Response of amidohydrolases in soils to chloroform fumigation

An ongoing challenge in enzymology is the differentiation between the various pools of enzymes in soils, i.e. between accumulated (extracellular) enzymes and enzymes associated with the microbial biomass (intracellular enzymes). In order to solve this problem, 10 surface soils representing a wide range of physico‐chemical properties and purified reference enzyme proteins were fumigated for 24 h at 25 °C. The activities of L‐asparaginase, L‐glutaminase, amidase, and L‐aspartase were assayed in chloroform fumigated soils, in reference enzyme proteins and in their nonfumigated counterparts in the presence and absence of toluene. Chloroform fumigation decreased the activities of L‐asparaginase, L‐glutaminase, and L‐aspartase in soils, on average, by 41, 78, and 78 %, respectively. The response of amidase activity towards chloroform fumigation of soils varied within the 10 soils studied. In five soils increases in activity values up to 40 % were observed. A loss of amidase activity, varying between 7 and 17 %, was found in four soils, whereas in one soil no effect of chloroform fumigation was determined. Enzyme activities of the four purified reference proteins were decreased by fumigation, with L‐glutaminase showing a nearly complete inhibition of 99 %, followed by amidase, L‐aspartase, and L‐asparaginase with an inhibition of 29, 18, and 7 %, respectively. Toluene treatment of the nonfumigated soils resulted in increases in the activity values of L‐asparaginase, L‐glutaminase, and L‐aspartase of 21 to 213 % (average of 10 soils). In contrast, amidase activity of soils was decreased in the presence of toluene by a mean of 32 %. Enzyme protein concentrations, calculated for the 10 soils, based on the specific activities of the purified enzymes (i.e., activity values per mg protein) and the activity values obtained in the soils, were, on average, 0.73, 0.50, 3.38, and 2.61 mg protein (kg soil)^—1 for L‐asparaginase, L‐glutaminase, amidase, and L‐aspartase, respectively. Comparison of activity values of soil amidohydrolases with the protein concentrations present in soils indicates that catalytic efficiency can vary greatly among different soil enzymes.     

Response of glycosidases in soils to chloroform fumigation

The purpose of this study was to differentiate between biotic and abiontic fractions of four important hydrolases involved in C cycling in soils. Therefore, ten different surface soils, which represent a wide range of physico-chemical properties were fumigated with chloroform for 24 h. The activities of !- and #-glucosidases and !- and #-galactosidases were assayed in these soils and in reference proteins purified from microbial sources before and after chloroform fumigation and in the presence and absence of toluene. Chloroform fumigation decreased the activities of !- and #-glucosidases and !- and #-galactosidases in soils, on average, by 42%, 22%, 43% and 53%, respectively. These results indicated that among the biochemical reactions involved in the degradation of carbohydrates in soils, the hydrolysis of maltose, melibiose and lactose are more inactivated by chloroform fumigation than that involved in the hydrolysis of cellobiose. The activities of all four purified enzyme proteins were decreased after chloroform fumigation, by 7% (#-galactosidase) to 40% (!-glucosidase). Enzyme protein concentrations, calculated for the ten soils were, on average, 3.72, 0.014, 0.027 and 1.56 mg protein kg^-1 soil for !- and #-glucosidases and !- and #-galactosidases, respectively. The results suggest that enzyme activity rates do not necessarily correspond to the amounts of enzyme proteins present in a soil, i.e., some enzymes have greater catalytic efficiencies than others. The activity values of the nonfumigated, toluene-treated soils were generally significantly correlated with contents of clay and microbial biomass C.     

Enzyme activities in agricultural soils fumigated with methyl bromide alternatives

Pre-plant fumigation of agricultural soils with a combination of methyl bromide (MeBr) and chloropicrin (CP) to control nematodes, soil-borne pathogens and weeds has been a common practice in strawberry (Fragaria X ananassa Duchesne) production since the 1960s. MeBr will be phased out by 2005, but little is known about the impacts of alternative fumigants on soil microbial processes. We investigated the response of microbial biomass and enzyme activities in soils fumigated over two years with MeBr+CP and the alternatives propargyl bromide (PrBr), InLine, Midas and CP. Results were compared to control soils, which were not fumigated for the last 4-5 years for Watsonville and Oxnard, respectively, but had a 10 year history of MeBr+CP fumigation (history soils). Soil samples (0-15 cm) were taken from two sites in the coastal areas of California, USA, in Watsonville and Oxnard, at peak strawberry production after two years of repeated application. In addition to the soil enzymes, the activities of purified reference enzymes of β-glucosidase, acid phosphatase and arylsulfatase were assayed before and after fumigation with MeBr+CP and alternative biocides. At the Oxnard site, microbial respiration significantly decreased in soils fumigated with MeBr+CP (P=0.036), while microbial biomass C and N showed no response to fumigation at both sites. These results may indicate that fumigation promotes the growth of resistant species or that soil microorganisms had recovered at the time of sampling. Repeated soil fumigation with MeBr+CP significantly decreased the activities of β-glucosidase and acid phosphatase at the Watsonville site, and dehydrogenase activity at the Oxnard site. Although, enzyme activities in soils fumigated with PrBr, InLine, Midas and CP were lower compared to the control soil, effects were, in general, not significant. Fumigation with MeBr+CP and alternatives reduced the activities of purified reference enzymes by 13, 76 and 28% for acid phosphatase, β-glucosidase and arylsulfatase, respectively. Mean enzyme protein concentrations in fumigated agricultural soils were 2.93, 0.105, and 2.95 mg protein kg⁻¹ soil for acid phosphatase, β-glucosidase and arylsulfatase, respectively, all lower than in control soils. Organic matter turnover and nutrient cycling, and thus, the long-term productivity of agricultural soils seem unaffected in soils repeatedly fumigated with PrBr, InLine, Midas and CP.     

Phosphatases in soils

Most studies on phosphatase activity in soils have been concerned with acid phosphatase. This study was conducted to determine the activity of phosphomonoesterases (acid and alkaline phosphatases), phosphodiesterase, and “phosphotriesterase”. The results indicate that acid phosphatase is predominant in acid soils and that alkaline phosphatase is predominant in alkaline soils. With universal buffer, the pH optima of phosphodiesterase and phosphotriesterase were at pH 10. The activities of these phosphatases in soils were much lower than those of the acid and alkaline phosphatases. Studies on the effects of various soil treatments on the activity of phosphatases in soils indicated that air-drying increased the activity of acid phosphatase and phosphotriesterase, decreased the activity of alkaline phosphatase, but did not affect the activity of phosphodiesterase. Steam sterilization of soils at 121 C for 1 h inactivated alkaline phosphatase, phosphodiesterase, and phosphotriesterase, but did not completely inactivate acid phosphatase. Addition of toluene to the incubation mixture did not markedly affect the activity of acid phosphatase, alkaline phosphatase, phosphodiesterase, but increased the activity of phosphotriesterase in soils.Studies of the kinetic parameters of phosphatases in the soils studied showed that the K_m values ranged from 1.11 to 3.40 mm for acid phosphatase. from 0.44 to 4.94 mm for alkaline phosphatase, and from 0.25 to 1.25 mm for phosphodiesterase. Expressed as μg p-nitrophenol released·h^?1·g^?1 soil, the V_max values ranged from 200 to 625 for acid phosphatase, from 124 to 588 for alkaline phosphatase, and from 46 to 127 for phosphodiesterase. The substrate of phosphotriesterase (tris-p-nitrophenyl phosphate) is insoluble in water; hence, the K_m and V_max values of this enzyme in soils could not be determined.     

Effect of cropping systems on phosphatases in soils

Phosphatases are widely distributed in nature and play a major role in phosphorus nutrition of plants. The effects of crop rotations and nitrogen fertilization on the activities of phosphatases (acid phosphatase, alkaline phosphatase, and phosphodiesterase) were studied in soils from two long‐term cropping systems at the Northeast Research Center (NERC) in Nashua and the Clarion Webster Research Center (CWRC) in Kanawha, Iowa, USA. Surface soils (0—15 cm) were taken in 1996 and 1997 from replicated field plots in corn, soybeans, oats, or meadow (alfalfa) that received 0 or 180 kg N ha^—1 before corn. Because of differences in organic C contents among soils of the two sites, the soils from the CWRC sites contained greater enzyme activity values than those from the NERC site. Plots under oats or meadow showed the greatest activity values, whereas those under continuous corn at the CWRC site and soybean at the NERC site showed the least activities. Analysis of variance indicated that the activities of the phosphatases were significantly affected by crop rotation (P < 0.001) in both years at the NERC site but not at the CWRC site. Nitrogen fertilization affected the activity of acid phosphatase in soils from the CWRC site in both years and alkaline phosphatase only in 1997; but it did not affect the activities of the phosphatases in the soils from the NERC site. With the exception of alkaline phosphatase (CWRC) and phosphodiesterase (NERC) in soils sampled in 1997, activities of alkaline phosphatase and phosphodiesterase were significantly correlated with microbial biomass C (C _mic) in soils from both sites and years, with r values ranging from 0.366* to 0.599***. Cropping systems and N fertilization affected the specific activities of phosphomonoesterases, especially acid phosphatase, but not of phosphodiesterase. Regression analysis showed that activities of phosphatases were significantly correlated with organic C contents of soils from the NERC site but not from the CWRC site.     

Determination of phosphatase activities of soils and animal wastes

A method is described to determine acid and alkaline phosphatase activities from the rate of decomposition of p-nitrophenylphosphate in the presence of large amounts of organic matter, such as occur in the surface layers of soils or in animal wastes. The p-nitrophenol formed is separated by high pressure liquid chromatography on a cellulose column from p-nitrophenylphosphate and other organic compounds present in the soil or waste extract. After separation, p-nitrophenol is measured on-line in a spectrophotometric flow cell at a wavelength of 405 nm. In this way p-nitrophenol concentrations down to 0.1 μm can be measured, making it possible to work with substrate concentrations of 1 μm.

The necessity of correcting the phosphatase activity measured in this way for adsorption of enzyme, substrate (p-nitrophenylphosphate) and product (p-nitrophenol) is discussed.

Acid and alkaline phosphatases are inhibited strongly at phosphate concentrations greater than 0.1 mm, consequently substrate concentrations in the range of 0.01 to 0.1 mm were used.

The method was applied to a number of sandy soils and to pig slurry. Air drying or freeze drying of soils was found to decrease the phosphatase activity. Freeze drying did not affect the phosphatase activity of pig slurry. Michaelis-Menten kinetics were found to apply reasonably well. The resulting kinetic parameters are compared with values from the literature. Phosphatase activities are correlated with organic P and organic matter contents of soils and pig slurry.     

Microbiological rates and enzyme activities as indicators of functionality in soils affected by the Aznalcóllar toxic spill

This study focused on the potential of using soil enzyme activities and general microbiological rates (respiration, N-mineralisation, nitrification) to evaluate the quality of soils affected by a pyrite mud spill which contained high concentrations of heavy metals. The quality of soils after restoration was estimated by comparing enzyme activities and general microbiological rates in three different types of experimental field plots: (i) non-polluted, (ii) polluted but restored, and (iii) polluted but un-restored soils. Non-polluted soils showed the highest levels of enzyme activity. Significant differences were detected for acid phosphatase, β-glucosidase and urease activities between all types of plots. However, arylsulfatase and alkaline phosphatase activities showed no significant differences between the restored plots and polluted but un-restored plots. Geometric mean statistics were used as an index of soil quality in terms of overall: (i) bioavailable heavy metal concentrations, (ii) assayed enzyme activities, and (iii) general microbiological rates, in order to compare plots differing in the degree of pyritic mud pollution. The results indicate that it is important to consider these three criteria in to estimate the soil quality of heavy-metal contaminated soils. Typically, enzyme activities were negatively correlated with bioavailable Cd, Cu and Zn concentrations, but positively with soil pH values. In contrast, pH values were negatively correlated with bioavailable concentrations of Cd, Cu and Zn. It is unclear if the generalised lower enzyme activities found in restored soils, compared to non-polluted soils, is promoted by pH or bioavailable heavy metals concentrations, or a combination of both.     

中药材龙胆GAP基地土壤酶活性的研究

分别采用硫代硫酸钠滴定法、高锰酸钾滴定法、TTC-脱氢酶活性测定法和磷酸苯二钠比色法测定龙胆GAP基地土壤中转化酶、过氧化氢酶、脱氢酶和磷酸酶的活性。对不同月份、种植不同年生龙胆根际土及非根际土中酶活性的测定结果进行分析表明:土壤过氧化氢酶活性在6月份出现一较高值,脱氢酶活性较高时期在7月份,土壤转化酶活性较大值出现在7、8月份,磷酸酶活性则逐月增高至9月份达到最大值,土壤总体酶活指标极大值出现在8月份;随着龙胆种植年限的增加,土壤过氧化氢酶和脱氢酶活性有所提高,而磷酸酶和转化酶活性没有明显变化,种植不同年生龙胆土壤中酶的活性随季节波动不尽相同。比较GAP基地龙胆根际土与非根际土中酶活性,土壤转化酶和过氧化氢酶的活性均表现为根际土非根际土,而土壤磷酸酶和脱氢酶的活性则为非根际土根际土;相关分析结果显示,过氧化氢酶活性与酸性及中性磷酸酶活性显著负相关;酸性、中性及碱性三种磷酸酶活性之间存在极显著正相关;总体酶活指标与转化酶、酸性磷酸酶、中性磷酸酶活性呈显著正相关。本研究完善了中药材龙胆GAP种植基地土壤酶的信息,为综合评价基地土壤肥力提供了科学数据,为药用植物龙胆的合理施肥、品质的提高提供了科学依据。     

Effect of tillage and residue management on enzyme activities in soils: III. Phosphatases and arylsulfatase

This study was carried out to investigate the effect of tillage and residue management on activities of phosphatases (acid phosphatase, alkaline phosphatase, phosphodiesterase, and inorganic pyrophosphatase) and arylsulfatase. The land treatments included three tillage systems (no-till, chisel plow, and moldboard plow) in combination with corn residue placements in four replications. The activities of these enzymes in no-till/double mulch were significantly greater than those in the other treatments studied, including no-till/bare, no-till/normal, chisel/normal, chisel/mulch, moldboard/normal, and moldboard/mulch. The effect of mulching on activities of phosphatases was not as significant as on activities of arylsulfatase. The lowest enzyme activities were found in soil samples form no-till/bare and moldboard/normal treatments, with the exception of inorganic pyrophosphatase, which showed the lowest activity in no-till/bare only. Among the same residue placements, no-till and chisel plow showed comparable arylsulfatase activity, whereas the use of moldboard plow resulted in much lower arylsulfatase activity. The activities of phosphatases and arylsulfatase were significantly correlated with organic C in the 40 soil samples studies, with r values ranging from 0.71*** to 0.92***. The activities of alkaline phosphatase, phosphodiesterase, and arylsulfatase were significantly correlated with soil pH, with r values of 0.85***, 0.78***, and 0.77***, respectively, in the 28 surface soil samples studied, but acid phosphatase and inorganic pyrophosphatase activities were not significantly correlated with soil pH. The activities of phosphatases and arylsulfatase decreased markedly with increasing soil depth and this decrease was associated with a decrease in organic C content. The activities of these enzymes were also significantly intercorrelated, with r values ranging from 0.50*** to 0.92***. Received: 4 October 1995     

Microbial biomass activities in urban soils in two consecutive years

Ecological soil functions are protected in Germany. Thus, for the sustainable use of urban soil resources data on the function of soils to serve as a habitat are required. Soil microbial biomass and activities were studied in two surface horizons in two consecutive years at nine sites in Stuttgart, Germany, differing in land use. Microbial biomass (chloroform‐fumigation extraction, substrate‐induced respiration) and microbial activities (potential N mineralization, potential ammonium oxidation, and enzyme activities of dehydrogenase, urease, arylsulfatase, and phosphatase) were determined in 2001 and 2002. DIN/ISO standard methods were applied as far as they were available. Furthermore, soil chemical properties were determined in the 2001‐samples. Large differences in chemical and microbiological properties among surface horizons were found. Concentrations of microbial biomass and microbial activities were, however, often comparable to agricultural or forest surface soils. The lowest microbial biomass and activities were observed at a highly disturbed railway area where vegetation was missing and total organic C (TOC) had been altered by anthropogenic organic particles. In contrast, microorganisms were promoted at vegetated sites and where organic impurities were negligible. As TOC was altered by obscure organic matter, total N (TN) and not TOC closely correlated with soil microbiological properties. Biomass and activity generally decreased with depth, but mixing of organic matter resulted in more uniform depth distribution of microbial properties in one garden soil. In 2002, microbial biomass and activity were often lower compared to 2001, but interpretation of this difference hampered as the number of samples taken was probably not sufficient to address the spatial variability in soil properties. Additional studies are needed to develop simple and cost‐effective procedures for the evaluation of ecological quality of urban soils by combined efforts of city planners and soil scientists.     

长期定位施肥土壤酶活性及其肥力变化研究

对小麦-玉米轮作区长期定位施肥土壤酶活性及其肥力变化的研究结果表明,与未施肥(对照)相比,长期施肥处理土壤脲酶、碱性磷酸酶、转化酶和过氧化氢酶活性均明显提高,其中有机肥(秸秆、厩肥)配施化肥效果明显优于单施化肥;施肥后休闲处理未提高土壤酶活性,表明施肥(化肥、有机肥)后作物根系及其分泌物具有刺激土壤酶活性的作用,且土壤酶活性高低与作物产量(即土壤肥力)相关性显著.     

鸡粪与木醋液配施对滨海盐碱土化学性质和酶活性的影响

施用有机肥是盐碱土改良与培肥地力的有效方式。选鸡粪和木醋液为改良剂,通过土壤培养试验,研究未施肥(CK)、单施鸡粪(CM)、单施木醋液(PA)、鸡粪+木醋液配施(CP)共4个处理对滨海盐碱土化学性质和酶活性的影响。结果表明:与CM相比,CP处理的pH值显著降低0.34个单位,电导率(EC)降低14.52%。与PA相比,施用鸡粪处理(CM和CP)的土壤养分含量和酶活性均显著提高。CP的全氮、有效磷、水溶性有机碳、水溶性有机氮和硝态氮含量较CM分别高出55.32%、103.35%、16.64%、55.68%和45.43%;而土壤α-葡萄糖苷酶、β-葡萄糖苷酶、几丁质酶、亮氨酸氨基肽酶、碱性磷酸酶、多酚氧化酶和脱氢酶活性分别显著增加49.58%、67.85%、40.84%、104.94%、17.66%、62.05%和37.50%。回归分析表明,土壤有机质、全氮、有效磷和水溶性有机碳、氮含量的增加促进酶活性的提高。综上所述,鸡粪与木醋液配施可显著降低盐碱土的pH值,并能显著提高盐碱土养分含量和酶活性。     

长期施肥对城市边缘区不同作物土壤酶活性的影响

以开封市为例,探讨了长期施肥条件下城市边缘区不同作物土壤酶活性的变化及其与土壤养分的关系。结果表明,土壤酶活性受施肥处理影响明显,其中蛋白酶、过氧化氢酶、转化酶和脲酶活性在化肥处理中均受到抑制,在有机肥中却得到大幅提升,碱性磷酸酶活性变化与之正好相反;在混施处理中各酶活性均有不同程度的增强,其中以脲酶活性增强尤为突出。土壤酶活性在各作物之间表现出一定的差异,但总的来说差异不显著。土壤各酶之间及酶与土壤肥力因素之间存在显著或极显著相关关系,因此土壤酶活性可以作为城市边缘区土壤环境质量评价的生物肥力指标之一。     

长期施肥土壤中酶活性的剖面分布及其动力学特征研究

对连续25年的长期培肥试验地中土壤剖面酶活性的分布及土壤酶的催化反应特性进行了研究,结果发现,土壤脲酶、碱性磷酸酶和蔗糖酶活性在土壤剖面中的分布从表层到深层,酶活性依次减小;而多酚氧化酶呈波浪型分布。土壤中脲酶、碱性磷酸酶、蔗糖酶活性与相应土层的有机质含量呈极显著正相关;多酚氧化酶无此相关性。土壤脲酶和碱性磷酸酶活性均随时间的延长而逐渐趋于一个稳定值,且各个时段酶活性均为施肥处理高于不施肥处理,说明施肥能显著提高土壤酶活性。土壤脲酶和碱性磷酸酶酶促反应初速度(V0)均随温度和底物浓度的增加而增加,至一定温度和底物浓度时,V0不再增加;不同培肥措施下V0为:厩肥秸秆化肥对照。     

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。     

不同树龄茶树根际土壤酶活性的变化分析

以不同种植年限黄金桂茶树根际土壤为研究对象,分析茶树树龄对土壤酶活性的影响。结果表明,茶树根际土壤中与养分循环相关的酸性磷酸酶、脲酶、蔗糖酶活性随着茶树树龄的增加而上升,且与茶树树龄呈显著正相关,中性磷酸酶、碱性磷酸酶则相反;茶树根际土壤中与抗性相关的多酚氧化酶活性随着茶树树龄的增加而上升且与茶树树龄呈显著正相关,而过氧化物酶、过氧化氢酶、脱氢酶活性则呈下降趋势,与茶树树龄呈显著负相关。土壤酶对茶树树龄的敏感性分析结果表明,不同土壤酶响应茶树树龄变化的趋势为过氧化氢酶脲酶脱氢酶蔗糖酶过氧化物酶多酚氧化酶酸性磷酸酶中性磷酸酶碱性磷酸酶。可见,在茶树生产管理过程中应适当提高磷肥的施用量,老茶树应当加强土壤松耕,以提高土壤中抗性酶活性。     

Enzyme activities along a climatic transect in the Judean Desert

Soil enzymes have an important influence on nutrient cycling. We examined spatial and temporal patterns in dehydrogenase, arylsulfatase, alkaline and acid phosphatase activities, and their relationships with organic carbon and microbial biomass nitrogen at three sites in Israel representing different climatic regions: Mediterranean (humid), mildly arid and arid. The sites were selected along a climatic transect from the Judean Mountains in the west to the Dead Sea in the east of Israel. With increasing aridity, soil organic carbon, soil microbial biomass nitrogen, dehydrogenase, phosphatase and different pools of arylsulfatase activities decreased significantly. A sharp change in enzyme activities existed between 260- and 120-mm mean annual rainfall. The arylsulfatase activity of the microbial biomass in the 0–2- and 5–10-cm soil layers usually accounted for more than 50% of the total activity, and the fraction of total activity in the 0–2-cm soil layer of the arid sites was significantly greater than that of the humid site. Dehydrogenase and total and microbial biomass arylsulfatase activities were sensitive indicators of the climatic change along the transect. At the humid and mildly arid sites, the activities of dehydrogenase were less in the winter than in the summer and spring, whereas total and microbial biomass arylsulfatase activities were less in both summer and winter. At the arid site, lower values were observed in the summer at 0–2-cm soil depth. At all sites, lower alkaline phosphatase activities at 0–2 cm were observed in the summer, but there were no significant seasonal differences in acid phosphatase activities. These different seasonal patterns of enzyme activities are attributed to the enzyme source, and specific seasonal soil moisture and temperature conditions at the studied sites. The low dehydrogenase and microbial biomass arylsulfatase activities in the winter at the humid and mildly arid sites are explained by the cold and wet soil conditions, and the low enzyme activity in the summer at the arid site is attributed to the dry and hot soil conditions.     

Changes in soil biological activities under reduced soil pH during Thlaspi caerulescens phytoextraction

Phytoextraction of soil Cd and Zn may require reduction in soil pH in order to achieve high metal uptake. Reducing the pH of high metal soil, however, could negatively affect soil ecosystem function and health. The objectives of this study were to characterize the quantitative causal relationship between pH and soil biological activities in two Zn and Cd contaminated soils and to investigate the relationship between metals and soil biological activities under low pH. Soils were adjusted to five or six different pH levels by sulfur addition, followed by salt leaching. Thlaspi caerulescens was grown for 6 months, and both the rhizosphere and non-rhizosphere soil biological activities were tested after harvest. Reducing pH significantly lowered soil alkaline phosphatase activity, arylsulphatase activity, nitrification potential, and respiration. However, acid phosphatase activity was increased with decreasing pH. The relationship between soil biological activities and pH was well characterized by linear or quadratic regression models with R² values ranging from 0.57 to 0.99. In general, the three enzyme activities, nitrification potential, and the ratio of alkaline phosphatase to acid phosphatase activity were very sensitive indicators of soil pH status while soil respiration was not sensitive to pH change. The rhizosphere soil had higher biological activities than non-rhizosphere soil. The negative effects observed in the non-rhizosphere soil were alleviated by the rhizosphere influence. However, rhizosphere soil after 6 months phytoextraction showed lower nitrification potential than non-rhizosphere soil, probably due to substrate limitation in our study.     

翻压不同绿肥品种对植烟土壤肥力及酶活性的影响

为了明确不同绿肥品种与土壤肥力及酶活性的关系,通过田间试验及简单相关分析、典型相关分析和主成分分析,研究种植翻压不同品种绿肥对植烟土壤酶活性及土壤肥力的影响。结果表明,不同品种绿肥种植翻压均可显著改善土壤的物理性状,提高土壤养分含量和土壤酶活性,在效应上具有相似的特点,主要影响土壤脲酶、过氧化氢酶与酸性磷酸酶活性及碱解氮和有效磷的含量,主要差异是土壤体积质量、孔隙度、pH、有机质、全氮、速效钾、过氧化氢酶的变化;脲酶、酸性磷酸酶、蔗糖酶、过氧化氢酶4种土壤酶不仅两两之间均呈极显著正相关,而且与土壤肥力指标均呈极显著相关;土壤肥力与土壤酶活性存在极显著的典型相关关系;此结果对当前的烤烟生产和土壤改良具有较大的意义。     

Additive effects of copper and zinc on cadmium toxicity on phosphatase activities and ATP content of soil as estimated by the ecological dose (ED50)

The ecological dose (ED₅₀) of Cd on alkaline and acid phosphatase activity and the ATP content of three contrasting forest soils was measured with or without Cu and Zn to assess the additive toxic effects of these two metals. Soils polluted with Cu and/or Zn were treated with increasing Cd concentrations to give the following metal combinations: Cd, Cd+Cu, Cd+Zn and Cd+Cu+Zn. Alkaline and acid phosphatase activities and ATP content of the three soils were analysed 4 h, 7 and 28 days after the metal additions. The ED₅₀ values were obtained by interpolating the enzyme activities or ATP data with a kinetic model and the goodness of fit was satisfactory.Generally, the ED₅₀ values of both acid and alkaline phosphatase activities for Cd were lower (higher toxicity) with than without Cu and Zn and the effect of Cu and Zn was particularly adverse when these two metals were both added to soils. The alkaline phosphatase was more sensitive in the acid and neutral soil whereas the acid phosphatase was more sensitive in the alkaline soil. Both phosphatase activities and the ATP content were more sensitive in the sandy than in the finer textured soils. The ATP content was less sensitive to the additive effects. Increasing toxicity was observed during the incubation.Analysis of 1 M NH₄NO₃-extractable Cd, Cu and Zn revealed that Cd competed with Zn for the adsorption sites but not with Cu. However, the lower ED₅₀ values for Cd of the two phosphatase activities and of the ATP content in the presence of heavy metal combinations could be not explained by the heavy metal solubility data. It is concluded that the ED₅₀ may be a sensitive tool for assessing additve toxic effects to soil biochemical parameters.