蒋家沟新银合欢人工林土壤养分分布及其与细根的关系

采用分层挖掘法对东川蒋家沟新银合欢人工林土壤养分分布特征及其与细根的关系进行了研究,结果表明:除全钾外,土壤表层养分含量相对优越,集聚现象明显,随土层深度的增加土壤养分含量降低且趋于贫瘠;3年生新银合欢林土壤养分表聚程度、土壤养分状况明显优于20年生,20年生与9年生基本一致;新银合欢细根主要集中于0—100cm土层,0—20 cm土层富集明显,且在垂直剖面上呈对数函数递减。回归分析显示,土壤养分(碱解氮、速效磷、有机质、速效钾和全氮)与细根质量间存在极显著的线性关系,其中速效磷同细根质量关系更为密切,在一定程度上决定着新银合欢细根根系的空间分布。     

泥石流源区新银合欢细根质量动态与垂直分布特征

 以中国科学院东川泥石流观测站人工林中3、5、9、14和20年生新银合欢为研究对象,采用分层挖掘法对距树干1.0 m处细根质量动态与细根质量密度分布进行研究。结果表明:新银合欢细根质量在相同范围剖面中并非随树龄的增加而单一增大,而是先减小后增大;不同树龄细根质量密度最大值都出现在0～20 cm土层,呈现出明显的表聚特征,但随树龄的增加,根系集中化特征减弱,表现为向深层化扩张、均匀化方向发展;细根质量密度与土层深度相关性关系明显,垂直分布特征遵循指数函数分布,其中根径D≤2 mm细根在细根分布特征中起主导作用,而2 mm<D≤5 mm细根对细根分布特性影响不大。研究结果可为生物措施防治泥石流提供重要依据。     

沙棘-侧柏混交林生物量、林地土壤特性及其根系分布特征的研究

选择黄土高原17 a生的侧柏纯林作为对照,对沙棘—侧柏混交林中的侧柏生长、林地土壤特性及根系分布特征进行了系统研究。研究结果表明,混交林中侧柏平均树高比纯林的高25.80%,平均胸径大36.88%,林分生物量高128.23%,地上各部分生物量都明显高于侧柏纯林;混交林地与侧柏纯林地相比,土壤各层容重减小,而总孔隙度、毛管空隙度、非毛管空隙度、自然含水量、最大含水量、毛管含水量、最小含水量均有不同程度的增大;根系分布特征研究表明,侧柏纯林中根径≤1 mm和1~3 mm的根系主要集中分布在0—60 cm土层内,而混交林在0—180 cm的范围内分布相对更深,更均匀;根径≥3 mm的根系侧柏纯林与混交林具有较为相似的垂直分布特征。混交林中根径≤1 mm和1~3 mm的根系水平分布范围相对纯林的更大,而根径≥3 mm的根系的分布范围较小。     

浙江安吉主要植被类型根系分布特征研究

采用土柱法对黄浦江源区—浙江省安吉县主要植被类型林木细根分布特征进行了研究,结果表明：不同植被类型细根分布有较大差异,茶园、毛竹林、灌木林的根长、根表面积都要明显高于其他几种植被类型,而落阔林的根体积最大,常阔林的根重最大;细根随土层深度的增加而减少,林地细根主要分布在0-40cm土层。草地主要分布在0-30cm土层,这对抵抗径流侵蚀、保持水土资源具有重要意义;各样地根长均以〈0．5mm径级的根长含量最高,0．5-1mm径级次之,而2-5mm径级的最少。根系体积和根重具有相同的分布趋势。大小顺序均为：2—5mm〉1—2mm〉0．5-1mm〉0．5mm,与根长的分布状况正好相反。不同径级根表面积分布差异较大。     

黄土丘陵沟壑区自然恢复坡面植物根系的分布特征

采用土钻法研究了黄土丘陵沟壑区自然恢复坡面土壤根系的分布特征及土壤养分含量与土壤水分含量对根系分布的影响。结果表明:根系的分布因坡向、侵蚀带、土层深度、植被类型等的不同而异。阳坡根系总生物量高于半阴坡,但差异不显著;沟谷地根系总生物量及≤1mm根系生物量与沟间地各侵蚀带存在显著性差异;随着土层深度的增加,根系生物量减小;不同植被类型及其盖度对根系生物量有很大影响。不同坡向、各侵蚀带、不同土层中各径级根系生物量的总体趋势是≤1mm根系生物量最大,1～2mm次之,2～3mm和>3mm根系生物量较小,且≤1mm根系生物量与2～3mm和>3mm根系生物量间存在显著差异。根系生物量与土壤养分(除全磷)总体为中度正相关,与土壤水分分布不一致。因此,根系分布不仅与植物自身特性有关,还受土壤环境的影响。     

泥石流频发区典型乔灌植物根系的固土效应

[目的]研究泥石流频发区云南省昆明市东川区蒋家沟两种典型生态修复物种新银合欢(Leucaena leucocephala)和马桑(Coriaria sinnica)的根系固土效应,为当地生物工程的应用及泥石流治理效益的评价提供理论依据和数据支撑。[方法]通过根系挖掘法查明根系分布特征,开展根系拉伸试验分析单根抗拉特征,运用修正后的Wu-Waldron模型(RWM)计算两种植物根系对土壤抗剪强度的增加值。[结果]①新银合欢和马桑的根面积比RAR均随着土壤深度的增加而减小。②新银合欢根系构型为垂直型,马桑根系构型为横走型。③新银合欢根系的抗拉强度与根径之间无明显规律性,马桑根系的抗拉强度与根径之间呈递减的对数函数关系。④新银合欢和马桑根系对土体抗剪强度增加值均随着土壤深度的增加而减少,新银合欢根系固土深度约为1.4 m,马桑根系固土深度约为0.6 m。[结论]新银合欢和马桑根系均能显著发挥固土作用。由于根系构型、固土深度、固土方式等原因,二者的固土作用不同,可将二者结合种植,不仅有利于边坡的稳定,也可提高土体的抗冲性。     

滨海盐化潮土台田对苹果根系分布的影响

为了探讨滨海盐化潮土台田对苹果根系分布的影响,采用改良壕沟法进行了调查。在滨海盐化潮土台田土壤中,12年生八棱海棠砧长富2号苹果根系水平分布距离6.02 m,为冠径的2.43倍。距离树干1、2、3、4 m处,根量分别占观察剖面根量的26.5%、20.4%、22.3%和18.7%,共占87.9%。根垂直分布深1.5 m,为树高的45.2%。根集中分布在5~120 cm土层内。根有分层分布的趋势,第一层分布在5~20 cm土层内,第二层在70~120 cm土层内。直径0.5、0.5~2.0、2.0~5.0、5.0~10.0和10.0 mm的根,分别占总根量的64.4%、30.3%、3.6%、1.0%和0.7%。不同粗度的根,水平分布都较远;0~5 cm土层只有直径2.0 mm的细根,5~120 cm土层中各类根都有,130 cm以下土层中也主要是直径2.0 mm的细根。在滨海盐化潮土台田中苹果根系的分布呈"综合型"。     

酸枣根系构型特征研究

对半干旱地区酸枣根系构型的研究结果表明:酸枣的根系水平分布可达300 cm,主要分布于0—60 cm范围内;60—240 cm范围根表面积和细根数量变化不大,二级侧根和细根分布比较均匀,在接近侧根末端,根长度、根表面积和细根长度数值明显增大,二级侧根数量增加。垂直方向根系分布可达120 cm,但主要分布在0—60 cm的土层中。0—60 cm土层含水量高,与根系在土层中的主要分布深度一致,因此,酸枣主要吸收土壤浅层和中层水分。尽管在深层土壤中细根的比例很少,但对酸枣吸收水分发挥着非常重要的作用,在干旱季节土壤浅层水分不足时,60 cm以下深层土壤中的水分能够维持酸枣的生存和生长。     

膜下滴灌条件下水分对棉花根系分布特征的影响

通过分层土柱挖掘法，研究膜下滴灌条件下不同滴灌量棉花（Gossypium hirsutum L．）根系的分布特征。结果表明：直径〉1mm的粗根只分布在40cm以上的土层；随着土层深度增加，棉花根系生物量逐渐减少；但随着滴灌量减少，土壤深层根系生物量有增加趋势。不同处理的根系生物量的分布与土层深度呈显著的负指数关系，棉花细根生物量、根长、根表面积在土壤中垂直分布都呈“单峰型”曲线变化规律；但随着滴灌量的减少，棉花根系消弱系数β呈增加趋势。     

贺兰山油松林根系空间分布特征研究

通过根钻法对贺兰山油松林木细根分布特征进行了研究,结果表明:在40 cm以上土层中,各径级根系均有大量分布,而在40 cm以下土层中根系分布逐渐减少;92.9％的＜2 mm的细根集中分布于0 60 cm土层中,0 10 cm表层中的细根量占30.8％;油松根系具有深根性特征,但粗根集中于40 cm以上土层中,占粗根总量的88.6％;在距油松样木不同距离处的土壤中,油松细根随着距样木距离的加大而不断减少,一般在距样木2.0m的位置,油松细根量减至最低,同时细根根长、表面积、体积及根尖数都在此处降至最低.     

Automated analysis of fine‐root dynamics using a series of digital images

Information related to the growth of fine roots is important for understanding C allocation in trees and the mechanisms of C cycling in ecosystems. Observations using a camera or scanner embedded in the soil enabled us to obtain continuous images of fine‐root‐growth dynamics. However, these methods are still labor‐intensive because the image analysis has to be conducted manually. We developed an automated method for tracking movement or elongation of fine roots using a sequence of scanner images. We also show how data obtained with these methods can be used for calculating fine‐root behavior. Two A4‐size scanners were buried in a mixed forest in Japan and images were taken continuously from within the soil. We preprocessed these images by extracting the fine‐root area from the images and developed an automated calculation plug‐in we named A‐root for tracking growth movement of the tips of fine roots. A‐root and manual‐tracking results were compared using the same images. The results show the A‐root and manual‐tracking methods yielded similar levels of accuracy. The average growth rate of 17 fine roots tracked using the program was 0.16 mm h^–1. The observation of the direction of growth in fine roots showed the direction may be influenced by the original root's growth where the fine roots branched, distribution of soil particles, other roots, and the force of gravity. The A‐root analysis also suggested there may be an interaction between speed of growth and changes in direction of growing fine roots.     

灌溉方式对杨树人工林细根分布特征的影响

[目的] 探究滴灌对北京市大兴区林场5—6年生欧美107杨树人工林细根分布的影响，为干旱沙地条件下营建人工林提供理论支持。[方法] 采用根钻取样法，对比滴灌和常规灌溉条件下细根生物量在不同方向、不同水平距离和不同土层深度的差异。[结果] 滴灌没有改变细根的空间分布格局，细根在水平方向的距树干50 cm内，垂直方向的0—40 cm土层集中分布，不同方向的细根分布表现为：株间>对角>行间。滴灌对细根生长和分布的影响受滴灌后形成的湿润带范围影响，株间方向细根生物量在水平和垂直方向的分布特征与对角和行间方向差异明显，湿润带范围内细根生物量均与常规灌溉差异极显著（p<0.01）。[结论] 滴灌条件下的杨树人工林较常规灌溉有更多的细根分布，可以更充分利用地下资源，促进林木生长，提高林地生产力。     

Tree roots in canopy soils of old European beech trees—An ecological reassessment of a forgotten phenomenon

The formation of adventitious roots in humus accumulations in tree canopies is widely acknowledged from tropical and temperate rainforests, while the occurrence of those canopy roots in temperate tree species under mesic climates has been largely disregarded for ca. 100 years. Moreover, almost nothing is yet known of the ecological growth conditions or the structure or morphology of such canopy root systems. This study reports on the occurrence of tree fine roots in crown humus pockets of old European beech (Fagus sylvatica L.) trees. The aim was to compare these canopy roots with the fine roots in the terrestrial organic layer soil in terms of fine root biomass density, root morphological traits, ectomycorrhizal colonisation and chemical composition of the root tissue, and to relate these root traits to the chemical properties of the respective soils. Fine root biomass density in crown humus pockets was ca. 7 times higher than in the terrestrial organic layer, even though soil chemical properties of both rooting media were similar. Fine roots in the canopy differed from terrestrial fine roots by lower specific root tip abundance, specific root length, and specific root surface area, all of which points to a longer lifespan of the fine roots in the canopy. Moreover, canopy roots revealed a lower percentage of root tips colonised by ectomycorrhizal fungi than terrestrial roots (87% vs. 93%). Chemical composition of the root tissue in canopy and terrestrial soils was similar for most elements, but canopy roots showed lower P, Fe, and Al concentrations and a higher N/P ratio than terrestrial roots. Root P concentrations of both canopy and terrestrial fine roots were closely related to soil P concentration, but not to soil C/P or N/P ratios. On the other hand, tissue N of canopy roots, but not of terrestrial roots, revealed a clear dependence on soil N and C/N values, suggesting a more limited N availability in the canopy soil compared to the terrestrial organic layer. However, the overall small differences in soil chemical properties between canopy and terrestrial organic layer soil cannot explain the markedly higher volumetric root density in the crown humus and the differences in ecomorphological traits between canopy and terrestrial soil. Instead, it is speculated that these differences are more likely a result of temporarily high water availability in crown humus pockets due to high water flow along the surface of branches to the central crown parts of the beech trees.     

The in situ root chamber: A novel tool for the experimental analysis of root competition in forest soils

Competition between the roots of mature trees in mixed forests is not well understood because adequate methods for studying this interaction under field conditions are not yet available. We present a novel root chamber (size: 90×70×30 mm) that allows growth monitoring of individual tree fine roots in the soil while altering root competition situations experimentally. Fine roots of mature trees that were carefully uncovered from the soil were allowed to grow for several months in the chamber which contained soil material from the root's close proximity. Fine root increment was quantified by optical root length determination at the beginning and the end of the experiment. By placing individual fine roots of a tree species together with a second conspecific or allospecific root, the chamber allows one to simulate conditions of intra- and interspecific competition, and to test hypotheses on intensity and direction of root competition in the soil of mixed forests.We investigated the applicability of the root chamber in a mature beech–oak mixed forest in which beech is known to be a superior competitor above-ground. One-hundred and six chambers with different combinations of beech and oak fine roots were exposed in the soil for 180 or 438 d. In two-species chambers, which contained one beech and one oak root allowing for interspecific competition, beech fine roots grew significantly faster than oak roots. Furthermore, beech roots tended to show a higher growth rate in two-species chambers than in single-species chambers (two beech roots: intraspecific competition). In contrast, oak roots tended to grow slower when placed together with beech than when growing together with oak. By expressing the competitive strength of beech and oak roots with the relative competition intensity (RCI) index, evidence of asymmetric interspecific root competition in favour of beech was obtained.The potentials of this technique are related to the fact that replicated experiments with fine roots of adult trees can be conducted in the field; a certain artificiality, which is inherent to all rhizosphere experiments, represents the main limitation. From this study we conclude that while there are some limitations, in situ root chambers represent an important step towards the experimental analysis of root competition in forests.     

Fine root decomposition,nutrient mobilization and fungal communities in a pine forest ecosystem

Despite its importance to energy flow and nutrient cycling the process of fine root decomposition has received comparatively little detailed research. Disruption of the fine root-soil interface during preparation of root litterbags for decomposition studies could affect decay rates and nutrient mobilization in part by altering the community of decay organisms. We compared rates of decomposition and nutrient release from fine roots of pine between litterbags and intact cores and characterized the fungal community in the decomposing roots. Fine root decomposition was about twice as fast overall for intact cores than litterbags, and rapid mobilization of N and P was observed for roots in cores whereas nutrients were immobilized in litterbags. Fungal communities characterized using 454 pyrosequencing were considerably different between decaying roots in intact cores and litterbags. Most interesting, taxa from ectomycorrhizal fungal orders such as Boletales, Thelephorales and Cantharellales appeared to be more common in decaying roots from cores than litterbags. Moreover, the rate of N and P mobilization from decaying fine roots was highly correlated with taxa from two orders of ectomycorrhizal fungi (Thelephorales, Cantharellales). Although we caution that DNA identified from the decaying roots cannot be conclusively ascribed to active fungi, the results provide tentative support for a significant role of ectomycorrhizal fungi in decomposition and nutrient mobilization from fine roots of pine.     

The influence of Mg fertilization on growth and mineral contents of fine roots in (Picea abies [Karst] L.) stands at different stages of decline in NE-Bavaria

The effect of various Mg-fertilizers (MgSO₄; calcined dolomite) on root growth and mineral composition of 40 yr old Norway spruce at different sites and stages of decline was studied. Two years after fertilization, density of living fine roots of Mg-deficient trees had significantly increased on fertilized compared to non-fertilized plots. Only fertilization of calcined dolomite appeared to induce new root formation in the upper mineral soil. No such changes were observed for healthy looking trees at a second experimental site, where base saturation of the bulk soil was also low but trees were sufficiently supplied with Mg. At the third experimental site where foliar analyses reflected a luxurious Ca and Mg but an insufficient K nutrition at high Mg and Ca saturation of the bulk soil, calcined dolomite caused an increase of root growth due to a reinforced antagonism between Ca and Mg competing with K uptake. In general, at the experimental sites the fine root necromass decreased when base saturation of the bulk soil increased. The elemental contents of fine roots from the minenal soil of all three sites under investigation indicated that fine root growth in the mineral soil is strongly related to the root Ca and Mg contents. Root Ca contents seemed to be mainly a function of the Ca availability in the soil. Since there was no close relationship between fine root growth and the Ca/Al molar ratio in living fine roots, Al toxicity may not completely account for the differences in root growth and nutrition on the experimental sites.     

The influence of Mg fertilization on growth and mineral contents of fine roots in (Picea abies [karst] L.) stands at different stages of decline in NE-Bavaria

The effect of various Mg-fertilizers (MgSO₄; calcined dolomite) on root growth and mineral composition of 40 yr old Norway spruce at different sites and stages of decline was studied. Two years after fertilization, density of living fine roots of Mg-deficient trees had significantly increased on fertilized compared to non-fertilized plots. Only fertilization of calcined dolomite appeared to induce new root formation in the upper mineral soil. No such changes were observed for healthy looking trees at a second experimental site, where base saturation of the bulk soil was also low but trees were sufficiently supplied with Mg. At the third experimental site where foliar analyses reflected a luxurious Ca and Mg but an insufficient K nutrition at high Mg and Ca saturation of the bulk soil, calcined dolomite caused an increase of root growth due to a reinforced antagonism between Ca and Mg competing with K uptake. In general, at the experimental sites the fine root necromass decreased when base saturation of the bulk soil increased. The elemental contents of fine roots from the mineral soil of all three sites under investigation indicated that fine root growth in the mineral soil is strongly related to the root Ca and Mg contents. Root Ca contents seemed to be mainly a function of the Ca availability in the soil. Since there was no close relationship between fine root growth and the Ca/AI molar ratio in living fine roots, Al toxicity may not completely account for the differences in root growth and nutrition on the experimental sites.     

Spatial Distribution Assessment of Maize Roots by 3D Monolith Sampling

Spatial distribution of roots is of paramount importance for nutrient acquisition by crop plants. The objective of this study was to assess the spatial distribution of root length density (RLD), root mass density (RMD), and root morphological parameters in maize. Soil monoliths were completely sampled in form of 84 cubic samples of 10-cm edge length. Total root length and mass were dominated by fine roots (<1 mm diameter). Root parameters revealed variability in all three spatial dimensions, notably also parallel to the plant row. Root morphological parameters depended more on the horizontal location with respect to location of plants than on depth. Multiple regression analysis indicated that RLD, proportion of fine roots, and root diameters can be predicted from RMD, soil depth, and distance to plant. These three-dimensional (3D) data could be utilized for evaluation of 3D root growth and nutrient uptake models.     

施氮对白羊草细根形态和生长的影响

细根作为植物吸收水分和养分的重要器官,其形态和生长也受到土壤资源有效性的影响。以多年生草本植物白羊草(Bothriochloa ischaemun)为研究对象,通过盆栽试验和连续扫描根系的方法,研究了6个施氮处理(0,0.02,0.04,0.08,0.16和0.32 g/kg)对白羊草1—4级根序根系形态特征的影响。结果表明:(1)随着根序增加,各级根序上根系的平均直径和平均根长呈显著增加趋势(p<0.05),但总根长和比根长显著下降(p<0.05);(2)除对1级根的平均直径没有显著影响外,施氮增加了白羊草其它各级根序的平均根长和平均直径,减小了比根长、总根长和生物量;(3)施氮提高了1—4级根序的根系伸长速率和直径增粗速率,且根系伸长速率和增粗速率随时间推移呈动态变化,尤其是对1,2级根序的影响较大。因此,全球氮沉降增加可能通过影响细根的平均根长、平均直径、比根长、生物量等形态特征而对草本植物地下特征产生影响,进而影响陆地生态系统的C,N循环。