Enzyme activities in Cerrado soils of Brazil

Abstract

Enzymes play an important role in cycling of organically bound nutrients in soils. Pyrophosphatase (PPi), acid phosphatase (AP), arylsulfatase (AS), urease (UR), and dehydrogenase (DH) activities were measured in air‐dry samples from the top 15 cm of two dark red Latosols and four red‐yellow Latosols from Cerrado regions of Minas Gerais (MG) and Goias (GO) Brazil. Relationships between enzyme activities and soil properties were examined. Among the six soils, the dark red Latosol from Sete Lagoas, MG, had the highest activities for AP, AS, and UR enzymes. The lowest activities for these enzymes were observed in a dark red Latosol from Uberaba, MG, and this soil also recorded the lowest DH activity. The red‐yellow Latosol from Sete Lagoas, MG, had the highest PPi and DH. The activities, whereas a red‐yellow Latosol from Felixlandia, MG, gave the lowest PPi activity. Activities of all enzymes were negatively correlated with sand and silt content and positively correlated with clay content. Overall, the enzyme activities were positively correlated with pH, organic carbon (C), Bray‐P, and exchangeable potassium (K), calcium (Ca), and magnesium (Mg). Soil organic C appears to have the greatest effect on the level of enzyme activities in acid soils. Each soil type has its own inherent levels of enzyme activities. Knowledge of relationships between enzyme activities and soil properties could be useful in development of sound fertilizer practices for Cerrado soils.     

Enzyme activities in Appalachian soils: 3. Pyro‐phosphatase

Abstract

The pyrophosphatase (PPi) enzyme catalyzes the hydrolysis of pyrophosphate to orthophosphate. The PPi activity was determined in 14 hill‐land soils of the Appalachian Region. The top two horizons from each soil were sampled and stored in a field‐moist state at 4°C (4°C) and in an air‐dry (AD) state prior to determination of PPi activity. Each soil type had its own level of PPi activity. The mean PPi activities of surface and subsurface horizons stored at 4°C were 1.3 and 1.7 times higher than those of AD samples. The average PPi activities of surface horizons were 6.2 and 4.6 times higher than subsurface horizons stored at AD and 4°C. respectively. The PPi activities were positively correlated with organic C, N, forms of S and P. exchangeable cations, original moisture by weight and volume, and percent air‐filled porosity. In both surface and subsurface horizons, significant positive correlationships were observed between PPi activities and Mn content, indicating the need for Mn in the activation of PPi. High PPi activities in surface horizons might induce a greater rate of hydrolysis of applied pyrophosphate (polyphosphate) fertilizers to orthophosphate and lead to undesirable fixation of P in acid soils.     

Enzyme activities in Appalachian soils: 4. Dehydrogenase

Abstract

Dehydrogenase enzymes significantly mediate biological oxidation of organic compounds in soil. Dehydrogenase activities were determined in surface and subsurface horizons of 14 major hill land soils of the Appalachian Region. Soil samples were stored air‐dry (AD) and field‐moist at 4°C prior to determination of dehydrogenase activities. Each soil type had its own level of dehydrogenase activity. The average dehydrogenase activities of surface and subsurface horizons stored at 4°C were 1.4 and 3.3 times higher than soil samples stored AD. Mean dehydrogenase activities of surface horizons were 5.3 and 2.2 times higher than subsurface horizons stored at AD and 4°C, respectively. Depending on storage method (AD or 4°C) and type of horizon (surface or subsurface). dehydrogenase activities were either positively or negatively related to soil moisture status, organic C, total N, soil texture, and forms of ? and S. Most of these relationships were nonsignificant. Dehydrogenase activities were positively related to exchangeable bases. CEC, and ratio of Mg/Mg+Ca; however. the relationships were mostly significant in surface horizons.     

The influence of acid soil factors on the growth of snapbeans in major appalachian soils

Abstract

Acid soil limitations to plant growth were assessed In 55 horizons of 14 major Appalachian hill land soils. Aluminum sensitive “Romano” and Al‐tolerant “Dade” snapbeans (Phaseolus vulgaris L.) were grown for 5 weeks in limed and unlimed treatments of the 55 horizons. Shoot and root growth was depressed >20% in unlimed relative to limed treatments in approximately 2/3 of the horizons. Dade snapbeans were generally more tolerant of the acid soil conditions and had higher Ca concentrations in the shoots than Romano snapbeans. However, the sensitive‐tolerant snapbean pair could not consistently be used to identify horizons with soil Al problems. Growth of both snapbeans was generally best in A horizons and worst in E horizons. The E horizons in this study were characterized by low Ca saturation (exchangeable Ca x 100/cation exchange capacity) and high Al saturation (exchangeable Al x 100/cation exchange capacity). Exchangeable Ca, soil Ca saturation and total soil solution Ca were positively correlated (p<0.01) with snapbean root and shoot growth. Soil Al saturation, total soil solution Al and soil solution Al reacting in 15 seconds with 8‐hydroxyquinoline were negatively correlated (p<0.01) with growth. The ratio of Ca/Al in soil solution was more closely related to snapbean growth than the soil solution concentration of any individual element. Soil and soil solution Mn were, in general, not significantly correlated with snapbean growth. Many of the horizons in this study had both Al toxicity and Ca deficiency problems and interaction between Ca and Al affected both snapbean growth and Ca uptake. These findings confirm the importance of considering Ca as well as Al when investigating Al phytotoxicity.     

Microbial community composition shapes enzyme patterns in topsoil and subsoil horizons along a latitudinal transect in Western Siberia

Soil horizons below 30 cm depth contain about 60% of the organic carbon stored in soils. Although insight into the physical and chemical stabilization of soil organic matter (SOM) and into microbial community composition in these horizons is being gained, information on microbial functions of subsoil microbial communities and on associated microbially-mediated processes remains sparse. To identify possible controls on enzyme patterns, we correlated enzyme patterns with biotic and abiotic soil parameters, as well as with microbial community composition, estimated using phospholipid fatty acid profiles. Enzyme patterns (i.e. distance-matrixes calculated from these enzyme activities) were calculated from the activities of six extracellular enzymes (cellobiohydrolase, leucine-amino-peptidase, N-acetylglucosaminidase, chitotriosidase, phosphatase and phenoloxidase), which had been measured in soil samples from organic topsoil horizons, mineral topsoil horizons, and mineral subsoil horizons from seven ecosystems along a 1500 km latitudinal transect in Western Siberia. We found that hydrolytic enzyme activities decreased rapidly with depth, whereas oxidative enzyme activities in mineral horizons were as high as, or higher than in organic topsoil horizons. Enzyme patterns varied more strongly between ecosystems in mineral subsoil horizons than in organic topsoils. The enzyme patterns in topsoil horizons were correlated with SOM content (i.e., C and N content) and microbial community composition. In contrast, the enzyme patterns in mineral subsoil horizons were related to water content, soil pH and microbial community composition. The lack of correlation between enzyme patterns and SOM quantity in the mineral subsoils suggests that SOM chemistry, spatial separation or physical stabilization of SOM rather than SOM content might determine substrate availability for enzymatic breakdown. The correlation of microbial community composition and enzyme patterns in all horizons, suggests that microbial community composition shapes enzyme patterns and might act as a modifier for the usual dependency of decomposition rates on SOM content or C/N ratios.     

我国主要土壤剖面酶活性状况

本世纪五十年代以来,由于科学的发展以及新技术的引入,土壤酶的研究愈来愈为人们所重视。试验研究已证明,土壤酶是土壤的组成分之一。     

Vertical gradients of potential enzyme activities in soil profiles of European beech,Norway spruce and Scots pine dominated forest sites

Management of forest sites has the potential to modulate soil organic matter decomposition by changing the catalytic properties of soil microorganisms within a soil profile. In this study we examined the impact of forest management intensity and soil physico-chemical properties on the variation of enzyme activities (β-glucosidase, β-xylosidase, α-glucosidase, phenol oxidase, N-acetyl-glucosaminidase, l-leucine aminopeptidase, phosphatase) in the topsoil and two subsoil horizons in three German regions (Schorfheide-Chorin, Hainich-Dün, Schwäbische Alb). The sandy soils in the Schorfheide-Chorin (SCH) showed lower ratios of the activity of carbon (C) acquiring enzymes (β-glucosidase) relative to nitrogen (N) acquiring enzymes (N-acetyl-glucosaminidase + l-leucine aminopeptidase), and activity of C acquiring enzymes relative to phosphorous (P) acquiring enzymes (phosphatase) than the finer textured soils in the Hainich-Dün (HAI) and Schwäbische Alb (ALB), indicating a shift in investment to N and P acquisition in the SCH. All enzyme activities, except phenol oxidase activity, decreased in deeper soil horizons as concentrations of organic C and total N did, while the decrease was much stronger from the topsoil to the first subsoil horizon than from the first subsoil to the second subsoil horizon. In contrast, phenol oxidase activity showed no significant decrease towards deeper soil horizons. Additionally, enzyme activities responsible for the degradation of more recalcitrant C relative to labile C compounds increased in the two subsoil horizons. Subsoil horizons in all regions also indicate a shift to higher N acquisition, while the strength of the shift depended on the soil type. Further, our results clearly showed that soil properties explained most of the total variance of enzyme activities in all soil horizons followed by study region, while forest management intensity had no significant impact on enzyme activities. Among all included soil properties, the clay content was the variable that explained the highest proportion of variance in enzyme activities with higher enzyme activities in clay rich soils. Our results highlight the need for large scale studies including different regions and their environmental conditions in order to derive general conclusions on which factors (anthropogenic or environmental) are most influential on enzyme activities in the whole soil profile in the long term at the regional scale.     

The use of polyethylene mulches to change soil microclimate as revealed by enzyme activity and biomass nitrogen,sulphur and phosphorus

Summary The effects of white, black and clear polyethylene mulches on temporal fluctuations in protease, sulphatase and phosphatase activities and levels of available and biomass N, S and P in raised beds of soil under a strawberry crop were investigated under field conditions. During spring, summer and early autumn, clear and, to a lesser extent black, polyethylene mulch increased both maximum and minimum mean monthly temperatures over those recorded with white mulch or no mulch. During summer and autumn, soil moisture content measured at monthly intervals was higher under mulched than unmulched conditions. Levels of extractable nitrate and sulphate in soils during autumn followed the order: clear mulch = black mulch > white mulch > no mulch. However, there were no significant differences in levels of enzyme activity or concentrations of biomass N, S or P between treatments. There were significant seasonal fluctuations in estimates of biomass N, S and P, but there was no close relationship between fluctuations in any estimate. This discrepancy was attributed to errors in the chloroform fumigation technique. Enzyme activities showed significant temporal fluctuations but the three enzymes did not show similar times of minimum and maximum activity. The complexity of interactions between soil microbial and biochemical properties and nutrient availability was exemplified by the absence of a discernible relationship between seasonal fluctuations in enzyme activities and levels of biomass N, S and P and/or levels of extractable mineral N, S and P in the soil. Strawberry fruit yields and vegetative growth followed the order : clear mulch = black mulch>white mulch>no mulch. Clear, and to a lesser extent black mulch increased the percentage of total yields produced in the first 2 months of cropping.     

Effects of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal fungus (Glomus intraradices) on enzyme activities of a sterilized soil–sand mixture and nutrient uptake by maize

A pot experiment was conducted to investigate the effect of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal (AM) fungi (Glomus intraradices) on soil enzyme activities and nutrient uptake by maize, which was grown on a mixture of sterilized soil and sand. Maize plants were grown in pots inoculated or not inoculated with AMF, treated or not treated with earthworms. Wheat straw was added as a feed source for earthworms. Mycorrhizal colonization of maize was markedly increased in AM fungi inoculated pots and further increased by addition of epigeic earthworms. AM fungi and epigeic earthworms increased maize shoot and root biomass, respectively. Soil acid phosphatase activity was increased by both earthworms and mycorrhiza, while urease and cellulase activities were only affected by earthworms. Inoculation with AM fungi significantly (p?<?0.001) increased the activity of soil acid phosphatase but decreased soil available phosphorus (P) and potassium (K) concentrations at harvest. Addition of earthworms alone significantly (p?<?0.05) increased soil ammonium-N content, but decreased soil available P and K contents. AM fungi increased maize shoot weight and root P content, while earthworms improved N, P, and K contents in shoots. AM fungi and earthworm interactively increased maize shoot and root biomass through their regulation of soil enzyme activities and on the content of available soil N, P, and K.     

有机物料还田对黑土胞外酶化学计量特征的影响

冷凉区有机物料（秸秆和有机肥）还田黑土胞外酶计量特征是否受年平均温度的影响，目前缺少定量研究和深入分析。根据气候条件，该研究在黑龙江省西部依据纬度特征选取了12个有机物料还田年限大于5 a的定位试验点，基于有机物料还田种类对土壤胞外酶计量学特征及驱动因子进行了区域性分析。结果表明土壤胞外酶C:N:P在1:0.97:0.61～1:1.13:0.71之间，即有机肥还田（M）和秸秆还田（S）处理下土壤微生物整体面临微生物碳和养分（氮）限制。研究发现随年均温度升高，M和S处理的碳获取酶活性降低，而氮获取酶活性增加。此外，年均温度升高还使得M处理磷获取酶活性降低，而S处理磷获取酶活性增加。总体而言，东北冷凉区有机物料还田黑土微生物能量和养分限制主要受年平均温度直接影响，间接受pH值，土壤C:P等影响。该研究为冷凉区黑土建立合理的碳氮磷施肥模式提供数据支撑，为土壤养分恢复提供理论依据。     

Soil Biological Activities in Monitoring the Bioremediation of Diesel Oil-Contaminated Soil

The effects of two different biological treatments on hydrocarbon degradation and on soil biological activities were determined during a 100-d incubation period. An evaluation of soil biological activities as a monitoring instrument for the decontamination process of diesel-oil contaminated soil was made using measurements of organic carbon content, soil microbial respiration, soil ATP and dehydrogenase, β-glucosidase, lipase enzyme activities. Five samples were used: S (control, uncontaminated soil), CS (contaminated soil), SCS (sterilized contaminated soil), CFS (contaminated soil plus N and P), CCS (contaminated soil plus compost). The relationships between soil parameters and the levels of total petroleum hydrocarbons (TPH) residues were investigated. Results showed that inorganic nutrients NP and compost stimulated hydrocarbon biodegradation but not all biological activities to a significant extent. The residual hydrocarbon trend was positively related with that of the organic C content, microbial respiration and with β-glucosydase activity, while both soil lipase and dehydrogenase activities were negatively related with the hydrocarbon trend. Lipase activity was found to be the most useful parameter for testing hydrocarbon degradation in soil.     

干湿交替灌溉改善稻田根际氧环境进而促进氮素转化和水稻氮素吸收

[目的]阐明不同水氮管理模式下水稻根际内外氧环境变化特征及其对土壤碳氮转化和水稻氮吸收利用的影响,以期从稻田"根际氧环境"调控角度揭示适宜水氮耦合促进水稻生长和提高氮素利用效率的内在机制.[方法]在长期定位试验基础上,采用根箱模拟培养以及Unisense微电极系统和15N同位素示踪相结合的研究方法,以常规粳稻日本晴和常...     

红壤旱地玉米开花期土壤酶活性对长期施肥的响应

【目的】 长期施肥条件下,土壤酶活性与土壤养分周转和作物生长密切相关,因此,研究驱动土壤速效氮磷钾养分和作物养分吸收的关键土壤酶活性因子十分重要。 【方法】 基于始于1986年的红壤旱地长期施肥定位试验,于试验进行31年时的早玉米开花期 (2017年6月18日) 采集不施肥 (CK)、氮磷钾化肥 (NPK)、两倍氮磷钾化肥 (2NPK)、氮磷钾化肥配施有机肥 (NPKM)、单施有机肥 (OM) 5个处理的土壤样品,分析土壤蔗糖转化酶 (INV)、脱氢酶 (DEH)、纤维素酶 (CEL)、脲酶 (UR)、多酚氧化物酶 (PHOX)、酸性磷酸酶 (ACP) 和β-葡萄糖苷酶 (BG) 的变化规律,并利用冗余分析 (RDA) 探讨了驱动红壤旱地速效养分和玉米氮磷钾含量的关键土壤酶活性因子。 【结果】 与CK处理相比,施肥可以显著增加红壤旱地的土壤酶活性,且以NPKM处理的土壤酶活性最高。NPKM处理下INV、DEH、UR、PHOX、ACP和BG活性分别比OM处理增加了13.7%、13.5%、10.6%、10.5%、5.6%和13.4%,比2NPK处理增加了32.4%、112.2%、22.8%、33.3%、27.6%和50.4%。但是,在氮磷钾化肥用量之间,呈现出2NPK处理的CEL和UR活性显著高于NPK处理 (增幅为26.0%和50.6%),而INV、DEH、PHOX、ACP和BG均无显著差异。土壤pH、有机碳、速效氮磷钾和植株氮磷钾含量也呈现出NPKM处理显著高于其他处理的规律。RDA结果表明,INV、CEL和UR是影响土壤速效氮磷钾和植株养分含量的关键酶活性因子 (R2 > 0.90, P < 0.001)。 【结论】 在红壤旱地上,玉米开花期土壤酶活性对不同施肥处理的响应规律不同,其中有机无机肥配施更有利于提高土壤酶活性,且纤维素酶和脲酶活性对氮磷钾化肥用量改变的响应比较敏感。土壤蔗糖转化酶、纤维素酶和脲酶可以作为关键酶活性因子表征玉米开花期红壤旱地的养分周转和迁移。      

土地利用方式对西南喀斯特土壤碳、氮、磷化学计量特征及酶活性的影响

  目的  探究西南喀斯特土壤碳（C）、氮（N）、磷（P）化学计量特征和酶活性对不同土地利用方式的响应,有利于为西南喀斯特的土地利用调控与生态修复提供决策支持。  方法  本研究以喀斯特高原峡谷（贵州省关岭县花江研究区）亚热带森林（SUF）、疏林（SPF）、灌木林（SHF）、草地（GL）、玉米地（CL）、裸地（BL）及弃荒地（AL）的土壤为研究对象,通过采集其0 ~ 15 cm土层样品,分析土壤C、N、P化学计量特征及酶活性的差异。  结果  ①土壤有机碳含量（SOC）和全氮（TN）含量表现为SPF > AL > BL > SHF > CL > SUF > GL,土壤全磷（TP）含量表现为AL > BL > CL > SPF > GL > SHF > SUF。C∶N表现为SUF > AL > SPF > SHF > CL > BL > GL,C∶P表现为SPF > SUF > SHF > CL > AL > GL > BL,N∶P表现为SPF > SHF > SUF > CL > GL > AL > BL。土壤微生物量碳（MBC）含量则是SPF > SHF > CL > AL > SUF > BL > GL。②脲酶（URE）活性表现为SUF > CL > SPF > SHF > AL > GL > BL,蔗糖酶（SUC）活性表现为BL > AL > SPF > CL > SHF > GL > SUF,碱性磷酸酶（ALP）活性表现为SUF > BL > SHF > SPF > AL > CL > GL,过氧化氢酶（CAT）活性则是CL > AL > BL > SHF > SPF > GL > SUF。③URE与C∶P、N∶P、MBC极显著正相关,与C∶N显著正相关,与TP显著负相关;SUC与TP极显著正相关,与SOC、TN显著正相关;ALP与C∶N、C∶P显著正相关;CAT与TP极显著正相关,与TN显著正相关,与C∶P显著负相关。④在前两个排序轴中土壤理化因子累计解释了土壤酶活性变化的84.83%,按重要性排序依次为pH > 土壤温度 > TP > C∶P > TN > 容重 > SOC > C∶N > N∶P > MBC。  结论  不同土地利用方式土壤C、N、P化学计量特征及酶活性存在显著差异,土壤N∶P < 14表明土壤养分主要受氮限制。影响酶活性的主要土壤理化因子为土壤pH、土壤温度和土壤全磷。     

转 AtPAP15基因大豆种植对根际土壤养分及酶活性的影响

以转入AtPAP15基因的两个磷养分高效转基因大豆株系AP15-1、AP15-3及其各自受体YC03-3、YC04-5为材料,在大田连续种植两季,通过在苗期、盛花期和成熟期采集根际土,对其进行pH和全磷、速效磷、有机磷、全氮、碱解氮、全钾、速效钾、及钼等八种微量元素含量的测定,并分析了盛花期AP15-1与其受体YC03-3根际土中酸性磷酸酶、过氧化氢酶、蔗糖酶和脲酶的活性变化,从而了解上述磷高效转基因大豆的种植是否会对根际土中主要养分和酶活性产生影响.研究结果显示:秋春两季根际土中除全钾和微量元素含量外,其他养分含量在个别时期,转基因大豆AP15-1或AP15-3与其受体之间,均存在显著性的差异,但这些显著性差异大部分出现在苗期,成熟期仅有机磷含量在AP15-1与其受体YC03-3、速效钾含量在AP15-3与其受体YC04-5之间呈显著差异,并且这些差异在两季中均未重复出现.根际土中四种土壤酶活性测定结果显示:同季转基因大豆与其受体之间差异不显著.总体结果表明,上述转AtPAP15基因磷高效大豆种植对根际土中磷、氮、钾等养分和四种土壤酶活性均未产生显著的影响.     

Microbial dynamics in Mediterranean Moder humus

There is a growing interest in the links between humus forms and soil biota, and little is known about these links in Mediterranean ecosystems. Culture-independent techniques, such as DNA extraction followed by DGGE and enzyme activities, allowed us to compare microbial communities in two horizons of a forest soil in different seasonal conditions. Direct in situ lysis was applied for extraction of DNA from soil; intracellular DNA was separated from extracellular and used to represent the composition of microflora. The aims were to describe how biochemical and microbiological parameters correlate with topsoil properties in typical Mediterranean Moder humus. Changes in bacterial and fungal community composition were evident from DGGE profiles. Degrees of similarity and clustering correlation coefficients showed that the seasonal conditions may affect the composition and activity of bacterial and fungal communities in the OH horizon, while in the E horizon the two communities were hardly modified. In the same season, OH and E horizons showed a different composition of bacterial and fungal communities and different enzyme activities, suggesting similar behaviour of eubacteria and fungi relatively to all the variables analysed. Evidently, different organic carbon content in soil horizons influenced microflora composition and microbial activities involved in the P and N cycles.     

不同污染方式下铅对茶园土壤氮素转化及其相关微生物和酶活性的影响

为探讨不同污染方式的Pb对茶园土壤氮素转化的影响，采用盆栽试验对累积和一次性添加不同浓度Pb条件下茶园土壤中氮素含量、相关微生物和酶活性进行了研究。结果表明：累积污染处理的土壤中Pb全量和有效态含量高于一次污染处理。Pb污染对土壤、茶苗植株的氮含量影响表现为：增加土壤中全氮和¹⁵N含量，减少茶苗地上部全氮和¹⁵N含量。添加Pb浓度为900 mg/kg时，累积污染处理促进根系全氮和¹⁵N含量，一次污染则显著抑制；累积污染处理的茶苗根和地上部中的氮含量显著高于一次污染(P<0.05)。Pb污染对氮循环相关微生物的影响表现为：氨化细菌、自生固氮菌、亚硝酸细菌和硝酸细菌的数量减少，反硝化细菌的数量增加。Pb的不同污染方式对茶园土壤与氮循环相关微生物数量的影响不显著(P>0.05)。Pb污染抑制脲酶、亚硝化还原酶和硝酸还原酶活性，对蛋白酶活性存在“低促高抑”现象；高浓度Pb(900 mg/kg)污染时，累积处理显著增加土壤羟胺还原酶活性，一次处理则显著抑制。两种污染方式对土壤脲酶、硝酸还原酶和羟胺还原酶活性的影响因Pb...     

Changes in enzyme activities of spruce (Picea balfouriana) forest soil as related to burning in the eastern Qinghai-Tibetan Plateau

The effect of forest fire on soil enzyme activity of spruce (Picea balfouriana) forest in the eastern Qinghai-Tibetan Plateau was assessed. Six specific enzymes were chosen for investigation: invertase, acid phosphatase, proteinase, catalase, peroxidase and polyphenoloxidase. It was found that the activities of invertase and proteinase were reduced by burning, but the activities of acid phosphatase, polyphenoloxidase and peroxidase increased. Meanwhile, burning significantly (P < 0.05) resulted in the decrease of concentrations of available N and K of 0–20 cm depth layer soil, and significantly (P < 0.05) decreased concentrations of organic matter content, total N and P, as well as available N, P and K in soil at both 20–40 and 40–60 cm depths except for available P at 20–40 cm soil depth. These results illustrated that burning could influence the enzyme activities and chemical properties of soil not only of upper but also lower soil layers. Correlation analysis indicated that invertase activities in 0–20 cm depth layer soil were significantly positively correlated with organic matter, total N and P, as well as available N and P. Furthermore, all six enzymes studied were sensitive to fire disturbance, and thus could be used as indicators of soil quality. Our study also showed that soil enzyme activities were associated with soil depth, decreasing from top to bottom in both burned and unburned spruce forests. The distribution pattern of soil enzyme activities suggested that the rate of organic matter decomposition and nutrient cycling depended on soil depth, which had important structural and functional characteristics in nutrient cycling dynamics and implications in plantation nutrient management. The finding that burning effects on enzyme activities and soil properties between different soil layers were homogenized was attributed to the 8-years’ regeneration of forest after burning.     

长期定位施肥对黄绵土酶活性及土壤养分状况的影响

本研究以25年的肥料长期定位试验为平台,探讨了长期不同施肥处理对土壤活性有机质、氮磷养分及土壤酶活性的影响。结果表明:长期施肥土壤活性有机质、全氮、碱解氮及速效磷含量显著提高,土壤转化酶和碱性磷酸酶活性增强,其中有机肥化肥配施(NPM)的作用明显大于施用化肥(N、NP);长期施肥不能增强土壤过氧化氢酶活性。相关分析表明,土壤脲酶、转化酶及碱性磷酸酶活性与土壤活性有机质、氮磷养分含量呈显著正相关,且三种酶活性间呈极显著正相关关系。综合土壤养分与土壤主要酶活性的密切关系,认为将土壤酶与土壤养分相结合进行土壤肥力研究,对该区培肥土壤具有重要的指导意义。     

长期不同施肥下褐土养分及酶活性的生态化学计量特征

  【目的】  研究长期不同施肥条件下褐土养分含量和与土壤有机质水解、碳氮磷有效性相关的酶活性及其化学计量变化特征,以深刻认识农田土壤元素循环的生物地球化学特征。  【方法】  依托1992年开始的山西寿阳旱地农田生态系统野外长期定位试验,选取其中不施肥对照(CK),4个单施无机肥处理(N₁P₁、N₂P₂、N₃P₃、N₄P₄),3个无机肥和有机肥配施处理 (N₂P₁M₁、N₃P₂M₃、N₄P₂M₂) 和1个单施有机肥处理 (M₆) 进行研究。于1992、2001、2006和2016年,分析了表层土壤 (0—20 cm) 中有机碳(C)、全氮(TN)、全磷(TP)、有效氮 (AN) 和有效磷 (AP) 含量及与碳氮磷循环相关的β-1,4-葡萄糖苷酶 (β-1,4-glucosidase, BG)、β-1,4-N-乙酰氨基葡萄糖苷酶(β-1,4-N-acetylglucosidase, NAG)和碱性磷酸酶(alkaline phosphatase, ALP)活性。计算土壤养分之间和酶之间的化学计量比 (C∶TN、C∶TP、TN∶TP和lnBG/lnNAG、lnBG/lnALP、lnNAG/lnALP)。计算酶向量角度 (vector angle) 和向量长度(vector length)。以向量角>45°或者<45°的多少来评价微生物受磷、氮限制的程度,向量角>45°越多表示微生物受磷限制越强,向量角<45°越多表示微生物受氮限制越强。以向量长度评价微生物受碳限制的程度,向量长度越长表示微生物受碳限制越强。  【结果】  1) 除N₄P₄处理土壤C : TN显著高于M₆处理外,其他化肥和有机肥处理之间C : TN和C : TP不存在显著差异,而土壤TN : TP在各施肥处理下显著低于M₆处理 (P<0.05)。与CK相比,M₆处理C∶TN显著降低了30.2% ,TN∶TP显著升高了41.0%;N₄P₄处理C∶TP显著降低了23.3%,TN∶TP降低了17.6% (P>0.05)。土壤C∶AN平均为2.11～2.29,处理之间无显著差异;土壤C∶AP和AN∶AP随化肥和有机肥投入量增加而降低,4个有机肥处理的土壤C∶AP和AN∶AP降幅大于4个化肥处理。2)长期N₂P₂、N₃P₃和N₄P₄处理下,土壤lnBG/lnNAG、酶向量角度和酶向量长度略高于各有机肥处理(P>0.05),而lnNAG/lnALP略低于各有机肥处理(P>0.05);与1992年 (试验开始年)相比,施肥处理后土壤lnBG/lnNAG均升高,lnNAG/lnALP均降低,向量角整体>45°,向量长度增加了11.1%～52.4%。3)相关性分析表明, AN与BG、NAG、ALP活性、lnBG/lnNAG及lnNAG/lnALP之间存在显著相关性;土壤C∶TN、C∶AN与酶活性lnBG/lnNAG、土壤TN∶TP与lnNAG/lnALP之间存在显著正相关,lnBG/lnALP与任何环境因子间都不存显著相关性。  【结论】  长期单施化肥易增加作物对有机碳的消耗和土壤稳定态磷素固持,微生物面临的碳、磷限制加剧;有机肥带入土壤的有机氮,加速了有机质分解,显著提高了土壤有效磷含量,有效缓解资源限制,促进褐土元素周转。综上,长期施肥显著改变了褐土元素化学计量特征,引起酶化学计量非稳态变化,土壤酶活性表现出强烈的资源依赖性。