川西高山森林不同时期土壤转化酶和脲酶活性对模拟气候变暖的响应

摘要

Not only do soil enzymes take part in carbon and nutrient cycles in soil ecosystems,but act as the sensitive bioindicators in indicating environmental changes.Consequently,climate change characterized by climate warming and seasonal snow cover decline might give to a certain extent effects on soil enzyme activity in high-altitude and high-latitude regions,and thereafter change the cycles of carbon and nutrients in soil ecosystems in cold biomes.However,the response of soil enzyme activity to climate warming at different critical periods remains unknown.In order to understand the effects of climate warming on soil ecological process in the alpine forest in western Sichuan,soil columns sampled from a primary Minjiang fir (Abies faxoniana) forest at 3582 m elevation was therefore in-situ incubated in the primary coniferous forest,transplanted and incubated in 3298 m and 3023 m sites in May 2010,respectively.Theoretically,the temperatures of soil and atmosphere would increase by 1.78 ℃ and 3.52 ℃,respectively.Based on the previous studies and simultaneous temperature monitoring,soil columns at three elevations were respectively retrieved at the early growing period (EGS),later growing period (LGS),onset of soil freezing period (OF),deeply frozen period (DF) and thawing period (TP) from August 2010 to April 2011,and the activities of invertase related to carbon cycle and urease related to nitrogen cycle in both soil organic layer (OL) and mineral soil layer (MS) were instantly measured in the lab.Different from the theoretical prediction values,annual mean air temperatures at 3298 m and 3023 m elevations were actually higher 1.39℃ and 2.64℃ than that at 3582 m elevation,respectively.As affected by seasonal snow cover,lowering 559 m elevation made the annual mean temperatures of OL and MS in soil columns increase 0.84℃ and 0.82℃,respectively,but lowering 284 m elevation made the temperatures of OL and MS in columns actually decrease 0.55℃ and 0.56℃,respectively.Regardless of soil column transplanting and sampling periods,the activities of both invertase and urease in OL were significantly higher than those in MS.Moreover,those activities in OL varied more sharply with critical periods and elevation lowering than those in MS.The activities of invertase and urease in soils fluctuated to some extent with critical periods,but the highest and lowest activities of soil enzymes varied with soil layers,enzyme types and the elevations.On the whole,the activities of invertase in both OL and MS decreased from EGS to LGS,and then increased during DF and TP.The activities of urease in both OL and MS increased from EGS to DF,and then decreased in TP.Soil column incubation with lowering 284 m elevation significantly improved the activities of invertase in both OL and MS at EGS,OF and DF,but the incubation with lowering 559 m elevation significantly improved the activities of urease in both OL and MS at DF.The elevation,soil layer,sampling period and their interactions gave strong effects on the activities of invertase and urease in the alpine forest soil,and the responses of soil invertase and urease activities in the alpine forest to simulated climate warming varied greatly with different critical periods as affected by seasonal snow cover.%为了解气候变化对不同时期川西高山森林土壤生态过程的影响,于2010年5月-2011年4月期间,通过原状土柱移位实验,模拟理论增温1.78℃和3.52℃对岷江冷杉原始林(3582 m)土壤转化酶和脲酶活性的影响.结果表明,海拔下降284 m和559 m分别使全年平均气温实际增高1.39:℃和2.64℃,但由于季节性雪被的影响,海拔降低559 m后土柱的土壤有机层和矿质土壤层的全年平均温度分别增加了0.84℃和0.82℃,而海拔降低284 m后土柱的土壤有机层和矿质土壤层的全年平均温度分别降低了0.55℃和0.56℃.随着海拔降低,土壤有机层和矿质土壤层的转化酶和脲酶活性均表现出明显的变化,且土壤有机层的变化幅度大于矿质土壤层.海拔降低284 m显著提高了两个土层生长季初期和冻结阶段(冻结初期和深冻期)的转化酶活性,而海拔降低559 m则显著提高了两个土层冻结阶段的脲酶活性.采样时期均温也在一定程度上影响了土壤转化酶和脲酶的活性,土壤有机层和矿质土壤层转化酶活性表现为从生长季初期到生长季末期显著下降,随后在冻结阶段和融化期显著升高并分别在深冻期和融化期达到全年最高;土壤脲酶活性表现为从生长季初期到深冻期显著增加,随后在融化期显著下降的过程.可见,受季节性雪被影响,不同关键时期的高山森林土壤转化酶和脲酶活性对模拟增温的响应不同.