Volume 37 Issue 3
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XU Chuanhong, LU Mingxing, FAN Diwu, CHENG Hu, HAN Jiangang. Effects of wetland reclamation on kinetic characteristics of soil alkaline phosphatase[J]. Journal of Zhejiang A&F University, 2020, 37(3): 522-530. doi: 10.11833/j.issn.2095-0756.20190388
Citation: XU Chuanhong, LU Mingxing, FAN Diwu, CHENG Hu, HAN Jiangang. Effects of wetland reclamation on kinetic characteristics of soil alkaline phosphatase[J]. Journal of Zhejiang A&F University, 2020, 37(3): 522-530. doi: 10.11833/j.issn.2095-0756.20190388
shu

Effects of wetland reclamation on kinetic characteristics of soil alkaline phosphatase

doi: 10.11833/j.issn.2095-0756.20190388
  • 1.

    College of Biology and Environment, Nanjing Forestry University, Nanjing 210037, Jiangsu, China

  • 2.

    Co-Innovation Center for the Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, Jiangsu, China

  • 3.

    National Positioning Observation Station of Hung-tse Lake Wetland Ecosystem in Jiangsu Province, Hongze 223100, Jiangsu, China

  • Received Date: 2019-06-26
  • Rev Recd Date: 2019-11-24
    • Available Online: 2020-05-21
  • Publish Date: 2020-06-01
  •   Objective  Enzyme kinetics study is a crucial method to reveal nutrient transformation in soil. The purpose of this study is to investigate the effects of wetland reclamation on transformation and availability of soil phosphorus and provide theoretical basis for nutrient conversion efficiency and quality improvement of wetland.  Method  Eight kinds of soil with different natural covers or land use patterns were collected in Hung-tse Lake estuary (shoal, Phragmites communis, Populus and paddy field) and Chongming Dongtan wetlands (shoal, Spartina alterniflora, P. communis and wheat field), and the soil alkaline phosphatase (ALP) was taken as an example to study kinetic characteristics of enzymatic reaction. One-Way ANOVA was used to compare the difference of soil ALP dynamic parameters under different land uses, and the correlation between physical and chemical properties of soil and kinetic parameters was explored by using redundancy analysis.  Result  Vmax (maximum reaction rate) and Km (Michaelis constant) of ALP kinetic parameters increased by 13.0%−313.4% and 21.0%−50.8%, respectively in Hung-tse Lake wetland, no matter whether the shoal naturally evolved into P. communis, or the reclaimed P. communis wetland into Populus plantation or paddy field. However, the Vmax/Km (catalytic efficiency) decreased by 25.0% during natural succession and increased by 2.3 times after artificial reclamation. For Chongming Dongtan wetland, Vmax and Km increased by 7.0 times and 6.2 times, and Vmax/Km increased by 11.1% after the transformation of shoal into P. communis. Moreover, the Vmax, Km and Vmax/Km decreased by 54.8%, 47.0% and 13.3% respectively after the conversion of P. communis into wheat field. Redundancy analysis results indicated that the Vmax/Km was positively correlated with total nitrogen (Hung-tse Lake) and organic carbon (Chongming Dongtan).  Conclusion  The total ALP significantly increased when the shoal was transformed into P. communis wetland, but the affinity between enzyme and substrate decreased. The Vmax/Km of ALP was significantly influenced by land use type and management mode after artificial reclamation. Increasing soil total nitrogen and organic carbon is beneficial to improvement of ALP catalytic efficiency no matter whether the land type is natural cover or artificial reclamation. [Ch, 1 fig. 3 tab. 43 ref.]
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Effects of wetland reclamation on kinetic characteristics of soil alkaline phosphatase

doi: 10.11833/j.issn.2095-0756.20190388
  • 1. College of Biology and Environment, Nanjing Forestry University, Nanjing 210037, Jiangsu, China
  • 2. Co-Innovation Center for the Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, Jiangsu, China
  • 3. National Positioning Observation Station of Hung-tse Lake Wetland Ecosystem in Jiangsu Province, Hongze 223100, Jiangsu, China
  • Received Date: 2019-06-26
  • Rev Recd Date: 2019-11-24
  • Available Online: 2020-05-21
  • Publish Date: 2020-06-01

Abstract:   Objective  Enzyme kinetics study is a crucial method to reveal nutrient transformation in soil. The purpose of this study is to investigate the effects of wetland reclamation on transformation and availability of soil phosphorus and provide theoretical basis for nutrient conversion efficiency and quality improvement of wetland.  Method  Eight kinds of soil with different natural covers or land use patterns were collected in Hung-tse Lake estuary (shoal, Phragmites communis, Populus and paddy field) and Chongming Dongtan wetlands (shoal, Spartina alterniflora, P. communis and wheat field), and the soil alkaline phosphatase (ALP) was taken as an example to study kinetic characteristics of enzymatic reaction. One-Way ANOVA was used to compare the difference of soil ALP dynamic parameters under different land uses, and the correlation between physical and chemical properties of soil and kinetic parameters was explored by using redundancy analysis.  Result  Vmax (maximum reaction rate) and Km (Michaelis constant) of ALP kinetic parameters increased by 13.0%−313.4% and 21.0%−50.8%, respectively in Hung-tse Lake wetland, no matter whether the shoal naturally evolved into P. communis, or the reclaimed P. communis wetland into Populus plantation or paddy field. However, the Vmax/Km (catalytic efficiency) decreased by 25.0% during natural succession and increased by 2.3 times after artificial reclamation. For Chongming Dongtan wetland, Vmax and Km increased by 7.0 times and 6.2 times, and Vmax/Km increased by 11.1% after the transformation of shoal into P. communis. Moreover, the Vmax, Km and Vmax/Km decreased by 54.8%, 47.0% and 13.3% respectively after the conversion of P. communis into wheat field. Redundancy analysis results indicated that the Vmax/Km was positively correlated with total nitrogen (Hung-tse Lake) and organic carbon (Chongming Dongtan).  Conclusion  The total ALP significantly increased when the shoal was transformed into P. communis wetland, but the affinity between enzyme and substrate decreased. The Vmax/Km of ALP was significantly influenced by land use type and management mode after artificial reclamation. Increasing soil total nitrogen and organic carbon is beneficial to improvement of ALP catalytic efficiency no matter whether the land type is natural cover or artificial reclamation. [Ch, 1 fig. 3 tab. 43 ref.]

XU Chuanhong, LU Mingxing, FAN Diwu, CHENG Hu, HAN Jiangang. Effects of wetland reclamation on kinetic characteristics of soil alkaline phosphatase[J]. Journal of Zhejiang A&F University, 2020, 37(3): 522-530. doi: 10.11833/j.issn.2095-0756.20190388
Citation: XU Chuanhong, LU Mingxing, FAN Diwu, CHENG Hu, HAN Jiangang. Effects of wetland reclamation on kinetic characteristics of soil alkaline phosphatase[J]. Journal of Zhejiang A&F University, 2020, 37(3): 522-530. doi: 10.11833/j.issn.2095-0756.20190388
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  • 土壤磷酸酶水解土壤有机磷，提高磷素有效性，在土壤磷素转化及生物利用过程中具有重要调节作用[1-3]。湿地生态系统不仅是重要的磷素储备库，在微生物主导的有机磷矿化过程中释放磷素，为植物生长供应重要的磷源，而且其独特的干湿交替水文条件增加了磷素转化的复杂性。自21世纪初以来，湿地磷素的转化过程越来越受到学者们的重视[4]，特别是湿地土地利用/覆被变化影响下土壤磷酸酶变化的研究日益增多[5-6]。宁沐蕾等[7]和KANG等[8]研究了崇明岛湿地土壤碱性磷酸酶(ALP)活性，表明转变稻田为樟树Cinnamomum camphora和水杉Metasequoia glyptostroboides林地后ALP活性增大。王树起等[9]以三江平原湿地为例，研究湿地土地利用变化下的土壤磷酸酶活性变化，表明草甸开垦为农田后ALP活性降低58.5%，而旱地农田转变为湿地草甸或白桦Betula platyphylla林地后，ALP活性分别增高31.7%和18.7%。与以上结果中农田利用下土壤酶活性低于林地和草甸不同的是，任勃等[10]对洞庭湖湿地的研究表明：水田土壤ALP活性高于杨树Populus林地和芦苇Phragmites communis地。刘云鹏等[11]对黄河中游湿地的研究也报道：棉田土壤ALP活性成倍(1.7倍)高于蒲草Typha orientalis植被。而刘琛等[12]则对海涂围垦区湿地的研究认为：农田(棉花Gossypium hirsutum、水稻Oryza sativa)与林地间土壤磷酸酶活性无明显差异。由此可见，目前有关湿地不同覆被类型与土地利用下土壤ALP活性变化的研究结论并不一致，有待进一步深入剖析。土地利用变化不但影响土壤酶活性，而且对酶促反应动力学特征产生重要影响，如NOURBAKHSH等[13]指出：天然草地转变为人工苜蓿Medicago sativa种植地后土壤脲酶的米氏常数(Km)提高。LOEPPMANN等[14]研究哥廷根下萨克森州农业区的草地转变为玉米Zea mays田后土壤酶的动力学特征，结果表明：酸性磷酸酶的最大酶促反应速率(Vmax)和Km减小，Vmax/Km增大，而β-葡萄糖苷酶的Vmax、Km和Vmax/Km均减小。北美原生态草原的草地和森林转变为耕地后，淀粉酶的Vmax和Km均减小[15]。以往有关围垦改变土地利用方式对土壤酶的酶促反应动力学特征影响的研究多在山地、草原等陆地生态系统进行，而对湿地土壤酶的酶促反应动力学特征的研究，特别是对ALP的研究还很不充分。全球气候变化与人为活动加速影响下，生产和生态两重压力下湿地资源保护与合理利用之间的矛盾愈加尖锐[16-17]。其中，湿地围垦对包括土壤磷素在内的养分转化的影响备受关注。本研究采集洪泽湖和崇明东滩湿地不同覆被或土地利用方式下共8种土壤，以ALP为例，研究自然演替和围垦利用对湿地ALP动力学参数的影响，为湿地养分转化效率及质量提升提供理论依据。

    • 1.   材料与方法

      1.1.   研究区概况

    • 洪泽湖(33°14′16″N，118°18′43″E)位于江苏省西部淮河下游，属于亚热带季风气候。由于泥沙淤积而在河湖交汇处形成光滩，随演替的推进，光滩演变为芦苇并成为当地优势种。随芦苇地的淤高，刈割芦苇栽种杨树(在人工林中占比达95%以上)或种植水稻，稻田和人工林取代芦苇而成为主要土地利用方式。

      崇明东滩(31°37′31″N，121°23′33″E)位于崇明岛东部，属长江口典型的河口湿地。随光滩的淤积，芦苇和互花米草Spartina alterniflora演变为优势物种。人为活动对土地利用方式的影响表现为人为刈割芦苇或互花米草，转变土地利用方式为小麦Triticum sestivum田。

      • 1.2.   土壤样品采集

    • 2017年4月采集崇明东滩的光滩、互花米草、芦苇和小麦样地土壤，于2017年7月采集洪泽湖的光滩、芦苇、杨树人工林和水稻样地土壤。2种样地的农田耕作和人工林种植时间均达20 a以上[18]。通过“S”形布点法(7个样点)在各样地(20 m×20 m)采集土样，各样点土壤通过“四分法”合并为1个土样，每个样地均取0~20 cm的表层土壤10 kg，自然风干后过2 mm的筛，保存于阴凉干燥处待用。

      • 1.3.   土壤理化性质的测定

    • pH值(水土比2.5∶1.0)通过雷磁pH计测定；有机碳(OC)使用高锰酸钾外加热法测定；全氮(TN)使用凯氏法，通过流动分析仪测定；电导率(EC，水土比5∶1)通过电导率测定仪测定；土壤粒径测定参考文献[19]；土壤全磷(TP)和无机磷(IP)通过灼烧法[20]测定，有机磷(OP)通过TP与IP的值相减得到，微生物量碳(MBC)采用氯仿熏蒸-硫酸钾浸提法[21]测定。结果见表1。

      湿地 土地类型 pH值 OC/(g·kg−1) TN/(g·kg−1) TP/(g·kg−1) MBC/(mg·kg−1) OP/(mg·kg−1) IP/(mg·kg−1)
      洪泽湖 光滩 8.65 15.2 0.58 0.42 108.5 114.1 306.1
      芦苇 8.60 17.7 0.56 0.36 82.1 37.2 324.6
      杨树 8.37 26.5 0.62 0.45 138.0 47.0 402.6
      水稻田 8.17 91.9 0.63 0.40 131.4 15.7 379.6
      崇明东滩 光滩 8.53 9.6 0.17 0.57 112.4 46.9 523.5
      互花米草 8.36 14.2 0.64 0.54 83.7 33.5 502.1
      芦苇 8.51 17.7 0.27 0.53 82.0 26.0 504.8
      小麦田 8.26 11.1 0.61 0.66 133.8 46.2 609.1
      湿地 土地类型 EC/(mS·cm−1) C∶N 不同土壤粒径分布/%
      0.1~2.0 2.0~63.0 63.0~200.0 200.0~2 000.0 μm
      洪泽湖 光滩 0.81 26 3.23 76.47 17.95 2.35
      芦苇 0.79 31 0.60 14.97 83.78 0.65
      杨树 2.08 42 1.35 75.68 20.79 2.18
      水稻田 1.14 146 2.16 77.93 18.67 1.24
      崇明东滩 光滩 0.86 55 7.94 88.80 2.08 1.18
      互花米草 0.78 22 0.02 87.55 8.63 3.80
      芦苇 0.39 65 4.93 77.36 17.63 0.08
      小麦田 0.14 18 0.14 95.87 2.31 1.68

      Table 1.  Soil basic physicochemical properties under different land uses

      • 1.4.   酶促反应动力学

    • ALP活性的测定参照文献[22]。称取2.0 g土样置于20 mL棕色小玻璃瓶中，设置3组平行，加入pH 8.4的氨基丁三醇盐酸(Tris-HCl)缓冲液3.0 mL，土样分别加入0、1.7、2.0、2.5、3.3、5.0和10.0 mmol·L−1对硝基苯磷酸二钠(PNPP)溶液1 mL，加入0.5 mol·L−1 氯化钙(CaCl2)溶液1 mL，摇匀，37 ℃水浴1 h(对照组不水浴)，取出玻璃瓶，立刻加入0.5 mol·L−1 氢氧化钠(NaOH)4.0 mL终止反应，过滤。取滤液5.0 mL于25 mL具塞比色管中，加入2.0 mol·L−1 氨基丁三醇(Tris)溶液2 mL，定容，采用紫外分光光度计(UV-2550型)在400 nm波长下测定对硝基苯酚(p-NP)吸光度(ALP活性以1 kg土壤1 h生成的p-NP的量表示)。ALP活性计算如下：

      式(1)中：V为ALP活性(mmol·kg−1·h−1)；C1和C0分别为25 mL具塞比色管中处理组和对照组p-NP浓度(mmol·L−1)；m为土壤质量(g)；t为水浴时间(h)。

      酶促反应动力学参数计算如下：

      式(2)中：V为酶促反应速率(mmol·kg−1·h−1)；Km为米氏常数(mmol·L−1)；Vmax为最大酶促反应速率(mmol·kg−1·h−1)；[S]为底物浓度(mmol·L−1)。

      • 1.5.   统计方法

    • 采用CANOCO 5.0进行数据的统计分析，使用Excel 2010制作表格。运用冗余分析方法分析酶促反应动力学参数与土壤基础理化性质的相关性，采用SPSS 20.0进行单因素方差分析。ALP活性以平均值±标准差的形式表示。

    2.   结果与分析

      2.1.   不同覆被/土地利用下ALP活性

    • 底物PNPP在0、1.7、2.0、2.5、3.3、5.0和10.0 mmol·L−1的不同浓度下，土壤ALP活性表现出随PNPP浓度的增加而增大的趋势(表2)。自然覆被和人为土地利用方式下ALP活性差异显著(P＜0.05)。光滩转变为芦苇湿地的自然演替过程中，洪泽湖湿地不同PNPP浓度下ALP活性平均减小约10.9%，而在崇明东滩湿地表现为增大74.0%。崇明东滩互花米草入侵光滩后，ALP活性仅增加10.7%。人类活动影响下，洪泽湖芦苇湿地转变为人为利用方式杨树林地或水稻田后，ALP活性增大约为2.2~2.3倍。而崇明东滩芦苇和互花米草湿地转变为小麦田后，ALP活性分别减小17.9%和增加23.3%。

      湿地 土地
      类型      		 不同PNPP浓度下ALP活性/(mmol·kg−1·h−1)
      0 1.7 2.0 2.5 3.3 5.0 10.0 mmol·L−1
      洪泽
      湖      		 光滩 0.001±0.001 Ag 0.090±0.001 Cf 0.096±0.004 Be 0.114±0.003 Bd 0.124±0.007 Cc 0.166±0.004 Bb 0.217±0.003 Ca
      芦苇 0.001±0.000 Af 0.074±0.003 De 0.086±0.005 Bde 0.097±0.002 Cd 0.115±0.014 Cc 0.148±0.004 Bb 0.223±0.010 Ca
      杨树 0.001±0.000 Ag 0.254±0.010 Af 0.307±0.008 Ae 0.351±0.019 Ad 0.431±0.006 Ac 0.554±0.010 Ab 0.784±0.018 Aa
      水稻 0.001±0.001 Ag 0.243±0.001 Bf 0.290±0.011 Ae 0.344±0.004 Ad 0.394±0.008 Bc 0.557±0.003 Ab 0.724±0.007 Ba
      崇明
      东滩      		 光滩 0.003±0.000 Ae 0.332±0.000 Dd 0.370±0.004 Dcd 0.443±0.004 Dbcd 0.510±0.008 Cbcd 0.624±0.010 Db 0.845±0.011 Ca
      互花
      米草      		 0.003±0.001 Ag 0.361±0.010 Cf 0.408±0.000 Ce 0.467±0.002 Cd 0.587±0.003 Cc 0.713±0.003 Cb 0.852±0.01 C6a
      芦苇 0.003±0.000 Ag 0.47±00.048 Af 0.568±0.019 Ae 0.713±0.018 Ad 0.950±0.005 Ac 1.362±0.051 Ab 2.002±0.011 Aa
      小麦 0.003±0.000 Ag 0.382±0.012 BDf 0.450±0.006 BDe 0.645±0.014 Bd 0.662±0.011 Bc 1.023±0.016 Bb 1.510±0.015 Ba
      　　说明：不同小写字母表示某一土地利用/覆被土壤不同PNPP浓度下ALP活性差异显著(P＜0.05)，不同大写字母表示某一PNPP浓度下不同　　　　　土地利用/覆被土壤ALP活性差异显著(P＜0.05)

      Table 2.  ALP activities with the concentration of PNPP in different land use changes

      • 2.2.   不同土地利用/覆被下ALP酶促反应动力学特征

    • ALP动力学参数的研究结果表明：洪泽湖和崇明东滩湿地自然覆被下的光滩、芦苇/互花米草和人为利用下的杨树、水稻和小麦土壤ALP的Vmax和Km差异显著(P＜0.05)(表3)。洪泽湖光滩转变为芦苇湿地的自然演变过程中，Vmax和Km分别增加13.0%和50.8%，Vmax/Km减少25.0%；土地利用类型由芦苇转变为稻田和杨树人工林后，Vmax、Km和Vmax/Km的增长幅度分别为290.6%~313.4%、21.0%~21.7%和224.4%~239.6%。相比较而言，崇明东滩湿地光滩演变为芦苇植被后，Vmax增加697.1%，Km 增加622.4%，Vmax/Km增加11.1%。而互花米草入侵光滩后，Vmax和Vmax/Km分别增加7.9%和10.2%，Km 变化不明显。刈割芦苇栽种小麦，Vmax、Km和Vmax/Km分别减少54.8%、47.0%和13.3%。不难发现，洪泽湖湿地光滩和芦苇植被土壤ALP的Vmax/Km显著小于稻田和杨树人工林(P＜0.05)，而崇明东滩湿地表现为麦田土壤ALP的Vmax/Km小于光滩、芦苇和互花米草植被，两地自然覆被与土地围垦利用后土壤ALP的Vmax/Km表现出较大的变化差异。

      湿地 土地类型 Vmax/(mmol·kg−1·h −1) Km/(mmol·L−1) Vmax/Km/(L·kg−1·h−1)
      洪泽湖　 光滩　　 0.28 b 3.74 c 0.08 b
      芦苇　　 0.32 b 5.64 b 0.06 b
      杨树　　 1.32 a 6.87 a 0.19 a
      水稻　　 1.26 a 6.83 a 0.18 a
      崇明东滩 光滩　　 1.19 d 4.32 c 0.27 a
      互花米草 1.28 c 4.23 c 0.30 a
      芦苇　　 9.44 a 31.22 a 0.30 a
      小麦　　 4.27 b 16.53 b 0.26 a
      　　说明：不同小写字母表示不同土地利用/覆被土壤下ALP动力学参数差异显著(P＜0.05)

      Table 3.  Kinetics of enzyme-catalyzed reactions of ALP under different land uses

      • 2.3.   Vmax、Km和Vmax/Km与土壤理化性质的关系

    • 洪泽湖和崇明东滩湿地土壤ALP的动力学参数受土壤磷素的存在形式和碳氮质量分数影响明显(图1)，洪泽湖湿地土壤IP质量分数的增加有利于Vmax的增大，土壤OP的增大抑制Km的增加，C∶N、OC的增大有利于Km的增大，TN和EC质量分数的增加有利于Vmax/Km的增大。崇明东滩湿地0.1~2.0 μm粒径土壤的增大对ALP的Vmax增大起到抑制作用，TN质量分数的减小有利于Km的增大，OC质量分数和63.0~200.0 μm粒径土壤的增大有利于Vmax/Km的增加，而MBC增大则抑制Vmax/Km的提高。

      Figure 1.  Redundancy analysis between Vmax, Km and Vmax/ Km of Hung-tse Lake (A) and Chongming Dongtan (B) ALP and soil physiochemical properties

    3.   讨论

      3.1.   覆被变化/围垦利用对ALP活性的影响

    • 杨文彬等[23]以漓江水陆交错带为例研究不同覆被下土壤酶活性变化，结果表明：苔藓植被自然演变为灌丛后，ALP活性增加30.9%~36.9%。HUANG等[24]发现盐城滨海湿地光滩转变为芦苇或互花米草植被后，ALP活性增大，其中土壤OC和TN的增加是导致ALP活性增大的重要因素。本研究中崇明东滩湿地光滩演变为芦苇或互花米草的自然演替过程中，土壤OC、TN和ALP活性均增大，与以往研究结果一致。有所不同的是洪泽湖光滩演变为芦苇湿地后，ALP活性降低10%，这可能与土壤OC和TN变化均不明显有关。

      天然湿地经过人为围垦利用后，ALP活性呈现增大趋势，如黄莉[25]研究人类活动影响下土壤酶的变化发现：鄱阳湖湿地经过围垦后土壤微生物活性提高，磷酸酶活性增大。湖北荆江天然河流湿地围垦为稻田后ALP活性增加72%[26]。本研究中，洪泽湖芦苇湿地转变杨树林地或水稻田，崇明东滩互花米草植被转变为小麦田后ALP活性显著增大(P＜0.05)，与以往研究结果一致。人为转变土地利用方式后，土壤MBC质量分数也表现为明显增大，表明微生物群落活跃程度提高，与ALP活性变化一致。值得指出的是，崇明东滩湿地芦苇湿地转变为农田后，ALP活性降低约17.7%，这可能受土壤C∶N的显著下降影响[27]。

      • 3.2.   覆被变化对Vmax、Km和Vmax/Km的影响

    • 酶促反应动力学参数中，Vmax表示酶被底物完全饱和时的反应速度，反映土壤酶的总量及酶-底物复合物分解为酶和产物的能力[28]，Km表征酶与底物亲和力[29]，Vmax/Km表征酶的催化效率[30-31]。本研究中洪泽湖和崇明东滩湿地光滩演变为芦苇植被，Vmax增大，植被增加使得由土壤微生物活动、植物根系分泌物和动植物残体腐解过程分泌的ALP含量增大[32-33]。刘存歧[34]也指出：崇明东滩潮滩沉积物中ALP的Vmax表现为芦苇湿地大于光滩土壤，本研究结果与其一致。值得指出的是，崇明东滩湿地光滩演变为互花米草(入侵物种)植被后，Vmax无明显变化，可能是因为崇明东滩互花米草入侵加快土壤有机质降解，而可培养微生物菌落数却显著降低[35-36]。光滩演变为芦苇植被后两地土壤ALP的Km均表现为显著增大(P＜0.05)，这可能与有机质对ALP的吸附有关[37]。TISCHER等[38]也发现：安第斯山脉草地自然演变为有机质含量更丰富的灌木林后土壤酸性磷酸酶的Km增大。本研究结果与其相似。

      • 3.3.   湿地围垦利用后Vmax、Km和Vmax/Km的变化

    • 人为转变土地利用方式后，土壤酶的Vmax和Vmax/Km减小，如KHALILI等[39]发现：伊朗中部扎格罗斯地区天然森林转变为耕地后，土壤纤维素酶Vmax和Vmax/Km减小；KNIGHT等[40]以俄勒冈州为例研究土地利用变化对土壤酶动力学特征的影响，结果表明：天然草地转变为农田后β-葡萄糖苷酶的Vmax和Vmax/Km减小。然而也有结果显示：人为土地利用变化可通过施肥等管理方式的影响使得土壤磷酸酶的Vmax和Vmax/Km增大。孔龙等[41]指出：农田耕作施加肥料而引起的土壤肥力增大可导致土壤磷酸酶的Vmax和Vmax/Km增大，邱莉萍等[31]也表明：小麦地土壤中OC和氮磷等营养指标的提高可促进ALP的Vmax增大。本研究中，洪泽湖湿地刈割芦苇栽植杨树或转变为稻田后，土壤OC质量分数均增加。常年农业化肥施用土壤TN质量分数提高的影响下，动力学参数Vmax和Vmax/Km显著增大(P＜0.05)，该结果与孔龙等[41]、邱莉萍等[31]的结果一致。此外，施肥作用影响下洪泽湖芦苇湿地转变为杨树人工林和水稻田后EC由0.79 mS·cm−1增加到2.08和1.14 mS·cm−1可能也是Vmax/Km增大的重要原因。相关性分析结果也表明：Vmax/Km与土壤TN和EC存在正相关关系。值得指出的是，崇明东滩湿地芦苇地转变为小麦田后ALP的Vmax和Vmax/Km均降低，可能受农业旱地土壤OC养分的淋失影响。其中Vmax的降低可能还与EC的淋失有关。相关性分析也表明：崇明东滩湿地土壤ALP的Vmax与EC存在正相关关系。小麦地在常年施肥影响下TN质量分数增大1.3倍，而OC质量分数降低37.3%，这可能是Vmax/Km下降的重要原因。相关性分析结果也显示：OC的减少不利于ALP的Vmax/Km增大。一方面，高质量分数OC有利于ALP的合成，有机质的吸附作用可减少酶的损失[42]，另一方面土壤中有机质是土壤酶促反应的重要能量来源[43]，因而低质量分数OC抑制ALP整体催化效率。人为围垦后崇明东滩土壤ALP的Km降低可能与土壤OC质量分数的降低有关，围垦芦苇湿地为麦田后OC质量分数降低，低质量分数有机质对ALP的吸附作用较小，增大酶与底物结合的机会[37]。

    4.   结论

    • 洪泽湖和崇明东滩湿地，在光滩自然演变为芦苇湿地过程中，Vmax和Km均增大，ALP的总量增加，但酶与底物亲和力下降。洪泽湖围垦芦苇湿地为杨树人工林或水稻田，Vmax/Km增加，崇明东滩围垦芦苇湿地为小麦田，Vmax/Km下降，林地和水稻田相比较于小麦田可能更有利于土壤酶催化效率的增加。相关性分析结果表明：洪泽湖和崇明东滩湿地土壤ALP的Vmax/Km分别与TN和OC密切正相关。可见，湿地围垦后的土地利用类型及管理方式可能对ALP的Vmax/Km产生显著影响，提高土壤TN和OC质量分数有利于ALP催化效率的提升。

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