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杨树Populus为中国重要的速生丰产林造林树种,其中欧美杨107 Populus × euramericana ‘Neva’因其材性好、干型美、抗性强和产量高等特点,在中国淮河、黄河流域及辽河流域以南等地区广泛栽植。灌溉是欧美杨人工林生产力维持的重要技术措施,滴灌可根据植物需水规律及时补充根部水分,显著促进林木生长,获得较高的经济效益和生态效益[1-3],该技术在国外的人工林培育方面已有较广泛的应用[4-5]。近年来,国内关于滴灌栽培人工林的研究也相继开展。贺勇等[6]研究发现:滴灌栽培条件下2、3年生欧美杨107幼龄林的蓄积量分别为沟灌的2.22和1.68倍。席本野等[7]研究指出:滴灌使6、7年生的毛白杨Populus tomentosa林分生产力分别较不灌溉平均提高了24%和28%。根系分布和形态特征反映了植物对土壤资源的利用状况,通常认为直径小于2 mm的细根是根系吸收功能的重要部分[8]。细根的生长和分布受树木自身生长特性、土壤的水养条件、温湿度及其他外界环境条件的影响[9-12],其分布也可以反映土壤中水分营养的分配格局[13]及地下部分对土壤资源的利用程度[14-15],这将直接影响林木地上部分的生长和生态效益的发挥[16]。滴灌可以大幅度提高根系数量,影响根系的分布特征[17-18],改善土壤条件[19],提高林地生产力[6-7]。但以往开展滴灌对林木细根的研究,多采用距树干特定距离或随机取样的方法,不能在空间维度反映细根的分布特征。本研究以滴灌和沟灌栽培的5年生欧美杨107为研究对象,对比分析在不同的取样方向、水平距离和土壤深度上细根的空间分布特征,探究不同灌溉方式对细根生长和分布的影响,为河流故道沙地等干旱地区人工林的灌溉调控和合理经营提供依据。
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研究地位于北京市大兴区林场,处于永定河故道沙地(39°26′~39°51′N,116°13′~116°43′E)。该区属暖温带半湿润大陆性季风气候,年均气温为11.6 ℃,年均降水量为550 mm,年均蒸发量为1 100 mm,无霜期为180~200 d。土壤为永定河故道冲积沙土,地下水位深为36 m,土壤容重为(1.46±0.15) g·cm−3,田间持水量为10%,蓄水能力差,土壤碱解氮质量分数为25.65 mg·kg−1,速效磷质量分数为2.36 mg·kg−1,速效钾质量分数为22.12 mg·kg−1,有机质质量分数为1.50 g·kg−1,从地表向地下1.2 m处均无明显腐殖质层。
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以5年生欧美杨107人工林为研究对象。该林分于2011年利用滴灌技术扦插造林,株行距3 m×5 m,滴头流量为4 L·h−1,滴头间距为60 cm,滴灌管沿株间铺设。结合土壤湿度传感器,于每年的5−9月,当20 cm土层土壤相对含水量低于60%时进行灌溉,灌溉量由灌溉时长控制,每次灌溉量为6~9 mm,灌溉总量为250 mm。滴灌后能在株间方向形成宽度为1.0~1.2 m,深度为60~70 cm的连续湿润带[19]。沟灌栽培的试验林于2012年造林成活后撤去滴灌管,沿株间方向挖宽1 m、深15 cm的灌溉沟进行灌溉。灌溉量由流量计控制,每次灌溉量为50 mm,春季、秋季各灌溉1次,夏季3次,灌溉总量为250 mm。
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于2015年10月下旬,分别在滴灌和沟灌栽培的试验林内设置3个面积为30 m×20 m的标准地,每个标准地内有样木40株,在各标准地内每木检尺后选取1株标准木作为研究对象(表1)。取样采用根钻法,根钻内径10 cm,高10 cm,以样木树干为中心,分别选取株间、行间和对角3个方向距树干20、50、100、150 cm处钻取土芯,取样深度为60 cm,每10 cm为1个土层。具体取样点位如图1所示,共计432个土样分别装入标号的塑封袋后带回实验室。
表 1 标准木基本特征
Table 1. Basic characteristics of standard wood
样木
编号滴灌 沟灌 胸径/cm 树高/m 冠幅/m 胸径/cm 树高/m 冠幅/m 1 15.6 17.26 3.63×3.42 13.4 15.24 3.12×2.57 2 15.8 16.87 3.13×3.50 13.6 15.86 3.03×2.61 3 15.8 17.63 3.35×3.17 13.4 15.47 3.07×2.70 将土样在清水中浸泡后,过0.8 mm孔径筛冲洗,分离土样中的根系并用镊子捡取所有活根系。按照传统的根系分类标准[20],以直径≤2 mm作为划分细根的阈值,应用Epson Twain Pro根系扫描系统和WinRhizo根系图像分析系统测定细根长(m);将细根在80 ℃烘箱中烘干至恒量(24 h),用电子天平(精确到0.001 g)测定细根生物量(g)。
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细根生物量密度(g·m−3)=M土芯/V土芯,细根根长密度(m·m−3)=L土芯/V土芯,比根长(m·g−1)=L土芯/M土芯。其中:M土芯为土芯内细根质量(g),L土芯为土芯内细根长(m),V土芯为土芯内土壤体积(m3)。V土芯=πr2h10−6,其中r为根钻半径,取值5 cm,h为根钻高度,取值10 cm。
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利用Excel和SPSS 19.0对数据进行统计分析,分别以同一水平距离处不同土层细根指标的累加值作为该水平距离处的细根特征值,采用单因素方差分析比较同一灌溉方式下细根的空间分布特征,采用t检验分析不同灌溉方式下同一水平距离处的细根分布特征。
Effects of drip irrigation and furrow irrigation on spatial distribution of fine roots of Populus
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摘要:
目的 探究不同灌溉方式对杨树Populus细根生长和分布的影响,为滴灌培育人工林提供理论和技术依据。 方法 以5年生欧美杨107 Populus × euramericana ‘Neva’为研究对象,在滴灌和沟灌栽培的人工林中选取标准木,分别在株间、对角和行间方向距树干20、50、100和150 cm处采用根钻法取样,比较其细根生物量密度、细根根长密度、细根比根长的差异。 结果 滴灌条件下株间方向的细根生物量密度与沟灌的差异随水平距离增加而增大(P<0.05),对角和行间方向随水平距离增加其差异减小。滴灌下细根生物量密度在株间方向距树干50 cm处最大,对角和行间方向在距树干20 cm处最大。滴灌下株间方向的细根根长密度与沟灌的差异随水平距离增加而增大(P<0.05),对角和行间方向的差异随水平距离增加而减小。滴灌下细根根长密度在株间方向距树干50 cm处最大,对角和行间方向在距树干20 cm处最大。滴灌和沟灌下0~40 cm土层的细根生物量分别占0~60 cm土层的81%和73%,细根根长分别占0~60 cm土层的85%和80%。滴灌和沟灌下的比根长随水平距离增加而增大,且均表现为沟灌大于滴灌,不同方向比根长的差异在距树干20 cm处最大,在距树干50 cm处最小。 结论 滴灌能促进杨树人工林细根的生长和周转,影响细根的空间分布,提高林地生产力。图4表1参28 Abstract:Objective This study aims to investigate the effects of different irrigation methods on the growth and spatial distribution of fine roots of Populus, so as to provide theoretical and technical basis for the cultivation of plantation by drip irrigation. Method The 5-year old ‘107’ Populus × euramericana ‘Neva’ was selected as the research object, and standard trees were selected from the plantations cultivated by drip irrigation and furrow irrigation. Root drills were used to sample trees at 20, 50, 100 and 150 cm from tree trunks in the directions of inter plant, diagonal and inter row. The differences of fine root biomass density, fine root length density and fine root specific root length were compared. Result In inter plant direction, the difference of fine root biomass density between drip irrigation and furrow irrigation increased with the increase of horizontal distance, and the difference was significant (P<0.05). With the increase of horizontal distance, the differences between diagonal and inter row directions decrease. Under drip irrigation, the fine root biomass density was the highest at 50 cm away from the trunk in the direction of inter plant, and the highest at 20 cm away from the trunk in the direction of diagonal and inter row. Under drip irrigation, the difference of fine root length density with furrow irrigation increased with the increase of the horizontal distance(P<0.05), while the difference of diagonal and row direction decreased with the increase of the horizontal distance. Under drip irrigation, the root length density of fine roots was the largest at 50 cm from the trunk in the direction of inter plant, and the largest at 20 cm away from the trunk in the direction of diagonal and inter row. Under drip and furrow irrigation, the fine root biomass of 0−40 cm soil layers accounted for 81% and 73% of that in 0−60 cm soil layers, respectively, while the fine root length accounted for 85% and 80%. The specific root length under drip irrigation and furrow irrigation increased with the increase of horizontal distance, and the difference of specific root length under furrow irrigation was greater than that under drip irrigation. The difference of specific root length in different directions was the largest at 20 cm away from the trunk and the smallest at 50 cm away from the trunk. Conclusion Drip irrigation can promote the growth and turnover of fine roots, affect their spatial distribution, and improve forest productivity. [Ch, 4 fig. 1 tab. 28 ref.] -
Key words:
- drip irrigation /
- furrow irrigation /
- Populus /
- fine roots /
- spatial distribution
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表 1 标准木基本特征
Table 1. Basic characteristics of standard wood
样木
编号滴灌 沟灌 胸径/cm 树高/m 冠幅/m 胸径/cm 树高/m 冠幅/m 1 15.6 17.26 3.63×3.42 13.4 15.24 3.12×2.57 2 15.8 16.87 3.13×3.50 13.6 15.86 3.03×2.61 3 15.8 17.63 3.35×3.17 13.4 15.47 3.07×2.70 -
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.20200808