马尾松与阔叶树种凋落叶混合分解初期的酶活性

Enzyme activities in the early stage of mixed leaf litter decomposition from Pinus massoniana and broad-leaved tree species

酶是凋落物养分释放过程中必不可少的催化剂,酶活性能迅速响应凋落物分解条件的改变,并在一定程度上反映分解快慢.以四川省低山丘陵区马尾松人工林为对象,研究马尾松（M）与香樟（X）、檫木（S）、香椿（T）阔叶树种混合凋落叶（MX、MS、MT;MSX、MXT、MST;MSXT）分解初期与碳（C）、氮（N）、磷（P）循环相关酶活性的变化特征,包括β-葡萄糖苷酶和纤维二糖水解酶（C循环水解酶）,β-N-乙酰氨基葡萄糖苷酶和亮氨酸氨基肽酶（N循环水解酶）,酸性磷酸酶（P循环水解酶）以及多酚氧化酶和过氧化物酶（C循环氧化酶）.结果显示：（1）树种组合对酶活性影响显著,相比单一M,MT、MXT、MST、MSXT组合有助于提高C、N循环水解酶活性,而MX、MS、MSX组合则对酶活性具有一定的抑制作用;（2）混合比例对酶活性影响显著,无论一针一阔、一针两阔还是一针三阔混合模式,皆在马尾松与总阔叶量之比为6：4时,C、N循环水解酶活性较高;（3）相比单一M,混合处理降低了P获得水解酶及C获得氧化酶活;MT6：4和MXT6：1：3、MST6：3：1及MSXT（6：1：1：2、6：1：2：1）处理则有助于C、N循环水解酶活性整体提高,其中又以MT6：4和MSXT6：1：2：1处理更佳,且分别提高了63.34%、22.12%、11.93%、105.80%和53.91%、50.94%、29.10%、140.93%;（4）CCA分析表明,酶活性对树种组合、混合比例、凋落叶初始质量及微环境因子的响应不同,其中树种组合对酶活性影响最大,凋落叶初始N、N/P次之,说明凋落叶化学组成及其物理性质的某些方面共同作用于酶活性.综上,MT6：4和MSXT6：1：2：1混合更利于C、N循环水解酶活性在分解初期的稳定及提高.

Enzymes are essential catalysts for the release of nutrients from litter. Enzyme activity can respond to changes in litter decomposition conditions, and it reflects the decomposition rate to some extent. To investigate the effects of mixed leaf litters on enzyme activities related to C, N, and P cycles in the soil at the early stage of decomposition, we set up a series of mixed defoliation treatments（MX, MS, MT, MSX, MXT, MST, and MSXT） from Pinus massoniana（M）, Cinnamomum camphora（X）, Sassafras tsumu（S）, and Toona sinensis（T）. Enzyme activities in leaf litter samples were determined after 75 days of decomposition, including two C cycle hydrolases（β-glucosidase and cellobiohydrolase）, two N cycle hydrolases（β-N-acetylglucosaminidase and leucine aminopeptidase）, one P cycle hydrolase（acid phosphatase）, and two C cycle oxidases（polyphenol oxidase and peroxidase）. The results showed that tree species combination significantly affected enzyme activities, and the MT, MXT, MST, and MSXT combinations contributed to the increase of C and N cycle hydrolase activity, while the MX, MS, and MSX combinations had a certain inhibitory effect on the enzyme activity. The mixed proportion had significant effects on enzyme activity. In all mixed models, C and N cycle hydrolase activity was relatively high when the ratio of M to broad-leaved litters was 6：4. Compared to single M, mixed treatments reduced P cycle hydrolases and C cycle oxidase activity, whereas MT6：4, MXT6：1：3, MST6：3：1, and MSXT（6：1：1：2, 6：1：2：1） contributed to the improvement of the overall C and N cycle hydrolase activities, and MT6：4 and MSXT6：1：2：1 were better collocations than the others. Compared to single M, the activity of the two C and two N cycle hydrolases in MT6：4 increased by 63.34%, 22.12%, 11.93%, and 105.80% and in MSXT6：1：2：1 by 53.91%, 50.94%, 29.10%, and 140.93%, respectively. Canonical correspondence analysis showed that the effects of tree species combination, mixed proportion, initial litter quality, and microenvironment on enzyme activity were different in the different mixed models, and among them, tree species combination had the greatest effect on enzyme activity, followed by initial N and N/P of leaf litters. These results indicated that both the chemical composition and physical properties of leaf litter play an important role in mediating enzyme activity. The findings of this study revealed that MT6：4 and MSXT6：1：2：1 are more conducive to the stability and improvement of hydrolase activity related to C and N in the early stage of litter decomposition.