Volume 37 Issue 2
Apr.  2020
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BO Huijuan, ZHU Jialei, WEN Chunyan, NIE Lishui, SONG Lianjun. Planting densities and vertical soil nutrients in a Populus tomentosa stand[J]. Journal of Zhejiang A&F University, 2020, 37(2): 266-272. doi: 10.11833/j.issn.2095-0756.2020.02.010
Citation: BO Huijuan, ZHU Jialei, WEN Chunyan, NIE Lishui, SONG Lianjun. Planting densities and vertical soil nutrients in a Populus tomentosa stand[J]. Journal of Zhejiang A&F University, 2020, 37(2): 266-272. doi: 10.11833/j.issn.2095-0756.2020.02.010

Planting densities and vertical soil nutrients in a Populus tomentosa stand

doi: 10.11833/j.issn.2095-0756.2020.02.010
  • Received Date: 2019-04-19
  • Rev Recd Date: 2019-07-22
  • Publish Date: 2020-04-20
  •   Objective  To explore the effects of planting densities on soil nutrients of different soil layers for a Populus tomentosa plantation.  Method  10-year-old S86 clones were used to study the soil nutrient characteristics with three planting densities (T1:2 m×2 m; T2:4 m×3 m; and T3:4 m×5 m) for six soil layers (0-5, 5-10, 10-20, 20-40, 40-60, and 60-100 cm). In mid-October 2016, soil samples were collected, and the contents of carbon (C), available nitrogen (N), available phosphorus (P), and available potassium (K) were determined and in total there were 3 treatments with 3 replicates, then one-way ANOVA and Duncan's multiple comparison tests were used to determine significant differences.  Result  The proportions of nutrients in the 0-20 cm layer compared to the 0-100 cm layer were:C(69%), N(79%), P(71%), and K (74%). The content of soil nutrients varied for the three planting densities. The highest C content found in T2 (15.44 g·kg-1 in the 0-5 cm layer) was significantly higher (P < 0.05) than T1; the C content in the 5-20 cm layer was significantly different (P < 0.05) than other densities in the order of T3 > T2 > T1; and in the 40-100 cm layer, the T1 content was significantly lower (P < 0.05) than other densities. The N content in T2 was 14.5-142.7 mg·kg-1. The P content was 1.3-12.4 mg·kg-1 with the content of T2 being significantly higher (P < 0.05) than other layers from 5-40 cm; however, in the 40-100 cm layers the content was T3 > T2 > T1. Planting density, though, had no significant effect on K content (P>0.05).  Conclusion  Nutrient content varied according to planting density and soil layers with the soil nutrient content of 10-year-old P. tomentosa clone S86 gathered in the 0-20 cm layer for the 2 m×2 m density having a lower nutrient content than the 4 m×3 m and 4 m×5 m densities.
  • [1] ZHANG Jianyun, WU Shengchun, WANG Minyan, SHAN Shengdao, CAO Zhihong, ZHANG Jin.  Tobacco stalk biochar in heavy metal contaminated soil amendments with tobacco production . Journal of Zhejiang A&F University, 2018, 35(4): 674-683. doi: 10.11833/j.issn.2095-0756.2018.04.013
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    [10] XU Qiu-fang, WU Jia-sen, JIANG Pei-kun.  Soil biological properties with weed removal in a Chinese chestnut (Castanea mollissima) plantation . Journal of Zhejiang A&F University, 2010, 27(5): 659-663. doi: 10.11833/j.issn.2095-0756.2010.05.004
    [11] LIU Wei-hua, ZHANG Gui-lian, XU Fei, WANG Ya-ping, YU Xue-qin, WANG Kai-yun.  Soil physical and chemical properties in Shanghai’s urban forests . Journal of Zhejiang A&F University, 2009, 26(2): 155-163.
    [12] YUAN Ying-hong, FANHou-bao, WANG Qiang, QIUXiu-qun2, CHENQiu-feng, LI Yan-yan, HUANG Yu-zi, LIAO Ying-chun.  Available nutrients with increased N deposition in soils of Cunninghamia lanceolata plantations . Journal of Zhejiang A&F University, 2007, 24(4): 437-444.
    [13] JIANG Pei-kun, XUQiu-fang, WUQi-feng, WUJia-sen.  Effects of fertilization on soil properties under Castanea mollissima plantation . Journal of Zhejiang A&F University, 2007, 24(4): 445-449.
    [14] GAO Zhi-qin, FU Mao-yi.  Characteristics of seasonal changes in soil carbon and nitrogen nutrients of different Phyllostachys pubescens stands . Journal of Zhejiang A&F University, 2006, 23(3): 248-254.
    [15] JIANG Pei-kun, XU Qiu-fang, CHU Jia-miao, WU Li-jun.  Soil nutrients in response to intensive management of Phyllostachys praecox . Journal of Zhejiang A&F University, 2006, 23(3): 242-247.
    [16] DAI Wen-sheng, LI Zhang-ju, CHENG Xiao-jian, YU Wei-wu, FU Qing-gong.  Mineral elements in Torreya grandis 'Merrillii' seeds and their forest soils . Journal of Zhejiang A&F University, 2006, 23(4): 393-399.
    [17] DAI Wen-sheng, LI Zhang-ju, CHENG Xiao-jian, YU Wei-wu, FU Qing-gong.  Soil nutrients in Torreya grandis `Merrillii' plantation . Journal of Zhejiang A&F University, 2006, 23(2): 140-144.
    [18] ZHOU Guo-mo, LIU En-bin, SHE Guang-hui.  Summary of estimated methods on forest soil's carbon pool . Journal of Zhejiang A&F University, 2006, 23(2): 207-216.
    [19] WANG Ji-yong, WANG Wen-quan, WU Hui-xiao.  Illumination domino effect and its influence on height growth of medicinal plant in intercropping system of Populus tomentosa and medicinal plants . Journal of Zhejiang A&F University, 2003, 20(1): 17-22.
    [20] WangShoudong, QinYuliang, YaoXin′ai.  Relationship between Planting Density and Yield in Early stage of Hawthorn. . Journal of Zhejiang A&F University, 1996, 13(1): 109-111.
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Planting densities and vertical soil nutrients in a Populus tomentosa stand

doi: 10.11833/j.issn.2095-0756.2020.02.010

Abstract:   Objective  To explore the effects of planting densities on soil nutrients of different soil layers for a Populus tomentosa plantation.  Method  10-year-old S86 clones were used to study the soil nutrient characteristics with three planting densities (T1:2 m×2 m; T2:4 m×3 m; and T3:4 m×5 m) for six soil layers (0-5, 5-10, 10-20, 20-40, 40-60, and 60-100 cm). In mid-October 2016, soil samples were collected, and the contents of carbon (C), available nitrogen (N), available phosphorus (P), and available potassium (K) were determined and in total there were 3 treatments with 3 replicates, then one-way ANOVA and Duncan's multiple comparison tests were used to determine significant differences.  Result  The proportions of nutrients in the 0-20 cm layer compared to the 0-100 cm layer were:C(69%), N(79%), P(71%), and K (74%). The content of soil nutrients varied for the three planting densities. The highest C content found in T2 (15.44 g·kg-1 in the 0-5 cm layer) was significantly higher (P < 0.05) than T1; the C content in the 5-20 cm layer was significantly different (P < 0.05) than other densities in the order of T3 > T2 > T1; and in the 40-100 cm layer, the T1 content was significantly lower (P < 0.05) than other densities. The N content in T2 was 14.5-142.7 mg·kg-1. The P content was 1.3-12.4 mg·kg-1 with the content of T2 being significantly higher (P < 0.05) than other layers from 5-40 cm; however, in the 40-100 cm layers the content was T3 > T2 > T1. Planting density, though, had no significant effect on K content (P>0.05).  Conclusion  Nutrient content varied according to planting density and soil layers with the soil nutrient content of 10-year-old P. tomentosa clone S86 gathered in the 0-20 cm layer for the 2 m×2 m density having a lower nutrient content than the 4 m×3 m and 4 m×5 m densities.

BO Huijuan, ZHU Jialei, WEN Chunyan, NIE Lishui, SONG Lianjun. Planting densities and vertical soil nutrients in a Populus tomentosa stand[J]. Journal of Zhejiang A&F University, 2020, 37(2): 266-272. doi: 10.11833/j.issn.2095-0756.2020.02.010
Citation: BO Huijuan, ZHU Jialei, WEN Chunyan, NIE Lishui, SONG Lianjun. Planting densities and vertical soil nutrients in a Populus tomentosa stand[J]. Journal of Zhejiang A&F University, 2020, 37(2): 266-272. doi: 10.11833/j.issn.2095-0756.2020.02.010
  • 土壤是森林生态系统的重要组成成分[1],也是维持林木健康生长的必要基质,其养分含量大小直接影响林木生长速度和质量[2]。在林地中由于养分输入、输出以及林木自身养分循环而表现出明显的垂直分布特征,且因养分类型不同具有显著差异[3],这种异质性影响整个生物学和生态学过程[4]。有关垂直方向养分的研究一般将土层划分为0~20、20~40、40~60和60~100 cm等4个层次[5],表土层作为整个土体的最上面,养分含量大小对林木生长和评价土壤肥力状况更有代表性,忽略对表土层更细致的研究,不利于精准地描述土壤养分垂直分布格局。栽植密度是营林措施中一项重要且容易操作的措施,密度大小不仅影响林分结构[6]、树冠大小[7]及各器官养分含量[8],进而影响林木对土壤养分的吸收[9];还会影响凋落物生物量及分解速率[10],最终对土壤养分状况产生深刻影响。很多学者对栽植密度与土壤养分含量之间的关系开展了研究[11-12]。有研究表明:马尾松Pinus massoniana林地土壤养分含量随密度增大而降低[13]。不同学者研究结论不尽相同,可能是由于研究对象、栽植密度及林龄不同所造成的。预计到2050年,人工林将提供75%的工业木材,其中50%由速生丰产林提供[14-15]。杨树Populus在中国的栽植面积已达850万hm2[16]。毛白杨Populus tomentosa适应性较强,具有扩大引栽栽培范围的潜力[17],S86品种相对于其他品种有较高的木材量[18]。目前,关于栽植密度对毛白杨S86的影响大多数为地上部分的研究[19]。人工林具有速生、短轮伐期、长期单一化栽植等特点,地力容易出现单一化问题[9]。为此,本研究以10年生毛白杨S86为研究对象,比较3种栽植密度林地土壤6个土层(0~5,5~10,10~20,20~40,40~60和60~100 cm)的养分情况,阐明在不同栽植密度下毛白杨土壤养分的差异情况,为人工林林地土壤的管理及施肥提供有效指导。

  • 试验地位于河北省威县苗圃场。该地属于华北平原中部,地势平坦,海拔30~50 m。年均气温为13.0 ℃,最低气温在1月,为-2.5 ℃,最高气温在7月,为27.0 ℃。气候为暖温带大陆性半干旱季风气候,全年日照总时数为2 574.8 h,无霜期198.0 d,平均降水量为497.7 mm,降水主要集中在7-8月。

  • 选择三倍体毛白杨无性系S86为试验材料,于2007年4月挑选长势大致相同的2年生毛白杨无性系幼苗(平均胸径为6.1 cm,树高为5.8 m)进行造林,栽植毛白杨时林地土壤养分概况为:有机质8.60 g·kg-1,全氮0.58 g·kg-1,碱解氮87.8 mg·kg-1,有效磷8.1 mg·kg-1,速效钾90.0 mg·kg-1,总孔隙度46.7%,田间持水量为26%。采用单因素完全随机设计。栽植密度3个水平(行距×株距),分别为2 m × 2 m(T1)、4 m × 3 m(T2)、4 m × 5 m(T3)。T1每行11株,T2每行7株,T3每行4株,分别为2行,3次重复共9个小区。小区以南北走向为长,东西走向为宽,保护行的栽植密度为4 m × 3 m,设置2行。表 1为2016年3种栽植密度下毛白杨生长状况统计。

    栽植密度(行距×株距) 树高/m 胸径/cm 蓄积量/(m3.hm-2) 凋落物量/(3hm-2)
    T1(2 m × 2 m) 14.60 ± 0.25 c 12.10 ± 0.31 b 157.97 ± 7.78 a 0.69 ± 0.14 b
    T2(4 m × 3 m) 18.08 ± 0.12 b 13.80 ± 0.24 a 86.80 ± 12.65 b 0.74 ± 0.18 a
    T3(4 m × 5 m) 21.04 ± 0.35 a 13.90 ± 0.13 a 64.75 ± 11.82 c 0.79 ± 0.04 a
    说明:同列不同小写字母表示不同栽植密度毛白杨生长状况差异显著(P<0.05)

    Table 1.  Growth status of P. tomentosa S86 under three different planting densities

  • 2016年11月中旬收集土样,随机选取试验小区中央位置的5株树木,在其东侧80 cm处定点取样。先剥开凋落物,用土钻分别取(0~5、5~10、10~20、20~40、40~60和60~100 cm)6个土层土壤样品,将每个小区5个取样点土层的40~60和60~100 cm的2个土层的5个土样分别混为1个样品,土层0~5、5~10、10~20和20~40 cm土样不混合。

    另采集3种栽植密度的凋落物,具体方法为每个小区取5个面积为60 cm × 60 cm凋落物样点,烘干称量得凋落物质量(表 1)。样品经室内风干、研磨、过筛后测定土壤养分。有机质采用重铬酸钾外加热法,碱解氮采用扩散法,有效磷采用钼锑抗比色法,速效钾采用火焰光度计法测定[20]

  • 采用Excel 2010计算和整理数据并进行图表绘制。数据间的方差分析(one-way ANOVA)、多重比较(Ducan检验法)采用SPSS 20.0进行分析。

  • 10年生毛白杨S86林地土层养分所占比例随土层深度增加而减少,从土层0~20 cm占整个土层的69%~79%减少到60~100 cm土层仅占4%~7%(图 1)。养分所占比例在0~5、5~10和10~20 cm有一定的区别,特别是碱解氮在3个土层间有明显差异,0~5 cm土层所占比例高达41%~45%。

    Figure 1.  Variation of constant element with soil profile

  • 3种栽植密度的毛白杨S86林地土壤有机质质量分数分别为1.72~8.57 g·kg-1(T1)、5.20~15.44 g·kg-1(T2)、4.58~14.86 g·kg-1(T3),且随土层深度的增加而减少(图 2)。0~5,5~10和10~20 cm有机质质量分数随土层变化较为缓慢,20~40,40~60和60~100 cm随土层增加下降较明显。方差分析显示:土层深度对有机质质量分数有显著影响(P < 0.05),0~5和5~10 cm土层有机质质量分数差异不显著,但均显著高于其他土层,10~20、20~40和60~100 cm之间有机质质量分数差异显著(P < 0.05)。有机质质量分数随栽植密度和土层变化而变化。0~5、20~40、40~60和60~100 cm土层,有机质质量分数从大到小依次为T2、T3、T1,0~5 cm土层,T2和T3有机质质量分数分别较T1增加80.16%和73.40%;5~10和10~20 cm土层,有机质质量分数从大到小依次为T3、T2、T1图 2)。总的来说,T1有机质质量分数显著低于T2和T3

    Figure 2.  Contents of organic matter in different soil layers of P. tomentosa S86 under three planting densities

  • 毛白杨S86林地碱解氮质量分数为6.8~142.7 mg·kg-1图 3),随土层深度的增加而减少。土层对碱解氮质量分数影响显著(P < 0.05),各土层之间(除60~100 cm)差异显著(P < 0.05)。3种栽植密度下碱解氮质量分数在0~5、10~20、20~40、40~60和60~100 cm土层从大到小依次为T2、T3、T1图 3);碱解氮质量分数在5~10 cm土层从大到小依次为T3、T2、T1。随土层深度增加,不同栽植密度间碱解氮质量分数差异越来越小,可能由于冬季淋溶作用较弱的原因所导致。

    Figure 3.  Contents of available nitrogen in different soil layers of P. tomentosa S86 under three planting densities

  • 3种栽植密度的毛白杨S86林地土壤有效磷质量分数分别为1.3~6.1 mg·kg-1(T1)、1.5~12.4 mg·kg-1(T2)和2.5~11.7 mg·kg-1(T3),随土层深度增加,有效磷质量分数呈下降趋势(图 4),从0~5 cm土层占整个土层的31%~37%减少到60~100 cm土层仅占4%~8%(图 1)。栽植密度对有效磷质量分数影响显著(P < 0.05)。0~5 cm土层有效磷质量分数大小依次为:T2(12.4 mg·kg-1)、T3(11.7 mg·kg-1)、T1(6.1 mg·kg-1),T1显著低于T2和T3。有效磷质量分数在土层5~10、10~20和20~40 cm表现为3条有差异的曲线(图 4)。多重比较结果表明:T2显著高于T1和T3,T1和T3差异不显著;40~100 cm土层T3显著高于T1和T2P < 0.05)。

    Figure 4.  Contents of available phosphorus in different soil layers of P. tomentosa S86 under three planting densities

  • 速效钾质量分数随土层增加呈下降趋势(图 5)。5~10 cm土层速效钾质量分数显著高于10~20 cm(P < 0.05),与0~5 cm土层差异不显著,20~40、40~60和60~100 cm土层间速效钾质量分数差异不显著。T2的土壤速效钾质量分数最高,为60.3~278.1 mg·kg-1。T1速效钾质量分数小于T2和T3图 5)。方差分析表明:栽植密度对土壤速效钾质量分数无显著影响(P>0.05)。

    Figure 5.  Contents of available potassium in different soil layers of P. tomentosa S86 under three planting densities

  • 10 a后毛白杨S86林地土壤养分质量分数发生变化,碱解氮和有效磷降低,栽植密度越大降低的程度越明显,特别是碱解氮,在T1处理下降低了60%(表 2)。表明随林龄增加,毛白杨从土壤中吸收越来越多的氮素来供地上部分生长,从而导致土壤氮库储量和供氮能力的下降。

    年份 w有机质/(g.kg-1) w碱解氮/(mg.kg-1) w有效磷/(mg.kg-1) w速效钾/(mg.kg-1)
    2016 T1 5.5 ± 0.1 c 34.8 ± 0.1c 3.3 ± 0.1 c 113.0 ± 0.1a
    T2 9.2 ± 0.1 a 53.3 ± 0.1b 6.6 ± 0.1 b 157.0 ± 0.2 a
    T3 10.0 ± 0.1 a 45.9 ± 0.1 b 5.2 ± 0.1 c 150.0 ± 0.2 a
    2007 8.6 ± 0.1b 87.8 ± 0.1 a 8.1 ± 0.1 a 90.0 ± 0.2 b
    说明:数据为平均值±标准差,同列不同字母表示不同处理间差异显著(P<0.05)

    Table 2.  Soil nutrient (mean) content in P. tomentosa S86 stand before and after 10 years

    速效钾质量分数增加,增加的幅度和栽植密度相关,T2增加幅度最大;有机质质量分数在T1处理下降低了3.12 g·kg-1,在T2和T3处理下分别增加了0.64和1.39 g·kg-1

  • 了解土壤养分垂直分布异质性是管理土壤养分和合理施肥的基础[21]。本研究发现:0~100 cm土层深度,毛白杨S86人工林有机质、碱解氮、有效磷和速效钾质量分数所占比例随土层深度增加呈降低的垂直分布特征,表层(0~20 cm)养分所占比例为69%~79%,富集了0~100 cm土层深度内大部分养分。戴奥娜等[22]在研究丝栗栲Castanopsis fargesii林下土壤养分时也充分证实这一点,原因是由于凋落物主要集中在表层[23]。在林木生长过程中,根系从土壤中吸取矿质营养供地上部分吸收,随后经凋落物分解返回到土壤中。总的来说,养分在不断地输出。本研究发现:10 a后毛白杨S86林地碱解氮和有效磷质量分数降低,可见在林木培育过程中,有必要对林地进行土壤养分管理[24]

    以往研究将土壤表层划分为0~20 cm或者0~10和10~20 cm[2, 25],本研究进一步将土层0~20 cm划分为0~5,5~10和10~20 cm,发现3个土层的养分所占比例不同,碱解氮在3个土层间存在显著差异(图 3),有机质在10~20 cm显著低于0~5和5~10 cm(图 2);有效磷和速效钾在0~5和10~20 cm差异显著(图 3图 4)。研究结果不仅精准地描述了养分在表层土的分布情况,而且为合理的水肥管理提供一定的依据,比如对0~20 cm土层施氮肥,可将大部分肥料施在10~20 cm土层中。

    林分栽植密度显著影响土壤有机质变化,有机质随密度的增加显著减少。这可能是由于有机质来源主要为凋落物和根系,栽植密度越低,凋落物越少(表 1)。同时,白毛杨S86在低栽植密度下有较高的根系生物量[26],从而导致有机质较高。林分密度对养分影响的研究结果表现不一致。对毛竹Phyllostachys edulis的研究发现:土壤营养元素随林分栽植密度的增加呈先逐渐增加后有所下降的趋势[27];油松Pinus tabulaeformis等树种土壤养分随林分栽植密度的增加而降低[28]。这些差异可能与林分类型、林分栽植密度或凋落物分解速率有关。

    本研究发现:有机质和碱解氮在表层对栽植密度的响应最激烈,有效磷在行距×株距为4 m × 3 m和4 m × 5 m显著高于2 m × 2 m,栽植密度对林地速效钾无显著影响。任丽娜等[29]在对油松Pinus tabulaeformis人工林研究后也得出类似的结果,不同土层养分量对栽植密度的响应不一致,可能是由于不同土层养分来源与流失方式不尽相同[30],比如微生物分布、根系分布以及淋溶和矿化作用等[31]。每一土层主导因素不一样,具体影响因素还有待进一步研究。

  • 10年生毛白杨S86林地土壤有机质和有效养分所占比例随土层增加而下降,碱解氮有较明显的垂直分布特征。栽植密度对10年生毛白杨S86林地土壤养分有一定的影响,整体来说行距×株距为4 m × 5 m和4 m × 3 m时养分高于2 m × 2 m,表层土壤有机质和碱解氮对栽植密度的响应最为激烈,有效磷在行距×株距为4 m × 3 m和4 m × 5 m时显著高于2 m × 2 m。栽植密度对速效钾没有显著影响。因此在华北平原砂壤土地区进行毛白杨林地管理时,结合培育目标在选择最初栽植密度后,建议对高栽植密度林地进行间伐或者施肥管理,低栽植密度林地可选择农作物进行套种。在今后将研究毛白杨林地凋落物在不同栽植密度下的分解状况,从而更准确地了解凋落物层与土壤养分之间的关系。

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