The search for a root economics spectrum (RES) has been sparked by recent interest in trait-based plant ecology. By analogy with the one-dimensional leaf economics spectrum (LES), fine-root traits ...are hypothesised to match leaf traits which are coordinated along one axis from resource acquisitive to conservative traits. However, our literature review and meta-level analysis reveal no consistent evidence of an RES mirroring an LES. Instead the RES appears to be multidimensional. We discuss three fundamental differences contributing to the discrepancy between these spectra. First, root traits are simultaneously constrained by various environmental drivers not necessarily related to resource uptake. Second, above- and belowground traits cannot be considered analogues, because they function differently and might not be related to resource uptake in a similar manner. Third, mycorrhizal interactions may offset selection for an RES. Understanding and explaining the belowground mechanisms and trade-offs that drive variation in root traits, resource acquisition and plant performance across species, thus requires a fundamentally different approach than applied aboveground. We therefore call for studies that can functionally incorporate the root traits involved in resource uptake, the complex soil environment and the various soil resource uptake mechanisms – particularly the mycorrhizal pathway – in a multidimensional root trait framework.
1. Although a major part of plant biomass is underground, we know little about the contribution of different species to root biomass in multispecies communities. We summarize studies on root ...distributions and plant responses to species‐specific soil biota and formulate three hypotheses to explain how root responses may drive species coexistence and ecosystem productivity. 2. Recent studies suggest that root growth of some species may be stimulated in species mixtures compared with monocultures without hampering the growth of other species, leading to below‐ground overyielding. Further studies suggest that these responses are the result of reduced impairment of growth by species‐specific plant pathogens that accumulate in monocultures. 3. First, we hypothesize that due to pathogen‐constrained growth, monocultures are ‘under‐rooted’, i.e. they do not have enough roots for optimal acquisition of nutrients. Although elevated root production in mixtures represents a cost to the plant, improved nutrition will eventually result in improved plant performance. 4. Second, due to the plant species specificity of the soil biotic communities, we suggest that plant species in mixtures develop an intransitive competitive network in which none of the species is competitively superior to all other species. Competitive intransitivity is proposed as a mechanism of species coexistence. 5. As a final hypothesis, we suggest that pathogen‐mediated root overproduction in species mixtures determines the patterns of community productivity and overyielding, both directly, by improving plant performance, and indirectly, by releasing more carbon into the soil, resulting in enhanced availability of nutrients. 6. Synthesis.Recent evidence suggests that species coexistence and ecosystem productivity may be the result of an interplay between pathogen‐driven plant responses and nutritional consequences. We suggest that responses of the roots are an important yet mostly overlooked intermediary between soil biota and plant community responses to biodiversity.
Timely perception of adverse environmental changes is critical for survival. Dynamic changes in gases are important cues for plants to sense environmental perturbations, such as submergence. In ...Arabidopsis thaliana, changes in oxygen and nitric oxide (NO) control the stability of ERFVII transcription factors. ERFVII proteolysis is regulated by the N-degron pathway and mediates adaptation to flooding-induced hypoxia. However, how plants detect and transduce early submergence signals remains elusive. Here we show that plants can rapidly detect submergence through passive ethylene entrapment and use this signal to pre-adapt to impending hypoxia. Ethylene can enhance ERFVII stability prior to hypoxia by increasing the NO-scavenger PHYTOGLOBIN1. This ethylene-mediated NO depletion and consequent ERFVII accumulation pre-adapts plants to survive subsequent hypoxia. Our results reveal the biological link between three gaseous signals for the regulation of flooding survival and identifies key regulatory targets for early stress perception that could be pivotal for developing flood-tolerant crops.
Background and aims Competition is an important force shaping plant communities. Here we test the hypothesis that high overall root length density and selective root placement in nutrient patches, as ...two alternative strategies, confer competitive advantage in species mixtures. Methods We performed a full-factorial pairwise competition experiment with eight grassland species in soil with homogeneously distributed nutrients, or with nutrients concentrated in a single patch. We measured species-specific relative growth rate, root length density, selective root placement, and ion uptake rates of all species in monocultures and in mixtures. Results Grasses showed higher specific root length overall and forbs a higher selective root placement in the nutrient patch. However, relative growth rate and root length density were more strongly related to competitive ability (measured as relative yield per plant), with little distinction between grasses and forbs. Conclusions Our results suggest that short-term competitive success was related to fast growth and high root densities, irrespective of nutrient heterogeneity. Developing a large root mass quickly may overwhelm the importance of other traits in the establishment phase of plants, although these other traits may prove to be important in the long run.
Flooding is expected to increase in frequency and severity in the future. The ecological consequences of flooding are the combined result of species-specific plant traits and ecological context. ...However, the majority of past flooding research has focused on individual model species under highly controlled conditions.
An early summer flooding event in a grassland biodiversity experiment in Jena, Germany, provided the opportunity to assess flooding responses of 60 grassland species in monocultures and 16-species mixtures. We examined plant biomass, species-specific traits (plant height, specific leaf area (SLA), root aerenchyma, starch content) and soil porosity.
We found that, on average, plant species were less negatively affected by the flood when grown in higher-diversity plots in July 2013. By September 2013, grasses were unaffected by the flood regardless of plant diversity, and legumes were severely negatively affected regardless of plant diversity. Plants with greater SLA and more root aerenchyma performed better in September. Soil porosity was higher in higher-diversity plots and had a positive effect on plant performance.
As floods become more frequent and severe in the future, growing flood-sensitive plants in higher-diversity communities and in soil with greater soil aeration may attenuate the most negative effects of flooding.
Root systems are highly plastic as they express a range of responses to acquire patchily distributed nutrients. However, the ecological significance of placing roots selectively in nutrient hotspots ...is still unclear. Here, we investigate under what conditions selective root placement may be a significant functional trait that determines belowground competitive ability. We studied two grasses differing in root foraging behaviour, Festuca rubra and Anthoxanthum odoratum. The plants were grown in stable and more dynamic heterogeneous environments, by switching nutrient patches halfway through the experiment. A. odoratum was a factor of two less selective in placing its roots into nutrient-rich patches than F. mbra. A. odoratum produced overall higher root length densities with higher specific root length than F. rubra and acquired more nutrients. A. odoratum appeared to be the superior competitor, irrespective of the nutrient dynamics. Our results suggest that root behaviour consisting of producing high root length densities at relatively low biomass investments can be a more effective foraging strategy than placing roots selectively in nutrient hotspots. When understanding the functionality of root traits among different species, specific root length may play a key role.
Two different plant strategies exist to deal with shade: shade avoidance and shade tolerance. All shade-exposed plants optimize photosynthesis to adapt to the decrease in light quality and quantity. ...When shaded, most species in open habitats express the shade-avoidance syndrome, a growth response to escape shade. Shade-tolerant species from forest understories cannot outgrow surrounding trees and adopt a tolerance response. Unlike shade avoidance, virtually nothing is known about regulation of shade tolerance. In this opinion article, we discuss potential modes of molecular regulation to adopt a shade-tolerance rather than a shade-avoidance strategy. We argue that molecular approaches using model and non-model species should help identify the molecular pathways that underpin shade tolerance, thus providing knowledge for further crop improvement.
The gaseous plant hormone ethylene modulates many internal processes and growth responses to environmental stimuli. Ethylene has long been recognized as a growth inhibitor, but evidence is ...accumulating that ethylene can also promote growth. Therefore, the concept of ethylene as a general growth inhibitor needs reconsideration: a close examination of recent literature can help to understand the two contrasting faces of growth control by ethylene. Here, we propose a hypothesis that integrates growth inhibition and growth stimulation into one biphasic ethylene response model. Focusing on photosynthesis and cell expansion, we highlight several mechanisms through which ethylene affects plant growth, thereby interacting with various other signal transduction routes.
Background and aims
The concept of plant-soil feedback is increasingly used to explain plant community assembly processes. Soil nutrient availability can be expected to play a critical role on these ...processes. However, little is known about the effects of nutrient availability on feedback direction and strength.
Methods
A plant-soil feedback experiment was performed with the grasses
Anthoxanthum odoratum
and
Festuca rubra
, and the forbs
Leontodon hispidus
and
Plantago lanceolata
, on soil with either low or high nutrient availability. Additionally, we tested if plant-soil feedback of the two forbs under these conditions changed by inoculation of the soil with spores of an arbuscular mycorrhizal fungus.
Results
Increased nutrient availability neutralised plant-soil feedback based on shoot biomass independent of its negative or positive direction, whereas the effects on root biomass were either not altered or turned negative. Mycorrhizal fungi spore addition decreased negative feedback and increased positive feedback.
Conclusions
Our results suggest that negative plant-soil feedback on low nutrient soil can be overcome with nutrient addition, and that positive soil biota associations on low nutrient soil may become superfluous with nutrient increase. We hypothesize that species-specific, microbial mediated plant community assembly processes occur in low rather than high nutrient environments.
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