不同年龄三倍体毛白杨纸浆林生长期间细根变化规律

以3、5、6及7年生三倍体毛白杨纸浆林为对象,于2008年研究生长期(4—11月)细根生物量、根长密度和细根表面积的月动态变化和垂直分布的变化。结果表明:细根生物量、根长密度或细根表面积在4—11月均表现为单峰曲线,其中细根生物量的峰值出现在8月,而根长密度和细根表面积的峰值出现在9月;细根生物量、根长密度及细根表面积的平均值随年龄的增加而增加,3、5、6及7年生的三倍体毛白杨细根生物量分别为658.3、750.6、1048.1和1115.0kg.hm-2,相应地根长密度分别为12.490×103、9.983×103、9.227×103和5.921×103m.m-3,细根表面积分别为12.17、18.68、22.23和25.28m2.m-3;细根生物量、根长密度及细根表面积的垂直分布表现为表层化,随年龄的增加表层细根增多,其中细根生物量的46.36%～51.12%、根长密度的62.77%～75.33%、细根表面积的61.74%～64.16%均分布在0～10cm土层。     

黄土高原不同演替阶段草地植被细根垂直分布特征与土壤环境的关系

研究了黄土区不同演替阶段草地植被细根垂直分布特征与土壤环境的关系,结果表明不同演替阶段草地植被细根生物量、根长密度、表面积、直径和比根长均具有明显的垂直分布特征。细根生物量、根长密度和细根表面积一般随土层加深而逐渐减少,且集中分布于0-40cm土层;随着演替的进行,除20a弃耕地外,0—80cm土层细根生物量、根长密度和细根表面积逐渐增加;除25a弃耕地外,细根直径随演替进行逐渐减小。0～100cm土层土壤含水量随演替进行而增加,不同演替阶段深层土壤水分较表层稳定。土壤容重的变化趋势为9〈4〈15〈20〈25a弃耕地,根系对表层土壤水分和容重的影响较大,而对深层土壤水分与容重影响较少。不同演替阶段细根各参数和土壤水分、容重差异均达到显著水平。各弃耕地细根参数之间,细根参数和土壤环境因子之间存在不同程度的相关关系,土壤含水量在草本植被的不同演替阶段均是影响其细根垂直分布的关键因素。土壤容重在演替早期对草本植被根系的影响较小,随着演替进行其影响作用进一步增强。     

亚热带不同演替树种米槠和马尾松细根性状对比研究

选择福建省三明市中亚热带演替前期树种马尾松和演替后期树种米槠两种人工林为研究对象,采用土芯法研究两个树种细根(直径2mm)的生物量及其垂直分布、形态以及分支结构等细根性状特征。结果表明:(1)0—80cm土层米槠的细根生物量密度(0.21±0.06)kg/m3、根表面积密度(3.15±1.25)m2/m3和根长密度(2202.84±517.03)m/m3分别为马尾松的1.6、1.2倍和2.2倍,并且3个指标均随土层深度增加而降低,但演替前期树种马尾松细根在土层间分布更均匀,而演替后期树种米槠细根更富集于表层。(2)马尾松细根的直径(0.86±0.04)mm、比表面积(191±32)cm2/g分别是米槠的1.4倍和1.3倍;米槠细根的比根长(10.73±0.46)m/g、组织密度(0.49±0.06)g/cm3分别是马尾松的1.4倍和2.0倍,马尾松细根的较大直径和低组织密度的形态结构能够迅速生长占领土壤空间和适应干旱环境,而米槠细根的较小直径、高比根长和较高的组织密度使其具有较强养分竞争能力和应对取食压力;(3)米槠的比根尖密度(4288±63)个/g、比分叉密度(1164±155)个/g均为马尾松的2.2倍,米槠细根的高分支系统能够迅速利用富养斑块。结论表明处于不同演替阶段的树种细根性状具有明显差异,可能反映了不同的资源获取策略。     

毛竹细根分布特征研究

为了解毛竹(Phyllostachys edulis)细根的分布规律,对不同水平距离和土层深度0~1 mm和1~2 mm细根的生物量、比根长、组织密度和根长密度进行了分析。结果表明,随着毛竹年龄的增加,细根生物量和根长密度先上升后降低,根组织密度先降低后升高,比根长呈降低的趋势。细根生物量和根长密度以距竹秆60 cm处最大,根组织密度以20 cm处最大,比根长在40 cm处最大,但他们在距竹秆不同距离间的差异不显著。细根生物量以10~20 cm土层最大,根组织密度以20~30 cm土层最大,细根生物量、比根长、组织密度和根长密度在不同土层间的差异不显著。与1~2 mm细根相比,0~1 mm细根生物量和根组织密度更小,比根长和根长密度更大。因此,毛竹年龄对细根生长具有显著的影响,1年生毛竹有最大的比根长和较大的根组织密度,具有更强的资源利用率。毛竹细根在一定的土层范围内呈均匀分布状态,可更有效地利用特定区域的水肥资源。     

干旱区绿洲灌溉条件下不同树龄轮台白杏根系的空间分布

采用田间分层挖掘法和图像扫描分析法,研究了干旱区绿洲灌溉条件下不同树龄轮台白杏根系的空间分布特征.结果表明:轮台白杏的根系主要由细根(d≤1 mm)构成,中粗根(1＜d≤2 mm)和粗根(d＞2 mm)所占比例较小,树龄5 a、10 a和15 a轮台白杏细根长度分别占根系总长度的90.9％、88.4％和79.9％.随树龄延长,根长密度增加,不同径级根长密度均为15 a＞10 a＞5 a.在垂直方向上,轮台白杏的根长密度呈现出先增加后减小的分布趋势,且各土层根系干质量密度差异显著,树龄5a、10 a和15 a轮台白杏根系干质量密度分布较集中的区域分别为距离树干200 cm以内的30 ～ 80 cm、30～100 cm和30～100 cm深度土层,轮台白杏根系的水平分布特征为距离树干越远根系干质量密度越小,且距树干不同距离处的差异显著.从减小相邻树行间树体根系的交错重叠和降低水肥竞争的角度考虑,在干旱区绿洲灌溉条件下,轮台白杏的栽植行距应≥6 m.     

喀斯特峰丛洼地不同植被恢复阶段细根生物量、形态特征及其影响因素

以喀斯特峰丛洼地不同植被恢复阶段的草丛、灌丛、次生林和原生林为研究对象,采用土芯法,分0~10、10~20、20~30 cm等3层获取群落活细根(直径≤2 mm),分析其生物量、形态特征及其与土壤性状的关系.结果表明:各恢复阶段细根生物量为194.63~255.19g·m^-2,集中分布在0~10 cm表层土壤中,占0~30 cm土层总生物量60%以上,不同恢复阶段群落生物量的差异不显著;细根比根长和比表面积在不同恢复阶段差异显著,随着植被由草丛向原生林正向恢复而逐渐降低;超过66%的根长和64%的根面积分布在0~10 cm表层土壤中,多数细根根长和根面积均在0~0.5 mm和0.5~1 mm径级,这两级根长和根面积占其总量的87%和72%以上.冗余分析表明,喀斯特峰丛洼地植物群落细根特征与土壤性状之间存在着不同的相关性,其中土壤有机碳、速效钾和全氮对细根特征影响较大.这是植物长期适应生境条件形成的有效策略.     

长白山阔叶红松林表层土壤木本植物细根生物量及其空间分布

2008年在长白山北坡原始阔叶红松林内选择3块50 m×50 m样地,采用地统计学方法对表层土壤中木本植物细根生物量及其分布特征进行了定量研究.结果表明：3块样地0～20 cm土层中木本植物活细根生物量分别为3.195、1.930和2.058 t·hm^-2,死细根生物量分别为0.971、0.581和0.790 t·hm^-2,0～10 cm土层中,死、活细根生物量之间无显著相关关系,而10～20 cm土层中,二者呈显著正相关关系(r=0.352,P<0.05）,死、活细根生物量的实际变异函数大多符合球状理论模型.空间自相关引起的空间异质性占总空间异质性的百分比平均大于70%,各样地活、死细根生物量变程分别为5.2、14.6、9.8 m和4.3、20.4、20.1 m.采用贝叶斯统计方法对3块样地活细根生物量空间自相关范围进行估计的结果与地统计学方法的统计结果一致.     

间伐对杉木不同根序细根形态、生物量和氮含量的影响

以25年生的杉木人工林为对象,研究了间伐对杉木1～5级根的生物量、形态和氮含量的影响.结果表明: 随着根序的增加,杉木细根的生物量、直径和组织密度(RTD)显著增加,而比根长(SRL)、根长密度(RLD)和根数(RN)显著降低.间伐显著提高了1～2级根的生物量、RLD和RN,以及1级和3～5级根的RTD,而对细根的SRL和氮含量无影响;1级和3～4级根的直径显著减小;表层(0～10 cm)土壤中的2级根直径明显小于亚表层(10～20 cm)土壤,而1～3级根的RLD和1～2级根的RN和氮含量均大于亚表层土壤.
间伐和土层的相互作用仅使1～2级根的直径减小.杉木细根的变化主要与间伐后的植被生长及更新密切相关.
     

小麦和玉米根系取样位置优化确定及根系分布模拟

为了确定小麦(Triticum aestivum)、玉米(Zea mays)根系的最优取样位置和更准确地模拟根长密度在土壤剖面的分布, 在冬小麦和夏玉米的灌浆后期, 采用根钻法取样, 比较了不同取样位置对根系分布的影响; 采用Gerwitz和Page模型对根长密度的分布进行了模拟。结果表明, 冬小麦行间和行上取样在0-10 cm土层根长密度差异显著, 在10 cm以下土层差异减少。在确定根长密度分布的取样中, 在0-20 cm土层应考虑根长密度分布的空间差异, 即行上密度大于行间密度; 而在20-100 cm土层, 需要考虑行间根长密度大于行上的空间差异; 在1 m以下土层两个位置的差异逐渐消失, 可不考虑空间差异。夏玉米根长密度在上层土壤表现出距离植株不同位置差异显著的特征。植株位置(株上)、距植株10 cm和距植株20 cm位置根长密度在土壤中的分布特征是: 0-10 cm土层3个位置根长密度差异在50%以上, 根长密度大小是株上>距植株10 cm>距植株20 cm; 而在10-30 cm层次, 根长密度表现为距植株10 cm>株上>距植株20 cm, 30-50 cm土层株上位置的根长密度最小, 50 cm以下各位置根长密度差异不明显。对于玉米根系取样, 50 cm以上土层需要考虑根长密度的空间差异, 50 cm以下土层可不考虑。采用Gerwitz和Page模型, 结合华北平原机械化耕作下形成的土壤犁底层变厚及其犁底层容重增加对根系分布的影响, 在模型中加入土壤容重参数订正可以使模型更准确地模拟根长密度在土壤剖面的分布。     

不同品种油茶细根时空分布动态

以赣无1、赣永5、长林4、长林40和赣447 等5个品种的油茶林为研究对象,采用微根管技术对0～40 cm土壤剖面的油茶细根进行了为期一年的观测,并分析了总根尖数(TRT)、平均根长密度(ARLD)、平均直径(ARD)的时空分布动态规律.结果表明: 2016年下半年,各品种的TRT和ARLD变化相对稳定,2017年上半年,各品种的TRT和ARLD变化幅度较大,尤其体现在赣无1与长林40中.赣无1的TRT和ARLD在2017年5月出现峰值,长林4的ARD在2017年3月出现峰值.赣无1的TRT和ARLD 以及长林4的ARD在整个观测期都显著大于其他品种.不同品种油茶细根在土层中的空间分布规律及动态变化存在明显差异,赣无1和赣447的细根主要分布在0～20 cm土层中,长林4和长林40的细根以20～40 cm土层居多,空间分布动态变化较其他3个品种稳定;赣永5的空间分布动态变化幅度较大,根量分布各土层无显著差异;长林4的ARD表现为20～40 cm土层>0～20 cm土层,其他品种的ARD在不同土层中无显著差异.赣无1的细根生物量最多,主要分布在上层;长林4的细根直径最粗,主要分布在下层.     

宽窄行栽植模式下三倍体毛白杨根系分布特征及其与根系吸水的关系

采用剖面法对宽窄行栽植模式下三倍体毛白杨(triploid Populus tomentosa)的根系分布特征进行了研究;采用管式TDR系统对土壤剖面含水率变化动态进行了连续观测,并据此计算林木根系吸水速率,以探讨土壤含水率、根系分布和根系吸水分布之间的相关关系。研究结果表明:毛白杨的总平均根长密度在林带两侧和不同径向距离处非常接近(P>0.05);但在不同土层间变化很大(P<0.01),其中0-20和60-150 cm土层为根系主要分布区域,其根系所占比例共达86%;不同径阶间的根长密度差异显著(P<0.01),且其比例关系会随空间位置的改变而发生变化。不同栽植方位下,林带东侧毛白杨根系分布的浅层化程度高于西侧,且在径向240-280 cm内其0-0.5 mm的极细根显著多于西侧(P<0.05)。因此,宽窄行栽植模式下,深度和径阶是毛白杨根系分布的主要影响因子,而栽植方位会对其形态构型产生影响。毛白杨根系吸水模式受细根分布的影响,但会随土壤剖面水分有效性分布的变化而变化:当表土层水分有效性增加时,根系吸水主要集中在表土层;当表土层水分有效性降低时,深层土壤根系的吸水贡献率会逐渐增加;当土壤剖面水分条件异质性较高时,根系吸水主要集中在根系密度与水分有效性均较高的区域;当土壤剖面水分分布均匀且不存在水分胁迫时,根系吸水分布与细根分布最为一致。     

Fine Root Distribution in Dehesas of Central-Western Spain

A Dehesa is a structurally complex agro-silvo-pastoral system where at least two strata of vegetation, trees and herbaceous plants coexist. We studied the root distribution of trees (Quercus ilex L.) and herbaceous plants, in order to evaluate tree and crops competition and complementarity in Dehesas of Central Western Spain. 72 soil cores of 10 cm diameter (one to two metre deep) were taken out around 13 trees. Seven trees were intercropped with Avena sativa L. and six trees were in a grazed pasture dominated by native grasses. Soil coring was performed at four distances from the tree trunks, from 2.5 (beneath canopy) till 20 m (out of the canopy). Root length density (RLD) of herbaceous plants and trees was measured using the soil core-break method. Additionally, we mapped tree roots in 51 profiles of 7 recently opened road cuts, located between 4 and 26 m of distance from the nearest tree. The depth of the road cuts varied between 2.5 and 5.5 m. Herbaceous plant roots were located mostly in the upper 30 cm, above a clayey, dense soil layer. RLD of herbaceous plants decreased exponentially with depth until 100 cm depth. Holm-oak showed a much lower RLD than herbs (on average, 2.4 versus 23.7 km m⁻³, respectively, in the first 10 cm of the soil depth). Tree RLD was surprisingly almost uniform with depth and distance to trees. We estimated a 5.2 m maximum depth and a 33 m maximum horizontal extension for tree roots. The huge surface of soil explored by tree roots (even 7 times the projection of the canopy) could allow trees to meet their water needs during the dry Mediterranean summers. The limited vertical overlap of the two root profiles suggests that competition for soil resources between trees and the herbaceous understorey in the Dehesa is probably not as strong as usually assumed.     

Analysis of Distribution of Root Length Density of Apple Trees on Different Dwarfing Rootstocks

This paper considers statistical analyses for comparing thedistribution of root length density (RLD) of apple trees underdifferent rootstocks and tree spacing. The source data includedRLD values (cm cm^-3) measured by soil coring the root systemsof eight trees in each of two seasons. We formulated a regressionmodel which assumed the RLD dropped exponentially with soildepth, and this relationship varied with the radial distancefrom the tree. The model fitted to the log transformed meandata described the RLD distribution well. Young trees (5-year-old)of M.26 (semi-dwarf) and MM.106 (semi-vigourous) had a highermean RLD and showed a more layered vertical distribution, comparedwith trees of the dwarf Mark rootstock. Differences among rootstockswere not evident in older (9-year-old) trees. In general, youngroot systems were more bowl shaped, whereas older trees hada higher RLD further away from the tree trunk. RLD is a positiveand continuous variable except for the possibility of an excessof exact zeros. A generalized linear model with a Poisson-gammatype distribution allows modelling of individual RLD data withzeros contributing to parameter estimation. It does not, however,provide simplicity of biological interpretation. In this paperwe present a model that assumes the realization of RLD datais due to a Bernoulli and an exponential process. The fittingof the Bernoulli-exponential model by maximum likelihood isillustrated, and further generalization suggested.Copyright1999 Annals of Botany Company Malus domestica(Borkh.), Fuji, rootstock, root system, soil core sampling, Bernoulli–exponential model.     

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

Fine root tumover 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 Mav 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 (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 soil layer.RLD and SRL in May were the highestthe other months,and RLD was the lowest in Septemberdynamics 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.     

Do propagation methods affect the fine root architecture of African plum (Dacryodes edulis)?

Belowground tree growth attributes determine whether associations will be complementary or competitive in an agroforestry context. A study on fine root (d?≤?2?mm) distribution patterns of Dacryodes edulis based on root density (RD), root length density (RLD) and root weight density (RWD) was conducted to evaluate the effect of propagation methods on rooting distribution. Results showed that D. edulis trees of seed origin had greater RD (P?≤?0.001) than trees of vegetative origin (cuttings and marcots) in the upper soil stratum (0–30?cm). Similarly, in the uppermost soil stratum (0–10?cm), RLD and RWDs varied significantly (P?<?0.01). Trees of seed origin had an exponential distribution pattern for fine RD, RLD and RWD with depth to 80?cm. In contrast, the distribution pattern of fine roots of trees of vegetative origin (cuttings and marcots) were quadratic for the same variables which increased in the 20–30?cm soil depth stratum before declining steadily to a depth of 80?cm. The findings of this study suggest that D. edulis trees of vegetative origin (cuttings and marots) are likely to be less competitive than trees of seed origin when intercropped with shallow-rooted annual plants in an agroforestry system for belowground resources.     

黄土丘陵半干旱区密植枣林随树龄变化的根系空间分布特征

该文研究了黄土丘陵半干旱区密植枣( Ziziphus jujuba ‘Lizao’)林群体根系随树龄变化的空间分布特征。对1年生、4年生、8年生和11年生4种树龄的密植枣林采用剖面法, 获得0-1 m土壤剖面上直径>3 mm、1-3 mm及<1 mm的根系数量和空间位置信息。利用方差分析, 评价了山地密植枣林林分根系随树龄变化的水平和垂直分布特征。结果表明: 3种直径的根系数量均随着树龄的增长而增加, 直径< 1 mm的根系增长速度最快; 随着土层加深, 根系数量递减, 1年生枣林的根系主要聚集在0-40 cm土层中, 4年生及以上树龄的根系主要分布在0-60 cm土层中; 0-1 m土层内, 1年生枣林(株距1.2 m)及4年以上树龄(株距2 m), 同树龄枣林中直径<1 mm的根系水平分布无差异; 同一土层中(0-20 cm, 20-40 cm, 40-60 cm), 无论树龄大小及离树干的水平位置如何, 不同直径根系的数量都无差异。研究表明: 在有水肥管理措施的条件下, 枣林根系垂直方向形成浅层型的适应模式; 在密植环境下, 枣林细根形成根网型的适应模式。     

陇东旱塬苹果根系分布规律及生理特性对地表覆盖的响应

为探明陇东旱塬区不同覆盖物对苹果园土壤理化性状、根系分布及根系生理活性的影响,以14年生苹果树为试材,采用土壤剖面分层取样法,调查根系空间分布,并对根系生物量、根长、表面积等进行分析,测定根系活力、抗氧化酶类、活性氧代谢等相关生理指标,同时测定不同深度土层土壤容重、孔隙度等.结果表明: 覆草可有效增大土壤含水量、孔隙度、有机质含量,增幅分别为2.7%～11.6%、3.2%～27.7%、5.1%～36.0%,但土壤容重降低,为清耕(CK)的88.7%～96.4%.CK根系主要分布在距树干30～120 cm范围内的0～60 cm深土层中;覆草、覆膜处理主要分布在距树干0～150 cm、0～60 cm水平范围内的0～100 cm深土层中,以20～40 cm根系最为密集;覆膜处理细根总量仅为CK的96.4%,根系水平分布范围较CK有所减小,0～60 cm内细根占根系总量的51.6%.不同覆盖处理显著增强0～80 cm土层根系活力及抗氧化酶活性,其中覆草处理根系活力为CK的111.3%～136.7%.综合分析根系生长分布与生理活性、土壤理化性状等,认为覆草处理是陇东旱塬区苹果园较为适宜的地表覆盖方式.     

柠条细根的空间分布特征及其季节动态

以晋西北黄土区30年生柠条(Caragana korshinskii Kom.)人工林为研究对象,2007年应用Minirhizotron技术,分别在距茎干水平距离0、50、100 cm处设点,对林地0-100 cm土层深度范围内的柠条细根空间分布及其生长季的动态进行了研究。结果表明:(1)生长季柠条细根根长密度(RLD)总平均值为1.3423 mm/cm²。在水平方向上,距茎干水平距离50 cm处分布最多(1.5369 mm/cm²),其次为0 cm处(1.3855 mm/cm²), 100cm处分布最少(1.1044 mm/cm²)。在垂直深度上,各土层RLD平均值大小顺序为40-60 cm>60-80 cm>20-40 cm>0-20 cm>80-100 cm;(2)在0-100 cm土层范围内,月平均RLD在生长季的波动范围为0.4405 2.1040 mm/cm²,其中9月份最多,4月份最少;RLD在5个土层深度3个水平距离处随季节变化均表现先增加后减少的趋势,且不同空间位置RLD峰值变化均在秋季(8 10月份)波动。细根的这种时空分布差异,可能主要受林下土壤资源空间异质性及其季节性变化的影响,但也不排除其它因素的影响(如真菌,植食性昆虫)。     

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]     

根区交替控制灌溉条件下玉米根系吸水规律

为了阐明根区交替控制灌溉(CRDAI)条件下玉米根系吸水规律,通过田间试验,在沟灌垄植模式下采用根区交替控制灌溉研究玉米根区不同点位(沟位、坡位和垄位)的根长密度(RLD)及根系吸水动态。研究表明,根区土壤水分的干湿交替引起玉米RLD的空间动态变化,在垄位两侧不对称分布,并存在层间差异;土壤水分和RLD是根区交替控制灌溉下根系吸水速率的主要限制因素。在同一土层,根系吸水贡献率以垄位最大,沟位最低;玉米营养生长阶段,10—30 cm土层的根系吸水速率最大;玉米生殖生长阶段,20—70 cm为根系吸水速率最大的土层,根系吸水贡献率为43.21%—55.48%。研究阐明了交替控制灌溉下根系吸水与土壤水分、RLD间相互作用的动态规律,对控制灌溉下水分调控机理研究具有理论意义。