南亚热带桉树混交林土壤酶活性及其化学计量比特征

Soil Enzyme Activity and Stoichiometry of Eucalyptus Mixed Plantations in Subtropical China

摘要:

针对当前桉树人工纯林林分的生产力下降问题，该研究以广东鹤山改造18 a后的尾叶桉(Eucalyptus urophylla)纯林和乡土树种株数占比分别为20%、30%、40%和50%的桉乡混交林为对象，通过测定凋落物生物量和碳(C)、氮(N)、磷(P)含量，0~10和10~20 cm土层的土壤pH值、C、N、P含量、可溶性C、N含量和微生物生物量C、N含量以及β-d-葡萄糖苷酶(BG)、N-乙酰葡萄糖苷酶(NAG)、酸性磷酸酶(AP)活性，探讨土壤酶活性及其化学计量比与凋落物和土壤理化性质关系。结果表明，随乡土树种混交比例增加，10~20 cm土层BG、NAG活性先降后增，0~10和10~20 cm土层AP活性先降后增，酶C:P和N:P先增后降，混交林一定程度上缓解土壤微生物碳氮限制，提升了土壤肥力和促进微生物活性。相关性和冗余分析表明, 0~ 10 cm土层土壤酶活性及其化学计量比主要与凋落物性质相关，10~20 cm土层主要与土壤理化性质相关。该研究阐明了混交林在改善土壤养分状况、调节土壤酶活性以及在不同土层的差异化调控途径，对指导低效桉树人工林改造和混交林经营具有应用价值。

Abstract:

In response to declining productivity in Eucalyptus monoculture plantations, the 18-year-old pure E. urophylla plantations and Eucalyptus-native mixed plantations with native tree species proportions of 20%, 30%, 40%, and 50% in Heshan, Guangdong were investigated. By measuring the biomass and carbon (C), nitrogen (N), and phosphorus (P) contents of litter, as well as the pH, C, N, P contents, soluble C and N contents, and microbial C and N contents in the 0–10 and 10–20 cm soil layers, and the activities of β-d-glucosidase (BG), N-acetylgluco- saminidase (NAG), and acid phosphatase (AP), the relationship between soil enzyme activities and their stoichiometric ratios and the physical and chemical properties of litter and soil was explored. The results showed that with the increase of the proportion of native tree species, the activities of BG and NAG in the 10–20 cm soil layer first decreased and then increased, while the activities of AP in both the 0–10 and 10–20 cm soil layers first decreased and then increased. The C:P and N:P ratios of enzymes first increased and then decreased. The mixed plantations to some extent alleviated the carbon and nitrogen limitations of soil microorganisms, improved soil fertility, and promoted microbial activity. Correlation and redundancy analysis indicated that the soil enzyme activities and their stoichiometric ratios in the 0–10 cm soil layer were mainly related to the properties of litter, while in the 10–20 cm soil layer, they were mainly related to the physical and chemical properties of soil. This study clarified the pathways of mixed plantations in improving soil nutrient status, regulating soil enzyme activities, and their differential regulation in different soil layers, which has application value for guiding the transformation of low-efficiency Eucalyptus plantations and the management of mixed plantations.