生态学报  2015, Vol. 35 Issue (14): 4604-4612

文章信息

杨文彬, 耿玉清, 王冬梅
YANG Wenbin, GENG Yuqing, WANG Dongmei
漓江水陆交错带不同植被类型的土壤酶活性
The activities of soil enzyme under different vegetation types in Li River riparian ecotones
生态学报, 2015, 35(14): 4604-4612
Acta Ecologica Sinica, 2015, 35(14): 4604-4612
http://dx.doi.org/10.5846/stxb201401140107

文章历史

收稿日期:2014-01-14
修订日期:2014-06-25
漓江水陆交错带不同植被类型的土壤酶活性
杨文彬1, 耿玉清1 , 王冬梅2    
1. 北京林业大学林学院, 北京 100083;
2. 北京林业大学水土保持学院, 北京 100083
摘要:水陆交错带是内陆水生生态系统与陆地生态系统之间的功能界面区,其包含了高地到低地直到水体的区域,是土壤有机质源、汇和转换器。土壤中有机物的分解以及营养物质的转化不仅影响到植物的生长,也对水体质量产生间接影响。土壤酶几乎参与土壤中有机物质的分解与合成的全过程,直接或间接影响着土壤一系列的生物化学反应,对生态系统的物质循环产生重要影响。不少学者围绕农田土壤、林地土壤以及湿地土壤探讨了不同植被下酶活性的变异。水陆交错带植被种类丰富,周期性的淹水条件加剧了土壤性质变异的复杂性。但目前水陆交错带不同植被类型土壤酶活性差异的研究不多。以漓江水陆交错带土壤为研究对象,对苔藓、草本和灌丛3种植被类型下的土壤溶解性化学成分、4种土壤水解酶即糖苷酶、几丁质酶、亮氨酸氨基肽酶和磷酸酶以及2种氧化还原酶即酚氧化酶和过氧化物酶的活性,以及土壤性质与酶活性之间的关系进行了研究。结果表明,苔藓植被下土壤的糖苷酶和酚氧化酶活性显著高于草本和灌丛,草本植被下土壤的过氧化物酶活性显著高于苔藓和灌丛,灌丛植被下土壤几丁质酶活性显著高于苔藓和草本,但不同植被类型的土壤亮氨酸氨基肽酶活性无显著差异。相关分析表明,土壤水分含量与糖苷酶和酚氧化酶活性呈显著正相关,而与几丁质酶和碱性磷酸酶活性呈显著负相关。土壤有机碳和易氧化碳均与糖苷酶和酚氧化酶活性呈极显著负相关,与几丁质酶活性呈显著正相关。土壤溶解性有机碳与亮氨酸氨基肽酶和酚氧化酶呈显著正相关。综合认为,水陆交错带不同种类土壤酶在不同植被类型间的差异有别,土壤水分含量和土壤有机碳显著影响土壤酶活性的变化。不同植被类型土壤酶活性的差异不仅与植被类型有关,与水陆交错带微地形以及土壤性质的空间异质性也有密切关系,需运用长期控制试验手段开展研究。
关键词水陆交错带    土壤水解酶    土壤氧化还原酶    土壤水分含量    溶解性有机碳    溶解性有机氮    
The activities of soil enzyme under different vegetation types in Li River riparian ecotones
YANG Wenbin1, GENG Yuqing1 , WANG Dongmei2    
1. College of Forestry, Beijing Forestry University, Beijing 100083, China;
2. School of Soil and Water Conservation, Beijing Forestry University, Beijing 100083, China
Abstract:"Riparian ecotone" refers to the functional-frontal-zone between an internal water-ecosystem and land-ecosystem, and riparian ecotones-as the sinks, sources or transformers of soil organic matter-contain the interference from the uplands, lowlands and aquatic zone. Riparian ecotones had played a critical role in regulating the conponents of chemical composition between terrestrial and aquatic zones. In addition, they have also had a significant effect on maintaining biodiversity, preventing pollutants from the land ecosystem entering the aquatic zone, and improving water quality or any other aspects. Soil offered essential nutrient substance for the growth of vegetation. The decomposition of organic matter and the transformation of nutrient substances in the soil have not only influenced the growth of vegetation but have also had an indirect effect on the quality of the water. The partial involvement of soil enzymes throughout process of soil organic matter decomposition and synthesis, has influenced all the biochemical reactions of soil, directly or indirectly, and has had a great impact on material circulation within the ecological system. Much debate has focused on the variation in soil enzyme activities with different vegetation types, e.g., farmland, forest land and wetland. Riparian ecotones have diverse vegetation types, complicated by the variation in soil properties aggravated by periodic flooding conditions. However, studies aimed at soil enzyme activity under different vegetation communities in riparian ecotones have been scare. In the riparian ecotones of the Lijiang River, soil water-soluble chemical composition, four types of soil hydrolase(glycosidase, chitinase, leucine aminopeptidase and phosphatase)and two types of oxidoreductase (phenol oxidase and peroxidase) were measured in relation to three vegetation types: mosses, herbs and shrubs. The relationship between the soil properties and enzyme activities was also studied. The results showed:(1) that the activity of soil glycosidase and phenol oxidase under mosses was significantly greater than that under herbaceous and shrubs;(2)that the soil glucosaminidase activity under shrubs was significantly higher than that under mosses and herbs;(3)that the peroxides activity under herbs was significantly higher than that under mosses and shrubs; and that there was no obvious difference in the activity of leucine amino peptidase among the three vegetation types. Among the six enzyme activities examined, soil water content was positively related to the activity of glucosidase and phenol oxidase, and negatively related to the activity of glucosaminidase and alkaline phosphatases. Soil organic carbon and readily oxidizable carbon were negatively associated with glucosidase and phenol oxidase, but positively associated with glucosaminidase. Dissolved organic carbon in soil was positively related to the activity of both glucosidase and phenol oxidase. In short, there were differences between different types of soil enzymes under different vegetation types in riparian ecotones, and soil water content and soil organic carbon significantly influenced the change in soil enzyme activities. In riparian ecotones enriching the plant diversity can accelerate soil ecological processes. The difference in soil enzyme activities under different vegetation communities was not only related to the vegetation types, but also to the micro-topography and spatial heterogeneity of the soil properties in riparian ecotones. Future research on soil enzyme activities under different kinds of vegetation types in the soil of riparian ecotones of the Lijiang River should incorporate long-term control-tests.
Key words: riparian ecotone    soil hydrolase    soil oxidoreductase    soil water content    dissolved organic carbon    dissolved organic nitrogen    

水陆交错带也称“河岸带”,是处于水域生态系统和陆地生态系统共同作用的重要环境界面区[1, 2],对维持生物多样性、拦截污染物以及改善水体质量有重要作用[3, 4]。但人为对植被的破坏,不仅影响到水陆交错带的景观,更重要的是影响到水体的质量[5]。土壤是维持植被生长的介质,土壤中有机物的分解以及营养物质的转化不仅影响到植物生长的养分途径,也对水质产生间接影响[6]

土壤酶是催化土壤有机物质分解的蛋白质,主要来源于微生物、植物根系及动物的分泌释放。它参与土壤中有机物质转化的全过程,直接或间接影响着土壤一系列的生物化学反应[7, 8],对生态系统的物质循环产生重要影响[9, 10]。植被可通过凋落物和根系分泌物对土壤酶活性产生影响[11]。已有不少学者围绕农田土壤[12, 13]、林地土壤[14, 15]以及湿地土壤[16, 17]探讨了不同植被下土壤酶活性的变异。水陆交错带土壤具有特殊的周期性淹水特征,在陆地和水域环境条件的交替作用下进行水陆生态系统间的物质转移和转换[7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18],是土壤有机质的源、汇和转换器[19]。但是针对水陆交错带的不同植被类型下土壤酶活性变异的研究却鲜有报道。

本文以漓江水陆交错带土壤为研究对象,主要探究不同植被类型下土壤酶活性的差异以及土壤因子对酶活性的影响。不同植被类型土壤,是基于自然植被种类的选择,是长期适应立地环境的结果。在水陆交错带,高程梯度的变化能直观反映地形梯度以及土壤基本性质的变异[20]。土壤酶种类丰富,本研究选取4种水解酶和2种氧化还原酶。其中糖苷酶(EC 3.2.1.21)能水解纤维素,是与土壤有机碳转化密切相关的酶,且国外研究较普遍;几丁质酶(EC3.2.1.52)与有机碳和氮的转化密切相关,其功能是催化几丁质转化为氨基糖;亮氨酸氨基肽酶(EC 3.4.11.1),参与土壤蛋白质的水解,其作用是从肽链的末端水解,形成氨基酸如亮氨酸和丙氨酸;碱性磷酸酶(EC3.1.3.1)在碱性土壤中占优势,参与土壤有机磷的转化,可将磷酸脂类水解形成磷酸及其他产物[21]。多酚氧化酶(EC 1.10.3.2)和过氧化物酶(EC 1.11.1.7)均为氧化还原酶,它们参与木质素的分解和芳香族化合物的氧化,影响土壤碳的积累[22]。本研究结果可为水陆交错带环境条件下土壤有机质转化过程的研究提供理论依据,同时也可进一步丰富我国土壤酶的研究内容。

1 研究区域

研究区域位于漓江桂林至阳朔河段,地处 E 109°45′—110°40′、N 24°18′—25°41′之间[23]。气候属中亚热带湿润季风气候,全年光照充足,平均气温17.8—19.1 ℃,年降雨量1 814—1 941 mm,年蒸发量1 377—1 857 mm,雨热基本同期;年径流量丰富但全年分布不均,水位在丰水期和枯水期有显著的不同。由于人为对原生植被的干扰破坏,目前植物区系为次生性质[24]。现存的植被种类主要有枫杨(Pterocarya tonkinensis)、水杨梅(Geum aleppicum)、黄荆(Vitex negundo)和一叶萩(Securinega suffruticosa)等木本植物;草本植被主要有狗牙根(Cynodon dactylon)、水蓼(Polygonum hydropiper L.)和葎草(Humulus scandens)等。在地势低洼或靠近江水的区域主要是以地钱(Marchantia polymorpha)、葫芦藓(Funaria hygrometrica)为主的苔藓植物。水陆交错带地形破碎,经过江水的持续冲刷以及土壤的淤积,土层厚度分布不均,一般在10—20 cm左右,厚的地方可达50 cm。

2 研究方法 2.1 样品采集

研究样地位于桂林市雁山区拓木镇龙门村,地处E 110°24′19″、N 25°10′50″,海拔高度145 m。据资料显示,漓江流域于9月至次年2月为枯水期,水陆交错带的宽度范围一般10—30 m[20]。经过野外踏查发现,水陆交错带存在比较明显的植被梯度变化。距离水边近、地势较低洼的地方植被多为苔藓;距离水边稍远、地势平坦的地方植被主要是草本;而远离水边地势较高的地方植被类型为灌丛,在灌丛中有呈零星分布的乔木。其中苔藓植被以地钱为主,也有零星分布的狗牙根,其平均高度为3 cm,土层厚度5—10 cm;草本植被以狗牙根为主,葎草和水蓼分布不均匀,植被平均高度为20 cm,土层厚度10—20 cm;灌丛植被则以水杨梅和一叶秋为主,其间有枫杨,土层厚度15—70 cm。

水陆交错带不同类型的植被呈零散分布。在2012年11月按照相近的原则,分别划定苔藓、草本和灌丛3种植被类型的样地,其面积分别为2 m×2 m,5 m×5 m和5 m×5 m。每种类型的样地按照植物盖度和多样性相似的原则设有6次重复。 对于苔藓和草本植被类型样地,首先除去地上部分,然后采集0—10 cm土层的土壤样本3份,混合成一个分析样本;对于灌丛植被类型样地,在植物附近采集0—10 cm土层的土壤样本3份,混合成一个分析样本。采集后的土样经除去石块和根系后,一部分装入布袋,经风干后磨细,供土壤理化性质分析(表 1);另一部分装于聚乙烯自封袋,并放置于冰盒中带回实验室,供溶解性化学成分和酶活性分析。

表1 样地基本概况 Table 1 Basic characteristic of plots
植被类型 Vegetation typespH 土壤容重 Soil bulk density/ (g/cm3)全氮 Total nitrogen/ (g/kg)全磷 Total phosphorus/ (g/kg)有效磷 Available phosphorus/ (mg/kg)全钾 Total potassium/ (g/kg)土壤质地 Soil texture
苔藓Mosses7.451.350.390.275.4220.59砂土及壤质砂土
草本Herbs7.551.280.520.423.5020.54砂质粘壤土
灌丛Shrubs7.571.250.750.671.6819.76砂质粘壤土
2.2 研究方法

土壤水分含量及土壤容重采用烘干法测定。土壤质地采用国际制土壤质地分类标准,用比重计法进行测定。土壤全氮测定采用硫酸钾-硫酸铜-硒粉消煮,凯氏定氮仪自动分析法。土壤全磷采用硫酸-高氯酸消煮-钼锑抗比色法。土壤全钾采用氢氟酸-高氯酸消煮火焰光度计法。土壤有机碳采用硫酸重铬酸钾氧化-容量法测得。土壤易氧化碳的测定采用0.02 mol/L的KMnO4-CaCl2溶液氧化方法,根据KMnO4浓度的变化计算土壤易氧化碳含量[25]。土壤溶解性有机碳(DOC)和溶解性总氮(DTN)的测定,采用0.5 mol/L纯水浸提(液体积与土质量比为10 ∶ 1),在180次/min的速度下间歇振荡1 h后静置15 min;混合液经过滤后,在12300 r/min条件下离心15 min,再用0.45 μm滤膜过滤,滤液用德国Multi N/C 3100分析仪直接测定。土壤铵态氮(NH+4-N) 和硝态氮 (NO-3-N)采用0.5 mol/L氯化钾溶液浸提(液体积与土质量比为5 ∶ 1),流动注射分析仪测定滤液的方法测得。土壤溶解性有机氮通过计算获得[26],公式为DON = DTN - (NH+4-N + NO-3-N)。

土壤水解酶活性的测定均采用对硝基苯酚(pNP)法[27, 28]。分别以对硝基苯-β-D-吡喃葡萄糖苷、对硝基苯酚乙酰基氨基葡萄糖苷、L-亮氨酸-4-硝基苯胺和对硝基苯磷酸二钠为底物测定糖苷酶、几丁质酶、亮氨酸氨基肽酶以及磷酸酶的活性。多酚氧化酶和过氧化物酶的测定分别以左旋多巴(DOPA)和DOPA加过氧化氢(H2O2)为底物[27],吸光系数用酪氨酸酶进行校正[29]。依据研究土壤 pH值的范围,本研究选择pH值为7.5的Tris缓冲液。在土壤酶测定的同时分别做无土空白试验和无底物对照试验。土壤有机碳是土壤研究的通用指标,基于有机碳基表示的酶活性可以反映微生物群落的特征,这一表示方法在国外也普遍应用[30, 31]。在本研究中,水解酶活性以每小时每克有机碳催化产生的对硝基苯酚的微摩尔浓度(μmol g-1 有机碳h-1)来表示。氧化还原酶采用每小时每克有机碳氧化底物的微摩尔浓度(μmol g-1 有机碳h-1)表示。

2.3 数据处理

所有数据使用Excel软件进行整理,应用SPSS for windows 软件19.0对数据进行分析。其中,土壤性质和土壤酶活性的差异显著性采用One-way ANOVA分析,土壤性质参数对土壤酶活性的相关分析采用Pearson法。

3 结果与分析 3.1 不同植被类型土壤水分含量的差异

土壤水分的梯度变化是水陆交错带的主要特征之一。从图 1来看,不同植被类型之间土壤水分含量的存在显著差异。其中苔藓植被下土壤水分含量为33.60%,显著高于草本植被下以及灌丛植被下的土壤水分含量(P<0.05)。草本植被土壤水分含量为30.11%,比灌丛植被下土壤水分含量高17.48%。

图1 不同植被类型下水分含量的差异 Fig.1 Soil water content under different vegetation types
3.2 不同植被类型土壤有机质和易氧化碳的差异

土壤有机碳是反映土壤质量的重要指标,在不同植被类型间的差异十分显著(P<0.05)。从表 2可知,灌丛植被土壤中土壤有机碳含量为13.09 g/kg,比草本植被高43.85%,比苔藓植被高99.24%。土壤易氧化碳的变化趋势与土壤有机碳一致,即灌丛植被土壤中含量最高,为726 mg/kg,而苔藓植被土壤含量最低为706 mg/kg。

表2 不同植被类型下土壤有机碳的含量 Table 2 Content of soil organic matter under different vegetation types
植被类型 Vegetation types土壤有机碳 Soil organic carbon/(g/kg)土壤易氧化碳 Soil readily oxidized organic carbon/(mg/kg)
苔藓 Mosses6.57±0.14c706±1.14c
草本Herbs9.10±0.64b717±2.57b
灌丛 Shrubs13.09±0.20a726±1.67a
数值为平均值±标准误,同列不同字母表示差异显著(P<0.05)
3.3 不同植被类型土壤溶解性化学成分的基本性质

土壤溶解性化学成分是最活跃的组分,对营养元素的生物地球化学过程以及微生物的生长代谢过程有着重要的作用。从表 3来看,不同植被类型之间土壤溶解性化学成分有一定的差异。苔藓植被土壤溶解性有机碳83.90 mg/kg,虽比草本植被高12.69%,但二者差异不显著。灌丛植被下土壤溶解性有机碳为48.14 mg/kg,显著低于苔藓和草本植被的溶解性有机碳含量。草本植被土壤溶解性总氮为5.85 mg/kg,显著地高于灌丛和苔藓植被;而苔藓植被的溶解性总氮为4.18 mg/kg,显著高于灌丛。土壤溶解性有机氮含量在不同植被类型间的差异与土壤溶解性总氮一致。灌丛植被土壤铵态氮含量显著高于苔藓植被土壤,但与草本植被土壤无显著差异。灌丛植被土壤硝态氮含量为0.12 mg/kg,但与其它植被无显著差异。

表3 不同植被类型下土壤溶解性化学成分的基本性质 Table 3 Basic properties of soil dissolved chemical composition under different vegetation types
植被类型 Vegetation types溶解性有机碳 Dissolved organic carbon/ (mg/kg)溶解性总氮 Dissolved total nitrogen/ (mg/kg)溶解性有机氮 Dissolved organic nitrogen/ (mg/kg)NH+4-N/ (mg/kg)NO-3-N/ (mg/kg)
苔藓 Mosses83.90±5.54a4.18±0.28b3.69±0.29b0.39±0.03b0.09±0.03a
草本Herbs74.45±5.56a5.85±0.37a5.31±0.30a0.48±0.05ab0.05±0.01a
灌丛 Shrubs48.14±5.50b2.80±0.19c1.98±0.18c0.70±0.17a0.12±0.04a
3.4 不同植被类型土壤酶活性的差异

表 4表明不同植被类型之间土壤酶活性有一定的差异。其中土壤糖苷酶活性在苔藓植被土壤中最高,为13.38 μmolpNP g-1有机碳h-1,显著高于草本和灌丛植被下的酶活性;但草本和灌丛植被下的酶活性差异未达到显著水平。灌丛植被土壤几丁质酶活性为3.00 μmolpNP g-1有机碳h-1,显著高于其它两种植被类型土壤,而草本植被土壤几丁质酶活性比苔藓植被并无显著差异。三种植被类型的土壤亮氨酸氨基肽酶活性均无显著性差异。就土壤碱性磷酸酶而言,苔藓植被类型下的土壤碱性磷酸酶活性为3.66 μmolpNP g-1有机碳h-1,显著低于草本和灌丛植被类型;但灌丛与草本植被类型土壤碱性磷酸酶活性差异不显著。酚氧化酶活性在不同植被类型土壤中均有显著性差异。其中苔藓植被的酚氧化酶活性为7.50 μmolDOPA g-1有机碳h-1,是灌丛植被土壤酶活性的1.92倍;草本植被土壤酚氧化酶活性为5.43 μmolDOPA g-1有机碳h-1,显著高于灌丛植被类型。就过氧化物酶而言,在草本植被类型中为11.07 μmolDOPA g-1有机碳h-1,显著高于其它两种植被类型,而苔藓植被与草本植被下土壤过氧化物酶活性无显著差异。

表4 不同植被类型下的土壤酶活性 Table 4 Soil enzyme activities under different vegetation types
植被类型 Vegetation types糖苷酶# Glucosidase 几丁质酶 Glucosaminidase/ (μmol pNP g-1 SOC h-1)亮氨酸氨 基肽酶# Leucine amino peptidase/ (μmol pNP g-1 SOC h-1)碱性磷酸酶 Alcaline phosphatase/ (μmol pNP g-1 SOC h-1)酚氧化酶δ Polyphenol oxidase/ (μmol DOP Ag-1 SOC h-1)过氧化物酶δ Peroxidase/ (μmol DOP Ag-1 SOC h-1)
苔藓Mosses13.38±0.28a2.05±0.24b2.61±0.24a3.66±0.16b7.50±0.18a8.28±0.48b
草本Herbs11.27±0.46b2.43±0.11b2.58±0.23a5.01±0.35a5.43±0.29b11.07±0.17a
灌丛Shrubs10.84±0.41b3.00±0.07a2.13±0.15a4.79±0.49a3.90±0.27c8.11±0.27b
4 讨论 4.1 植被类型对土壤酶活性的影响

水陆交错带所形成的特定空间是众多植物的栖息地,植物种类数量要明显高于其它生态系统[32, 33]。不同类型的植被通过凋落物和根系分泌物来影响土壤微生物,从而影响土壤酶活性的高低。Ekaterina发现草本植被下土壤糖苷酶、几丁质酶、磷酸酶、氨基肽酶和酚氧化酶活性高于在苔藓和地衣[34]。刘存歧也发现草本植被土壤碱性磷酸酶活性和过氧化物酶活性高于藻类苔藓带[35]。刘艳等发现植被类型由草本演替为灌丛和乔木林,土壤酶活性也在发生显著的变化[36]。综合来看,不同植被对土壤酶活性的影响有显著差异。

本研究发现,不同酶种类在不同植被类型间的差异有别,其中苔藓植被下土壤的糖苷酶和酚氧化酶活性显著高于草本和灌丛。这表明苔藓植被有利于有机物质的水解。表 2中苔藓植被土壤有机碳含量显著低于灌丛植被,但表 3中的土壤溶解性有机碳却显著高于灌丛植被。这充分说明苔藓植被下,土壤微生物对有机碳的利用率高,进而对土壤复杂有机碳转化的速度要高于灌丛土壤。由于几丁质酶和亮氨酸氨基肽酶均参与有机氮化合物的转化,因此酶活性的高低可影响无机氮含量的变化。研究结果显示灌丛植被下土壤几丁质酶活性显著高于苔藓和草本,但亮氨酸氨基肽酶活性与苔藓和草本植被没有显著差异;另外,土壤溶解性化学成分的数据表明,灌丛植被的有机氮含量比其它植被类型低,但无机氮的含量与其它植被无显著差异。这说明在灌丛植被土壤中有机氮的转化速度快。因此,几丁质酶在灌丛土壤有机氮的转化中的作用要高于亮氨酸氨基肽酶。

4.2 土壤性质对酶活性的影响

土壤性质可通过不同途径影响土壤微生物的生长发育进而影响酶的分泌。在水陆交错带,由于地形以及水位的变化,使得土壤水分发生剧烈的变化。土壤水分被认为是影响酶活性的主要因子[37]。Hackl等认为土壤湿度与土壤水解酶呈显著负相关关系[38];但Waldrop发现土壤水分的增加会降低部分酶的活性,其中酚氧化酶和过氧化物酶活性降低显著,而水解酶活性变化不明显[39]。因此,土壤水分对酶活性的影响是复杂的。本研究中糖苷酶和酚氧化酶活性是随着水分含量的增加而升高的(表 5),几丁质酶和碱性磷酸酶活性则是随着水分含量的增加而降低,其它酶活性与水分含量并无相关性。

表5 土壤性质参数与酶活性相关关系 Table 5 Pearson′s correlation of soil property parameters and soil enzyme activities
土壤性质参数 Parameter of soil properties糖苷酶 Glucosidase几丁质酶 Glucosaminidase亮氨酸氨 基肽酶 Leucine amino peptidase碱性磷酸酶 Alcaline phosphatase酚氧化酶 Polyphenol oxidase过氧化物酶 Peroxidase
土壤水分含量 Soil water content0.572*-0.611* *0.461-0.501*0.701* *0.163
土壤有机碳 Soil organic carbon-0.667* *0.701* *-0.3910.345-0.868* *-0.133
易氧化碳ROC-0.745* *0.726* *-0.2910.396-0.920* *0.032
溶解性有机碳DOC0.458-0.3810.600* *-0.3450.561*0.160
溶解性总氮DTN0.012-0.3770.2380.0670.3290.671* *
溶解性有机氮DON0.071-0.4250.2380.0650.4080.653* *
NH+4-N-0.3230.360-0.072-0.043-0.570*-0.070
NO-3-N-0.0470.127-0.0230.1000.051-0.158
*表示在P<0.05水平显著相关,* *表示在P0.01水平极显著相关

土壤有机碳是土壤微生物的能源和营养源,土壤易氧化碳是有机碳中的活性部分,对土壤生物学性质的影响较有机碳指标敏感[40]。有学者认为较高的有机碳含量能促进糖苷酶、磷酸酶以及几丁质酶的合成[41, 42, 16],也有研究认为土壤有机碳与β-糖苷酶、几丁质酶和酚氧化酶不存在相关性[43]。这与有机碳是土壤长期积累的产物,而土壤酶活性受环境因素的影响而产生短时间的变化有关[44]。有关易氧化碳与酶活性的相关性的研究相对较少。有研究表明,磷酸酶与易氧化碳呈显著正相关[16]。也有研究表明,易氧化碳与酚氧化酶呈正相关,而与过氧化物酶呈负相关[45]。但本研究中土壤糖苷酶和酚氧化酶活性随着有机碳和易氧化碳的增加而降低,几丁质酶活性随着有机碳和易氧化碳的增加而增加,其它酶活性与有机碳和易氧化碳没有相关性。

土壤溶解性碳氮的生物有效性可通过影响微生物来影响土壤酶活性[46, 47];另一方面,土壤溶解性碳氮是复杂大分子如纤维素和蛋白质经酶催化的产物。从理论上推断,土壤溶解性碳氮与酶活性存在一定的相关性。一些研究表明糖苷酶和酸性磷酸酶与溶解性有机碳有显著正相关[16],但也有研究发现溶解性碳氮与酶活性并没有显著的相关性[44]。本研究表明,土壤溶解性有机碳与亮氨酸氨基肽酶呈极显著的正相关,与酚氧化酶呈显著正相关;溶解性有机氮与过氧化物酶均呈极显著正相关;但土壤溶解性碳氮与几丁质酶、糖苷酶和碱性磷酸酶相关性均不显著。此外,除铵态氮与酚氧化酶有显著负相关性外,无机氮与各种酶活性之间的关系均不显著。

5 结论

(1) 不同种类的酶活性在不同植被类型间的差异有一定的区别,但这种区别并没有一致的规律。研究表明苔藓植被下土壤的糖苷酶和酚氧化酶活性显著高于草本和灌丛,这说明苔藓植被土壤有利于有机碳的转化。由于草本植被的过氧化物酶活性显著高于苔藓和灌丛,因此,草本植被可促进土壤有机碳的积累。灌丛植被下土壤几丁质酶活性显著高于苔藓和草本,这表明灌丛植被下土壤中几丁质酶水解的速度要高于其它植被类型。针对不同植物类型土壤影响有机质转化的差异,丰富植物的多样性可加速土壤的生态过程。

(2) 不同植物类型间土壤酶活性的差异受土壤多因子的影响。本研究表明土壤水分含量是影响水陆交错带土壤酶活性的主要因素,它有利于糖苷酶和酚氧化酶活性的提高,但抑制几丁质酶和碱性磷酸酶活性。其次,土壤有机碳也影响着土壤酶活性的变化,但有机碳类型不同,影响的程度也不一致。土壤总有机碳和易氧化碳可以诱导几丁质酶的生成,但降低了糖苷酶、酚氧化酶的活性;而土壤溶解性有机碳的升高,可诱导亮氨酸氨基肽酶和酚氧化酶活性的提高。土壤溶解性有机氮则能提高过氧化物酶的活性,但对其它酶活性均无影响。

在漓江水陆交错带,由于水的冲刷引起地表微地形起伏不定,引起了土壤性质的空间变异。土壤性质的变异,又是影响酶活性的主要因素。因此不同植被类型之间酶活性的差异,不仅与植被类型有关,也与微地形以及土壤性质的空间异质性有密切关系。对不同植被类型影响土壤酶活性的研究,需运用土壤控制试验手段,开展长期研究。

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