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）.     

落叶松和水曲柳不同根序细根形态结构、组织氮浓度与根呼吸的关系

根系具有高度的形态和生理功能异质性, 在森林生态系统碳和养分循环中起重要作用。根系分枝的顺序构成根序,是根系最基本的构型特征, 根序代表根系不同的发育阶段。然而, 目前直接测定不同根序细根生理功能的研究很少。以落叶松(Larix gmelinii)和水曲柳(Fraxinus mandshurica)的细根为研究对象, 使用气相氧电极测定不同根序细根的呼吸速率, 探讨根系呼吸速率与其形态、结构和组织氮浓度的关系。结果表明: 落叶松和水曲柳细根的直径、根长和维管束直径均随着根序的增加(1–5级)而增加, 而比根长、组织氮浓度和呼吸速率随着根序的增加而降低, 各根序之间差异显著(P < 0.05); 1级根比根长最大、皮层组织发达、组织氮浓度最高且呼吸速率也最高, 其呼吸速率分别为17.57 nmolO₂·g^–1·s^–1(落叶松)和18.80 nmolO₂·g^–1·s^–1(水曲柳), 比5级根分别高148%(落叶松)和124%(水曲柳); 并且, 落叶松根的呼吸速率几乎有96%与根系组织氮浓度相关, 而水曲柳根的呼吸速率则有89%与根系组织氮浓度相关。上述结果说明, 细根的形态和生理功能异质性是紧密相连的, 低级根的形态、结构决定其功能是吸收养分和水, 而高级根的形态、结构决定其功能是运输和贮存养分。     

水曲柳和落叶松细根形态及母根与子根比例关系

细根（直径〈2mm）的分枝是根系重要的结构特征,不同根序等级的细根在养分和水分吸收、C的消耗和寿命方面具有较大的差异,定量研究各根序等级之间的比例关系对认识细根死亡的顺序具有重要的理论意义。根据Pregitzer等2002年提供的方法,研究了17年生水曲柳（Fraxinus mandshurica Rupr．）和落叶松（Larix gmelinii Rupr．）人工纯林1-5级细根的直径、长度、比根长、生物量和数量。结果表明,两树种细根中1级根序的数量占总根系数量80％-90％,它们直径小、长度短、比根长高。随着根序等级（1级-5级）的增加细根直径增粗和长度增加、比根长减小。细根的数量和生物量在上下土层的分布受土壤资源有效性的影响。水曲柳5级根序-2级根序之间母根与子根的数量关系是1：3,落叶松是1：2-3。2级根序与1级根序之间母根与子根的数量关系,水曲柳是1：10—12,落叶松是1：8。如果当年生长的1级细根当中保持1：3的比例,将有65％-75％的1级细根死亡,占根系总数的55％～65％,总长度的40％-50％,以及总生物量的20％-30％。     

不同水稻品种产量形成过程的能量积累与热值特征

通过测定晚季稻汕优63 (三系杂交稻)、两优2186（两系杂交稻）和IR64（常规稻）生长过程中的干物质和热值,研究了不同水稻品种生长过程中的热值动态和能量固定特征.结果表明,完熟期汕优63、两优2186和IR64 3种水稻的干物质积累量分别为1926.38、1933.80和1842.30 g·m^-2,能量积累量分别为31137.05、31060.63和30454.89 kJ·m^-2,不同水稻品种的干物质及能量积累量间无显著差异.在灌浆过程中,汕优63、两优2186和IR64总的能量表观转化率分别为38.95%、 28.38%和32.66%,汕优63和IR64的能量流动比两优2186顺畅,两优2186茎器官能量输出受阻.完熟期3种水稻分配到籽粒中的能量依次占53.03%、46.43%和50.11%,三系杂交稻汕优63具有能量分配优势.热值分析表明,3种水稻各生育期间的热值平均值间无显著差异;不同器官热值大小依次为：叶＞籽粒＞鞘＞茎＞根,热值范围为：叶16.81～17.25 kJ·g^-1,籽粒15.89～16.54 kJ·g^-1,鞘14.33～15.49 kJ·g^-1,茎14.23～15.15 kJ·g^-1,根11.51～13.25 kJ·g^-1,叶片的热值显著高于其它器官,而根的热值显著低于其它器官.水稻叶片热值与其碳含量、叶绿素a含量、氮含量存在显著正相关,确定系数R²分别为0.609、0.471和0.485.     

落叶松和水曲柳不同根序细根形态结构、组织氮浓度与根呼吸的关系

根系具有高度的形态和生理功能异质性,在森林生态系统碳和养分循环中起重要作用。根系分枝的顺序构成根序,是根系最基本的构型特征,根序代表根系不同的发育阶段。然而,目前直接测定不同根序细根生理功能的研究很少。以落叶松（Larix gmelinii）和水曲柳（Fraxinus mandshurica）的细根为研究对象,使用气相氧电极测定不同根序细根的呼吸速率,探讨根系呼吸速率与其形态、结构和组织氮浓度的关系。结果表明：落叶松和水曲柳细根的直径、根长和维管束直径均随着根序的增加（1–5级）而增加,而比根长、组织氮浓度和呼吸速率随着根序的增加而降低,各根序之间差异显著（P〈0.05）;1级根比根长最大、皮层组织发达、组织氮浓度最高且呼吸速率也最高,其呼吸速率分别为17.57nmolO2·g^–1·s^–1（落叶松）和18.80 nmolO2·g^–1·s^–1（水曲柳）,比5级根分别高148%（落叶松）和124%（水曲柳）;并且,落叶松根的呼吸速率几乎有96%与根系组织氮浓度相关,而水曲柳根的呼吸速率则有89%与根系组织氮浓度相关。上述结果说明,细根的形态和生理功能异质性是紧密相连的,低级根的形态、结构决定其功能是吸收养分和水,而高级根的形态、结构决定其功能是运输和贮存养分。     

瓦屋山常绿阔叶次生林建群种扁刺栲的细根分布及其碳氮特征

四川瓦屋山国家森林公园是我国西部的中亚热带湿性常绿阔叶林的典型代表,具有四川现存的较为完好的扁刺栲(Castanopsis platyacantha)-华木荷(Schima sinensis)群系,该研究利用土钻法探讨了该群系内主要建群种扁刺栲标准木的细根分布及其碳氮特征。结果表明:(1)扁刺栲细根总生物量为173.62 g·m~(-2),其中活根生物量为135.29 g·m~(-2)。(2)随着土层深度的增加,扁刺栲细根生物量、根长密度、根系表面积和比根长呈下降趋势,0~30 cm土层所占比例分别为67.23%、69.53%、69.48%和57.20%;根长密度、根系表面积和比根长均随细根直径的增加而显著下降,直径小于1 mm的根系所占比例分别为58.84%、52.59%和51.36%。(3)扁刺栲细根生物量、根长和表面积消弱系数β均随根系直径的增加而增加。(4)根系C含量在第Ⅰ土层中随细根直径的增加而显著增加,在其他土层则无显著差异;直径小于2 mm的根系C含量在第Ⅰ土层中显著低于其他土层,大于2 mm的根系C含量在各土层间的差异不大。(5)根系N含量随根系直径和土层深度的增加而减少,C/N值则与之相反。该研究结果在一定程度上反映了该次生林地下细根的垂直分布及养分特征,为揭示该生态系统地下生态过程及今后在该生态系统研究环境变化对地下生态过程的影响提供了基础数据。     

青杨人工林根系生物量、表面积和根长密度变化

在植物生长季节,采用钻取土芯法对秦岭北坡50年生青杨人工林根径≤2 mm和2～5 mm根系的生物量、表面积和根长密度进行测定.结果表明：在青杨人工林根系(＜5 mm)中,根径≤2 mm根系占总生物量的77.8%,2～5 mm根系仅占22.2%;根径≤2 mm根系表面积和根长密度占根系总量的97%以上,而根径2～5 mm根系不足3%.随着土层的加深,根径≤2 mm根系生物量、表面积和根长密度数量减少,根径2～5 mm根系生物量、表面积和根长密度最小值均分布在20～30 cm土层.≤2 mm根系生物量、表面积和根长密度与土壤有机质、有效氮呈极显著相关,而根径2～5 mm根系的相关性不显著.     

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.     

施肥对日本落叶松人工林细根直径、根长和比根长的影响

以辽宁东部山区16年生日本落叶松人工林为研究对象,探讨施肥对日本落叶松1～5级根序中细根直径、根长和比根长的影响.结果表明：随着根序等级的增加,日本落叶松细根平均直径和根长显著增加（P<0。05,P<0。01）、比根长则显著下降（P<0。01）.在日本落叶松的5级根序中,1级根的平均直径最细、根长最短、比根长最高,而5级根则相反;随着根序等级的增加,日本落叶松细根平均直径、根长和比根长的变异系数逐渐增大.除1级根外,土层对细根的平均直径、根长和比根长没有显著影响(P>0。05).与对照样地相比,施肥对各级细根平均直径、根长和比根长的影响主要表现在1～2级根上,对3级根序以上的细根影响不显著（P>0.05）.其中,施氮肥显著降低了1～2级根的平均直径（P<0.05）,施氮肥以及氮磷肥显著降低了表层土壤（0～10 cm）中1级根的平均根长（P<0.05）,表层土壤中细根的比根长在施氮肥的条件下显著增加（P<0.05）.     

深圳湾红树木榄根系生物量及空间分布格局

采用分层挖掘法,对深圳湾乡土种红树植物木榄不同活力和径级根系生物量及相关底泥性质的空间分布格局进行了研究。结果表明:木榄人工林平均总根系生物量为61.23 t·hm~(-2),其中活根生物量占86.42%,死根占13.58%。在活根中,粗根(直径10 mm)所占比例最高(84.57%),其次为细根(2~5 mm,5.84%)、极细根(2 mm,4.94%)和中根(5~10 mm,4.66%)。木榄总根系生物量从基部到树冠落水线处递减,生物量分别为77.54 t·hm~(-2)(基部)、22.88 t·hm~(-2)(中部)和16.15 t·hm~(-2)(边缘);基部直径10 mm的活根生物量为中部和边缘活根生物量的5倍以上;随着水平距离的增加,2 mm根系生物量占相应距离处活根生物量的比例增加。垂直分布以中下层(20~60 cm)居多,分别占相应水平距离处总根系生物量的80.89%(基部)、73.41%(中部)和71.76%(边缘);总根系生物量分布主要受水平距离的影响(P0.05)。底泥含水量、容重、p H和电导率的变化范围分别为30.66%~35.86%、1.23~1.40 g·cm-3、5.75~7.01 S·m~(-1)和0.22~0.37 S·m~(-1),其中底泥容重与不同活力根系生物量呈显著负相关(P0.05),是影响木榄根系生物量及其空间分布的主要环境因子。该研究结果为福田红树林地下碳分配、储量及周转速率等进一步研究提供了科学依据。     

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.     

落叶松人工林细根动态与土壤资源有效性关系研究

树木细根在森林生态系统C和养分循环中具有重要的作用。由于温带土壤资源有效性具有明显的季节变化, 导致细根生物量、根长密度 (Rootlengthdensity, RLD) 和比根长 (Specificrootlength, SRL) 的季节性变化。以 17年生落叶松 (Larixgmelini) 人工林为研究对象, 采用根钻法从 5月到 10月连续取样, 研究了不同土层细根 (直径≤ 2mm) 生物量、RLD和SRL的季节动态, 以及这些根系指标动态与土壤水分、温度和N有效性的关系。结果表明 :1) 落叶松细根年平均生物量 (活根 +死根 ) 为 189.1g·m-2 ·a-1, 其中 5 0 %分布在表层 (0~ 10cm), 33%分布在亚表层 (11~ 2 0cm), 17%分布在底层 (2 1~ 30cm) 。活根和死根生物量在 5~ 7月以及 9月较高, 8月和 10月较低。从春季 (5月 ) 到秋季 (10月 ), 随着活细根生物量的减少, 死细根生物量增加 ;2 ) 土壤表层 (0~ 10cm) 具有较高的RLD和SRL, 而底层 (2 1~ 30cm) 最低。春季 (5月 ) 总RLD和SRL最高, 分别为 10 6 2 1.4 5m·m-3 和 14.83m·g-1, 到秋季 (9月 ) 树木生长结束后达到最低值, 分别为 2 198.2 0m·m-3 和 3.77m·g-1;3) 细根生物量、RLD和SRL与土壤水分、温度和有效N存在不同程度的相关性。从单因子分析来看, 土壤水分和有效N对细根的影响明显大于温度, 对活根的影响大于死根。由于土壤资源有效性的季节变化, 使得C的地下分配格局发生改变。各土层细根与有效性资源之间的相关性反映了细根功能季节性差异。细根 (生物量、RLD和SRL) 的季节动态 (5 8%~ 73%的变异 ) 主要由土壤资源有效性的季节变化引起。     

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]     

黄土高原白羊草、沙棘和辽东栎细根比根长特性

以黄土高原地区典型草本（白羊草）、灌木（沙棘）和乔木（辽东栎）为对象,研究了3种植物细根比根长在不同土层的分布状况以及与其它细根参数和土壤物理因子之间的相关性。结果表明,3种植物细根比根长的变化范围为6～55ram／rag。在0,80cm土层,白羊草、沙棘和辽东栎细根比根长变化范围分别为18—55mm／mg,14—4JDmm／mg,6—33mm／mg。3种植物0--80cm土层平均细根比根长从大到小依次为白羊草〉沙棘〉辽东栎。3种植物0-10cm土层细根比根长依次为沙棘〉辽东栎〉白羊草,10-80cm依次为白羊草〉辽东栎〉沙棘,表明3种植物细根比根长不仅在这两土层中的分布不具一致性,而且与0-80cm土层平均比根长也不具有一致性,进一步说明3种植物沿土壤剖面的生物量分配策略不同。相关分析表明,3种植物细根比根长与其它细根参数之间的相互关系各不相同,制约程度存在差异。与土壤物理因子的相关分析表明,3种植物细根比根长均随土壤含水量的增加而减少。土壤各级水稳性团聚体和土壤颗粒对3种植物细根比根长并无一致的影响。     

Long-term warming effects on root morphology, root mass distribution, and microbial activity in two dry tundra plant communities in northern Sweden

Effects of warming on root morphology, root mass distribution and microbial activity were studied in organic and mineral soil layers in two alpine ecosystems over>10 yr, using open-top chambers, in Swedish Lapland. Root mass was estimated using soil cores. Washed roots were scanned and sorted into four diameter classes, for which variables including root mass (g dry matter (g DM) m(-2)), root length density (RLD; cm cm(-3) soil), specific root length (SRL; m g DM(-1)), specific root area (SRA; m2 kg DM(-1)), and number of root tips m(-2) were determined. Nitrification (NEA) and denitrification enzyme activity (DEA) in the top 10 cm of soil were measured. Soil warming shifted the rooting zone towards the upper soil organic layer in both plant communities. In the dry heath, warming increased SRL and SRA of the finest roots in both soil layers, whereas the dry meadow was unaffected. Neither NEA nor DEA exhibited differences attributable to warming. Tundra plants may respond to climate change by altering their root morphology and mass while microbial activity may be unaffected. This suggests that carbon may be incorporated in tundra soils partly as a result of increases in the mass of the finer roots if temperatures rise.     

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)。     

Root length and biomass losses during sample preparation with different screen mesh sizes

Data are presented on the differences in root length density (RLD), dry matter (DM), and root diameter values determined on wheat and faba bean using sieves of different mesh size to separate roots from soil during sample preparation. Screens with 0.2, 1, and 2 mm (0.04, 1, and 4 mm²) aperture were used. Roots collected on the 2-mm sieve represented on average 55% of the weight and only 10% of the total length collected using a 0.2-mm sieve. With a 1-mm sieve 75% of weight was retained, but only 34% of the length. In the 0–20 cm soil layer average RLD and DM values ranged between 1.3 and 2.5 cm cm^-3 and 215 and 136 g m^-2 for faba bean and wheat respectively with 2 mm screens and 14.6 and 18.1 cm cm^-3 and 313 and 202 g m^-2 with 0.2 mm sieves. RLD was more affected than weight since losses from coarse screens were largely due to fine root fractions, although the 1-and 2-mm screens retained a small amount of fine roots that were long or attached to main structures. Variability was higher for measurements on coarser screens. The use of screens much coarser than the diameter of fine roots is not recommended for the study of surface-related phenomena in which root length quantification is necessary, while it may be acceptable for gross comparisons of root weight and spatial extent.     

Specific root length as an indicator of environmental change

Abstract

Specific root length (SRL, m g^?1) is probably the most frequently measured morphological parameter of fine roots. It is believed to characterize economic aspects of the root system and to be indicative of environmental changes. The main objectives of this paper were to review and summarize the published SRL data for different tree species throughout Europe and to assess SRL under varying environmental conditions. Meta-analysis was used to summarize the response of SRL to the following manipulated environmental conditions: fertilization, irrigation, elevated temperature, elevated CO₂, Al-stress, reduced light, heavy metal stress and physical disturbance of soil. SRL was found to be strongly dependent on the fine root classes, i.e. on the ectomycorrhizal short roots (ECM), and on the roots <0.5 mm, <1 mm, <2 mm and 1 – 2 mm in diameter SRL was largest for ECM and decreased with increasing diameter. Changes in soil factors influenced most strongly the SRL of ECM and roots <0.5 mm. The variation in the SRL components, root diameter and root tissue density, and their impact on the SRL value were computed. Meta-analyses showed that SRL decreased significantly under fertilization and Al-stress; it responded negatively to reduced light, elevated temperature and CO_2. We suggest that SRL can be used successfully as an indicator of nutrient availability to trees in experimental conditions.