甘肃省盐碱草地主要植物群落土壤酶活性研究

对甘肃省盐碱地主要植物群落土壤脲酶、过氧化氢酶、碱性磷酸酶、脱氢酶及硝酸还原酶活性的季节动态进行研究。结果表明,5种土壤酶活性季节变化趋势不同,脲酶、过氧化氢酶及碱性磷酸酶活性均在夏季达到最高,硝酸还原酶在秋季最高,脱氢酶在春季最高;不同植物群落土壤酶活性变化趋势不同,脲酶、碱性磷酸酶、过氧化氢酶活性在狗尾草群落(Setaria viridis)具最大活性,硝酸还原酶、脱氢酶活性在芦苇群落(Phragmites australis)均最高,5种酶活性在盐爪爪群落(Kalidium foliatum)均最低;各植物群落的土壤酶活性多表现为随着土壤深度的加深呈递减趋势,在表层0—5cm土层,土壤酶活性最强。对5种酶之间的相关性进行分析,研究发现碱性磷酸酶与脲酶、过氧化氢酶间呈极显著相关,脲酶与过氧化氢酶、硝酸还原酶与脱氢酶间呈显著相关。     

黄土丘陵区植被恢复过程中土壤酶活性的响应与演变

对宁夏南部丘陵区不同植被自然恢复阶段土壤脲酶、碱性磷酸酶、蔗糖酶、脱氢酶和过氧化氢酶活性的变化特征进行了研究。结果表明：土壤脲酶、碱性磷酸酶、蔗糖酶和脱氢酶基本上随着植被封育年限的增加而增大,过氧化氢酶活性对于植被恢复年限的响应不明显。植被封育的前23年中,土壤脲酶、碱性磷酸酶、蔗糖酶和脱氢酶的活性增加明显,23年后基本趋于稳定,增加不明显。封育78年的大针茅群落下的土壤脲酶和蔗糖酶（转化酶）活性最强,其土壤中碳素和氮素营养循环强度最大。脲酶与蔗糖酶、碱性磷酸酶和脱氢酶的活性极显著相关,表明土壤酶在促进土壤有机物转化中存在共性关系。这几种酶能够在一定程度上反映植被群落的演替和植被的恢复程度,自然封育对提高土壤生物学质量有重要的作用。     

太湖地区稻麦二熟制下长期秸秆还田对土壤酶活性的影响

摘要：研究了长期秸秆还田情况下太湖水稻土中与C、N、P、S养分循环及微生物活动有关的荧光素二乙酸酯（FDA）水解酶、酸性磷酸酶、碱性磷酸酶、芳基硫酸酯酶、β-葡糖苷酶、脲酶和脱氢酶等7种酶的活性。结果表明：秸秆还田与无机肥处理都明显增强了所有酶的活性,与对照无肥区的差异达到了显著水平。酶活性对化肥或秸秆还田的敏感度为：β-葡糖苷酶〉脱氢酶、脲酶〉FDA水解酶、碱性磷酸酶〉芳基硫酸酯酶〉酸性磷酸酶。各处理间酶活性顺序为：NPKS2（NPK＋稻秆4500kg/hm^2）〉NPKSI（NPK＋稻秆2250kg/hm^2）〉NPK（N120kg/hm^2,P75kg／hm^2,K150kg/hm^2）〉CK。     

双季稻田马铃薯不同覆盖栽培对土壤酶活性的影响

为探讨双季稻区春马铃薯不同覆盖模式下稻田土壤酶活性的变化情况, 在大田条件下, 以露地处理为对照, 设置稻草、无纺布、稻草+无纺布、黑膜、稻草+黑膜5 种覆盖处理。结果表明: 地表覆盖显著影响土壤酶活性。其中, 稻草覆盖显著(P<0.05)提高碱性磷酸酶、芳基硫酸酯酶和脱氢酶酶活性, 分别较对照提高17.55%、24.77%和87.2%; 稻草+无纺布覆盖显著(P<0.05)提高芳基酰胺酶和脱氢酶活性, 分别较对照提高8.03%和71.05%; 黑膜覆盖显著(P<0.05)提高β-葡萄糖苷酶、碱性磷酸酶、芳基硫酸酯酶和脱氢酶活性, 分别较对照提高23.44%、22.70%、37.43%和146.30%; 稻草+黑膜覆盖显著(P<0.05)提高β-葡萄糖苷酶、芳基酰胺酶、碱性磷酸酶、芳基硫酸酯酶和脱氢酶活性, 分别较对照提高34.76%、19.31%、19.03%、51.98%和125.62%。由此得出, 覆盖稻草并加盖黑膜可显著提高与土壤养分循环有关的主要土壤酶活性, 利于提高土壤质量。     

尾矿区土壤重金属污染对土壤酶活性的影响

为研究铜陵尾矿区土壤重金属污染状况以及土壤重金属污染对土壤酶活性的影响,按照距离矿口远近不同进行土壤样品的采集。结果表明,尾矿区及其周边土壤受到不同程度的Cu、Zn、Pb、Mn污染,尾矿区土壤酶活性随着重金属污染程度的加剧而显著降低,其中蔗糖酶和脲酶活性下降最明显。多元回归分析表明,在土壤重金属复合污染影响下,Cu、Pb、Mn 3种重金属对土壤脲酶、蔗糖酶、脱氢酶活性均有抑制作用,而Zn对土壤脲酶、蔗糖酶、脱氢酶有一定的刺激作用。     

广西平果县岩溶山地不同植物群落的土壤酶活性

为探讨平果县岩溶山地典型植物群落的土壤酶活性特征,基于调查取样与试验分析,采用相关分析、多重比较以及主成分分析方法,研究了不同植物群落间土壤酶活性的差异,分析了土壤酶活性与土壤化学性质的关系。结果表明:(1)土壤过氧化氢酶、脲酶及蔗糖酶活性的群落间差异达显著水平,显示不同植物群落对土壤酶活性产生一定影响;(2)土壤pH值与过氧化氢酶、脲酶间呈极显著正相关(p0.01),与碱性磷酸酶间呈显著负相关(p0.05);(3)4个酶活性与代表土壤肥力的土壤有机质、全氮、全磷、全钾、碱解氮及速效钾之间具有较强的相关性,但速效磷与4个土壤酶之间的相关性均未达显著水平(p0.05);(4)过氧化氢酶、脲酶及碱性磷酸酶能敏感反映土壤质量的变化,可作为本区域土壤质量评价的指标。     

松嫩盐碱草地主要植物群落土壤酶活性研究

对松嫩盐碱草地不同植物群落土壤酶活性及其与土壤养分的关系进行了研究,结果表明,不同植物群落土壤酶活性变化趋势不同,过氧化氢酶在碱蓬群落中具最大活性.多酚氧化酶、过氧化物酶活性在碱斑裸地、碱蓬群落、碱蓬-虎尾草群落中活性较高,蛋白酶、转化酶及碱性磷酸酶活性在羊草-寸草苔群落及双子叶杂草群落中的活性较高;多酚氧化酶、过氧化物酶、蛋白酶、转化酶及碱性磷酸酶活性间有显著的相关关系;多酚氧化酶、过氧化物酶、蛋白酶、转化酶、碱性磷酸酶和土壤全氮、碱解氮、有机质、速效磷间有显著相关关系.     

东寨港红树林湿地土壤因子与酶活性的关系

[目的] 红树林是热带、亚热带典型的海岸带湿地生态系统。分析不同植物群落条件下红树林湿地的土壤活性有机碳组成、土壤酶活性现状以及两者间的相互作用,进而预测东寨港红树林片区的生态结构和功能发展趋势,为东寨港红树林湿地的生态恢复与保护提供科学依据。[方法] 通过实地采样,对9种红树植物群落类型〔红海榄(Type 1)、白骨壤(Type 2)、角果木(Type 3)、海莲+角果木(Type 4)、桐花树+海莲+秋茄(Type 5)、海莲+榄李+桐花树(Type 6)、秋茄+海莲+榄李(Type 7)、海莲+无瓣海桑+桐花树+秋茄(Type 8)、海莲+无瓣海桑(Type 9)〕的土壤酶活性、土壤活性有机碳组分含量和理化性质进行化验分析。[结果] ①该区表层土壤有机碳介于6.57~74.87 g/kg之间,在不同群落类型间以Type 7群落显著最高,Type 1群落低至6.57 g/kg。②各群落类型湿地表层土壤酶活性变化规律为：脲酶＞磷酸酶＞过氧化氢酶＞蔗糖酶,其中脲酶以Type 8群落最高,显著高于Type 1—6群落;磷酸酶以Type 8群落最高,显著高于Type 1—3群落;过氧化氢酶以Type 5最高,显著高于其余群落(Type 6和Type 7除外);蔗糖酶以Type 9群落最高,显著高于Type 2,Type 5和Type 8群落。③土壤脲酶、磷酸酶和过氧化氢酶与土壤活性有机碳各组分含量呈显著及极显著正相关;土壤脲酶、磷酸酶与土壤pH值呈极显著负相关,与全氮、全磷呈极显著正相关;土壤过氧化氢酶与全氮、全磷呈极显著正相关;土壤蔗糖酶与全氮、全磷呈显著正相关。④冗余分析结果显示：土壤轻组有机碳、土壤总有机碳、土壤颗粒有机碳和土壤微生物生物量碳是影响东寨港红树林植物群落土壤酶活性的主要因子。[结论] 土壤酶活性与多种土壤活性有机碳组分呈紧密正相关,因此可用土壤酶活来表征东寨港红树林湿地土壤碳库活跃程度。     

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。     

土壤锗污染对土壤酶活性的生态毒理效应

通过室内培养和盆栽试验,研究了土壤添加锗(Ge)对黄棕壤过氧化氢酶、脱氢酶、脲酶、碱性磷酸酶、转化酶的生态毒理效应。结果表明,在土壤Ge含量2~200 mg kg-1范围,土壤Ge对脱氢酶、碱性磷酸酶、转化酶活性抑制作用不明显。土壤Ge对土壤过氧化氢酶和脲酶活性有明显抑制作用,脲酶受Ge的抑制作用最强。土壤Ge含量与脲酶活性之间具有显著负相关,脲酶抑制率可作为Ge生态风险评价的一项生物指示物。     

Clonal and seasonal shifts in communities of saprotrophic microfungi and soil enzyme activities in the mycorrhizosphere of Salix spp.

The species‐specific microbial root and rhizosphere colonization contributes essentially to the plant nutrient supply. The species number and colonization densities of cultivable saprotrophic microfungi and the activities of nutrient‐releasing soil enzymes (protease, acid and alkaline phosphatase, arylsulfatase) were investigated in the rhizosphere of one low mycorrhizal (Salix viminalis) and one higher mycorrhizal (S. × dasyclados) willow clone at a Eutric Cambisol in N Germany. After soil washing, in total 32 and 28 saprotrophic microfungal species were isolated and identified microscopically from the rhizosphere of S. viminalis and S. × dasyclados, respectively. The fungal species composition changed within the growing season but the species number was always lower under S. × dasyclados than under S. viminalis. Under both willow clones, the fungal colonization density was largest in spring, and the species number was largest in autumn. Acid‐phosphatase activity (p < 0.001) and protease activity (p < 0.003) were significantly affected by the Salix clone, whereas arylsulfatase and alkaline‐phosphatase activities did not show clone‐specific differences. All enzyme activities reached their maxima in the summer sampling. Rhizosphere colonization with Acremonium butyri, Cladosporium herbarum, and Penicillium janthinellum contributed significantly to explain the activities of acid phosphatase. Rhizosphere colonization with Cylindrocarpon destructans, Penicillium spinulosum, Plectosphaerella cucumerina, and Trichoderma polysporum contributed significantly to explain the arylsulfatase activities. Effects of the saprotrophic fungal colonization densities on the protease activities in the rhizosphere were low. Acid‐ and alkaline‐phosphatase and arylsulfatase activities in the rhizosphere soil were stronger affected by the composition of the saprotrophic fungal communities than by the Salix clone itself. In conclusion, the colonization density of some saprotrophic microfungi in the rhizosphere contributed to explain shifts in soil‐enzyme activities of the P and S cycles under different willow clones.     

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     

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.     

Responses of phosphatases and arylsulfatase in soils to liming and tillage systems

This study was carried out to investigate the long‐term influence of lime application and tillage systems (no‐till, ridge‐till, and chisel plow) on the activities of phosphatases and arylsulfatase in soils at four research sites in Iowa, USA. The activities of the following enzymes were studied: acid and alkaline phosphatases, phosphodiesterase, and arylsulfatase at their optimal pH values. With the exception of acid phosphatase, which was significantly (P < 0.001) but negatively correlated with soil pH (r ranged from –0.65** to –0.98***), the activities of other enzymes were significantly (P < 0.001) and positively correlated with soil pH, with r values ranging from 0.65** to 0.99*** for alkaline phosphatase, from 0.79*** to 0.97*** for phosphodiesterase, and from 0.66*** to 0.97*** for arylsulfatase. The Δ activity/Δ pH values were calculated to determine the sensitivity of each enzyme to changes in soil pH. Acid phosphatase was the most sensitive and arylsulfatase the least sensitive to changes in soil pH. Activities of the enzymes were greater in the 0 – 5 cm depth samples than those in 0 – 15 cm samples under no‐till treatment. With the exception of acid phosphatase, enzyme activities were mostly significantly (P < 0.001) and positively correlated with microbial biomass C (C_mic), with r values ranging from 0.28 (not significant) to 0.83*** and with microbial biomass N (N_mic), with r values ranging from 0.31 (not significant) to 0.94***. Liming and tillage systems significantly affected the activities of some enzymes but not others, as was evident from the specific activity values (g of p‐nitrophenol released kg^–1 C_org h^–1).     

Tebuconazole application decreases soil microbial biomass and activity

A short-term mesocosm experiment was conducted to ascertain the impact of tebuconazole on soil microbial communities. Tebuconazole was applied to soil samples with no previous pesticide history at three rates: 5, 50 and 500 mg kg⁻¹ DW soil. Soil sampling was carried out after 0, 7, 30, 60 and 90 days of incubation to determine tebuconazole concentration and microbial properties with potential as bioindicators of soil health [i.e., basal respiration, substrate-induced respiration, microbial biomass C, enzyme activities (urease, arylsulfatase, β-glucosidase, alkaline phosphatase, dehydrogenase), nitrification rate, and functional community profiling]. Tebuconazole degradation was accurately described by a bi-exponential model (degradation half-lives varied from 9 to 263 days depending on the concentration tested). Basal respiration, substrate-induced respiration, microbial biomass C and enzyme activities were inhibited by tebuconazole. Nitrification rate was also inhibited but only during the first 30 days. Different functional community profiles were observed depending on the tebuconazole concentration used. It was concluded that tebuconazole application decreases soil microbial biomass and activity.     

Relationship between vegetation diversity and soil functional diversity in native mixed-oak forests

Most studies on the interactions between aboveground vegetation and belowground soil diversity have been carried out in microcosms or manipulated field plots. In the current study, we investigated the relationship between forest vegetation diversity and soil functional diversity (calculated from the activity of soil enzymes) in naturally developed plant communities of native mixed-oak forests without imposing any disturbances to already existing plant–soil relationships. In order to do so, five different vegetation types, i.e., herbaceous plants, climbing plants, trees, shrubs, and ferns, were considered. Correlations between plant diversity, soil physicochemical properties, and soil enzyme activities were determined. Soil physicochemical parameters appeared strongly correlated with both enzyme activities (e.g., pH was positively correlated with amidase and arylsulphatase, and negatively with acid phosphatase; OM content was positively correlated with β-glucosidase, acid and alkaline phosphatase and urease, and negatively with amidase; total N was positively correlated with β-glucosidase, and acid and alkaline phosphatase, and negatively with amidase) and soil functional diversity. For ferns, strong correlations between enzyme activities and plant diversity indexes were found (i.e., dehydrogenase was positively correlated with species richness and Shannon's diversity; acid and alkaline phosphatase were negatively correlated with Shannon's diversity; acid phosphatase was also negatively correlated with species richness). Most interestingly, herbaceous plants and ferns showed a strong positive correlation between Shannon's plant diversity and soil functional diversity. Furthermore, herbaceous plants showed a strong positive correlation between species richness and soil functional diversity. Although these correlations between plant diversity and soil functional diversity might possibly be due to the fact that higher values of plant richness and diversity result in a greater habitat heterogeneity in the soil, current knowledge on the topic is mixed and very incomplete and, then, one must be extremely cautious when interpreting such correlations.     

宁夏黄土区不同植物群落土地利用方式对土壤质量的影响

本文研究了宁夏南部山区典型植物群落土地不同利用方式下土壤质量的变化。结果表明:（1）典型长芒草群落土地,开垦地比封禁地土壤有机质、全氮、全磷、速效氮、速效磷、速效钾养分含量明显降低,降低幅度分别为19.5%、20.1%、17.6%、13.0%、77.8% 和47.5%。脲酶活性为开垦地封禁地,蔗糖酶则表现为封禁地开垦地,中性磷酸酶差异不明显。（2）铁杆蒿群落土地三种利用方式下:放牧地土壤有机质、全氮、全磷、速效钾等养分含量较封禁地与开垦地有一定幅度的增加;放牧地的土壤脲酶、蔗糖酶和中性磷酸酶活性均高于封禁和开垦的同土层土壤,封禁地的脲酶和蔗糖酶次之,开垦地的脲酶和蔗糖酶活性最小,开垦地的中性磷酸酶活性高于封禁地。脲酶活性在土层之间变化较小,最高为放牧地表层177.6 mg/(kg.h),最低为开垦地表下层114.5 mg/(kg#8226;h),蔗糖酶活性层次之间变化明显,其中放牧地表层为表下层的3倍左右。长芒草群落土壤表层各级微团聚体表现为封禁地远大于开垦地,铁杆蒿群落土地不同利用方式下各级微团聚体表现不同,结构系数表现为表层表下层,保持率则为表层表下层。结构系数与保持率均表现为封禁地放牧地开垦地。（3）在轻度放牧条件下,土壤养分状况、酶活性有所提高,但土壤微团聚体中的结构系数与保持率则明显降低。     

黄土高原油松根际土壤酶活性及真菌群落多样性研究——以黄龙山林场为例

为了解黄土高原油松林根际土壤酶活性和真菌群落多样性,本研究分析了陕西黄龙县不同样区油松根际土壤脲酶、碱性磷酸酶、多酚氧化酶和过氧化氢酶活性,并采用巢式PCR-变性梯度凝胶电泳(PCR-DGGE)技术研究了油松根际土壤中真菌群落多样性。结果表明,该地区油松根际真菌群落相似性较高,但受坡向、海拔、土壤水分及人类扰动等诸多因素的影响,不同样区的真菌群落多样性和土壤酶活性存在差异。油松根际各土壤酶活性均表现出坡顶样地高于坡底样地,阴面样地高于阳面样地,林区路旁样地由于采样环境不同于林中样地,酶活性介于其他样地之间;丰富度(S)、Shannon-Wiener指数(H)、Simpson指数(D)、均匀度指数(EH)分析表明,该区域油松根际土壤真菌群落多样性分布特征与酶活性分布特征相一致。相关性分析表明,除过氧化氢酶外,其余酶活性之间、以及与真菌多样性均呈显著正相关(p0.05);土壤含水量与真菌多样性和土壤酶活性除多酚氧化酶外均呈显著正相关(p0.05);而土壤p H与各种酶活性之间均未达显著相关水平(p0.05)。土壤含水量是影响该地区真菌群落多样性与土壤酶活性主要因素之一。     

Long term CO2 enrichment stimulates N-mineralisation and enzyme activities in calcareous grassland

Elevated concentration of atmospheric carbon dioxide will affect carbon cycling in terrestrial ecosystems. Possible effects include increased carbon input into the soil through the rhizosphere, altered nutrient concentrations of plant litter and altered soil moisture. Consequently, the ongoing rise in atmospheric carbon dioxide might indirectly influence soil biota, decomposition and nutrient transformations.N-mineralisation and activities of the enzymes invertase, xylanase, urease, protease, arylsulfatase, and alkaline phosphatase were investigated in spring and summer in calcareous grassland, which had been exposed to ambient and elevated CO₂ concentrations (365 and 600 μl l⁻¹) for six growing seasons.In spring, N-mineralisation increased significantly by 30% at elevated CO₂, while there was no significant difference between treatments in summer (+3%). The response of soil enzymes to CO₂ enrichment was also more pronounced in spring, when alkaline phosphatase and urease activities were increased most strongly by 32 and 21%. In summer, differences of activities between CO₂ treatments were greatest in the case of urease and protease (+21 and +17% at elevated CO₂).The stimulation of N-mineralisation and enzyme activities at elevated CO₂ was probably caused by higher soil moisture and/or increased root biomass. We conclude that elevated CO₂ will enhance below-ground C- and N-cycling in grasslands.     

Enzyme activities in a limed agricultural soil

 This study assessed the effect of eight lime application rates, with four field replications, on the activities of 14 enzymes involved in C, N, P, and S cycling in soils. The enzymes were assayed at their optimal pH values. The soil used was a Kenyon loam located at the Northeast Research Center in Nashua, Iowa. Lime was applied in 1984 at rates ranging from 0 to 17,920 kg effective calcium carbonate equivalent (ha^–1), and surface samples (0–15 cm) were taken after 7 years. Results showed that organic C and N were not significantly affected by lime application, whereas the soil pH was increased from 4.9 to 6.9. The activities of the following enzymes were assayed: α- and β-glucosidases, α- and β-galactosidases, amidase, arylamidase, urease, l-glutaminase, l-asparaginase, l-aspartase, acid and alkaline phosphatases, phosphodiesterase, and arylsulfatase. With the exception of acid phosphatase, which was significantly (P<0.001) but negatively correlated with soil pH (r=–0.69), the activities of all the other enzymes were significantly (P<0.001)and positively correlated with soil pH, with r values ranging from 0.53 for the activity of α-galactosidase to 0.89 for alkaline phosphatase and phosphodiesterase. The Δ activity/Δ pH values ranged from 4.4 to 38.5 for the activities of the glycosidases, from 1.0 to 107 for amidohydrolases and arylamidase, 97 for alkaline phosphatase, 39.4 for phosphodiesterase, and 11.2 for arylsulfatase. This value for acid phosphatase was –35.0. The results support the view that soil pH is an important indicator of soil health and quality. Received: 3 May 1999