Reproductive phenology as a dimension of the phenotypic space in 139 plant species from the Mediterranean.

Phenology, the study of seasonal timing of events in nature, plays a key role in the matching between organisms and their environment. Yet, it has been poorly integrated in trait-based descriptions of the plant phenotype. Here, we focus on three phases of reproductive phenology - time of flowering, time of seed dispersal and duration of seed maturation - to test how these traits relate to other recognized dimensions of plant functioning. Traits describing reproductive phenology, together with reproductive plant height, seed mass, area of a leaf, and traits involved in leaf economics, were compiled for 139 species growing under Mediterranean climate conditions. Across all species, flowering time was positively related to reproductive height, while the duration of seed maturation was related to leaf economics. Relationships differed among growth forms, however: flowering time and reproductive height were related both in annuals and in herbaceous perennials, whereas the duration of seed maturation was related to seed mass only in annuals; no correlations were found for woody species. Phenology relates to other dimensions of plant functioning in a complex manner, suggesting that it should be considered as an independent dimension in the context of plant strategies.

Fast-growing willows significantly reduce invasive knotweed spread.

Competitive interactions seem to play a major role in invasive plant success. However, they have mostly been addressed through the invader impacts on other species of the plant community and rarely through the way plant communities can contain alien species. Understanding such mechanisms would help in designing restoration projects using plant community competitive properties to control invasive populations. In this study, we looked at the role of competitive interactions in the success of Fallopia japonica (Houtt.) Ronse Decraene using a native willow frequently used in bioengineering techniques: Salix viminalis L. S. viminalis has a high growth rate and is, as such, a potential candidate to compete with F. japonica in restoration projects of invaded areas. Both species were grown in semi-controlled conditions in mesocosms (truck dumpsters), alone or in competition. Morphological traits (plant height, specific leaf area) as well as biomass (aboveground and underground) were measured on each species during two growing seasons. We also quantified spatial expansion of F. japonica. Even under a dense canopy of S. viminalis, F. japonica was able to survive and grow. However, its performance was significantly reduced compared to monocultures and its spatial colonization was less extended. Although S. viminalis biomass was affected by F. japonica, F. japonica expressed competitive stress through a modification of ramet density and height. There was no significant effect of F. japonica on S. viminalis height, enabling this species to dominate. Synthesis and applications: We conclude that S. viminalis succeeded in reducing F. japonica growth by developing a competitive canopy. Bioengineering techniques aiming at restoring a competitive neighborhood can control F. japonica. However, F. japonica's broad underground extension should be taken into account in any management strategy in order to successfully limit its development and spatial spread.

Differential allelopathic effects of Japanese knotweed on willow and cottonwood cuttings used in riverbank restoration techniques.

Using bioengineering techniques to restore areas invaded by Fallopia japonica shows promising results. Planting tree cuttings could allow both rapidly re-establishing a competitive native plant community and reducing F. japonica performance. However, F. japonica has been shown to affect native plant species through different mechanisms such as allelopathy. This article investigates the phytotoxic effect of F. japonica on the resprouting capacity and the growth of three Salicaceae species with potential value for restoration. An experimental design which physically separates donor pots containing either an individual from F. japonica or bare soil from target pots containing cuttings of Populus nigra, Salix atrocinerea or Salix viminali was used. Leachates from donor pots were used to water target pots. The effects of leachates were evaluated by measuring the final biomass of the cuttings. F. japonica leachates inhibited the growth of cuttings, and this effect is linked to the emission of polyphenol compounds by F. japonica. Leachates also induced changes in soil nitrogen composition. These results suggest the existence of allelopathic effects, direct and/or indirect, of F. japonica on the growth of Salicaceae species cuttings. However, the three species were not equally affected, suggesting that the choice of resistant species could be crucial for restoration success.

PhenoSpace: A Shiny application to visualize trait data in the phenotypic space of the global spectrum of plant form and function.

A recent analysis of variation in six major traits conducted on a large worldwide sample of vascular plant species showed that three-quarters of trait variation was captured by a two-dimensional global spectrum of plant form and function ("global spectrum" hereafter). We developed the PhenoSpace application, whose aim is to visualize and export the position of any individual/population/species in the phenotypic space of the global spectrum.PhenoSpace is a Shiny application that helps users to manipulate and visualize data pertaining to the global spectrum of plant form and function. It is freely accessible at the following URL: https://shiny.cefe.cnrs.fr/PhenoSpace/.PhenoSpace has three main functionalities. First, it allows users to visualize the phenotypic space of the global spectrum using different combinations of traits and growth forms. Second, trait data from any new user-defined dataset can be projected onto the phenotypic space of the global spectrum, provided that at least two of the six traits are available. Finally, figures produced and loadings of the imported data on the PCA axes can be downloaded, allowing users to conduct further analyses.PhenoSpace fulfills the practical goal of positioning plants in the phenotypic space of the global spectrum, making it possible to compare trait variation at any level of organization against the worldwide background. This serves a major aim of comparative plant ecology, which is to put specific sets of individuals, populations or species into a broader context, facilitating comparison and synthesis of results across different continents and environments using relevant indicators of plant design and function.

The worldwide leaf economics spectrum.

Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.

Differential impacts of plant interactions on herbaceous species recruitment: disentangling factors controlling emergence, survival and growth of seedlings.

Recruitment is a crucial event in the plant life cycle that is very sensitive to interaction with established vegetation. Based on a large comparative experiment, we tested the hypothesis that the components of recruitment--emergence time and rate, seedling survival and biomass--differ in response to plant-plant interactions during recruitment. The consequences for the population are predicted with a simple demographic model assessing the response of seed production. In a common garden experiment, we recorded the recruitment of four target species in an individual-based survey protocol. A total of 7,680 seeds were sown within 20 neighbourhoods, consisting of 19 mono-specific herbaceous stands and a control treatment without vegetation. We measured transmitted light, temperature and moisture at soil surface to characterise the environmental conditions within neighbourhoods. The mean height of neighbours controlled temperature buffering and light interception and thus depicted the interaction gradient. Emergence rate and time increased with neighbour height in two of the four target species, while seedling survival and biomass significantly decreased with neighbour height in three and all four target species, respectively. We recorded a shift in seedling neighbour interactions under the tallest neighbours that largely favoured emergence but strongly depressed seedling survival and biomass. The components of recruitment were predicted to differ in their impact on later adult performance. Biomass strongly contributed to predicted seed production in three target species, and emergence had an equal or greater impact on a fourth species. These results confirm the fundamental role of plant-plant interactions in the recruitment of herbaceous species through a complex combination of habitat amelioration, which facilitates emergence and light competition, which in turn limits seedling survival and biomass.

Competition, traits and resource depletion in plant communities.

Although of primary importance to explain plant community structure, general relationships between plant traits, resource depletion and competitive outcomes remain to be quantified across species. Here, we used a comparative approach to test whether instantaneous measurements of plant traits can capture both the amount of resources depleted under plant cover over time (competitive effect) and the way competitors perceived this resource depletion (competitive response). We performed a large competition experiment in which phytometers from a single grass species were transplanted within 18 different monocultures grown in a common-garden experiment, with a time-integrative quantification of light and water depletion over the phytometers' growing season. Resource-capturing traits were measured on both phytometers (competitive response traits) and monocultures (competitive effect traits). The total amounts of depleted light and water availabilities over the season strongly differed among monocultures; they were best estimated by instantaneous measurements of height and rooting depth, respectively, performed when either light or water became limiting. Specific leaf area and leaf water potential, two competitive response traits measured at the leaf level, were good predictors of changes in phytometer performance under competition, and reflected the amount of light and water, respectively, perceived by plants throughout their lifespan. Our results demonstrated the relevance of instantaneous measures of plant traits as indicators of resource depletion over time, validating the trait-based approach for competition ecology.

Plant growth and competition at elevated CO2 : on winners, losers and functional groups.

The effects of increased atmospheric CO2 concentrations on vegetative growth and competitive performance were evaluated, using five meta-analyses. Paying special attention to functional groups, we analysed responses at three integration levels: carbon economy parameters, vegetative biomass of isolated plants, and growth in competition. CO2 effects on seed biomass and plant-to-plant variability were also studied. Underlying the growth stimulation is an increased unit leaf rate (ULR), especially for herbaceous dicots. This is mainly caused by an increase in the whole-plant rate of photosynthesis. The increased ULR is accompanied by a decrease in specific leaf area. The net result of these and other changes is that relative growth rate is only marginally stimulated. The biomass enhancement ratio (BER) of individually grown plants varies substantially across experiments/species, and size variability in the experimental populations is a vital factor in this. Fast-growing herbaceous C3 species respond more strongly than slow-growing C3 herbs or C4 plants. CAM species and woody plants show intermediate responses. When grown in competition, C4 species show lowest responses to elevated CO2 at high nutrient conditions, whereas at low nutrient levels N2 -fixing dicots respond relatively strongly. No systematic differences were found between slow- and fast-growing species. BER values obtained for isolated plants cannot be used to estimate BER of the same species grown in interspecific competition - the CO2 response of monocultures may be a better predictor. Contents Summary 175 I. Introduction 176 II. Materials and Methods 177 III. Factors underlying the growth response 178 IV. Variation in biomass enhancement ratio 181 V. Functional groups of species 184 VI. The response in a more natural environment 188 VII. An outlook 192 VIII. Conclusions 193 Acknowledgements 193 References 193 Appendices 196.

Leaf life span, dynamics and construction cost of species from Mediterranean old-fields differing in successional status.

• Variations in leaf life span (LLS), construction cost (CC) and dynamics patterns (periods of leaf production, tp , and loss, tL , time lag separating the end of leaf production and the beginning of leaf loss, t) were investigated in species differing in successional status and life forms. We tested how those traits varied along the succession and how these were interrelated. A new graphical framework is proposed to assess the influence of dynamics traits on LLS. • The study was conducted on 42 species of contrasted life forms, typical of various stages of secondary succession, under the Mediterranean climate of southern France. • LLS increased along the succession, tp was shorter and t longer in species from the later stage, without significant change in CC or tL . Herbaceous species, mostly of early successional status, had short-lived, low-CC leaves, produced and lost continuously. Woody species, of later successional status, had long-lived leaves, with slightly higher CC than herbs. LLS and CC or payback time were weakly correlated. • Variations in LLS and leaf dynamics along the succession were related to changes in plant stature and growth potential of species, captured by leaf traits. Whether this is the consequence of a decrease in frequency of disturbance or of a change in the level of resources remains an open question.

Specific leaf area and dry matter content estimate thickness in laminar leaves.

BACKGROUND AND AIMS: Leaf thickness plays an important role in leaf and plant functioning, and relates to a species' strategy of resource acquisition and use. As such, it has been widely used for screening purposes in crop science and community ecology. However, since its measurement is not straightforward, a number of estimates have been proposed. Here, the validity of the (SLA x LDMC)(-1) product is tested to estimate leaf thickness, where SLA is the specific leaf area (leaf area/dry mass) and LDMC is the leaf dry matter content (leaf dry mass/fresh mass). SLA and LDMC are two leaf traits that are both more easily measurable and often reported in the literature. METHODS: The relationship between leaf thickness (LT) and (SLA x LDMC)(-1) was tested in two analyses of covariance using 11 datasets (three original and eight published) for a total number of 1039 data points, corresponding to a wide range of growth forms growing in contrasted environments in four continents. KEY RESULTS AND CONCLUSIONS: The overall slope and intercept of the relationship were not significantly different from one and zero, respectively, and the residual standard error was 0.11. Only two of the eight datasets displayed a significant difference in the intercepts, and the only significant difference among the most represented growth forms was for trees. LT can therefore be estimated by (SLA x LDMC)(-1), allowing leaf thickness to be derived from easily and widely measured leaf traits.