Climate change is projected to increase the incidence of severe drought in many regions, potentially requiring selection for different traits in crop species to maintain productivity under water ...stress. In this study, we identified a suite of hydraulic traits associated with high productivity under water stress in four genotypes of S. melongena L. We also assessed the potential for recovery of this suite of traits from drought stress after re-watering. We observed that two genotypes, PHL 4841 and PHL 2778, quickly grew into large plants with smaller, thicker leaves and increasingly poor hydraulic status (a water-spender strategy), whereas PHL 2789 and Mara maintained safer water status and larger leaves but sacrificed large gains in biomass (a water-saver strategy). The best performing genotype under water stress, PHL 2778, additionally showed a significant increase in root biomass allocation relative to other genotypes. Biomass traits of all genotypes were negatively impacted by water deficit and remained impaired after a week of recovery; however, physiological traits such as electron transport capacity of photosystem II, and proportional allocation to root biomass and fine root length, and leaf area recovered after one week, indicating a strong capacity for eggplant to rebound from short-term deficits via recovery of physiological activity and allocation to resource acquiring tissues. These traits should be considered in selection and breeding of eggplant hybrids for future agricultural outlooks.
Geneticists and breeders are positioned to breed plants with root traits that improve productivity under drought. However, a better understanding of root functional traits and how traits are related ...to whole plant strategies to increase crop productivity under different drought conditions is needed. Root traits associated with maintaining plant productivity under drought include small fine root diameters, long specific root length, and considerable root length density, especially at depths in soil with available water. In environments with late season water deficits, small xylem diameters in targeted seminal roots save soil water deep in the soil profile for use during crop maturation and result in improved yields. Capacity for deep root growth and large xylem diameters in deep roots may also improve root acquisition of water when ample water at depth is available. Xylem pit anatomy that makes xylem less "leaky" and prone to cavitation warrants further exploration holding promise that such traits may improve plant productivity in water-limited environments without negatively impacting yield under adequate water conditions. Rapid resumption of root growth following soil rewetting may improve plant productivity under episodic drought. Genetic control of many of these traits through breeding appears feasible. Several recent reviews have covered methods for screening root traits but an appreciation for the complexity of root systems (e.g., functional differences between fine and coarse roots) needs to be paired with these methods to successfully identify relevant traits for crop improvement. Screening of root traits at early stages in plant development can proxy traits at mature stages but verification is needed on a case by case basis that traits are linked to increased crop productivity under drought. Examples in lesquerella (Physaria) and rice (Oryza) show approaches to phenotyping of root traits and current understanding of root trait genetics for breeding.
•We evaluated canopy temperature on six deficit irrigation treatments of corn.•Corn canopy temperature was highly correlated with midday leaf water potential.•Three previously used and three new ...water stress indices were evaluated.•All indices showed linear relationship with soil water deficit at high temperatures.•Indices that require canopy temperature only are highly correlated with CWSI.
Infrared thermal radiometers (IRTs) are an affordable tool for researchers to monitor canopy temperature. In this maize experiment, six treatments of regulated deficit irrigation levels were evaluated. The main objective was to evaluate these six treatments in terms of six indices (three previously proposed and three introduced in this study) used to quantify water stress. Three are point-in-time indices where one daily reading is assumed representative of the day (Crop Water Stress Index – CWSI, Degrees Above Non-Stressed – DANS, Degrees Above Canopy Threshold – DACT) and three integrate the cumulative impact of water stress over time (Time Temperature Threshold – TTT, Integrated Degrees Above Non-Stressed – IDANS, Integrated Degrees Above Canopy Threshold – IDACT). Canopy temperature was highly correlated with leaf water potential (R2=0.895). To avoid potential bias, the lowest observation from the non-stressed treatment was chosen as the baseline for DANS and IDANS indices. Early afternoon temperatures showed the most divergence and thus this is the ideal time to obtain spot index values. Canopy temperatures and stress indices were responsive to evapotranspiration-based irrigation treatments. DANS and DACT were highly correlated with CWSI above the corn threshold 28°C used in the TTT method, and all indices showed linear relationship with soil water deficit at high temperatures. Recommendations are given to consider soils with high water-holding capacity when choosing a site for non-stressed reference crops used in the DANS method. The DACT may be the most convenient index, as all it requires is a single canopy temperature measurement yet has strong relationships with other indices and crop water measurements.
1. Ecosystem functioning relies heavily on below-ground processes, which are largely regulated by plant fine-roots and their functional traits. However, our knowledge of fine-root trait distribution ...relies to date on local- and regional-scale studies with limited numbers of species, growth forms and environmental variation. 2. We compiled a world-wide fine-root trait dataset, featuring 1115 species from contrasting climatic areas, phylogeny and growth forms to test a series of hypotheses pertaining to the influence of plant functional types, soil and climate variables, and the degree of manipulation of plant growing conditions on species fine-root trait variation. Most particularly, we tested the competing hypotheses that fine-root traits typical of faster return on investment would be most strongly associated with conditions of limiting versus favourable soil resource availability. We accounted for both data source and species phylogenetic relatedness. 3. We demonstrate that: (i) Climate conditions promoting soil fertility relate negatively to fine-root traits favouring fast soil resource acquisition, with a particularly strong positive effect of temperature on fine-root diameter and negative effect on specific root length (SRL), and a negative effect of rainfall on root nitrogen concentration; (ii) Soil bulk density strongly influences species fine-root morphology, by favouring thicker, denser fine-roots; (iii) Fine-roots from herbaceous species are on average finer and have higher SRL than those of woody species, and N2-fixing capacity positively relates to root nitrogen; and (iv) Plants growing in pots have higher SRL than those grown in the field. 4. Synthesis. This study reveals both the large variation in fine-root traits encountered globally and the relevance of several key plant functional types and soil and climate variables for explaining a substantial part of this variation. Climate, particularly temperature, and plant functional types were the two strongest predictors of fine-root trait variation. High trait variation occurred at local scales, suggesting that wide-ranging below-ground resource economics strategies are viable within most climatic areas and soil conditions.
Summary
In the context of a recent massive increase in research on plant root functions and their impact on the environment, root ecologists currently face many important challenges to keep on ...generating cutting‐edge, meaningful and integrated knowledge. Consideration of the below‐ground components in plant and ecosystem studies has been consistently called for in recent decades, but methodology is disparate and sometimes inappropriate. This handbook, based on the collective effort of a large team of experts, will improve trait comparisons across studies and integration of information across databases by providing standardised methods and controlled vocabularies. It is meant to be used not only as starting point by students and scientists who desire working on below‐ground ecosystems, but also by experts for consolidating and broadening their views on multiple aspects of root ecology. Beyond the classical compilation of measurement protocols, we have synthesised recommendations from the literature to provide key background knowledge useful for: (1) defining below‐ground plant entities and giving keys for their meaningful dissection, classification and naming beyond the classical fine‐root vs coarse‐root approach; (2) considering the specificity of root research to produce sound laboratory and field data; (3) describing typical, but overlooked steps for studying roots (e.g. root handling, cleaning and storage); and (4) gathering metadata necessary for the interpretation of results and their reuse. Most importantly, all root traits have been introduced with some degree of ecological context that will be a foundation for understanding their ecological meaning, their typical use and uncertainties, and some methodological and conceptual perspectives for future research. Considering all of this, we urge readers not to solely extract protocol recommendations for trait measurements from this work, but to take a moment to read and reflect on the extensive information contained in this broader guide to root ecology, including sections I–VII and the many introductions to each section and root trait description. Finally, it is critical to understand that a major aim of this guide is to help break down barriers between the many subdisciplines of root ecology and ecophysiology, broaden researchers’ views on the multiple aspects of root study and create favourable conditions for the inception of comprehensive experiments on the role of roots in plant and ecosystem functioning.
Root traits vary enormously among plant species but we have little understanding of how this variation affects their functioning. Of central interest is how root traits are related to plant resource ...acquisition strategies from soil. We examined root traits of 33 woody species from northeastern US forests that form two of the most common types of mutualisms with fungi, arbuscular mycorrhizas (AM) and ectomycorrhizas (EM). We examined root trait distribution with respect to plant phylogeny, quantifying the phylogenetic signal (K statistic) in fine root morphology and architecture, and used phylogenetically independent contrasts (PICs) to test whether taxa forming different mycorrhizal associations had different root traits. We found a pattern of species forming roots with thinner diameters as species diversified across time. Given moderate phylogenetic signals (K = 0.44–0.68), we used PICs to examine traits variation among taxa forming AM or EM, revealing that hosts of AM were associated with lower branching intensity (rPIC = −0.77) and thicker root diameter (rPIC = −0.41). Because EM evolved relatively more recently and intermittently across plant phylogenies, significant differences in root traits and colonization between plants forming AM and EM imply linkages between the evolution of these biotic interactions and root traits and suggest a history of selection pressures, with trade‐offs for supporting different types of associations. Finally, across plant hosts of both EM and AM, species with thinner root diameters and longer specific root length (SRL) had less colonization (rPIC = 0.85, −0.87), suggesting constraints on colonization linked to the evolution of root morphology.
We examined root traits of 33 woody species co‐existing in Northeastern US forests that form two of the most common types of mutualisms with fungi, arbuscular mycorrhizas (AM) and ectomycorrhizas (EM). We found patterns of plants forming roots with thinner diameters as species diversified across time; and that the AM habit was associated with lower branching intensity (rPIC = −0.77) and thicker root diameter (rPIC = −0.41) and the EM habit. We discuss findings in light of selection pressures on root traits and trade‐offs for supporting different types of fungal symbionts.
Summary
The effects of plants on the biosphere, atmosphere and geosphere are key determinants of terrestrial ecosystem functioning. However, despite substantial progress made regarding plant ...belowground components, we are still only beginning to explore the complex relationships between root traits and functions. Drawing on the literature in plant physiology, ecophysiology, ecology, agronomy and soil science, we reviewed 24 aspects of plant and ecosystem functioning and their relationships with a number of root system traits, including aspects of architecture, physiology, morphology, anatomy, chemistry, biomechanics and biotic interactions. Based on this assessment, we critically evaluated the current strengths and gaps in our knowledge, and identify future research challenges in the field of root ecology. Most importantly, we found that belowground traits with the broadest importance in plant and ecosystem functioning are not those most commonly measured. Also, the estimation of trait relative importance for functioning requires us to consider a more comprehensive range of functionally relevant traits from a diverse range of species, across environments and over time series. We also advocate that establishing causal hierarchical links among root traits will provide a hypothesis‐based framework to identify the most parsimonious sets of traits with the strongest links on functions, and to link genotypes to plant and ecosystem functioning.
While there are many theories and a variety of innovative datasets contributing to our understanding of the mechanism generating root pressure in vascular plants, we are still unable to produce a ...specific cellular mechanism for any species. To discover these mechanisms, we used RNA-Seq to explore differentially expressed genes in three different tissues between individual Zea mays plants expressing root pressure and those producing none. Working from the perspective that roots cells are utililizing a combination of osmotic exudation and hydraulic pressure mechanisms to generate positively-pressured flow of water into the xylem from the soil, we hypothesized that differential expression analysis would yield candidate genes coding for membrane transporters, ion channels, ATPases, and hormones with clear relevance to root pressure generation. In basal stem and coarse root tissue, we observed these classes of differentially expressed genes and more, including a strong cytoskeletal remodeling response. Fine roots displayed remarkably little differential expression relevant to root pressure, leading us to conclude that they either do not contribute to root pressure generation or are constitutively expressing root pressure mechanisms regardless of soil water content.
Abstract
Water and nitrogen (N) are the most limiting factors to plant productivity globally, but we lack a critical understanding of how water availability impacts N dynamics in agricultural ...systems. Plant N requirements are particularly uncertain when water is limited because of the interactive effect of water and N on plant growth, N demand, and plant uptake. We investigated impacts of N application and water availability on plant growth and N movement, including above and belowground growth, water productivity, N productivity, N uptake, N recovery, and greenhouse gas emissions within a semi-arid system in northeastern Colorado, USA. Moderately high soil N availability depressed grain yield and shoot growth under both limited and full water availability, despite no indication of physical toxicity, and came with additional risk of deleterious N losses. Under low N availability, plant N concentrations in aboveground tissues showed greater recovery of N than what was applied in the low N treatments under both full and limited water availability. This enhanced recovery underscores the need to better understand both plant soil foraging and processes governing resource availability under these conditions. Finally, limited water availability reduced N uptake across all N treatments and left 30% more soil nitrate (NO
3
−
) deep in the soil profile at the end of the season than under full water availability. Our results show that plant N needs are not linearly related to water use and emphasize the need for an integrated understanding of water and N interactions, plant foraging for these resources, and the dynamics of processes that make N available to plants.
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