极端干旱区多枝柽柳幼苗对人工水分干扰的形态及生理响应

在塔里木河下游断流河道人工生态输水的大背景下,多枝柽柳(Tamarix ramosissima )作为当地优势物种,其更新恢复研究对下游荒漠河岸林的恢复尤为重要。通过研究多枝柽柳幼苗形态、水分和光合生理对不同灌溉处理的响应,分析不同人工水分干扰模式对柽柳幼苗生长发育的影响。实验设计了侧渗分层(LSI)和地表灌溉(AGI)两种给水方式,以及高灌(W1,50 L/株)、中灌(W2,25 L/株)、低灌(W3,12.5 L/株)3 个给水水平,并在整个生长季定期监测幼苗的形态参数变化、生物量、水势和光合速率。结果显示:(1)侧渗分层灌溉方式对幼苗基径、株高、冠幅以及前期生长速率都有促进作用;(2)在侧渗分层灌溉高灌下,幼苗地下及总生物量都显著高于地表灌溉(P < 0.05),且地表灌溉下根冠比(R/S:Root shoot ratio)明显高于侧渗分层灌溉;(3)侧渗分层灌溉下,幼苗茎水势高于地表漫灌,且在中灌和低灌下达到显著水平(P < 0.05),表明侧渗分层灌溉下幼苗的水分吸收效率更高;(4)在侧渗分层高灌及中灌下,实际光化学光量子产量值高于地表灌溉处理,并在高灌时差异极显著(P < 0.01)。研究表明,侧渗分层灌溉方式对多枝柽柳幼苗早期生长及水分和光合生理都具有显著促进作用。     

不同灌溉量对绿洲-荒漠过渡带多枝柽柳幼苗根系生长和分布的影响

为了探讨绿洲-荒漠过渡带上受损柽柳群落幼苗适宜生长的土壤水分条件,在塔南策勒绿洲外围设置A（不灌溉）、B（适度灌溉）、C（充分灌溉）3个处理的田间试验,于7～10月份考察了各处理柽柳幼苗粗根（>2 mm）和细根（<2 mm）生物量积累、空间分布等变化特征。结果显示:（1）随着灌溉量的增加,柽柳根系生物量积累不断增加,且在生长季末（10月份）增速最大,同时细根占总根重的比例从20.5%上升到29.8%,显著提高了幼苗吸收养分和水分的能力。（2）干旱胁迫（处理A）下柽柳幼苗根系的下扎深度大,但水平根幅的扩展却有限;适度灌溉（处理B）的生物量较处理A大,但小于处理C;根系扎根深度表现为处理A>处理B>处理C,各指标均处于中间状态;水分条件最好（处理C）时虽然垂直扎根深度小,但水平根幅最大,可以更有效利用浅层土壤资源。（3）柽柳幼苗大量根系集中在0～40 cm的土壤表层,而且水分条件越好,这种集中趋势越明显;根系生物量随土壤深度的增加呈递减变化,细根的根长密度也有相似变化,但细根的比根长变化规律不明显,这可能与各层土壤微观环境的变化有关。研究表明,灌溉对柽柳幼苗根系的生长和分布有显著影响,充分灌溉下柽柳幼苗根系生物量积累最多且空间分布最大,该灌溉量有利于柽柳幼苗根系的正常生长和合理分布。     

毛竹种群向常绿阔叶林扩张的细根策略

为了探讨毛竹(Phyllostachys pubescens)种群向常绿阔叶林扩张的根系策略, 该文采用根钻法和内生长法, 在江西大岗山选取毛竹林与阔叶林的交错区——竹阔界面(bamboo-broad-leaved forest interface), 并垂直于界面连续设置毛竹林、毛竹与阔叶树的混交林(以下简称为竹阔混交林)、常绿阔叶林3种样地, 比较分析其细根的空间分布格局、比根长、根长密度、生长速率和周转率等指标。结果表明: 毛竹林细根生物量(1201.60 g·m^-2) >竹阔混交林(601.18 g·m ^-2) >常绿阔叶林(204.88 g·m ^-2); 在毛竹与阔叶树竞争的混交林中, 毛竹细根分布趋向于上层土壤(与毛竹林细根相比), 且其比根长也显著增加, 平均增幅高达123.42%, 总根长密度比阔叶树大2.1倍; 同时, 毛竹细根生长速率和周转率均高于阔叶树。这些结果说明毛竹可通过广布、精准、灵活、快速等细根竞争策略, 提高资源获取能力, 实现种群扩张。     

翠菊根系养分捕获形态塑性及其生理机制

为验证以下3个假设: 1) NO₃ ^-和NH₄ ⁺及其不同供给方式显著影响根系生长; 2) NO₃ ^-和NH₄ ⁺以及不同供给方式对根内激素含量影响显著; 3)根构型(1级根长、单位2级根上1级侧根密度(分枝强度)和1级根在2级根上的根间距)与根内激素(生长素(IAA)、脱落酸(ABA)和细胞分裂素(玉米素核苷+玉米素) (CK (ZR + Z))含量显著相关, 采用营养液培养方法, 使实验植物翠菊(Callistephus chinensis)在两种氮肥(NO₃ ^-和NH₄ ⁺)、不同施氮浓度(NO₃ ^-: 0.2、1.0和18.0 mmol·L ^-1; NH₄ ⁺: 0.2、4.0和20.0 mmol·L ^-1), 以及脉冲和稳定两种施用方式处理下生长。在处理35天后收获植物, 测定根系生物量、根系构型指标(根系1级根长、单位2级根上1级侧根数和1级根在2级根上的根间距)和根系中激素含量(IAA、ABA和CK (ZR + Z))。结果显示: 1)实验处理对根生物量和根系中IAA、ABA和CK (ZR + Z)含量均有不同程度的显著影响: 施用NH₄ ⁺使根生物量和根内IAA含量显著低于施用NO₃ ^-; 高浓度NO₃ ^-和NH₄ ⁺处理亦使根生物量和IAA降低; 相对于稳定处理, 脉冲施氮显著降低根生物量和根内IAA含量; NO₃ ^-使根内CK (ZR + Z)含量显著高于施用NH₄ ⁺, 且与施氮浓度及施氮方式无关; NO₃ ^-处理下, 高浓度使根内ABA含量提高, 且脉冲处理使ABA含量升高。NH₄ ⁺处理下, 高浓度使根内ABA含量降低, 而施氮方式对其没有显著影响。2)根构型因素与根内激素关系各异: 各激素与1级根间距无显著关系; IAA和CK (ZR + Z)与1级根长和侧根密度有显著回归关系。3)根构型因素与根生物量的关系是根生物量与1级根长和侧根密度有显著正回归关系, 与1级根间距无显著回归关系。实验结果表明翠菊根生长的 “反常”可能是由于其对脉冲高浓度NH₄ ⁺耐受阈值低所致。该研究通过实验建立了氮养分种类/供应方式通过改变激素、影响根构型而影响根生长的联系, 进一步探究了植物根养分捕获塑性机制。     

不同水分处理对甘蒙柽柳幼苗根系生长特性的影响

以1年生甘蒙柽柳幼苗为对象,采用人工壕沟挖掘法,对柽柳幼苗在不同水分处理条件下(干旱处理、适度灌溉、充分灌溉)根系生态学特征的季节变化进行了研究.结果表明,不同水分处理对柽柳幼苗根系生长影响显著,垂直根扎根深度和生长速率随着灌溉量的减小而增加.地面灌溉量的增加会导致根系分布的浅表化和根系消弱系数的减小,根系生物量与土壤深度呈显著负对数关系.不同水分处理条件下,7-10月的根/冠比平均值分别为0.43、0.60、0.90、1.12,其根、冠间存在典型的异速生长关系.根/冠比随土壤水分的减小而增加,且生长季后期大于初期.     

生活污水尾水灌溉对麦秸还田水稻幼苗及土壤环境的影响

通过盆栽试验研究了麦秸还田下生活污水尾水灌溉对水稻幼苗和土壤环境的影响.测定了不同处理水稻幼苗根系形态、根系活力、分蘖、株高、干物质累积量、土壤亚铁、有机酸、酶活性.结果表明: 与自来水灌溉相比,不施化肥氮时,生活污水尾水灌溉显著提高了水稻移栽后41 d的分蘖数和根系活力;正常施氮肥时,生活污水尾水灌溉显著促进了水稻根系和植株生长,根长、根表面积、根体积、根系活力、水稻分蘖数和干物质累积量均显著高于自来水灌溉处理.生活污水尾水灌溉处理显著降低了土壤Fe²⁺和有机酸含量,土壤脲酶、过氧化氢酶活性等显著提高.生活污水尾水灌溉和施氮耦合能有效缓解秸秆还田初期对水稻幼苗生长的不利影响,改善水稻生长状况,提升土壤肥力和质量.     

短期氮-水处理对刨花楠幼苗细根根序形态的影响

以种子来源于江西遂川的1年生刨花楠扦插苗为材料,设置田间持水量的80%、40% 2个水分水平,以及不添加(0 kg N·hm^-2)、低氮(50 kg N·hm^-2)、高氮(100 kg N·hm^-2) 3个氮添加水平共6种处理的氮-水交互受控试验,测定不同处理刨花楠幼苗3个根序细根比根长、比表面积、平均直径和根组织密度,分析短期氮添加、干旱胁迫及两者交互作用对刨花楠幼苗细根的影响.结果表明: 刨花楠幼苗细根平均直径、比根长在不同根序间差异显著.随根序的增加,刨花楠幼苗细根平均直径增加,其中3级根最大,为0.97 mm;而比根长降低,3级根最小,为238.99 cm·g^-1.氮添加对刨花楠细根的比表面积、平均直径、比根长和根组织密度无显著影响,而水分对刨花楠细根平均直径、比根长、根组织密度影响显著.干旱胁迫明显促进幼苗3级细根直径的增加,降低了1、2级细根根组织密度.干旱环境下幼苗3级根的比根长明显低于正常供水环境下幼苗.氮水交互作用对刨花楠细根形态影响不显著.     

氮添加对稀土尾砂地猴樟幼苗根系生长、生物量分配及非结构性碳水化合物的影响

为探究氮添加对稀土矿尾砂地猴樟(Cinnamomun bodinieri)幼苗生长及非结构性碳水化合物(NSC)含量的影响，以1年生猴樟扦插苗为研究对象，选用硝酸铵钙作为氮肥(含N 15%)，设置3种氮肥水平(CK(0)、N1(1.8 g·株^-1)、N2(3.6 g·株^-1))，分析不同氮添加水平下猴樟幼苗根系生长、生物量分配和NSC等指标的差异，探讨稀土尾砂地猴樟对氮添加的响应。结果发现：稀土尾砂地氮添加均增加了猴樟幼苗不同组织的生物量积累，其中N1处理下叶生物量、冠层生物量分别较N2处理下显著提升了44.75%、57.43%(P<0.05);N2处理下叶比重分别较CK、N1处理显著提升了123.53%、15.85%(P<0.05)。不论是粗根(直径>2 mm)，还是细根(直径≤2 mm)，氮添加均显著增加了植物的根长和根表面积(P<0.05)，其中N1处理的促进效果最显著(P<0.05);N2处理下的比根长、比表面积均高于CK与N1，且与CK显著差异(P<0.05)。对NSC来说，N1处理提升了叶、茎中...     

亚硒酸盐对油菜幼苗硒吸收、根系形态及生理指标的影响

以甘蓝型油菜(湘农油571)为试验材料,通过溶液培养研究了外源四价硒条件下,油菜幼苗硒吸收分配、生理特性及根系形态的变化.结果表明： 油菜幼苗的硒富集能力随施硒量增加显著降低,而硒分配系数一直稳定在0.9左右,不受硒浓度影响.10 μmol·L^-1硒可以通过显著改善油菜幼苗根系生理指标和根系形态来促进油菜幼苗的生长,其对生理指标的影响主要表现为：显著降低油菜幼苗根系超氧阴离子自由基(O₂^-_·)产生速率,并显著提高超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性,从而显著降低根系的膜脂过氧化物质(MDA)含量,降幅达26.0%,进〖JP2〗而显著提高根系活力,增幅达17.4%;其对构型指标促进程度依次为：根体积>总表面积>分根数>总根长>根尖数>平均直径,但这些正效应均与1 μmol·L^-1硒处理无显著差异,表明少量硒(≤10 μmol·L^-1)可以通过提高油菜幼苗根系抗氧化酶活性和降低膜脂过氧化物含量,来提高根系活力和改善根系构型,最终促进油菜幼苗生长.     

红砂幼苗根系形态特征和水分利用效率对土壤水分变化的响应

为探讨干旱与半干旱区受损红砂种群幼苗适宜生长的土壤水分条件,采用盆栽方法,研究了红砂幼苗在充分灌溉(FI)、适度灌溉(MI)、干旱处理(DT)3个水分处理下根系形态和水分利用效率的变化特征。结果表明:(1)红砂幼苗根系形态因水分条件和根序的不同而各异;随灌溉量的减少红砂幼苗根系直径和根体积均表现为FIMIDT,但干旱处理促进了根系的伸长生长和比表面积和比根长增加,根系形态的可塑性是红砂幼苗获取水分适应干旱环境的重要策略之一。(2)随根序的升高,各处理水平下红砂幼苗根长、比根长均显著减少,而其根直径和体积却显著增加,表明红砂幼苗根系内部具有高度的形态异质性。(3)与FI处理相比,MI和DT处理下红砂幼苗根系总生物量分别增加了50.00%、19.23%,但MI和DT处理却显著降低了红砂幼苗地上生物量,特别是叶片生物量下降幅度最大,分别降低了62.15%、83.28%,导致根冠比随灌溉量的减少而逐渐增加。(4)干旱处理显著提高了红砂幼苗的水分利用效率。研究认为,在灌溉量减少的情况下,红砂幼苗可通过根长、根系表面积和体积、直径等形态变化来优化其空间分布构型,以调节植株对水分的利用,提高水分利用效率。     

宁夏平原北部地下水埋深浅地区不同灌木的水分来源

宁夏平原北部引黄灌区地下水埋深浅是该地区土壤盐碱化的主要原因, 种植耐盐植物可以吸收利用地下水, 在降低地下水位的同时可以减少对地面灌溉的依赖。为了分析银川平原北部4种灌木对不同水源的利用特征, 于2010年生长季测定了灌溉前后20年生多枝柽柳(Tamarix ramosissima)、3年生多枝柽柳、3年生宁夏枸杞(Lycium barbarum)和3年生四翅滨藜(Atriplex canescens)木质部水及不同潜在水源稳定氧、氢同位素组成(δ¹⁸O和δD), 应用IsoSource同位素线性混合模型估算了不同灌木对不同水源的利用率。同时测定了0-200 cm土壤剖面的全盐含量、含水量和pH值以及灌溉前后光合气体交换参数。结果表明: 不同深度土壤水δ¹⁸O和δD值存在较大差异, 并呈规律性变化。土壤水δ¹⁸O和δD值随深度加深呈逐渐降低的趋势。灌溉后80 cm以上土壤水δ¹⁸O和δD值低于灌溉前。无论灌溉前还是灌溉后, 20年生多枝柽柳与3年生灌木相比具有更低的δ¹⁸O和δD值。灌溉前, 3年生多枝柽柳、宁夏枸杞和四翅滨藜主要利用表层土壤水(70.1%、52.3%和48.9%); 20年生多枝柽柳对地下水的利用率最高(21.5%)。灌溉后, 3年生多枝柽柳和宁夏枸杞对80-140 cm土壤水利用率较高(59.5%和58.8%)。20年生多枝柽柳对地下水的利用率最高(18.3%)。灌溉前, 20年生多枝柽柳净光合速率、气孔导度和蒸腾速率显著高于其他3种灌木, 灌溉后3年生四翅滨藜净光合速率最高。灌溉对3年生多枝柽柳和宁夏枸杞的净光合速率和气孔导度有显著影响。无论灌溉前还是灌溉后, 3年生四翅滨藜瞬间水分利用效率均高于其他3种灌木。研究表明, 不同灌木在不同水分条件下水分利用策略不同, 这主要与植物种类及树龄有关。灌溉前幼龄多枝柽柳凭借其对干旱较强的忍耐能力利用浅层不饱和土壤水, 灌溉后其又转而利用中层土壤水, 表现出潜水湿生植物的特征, 主要吸收利用深层土壤水分, 对灌溉反应不明显。     

华北落叶松林细根生物量对土壤水分、氮营养空间异质性改变的响应

在华北落叶松(Larix principis-rupprechtii)林选取采伐干扰样地和未采伐干扰样地进行对比研究, 分析采伐干扰造成林下土壤水分和氮营养空间异质性的改变对细根生物量空间变异的影响。采用空间格局分析的小支撑、多样点的设计原则, 对每个样点的土壤分3层取样(0-10 cm、10-20 cm、20-30 cm)。进行细根(≤1 mm和1-2 mm)生物量与土壤含水量、全氮、硝态氮、铵态氮和土壤pH的偏相关分析, 以及细根生物量变异函数值和土壤各因子变异函数值的线性回归分析。研究结果表明, 在不同样地, 细根生物量与土壤各因子均表现为正相关关系, 不同土层相关性强弱表现各异, 其中土壤含水量与细根生物量的相关性显著。受采伐干扰后, 细根生物量与土壤含水量、全氮、土壤硝态氮空间变异的关联性更趋于明显。多元线性回归分析结果表明, 采伐干扰样地细根生物量的空间变异更多地受到土壤多因子的综合影响, 而未采伐干扰样地的细根生物量受土壤水分、全氮和硝态氮单独效应的影响更大。     

沙丘多枝柽柳灌丛根层土壤含水量变化特征与根系水力提升证据

分析干旱区深根型荒漠植物的根层土壤水分是揭示荒漠植物与土壤水分关系机理的重要方面。在黑河中游一片风沙侵蚀区域的多枝柽柳(Tamarix ramosissima)人工林地中, 对表层0.3 m到3 m深的土壤不同深度的含水量进行了连续的动态观测。结果显示, 多枝柽柳根系层土壤含水量可以分为明显不同的3层: 浅层(0.2-1.7 m深)相对湿润层、中间(1.7-2.7 m深)相对干层和深层(2.7 m以下)有效含水层。在多枝柽柳生长盛期, 浅层相对湿润层土壤含水量呈现明显的昼夜变化特征, 同时, 在晚上植物根系与浅层土壤之间存在正水势梯度, 这说明存在根系水力提升现象。水力提升是干旱气候下根层浅层土壤含水量保持相对湿润的主要原因, 并因此维系浅层根系的发育, 也为多枝柽柳具备的防风固沙功能提供了可能的解释。据初步估算, 多枝柽柳根系水力提升占每天耗水量的5%-8%, 耗水的主要水分来源仍然是充足的土壤深层有效含水层。     

Fine-root vitality in a Norway spruce stand subjected to various nutrient supplies

The vitality of fine roots in a Norway spruce stand subjected to application of ammonium sulphate (NS), wood ash (A) and nitrogen-free fertilizer (V) respectively, was investigated using i) vitality classification of fine roots based on morphological characteristics and ii) the triphenyl tetrazolium chloride (TTC) method of estimating dehydrogenase activity.Although the NS-treated areas showed a 30% increase in above-ground production in response to the NS-application, the vitality of the fine-root system in the humus layer appeared to be in a state of deterioration, as indicated by a decrease in fine-root biomass, an increased amount of dead fine (0–1 mm) and small (1–2 mm) roots, a decreased specific root length (SRL = fine root length/fine root dry weight) and an increased dehydrogenase activity. The impact of the the A and V treatments was reflected in a decrease in fine-root biomass and an increase in SRL. The results make it clear that in order to study the vitality of forest trees, both fine-root studies and studies of above-ground tree parts are necessary.     

Fine-root morphology and uptake of 32P and 35S in a Norway spruce (Picea abies (L.) Karst.) stand subjected to various nutrient and water supplies

An investigation of fine (< 1 mm in diameter) and small (1–2 mm in diameter) roots in the organic soil layer was carried out in a Norway spruce forest stand with different treatments of water and nutrients, including control (C); ammonium sulphate application (NS); nitrogen-free fertilization (V); irrigation with liquid fertilization (a complete nutrient solution) (IF); NS followed by artificial drought (ND); V followed by artificial drought (VD). In order to evaluate the vitality and function of the fine roots, the following approaches were used: i) classification of fine roots, based on morphological characteristics; ii) nutrient uptake bioassay, using ³²P-phosphate and ³⁵S-sulphate; iii) nutrient concentration in fine roots and its relation to nutrient uptake. The NS treatment showed effects on the fine and small roots, with a decrease in amount of living roots, and a decrease in the total amount of fine and small roots. The VD treatment resulted in increased amounts of living small roots, while the ND treatment showed the opposite, as compared with the V and NS treatments, respectively. The uptake of P was negatively related to the P supply, with a higher P uptake for C and NS fine roots than for IF and V fine roots. The specific root length (SRL, m g^-1 DW) decreased for NS fine roots and increased for IF fine roots, indicating a further increase in uptake for NS roots and a decreased uptake for IF roots if calculated on a root length basis. So far, the NS and IF treatments maintain a considerable increase in above-ground biomass with a significantly reduced root biomass and standing crop.     

Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation

Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive to many global change factors. Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics and the tremendous research efforts in the past, our understanding of it remains limited. This is because the dynamics processes associated with soil resources availability are still poorly understood. Soil moisture, temperature, and available nitrogen are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch and at the ecosystem level. In temperate forest ecosystems, seasonal changes of soil resource availability will alter the pattern of carbon allocation to belowground. Therefore, fine root biomass, root length density (RLD) and specific root length (SRL) vary during the growing season. Studying seasonal changes of fine root biomass, RLD, and SRL associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover. The objective of this study was to understand whether seasonal variations of fine root biomass, RLD and SRL were associated with soil resource availability, such as moisture, temperature, and nitrogen, and to understand how these soil components impact fine root dynamics in Larix gmelinii plantation. We used a soil coring method to obtain fine root samples (⩽2 mm in diameter) every month from May to October in 2002 from a 17-year-old L. gmelinii plantation in Maoershan Experiment Station, Northeast Forestry University, China. Seventy-two soil cores (inside diameter 60 mm; depth intervals: 0–10 cm, 10–20 cm, 20–30 cm) were sampled randomly from three replicates 25 m × 30 m plots to estimate fine root biomass (live and dead), and calculate RLD and SRL. Soil moisture, temperature, and nitrogen (ammonia and nitrates) at three depth intervals were also analyzed in these plots. Results showed that the average standing fine root biomass (live and dead) was 189.1 g·m⁻²·a⁻¹, 50% (95.4 g·m⁻²·a⁻¹) in the surface soil layer (0–10 cm), 33% (61.5 g·m⁻²·a⁻¹), 17% (32.2 g·m⁻²·a⁻¹) in the middle (10–20 cm) and deep layer (20–30cm), respectively. Live and dead fine root biomass was the highest from May to July and in September, but lower in August and October. The live fine root biomass decreased and dead biomass increased during the growing season. Mean RLD (7,411.56 m·m⁻³·a⁻¹) and SRL (10.83 m·g⁻¹·a⁻¹) in the surface layer were higher than RLD (1 474.68 m·m⁻³·a⁻¹) and SRL (8.56 m·g⁻¹·a⁻¹) in the deep soil layer. RLD and SRL in May were the highest (10 621.45 m·m⁻³ and 14.83m·g⁻¹) compared with those in the other months, and RLD was the lowest in September (2 198.20 m·m⁻³) and SRL in October (3.77 m·g⁻¹). Seasonal dynamics of fine root biomass, RLD, and SRL showed a close relationship with changes in soil moisture, temperature, and nitrogen availability. To a lesser extent, the temperature could be determined by regression analysis. Fine roots in the upper soil layer have a function of absorbing moisture and nutrients, while the main function of deeper soil may be moisture uptake rather than nutrient acquisition. Therefore, carbon allocation to roots in the upper soil layer and deeper soil layer was different. Multiple regression analysis showed that variation in soil resource availability could explain 71–73% of the seasonal variation of RLD and SRL and 58% of the variation in fine root biomass. These results suggested a greater metabolic activity of fine roots living in soil with higher resource availability, which resulted in an increased allocation of carbohydrate to these roots, but a lower allocation of carbohydrate to those in soil with lower resource availability. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(3): 403–410 [译自: 植物生态学报, 2005, 29(3): 403–410]     

Early taproot development of a xeric shrub (<Emphasis Type="Italic">Larrea tridentata</Emphasis>) is optimized within a narrow range of soil moisture

Effects of watering amount and frequency on root biomass accumulation and taproot elongation were examined 16–17 days post-germination in seedlings of Larrea tridentata, a dominant shrub in North American hot deserts. Two experimental variables manipulated in a full factorial design greenhouse study were (i) number of “triggering” days: consecutive days (2, 3, 4 or 5) at the start of the experiment on which seedlings received 10 mm of water per day; and (ii) “post-trigger” watering frequency: 5 mm of water either daily or every other day. We hypothesized that taproot elongation would increase with greater numbers of triggering days, whereas higher post-trigger watering frequency would enhance root biomass development. Increasing the number of triggering days from two to four promoted taproot extension without affecting root biomass, and higher watering frequency in the post-trigger phase generally increased root biomass, as expected. Contrary to expectations, root biomass and taproot length were significantly reduced when daily watering followed five consecutive triggering days. Taproot length correlated with root biomass, but irrigation regime also had a biomass-independent effect: with either two or five triggering days, taproots were shorter than expected based on root biomass. Thus, both too little and too much water stymied taproot extension. In natural settings, the adverse response of taproots to too little or too much water could reduce seedling survivorship and restrict establishment to a narrow range of environmental conditions.     

Responses of the fine root morphology and vertical distribution of Populus × euramericana ‘Guariento’ to the coupled effect of water and nitrogen

Aims Irrigation and fertilization have great potentials to enhance yield in forest plantations. The integrated effect of water and nitrogen management on fine roots morphology and distribution of Populus × euramericana ‘Guariento’, however, remains unclear. The objective of this study was to evaluate the effect of water and nitrogen addition on fine root morphology and distribution in poplar plantations for developing the best water and nitrogen strategy for promoting fine root. Methods The soil core method was used to quantify the morphology and distribution of fine roots in the 0–60 cm in a poplar plantation with surface dripping irrigation and fertilization technologies. The experiment included nine treatments, which were a combination of three irrigation treatments where dripping irrigation was applied when soil water potential (ψ_soil) reached –75, –50, or –25 kPa, and three fertilization treatments at nitrogen additions of 150, 300, or 450 g·tree–1·a–1, respectively). A control plot with non-irrigation and non-fertilizationtreatment in growing season (CK) was also included in the study. Important findings The fine roots biomass density, fine root surface area density, average root diameter in all treatments were mainly found at 0–10 cm and 10–20 cm depths, with root biomass density in the 10–20 cm of 1.03 to 1.21 times of that in the 0–10 cm, 1.25 to 1.80 times of that in the 20–30 cm, 1.62 to 22.10 times of that in the 30–40 cm, 2.77 to 54.35 times of that in the 40–50 cm, and 6.48 to 293.09 times of that in the 50–60 cm. The root biomass density in the 10–20 cm accounted for 27%–37% of the total biomass density in the top 60 cm. For root biomass density and average diameter, there were no significant differences between 0–10 cm and 10–20 cm depths, and between 40–50 cm and 50–60 cm depths. Fine roots in the irrigation and fertilization treatments were significantly higher than that of the CK, except the D1F1 treatment (i.e., with low water and low nitrogen level). Additionally, fine roots in the D2F3 treatment (i.e., with intermedia irrigation and high nitrogen level) and the D3F3 treatment (i.e., with high water and high nitrogen level) were significantly higher than those in other treatments, but not significantly different between D2F3 and D3F3. Compared with the CK, the fine roots biomass density in six soil layers were significantly enhanced at 359%, 388%, 328%, 3823%, 4774% and 2866%, respectively, for the treatment with high water and high nitrogen levels. The vertical distributions of fine roots appeared not affected by the interaction of irrigation and nitrogen addition. However, the surface dripping irrigation and fertilization treatments increased fine roots significantly. Finally, we found that the response of fine root growth and distribution was stronger to fertilization than to the irrigation in this poplar plantation.     

Very fine roots respond to soil depth: biomass allocation,morphology, and physiology in a broad-leaved temperate forest

Very fine roots (<0.5 mm in diameter) of forest trees may serve as better indicators of root function than the traditional category of <2 mm, but how these roots will exhibit the plasticity of species-specific traits in response to heterogeneous soil nutrients is unknown. Here, we examined the vertical distribution of biomass and morphological and physiological traits of fine roots across three narrow diameter classes (<0.5, 0.5–1.0, and 1.0–2.0 mm) of Quercus serrata and Ilex pedunculosa at five soil depths down to 50 cm in a broad-leaved temperate forest. In both species, biomass and the allocation of very fine roots were higher in the surface soil but lower below 10-cm soil depth compared to values for larger roots (0.5–2.0 mm). When we applied these diameter classes, only very fine roots of Q. serrata exhibited significant changes in specific root length (SRL; m g⁻¹) and root nitrogen (N) concentrations with soil depth, whereas the N concentrations only changed significantly in I. pedunculosa. The SRL and root N concentrations of larger roots in the two species did not significantly differ among soil depths. Thus, very fine roots may exhibit species-specific traits and change their potential for nutrient and water uptake in response to soil depth by plasticity in root biomass, the length, and the N in response to available resources.