亚热带人工林下植被根际土壤酶化学计量特征

Characteristics of soil enzymes stoichiometry in rhizosphere of understory vegetation in subtropical forest plantations

为探讨林下植被根际土壤酶化学计量特征及其对林分类型和季节的响应,该研究以江西省泰和县千烟洲试验站典型人工杉木(Cunninghamialanceolata)、马尾松(Pinusmassoniana)和湿地松(Pinuselliottii)林林下优势灌草檵木(Loropetalum chinense)、杨桐(Adinandra millettii)、格药柃(Eurya muricata)、狗脊蕨(Woodwardia japonica)和暗鳞鳞毛蕨(Dryopteris atrata)为对象,在植被生长初期(4月)和旺盛期(7月)测定优势灌草根际土壤与碳(C)循环相关的β-1,4-葡萄糖苷酶(BG)、与氮(N)循环相关的β-1,4-N-乙酰葡糖氨糖苷酶(NAG)和亮氨酸氨基肽酶(LAP)、与磷(P)循环相关的酸性磷酸酶(AP)活性、酶化学计量比及土壤理化性质。结果发现:(1)根际土壤与C和N循环相关的酶活性以及BG:AP(酶C:P)在不同林下植被之间存在显著差异,而与P循环相关的酶活性差异不显著。林分类型和取样季节显著影响BG:(NAG+LAP)(酶C:N),且林下植被类型、林分类型和取样季节交互影响酶C:P。主成分分析表明,根际土壤酶的活性及计量比在不同林下植被(檵木不同于格药柃,且二者显著区别于其他物种)、林分类型(杉木林区别于马尾松、湿地松林)和取样季节之间均存在显著差异。土壤硝态氮(NO3--N)、铵态氮(NH4+-N)、可溶性有机碳(DOC)含量和碳氮比(C:N)是影响林下植被根际土壤酶的活性及化学计量比的主要因素。(2)标准主轴回归分析表明,林下植被根际土壤lg(BG)、lg(NAG+LAP)和lg(AP)之间存在显著线性关系,lg BG:lg(NAG+LAP):lg AP(酶C:N:P)约为1:1:1.3,酶C:P及(NAG+LAP):AP(酶N:P)分别为0.14和0.15。AP远大于BG和NAG+LAP的活性,导致lg(BG)和lg(NAG+LAP)与lg(AP)的回归斜率极显著偏离1。说明林下植被根际土壤酶的活性及计量比受植被种类、林分类型及取样季节影响,且基质有效性在其中发挥重要作用。相较于C循环和N循环,微生物会分配更多资源用于P循环相关酶的生产,暗示亚热带人工林林下植被根际土壤微生物生长和活性更易受P限制。

Aims The objective was to explore the stoichiometry of rhizosphere soil enzymes under major understory vegetation and their responses to plantation types and seasons.Methods Rhizosphere soils of understory shrubs(Loropetalum chinense, Adinandra millettii and Eurya muricata) and herbs(Woodwardia japonica and Dryopteris atrata) were sampled in the early growth stage(April) and the vigorous growth stage(July) in Cunninghamia lanceolata, Pinus massoniana and Pinus elliottii plantations at Qianyanzhou Ecological Research Station, Taihe, Jiangxi. Potential activities of β-1,4-glucosidase(BG, carbon(C) acquiring enzyme),β-1,4-N-acetylglucosaminidase(NAG, nitrogen(N) acquiring enzyme) and leucine aminopeptidase(LAP, N-acquiring enzyme), acid phosphatase(AP, phosphorus(P) acquiring enzyme) and their stoichiometric ratios were measured. Soil physical and chemical properties were also analyzed.Important findings The results found that(1) rhizosphere soil extracellular enzyme activities associated with C and N acquisition and BG:AP(enzyme C:P) were significantly different among understory species, but P acquisition were not. Both forest stand types and sampling seasons influenced BG:(NAG+LAP)(enzyme C:N). Interactions of understory species, forest stand types and seasons observably affected enzyme C:P. Principal component analysis showed that rhizosphere soil enzyme activities and ecoenzymatic stoichiometry differed significantly among different understory species(Loropetalum chinense was obviously different from Eurya muricata, and both of them were evidently different from other understory species), forest stand types(Cunninghamia lanceolata was different from Pinus massoniana and Pinus elliottii plantations) and sampling seasons. Soil NO3--N,NH4+-N, DOC content and C:N were the main edaphic abiotic factors influencing the rhizosphere soil enzyme activities and ecoenzymatic stoichiometry.(2) Standardized major axis analysis showed that there were significantly linear relationship among lg(BG), lg(NAG+LAP) and lg(AP) of rhizosphere soils of understory species.lgBG:lg(NAG+LAP):lgAP(enzyme C:N:P) was approximately 1:1:1.3. Rhizosphere soil enzyme C:P and(NAG+LAP):AP(enzyme N:P) of understory species were 0.14 and 0.15, respectively. The regression slopes of lg(BG), lg(NAG+LAP) and lg(AP) deviated significantly from 1 because AP activities were much higher than BG activities and NAG+LAP activities. This study found that rhizosphere soil enzyme activities and ecoenzymatic stoichiometry were affected by understory species, forest stand types and sampling seasons in which substrate availability played an important role. Compared with C-and N-acquiring enzymes, microorganisms allocated more resources to the production of P-acquiring enzymes, which implied that the growth and activity of soil microorganisms were much more limited by P in rhizosphere soil of understory vegetation in subtropical plantations.