Suites of root traits differ between annual and perennial species growing in the field

Here, we tested whether root traits associated with resource acquisition and conservation differed between life histories (annuals, perennials) and families (Fabaceae, Asteraceae and Poaceae). Root topology, morphology, chemistry and mycorrhizal colonization were measured on whole root systems of 18 field-grown herbaceous species grown and harvested in central Argentina. Annuals differed from perennials in several root traits important in resource uptake and conservation. They exhibited higher specific root length (SRL), root nitrogen concentration (RNC) and mycorrhizal colonization but had lower root tissue density (RTD) than perennials. They did not differ in topology or construction cost. These differences were consistent among families. Families differed only in a few root traits known to be strongly associated with certain lineages such as topology and nitrogen concentration. There was a strong parallel between root traits and analogous leaf traits described in the literature for annuals and perennials. Our results suggest the existence at the root level of an acquisitive vs conservative syndrome consistent among families similar to that previously reported for above-ground traits.     

Root exudation rate as functional trait involved in plant nutrient‐use strategy classification

Plants adopt a variety of life history strategies to succeed in the Earth's diverse environments. Using functional traits which are defined as “morphological, biochemical, physiological, or phonological” characteristics measurable at the individual level, plants are classified according to their species’ adaptative strategies, more than their taxonomy, from fast growing plant species to slower‐growing conservative species. These different strategies probably influence the input and output of carbon (C)‐resources, from the assimilation of carbon by photosynthesis to its release in the rhizosphere soil via root exudation. However, while root exudation was known to mediate plant‐microbe interactions in the rhizosphere, it was not used as functional trait until recently. Here, we assess whether root exudate levels are useful plant functional traits in the classification of plant nutrient‐use strategies and classical trait syndromes? For this purpose, we conducted an experiment with six grass species representing along a gradient of plant resource‐use strategies, from conservative species, characterized by low biomass nitrogen (N) concentrations and a long lifespans, to exploitative species, characterized by high rates of photosynthesis and rapid rates of N acquisition. Leaf and root traits were measured for each grass and root exudate rate for each planted soil sample. Classical trait syndromes in plant ecology were found for leaf and root traits, with negative relationships observed between specific leaf area and leaf dry matter content or between specific root length and root dry matter content. However, a new root trait syndrome was also found with root exudation levels correlating with plant resource‐use strategy patterns, specifically, between root exudation rate and root dry matter content. We therefore propose root exudation rate can be used as a key functional trait in plant ecology studies and plant strategy classification.     

Mycorrhizal associations in the Patagonian steppe,Argentina

The mycorrhizal status of plant species in north-west Patagonia was examined. Communities representative of Patagonian steppe and marshes were compared with respect to the mycorrhizal status of their species.Most of both native and exotic plant species sampled were arbuscular mycorrhizal (AM). The percentage of species with mycorrhizal association was higher for perennial herbs and shrubs than for annual herbs. The higher ratio of mycorrhizal/nonmycorrhizal (NM) species found for dicotyledons than for monocotyledons, could reflect the presence of a considerable number of NM monocotyledons in the marsh. The mycorrhizal status of plants differed slightly between the steppe and the marsh. In the steppe, native AM species were more frequent than in the marsh. In contrast, in the marsh, the NM species were proportionally more represented than in the steppe. The Juncaceae and Cyperaceae, which include hydrohytic NM plants, accounted for many of these differences. Moreover, the dominant species in the marshes, Juncus arcticus, is a NM species.In the present study, most of species belonging to the same taxonomic family tended to have the same mycorrhizal associations, in agreement with studies on plants from other regions. Exceptions to this general behaviour were observed in the families Cyperaceae, Scrophulariaceae, Berberidaceae and Amaryllidaceae. The most represented families in which mycorrhizal behaviour differed between species of the same family were Asteraceae, Fabaceae and Poaceae. Senecio neaei (Asteraceae) and Boopis australis (Calyceraceae) showed facultative mycorrhizal behaviour.     

How do nitrogen and phosphorus deficiencies affect strigolactone production and exudation?

Plants exude strigolactones (SLs) to attract symbiotic arbuscular mycorrhizal fungi in the rhizosphere. Previous studies have demonstrated that phosphorus (P) deficiency, but not nitrogen (N) deficiency, significantly promotes SL exudation in red clover, while in sorghum not only P deficiency but also N deficiency enhances SL exudation. There are differences between plant species in SL exudation under P- and N-deficient conditions, which may possibly be related to differences between legumes and non-legumes. To investigate this possibility in detail, the effects of N and P deficiencies on SL exudation were examined in Fabaceae (alfalfa and Chinese milk vetch), Asteraceae (marigold and lettuce), Solanaceae (tomato), and Poaceae (wheat) plants. In alfalfa as expected, and unexpectedly in tomato, only P deficiency promoted SL exudation. In contrast, in Chinese milk vetch, a leguminous plant, and in the other non-leguminous plants examined, N deficiency as well as P deficiency enhanced SL exudation. Distinct reductions in shoot P levels were observed in plants grown under N deficiency, except for tomato, in which shoot P level was increased by N starvation, suggesting that the P status of the shoot regulates SL exudation. There seems to be a correlation between shoot P levels and SL exudation across the species/families investigated.     

Plant growth strategy determines the magnitude and direction of drought-induced changes in root exudates in subtropical forests

Root exudates are an important pathway for plant–microbial interactions and are highly sensitive to climate change. However, how extreme drought affects root exudates and the main components, as well as species-specific differences in response magnitude and direction, are poorly understood. In this study, root exudation rates of total carbon (C) and its components (e.g., sugar, organic acid, and amino acid) were measured under the control and extreme drought treatments (i.e., 70% throughfall reduction) by in situ collection of four tree species with different growth rates in a subtropical forest. We also quantified soil properties, root morphological traits, and mycorrhizal infection rates to examine the driving factors underlying variations in root exudation. Our results showed that extreme drought significantly decreased root exudation rates of total C, sugar, and amino acid by 17.8%, 30.8%, and 35.0%, respectively, but increased root exudation rate of organic acid by 38.6%, which were largely associated with drought-induced changes in tree growth rates, root morphological traits, and mycorrhizal infection rates. Specifically, trees with relatively high growth rates were more responsive to drought for root exudation rates compared with those with relatively low growth rates, which were closely related to root morphological traits and mycorrhizal infection rates. These findings highlight the importance of plant growth strategy in mediating drought-induced changes in root exudation rates. The coordinations among root exudation rates, root morphological traits, and mycorrhizal symbioses in response to drought could be incorporated into land surface models to improve the prediction of climate change impacts on rhizosphere C dynamics in forest ecosystems.     

Functional aspects of root architecture and mycorrhizal inoculation with respect to nutrient uptake capacity

The aim of this research was to investigate the effect of arbuscular mycorrhizal (AM) colonisation on root morphology and nitrogen uptake capacity of carob ( Ceratonia siliqua L.) under high and low nutrient conditions. The experimental design was a factorial arrangement of presence/absence of mycorrhizal fungus inoculation ( Glomus intraradices) and high/low nutrient status. Percent AM colonisation, nitrate and ammonium uptake capacity, and nitrogen and phosphorus contents were determined in 3-month-old seedlings. Grayscale and colour images were used to study root morphology and topology, and to assess the relation between root pigmentation and physiological activities. AM colonisation lead to a higher allocation of biomass to white and yellow parts of the root. Inorganic nitrogen uptake capacity per unit root length and nitrogen content were greatest in AM colonised plants grown under low nutrient conditions. A better match was found between plant nitrogen content and biomass accumulation, than between plant phosphorus content and biomass accumulation. It is suggested that the increase in nutrient uptake capacity of AM colonised roots is dependent both on changes in root morphology and physiological uptake potential. This study contributes to an understanding of the role of AM fungi and root morphology in plant nutrient uptake and shows that AM colonisation improves the nitrogen nutrition of plants, mainly when growing at low levels of nutrients.     

Effect of mutations in the pea genes <Emphasis Type="Italic">Sym33</Emphasis> and <Emphasis Type="Italic">Sym40</Emphasis>

Two pea (Pisum sativum L.) symbiotic mutants SGEFix(-)-1 (sym40) and SGEFix(-)-2 (sym33) with abnormalities in infection thread development and function in symbiotic root nodules have been characterised in terms of mycorrhizal colonisation of roots, shoot and root biomass accumulation and shoot and root phosphorus (P) content. The mutation in gene sym33 decreased mycorrhizal colonisation of roots (except arbuscule abundance in mycorrhizal root fragments, which increased) but did not change the effectiveness of mycorrhiza function. The mutation in sym40 did not affect either of these processes. Both mutants showed differences in plant development compared with the wild-type line SGE. The mutants had delayed flowering and pod ripening, and shoot/root biomass ratios and P accumulation also differed from those of SGE. These observations suggest that the gene mutations cause systemic changes in plant development.     

Insights into mycorrhizal colonisation at elevated CO2: a simple carbon partitioning model

A simulation model was used to investigate the effect of an increased rate of plant photosynthesis at enhanced atmospheric CO2 concentration on a non-leguminous plant-mycorrhizal fungus association. The model allowed the user to modify carbon allocation patterns at three levels: (1) within the plant (shoot–root), (2) between the plant and the mycorrhizal fungus and (3) within the mycorrhizal fungus (intraradical–extraradical structures). Belowground (root and fungus) carbon losses via respiration (and turnover) could also be manipulated. The specific objectives were to investigate the dynamic nature of the potential effects of elevated CO2 on mycorrhizal colonisation and to elucidate some of the various mechanisms by which these effects may be negated. Many of the simulations showed that time (i.e. plant age) had a more significant effect on the observed stimulation of mycorrhizal colonisation by elevated CO2 than changes in carbon allocation patterns or belowground carbon losses. There were two main mechanisms which negated a stimulatory effect of elevated CO2 on internal mycorrhizal colonisation: an increased mycorrhizal carbon allocation to the external hyphal network and an increased rate of mycorrhizal respiration. The results are discussed in relation to real experiments. The need for studies consisting of multiple harvests is emphasised, as is the use of allometric analysis. Implications at the ecosystem level are discussed and key areas for future research are presented.     

Positive association between mycorrhiza and foliar endophytes in Poa bonariensis, a native grass

The interaction between mycorrhiza and leaf endophytes (Neotyphodium sp.) was studied in three Poa bonariensis populations, a native grass, differing significantly in endophyte infection. The association between endophytes and mycorrhizal fungi colonisation was assessed by analysing plant roots collected from the field. We found that roots from endophyte-infected populations showed a significantly higher frequency of colonisation by mycorrhizal fungi and that soil parameters were not related to endophyte infection or mycorrhiza colonization. In addition, we did not observe significant differences in the number of AM propagules in soils of the three populations sites. We also report the simultaneous development of Paris-type and Arum-type mycorrhiza morphology within the same root systems of P. bonariensis. The co-occurrence of both colonisation types in one and the same root system found in the three populations, which differed in Neotyphodium infection, suggests that foliar endophytes do not determine AM morphology. The percentage of root length colonised by different types of fungal structures (coils, arbuscules, longitudinal hyphae and vesicles) showed significant and positive differences in arbuscular frequency associated with endophyte infection, whereas the much smaller amounts of vesicles and hyphal coils did not differ significantly.     

Multifunctionality is affected by interactions between green roof plant species,substrate depth,and substrate type

Green roofs provide ecosystem services through evapotranspiration and nutrient cycling that depend, among others, on plant species, substrate type, and substrate depth. However, no study has assessed thoroughly how interactions between these factors alter ecosystem functions and multifunctionality of green roofs. We simulated some green roof conditions in a pot experiment. We planted 20 plant species from 10 genera and five families (Asteraceae, Caryophyllaceae, Crassulaceae, Fabaceae, and Poaceae) on two substrate types (natural vs. artificial) and two substrate depths (10 cm vs. 30 cm). As indicators of major ecosystem functions, we measured aboveground and belowground biomasses, foliar nitrogen and carbon content, foliar transpiration, substrate water retention, and dissolved organic carbon and nitrates in leachates. Interactions between substrate type and depth strongly affected ecosystem functions. Biomass production was increased in the artificial substrate and deeper substrates, as was water retention in most cases. In contrast, dissolved organic carbon leaching was higher in the artificial substrates. Except for the Fabaceae species, nitrate leaching was reduced in deep, natural soils. The highest transpiration rates were associated with natural soils. All functions were modulated by plant families or species. Plant effects differed according to the observed function and the type and depth of the substrate. Fabaceae species grown on natural soils had the most noticeable patterns, allowing high biomass production and high water retention but also high nitrate leaching from deep pots. No single combination of factors enhanced simultaneously all studied ecosystem functions, highlighting that soil–plant interactions induce trade‐offs between ecosystem functions. Substrate type and depth interactions are major drivers for green roof multifunctionality.     

Effects of vesicular-arbuscular mycorrhizal infection and phosphate on Plantago major ssp. pleiosperma in relation to the internal phosphate concentration

Two experiments were carried out to study physiological effects of vesicular-arbuseular mycorrhizal infection on Plantago major L., ssp. pleiosperma (Pilger). In the first experiment, infection by the Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe increased growth, shoot to root ratio, P concentrations in both shoot and roots and total uptake of P per plant. The percentages of dry matter in both shoot and roots were lower in mycorrhizal plants.
In the second experiment different P treatments were applied to both mycorrhizal and non-mycorrhizal P. major plants to separate any effects of mycorrhizal infection from increased uptake of P. In addition to the effects found in the first experiment, mycorrhizal, P, and mycorrhizal x P interaction effects were found on root respiration rate and the concentration of soluble sugars in the roots. No clear effects on total dry weight, N and starch concentrations in shoot and roots and sugar concentraion in the shoot were found. Irrespective of the mycorrhizal treatment, increased P concentration in the shoot correlated with an increased shoot to root ratio and root respiration rate, and a decreased percentage dry matter and sugar concentration in the roots. However, the root respiration rate and the P concentration in the roots of mycorrhizal plants were enhanced more than expected from the increased P concentrations in the shoots of these plants.     

Mycorrhizal respiration: implications for global scaling relationships

Most plant species form mycorrhizas, yet these are neglected by plant physiologists. One consequence of this neglect is reduced ability to predict plant respiration, because respiration rate (R) in mycorrhizal roots might be higher than in non-mycorrhizal roots owing to increased substrate availability associated with enhanced nutrient uptake, coupled with increased respiratory product demand. Other predictions include that mycorrhizal colonization will affect scaling of R with tissue nitrogen concentrations; that mycorrhizal and non-mycorrhizal root R differ in their response to nutrient supply; and that the impact of colonization on R is related to fungal biomass. Failure to examine properly the role of colonization in determining root R means that current interpretations of root and soil respiration data might be flawed.     

Auxin influences strigolactones in pea mycorrhizal symbiosis

Hormone interactions are essential for the control of many developmental processes, including intracellular symbioses. The interaction between auxin and the new plant hormone strigolactone in the regulation of arbuscular mycorrhizal symbiosis was examined in one of the few auxin deficient mutants available in a mycorrhizal species, the auxin-deficient bsh mutant of pea (Pisum sativum). Mycorrhizal colonisation with the fungus Glomus intraradices was significantly reduced in the low auxin bsh mutant. The bsh mutant also exhibited a reduction in strigolactone exudation and the expression of a key strigolactone biosynthesis gene (PsCCD8). Strigolactone exudation was also reduced in wild type plants when the auxin content was reduced by stem girdling. Low strigolactone levels appear to be at least partially responsible for the reduced colonisation of the bsh mutant, as application of the synthetic strigolactone GR24 could partially rescue the mycorrhizal phenotype of bsh mutants. Data presented here indicates root auxin content was correlated with strigolactone exudation in both mutant and wild type plants. Mutant studies suggest that auxin may regulate early events in the formation of arbuscular mycorrhizal symbiosis by controlling strigolactone levels, both in the rhizosphere and possibly during early root colonisation.     

Mechanism of application nursery cultivation arbuscular mycorrhizal seedling in watermelon in the field

Arbuscular mycorrhizal fungi (AMF) colonisation of plant root facilitates the absorption of nutrients such as phosphorus (P) and enhances plant biotic and abiotic resistance generally. However, arbuscular mycorrhiza (AM) colonisation decreases with application of chemical fertiliser. Here, we investigated whether AMF inoculation in nurseries would facilitate AM colonisation and take physiological and ecological functions in watermelon (Citrullus lanatus) in the field. Pot experiments were carried out to study the change of AMF colonised seedling on physiology and gene expression in nursery site. Field experiments were performed to investigate the effect of nursery AMF inoculation on yield, quality and disease resistance of watermelon in the field. The results showed that nursery‐inoculated seedlings produced more dry matter and root surface area than non‐inoculated seedlings. Expression of the secretory purple acid phosphatase (PAP) genes ClaPAP10 and ClaPAP26 was up‐regulated following AMF colonisation. Accordingly, acid phosphatase activities at the root surface and P concentrations in seedling were enhanced. After transplantation to the field, the shoot dry matter and P concentration in old stem were higher in the nursery AMF inoculated seedlings than that in non‐AMF inoculated seedling. AMF inoculation also induced increase of yields and decrease of wilt disease indexes and soluble sugar content. In addition, acid phosphatase activities and AMF spore densities were increased by nursery‐inoculation in watermelon rhizosphere soil in the field. In conclusion, nursery colonisation AMF seedling enhanced watermelon growth and yield by improving the root growth and P acquisition in nursery cultivating stage, as well as optimised soil properties in the field. Nursery cultivation of watermelon seedling with AMF was an effective technique to reduce wilt disease in continuous cropped management in watermelon.     

Ancient whole genome duplications, novelty and diversification: the WGD Radiation Lag-Time Model

Many large and economically important plant groups (e.g. Brassicaceae, Poaceae, Asteraceae, Fabaceae and Solanaceae) have had ancient whole genome duplications (WGDs) occurring near or at the time of their origins, suggesting that WGD contributed to the origin of novel key traits and drove species diversification. However, these large clades show phylogenetic asymmetries with a species-rich crown group and a species-poor sister clade, suggesting significant 'lag-times' between WGDs and radiations. The species-poor sister groups share many key traits, but are often restricted to the hypothesized center of origin for the larger clade. Thus, the ultimate success of the crown group does not only involve the WGD and novel key traits, but largely subsequent evolutionary phenomena including later migration events, changing environmental conditions and/or differential extinction rates.     

Effect of plant nitrogen status on the contribution of arbuscular mycorrhizal hyphae to plant nitrogen uptake

The contribution of hyphae of Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) to the acquisition of mineral nitrogen by Triticum aestivum L. cv. Hano (wheat) was tested under conditions of low P and high N (+N−P) or low N (−N−P). Mycorrhizal colonisation increased the shoot dry weight and plant tissue concentrations of P and cations. However, N tissue concentrations of mycorrhizal plants were not increased, although nitrate reductase activities were significantly higher (in vivo activity) in +N−P mycorrhizal compared to non-mycorrhizal roots. Severe plant N deficiency reduced the percentage root length colonised (but not the percentage viable colonisation), hyphal length, total 15 N uptake by hyphae and dry weight of mycorrhizal plants. Although mycorrhizal colonisation did not affect the overall plant N status, hyphae transported 1% (−N−P) and 7% (+N−P) of the 15 N-labelled NH₄NO₃ to mycorrhizal plants over 48 h. The higher rate of hyphal N uptake was apparently related to the more extensive hyphal growth at the higher level of plant N supply. However, the hyphal N supply was not sufficiently high to sustain adequate N nutrition of the plants supplied with very low amounts of N to the roots. Conversely, a sufficient N supply to the roots was important for the development of an extensive mycelium.     

Functional traits and root morphology of alpine plants

Background and Aims

Vegetation has long been recognized to protect the soil from erosion. Understanding species differences in root morphology and functional traits is an important step to assess which species and species mixtures may provide erosion control. Furthermore, extending classification of plant functional types towards root traits may be a useful procedure in understanding important root functions.

Methods

In this study, pioneer data on traits of alpine plant species, i.e. plant height and shoot biomass, root depth, horizontal root spreading, root length, diameter, tensile strength, plant age and root biomass, from a disturbed site in the Swiss Alps are presented. The applicability of three classifications of plant functional types (PFTs), i.e. life form, growth form and root type, was examined for above- and below-ground plant traits.

Key Results

Plant traits differed considerably among species even of the same life form, e.g. in the case of total root length by more than two orders of magnitude. Within the same root diameter, species differed significantly in tensile strength: some species (Geum reptans and Luzula spicata) had roots more than twice as strong as those of other species. Species of different life forms provided different root functions (e.g. root depth and horizontal root spreading) that may be important for soil physical processes. All classifications of PFTs were helpful to categorize plant traits; however, the PFTs according to root type explained total root length far better than the other PFTs.

Conclusions

The results of the study illustrate the remarkable differences between root traits of alpine plants, some of which cannot be assessed from simple morphological inspection, e.g. tensile strength. PFT classification based on root traits seems useful to categorize plant traits, even though some patterns are better explained at the individual species level.     

黑果枸杞功能性状对氮磷添加的响应及其可塑性

分析养分添加对荒漠植物功能性状的影响,对揭示其响应和适应环境变化的规律至关重要.本研究以黑果枸杞为材料,设置3个氮磷(NP)添加量(低、中、高)和N/P(5∶1、15∶1、45∶1),量化分析了整株、根、茎、叶和果实性状对NP添加的响应.结果 表明:黑果枸杞功能性状差异化响应了NP添加量和比例,随NP添加量的增加,生物...     

Does responsiveness to arbuscular mycorrhizal fungi depend on plant invasive status?

Differences in the direction and degree to which invasive alien and native plants are influenced by mycorrhizal associations could indicate a general mechanism of plant invasion, but whether or not such differences exist is unclear. Here, we tested whether mycorrhizal responsiveness varies by plant invasive status while controlling for phylogenetic relatedness among plants with two large grassland datasets. Mycorrhizal responsiveness was measured for 68 taxa from the Northern Plains, and data for 95 taxa from the Central Plains were included. Nineteen percent of taxa from the Northern Plains had greater total biomass with mycorrhizas while 61% of taxa from the Central Plains responded positively. For the Northern Plains taxa, measurable effects often depended on the response variable (i.e., total biomass, shoot biomass, and root mass ratio) suggesting varied resource allocation strategies when roots are colonized by arbuscular mycorrhizal fungi. In both datasets, invasive status was nonrandomly distributed on the phylogeny. Invasive taxa were mainly from two clades, that is, Poaceae and Asteraceae families. In contrast, mycorrhizal responsiveness was randomly distributed over the phylogeny for taxa from the Northern Plains, but nonrandomly distributed for taxa from the Central Plains. After controlling for phylogenetic similarity, we found no evidence that invasive taxa responded differently to mycorrhizas than other taxa. Although it is possible that mycorrhizal responsiveness contributes to invasiveness in particular species, we find no evidence that invasiveness in general is associated with the degree of mycorrhizal responsiveness. However, mycorrhizal responsiveness among species grown under common conditions was highly variable, and more work is needed to determine the causes of this variation.     

Quantitative estimation of root exudation of maize plants

Summary The rate of root exudation of maize plants was estimated by measuring the rate of denitrification in a hermetically sealed root system. While CO₂ production measured in the rhizosphere results both from root respiration and microbial respiration N₂O production during nitrate respiration is solely related to the amount of root exudates available for bacterial degradation. With 4 week old plants growing in quartz sand or soil root exudation amounted to 7% of the net photosynthates. Calculations revealed that about 25% of the organic matter flowing into the root system was excreted into the rhizosphere.