogeochemical cycle model. 参考文献 相似文献 引证文献

Extracellular Enzyme Patterns Provide New Insights Regarding Nitrogen Transformation Induced by Alkaline Amendment of Acidic Soil

Nitrogen (N) availability is generally a limiting factor in highly acidic soil, which could be improved by amending these soils with alkaline materials. Soil extracellular enzyme activity (EEA) plays an important role in N transformation; a current knowledge gap is how this occurs in acidic soils amended with alkaline material. The present 45-day incubation experiment was designed to examine the effects of different amounts of alkaline materials (urea and/or calcium–silicon–magnesium–potassium fertilizer (CSMP)) on N transformation. The results show that soil pH significantly increased after the CSMP amendment (1.2 units) and increased soil net N mineralization (Rmin), net nitrification (Rnit) rates, and net ammonification (Ramo) rates. CSMP amendment changed the different soil EEA but with differing or opposing effects, e.g., Rnit was positively correlated with the activities of L-leucine aminopeptidase, β-xylosidase, α-glucosidase, and N-acetyl-β-glucosaminidase but negatively correlated with β-1, 4-glucosidase and β-cellobiosidase. A machine learning analysis indicated that the best predictor for Rmin and Ramo was soil pH, and for Rnit, it was nitrate. The results of the present study improve our understanding of N availability in acidic soils amended with materials to control soil pH. Such knowledge could lead to more bespoke nutrient management planning at the field scale, leading to better agronomic and environmental outcomes.

Response of soil C-, N-, and P- acquisition enzymes to moisture pulses in desert grassland to shrubland state transition

Grassland-shrubland state transition causes profound effects on soil nutrients and microorganisms, yet little is known about how these soil characteristics are influenced by rainfall and litter changes during transition. Here, we examined water (high or low moisture pulse) and litter (grass or shrub) effects on these soil characteristics in grassland-shrubland mosaics consisting of desert grassland (DG), grassland edge (GE), shrubland edge (SE), and shrubland (SL) sites. The results showed that the transition of DG-GE-SE-SL significantly reduced soil moisture, total carbon (C), total nitrogen (N), total phosphorus (P), microbial biomass carbon, and microbial biomass nitrogen, revealing evident soil degradation during this transition. After applying water and litter, soil microbial respiration (SMR) and the activities of all enzymes were promoted to varying degrees among the sites. Specifically, SMR was promoted under a low moisture pulse but suppressed under a high moisture pulse along the transition from DG to SL. Two C-acquisition enzymes, cellobiohydrolase and β-1,4-glucosidase, became increasingly active from DG to SL. Another C-acquisition enzyme of β-1,4-xylosidase and an N-acquisition enzyme of leucine aminopeptidase showed the strongest preferences for low moisture pulses in SL. These results indicated that shrub encroachment retained certain microbes with an advanced ability to acquire to C and N from dry and infertile soil in SL. Although a P-acquisition enzyme of alkaline phosphatase showed a decreasing trend along the transition from DG to SL, similar like those C- and N- acquisition enzymes, it was not sensitive to varying moisture levels, suggesting that alkaline phosphatase was affected by other soil physicochemical properties rather than soil moisture. The joint analysis of soil extracellular enzymes and nutrients indicated that microbial biomass carbon played a more important role than other soil characteristics in determining soil extracellular enzyme activities along the transition from DG to SL. Future research on dissecting soil microbial communities is warranted to better understand the microbiological mechanisms behind these phenomena in the shrub encroachment process.

Distinct roles of bacteria and fungi in mediating soil extracellular enzymes under long-term nitrogen deposition in temperate plantations

Soil microbes decompose soil organic matter by producing various extracellular enzymes, and also regulate soil carbon (C) and nutrient cycles. However, how shifts in soil microbial community under long-term nitrogen (N) deposition govern soil extracellular enzyme activities (EEAs) is not known. Here, we conducted a decade-long N fertilization experiment consisting of control, low-N (2 g N m−2 year−1), medium-N (5 g N m−2 year−1), and high-N (10 g N m−2 year−1) treatments in a N-limited temperate plantation in northern China. The diversity and community composition of fungi and bacteria were determined with bacterial 16S rRNA genes and fungal internal transcribed spacer genes sequencing. Soil EEAs involved in C, N, and phosphorus (P) cycles were also measured. The results showed that high-N addition increased fungal diversity and altered microbial community composition. In particular, rare fungal diversity and rare bacterial community composition were more sensitive to N addition. N addition improved β-1,4-glucosidase (BG) and acid phosphatase (AP) activities by altering bacterial community composition, and inhibited leucine aminopeptidase (LAP) and polyphenolic oxidase (PPO) activities by affecting fungal functional groups. Specifically, shifts in bacterial community composition caused by N addition were reflected in the significant increase in the dominant class Thermoleophilia, which could be an indicator of secreted hydrolase involved in C and P cycles. Symbiotrophic fungi were more closely associated with LAP for acquiring N and PPO. Our data provide a novel view of the link between major extracellular enzymes and specific microbial taxa under the background of N deposition.

Soil Organic Carbon Distribution, Enzyme Activities, and the Temperature Sensitivity of a Tropical Rainforest in Wuzhishan, Hainan Island

Soil carbon (C) distribution, which is deeply correlated with soil extracellular enzyme activity and its temperature sensitivity (Q10), are important for predicting the soil organic carbon (SOC) pools under climate warming. However, the high spatial heterogeneity in tropical forest soils makes the predicted results vary significantly. Thus, a total of 87 soil samples of three forest types, eight slope orientations, and four vegetation types were selected from Wuzhishan in Hainan Island, China. SOC distribution, the activities of six soil enzymes, and Q10 at 10, 20, 30, and 40 °C were investigated to supplement the tropical data. The results showed that: (1) SOC ranged from 24.82 to 87.72 g/kg. SOC in the primary forest was significantly higher than that of the secondary forest, and SOC of the cloud forests and hilltop scrub at higher elevations was significantly higher than that of the lowland rainforests and montane rainforests at lower elevations. However, the amount of recalcitrant carbon in the primary forest was the lowest. (2) Under lab temperature conditions, the acid phosphatase and β-1,4-glucosidase in the plantation forest were significantly higher than that of the secondary forest, and the polyphenol oxidase and catalase in the plantation forest were significantly higher than that of the primary forest. Enzyme stoichiometry analysis indicated that microbials were limited by nitrogen in the study area. The six soil enzyme activities were strongly correlated with SOC and total nitrogen. (3) The Q10 of soil enzymes ranged from 0.61 to 1.92 under three temperature gradients. Most hydrolases enzymes (Q10 &gt; 1) showed a positive response with temperatures from 10 to 30 °C, and showed a negative response (Q10 &lt; 1) with temperatures from 30 to 40 °C. We concluded that the negative response of enzyme Q10 with global warming would slow down the SOC decomposition. Primary tropical forests could still sequester SOC; however, their ability to do so may be vulnerable to climate change, as the amount of soil C quality index was low.

Soil extracellular enzyme stoichiometry reflects the unique habitat of karst tiankeng and helps to alleviate the P-limitation of soil microbes

Soil microbial resource limitation is an important indicator of the ecosystem function and process, especially the response mechanism of the ecosystem under global change. Known as an oasis in the degraded karst landscape, the microbial resource limitations of the karst tiankeng ecosystem are still unclear. In this study, the soil extracellular enzyme activities (EEAs) and stoichiometry (EES) related to carbon (C), nitrogen (N), and phosphorus (P) acquisition were assayed in karst tiankeng. Soil samples were collected from the sunny slope of tiankeng (TSU), the shady slope of tiankeng (TSH), the base of tiankeng (TB), and outside tiankeng (OT). The results showed that the soil enzymatic acquisition of C: N: P in karst tiankeng was deviated by 1: 1: 1, indicating that the stoichiometry of soil enzymes in karst tiankeng was in an unstable state. Soil microbial communities in karst tiankeng were limited by soil C and P, which were mainly achieved by altering soil nutrient stoichiometry. At the TSH site, soil microbes were minimally limited by C and P. The P-limitation was more evident outside karst tiankeng than inside karst tiankeng. These results showed that the unique habitat of karst tiankeng can alleviate microbial community P-limitation in karst land. This study highlights the characteristics of karst tiankeng ecosystems and their role in maintaining microbial survival and ecological function in karst fragile ecosystems.

Vegetation Restoration with Mixed N2-Fixer Tree Species Alleviates Microbial C and N Limitation in Surface Soil Aggregates in South Subtropical Karst Area, China

Soil extracellular enzyme stoichiometry (EES) is the essential predictor in nutrient status and resource limitation of soil microorganisms, whose metabolism has a vital role in biogeochemical cycling and ecosystem function. However, little is known about how N2-fixer tree species with different planting patterns affect soil nutrient resources in terms of extracellular enzyme activity (EEA) or EES within aggregates in degraded karst ecosystems. In this study, we evaluated soil EEA and EES related to carbon (C), nitrogen (N), and phosphorus (P) cycles across two eight-year-old pure plantations of legume species [Dalbergia odorifera T. Chen (PD) and Acrocarpus fraxinifolius Wight ex Arn. (PA)] and a mixed plantation of the two tree species listed above (MP). Meanwhile, a nearby undisturbed shrubland was used as a control (CK). We concluded that the activities of C-, N-, and P-acquiring enzyme increased to different degrees in the N2-fixer tree species stands (particularly in MP) compared to CK in all aggregates. Compared to CK, MP significantly increased by 39.0%, 54.0%, 39.3%, and 24.8% in total C-acquiring EEA, 41.1%, 60.5%, 47.8%, and 12.5% in total N-acquiring EEA, and 100.4%, 79.7%, 69.2%, and 56.4% in total P-acquiring EEA within &gt;2 mm, 1–2 mm, 0.25–1 mm, and &lt;0.25 mm aggregates, respectively. Furthermore, the logarithmic transformed ratio of C-, N-, and P-acquiring enzyme activities was 1.20:1.08:1, which deviated from the global ratio (1:1:1). Vector analysis of EEA showed that the vector length (VL) within aggregates was significantly lower than that of CK in all stands of N2-fixer species except PD; while in all treatments, vector angle (VA) was &lt;45° for all aggregate sizes, except in MP, where VA reached 45° for &lt;0.25 mm aggregate. These indicated soil microbes were limited by C and N together. However, MP significantly alleviated microbial C and N limitation than CK (p &lt; 0.05). There were obvious positive relationships between enzyme C:N, C:P, and N:P ratios. VL was markedly negatively linked to VA. EES was markedly related to most soil nutrients and microbial biomass stoichiometry ratios. Changes in soil EEA and EES were primarily driven by available phosphorus (AP), microbial biomass carbon (MBC), soil C:N and MBN:MBP ratios. Together, our results demonstrate the influences after introducing N2-fixer tree species (particularly MP) for vegetation recovery on soil microbial nutrient limitation and ecological processes in aggregate level and will contribute to the development of ecological restoration practices and fertility management in degraded karst ecosystems of southwest China.

Effects of vegetation shift from needleleaf to broadleaf species on forest soil CO2 emission

Forest soil harbors diverse microbial communities with decisive roles in ecosystem processes. Vegetation shift from needleleaf to broadleaf species is occurring across the globe due to climate change and anthropogenic activities, potentially change forest soil microbial communities and C cycle. However, our knowledge on the impact of such vegetation shift on soil microbial community and activities, and its consequences on forest soil C dynamics are still not well established. Here, we examined the seasonal variation of soil CO2 emission, soil extracellular enzyme activities (EEAs), and soil bacterial, fungal communities in subtropical forest from broadleaf, needleleaf, and mixed stands. In addition, soil CO2 emission and soil EEAs were measured in temperate forest during the growing season. Soil organic matter (SOM) content significantly differs between broadleaf and needleleaf forests and primarily distinguish various soil chemical and microbial characteristics. Significantly higher EEAs and soil CO2 emission in broadleaf forest compared to needleleaf forest were observed both in subtropical and temperate forests. The relative abundance of Basidiomycota positively correlated with SOM and EEAs and indirectly increase soil CO2 emission whereas the relative abundance of Ascomycota exhibits opposite trend, suggesting that soil fungal communities play a key role in determining the different microbial activities between broadleaf and needleleaf stands. The temperature sensitivity of soil CO2 emission was significantly higher in broadleaf forest compared to needleleaf forest, further suggesting that the soil organic carbon in broadleaf forests is more vulnerable to warming.

Effects of Amaranthus palmeri Invasion on Soil Extracellular Enzyme Activities and Enzymatic Stoichiometry

Effects of Amaranthus palmeri Invasion on Soil Extracellular Enzyme Activities and Enzymatic Stoichiometry

Long-term organic fertilizer additions elevate soil extracellular enzyme activities and tobacco quality in a tobacco-maize rotation.

Organic fertilizer is effective in improving soil quality, and promoting crop growth. Combined organic and inorganic fertilization has been proved as a more favorable way to tobacco yield and quality. However, the mechanisms underlying tobacco yield and quality under combinations of different organic and inorganic fertilizer remain unclear. We conducted a 12-year tobacco (Nicotiana tabacum L.)-maize crop rotation field experiment in Yanhe experimental station, China to examine the yields and qualities of tobacco, soil nutrients, and extracellular enzyme activities associated with carbon, nitrogen, and phosphorus cycles in response to different fertilization treatments. Five fertilization treatments (no fertilization; 75 kg N fertilizer ha–1; 450 kg oil cake ha–1 + 75 kg N fertilizer ha–1; 15,000 kg pig dung ha–1 + 60 kg N fertilizer ha–1; 3,000 kg straw ha–1 + 75 kg N fertilizer ha–1) were applied to tobacco while maize was fertilized with inorganic compound fertilizers. After 12 years of tobacco-maize rotation, the results showed that organic fertilizer additions elevate tobacco yield and quality, and the soil extracellular enzymes activities. Gram-negative bacteria, actinomycetes, and total soil microbial biomass were increased by organic fertilizer additions, both plant-based (oil cake and straw) and animal-based (pig dung) organics. The levels of soil organic matter, total organic carbon, total phosphorus and available phosphorus are higher in pig dung addition treatment than oil cake and straw additions. By variance analysis with respect to fertilization treatments, organic sources differentially affected the activities of diverse soil enzymes. The redundancy analysis gave that yield and quality of tobacco leaves (upper, middle, and lower leaves) positively related to soil extracellular enzyme activities. Based on analysis of yield and quality of tobacco leaves with extracellular enzyme activities and soil nutrients, it is suggested animal-based organic fertilizer, thus pig dung, should be used in combining with chemical fertilizers to improve the quality of tobacco and soil nutrients.

Effects of Nitrogen Addition on Soil Microbial Functional Diversity and Extracellular Enzyme Activities in Greenhouse Cucumber Cultivation

Greenhouses, commonly used for vegetable production, are experiencing large nitrogen (N) inputs in North China, which leads to soil acidification, increases soil N availability, and affects microbial community structure and composition. However, it remains unclear how N enrichment influences soil microbial functional activities in this region. In this study, we conducted a two-year pot experiment in a greenhouse to evaluate the effects of four different rates of N addition (0, 334, 668, and 1002 kg N ha−1 year−1) on cucumber soil properties, extracellular enzyme activities, and community level physiological profiles (CLPP). We found that high-N addition (1002 kg N ha−1) caused a massive accumulation of inorganic nitrogen and soil acidification, which was not beneficial to soil microbial activities. The color development (AWCD) values for the metabolism of microbial carbon sources and the activities of soil extracellular enzymes also showed a significant decrease in high N(N3) treatment. Additionally, the activity of leucine aminopeptidase (LAP) and polyphenol oxidase (PPO) of N3 decreased by 36% and 50% compared to the N0 and could be a good predictor for microbial functional diversity and microbial biomass carbon (MBC). Structural equation modeling (SEM) confirmed that the reduction of microbial functional diversity is mainly coregulated by the decline of soil pH and the change of cucumber BGB (belowground biomass) resulting from soil C and N imbalance. Overall, excessive N-fertilizer amendment can be more dangerous to microbial community functional diversity, especially for carbohydrate utilization which adversely affects cucumber yield in current intensive management.

Changes in microbial community composition drive the response of ecosystem multifunctionality to elevated ozone

Increasing tropospheric ozone poses a potential threat to both above- and belowground components of the terrestrial biosphere. Microorganisms are the main drivers of soil ecological processes, however, the link between soil microbial communities and ecological functions under elevated ozone remains poorly understood. In this study, we assessed the responses of three crop seedlings (i.e., soybean, maize, and wheat) growth and soil microbial communities to elevated ozone (40 ppb O3 above ambient air) in a pot experiment in the solardomes. Results showed that elevated ozone adversely affected ecosystem multifunctionality by reducing crop biomass, inhibiting soil extracellular enzyme activities, and altering nutrient availability. Elevated ozone increased bacterial and fungal co-occurrence network complexity, negatively correlated with ecosystem multifunctionality. Changes in the relative abundance of some specific bacteria and fungi were associated with multiple ecosystem functioning. In addition, elevated ozone significantly affected fungal community composition but not bacterial community composition and microbial alpha-diversity. Crop type played a key role in determining bacterial alpha-diversity and microbial community composition. In conclusion, our findings suggest that short-term elevated ozone could lead to a decrease in ecosystem multifunctionality associated with changes in the complexity of microbial networks in soils.

Fire decreases soil enzyme activities and reorganizes microbially mediated nutrient cycles: A meta-analysis.

The biogeochemical signature of fire shapes the functioning of many ecosystems. Fire changes nutrient cycles not only by volatilizing plant material, but also by altering organic matter decomposition, a process regulated by soil extracellular enzyme activities (EEAs). However, our understanding of fire effects on EEAs and their feedbacks to nutrient cycles is incomplete. We conducted a meta-analysis with 301 field studies and found that fire significantly decreased EEAs by ~20%-40%. Fire decreased EEAs by reducing soil microbial biomass and organic matter substrates. Soil nitrogen-acquiring EEA declined alongside decreasing available nitrogen, likely from fire-driven volatilization of nitrogen and decreased microbial activity. Fire decreased soil phosphorus-acquiring EEA but increased available phosphorus, likely from pyro-mineralization of organic phosphorus. These findings suggest that fire suppresses soil microbes and consumes their substrates, thereby slowing microbially mediated nutrient cycles (especially phosphorus) via decreased EEAs. These changes can become increasingly important as fire frequency and severity in many ecosystems continue to shift in response to global change.

Litter Inputs Control the Pattern of Soil Aggregate-Associated Organic Carbon and Enzyme Activities in Three Typical Subtropical Forests

Soil extracellular enzyme activities among aggregate fractions are critical to short-term microbial activity and long–term carbon dynamics in forest ecosystems, but little is known regarding the effects of forest types on the soil enzyme activities in different soil aggregate fractions. Three typical subtropical forest types (Broadleaved forest, Moso bamboo forest and Chinese fir forest) were selected, and undisturbed soil samples (0–15 cm) were collected. We investigated the effects of forest types on aggregate stability (mean weight diameter, geometric mean diameter and fractal dimension), aggregate–associated organic carbon (OC) and the functionality of five enzymes (cellobiohydrolase, β-glucosidase, β-xylosidase, N–acetylglucosaminidase, leucine aminopeptidase) of different aggregate fractions (&gt;2 mm, 0.25–2 mm, 0.053–0.25 mm and &lt;0.053 mm). The results showed that the proportion of macro-aggregates, aggregate stability and macro–aggregates associated–carbon content and storage were higher in broadleaved and Moso bamboo forests than in Chinese fir forests, indicating that forest types influence the distribution of total soil OC among aggregate fraction classes and would delay the loss of OC in broadleaved and Moso bamboo forests. We also found that the extracellular enzymes were higher in aggregates of broadleaved forests and Moso bamboo forests. SEM (structural equation model) analysis also supported significantly positive relationships between litter quantity and aggregate enzyme activity, and indirect impact of litter quantity and litter C/N ratio together with soil organic carbon (SOC) and soil aggregate organic C content (SAOCC) on aggregate enzyme activity. The results of this study indicate that forest types showed large impact on aggregate-associated OC and enzyme activities, and the litter input of different forest types is the main control on enzyme activity among different aggregate fractions, and thus may play an important role in adjusting the sink capacity and stability of SOC.

Short-term vs. long-term effects of warming and nitrogen addition on soil extracellular enzyme activity and litter decomposition in a grass-dominated system

Short-term vs. long-term effects of warming and nitrogen addition on soil extracellular enzyme activity and litter decomposition in a grass-dominated system

Effects of Plastic Film Mulching on Soil Enzyme Activities and Stoichiometry in Dryland Agroecosystems.

Soil extracellular enzymes are pivotal for microbial nutrient cycling in the ecosystem. In order to study the effects of different nitrogen application rates under plastic film mulching on soil extracellular enzyme activities and stoichiometry, five nitrogen application levels (i.e., 0, 90, 150, 225 and 300 kg·hm−2) were set based on two treatments: plastic film mulching (PM) and no film mulching (LD). We measured the soil extracellular enzyme activities (EEAs) and stoichiometry (EES) of four enzymes (i.e., β-1,4-glucosidase (βG), leucine aminopeptidase (LAP), β-1,4-N-acetylaminoglucosidase (NAG) and alkaline phosphatase (AP)) involved in the C, N and P cycles of soil microorganisms in surface soil at five maize growth stages (seedling stage, jointing stage, trumpet stage, grout stage and harvest stage). The results showed that there were significant differences in soil EEA at different maize growth stages. The soil nutrient content and soil EEA were significantly improved under PM, and the stoichiometric ratio of extracellular enzymes (EC:N:P) was closer to 1:1:1, which indicated that PM was beneficial to the balance of soil nutrients and the activity of microorganisms. At each stage, with the increase in nitrogen application levels, the soil EEA showed a trend of increasing first and then decreasing (or remained unchanged), and both LD and PM treatments reached their highest activity at the 225 kg·hm−2 nitrogen application rate. When the nitrogen application level was less than 225 kg·hm−2, the soil enzyme activity was mainly limited by the N nutrient, and when the nitrogen application level reached 300 kg·hm−2, it was mainly limited by the P nutrient. RDA and correlation analysis showed that the soil C:P, C:N, N:P and pH had significant effects on soil βG, NAG + LAP and AP activities as well as EC:N, EC:P and EN:P.

Effect of N deposition on the home-field advantage of wood decomposition in a subtropical forest

Nitrogen (N) can influence the functions of forest ecosystems by altering the abundance and activity of microbial and faunal communities. The impact of N deposition on the home-field advantage (HFA) effect of dead wood decomposition remains unclear. In this study, a 24-month field reciprocal wood translocation experiment was conducted with three levels of N deposition (control (N0), 60 (N1) and 120 (N2) kg N ha−1 yr−1) in both Platycarya strobilacea (PL) forest and Cryptomeria japonica (CR) forest in subtropical China, where anthropogenic N deposition is among the highest in the world. The influence of soil biota groups on the HFA effect was partitioned using different sizes of mesh bags. We found that N1 facilitated wood decomposition by enhancing wood faunal and microbial community abundance and soil extracellular enzyme activity. However, N2 promoted wood decomposition in coarse-mesh bags by attracting more fauna and in fine-mesh bags by increasing fungal growth. In the control (CK) treatments, we found a 4.55-fold greater HFA effect in fine-mesh bags than in coarse-mesh bags. On average, a 6.6- and 4.8-fold greater HFA effect was observed with N1 treatment than with N2 and control treatments, respectively, and these differences were associated with greater differences in microbial and faunal communities between home and away fields. In summary, our results indicated that low levels of anthropogenic N enrichment could increase the HFA effect on wood decomposition through the modification of microbial and faunal communities in the wood decomposition process and thereby influence C sequestration, with peak carbon emissions and carbon neutrality reached in the next few decades in the forests of subtropical regions.

Ecoenzymatic stoichiometry reveals stronger microbial carbon and nitrogen limitation in biochar amendment soils: A meta-analysis

Soil extracellular enzyme activities of microbes to acquire carbon (C), nitrogen (N) and phosphorus (P) exert great roles on soil C sequestration and N, P availability. However, a lack of biochar-induced changes of C, N and P acquisition enzyme activities hinders us from understanding if biochar application will lead to microbial C, N and P limitation based on ecoenzymatic stoichiometry. In this study, through ecoenzymatic stoichiometry, a meta-analysis was conducted to evaluate responses of microbial metabolic limitation to biochar amendment by collecting data of ecoenzymatic activities (EEAs) of the C, N and P acquisition from peer-reviewed papers. The results showed that biochar application increased activities of C, N acquisition enzymes significantly by 9.3 % and 15.1 % on average, respectively. But the influence on P acquisition enzymes activities (Acid, neutral or alkaline phosphatase, abbreviated wholly as PHOS) was not significant. Biochar increased ratio of C acquisition enzymes activities (EC) over P enzymes activities (EP) and ratio of N enzymes activities (EN) over EP, but decreased EC:EN, indicating an increased N limitation or a shift from P limitation to N limitation in microbial metabolism. Enzyme vector analysis showed that soil microbial metabolism was limited by C relative to nutrients (N and P) under biochar amendment according to the overall increased vector length (~1.5 %). Wood biochar caused the strongest microbial C limitation, followed by crop residue biochar as indicated by increased enzyme vector length of 3.6 % and 1.2 % on average, respectively. The stronger microbial C limitation was also found when initial soil total organic carbon (SOC) was <20 g·kg−1. Our results illustrated that available nitrogen and organic carbon should be provided to meet microbial stoichiometric requirements to improve plant productivity, especially in low fertile soils under biochar amendment.

Differential Responses of Soil Extracellular Enzyme Activities to Salinization: Implications for Soil Carbon Cycling in Tidal Wetlands

AbstractRising sea levels are expected to cause salinization in many historically low‐salinity tidal wetlands. However, the response of soil extracellular enzyme activities to salinization in tidal wetlands and their links to soil organic carbon (SOC) decomposition are largely unknown. Here, we conducted a global meta‐analysis to examine the effect of salinization on hydrolytic and oxidative carbon‐acquiring enzyme activities and their relationships with SOC storage in tidal wetlands. The results showed that salinization reduced hydrolytic carbon‐acquiring enzyme activities by 33% but increased oxidative carbon‐acquiring enzyme activities by 15%. Meanwhile, salinization decreased SOC storage by 14%, and the change in SOC storage was negatively associated with oxidative carbon‐acquiring enzyme activities. These results indicate an important role for oxidative carbon‐acquiring enzymes in SOC loss in tidal wetlands. Moreover, the effect of salinization on oxidative carbon‐acquiring enzyme activities logarithmically declined with increasing salinization, implying that SOC loss was highly sensitive to even minor increases in salinity at the initial stage of salinization. Given increasing salinization over time with rising sea levels in most global tidal wetlands, our results suggest that SOC loss might be greater during early than later stages. Consequently, salinization‐induced SOC loss may be overstated in the long term if extrapolations are merely based on a constant SOC loss rate determined from short‐term studies. Future modeling frameworks should account for this changing sensitivity of microbially mediated SOC loss with increasing salinization over time.