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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 2mm) 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.

The variation and correlation among desert plant traits are helpful to understanding the adaptation strategies of plants to the environment and the mechanism of community assembly. However, the diversity and covariation among fine root traits of desert plants and their phylogenetic relationships remain unclear. Principal component analysis, Pearson’s correlations, phylogenetic independent comparison, mixed linear model, and variance decomposition were used to investigate the variation and correlation among 10 fine root traits of 25 common desert plants in arid areas. The results are as follows: (1) We found that all fine root traits varied more among interspecific variation, with the coefficient of variation ranging from 21.83% to 105.79%. Most traits were predominantly shaped by interspecific variation, whereas root phosphorus content (RPC) and intraspecific variation in root carbon/nitrogen ratio (RCN) were more important. (2) Root traits were correlated with four axes of variation. Root nitrogen content (RNC) correlated positively with root diameter (AD) and tissue density (RTD) but negatively with specific root length (SRL), which was inconsistent with the inference of the root economics spectrum (RES). (3) Covariance and trade-off strategies of fine root traits in different life forms of plants were different. Herb RNC was negatively correlated with SRL and positively correlated with AD, while this relationship did not exist in shrubs. Moreover, shrub AD was negatively correlated with RTD, but herbs showed no significant correlation. (4) Influenced by phylogenetic factors, fine root traits exhibited a covariant or trade-off pattern. Taken together, fine root traits were predominantly shaped by interspecific variation, but intraspecific variation also played a significant role. Concurrently, distinct patterns in fine root covariation and trade-off strategies among different life forms of plants were also observed. Future studies should explore the variation and correlation among traits at different scales within and between species from the perspective of life form.

1.Quantifying the variation in community-level fine root (<2mm) 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 (i) there is variation and covariation in community-level fine root traits along the succession and in response to mowing and (ii) 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 to 20% of the variation) represented variations in RNC, potentially related to root respiration and metabolism.5.SRL and SLA (specific leaf area) were correlated regardless of the mowing regime, but there was no analogous relationship between LDMC (leaf dry matter content) and RDMC in mown communities, showing a decoupling in the investment in tissue density above and belowground.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 LDMC and RDMC observed in unmown communities was modified by mowing, reflecting an uncoupled response to mowing.

Fine roots, and their functional traits, influence associated rhizosphere microorganisms via root exudation and root litter quality. However, little information is known about their relationship with rhizosphere microbial taxa and functional guilds. We investigated the relationships of 11 fine root traits of 20 sub-arctic tundra meadow plant species and soil microbial community composition, using phospholipid fatty acids (PLFAs) and high-throughput sequencing. We primarily focused on the root economics spectrum , as it provides a useful framework to examine plant strategies by integrating the co-ordination of belowground root traits along a resource acquisition-conservation trade-off axis. We found that the chemical axis of the fine root economics spectrum was positively related to fungal to bacterial ratios, but negatively to Gram-positive to Gram-negative bacterial ratios. However, this spectrum was unrelated to the relative abundance of functional guilds of soil fungi. Nevertheless, the relative abundance of arbuscular mycorrhizal fungi was positively correlated to root carbon content, but negatively to the numbers of root forks per root length. Our results suggest that the fine root economics spectrum is important for predicting broader groups of soil microorganisms (i.e. fungi and bacteria), while individual root traits may be more important for predicting soil microbial taxa and functional guilds.

Background and aims The quantification of plant roots from soil represents a pivotal step in many studies in plant ecology and soil science. However, the substantial time investment required for this process often represents a considerable impediment to research progress. The objective of this study is to evaluate and propose a time-saving method to minimize the time required for collecting roots without compromising data integrity compared to traditional approaches. Methods The proposed Sub-sample Approach (SA) requires collecting fine roots from a sub-sample and subsequently leading calculations to estimate total root traits (mass, length, and length distribution among diameters) within the sampled soil core. A comparative analysis was carried out on root harvesting time between meticulous sample cleaning (Conventional Approach, CA) and SA. Moreover, these methods were assessed across different sites including grassland, oak forest, and olive orchard. Results The analysis conducted across many sites resulted in high heterogeneity of processing time when employing the CA (ranging from 2.6 to 27.6 h per sample). Conversely, the adoption of SA reduced processing time and resulted in less variation between samples (ranging from 37 to 112 min per sample). Remarkably, root trait data obtained using SA showed similarity to those obtained through the CA. Conclusion The SA offers a remarkable advantage over the CA by significantly reducing the time needed for root collection from soil core samples. Moreover, SA exhibits lower variability among different collection sites, while maintaining consistency in qualitative and quantitative data compared to the CA.

Background and aims Coordination between leaf and root traits is crucial to plant performance and ecosystem functioning, but how leaves and roots coordinate in ectomycorrhizal (ECM)-dominated alpine forests remains unclear. Therefore, the covariation patterns of leaf and root traits of ECM-dominated alpine conifers and the environmental drivers were examined. Methods Five pairs of key leaf (i.e., leaf thickness [LT], specific leaf area [SLA], leaf tissue density [LTD], leaf N and P concentrations) and fine-root traits (i.e., root diameter [RD], specific root length [SRL], root tissue density [RTD], root N and P concentrations) were measured across 49 alpine coniferous populations (including 8 coniferous species) on the Tibetan Plateau. Results Root traits including RTD, root N and P concentrations and leaf traits such as LT, SLA, LTD, leaf N and P concentrations were correlated. The root-leaf relationships represent a tradeoff between resource conservation and fast plant growth, i.e., plant economic spectrum. RD and SRL were independent from the plant economic spectrum. Temperature drove variations in the leaf traits, RTD, root N and P concentrations, and conifers under low temperature had denser leaves and roots (i.e., larger LT, LTD, RTD) and lower nutrient contents. Precipitation primarily controlled variations in RD and SRL, and roots became thinner with decreasing precipitation. Conclusion Our study demonstrates divergent roles of temperature and precipitation in driving the coordination of leaf and root economic traits in the ECM-dominated alpine coniferous ecosystems. This is insightful for a comprehensive understanding of the adaptation and responses of alpine forests to climate change.

Summary Plant functional traits have revealed trade‐offs related to life‐history adaptations, geographical distributions, and ecosystem processes. Fine roots are essential in plant resource acquisition and play an important role in soil carbon cycling. Nonetheless, root trait variation is still poorly quantified and rarely related to the rest of the plant. We examined chemical and morphological traits of 34 temperate arbuscular mycorrhizal tree species, representing three main angiosperm clades (super‐orders asterid, magnoliid and rosid). We tested to what extent fine root chemical and morphological traits were correlated similarly to the leaf economical spectrum (LES) or were structured by ancestral affiliations among species. Root traits did not display the same trade‐offs as leaves (e.g. specific root length was not correlated with root N, whereas specific leaf area was correlated with leaf N). Moreover, 75% of below‐ground traits were phylogenetically structured according to Pagel's λ and Abouheif's Cmean autocorrelation tests, as opposed to 28% of above‐ground traits. Magnoliids showed thicker, less branched roots than asterids or rosids, but rosid roots exhibited lower N and higher non‐acid‐hydrolysable (e.g. lignin) content than other species. In contrast, leaf traits did not differ significantly among super‐orders. At the whole‐tree level, chemical traits such as nitrogen tissue content and lignin content were correlated between above and below‐ground organs. The distribution of root traits in woody temperate trees was better explained by shared ancestry than by the nutrient content and structural trade‐offs expected by the LES hypothesis. Root chemistry and morphology differed substantially among species belonging to different super‐orders, suggesting deep divergences in resource acquisition strategies among major angiosperm groups. Although we found partial support for the idea of whole‐plant integration based on corresponding nitrogen content across all organs (i.e. a plant economics spectrum), our study stresses phylogenetic affiliation as the primary driver of root trait distributions among angiosperms, a pattern that could be easily overlooked based solely on above‐ground observations. Lay Summary

Global vegetation models use conceived relationships between functional traits to simulate ecosystem responses to environmental change. In this context, the concept of the leaf economics spectrum (LES) suggests coordinated leaf trait variation, and separates species which invest resources into short-lived leaves with a high expected energy return rate from species with longer-lived leaves and slower energy return. While it has been assumed that being fast (acquisitive) or slow (conservative) is a general feature for all organ systems, the translation of the LES into a root economics spectrum (RES) for tree species has been hitherto inconclusive. This may be partly due to the assumption that the bulk of tree fine roots have similar uptake functions as leaves, despite the heterogeneity of their environments and resources. In this study we investigated well-established functional leaf and stature traits as well as a high number of fine root traits (14 traits split by different root orders) of 13 dominant or subdominant temperate tree species of Central Europe, representing two phylogenetic groups (gymnosperms and angiosperms) and two mycorrhizal associations (arbuscular and ectomycorrhizal). We found reflected variation in leaf and lower-order root traits in some (surface areas and C:N) but not all (N content and longevity) traits central to the LES. Accordingly, the LES was not mirrored belowground. We identified significant phylogenetic signal in morphological lower-order root traits, i.e., in root tissue density, root diameter, and specific root length. By contrast, root architecture (root branching) was influenced by the mycorrhizal association type which developed independent from phylogeny of the host tree. In structural equation models we show that root branching significantly influences both belowground (direct influence on root C:N) and aboveground (indirect influences on specific leaf area and leaf longevity) traits which relate to resource investment and lifespan. We conclude that branching of lower order roots can be considered a leading root trait of the plant economics spectrum of temperate trees, since it relates to the mycorrhizal association type and belowground resource exploitation; while the dominance of the phylogenetic signal over environmental filtering makes morphological root traits less central for tree economics spectra across different environments.

Trees adjust multiple structural and functional organ-specific characteristics, \"traits\", to cope with diverse soil conditions. Studies on traits are widely used to uncover ecological species adaptability to varying environments. However, fine-root traits are rarely studied for methodological reasons. We analyzed the adaptability of the fine-root systems of European beech and Norway spruce to extreme drought within species-specific tree groups at Kranzberger Forst (Germany), focusing on the seasonality of morphological, physiological, and biochemical key traits in view of carbon (C) and nitrogen dynamics. We hypothesized that fine roots of both species adjust to seasonal drought: with beech representing a \"fast\" (i.e. with fast C turnover), and spruce a \"slow\" (i.e. with long-term C retention) ecological strategy. We identified three functional fine-root categories, based on root function (absorptive or transport fine roots), and mycorrhizal status of the absorptive fine-roots (mycorrhizal or non-mycorrhizal). Solely the non-mycorrhizal absorptive roots adjusted in a species-specific manner supporting fine-root ecological strategy hypothesis. During drought, beech produced thin ephemeral (absorptive non-mycorrhizal) fine roots with high specific fine-root area and high respiratory activity, representing fast C turnover and enabling effective resource exploitation. These adjustments reflect a \"fast\" ecological strategy. Conversely, spruce absorptive fine roots did not respond to the soil moisture deficit by growth but instead increased root suberization. Drastically lowered respiratory activity of this functional category facilitated C retention and structural persistence during drought, indicating a \"slow\" ecological strategy in spruce. Absorptive mycorrhizal fine roots maintained respiration throughout the drought event in both tree species, but in spruce this was the only fine-root category with high respiration. This suggests, that spruce relies heavily on mycorrhizal associations as a method of drought resistance. Accumulation of non-structural carbohydrates and high C concentrations were observed in the transport fine roots of both species, indicating drought-induced osmotic protection of these roots. Thus, functional classification enabled us to determine that fine-root branches of each species are not tied to one sole ecological strategy. The suggested approach helps to better understand the complex interplay between structure and function belowground.

Background and aims Roots and their rhizosphere considerably influence soil structure by regulating soil aggregate formation and stabilization. This study aimed to examine the rhizosphere effects on soil aggregation and explore potential mechanisms along secondary forest successions. Methods Effects of roots and their rhizosphere on soil aggregation in two subtropical secondary forest successions were examined by separating soils into rhizosphere and bulk soils. Soil aggregate mean weight diameter (MWD), soil organic carbon (SOC), soil nutrients, and fine-root traits were simultaneously measured. Results Soil aggregate MWD increased significantly in the bulk soils along secondary forest successions, but did not differ in the rhizosphere soils. Rhizosphere effects on soil aggregate MWD (i.e., root-induced differences between the rhizosphere and bulk soils) were thus significantly higher at the early-successional stage of subtropical forest with low soil fertility than those at the late stages with high fertility. Rhizosphere significantly increased SOC and soil total nitrogen (TN) throughout the entire secondary forest successions, which was nonlinearly correlated with soil aggregate MWD. Principal components regression analysis showed that SOC was the primary abiotic factor and positively correlated with soil aggregate MWD. As for biotic factors, fine-root length density and N concentration were two important root traits having significant effects on soil aggregate stability. An improved conceptual framework was developed to advance our understanding of soil aggregation and rhizosphere effects, highlighting the roles of soil fertility (i.e., SOC and available nutrients), root traits, and forest age in driving soil aggregation. Conclusions Impacts of root-derived organic compounds inputs to rhizosphere on soil aggregation were stronger at the early-successional stage of subtropical forest than those at the late stages. This succession-specific pattern in rhizosphere effects largely resulted from the nonlinear relationships between soil aggregate MWD and SOC concentration with a plateau at high SOC. Incorporating the SOC-dependent rhizosphere effects on biogeochemical cycle into Earth system models might improve the prediction of forest soil C dynamics.