川西亚高山/高山森林土壤氧化还原酶活性及其对季节性冻融的响应

川西亚高山/高山森林土壤通常具有明显的季节性冻融特征。为深入了解川西亚高山/高山森林冬季土壤生态过程,于2008年11月-2009年10月,在土壤初冻期、冻结期和融化期及生长季节,研究了不同海拔(3582 m、3292 m和3023 m)岷江冷杉林的土壤氧化还原酶活性及其对土壤冻融的响应。土壤冻结时间和冻融循环次数随海拔的增加而增加。冻融格局显著影响了土壤氧化还原酶活性,但不同土壤酶在不同海拔表现出明显差异。土壤过氧化物酶和脱氢酶活性受初冻期冻融循环和温度降低影响显著下降,而过氧化氢酶活性明显上升。3种土壤氧化还原酶活性在土壤温度相对稳定的冻结期变化不显著,但在融化期随着土壤温度急剧增加经历一个明显的活性高峰后快速降低,且冻结时间最长和冻融循环次数最多的3582 m变化更为显著。此外,海拔和土层的交互作用显著影响了过氧化物物活性,但对脱氢酶和过氧化氢酶活性不显著。脱氢酶活性与土壤温度极显著相关,但过氧化物酶和过氧化氢酶活性与土壤温度的相关性随海拔差异而不同。这些结果表明川西亚高山/高山森林冬季土壤氧化还原酶仍然具有较高的活性,但受到季节性冻融及其变化的显著影响。

Activities of soil oxidordeuctase and their response to seasonal freeze-thaw in the subalpine/alpine forests of western Sichuan

Soil enzyme, the sensitive bio-indictor to environmental change in soil ecosystem, plays an essential role in soil ecological processes, such as litter decomposition, organic matter accumulation and nutrient cycling. Including others, climate change with temperature dynamics always have a great effect on soil enzyme activity. Seasonal freeze-thaw cycle in the subalpine/alpine region is a common climate phenomenon, which could change soil enzyme activity, and then soil ecological processes. However, little information has been available. In order to understand soil oxidordeuctases activities and their responses to seasonal freeze-thaw cycle in the subalpine/alpine forests of western Sichuan, three fir (Abies faxoniana) forests were selected covering a 600 m vertical transition zone. The primary fir forest at 3852 m of altitude, fir and birch mixed forest at 3298 m of altitude, and secondary fir forest at 3023 m of altitude are representative forests in the subalpine and alpine region of west Sichuan. Based on the simultaneous monitoring of soil temperature, soils were sampled in different stages as the onset of soil freezing period, soil frozen period, soil thawing period and growing period from November 2008 to October 2009. The activities of soil peroxidase, dehydrogenase, and catalase were measured. There were obvious seasonal freeze-thaw processes in sampled forests at different altitudes, and the length of seasonal freeze-thaw and the number of freeze-thaw cycle increased with the increase of altitude. Seasonal freeze-thaw cycle significantly affected the activities of soil oxidordeuctases, but the responses of soil oxidordeuctase activities were varied with soil enzyme types. The activities of soil peroxidase and dehydrogenase decreased in the onset of soil freezing period with the decrease of soil temperature, but soil catalase activity increased. Soil oxidordeuctases activities displayed few changes in soil frozen period. However, soil oxidordeuctases activities sharply increased with the increase of soil temperature in soil thawing period. The activities of all investigated soil oxidordeuctases reached to an obvious peak in soil thawing period. The changes of soil oxidordeuctases activity at 2583 m were more significant in comparison with those at 3298 m and 3023 m due to longer freezing length and more freeze-thaw cycles. Meanwhile, the interaction of altitude and soil layer had significant effects on soil peroxidase activities, but had insignificant effects on soil dehydrogenase and catalase activities. Additionally, soil dehydrogenase activities were significantly correlated with soil temperature, but the correlations between soil temperature and the activity of soil peroxidase and catalase differed with altitudes. The results suggest that soil oxidordeuctases in wintertime still keep relative higher activities in the subalpine and alpine forest of western Sichuan, although the seasonal freeze-thaw cycle and its changes have significant effects on the activities of soil oxidordeuctases.