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土壤微生物是土壤有机质分解和养分周转的主要参与者[1]。土壤酶作为微生物代谢的指标,推动着土壤微生物分解有机质,在土壤碳、氮、磷循环过程中发挥着重要的作用[2]。Sinsabaugh等研究认为,水解酶的活性可以作为微生物营养需求的指标,而且在C、N和P周转相关的酶活性之间也存在化学计量关系[3]。相关研究将微生物用于获取碳、氮、磷养分的主要水解酶的比值 (βG∶NAG∶AP),称为生态酶化学计量比,能够反映土壤微生物群落的养分需求和利用能力,并与土壤养分循环、转化及其有效性联系起来,可用来衡量土壤微生物能量和养分资源的限制状况[3-5]。已有的研究表明生态酶活性及其计量比受到温度、水分、pH值、养分有效性、微生物生物量以及植被特征等因素的影响[6-10],而将土壤-微生物生物量-酶化学计量比结合起来的研究鲜有报道。
杉木 (Cunninghamia lanceolata (Lamb.) Hook.) 为我国南方主要造林树种,栽培面积大 [11]。近几十年来,由于杉木林长期单一的纯林经营,造成连栽杉木人工林的土壤肥力退化、生产力下降等问题[12-15]。已有研究表明,对杉木人工林进行间伐、套种等改造,能够改善林分质量,丰富生物多样性[16];杉木纯林在套种改造后形成混交林的土壤微生物生物量[17]、土壤肥力和土壤酶活性[18]也得到提高。但过去关于杉木林下套种阔叶树的研究更多地仅关注套种后土壤理化性质及养分的变化,从土壤酶活性及其化学计量比角度的研究较少。为此,本研究在三明格氏栲自然保护区建立杉木林下套种阔叶树试验,研究套种后土壤酶活性及生态酶计量比的特征,以探讨杉木林下套种阔叶树对提高土壤肥力、促进土壤养分周转的效果。
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试验区位于福建省三明市格氏栲自然保护区 (117°28′ E,26°11′ N) 内,该区属于中亚热带季风气候,夏热冬冷且雨热同季,年均温19~20 ℃,年降水量达1 740 mm。保护区内平均海拔300~350 m,以低山丘陵为主,植物群落种类丰富且分层明显。土壤主要以红壤和黄壤为主,多呈酸性,土壤厚度超过1 m。
自2014年4月开始,在三明格氏栲自然保护区建立杉木林下套种阔叶树的杉木林试验区。套种前先对林地进行疏伐、清除林下杂草、穴状整地,每个处理的立地条件、坡向、坡位等条件基本一致,明穴规格为40 cm × 30 cm × 30 cm,林分株行距为2 m × 3 m。设置3种套种处理,分别为杉木成熟林套种阔叶树 (套种成熟林)、杉木幼林套种阔叶树(套种幼林)和杉木纯林(对照),每种处理设置20 m × 20 m的标准样地5个。套种阔叶树种的杉木林龄分别为51年生和4年生,杉木纯林的林龄为4年生。林下套种的种植密度以各阔叶树种生长后能覆盖地表为宜,套种的阔叶树均为3年生,包括马褂木 (Liriodendron chinense (Hemsl.) Sarg.)、火力楠(Michelia macclurei Dandy)和乐昌含笑(Michelia chapensis Dandy),三者比例为1∶1∶1。栽植后于当年8—9月抚育1次,次年8—9月进行第二次抚育,抚育内容主要包括松土、清除林地杂草等,以促进幼林良好地生长[19]。
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2018年10月,在套种的每个样地内按“S” 型选5个点,用土钻取表层土壤 (0~10 cm),将土壤分别充分混合均匀并去除可见的细根和石砾等,再将土样过2 mm筛装入自封袋。一部分存在 4℃冰箱中,用于测定土壤含水量、微生物生物量、碳、氮、磷 (MBC、MBN、MBP)含量、土壤酶活性等,另外一部分自然风干,主要用来测定土壤pH值和土壤全碳 (TC)、全氮 (TN)、全磷 (TP) 含量等。
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土壤含水量运用铝盒烘干衡定法测定,采用ElementarVario MAX碳氮元素分析仪 (GmbH,Hanau,Germany) 测定土壤TC和TN含量;土壤TP 含量的测定则加入浓硫酸-高氯酸消煮后提取待测溶液,使用连续流动分析仪 (Skalar san++,Skalar,荷兰) 测定。
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土壤微生物量运用氯仿熏蒸-浸提法,每个鲜土样各称取5份(5 × 5 g),两组土样放到50 mL小烧杯中做熏蒸处理,另两组土样放到离心管中,放不含氯仿的干燥器中做未熏蒸处理,剩余一组加入62.5 μL的1 000 mg· kg−1磷标液,放置24 h进行加标回收实验。24 h后,将烧杯中的熏蒸土样取出,土壤微生物生物量碳和氮 (MBC、MBN) 用2 mL 0.5 mol·L−1 K2SO4洗至离心管中,土壤微生物生物量磷 (MBP) 用20 mL 0.5 mol·L−1 NaHCO3洗至离心管中。未熏蒸的土样则分别直接加入20 mL 0.5 mol·L−1 K2SO4和20 mL 0.5 mol·L−1 NaHCO3。MBC含量用总有机碳分析仪 (TOC-VCPH/CPN,Shimadzu,日本)测定,MBN、MBP含量用连续流动分析仪 (San++,Skalar,荷兰)测定。
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土壤酶活性测定参考Saiya-Cork等[20-21]的方法,各样品分别称取 1 g 土壤加入125 mL 50 mmol·L−1且pH 值为5.0的醋酸缓冲液中,制成悬浮液,静置30 min取上清液200 µL加入96孔微孔板中。每个样品有16个重复 (200 µL样品溶液+50 µL 200 µmol·L–1底物溶液),8个阴性对照 (200 µL醋酸缓冲溶液+50 µL底物溶液)、8个空白 (200 µL样品溶液+50 µL缓冲溶液) 和8个淬火标准液 (200 µL样品溶液+50 µL标准液) 及淬火标准对照液(200 µL缓冲液+50 µL标准液)进行校正。再将微孔板置于20℃黑暗培养箱中恒温培养4 h后取出,加入1 mol·L–1 NaOH至每个微孔井使其终止反应。最后采用Synergy H4多功能酶标仪 (Molecular Devices, San Jose, USA) 检测荧光度,酶活性以每小时每克干物质产生底物的摩尔数 (nmol·g–1·h–1) 来表达。各种土壤酶的名称、缩写、类型及所用标定底物详细见表1。
表 1 土壤酶的种类、缩写、类型和所用底物
Table 1. The abbreviations,type and substrates of soil enzyme
酶
Enzyme缩写
Abbreviation类型
Type底物
Substrate酸性磷酸酶 Acid phosphatase AP P-targetinghydrolytic 4-MUB-phosphate β-葡萄糖苷酶 β-glucosidase βG C-targeting hydrolytic 4-MUB-β-D-glucoside β-N-乙酰氨基葡萄糖苷酶 β-N-acetylglucosaminidase NAG N-targeting hydrolytic 4-MUB-N-acetyl-β-D-glucosaminide -
数据经Microsoft Excel 2019软件处理后,使用SPSS 22.0软件进行分析,通过单因素方差分析(One-way ANOVA) 检验不同套种处理下土壤理化性质、土壤微生物生物量、生态酶活性及其化学计量比的差异显著性,并用Pearson相关分析法分析土壤酶活性及其化学计量比与土壤理化性质和微生物生物量碳氮等指标的相关性。使用Canoco Software5.0 软件对生态酶活性及其化学计量与土壤理化因子和微生物生物量的关系进行冗余分析(RDA)。
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如表2所示,杉木成熟林套种后土壤pH值、TC、TN含量显著高于套种幼林以及杉木纯林,而后两者之间无显著差异。不同的套种处理对土壤TP的含量无显著影响。不同处理之间土壤C:N、C:P、N:P差异显著,其中C:N的范围为13.31~9.36,变化趋势是套种成熟林 > 套种幼林 > 杉木纯林,C:P和N:P的范围分别是260.67~103.38和19.74~9.94,变化趋势则是套种成熟林的比值显著高于套种幼林和杉木纯林,而套种幼林与杉木纯林之间无显著差异。
表 2 不同套种处理土壤理化性质
Table 2. Physical and chemical properties of soil under different interplanting treatments
处理
Treatments套种幼林
Young interplanting forest套种成熟林
Mature interplanting forest杉木纯林
Pure Chinese fir plantation酸碱度 pH 4.308 ± 0.03 b 4.46 ± 0.07 a 4.16 ± 0.03 b 含水量 Soil water content/% 0.99 ± 0.11 a 0.92 ± 0.06 a 0.86 ± 0.13 a 总碳 Total carbon/(g·kg−1) 12.93 ± 0.90 b 19.84 ± 0.14 a 11.62 ± 0.79 b 总氮 Total nitrogen/(g·kg−1) 1.23 ± 0.06 b 1.51 ± 0.01 a 1.15 ± 0.03 b 总磷 Total phosphorus/(g·kg−1) 0.19 ± 0.08 a 0.08 ± 0.01 a 0.09 ± 0.01 a 碳氮比 C:N 10.68 ± 0.17 b 13.31 ± 0.14 a 9.36 ± 0.10 c 碳磷比 C:P 103.38 ± 22.12 b 260.67 ± 21.52 a 133.34 ± 17.6 6b 氮磷比 N:P 9.94 ± 2.16 b 19.74 ± 1.51 a 13.20 ± 1.59 b 注:表中数据为平均值 ± 标准差(n = 5),同一行不同小写字母表示不同处理间差异显著(P < 0.05)。
Notes: The data in the table are mean ± standard deviation (n = 5). Different lowercase letters in the same row indicate significant differences between different treatments (P < 0.05). -
土壤微生物生物量碳、氮、磷在不同套种处理间变化显著 (表3)。套种成熟林的微生物生物量碳(MBC)含量分别比套种幼林和杉木纯林高8.07%和14.90%。套种成熟林的微生物生物量磷(MBP)含量分别比套种幼林和杉木纯林高15.54%和36.75%。但是微生物生物量氮(MBN)含量在三者之间没有显著差异。杉木纯林土壤的MBN:MBP明显高于套种幼林,而与套种成熟林差异不显著。MBC:MBN以及MBC:MBP在不同套种处理之间的差异均不显著。
表 3 不同套种处理下微生物生物量及其计量比
Table 3. Microbial biomass and its metering ratio under different interplanting treatments
处理
Treatments套种幼林
Young interplanting forest套种成熟林
Mature interplanting forest杉木纯林
Pure Chinese fir plantation微生物生物量碳 MBC/(mg·kg−1) 317.16 ± 40.88 b 342.76 ± 15.56 a 298.31 ± 16.08 b 微生物生物量氮 MBN/(mg·kg−1) 13.11 ± 0.72 a 18.42 ± 1.86 a 15.64 ± 1.51 a 微生物生物量磷 MBP/(mg·kg−1) 43.00 ± 0.94 b 49.68 ± 0.94 a 36.33 ± 0.94 b MBC:MBN 25.03 ± 4.39 a 14.51 ± 2.38 a 24.24 ± 1.68 a MBC:MBP 7.34 ± 0.85 a 6.89 ± 0.23 a 8.26 ± 0.61 a MBN:MBP 0.31 ± 0.02 b 0.37 ± 0.04 ab 0.43 ± 0.05 a 注:表中数据为平均值 ± 标准差(n = 5),同一行不同小写字母表示不同处理间差异显著(P < 0.05)。
Notes: The data in the table are mean ± standard deviation (n = 5). Different lowercase letters in the same row indicate significant differences between different treatments (P < 0.05). -
不同的套种处理显著影响土壤酸性磷酸酶(AP)、β-葡萄糖苷酶(βG)和β-N-乙酰氨基葡萄糖苷酶(NAG)这3种土壤水解酶活性 (图1),其变化范围分别为93.29~60.81、0.70~0.22、0.96~0.71 nmol·g−1·h−1。其中AP酶活性在不同处理间的变化趋势是套种成熟林 > 套种幼林 > 杉木纯林;杉木纯林的βG酶活性显著高于套种成熟林和套种幼林,而套种成熟林和套种幼林之间没有显著差异性;套种成熟林的NAG酶活性最高且与套种幼林差异显著,而杉木纯林与其他两个处理间没有显著差异。如图2所示,杉木纯林βG:NAG和βG:AP显著高于套种成熟林和套种幼林,但βG:NAG和βG:AP在套种成熟林和套种幼林之间差异不显著。NAG:AP在各个处理之间的差异均不显著。
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Pearson相关分析(表4)表明土壤AP、NAG酶活性分别与土壤pH、TC、TN、MBP含量以及C:N、C:P、N:P和MBN:MBP显著正相关。其中土壤AP酶活性与土壤pH、TC、TN、MBP含量以及C:N、C:P和N:P呈极显著正相关 (P < 0.01),土壤NAG酶活性与pH值以及MBN:MBP呈显著正相关。而土壤生态酶计量比中NAG:AP与土壤理化性质相关性不显著,βG:NAG与MBP呈显著负相关、与MBN:MBP呈显著正相关,βG:AP与pH值和C:N 呈显著负相关,与MBP呈极显著负相关,而与MBN:MBP呈显著正相关。冗余分析表明土壤生态酶活性及其计量比与土壤C:N和MBC:MBN显著相关。如图3所示,第一轴解释了变量的98.72%,第二轴解释了变量的0.03%,其中土壤C:N、MBC:MBN和C:P分别解释土壤酶活性和生态酶化学计量比变化的92.3%、4.4%和1.6%。此外,土壤生态酶活性及其化学计量比可以将3种处理明显地区分开。
图 3 土壤酶活性和生态酶化学计量比与土壤理化因子的冗余分析
Figure 3. Redundant analysis of soil enzyme activity and ecological enzyme stoichiometry and soil physical and chemical factors
表 4 土壤酶活性、酶化学计量比与理化性质及土壤化学计量相关性
Table 4. Correlation between soil enzyme activity, enzyme stoichiometry and physicochemical properties and soil stoichiometry
相关性 Correlation AP βG NAG βG:NAG βG:AP NAG:AP pH 0.849** −0.352 0.590* −0.490 −0.532* −0.229 SWC −0.189 0.076 0.200 −0.048 0.125 0.383 TN 0.881** −0.226 0.455 −0.346 −0.404 −0.359 TC 0.946** −0.233 0.461 −0.315 −0.429 −0.427 TP −0.214 −0.296 −0.277 −0.244 −0.225 −0.122 C:N 0.968** −0.391 0.485 −0.500 −0.580* −0.422 C:P 0.809** 0.062 0.481 −0.028 −0.120 −0.238 N:P 0.667** 0.191 0.463 0.088 0.035 −0.104 MBC 0.605* −0.196 0.421 −0.301 −0.311 −0.141 MBN 0.462 0.346 0.256 0.222 0.198 −0.081 MBP 0.883** −0.487 0.432 −0.609* −0.651** −0.402 MBC:MBN −0.211 0.027 −0.218 −0.190 −0.219 −0.050 MBC:MBP −0.413 −0.131 0.397 0.476 0.401 0.096 MBN:MBP −0.061 −0.049 0.628* 0.587* 0.616* 0.229 注:*在0.05水平上显著相关;**在0.01水平上显著相关。
Notes:*Correlation is highly significant at the 0.05 level; ** Correlation is significant at the 0.01 level.
杉木林下套种阔叶树对土壤生态酶活性及其化学计量比的影响
Effects of Chinese Fir Interplanted with Broadleaved Trees on Soil Ecological Enzyme Activity and Stoichiometry
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摘要:
目的 研究杉木林下套种阔叶树的土壤生态酶活性及其化学计量比,评估该林分土壤养分和肥力状况。 方法 在福建省三明市格氏栲自然保护区杉木林试验示范区设置3种处理,分别是杉木成熟林套种阔叶树、杉木幼林套种阔叶树,以及不套种阔叶树的杉木纯林 (对照),测定其表层 (0~10 cm) 土壤的理化性质、土壤微生物生物量碳氮磷含量及土壤酶活性,并计算酶化学计量比。 结果 杉木林下套种阔叶树后,尤其是杉木成熟林套种阔叶树,土壤全碳 (TC)、全氮 (TN)、微生物生物量碳 (MBC) 含量增加。套种处理之后,土壤β-N-乙酰氨基葡萄糖苷酶 (NAG) 和酸性磷酸酶 (AP) 酶活性显著升高,β-葡萄糖苷酶 (βG) 酶活性显著降低;βG: AP和NAG: AP的平均值分别为0.006 4和0.011 3,远低于全球平均水平,表明该区域土壤微生物受磷限制,AP酶和NAG酶的活性提高,使得βG: AP和βG: NAG值在套种处理之后显著降低。冗余分析表明土壤C: N和MBC: MBN分别解释土壤酶活性和生态酶化学计量比变异的92.3%和4.4%。 结论 杉木套种阔叶树有助于土壤养分积累,改良土壤性状。 Abstract:Objective To study the soil enzyme activities and their stoichiometry in Chinese fir (Cunninghamia lanceolata) forests interplanted with broadleaved trees, and assess the soil nutrient and fertility conditions in these forests. Method Soil physicochemical properties, soil microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), and soil enzyme activities in surface soil (0~10 cm in depth) were determined in different interplanting forests (young Chinese fir interplanting forest, mature Chinese fir interplanting forest) and pure Chinese fir plantation in Sanming, Fujian Province. Result The contents of total C, total N and MBC increased significantly after interplanted with broadleaved trees, especially in mature Chinese fir interplanting forest. After interplanting, the activities of: β-N-Acetylglucosaminidase (NAG) and acid phosphatase (AP) increased significantly, and the activity ofβ-glucosidase (βG) decreased significantly. The ratios of βG:AP and NAG:AP were lower than global average, which showed that the soil microorganisms in this area were in the state of phosphorus restriction. The activities of AP and NAG increased after interplanting and thus βG:AP and βG:NAG ratios decreased significantly. Redundancy analysis showed that soil C:N and MBC:MBN explained 92.3% and 4.4% of soil enzyme activity and enzyme stoichiometric ratio variation, respectively. Conclusion Chinese fir interplanted with broadleaved trees can help to accumulate soil nutrients and improve soil properties. -
表 1 土壤酶的种类、缩写、类型和所用底物
Table 1. The abbreviations,type and substrates of soil enzyme
酶
Enzyme缩写
Abbreviation类型
Type底物
Substrate酸性磷酸酶 Acid phosphatase AP P-targetinghydrolytic 4-MUB-phosphate β-葡萄糖苷酶 β-glucosidase βG C-targeting hydrolytic 4-MUB-β-D-glucoside β-N-乙酰氨基葡萄糖苷酶 β-N-acetylglucosaminidase NAG N-targeting hydrolytic 4-MUB-N-acetyl-β-D-glucosaminide 表 2 不同套种处理土壤理化性质
Table 2. Physical and chemical properties of soil under different interplanting treatments
处理
Treatments套种幼林
Young interplanting forest套种成熟林
Mature interplanting forest杉木纯林
Pure Chinese fir plantation酸碱度 pH 4.308 ± 0.03 b 4.46 ± 0.07 a 4.16 ± 0.03 b 含水量 Soil water content/% 0.99 ± 0.11 a 0.92 ± 0.06 a 0.86 ± 0.13 a 总碳 Total carbon/(g·kg−1) 12.93 ± 0.90 b 19.84 ± 0.14 a 11.62 ± 0.79 b 总氮 Total nitrogen/(g·kg−1) 1.23 ± 0.06 b 1.51 ± 0.01 a 1.15 ± 0.03 b 总磷 Total phosphorus/(g·kg−1) 0.19 ± 0.08 a 0.08 ± 0.01 a 0.09 ± 0.01 a 碳氮比 C:N 10.68 ± 0.17 b 13.31 ± 0.14 a 9.36 ± 0.10 c 碳磷比 C:P 103.38 ± 22.12 b 260.67 ± 21.52 a 133.34 ± 17.6 6b 氮磷比 N:P 9.94 ± 2.16 b 19.74 ± 1.51 a 13.20 ± 1.59 b 注:表中数据为平均值 ± 标准差(n = 5),同一行不同小写字母表示不同处理间差异显著(P < 0.05)。
Notes: The data in the table are mean ± standard deviation (n = 5). Different lowercase letters in the same row indicate significant differences between different treatments (P < 0.05).表 3 不同套种处理下微生物生物量及其计量比
Table 3. Microbial biomass and its metering ratio under different interplanting treatments
处理
Treatments套种幼林
Young interplanting forest套种成熟林
Mature interplanting forest杉木纯林
Pure Chinese fir plantation微生物生物量碳 MBC/(mg·kg−1) 317.16 ± 40.88 b 342.76 ± 15.56 a 298.31 ± 16.08 b 微生物生物量氮 MBN/(mg·kg−1) 13.11 ± 0.72 a 18.42 ± 1.86 a 15.64 ± 1.51 a 微生物生物量磷 MBP/(mg·kg−1) 43.00 ± 0.94 b 49.68 ± 0.94 a 36.33 ± 0.94 b MBC:MBN 25.03 ± 4.39 a 14.51 ± 2.38 a 24.24 ± 1.68 a MBC:MBP 7.34 ± 0.85 a 6.89 ± 0.23 a 8.26 ± 0.61 a MBN:MBP 0.31 ± 0.02 b 0.37 ± 0.04 ab 0.43 ± 0.05 a 注:表中数据为平均值 ± 标准差(n = 5),同一行不同小写字母表示不同处理间差异显著(P < 0.05)。
Notes: The data in the table are mean ± standard deviation (n = 5). Different lowercase letters in the same row indicate significant differences between different treatments (P < 0.05).表 4 土壤酶活性、酶化学计量比与理化性质及土壤化学计量相关性
Table 4. Correlation between soil enzyme activity, enzyme stoichiometry and physicochemical properties and soil stoichiometry
相关性 Correlation AP βG NAG βG:NAG βG:AP NAG:AP pH 0.849** −0.352 0.590* −0.490 −0.532* −0.229 SWC −0.189 0.076 0.200 −0.048 0.125 0.383 TN 0.881** −0.226 0.455 −0.346 −0.404 −0.359 TC 0.946** −0.233 0.461 −0.315 −0.429 −0.427 TP −0.214 −0.296 −0.277 −0.244 −0.225 −0.122 C:N 0.968** −0.391 0.485 −0.500 −0.580* −0.422 C:P 0.809** 0.062 0.481 −0.028 −0.120 −0.238 N:P 0.667** 0.191 0.463 0.088 0.035 −0.104 MBC 0.605* −0.196 0.421 −0.301 −0.311 −0.141 MBN 0.462 0.346 0.256 0.222 0.198 −0.081 MBP 0.883** −0.487 0.432 −0.609* −0.651** −0.402 MBC:MBN −0.211 0.027 −0.218 −0.190 −0.219 −0.050 MBC:MBP −0.413 −0.131 0.397 0.476 0.401 0.096 MBN:MBP −0.061 −0.049 0.628* 0.587* 0.616* 0.229 注:*在0.05水平上显著相关;**在0.01水平上显著相关。
Notes:*Correlation is highly significant at the 0.05 level; ** Correlation is significant at the 0.01 level. -
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