不同优势树种菌根类型差异对土壤胞外酶活性的影响

Effects of different mycorrhizal types in dominant tree species on soil extracellular enzyme activity

土壤酶作为微生物代谢指标,在森林生态系统土壤碳和养分循环过程中发挥着重要作用,是土壤质量的重要指标。针对不同优势树种的内生菌根(AM)和外生菌根(ECM)所占比例差异,设置4种菌根类型比例梯度(即林分中ECM树种所占比例为<25%、25%—50%、50%—75%、>75%),分析4种林分中土壤水解酶[β-葡糖苷酶(BG)、β-N-乙酰氨基葡萄糖苷酶(NAG)、亮氨酸氨基肽酶(LAP)、酸性磷酸酶(AP)]和过氧化物酶(PER)活性差异,运用方差分析和多重比较分析方法,探究水解酶和氧化酶沿菌根类型梯度的变化规律及原因。结果表明:(1)lnBG和ln(NAG+LAP)与lnAP的回归斜率小于1,且AP远大于BG和NAG+LAP,这表明森林土壤微生物受磷(P)限制更严重,随着林分中ECM优势树种的增加,微生物受碳(C)和P限制的状况得到缓解;(2)土壤有机碳(SOC)随着ECM树种占比的增加而增加,ECM森林比AM森林表现出更高的全氮(TN)和全磷(TP)含量;(3)随着林分中ECM树种占比的增加,BG、AP和NAG+LAP呈逐渐显著增加的趋势(P<0.05);但氧化酶活性差异不显著;(4)土壤水解酶活性与铵态氮、硝铵比、TN、TP、SOC有显著相关关系,氧化酶活性只与土壤水分(SM)含量呈现显著相关性。研究支持资源分配理论,验证了土壤胞外酶活性随AM和ECM菌根比例变化而呈现梯度变化,证实了菌根——养分经济模型的适用性,研究结果可加强对不同菌根梯度林分土壤理化性质和酶活性的可预测性,有助于生物地球化学循环模型的补充与完善。

Soil enzyme is a crucial indicator of microbial metabolic activity and soil quality monitoring, playing an important role in the soil carbon and nutrient cycle. Global change could alter tree species composition, leading the transfer of dominant mycorrhizal at the individual or ecosystem level. In order to investigate the effect of mycorrhizal types on soil extracellular enzyme activity, four stands with percentage of different mycorrhizal type(the percentage of ECM trees was <25%, 25%—50%, 50%—75% and >75%, respectively) were set up in pure Cunninghamia lanceolata stand, pure Quercus acutissima stand, and the two species mixed forest. We measured the soil hydrolase activities [β-glucosidase(BG), β-N-acetylglucosaminidase(NAG), leucine aminopeptidase(LAP), acid phosphatase(AP)], and soil peroxidase(PER) activity and analyzed the pattern of hydrolase and oxidase activities along the gradient of mycorrhizal types using one-way ANOVA and multiple comparisons. The results showed that:(1) the regression slope of the ratio of lnBG to ln(NAG+LAP) and to lnAP were less than 1, indicating that AP activity was much higher than that of BG and NAG+LAP. This indicated that forest soil microorganisms were more severely restricted by phosphorus(P). The increase of ECM-associated tree species relieved the limitation of C and P for microorganisms.(2) Soil organic carbon(SOC) increased as the proportion of ECM-associated tree species increased. While ECM-dominated forests had higher total soil nitrogen(TN) and total soil phosphorus(TP) contents than AM-dominated forests.(3) With the increase in the proportion of ECM-associated tree species in the forest, activities of BG, AP, and NAG+LAP showed a gradual increase trend(P<0.05)except for soil oxidase activity.(4) Soil hydrolase activity exhibited a significant correlation with ammonium nitrogen, nitrate-ammonium ratio, TN, TP, and SOC, while the oxidase activity only exhibited a significant correlation with the content of soil moisture(SM). These results support the theory of resource allocation, verify that the activity of soil extracellular enzymes changes gradually with the percent of AM-associated and ECM-associated tree species, and confirm the applicability of the mycorrhizal-associated nutrient economy pattern. The results also strengthen the predictability of the soil physical and chemical properties as well enzyme activities in the forest with different percentages of AM-associated and ECM-associated tree species, and thus contributing to the improvement of biogeochemical cycle model.