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GUO Jiahuan, SUN Jiejie, FENG Huili, CAO Penghe, YU Yuanchun. Research progress on evolution trends and maintenance measures of soil fertility quality in Cunninghamia lanceolata plantations[J]. Journal of Zhejiang A&F University. doi: 10.11833/j.issn.2095-0756.20190478
Citation: GUO Jiahuan, SUN Jiejie, FENG Huili, CAO Penghe, YU Yuanchun. Research progress on evolution trends and maintenance measures of soil fertility quality in Cunninghamia lanceolata plantations[J]. Journal of Zhejiang A&F University. doi: 10.11833/j.issn.2095-0756.20190478

Research progress on evolution trends and maintenance measures of soil fertility quality in Cunninghamia lanceolata plantations

doi: 10.11833/j.issn.2095-0756.20190478
  • Received Date: 2019-08-15
  • Rev Recd Date: 2019-12-02
  • Available Online: 2019-12-17
  • In recent years, the growing contradiction between degradation of soil fertility quality and forestry production has seriously threatened the survival and development of human beings. Aiming at the hot issue of degradation and maintenance of soil fertility quality in plantations, this paper systematically elaborates the evolution trend of soil fertility quality in management of Cunninghamia lanceolata plantations from the perspectives of soil physical property, soil chemical property, soil microorganism, soil enzyme activity and allelopathy. Many studies have shown that degradation of soil fertility quality and continuous decrease of productivity are common problems in C. lanceolata plantations, and the main contributing factor is unsustainable forestry practice. The results of soil fertility maintenance in C. lanceolata plantations are reviewed from such aspects as rotation management, mixed compound afforestation, forest density adjustment, fertility compensation and sustainable forest management. The research on soil fertility quality maintenance in C. lanceolata plantations is prospected. [Ch, 1 tab. 48 ref.]
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Research progress on evolution trends and maintenance measures of soil fertility quality in Cunninghamia lanceolata plantations

doi: 10.11833/j.issn.2095-0756.20190478

Abstract: In recent years, the growing contradiction between degradation of soil fertility quality and forestry production has seriously threatened the survival and development of human beings. Aiming at the hot issue of degradation and maintenance of soil fertility quality in plantations, this paper systematically elaborates the evolution trend of soil fertility quality in management of Cunninghamia lanceolata plantations from the perspectives of soil physical property, soil chemical property, soil microorganism, soil enzyme activity and allelopathy. Many studies have shown that degradation of soil fertility quality and continuous decrease of productivity are common problems in C. lanceolata plantations, and the main contributing factor is unsustainable forestry practice. The results of soil fertility maintenance in C. lanceolata plantations are reviewed from such aspects as rotation management, mixed compound afforestation, forest density adjustment, fertility compensation and sustainable forest management. The research on soil fertility quality maintenance in C. lanceolata plantations is prospected. [Ch, 1 tab. 48 ref.]

GUO Jiahuan, SUN Jiejie, FENG Huili, CAO Penghe, YU Yuanchun. Research progress on evolution trends and maintenance measures of soil fertility quality in Cunninghamia lanceolata plantations[J]. Journal of Zhejiang A&F University. doi: 10.11833/j.issn.2095-0756.20190478
Citation: GUO Jiahuan, SUN Jiejie, FENG Huili, CAO Penghe, YU Yuanchun. Research progress on evolution trends and maintenance measures of soil fertility quality in Cunninghamia lanceolata plantations[J]. Journal of Zhejiang A&F University. doi: 10.11833/j.issn.2095-0756.20190478
  • 近几十年来,中国人工林迅速发展,逐步替代天然林成为工业木材的主要供应源。《第8次全国森林资源清查报告》[1]显示:中国现有人工林面积6.933×107 hm2,占有林地面积的64%,林地面积居世界首位。人工林蓄积24.830×108 m3,占森林蓄积的17%。人工林面积、蓄积增量分别占有林地面积、蓄积增量的78%、37%,人工林对中国森林资源增长的贡献明显。报告指出:中国人工林年均采伐1.550×108 m3,比上次清查增加了3.221×107 m3,采伐量占全国森林采伐量的46%,比上次清查提高了7%,采伐比例持续上升。然而,由于长期的纯林化连栽和掠夺式经营,人工林生态系统的脆弱性愈加明显,接连出现了土壤退化、生物多样性减少、生产力降低、生态系统稳定性下降等复杂的生态问题,人工林土壤肥力退化问题受到广泛关注。土壤退化被首次报道是在19世纪初,又被称作“地力衰退”和“第2代效应”[2]。人工林土壤肥力退化是指营林过程中,人为不利因素干扰引起土壤属性的改变而无法实现其对人类有价值的特定功能,主要表现为土壤理化性质恶化及其环境调节能力的持续降低、土壤微生物数量减少、营养元素缺失、生物和森林生产力下降等。杉木Cunninghamia lanceolata的地理分布范围为19°30′~34°03′N,101°30′~121°53′E,遍及中国亚热带地区18个省(市、自治区),是中国主要的速生工业用材和造林灭荒优势树种,具生长快、材质好、用途广等特点。目前,栽植面积占全国人工林面积的30%以上[3],在中国林业生产和森林生态系统中发挥着重要作用。为此,本研究对近几年的杉木研究成果进行综述,阐述了杉木人工林土壤肥力质量的演变趋势及维护措施,为实现杉木人工林的可持续高产和维持人工林生态系统稳定提供参考。

    • 近年来,桉树Eucalyptus、杨树Populus、落叶松Larix gmelinii、杉木等人工林在经营过程中出现土壤质量退化、生产力降低等问题,人工林土壤肥力变化受到广泛关注。本研究对1989−2018年发表的50余篇中国杉木主要产区土壤肥力相关论文数据综合分析后发现:中国杉木人工林主产区不同程度出现了土壤退化,土壤肥力朝着持续降低的方向发展(表1)。

      省份 林龄/a 平均树高/m 平均胸径/cm 土壤类型 土壤肥力 代表性参考文献
      福建 14~17 12.75 16.76 山地红壤 下降 [4]
      湖南 14 11.23 12.86 山地黄壤 下降 [5]
      江西 7~49 13.68 17.24 丘陵红壤 下降 [6]
      浙江 9~20 8.01 9.48 山地黄壤 下降 [7]
      广西 4~6 赤红壤  下降 [8]
      广东 15 8.11 11.2 赤红壤  下降 [9]
      贵州 18 14.18 16.02 黄壤   下降 [10]
      河南 12 黄棕壤  下降 [11]
        说明:表中土壤类型按中国农业农村部土壤分类学分类;“−”代表无数据

      Table 1.  Basic situation of soil fertility in main production area of C. lanceolata plantations

    • 土壤作为人工林根系伸展、固持的一种介质,它的物理性质决定了土壤的基本性状和运动过程,影响着土壤与人工林之间的物质和能量交换,对维持、调节和控制林地生态系统的稳定至关重要。研究表明:杉木生长状况与土壤物理性质变化有很强的联系,尤其以表层土(0~20 cm)的变化最为明显。王丹等[5]研究发现:不同生长发育阶段(幼龄、中龄、近熟、成熟、过熟)杉木人工林的土壤孔隙度、紧实度、全蓄水量、田间持水量都达到显著差异水平(P<0.05)。俞元春等[12]研究发现:杉木人工林2、3代林土壤容重较1代林分别增加了43.48%和52.17%;在土壤总孔隙度、毛管孔隙度和非毛管孔隙度均呈下降趋势的指标中,2代林相对于1代下降了23.12%、23.33%和22.30%,3代林相对于1代则下降了27.74%、43.91%和33.02%。王刚[13]研究不同林龄(8、11、15 a)杉木人工林后发现:随着杉木林龄增加,林地土壤容重增加5.0%~8.5%、含水量持续上升2.1%~3.3%,土壤孔隙度下降2.4%~3.5%,土壤变得紧实,容蓄能力变小。盛炜彤等[14]在对不同立地条件(立地指数为12、14、16)的杉木人工林林地土壤调查后发现,随着栽植代数的增加,不同立地条件下的杉木人工林呈土壤容重上升、毛管持水量及非毛管孔隙度下降,土壤变得坚实,杉木人工林土壤物理性质逐渐变劣。

      与此同时,也有学者持不同意见。胡慧蓉等[6]调查了云南不同林龄(6、13、18 a)杉木人工林土壤理化性质后指出:营造杉木人工林之后,土壤含水量上升,容重降低,紧实度减小,土壤物理性质逐步得到改善,这与高志强等[15]的研究结论相类似。陈欣凡等[16]、李晨晨等[17]则指出:相对于杉木纯林,针阔混交、林农复合经营更能有效降低林地土壤容重、改善土壤通气状况和土壤物理性质。

    • 从生态系统功能的角度来看,土壤肥力很大程度上取决于土壤的养分循环和平衡,这与土壤的化学性质紧密相关。长期连续营造杉木人工林对土壤养分周转能力、土壤养分含量及土壤pH产生负面影响。已有研究显示:杉木人工林连栽后的2代林土壤养分周转能力下降,养分丢失比率为1代林的200%,养分积累率不足1代林的60%[18]。随着林龄的增加,杉木人工林的年养分吸收和养分利用效率(氮除外)增加,生态系统养分产量下降,土壤养分输出超过了各龄期林分的投入,土壤净养分损失增加,氮、磷、钙等净养分流失显著[19]。王清奎等[20]研究表明:福建来周林场杉木人工林随着连栽次数增加,林地土壤可溶性有机碳(DOC)和可溶性有机氮(DON)、全氮(TN)、全钾(TK)、铵态氮(${\rm{NH}}_4^{+} $)、速效钾(AK)以及可溶性有机质(DOM)等均呈递减的变化趋势,土壤肥力质量逐代降低。盛炜彤等[14]调查了福建南平杉木人工林后发现:连栽后的2、3代林与1代林相比,速效磷(AP)、碱解氮(AN)含量平均降幅达20%~30%;铜、锌等微量元素含量也呈递减趋势;土壤有机质(SOM)在2代林中有所降低,2、3代林土壤中的胡敏酸含量及土壤腐殖化系数均低于1代林,连栽后土壤肥力下降趋势明显。王刚[13]在调查江西景德镇枫树山林场内不同栽植代数杉木人工林时发现:连栽后林地土壤有机质、氮(N)、磷(P)、钾(K)含量以及钙离子(Ca2+)和镁离子(Mg2+)交换量均呈下降的变化趋势。然而,也有学者持不同的观点。张志才[9]对福建洋口林场连栽杉木林土壤肥力调查发现:2代杉木林土壤化学性质与1代林相比无显著差异。唐健等[4]对广西大桂山林场1、2代杉木人工林土壤有机质、全氮含量等15个指标综合分析后指出:2代幼龄林土壤肥力高于1代幼龄林,连栽并没有引起林地土壤肥力下降。研究结论的不同可能由于不同的杉木种源和区域环境条件以及经营管理方式的差别,也可能是不同地域杉木的林下植物群落组成、微生物种类、根际分泌物等环境因子的差异,从而导致土壤养分储量及有效性不同。关于土壤pH,众多研究均显示杉木连栽会导致土壤pH降低,引起土壤酸化[4,13-14]

      此外,凋落物的分解、养分归还量的平衡对杉木林地土壤养分循环也具有重要影响。研究发现:随着杉木人工林连栽次数增加,杉木林分养分的年归还量、年吸收量以及归还吸收比均呈逐代下降的变化趋势,养分循环速效减缓,多代连栽不利于杉木林地肥力的恢复[21]。随着杉木林龄的增长,养分年积累量显著降低,年归还量、年吸收量和归还吸收比逐渐增加。因此,可采取杉木林早期施肥、适当延长轮伐周期等手段来补偿杉木早期生长所消耗养分,以维持土壤养分的动态平衡。

    • 土壤微生物作为土壤隐形的管理者,直接参与土壤的形成、有机物降解和土壤养分循环等过程,对维持土壤肥力质量至关重要。杉木人工纯林连栽对土壤质量变化及土壤微生物种群有较大的影响,容易改变土壤微生物区系,导致土壤肥力退化。研究发现:杉木人工林连栽将会加剧杉木根际土壤微生态失衡,明显降低土壤微生物的多样性和代谢活性,造成了土壤营养元素的耗竭[8]。另外,刘丽等[22]研究发现:杉木第3代人工林土壤真菌群落结构相较于天然林变化剧烈,出现了核盘菌属Sclerotinia sclerotiorum、球壳菌属Mycosphaerella sp.和小皮伞菌属Marasmius sp.等致病菌群。这些菌群的存在是引起林地土壤退化和肥力下降的主要诱因之一。李延茂等[23]在调查连栽杉木根际土壤微生物多样性后指出:随着连栽代数增加,真菌DGGE图谱带减少,生物多样性降低,病原真菌和产毒真菌数量明显增加,这可能是导致林地土壤肥力下降的直接原因。杉木连栽后,土壤微生物总数下降,土壤生物活性降低[24]。除此之外,杜国坚等[25]研究了杉木混交林后发现:杉阔混交林土壤微生物数量要比杉木纯林高7.19%~41.31%。石丽娜等[26]指出:近自然模式经营杉木林(老龄林、萌芽林)更利于土壤微生物生存与发展,可有效改善土壤肥力质量。

    • 土壤酶活性不仅反映了土壤微生物状态,同时又综合了土壤理化条件和营养物质的有效性等相关信息,因此常被用作土壤处理对土壤肥力影响研究的“传感器”,成为衡量土壤退化程度的关键指标之一。杉木人工林的土壤酶活性随着栽植代数增加呈下降的趋势,土壤肥力效果与土壤酶活性密切相关,多种土壤酶相互作用对土壤养分产生影响。俞新妥等[7]对杉木连栽林和不同混交林土壤酶活性研究发现:在垂直分布上,土壤酶活性从强到弱均表现为0~20、20~40、40 cm以下,且连栽多代杉木林地土壤酶活性下降幅度更大。此外,杉木混交林各层次土壤酶活性显著高于连栽多代杉木纯林。秦国宣等[27]调查了2代杉木人工林土壤酶活性与土壤肥力的关系后发现:杉木人工林土壤酶活性随着林分年龄增长呈递减趋势,且自然恢复的杉木林地土壤酶活性显著高于林龄为20 a的2代人工林。

      与此同时,杉木连栽对不同类型的土壤酶活性影响也不同。罗飞等[28]在研究酸雨区不同林龄杉木人工林土壤酶活性季节动态基础上,分析了土壤养分与酶活性的相关关系后发现:多酚氧化酶(PPO)、过氧化氢酶(CAT)、过氧化物酶(POD)活性从强到弱表现为成熟林、中龄林、幼龄林,蔗糖酶活性随林龄增加表现出先升后降的变化趋势。随着林龄的增加,土壤pH逐渐降低导致土壤酶活性大幅下降,凋落物分解速度变缓,全氮、全磷、碱解氮、速效磷、速效钾、土壤有机质含量显著降低,土壤肥力下降。

      杉木连栽引起的土壤有机质减少也往往伴随着土壤酶活性的下降;间伐将提高杉木林土壤酶活性并持续改善土壤肥力。胡亚林等[29]研究发现:杉木人工林替代天然次生阔叶林后表层土壤有机碳下降44.87%,土壤酸度增加,全氮、全磷等养分减少,土壤酶活性和土壤呼吸强度显著降低,表层土壤质量恶化。林地土壤有机质减少是土壤养分降低、酶活性下降的驱动因素之一。丁波等[30]通过研究不同间伐强度对18年生杉木人工林土壤酶活性的影响认为:间伐可显著提高土壤过氧化氢酶、碱性磷酸酶(ALP)、脲酶和蔗糖酶的活性,且在3 a后的综合表现表明:这类土壤酶活性的提升可有效改善土壤肥力质量。

    • 化感作用是一种存在于大自然和生态系统管理中的重要生态机制。有害化感物质是造成杉木人工林土壤肥力质量下降的重要因子之一。陈龙池等[10-11]研究发现:杉木凋落物所释放的香草醛等酚类物质积累到一定浓度时对幼龄杉木根系具有化学毒害效果,严重影响根部细胞对土壤中${\rm{NO}}_3^{-} $${\rm{HPO}}_4^{2-} $${\rm{NH}}_4^{+} $${\rm{SO}}_4^{2-} $离子的交换吸收,同时促使大量氮素被分配至根部,茎、叶中氮素分配严重不足,导致杉木长期处于养分亏缺状态,降低了杉木生产力。XIA等[31]在调查化感物质对土壤微生物的影响时发现:长期单一栽植杉木林地土壤中含有大量的化感物质环二肽,且2代林的含量明显高于1代林。该物质不仅对杉木根系有直接的毒害作用,严重抑制了根系的生长,同时还会间接改变土壤微生物群落组成,最终引起林地土壤生态失衡,导致土壤质量逐渐恶化。HUANG等[32]对杉木根桩分解过程中酚类物质化感效应的研究表明:微生物在分解根桩的过程中会向周围土壤释放多种类型的次生代谢产物,包括酚类物质,当酚类物质在土壤中积累到一定浓度时会抑制杉木根和叶的生长,降低水分利用效率,破坏土壤微生物生态循环系统,导致土壤养分流失、肥力下降。

    • 轮作能有效避免长期经营单一纯林所引起的土壤养分耗竭,有助于恢复林地土壤功能,有效提升土壤肥力质量,防止土壤肥力退化。张鼎华等[33]调查杉木、马尾松Pinus massoniana人工林轮作对土壤肥力和林木生长的影响发现:轮作过程中后茬林地土壤微生物生物量大幅增加,酶活性明显增强,有毒化感物质含量降低,土壤pH上升,林地土壤肥力改善效果良好,林分生产力明显提高。张剑等[34]指出:杉木与火力楠Michelia macclurei轮作显著增加了土壤微生物量碳、土壤微生物熵、易氧化有机碳和碳库管理指数,提高了土壤微生物对底物的利用效率。在今后的杉木轮作研究中,应合理利用部分树种间协同促进的生物学特性,选择合适的树种,避免有害化感作用,确定正确的轮作顺序以及合理的轮作年限,构建合理的轮作系统,最大限度发挥轮作系统的生态效果。

    • 通常情况下,混交林凋落物比针叶纯林要高很多,土壤中微生物群落组成也更复杂,酶活性也更高,因此,凋落物分解和速效养分的释放也将更快。混交造林更有利于降低土壤养分损失,有助于人工林土壤肥力的长期维持。曹小玉等[35]对不同林龄(幼龄林、中龄林、近熟林)的杉木人工林补栽栾树Koelreuteria bipinnata、鹅掌楸Liriodendron tulipifera等阔叶树种调查发现:混交改造后的3个林龄杉木人工林土壤养分含量均有提高,土壤肥力质量得到改善。田晓等[36]运用FORECAST模型模拟研究了桢楠Phoebe zhennan与杉木混交林未来300 a内林分的时空演变后发现:往杉木人工林内引入一定数量的桢楠可有效遏止土壤退化。当楠-杉混交比例为3:1时,森林可获得蓄积量最高,土壤肥力维持效果最好。WANG等[37]研究杉木纯林中补植阔叶树后发现:土壤全氮、硝态氮(${\rm{NO}}_3^{-} $)、全磷和速效磷等养分增加,土壤微生物活性增强,土壤肥力恢复效果明显。此外,黄云鹏[38]在研究杉木-红锥Castanopsis hystrix混交林时发现:不同混交比例的人工林林分生产力、土壤肥力均有显著差异。土壤中全氮、铵态氮$({\rm{NH}}_4^{+}) $、速效磷、土壤有机质随着杉木比例降低而显著增加,杉木-红锥混交比为7︰3时林地土壤肥力提升效果最好。因此,混交复合造林,尤其与阔叶树混交是杉木人工林土壤肥力质量维持的有效手段。

    • 合理调节林分密度可促进林下植被的发展,增加林地生物多样性,改善群落结构,提高生态功能稳定性,而且对维护林地土壤质量,促进养分循环,维持生产力方面具有重要作用。已有研究发现:中度间伐后林下植物种类、林下死地被植物量增加,土壤温度上升,死地被物分解速度加快;重度间伐后表层土壤(0~10、10~20 cm)容重下降,含水量和孔隙度增加,土壤全氮、碱解氮、锌含量上升,并且不同程度间伐对土壤肥力质量均有积极影响[39]。另外,随着时间推移,间伐抚育在1~2 a内林下植被的组成、多样性和生物量相对于杉木人工纯林有显著的提高,间伐林土壤性状明显改善,林分蓄积量并未降低[40]。还有研究发现:适度间伐后的林分环境和光环境得到改善,林下植被得以发展,土壤微生物群落组成更加稳定。其中,间伐率为33.3%(1 200株·hm−2)时土壤肥力提升效果最为显著,有利于杉木人工林土壤肥力质量的维持[30]。此外,间伐后林下植被的生长导致土壤含水量上升,促进了可溶性有机碳的溶解,可溶性有机碳含量上升使得β-1,4-葡萄糖苷酶(β-G)、β-1,4-N-乙酰葡糖氨糖苷酶(NAG)活性增强,加速了土壤有机质的分解和养分的释放,土壤肥力因此提升[41]。与此同时,减少林分密度有助于改善磷的内部循环,提高土壤速效磷含量,满足树体营养需求[42]。综上所述,林分密度是影响杉木人工林养分循环的关键因子之一,合理调节林分密度可增加杉木人工林林地生态系统的稳定性,有助于林地土壤肥力质量的维持。其中,中度间伐(25%~30%)后土壤肥力质量的维持效果最好,有利于杉木人工林的经营。

    • 肥力补偿能有效补充土壤养分,改善土壤质量,提高林分生产力。杉木人工林林地肥力补偿应在营养诊断基础上,结合林地土壤养分状况,以自然补偿为主,人为补偿为辅,做到缺素补偿、适量补偿。研究显示:施肥可有效补充土壤养分,增强土壤酶活性,提升土壤肥力水平,缓解杉木缺素病症[43]。与此同时,不同林龄、不同种源的杉木对肥料的需求也不同。牛宁[44]利用DRIS营养诊断法对3代种子园后代杉木植株养分元素诊断后发现:杉木植株中氮、磷、钾养分最佳比值区间为rP/N=0.145 8±0.026 1,rK/N=0.932 4±0.044 4,rK/P=6.643 2±0.883 3,杉木对氮、磷、钾三大营养元素的需求从大到小表现为钾、磷、氮。WANG等[45]研究发现:在杉木幼龄期施氮、磷肥后,土壤微生物生物量减少,SOM分解速度上升,土壤养分有效性增加。陈胜进等[46]研究指出:连栽后土壤pH逐渐降低,施肥可有效改善这种状况。同时,在杉木林幼龄阶段增施磷肥可促进植株的营养生长,中龄阶段补偿氮、磷、钾、锌可显著提高蓄积量,近熟期补偿铜和锌可有效提高林木养分利用效率,缓解前期养分耗竭现象。除此之外,杉木早期耗尽土壤养分保持增长,并随着林龄增加提高土壤养分的利用效率,减少对土壤的依赖。杉木的养分归还量、养分利用效率、养分周转时间和归还比率也随着林龄的增加而增加[47]

    • 可持续森林管理(sustainable forest management, SFM)是指在管理和利用森林和林地过程中,保持其现有和未来的生物多样性、生产力、再生能力、活力及其潜力,以实现在地区、国家和全球范围内的相关生态、经济和社会功能,并且不对其他生态系统造成损害[48]。人工林替代天然林后,人为因素的增加,加剧了对森林生态系统的干扰,打乱了原有森林生态位,破坏了林地生物地化循环,给土壤生态系统带来一定的负面影响。因此,开展可持续管理,采用近自然模式营造和管理人工林,造林时避免破坏性炼山、整地等不合理的生产行为,营造林分结构复杂、生物多样性丰富稳定的森林生态系统,合理延长轮伐周期,注重择伐,限制皆伐,注重养分的自然补偿,避免土壤养分过度流失。通过上述措施,协调好林地系统与其他生态系统的关系,既能保证杉木人工林持续的木材产量,又可以维持人工林地的土壤生态功能。

    • 目前,人工林土壤肥力维持是全世界所面临的重点难点问题,涉及土壤、微生物、生物化学、植物生理等众多领域,无论采取何种解决方式和手段,现阶段杉木人工林土壤肥力维持都面临诸多困难。针对现存问题,未来关于杉木人工林土壤肥力质量维持的研究重点如下:①土壤退化是气候变化的主导因素之一,而气候变化对人工林土壤退化的影响也是亟待解决的问题。未来可运用科学的监测手段,以对气候变化敏感的土壤微生物为“传感器”,探索全球气候变化对杉木人工林土壤微生物群落的组成、多样性以及功能的时空演变及其对土壤肥力变化的影响。②目前,关于杉木人工林的研究较多,但多数研究还是建立在以“空间换时间”的基础上,缺乏长期系统的跟踪监测,而土壤变化是长期且复杂的过程。今后可在杉木人工林中心产区建立长期的定位研究站,对土壤养分的释放、活化和植物对养分的吸收、运输、储存、归还等方面展开系统调查,为杉木人工林的土壤肥力质量的维持提供理论依据。③大气氮沉降的增加是全球气候变化的主要驱动因素,氮素作为森林和土壤中最主要的营养元素之一,其沉降不可避免地对森林生态系统产生影响。目前,氮沉降对土壤微生物组成、生物量及呼吸作用的影响仍不清楚。因此,有必要研究大气氮的沉降尺度及其与林地生态系统的交互作用对土壤微生物和土壤酶活性的影响,调查氮沉降对土壤肥力变化的影响,为杉木人工林土壤肥力质量维持提供参考。④当前,虽然已有较多研究显示杉木人工林施肥可改善土壤质量,然而却很少有研究区分化肥和有机肥对杉木人工林土壤作用效果的不同,也并未探讨过度施肥是否会导致杉木人工林土壤板结和酸化等问题。这有待进一步的研究去论证。

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