Roberta M. Ceriani

Seed size, shape and persistence in soil: a test on Italian flora from Alps to Mediterranean coasts

Seed size is a good predictor of seed persistence in soil for British, Argentinean, Iranian and – to some extent – New Zealand species. It has been suggested that seed shape should also be linked to the ease of burial and, thus, to seed persistence, even if some studies failed to show this. The relationship between seed size and shape and persistence in soil was analysed for 259 species of the Italian flora, belonging to a wide range of habitats, from alpine pasture to limestone prairies and meadows of the Prealps, and from woodlands to Mediterranean maquis and garigues. Seed size was related to persistence in soil in the same way as in most other floras examined. Furthermore, seed shape was highly related to persistence in soil among the species analysed, when considered both altogether and divided among the different habitats. Our results suggest that not only seed size, but also seed shape, are key factors in determining seed fate and seed persistence in soil.

The leaf economics spectrum of Poaceae reflects variation in survival strategies

Abstract Leaf morphology reflects a trade-off between maximising resource acquisition and investment in structural/metabolic durability, and continuous variation in such leaf economics is apparent even within traditional plant functional type categories such as ‘grasses’. We hypothesised that the leaf economics spectrum of ‘grasses’ reflects a spectrum of survival strategies, with functional divergence apparent both within and between ecozones. CSR classification and histology of 30 Poaceae with ranges restricted to either the southern Alps or Po plain of Italy demonstrated that alpine species were predominantly stress-tolerators (mean C:S:R = 26.7:46.1:27.2%) but included some competitive ruderals (e.g. Agrostis schraderana). Lowland species were predominantly competitive ruderals but included some stress-tolerators (e.g. Stipa pennata). Functional relationships were confirmed by PCA: PCA1 represented a trade-off between high SLA, high foliar N, rapid phenology (competitive ruderals) and high foliar C:N and dry matter content (stress-tolerators). Stress-tolerance was negatively correlated with the extent of intercellular airspace, and positively with mesophyll, schlerenchyma and vascular tissues (a trade-off between internal conductivity and durability). The leaf economics spectrum of Poaceae reflects a spectrum of whole plant function, but only the overall plant strategy can elucidate the extent to which vegetative or reproductive phases are critical for survival.

How well do seed production traits correlate with leaf traits, whole-plant traits and plant ecological strategies?

AbstractThe principal axes of variation in plant function include the economics spectrum and size variation, both of which are implicated in primary ecological strategies. However, it is unclear to what extent vegetative traits and primary strategies correlate with reproductive traits, particularly for seed production. Fifteen traits, including whole-plant, leaf and seed traits (mass, number, total mass of seeds, volume and variance), were measured for 371 species from a range of habitats in Italy. Classification of Grime’s competitor, stress-tolerator, ruderal (CSR) strategies was applied from leaf area, leaf dry matter content and specific leaf area data. Relationships between vegetative traits, CSR values and seed traits were determined using principal components analysis (PCA) and Pearson’s correlation coefficients. PCA1 was an axis of economics, significantly correlated (positively) with leaf carbon concentration and S-selection, and (negatively) with leaf nitrogen concentration, flowering period and R-selection, but not seed traits. PCA2 was a plant size axis, significantly positively correlated with canopy height, leaf mass, C-selection and to a lesser extent seed size traits and total mass of seeds. PCA3 was a specific seed size-seed output axis, correlated positively with seed mass and volume, and negatively with seed number and variance. The loading of seed production traits on a general plant size axis alongside C-selection demonstrates that seed production traits are integral to CSR strategies. However, the stronger contribution of seed traits to a specific axis of variability is suggestive of reproductive variability beyond the CSR strategy, as predicted by the twin-filter model.

Are morpho-functional traits reliable indicators of inherent relative growth rate for prealpine calcareous grassland species?

Abstract Relative growth rate (RGR) is a fundamental trait for comparative plant ecology but cannot be measured in situ, leading to problems in interpreting vegetation function. However, the components of RGR (net assimilation rate (NAR), leaf area ratio (LAR), leaf weight ratio (LWR), and specific leaf area (SLA)) can be calculated for wild plants from morphological measurements (leaf area, leaf dry mass, whole plant dry mass), which potentially reflect RGR. Seeds of 19 species from Italian prealpine calcareous grasslands were collected and seedlings were cultivated under controlled conditions. RGR, NAR, LAR, LWR and SLA were analysed. The results demonstrated that RGR was positively correlated with SLA and LAR (p < 0.01). Furthermore, LAR was positively correlated with LWR and negatively with NAR (p < 0.05). Monocotyledons showed significantly higher LAR, LWR and NAR than dicotyledons, as the latter allocated a greater proportion of biomass to stems, but RGR and SLA showed no such phylogenetic constraint. Therefore SLA is the most reliable indicator of RGR in ecological and functional surveys of prealpine calcareous grasslands, and has the additional advantage that it can be measured from leaf material alone. Lower mean RGR and SLA for calcareous grassland species suggests that this vegetation is less likely to recover from the effects of disturbance than meadows and dry meadows.

Why are many anthropogenic agroecosystems particularly species-rich?

Species-rich meadow and pasture habitats are recognised by the European Union Habitats Directive as targets for biodiversity conservation. High species richness is hypothesised to be associated with diversity in plant functional traits and life-history strategies, which are potentially restricted in situations of extremely high and low biomass production. However, variability in functional traits has yet to be investigated across a broad biomass range in nature. We measured variability in a range of functional traits and Grimes competitor, stress-tolerator, ruderal (CSR) strategies for species comprising lowland meadows, subalpine pastures, abandoned grassland and field margins at sites in northern Italy, alongside peak above-ground biomass. The factor most highly and positively correlated with species richness was strategy richness (the number of CSR strategies; Pearsons r = 0.864, P < 0.0001, n = 39), followed by variance in traits involved in leaf resource economics and the timing of flowering. Species richness, trait variance and strategy richness were greatest at intermediate biomass. Thus whilst extremes of biomass production were associated with relatively few taxa exhibiting similar trait values and specialised strategies, greater species richness was apparent in meadows and pastures in which species exhibited divergence in resource economics trait values, reproductive timing and strategy richness.

Seed germination in a narrow endemic species (Telekia speciosissima, Asteraceae): Implications for ex situ conservation

Abstract Telekia speciosissima is an endemic chasmophyte of limestone and dolomite boulders in the Lombardy Prealps. It is included in the Italian Red List as a low-risk species. Seed germination dynamics of this plant were studied with the aim of producing germination protocols to use in ex situ conservation and recovery projects. Cold stratification and light requirements were investigated as potential factors improving seed germination. Seed samples were therefore stratified at 6 – 10°C during 15, 30, 45, 60, 90 and 180 days and then tested at higher temperature in continuous darkness or in a light/dark regime. Germination tests showed that seed dormancy was broken by cold stratification, while light promoted germination itself. These two factors strongly influenced germination dynamics and parameters. The highest germination percentage (91.8%) was attained after 90 days of cold stratification before testing seeds in light condition. However, a decrease in germination percentages occurred after a stratification of 150 days. An interpretation of these results is given according to the biological and ecological characters of the species, especially with respect to the need for establishing a transient seed bank.

Pea seed extracts stimulate germination of the terrestrial orchid Ophrys apifera Huds. during a habitat restoration project

Novel methods are required to break the seed dormancy of temperate-zone orchids and aid the conservation of rare species. Zeatin is produced in increasing concentrations during the development of pea (Pisum sativum) seeds. We hypothesised that hot water extracts of pea seeds stimulate germination of the orchid Ophrys apifera in vitro, particularly for extractions made during later pea development. Pea seeds, exposed to 0, 3, 6, 9, 12 or 15 days of periodic wetting, were extracted in hot water and the extracts were added to Malmgrens growth medium. Germination of O. apifera on this medium was quantified after 7 months, stimulated by a range of pure hormones. Pea seed extract collected later in pea development (at 6–15 days) inhibited germination of O. apifera. However, extracts taken at 0 and 3 days significantly increased germination from 3.8 ± 0.32% in the control to 9.1 ± 1.84% and 7.6 ± 0.79%, respectively: increases comparable to the most effective of the pure hormones. Dried peas therefore provide an economical alternative source of germination stimulants for orchids. We briefly report how sufficient mature plants of O. apifera were produced to allow a population to be multiplied to 15 times its original size during a habitat restoration project.

Ecology and floristic composition of heathlands in the Po basin and the Southern Alps (NW Italy)

Abstract The importance of heathlands as habitats for plants and thus for nature conservation is recognized by European Directive 92/43 (Habitats Directive). However, heathlands are threatened by habitat loss and quality degradation due to several drivers. Temperate Calluna vulgaris communities in the Po basin and in the Southern Alps (NW Italy) are disjunct from the core distribution area in Western Europe and occur at their climatic limits. This study aimed to analyze floristic patterns of heather communities in NW Italy in order to provide detailed recommendations for local conservation needs. Data on plant species composition (phytosociological relevés) and abiotic (environmental and geographical) factors were jointly analyzed using multivariate statistical analyses, to provide a quantitative and statistical interpretation of variation among heathland communities. We show that diversity in species composition was associated with variation in abiotic factors, and we sorted an initial list of “typical species” of the heather’s habitat among indicator species. Several subtypes of heathlands were also recognized and related to habitats “élémentaires”, which require specific conservation measures to preserve their floristic diversity. Finally, we proposed a revised syntaxonomy of heathlands for NW Italy.