不同供氮水平下水曲柳（Fraxinus mandushurica Rupr.）幼苗根系呼吸季节动态

根呼吸是林木根系获得吸收养分和水分所需能量的重要生理活动.为了探讨林木根系呼吸速率的季节变化及其影响因素,采用离体根系法(Li-6400-06叶室连接到Li-6400便携式CO2/H2O分析系统)研究了水曲柳(Fraxinus mandushurica Rupr.)苗木各径级根呼吸速率在不同供氮水平下季节变化规律.结果表明:水曲柳苗木根呼吸速率表现出明显的季节动态,且与气温的季节变化规律相同,其中比根呼吸速率在0.5732 μmolCO2 · g-1 · s-1(直径≤2 mm,10月份)～7.1861 μmolCO2 · g-1 · s-1(直径≤2 mm,7月份)之间变化,表面积呼吸速率也是7月份最高,达到0.6848 μmolCO2 · cm-2 · s-1(直径>5 mm),10月份最低,仅为0.0132 μmolCO2 · cm-2 · s-1(直径≤2 mm);比根呼吸速率随根直径变大而降低,表面积呼吸速率变化规律则完全相反.供氮水平对水曲柳苗木根呼吸速率的影响随气温升高明显增强,其在6～8月份各径级根系中均达到显著水平(0.00072mm)Q10值范围为2.07～2.96,Q10值随根系径级增大而降低的现象表明水曲柳苗木细根对温度变化反应更为敏感;细根Q10值在供氮水平间差异显著(P=0.0392<0.05),粗根则不明显,表明土壤供氮水平主要影响细根的Q10值变化.     

不同耐盐品种棉花根系主要指标对盐分胁迫的响应

以盐敏感品种‘中棉所45’(CCRI45)、弱耐盐品种‘新陆早17号’(XLZ17)、中等耐盐品种‘新陆早13号’(XLZ13)和耐盐品种‘中棉所35’(CCRI35)为试验材料,利用根系分析系统研究盐分胁迫下棉花根系形态特征及其与棉株耐盐性的关系.结果表明:盐分胁迫显著降低棉花根和叶的干质量以及K^+/Na^+,其中耐盐品种CCRI35和中等耐盐品种XLZ13的根干质量、叶干质量以及根中K^+/Na^+分别比盐敏感品种CCRI45提高了69.3%~104.4%、24.8%~45.3%和25.0%~45.8%;盐分胁迫显著抑制棉花根系生长发育,其中CCRI 35和XLZ13的总根长、根系总表面积、根系总体积以及0~10 cm土层中直径为0~1.2 mm内的根长、根表面积和根体积均显著高于CCRI45,分别增加了15.2%~85.8%、12.0%~68.5%、31.7%~217.8%、27.2%~73.9%、39.6%~74.3%和99.0%~309.7%.主成分分析表明,比根长、浅层根长比例和细根比例受基因型差异的影响较为明显,是区分不同耐盐品种棉花根系形态差异的主要指标.逐步回归分析显示,比根长、0~10 cm土层的粗根根长、细根根表面积、粗根根表面积、粗根体积、中根比例,以及10~20 cm粗根根长、粗根表面积、粗根体积等根系参数对盐分响应敏感.耐盐棉花品种可通过维持表层根长比例、细根比例和比根长的增加来适应盐分胁迫.     

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。     

云南松林的根系生物量及其分布规律的研究

利用平均标准木机械布点法测定了云南省永仁林业局云南松不同龄组林分的根系生物量及其沿土壤剖面深度的分布规律.结果表明,林分根系总生物量随林龄而增加,幼龄林(15～17年)的根系生物量为8.50 t·hm^-2,中龄林(30～32年)为11.70 t·hm^-2,成熟林为(＞62年)18.91 t·hm^-2.在不同龄组林分中,粗根(＞10mm)生物量差异最大(1.5～12.3 t·hm^-2),而中根(5～10 mm)(1.4～1.6 t·hm^-2)及小根(＜5 mm)(5.3～6.2 t·hm^-2)的生物量差异最小.根系生物量沿土壤深度迅速减少,约93%的根系生物量集中分布在0～30 cm土层中,深土层(30～115 cm)的根系生物量仅占7%左右.     

转Bt基因抗虫棉根际微生物区系和细菌生理群多样性的变化

在大田栽培条件下 ,以转 Bt基因抗虫棉 GK-12和常规棉花泗棉 3号作为材料 ,在棉花不同发育时期 ,于 2 0 0 1和 2 0 0 2连续两年测定棉花根际土壤细菌、放线菌和真菌数量的变化 ,并在 2 0 0 2年棉花的花铃期和吐絮期对根际细菌生理群的数量和多样性进行了分析 ,结果表明 :虽然不同年份和生育期棉花根际微生物数量存在差异 ,但是 ,年度间和相同的发育时期棉花根际微生物的数量变化趋势一致。在棉花的苗期和吐絮期 ,转 Bt基因抗虫棉根际微生物的数量与对照差异不显著 ;在棉花的花铃期 ,转 Bt基因抗虫棉根际细菌的数量比对照增加 ,放线菌的数量差异不显著 ,而真菌的数量变化没有规律。在棉花发育的花铃期和吐絮期 ,Bt棉根际细菌生理群的总数量比常规棉增加 ,但是根际细菌生理群的 Simpson指数、Shannon-Wiener指数和细菌生理群分布的均匀度下降     

半干旱地区小麦群体的根系特征与抗旱性的关系

对抗旱性能不同的 5个春小麦品种 (分别为A、B、C、D、E)的试验表明 ,在 0～ 1 2 0cm土层中 ,其根密度分别为 66、1 0 4、1 37、1 0 2和 99μg·cm- 3;总根量分别为 78.7、1 2 4 .3、1 64.3、1 2 1 .8和 1 1 8.7g·m- 2 ;产量分别为 2 0 1、2 0 7、1 41、2 1 8和 1 90g·m- 2 .在水分为主导因子的旱作条件下 ,根系过大的品种 ,个体间竞争激烈 ,其群体的抗旱性较差 ;根系较小的品种 ,个体间竞争较弱或无竞争 ,故群体抗旱性较强 .     

氮素对花铃期干旱再复水后棉花根系生长的影响

于2005~2006年在江苏南京农业大学卫岗试验站进行盆栽试验, 设置正常灌水(土壤含水量为田间持水量的75%左右)和棉花(Gossypium hirsutum)花铃期土壤短期干旱处理(将正常灌水的棉花自然干旱持续8 d, 以棉株出现萎蔫症状为标准, 之后复水至正常灌水水平), 每个处理再设置3个氮素水平(0、3.73、7.46 g N·pot^-1, 分别相当于0、240、480 kg N·hm^-2), 研究氮素对花铃期干旱及复水后棉花根系生长的影响。结果表明, 花铃期干旱条件下, 土壤相对含水量迅速减少, 并随氮素水平的提高而降低。在干旱处理结束时, 与正常灌水处理相比, 干旱处理棉花根重与氮素累积量显著降低, 但干物质根冠比(R/S)与氮素累积量根冠比(R_N/S_N)增大; 根系超氧化物歧化酶(SOD)和过氧化物酶(POD)活性明显升高, 而过氧化氢酶(CAT)活性降低, 同时, 丙二醛(MDA)含量相应增大。花铃期短期干旱亦显著降低棉花根系活力与叶片净光合速率。施氮可提高干旱处理棉花根重与氮素累积量, 降低SOD活性, 增强POD与CAT活性, 但以240 kg N·hm^-2水平最有利于根系生长, 其内在生理机制表现为R/S与R_N/S_N最小, 膜脂过氧化程度最低, 而根系活力最强, 其叶片的净光合速率亦最高。复水后, 干旱处理棉花根重与氮素累积量显著高于正常灌水处理; 内源保护酶活性相应变化, 其根系MDA含量与正常灌水处理已无显著差异; 根系活力显著高于正常灌水处理。施氮有助于增加复水后棉花根重与氮素累积量, 提高POD与CAT活性, 降低膜脂过氧化程度, 增强棉花根系活力, 从而提高叶片净光合速率。综合分析认为, 过量施氮或施氮不足均不利于棉花根系生长, 两年的试验结果表明, 在本试验设置的3个氮素水平中, 花铃期干旱胁迫下以240 kg N·hm^-2, 且基施50%, 初花期追施50%较适宜。     

毛乌素沙地臭柏（Sabina vulgaris）和油蒿（Artemisia ordosica）群落的细根分布特征

用根钻法和细根分级的方法研究了毛乌素沙地臭柏群落、臭柏灌丛、油蒿群落的细根(D≤2 mm, D为根直径)垂直分布,并用渐近线方程Y=1-βd[Y为从地表到一定深度的根量百分比累积值(0～1),d表示土层深度(cm),β为根系削弱系数]描述根系分布与土壤深度的关系.对不同径级臭柏、油蒿细根的β值、根长密度及根面积指数进行计算,结果表明:以15 cm为取样深度级,臭柏和油蒿群落活细根(D≤2 mm)的各月生物量平均值,在0～15 cm 范围内最大,并且随土壤深度增加而减少.臭柏群落、臭柏灌丛、油蒿群落细根生物量垂直分布的β值差异不显著(P＞0.5),但相应层次上的月平均细根生物量,臭柏群落是油蒿群落的6.7～14.6倍(P＜0.05),臭柏灌丛是油蒿群落的14.0～19.2倍(P＜0.05).D≤1 mm与1 mm＜D≤2 mm的细根重量百分比与土壤深度都呈对数关系,但D≤1 mm的细根与土壤深度的相关程度更高.根长密度与根面积指数在各土层的分布有极大的相似性.在臭柏群落、臭柏灌丛、油蒿群落中,D≤2 mm的细根根长密度和根面积指数随土壤深度的增加而减小.月平均值中, D≤2 mm、D≤1 mm、1 mm＜D≤2 mm的细根在0～90 cm的根面积指数总和的大小都是:臭柏灌丛＞臭柏群落＞油蒿群落.     

科尔沁沙地3种草本植物根系生长动态

利用微管对狗尾草(Setaria viridis)、黄蒿(Artemisia scoparia)和沙米(Agriophyllum squarrosum)根系生长动态进行了观测。结果表明:1)在观察期内,狗尾草和黄蒿的根系生长表现出先增后减的“抛物线”型,而沙米的根系成指数生长。在7月末至8月初狗尾草、黄蒿和沙米根系具有最高的生产量,其根量密度分别为4 690.91、2 975.76和2 354.55条·m^-2;在8月末,狗尾草和黄蒿根系都表现出不同程度的衰减,沙米根数保持增加。2)狗尾草优先生长表层根系,根系主要生长在0~30 cm的土层内,根长密度最大时为2.23 cm·cm^-2;黄蒿生长前期表层根长密度大,生长后期下层根长密度开始增加;沙米优先发展下层根系,快速生长期后,地下30~50 cm处的根长密度增加高于上层。3)生长前期和快速生长期,0~50 cm狗尾草根长密度最大,黄蒿次之,沙米最小,生长末期,沙米根长密度大于狗尾草。     

旱涝胁迫对棉花根系生长的影响

为探究旱涝胁迫对棉花花铃期及吐絮期根系的影响,于2016年在武汉大学灌溉排水试验场开展了受旱、受涝及旱涝急转胁迫测坑试验,使用微根管系统对根系进行了原位生长过程监测,并用挖掘法对结果进行了验证。结果表明:通过微根管观测图片所获取的根系信息,代表了根管周围3.3 mm透视厚度土层的根系状况;从蕾期至吐絮期内,根系生长呈"S"型曲线,其中花铃期根系生长发育最快;0~30 cm是根系主要分布区域,约占根系总量的70%~80%;不同旱涝胁迫处理下总根长及总根表面积从大到小的顺序为受涝组旱转涝组正常组受旱组;涝渍导致表层根系大量繁殖,特别是根粗为0.2~0.4 mm的根系生长;干旱使得棉花根长密度变小,径变粗,深层根系生长加速、占比上升,根系重心下移;旱转涝后根系指标增速大于对照组,证明后期受涝对前期受旱在根系生长方面具有补偿效应。     

Genotype and Planting Density Effects on Rooting Traits and Yield in Cotton （Gossypium hirsutum L,）

Root density distribution of plants is a major Indicator of competition between plants and determines resource capture from the solh This experiment was conducted in 2005 at Anyang, located in the Yellow River region, Henan Province, China. Three cotton （Gossyplum hlrsutum L.） cultivars were chosen： hybrid Btcultlvar CRI46, conventional Btcultlvars CRI44 and CRI45. Six planting densities were designed, ranging from 1.5 to 12.0 plants/m^2. Root parameters such as surface area, diameter and length were analyzed by using the DT-SCAN Image analysis method. The root length density （RLD）, root average diameter and root area Index （RAI）, root surface area per unit land area, were studied. The results showed that RLD and RAI differed between genotypes; hybrid CRI46 had significantly higher （P 〈0.05） RLD and RAI values than conventlonal cultlvars, especially under low planting densities, less than 3.0 plants/m^2. The root area index （RAI） of hybrid CRI46 was 61% higher than of CRI44 and CRI45 at the flowering stage. The RLD and RAI were also significantly different （P = 0.000） between planting densities. The depth distribution of RAI showed that at Increasing planting densities RAI was Increasingly distributed in the soil layers below 50 cm. The RAI of hybrid CRI46 was for all planting densities, obviously higher than other cultivars during the flowering and boll stages. It was concluded that the hybrid had a strong advantage in root maintenance preventing premature senescence of roots. The root diameter of hybrid CRI46 had a genetically higher root diameter at planting densities lower than 6.0 plants/m^2. Good associations were found between yield and RAI In different stages. The optimum planting density ranged from 4.50 plants/m^2 to 6.75 plants/m^2 for conventional cultlvars and around 4.0-5.0 plants/m^2 for hybrids.     

Sorghum root length density and the potential for avoiding striga parasitism

Striga hermonthica is a serious root parasite of sorghum in the semiarid tropics. Successful parasitism is dependent on interactions of Striga seeds and host roots. Several sorghum cultivars have been found which resist parasitism. The basis of resistance is not well known. One possible method for reducing the chances of parasitism is by restricted host root development. This research was conducted to evaluate this hypothesis in sorghum known to possess resistance to parasitism by Striga.Root length density of 21-day-old pot-grown resistant cultivars, Framida, N-13, IS-9830, Tetron and P-967083, were compared to that of the susceptible check, Dabar, using the line intercept method of measuring root length. There was no significant difference between resistant cultivars and the susceptible cultivar Dabar. The RLD of resistant P-967083 however was significantly less than Framida, another resistant cultivar.The RLD of Dabar was compared to that of Framida and P-967083 in USA and Niger field trials. Root length density was determined on soil cores taken at flowering with a Giddings Soil Sampler. Each core was divided into 10-cm fractions for estimating RLD by the line intercept method. In the USA Dabar had significantly greater RLD than the two resistant cultivars in the upper 10-cm portion of the soil profile, but only significantly greater than P-967083 in the 10–20-cm portion. Significant differences in RLD between susceptible and resistant cultivars were not found at depths between 20–60 cm. In field trials in Niger, RLD of Dabar was significantly greater than either resistant cultivar in the (0 to 30 cm) portion of the soil core. These results suggest that part of the Striga resistance of P-967083 and perhaps Framida may be a result of avoiding interactions between parasitic seeds and host roots.     

干旱区膜下滴灌条件下土壤深层水对棉花根系生长、分布及产量的影响

在土柱栽培条件下研究膜下滴灌土壤深层水对棉花根系生长的影响及与植株地上部生长的关系,设置土壤(60～120 cm)有深层水和无深层水2个处理,每处理设2个生育期间灌溉处理,分别为田间持水量70%和55%.结果表明：棉花总根质量密度、40～120 cm土层根长密度、根系活力等与地上部干质量间均具有显著的相关关系.生育期间耕层70%田间持水量条件下,土壤有深层水处理的总根质量密度与无深层水处理无明显差异,但40～120 cm土层的根长密度增加,根系活力增强,提高了土壤贮备水消耗量,增加了地上部干质量,最终获得较高的经济产量及水分利用效率.土壤有深层水条件下,生育期间耕层55%田间持水量处理的根冠比较大,40～120 cm土层根长密度和80～120 cm土层根系活力相对较高,土壤贮备水消耗量大幅提高,但仍无法弥补生育期间水分亏缺对根系及地上部生物量造成的负面影响,导致经济产量显著低于70%田间持水量处理.综上,充足的土壤深层水配合生育期间耕层65%～75%田间持水量,可促进棉花根系向下生长,有利于实现膜下滴灌棉花节水高产高效生产.     

Root distribution,standing crop biomass and belowground productivity in a semidesert in México

In a semidesert community in México (Zapotitlán de las Salinas, Puebla) the vertical distribution of roots and root biomass was estimated at 0–100 cm depth on two sampling dates, November 1995 (wet season) and January 1998 (dry season). Root productivity at 7 to 14.5 cm depth was estimated with the in-growth core technique every two months from March 1996 to February 1998. The relationship between environmental factors and seasonal root productivity was analyzed. Finally, we tested the effect of an irrigation equivalent to 20 mm of rain on root production. Seventy four percent of the total number of roots were found at 0-40 cm depth. Very fine roots (<1 mm diameter) were found throughout the soil profile (0-100 cm). In contrast, fine roots (1-3 mm diameter) were found only from 0–90 cm depth, and coarse roots (>3 mm diameter) from 0–60 cm depth. The root biomass was 971.5 g m^–2 (S.D. = 557.39), the very fine and fine roots representing 62.9% of the total. Total root productivity, as estimated with the ingrowth core technique, was 0.031 Mg ha^–1 over the dry season and 0.315 Mg ha^–1 over the wet season. Only very fine roots were obtained at all sampling dates. Rainfall was significantly correlated with very fine root production. The difference between fine root production in non-watered (0.054 g m^–2) and watered (0.429 g m^–2) treatments was significant. The last value was the same as that predicted for a rain of 20 mm, according to the exponential model describing the relation between the production of very fine roots and rainfall at the site.     

Root System Development of Oak Seedlings Analysed using an Architectural Model. Effects of Competition with Grass

A dynamic 3D model of root system development was adapted to young sessile oak seedlings, in order to evaluate the effects of grass competition on seedling root system development. The model is based on a root typology and the implementation of a series of developmental processes (axial and radial growth, branching, reiteration, decay and abscission). Parameters describing the different processes are estimated for each root type. Young oak seedlings were grown for 4 years in bare soil or with grass competition and were periodically excavated for root system observation and measurements (topology of the root system, length and diameter of all roots with a diameter greater than 0.3 mm). In the fourth year, 40 cm×20 cm×20 cm soil monoliths were excavated for fine root measurement (root density and root length). Root spatial development was analysed on a sub-sample of roots selected on four seedlings. The model was a guideline that provided a complete and consistent set of parameters to represent root system development. It gave a comprehensive view of the root systems and made it possible to quantify the effects of competition on the different root growth processes. The same root typology was used to describe the seedlings in bare soil and in grass. Five root types were defined, from large tap roots to fine roots. Root system size was considerably reduced by grass competition. Branching density was not affected but the branch roots were always smaller for the seedlings grown in competition. Reiteration capacity was also reduced by competition. Cross sectional areas before and after branching were linearly related with a scaling coefficient close to 1, as predicted by the pipe model theory. This relationship was not affected by grass competition.     

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）.     

高温胁迫对Bt棉铃壳中Bt蛋白含量及氮代谢的影响

以Bt基因来源于中国的棉花品种泗抗1 号(常规种)、泗抗3 号(杂交种)和来源于美国的棉花品种99B(常规棉)、岱杂1 号(杂交棉)为材料,研究了不同高温水平下Bt 棉盛铃期铃壳中Bt 蛋白含量变化及氮代谢生理特征.结果表明: 铃壳中Bt 蛋白含量随温度升高而降低,与对照相比(32 ℃),常规棉品种在38 ℃、杂交棉品种在40 ℃以上时,铃壳中Bt 蛋白含量大幅度下降.其中,常规种泗抗1号和99B在38 ℃时分别下降53.0%和69.5%;杂交种泗抗3号和岱杂1号在40 ℃时下降64.8%和54.1%.铃壳Bt 杀虫蛋白含量下降显著时,其可溶性蛋白含量明显下降,游离氨基酸含量明显提高,GPT活性显著下降,蛋白酶活性显著增加.高温影响铃壳的氮代谢引起Bt蛋白的分解加剧,合成减弱,从而造成Bt蛋白含量减少,抗虫性下降.     

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。     

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.
     

Root size and soil environments determine root lifespan: evidence from an alpine meadow on the Tibetan Plateau

We used a minirhizotron system to investigate the influence of three major factors—root morphology, root depth, and season of root emergence—on root survivorship and longevity in a Kobresia humilis meadow on the Tibetan Plateau during the growing season of 2009. Root longevity was assessed by survival analysis, Kaplan–Meier analysis, and Cox proportional hazards regression. Root longevity was correlated positively with root diameter. A 17.5 % decrease in the risk of mortality was associated with a 0.1-mm increase in diameter. Roots distributed in the top 10 cm of the soil had significantly shorter longevities than roots at greater depths, with a 48 % decrease of mortality risk for each 10-cm increase in soil depth from the surface to 40 cm. Of all the factors examined, the season of root emergence had the strongest effect on root lifespan. Roots that emerged in May and June had shorter longevity than roots that emerged later in the year, and roots that emerged in September and October were more likely to survive over winter. Our findings indicated that life-history traits of roots in K. humilis meadows are highly heterogeneous, and this heterogeneity should be considered when modeling the contribution of roots to carbon and nitrogen fluxes in this type of meadow ecosystem. Moreover, temporal, spatial, and compositional variations in root longevity must be considered.