Soil Microorganisms Alleviate the Allelochemical Effects of a Thyme Monoterpene on the Performance of an Associated Grass Species

Background: Plant allelochemicals released into the soil can significantly impact the performance of associated plant species thereby affecting their competitive ability. Soil microbes can potentially affect the interaction between plant and plant chemicals by degrading the allelochemicals. However, most often plant-plant chemical interactions are studied using filter paper bioassays examining the pair-wise interaction between a plant and a plant chemical, not taking into account the potential role of soil microorganisms. Methodology/Principal findings: To explore if the allelopathic effects on a grass by the common thyme monoterpene ‘‘carvacrol’ ’ are affected by soil microorganisms. Seedlings of the grass Agrostis capillaris originating from 3 different thyme sites were raised in the greenhouse. Seedlings were grown under four different soil treatments in a 2*2 fully factorial experiment. The monoterpene carvacrol was either added to standard greenhouse soil or left out, and soil was either sterilized (no soil microorganisms) or not (soil microorganisms present in soil). The presence of carvacrol in the soil strongly increased mortality of Agrostis plants, and this increase was highest on sterile soil. Plant biomass was reduced on soil amended with carvacrol, but only when the soil was also sterilized. Plants originating from sites where thyme produces essential oils containing mostly carvacrol had higher survival on soil treated with that monoterpene than plants originating from a site where thyme produced different types of terpenes, suggesting an adaptive response to the locally occurrin

"Menage à trois": the presence/absence of thyme shapes the mutualistic interaction between the host plant [i]Medicago truncatula[/i] (Fabaceae) and its symbiotic bacterium [i]Sinorhizobium meliloti[/i]

UMR 1334 AGAP : Equipe DAVEM Diversité et adaptation de la vigne et des espèces méditerranéennesThe long-term maintenance of specialized mutualisms remains an evolutionary puzzle. Recent focus has been on factors governing the stability of these mutualisms, including sanctions by the host, partner choice, and coevolutionary constraint, that is, the genetic correlation (r(G)) between fitness of both partners. So far these studies have been typically carried out in a single environment. Here, we ask if the genetic correlation between fitness of the host plant Medicago truncatula (Fabaceae) and its bacterial symbiont Sinorhizobium meliloti is affected by the presence/absence of a monoterpene (carvacrol) leached into the soil by Thymus vulgaris-a common plant of the Mediterranean vegetation, often co-occuring with Medicago. We show that the presence of carvacrol in the soil dramatically affects fitness of the rhizobial partner and increases the magnitude of rG between plant and rhizobia fitness (r(G) = 0.02 +/- 0.05 vs. r(G) = 0.57 +/- 0.02). This finding emphasizes the importance of heterogeneity in the biotic environment for understanding the evolution of species interactions

Summary of the logistic regression analysis on survival of <i>Agrostis</i> plants.

<p>Significance of test deviance is indicated by:</p><p>*P<0.05;</p><p>**P<0.01;</p><p>***P<0.001.</p

Biomass of <i>Agrostis capillaris</i> plants.

<p>Biomass (+/− SE) of plants growing in pots with the thyme monterpene carvacrol added to the soil (T) or not (no T) and on soil which was either sterilized or not.</p

Summary of ANOVA on plant biomass.

<p>Significance of F ratio is indicated by:</p><p>*P<0.05;</p><p>**P<0.01;</p><p>***P<0.001.</p

Survival of <i>Agrostis capillaris</i> plants.

<p>Observed probability (+/− SE) of survival of plants growing in pots where the thyme monoterpene carvacrol is either added to the soil (T) or not added (No T) and where the soil is either sterilized or not. Grey dots: <i>Agrostis</i> originating from populations where it co-occurs with <i>Thymus pulegiodes</i> (TP), black dots: <i>Agrostis</i> originating from a single population where is co-occurs with <i>T. serpyllum</i> (TS).</p

Water availability and population origin affect the expression of the tradeoff between reproduction and growth in Plantago coronopus

[EN] Investment in reproduction and growth represent a classic tradeoff with implication for life history evolution. The local environment can play a major role in the magnitude and evolutionary consequences of such a tradeoff. Here, we examined the investment in reproductive and vegetative tissue in 40 maternal half-sib families from four different populations of the herb Plantago coronopus growing in either a dry or wet greenhouse environment. Plants originated from populations with an annual or a perennial life form, with annuals prevailing in drier habitats with greater seasonal variation in both temperature and precipitation. We found that water availability affected the expression of the tradeoff (both phenotypic and genetic) between reproduction and growth, being most accentuated under dry condition. However, populations responded very differently to water treatments. Plants from annual populations showed a similar response to drought condition with little variation among maternal families, suggesting a history of selection favouring genotypes with high allocation to reproduction when water availability is low. Plants from annual populations also expressed the highest level of plasticity. For the perennial populations, one showed a large variation among maternal families in resource allocation and expressed significant negative genetic correlations between reproductive and vegetative biomass under drought. The other perennial population showed less variation in response to treatment and had trait values similar to those of the annuals, although it was significantly less plastic. We stress the importance of considering intraspecific variation in response to environmental change such as drought, as conspecific plants exhibited very different abilities and strategies to respond to high versus low water availability even among geographically close populations.The authors are grateful to R. Nielsen for her help in the greenhouse, J. Villelas for field assistance, and to J.G. Sørensen, T. Bataillon, M. Mend ez and R. Wesselingh for comments and suggestions to improve the manuscript. MBG benefited from the support of two Spanish National projects (CGL2006-08 507 and CGL2010-21 642), BKE had support from a research project supported by the Villum Foundation.Peer reviewe

Sex inheritance in gynodioecious species: a polygenic view

International audienceGynodioecy is defined as the coexistence of two different sexual morphs in a population: females and hermaphrodites. This breeding system is found among many different families of angiosperms and is usually under nucleo-cytoplasmic inheritance, with maternally inherited genes causing male sterility and nuclear factors restoring male fertility. Numerous theoretical models have investigated the conditions for the stable coexistence of females and hermaphrodites. To date, all models rest on the assumption that restoration of a given male sterile genotype is controlled by a single Mendelian factor. Here, we review data bearing on the genetic determinism of sex inheritance in three gynodiecious plant species. We suggest that restoration of male fertility is probably best viewed as a quantitative trait controlled by many loci. We develop a threshold model that accommodates an underlying polygenic trait, which is resolved at the phenotypic level in discrete sexual morphs. We use this model to reanalyse data in Thymus vulgaris, Silene vulgaris and Plantago coronopus. A simple Mendelian inheritance of sex determinism is unlikely in all three species. We discuss how our model can shed additional light on the genetics of restoration and point towards future efforts in the modelling of gynodioecy

Species-specific interference exerted by the shrub Cistus clusii Dunal in a semi-arid Mediterranean gypsum plant community

[Background]: The gypsovag shrub Cistus clusii is locally dominant in semi-arid gypsum plant communities of North-Eastern Spain. This species commonly grows in species-poor patches even though it has nurse potential, suggesting interference on neighbouring species. Other Cistus species exert a chemically mediated interference on plant communities, suggesting that it might be a common phenomenon in this genus. This study aimed investigating whether C. clusii exerts chemically mediated interference on neighbouring species in gypsum plant communities. We tested in a greenhouse whether aqueous extracts from C. clusii leaves (L), roots (R) and a mixture of both (RL) affected germination, seedling survival, and growth of nine native species of gypsum communities, including C. clusii itself. We further assessed in the field richness and abundance of plants under the canopy of C. clusii compared to Gypsophila struthium (shrub with a similar architecture having a nurse role) and in open patches. Finally, we specifically assessed in the field the influence of C. clusii on the presence of the species tested in the greenhouse experiment.[Results]: Aqueous extracts from C. clusii (R and RL) negatively affected either germination or survival in four of nine species. In the field, richness and abundance of plants were lower under the canopy of C. clusii than under G. struthium, but higher than in open patches. Specifically, five of nine species were less frequent than expected under the canopy of C. clusii.[Conclusions]: Cistus clusii shows species-specific interference with neighbouring species in the community, which may be at least partially attributable to its phytotoxic activity. To our knowledge, this is the first report of species-specific interference by C. clusii.This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (CGL2012-37508, CGL2016-80783-R). Funding provided by CGL2012-37508, CGL2016-80783-R research projects was used to pay the expenses derived from the field surveys and the laboratory analyses. This ministry also supported A. Foronda with a Ph.D. Grant (BES-2013-063852), favouring the data analyses and interpretation and the writing of the manuscript. A. Foronda also received a Grant from this ministry for a short research stay in Denmark (EEBB-I-15-10298), which allowed the collaboration with B. K. Ehlers and the performance of the greenhouse experiment and the laboratory analyses