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Fine roots of plants play an important role in terrestrial ecosystems. There is a close association between the anatomical characteristics and physiological and ecological functions of plants, but we still have a very limited knowledge of anatomical traits. For example, (1) we do not know if herbs and grasses have anatomical patterns similar to those of woody plants, and (2) the variation among different woody plants in the same ecosystem is unclear. In the present study, we analysed the anatomical structures of the fine root systems of various groups of vascular plants (ferns, eudicot herbs, monocots and woody plants) from the same ecosystem (a natural secondary forest on Mao'er Mountain, Heilongjiang, China) to answer the following questions: (1) How does the anatomy of the fine roots change with root order in various plant groups in the same ecosystem? (2) What is the pattern of variation within group? The results show that anatomical traits can be divided into 3 categories: traits that indicate the root capacity to transport resource along the root (stele diameter, xylem cell diameter and xylem cell area); traits that indicate absorptive capacity cortical thickness, (the number of cortical cell layers and the diameter of cortical cells); and traits that are integrated indicators (diameter and the stele to root diameter ratio). The traits indicate the root capacity to transport resource along the root order is generally similar among groups, but absorptive capacity is very different. The shift in function is the main factor influencing the fine root anatomy. Some traits show large variation within groups, but the variations in other traits are small. The traits indicate that the lower-order roots (absorbing roots) in distinct groups are of the first one or two root order in ferns, the first two or three orders in eudicot herbs, the first (only two root orders) or first two orders (more than three root orders) in monocots and the first four or five root orders in woody plants and the other roots are higher-order roots (transport roots). The result will helpful to understand the similarities and differences among groups and the physiological and ecological functions of plant roots. [ABSTRACT FROM AUTHOR]

Fine root life span is a key variable influencing the belowground dynamics of forest ecosystems and is known to be associated with a complex suite of endogenous and environmental factors. We investigated how root life span is influenced by root diameter, branch order, season of birth and soil depth of birth for five temperate tree species growing in monoculture plantations at a common site in northeastern China. The minirhizotron approach was used to estimate root life span from April 2008 to October 2009. Cox proportional hazards regression analysis was employed to determine the impact of those four factors on root life span of each species. There was no consistent difference in fine root life span between evergreen conifers and deciduous hardwoods. A bimodal frequency distribution of root life span was observed for all the species; the majority of roots born in summer and autumn survived to the following year, while roots born in spring mostly died in the current growing season. Root life span tended to increase with root diameter across all species, except Juglans mandshurica. The first two root branch orders within each species generally shared similar life span, with the exception of Picea koraiensis. Root life span tended to be longer at greater depths in the soil profile across all five species. Our results suggest that root life span generally depends on complex interrelations among root anatomy, soil environment and seasonal climatic conditions. [ABSTRACT FROM AUTHOR]

Fine root survivorship is an important aspect of root ecology and is known to be influenced by a suite of covariates. However, the relative importance of each covariate on root survivorship is not clear. Here, we used minirhizotron-based data from 18 woody species to evaluate the relative strength of influence on root survivorship by root diameter, branch order, soil depth, and season of root birth, and to examine how the relationship between each covariate and root survivorship differed across species. We extracted hazard ratio estimates for 16 species from published studies that performed Cox proportional hazards regression analysis, and from our own unpublished data for two Chinese temperate tree species. The mean change in hazard ratio (CHR) and corresponding coefficient of variation for each factor were calculated across species. On average, root diameter and season of root birth had stronger effects on root survivorship than branch order and soil depth. However, the effects of season varied with species and were stronger in temperate forests, whereas the influence of diameter and order were relatively consistent across species. These results suggest that root structures such as diameter and branch order should be carefully considered in root classification and sampling, and adding season of birth (particularly in temperate forests) as a covariate in root survivorship analysis should further enhance our ability in achieving a better understanding of root demography and more accurate estimates of root turnover in forests of different climate zones. [ABSTRACT FROM AUTHOR]

• Elevated [CO 2 ] significantly modify leaf morphology, anatomy and physiology. • Absorptive roots become thicker under elevated [CO 2 ], accompanied with greater cortex. • Functional traits of leaf and root coordinately respond to elevated [CO 2 ]. • Trait-responses to elevated [CO 2 ] are more sensitive in woody than herbaceous plants. Elevated atmospheric CO 2 concentration (e[CO 2 ]) profoundly affects the growth and physiological activities of plants. However, the responses of leaf and root functional traits to e[CO 2 ] are rarely investigated together, limiting our understanding of the whole-plant adaptive strategies to climate change. In this study, 17 temperate woody (nine) and herbaceous (eight) plant species were grown under ambient [CO 2 ] (a[CO 2 ], 380 ppm) and e[CO 2 ] (720 ppm) conditions in the chamber (Percival Scientific, Perry, USA), and the responses of 16 key functional traits (anatomy, morphology, physiology) of leaves and typical absorptive roots (the 1st order root) and their relationships were studied. Averagely, we found that e[CO 2 ] increased leaf thickness (LT, +13 %), reduced specific leaf area (SLA, -14 %), increased palisade tissue thickness (PT, +23 %) and the ratio of palisade tissue to spongy tissue thickness (P/S, +14 %) across species, which were accompanied by physiological changes. For absorptive root, root diameter (RD) increased by 15 %, specific root length (SRL) decreased by 12 %, and root tissue density (RTD) decreased by 14 % across species under e[CO 2 ], indicating that plants tend to construct thicker roots with looser tissue under e[CO 2 ] compared to a[CO 2 ]. Also root cortical thickness (CT) and the ratio of cortical thickness to stele radius (C/S) increased by 20 % and 13 % under e[CO 2 ], respectively, implying an increase in root potential absorption capacity. More importantly, the corresponding functional traits of leaf and absorptive root, i.e., LT and RD, SLA and SRL, PT and CT, P/S and C/S, showed positive correlations in their magnitudes of the responses to e[CO 2 ] in both woody and herbaceous species. Our study revealed the coordinated changes of corresponding functional traits in leaf and absorptive root under e[CO 2 ] condition, which provide some insights into the whole-plant resources acquisition strategy under changing environment. [ABSTRACT FROM AUTHOR]