三峡库区马尾松林土壤-凋落物层酶活性对凋落物分解的影响

凋落物的彻底降解是在凋落物和土壤酶系统的综合作用下完成,酶活性的提高有利于凋落物-土壤有机物质的分解和养分释放。通过对三峡库区30年生马尾松林凋落物分解、凋落物-土壤层酶活性季节动态及其对分解的影响进行研究,结果表明:30年生马尾松林凋落物经过540 d的分解后干重剩余率是59.80%;凋落物层酶活性季节动态明显,氧化还原酶活性均是11月最低,3月最高;土壤过氧化物酶活性季节变化显著且均是11月最低,多酚氧化酶活性9月较高,而过氧化物酶活性则是6月较高。马尾松林凋落物层酶活性与土壤层酶活性差异较大,且水解酶活性差异较氧化还原酶活性差异大,凋落物层脲酶活性、纤维素酶活性和蔗糖酶活性11月、6月、9月分别是0—5 cm土壤层的6.33倍、3.24倍、10.29倍,68.14倍、16.16倍、24.81倍,25.07倍、31.88倍、29.20倍。凋落物分解速率均与土壤、凋落物层氧化还原酶活性呈极显著"S"形曲线,与凋落物层水解酶活性呈二次函数关系,与土壤层水解酶均呈极显著的线性关系。凋落物质量能引起凋落物-土壤层酶活性变化,酶活性的改变反过来影响凋落物的分解,因此,凋落物-土壤层酶活性差异与凋落物分解阶段和对共同影响因素(凋落物质量、土壤温度、水分含量和土壤养分等)的敏感性不同有关,凋落物-土壤层酶的相互作用共同影响森林生态系统的物质循环和养分循环过程。

Effect of soil-litter layer enzyme activities on litter decomposition in Pinus massoniana plantation in Three Gorges Reservoir Area

The complete degradation of litter results from the combined enzyme activities in litter layer and soil layer, and their improvement is helpful to organic matter decomposition and nutrient release. Litter decomposition and the seasonal dynamic of soil-litter layer enzyme activities were studied on 30-year-old P. massoniana forest in Three Gorges Reservoir Area. The results showed that the remaining mass was 59.80% after 540 days decomposition. The decomposition rate was relatively fast during the decomposition 0-180 d, and relatively slow during 180-270 d. The period of 50% mass loss and 95% mass loss was 2.11 a and 9.15 a, respectively. The litter layer enzyme activities exhibited a remarkable seasonal dynamics, with the lowest enzyme activity occurring in November and the highest in March for oxidoreductase activity. Polyphenoloxidase activity and peroxidase activity of litter layer in March were 4.60 times and 6.07 times as high as those in November, respectively, while the dynamic of hydrolase activity in litter layer was irregular variation. The seasonal dynamics of soil layer peroxidase activity was remarkable with the lowest value occurring in November, and the highest in June. Polyphenoloxidase activity was the highest in September. The seasonal dynamics of soil layer hydrolase activity was irregular variation, the seasonal dynamical of soil urease activity was not significant (P>0.05), while the cellulose activity and sucrase activity was significant (P<0.05) with the sequence of September < June < November for sucrase activity, and the sequence of November < September < June for cellulose activity. Soil enzyme activity in the vertical direction was decreased gradually with soil depth except peroxidase activity. There was a notable difference in enzyme activity between litter layer and soil layer, and the difference in hydrolase activity was greater than in oxidoreductase activity. Litter layer urease activity, cellulase activity and sucrase activity were 6.33 times, 3.24 times, 10.29 times as high as those in 0-5 cm soil layer in November; 68.14 times, 16.16 times, 24.81 times in June, and 25.07 times, 31.88 times, 29.20 times in September, respectively. Litter polyphenoloxidase activity in November, June and September were 1.76 times, 1.45 times and 2.07 times as high as those in 0-5 cm soil layer, and the corresponding value were 0.40 times, 0.64 times and 0.56 times for peroxidase activity, respectively. There was a close relationship between litter-soil enzyme activities. Litter decomposition rate was significantly correlated in S-shaped curve with oxidereductase activity both in litter and soil layer, probably because oxidoreductase activity dynamic is complex and influenced by soil pH value, nutrient content, soil layer distribution and so on. There were significant quadratic function (P<0.01) between litter decomposition rate and hydrolase activity in litter layer, while litter decomposition rate was significantly linearly related (P<0.01) to the hydrolase in soil layer. Litter quality could change the enzyme activity in litter and soil layer, in return, enzyme activity could affect litter decomposition rate. Therefore, the difference of enzyme activity between litter and soil layer is related with litter decomposition stage and the different sensitivity of the common impact factors including litter quality, soil temperature, water content and soil nutrients. The interactions of litter-soil layer enzyme activity influence material circulation and nutrient cycling process of forest ecosystem.