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在森林生态系统中,根系是植物与土壤之间进行物质交换和能量流动的桥梁[1-2]。林木细根(≤ 2 mm)吸收水分和养分的表面积大且生理活性强,对保持水土、改善土壤结构、促进养分循环和碳平衡等有不可或缺的作用[2-4],且对气候变化有重要指示意义[5]。细根作为林木根系中最活跃、最敏感的组成部分,其结构与功能特征往往因外界环境条件的变化而改变,其中,细根生物量高低与林木生产力密切相关,细根形态变化影响其功能发挥[6-7]。
林木根系的研究倍受人们关注[8],以往有关根系的研究主要解决自然因素对细根的影响[6,9],而人为采伐干扰对细根生长和分布影响的研究资料仍然十分有限,特别是对细根形态特征研究尤为不足[10],研究结论也存在较大差异。Noguchi等[11]研究表明,10年生日本扁柏(Chamaecyparis obtusa (Sieb. et Zucc.) Endl.)间伐3 a后(间伐强度65%),小于1 mm细根总生物量明显降低,但对细根形态的影响不明显;尤健健等[7]研究表明,中度间伐(保留郁闭度0.7)条件下,油松(Pinus tabuliformis Carr.)林细根总生物量、根长密度和根表面积密度都达到最大;张犇等[12]研究表明,阔叶红松林择伐40 a后(择伐强度40%),生长季未采伐和择伐的年平均细根生物量差异不显著;杨秀云等[10]研究表明,华北落叶松(Larix principis-rupprechtii Mayr)间伐10 a后(间伐强度20%),细根生物量降低,波动范围变窄。
杉木(Cunninghamia lanceolata (Lamb.) Hook.)是我国南方重要的造林和用材树种,在我国森林资源和亚热带森林生态系统中占有重要地位,在林业生产上也有重要战略意义[13]。我国人工林经营长期沿用传统的皆伐方式,近年来,人工林择伐理念才得到重视[13-14]。探讨采伐强度对林木细根的影响程度及其影响机制,对于推进人工林采伐经营方式由皆伐向择伐转变,准确评估人工林采伐经营对人工林生产力和生态稳定性的影响至关重要。为此,以闽北杉阔混交人工林为研究对象,比较不同采伐强度5 a后细根生物量及形态特征差异,旨在探究采伐强度对细根生长的影响以及适宜采伐强度,为该区域杉阔混交人工林科学经营提供基础数据和理论参考。
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福建省建瓯市(117°58′~118°57′ E,26°38′~27°20′ N),地处闽江上游,武夷山脉东南面、鹫峰山脉西北侧。该区气候条件为中亚热带海洋性季风气候,年均气温18.7℃,年均降水量1 733 mm,年均蒸发量1 450 mm,年均相对湿度80%,年日照时数1 612 h,年均无霜期286 d [15]。
福建省建瓯市墩阳林业采育场47林班08大班40小班,属山地丘陵地形,海拔250~350 m,土壤为山地黄红壤;小班面积为8.4 hm2,造林密度为3 300株·hm−2,造林树种为杉木和木荷(Schima superba Gardn. et Champ.),株数比例为1:1.53。于2011年7月建立杉阔混交人工林择伐与更新长期跟踪试验基地,试验林为18年生杉阔混交人工林,林分和立地条件基本一致[15-16]。按胸高断面积计算树种组成为51.88%阔叶树、46.78%杉木、1.34%马尾松(Pinus massoniana Lamb.);主要灌木有檵木(Loropetalum chinense (R. Br.) Oliv.)、黄瑞木(Adinandra millettii (Hook. et Arn.) Benth. et Hook. f. ex Hance)、三花冬青(Ilex triflora Bl.)、尖连蕊茶(Camellia cuspidata (Kochs) Wright ex Gard.)和山樱花(Cerasus serrulata (Lindl.) G. Don ex London)等;主要草本有细齿叶柃(Eurya nitida Korthals)、五节芒(Miscanthus fIoridulus (Lab.) Warb. ex Schum. et Laut.)、狗脊(Woodwardia japonica (L. f.) Sm.)、芒萁(Dicranopteris dichotoma (Thunb.) Berhn.)和淡竹叶(Lophatherum gracile Brongn.)等。
因为该试验林2011年8月前从未间伐,林分密度过大,为使择伐后释放充足的林分生长空间,所以没设置弱度择伐。于2011年8月实施中度择伐(MI)、强度择伐(HI)、极强度择伐(EHI) 和皆伐(CC),蓄积量择伐强度分别为34.6%、48.6%、67.6%、100%,断面积择伐强度分别为35.9%、50.1%、74.8%、100%,并以未采伐(NC)为对照。各种采伐强度试验样地面积为800 m2(在上、下坡位各设1块20 m × 20 m标准样地,每块样地四角用水泥桩长期固定),试验林采伐后均保持自然恢复[16]。采伐5 a后于2016年7月进行了复查,试验林地林分和土壤概况见表1。
表 1 不同采伐强度5 a后试验林地概况
Table 1. Geophysical characteristics of the experimental forestland under different harvesting intensities after 5 years
采伐强度
Harvesting
intensity坡度
Slope gradient/(°)坡向
Slope aspect林分因子
Forest factors土壤理化性质
Soil physical and chemical properties上坡
Top下坡
Bottom上坡
Top下坡
Bottom胸径
DBH/
cm树高
Height/
m密度
Density/
(株·hm−2)温度
Temperature/
℃湿度
Moisture/
%有机质
Organic matter/
(g·kg−1)全N
Total N/
(g·kg−1)全P
Total P/
(g·kg−1)NC 31 32 W S 12.7 12.0 3 213 18.52 30.67 34.20 1.07 0.18 MI 32 32 W S 14.8 13.2 1 638 19.50 31.01 35.31 0.99 0.22 HI 31 31 SW S 13.5 12.2 1 717 20.52 29.46 35.11 0.75 0.15 EHI 32 29 SW SW 12.9 11.0 1 313 21.33 28.50 34.77 0.85 0.12 CC 29 30 SW SW — — — 23.18 26.69 21.65 0.41 0.05 注:NC:未采伐;MI:中度择伐;HI:强度择伐;EHI:极强度择伐;CC:皆伐。S:南;W:西;SW:西南。下同。
Notes: NC: Non-cutting; MI: Selective harvesting at medium intensity; HI: Selective harvesting at high intensity; EHI: Selective harvesting at extra-high intensity; CC: Clear-cut harvesting. S: South; W: Western; SW: Southwest. The same below. -
表2表明:在0~10 cm土层中,随着采伐强度的增大,细根生物量呈先增大后减小的变化规律,中度择伐最大(175.40 g·m−2),皆伐最小(45.51 g·m−2);在10~20 cm土层中,细根生物量随采伐强度增大呈波动变化,中度择伐降低,强度择伐最大(116.64 g·m−2),极强度择伐和皆伐呈明显下降趋势;各种采伐强度下,细根生物量表现为0~10 cm土层高于10~20 cm土层;中度和强度择伐0~20 cm土层细根总生物量略有增大,但均与未采伐差异不显著(P > 0.05),极强度择伐和皆伐显著降低(P < 0.05),分别比未采伐降低了47.0%和66.3%。
表 2 不同采伐强度5 a后细根生物量变化
Table 2. The change of fine root biomass under different harvesting intensities after 5 years
g·m−2 土层
Soil layer/cm采伐强度 Harvesting intensity NC MI HI EHI CC 0~10 141.66 ± 10.64 175.40 ± 19.35 141.32 ± 9.80 92.17 ± 16.79 45.51 ± 16.16 10~20 77.69 ± 10.66 49.91 ± 4.84 116.64 ± 25.33 24.07 ± 5.18 28.37 ± 6.06 0~20 219.35 ± 19.39 a 225.31 ± 23.44 a 257.96 ± 22.20 a 116.24 ± 21.10 b 73.88 ± 21.15 b 注:均值 ± 标准误;同一行不同字母表示差异显著(P < 0.05)。下同。
Notes:Mean ± S.E. Different letters of same row indicated significant difference (P < 0.05). The same below. -
由表3可知:在0~10 cm土层中,随着采伐强度增大,细根比根长和比表面积均呈先减小后增大的变化趋势,强度择伐最小,皆伐最大;根长密度和根表面积密度随采伐强度的增大均呈先增大后减小的变化趋势,中度择伐最大,皆伐最小。在10~20 cm土层中,细根比根长和比表面积随采伐强度的增大而变化的规律与0~10 cm土层的变化规律相似;根长密度和根表面积密度随采伐强度的增大呈波动变化,规律性不甚明显,其中,极强度择伐和皆伐均明显减小。
表 3 不同采伐强度5 a后细根形态特征变化
Table 3. The change of fine root morphological characteristic under different harvesting intensities after 5 years
土层
Soil Layer/
cm采伐强度
Harvesting
intensity细根形态特征 Fine root morphological characteristic 比根长
Specific root length/
(m·g−1)比表面积
Specific root surface area/
(cm2·g−1)根长密度
Root length density/
(m·m−3)根表面积密度
Root surface area density/
(m2·m-3)0~10 NC 11.15 ± 1.34 154.29 ± 15.67 14 474.90 ± 1 396.24 20.24 ± 1.53 MI 10.84 ± 0.58 155.14 ± 7.01 18 629.82 ± 1 841.71 26.59 ± 2.63 HI 7.82 ± 0.65 123.72 ± 12.90 10 528.82 ± 515.24 16.38 ± 0.86 EHI 8.31 ± 0.57 135.25 ± 8.07 7 341.33 ± 1 321.97 11.60 ± 1.82 CC 17.14 ± 2.09 273.26 ± 29.56 6 626.72 ± 2 058.15 10.11 ± 2.92 10~20 NC 10.48 ± 1.97 156.12 ± 23.07 6 141.37 ± 199.10 9.73 ± 0.22 MI 9.34 ± 1.11 158.95 ± 15.33 4 566.11 ± 765.31 7.50 ± 0.89 HI 8.10 ± 0.96 127.11 ± 13.69 9 146.54 ± 2 453.84 13.96 ± 3.49 EHI 10.94 ± 1.23 192.47 ± 16.86 2 581.45 ± 711.69 4.33 ± 1.04 CC 12.04 ± 1.72 236.51 ± 33.24 2 674.24 ± 441.28 5.13 ± 0.73 在0~20 cm土层中,细根比根长和比表面积(图1A)多重比较结果表明:二者随采伐强度的变化规律相似,均表现为各种强度的择伐都与未采伐差异不显著(P > 0.05),但皆伐显著大于未采伐(P < 0.05),皆伐细根比根长和细根比表面积分别比未采伐提高了41.5%和71.2%;根长密度和根表面积密度(图1B)多重比较结果表明:二者随采伐强度的变化规律相似,均表现为中度和强度择伐均与未采伐差异不显著(P > 0.05),但极强度择伐和皆伐均显著降低(P < 0.05),极强度择伐根长密度和根表面积密度分别比未采伐降低了51.9%和46.9%,皆伐根长密度和根表面积密度分别比未采伐降低了54.9%和49.2%。
采伐强度对杉阔混交人工林细根生物量及形态特征影响
Effects of Harvesting Intensity on Fine Root Biomass and Morphological Characteristics of Mixed Plantations of Cunninghamia lanceolata and Broadleaved Trees
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摘要:
目的 比较杉阔混交人工林在不同采伐强度下细根生物量及形态特征的差异,探究林木细根生长与采伐强度的关系,以期为区域杉阔混交人工林科学经营提供基础数据和理论参考。 方法 以闽北杉阔混交人工林为研究对象,2011年8月实施4种不同采伐强度(按蓄积量计算分别为中度择伐34.6%、强度择伐48.6%、极强度择伐67.6%和皆伐100%)试验,并与未采伐对照;经自然恢复5 a后,采用根钻法分2层(0~10、10~20 cm)获取乔木树种活细根(≤ 2 mm),分析采伐强度对0~20 cm土层细根总生物量及形态特征的影响。 结果 中度和强度择伐细根总生物量分别为225.31、257.96 g·m−2,与未采伐(219.35 g·m−2)差异不显著(P > 0.05),极强度择伐和皆伐分别比未采伐显著降低了47.0%和66.3%( P < 0.05);各种强度的择伐下细根比根长和比表面积与未采伐无显著差异(P > 0.05),皆伐比未采伐分别显著增大了41.5%和71.2%(P < 0.05);细根根长密度和根表面积密度随采伐强度增大而变化的规律与细根总生物量的变化规律一致,极强度择伐比未采伐分别显著降低了51.9%和46.9%(P < 0.05),皆伐比未采伐分别显著降低了54.9%和49.2%(P < 0.05)。 结论 杉阔混交人工林不同采伐强度5 a后,中度和强度择伐仍能维持林木细根生物量和吸收水分与养分能力,而极强度择伐和皆伐都出现显著降低;从有效维持和促进林木细根生长的角度,建议类似林分适宜采伐强度不超过强度择伐。 Abstract:Objective To compare the differences in fine root biomass and morphological characteristics of mixed plantation of Cunninghamia lanceolata and broadleaved trees under different harvesting intensities, reveal the relationship between fine root growth and harvesting intensity, and provide basic data and theoretical references for the management of regional mixed plantation of Cunninghamia lanceolata and broadleaved trees. Method A mixed plantation of Cunninghamia lanceolata and broadleaved trees in northern Fujian Province in China was used as the research object. Selective harvesting at medium intensity (34.6% removal of growing stock volume), high intensity (48.6%), at extra-high intensity (67.6%), and clear-cut harvesting (100%) were conducted and non-cutting as the control in August 2011. After 5 years of natural recovery, the basic data of biomass and morphological characteristics of living fine root (≤ 2 mm) of tree species were collected from two soil depths (0-10 cm and 10-20 cm) via root drilling methods. The influence of harvesting intensity on the total biomass and morphological characteristics of fine root in the 0-20 cm soil layer was analyzed. Result For the total fine root biomass, non-cutting, selective harvesting at medium and high intensities were 219.35, 225.31 and 257.96 g·m−2, there was no significant difference among them (P > 0.05). But the total fine root biomass under selective harvesting at extra-high intensity and clear-cut harvesting were significantly reduced by 47.0% and 66.3% respectively compared with non-cutting (P < 0.05). For the specific root length and specific root surface area, there was no significant difference between selective harvesting at various intensities and non-cutting (P > 0.05). The specific root length and specific root surface area under clear-cut harvesting were significantly increased by 41.5% and 71.2% respectively compared with non-cutting (P < 0.05). The changes of root length density and root surface area density with harvesting intensity increasing were consistent with their change of total fine root biomass. The root length density and root surface area density under selective harvesting at extra-high intensity were significantly reduced by 51.9% and 46.9% respectively compared with non-cutting (P < 0.05). The root length density and root surface area density under clear-cut harvesting were significantly reduced by 54.9% and 49.2% respectively compared with non-cutting (P < 0.05). Conclusion 5 years after harvesting, the fine root biomass and the ability to absorb water and nutrients of the mixed plantation of Cunninghamia lanceolata and broadleaved trees can be maintained under selective harvesting at medium and high intensities, but will be significantly reduced under selective harvesting at extra-high intensity and clear-cut harvesting. From the perspective of effectively maintaining and promoting the growth of fine roots of forest trees, it is recommended that suitable harvesting intensity of similar forests should not exceed the selective harvesting at high intensity. -
表 1 不同采伐强度5 a后试验林地概况
Table 1. Geophysical characteristics of the experimental forestland under different harvesting intensities after 5 years
采伐强度
Harvesting
intensity坡度
Slope gradient/(°)坡向
Slope aspect林分因子
Forest factors土壤理化性质
Soil physical and chemical properties上坡
Top下坡
Bottom上坡
Top下坡
Bottom胸径
DBH/
cm树高
Height/
m密度
Density/
(株·hm−2)温度
Temperature/
℃湿度
Moisture/
%有机质
Organic matter/
(g·kg−1)全N
Total N/
(g·kg−1)全P
Total P/
(g·kg−1)NC 31 32 W S 12.7 12.0 3 213 18.52 30.67 34.20 1.07 0.18 MI 32 32 W S 14.8 13.2 1 638 19.50 31.01 35.31 0.99 0.22 HI 31 31 SW S 13.5 12.2 1 717 20.52 29.46 35.11 0.75 0.15 EHI 32 29 SW SW 12.9 11.0 1 313 21.33 28.50 34.77 0.85 0.12 CC 29 30 SW SW — — — 23.18 26.69 21.65 0.41 0.05 注:NC:未采伐;MI:中度择伐;HI:强度择伐;EHI:极强度择伐;CC:皆伐。S:南;W:西;SW:西南。下同。
Notes: NC: Non-cutting; MI: Selective harvesting at medium intensity; HI: Selective harvesting at high intensity; EHI: Selective harvesting at extra-high intensity; CC: Clear-cut harvesting. S: South; W: Western; SW: Southwest. The same below.表 2 不同采伐强度5 a后细根生物量变化
Table 2. The change of fine root biomass under different harvesting intensities after 5 years
g·m−2 土层
Soil layer/cm采伐强度 Harvesting intensity NC MI HI EHI CC 0~10 141.66 ± 10.64 175.40 ± 19.35 141.32 ± 9.80 92.17 ± 16.79 45.51 ± 16.16 10~20 77.69 ± 10.66 49.91 ± 4.84 116.64 ± 25.33 24.07 ± 5.18 28.37 ± 6.06 0~20 219.35 ± 19.39 a 225.31 ± 23.44 a 257.96 ± 22.20 a 116.24 ± 21.10 b 73.88 ± 21.15 b 注:均值 ± 标准误;同一行不同字母表示差异显著(P < 0.05)。下同。
Notes:Mean ± S.E. Different letters of same row indicated significant difference (P < 0.05). The same below.表 3 不同采伐强度5 a后细根形态特征变化
Table 3. The change of fine root morphological characteristic under different harvesting intensities after 5 years
土层
Soil Layer/
cm采伐强度
Harvesting
intensity细根形态特征 Fine root morphological characteristic 比根长
Specific root length/
(m·g−1)比表面积
Specific root surface area/
(cm2·g−1)根长密度
Root length density/
(m·m−3)根表面积密度
Root surface area density/
(m2·m-3)0~10 NC 11.15 ± 1.34 154.29 ± 15.67 14 474.90 ± 1 396.24 20.24 ± 1.53 MI 10.84 ± 0.58 155.14 ± 7.01 18 629.82 ± 1 841.71 26.59 ± 2.63 HI 7.82 ± 0.65 123.72 ± 12.90 10 528.82 ± 515.24 16.38 ± 0.86 EHI 8.31 ± 0.57 135.25 ± 8.07 7 341.33 ± 1 321.97 11.60 ± 1.82 CC 17.14 ± 2.09 273.26 ± 29.56 6 626.72 ± 2 058.15 10.11 ± 2.92 10~20 NC 10.48 ± 1.97 156.12 ± 23.07 6 141.37 ± 199.10 9.73 ± 0.22 MI 9.34 ± 1.11 158.95 ± 15.33 4 566.11 ± 765.31 7.50 ± 0.89 HI 8.10 ± 0.96 127.11 ± 13.69 9 146.54 ± 2 453.84 13.96 ± 3.49 EHI 10.94 ± 1.23 192.47 ± 16.86 2 581.45 ± 711.69 4.33 ± 1.04 CC 12.04 ± 1.72 236.51 ± 33.24 2 674.24 ± 441.28 5.13 ± 0.73 -
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