Root length and diameter measurement using NIH Image: application of the line-intercept principle for diameter estimation

The objective of this study was to develop an image analysis algorithm for estimating the length versus diameter distribution of washed root samples. Image analysis was performed using a Macintosh computer and the public domain NIH Image program. After an appropriate binary image of roots was obtained, the image was processed to get the thinned image to calculate the length of the roots. The edge pixel of the binary image was then deleted and root length was calculated again. This `edge deletion–length calculation' cycle was repeated until no root pixel was left in the image. Repeated edge deletion removed one pixel layer from around the periphery of root objects in each iteration. The number of edge deletions, which is equivalent to the intercept length, can be used to estimate the root diameter. We used the vertical or horizontal intercept length, whichever was shorter. The accuracy of diameter estimation due to orientation of objects varied from 89.1 to 126.0%. Branching root systems consist of several orders of laterals, and as the root branches to a higher order, the diameter of the roots becomes smaller. Therefore, edge deletions eliminate sequentially from the highest order roots, which have the smallest diameter, to the lowest order roots, which have the widest diameter. Thus, the length and diameter of each root order can be calculated by the proposed method. For verification, images of copper wire of 0.23, 0.50, and 1.0 mm diameter were analyzed. The results showed reasonable agreement with the expected distribution of length versus diameter for randomly oriented objects, and consequently the wire length of each diameter could be estimated. The proposed method was tested for primary and secondary roots of water-cultured rice (Oryza sativa L.), and it was proven that the method can provide accurate length and diameter measurements for each root order.     

Accurate root length measurement by image analysis

Algorithms for estimating root length by image analysis should lead to results that have no systematic error (bias), be insensitive to preferential root orientation, valid across a wide range of sample sizes and adjust for overlap between roots in samples, to reduce the effort needed in spreading out root systems. We propose a new algorithm that forms a compromise between small bias and robustness (insensitivity to variation in sample size and preferential root orientation), and provide a simple way of dealing with root overlap. Image analysis was performed on a Macintosh computer using the public domain NIH Image program. The digital image of the root was processed to get the thinned image (skeleton). The numbers of orthogonally and diagonally connected pairs of pixels (N _o and N _d, respectively) in the skeleton were counted separately and used for length (L) calculation. A new length calculation equation was introduced so that the effect of orientation on length calculation was minimized; L=[N d ²+(N _d+N _o/2)²]^1/2+N _o/2. The maximum error due to orientation of a single line was evaluated for an ideal line, and the analysis revealed that the new equation was less affected by orientation than previous equations. Copper wire and rice (Oryza sativa L.) roots containing both primary and fine secondary root were measured manually and with image analysis. The two methods showed good agreement within 1.5%. The proposed image analysis method yielded length estimates with CV from 0.23 to 0.88%, which was lower than the CVs of the line-intersect method. Moreover, the lengths of overlapping samples were calculated correctly because the image analysis method distinguished an overlapping pixel from a thinned image, while the calculation with the line-intersect method showed underestimation because overlaps were not considered in that method. This revised version was published online in June 2006 with corrections to the Cover Date.     

Morphological and anatomical relationships of loblolly pine fine roots

 Suberized or brown roots have been traditionally considered secondary or woody tissues. The validity of using morphological features such as color to infer root anatomy for southern pines is questionable and unproven. The objectives of this study were (i) to establish relationships between root color, diameter, and developmental stage (i.e., primary or secondary tissues) for loblolly pine, (ii) to determine the percentages of primary and secondary brown roots by diameter class, and (iii) to use these percentages to make first order estimates of the amount of brown root length and surface area that is in the primary and secondary developmental stages for sampled roots of a semi-mature loblolly pine stand. ”Unsectioned” roots were collected by coring to a 25-cm depth 3 times a year and measuring roots for length and surface area by diameter class. ”Sectioned” roots were sampled from a one-time core and from periodic grab samples. These roots were sectioned and characterized by their color, diameter and developmental stage. Diameters of sectioned roots (n=353) ranged from 0.21 to 8.24 mm. White and orange roots ranged from 0.23 to 2.50 mm, while brown roots spanned the range. White roots were developmentally primary, whereas orange/brown roots were either primary (from 0.21 to 2.50 mm), secondary (from 0.33 to 8.24 mm), or in transition (from 0.27 to 0.76). Total live root length of the sampled stands was estimated to be composed of 38% primary tissue, 58% secondary tissue, and 4% transition tissue. Lastly, neither root color nor diameter was a reliable predictor of developmental stage unless roots were white (primary), or orange/brown and >2.5 mm in diameter (secondary). Received: 30 June 1997 / Accepted: 28 January 1998     

Decomposition of roots and twigs: Effects of wood type (beech and ash), diameter,site of exposure and macrofauna exclusion

Carbon loss and nitrogen dynamics in beech roots (Fagus sylvatica L.), beech twigs and ash roots (Fraxinus excelsior L.) of 0–3, 3–10 and 10–40 mm diameter were investigated during 36 months of exposure in litter bags of 1 and 4 mm mesh. Four experiments were set up: (1) Beech and ash roots (three size classes) were placed in a soil depth of ca 5 cm in a beechwood on limestone; (2) beech twigs (three size classes) were placed on the soil surface of the beechwood; (3) beech roots (3–10 mm) were placed on the soil surface of the beechwood: (4) beech twigs (3–10 mm) were placed on the soil surface of four sites representing different stages of secondary succession (wheat field, 13 year old fallow, ca 50 year old fallow, beechwood). Ash roots generally lost more C than beech roots. Loss in C of ash roots was similar for each of the size classes, whereas in beech roots and beech twigs C loss was in the order large roots > medium roots > small roots. Beech roots (3–10 mm) placed on the soil surface lost considerably less C than beech twigs (3–10 mm). Decomposition of beech twigs varied among ecosystems but generally did not follow clear patterns with successional stages. The fit of linear vs exponential models of decay is compared and in most materials exponential models fitted the data better. In each of the wood materials an accumulation of N occurred. Irrespective of wood type, root and twig diameter, mineralization of N of wood materials placed in the beechwood started uniformly after 12 months. Multiple regression analysis indicated a negative relationship between initial N content and C loss in beech roots and twigs but not in ash roots. The analysis also indicated a significant influence of the degree of white rot and of the amount of mineral soil deposited in the litter bags on C loss of certain wood materials. Generally, mesh size affected C loss and N dynamics only slightly, which is attributed to the comparatively short exposure time.     

Longevity and turnover of roots in the shortgrass steppe: influence of diameter and depth

We used minirhizotrons to determine patterns of root longevity andturnover for the perennial bunchgrass Bouteloua gracilisinthe shortgrass steppe of eastern Colorado, USA. We hypothesized that rootlongevity would be partially controlled by root diameter, following previouslyobserved patterns in woody plants. In addition, we hypothesized that rootturnover would be greatest in surface soil horizons and decrease with depth dueto variation in soil moisture availability and temperature. Root longevity wascorrelated with root diameter. Median life span of roots > 0.4mm was approximately 320 days, while roots < 0.2mmhad a median life span of 180 days. There was approximately a 6%decreasein the likelihood of mortality with a 0.10-mm increase inroot diameter, controlling for the effect of depth in the soil profile. Rootlength production and mortality were highest in the upper20 cm of the soil profile and decreased with depth.However,because root length density also decreased with depth, there were nosignificantdifferences in turnover rate of root length among sampling intervals. Turnoverwas approximately 0.86 yr^–1 based on root length production,while turnover was 0.35 yr^–1 using root length mortality as ameasurement of flux. The imbalance between turnover estimates may be aconsequence of the time the minirhizotrons were in place prior to imaging or mayresult from our lack of over-winter measures of mortality. Our worksuggests that Bouteloua gracilis roots have complex lifehistory strategies, similar to woody species. Some portion of the root systemishighly ephemeral, while slightly larger roots persist much longer. Thesedifferences have implications for belowground carbon and nitrogen cycles in theshortgrass steppe.     

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。     

Distinguishing between metabolically active and inactive roots by combined staining with 2,3,5-triphenyltetrazolium chloride and image colour analysis

The objective of the present work was to develop a method to distinguish between metabolically inactive and active parts of plant roots. White clover (Trifolium repens L.) roots were stained with 2,3,5-triphenyltetrazolium chloride (TTC) followed by root colour classification with an interactive scanner-based image analysis programme (WinRHIZO). Roots inactivated by boiling were unstained and pale brown, whereas fresh samples with predominantly metabolically active roots turned dark red, red or pale red after staining. A small amount of very young, presumable active roots (0.8% of total active root length) failed to stain red with TTC. The colour analysis of inactive and active roots was based on four colour classes for boiled roots and seven classes for fresh roots, respectively, as defined upon visual examination of images. Pixel colours falling outside the defined classes were allocated to the nearest defined class – an option that increased objectivity and stability and reduced the required number of colour classes. For the fresh white clover roots, 75–86% of the total root length was determined as active, while 3–7% of the boiled roots fell into the same category. The percentage of total root length measured by WinRHIZO that was identified as metabolically active was linearly correlated with the percentage of fresh roots in mixtures of fresh and boiled roots (R²=0.99). Colour classes chosen à priori from one experiment could be used to distinguish fairly satisfactorily between active and inactive roots of another white clover cultivar grown under other conditions, but failed to classify activity in ryegrass (Lolium multiflorum Lam.) root samples. In the latter case, colour classes needed to be re-defined in order to produce reliable data. Our work shows that WinRHIZOs colour identification sub-module provides a new promising tool to classify root activity as identified after staining with TTC, but colour classes must be carefully evaluated on every new occasion.     

Analysis of root images from auger sampling with a fast procedure: a case of application to sugar beet

Manual line-intersect methods for estimating root length are being progressively replaced by faster and more accurate image analysis procedures. These methods even allow the estimation of some more root parameters (e.g., diameter), but still require preliminary labour-intensive operations. Through a task-specific macro function written in a general-purpose image analysis programme (KS 300 – Zeiss), the processing time of root images was greatly reduced with respect to skeletonisation methods by using a high-precision algorithm (Fibrelength). This has been previously proposed by other authors, and estimates length as a function of perimeter and area of the digital image of roots. One-bit binary images were acquired, aiming at large savings in computer memory, and automatic discrimination of roots against extraneous objects based on their elongation index (perimeter²/area), was performed successfully. Of four tested spatial resolutions (2.9, 5.9, 8.8, 11.8 pixel mm^–1), in clean samples good accuracy in root length estimation was achieved at 11.8 pixel mm^–1, up to a root density of 5 cm cm^–2 on the scanner bed. This resolution is theoretically suitable for representing roots at least 85 m wide. When dealing with uncleaned samples, a thick layer of water was useful in speeding up spreading of roots on the scanner bed and avoiding underestimation of their length due to overlaps with organic debris. A set of fibrous root samples of sugar beet (Beta vulgaris var. saccharifera L.) collected at harvest over two years at Legnaro (NE Italy) was analysed by applying the above procedure. Fertilisation with 100 kg ha^–1 of nitrogen led to higher RLD (root length density in soil) in shallow layers with respect to unfertilised controls, whereas thicker roots were found deeper than 80 cm of soil without nitrogen.     

Biomass and production of fine and coarse roots during regrowth of a disturbed subtropical humid forest in north-east India

Seasonal variation and depthwise distribution of dry matter in roots of different diameter classes and their annual production were studied using sequential core sampling. The investigations were carried out in three stands of a subtropical humid forest of north-east India representing different stages of regrowth after tree cutting. The mean annual standing crop of fine (<2 mm in diameter) and coarse (2–15 mm diameter) roots increased gradually from 5.4 Mg ha^-1 and 0.7 Mg ha^-1 in 7-yr old regrowth to 9.4 Mg ha^-1 and 2.8 Mg ha^-1 in 16-yr old regrowth, respectively. The contribution of fine roots to the total root mass declined from 88% in 7-yr old regrowth to 77% in both 13 and 16-yr old regrowths, while that of coarse roots increased from 12 to 23%. A major portion of fine roots (59–62%) was present in 0–10 cm soil layer, but the coarse roots were concentrated in 10–20 cm soil depth (38–48%). In all the three stands, biomass of both fine and coarse roots followed a unimodal growth curve by showing a gradual increase from spring/pre-rainy season to autumn/post-rainy season. Biomass to necromass ratio increased from 2.5 in the 7-yr old to 3.2 in the 16-yr old stand. The annual fine root production increased from 5.9 Mg ha^-1 to 7.7 Mg ha^-1 and total root production from 7.6 Mg ha^-1 to 14.7 Mg ha^-1 from 7-yr to 16-yr old regrowth.     

Patterns of variability in the diameter of lateral roots in the banana root system

The relative importance of root system structure, plant carbon status and soil environment in the determination of lateral root diameter remains unclear, and was investigated in this study. Banana (Musa acuminata) plants were grown at various moderate levels of soil compaction in two distinct experiments, in a field experiment (FE) and in a glasshouse experiment (GE). Radiant flux density was 5 times lower in GE. The distribution of root diameter was measured for several root branching orders. Root diameters ranged between 0.09 and 0.52 mm for secondary roots and between 0.06 and 0.27 mm for tertiary roots. A relationship was found between the diameter of the parent bearing root and the median diameter of its laterals, which appears to be valid for a wide range of species. Mean lateral root diameter increased with distance to the base of the root and decreased with branching density [number of lateral roots per unit length of bearing root (cm(-1))]. Typical symptoms of low light availability were observed in GE. In this case, lateral root diameter variability was reduced. Although primary root growth was affected by soil compaction, no effects on lateral root diameter were observed.     

Relationships between root diameter,root length and root branching along lateral roots in adult,field-grown maize

Background and Aims Root diameter, especially apical diameter, plays an important role in root development and function. The variation in diameter between roots, and along roots, affects root structure and thus the root system’s overall foraging performance. However, the effect of diameter variation on root elongation, branching and topological connections has not been examined systematically in a population of high-order roots, nor along the roots, especially for mature plants grown in the field.Methods A method combining both excavation and analysis was applied to extract and quantify root architectural traits of adult, field-grown maize plants. The relationships between root diameter and other root architectural characteristics are analysed for two maize cultivars.Key Results The basal diameter of the lateral roots (orders 1–3) was highly variable. Basal diameter was partly determined by the diameter of the bearing segment. Basal diameter defined a potential root length, but the lengths of most roots fell far short of this. This was explained partly by differences in the pattern of diameter change along roots. Diameter tended to decrease along most roots, with the steepness of the gradient of decrease depending on basal diameter. The longest roots were those that maintained (or sometimes increased) their diameters during elongation. The branching density (cm^–1) of laterals was also determined by the diameter of the bearing segment. However, the location of this bearing segment along the mother root was also involved – intermediate positions were associated with higher densities of laterals.Conclusions The method used here allows us to obtain very detailed records of the geometry and topology of a complex root system. Basal diameter and the pattern of diameter change along a root were associated with its final length. These relationships are especially useful in simulations of root elongation and branching in source–sink models.     

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.     

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）.     

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）.     

Root productivity in a lowland tropical rain forest in Mexico

Fine root productivity was estimated in a lowland tropical rain forest at Los Tuxtlas (SE Mexico) and examined in relation to climatic factors. Two root diameter classes were defined (class I,<1 mm; class II, 1–3 mm). Total root productivity was estimated to 1.95 t ha^–1 year^–1, a value which is lower than those reported from other rain forest sites. Significant differences in root dry weight were found among months and between diameter classes throughout the year. Class I monthly means formed two groups: one corresponding to the months of highest precipitation, and the other to the relatively dry season. Class II monthly means also formed two groups, although these were unrelated to the regional precipitation pattern. A multiplicative regression model of productivity on precipitation was significant for both root classes when rainfall data of the previous month were used, while a linear regression model was significant only for class I roots when temperature data of two months before were used; these results suggest a delay in the effect of climatic conditions on root productivity. While the seasonal pattern of root productivity is clearly related to the annual rainfall distribution, the low total annual productivity may be related to the very high soil fertility at Los Tuxtlas.     

水曲柳和落叶松不同根序之间细根直径的变异研究

细根直径大小和根序高低对细根寿命和周转估计具有重要的影响,研究不同根序之间的直径变异对认识细根直径与根序的关系具有重要意义。该文根据Pregitzer等(2002)提供的方法,研究了位于东北林业大学帽儿山实验林场尖砬沟森林培育实验站17年生水曲柳(Fraxinus mandshurica)和落叶松(Larix gmelinii)人工林细根1~5级根序的平均直径的变化、直径的最小值和最大值范围、直径的变异系数。结果表明,水曲柳和落叶松细根直径<2 mm时,包含5个根序,随着根序由小到大的增加,细根直径也在增大。各根序平均直径之间,存在较大的差异。在同一根序内,细根直径范围很大,水曲柳和落叶松一级根最小直径均<0.20 mm,最大直径分别<0.50 mm(水曲柳)和<0.70 mm(落叶松)左右。2~3级根序直径最小值在0.20~0.30 mm之间,最大值≤1.0 mm。5级根直径最小值<1.0 mm,最大值超过2.0 mm。随着根序等级增加,直径变异系数增大。一级根序的直径平均变异系数<10%,2~3级根序直径平均变异系数在10%~15%左右,4~5级根序直径的平均变异系数在20%~30%之间。因此,在细根寿命与周转研究过程中,必须同时考虑直径和根序对细根的寿命估计的影响。     

Fine-root vitality in a Norway spruce stand subjected to various nutrient supplies

The vitality of fine roots in a Norway spruce stand subjected to application of ammonium sulphate (NS), wood ash (A) and nitrogen-free fertilizer (V) respectively, was investigated using i) vitality classification of fine roots based on morphological characteristics and ii) the triphenyl tetrazolium chloride (TTC) method of estimating dehydrogenase activity.Although the NS-treated areas showed a 30% increase in above-ground production in response to the NS-application, the vitality of the fine-root system in the humus layer appeared to be in a state of deterioration, as indicated by a decrease in fine-root biomass, an increased amount of dead fine (0–1 mm) and small (1–2 mm) roots, a decreased specific root length (SRL = fine root length/fine root dry weight) and an increased dehydrogenase activity. The impact of the the A and V treatments was reflected in a decrease in fine-root biomass and an increase in SRL. The results make it clear that in order to study the vitality of forest trees, both fine-root studies and studies of above-ground tree parts are necessary.     

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.     

高寒草地不同径级根形态对围封年限的响应

以根径级表征根系形态结构,可以反映植物资源利用和生物量分配状况。研究高寒草地不同径级根形态,对了解地下碳分配、水分和养分吸收及生产力具有重要意义。围封被认为是防治草地退化的最有效措施之一,但目前有关围封年限对不同径级根形态影响的研究还极度缺乏,以致无法确定有利于根生态效益,即资源吸收利用能力最大化的围封年限。以位于青海省海北台站围封5、13、22、39 a的高寒草地为研究对象,季节性放牧草地为对照,探讨围封年限对不同径级根形态(包括根长、根表面积和根尖数)的影响。结果表明：在0—15 cm土层中,径级小于0.5 mm时,围封13 a的根尖数显著高于围封5 a的草地,其对应的生物量也最大;径级小于0.6 mm时,围封13 a的根长和根表面积均显著高于围封5 a和放牧草地,且其对应的生物量也达最大;径级大于0.5 mm时,各草地之间的根尖数均无差异;径级大于0.6 mm时,围封39 a的根长和根表面积均显著高于放牧草地,且其对应的生物量最大。在15—30 cm土层中,各径级下,围封5 a的根长、根表面积和根尖数均显著大于围封39 a和放牧草地,但其对应的生物量在围封13 a时达最大。土壤硝...