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Fine root lifespan is a critical trait associated with contrasting root strategies of resource acquisition and protection. Yet, its position within the multidimensional "root economics space" synthesizing global root economics strategies is largely uncertain, and it is rarely represented in frameworks integrating plant trait variations. Here, we compiled the most comprehensive dataset of absorptive median root lifespan (MRL) data including 98 observations from 79 woody species using (mini-) rhizotrons across 40 sites and linked MRL to other plant traits to address questions of the regulators of MRL at large spatial scales. We demonstrate that MRL not only decreases with plant investment in root nitrogen (associated with more metabolically active tissues) but also increases with construction of larger diameter roots which is often associated with greater plant reliance on mycorrhizal symbionts. Although theories linking organ structure and function suggest that root traits should play a role in modulating MRL, we found no correlation between root traits associated with structural defense (root tissue density and specific root length) and MRL. Moreover, fine root and leaf lifespan were globally unrelated, except among evergreen species, suggesting contrasting evolutionary selection between leaves and roots facing contrasting environmental influences above vs. belowground. At large geographic scales, MRL was typically longer at sites with lower mean annual temperature and higher mean annual precipitation. Overall, this synthesis uncovered several key ecophysiological covariates and environmental drivers of MRL, highlighting broad avenues for accurate parametrization of global biogeochemical models and the understanding of ecosystem response to global climate change. [ABSTRACT FROM AUTHOR]

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In the Amazon basin, approximately 60% of rainforest thrives on geologically old and highly weathered soils, thus decomposition represents an important mechanism for recycling nutrients from organic matter. Although dead logs and branches constitute up to 14% of the carbon stored in terrestrial ecosystems, woody debris decomposition and mainly the effect of direct nutrient cycling by plant root interaction is poorly studied and often overlooked in ecosystem carbon and nutrient budgets. Here we monitored the decomposition of five different local woody species covering a range of wood density by conducting a long‐term wood decomposition experiment over two years with factorial root presence and phosphorous (P) addition treatments in a central Amazonian rainforest. We hypothesized that woody debris decomposition is accelerated by colonizing fine roots mining for nutrients, possibly strongly affecting wood debris with lower density and higher nutrient concentration (P). We found that root colonization and P addition separately increased wood decay rates, and although fine root colonization increased when P was added, this did not result in a change in wood decay. Nutrient loss from wood was accelerated by P addition, whereas a root presence effect on nutrient mobilization was only detectable at the end of the experiment. Our results highlight the role of fine roots in priming wood decay, although direct nutrient acquisition by plants seems to only occur in more advanced stages of decomposition. On the other hand, the positive effect of P addition may indicate that microbial nutrient mobilization in woody material is driven mainly by wood stoichiometry rather than priming by root activity. [ABSTRACT FROM AUTHOR]

The ecology of plant species relies on the synchronous functioning of leaves and roots, but few studies have simultaneously examined the community trait dispersion (CTD) patterns of both organs. We measured 16 analogous leaf and root traits on 44 co-occurring woody species in a subtropical forest in southern China, aiming to examine whether leaf and root traits were coordinated, organized into parallel trait axes, exhibited similar CTD, and displayed consistent responses in CTD and community-weighted means of (CWM) traits over environmental gradients. While the first axes of leaf and root trait variation similarly exhibited a fast–slow continuum, leaf traits covered a secondary "carbon economics" axis, contrasting to root traits depicting a collaboration axis reflecting species' mycorrhizal dependency. Analogous leaf and root chemical traits were generally coordinated but less so for morphological traits. At the community level, changes in the CWM of the first axes were generally consistent among organs with more conservative traits found as increasing elevation but not for the second axis. While root traits became thinner and more conservative as soil phosphorus concentration decreased, leaf traits rarely varied. When different trait axes were combined, leaf traits were overdispersed but tended to converge with increased elevation and soil potassium and phosphorus levels, whereas root traits were clustered but tended to diverge along the same gradients. Our study highlights fine filtering of different suites of traits above- and belowground, which in turn might reduce overall niche overlap among species and promote coexistence with diverse functional designs. [ABSTRACT FROM AUTHOR]

The interactions between roots and mycorrhizal fungi are critical for our understanding of the multidimensional root economics space. Our knowledge on their relationships comes mainly from arbuscular mycorrhizal (AM) plants, and less is known about how roots are coordinated with ectomycorrhizal (ECM) fungal communities, especially in ECM‐dominated alpine forests that are highly sensitive to climate change worldwide.Here, we investigated the coordination between roots and ECM fungi and their drivers by measuring multiple root traits, ECM fungal composition and environmental factors of 47 coniferous populations across the alpine coniferous forests on the Tibetan Plateau.Our results reveal two independent fine‐root trait dimensions, that is root foraging dimension and root uptake dimension, which are represented by root diameter‐specific root length, root tissue density‐root N concentration. Importantly, the hyphal exploration type based ECM foraging correlated significantly with both root foraging and root uptake dimension. Further, in the low temperature plateau, it is precipitation‐induced changes in soil moisture, soil nutrients and pH that drive the proportion of longer‐distance hyphal exploration types to increase with higher root foraging by higher specific root length, and to decrease with higher uptake by higher root N concentration.Synthesis. The coordination of multidimensional root traits with ECM fungi differs greatly from the well‐recognized pattern in AM plants that mycorrhizal fungi connect predominantly with root foraging and that roots and mycorrhizal fungi are temperature sensitive. These findings provide a new insight for our holistic understanding of how roots and mycorrhizal fungi vary collaboratively and hence driving plant community assembly and responses to the changing climate. [ABSTRACT FROM AUTHOR]

Summary: Forest fungal communities are shaped by the interactions between host tree root systems and the associated soil conditions. We investigated how the soil environment, root morphological traits, and root chemistry influence root‐inhabiting fungal communities in three tropical forest sites of varying successional status in Xishuangbanna, China.For 150 trees of 66 species, we measured root morphology and tissue chemistry. Tree species identity was confirmed by sequencing rbcL, and root‐associated fungal (RAF) communities were determined using high‐throughput ITS2 sequencing.Using distance‐based redundancy analysis and hierarchical variation partitioning, we quantified the relative importance of two soil variables (site average total phosphorus and available phosphorus), four root traits (dry matter content, tissue density, specific tip abundance, and forks), and three root tissue elemental concentrations (nitrogen, calcium, and manganese) on RAF community dissimilarity. The root and soil environment collectively explained 23% of RAF compositional variation. Soil phosphorus explained 76% of that variation. Twenty fungal taxa differentiated RAF communities among the three sites.Soil phosphorus most strongly affects RAF assemblages in this tropical forest. Variation in root calcium and manganese concentrations and root morphology among tree hosts, principally an architectural trade‐off between dense, highly branched vs less‐dense, herringbone‐type root systems, are important secondary determinants. [ABSTRACT FROM AUTHOR]

1 would adjust (combinations of) these traits whilst keeping the four key RES traits (root N, specific root length, root tissue density and root diameter) constant, it may remain at the same position at the RES, but still display considerable belowground adjustments in their belowground strategies. The establishment of this root economics space - and its four key traits (root diameter, SRL, root tissue density and root nitrogen concentration) - provides novel and important insights into the formation of diverse belowground strategies and hence, species coexistence and community diversity. A second, independent "conservation axis", in turn, separates species with mass-dense (and presumably long-lived) roots that permits long-term resource conservation, from species with roots that are high in nitrogen concentration indicating active root metabolism and fast turnover. For instance, species sampled in different seasons may display different root traits: under adverse conditions, acquisitive, lower-order roots may be shed and only higher order roots (with distinct traits, such as higher root diameter; McCormack et al. 2015) may be sampled, and root traits themselves (like nitrogen concentration) may change over the seasons (Zadworny et al. 2015). [Extracted from the article]

Summary: Lignin is an important root chemical component that is widely used in biogeochemical models to predict root decomposition. Across ecological studies, lignin abundance has been characterized using both proximate and lignin‐specific methods, without much understanding of their comparability. This uncertainty in estimating lignin limits our ability to comprehend the mechanisms regulating root decomposition and to integrate lignin data for large‐scale syntheses.We compared five methods of estimating lignin abundance and composition in fine roots across 34 phylogenetically diverse tree species. We also assessed the feasibility of high‐throughput techniques for fast‐screening of root lignin.Although acid‐insoluble fraction (AIF) has been used to infer root lignin and decomposition, AIF‐defined lignin content was disconnected from the lignin abundance estimated by techniques that specifically measure lignin‐derived monomers. While lignin‐specific techniques indicated lignin contents of 2–10% (w/w) in roots, AIF‐defined lignin contents were c. 5–10‐fold higher, and their interspecific variation was found to be largely unrelated to that determined using lignin‐specific techniques. High‐throughput pyrolysis–gas chromatography–mass spectrometry, when combined with quantitative modeling, accurately predicted lignin abundance and composition, highlighting its feasibility for quicker assessment of lignin in roots.We demonstrate that AIF should be interpreted separately from lignin in fine roots as its abundance is unrelated to that of lignin polymers. This study provides the basis for informed decision‐making with respect to lignin methodology in ecology. [ABSTRACT FROM AUTHOR]

Summary: The root economics space (RES) is multidimensional and largely shaped by belowground biotic and abiotic influences. However, how root–fungal symbioses and edaphic fertility drive this complexity remains unclear.Here, we measured absorptive root traits of 112 tree species in temperate and subtropical forests of China, including traits linked to functional differences between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) hosts.Our data, from known mycorrhizal tree species, revealed a 'fungal‐symbiosis' dimension distinguishing AM from ECM species. This divergence likely resulted from the contrasting mycorrhizal evolutionary development of AM vs ECM associations. Increased root tissue cortical space facilitates AM symbiosis, whereas increased root branching favours ECM symbiosis. Irrespective of mycorrhizal type, a 'root‐lifespan' dimension reflecting aspects of root construction cost and defence was controlled by variation in specific root length and root tissue density, which was fully independent of root nitrogen content. Within this function‐based RES, we observed a substantial covariation of axes with soil phosphorus and nitrate levels, highlighting the role played by these two axes in nutrient acquisition and conservation.Overall, our findings demonstrate the importance of evolved mycorrhizal symbiosis pathway and edaphic fertility in framing the RES, and provide theoretical and mechanistic insights into the complexity of root economics. [ABSTRACT FROM AUTHOR]

Abstract: Although significant advances have been made in understanding terrestrial carbon cycling, there is still a arge uncertainty about the variability of carbon (C) fluxes at local scales. Using a [...]

Summary: Recent studies on fine root functional traits proposed a root economics hypothesis where adaptations associated with mycorrhizal dependency strongly influence the organization of root traits, forming a dominant axis of trait covariation unique to roots. This conclusion, however, is based on tradeoffs of a few widely studied root traits. It is unknown how other functional traits fit into this mycorrhizal‐collaboration gradient. Here, we provide a significant extension to the field of root ecology by examining how fine root secondary compounds coordinate with other root traits.We analyzed a dataset integrating compound‐specific chemistry, morphology and anatomy of fine roots and leaves from 34 temperate tree species spanning major angiosperm lineages.Our data uncovered previously undocumented coordination where root chemistry, morphology and anatomy covary with each other. This coordination, aligned with mycorrhizal colonization, reflects tradeoffs between chemical protection and mycorrhizal dependency, and provides mechanistic support for the mycorrhizal‐collaboration gradient. We also found remarkable phylogenetic structuring in root chemistry. These patterns were not mirrored by leaves. Furthermore, chemical protection was largely decoupled from the leaf economics spectrum.Our results unveil broad organization of root chemistry, demonstrate unique belowground adaptions, and suggest that root strategies and phylogeny could impact biogeochemical cycles through their links with root chemistry. [ABSTRACT FROM AUTHOR]

It remains unclear how evolutionary and ecological processes have shaped the wide variety of plant life strategies, especially in highly diverse ecosystems like tropical forests. Some evidence suggests that species have diversified across a gradient of ecological strategies, with different plant tissues converging to optimize resource use across environmental gradients. Alternative hypotheses propose that species have diversified following independent selection on different tissues, resulting in a decoupling of trait syndromes across organs. To shed light on the subject, we assembled an unprecedented dataset combining 19 leaf, stem and root traits for 1467 tropical tree species inventoried across 71 0.1‐ha plots spanning broad environmental gradients in French Guiana. Nearly 50% of the overall functional heterogeneity was expressed along four orthogonal dimensions, after accounting for phylogenetic dependences among species. The first dimension related to fine root functioning, while the second and third dimensions depicted two decoupled leaf economics spectra, and the fourth dimension encompassed a wood economics spectrum. Traits involved in orthogonal functional strategies, five leaf traits in particular but also trunk bark thickness, were consistently associated with a same gradient of soil texture and nutrient availability. Root traits did not show any significant association with edaphic variation, possibly because of the prevailing influence of other factors (mycorrhizal symbiosis, phylogenetic constraints). Our study emphasises the existence of multiple functional dimensions that allow tropical tree species to optimize their performance in a given environment, bringing new insights into the debate around the presence of a whole plant economic spectrum in tropical forest tree communities. It also emphasizes the key role that soil heterogeneity plays in shaping tree species assembly. The extent to which different organs are decoupled and respond to environmental gradients may also help to improve our predictions of species distribution changes in responses to habitat modification and environmental changes. [ABSTRACT FROM AUTHOR]

Premise: Studying the organization of functional traits in plant leaves and stems has revealed notable patterns linking function and form; however, evidence of similarly robust organization in root tissues remains controversial. We posit that anatomical traits in roots can provide insight on the overall organization of the root system. We hypothesized that size variation in the tissue outside the stele is related in a nonlinear fashion with functional traits associated with direct resource uptake, including a negative relationship with root architectural traits, and that similar relationships detected in tropical areas also hold true in other biomes. Methods: We addressed our hypotheses using empirical data from 24 tropical tree species in French Guiana, including anatomical measurements in first order roots and functional trait description for the entire fine root system. In addition, we compiled a global meta‐analysis of root traits for 500+ forest species across tropical, subtropical, and temperate forests. Results: Our results supported the expected nonlinear relationships between cortical size and morphological traits and a negative linear trend with architectural traits. We confirmed a global negative relationship among specific root length (SRL), diameter, and tissue density, suggesting similar anatomical constraints in root systems across woody plants. However, the importance of factors varies across biomes, possibly related to the unequal phylogenetic representation across latitudes. Conclusions: Our findings imply that the rhizocentric hypothesis can be a valuable approach to understand fine root trait syndromes and the evolution of absorptive roots in vascular plants. [ABSTRACT FROM AUTHOR]

Summary: Soil nutrient availability can strongly affect root traits. In tropical forests, phosphorus (P) is often considered the main limiting nutrient for plants. However, support for the P paradigm is limited, and N and cations might also control tropical forests functioning.We used a large‐scale experiment to determine how the factorial addition of nitrogen (N), P and cations affected root productivity and traits related to nutrient acquisition strategies (morphological traits, phosphatase activity, arbuscular mycorrhizal colonisation and nutrient contents) in a primary rainforest growing on low‐fertility soils in Central Amazonia after 1 yr of fertilisation.Multiple root traits and productivity were affected. Phosphorus additions increased annual root productivity and root diameter, but decreased root phosphatase activity. Cation additions increased root productivity at certain times of year, also increasing root diameter and mycorrhizal colonisation. P and cation additions increased their element concentrations in root tissues. No responses were detected with N addition.Here we showed that rock‐derived nutrients determined root functioning in low‐fertility Amazonian soils, demonstrating not only the hypothesised importance of P, but also highlighting the role of cations. The changes in fine root traits and productivity indicated that even slow‐growing tropical rainforests can respond rapidly to changes in resource availability. [ABSTRACT FROM AUTHOR]

Summary: Environmental filtering and limiting similarity mechanisms can simultaneously structure community assemblages. However, how they shape the functional and phylogenetic structure of root neighborhoods remains unclear, hindering the understanding of belowground community assembly processes and diversity maintenance.In a 50‐ha plot in a subtropical forest, China, we randomly sampled > 2700 root clusters from 625 soil samples. Focusing on 10 root functional traits measured on 76 woody species, we examined the functional and phylogenetic structure of root neighborhoods and linked their distributions with environmental cues.Functional overdispersion was pervasive among individual root traits (50% of the traits) and accentuated when different traits were combined. Functional clustering (20% of the traits) seemed to be associated with a soil nutrient gradient with thick roots dominating fertile areas whereas thin roots dominated infertile soils. Nevertheless, such traits also were sorted along other environmental cues, showing multidimensional adaptive trait syndromes. Species relatedness also was an important factor defining root neighborhoods, resulting in significant phylogenetic overdispersion.These results suggest that limiting similarity may drive niche differentiation of coexisting species to reduce competition, and that alternative root strategies could be crucial in promoting root neighborhood resource use and species coexistence. [ABSTRACT FROM AUTHOR]