Fourth-order Roots Research Articles

Responses of Fine Root Morphological and Chemical Traits among Branch Orders to Forest Thinning in Pinus massoniana Plantations

Fine roots play an essential role in biogeochemical cycling in forest ecosystems; however, little is known about the response of fine root morphology and chemistry in different root orders to forest management activities such as forest thinning. We investigated the fine root morphological and chemical traits in different root orders of Pinus massoniana under different thinning intensities, namely no thinning, low-intensity thinning (LIT), middle-intensity thinning (MIT), and high-intensity thinning (HIT) (0%, 25%, 45%, and 65% of individual trees eliminated, respectively). We found that forest thinning increased the root diameter (RD) of absorptive roots and decreased that of transport roots, while the trend for the specific root length (SRL) was the opposite. LIT and MIT could increase specific surface area (SSA), especially the SSA of absorptive roots in the MIT treatment. The root tissue density (RTD) of all root sequences in the LIT treatment decreased but increased in the HIT treatment. For the fine root chemical traits, thinning increased the root carbon concentration (RCC) of absorptive roots. The root nitrogen concentration (RNC) and root phosphorus concentration (RPC) of first- to fourth-order roots increased in the LIT and MIT treatments after thinning. Meanwhile, thinning increased root lignin, cellulose, and non-structural carbohydrate (NSC) concentrations. Soil temperature, nitrate, and microbial biomass carbon were factors affecting variations in fine root morphology and chemistry. Forest thinning was likely to shift the absorptive roots’ foraging strategy into a resource-conserving one. Thinning increased fine root chemical traits in most root orders. These findings contributed to our ability to predict how belowground ecological processes are mediated by fine roots under forest management activities.

Rock fragment content in soils shift root foraging behavior in xerophytic species

Root traits associated with resource foraging, including fine-root branching intensity, root hair, and mycorrhiza, may change in soils that vary in rock fragment content (RFC), while how these traits covary at the level of individual root branching order is largely unknown. We subjected two xerophytic species, Artemisia vestita (subshrub) and Bauhinia brachycarpa (shrub), to increasing RFC gradients (0%, 25%, 50%, and 75%, v v− 1) in an arid environment and measured fine-root traits related to resource foraging. Root hair density and mycorrhizal colonization of both species decreased with increasing root order, but increased in third- or fourth-order roots at high RFCs (50% or 75%) compared to low RFCs. The two species tend to produce more root hairs than mycorrhizas under the high RFCs. For both species, root hair density and mycorrhizal colonization intensity were negatively correlated with root length and root diameter across root order and RFCs. Rockiness reduced root branching intensity in both species comparing with rock-free soil. At the same level of RFC, A. vestita had thicker roots and lower branching intensity than B. brachycarpa and tended to produce more root hairs. Our results suggest the high RFC soil conditions stimulated greater foraging functions in higher root orders. We found evidence for a greater investment in root hairs and mycorrhizal symbioses as opposed to building an extensive root system in rocky soils. The two species studied, A. vestita and B. brachycarpa, took different approaches to foraging in the rocky soil through distinctive trait syndromes of fine-root components.

Anatomical patterns of condensed tannin in fine roots of tree species from a cool-temperate forest

Condensed tannin (CT) is an important compound in plant biological structural defence and for tolerance of herbivory and environmental stress. However, little is known of the role and location of CT within the fine roots of woody plants. To understand the role of CT in fine roots across diverse species of woody dicot, we evaluated the localization of CT that accumulated in root tissue, and examined its relationships with the stele and cortex tissue in cross-sections of roots in 20 tree species forming different microbial symbiotic groups (ectomycorrhiza and arbuscular mycorrhiza). In a cool-temperate forest in Japan, cross-sections of sampled roots in different branching order classes, namely, first order, second to third order, fourth order, and higher than fourth order (higher order), were measured in terms of the length-based ratios of stele diameter and cortex thickness to root diameter. All root samples were then stained with ρ-dimethylaminocinnamaldehyde solution and we determined the ratio of localized CT accumulation area to the root cross-section area (CT ratio). Stele ratio tended to increase with increasing root order, whereas cortex ratio either remained unchanged or decreased with increasing order in all species. The CT ratio was significantly positively correlated to the stele ratio and negatively correlated to the cortex ratio in second- to fourth-order roots across species during the shift from primary to secondary root growth. Ectomycorrhiza-associated species mostly had a higher stele ratio and lower cortex ratio than arbuscular mycorrhiza-associated species across root orders. Compared with arbuscular mycorrhiza species, there was greater accumulation of CT in response to changes in the root order of ectomycorrhiza species. Different development patterns of the stele, cortex and CT accumulation along the transition from root tip to secondary roots could be distinguished between different mycorrhizal associations. The CT in tissues in different mycorrhizal associations could help with root protection in specific branching orders during shifts in stele and cortex development before and during cork layer formation.

Morphological traits of Chamaecyparis obtusa fine roots are sensitive to soil acid buffering capacity

The purpose of this study was to clarify how the morphological traits of Chamaecyparis obtusa (Sieb. & Zucc.) Endl. roots vary with soil acid buffering capacity (ABC), i.e., along a gradient in soil acidification. We used an order-based root classification system instead of a diameter-based root classification system, as the former relates better to root function. We sampled 210 intact fine root systems up to the fourth order and measured the morphological traits of a total of 16,657 individual branch-order roots in three C. obtusa stands with high soil ABC and four stands with low soil ABC. We found significant differences in the morphological traits of the first- to fourth-order roots between the soil ABCs. In the low-ABC soils, the fine root systems consisted of more and thinner roots than in the high-ABC soils. The diameter of the second-order roots was positively correlated with the soil pH and the concentration of base cations, but negatively with soil aluminum. Morphological traits of fine roots are sensitive indicators of soil acidification in C. obtusa forests.

Variation in the morphology of fine roots in Cryptomeria japonica determined by branch order-based classification

This study assessed intraspecific variation in morphological traits of the fine root branch orders of Cryptomeria japonica, and identified variation in the diameter of the first three-order roots among species types with mycorrhiza, and the diameter of first-order roots at the family level. Diameter, length, and specific root length of branch order roots (up to the fourth-order) were measured in intact fine root systems collected in four C. japonica stands. Relationships between soil chemical properties and morphological traits of the first- to fourth-order roots were investigated. The diameter of roots of 52 tree species reported in previous studies was compared at species types with mycorrhiza and at family level. The diameter of first-order roots in C. japonica varied by 1.2 times among stands. Negative correlations between soil NH4+ content and specific root length of the second- and third-order roots were observed in C. japonica. The diameter of first- and second-order roots forming arbuscular mycorrhiza in coniferous trees were significantly higher than those of roots forming ectomycorrhiza in coniferous and broadleaf trees. The diameter of first-order roots in Cupressaceae were significantly larger than those of Pinaceae, Sapindaceae, Betulaceae, and Fagaceae. Clarifying intraspecific variation in morphological traits of C. japonica lower-order roots may contribute to understanding their responses to different site conditions such as soil inorganic nitrogen contents.

不同土壤深度落叶松细根分解及N动态变化

PDF HTML阅读 XML下载 导出引用 引用提醒 不同土壤深度落叶松细根分解及N动态变化 DOI: 10.5846/stxb201806251392 作者: 作者单位: 森林植物生态学教育部重点实验室,东北林业帽儿山实验林场,中国科学院森林生态与管理重点实验室沈阳应用生态研究所;中国科学院森林生态与管理重点实验室沈阳应用生态研究所,中国科学院森林生态与管理重点实验室沈阳应用生态研究所;中国科学院森林生态与管理重点实验室沈阳应用生态研究所,森林植物生态学教育部重点实验室,森林植物生态学教育部重点实验室,森林植物生态学教育部重点实验室,黑龙江省密山市第一中学,森林植物生态学教育部重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31500361，31700397，31270494）；博士研究生自主创新基金（2572017AA21） Fine root decomposition and N dynamics of Larix gmelinii at different soil depths Author: Affiliation: Northeast Forestry University,Harbin,Maoershan Experimental Forest Farm of Northeast Forestry University,Shangzhi,Shenyang Institute of Applied Ecology,Chinese Academy of Sciences,Shenyang,Shenyang Institute of Applied Ecology,Chinese Academy of Sciences,Shenyang,Northeast Forestry University,Harbin,Northeast Forestry University,Harbin,Northeast Forestry University,Harbin,,Northeast Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:细根分解受根序和土壤深度的潜在影响。使用根序法分根，将落叶松Larix gmelini根系分为两类：一级根、二级根为一类（1-2级根），即低级根；三级根和四级跟为另一类（3-4级根），即高级根。采用埋袋法对落叶松低级根和高级根在不同土壤深度（0-10 、10-20 cm和20-30 cm）进行了为期862 d的分解实验，探讨不同根序细根分解规律，养分释放及其影响。结果表明：1-2级根的分解速率比3-4级分解速率慢，这种规律同时存在于不同深度的土壤中。在空间上，低级根和高级根的分解速率均随土壤深度的增加而降低，高级根的降低趋势更明显。随着分解时间的进行，各个土层之间的分解率在低级根之间差异更大。细根分解过程中，落叶松不同根序养分的释放特征不同。N释放速率总体上随细根根序增加而增大，随土壤深度的增加而降低。 Abstract:Fine root decomposition can be affected by root order and soil depth. Using a branch-order classification, we separated the fine root systems of Larix gmelinii into two classes: first- and second-order roots were combined into one lower order (1-2 order); third- and fourth-order roots were combined into another higher order (3-4 order). Using the litterbag method, we conducted an 862-day decomposition experiment of lower-order and higher-order roots at different depths (0-10, 10-20, and 20-30 cm) to study decomposition and the nutrient dynamics of fine roots among different root branching orders. Our results showed that the decomposition rate of the 1-2 order was slower than that of the 3-4 order, and this pattern also held true at different soil depths. Spatially, the decomposition rate of both lower and higher roots decreased with increasing soil depth, and the decreasing trend in the higher roots was more obvious. With the process of decomposition, there were larger differences in the decomposition rates of each soil layer among the lower-order roots. The patterns of root nutrient release also varied depending on different stages of decomposition. In conclusion, the N release rate generally increased with root order, and decreased with increasing soil depth. 参考文献 相似文献 引证文献

Huanglongbing-induced Anatomical Changes in Citrus Fibrous Root Orders

Citrus fibrous roots are vital for absorption and transport of water, nutrients, and other endogenous plant growth regulators. Efficient functioning of these roots in Huanglongbing (HLB)-affected citrus trees is important for their survival. One-year-old ‘Valencia’ sweet orange (Citrus sinensis L. Osbeck) trees on Swingle citrumelo were budded with HLB-infected budwood to determine the HLB-induced pathological responses at the ultrastructural level of different fibrous root orders. The fibrous root mass was dissected into four root orders: fourth-order (attached to a thick rudimentary taproot), third-order (attached to the fourth-order root), and second-order roots (attached to the third-order root). We were not able to study the ultrastructure of the first-order (attached to the second-order root) roots in this study. Severe loss in fibrous root mass was observed within 1 year following HLB infection. All root orders displayed various degrees of HLB symptoms. The fourth-order roots comprised normal phloem and disintegrated phloem. Some vascular bundles had completely disintegrated phloem tissue, whereas others showed normal ultrastructure. The fourth-order roots were also deficient in starch granules compared with controls. The pattern of phloem disintegration was similar in the third- and second-order roots. A thick layer of necrotic phloem developed near cortical cells, while the rest of the phloem structure remained normal in the third- and second-order roots. Cortical cells of both third and second orders were enriched with starch granules; therefore, soluble carbohydrates are most likely not the limiting factor for root decline in these root orders. The xylem anatomy displayed heptarch to pentarch morphology in the various root orders. These observations confirmed that various root orders in the fibrous root system are distinct and exhibit varied pathological responses during HLB pathogenesis. We propose that photosynthates deprived fourth-order roots in conjunction with necrotic phloem promoted decline in all root orders and impaired the translocation process to aboveground plant parts.

短期氮磷配施对刨花楠细根形态及其土壤微生物的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 短期氮磷配施对刨花楠细根形态及其土壤微生物的影响 DOI: 10.5846/stxb201704240735 作者: 作者单位: 福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31170596，31170374，31370589）；福建省种业创新和产业化工程项目（2014S1477-4）；福建省科技厅重大项目（2014N5008） Effect of adding a combination of nitrogen and phosphorus on fine root morphology and soil microbes of Machilus pauhoi seedling Author: Affiliation: School of Geographical Science, Fujian Normal University,School of Geographical Science, Fujian Normal University,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以1年生刨花楠幼苗为研究对象，通过不同的氮磷配施实验，采用扫描根系法和磷脂脂肪酸法，研究不同氮磷配施处理对刨花楠幼苗1-4级细根根序形态特征及其土壤微生物的影响。结果表明：（1）4种氮磷配施处理均显著增加了刨花楠1-2级根的比根长和比根面积（P < 0.05），降低了3-4级根的比根面积（P < 0.05）；（2）通过不同梯度的氮磷配施，1-2级细根的根组织密度呈下降态势，而3-4级根的组织密度则显著增加（P < 0.05），体现低级根与高级根之间的权衡；（3）4种氮磷配施处理都显著降低刨花楠1-4级细根的平均直径（P < 0.05）；（4）随着氮磷比的增加，微生物总量及细菌、真菌与放线菌数量等均呈现先增加后降低的趋势，并均在N：P为10：1时达到最大；（5）氮磷配施条件下，细菌、真菌等与1-2级细根的比根长和比根面积呈显著正相关，而与4级根的比根长和比根面积则呈显著负相关，革兰氏阳性菌、真菌等与3-4级根的组织密度存在显著正相关，而与1-2级根的组织密度无显著相关性。各级根序的平均直径均与土壤微生物无显著相关性。研究结果表明，短期氮磷配施以N：P为10：1的效果最好，其最有利于提高刨花楠苗木细根的养分吸收能力与养分吸收效率，苗木通过调整细根形态来适应氮沉降，其地下生物群落如土壤微生物及其与细根的关系也发生变化，进而影响地下生态系统碳氮循环和养分流动。 Abstract:One-year old seedlings of Machilus pauhoi were used to determine the effect of adding a combination of N and P on the morphology of different orders of fine roots and soil microbes. For this, the phospholipid fatty acid (PLFA) analysis and root system scanning methods were used. The results were as follows:(1) Combined addition of N and P significantly improved (P < 0.05) specific root length and specific root area of the first-order and second-order fine roots, while it reduced specific root area of the third-order and fourth-order roots. (2) Root tissue density for the first-order and second-order fine roots tended to decline, contrary to that for the third-order and fourth-order. (3) Root average diameter of the first-order to the fourth-order roots was significantly reduced (P < 0.05). (4) Total microbial, fungal, and bacterial biomass all showed a tendency to reduce after first increasing, all reaching the maximum when treated with N:P in the ratio of 10:1. (5) Although the bacterial and fungal and actinomycetes biomass and total microbial were significantly and positively correlated with specific root length and specific root area for the first-and second-order roots, they were negatively correlated for the fourth-order roots. Although Gram-positive bacteria and fungal biomass were positive correlated with root tissue density for the third-order and the fourth-order, no significant correlations with the first-and second-order roots were observed. Root average diameter for all orders had no significant correlation with soil microbes. Our results suggest that the effect of short-term addition of a combination of N and P was the best when treated with N:P in the ratio of 10:1, which can improve the efficiency of nutrient uptake of Machilus pauhoi seedlings' fine roots. Plants may adapt to N deposition by adjusting the fine root morphological characteristics. Meanwhile, the response of underground biological communities such as soil microbes, and the relationship of microbes with fine roots, to N deposition also changes, which affects C and N cycles and the nutrient flow in underground ecosystem. 参考文献 相似文献 引证文献

Intraspecific variation in morphological traits of root branch orders in Chamaecyparis obtusa

We aimed to clarify the intraspecific variation in the morphological traits of branch orders under different soil conditions in Chamaecyparis obtusa (Siebold & Zucc.) Endl. We investigated the morphological traits of branch orders, based on 16,351 individual roots that were dissected from 12 intact fine root systems, up to a diameter of 2 mm at three C. obtusa stands. We also measured the concentrations of soil carbon, nitrogen, and inorganic nitrogen. The intact fine root systems up to the diameter of 2 mm had branched into between five and seven orders. The diameter of first- to fourth-order roots and the lengths of second- and third-order roots were significantly different among the three stands. The morphological traits of lower order (first to third) roots correlated with soil inorganic nitrogen concentrations, but higher order (fourth to sixth) roots correlated with soil carbon concentrations. We clarified the possible ranges of intraspecific variation in the morphological traits of root branch orders within C. obtusa. Both the lower and higher orders of the intact fine root systems were tightly related to the surrounding soil conditions.

On the denesting of nested square roots

ABSTRACTWe present the basic theory of denesting nested square roots, from an elementary point of view, suitable for lower level coursework. Necessary and sufficient conditions are given for direct denesting, where the nested expression is rewritten as a sum of square roots of rational numbers, and for indirect denesting, where the nested expression is rewritten as a sum of fourth-order roots of rational numbers. The theory is illustrated with several solved examples.

Early Stage Fine-Root Decomposition and Its Relationship with Root Order and Soil Depth in a Larix gmelinii Plantation

Characterization of decomposition dynamics of fine roots is essential for understanding vegetation–soil feedbacks and predicting ecosystem responses to future climate scenarios, given their more rapid turnover rates. Using a branch-order classification, we separated the fine root systems of Larix gmelinii into two classes: first- and second-order roots combined into one (lower-order); third- and fourth-order roots combined into another (higher-order). In a field experiment, we conducted a litterbag study to investigate fine root decomposition and its relationship with root order class and soil depth over 17 months. Despite their lower C:N ratio and smaller diameter, lower-order roots decomposed more slowly compared with higher-order roots over this period. This pattern also seems to hold true at each different depths (10, 20 and 30 cm) in the soil profile. Our data suggest that the slow decomposition rate of lower-order roots may result from their poor carbon quality. Moreover, we found that the decomposition rates of both lower-order and higher-order roots decreased linearly from 10 cm to 30 cm, which implied that a substantially larger fraction of fine root mass would be stabilized as soil organic carbon in the deeper rather than the upper soil layers.

Fine roots – functional definition expanded to crop species?

Fine roots – functional definition expanded to crop species?

Is root nutrient uptake a modular function? A test using Solidago canadensis

Plant roots have been recognized to be modular, and a third order root cluster has been proposed to be the basic root module unit based upon the life cycle. This experiment examines root modularity of the nutrient-uptake function using stable isotope 15N. Solidago canadensis root clusters of second or third orders—from the same third or fourth order roots, respectively—were treated with 15NH415NO3, NH4NO3, and de-ionized water for 15 and 180 min. The δ15N values of the root clusters were then analyzed and compared. The δ15N values of 15N-treated root clusters of both second and third orders were hundreds of times higher than that of the 15N untreated root clusters. However, the differences of the δ15N values among 15N untreated root clusters (though expressed some significant variations), did not indicate the 15N shared by the sister root clusters came from a common higher-order root. These results demonstrated functional modularity of root nutrient uptake, revealed a second order root, perhaps even a first order root to be a base module unit in terms of root nutrient uptake. The results also suggested that the concept of root modularity is function-specific. This experiment further revealed the importance of treatment timing in stabilizing the internal 15N/14N ratio in roots and avoiding top-down transportation of 15N back into roots to secure unbiased measurements.

Simulated Atmospheric Nitrogen Deposition Alters Decomposition of Ephemeral Roots

Roots concentrated on the smallest distal branching orders have short life spans and thus dominate root mortality, and may contribute predominately to plant carbon and nutrient transfer into soil. Yet the effects of nitrogen (N) enrichment on decomposition of the finest root branching orders have not yet been examined. Resolving such N effects is critical for predicting the ecosystem consequences of increased anthropogenic N deposition. The first four root orders were separated into two classes: first- and second-order roots; third- and fourth-order roots. We studied the effects of N addition on decomposition of different root order classes in four temperate tree species over 4 years. Asymptotic decay models best fit the decomposition and allowed us to examine effects of N on initial versus later stages of decomposition separately. Very early in decomposition, N fertilization stimulated decomposition rates in higher-order roots, but had no effects on initial rates of decomposition in lower-order roots. In contrast, later in decomposition, N fertilization inhibited decomposition, ultimately resulting in a larger, slowly decomposing fraction in both lower-order and higher-order roots. Inhibitory effects of N addition on lignin-degrading enzyme activity might be an important mechanism explaining the negative effects of N on decomposition here. This study highlights the importance of long-term studies for understanding N effects on decomposition, and suggests that contrasting effects of N on different decomposition processes and carbon pools should be widely considered in biogeochemical models. Furthermore, the inhibitory effects of elevated atmospheric N deposition on decomposition of lower-order roots suggest that these roots may provide a critical mechanism of carbon and nutrient retention in soil because of their rapid input via root mortality.

Optimal root system strategies for desert phreatophytic seedlings in the search for groundwater

Desert phreatophytes are greatly dependent on groundwater, but how their root systems adapt to dif- ferent groundwater depths is poorly understood. In the present study, shoot and root growths of Alhagi sparsifolia Shap. seedlings were studied across a gradient of groundwater depths. Leaves, stems and roots of different orders were measured after 120 days of different groundwater treatments. Results indicated that the depth of soil wetting front and the vertical distribution of soil water contents were highly controlled by groundwater depths. The shoot growth and biomass of A. sparsifolia decreased, but the root growth and rooting depth increased under deeper groundwater conditions. The higher ratios of root biomass, root/shoot and root length/leaf area under deeper groundwater conditions implied that seedlings of A. sparsifolia economized carbon cost on their shoot growths. The roots of A. sparsifolia distributed evenly around the soil wetting fronts under deeper groundwater conditions. Root diameters and root lengths of all orders were correlated with soil water availabilities both within and among treat- ments. Seedlings of A. sparsifolia produced finer first- and second-order roots but larger third- and fourth-order roots in dry soils. The results demonstrated that the root systems of desert phreatophytes can be optimized to acquire groundwater resources and maximize seedling growth by balancing the costs of carbon gain.

Variation of the linkage of root function with root branch order.

Mounting evidence has shown strong linkage of root function with root branch order. However, it is not known whether this linkage is consistent in different species. Here, root anatomic traits of the first five branch order were examined in five species differing in plant phylogeny and growth form in tropical and subtropical forests of south China. In Paramichelia baillonii, one tree species in Magnoliaceae, the intact cortex as well as mycorrhizal colonization existed even in the fifth-order root suggesting the preservation of absorption function in the higher-order roots. In contrast, dramatic decreases of cortex thickness and mycorrhizal colonization were observed from lower- to higher-order roots in three other tree species, Cunninghamia lanceolata, Acacia auriculiformis and Gordonia axillaries, which indicate the loss of absorption function. In a fern, Dicranopteris dichotoma, there were several cortex layers with prominently thickened cell wall and no mycorrhizal colonization in the third- and fourth-order roots, also demonstrating the loss of absorptive function in higher-order roots. Cluster analysis using these anatomic traits showed a different classification of root branch order in P. baillonii from other four species. As for the conduit diameter-density relationship in higher-order roots, the mechanism underpinning this relationship in P. baillonii was different from that in other species. In lower-order roots, different patterns of coefficient of variance for conduit diameter and density provided further evidence for the two types of linkage of root function with root branch order. These linkages corresponding to two types of ephemeral root modules have important implication in the prediction of terrestrial carbon cycling, although we caution that this study was pseudo-replicated. Future studies by sampling more species can test the generality of these two types of linkage.

Decomposition of the finest root branching orders: linking belowground dynamics to fine-root function and structure

Root turnover is fastest in the finest roots of the root system (first root order). Additionally, tissue chemistry varies among even the finest root orders and between white roots and older, pigmented roots. Yet the effects of pigmentation and order on root decomposition have rarely been examined. We separated the first four root orders (all <1 mm) of four temperate tree species into three classes: white first- and second-order roots; pigmented first- and second-order roots; and pigmented third- and fourth-order roots. Roots were enclosed in litterbags and buried under their own and under a common species canopy in a 34-year-old common garden in Poland. When comparing decomposition of different root orders over 36 months, pigmented third- and fourth-order roots with a higher C:N ratio decomposed more rapidly, losing 20–40% of their mass, than pigmented first- and second-order roots, which lost no more than 20%. When comparing decomposition of roots of different levels of pigmentation within the same root order over 14 months, pigmented (older) first- and second-order roots lost ∼10% of their mass, while white (younger) first- and second-order roots lost ∼30%. In contrast to root mass loss, root N content declined more rapidly in the first- and second-order roots than in third- and fourth-order roots. In higher-order roots, N increased in the first 10 months from ∼110% to nearly 150% of initial N content, depending on species; by the end of the study N content had returned to initial levels. These findings suggest that, in plant communities where root mortality is primarily of pigmented first- and second-order roots, microbial decomposition may be slower than estimates derived from bulk fine-root litterbag experiments, which typically contain at least four root orders. Thus, a more mechanistic understanding of root decomposition and its contribution to ecosystem carbon and nutrient dynamics requires a fundamental shift in experimental methods that stratifies root samples for decomposition along more functionally based criteria such as root order and pigmentation, which parallel the markedly different longevities of these different root classes.

Tree species fine‐root demography parallels habitat specialization across a sandhill soil resource gradient

Single species can substantially alter belowground processes in ecosystems via differential root production and death. However, information on species differences in fine-root demography is virtually absent for natural communities. In this field study, we recorded species-specific fine-root (<2 mm in diameter) demography in adults of four tree species (Pinus palustris, Quercus laevis, Q. incana, and Q. margaretta) that are distributed differentially along soil resource gradients in the fall-line sandhills of the southeastern United States. At a subxeric habitat where all four species co-occur, roots of individual trees of each species were isolated in rhizotrons and tracked individually for three years. Quercus species had similar fine-root morphology but differed substantially for fine-root demography and architecture. Quercus laevis and Q. incana, the species from xeric habitats, showed lower fine-root production, death, percentage mortality, turnover rates, and risk of death, and greater life span and mean root segment length (MRSL) than Q. margaretta, the species from subxeric habitats. Fine roots of P. palustris (a generalist) showed high production and intermediate mortality, turnover rate, longevity, and MRSL. Fine-root survival increased with root order (first to fourth in centripetal order), but the degree of change was species specific. Q. margaretta showed greater increases in survival with order, but all species had similar demography of third- and fourth-order roots. Mycorrhizal roots had greater longevity than non-mycorrhizal roots only in Q. laevis. Species differences were also seasonal. Although these Quercus species are leaf deciduous, some growth of fine roots occurred in Q. margaretta during the "leaf-dormant" season. In our narrow-scale species comparison, species differences in ecological distribution were consistent with the observed variation in fine-root demography and architecture with greater resolution than leaf characters or other root traits such as morphology. Our results also show that narrow-scale variation in fine-root demography (including intra-generic differences) can be as large as broad-scale variation across biomes and vegetation types. Hence, small shifts in community composition have the potential to produce substantial changes below ground.

ANATOMICAL AND FUNCTIONAL HETEROGENEITY AMONG DIFFERENT ROOT ORDERS OF PHELLODENDRON AMURENSE

Aims Fine roots are the primary organs for nutrient and water uptake in trees. The growth and turnover of fine roots significantly influence productivity and matter cycles in forest ecosystems. Our objective was to elucidate the basic structure, function and allocation of fine roots in Phellodendron amurense. Methods We made paraffin slices stained by safranin and fast green to observe anatomical structures (such as diameter, cortex, number of passage cells, development of vascular bundle, mycorrhizae of roots, etc.) of the first five orders of roots of P. amurense. Bright-light and fluorescence microscopes were used to observe and take photos. Important findings Root diameter (R), vascular bundle diameter (V) and V/R increased as root order increased. The thickness and layers of cortex were similar in the first three orders. Few cortical cells were in fourth-order roots and almost none in fifth-order roots. There were higher mycorrhizae infections in the first three order roots than the last two orders, and the later had almost no fungi. Primary growth occurred in all first-and second-order roots, an secondary growth occurred in all fourth and fifth order roots. Some third-order roots had only primary growth, but some had secondary growth with inconsecutive phellogen. All results suggested that the ability of roots to absorb nutrients and water decreased but transport ability and longevity increased as root orders increased. According to the relation- ships among anatomical characteristics, diameters and root orders, the fine roots of P. amurense should be involved in the first three orders at most; these have passage cells but lack successive phellogen and have diameters less than 0.8 mm.

CONTRIBUIÇÃO AO CONHECIMENTO DO SISTEMA RADICULAR DA PUPUNHEIRA (Bactris gasipaes KUNTH, PALMAE). II. SOLO LATOSSOLO AMARELO, TEXTURA ARGILOSA

A distribuição da biomassa e da área absorvente do sistema radicular da pupunheira (Bactris gasipaes)foram estudadas num latossolo amarelo, textura argilosa, perto de Manaus, Amazonas, Brasil. Aproximadamente 80% da biomassa se encontrava no horizonte Ap, da qual 90% se encontrava dentro da área de projeção da copa. A biomassa total estimada pesou 72 kg, excluindo-se a massa logo abaixo do estipe. A área superficial das raízes aumentou significativamente conforme se afastava do estipe, devido a proporção cada vez maior de raízes terciárias e quartenárias, embora sua abundância por m3 diminuiu de forma similar à biomassa. A área superficial total estimada chegou a 545 m2, da qual se supõe que 50% é ativa na absorção de nutrientes. Supõe-se ainda que existam raízes absorventes até 8-9 m do estipe das plantas. Recomenda-se que a adubação seja feita dentro e logo fora da projeção da copa.