張 麗,吳福忠,徐振鋒,譚 波,劉 洋,楊玉蓮,3,王 奧,4,楊萬(wàn)勤,*

1 四川農(nóng)業(yè)大學(xué)生態(tài)林業(yè)研究所,高山森林生態(tài)系統(tǒng)定位研究站,成都 611130 2 四川省長(zhǎng)江上游生態(tài)安全協(xié)同創(chuàng)新中心,成都 611130 3 綿陽(yáng)師范學(xué)院,生態(tài)安全與保護(hù)四川省重點(diǎn)實(shí)驗(yàn)室,綿陽(yáng) 621000 4 遵義市產(chǎn)品質(zhì)量檢驗(yàn)檢測(cè)院,遵義 563000

川西高山森林不同時(shí)期土壤轉(zhuǎn)化酶和脲酶活性對(duì)模擬氣候變暖的響應(yīng)

張 麗1,2,吳福忠1,2,徐振鋒1,2,譚 波1,2,劉 洋1,2,楊玉蓮1,2,3,王 奧1,2,4,楊萬(wàn)勤1,2,*

1 四川農(nóng)業(yè)大學(xué)生態(tài)林業(yè)研究所,高山森林生態(tài)系統(tǒng)定位研究站,成都 611130 2 四川省長(zhǎng)江上游生態(tài)安全協(xié)同創(chuàng)新中心,成都 611130 3 綿陽(yáng)師范學(xué)院,生態(tài)安全與保護(hù)四川省重點(diǎn)實(shí)驗(yàn)室,綿陽(yáng) 621000 4 遵義市產(chǎn)品質(zhì)量檢驗(yàn)檢測(cè)院,遵義 563000

為了解氣候變化對(duì)不同時(shí)期川西高山森林土壤生態(tài)過(guò)程的影響,于2010年5月—2011年4月期間,通過(guò)原狀土柱移位實(shí)驗(yàn),模擬理論增溫1.78℃和3.52℃對(duì)岷江冷杉原始林(3582 m)土壤轉(zhuǎn)化酶和脲酶活性的影響。結(jié)果表明,海拔下降284 m和559 m分別使全年平均氣溫實(shí)際增高1.39℃和2.64℃,但由于季節(jié)性雪被的影響,海拔降低559 m后土柱的土壤有機(jī)層和礦質(zhì)土壤層的全年平均溫度分別增加了0.84℃和0.82℃,而海拔降低284 m后土柱的土壤有機(jī)層和礦質(zhì)土壤層的全年平均溫度分別降低了0.55℃和0.56℃。隨著海拔降低,土壤有機(jī)層和礦質(zhì)土壤層的轉(zhuǎn)化酶和脲酶活性均表現(xiàn)出明顯的變化,且土壤有機(jī)層的變化幅度大于礦質(zhì)土壤層。海拔降低284 m顯著提高了兩個(gè)土層生長(zhǎng)季初期和凍結(jié)階段(凍結(jié)初期和深凍期)的轉(zhuǎn)化酶活性,而海拔降低559 m則顯著提高了兩個(gè)土層凍結(jié)階段的脲酶活性。采樣時(shí)期均溫也在一定程度上影響了土壤轉(zhuǎn)化酶和脲酶的活性,土壤有機(jī)層和礦質(zhì)土壤層轉(zhuǎn)化酶活性表現(xiàn)為從生長(zhǎng)季初期到生長(zhǎng)季末期顯著下降,隨后在凍結(jié)階段和融化期顯著升高并分別在深凍期和融化期達(dá)到全年最高；土壤脲酶活性表現(xiàn)為從生長(zhǎng)季初期到深凍期顯著增加,隨后在融化期顯著下降的過(guò)程。可見,受季節(jié)性雪被影響,不同關(guān)鍵時(shí)期的高山森林土壤轉(zhuǎn)化酶和脲酶活性對(duì)模擬增溫的響應(yīng)不同。

高山森林；土壤轉(zhuǎn)化酶；土壤脲酶；原狀土柱移位；模擬增溫；季節(jié)性雪被

Abstract： 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 (Abiesfaxoniana) 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.

KeyWords: alpine forest; soil invertase; soil urease; soil column transplanting; simulated climate warming; seasonal snow cover

以氣候變暖和季節(jié)性雪被減少為主要特征的氣候變化正在改變著陸地生態(tài)系統(tǒng)過(guò)程[1]。據(jù)IPCC(2014)預(yù)測(cè),到21世紀(jì)末,全球平均氣溫將升高0.3—4.8℃,在高緯度和高海拔地區(qū)溫度的增幅將更大[2]。土壤酶不僅是土壤生態(tài)系統(tǒng)物質(zhì)循環(huán)和能量流動(dòng)的重要參與者,而且是指示環(huán)境變化的敏感生物學(xué)指標(biāo)之一[3-4]。溫度是控制土壤酶活性的一個(gè)重要環(huán)境因子[5-6],全球氣候變暖可能對(duì)陸地生態(tài)系統(tǒng)土壤酶活性產(chǎn)生影響。一方面,升高溫度可以影響土壤酶的動(dòng)力學(xué),直接影響土壤酶活性[7]；另一方面,升高溫度也可能通過(guò)影響土壤的水熱條件、土壤微生物的群落結(jié)構(gòu)、微生物生物量、有機(jī)物質(zhì)分解等因素間接影響土壤酶的活性[6,8-10]。已有的研究表明,土壤溫度升高能增加土壤酶活性[11-13],但不同生態(tài)系統(tǒng)及不同種類的土壤酶對(duì)溫度敏感性存在一定差異[14-17],且同一種酶在不同生態(tài)系統(tǒng)下對(duì)土壤溫度的敏感性也表現(xiàn)不一致[18]。因此,未來(lái)氣候變化可能對(duì)陸地生態(tài)系統(tǒng)中土壤酶系統(tǒng)產(chǎn)生復(fù)雜的影響,從而影響相關(guān)的土壤碳氮過(guò)程。

川西高山森林位于長(zhǎng)江上游和青藏高原東緣,在區(qū)域氣候調(diào)節(jié)、涵養(yǎng)水源、水土保持、生物多樣性保育和全球碳循環(huán)等方面具有十分重要的作用和地位[19-20]。每年11月至次年4月,受季節(jié)性雪被等因素的影響,土壤表現(xiàn)出明顯的季節(jié)性凍融過(guò)程,且由于氣溫隨海拔降低而升高,因而季節(jié)性雪被和凍融循環(huán)也隨海拔垂直分異連續(xù)變化[21]。這為研究高海拔森林土壤生態(tài)過(guò)程及其對(duì)環(huán)境變化的響應(yīng)提供了理想的天然實(shí)驗(yàn)室。因此,采用原狀土柱移位實(shí)驗(yàn),將岷江冷杉(Abiesfaxoniana)原始林(3582 m)的原狀土柱分別培養(yǎng)在岷江冷杉原始林(3582 m)、岷江冷杉和紅樺(Betulaalbo-sinensis)混交林(3298 m)和岷江冷杉次生林(3023 m)的森林地表,研究了不同關(guān)鍵時(shí)期的土壤酶活性動(dòng)態(tài)特征,以期深入理解全球變暖情景下的高海拔森林土壤生態(tài)過(guò)程。

1 材料與方法

1.1 研究區(qū)域概況

研究區(qū)域位于四川省理縣畢棚溝自然保護(hù)區(qū)(102°53′—102°57′ E,31°14′—31°19′N,海拔2458—4619 m),地處青藏高原東緣與四川盆地的過(guò)渡帶。年降雨量約850 mm,年平均氣溫2—4℃,最高氣溫23℃(7月),最低氣溫 -18℃ (1月)。土壤季節(jié)性凍結(jié)期為每年11月初至次年4月中旬,凍結(jié)時(shí)間長(zhǎng)達(dá)5—6個(gè)月,土壤凍結(jié)初期和融化期間具有比較明顯的凍融循環(huán)[21]。研究區(qū)域的主要森林植被類型為針葉林和針闊混交林,主要森林樹種包括岷江冷杉、川西云杉(Picealikiangensisvar.balfouriana)和紅樺。林下灌木主要為箭竹(Fargesiaspathacea)、高山杜鵑(Rhododendrondelavayi)、三顆針(Berberisjulianae)等；草本主要有蟹甲草(Cacaliaauriculata)、高山冷蕨(Cystopterismontana)、苔草屬(Carexspp.)和莎草屬(Cyperusspp.)等[21]。

1.2 樣地設(shè)置與樣品采集

2010年5月在岷江冷杉原始林(3582 m)內(nèi)選取坡向、坡度和海拔高度基本一致(30 m×30 m)的樣地,先清除地面上的植物與新鮮凋落物,再將PVC管(長(zhǎng)20 cm、內(nèi)徑5 cm)垂直打入土壤中,在盡量不破壞土壤的原狀結(jié)構(gòu)情況下,保持PVC管上端與土壤表面平行,然后挖出裝有土壤的PVC管,將兩端用尼龍布封口,其中上層為土壤有機(jī)層(OL),下層為礦質(zhì)土壤層(MS)。

原狀土柱移位實(shí)驗(yàn)：將采自原始冷杉林下的原狀土柱進(jìn)行原位培養(yǎng),其余土柱分別培養(yǎng)在海拔3298 m的岷江冷杉和紅樺混交林(海拔降低284 m,理論氣溫增加1.78℃)和海拔3023 m的岷江冷杉次生林(海拔降低559 m,理論氣溫增加3.52℃)地表。在3個(gè)海拔梯度上分別選擇5個(gè)具有代表性且環(huán)境條件基本一致的標(biāo)準(zhǔn)樣地,每個(gè)樣地劃分3個(gè)小區(qū),在每個(gè)小區(qū)內(nèi)埋入5根已經(jīng)裝好土壤的PVC管,即每個(gè)海拔梯度埋設(shè)75根PVC管。

根據(jù)土壤溫度動(dòng)態(tài)、冬季土壤凍融過(guò)程以及前期的實(shí)驗(yàn)觀察結(jié)果[22],于2010年8月12日生長(zhǎng)季初期(EGS)、2010年10月17日生長(zhǎng)季末期(LGS)、2010年12月23日凍結(jié)初期(OF)、2011年3月3日深凍期(DF)和2011年4月19日融化期(TP)進(jìn)行土壤樣品采集。在每個(gè)樣地內(nèi)的各小區(qū)采集1根PVC管,每根PVC管內(nèi)的土壤分別分層處理,其中0—10 cm為土壤有機(jī)層,10—20 cm為礦質(zhì)土壤層,各樣地內(nèi)的樣品分別混勻后裝入無(wú)菌樣品袋低溫保存,即時(shí)運(yùn)回實(shí)驗(yàn)室。隨后將每個(gè)樣品去掉石塊、動(dòng)植物殘?bào)w和根系后過(guò)2 mm篩,混勻裝入保鮮袋,貯存4℃的冰箱中備用,用于土壤轉(zhuǎn)化酶和脲酶活性測(cè)定。

1.3 測(cè)定方法

2010年5月,分別在樣地內(nèi)地表及土壤5 cm和15 cm處埋設(shè)紐扣式溫度記錄器(DS1923-F5#,Maxim/Dallas semiconductor Inc., USA) 連續(xù)監(jiān)測(cè)空氣及土壤溫度,設(shè)定為每1 h記錄一次數(shù)據(jù)。

土壤酶活性參照關(guān)松蔭[23]的方法測(cè)定。轉(zhuǎn)化酶(INV)采用3,5-二硝基水楊酸比色法測(cè)定,一個(gè)酶活性單位(EUINV)以1 g土壤樣品在37℃條件下,24 h內(nèi)水解產(chǎn)生葡萄糖的毫克數(shù)表示；土壤脲酶(URE)采用尿素比色法測(cè)定,一個(gè)酶活性單位(EUURE)以1 g土壤在37℃條件下,24 h內(nèi)水解減少的尿素毫克數(shù)表示。

1.4 統(tǒng)計(jì)分析

采用重復(fù)測(cè)量方差分析(repeated-analysis ANOVA)檢驗(yàn)海拔、土層、采樣時(shí)期及各因子交互作用對(duì)土壤轉(zhuǎn)化酶和脲酶活性的影響。采用單因素方差分析(one-way ANOVA)和Tukey法檢驗(yàn)同一采樣時(shí)期不同海拔和同一海拔的不同采樣時(shí)期對(duì)土壤轉(zhuǎn)化酶和脲酶活性的影響。采用Excel 2007和SPSS 16.0對(duì)實(shí)驗(yàn)數(shù)據(jù)進(jìn)行統(tǒng)計(jì)與分析,顯著性水平設(shè)定為P<0.05。

2 結(jié)果與分析

2.1 土壤溫度特征

圖1 3個(gè)海拔梯度的大氣及土壤溫度動(dòng)態(tài)變化(2010-05-24—2011-04-19)Fig.1 Temperature dynamic of air and soil in three elevations from May 24, 2010 to April 19, 2011. A is daily dynamic of atmosphere temperature, and B is the temperature difference at different critical periods

2010年5月24日—2011年4月19日期間,3個(gè)海拔的森林群落中,空氣和土壤溫度變化特征如圖1所示。隨著海拔降低,即與3582 m相比,海拔降低284 m和559 m使空氣溫度表現(xiàn)出增高的趨勢(shì),全年平均氣溫實(shí)際增高分別為1.39℃和2.64℃。土壤溫度在不同增溫模式下表現(xiàn)出一定的差異,海拔下降284 m后土柱的土壤有機(jī)層和礦質(zhì)土壤層溫度在生長(zhǎng)季初期和融化期表現(xiàn)為升高,而在生長(zhǎng)季末期到深凍期則表現(xiàn)為下降,全年平均溫度實(shí)際分別降低了0.55℃和0.56℃；海拔降低559 m,土柱的土壤有機(jī)層和礦質(zhì)土壤層溫度在整個(gè)研究期間均表現(xiàn)為升高,全年平均溫度實(shí)際分別增加了0.84℃和0.82℃。

2.2 土壤轉(zhuǎn)化酶活性動(dòng)態(tài)

土柱原位培養(yǎng)、海拔降低284 m和559 m移位培養(yǎng)的土壤有機(jī)層和礦質(zhì)土壤層的轉(zhuǎn)化酶活性均隨著關(guān)鍵時(shí)期而變化(圖2)。其中,土壤有機(jī)層的轉(zhuǎn)化酶活性明顯高于礦質(zhì)土壤層。土壤有機(jī)層的轉(zhuǎn)化酶活性均表現(xiàn)為從生長(zhǎng)季初期到生長(zhǎng)季末期顯著下降,隨后在凍結(jié)階段顯著升高并在深凍期達(dá)到全年最高,并與土壤采樣時(shí)期均溫呈極顯著負(fù)相關(guān)關(guān)系(表1)。土柱位移對(duì)生長(zhǎng)季節(jié)末期的土壤有機(jī)層轉(zhuǎn)化酶活性沒有顯著影響,但降低了其它關(guān)鍵時(shí)期土壤有機(jī)層的轉(zhuǎn)化酶活性。不管土柱位移培養(yǎng)與否,礦質(zhì)土壤層的轉(zhuǎn)化酶活性均表現(xiàn)為從生長(zhǎng)季初期到生長(zhǎng)季末期顯著下降,在隨后的凍結(jié)階段和融化期顯著升高并在融化期升至全年最高。海拔降低284m提高了土壤凍結(jié)階段(OF和DF期)的轉(zhuǎn)化酶活性,但海拔降低559m降低了土壤凍結(jié)期間礦質(zhì)土壤層的轉(zhuǎn)化酶活性；土柱的海拔位移顯著降低了生長(zhǎng)季初期和融化期礦質(zhì)土壤層的轉(zhuǎn)化酶活性。海拔、土層和采樣時(shí)期及其相互間的交互作用均顯著影響了土壤轉(zhuǎn)化酶活性(表2)。

圖2 土柱海拔位移對(duì)高山森林土壤有機(jī)層和礦質(zhì)土壤層轉(zhuǎn)化酶活性動(dòng)態(tài)的影響Fig.2 Effects of soil column transplanting on soil invertase activity in soil organic layer (OL) and mineral soil layer (MS) in the alpine forest from May 24, 2010 to April 19, 2011不同大寫字母表示不同采樣時(shí)期下同一海拔及土層間的土壤轉(zhuǎn)化酶活性差異顯著；不同小寫字母表示不同海拔間同一采樣時(shí)期及土層間的土壤轉(zhuǎn)化酶活性差異顯著(P<0.05)

因子FactorOLMS轉(zhuǎn)化酶Invertase脲酶Urease轉(zhuǎn)化酶Invertase脲酶Urease水分Mositure0.000-0.0030.2940.369pH-0.1380.2190.200-0.255采樣時(shí)期均溫Du-AT-0.706**-0.608*-0.470-0.639*海拔間溫差(同一采樣時(shí)期)(E-TD)-0.165-0.154-0.070-0.242

OL: 土壤有機(jī)層; MS: 礦質(zhì)土壤層; Du-AT: Duration average temperature; E-TD: Elevation temperature difference;*P<0.05;**P<0.01

2.3 土壤脲酶活性動(dòng)態(tài)

土柱原位培養(yǎng)、海拔降低284 m和559 m移位培養(yǎng)的土壤有機(jī)層和礦質(zhì)土壤層脲酶活性表現(xiàn)出從生長(zhǎng)季初期到深凍期顯著增加,隨后在融化期顯著降低的動(dòng)態(tài)變化,且土壤有機(jī)層的脲酶活性高于礦質(zhì)土壤層(圖3)。土壤脲酶活性與土壤時(shí)期均溫呈極顯著負(fù)相關(guān)關(guān)系(表1)。土柱位移對(duì)土壤有機(jī)層脲酶活性產(chǎn)生了顯著影響,海拔降低284 m提高了生長(zhǎng)季初期的脲酶活性,而海拔降低559 m則提高了其他關(guān)鍵時(shí)期的脲酶活性。礦質(zhì)土壤層在生長(zhǎng)季末期和土壤凍結(jié)期表現(xiàn)出與有機(jī)層相似的趨勢(shì),而海拔降低284 m則提高了融化期的脲酶活性。海拔、土層和采樣時(shí)期顯著影響了土壤脲酶活性(表2)。

表2海拔、土層和采樣時(shí)期對(duì)土壤轉(zhuǎn)化酶和脲酶活性影響的重復(fù)方差分析結(jié)果

Table2ResultsofrepeatedmeasuresANOVAfortheeffectsofelevation,soillayer,andsamplingperiodonsoilinvertaseandureaseactivities

轉(zhuǎn)化酶Invertase脲酶Urease因子Factors樣本自由度df(n)誤差自由度df(error)FP因子Factors樣本自由度df(n)誤差自由度df(error)FPE21239.012<0.001E212108.377<0.001L1120.0089<0.001L1120.0058<0.001SP448705.781<0.001SP448574.376<0.001E×L21219.271<0.001E×L21218.236<0.001E×SP84817.036<0.001E×SP84820.679<0.001L×SP448318.542<0.001L×SP44857.155<0.001E×L×SP84813.053<0.001E×L×SP84835.321<0.001

E: 海拔elevation;L: 土層soil layer; SP: 采樣時(shí)期sampling period

圖3 土柱海拔位移對(duì)高山森林土壤有機(jī)層和礦質(zhì)土壤層脲酶活性動(dòng)態(tài)的影響Fig.3 Effects of soil column transplanting on urease activity in both soil organic layer (OL) and mineral soil layer (MS) in the alpine forest from May 24, 2010 to April 19, 2011圖中不同大寫字母表示不同采樣時(shí)期下同一海拔及土層間的土壤脲酶活性差異顯著；不同小寫字母表示不同海拔間同一采樣時(shí)期及土層間的土壤脲酶活性差異顯著(P<0.05)

3 討論

利用土柱在自然海拔梯度上研究模擬大氣溫度增加對(duì)土壤溫度的影響發(fā)現(xiàn),不同模擬增溫幅度對(duì)土壤溫度的影響存在一定差異(圖1)。與前人的研究結(jié)果一致,在受季節(jié)性雪被影響的高緯度高海拔地區(qū),冬季土壤溫度表現(xiàn)出降低的現(xiàn)象[24-27]。海拔降低284 m的土壤有機(jī)層和礦質(zhì)土壤層溫度在生長(zhǎng)季初期和融化期表現(xiàn)出升高的趨勢(shì),在生長(zhǎng)季末期、凍結(jié)期和深凍期則表現(xiàn)出下降的趨勢(shì)。海拔降低284 m的森林群落普遍存在的雪被覆蓋現(xiàn)象對(duì)土壤起到一定的絕緣和隔熱作用,同時(shí),雪被還可能干擾了太陽(yáng)輻射對(duì)土壤的增溫效應(yīng)[26,28-29],從而使得海拔降低284 m的土壤溫度在冬季并不隨氣溫的增加而增加。而海拔降低559 m的雪被覆蓋時(shí)間和雪被厚度均明顯降低[30],土壤溫度對(duì)太陽(yáng)輻射響應(yīng)更敏感,使得土壤平均溫度升高。

土壤酶是土壤生態(tài)系統(tǒng)代謝的一類重要?jiǎng)恿?主要來(lái)源于動(dòng)植物的分泌及其殘?bào)w和微生物的分泌。土壤酶活性是土壤生物和非生物環(huán)境變化的“感應(yīng)器”[31-32],在凋落物分解、碳氮礦化、土壤養(yǎng)分轉(zhuǎn)化和循環(huán)過(guò)程中具有重要的作用。川西高山森林土壤轉(zhuǎn)化酶活性從生長(zhǎng)季初期到生長(zhǎng)季末期顯著下降,可能是由于：1)土壤溫度的急劇降低,抑制了土壤生物活性及酶合成[33-34]；2)由于土柱實(shí)驗(yàn)排除了植物根系的影響,導(dǎo)致植物輸入地下的有機(jī)物及根系分泌物減少,影響土壤轉(zhuǎn)化酶活性[35]。由于深凍期相對(duì)穩(wěn)定的環(huán)境在一定程度上有利于對(duì)低溫適應(yīng)性更好的物種生長(zhǎng)[36],提高了土壤微生物群落的多樣性,以及融化期凋落物的解凍等釋放的胞內(nèi)酶在短期內(nèi)對(duì)酶活性的促發(fā)[34,37],導(dǎo)致轉(zhuǎn)化酶活性在隨后的凍結(jié)階段和融化期表現(xiàn)出升高的趨勢(shì)。前人的研究表明,酶活性對(duì)小幅度的土壤增溫響應(yīng)并不敏感[11,38-39]。本研究中,酶活性對(duì)增溫的響應(yīng)明顯小于季節(jié)性溫度變化引起的響應(yīng)(表1和圖1,圖2), 與前人的研究結(jié)果一致[11,39]。不同模擬增溫條件下土壤轉(zhuǎn)化酶活性在不同采樣時(shí)期表現(xiàn)也不一致,與土柱原位培養(yǎng)相比,海拔降低284 m和海拔降低559 m處的土壤轉(zhuǎn)化酶活性在凍結(jié)階段的兩個(gè)土層中分別表現(xiàn)出升高和降低的趨勢(shì),可能是由于凍結(jié)作用導(dǎo)致的死亡生物細(xì)胞破裂釋放出的胞內(nèi)酶在短期內(nèi)提高土壤酶活性[34,37],以及雪被的保溫作用為那些對(duì)低溫適應(yīng)性更好的土壤微生物提供了較為穩(wěn)定的微環(huán)境[36],改變了土壤微生物群落組成結(jié)構(gòu),更有利于增加土壤酶生產(chǎn)和活性。

土壤酶活性與土壤水熱條件之間有著十分密切的關(guān)系,不同季節(jié)水分的差異導(dǎo)致了它們對(duì)增溫的響應(yīng)不同,如土壤蛋白酶更易受土壤水分影響,而在土壤水分保持穩(wěn)定的條件下,土壤脲酶對(duì)溫度的敏感性則更高[6,40]。本研究中,由于生長(zhǎng)季內(nèi)降水較多,適宜的小氣候促進(jìn)微生物的生長(zhǎng),模擬增溫顯著增加了土壤脲酶的活性,這一結(jié)果與徐振鋒等[41]的研究相似。在凍融季節(jié),土壤脲酶先顯著升高,然后在融化期顯著降低,且海拔降低559 m脲酶活性相對(duì)較高,可能是由于凍融交替作用使土壤疏松度增加,水穩(wěn)性團(tuán)聚體降低,促進(jìn)有機(jī)物質(zhì)和微生物接觸進(jìn)而增強(qiáng)酶的激活效應(yīng)[42]；同時(shí),凍融交替導(dǎo)致土壤水分滲透壓變化,大量土壤生物死亡也可促進(jìn)死亡細(xì)胞內(nèi)酶向土壤中釋放,在短期內(nèi)也提高土壤酶活性[37,43]。但當(dāng)土壤融化時(shí),強(qiáng)烈的淋溶作用使養(yǎng)分大量流失[44-45],通過(guò)限制土壤生物的生長(zhǎng)和復(fù)蘇而使土壤酶活性有所下降。

綜上所述,土壤酶活性除受溫度的影響外,土壤凍融格局、微生物的活性等的改變也會(huì)直接或間接影響土壤酶的活性,由于研究環(huán)境的差異,不同因子的共同作用可能導(dǎo)致土壤酶活性受增溫的影響不同。川西高山森林土壤酶活性對(duì)季節(jié)性溫度變化和不同增溫幅度的響應(yīng)有所差異,且土壤酶活性對(duì)溫度的響應(yīng)與采樣時(shí)期均溫呈顯著的負(fù)相關(guān)關(guān)系。在土壤凍結(jié)期出現(xiàn)一個(gè)明顯的酶活性高峰,顯著高于生長(zhǎng)季(或與之相當(dāng)),表明冬季低溫環(huán)境維持的土壤酶活性對(duì)川西高山森林土壤生態(tài)過(guò)程具有重要作用。

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ResponsesofsoilinvertaseandureaseactivitiesinanalpineforestofwesternSichuantosimulatedclimatewarmingatdifferentcriticalperiods

ZHANG Li1,2, WU Fuzhong1,2, XU Zhenfeng1,2, TAN Bo1,2, LIU Yang1,2, YANG Yulian1,2,3, WANG Ao1,2,4, YANG Wanqin1,2,*

1Long-termResearchStationofAlpineForestEcosystems,InstituteofEcology&Forestry,SichuanAgriculturalUniversity,Chengdu611130,China2CollaborativeInnovationCenterofEcologicalSecurityintheUpperReachesofYangtzeRiver,Chengdu611130,China3SichuanProvincialKeyLaboratoryofEcologicalSecurityandProtection,MianyangNormalUniversity,Mianyang621000,China4InstituteofProductQualityInspectionandTestingofZunyi,Zhunyi563000,China

國(guó)家自然科學(xué)基金項(xiàng)目(31570445, 31270498, 31500509, 31570601);教育部博士點(diǎn)基金項(xiàng)目(20105103110002);四川省教育廳重點(diǎn)項(xiàng)目(15ZA0009);四川省杰出青年學(xué)術(shù)與技術(shù)帶頭人培育項(xiàng)目(2012JQ0008)

2016- 05- 18; < class="emphasis_bold">網(wǎng)絡(luò)出版日期

日期:2017- 03- 27

*通訊作者Corresponding author.E-mail: scyangwq@163.com

10.5846/stxb201605180960

張麗,吳福忠,徐振鋒,譚波,劉洋,楊玉蓮,王奧,楊萬(wàn)勤.川西高山森林不同時(shí)期土壤轉(zhuǎn)化酶和脲酶活性對(duì)模擬氣候變暖的響應(yīng).生態(tài)學(xué)報(bào),2017,37(16):5352- 5360.

Zhang L, Wu F Z, Xu Z F, Tan B, Liu Y, Yang Y L, Wang A, Yang W Q.Responses of soil invertase and urease activities in an alpine forest of western Sichuan to simulated climate warming at different critical periods.Acta Ecologica Sinica,2017,37(16):5352- 5360.