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•We propose a framework and experimental approach to study stemflow funnelling.•We studied tree traits and stemflow under three sycamore trees in Scotland.•We studied soil-water ...dynamics with and without stemflow.•Soil-water dynamics were highly influenced by stemflow but also by air temperature.•The framework detected the influence of tree traits on stemflow yield.•Sample size was small, so the trends observed need further verification.
A novel experimental approach and numerical framework are proposed to study the effect of tree architectural traits on stemflow yield and its effects on soil-water dynamics. The framework includes a data mining workflow employing information from two experimental steps: (i) evaluation of the effect of tree aboveground architecture on stemflow yield and (ii) quantification of specific parameters for soil-water dynamics with and without stemflow. We studied double-funnelling (stemflow and root-induced preferential flow) under three sycamore (Acer pseudoplatanus L.) trees growing on a slope in Scotland during the summer season and measured architectural traits. Stemflow yield ranged from 1.3 to 3.8% of the incident rainfall, with funnelling ratios of between 2.2 ± 2.1 and 5.2 ± 3.9. Double-funnelling to a depth of up to 400 mm beneath the soil surface occurred as matrix flow and was significantly and positively correlated with the vertical root distribution. Soil-water dynamics were distinctly different with and without stemflow. Our framework revealed that the number of tree branches, their insertion angle, leaf number, and stem basal diameter influenced stemflow yield within rainfall thresholds of 1.1 and 3.5 mm d-1. The framework also showed that stemflow yield had a negative impact on soil matric suction, while air temperature was the most influential covariate affecting soil-water dynamics, likely due to its strong correlation to evapotranspiration during the summer season. In spite of the study limitations, such as small sample size and differences between individuals, we show that the proposed framework and experimental approach can contribute to our knowledge of how stemflow generated aboveground triggers major responses in soil-water dynamics belowground.
Background and aims Vegetation can be used to stabilise slopes with regard to shallow landslides, but the optimal plant architecture for conferring resistance is not known. This study aims at ...identifying root morphological traits which confer the most resistance to soil during shearing. Methods Three species used for slope stabilisation (Ricinus communis L., Jatwpha curcas L. and Rhus chinensis Mill.) were grown for 10 months in large shear boxes filled with silty clay similar to that found in Yunnan, China. Direct shear tests were then performed and compared to fallow soil. Root systems were excavated and a large number of traits measured. Results Shear strength and deformation energy were enhanced by the presence of roots. Regardless of confining pressure, R. communis conferred most resistance due to its taprooted system with many vertical roots. J. curcas possessed oblique and vertical roots which created fragile zones throughout the soil profile. The least efficient root system was R. chinensis which possessed many horizontal lateral roots. Soil mechanical properties were most influenced by (i) density of roots crossing the shear plane, (ii) branching density throughout the soil profile, (iii) total length of coarse roots above the shear plane and (iv) total volume of coarse roots and fine root density below the shear plane. During failure, fine, short and branched roots slipped through soil rather than breaking. Conclusion Root morphological traits such as density, branching, length, volume, inclination and orientation influence significantly soil mechanical properties.
Although fine roots are important components of the global carbon cycle, there is limited understanding of root structure–function relationships among species. We determined whether root respiration ...rate and decomposability, two key processes driving carbon cycling but always studied separately, varied with root morphological and chemical traits, in a coordinated way that would demonstrate the existence of a root economics spectrum (RES).
Twelve traits were measured on fine roots (diameter ≤ 2 mm) of 74 species (31 graminoids and 43 herbaceous and dwarf shrub eudicots) collected in three biomes.
The findings of this study support the existence of a RES representing an axis of trait variation in which root respiration was positively correlated to nitrogen concentration and specific root length and negatively correlated to the root dry matter content, lignin : nitrogen ratio and the remaining mass after decomposition. This pattern of traits was highly consistent within graminoids but less consistent within eudicots, as a result of an uncoupling between decomposability and morphology, and of heterogeneity of individual roots of eudicots within the fine-root pool.
The positive relationship found between root respiration and decomposability is essential for a better understanding of vegetation–soil feedbacks and for improving terrestrial biosphere models predicting the consequences of plant community changes for carbon cycling.
Fundamental plant traits such as support, anchorage, and protection against environmental stress depend substantially on biomechanical design. The costs, subsequent trade-offs, and effects on plant ...performance of mechanical traits are not well understood, but it appears that many of these traits have evolved in response to abiotic and biotic mechanical forces and resource deficits. The relationships between environmental stresses and mechanical traits can be specific and direct, as in responses to strong winds, with structural reinforcement related to plant survival. Some traits such as leaf toughness might provide protection from multiple forms of stress. In both cases, the adaptive value of mechanical traits may vary between habitats, so is best considered in the context of the broader growth environment, not just of the proximate stress. Plants can also show considerable phenotypic plasticity in mechanical traits, allowing adjustment to changing environments across a range of spatial and temporal scales. However, it is not always clear whether a mechanical property is adaptive or a consequence of the physiology associated with stress. Mechanical traits do not only affect plant survival; evidence suggests they have downstream effects on ecosystem organization and functioning (e.g., diversity, trophic relationships, and productivity), but these remain poorly explored.
There is a fundamental trade‐off between leaf traits associated with either resource acquisition or resource conservation. This gradient of trait variation, called the economics spectrum, also ...applies to fine roots, but whether it is consistent for coarse roots or at the plant community level remains untested. We measured a set of morphological and chemical root traits at a community level (functional parameters; FP) in 20 plant communities located along land‐use intensity gradients and across three climatic zones (tropical, mediterranean and montane). We hypothesized (i) the existence of a root economics spectrum in plant communities consistent within root types (fine, < 2 mm; coarse, 2–5 mm), (ii) that variations in root FP occur with soil depths (top 20 cm of soil and 100–150 cm deep) and (iii) along land‐use gradients. Root FP covaried, in line with the resource acquisition–conservation trade‐off, from communities with root FP associated with resource acquisition (e.g. high specific root length, SRL; thin diameters and low root dry matter contents, RDMC) to root FP associated with resource conservation (e.g. low SRL, thick diameters and high RDMC). This pattern was consistent for both fine and coarse roots indicating a strong consistency of a trade‐off between resource acquisition and conservation for plant roots. Roots had different suites of traits at different depths, suggesting a disparity in root function and exploitation capacities. Shallow, fine roots were thinner, richer in nitrogen and with lower lignin concentrations associated with greater exploitation capacities compared to deep, fine roots. Shallow, coarse roots were richer in nitrogen, carbon and soluble concentrations than deep, coarse roots. Fine root parameters of highly disturbed, herbaceous‐dominated plant communities in poorer soils were associated with foraging strategies, that is greater SRL and lower RDMC and lignin concentration than those from less disturbed communities. Coarse roots, however, were less sensitive to the land‐use gradient. Synthesis. This study demonstrates the existence of a general trade‐off in root construction at a community level, which operates within all root types, suggesting that all plant tissues are controlled by the trade‐off between resource acquisition and conservation.
1. Quantifying the variation in community-level fine root (<2 mm) traits along ecological gradients or in response to disturbances is essential to unravel the mechanisms of plant community assembly, ...but available surveys are scarce. Whether fine root traits covary along a one-dimensional economic spectrum, as previously shown for leaves, is highly debated. 2. We measured six fine root traits at the community level along a 69-year succession, with or without annual mowing, offering a unique design of two nested disturbances. We examined whether (1) there is variation and covariation in community-level fine root traits along the succession and in response to mowing and (2) morphological root traits mirrored analogous leaf traits (using previously acquired data). 3. Early-successional communities were herbaceous-dominated (48 ± 6% in < 10-year-old plots) and possessed fine roots with high specific root length (SRL), low root dry matter content (RDMC) and low root carbon concentration (RCC), while later successional communities were dominated by woody species (56 ± 9% in >40-year-old plots) and possessed opposite trait values. Root nitrogen concentration (RNC) did not vary across communities along the succession. The trait values at community level were not affected by mowing, except for a reduction in root mass density. 4. We found covariation of fine root traits across communities along two dimensions: the first dimension (60% of total variation) represented changes in root foraging capacity (related to SRL) and resource conservation (related to RDMC, RCC, mean root diameter), whereas the second dimension (17%-20% of the variation) represented variations in RNC, potentially related to root respiration and metabolism. 5. Specific root length and specific leaf area were correlated regardless of the mowing regime, but there was no analogous relationship between leaf dry matter content and RDMC in mown communities, showing a decoupling in the investment in tissue density above- and below-ground. 6. Synthesis. Our study demonstrates coordinated variations of community-level fine root traits along a succession gradient and provides evidence that fine root traits covaried along two dimensions, regardless of mowing regime. The relationship between leaf dry matter content and root dry matter content observed in unmown communities was modified by mowing, reflecting an uncoupled response to mowing.
Major reforestation programs have been initiated on hillsides prone to erosion and landslides in China, but no framework exists to guide managers in the choice of plant species. We developed such a ...framework based on the suitability of given plant traits for fixing soil on steep slopes in western Yunnan, China. We examined the utility of 55 native and exotic species with regard to the services they provided. We then chose nine species differing in life form. Plant root system architecture, root mechanical and physiological traits were then measured at two adjacent field sites. One site was highly unstable, with severe soil slippage and erosion. The second site had been replanted 8 years previously and appeared to be physically stable. How root traits differed between sites, season, depth in soil and distance from the plant stem were determined. Root system morphology was analysed by considering architectural traits (root angle, depth, diameter and volume) both up- and downslope. Significant differences between all factors were found, depending on species. We estimated the most useful architectural and mechanical traits for physically fixing soil in place. We then combined these results with those concerning root physiological traits, which were used as a proxy for root metabolic activity. Scores were assigned to each species based on traits. No one species possessed a suite of highly desirable traits, therefore mixtures of species should be used on vulnerable slopes. We also propose a conceptual model describing how to position plants on an unstable site, based on root system traits.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Background and Aims Fine roots play a major role in the global carbon cycle through respiration, exudation and decomposition processes, but their dynamics are poorly understood. Current estimates of ...root dynamics have principally been observed in shallow soil horizons (<1 m), and mainly in forest systems. We studied walnut (Juglans regia×nigra L.) fine root dynamics in an agroforestry system in a Mediterranean climate, with a focus on deep soils (down to 5 m), and root dynamics throughout the year. Methods Sixteen minirhizotron tubes were installed in a soil pit, at depths of 0.0–0.7, 1.0–1.7, 2.5–3.2 and 4.0–4.7 m and at two distances from the nearest trees (2 and 5 m). Fine root (diameter≤2 mm) dynamics were recorded across three diameter classes every 3 weeks for 1 year to determine their phenology and turnover in relation to soil depth, root diameter and distance from the tree row. Results Deep (>2.5 m) root growth occurred at two distinct periods, at bud break in spring and throughout the winter i.e., after leaf fall. In contrast, shallow roots grew mainly during the spring–summer period. Maximum root elongation rates ranged from 1 to 2 cm day⁻¹ depending on soil depth. Most root mortality occurred in upper soil layers whereas only 10 % of fine roots below 4 m died over the study period. Fine root lifespan was longer in thicker and in deeper roots with the lifespan of the thinnest roots (0.0–0.5 mm) increasing from 129 days in the topsoil to 190 at depths>2.5 m. Conclusions The unexpected growth of very deep fine roots during the winter months, which is unusual for a deciduous tree species, suggests that deep and shallow roots share different physiological strategies and that current estimates based on the shortest root growth periods (i.e., during spring and summer) may be underestimating root production. Although high fine root turnover rates might partially result from the minirhizotron approach used, our results help gain insight into some of the factors driving soil organic carbon content.
The role of vegetation in preventing shallow soil mass movement is now fairly well understood, particularly at the individual plant level. However, how soil is reinforced on a larger scale and the ...influence of changes in vegetation over time has rarely been investigated. Therefore we carried out a study on the temporal and spatial changes within stands of
Cryptomeria japonica D. Don, growing in the Sichuan province of China, an area where shallow landslides are frequent.
Soil cores were taken from three neighbouring stands of
C. japonica aged 9, 20 and 30 years old and growing on steep slopes. Cores were taken from around trees and the root (<10
mm in diameter) biomass density (root density (RD)) present in each core was measured at different depths. The spatial position of trees at each site was noted and soil shear strength was measured. The tensile strength of a sample of roots from each stand was measured. Using the RD data, the root area ratio (RAR) could be estimated. RAR and root tensile strength were used as input to a model of root reinforcement which determines the additional cohesion,
c
r, or contribution of vegetation to soil. Data were then incorporated into a two-dimensional model of slope stability developed in the finite element (FE) code, Plaxis, which calculates the safety factor (FOS), or likelihood of a slope to fail under certain circumstances. We calculated the FOS of slopes with and without
C. japonica, taking into account the spatial position of trees at each stand.
Results showed that RD was highest in the 9-year-old stand, but that root tensile strength was lowest. In the 30-year-old stand, RD was low but a higher root tensile strength compensated for the decrease in RAR. The FOS increased by only 15–27% when vegetation was present, with the greatest augmentation in the 9-year-old stand. The older stands had been thinned over the years, resulting in large gaps between trees, which would be prone to local soil slippage. This spatial effect was reflected in the FE analysis, which showed a significant relationship between the number of trees and distance between groups of trees in the 20- and 30-year-old stands only. Therefore, when managing fragile slopes, care should be taken when thinning, so that large gaps do not exist between trees, the influence of which is accrued over time.
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