高山森林林窗對(duì)凋落葉分解的影響

吳慶貴, 吳福忠,譚　波,楊萬勤,*,何　偉,倪祥銀

1 四川農(nóng)業(yè)大學(xué), 生態(tài)林業(yè)研究所,林業(yè)生態(tài)工程省級(jí)重點(diǎn)實(shí)驗(yàn)室, 成都　611130 2 綿陽師范學(xué)院, 生態(tài)安全與保護(hù)四川省重點(diǎn)實(shí)驗(yàn)室, 綿陽　621000

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高山森林林窗對(duì)凋落葉分解的影響

吳慶貴1,2, 吳福忠1,譚波1,楊萬勤1,*,何偉1,倪祥銀1

1 四川農(nóng)業(yè)大學(xué), 生態(tài)林業(yè)研究所,林業(yè)生態(tài)工程省級(jí)重點(diǎn)實(shí)驗(yàn)室, 成都611130 2 綿陽師范學(xué)院, 生態(tài)安全與保護(hù)四川省重點(diǎn)實(shí)驗(yàn)室, 綿陽621000

摘要:林窗對(duì)降水和光照等環(huán)境條件的再分配以及分解者群落的影響可能深刻作用于森林凋落物分解過程，但有關(guān)高山森林林窗大小對(duì)凋落物分解的影響尚無研究報(bào)道。采用凋落物分解袋法，研究了川西高山森林不同大小林窗對(duì)非生長(zhǎng)季節(jié)和生長(zhǎng)季節(jié)紅樺(Betula albo-sinensis)和岷江冷杉(Abies faxoniana)凋落葉質(zhì)量損失的影響。結(jié)果顯示，經(jīng)過1a的分解，不同生境下紅樺和岷江冷杉凋落葉分別分解了27.25%—30.12%和27.04%—27.96%，其中非生長(zhǎng)季節(jié)占53.83%—60.18%和50.23%—59.09%。林窗對(duì)紅樺和岷江冷杉凋落葉質(zhì)量損失的影響因物種不同而呈現(xiàn)季節(jié)差異?？傮w上，林窗加快了岷江冷杉凋落葉的分解而延緩了紅樺凋落葉的分解。與郁閉林下相比，林窗顯著增加了2種凋落葉非生長(zhǎng)季節(jié)的質(zhì)量損失速率，顯著降低了生長(zhǎng)季節(jié)2種凋落葉的質(zhì)量損失速率；2種凋落葉質(zhì)量損失速率在非生長(zhǎng)季節(jié)隨林窗面積增大而加快，在生長(zhǎng)季節(jié)隨林窗面積增大而減慢。林窗顯著影響了初凍期、深凍期和融化期岷江冷杉凋落葉的質(zhì)量損失率，但對(duì)紅樺凋落葉質(zhì)量損失率影響不顯著?？梢?，高山森林凋落物分解過程受到林窗的顯著影響，并且闊葉和針葉凋落葉在非生長(zhǎng)季節(jié)和生長(zhǎng)季節(jié)對(duì)林窗的響應(yīng)具有明顯差異。

關(guān)鍵詞：林窗; 凋落物分解; 質(zhì)量損失; 非生長(zhǎng)季節(jié); 針葉林; 高寒地區(qū)

林窗是川西高山森林生態(tài)系統(tǒng)普遍存在的干擾形式[1]。與郁閉林下相比，林窗改變了林內(nèi)水熱條件(光照、溫度、降水)和分解者群落結(jié)構(gòu)[2]，可能對(duì)凋落物分解過程具有強(qiáng)烈影響。在高寒森林生態(tài)系統(tǒng)，不同大小的林窗內(nèi)冬季雪被厚度和持續(xù)時(shí)間的變異可能深刻作用于凋落物分解[3- 4]。一方面，林窗內(nèi)雪被的絕熱保溫作用能使土壤微生物維持相對(duì)較高的活性[5]；另一方面，郁閉林冠下由于缺乏雪被覆蓋，微生物活性受低溫和凍結(jié)作用抑制[6]。因而，林窗可能促進(jìn)冬季凋落葉分解，并且不同大小林窗對(duì)雪被厚度和凍融循環(huán)格局的改變也可能不同程度地作用于凋落葉分解[7- 8]。與此相反，盡管生長(zhǎng)季節(jié)適宜的溫濕度條件更有利于凋落物分解，但林窗內(nèi)相對(duì)更高的光照強(qiáng)度和光輻射效率[9]可導(dǎo)致凋落物地表溫度升高[10]，水分蒸發(fā)增加[11]，進(jìn)而影響土壤微生物活性和土壤動(dòng)物活動(dòng)能力[12]。因此，相比于郁閉林下，林窗可能抑制生長(zhǎng)季節(jié)凋落葉分解。這意味著，林窗對(duì)高寒森林生態(tài)系統(tǒng)不同季節(jié)凋落物的分解具有截然不同的影響，但迄今的研究一直缺乏相應(yīng)的關(guān)注，這極大地限制了對(duì)高寒森林地下生態(tài)過程的認(rèn)識(shí)。

川西高山森林在調(diào)節(jié)區(qū)域氣候、涵養(yǎng)水源、保育生物多樣性等方面具有突出的戰(zhàn)略地位。前期研究表明，林窗是川西高山森林群落最主要的自然更新方式[13]，影響凋落物分解的生物和非生物因素與林窗密切相關(guān)[14]。因此，可以假設(shè)，林窗能顯著影響川西高山森林凋落葉分解過程，在冬季促進(jìn)凋落葉分解，在生長(zhǎng)季節(jié)制約凋落葉分解；且闊葉和針葉凋落葉對(duì)林窗的響應(yīng)不同。為驗(yàn)證上述假設(shè)，本研究采用凋落物分解袋法，以區(qū)域內(nèi)代表性針葉樹種岷江冷杉(Abiesfaxoniana)和闊葉樹種紅樺(Betulaalbo-sinensis)凋落葉為研究對(duì)象，研究林窗面積大小對(duì)針、闊樹種凋落葉在非生長(zhǎng)季節(jié)和生長(zhǎng)季節(jié)分解的影響，以期為深入認(rèn)識(shí)高寒森林生態(tài)系統(tǒng)物質(zhì)循環(huán)過程提供科學(xué)依據(jù)。

1材料與方法

1.1研究區(qū)域與樣地概況

研究區(qū)域位于四川省理縣畢棚溝自然保護(hù)區(qū)(31°14′—31°19′ N，102°53′—102°57′ E， 2458—4619 m a.s.l.)，地處青藏高原東緣與四川盆地的過渡帶。年平均氣溫2—4℃，最高氣溫23℃ (7月)，最低溫度為-18℃ (1月)，年降水量約850 mm。該區(qū)域冬季具有明顯的季節(jié)性雪被覆蓋和凍融過程，雪被厚度達(dá)50 cm，凍融時(shí)間長(zhǎng)達(dá)約120 d[3]。區(qū)域內(nèi)典型植被為岷江冷杉(A.faxoniana) 、紅樺(B.albo-sinensis)和川西云杉(Piceabalfouriana)。土壤為發(fā)育于坡積物上的雛形土，基本理化性質(zhì)見楊玉蓮等[15]。

表1　樣地內(nèi)不同林窗的面積、形成木、邊界木和形成方式

圖1　不同林窗下的日平均溫度　Fig. 1　Daily means temperature in sampled gaps and the closed canopyLG: 大林窗l(fā)arge gap;IG: 中林窗intermediate gap; SG: 小林窗small gap; CC: 郁閉林下the closed canopy; BGS: 非生長(zhǎng)季節(jié)beyond growing season; GS: 生長(zhǎng)期季節(jié)growing season

基于前期研究，在海拔3598m 原始岷江冷杉林內(nèi)設(shè)置1 hm2樣地(坡向NE 38°，坡度24°)。喬木層岷江冷杉占據(jù)絕對(duì)優(yōu)勢(shì)，其次是紅樺，伴生少量野櫻桃(P.tatsienensis)；灌木主要有高山杜鵑(Rhododendrondelavayi)、三顆針(Berberissargentiana)和絹毛薔薇(Rosasericea)等；草本以鐵線蓮(Clematis)、苔草(Carex)和羊茅(Festuca)等為主，林窗內(nèi)草本蓋度約85%。按照林窗面積大小在樣地內(nèi)分別選取大林窗(large gap, LG)、中林窗(intermediate gap, IG)和小林窗(small gap, SG)各3個(gè)。同時(shí)，在岷江冷杉郁閉林下(the closed canopy, CC)設(shè)置3個(gè)10 m×10 m的樣方作為對(duì)照。然后調(diào)查林窗的基本性質(zhì) (表1)，并進(jìn)行整理和清除工作。

1.2凋落物分解試驗(yàn)

2011年秋季搜集岷江冷杉和紅樺新鮮凋落葉，室溫下自然風(fēng)干，稱取10 g風(fēng)干凋落葉裝入分解袋(大小為20 cm×20 cm，貼地面孔徑0.50 mm，上表面孔徑1 mm)，于2011年11月埋設(shè)于樣地，分解試驗(yàn)為期1a，共埋設(shè)分解袋1440袋=每次取樣 (10) × 林窗 (4) × 3 (重復(fù)) × 2 (物種) × 6次。同時(shí)，采用紐扣式溫度記錄器(iButton DS1923-F5, Maxim/Dallas Semiconductor, Sunnyvale, USA)記錄空氣和各林窗下凋落袋內(nèi)溫度，設(shè)定每2 h記錄1次溫度數(shù)據(jù)。此外，采用鋼尺測(cè)量各海拔林窗及林下雪被厚度。各林窗溫度和雪被變化見圖1、圖2和表2。

根據(jù)前期監(jiān)測(cè)，按高山植物的物候期分非生長(zhǎng)季節(jié)(冬季)和生長(zhǎng)季節(jié)進(jìn)行樣品采集，具體為：非生長(zhǎng)季節(jié)的初凍期(12月27日，onset of soil freezing period, OF)、深凍期(3月7日，soil deep freezing period, DF)、融化期(4月27日，soil thawing period, TP)；生長(zhǎng)季節(jié)的初期(6月16日，early growth period, EP)、中期(8月25日mid-growing period, MP)和后期(10月29日，later growth period, LP)。每次采樣時(shí)隨機(jī)從每個(gè)樣方撿回10袋凋落葉，去除雜物后，于65℃烘干至恒重并稱量，計(jì)算凋落葉失重率。2種凋落葉的初始化學(xué)特征見表3。

圖2　不同大小林窗和郁閉林下的雪被厚度Fig. 2　Snow depths in forest gaps and the closed canopy

林窗類型Typesofgap初凍期Onsetofsoilfreezingperiod深凍期Soildeepfreezingperiod融化期Soilthawingperiod生長(zhǎng)初期Earlygrowthperiod生長(zhǎng)中期Mid-growingperiod生長(zhǎng)后期Latergrowthperiod大林窗Largegap-0.56±0.16a-1.39±0.19a2.98±0.41a9.78±1.04a12.51±0.41a7.94±0.74a中林窗Intermediategap-1.60±0.13b-2.12±0.29b2.16±0.36b9.40±1.08a12.34±0.54ab5.68±0.51b小林窗Smallgap-1.98±0.15c-2.13±0.33b1.95±0.34b6.16±0.96b11.63±0.44b5.66±0.63b郁閉林下Closedcanopy-2.40±0.12d-3.14±0.45c0.59±0.14c6.04±0.53b10.13±0.55c4.37±0.55c

不同小寫字母表示差異顯著(獨(dú)立樣本t檢驗(yàn),P< 0.05)

表3　紅樺和岷江冷杉凋落葉初始質(zhì)量特征(平均值±標(biāo)準(zhǔn)偏差, n=5)

1.3數(shù)據(jù)處理與統(tǒng)計(jì)分析

半分解時(shí)間(T50%)、95%分解時(shí)間(T95%)、質(zhì)量損失率和質(zhì)量損失速率[16- 17]按如下公式計(jì)算：

50%分解時(shí)間=-ln(1-0.50)/(k)

95%分解時(shí)間=-ln(1-0.95)/(k)

質(zhì)量損失率Lt(%)=100× (Mt-M0)/ M0

各關(guān)鍵時(shí)期每30d質(zhì)量損失速率Vt(%/d)= 30 ×(Mt-1-Mt)/ M0×100/DΔt

各關(guān)鍵時(shí)期質(zhì)量損失占全年比率Rt(%) = 100× (Mt-1-Mt) /(M0-M6)

式中，Mt為t時(shí)刻凋落葉干質(zhì)量(g)，M0為初始干重(g)，(Mt-1-Mt)為相鄰采樣時(shí)間凋落葉殘留量差(t=1，2，3,…,6)，DΔt為相鄰采樣時(shí)間間隔天數(shù)。

用單因素方差分析(one-way ANOVA)檢驗(yàn)凋落葉日均溫、質(zhì)量損失率、損失速率在不同林窗間的差異顯著性；用Pearson相關(guān)分析檢驗(yàn)日均溫、凍融循環(huán)次數(shù)與質(zhì)量損失速率之間的相關(guān)關(guān)系。顯著性水平設(shè)為P= 0.05，數(shù)值以平均值±標(biāo)準(zhǔn)誤(mean ± SE)表示。數(shù)據(jù)分析采用SPSS 20.0 (IBM SPSS Statistics Inc., Chicago, IL, USA)軟件包進(jìn)行。

2結(jié)果與分析

2.1質(zhì)量損失率

分解1a后，紅樺和的岷江冷杉凋落葉質(zhì)量損失率分別為27.25—30.12%和27.04—27.96% (圖3)。2種凋落葉半分解和95%分解時(shí)間分別為2.015—2.413 a、2.110—2.557 a和8.708—10.428 a、9.121—11.053 a，紅樺凋落葉分解周期隨林窗面積增加而增加，岷江冷杉凋落葉則相反(表4)。與郁閉林下相比，林窗形成顯著(P<0.05)影響非生長(zhǎng)季節(jié)(初凍期、深凍期和融化期)岷江冷杉凋落葉的質(zhì)量損失率，且林窗面積越大其質(zhì)量損失率越高；而對(duì)紅樺凋落葉質(zhì)量損失率無顯著影響(P>0.05)。

圖3　不同大小林窗和郁閉林下的凋落葉質(zhì)量損失Fig. 3　Mass losses of foliar litter in forest gaps and the closed canopy

物種Species林窗類型Typesofgap回歸方程Regressionmodels分解系數(shù)kDecompositionconstantk相關(guān)系數(shù)R2CorrelationcoefficientR2半分解時(shí)間/aTimeofhalfdecomposition95%分解時(shí)間/aTimeof95%decomposition紅樺大林窗y=96.476e-0.287t0.2870.9872.41310.428Betulaalbo-sinensis中林窗y=97.412e-0.306t0.3060.9942.2669.794小林窗y=96.927e-0.321t0.3210.9912.1579.324郁閉林下y=97.503e-0.344t0.3440.9952.0158.708岷江冷杉大林窗y=97.494e-0.328t0.3280.9922.1109.121Abiesfaxoniana中林窗y=97.684e-0.307t0.3070.9932.2569.751小林窗y=97.182e-0.283t0.2830.9862.44910.585郁閉林下y=97.286e-0.271t0.2710.9802.55711.053

2.2質(zhì)量損失速率

2種凋落葉分解速率總體上呈現(xiàn)逐漸減慢再增加的趨勢(shì)(圖4)。林窗形成顯著(P<0.05)影響了深凍期、融化期和生長(zhǎng)后期紅樺凋落葉的質(zhì)量損失速率，顯著增加了融化期質(zhì)量損失速率，且隨林窗面積增大而增加。對(duì)岷江冷杉而言，林窗形成顯著(P<0.05)影響了初凍期、融化期和生長(zhǎng)初期凋落葉的質(zhì)量損失速率。林窗形成后顯著(P<0.05)增加了初凍期、深凍期和融化期岷江冷杉凋落葉的質(zhì)量損失速率，且質(zhì)量損失速率隨林窗面積增大而增加；顯著降低了減小降低了生長(zhǎng)季節(jié)后期岷江冷杉凋落葉的質(zhì)量損失速率，且質(zhì)量損失速率隨林窗面積增大而降低。

圖4　不同大小林窗和郁閉林下的凋落葉分解速率Fig. 4　Mass loss rates of foliar litter in forest gaps and the closed canopy

由圖5可得，林窗顯著(P<0.05)影響了2種凋落葉第1年的質(zhì)量損失速率。林窗形成后顯著降低了2種凋落葉第1年生長(zhǎng)季節(jié)質(zhì)量損失速率，且林窗面積越大質(zhì)量損失速率越低；顯著增加了紅樺凋落葉非生長(zhǎng)季節(jié)和岷江冷杉凋落葉非生長(zhǎng)季節(jié)以及第1年的質(zhì)量損失速率，且林窗面積越大質(zhì)量損失速率越高?？傮w上，2種凋落葉質(zhì)量損失速率在第1年非生長(zhǎng)季節(jié)顯著(P<0.05)高于生長(zhǎng)季節(jié)。

圖5　冬季和生長(zhǎng)季節(jié)凋落葉分解速率Fig. 5　Mass loss rates of foliar litters in forest gaps and the closed canopy in winter and the growing season

2.3各關(guān)鍵時(shí)期的質(zhì)量損失比率

由圖6可得，2種凋落葉各關(guān)鍵時(shí)期質(zhì)量損失所占比例為第1年深凍期>生長(zhǎng)中期>初凍期>生長(zhǎng)初期>生長(zhǎng)后期>融化期。4種不同面積林窗內(nèi)(從大林窗、中林窗、小林窗到林下)紅樺和岷江冷杉凋落葉第1年非生長(zhǎng)季節(jié)質(zhì)量損失分別占第1年的60.18%、54.46%、55.34%、53.83%和59.09%、54.37%、52.22%、50.23%，非生長(zhǎng)季節(jié)顯著(P<0.05)高于生長(zhǎng)季節(jié)。

圖6　各關(guān)鍵時(shí)期質(zhì)量損失在全年分解過程中所占的比率Fig. 6　Ratios of mass losses at each critical stage compared to the entire decomposition year

3討論

與假設(shè)基本一致，川西高山森林林窗對(duì)凋落葉分解有顯著影響：促進(jìn)了冬季凋落葉分解，抑制生長(zhǎng)季節(jié)的凋落葉分解，尤其是對(duì)岷江冷杉凋落葉分解過程作用更為明顯。一方面，林窗面積越大，冬季形成雪被的厚度也越厚，林窗內(nèi)雪被覆蓋的時(shí)間也越長(zhǎng)(圖2)，雪被的保溫作用能持續(xù)促進(jìn)凋落葉分解。并且，大林窗內(nèi)的凋落葉在雪被融化期可接收更多雪融水和降水的淋洗作用，促進(jìn)凋落葉內(nèi)可溶解性組分的流失。另一方面，在生長(zhǎng)季節(jié)，由于缺乏林冠對(duì)光照的過濾和攔截作用，林窗內(nèi)的太陽輻射顯著高于郁閉林下，且這種作用隨林窗面積增加和增強(qiáng)[18]。這促進(jìn)了林窗內(nèi)凋落葉水分的蒸發(fā)，不利于土壤無脊椎動(dòng)物和微生物對(duì)凋落物分解的貢獻(xiàn)，進(jìn)而抑制凋落葉分解。這表明林窗形成對(duì)微環(huán)境的改變能深刻影響高寒森林地下生態(tài)系統(tǒng)的物質(zhì)循環(huán)。

在高寒森林生態(tài)系統(tǒng)中，盡管冬季低溫不利于土壤動(dòng)物[19]和微生物[17]對(duì)凋落葉的降解，但季節(jié)性雪被[3]和凍融循環(huán)[14,16]能顯著作用于冬季凋落葉分解。已有的研究表明，雪被融化的淋洗作用和凍融循環(huán)的物理破碎[3, 14, 16]都能顯著促進(jìn)凋落葉分解。同時(shí)，雪被覆蓋環(huán)境中存活的土壤動(dòng)物[20- 21]和微生物活性[5]也能促進(jìn)冬季凋落葉分解。本研究中，紅樺和岷江冷杉冬季凋落葉分解占全年分解的比例分別為53.83%—60.18%和50.23%—59.09%，高于生長(zhǎng)季節(jié)(圖6)。這說明冬季凋落葉分解對(duì)高山森林物質(zhì)循環(huán)具有十分重要的作用[17]。另一方面，林窗形成能改變雪被環(huán)境、土壤凍融格局[22]和耐寒微生物的活性[23]，直接或間接影響冬季凋落葉分解[12]。本研究中，林窗形成顯著提高了非生長(zhǎng)季節(jié)2種凋落葉質(zhì)量損失速率。地表凋落葉日均溫度和土壤凍融循環(huán)與深凍期等關(guān)鍵時(shí)期質(zhì)量損失速率顯著相關(guān)(表5),這表明林窗形成改變了林窗內(nèi)冬季環(huán)境條件，對(duì)川西高山森林冬季凋落葉分解產(chǎn)生了重要影響[2, 24]。

表5日均溫度(T)和凍融循環(huán)次數(shù)(F)與凋落葉各關(guān)鍵時(shí)期質(zhì)量損失速率的相關(guān)性分析

Table 5Correlation analyses between daily mean temperature and frequencies of freeze-thaw cycle and mass loss rates of foliar litters at critical decomposition period

類別Types物種Species初凍期Onsetofsoilfreezingperiod深凍期Soildeepfreezingperiod融化期Soilthawingperiod生長(zhǎng)初期Earlygrowthperiod生長(zhǎng)中期Mid-growingperiod生長(zhǎng)后期Latergrowthperiod日均溫(T)紅樺Betulaalbo-sinensis-0.2010.607**0.687**-0.139-0.2360.077Averagetemperature岷江冷杉Abiesfaxoniana0.691**0.422*-0.2300.564**-0.182-0.007凍融循環(huán)(F)紅樺Betulaalbo-sinensis-0.1730.1510.355*0.079-0.085Frequencyofsoilfreeze-thawcy-cle岷江冷杉Abiesfaxoniana0.581**0.587**0.650**0.280-0.023

*P<0.05; **P<0.01

林窗對(duì)凋落物分解的影響常常隨林窗面積大小而發(fā)生變化，但已有的研究結(jié)果具有不確定性[24- 28]。有研究者發(fā)現(xiàn)，大林窗中凋落物的質(zhì)量損失速率比小林窗和林下低[25- 26]，也有研究者認(rèn)為林窗面積大小對(duì)凋落物分解影響不顯著[27- 28]，甚至在大林窗中凋落物分解更快[29]。本研究發(fā)現(xiàn)，在1a分解過程中，2種凋落葉在生長(zhǎng)季節(jié)的質(zhì)量損失速率隨林窗面積增加而減小，在非生長(zhǎng)季節(jié)的岷江冷杉凋落葉以及融化期的紅樺凋落葉的質(zhì)量損失速率隨林窗面積增加而增加，而初凍期和深凍期紅樺凋落葉質(zhì)量損失速率在不同面積林窗內(nèi)差異不顯著(中林窗除外)。如前所述，不同面積林窗由于冬季雪被覆蓋以及生長(zhǎng)季節(jié)水分蒸發(fā)量差異等限制著分解者群落的定著，直接影響林內(nèi)凋落葉的分解過程。研究表明，凋落物質(zhì)量(quality)是植物殘?bào)w自身分解的關(guān)鍵因子[30]，控制著中小尺度上凋落物的分解過程[31]。本研究中紅樺和岷江冷杉分別是闊葉和針葉凋落葉，其基質(zhì)質(zhì)量存在顯著差異(表3)，因此對(duì)環(huán)境變化的響應(yīng)過程和時(shí)間也存在不同(圖3)。綜上所述，川西高山森林林窗面積大小對(duì)凋落葉分解產(chǎn)生顯著影響，且闊葉和針葉凋落葉在非生長(zhǎng)季節(jié)與生長(zhǎng)季節(jié)對(duì)林窗的響應(yīng)存在明顯差異。

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基金項(xiàng)目:國家自然科學(xué)基金項(xiàng)目(31170423, 31270498); 國家“十二五”科技支撐計(jì)劃(2011BAC09B05); 四川省杰出青年學(xué)術(shù)與技術(shù)帶頭人培育項(xiàng)目(2012JQ0008, 2012JQ0059); 中國博士后科學(xué)基金(2012T50782); 四川省教育廳青年基金(2013SZB0553, 13TD0015); 生態(tài)安全與保護(hù)四川省重點(diǎn)實(shí)驗(yàn)室開放基金項(xiàng)目(ESP201309, ESP1404)

收稿日期:2014- 10- 19; 網(wǎng)絡(luò)出版日期:2015- 05- 20

*通訊作者

Corresponding author.E-mail: scyangwq@163.com

DOI:10.5846/stxb201410192049

Effects of gap sizes on foliar litter decomposition in alpine forests

WU Qingui1, 2, WU Fuzhong1, TAN Bo1, YANG Wanqin1,*, HE Wei1, NI Xiangyin1

1Long-termResearchStationofAlpineForestEcosystem,KeyLaboratoryofEcologicalForestryEngineering,InstituteofEcology&Forestry,SichuanAgriculturalUniversity,Chengdu611130,China2EcologicalSecurityandProtectionKeyLaboratoryofSichuanProvince,Mianyang621000,China

Abstract：Forest gaps are one of the most normal interferences in primary forest ecosystems, and they play an important role in not only aboveground processes but also belowground processes. However, many studies have paid more attention to the effects of forest gaps on aboveground processes. Increasing evidence has demonstrated that forest gaps have a strong effect on mass loss and carbon and nutrient release in litter by redistributing precipitation, light, and other environmental factors. At high latitudes and altitudes, litter decomposition due to forest gaps may be more complex because of seasonal snow cover and freeze-thaw cycles. Theoretically, interception of rainfall and snowfall in the winter by the canopy and canopy shading may cause the hydrothermal dynamics on the forest floor to vary with respect to gap sizes and critical periods. Currently, little information is available on the effects of gap sizes on litter decomposition at different critical periods. In order to understand the effects of forest gaps on litter decomposition in forest ecosystems at high altitudes, litterbags with red birch (Betula albosinensis) and Minjiang fir (Abies faxoniana) foliar litter were incubated on the forest floor in small, medium, and large gaps and the adjacent closed canopy from November 21, 2011 to October 29, 2012. Then, the litterbags were sampled at the periods of onset of soil freezing (OF), soil deep-freezing (DF), soil thawing (TP), early growth (EP), mid-growth (MP), and late growth (LP), and the mass loss was calculated. After a year of litter decomposition, red birch and Minjiang foliar litter lost 27.25—30.12% and 27.04—27.96% mass, respectively. The mass loss of red birch and Minjiang fir foliar litter in the non-growing season accounted for 53.8—60.18% and 50.23—59.09% of the total mass loss, respectively. Gap sizes have strong effects on the mass loss of Minjiang fir and red birch foliar litter, depending on tree species and sampling periods. Forest gaps accelerated the litter decomposition of Minjiang fir, but slowed down the litter decomposition of red birch. Regardless of tree species, forest gaps significantly accelerated the rates of mass loss of foliar litter in the non-growing season (P < 0.05), but significantly lowered them in the growing season (P < 0.05). The rates of mass loss of foliar litter increased with gap sizes in the non-growing season, but decreased with gap sizes in the growing season. Moreover, the rates of mass loss of Minjiang fir foliar litter in the periods of OF, DF, and TP increased significantly with gap sizes (P < 0.05), but the effects on red birch foliar litter were not significant (P > 0.05). In addition, the contribution of litter mass loss at different critical periods to a year of mass loss was in the order of DF > MP > OF > EP > LP > TP. Mass loss of red birch foliar litter in the non-growing season accounted for 60.18%, 54.46%, 55.34%, and 53.83% of the one-year mass loss in large gaps, middle gaps, small gaps, and closed canopy, respectively; similarly, the contributions of mass loss of Minjiang fir foliar litter to the one-year mass loss in the non-growing season were 59.09%, 54.37%, 52.22%, and 50.23%, respectively. These results suggest that forest gaps accelerated the mass loss of foliar litter in the snow-cover season, but slowed down the mass loss in the growing season. The responses of litter decomposition to gap sizes in the snow-cover season were different from those in the growing season, implying that gap sizes could have strong effects on litter decomposition at different critical periods in the coniferous forest ecosystem of alpine regions.

Key Words:forest gap; litter decomposition; mass loss; non-growing season; coniferous forest; alpine region

吳慶貴, 吳福忠,譚波,楊萬勤,何偉,倪祥銀.高山森林林窗對(duì)凋落葉分解的影響.生態(tài)學(xué)報(bào),2016,36(12):3537- 3545.

Wu Q G, Wu F Z, Tan B, Yang W Q, He W, Ni X Y.Effects of gap sizes on foliar litter decomposition in alpine forests.Acta Ecologica Sinica,2016,36(12):3537- 3545.