Distribution of roots and root nodules and biomass allocation in young intensively managed grey alder stands on a peat bog

Development of below-ground biomass and biomass allocation were studied in two different stands of young grey alder stands growing on a peat bog. Both stands were given the same fertilization and irrigation treatment. The roots were investigated from 1) open plastic tubes enclosing the complete root systems in 1982, and 2) root cores 1984–86. Coarse roots (diameter>1 mm) were mainly found close to the trunk of the trees while fine roots (≤1 mm) were more evenly distributed in the stands. Root nodules were intermediate in distribution. The root systems were shallow, with more than 90% of the biomass in the uppermost 9–10 cm of the soil, probably because of low oxygen availability in the peat soil. The biomass allocation to the above-ground parts increased during the study period.     

Sieve size effects on root length and biomass measurements of maize (Zea mays) and Grevillea robusta

The purpose of this study was to investigate the effects of different mesh sizes on the recovery of root length and biomass and to determine whether the degree of recovery was influenced by plant species and sample location. Sieves of 2.0, 1.0, 0.5 and 0.25 mm (4.0, 1.0, 0.25 and 0.06 mm2) mesh sizes were used to recover and measure the root length and biomass of Zea mays L. (maize) at 0–15 cm and 30–45 cm depths and of Grevillea robusta A. Cunn. ex R. Br. (grevillea) at the same depths 1.0 m and 4.5 m from a line of grevillea trees. At 0–15 cm, the coarser sieves (sum collected with 2.0 and 1.0 mm sieves) recovered approximately 80% of the total root biomass measured, but only 60% of the root length. The proportion of total maize root length and biomass recovered by the coarser sieves decreased with soil depth. The proportion of total grevillea root length recovered by the coarser sieves was similar at the two soil depths, but increased slightly with distance from the tree line. The ≥ 0.5 mm sieves recovered between 93 and 96% of grevillea and maize root biomass and between 73 and 98% of their root length, depending on the sample location. Roots passing through the 0.5 mm sieve, but recovered by the 0.25 mm sieve were about 20% of total maize root length and grevillea root length at 1.0 m from the tree line but < 5% of the total grevillea root length at 4.5 m from the tree. Roots passing through the 0.5 mm sieve but recovered by the 0.25 mm sieve contributed only slightly to root biomass. Although the ≥ 0.5 mm sieves provided adequate measurements of root biomass, the ≥ 0.25 mm sieves were required for accurate measurement of fine root length. There was no universal correction for root length and biomass underestimation when large sieve sizes were used because the proportions of length and biomass recovered depended on the plant species and on soil depth and distance from the plant. This revised version was published online in August 2006 with corrections to the Cover Date.     

水曲柳根系生物量、比根长和根长密度的分布格局

采用连续钻取土芯法在生长季内对东北林业大学帽儿山实验林场17年生水曲柳人工林根系取样,研究水曲柳不同直径根系现存生物量、比根长和根长密度及垂直分布状况.结果表明,水曲柳人工林根系总生物量为1 637.6 g·m^-2,其中活根生物量占85%,死根占15%.在活根生物量当中,粗根(直径5～30 mm)占的比例最高（69.95%）,其次为活细根（直径<1 mm,13.53%）,小根(1～2 mm)和中等直径的根(2～5 mm)比例较小（分别为7.21%和9.31%）.直径<1 mm活细根的比根长为32.20 m·g^-1,直径5～30 mm粗根的比根长为0.08 m·g^-1.单位面积上活根的总长度为6 602.54 m·m^-2,其中直径<1 mm的细根占92.43%,其它直径等级则不到活根总长度的8%.直径<1 mm的细根生物量与根长密度具显著线性关系（R²=0.923）,但与比根长无显著相关关系（R²=0.134）.     

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.     

三峡库区马尾松根系生物量的空间分布

以三峡库区主要植被马尾松人工林为研究对象,用内径为10 cm的根钻,分别在马尾松中龄林、近熟林和成熟林内,据树干0.5、1.0、1.5 m和2.0 m处设置取样点,各样点按0-10、10-20、20-30、30-40、40-60 cm将土壤分为5个垂直层次,对马尾松根系的空间分布格局进行调查。结果表明:(1)三峡库区马尾松总根系生物量(0-10 mm)为中龄林(4.72 t/hm²)显著高于成熟林(2.94 t/hm²)和近熟林(2.40 t/hm²)(P<0.05)。细根(0-2 mm)生物量随年龄增加而递减,差异不显著(P>0.05);(2)马尾松3个林龄中根系生物量表现出一定的水平分布特征,但具体趋势表现各异,细根生物量最大值均出现在距离样木1.0 m处;(3)细根主要分布在土壤上层,其中47.53%-71.73%的活细根集中在0-20 cm土壤深度内,且随土层的加深,其生物量明显减少。粗根(2-10 mm)则主要分布于20-60 cm土层范围内;(4)根系直径越小,受环境变化越明显。马尾松细根生物量分布主要受土壤深度的影响,树龄和不同水平距离对细根分布格局影响不显著(P>0.05),各因素对粗根生物量的影响均未达到显著水平(P>0.05)。     

水曲柳根系生物量、比根长和根长密度的分布格局

采用连续钻取土芯法在生长季内对东北林业大学帽儿山实验林场17年生水曲柳人工林根系取样,研究水曲柳不同直径根系现存生物量、比根长和根长密度及垂直分布状况.结果表明,水曲柳人工林根系总生物量为1 637.6 g·m^-2,其中活根生物量占85%,死根占15%.在活根生物量当中,粗根(直径5～30 mm)占的比例最高（69.95%）,其次为活细根（直径<1 mm,13.53%）,小根(1～2 mm)和中等直径的根(2～5 mm)比例较小（分别为7.21%和9.31%）.直径<1 mm活细根的比根长为32.20 m·g^-1,直径5～30 mm粗根的比根长为0.08 m·g^-1.单位面积上活根的总长度为6 602.54 m·m^-2,其中直径<1 mm的细根占92.43%,其它直径等级则不到活根总长度的8%.直径<1 mm的细根生物量与根长密度具显著线性关系（R²=0.923）,但与比根长无显著相关关系（R²=0.134）.     

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]     

Below‐ground biomass and productivity of a grazed site and a neighbouring ungrazed exclosure in a grassland in central Argentina

Abstract We estimated the below‐ground net plant productivity (BNPP) of different biomass components in an intensively and continuously 45‐ha grazed site and in a neighbouring exclosure ungrazed for 16 years for a natural mountain grassland in central Argentina. We measured approximately twice as much dead below‐ground biomass in the grazed site as in the ungrazed site, with a strong concentration of total below‐ground biomass towards the upper 10 cm of the soil layer in both sites. The main contribution to total live biomass was accounted for by very fine (<0.5 mm) and fine roots (0.5–1.0 mm) both at the grazed (79%) and at the ungrazed (81%) sites. We measured more dead biomass for almost all root components, more live biomass of rhizomes, tap roots and bulbs, and less live biomass of thicker roots (>1 mm) in the grazed site. The seasonal variation of total live below‐ground biomass mainly reflected climate, with the growing season being limited to the warmer and wetter portion of the year, but such variation was higher in the grazed site. Using different methods of estimation of BNPP, we estimated maximum values of 1241 and 723 g m^?2 year^?1 for the grazed and ungrazed sites, respectively. We estimated that very fine root productivity was almost twice as high at the grazed site as at the ungrazed one, despite the fact that both sites had similar total live biomass, and root turnover rate was twofold at the grazed site.     

Lorentzian model of roots for understory yellow birch and sugar maple saplings

Total 66 small (<50m(2)), 24 medium (101-200m(2)) and 36 large (201-500m(2)) canopy gaps at the three sites of yellow birch (Betula alleghaniensis Britton) and sugar maple (Acer saccharum Marsh) forests were established in southern Québec, Canada. Half of the gaps were covered by 8x8m(2) shading cloths to mimic a closed canopy. From these gaps, 46 understory yellow birch and 46 sugar maple saplings with different tree ages and sizes were sampled. Single- and multi-variable linear and nonlinear models of root biomass and traits (root surface area, volume, length and endings) were developed and examined. Lorentzian model as a multi-variable nonlinear model was firstly applied to the simulations using both base diameter and height, and performed the best fit to total root biomass in both species with the highest correlation coefficients (R(2)=0.96 and 0.98) and smallest root mean squared deviations (RMSD=7.85 and 7.02) among all the examined models. The model also accurately simulated small fine root (2.0mm in diameter), coarse fine root (>2.0-5.0mm) and coarse root (>5.0mm) biomass (R(2)=0.87-0.99; RMSD=2.24-6.41), and the root traits (R(2)=0.71-0.99; RMSD=0.19-19.38). The study showed yellow birch roots were longer, larger, had more endings (tips) and grew faster than sugar maple roots. The root traits were largely distributed to small fine roots, sharply decreased from small fine roots to coarse fine roots, the fewest in coarse roots except for root volume. When trees were large, coarse root biomass increased more rapidly than fine root biomass, but vise versa when the trees were small.     

Root biomass and nutrient dynamics in a scrub-oak ecosystem under the influence of elevated atmospheric CO2

Elevated CO₂ can increase fine root biomass but responses of fine roots to exposure to increased CO₂ over many years are infrequently reported. We investigated the effect of elevated CO₂ on root biomass and N and P pools of a scrub-oak ecosystem on Merritt Island in Florida, USA, after 7 years of CO₂ treatment. Roots were removed from 1-m deep soil cores in 10-cm increments, sorted into different categories (<0.25 mm, 0.25–1 mm, 1–2 mm, 2 mm to 1 cm, >1 cm, dead roots, and organic matter), weighed, and analyzed for N, P and C concentrations. With the exception of surface roots <0.25 mm diameter, there was no effect of elevated CO₂ on root biomass. There was little effect on C, N, or P concentration or content with the exception of dead roots, and <0.25 mm and 1–2 mm diameter live roots at the surface. Thus, fine root mass and element content appear to be relatively insensitive to elevated CO₂. In the top 10 cm of soil, biomass of roots with a diameter of <0.25 mm was depressed by elevated CO₂. Elevated CO₂ tended to decrease the mass and N content of dead roots compared to ambient CO₂. A decreased N concentration of roots <0.25 mm and 1–2 mm in diameter under elevated CO₂ may indicate reduced N supply in the elevated CO₂ treatment. Our study indicated that elevated CO₂ does not increase fine root biomass or the pool of C in fine roots. In fact, elevated CO₂ tends to reduce biomass and C content of the most responsive root fraction (<0.25 mm roots), a finding that may have more general implications for understanding C input into the soil at higher atmospheric CO₂ concentrations.     

中亚热带杉木人工林细根生物量空间变异与取样数量估算

林木细根生物量具有一定的空间异质性,因此采用合理的细根取样策略对精确估算细根生物量十分重要。通过在福建省三明杉木人工林林内采用土钻法随机选取100个取样点,分析不同细根类型(杉木、林下植被、总细根)生物量的空间变异特征,并对细根生物量所需的取样数量进行估计。结果表明:不同细根类型单位面积生物量随径级(0—1、1—2 mm)及土层深度的增加变异增大,所需的取样数量也相应增加。Shapiro-Wilk检验表明,仅0—2 mm杉木细根和总细根单位面积生物量符合正态分布,其余各个细根类型不同径级不同土层单位面积生物量均不符合正态分布,均呈明显的右偏分布。蒙特卡罗统计模拟分析表明:在置信水平为95%、精度为80%的条件下,直径为0—1 mm、1—2 mm和0—2 mm的细根,杉木采集95、96、32个样品可以满足测定单位面积生物量的需要,林下植被分别采集98、98、63个样品可以满足测定单位面积生物量的需要,而总细根分别采集93、93、18个样品可以满足测定单位面积生物量的需要。     

不同分类系统下油松幼苗根系特征的差异与联系

植物根序和径级不仅反映细根的形态结构, 而且能反映根系的一些生理特征, 如细根寿命和周转等。该文以二年生油松(Pinus tabulaeformis)幼苗根系为研究对象, 系统比较了根序分类方法和径级分类方法在描述根系特征上的优缺点, 探索了两者之间的内在联系。结果表明: 二年生油松幼苗最多可包括6级根序, 直径的变化范围为0.169-3.877 mm。按根序划分, I-VI级根序的总根长和总根表面积主要集中在前3级根序, 这3级根序的根占总根长的78.77%和总根表面积的62.72%。前3级根序的比根长是后3级根序比根长的1.3-3.0倍, 比根面积是后3级比根面积的1.0-1.5倍。按常用的径级(以0.5、1.0、1.5和2.0 mm为阈值)划分方法, 油松幼苗大部分根系直径≤1.5 mm, 此区间细根的根长和根表面积占总根长的93.76%和总根表面积的84.35%。直径≤1.5 mm的细根平均比根长是>1.5 mm细根比根长的3-7倍, 比根面积的1.5-3.0倍。由于油松根序和径级之间有显著的指数关系, 依据径级最大程度反映根序的原则, 提出了新的径级划分方法, 即以0.4、0.8、1.3和2.0 mm为阈值对油松幼苗根系径级重新进行划分。此时, 上述区间可分别包括I级、II级、III级、IV级、V级根序中根尖数的93.22%、86.37%、75.96%、70.47%和76.67%。同时也可分别涵盖各径级根长的89.34%-70.83%、根面积的86.01%-76.12%以及体积的87.73%-76.12%。此时, 根系不同径级与根序之间可以建立起良好的对应关系。这些结果表明, 通过合理划分径级区间可以较好地反映根序 特征。     

Biomass, morphology and nutrient contents of fine roots in four Norway spruce stands

Fine root systems may respond to soil chemical conditions, but contrasting results have been obtained from field studies in non-manipulated forests with distinct soil chemical properties. We investigated biomass, necromass, live/dead ratios, morphology and nutrient concentrations of fine roots (<2 mm) in four mature Norway spruce (Picea abies [L.] Karst.) stands of south-east Germany, encompassing variations in soil chemical properties and climate. All stands were established on acidic soils (pH (CaCl₂) range 2.8–3.8 in the humus layer), two of the four stands had molar ratios in soil solution below 1 and one of the four stands had received a liming treatment 22 years before the study. Soil cores down to 40 cm mineral soil depth were taken in autumn and separated into four fractions: humus layer, 0–10 cm, 10–20 cm and 20–40 cm. We found no indications of negative effects of N availability on fine root properties despite large variations in inorganic N seepage fluxes (4–34 kg N ha⁻¹ yr⁻¹), suggesting that the variation in N deposition between 17 and 26 kg N ha⁻¹ yr⁻¹ does not affect the fine root system of Norway spruce. Fine root biomass was largest in the humus layer and increased with the amount of organic matter stored in the humus layer, indicating that the vertical pattern of fine roots is largely affected by the thickness of this horizon. Only two stands showed significant differences in fine root biomass of the mineral soil which can be explained by differences in soil chemical conditions. The stand with the lowest total biomass had the lowest Ca/Al ratio of 0.1 in seepage, however, Al, Ca, Mg and K concentrations of fine roots were not different among the stands. The Ca/Al ratio in seepage might be a less reliable stress parameter because another stand also had Ca/Al ratios in seepage far below the critical value of 1.0 without any signs of fine root damages. Large differences in the live/dead ratio were positively correlated with the Mn concentration of live fine roots from the mineral soil. This relationship was attributed to faster decay of dead fine roots because Mn is known as an essential element of lignin degrading enzymes. It is questionable if the live/dead ratio can be used as a vitality parameter of fine roots since both longevity of fine roots and decay of root litter may affect this parameter. Morphological properties were different in the humus layer of one stand that was limed in 1983, indicating that a single lime dose of 3–4 Mg ha⁻¹ has a long-lasting effect on fine root architecture of Norway spruce. Almost no differences were found in morphological properties in the mineral soil among the stands, but vertical patterns were apparently different. Two stands with high base saturation in the subsoil showed a vertical decrease in specific root length and specific root tip density whereas the other two stands showed an opposite pattern or no effect. Our results suggest that proliferation of fine roots increased with decreasing base saturation in the subsoil of Norway spruce stands.     

Measuring Fine Root Turnover in Forest Ecosystems

Development of direct and indirect methods for measuring root turnover and the status of knowledge on fine root turnover in forest ecosystems are discussed. While soil and ingrowth cores give estimates of standing root biomass and relative growth, respectively, minirhizotrons provide estimates of median root longevity (turnover time) i.e., the time by which 50% of the roots are dead. Advanced minirhizotron and carbon tracer studies combined with demographic statistical methods and new models hold the promise of improving our fundamental understanding of the factors controlling root turnover. Using minirhizotron data, fine root turnover (y⁻¹) can be estimated in two ways: as the ratio of annual root length production to average live root length observed and as the inverse of median root longevity. Fine root production and mortality can be estimated by combining data from minirhizotrons and soil cores, provided that these data are based on roots of the same diameter class (e.g., < 1 mm in diameter) and changes in the same time steps. Fluxes of carbon and nutrients via fine root mortality can then be estimated by multiplying the amount of carbon and nutrients in fine root biomass by fine root turnover. It is suggested that the minirhizotron method is suitable for estimating median fine root longevity. In comparison to the minirhizotron method, the radio carbon technique favor larger fine roots that are less dynamics. We need to reconcile and improve both methods to develop a more complete understanding of root turnover.     

三峡库区马尾松细根生产和周转及其影响因子

采用连续根钻法、分解袋法、分室通量模型法计算三峡库区马尾松细根的年生产量和周转率,分析细根生产量和周转率与各影响因子的关系.结果表明: 马尾松<0.5、0.5～1和1～2 mm细根年均生物量分别为0.29、0.59、0.76 t·hm^-2,细根年生产量分别为0.13、0.49、0.37 t·hm^-2,细根年周转率分别为1.49、1.01、0.40 a^-1.各影响因子对不同径级细根生产与周转的影响不同.土壤温度、土壤钙含量显著影响<0.5 mm细根生产量与细根周转,且土壤温度解释生产量和周转率32.8%和25.0%的变异,土壤钙含量解释65.6%和73.1%的变异;细根生物量与细根生产量呈显著正相关,细根生物量分别解释<0.5、0.5～1和1～2 mm细根生产量41.0%、41.1%和54.5%的变异;细根P、K含量与<0.5 mm细根生产量具有显著相关性,分别解释<0.5 mm细根生产量32.2%、39.2%的变异.<0.5 mm细根与各影响因子的关系最为密切,土壤温度、土壤钙含量是细根生物量的主要影响因子.     

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.     

Fine-root morphological and growth traits in a Turkey-oak stand in relation to seasonal changes in soil moisture in the Southern Apennines, Italy

We investigated the effects of seasonal changes in soil moisture on the morphological and growth traits of fine roots (<2?mm in diameter) in a mature Turkey-oak stand (Quercus cerris L.) in the Southern Apennines of Italy. Root samples (diameter:?<0.5, 0.5?C1.0, 1.0?C1.5, and 1.5?C2.0?mm) were collected with the Auger method. Mean annual fine-root mass and length on site was 443?g?m^?2 (oak fine roots 321?g?m^?2; other species 122?g?m^?2) and 3.18?km?m^?2 (oak fine roots 1.14?km?m^?2; other species 2.04?km?m^?2), respectively. Mean specific root length was 8.3?m?g^?1. All fine-root traits displayed a complex pattern that was significantly related to season. In the four diameter classes, both fine-root biomass and length peaked in summer when soil water content was the lowest and air temperature the highest of the season. Moreover, both fine-root biomass and length were inversely related with soil moisture (p?<?0.001). The finest roots (<0.5?mm in diameter) constituted an important fraction of total fine-root length (79?%), but only 21?% of biomass. Only in this root class, consequent to change in mean diameter, specific root length peaked when soil water content was lowest showing an inverse relationship (p?<?0.001). Furthermore, fine-root production and turnover decreased with increasing root diameter. These results suggest that changes in root length per unit mass, and pulses in root growth to exploit transient periods of low soil water content may enable trees to increase nutrient and water uptake under seasonal drought conditions.     

Influence of cultivation method on root grafting in Norway spruce (Picea abies (L.) Karst.)

Root grafting is the process by which a functional union of two or more roots subsequent to their formation is formed. The above- and below-ground parts of three Norway spruce stands (natural stand, Umbric Luvisol; row-culture and group-culture, Planosol; stand ages 40, 43 and 43, respectively) of high site quality (I) were investigated. Stand densities were 1550, 1783 and 1722 stems ha^-1, respectively. In all investigated stands, root grafting was most sensitive to tree spacing. Grafts were observed in case the distance between the trees was 0.7–1.2 m. Grafts occurred always in areas of higher rooting density, in a row of the row-culture and within a tree group in the group-culture. Root grafting was enhanced in case of a narrower humus horizon in the group culture compared with the row-culture, 16.5 and 30 cm, respectively; the humus horizon contained 99% and 95% of conducting roots with d ≥ 5 mm, respectively. Root graftings occurred in 75% of excavated trees in the group-culture, in 37.5% of excavated trees in the row-culture and in 33.3% of excavated trees in the natural stand. Stand age was 24 years in the row-culture and 22 years in the group-culture at the beginning of root grafting. No grafts occurred between two suppressed trees, whereas in 86–100% of all cases, at least one tree was dominant or codominant. In row- and group-cultivated Norway spruce stands, the initial minimum diameter of the grafted root without bark was from 1 to 3 cm in 63% of cases. Grafting of roots with d < 1 cm or d > 10 cm was rare or absent. Root grafting had usually begun at the root age of 10–20 years (46% of cases). This revised version was published online in June 2006 with corrections to the Cover Date.     

模拟氮沉降对中亚热带杉木幼树根系生物量的影响

植物根系是全球陆地生态系统碳储量的重要组成部分,在全球生态系统碳循环中起着重要作用,日益加剧的氮沉降会影响根系生物量在空间和不同径级的分配,进而影响森林生态系统的生产力和土壤养分循环。以杉木幼树为研究对象,通过野外氮沉降模拟实验,研究氮沉降四年后对不同土层、不同径级根系生物量的影响。结果发现：（1）低氮和高氮处理总细根生物量较对照均无显著差异（P > 0.05）,高氮处理粗根生物量及总根系生物量较对照分别增加45%和40%（P < 0.05）;（2）与对照相比,施氮处理显著增加20-40 cm与40-60 cm土层细根和粗根生物量,且在低氮处理下,20-40 cm土层细根、粗根在总土层细根与粗根生物量的占比显著提高。（3）与对照相比,高氮处理显著增加了2-5 mm、5-10 mm及10-20 mm径级的根系生物量,低氮处理显著增加2-5 mm、5-10 mm径级根系生物量,且显著降低20-50 mm径级根系生物量。综上所述表明：氮沉降后杉木幼树通过增加较粗径级根系来增加对养分及水分的输送,同时通过增加深层根系生物量及其比例的策略来维持杉木幼树的快速生长;而根系生物量的增加,在一定程度上会增加根系碳源的输入,影响土壤碳循环过程。     

Root distribution of a Mediterranean shrubland in Portugal

The distribution of roots of an Erica (Erica scoparia and Erica lusitanica) dominated Mediterranean maquis was studied using three different approaches: root counts on trench walls (down to 120 cm), estimation of the maximum rooting depth using an allometric relationship and estimation of fine root biomass and fine root length using soil cores (down to 100 cm). Roots were classified according to diameter (fine, 1.0 mm; small, 1.1–5.0 mm; medium, 5.1–10.0 mm; coarse, >10.0 mm) and species (Erica sp., Pteridium aquilinum, Rubus ulmifolius and Ulex jussiaei). The depth corresponding to 50% of all roots (D ₅₀) was determined by fitting a new model to the cumulative root distribution. Fine roots represented 96% of root counts. Root counts of Erica represented 59%, Ulex 34%, Rubus 6% and Pteridium 1%. Overall root counts showed a D ₅₀ of 26 cm. D ₅₀ was higher for Ulex (40 cm) and Erica (22 cm), than for Pteridium (9 cm) and Rubus (3 cm). D ₅₀ for fine roots was 27 cm, for small roots 11 cm, for medium roots 6 cm and for coarse roots 4 cm. The estimated average maximum rooting depth of the 28 deepest Erica roots was 222 cm. The deepest Erica root was estimated to reach 329 cm. A total of 82% of roots growing deeper than 125 cm were not reaching more than 175 cm. The overall fine root length density ranged from 4.6 cm/cm³ at 10 cm to 0.8 cm/cm³ at 80 cm. The overall fine root biomass ranged from 7.7 mg/cm³ at 10 cm to 0.6 mg/cm³ at 40 cm. D ₅₀ for root biomass was 12 cm and D ₅₀ for root length was 14 cm. Fine root biomass was estimated as 1.6 kg/m² and the respective root length as 18.7 km/m².