Importance de l'agriculture dans la dynamique spatio-temporelle du paysage (exemple du Causse Méjean)

MONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF

Genetic diversity and clonal structure of Rubia peregrina in mediterranean vineyard and unmanaged habitats

38 ref.International audienc

Compétition, réduction des ressources et traits fonctionnels dans les communautés herbacées

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

PLANT TRAITS RELATED TO COMPETITION: HOW DO THEY SHAPE THE FUNCTIONAL DIVERSITY OF COMMUNITIES?

International audienceThe identification of functional traits critical to plant responses to the environment is renewing community ecology by giving an understanding of the assembly of communities that relies on environmental filtering. However, the recent trait-community approaches mostly ignore the influence of plant-plant interactions by mainly focusing on traits related to abiotic filtering processes. The conceptual framework we propose aims at clarifying how the functional diversity of communities depends on the filtering effect of competition on relevant traits. We define two types of competition-related traits: competitive effect traits reflect the changes in local resource levels due to plant activity while competitive response traits are related to plant response to these resource depletions. We then suggest that the contribution of both types of competition-related traits to functional diversity depends on the importance of competition, previously defined as the effect of competition on plant fitness relative to that of other environmental factors. Therefore, the divergence of functional diversity is predicted to be maximized at intermediate levels of competition in relation to the coexistence of species with different strategies characterized by highly contrasted values of competition-related traits

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 neigbourhoods, 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.GEOTRAITS project (French National Programme ECCO-PNBC

Les mécanismes du recrutement des plantules et leurs effets sur la vitesse d'invasion des ligneux pionniers dans les pelouses (comparaison d'une espèce indigène (Pinus sylvestris L.) et d'une espèce introduite (Pinus nigra Arn. subsp. nigra) dans les grands Causses)

MONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF

Effect of date of emergence on the growth of the clonal perennial Cyperus esculentus in the Haute Lande, south-western France

International audienceIn order to develop management strategies in an intensive agricultural region of south-western France, we examined in a two-year experiment, the consequences of change in emergence date on the growth and development of the clonal perennial Cyperus esculentus. Germinated tubers emerged in early May, June and late July and were harvested 4, 5 or 6 months after emergence. Total shoot and tuber number per individual increased throughout the growing season, then significantly decreased in autumn. All plants produced tubers, the primary means of reproduction, including the smallest and latest emerging cohorts, but the allocation to tubers decreased with emergence date. However, emergence date had no effect on the emergence rate of the shoots, indicating that the reduction in total shoot production was not counterbalanced by an acceleration of this production when the growing season shortened. Consequently, management programs should advantageously integrate agricultural practices (i) that avoid periods without crops between April and October, (ii) that delay C. esculentus emergence and (iii) that include interventions on the newly emerged individuals

How relevant are instantaneous measurements for assessing resource depletion under plant cover? A test on light and soil water availability in 18 herbaceous communities

International audience1. Quantifying the amount of resources remaining under plant cover is essential for assessing plant–plant interactions or biological invasions. Although resource levels fluctuate in time, their quantification is performed mainly by instantaneous measurements. We investigated how instantaneous measurements are related to the amount of resources cumulated throughout one growing season, measuring parameters of both light and soil water depletion. 2. During a growing season, we measured regularly light and soil water levels under the cover of 18 plant species grown as monocultures in a common garden. The temporal dynamics of light and soil water depletion were assessed within each monoculture using mechanistic modelling approaches. 3. The total amounts of resources remaining over the year under the range of communities were best predicted by instantaneous measurements performed at critical periods, differing among resources. The significance of prediction decreased dramatically for other dates, including the period of peak production, but without changing the ranking of communities according to ability to deplete resources. We therefore recommend that such measurements should be limited to qualitative studies, and that mechanistic modelling for quantitative assessments should be developed

Mécanismes de régénération des espèces végétales dans les prairies subalpines sur un gradient d extensification des pratiques agricoles

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Questioning the reliability of the point intercept method for assessing community functional structure in low-productive and highly diverse Mediterranean grasslands

Quantifying species relative abundances in plant communities remains a key issue for the assessment of community functional structure. This is particularly challenging when non-destructive estimates are required over time. We tested whether the point intercept method (PIM), originally developed for low-diverse communities, is relevant for assessing the aboveground biomass and functional structure of highly diverse, low-productive Mediterranean grasslands. We sampled 18 communities with the PIM along a gradient of soil depth and texture, twice over the growing season. After each sampling period, we harvested the aboveground biomass in order to measure species biomass and to assess species richness and community functional structure with plant height, leaf area and leaf dry matter content (LDMC). We investigated the relationship between point intercept measurements and aboveground biomass at three hierarchical levels (species, growth-form and community) to find generalizable calibration equations for estimating community biomass and tested for sensitivity of estimates to community structure. We then compared the community weighted mean (CWM) and variance (CWV) of LDMC, calculated with and without calibration. Differences in species growth strategy and phenology strongly impacted biomass estimates at both the species and the community level. These differences were, however, successfully accounted for by growth-form specific calibrations, which provided accurate estimates without any influence of community structure. Lack of calibration may have dramatic consequences on functional structure assessment by inducing errors in estimates of CWV up to 80 %, depending on growth-form proportions. This work contributes to a better understanding of the possible methodological biases induced during sampling with the PIM, when quantifying species relative abundances for functional structure assessment in complex communities