摘要
为考察平茬措施对根系力学特性的影响,以内蒙古干旱半干旱地区水土保持先锋灌木沙棘(Hippophae rhamnoides)根系为研究对象,使用TY-8000拉力机,进行单根极限拉伸试验和根土界面拉拔摩阻试验,并分析平茬对沙棘根系固土力学特性的影响。试验结果显示,在测试根径为0~5 mm时,平茬和未平茬条件下,沙棘单根极限抗拉力、抗阻拉力均与直径呈幂函数正相关;单根极限抗拉强度、根-土界面拉拔抗剪强度均与直径呈幂函数负相关。在代表根径级0.5~1.5 mm,沙棘平茬较未平茬平均单根极限抗拉力值提高31%;平均单根极限抗拉强度提高37%;平均拉拔抗剪强度提高30%。研究结果表明,直径对沙棘根系抗拉强度和抗剪强度均有影响,且沙棘经平茬处理后,抗拉特性和抗剪特性均有所提高。
水土流失是目前世界上最重要的土地退化问题之
平茬是伐除植株地上部分以促使新枝萌发的一种营林措施,通过平茬可以有效地维持灌木林的生态和经济效益。灌木平茬不但可以获得大量的燃料和饲料,而且还能够促进根系萌蘖,从而达到更新、复壮的目
本研究以内蒙古砒砂岩区典型水土保持先锋树种沙棘根系为对象,进行单根极限拉伸试验和根土界面拉拔摩阻试验,分析平茬复壮措施对沙棘根系抗拉力学特性和根土界面摩阻特性的影响,进一步从力学方面探究平茬对沙棘生长的影响,以期为沙棘人工灌木林的可持续经营和管理提供理论支撑。
试验地点位于内蒙古鄂尔多斯市准格尔旗暖水乡,该地受季风影响,冬季寒冷漫长。试验于2021年8月下旬进行,选择10 a生人工沙棘林进行根系的挖掘和采样。平茬样地内沙棘株行距为2 m。试验前1年的2020年8月下旬,在待平茬样地内随机选择40株植株测量其株高、冠幅、地径(最粗)等指标,计算其平均值,测量结果显示,待平茬样地沙棘株高(95.0±6.7) cm、南北冠幅(105.0±7.2) cm、东西冠幅(123.0±11.3) cm、地径(5.21±0.70) cm。根据平均值找出与平均值最接近的8株植株作为标准株(丛)进行标记,其中4株进行全面平茬,留茬高度为10 cm,另外4株不进行平茬处理,待翌年进行根系的挖掘和取样。
挖掘根系时,以标准株为中心,在半径为2 m的圆圈内采用由外向内方法进行收缩式挖掘,当露出根系时立即停止挖掘,采用便携式小铲顺着根系走向轻轻挖掘,待根系裸露长度和根径达到测试要求的长度和直径时停止挖掘,再用毛刷轻轻刷去根表面粘连土体。挖掘过程中每隔3~5 min喷1次水,尽量使露出根周围保持湿润。所需根系采集完后,放入黑色塑料袋覆土、喷水,防止根系失水。将待测根系带回实验室,放入4 ℃恒温箱保存,并尽快完成试验以保证根系的鲜活状态。根系挖掘采集的同时在标准植株下修整土壤剖面,并在根系集中分布土层内收集土壤样品,选取10个样品测定土壤干密度和自然含水率,取平均值,试验样品的干密度和含水率依据上述方法进行制作。另取5~8 kg根系集中分布土层内的土壤带回实验室用于根-土复合体重塑土样的制备,确保尽可能地还原根系生长状况。
单根极限拉伸式样制备:将取得的根系以0.5 mm为1个间隔进行分级装袋,分为10个级别,具体见
径级/mm Diameter class | 未平茬No mowing | 平茬Mowing |
---|---|---|
0~0.5 | 11.15Aa | 16.47Aa |
0.5~1.0 | 25.41Ba | 36.32Bb |
1.0~1.5 | 61.29Ca | 77.01Cb |
1.5~2.0 | 97.87Da | 125.77Db |
2.0~2.5 | 155.83Ea | 156.02Ea |
2.5~3.0 | 179.31Fa | 174.99Fa |
3.0~3.5 | 211.66Ia | 199.92Ga |
3.5~4.0 | 196.94Ha | 228.20Hb |
4.0~4.5 | 187.62Ga | 309.76Jb |
4.5~5.0 | 247.32Ja | 279.78Ib |
注: 大写字母表示相同处理下不同径级之间的差异性;小写字母表示相同径级下平茬与未平茬之间的差异性,P<0.05,下同。Note:Capital letters represent the difference between different diameter classes under the same treatment;small letters represent the difference between mowing and non mowing under the same diameter class (P<0.05), the same as below.
根-土复合体重塑土样制备的PVC圆柱状塑料管,直径为6 cm,长度为8 cm。先在PVC管内盛满土样,然后在塑料管横向中心处开通1个直径约1 cm的圆孔,圆孔用于固定穿插根系。将植物根系插入圆孔后,继续加载土壤样品,并用相同的力交替敲打PVC管的两端,使得根土紧密接触,直至达到试验所需土体密度。
用烘干法测得的原状土含水率为6.35%,用环刀法测得的干密度为1.52 g/c
(1) |
m=(1+0.010)Vρd | (2) |
(3) |
单根极限拉伸试验和根土界面拉拔摩阻特性试验仪器均为TY-8000伺服式力学实验机。实验机夹具距离为60 mm,加载速度为150 mm/min。由于植物根系直径沿轴向变化,在计算单个根系的极限抗拉强度时,取断裂点处的根径作为直径带入公式计算。试验时在根段中心处发生断裂的数据视为有效,在两端发生断裂的数据视为无效。
P=4F/π | (4) |
在进行根-土复合体的单根拉拔试验必须假定根被拔动时,根土界面摩擦应力是均匀分布的;并且根土界面处拉拔剪应力与摩擦应力相同,合力为零,即:
τπdl-F=0 | (5) |
由

图1 沙棘单根极限抗拉力与直径关系
Fig.1 Ultimate anti-tension of a single Hippophae rhamnoides root with diameter
y1和y2分别代表未平茬和平茬,下同。y1 and y2 represent no mowing and mowing,respectively.The same as below.
由
由

图2 平茬和未平茬沙棘单根极限抗拉强度与直径关系
Fig.2 Ultimate tensile resistance of single Hippophae rhamnoides root with diameter between mowing and no mowing
由
径级/mmDiameter class | 未平茬No mowing | 平茬Mowing |
---|---|---|
0~0.5 | 75.41Aa | 127.44Ab |
0.5~1.0 | 68.91Ba | 109.41Bb |
1.0~1.5 | 50.83Ca | 55.16Ca |
1.5~2.0 | 42.37Da | 52.91Cb |
2.0~2.5 | 38.83Da | 37.69Da |
2.5~3.0 | 31.17Ea | 31.53Ea |
3.0~3.5 | 25.61Fa | 23.60Fa |
3.5~4.0 | 18.20Ga | 21.50Fa |
4.0~4.5 | 13.22Ha | 20.45Fa |
4.5~5.0 | 13.20Ha | 16.30Ga |
1)沙棘单根抗阻拉力。从

图3 平茬和未平茬沙棘单根抗阻拉力与根径的关系
Fig.3 Resistance tension of single Hippophae rhamnoides root with diameter between mowing and no mowing
由
径级/mm Diameter class | 未平茬No mowing | 平茬Mowing |
---|---|---|
0~0.5 | 7.28Aa | 9.61Aa |
0.5~1.0 | 14.37Ba | 15.03Ba |
1.0~1.5 | 20.40Ca | 24.59Cb |
1.5~2.0 | 31.88Da | 31.73Da |
2.0~2.5 | 42.35Ea | 43.56Ea |
2.5~3.0 | 49.45Fa | 44.60Eb |
3.0~3.5 | 53.58Ga | 49.94Fa |
3.5~4.0 | 55.97Ga | 76.41Ib |
4.0~4.5 | 75.14Ha | 56.42Gb |
4.5~5.0 | 83.25Ia | 72.89Hb |
2)沙棘单根拉拔抗剪强度。由

图4 平茬和未平茬沙棘单根拉拔抗剪强度均值与根径关系
Fig.4 Pull-out shear strength of single Hippophae rhamnoides root with diameter between mowing and no mowing
径级/mmDiameter class | 未平茬No mowing | 平茬Mowing |
---|---|---|
0~0.5 | 135.13Aa | 223.30Ab |
0.5~1.0 | 92.52Ba | 120.88Bb |
1.0~1.5 | 88.00Ca | 109.11Db |
1.5~2.0 | 94.18Ba | 104.93Eb |
2.0~2.5 | 95.83Ba | 88.87Fa |
2.5~3.0 | 89.57Ca | 76.50Gb |
3.0~3.5 | 85.27Da | 75.25Gb |
3.5~4.0 | 81.40Ea | 77.44Ga |
4.0~4.5 | 85.52Da | 88.72Fa |
4.5~5.0 | 97.69Ba | 110.15Cb |
本研究表明,在测试根径为0~5.0 mm时,在平茬和未平茬条件下沙棘单根极限抗拉力、单根抗阻拉力与直径均呈幂函数正相关。在代表根根径为0.5~1.5 mm时,平茬和未平茬条件下沙棘单根极限抗拉力均值分别为56.67、43.35 N,平茬较未平茬值提高31%;平茬和未平茬条件下沙棘单根抗阻拉力均值分别是17.39、19.81 N。在测试根径为0~5 mm时,在平茬和未平茬条件下沙棘单根极限抗拉强度、沙棘根-土界面拉拔抗剪强度与直径均呈幂函数负相关。在代表根径级为0.5~1.5 mm时,平茬和未平茬条件下沙棘单根极限抗拉强度均值分别为82.28、59.87 MPa,即平茬值较未平茬值提高37%;平茬和未平茬条件下沙棘拉拔抗剪强度均值分别为117.50、90.26 kPa,平茬值较未平茬值提高30%。因此,直径对沙棘根系抗拉强度和抗剪强度均有影响,且经平茬处理后,抗拉特性和抗剪特性均有所提高。
在根径为0~5.0 mm时,在平茬与未平茬条件下沙棘单根极限抗拉力均随着根径的不断增长而增大,这是由于根系中化学物质成分含量不同所致。研究表明,根系抗拉力与纤维素和半纤维素含量呈正相关,与木质素含量呈负相关;随着根径的增加,纤维素和半纤维素含量逐渐增加,而木质素的含量逐渐减少,因此单根极限抗拉力就会增
沙棘经平茬处理后,单根极限抗拉力、抗拉强度和根-土界面拉拔抗剪强度值有所提高。研究表明,植物在遭遇外力的损伤和破坏后,会出现生长加快和生物量迅速恢复的现
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