千家寨不同海拔野生古茶树根际土壤微生物胞外酶活性特征

Microbial extracellular enzyme activity in the rhizosphere soil of ancient wild tea trees at different altitudes in the Qianjiazhai Reserve

野生古茶树是亟需保护的珍稀种质资源.为了解野生古茶树根际土壤碳氮磷生态化学计量、微生物量碳氮和胞外酶活性的垂直分布格局,以千家寨野生古茶树群落为对象,采集千家寨4个海拔2050 m(E1)、2200 m(E2)、2350m(E3)、2500m(E4)的野生古茶树群落的根际土壤,测定并分析其碳氮磷(C、N、P)生态化学计量、微生物量碳和氮(MBC和MBN)和胞外酶活性[磷素获取酶碱性磷酸酶(AKP)、碳素获取酶β-1,4-葡萄糖苷酶(βG)、氮素获取酶β-1,4-N-乙酰基氨基葡萄糖苷酶(NAG)和水解酶亮氨酸氨基肽酶(LAP)、多酚氧化酶(PPO)、过氧化物酶(PER)]的变化及其影响因素.结果显示,千家寨野生古茶树根际土壤C:N较高(11.27-13.35),并随海拔升高而增加;C:P和N:P均随海拔升高呈先升高后降低的变化规律.根际土壤MBC和MBN随海拔升高呈先上升后下降的规律,分别受根际土壤含水量和铵态氮(NH4+)的影响.根际土壤AKP、βG和NAG活性随海拔升高均显著增加并与总磷含量(TP)密切相关,LAP活性在海拔上无显著变化,PPO活性随海拔升高而显著下降(P<0.05).根际土壤胞外酶活性生态化学计量大小顺序是βG:(NAG+LAP)>βG:AKP>(NAG+LAP):AKP,其中βG:AKP和(NAG+LAP):AKP值均小于1.综上所述,不同海拔梯度上土壤碳氮磷生态化学计量、微生物量碳氮和胞外酶活性及其计量学差异显著,而TP是影响海拔梯度上野生古茶树根际土壤胞外酶活性大小的关键因子;千家寨野生古茶树根际土壤微生物受磷限制和碳限制相对于氮限制程度更高,在不同海拔中受碳氮磷限制的程度有差异;本研究结果对了解野生古茶树的养分循环和生态适应机制有重要意义.(图6表3参54)

This study aimed to explore the vertical distribution of carbon, nitrogen, and phosphorus, microbial biomass(carbon and nitrogen), and extracellular enzyme activities in the rhizosphere soil of an ancient wild tea tree species, which urgently needs protection as it is a rare genetic resource. Ancient wild tea communities at different altitudes of 2 050 m(E1), 2 200 m(E2), 2 350 m(E3), and 2 500 m(E4) in the Qianjiazhai Reserve were used to study the variation of rhizosphere soil C:N:P stoichiometry, microbial biomass carbon and nitrogen(MBC and MBN), and rhizosphere soil extracellular enzyme activities(phosphorus acquisition: alkaline phosphatase(AKP);carbon acquisition: β-glucosidase(βG);nitrogen acquisition: N-acetyl-β-D-glucosaminidase(NAG);and leucyl aminopeptidase(LAP), polyphenol oxidase(PPO), and peroxidase activity(PER)). Our results revealed that C:N was relatively high(11.27-13.35) in rhizosphere soil of ancient wild tea trees in the Qianjiazhai Reserve. With an increase in altitude, C:N increased whereas C:P and N:P increased initially and then decreased. MBC and MBN followed a similar pattern as altitude increased, which were affected by rhizosphere soil water content and ammonium nitrogen(NH4+), respectively. The activities of AKP, βG, and NAG in rhizosphere soil increased significantly with an increase in altitude and were closely related to total phosphorus content(TP). The LAP activity had no significant change owing to altitude, and the PPO activity decreased as altitude increased. The rank of extracellular enzyme stoichiometry was βG:(NAG + LAP) > βG:AKP >(NAG + LAP):AKP;both βG:AKP and(NAG + LAP):AKP were less than 1. The C:N:P stoichiometry, microbial biomass, and soil extracellular enzyme activity were significantly affected by an increase in the altitude gradient. The TP was a key factor affecting the activities of extracellular enzymes in rhizosphere soil. P and C were the main limiting elements in the determination and variation of the microbial community in the rhizosphere soil of ancient wild tea trees in the Qianjiazhai Reserve. This study provides significant information to better understand the regulatory mechanisms of nutrient cycles and ecological adaptation of wild ancient tea plants and aids in the preservation of this genetically rare resource.