不同土地利用方式土壤化学性状与酶学指标分析

在黄河三角洲地区，由于河水携带大量泥沙在人海口淤积，每年形成一定面积的陆地。新生陆地一般营养丰富，适宜耕作．常常被开垦为耕地。由于干旱，天然降雨少，土壤蒸发量大，导致深层土壤水分沿毛细管上升，可溶性盐分离子随之上升到土壤表层，水分蒸发后，盐分离子在土壤表层积累，从而发生土壤盐渍化。进行农业耕作20年后，土壤返盐严重，不再适宜继续耕种。除此之外，还有不同的土地利用方式。本研究选择了5种利用方式，分别测定了土壤溶液电导率、N、P、K、有机质含量等营养状况以及几种土壤酶活性，结果表明：耕地（E）的土壤含盐量最低，营养水平最高，土壤酶活性也最高。草地（G）的土壤含盐量比较高，而营养水平、土壤酶活性也比较高。灌木林地（S）的土壤含盐量比较高，而营养水平、土壤酶活性却比较低，属于立地条件较差的地块。与盐碱荒地（U）相比，它的含盐量降低不少，而营养水平、土壤酶活性也有所改善，说明通过栽植耐盐树木，提高植被覆盖率来改良盐碱荒地是可行的。林地（F和MF）的土壤含盐量比较低，营养水平、土壤酶活性比较高。另外，刺槐与紫穗槐混交林的效果很好，一方面它们都有一定的耐盐性，另一方面都是固氮植物，能够自我积累营养。     

氮素形态对小麦生长中后期保护酶等生理特性的影响

在水培条件下,探究了氮素形态对小麦营养生殖并进生长时期保护酶的影响。结果表明:铵、硝态氮单供和混合供应对小麦保护酶活性影响不同。在铵、硝态氮混合供应下,叶片SOD、CAT,根系SOD活性最高,同时叶片、根系可溶性蛋白含量最大,根系活力和根系表面K3Fe(CN)6还原活性最高,但MDA含量最高;单供硝态氮时叶片POD活性最高,根系MDA含量最高;单供铵态氮时根系POD、CAT活性最高。单供尿素时叶片仅CAT活性高于铵和硝态氮混合供给,但同时叶片MDA含量也高于铵和硝态氮混合供给。叶片以SOD、CAT和POD为主清除自由基,而根系以SOD和POD为主清除自由基。铵和硝态氮混合供给下,小麦成熟后,地上部干重,籽粒产量最大,根冠比最小。     

Areal activities and stratification of hydrolytic enzymes involved in the biochemical cycles of carbon, nitrogen, sulphur and phosphorus in podsolized boreal forest soils

A novel approach allowing on-site high throughput enzyme activity measurements by fluorogenic model substrates was applied to study the functioning of enzymes involved in biochemical cycling of nutrients in boreal forest soil ecosystems. The examined enzymes comprised α-glucosidase, β-glucosidase, β-xylosidase, β-cellobiosidase, N-acetyl-glucosamidase, acetate-esterase, butyrate-esterase, phosphomonoesterase, sulphatase and aminopeptidase, whereby spatial and seasonal variation of their activity was investigated over nine seasons in 2 years. The studied sites of boreal podzolized soil of Pinus sylvestris and Picea abies forest were located in central Finland. Activity of all enzymes except sulphatase was highest in the humus layer in all seasons. Maximum sulphatase activity was located below the humus layer in the soil column. Annual activities of acetate-esterase, butyrate-esterase, β-glucosidase and phosphomonosterase calculated to in situ temperature during the year were 480-700, 690-950, 110-190 and 110-200 mol m⁻² year⁻¹, respectively. They were up to 100 fold higher than the other six measured activities. The overall turnover capacity of the enzymes was >1000 mol of ester linked carbon, >700 mols carbon from different carbohydrates, 100-200 mol of ester linked phosphate, 10-40 mol of ester linked sulphate m⁻² year⁻¹. Winter time (November-April) contributed from 7 to 32% to the annual turnover capacity indicating important enzyme activities also during a cold period of the year. Clear-cutting of the tree stand did not adversely affect enzyme activities related to the cycling of carbon, nitrogen, sulphur and phosphorus during the year. The pH optimum for hemicellulose and cellulose hydrolysing enzymes was pH 3-4 and the pH optimum of phosphomonoesterase, sulphatase, aminopeptidase and N-acetyl-glucosamidase was 4-5. This shows that the hydrolytic activities were adapted to the acid pH-values of the soils. The soil hydrolytic potential was many fold higher as compared to the actual amount of litter it received in the P. sylvestris and P. abies forests.     

Enzyme activities and litter decomposition in agricultural soils in northern,central, and southern Germany

Although enzyme activities were extensively investigated in soils with reference to abiotic environmental conditions and human impact, their role in litter decomposition is not fully understood. Therefore, decomposition rates and enzyme activities were studied using nylon bags and three litter types buried in silty‐loamy Cambisols and Luvisols in northern, central, and southern Germany under similar averaged temperature and precipitation and a maritime to continental gradient. After 180 d, the ash‐free mass remaining ranged between 15% and 68% for the Triticum, Secale, and Lolium litter. The enzyme activities were mainly controlled by the litter type and the decomposition time and less but significant by site. The highest decomposition rate occurred at the central German site for Lolium litter associated with highest arginine ammonification and urease activity in litter. In contrast, the recalcitrant Secale and Triticum litter were decomposed more rapidly at the northern and southern site where urease, protease, and arginine ammonification was high in the bulk soil. The β‐glucosidase activity was similar in soil and litter at the three locations and was not correlated to the velocity of litter decomposition. Since the abiotic environmental factors at the maritime to continental gradient did not explain the site‐specific velocity of both rapidly decomposing and refractory litter, enzyme activities related to the N cycling like arginine ammonification and urease activity were recognized to velocity of litter decomposition.     

Extraction of humic-β-glucosidase fractions from soil

Humic compounds with -glucosidase activity were extracted from soil using tetrasodium pyrophosphate as extracting solution. Mixture of soil samples with 0.01 M pyrophosphate in a ratio of 1:5 (w/v), adjustment to pH 7.0–7.3, extraction for 18 h with reciprocating agitation, and bacteriological filtration after centrifugation were the optimum conditions for extraction of the -glucosidase complexes. Otherwise, experimental conditions for extraction indicated that the concentration and pH of pyrophosphate were the factors with the most influence on enzymatic extraction yields. The results indicated that the -glucosidase was extracellular and associated with soil humates.     

Effects of some environmental factors on ammonia volatilization from simulated livestock urine applied to soil

Summary The proportion of the N that was volatilized as ammonia during 8 days, following the application of simulated livestock urine to soil, increased from 25 to 38% as the temperature of incubation was increased from 4° to 20°C in a system with a continuous flow of air at 70% relative humidity. However, volatilization was reduced if the application was followed by simulated rain; the reduction was greater as the amount of rain increased (up to at least 16 mm) and became less with an increasing length of time (up to 2–3 days) after the application of the urine. The effects of the soil water content before application of the urine, and of the relative humidity of the air, were generally small but volatilization was reduced by a combination of air-dry soil with a low relative humidity. Volatilization was slight (7%) when the flow of air was restricted to 0.5 h in every 12 h but, with an air flow for 12 h in every 24 h, the volatilization was much closer to that with a continuous flow for the whole 8-day period. When cool or dry conditions were imposed for 8 days and then more favourable conditions were instituted for a second period of 8 days, there was a substantial increase in volatilization following the change.     

Alkaline Hydrolyzable Organic Nitrogen as an Index of Nitrogen Mineralization in Soils: Relationship with Activities of Arylamidase and Amidohydrolases

ABSTRACT

This study investigated the relationship between a recently proposed alkaline hydrolysis method for estimating the chemical index of nitrogen (N) mineralization potential of soils and the activities of arylamidase and four amidohydrolases involved in hydrolysis of organic N (ON) in soils. Nitrogen mineralization was studied in 13 soils from uncultivated fields in Iowa, USA, by direct steam distillation of 1 g field-most soil treated with 1 M KOH or 1 M NaOH. The distillate was collected in boric acids, which was changed every 5 min for a total of 40 min. The NH₄ ⁺-N in the distillate was determined by titration with 0.005 M H₂SO₄. The cumulative amounts of N hydrolyzed were fitted to the first-order exponential equation to determine the “potentially hydrolyzable N (N_max )” for the soils. The activities of arylamidase, L-asparaginase, L-glutaminase, amidase, and L-aspartase were assayed at their optimal pH values. Results showed that estimated N_max values were strongly correlated with the activities of arylamidase and amidohydrolases. The activities of arylamidase and the amidohydrolases were significantly correlated, indicating that the activities of the two groups of enzymes are coupled in mineralization of ON in soils. Based on the specificity of enzyme reactions and the strong relationship between estimated N_max values and the activities of arylamidase and amidohydrolases, we concluded that similar amide-N bonds were susceptible to enzymatic and alkaline hydrolysis, and that alkaline hydrolyzable ON can be used as an index of N mineralization in soils.     

番茄果实生长发育过程中糖的代谢

通过测定番茄果实生长发育过程中蔗糖、果糖、可溶性总糖、淀粉的含量和糖代谢中涉及到的蔗糖合成酶、蔗糖磷酸合成酶、酸性转化酶、中性转化酶的活性,研究了番茄果实生长发育过程中糖的代谢过程。根据番茄果实的生长发育曲线和相对日生长率,可以将番茄的生长发育过程按开花后39 d作为分界点分为2个阶段,39 d之前为产量形成期,之后为品质形成期。在产量形成期内,果糖和可溶性总糖含量逐渐升高,淀粉含量逐渐下降,蔗糖含量先升高后下降,变化不剧烈,以积累淀粉为主。同期AI和NI的活性较低,SS和SPS的活性较高。在品质形成期,果糖含量升高,淀粉含量下降,蔗糖和可溶性总糖变化不明显,以积累果糖为主。AI和NI的活性急剧升高,SS和SPS的活性很低。统计分析表明,番茄果实单果重量与淀粉含量、淀粉含量与NI活性呈显著负相关,可以参考淀粉的含量和NI的活性进行番茄高产研究。果糖含量与淀粉含量呈显著负相关,与SS和AI,NI的活性均为显著正相关;番茄果实中的可溶性总糖与淀粉含量呈显著负相关,与SS的活性呈显著正相关,可以参考SS和AI,NI的活性进行高果糖含量的品质研究。     

不同年龄大熊猫肠道菌群及其酶活特征分析

旨在探究年龄对大熊猫个体肠道微生态的影响。本研究采集大熊猫（Ailuropoda melanoleuca）（J₁（亚成年大熊猫个体）、J₂（成年大熊猫个体）、J₃（老年大熊猫个体））的新鲜粪便,基于16S rRNA基因技术,测定不同年龄的大熊猫个体肠道细菌组成,分析其物理和化学特征及酶活特异性,利用冗余分析（redundant analysis,RDA）分析大熊猫肠道微生物菌群丰度与其环境因子之间的关系。结果表明：在门水平上,变形菌门的相对丰度随着年龄的增加而升高,厚壁菌门的相对丰度随着年龄的增加而降低;在属水平上,链球菌属的相对丰度随着年龄的增加而降低;淀粉酶和纤维素酶的酶活力在J₂肠道最高,淀粉酶活力在J₃肠道最低,纤维素酶活力在J₁肠道最低,蛋白酶活力在J₁肠道最高,在J₃肠道最低;厚壁菌门和拟杆菌门的相对丰度均与淀粉酶活力和还原糖含量呈正相关,变形菌门的相对丰度与还原糖含量和氨基酸含量呈负相关。研究表明,不同年龄大熊猫个体的肠道微生物菌群的表现特征不同,其肠道细菌优势菌的相对丰度与其消化酶等环境因子存在相关性;建议需对亚成年大熊猫加强饮食和生活环境管理,并可以通过添加益生菌等方式加强对老年大熊猫肠道健康的管理。     

酸胁迫对夏枯草叶绿素荧光特性和根系抗氧化酶活性的影响

为了阐明夏枯草幼苗对酸性环境的耐受性,采用不同pH值(pH=4.5、4.0、3.5、3.0)的Hoagland营养液模拟酸胁迫环境,研究酸胁迫对夏枯草幼苗叶绿素荧光特性及根系抗氧化酶活性的影响。结果表明,随着pH值下降,代表供体与受体侧参数的K点相对可变荧光(W_K)、J点相对可变荧光(V_J)和电子受体QA-被还原的最大速率(dV/dt_o)逐渐升高,光系统Ⅱ(PSⅡ)电子传递的量子效率(φE_o)降低;表示单位反应中心吸收(ABS/RC)、捕获(TR_o/RC)、热耗散(DI_o/RC)的能量逐渐增加;用于电子传递的能量(ET_o/RC)逐渐下降;表示PSⅡ的最大光化学效率(F_v/F_m)、吸收光能为基础的光合性能指数(PI_abs)、表征光系统Ⅰ(PSⅠ)的最大氧化还原活性(ΔI/I_o)及PSⅡ与PSⅠ协调性(Φ_PSⅠ/PSⅡ)随酸胁迫程度增加逐渐下降。夏枯草根系超氧化物歧化酶(SOD)与过氧化物酶(POD)活性呈下降趋势,而根系抗坏血酸过氧化物酶(APX)活性先升高后降低;夏枯草叶片可溶性糖、脯氨酸含量逐渐上升。酸胁迫下,夏枯草PSⅡ反应中心受损,电子传递受阻,光系统性能及PSⅡ与PSⅠ的协调性降低,根系SOD与POD活性受到抑制,在pH 3.0处理下表现较为明显。夏枯草通过提高单位反应中心的热耗散能力来减少过剩光能对叶片光合机构的破坏,通过提高根系APX抗氧化酶及叶片渗透调节物质含量来减少酸胁迫带来的伤害。