Phylogenetic variation in the shoot mineral concentration of angiosperms

The calcium (Ca) concentration of plant shoot tissues varies systematically between angiosperm orders. The phylogenetic variation in the shoot concentration of other mineral nutrients has not yet been described at an ordinal level. The aims of this study were (1) to quantify the shoot mineral concentration of different angiosperm orders, (2) to partition the phylogenetic variation in shoot mineral concentration between and within orders, (3) to determine if the shoot concentration of different minerals are correlated across angiosperm species, and (4) to compare experimental data with published ecological survey data on 81 species sampled from their natural habitats. Species, selected pro rata from different angiosperm orders, were grown in a hydroponic system under a constant external nutrient regime. Shoots of 117 species were sampled during vegetative growth. Significant variation in shoot carbon (C), calcium (Ca), potassium (K), and magnesium (Mg) concentration occurred between angiosperm orders. There was no evidence for systematic differences in shoot phosphorus (P) or organic-nitrogen (N) concentration between orders. At a species level, there were strong positive correlations between shoot Ca and Mg concentration, between shoot P and organic-N concentration, and between shoot K concentration and shoot fresh weight:dry weight ratio. Shoot C and cation concentration correlated negatively at a species level. Species within the Poales and the Caryophyllales had distinct shoot mineralogies in both the designed experiment and in the ecological survey.     

Phylogenetic variation in the silicon composition of plants

BACKGROUND AND AIMS: Silicon (Si) in plants provides structural support and improves tolerance to diseases, drought and metal toxicity. Shoot Si concentrations are generally considered to be greater in monocotyledonous than in non-monocot plant species. The phylogenetic variation in the shoot Si concentration of plants reported in the primary literature has been quantified. METHODS: Studies were identified which reported Si concentrations in leaf or non-woody shoot tissues from at least two plant species growing in the same environment. Each study contained at least one species in common with another study. KEY RESULTS: Meta-analysis of the data revealed that, in general, ferns, gymnosperms and angiosperms accumulated less Si in their shoots than non-vascular plant species and horsetails. Within angiosperms and ferns, differences in shoot Si concentration between species grouped by their higher-level phylogenetic position were identified. Within the angiosperms, species from the commelinoid monocot orders Poales and Arecales accumulated substantially more Si in their shoots than species from other monocot clades. CONCLUSIONS: A high shoot Si concentration is not a general feature of monocot species. Information on the phylogenetic variation in shoot Si concentration may provide useful palaeoecological and archaeological information, and inform studies of the biogeochemical cycling of Si and those of the molecular genetics of Si uptake and transport in plants.     

The relationship between nuclear DNA content and leaf strategy in seed plants

BACKGROUND AND AIMS: Species' 2C-values (mass of DNA in G(1) phase 2n nuclei) vary by at least four orders of magnitude among seed plants. The 2C-value has been shown to be co-ordinated with a number of other species traits, and with environmental variables. A prediction that species 2C-values are negatively related to leaf life span (LL) and leaf mass per area (LMA) is tested. These leaf traits are components of a major dimension of ecological variation among plant species. METHODS: Flow cytometry was used to measure the 2C-values for 41 Australian seed plant species, 40 of which were new to the literature. Where possible, LL and LMA data from the global literature were combined with 2C-values from our data set and online C-value databases. KEY RESULTS: Across all species, weak positive relationships were found between 2C-values and both LL and LMA; however, these did not reflect the relationships within either angiosperms or gymnosperms. Across 59 angiosperm species, there were weak negative relationships between 2C-values and both LL (r2 = 0.13, P = 0.005) and LMA (r2 = 0.15, P = 0.002). These relationships were the result of shifts to longer LL and greater LMA in woody compared with herbaceous growth forms, with no relationships present within growth forms. It was not possible to explain a positive relationship between 2C-values and LMA (r2 = 0.30, P = 0.024) across 17 gymnosperm species. The 2C-value was not related to LL or LMA either across species within orders (except for LMA among Pinales), or as radiation divergences in a model phylogeny. CONCLUSIONS: Gymnosperms appear to vary along a spectrum different from angiosperms. Among angiosperms, weak negative cross-species relationships were associated with growth form differences, and traced to a few divergences deep in the model phylogeny. These results suggest that among angiosperms, nuclear DNA content and leaf strategy are unrelated.     

Phyletic hot spots for B chromosomes in angiosperms

We determined whether supernumerary B chromosomes were nonrandomly distributed among major angiosperm lineages and among lineages within families, as well as the identity of lineages with unusually high B-chromosome frequencies (hot spots). The incidence of B chromosomes for each taxon was gathered from databases showing species with and without these chromosomes (among species with known chromosome numbers). Heterogeneity was found at all ranks above the species level. About 8% of monocots had B chromosomes versus 3% for eudicots; they were rare in nonmonocot basal angiosperms. Significant heterogeneity in B-chromosome frequency occurred among related orders, families within orders, and major taxa within families. There were many B-chromosome hot spots, including Liliales and Commelinales at the order level. At the family level, there was a trend suggesting that B-chromosome frequencies are positively correlated with genome size.     

Physiological mechanisms drive differing foliar calcium content in ferns and angiosperms

Recent evidence points to ferns containing significantly lower contents of foliar calcium and other cations than angiosperms. This is especially true of more ancient ‘non-polypod’ fern lineages, which predate the diversification of angiosperms. Calcium is an important plant nutrient, the lack of which can potentially slow plant growth and litter decomposition, and alter soil invertebrate communities. The physiological mechanisms limiting foliar calcium (Ca) content in ferns are unknown. While there is a lot we do not know about Ca uptake and transport in plants, three physiological processes are likely to be important. We measured transpiration rate, cation exchange capacity, and leaching loss to determine which process most strongly regulates foliar Ca content in a range of fern and co-occurring understory angiosperm species from a montane Hawaiian rainforest. We found higher instantaneous and lifetime (corrected for leaf lifespan) transpiration rates in angiosperms relative to ferns. Ferns preferentially incorporated Ca into leaves relative to strontium, which suggests that root or stem cation exchange capacity differs between ferns and angiosperms, potentially affecting calcium transport in plants. There were no differences in foliar Ca leaching loss between groups. Among the physiological mechanisms measured, foliar Ca was most strongly correlated with leaf-level transpiration rate and leaf lifespan. This suggests that inter-specific differences in a leaf’s lifetime transpiration may play a significant role in determining plant nutrition.     

Variation in nuclear DNA content across environmental gradients: a quantile regression analysis

The nuclear DNA content of angiosperms varies by several orders of magnitude. Previous studies suggest that variation in 2C DNA content (i.e. the amount of DNA in G1 phase nuclei, also referred to as the 2C-value) is correlated with environmental factors, but there are conflicting reports in the literature concerning the nature of these relationships. We examined variation in 2C DNA content for 401 species in the ecologically diverse California flora in relation to the mean July maximum temperature, January minimum temperature, and annual precipitation within the geographical ranges of these species. Species with small 2C-values predominate in all environments. Species with large 2C-values occur at intermediate July maximum temperatures, and decline in frequency at both extremes of the July temperature gradient, and with decreasing annual precipitation. Our analysis demonstrates the utility of quantile regression for statistical inference of complex distributions such as these. The method supports our observation that relationships between nuclear DNA content and environmental factors are stronger for species with large 2C-values.     

Testing the distinctness of shoot ionomes of angiosperm families using the Rothamsted Park Grass Continuous Hay Experiment

? The ionome is the elemental composition of a tissue or organism. Phylogenetic variation in the ionomes of plant shoots has been widely reported based on controlled experiments, vegetation surveys and literature meta-analyses. However, environmental effects on phylogenetic variation in shoot ionomes have not been quantified. This study tests the hypothesis that phylogenetic variation in shoot ionomes is robust to environmental perturbation and that plant families can be distinguished by their shoot ionomes. ? Herbage was sampled from six subplots of the Rothamsted Park Grass Experiment. Subplots had received contrasting fertilizer treatments since 1856. Herbage was separated into its constituent species (n?=?21) and concentrations of eleven mineral elements were determined in dried shoot material. ? Shoot concentrations of calcium (Ca), zinc (Zn), manganese (Mn), magnesium (Mg) and sodium (Na) showed significant variation associated with plant species, and responded similarly to fertilizer treatments in diverse plant species. Species?×?treatment interactions were indicated for phosphorus (P), potassium (K), nickel (Ni), copper (Cu) and iron (Fe). Plant families could be distinguished by their shoot ionomes. The most informative elements for discriminant analysis were Ca?>?Mg?>?Ni?>?S?>?Na?>?Zn?>?K?>?Cu?>?Fe?>?Mn?>?P. ? Whilst shoot ionomes were sensitive to fertilizer treatment, phylogenetic variation in a subset of the shoot ionome (Ca, Zn, Mn, Mg) was robust to this environmental perturbation.     

Natural quantitative genetic variance in plant growth differs in response to ecologically relevant temperature heterogeneity

Adaptation to large‐scale spatial heterogeneity in the environment accounts for a major proportion of genetic diversity within species. Theory predicts the erosion of adaptive genetic variation on a within‐population level, but considerable genetic diversity is often found locally. Genetic diversity could be expected to be maintained within populations in temporally or spatially variable conditions if genotypic rank orders vary across contrasting microenvironmental settings. Taking advantage of fine‐resolution environmental data, we tested the hypothesis that temperature heterogeneity among years could be one factor maintaining quantitative genetic diversity within a natural and genetically diverse plant population. We sampled maternal families of Boechera stricta, an Arabidopsis thaliana relative, at one location in the central Rocky Mountains and grew them in three treatments that, based on records from an adjacent weather station, simulated hourly temperature changes at the native site during three summers with differing mean temperatures. Treatment had a significant effect on all traits, with 2–3‐fold increase in above‐ and belowground biomass and the highest allocation to roots observed in the treatment simulating the warmest summer on record at the site. Treatment affected bivariate associations between traits, with the weakest correlation between above‐ and belowground biomass in the warmest treatment. The magnitude of quantitative genetic variation for all traits differed across treatments: Genetic variance of biomass was 0 in the warmest treatment, while highly significant diversity was found in average conditions, resulting in broad‐sense heritability of 0.31. Significant genotype × environment interactions across all treatments were found only in root‐to‐shoot ratio. Therefore, temperature variation among summers appears unlikely to account for the observed levels of local genetic variation in size in this perennial species, but may influence family rank order in growth allocation. Our results indicate that natural environmental fluctuations can have a large impact on the magnitude of within‐population quantitative genetic variance.     

Shoot calcium and magnesium concentrations differ between subtaxa, are highly heritable, and associate with potentially pleiotropic loci in Brassica oleracea

Calcium (Ca) and magnesium (Mg) are the most abundant group II elements in both plants and animals. Genetic variation in shoot Ca and shoot Mg concentration (shoot Ca and Mg) in plants can be exploited to biofortify food crops and thereby increase dietary Ca and Mg intake for humans and livestock. We present a comprehensive analysis of within-species genetic variation for shoot Ca and Mg, demonstrating that shoot mineral concentration differs significantly between subtaxa (varietas). We established a structured diversity foundation set of 376 accessions to capture a high proportion of species-wide allelic diversity within domesticated Brassica oleracea, including representation of wild relatives (C genome, 1n = 9) from natural populations. These accessions and 74 modern F(1) hybrid cultivars were grown in glasshouse and field environments. Shoot Ca and Mg varied 2- and 2.3-fold, respectively, and was typically not inversely correlated with shoot biomass, within most subtaxa. The closely related capitata (cabbage) and sabauda (Savoy cabbage) subtaxa consistently had the highest mean shoot Ca and Mg. Shoot Ca and Mg in glasshouse-grown plants was highly correlated with data from the field. To understand and dissect the genetic basis of variation in shoot Ca and Mg, we studied homozygous lines from a segregating B. oleracea mapping population. Shoot Ca and Mg was highly heritable (up to 40%). Quantitative trait loci (QTL) for shoot Ca and Mg were detected on chromosomes C2, C6, C7, C8, and, in particular, C9, where QTL accounted for 14% to 55% of the total genetic variance. The presence of QTL on C9 was substantiated by scoring recurrent backcross substitution lines, derived from the same parents. This also greatly increased the map resolution, with strong evidence that a 4-cM region on C9 influences shoot Ca. This region corresponds to a 0.41-Mb region on Arabidopsis (Arabidopsis thaliana) chromosome 5 that includes 106 genes. There is also evidence that pleiotropic loci on C8 and C9 affect shoot Ca and Mg. Map-based cloning of these loci will reveal how shoot-level phenotypes relate to Ca(2+) and Mg(2+) uptake and homeostasis at the molecular level.     

Which factors contribute most to genome size variation within angiosperms?

Genome size varies greatly across the flowering plants and has played an important role in shaping their evolution. It has been reported that many factors correlate with the variation in genome size, but few studies have systematically explored this at the genomic level. Here, we scan genomic information for 74 species from 74 families in 38 orders covering the major groups of angiosperms (the taxonomic information was acquired from the latest Angiosperm Phylogeny Group (APG IV) system) to evaluate the correlation between genome size variation and different genome characteristics: polyploidization, different types of repeat sequence content, and the dynamics of long terminal repeat retrotransposons (LTRs). Surprisingly, we found that polyploidization shows no significant correlation with genome size, while LTR content demonstrates a significantly positive correlation. This may be due to genome instability after polyploidization, and since LTRs occupy most of the genome content, it may directly result in most of the genome variation. We found that the LTR insertion time is significantly negatively correlated with genome size, which may reflect the competition between insertion and deletion of LTRs in each genome, and that the old insertions are usually easy to recognize and eliminate. We also noticed that most of the LTR burst occurred within the last 3 million years, a timeframe consistent with the violent climate fluctuations in the Pleistocene. Our findings enhance our understanding of genome size evolution within angiosperms, and our methods offer immediate implications for corresponding research in other datasets.     

The leaf size/number trade-off in herbaceous angiosperms

Aims In this study, we examined the extent to which between-species leaf size variation relates to variation in the intensity of leaf production in herbaceous angiosperms. Leaf size variation has been most commonly interpreted in terms of biomechanical constraints (e.g. affected by plant size limitations) or in terms of direct adaptation associated with leaf size effects in optimizing important physiological functions of individual leaves along environmental gradients (e.g. involving temperature and moisture). An additional interpretation is explored here, where adaptation may be more directly associated with the number of leaves produced and where relatively small leaf size then results as a trade-off of high 'leafing intensity'—i.e. number of leaves produced per unit plant body size.Methods The relationships between mean individual leaf mass, number of leaves and plant body size were examined for 127 species of herbaceous angiosperms collected from natural populations in southern Ontario, Canada.Important findings In all, 88% of the variation in mean individual leaf mass across species, spanning four orders of magnitude, is accounted for by a negative isometric (proportional) trade-off relationship with leafing intensity. These results parallel those reported in recent studies of woody species. Because each leaf is normally associated with an axillary bud or meristem, having a high leafing intensity is equivalent to having a greater number of meristems per unit body size—i.e. a larger 'bud bank'. According to the 'leafing intensity premium' hypothesis, because an axillary meristem represents the potential to produce either a new shoot or a reproductive structure, high leafing intensity should confer greater architectural and/or reproductive plasticity (with relatively small leaf size required as a trade-off). This greater plasticity, we suggest, should be especially important for smaller species since they are likely to suffer greater suppression of growth and reproduction from competition within multi-species vegetation. Accordingly, we tested and found support for the prediction that smaller species have not just smaller leaves generally but also higher leafing intensities, thus conferring larger bud banks, i.e. more meristems per unit plant body size.     

Macroecological explanations for differences in species richness gradients: a canonical analysis of South American birds

Aim To evaluate how spatial variation of species richness in different bird orders responds to environmental gradients and determine which order level trait best predicts these relationships. Location South America. Methods A canonical correlation analysis was performed between the species richness in each of 17 bird orders and eight environmental variables in 374, 220 × 220 km cells. Loadings associated with the first two canonical variables were regressed against six order‐level predictors, including diversification level (number of species in each order), body size, median geographical range size and characteristics included in the model to control Type I error rates (the phylogenetic relationship among orders and levels of local‐scale spatial autocorrelation). Results Richness patterns of 14 bird orders were highly correlated with the first canonical axis, indicating that most orders respond similarly to energy‐water gradients (primarily actual evapotranspiration, minimum temperature and potential evapotranspiration). In contrast, species richness within Trochiliformes, Apodiformes and Galliformes were also correlated with the second canonical variable, representing measures of mesoscale climatic variation (range in elevation within cells, minimum temperature, and the interaction term between them) and landcover (habitat diversity). We also found that total diversification within orders was the best predictor of the loadings associated with the first canonical axis, whereas body size of each order best predicted loadings on the second axis. Conclusion Our results broadly support climatic‐related hypotheses as explanations for spatial variation in species richness of different orders. However, both historical (order‐specific variation in speciation rates) and ecological (dispersal of species that evolved by independent processes into areas amenable to birds) processes can explain the relationship between order level traits, such as body size and diversification level, and magnitude of response to current environment, furnishing then guidelines for a further and deeper understanding of broad‐scale diversity gradients.     

Sexual size dimorphism within species increases with body size in insects

Studies examining interspecific differences in sexual size dimorphism (SSD) typically assume that the degree of sexual differences in body size is invariable within species. This work was conducted to assess validity of this assumption. As a result of a systematic literature survey, datasets for 158 insect species were retrieved. Each dataset contained adult or pupal weights of males and females for two or more different subsets, typically originating from different conditions during immature development. For each species, an analysis was conducted to examine dependence of SSD on body size, the latter variable being used as a proxy of environmental quality. A considerable variation in SSD was revealed at the intraspecific level in insects. The results suggest that environmental conditions may strongly affect the degree, though not the direction of SSD within species. In most species, female size appeared to be more sensitive to environmental conditions than male size: with conditions improving, there was a larger relative increase in female than male size. As a consequence, sexual differences in size were shown to increase with increasing body size in species with female-biased SSD (females were the larger sex in more than 80% of the species examined). The results were consistent across different insect orders and ecological subdivisions. Mechanisms leading to intraspecific variation in SSD are discussed. This study underlines the need to consider intraspecific variation in SSD in comparative studies.     

Decline of charophytes during eutrophication: comparison with angiosperms

1. Charophytes have disappeared from several enriched lakes in Scania (southern Sweden) since the 1940s. Poor light conditions, rather than a toxic effect of phosphorus or negative impact of fish, are the most probable reason for this decline. 2. Small species of charophytes (shoot diameter 0.5–1.0 mm), which are able to form dense, low mats, still occur in eutrophic lakes with high phosphorus concentrations, but are restricted to areas of shallow water. In contrast, large species (shoot diameter 1–4 mm) have totally disappeared from the most turbid lakes. I suggest that these species are unable to grow in very shallow water because of damage by ice and wave action. 3. Maximum depth distribution (z_e) and Secchi depth (D) were measured in Scanian lakes for both charophytes and angiosperms and combined with data obtained from Chambers & Kalff (1985). According to the combined data, z_c and D are closely correlated with each other for both angiosperms and charophytes. 4. The z_c of charophytes is higher than z_c of angiosperms in clear lakes but lower in turbid lakes. Higher z_c of angiosperms in the most turbid lakes is explained by special adaptations of these species to poor light availability (shoot elongation, canopy formation, rapid growth during spring).     

Ovule number per flower in a world of unpredictable pollination

The number of ovules per flower varies over several orders of magnitude among angiosperms. Here we consider evidence that stochastic uncertainty in pollen receipt and ovule fertilization has been a selective factor in the evolution of ovule number per flower. We hypothesize that stochastic variation in floral mating success creates an advantage to producing many ovules per flower because a plant will often gain more fitness from occasional abundant seed production in randomly successful flowers than it loses in resource commitment to less successful flowers. Greater statistical dispersion in pollination and fertilization among flowers increases the frequency of windfall success, which should increase the strength of selection for greater ovule number per flower. We therefore looked for evidence of a positive relationship between ovule number per flower and the statistical dispersion of pollen receipt or seed number per flower in a comparative analysis involving 187 angiosperm species. We found strong evidence of such a relationship. Our results support the hypothesis that unpredictable variation in mating success at the floral level has been a factor in the evolution of ovule packaging in angiosperms.     

Macrophytes of the River Tweed

Summary

An account is given of the 5 lichens, 76 bryophytes, 40 angiosperms and the ‘sewage-fungus’ community recorded from a survey of the River Tweed, Scotland, together with historical and environmental data. For most of its length the river water is relatively soft and low in key nutrients, although phosphate levels in the past were probably higher due to the effluents from wool mills. The presence or absence of each macrophyte was recorded for successive 0.5 km lengths of the river, and histograms are included which summarise the distribution of individual species. In addition, a subjective estimate of the relative abundance within each length was made for each species, and some of these data have been included in an ordination table. Some comparison is also made with data from the literature on rivers in North-east England.     

Life histories of Clethrionomys and Microtus (Microtinae)

Although there have been numerous life-history reviews of mammals at high taxonomic levels (e.g. among families within orders), there are far fewer studies at lower taxonomic levels (e.g. among species within genera). Data on adult weights, litter size, gestation length, neonate weight, age and weight at weaning, growth rate to weaning, maximum life span, and length of the breeding season were compiled from the literature on five species of Clethrionomys and 33 species of Microtus. Variability in litter size and male body weights was not significantly different when compared between cyclic and non-cyclic populations. Coefficients of variation were also calculated for the three species with the most data (C. gapperi, C. glareolus and M. pennsylvanicus ). These values showed that the amount of intraspecific variation differed among traits as well as among species. Gestation length was the most invariable of all traits and variation in adult weights, neonate weight, gestation length, and litter size had similar values to those reported for Peromyscus maniculatus. Five and eight traits differed among Clethrionomys and Microtus species, respectively. Differences in litter size, adult weights and length of the breeding season were common to both genera. Male weight, gestation length and neonate weight as well as length of the breeding season were different between genera. Very few traits covaried within C. gapperi, C. glareolus or M. pennsylvanicus. Similarly, few traits covaried among all Clethrionomys populations. However, among all Microtus populations and Microtus species, 11 and 12 correlations were significant. Many of the patterns found in Microtus involved positive relationships between female weight and some other trait. These patterns have also been found by broader surveys at higher taxonomic levels. Large species of Microtus had larger offspring, a greater litter size and occurred in short-season environments relative to small species of this genus.     

Mineral nutrient economy in competing species of Sphagnum mosses

Bog vegetation, which is dominated by Sphagnum mosses, depends exclusively on aerial deposition of mineral nutrients. We studied how the main mineral nutrients are distributed between intracellular and extracellular exchangeable fractions and along the vertical physiological gradient of shoot age in seven Sphagnum species occupying contrasting bog microhabitats. While the Sphagnum exchangeable cation content decreased generally in the order Ca²⁺ ≥ K⁺, Na⁺, Mg²⁺ > Al³⁺ > NH₄ ⁺, intracellular element content decreased in the order N > K > Na, Mg, P, Ca, Al. Calcium occurred mainly in the exchangeable form while Mg, Na and particularly K, Al and N occurred inside cells. Hummock species with a higher cation exchange capacity (CEC) accumulated more exchangeable Ca²⁺, while the hollow species with a lower CEC accumulated more exchangeable Na⁺, particularly in dead shoot segments. Intracellular N and P, but not metallic elements, were consistently lower in dead shoot segments, indicating the possibility of N and P reutilization from senescing segments. The greatest variation in tissue nutrient content and distribution was between species from contrasting microhabitats. The greatest variation within microhabitats was between the dissimilar species S. angustifolium and S. magellanicum. The latter species had the intracellular N content about 40% lower than other species, including even this species when grown alone. This indicates unequal competition for N, which can lead to outcompeting of S. magellanicum from mixed patches. We assume that efficient cation exchange enables Sphagnum vegetation to retain immediately the cationic nutrients from rainwater. This may represent an important mechanism of temporal extension of mineral nutrient availability to subsequent slow intracellular nutrient uptake.     

小麦地上部和根系生长的相关性及其在耐Al性筛选中的作用

1　引　　言以往的研究中 ,测定植物根系长度或重量通常以相对根长或相对根系干重作为耐性指标进行耐Ａｌ性的筛选[2 ,4 ,5,8] .但是根系性状在土培或田间试验中不仅取样和测定困难 ,而且易造成根系损伤 ,影响测定的精度 .因此 ,有必要建立简便、可靠且易于测定的筛选指标 .能否采用植株地上部耐性指标来衡量不同小麦基因型的耐Ａｌ性 ?以往涉及植物在铝毒胁迫下地上部和根系生长的耐性指标间的相关性 ,以及地上部耐性指标用于耐Ａｌ性筛选方面的研究甚少 .本研究采用两种筛选方法探讨了 2 4个小麦基因型地上部和根系耐性指标间的相关性 ,旨…     

Anatomical traits associated with absorption and mycorrhizal colonization are linked to root branch order in twenty-three Chinese temperate tree species

* Different portions of tree root systems play distinct functional roles, yet precisely how to distinguish roots of different functions within the branching fine-root system is unclear. * Here, anatomy and mycorrhizal colonization was examined by branch order in 23 Chinese temperate tree species of both angiosperms and gymnosperms forming ectomycorrhizal and arbuscular-mycorrhizal associations. * Different branch orders showed marked differences in anatomy. First-order roots exhibited primary development with an intact cortex, a high mycorrhizal colonization rate and a low stele proportion, thus serving absorptive functions. Second and third orders had both primary and secondary development. Fourth and higher orders showed mostly secondary development with no cortex or mycorrhizal colonization, and thus have limited role in absorption. Based on anatomical traits, it was estimated that c. 75% of the fine-root length was absorptive, and 68% was mycorrhizal, averaged across species. * These results showed that: order predicted differences in root anatomy in a relatively consistent manner across species; anatomical traits associated with absorption and mycorrhizal colonization occurred mainly in the first three orders; the single diameter class approach may have overestimated absorptive root length by 25% in temperate forests.