福建柏和杉木人工林细根生产力、分布及周转的比较

对福建三明福建柏和杉木人工林细根生产力、分布及周转进行了为期 3年的研究 ,结果表明 ,福建柏年均细根生物量达 389 7g·m- 2 ,是杉木林 (2 77 2g·m- 2 )的 1 4 1倍 ;活细根年均生物量达 2 16 3g·m- 2 ,是杉木林(14 8 4g·m- 2 )的 1 4 6倍 ;<0 5mm细根生物量 (2 4 2 2g·m- 2 )则是杉木林 (12 4 7g·m- 2 )的 1 94倍 ,其占总细根生物量比例 (6 1 2 % )比杉木林 (4 5 0 % )的高出 16 2 %。福建柏和杉木细根垂直分布在 0～ 10cm土层差异最大 ,该层福建柏总细根密度 (14 4 2g·m- 2 )是杉木 (70 2g·m- 2 )的 2 1倍。福建柏林活细根生物量 1年只出现 1次峰值 (3月 ) ,而杉木林活细根则出现 2次 (3月和 9月 )。福建柏不同径级细根第 1年分散速率及分解系数均低于杉木的。福建柏林细根年净生产量 (32 0 2g·m- 2 a- 1 )和细根年死亡量 (32 6 5g·m- 2 a- 1 ) ,分别是杉木林 (2 5 1 3和 2 4 9 2g·m- 2 a- 1 )的 1 2 7倍和 1 31倍。福建柏细根年均周转速率为 1 4 8a- 1 ,低于杉木林的 (1 6 9a- 1 )。福建柏和杉木细根生物量分别仅占其乔木层生物量的 1 70 %和 1 18% ,但细根净生产力却分别占其乔木层总净生产力的 19 84 %和19 2 1% ,细根年死亡量分别占地上部分凋落物量的 4 8 74 %和 5 1 0 0     

帽儿山林区6种林分细根生物量的时空动态

采用根钻法对以上6种森林类型细根现存量进行动态研究.对0～30 cm土层的细根(≤5 mm)现存生物量和死亡量的动态变化进行比较.结果表明:1)不同林分的细根现存量差别很大,6种林分中细根现存量为水曲柳林(1 030.0 g·m-2)＞蒙古栎林(973.4 g·m-2)＞红松林(780.9g·m-2)＞落叶松林(718.2 g·m-2)＞山杨林(709.1 g·m-2)＞樟子松林(470.4 g·m-2);2)除落叶松外,其他林分活细根现存量与总细根现存量变化趋势相一致.红松林、落叶松林活细根现存量最大值出现在5月,其余4种均出现在6月,水曲柳林最小值出现在9月,其他5种林分均出现在7月或8月;3)不同林分死细根所占的比率不同;4)从细根的垂直分布来看,由于温度、水分、养分等在不同土壤层中分配比率不同,细根的现存量主要集中在0～10 cm土层中,在各林分中占细根总现存量的比率都超过40%,其中水曲柳林最高,达到60.3%.由此可见,不同森林类型的细根时空动态具有种的特殊性,在进行整个地区森林生态系统物质循环和能量流动研究时,应考虑不同森林类型的特性.     

混交条件下水曲柳落叶松根系的生长与分布

用土钻法调查了水曲柳、落叶松纯林及其混交林的根系分布 ,并在温室内用盆栽和床栽方法测定了混栽及纯栽水曲柳、落叶松的根系生长。野外调查结果表明 :在混交林中 ,水曲柳、落叶松根系的水平分布不同 ,在水曲柳、落叶松相邻行间和水曲柳带内 1、2行间 ,水曲柳根密度分别为 32 37 2g·m- 3 和 3130 2g·m- 3 ,无明显差异。而在水曲柳落叶松相邻行间和落叶松带内 1、2行间 ,落叶松的根密度分别为 939 4g·m- 3 和2 745 3g·m- 3 ,差异明显。水曲柳根系有向落叶松带伸展的趋势 ,而落叶松根系的分布则受到水曲柳的抑制。混交林中根系的垂直分布更加均匀 ,在水曲柳落叶松相邻行间 ,0～ 10cm、10～ 2 0cm和 2 0～ 30cm土层内根量分别占总根量的 41 9%、2 8 7%和 2 9 4%。而水曲柳纯林中分别为 6 1 0 %、31 6 %和 7 4% ;落叶松纯林中分别为 5 5 6 %、2 7 9%和 16 5 %。温室栽培实验表明 :无论盆栽和床栽 ,混栽水曲柳的根生物量和地上生物量均高于纯栽 ,尤其是≤ 2mm细根生物量增加明显 ,盆栽时增加 2 8 8% ,床栽时增加 36 5 %。而混栽时落叶松的根生物量和地上生物量均低于纯栽。水曲柳的地下 地上比较高 ,约是落叶松的 2倍。水曲柳的根生物量约是落叶松的 4～ 6倍。上述结果说明 ,水曲柳的地下竞争能力     

不同密度水曲柳人工林细根生物量对邻近树木胸径和距离的响应

【目的】研究不同密度水曲柳人工林细根生物量对邻近树木胸径和距离的响应,为制定合理的水曲柳根系取样方案提供理论依据。【方法】在4种林分密度(Ⅰ:3 572株·hm~(-2),Ⅱ:3 128株·hm~(-2),Ⅲ:2 215株·hm~(-2),Ⅳ:1 468株·hm~(-2))的水曲柳人工林内,随机布点取样,测定0～10、10～20和20～30 cm土层吸收根(直径≤0.05 mm)和细根(直径≤2.0 mm)生物量及0～30 cm土层的吸收根总生物量和细根总生物量,并记录距取样点最近的1株和4株树的距离及胸径。采用线性回归分析,检验细根生物量与邻近树木距离和胸径的关系。【结果】0～30 cm土层吸收根和细根总生物量受林分密度影响显著,二者均在密度最小林分中最大;从林分密度Ⅰ～Ⅳ,吸收根占细根生物量的比例分别为61.6%、54.3%、52.9%和63.4%;在所有林分中,50%以上的细根和吸收根生物量分布在0～10 cm土层;在4种密度林分中,吸收根和细根总生物量与最近1株或4株树的距离均相关性不显著(P0.05),仅有密度Ⅲ林分10～20 cm土层细根生物量与最近4株树的平均距离显著正相关(P0.05);与细根总生物量相比,0～30 cm土层吸收根总生物量与邻近树木胸径之间呈现出更普遍的相关,但相关性显著水平与林分密度有关;密度Ⅰ林分吸收根和细根生物量均与最近1株树胸径显著正相关(均R~2 0.19),而密度Ⅱ林分吸收根和细根生物量均与最近4株树的平均胸径显著正相关(均R~2 0.21);密度Ⅲ林分中吸收根生物量与最近1株或4株树的胸径均显著相关(均R~2 0.16);而密度Ⅳ林分中吸收根和细根生物量与邻近树木胸径均不显著相关;在调查的3个土层中,细根和吸收根生物量与邻近树木胸径的相关性主要出现在0～10 cm土层,并呈现出与0～30 cm土层细根总生物量相似的规律。【结论】基于对不同密度水曲柳人工林细根生物量的研究结果,认为可在东北林区不同密度水曲柳人工林内灵活设置细根取样点,不必考虑与附近林木的距离,但需考虑邻近树木胸径大小的影响,在平均木周围设置取样点是可选途径。     

海南岛尖峰岭鸡毛松人工林乔木层生物量和生产力研究

对海南岛尖峰岭35年生鸡毛松人工林生物量的结构与分布特点、净初级生产力和林分生长的动态变化进行了研究。结果表明,鸡毛松人工林乔木层生物量达285 53t·hm-2,其中树干为190 82t·hm-2,树皮为19 19t·hm-2,树枝为35 93t·hm-2,树叶为7 96t·hm-2,根为31 63t·hm-2,鸡毛松不同器官生物量的比例为树干∶树枝∶根∶树皮∶树叶=24 0∶4 5∶4 0∶2 4∶1 0。12～22cm径级的立木生物量占总生物量的70 9%,而8m以下的树干生物量占其总生物量的80%以上。1～25a内生物量增长迅速,年平均净生产量随年龄的增加而增大,25a后生物量增长相对较慢,进入生长的平稳期。35a鸡毛松人工林乔木层年平均净生产力可达10 34t·hm-2·a-1,最大可达13 99t·hm-2·a-1,表现出较高的生产力。     

杉木观光木混交林群落细根净生产力及周转

本文系统地研究了27a生杉木观光木混交林和杉木纯林群落细根(＜2mm)的生物量、净生产力和年周转率.结果表明,混交林和纯林群落活细根现存量分别为3.872和3.315 t@hm-2,活细根现存量变化呈双峰型,在3月和9月出现两次高峰;死细根现存量为1.509和1.269 t@hm-2,数量变化呈现单谷型,在5月或3月出现最低值;细根净生产力分别为4.124和3.528t@hm-2a-1,分别占各自群落净第一性生产力的22.9%和20.9%;细根年死亡量分别为2.119和1.894t@hm-2,相当于各自群落地上部分凋落物量的31.4%和27.8%;细根周转率分别为1.07和1.06,观光木、混交林杉木、纯林杉木的细根周转速率依次降低,而林下植被层细根周转率高于乔木层.表明细根周转是群落有机质归还的重要途径,对维持和改良地力有重要作用.     

1901-2008年小兴安岭森林NPP估算

根据黑龙江省森林收获表、生物量相容性相对生长方程及叶片与细根周转率数据,估算小兴安岭林区森林主要树种净初级生产力( NPP)与年龄的关系,并结合森林生态系统碳循环模型 InTEC 模型和 NPP 与年龄的关系,估算1901—2008年间小兴安岭森林 NPP的时空变化。结果表明：幼龄林 NPP随林分年龄的增长而迅速增加,进入成熟年龄 NPP达到最大,随后逐渐减少,直至达到稳定值;小兴安岭人工林的 NPP大于天然林,天然针叶林的固碳能力大于天然阔叶林与针阔混交林;1901—2008年间小兴安岭森林NPP整体呈现增加趋势,与工业前期1901年相比,2008年小兴安岭森林NPP增加了30%;森林NPP受海拔影响,呈现出中部偏高、北部与南部偏低的趋势。     

川西高原光果西南杨人工林生物量及生产力的研究

采用标准木和回归分析法 (乔木层 )及样方收获法 (灌木、草本 )研究了川西高原丘陵宽谷地带光果西南场人工林的生产力生物量及其分配规律。1 根据各径阶标准木资料 ,对 4个回归模型 (a)Y =a +bX ,(b)Y =aXb,(c)Y =aebX,(d)Y =a +b1nX 的适应性进行评价、筛选 ,结果以 (b)的相关系数最高 ,精度符合要求。2 林分总生物量为 6 1 371t·hm-2 ,其中乔木层 5 8 391t·hm-2 (95 14 0 % ) ,灌木层 1 0 90t·hm-2 (1 780 % ) ,草本层 1 890t·hm-2 (3 0 8% ) ;乔木层净生产量为 9 342t·hm-2 ·a-1,约 38 5 14 %分配到树干。3 林分总生物量及树干生物量随高度分布呈金字塔型 ,枝、叶生物量主要集中分布在树冠中上部 ;根系生物量随土壤深度的增加逐渐减少 ,呈倒金字塔形 ,根生物量占林分总生物量的 2 8 84 % ,主要分布于 0～ 6 0cm的土层中。4 地上部分生物量和总生物量分别是树干生物量的 1 2 8倍和 1 8倍 ,和其它热带、亚热带森林分析的结果相似。     

新疆三工河流域柽柳群落细根生产与周转对土壤有机碳的贡献

在2010年整个生长季内,采用土钻法和内生长法,对新疆干旱区柽柳细根生物量、季节动态、分解与周转进行了研究。结果表明:柽柳群落土壤含水量随着土层深度的增加而增加。10~20cm土层土壤有机碳储量最大,随后随着土壤深度的增加,有机碳含量逐渐降低。方差分析表明:不同土层有机碳含量差异显著。细根生物量的月平均值为54.51g·m–2,群落细根生产量为58.64g·m–2。细根生物量呈明显的季节变化趋势,即5—9月逐渐增加,9月达到最大值,9—10月逐渐下降;在土壤剖面垂直变化上,细根生物量随土层深度的增加呈先增加后降低的趋势,0~10、10~20、20~30、30~40、40~50、50~60cm各土层细根生物量所占比例分别为19.53%、30.05%、26.41%、12.01%、7.33%、4.67%。双因素方差分析表明:不同取样时间、不同土层之间的活细跟生物量、死细根生物量均差异极显著。柽柳群落细根年分解量、年死亡量、净生产力分别为17.41、33.75、83.60g·m-2·a-1,年周转率为1.98次·a-1,通过细根死亡进入土壤中的有机碳为(42.68±5.40)g·m–2·a–1,占土壤有机碳含量的2.12%。这表明,尽管柽柳群落通过细根周转进入土壤中的有机碳仅占现存土壤有机碳的一小部分,但从较长的时间尺度来看,柽柳群落细根对干旱区生态系统地下有机碳的补充具有重要作用。     

西双版纳橡胶林细根生物量及其周转

用土钻法研究了西双版纳橡胶Hevea brasiensis林0～20cm土层中≤2mm细根的生物量和生长量,用分解袋法研究了橡胶林细根的分解,结果表明:0～10cm的细根生物量显著高于10～20cm的细根生物量(p<0.01);在0～20cm土层中,橡胶林活细根和死细根现存量分别为2 206 kg·hm~(-2)和345 kg·hm~(-2);活细根现存量的最大值出现在5月份,最小值出现在11月份;死细根现存量的最大值出现在2月份,最小值出现在8月份;年分解量、年死亡量、年生长量和年周转率分别为213 kg·hm~(-2)、733 kg·hm~(-2)、1 801 kg·hm~(-2)和82%。     

Biomass and net primary production of a <Emphasis Type="Italic">Pinus densiflora</Emphasis> forest established on a lava flow of Mt. Fuji in central Japan

We assessed the above- and below-ground biomass and net primary production (NPP) in a mature (85-year-old) Pinus densiflora forest established on a lava surface of Mt. Fuji in central Japan. The nitrogen (N) concentration of the forest soil was low (1.25%), and the mean soil carbon/nitrogen (C/N) ratio was 34.2; therefore, both plants and microorganisms would compete for N in our research forest. The total biomass was 192.62Mgha^–1, of which 67.28% was in the stems and 25.71% was in the roots. The fine-root biomass was 1.12% of the total biomass. The total NPP of the forest reached 11.89Mgha^–1 year^–1, which fell within the values reported for other cool temperate P. densiflora forests established on non-volcanic-related substrata. The below-ground production was about 39% of the total NPP; the value was relatively small under the conditions of low total N concentration and high soil C/N ratio. Our study suggested that P. densiflora could recruit and grow on geologically new substrata without increasing the allocation of its annual carbon budget to below-ground organs (i.e., roots).     

莲花山白盆珠自然保护区 3 种森林土壤养分含量比较

以莲花山白盘珠自然保护区针阔混交林、季风常绿阔叶林和山地常绿阔叶林表层土壤（0~20 cm）为对象，测定了土壤pH 值及主要养分含量，并应用相关分析法，探究了不同养分间的相关性。结 果表明：（1）山地常绿阔叶林土壤pH 值显著低于针阔混交林和季风常绿阔叶林；（2）森林土壤有机质、 全氮（N）、全磷（P）、速效N、有效P 含量在不同森林类型间差异显著：山地常绿阔叶林土壤有机质、 全 N、全P 显著高于针阔混交林和季风常绿阔叶林；针阔混交林土壤速效 N 含量最高，但有效 P 含量最 低；（ 3）3 种森林土壤全N 与全P 含量均存在极显著相关性，但其它养分间的相关性随森林类型而异， 表明森林类型对土壤养分的影响既有普遍性，又有特异性。     

Above- and belowground biomass and primary productivity of a Larix gmelinii stand near Tura, central Siberia

We assessed above- and belowground biomass and net primary production (NPP) of a mature Larix gmelinii (Rupr.) Rupr. forest (240-280 years old) established on permafrost soils in central Siberia. Specifically, we investigated annual carbon budgets in roots in relation to root system development and availability of soil resources. Total stand biomass estimated by allometry was about 39 Mg per ha. Root biomass (17 Mg per ha) comprised about 43% of total biomass. Coarse root (>/= 5 mm in diameter) biomass was about twice that of fine roots (< 5 mm). The aboveground biomass/root biomass ratio (T/R) of the larch stand was about unity, which is much less than that of other boreal and subalpine conifer forests. The proportion of fine roots in total root biomass (35%) was relatively high compared with other cold-climate evergreen conifer forests. Total NPP, defined as the sum of annual biomass increment of woody parts and needle biomass, was estimated to be 1.8 Mg per ha per year. Allocation of total NPP to needle production was 56%. The proportion of total NPP in belowground production (27%) was less than for evergreen taiga forests. However, belowground NPP was probably under-estimated because root mortality was excluded. We conclude that L. gmelinii trees invested annual carbon gains largely into needle production or roots, or both, at the expense of growth of aboveground woody parts. This carbon allocation pattern, which resulted in the construction of exploitative root networks, appeared to be a positive growth response to the nutrient-poor permafrost soil of central Siberia.     

高黎贡山南段2种森林类型的土壤特性研究

对设于高黎贡山自然保护区南段中山湿性常绿阔叶林的5块样地和季风常绿阔叶林3块样地的土壤进行了调查研究,结果表明:2种森林类型主要有黄红壤、黄壤、黄棕壤、棕壤4种土壤。样地土壤的有机质等养分含量丰富,而土壤盐基饱和度较低。中山湿性常绿阔叶林样地的土壤养分含量、阳离子交换量明显高于季风常绿阔叶林。2块中山湿性常绿阔叶林样地的土壤总孔隙度大于50%,通透性尚好,其余样地土壤通透性稍差,样地土壤的交换性能较好。     

Regional assessment of boreal forest productivity using an ecological process model and remote sensing parameter maps

An ecological process model (BIOME-BGC) was used to assess boreal forest regional net primary production (NPP) and response to short-term, year-to-year weather fluctuations based on spatially explicit, land cover and biomass maps derived by radar remote sensing, as well as soil, terrain and daily weather information. Simulations were conducted at a 30-m spatial resolution, over a 1205 km(2) portion of the BOREAS Southern Study Area of central Saskatchewan, Canada, over a 3-year period (1994-1996). Simulations of NPP for the study region were spatially and temporally complex, averaging 2.2 (+/- 0.6), 1.8 (+/- 0.5) and 1.7 (+/- 0.5) Mg C ha(-1) year(-1) for 1994, 1995 and 1996, respectively. Spatial variability of NPP was strongly controlled by the amount of aboveground biomass, particularly photosynthetic leaf area, whereas biophysical differences between broadleaf deciduous and evergreen coniferous vegetation were of secondary importance. Simulations of NPP were strongly sensitive to year-to-year variations in seasonal weather patterns, which influenced the timing of spring thaw and deciduous bud-burst. Reductions in annual NPP of approximately 17 and 22% for 1995 and 1996, respectively, were attributed to 3- and 5-week delays in spring thaw relative to 1994. Boreal forest stands with greater proportions of deciduous vegetation were more sensitive to the timing of spring thaw than evergreen coniferous stands. Similar relationships were found by comparing simulated snow depth records with 10-year records of aboveground NPP measurements obtained from biomass harvest plots within the BOREAS region. These results highlight the importance of sub-grid scale land cover complexity in controlling boreal forest regional productivity, the dynamic response of the biome to short-term interannual climate variations, and the potential implications of climate change and other large-scale disturbances.     

Incorporation and remobilization of ¹³C within the fine-root systems of individual Abies alba trees in a temperate coniferous stand

Forest ecosystems have a large carbon (C) storage capacity, which depends on their productivity and the residence time of C. Therefore, the time interval between C assimilation and its return to the atmosphere is an important parameter for determining C storage. Especially fine roots (≤2 mm in diameter) undergo constant replacement and provide a large biomass input to the soil. In this study, we aimed to determine the residence time of C in living fine roots and the decomposition rates of dead fine roots. Therefore, we pulse-labelled nine 20-year-old individual silver fir trees (Abies alba Miller; ～70 cm tall) with 13CO? in situ to trace the assimilated C over time into the fine-root systems. Whole trees were harvested at different time points after labelling in autumn, biomass was determined and cellulose and starch of fine roots were extracted. Moreover, soil cores were taken and ingrowth cores installed, in which fine roots were genetically identified, to assess incorporation and remobilization of 13C in the fine roots of silver fir trees; litterbags were used to determine fine-root decomposition rates. The 13C label was incorporated in the fine-root system as cellulose within 3 days, with highest values after 30 days, before reaching background levels after 1 year. The highest δ13C values were found in starch throughout the experiment. 13C recovery and carbon mean residence times did not differ significantly among fine-root diameter classes, indicating size-independent C turnover times in fine roots of A. alba trees of ～219 days. Furthermore, carbon was remobilized from starch into newly grown fine roots in the next spring after our autumn labelling. One year after installation, litterbags with fine roots revealed a decrease of biomass of ～40% with relative 13C content in fine-root bulk biomass and cellulose of ～50%, indicating a faster loss of 13C-labelled compounds compared with bulk biomass. Our results also suggest that genetic analysis of fine-root fragments found in soil and ingrowth cores is advisable when working in mixed forest stands with trees of similar fine-root morphology. Only then can one avoid dilution of the labelling signal by mistake, due to analysis of non-labelled non-target species roots.     

东北地区森林植被生产力遥感定量估测

以辽宁、吉林和黑龙江3省为研究区,引入一种过程模型(Forest-BGPG),以2003年1 km的MODIS影像为遥感数据,估测森林植被净第一性生产力(NPP)。结果表明:2003年森林植被NPP为3.7 MgC/hm2,其中,常绿针叶林4.1 mgC/hm2、落叶阔叶林4.0 mgC/hm2、常绿阔叶林3.8 mgC/hm2、针阔混交林3.9 mgC/hm2和落叶针叶林3.5 mgC/hm2;辽宁东部及长白山地区森林植被NPP超过6.3mg C/hm2,大兴安岭地区不足3.2 mgC/hm2,区域时空分布格局明显。通过与国内现有研究结果和2003年全球陆地植被NPP产品对比分析,表明估测结果准确反映了森林植被现实生长过程,Forest-BGPG为区域尺度森林植被NPP和碳储量动态监测提供了连续的测量手段。     

太行山石灰岩区水保林林分结构模式研究

通过对太行山石灰岩区乔灌、灌木、灌草三类水土保持林林地上现存 19种林分模式调查 ,并通过典型林分模式水土保持功能、生物量比较研究 ,得出乔灌、灌木、灌草三种类型林地上现存林分模式应是针阔、乔灌、灌草混交林分     

Reliable data on fine-root turnover from sequential soil coring in an old carbon budget for a 14-year-old Scots pine from the late 1970s: Comments on Majdi et al., Scandinavian Journal of Forest Research 22: 299–303

Abstract

Comprehensive data from different research workers were included in the compilation of a carbon budget for a 14-year-old Scots pine (Pinus sylvestris) in the late 1970s, within the SWECON project (the Swedish Coniferous Forest Project). In a recent paper in the Scandinavian Journal of Forest Research, the authors published a surprisingly high turnover rate of fine roots (7.4 year^?1), maintaining that they had used our old SWECON data from our sequential soil coring. However, a close examination of our original data suggests a turnover of fine-root biomass of 2.3 and for fine-root standing crop (biomass+necromass) of 2.0 year^?1. Supporting evidence is available from other forest sites suggesting that our turnover rates were correctly estimated. Certain errors may exist in different parts of our old carbon budget, e.g. some measurements were carried out for different parts of the tree, while others were attributed to the whole stand. The sequential soil coring technique still remains the best technique available for fine-root growth and turnover estimates in forest stands.     

Discrepancy in fine root turnover estimates between diameter-based and branch-order-based approaches: a case study in two temperate tree species

Fine root turnover plays a key role in carbon(C) budgets and nutrients cycles in forest ecosystems.However,the difference between branch-order-based and diameter-based approaches in estimating fine root turnover is still unclear.We studied root biomass turnover based on multiplying root standing biomass by turnover rate(inverse of median root longevity) in two Chinese temperate tree species,Fraxinus mandshurica Rupr.and Larix gmelinii Rupr.The minirhizotron(MR) technique was used to estimate longevities for first and second order roots,and total roots(R total) apparent on the MR tube surface.The corresponding biomass for each root group was estimated by soil monolith.The difference in biomass turnover between R total and the sum of the first and second order roots was used to represent the discrepancy between diameter-and order-based approaches.First order roots had shorter life spans and higher biomass turnover rates than the second order roots in both species.Biomass turnover estimated by the order-based method for F.mandshurica and L.gmelinii were 155.4 g m-2 a-1 and 158.9 g m-2 a-1,respectively,in comparison with 99.5 g m-2 a-1 and 117.7 g m-2 a-1 estimated by the diameter-based method,indicating that the diameter-based approach underestimated biomass turnover.The most probable reason was that the order-based method enhanced separation of the heterogeneous root population into relatively homogenous root groups with varying turnover rates.We conclude that separating fine root pool into different branch orders can improve the accuracy of estimates for fine root turnover,as well as the understanding of the belowground C allocation and nutrient cycling at ecosystem level.