Bruno Enrico Leone Cerabolini

The global spectrum of plant form and function

Earth is home to a remarkable diversity of plant forms and life histories, yet comparatively few essential trait combinations have proved evolutionarily viable in today’s terrestrial biosphere. By analysing worldwide variation in six major traits critical to growth, survival and reproduction within the largest sample of vascular plant species ever compiled, we found that occupancy of six-dimensional trait space is strongly concentrated, indicating coordination and trade-offs. Three-quarters of trait variation is captured in a two-dimensional global spectrum of plant form and function. One major dimension within this plane reflects the size of whole plants and their parts; the other represents the leaf economics spectrum, which balances leaf construction costs against growth potential. The global plant trait spectrum provides a backdrop for elucidating constraints on evolution, for functionally qualifying species and ecosystems, and for improving models that predict future vegetation based on continuous variation in plant form and function.

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.

Allocating CSR plant functional types: the use of leaf economics and size traits to classify woody and herbaceous vascular plants

Summary 1. Three main directions of adaptive specialization are evident in the world flora, reflecting fundamental trade-offs between economics (conservative vs. acquisitive investment of resources) and size. The current method of ordinating plants according to these trade-offs, CSR classification, cannot be applied to the woody species that dominate many terrestrial ecosystems. 2. We aimed to produce a novel CSR classification method applicable to vascular plants in general. 3. Principal components analysis (PCA) of variation in a range of plant traits for 678 angiosperm, gymnosperm and pteridophyte species was used to determine the limits to multivariate space occupied by functionally diverse species. From this calibration, correlations between PCA axes and values of leaf dry matter content (LDMC; as an index of conservatism in life history), specific leaf area (SLA; indicative of acquisitive economics) and leaf area (LA; photosynthetic organ size) were used to produce predictor regressions from which target species could be compared against the multivariate space. A spreadsheet was developed that returned ternary coordinates and tertiary CSR strategies for target subjects based on LA, LDMC and SLA values. 4. The method allowed classification of target species within a triangular space corresponding to Grime’s theoretical CSR triangle and was sufficiently precise to distinguish strategies between species within genera and within populations of species. It was also largely in agreement with previous methods of CSR classification for herbaceous species. 5. Rapid CSR classification of woody and herbaceous vascular plants is now possible, potentially allowing primary plant functional types and ecosystem processes to be investigated over landscape scales.

Conifer needles as passive biomonitors of the spatial and temporal distribution of DDT from a point source

Needles of two conifer species, Picea abies and Pinus nigra, were used as passive samplers for monitoring air contamination by sampling at increasing distances from a suspected point source of DDT. Needle concentrations declined with increasing distance downwind of the point source allowing to identify spatial and temporal trends of accumulation. This suggested that conifer needles are effective biomonitors of contamination levels in areas characterized by the presence of semi-volatile substances. Differences in uptake were apparent between the species. Needle morphology and structure were studied with scanning electron microscope (SEM) as were dimensional parameters (surface area, volume). The results suggest that the concentrations depend on a mechanism involving the inner structure of the needles, specifically the number and accessibility of resin channels rather than their surface area. Pine needles have more channels with greater accessibility than spruce. The results suggest that spruce is more suitable for short term measurement while pine for determining long term cumulative exposure.

Measuring the functional redundancy of biological communities: a quantitative guide

Summary The preservation of ecosystem processes under ongoing biotic erosion requires that some species within affected communities perform similar functions, a property that is usually defined as functional redundancy. Although functional redundancy has recently become a relevant part of ecological research, so far there is no agreement on its measurement. The scope of this work is thus to propose a consistent framework based on functional dissimilarities among species for summarizing different facets of functional redundancy. The behaviour of the proposed measures is illustrated with one small artificial data set, together with actual examples on the species functional turnover along successional gradients. We believe this new framework provides an important contribution for the clarification and quantification of key metrics of community redundancy and vulnerability. The method, for which we provide a simple r function called ‘uniqueness’, further allows summarizing the functional contribution of single species to the overall redundancy of any type of biological community.

Vegetation and environmental factors during primary succession on glacier forelands: Some outlines from the Italian Alps

ABSTRACT Relationships between plant communities and the physical environment during primary succession on recently deglaciated glacier forelands were studied in 3 areas of the Italian Alps. The aim of the research was to relate traditional phytosociological data with environmental variables. Twenty-eight phytosociological relevés were performed, each associated with twenty-six environmental variables; quantitative parameters of richness and diversity were also calculated. Species/relevés, environmental variables/relevés and species/environmental variables matrices were analyzed by cluster analysis, PCA and Spearman correlation coefficient. Three main stages of succession were identified by floristic composition and confirmed by environmental parameter evaluation. A complex of environmental variables seems to be closely correlated with terrain age and richness/diversity parameters, even though diversity decreases in late successional stages. The phytosociological significance of species is in accordance with their position in the context of succession.

Combined use of leaf size and economics traits allows direct comparison of hydrophyte and terrestrial herbaceous adaptive strategies

BACKGROUND AND AIMS Hydrophytes generally exhibit highly acquisitive leaf economics. However, a range of growth forms is evident, from small, free-floating and rapidly growing Lemniden to large, broad-leaved Nymphaeiden, denoting variability in adaptive strategies. Traits used to classify adaptive strategies in terrestrial species, such as canopy height, are not applicable to hydrophytes. We hypothesize that hydrophyte leaf size traits and economics exhibit sufficient overlap with terrestrial species to allow a common classification of plant functional types, sensu Grimes CSR theory. METHODS Leaf morpho-functional traits were measured for 61 species from 47 water bodies in lowland continental, sub-alpine and alpine bioclimatic zones in southern Europe and compared against the full leaf economics spectrum and leaf size range of terrestrial herbs, and between hydrophyte growth forms. KEY RESULTS Hydrophytes differed in the ranges and mean values of traits compared with herbs, but principal components analysis (PCA) demonstrated that both groups shared axes of trait variability: PCA1 encompassed size variation (area and mass), and PCA2 ranged from relatively dense, carbon-rich leaves to nitrogen-rich leaves of high specific leaf area (SLA). Most growth forms exhibited trait syndromes directly equivalent to herbs classified as R adapted, although Nymphaeiden ranged between C and SR adaptation. CONCLUSIONS Our findings support the hypothesis that hydrophyte adaptive strategy variation reflects fundamental trade-offs in economics and size that govern all plants, and that hydrophyte adaptive strategies can be directly compared with terrestrial species by combining leaf economics and size traits.

Species evenness affects ecosystem processes in situ via diversity in the adaptive strategies of dominant species

Community biomass production reflects species evenness (relative abundance), suggesting that particular adaptive/survival strategies contribute disproportionately to ecosystem processes. We hypothesized that diversity in the strategies of dominant species would be a better predictor of biomass production than species diversity per se. We compared species diversity, strategy diversity, peak biomass, soil and leaf nutrient status, and leaf area index (LAI) in situ for related sub-alpine plant communities differing only in the intensity of cattle grazing and manuring; with identical climatic exposure, slope, aspect and parent material. Greater total biomass was associated with greater strategy richness and evenness and, to a lesser extent, species evenness—but species richness and aboveground biomass were not significantly different. Diversity in the adaptive strategies of dominant species allowed more effective deployment of canopy biomass (greater LAI), providing superior photosynthetic nutrient use efficiencies and greater total biomass despite lower nutrient status. This was reflected in species evenness, but not species richness.

Towards more ecologically realistic scenarios of plant uptake modelling for chemicals: PAHs in a small forest

The importance of plants in the accumulation of organic contaminants from air and soil was recognized to the point that even regulatory predictive approaches now include a vegetation compartment or sub-compartment. However, it has recently been shown that many of such approaches lack ecological realism to properly evaluate the dynamic of air/plant/soil exchange, especially when environmental conditions are subject to sudden variations of meteorological or ecological parameters. This paper focuses on the development of a fully dynamic scenario in which the variability of concentrations of selected chemicals in air and plant leaves was studied weekly and related to the corresponding meteorological and ecological parameters, to the evaluate their influence. To develop scenarios for modelling purposes, two different sampling campaigns were performed to measure temporal variability of: 1) polycyclic aromatic hydrocarbon (PAH) concentrations in air of a clearing and a forest site, as well as in leaves of two broadleaf species and 2) two important leaf and canopy traits, specific leaf area (SLA) and leaf area index (LAI). The aim was to evaluate in detail how the variability of meteorological and ecological parameters (SLA and LAI) can influence the uptake/release of organic contaminants by plants and therefore air concentrations. A principal component analysis demonstrated how both meteorological and ecological parameters jointly influence PAH air concentrations. SLA, LAI, as well as leaf density were showed to change over time and among species and to be directly proportional to leaf/canopy uptake rate. While hazelnut had the higher leaf uptake rate, maple became the most important species when considering the canopy uptake rate due to its higher LAI. Other species specific traits, such as the seasonal variation in production of new leaves and the timing of bud burst, were also shown to influence the uptake rate of PAHs by vegetation.

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.