Minirhizotron Technique Research Articles

Root growth dynamics linked to above-ground growth in walnut (Juglans regia).

Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature. Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia 'Chandler') using minirhizotron techniques. Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production. The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs.

Visualization of peanut nodules and seasonal nodulation pattern in different tillage systems using a minirhizotron system

Abstract Nodulation is essential for providing the nitrogen (N) needs of peanut, but little is known about the time course of nodule development with soil depth in a field production system. A minirhizotron system allows for non-destructive, periodic digital imaging of identical locations in the crop root system in situ, including the associated nodules. Because the system allows imaging at the same location over time, individual nodule development and subsequent senescence can be followed throughout the growing season. To test the proof of concept for the use of a minirhizotron system to observe peanut nodule development, a case study was conducted in 2012 in Citra, FL in a sod-based production system managed with both conservation and conventional tillage at two different timings. Images were taken to a soil depth of 90 cm on four dates during the growing season, and nodule number, surface area, and senescence were determined. Most nodules occurred at depths spanning 5-30 cm with very few outside of this range; however, individual nodules were noted as deep as 90 cm. In this case study, tillage operation and timing had no impact on the total number of nodules produced, and the peak seasonal nodule number was formed relatively early in the season (9 July - 61 days after planting) and stayed constant until harvest. Nodule number varied by soil depth with the majority of nodules formed in the 0-20 cm depth. Nodule surface area was impacted by tillage type with conservation tillage treatments having larger nodule size (average 2.6 mm2) than nodules in conventional tillage (1.9 mm2). Maximum nodule surface area was achieved by mid-season on 1 August. This study gave a unique visual assessment of nodule development for field grown peanut over time and provided data that has rarely been reported. In addition, this study also illustrated that the minirhizotron technique could be successfully utilized in studies examining the development of nodules in peanut and would likely be applicable for similar studies in other legume crops.

Fine root lifespan dynamics in four sour cherry (Prunus cerasus) cultivars grown in Central Poland using the minirhizotron technique

Sour cherry (Prunus cerasus L.) is one of the most important fruit crops in Poland. There are many varieties cultivated in orchards, but only a few of them play an important role in commercial production. These few varieties have been the object of numerous studies focused on practical aspects like growth performance, yielding, or resistance to diseases. Recently more belowground research has been carried out in pomological plants using the minirhizotron research allowing to observe roots in short and long term experiments. There have been very few studies concerning root growth dynamics of sour cherry cultivars. Here we studied the influence of four major factors on root growth: the cultivar, root diameter, soil depth, and season on the survivorship of fine roots. We used the minirhizotron technique (MR) to examine fine roots dynamics of four sour cherry cultivars grafted on the Mahaleb rootstock, grown in an experimental orchard in Central Poland. The results revealed that the greatest impact on root survivorship was exerted by root diameter, depth of root formation and the season, whereas cultivars had no obvious influence. The finest roots (with a diameter 0.75mm) and roots formed at a depth of more than 50 cm below the soil surface have the longest survivorship. The season of root growth has little impact on root survivorship, but has a big influence on the number of the roots formed. There is no impact of the cultivar on the differences in observed roots survivorship.

Root growth of maize as studied with minirhizotrons and monolith methods

The root minirhizotron technique (MT) has been used to monitor nondestructively the root growth of field crops. The objective of this study was to compare the ability of MT to measure the root length density (RLD) of maize (Zea mays L.) as compared to the quadrate monolith method (QMM). The experiment was conducted at the Gucheng Ecological-Meteorological Experiment Station in China during the summer of 2007. RLD was estimated using MT and QMM. Results showed that the vertical distribution of RLD decreased top–down gradually, starting at the top of the root zone. The growth rate of RLD decreased as soil depth increased based on both methods. RLD was underestimated by MT at depths between 0 and 40 cm at the milk and maturity stages and overestimated by MT at depths between 0 and 20 cm at the jointing and tasseling stages. There was a significant correlation (r2 = 0.715, = 0.05) between RLD estimates based on QMM and MT. The results of this study indicate that properly calibrated MT is a reliable method to screen nondestructively the root growth of maize.

Visualization of Peanut Nodules and Seasonal Nodulation Pattern in Different Tillage Systems Using a Minirhizotron System

ABSTRACT Nodulation is essential for providing the nitrogen (N) needs of peanut, but little is known about the time course of nodule development with soil depth in a field production system. A minirhizotron system allows for non-destructive, periodic digital imaging of identical locations in the crop root system in situ, including the associated nodules. Because the system allows imaging at the same location over time, individual nodule development and subsequent senescence can be followed throughout the growing season. To test the proof of concept for the use of a minirhizotron system to observe peanut nodule development, a case study was conducted in 2012 in Citra, FL in a sod-based production system managed with both conservation and conventional tillage at two different timings. Images were taken to a soil depth of 90 cm on four dates during the growing season, and nodule number, surface area, and senescence were determined. Most nodules occurred at depths spanning 5-30 cm with very few outside of this range; however, individual nodules were noted as deep as 90 cm. In this case study, tillage operation and timing had no impact on the total number of nodules produced, and the peak seasonal nodule number was formed relatively early in the season (9 July – 61 days after planting) and stayed constant until harvest. Nodule number varied by soil depth with the majority of nodules formed in the 0-20 cm depth. Nodule surface area was impacted by tillage type with conservation tillage treatments having larger nodule size (average 2.6 mm2) than nodules in conventional tillage (1.9 mm2). Maximum nodule surface area was achieved by mid-season on 1 August. This study gave a unique visual assessment of nodule development for field grown peanut over time and provided data that has rarely been reported. In addition, this study also illustrated that the minirhizotron technique could be successfully utilized in studies examining the development of nodules in peanut and would likely be applicable for similar studies in other legume crops.

Effects of warming on root diameter, distribution, and longevity in an alpine meadow

Roots form one of the most important carbon (C) pools in alpine ecosystems. Uncertainty about the effects of warming on root dynamics limits our ability to predict how C will transfer between biological and atmospheric pools in alpine regions under global warming. We used a minirhizotron technique to gain a better understanding of the response of alpine plant roots to warming. We looked for effects on root diameter, root depth in the soil, and root lifespan under a controlled asymmetrical warming (1.2/1.7 °C during daytime/nighttime) experiment during the growing season of 2009 in an alpine meadow on the northern Tibetan plateau. Roots became smaller in diameter, moved toward the upper soil layers, and showed significantly shorter lifespans in heated (H) than in unheated (UH) plots. Furthermore, in H treatment plots root lifespan was more strongly influenced by the time of root emergence rather than by root diameter. These results provide evidence that alpine plants may respond to climate change by altering their roots so that they are thinner, distributed shallower and turning over faster, suggesting that soil C flow and nutrient cycling would be accelerated resulting from the fast turnover of fine roots under elevated temperatures.

APPLICATION OF THE MINIRHIZOTRON TECHNIQUE TO STUDYING THE ROOTS OF FRUIT PLANTS

Minirhizotron, a non-destructive technique is based on the application of transparent tubes, located in plant’s root zone. This method has been known since the beginning of 20 th century and is used for plant root’s observations, especially in forest trees (Scots pine, Norway spruce, silver fir, birch), steppe grasses, vegetables and cereals. Minirhizotron technique is also applicable to pomological plants observations, mostly apples, but many others orchard species were observed with this method last years. The study of root growth dynamics in fruit plants using the non-destructive, minirhizotron method is conducted in the Pomological Orchard in Skierniewice. The objects of the observations are the roots of: apple trees cultivar. ‘Gold Milenium’, blackcurrant bushes cultivar ‘Tiben’ and sweet cherry cultivar ‘Vanda’. The observations were carried out monthly over a period of from March to November.

Root Growth of Neighboring Maize and Weeds Studied with Minirhizotrons

Competition between crops and weeds may be stronger at the root than at the shoot level, but belowground competition remains poorly understood, due to the lack of suitable methods for root discrimination. Using a transgenic maize line expressing green fluorescent protein (GFP), we nondestructively discriminated maize roots from weed roots. Interactions between GFP-expressing maize, common lambsquarters, and redroot pigweed were studied in two different experiments with plants arranged in rows at a higher plant density (using boxes with a surface area of 0.09 m2) and in single-plant arrangements (using boxes with a surface area of 0.48 m2). Root density was screened using minirhizotrons. Relative to maize that was grown alone, maize root density was reduced from 41 to 87% when it was grown with redroot pigweed and from 27 to 73% when it was grown with common lambsquarters compared to maize grown alone. The calculated root : shoot ratios as well as the results of shoot dry weight and root density showed that both weed species restricted root growth more than they restricted shoot growth of maize. The effect of maize on the root density of the weeds ranged from a reduction of 25% to an increase of 23% for common lambsquarters and a reduction of 42 to 6% for redroot pigweed. This study constitutes the first direct quantification of root growth and distribution of maize growing together with weeds. Here we demonstrate that the innovative use of transgenic GFP-expressing maize combined with the minirhizotron technique offers new insights on the nature of the response of major crops to belowground competition with weeds.

Root growth and survivorship in cow manure and compost amended soils

The effect of the application of compost and cow manure on nectarine (Prunus persica L.) root growth and survivorship was investigated in a commercial orchard during the growing seasons 2003, 2004 and 2005. Our main objective was to determine whether compost affects root dynamics differently than cow manure. The experiment was a complete randomized block design with four replicates of two treatments: cow manure and compost applied at planting in 2001 at 10 t dry weight (DW)/ha and from 2004 at the rate of 5 t DW/ha. The compost fertilization represented a yearly rate of 120 kg N/ha, while cow manure was approximately 80 kg N/ha/year. Both root growth and survival were evaluated at 20-day intervals during the growing season by the minirhizotron technique. Cow manure increased the production of new roots compared with compost (P ≤ 0.001). Roots were mainly produced at a depth of 21–40 cm for compost and 61–80 cm for cow manure. The root lifespan was longer in compost than in cow manure treated trees (P ≤ 0.05) and was strongly affected by depth. No differences were observed in root length and diameter.

Root distribution and demography in an avocado (Persea americana) orchard under groundcover management systems.

The effect of groundcover management systems on root demography and distribution of newly planted avocado (Persea americana Mill) trees was examined using minirhizotron techniques. We evaluated three groundcover systems: (1) bare soil (BS), pre- and post-emergence herbicides; (2) vegetation strip (VS), post-emergence herbicide applied in a 1-m wide strip centred on the tree row plus a groundcover mixture seeded between tree rows; and (3) complete groundcover (GC), covering the entire surface of the plots. Root production was higher in the non-bearing year (2009-10) than in the bearing year (2010-11). Trees in the BS plots had more roots of bigger diameter in the top 30cm of soil and trees in VS and GC plots had more roots in the 30-60cm depth and of smaller diameter. Lifespan of spring-born roots were 61 and 59% greater than those born during autumn and summer, respectively and soil depth and root diameter were positively correlated with root longevity. Lifespan of thinner roots (<0.2mm) in the BS and VS plots were 49 and 33% greater than GC respectively. Avocado trees grown in contrasting condition compared with their native habitat show high morphological root plasticity, in response to resource and non-resource competition when grown in mixed stands.

5种温带森林生态系统细根的时间动态及其影响因子

细根(直径≤ 2 mm)的生长和死亡动态及其影响因子是森林生态系统能量流动和物质循环的重要研究内容,但因受到研究方法的限制而了解甚少。于2010年5-10月采用微根管技术对东北东部山区5种温带森林生态系统的细根生长量(FRP)和死亡量(FRM)进行了动态跟踪测定,并同步测定了土壤温度(<em>T</em>s)、土壤湿度(<em>M</em>s)、叶面积指数(LAI)等相关因子。结果表明: 不同林型和取样时间的FRP和FRM均差异显著(<em>P</em> < 0.001)。杨桦林、硬阔叶林、兴安落叶松林、红松林、蒙古栎林的FRP和FRM分别为:(13.34±0.90) μm·cm^-2·d^-1(平均值±标准误)和(5.02±0.36) μm·cm^-2·d^-1、(13.04±0.82) μm·cm^-2·d^-1 和(6.85±0.32) μm·cm^-2·d^-1、(8.74±1.44) μm·cm^-2·d^-1和(5.05±0.61) μm·cm^-2·d^-1、(8.02±2.27) μm·cm^-2·d^-1和(3.88±0.35) μm·cm^-2·d^-1、(7.59±0.82) μm·cm^-2·d^-1和(3.88±0.61) μm·cm^-2·d^-1。所有林型生长季期间FRP的时间变化均呈现明显的单峰型,但峰值出现的时间却因林型而异。FRM随生长季的进程而逐渐增加,杨桦林和硬阔叶林FRM在8月初出现峰值,而红松林、兴安落叶松林和蒙古栎林的FRM峰值均出现在生长季末期。<em>T</em>s、<em>M</em>s和LAI对FRP和FRM均存在显著的正效应(<em>P</em> < 0.05),3个因子的综合作用对各个林型FRP和FRM变异性的解释率分别达68%和53%以上,表明这些温带森林生态系统细根生长和死亡的时间动态主要受土壤温湿度和叶面积变化的联合影响。;Production and mortality of fine roots (diameter ≤ 2mm) and influencing factors are important to energy flow and nutrient cycling in forest ecosystems, but remain poorly understood mainly due to the limitation of methodology. In this study, we used a minirhizotron technique to investigate the temporal dynamics in fine root length production (FRP) and mortality (FRM) of five representative forest ecosystems in Northeast China during the period between May and October of 2010. Soil temperature (<em>T</em>s), soil moisture (<em>M</em>s), and leaf area index(LAI)were simultaneously measured for each stand. The stands were aspen-birch forest dominated by <em>Populus davidiana</em> and <em>Betula platyphylla</em>, hardwood forest dominated by <em>Fraxinus mandshurica</em> and <em>Juglans mandshurica</em>, Mongolian oak forest dominated by<em> Quercus mongolica</em>, Korean pine (<em>Pinus Koraiensis</em>) plantation, and Dahurian larch (<em>Larix gmelinii</em>) plantation. The experimental design included five forest types, three 20 m×30 m replicate plots in each forest type. The results showed that the FRP and FRM were significantly (<em>P</em> < 0.001) affected by forest types, sampling times and their interactions. The FRP was (13.34±0.90) μm·cm^-2·d^-1(mean±SE), (13.04±0.82) μm·cm^-2·d^-1, (8.74±1.14) μm·cm^-2·d^-1, (8.02±2.77) μm·cm^-2·d^-1, and (7.59±0.82) μm·cm^-2·d^-1 for the aspen-birch, hardwood, larch, pine, and oak stands, respectively; and the FRM was (5.02±0.36) μm·cm^-2·d^-1, (6.85±0.32) μm·cm^-2·d^-1, (5.05±0.61) μm·cm^-2·d^-1, (3.88±0.35) μm·cm^-2·d^-1, and (3.88±0.61) μm·cm^-2·d^-1, correspondingly. The FRP showed a unimodal seasonal pattern with peaks varying with forest types. The FRM increased gradually as the growing season proceeded, and reached its maximum at the end of the growing season for all the stands except for the aspen-birch and hardwood stands where it peaked in early August. <em>T</em>s, <em>M</em>s, and LAI all exerted significant positive effects on FRP and FRM (<em>P</em> < 0.05), which, together, explained more than 68% and 53% of variability in FRP and FRM, respectively. These results illustrated that the temporal dynamics of fine root production and mortality in these temperate forest ecosystems were jointly influenced by changes in soil temperature, moisture and leaf area index.

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 (Rtotal) apparent on the MR tube surface. The corresponding biomass for each root group was estimated by soil monolith. The difference in biomass turnover between Rtotal 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.

A novel pre-treatment for rapidly separating willow roots from high clay content soil

Numerous studies have examined the root dynamics of willow biomass energy crops growing on medium to light-textured soils, using either soil coring, minirhizotron techniques, or a combination thereof. However, neither approach is well suited for studying roots in expansive high clay content soil. Our objective was to test the efficacy of a novel inexpensive root washing pre-treatment, using baking soda (NaHCO3), for facilitating the separation of willow roots from a Vertisol (70% clay). Soil cores were collected from within a willow variety trial plot of Tully Champion (Salix viminalis × Salix miyabeana) and were either conventionally washed (i.e., no pre-treatment) or washed following a pre-treatment consisting of shaking the sample for 15 min with either deionized water or 1.2 mol dm−3 NaHCO3. Measurement variables included washing duration, water usage, and recovery of fine (<2 mm) and coarse roots. The ranking of washing duration and water usage was NaHCO3 pre-treatment < deionized water pre-treatment < conventional washing. Compared to conventional washing, the NaHCO3 pre-treatment reduced the washing duration and water usage by 45 and 61%, respectively, while increasing the fine root recovery by 26%. There was no significant difference (P > 0.05) in the fine root recovery between the deionized water and NaHCO3 pre-treatments or the coarse root recovery among the three washing methods. Developing a quicker technique of separating willow roots from high clay content soil, which conserves water and increases fine root recovery, should promote further investigations of root growth dynamics within this traditionally difficult soil type.

Fine-root dynamics in sugi (Cryptomeria japonica) under manipulated soil nitrogen conditions

Nitrogen deposition affect fine-root dynamics, a key factor in forest carbon and nutrient dynamics. This study aimed to elucidate the effects of increased soil inorganic nitrogen (N) levels on the fine-root dynamics of Cryptomeria japonica, which is tolerant to excess N load. An ammonium nitrate solution (28 kg ha−1 month−1) was applied for 3 years to plots (1 m × 2 m) in a C. japonica plantation. The elongation and disappearance of the fine roots were examined using the minirhizotron technique. The N fertilization increased soil inorganic N content and lowered the soil pH. Fine-root elongation rates increased with fertilization, whereas patterns of their seasonal changes were not affected. The ratio of cumulative disappearance to cumulative elongation of fine roots was lower in the N-fertilized plots than in the control plots. The mean diameter of the fine roots was not affected by N fertilization. Our results suggest that C. japonica can respond to increased levels of soil inorganic N by increasing both the production and residence time of the fine roots. However, the effects of the changing soil N content are less evident for the phenology and morphology of the fine roots in C. japonica.

Root‐growth characteristics contributing to genotypic variation in nitrogen efficiency of oilseed rape

AbstractA 3‐year field experiment was carried out to determine the significance of root‐growth characteristics contributing to N‐uptake efficiency of two oilseed rape (Brassica napusL.) cultivars differing in N efficiency. Two N treatments were applied, and the core and minirhizotron techniques were used to study root‐length density and number of living roots, respectively. Fertilizer‐N supply increased shoot dry matter, grain yield, total N uptake, and total soil Nmincontents particularly in the top soil. Although significant differences occurred in all parameters between years, the interactions between years and cultivars were mostly not significant. Compared to cv. Capitol, the N‐efficient cv. Apex was characterized by a higher grain yield at N0 and a higher N uptake during reproductive growth. This genotype also had a higher root‐length density and more living fine roots particularly in the topsoil layer. Root growth of this genotype was especially high from beginning of shooting to beginning of flowering, while shoot growth and N uptake during vegetative growth were comparatively low. Our results suggest that N‐efficient cultivars can be characterized by a high investment in root growth during the vegetative stage with a comparatively slow shoot growth and N‐uptake rate until beginning of flowering, which, however, continues during reproductive growth. High root production only during reproductive growth seems to be less effective to achieve high N efficiency, because this may lead to a shortage of assimilates for seed filling. High root‐length density at vegetative stages may thus be advantageous for N uptake and reproductive growth and could be a useful morphological character for the selection and breeding of N‐efficient cultivars.

Preliminary study on estimating fine root growth in a natural Pinus densiflora forest using a minirhizotron technique

The minirhizotron technique was used to investigate the spatial (soil depth) and temporal (season) changes of fine roots (≤2 mm) in a mature Pinus densiflora forest. Length, production, and mortality of fine roots were measured at different depths on seven dates between March and October 2011. Average fine root length (mm cm−2), production, and mortality (μm cm−2) during the growing seasons were 2.54 ± 0.82, 84 ± 27, and 7 ± 4 at 0–20 cm depth, 0.85 ± 0.37, 39 ± 13, and 14 ± 9 at 20–40 cm depth, and 1.26 ± 0.92, 45 ± 28, and 34 ± 16 at 40–60 cm depth, respectively. There was no significant difference in length, production, or mortality of fine roots among the different seasons and depths (P > 0.05). The seasonal pattern in fine root length generally increased during the growing seasons. The fine root production was high in summer, whereas the mortality was high in autumn. This preliminary result using a minirhizotron technique can be used for quantifying and understanding the fine root dynamics in P. densiflora forests.

Cattle Grazing Affects Cotton Root Dimensions and Yield in a Bahiagrass-based Crop Rotation

With increasing production costs in the southeastern US, cropping systems that improve agronomic and economic sustainability are critical. A sod-based system utilizing a two year rotation of establishing and grazing bahiagrass (Paspalum notatum Fluegge) followed by a year of peanut (Arachis hypogaea L.) and a year of cotton (Gossypium hirsutum L.) was established in Marianna, FL. The effect of grazing in this system on root dimensions (length, diameter, and surface area) of cotton was monitored using a mini-rhizotron technique. There were differences in several root parameters between grazed and non-grazed plots (256 m²) including: cotton root length (1260 mm grazed vs. 844 mm non-grazed), surface area (1727 mm² grazed vs. 1105 mm² non-grazed), and diameter (3.09 mm grazed vs. 2.51 mm non-grazed). The roots in the 15 to 30-cm-depth profile had greater length and surface area in the grazed plots with the greatest root surface areas in the deepest soil profile (75-90 cm). Grazed plots also exceeded nongrazed plots in seed cotton yield (3967 kg/ha vs. 3335 kg/ha) and lint (1672 kg/ha vs. 1444 kg/ha). Increases in root architecture associated with cattle grazing in this system may enable cotton to better withstand adverse environmental conditions such as drought stress, thereby improving long-term sustainability. (Resume d'auteur)

幼龄柠条细根的空间分布和季节动态

以晋西北黄土高原区5年生柠条(<em>Caragana korshinskii</em>)人工林为研究对象,应用Minirhizotron技术,分别在距茎干水平距离0 cm和50 cm处设点(以下简称为0 cm位点和50 cm位点),对林地0-100 cm土层深度范围内的柠条细根进行了观测。以2009年生长季(4-10月)的细根根长密度(<em>RLD</em>,mm /cm²)和表面积密度(<em>RAD</em>,mm²/cm²)数据为基础,结合同期环境因子(气温、降雨量、土壤温度和土壤含水量等)数据,对0 cm和50 cm两个位点的细根动态特点进行了比较研究。结果表明:(1)两个水平位点的细根垂直分布和季节变化趋势均具有一定差异,主要差异是0 cm位点0-60 cm各土层的<em>RLD</em>均大于50 cm位点,前者各测定期的<em>RLD</em>(<em>RAD</em>)均大于后者。因此,0 cm位点的细根分布量(4.04 mm/ cm²和4.67 mm²/ cm²)显著大于50 cm位点(3.07 mm/ cm²和2.99 mm²/ cm²)。(2)就整体(两个位点平均值)而言,<em>RLD </em>(<em>RAD</em>)的垂直分布以40-50cm土层最大,以60-70cm土层最小。<em>RLD</em>(<em>RAD</em>)的季节变化具有由小变大再变小的趋势。年生长季幼龄柠条细根的<em>RLD</em>和<em>RAD</em>总平均值分别为3.55 mm/ cm²和3.83 mm²/ cm²。(3)就0 cm位点、50 cm位点或整个林地而言,细根<em>RLD</em>的季节变化与气温和土壤温度的季节变化均具有显著正相关性。以上结果表明,幼龄柠条细根的水平分布具有"近主根"特点;<em>RLD</em>的季节变化与温度因子的季节变化具有高度一致性。;It is important and significant to know the spatial distribution pattern of fine roots for understanding the utilization status of the available resources belowground. The objective of this study was to investigate the fine root dynamics of <em>Caragana korshinskii </em>Kom, a shrub species widely planted to control soil erosion and land desertification in the semiarid area of China, in a 5-year-old plantation in the Loess Plateau area of Northwest Shanxi, China. Using the minirhizotron technique. The minirhizotron tubes were installed at two horizontal distances (0 cm and 50 cm) from the plant stems in the top 100-cm of soil. Based on the data sampled in the growing season (from April to September) of 2009, we analyzed the spatial-temporal patterns of fine root length density (<em>RLD</em>, mm/cm²) and fine root surface area density (<em>RAD</em>, mm²/cm²) in the plantation, and explored the relationships of <em>RLD</em> and <em>RAD</em> with the environment factors such as air temperature, soil temperature, rainfall and soil water content. The results showed that (1) there were certain differences in both vertical distribution patterns and seasonal change trends of fine roots between the two horizontal sites, and the obvious difference was that the values of<em> RLD</em> in the upper 0-60cm soil layers at the 0cm horizontal site were greater than those at the 50 cm horizontal site, and that the values of<em> RLD</em> (<em>RAD</em>) measured in every month for the former were larger than those for the latter. Therefore the <em>RLD</em> and<em> RAD</em> for the former (4.04 mm/cm² and 4.67 mm²/cm²) were significantly larger than those for the latter (3.07 mm/cm² and 2.99 mm²/cm²). (2) As a whole (for the average of two horizontal sites), the maximum value of <em>RLD</em> (<em>RAD</em>) appeared in 40-50 cm soil layer while the minimum value in 60-70 cm soil layer in the 100 cm soil profile. The <em>RLD</em> (<em>RAD</em>) showed a common seasonal trend with the peak value in the middle period of growing season. The total averages of <em>RLD</em> and <em>RAD</em> of fine roots in the growing season were 3.55 mm/cm² and 3.83 mm²/cm², respectively. (3) For 0 cm horizontal site, 50 cm horizontal site or the average of two horizontal sites (i.e. the plantation), the seasonal change course of <em>RLD</em> was significantly and positively related with air temperature and soil temperature, respectively. The above results showed that the horizontal distribution of the fine roots of young <em>Caragana korshinskii</em> was characterized by appearing mainly around the taproots, and the seasonal change trend of <em>RLD</em> was highly consistent with the change of temperature factor. Although the correlation coefficients between the seasonal change courses of <em>RLD</em> (<em>RAD</em>) and water indices (rainfall and soil water content) were not significant, this did not imply that fine root growth was not affected by water factor. Further research is required on the mechanisms of fine root dynamics in the annual growing season because of the internal and external controls of fine root growth.

Fine root dynamics and longevity of Artemisia halodendron reflect plant growth strategy in two contrasting habitats

Fine root dynamics and longevity may reflect the results of plant adaptation. The minirhizotron technique was applied to investigate the fine root dynamics and longevity of Artemisia halodendron Turcz. ex Bess. in the mobile and fixed sand dunes in Inner Mongolia, Northern China. For over two years of study, the cumulative fine root length production and turnover were all significantly higher in the mobile than the fixed sand dunes at soil depths of 0–20, 20–40, and 40–60 cm. The annual fine root production (8.46 mm cm −2 y −1) and annual fine root turnover (7.38 mm cm −2 y −1) of shrubs in the mobile sand dunes are about 38 and 70 percent higher than those in the fixed sand dunes. The fine root lifespan is higher for those in the fixed (47 days) than in the mobile (33 days) sand dunes, consistent with the higher ratio of first- (distal) to second-order roots of the former. The root production and lifespan are consistent with the adaptive responses of A. halodendron in the two habitats. The differences in root dynamics and lifespan between the mobile and fixed sand dunes may significantly explain the changes in the C fixation rate with the restoration of desert soils.

Fine-root dynamics in a young hinoki cypress (Chamaecyparis obtusa) stand for 3 years following thinning

Fine roots play a key role in carbon and nutrient dynamics in forested ecosystems. Fine-root dynamics can be significantly affected by forest management practices such as thinning, but research on this topic is limited. This study examined dynamics of fine roots <1 mm in diameter in a 10-year-old stand of hinoki cypress (Chamaecyparis obtusa) for 3 years following thinning (65% in basal area). Fine-root production and mortality rates were estimated using a minirhizotron technique in combination with soil coring. In both thinned and un-thinned control plots, fine-root elongation occurred from early spring to winter (March to December) and fluctuated seasonally. In the thinned and the control plots, the annual fine-root production rates were estimated to be 101 and 120 g m−2 year−1, respectively, whereas the estimated annual fine-root mortality rates were 77 and 69 g m−2 year−1, respectively. At 3 years after thinning, live fine-root biomass was significantly smaller in the thinned plot (143 g m−2) than in the control plot (218 g m−2), whereas dead fine-root biomass was not (147 and 103 g m−2, respectively). Morphological and physiological indices of fine roots such as diameter, specific root length, and root tissue density of the live fine roots was similar in both plots. These results suggested that thinning tended to decrease biomass and production of fine roots, but the effects on characteristics of fine roots would be less evident.