Highly Species-Specific Foliar Metabolomes of Diverse Woody Species and Relationships with the Leaf Economics Spectrum

Plants show an extraordinary diversity in chemical composition and are characterized by different functional traits. However, relationships between the foliar primary and specialized metabolism in terms of metabolite numbers and composition as well as links with the leaf economics spectrum have rarely been explored. We investigated these relationships in leaves of 20 woody species from the Mediterranean region grown as saplings in a common garden, using a comparative ecometabolomics approach that included (semi-)polar primary and specialized metabolites. Our analyses revealed significant positive correlations between both the numbers and relative composition of primary and specialized metabolites. The leaf metabolomes were highly species-specific but in addition showed some phylogenetic imprints. Moreover, metabolomes of deciduous species were distinct from those of evergreens. Significant relationships were found between the primary metabolome and nitrogen content and carbon/nitrogen ratio, important traits of the leaf economics spectrum, ranging from acquisitive (mostly deciduous) to conservative (evergreen) leaves. A comprehensive understanding of various leaf traits and their coordination in different plant species may facilitate our understanding of plant functioning in ecosystems. Chemodiversity is thereby an important component of biodiversity

Qual è il ruolo dell'anatomia dello xilema nei processi di embolizzazione e ripristino della conducibilità idraulica degli elementi vascolari? Any role of xylem anatomy in hydraulic vulnerability and recovery?

In the xylem, water is transported in a metastable state under tension. During drought, this tension increases causing embolism formation and reducing plant productivity. Hypothetically, as embolism reversal mechanism may rely upon the sugars provided by parenchyma cells, vulnerable species should have a high parenchyma amount providing an efficient refilling mechanism to recover from embolism formation. We measured total parenchyma amount (PAtot), fibres area (FA), volume of wood occupied by vessels (VA), mean conduit area (MCA), conduit density (CD), theoretical hydraulic conductivity (KS), hydraulic vulnerability to embolism (P50), and other qualitative traits. Published anatomical and hydraulic data were also used. Angiosperm species more vulnerable to cavitation (i.e. less negative P50) have higher PAtot that is inversely related with FA and a higher MCA that is inversely related with CD. These relations were not significant in gymnosperms. P50 is strongly related with conduits properties as wider and therefore less dense vessels determine a higher vulnerability to embolism. Angiosperms therefore tend to produce a greater amount of PAtot allowing to both storage and utilize more efficiently a greater sugars amount throughout the xylem, relying on more efficient refilling mechanism to compensate for the low safety of the water transport system

The potential of Mid-Infrared spectroscopy for prediction of wood density and vulnerability to embolism in woody angiosperms

Xylem resistance to embolism formation determines the species-specific drought tolerance and the survival prospects of plants under extreme climatic conditions. Fourier Transform-Infrared (FTIR) spectroscopy is a cost-effective and rapid analytical tool with potential beyond its current use in plant physiology. We tested the use of FTIR spectroscopy as a method for estimating wood density (WD) and xylem resistance to embolism formation (P50) in 24 angiosperm species. Higher WD was associated with more negative P50 (r2 = 0.41). Partial least squares regression was applied to establish models of FTIR spectra and the reference data. They showed a high predictive quality for WD (r2 = 0.73), whereas the prediction of P50 was weaker (r2 = 0.49). By including WD in the model as an additional factor influencing P50, its predictive power significantly increased (r2 = 0.59). The spectral range in the model elaboration has been also narrowed (bands of lignin, cellulose, hemicellulose), but this did not influence the model descriptors, suggesting that for P50 prediction broad spectral range is more informative than narrow band regions reflecting main wood constituents. In conclusion, FTIR spectroscopy associated with WD measurements has proven to be a promising alternative to traditional methods for screening of individual- or species-specific resistance to embolism in angiosperms

Functional balance between leaf and xylem tissues is maintained under different soil water availability in Pinus sylvestris and Picea abies

Plants are composed by tight connected different tissues and organs that work in synchrony among each other guiding all physiological processes. The functionality of the entire organism depends on the resources allocation for the different organs that have to balance the cost and the benefit of the plant. The ratio between leaf biomass and xylem biomass is an extremely important plant trait since it links photosynthesis to transpiration efficiency and to respiratory costs. Resource availability have been reported to significantly affect the growth of trees. In limited resource environment trees present smaller leaves and shorter braches than plants grown in non-limiting conditions. The aim of this work is to evaluate if the resource allocation is maintained constant during ontogeny and if the ratio between leaf and xylem is preserved in different environmental conditions to guarantee the functionality of the system. We sampled branches of Pinus sylvestris and Picea abies grown on arid and mesic soils. For each the branch we measured the xylem volume and the leaf biomass produced each year and how they cumulate from the branch apex to the base. Our results showed that the cumulated leaf biomass and xylem volume scale linearly with the distance from the branch apex and the branches from the wet site, especially P. sylvestris\u2019 s, had more leaf biomass and xylem volume. This confirms that carbon allocation is conserved during the ontogeny and that the trees grown in non-limiting conditions have higher production. Moreover, the relation among leaf biomass and xylem volume showed a conserved allocation pattern in the two species with no effect of the environmental conditions. This demonstrates that these two traits are highly correlated and dependent on each other and that their functional balance is highly preserved to sustain the functionality of the tree independently by the resource availability

Vulnerability to xylem embolism correlates to wood parenchyma fraction in angiosperms but not in gymnosperms

Understanding which structural and functional traits are linked to species\u2019 vulnerability to embolism formation (P50) may provide fundamental knowledge on plant strategies to maintain an efficient water transport. We measured P50, wood density (WD), mean conduit area, conduit density, percentage areas occupied by vessels, parenchyma cells (PATOT) and fibers (FA) on branches of angiosperm and gymnosperm species. Moreover, we compiled a dataset of published hydraulic and anatomical data to be compared with our results. Species more vulnerable to embolism had lower WD. In angiosperms, the variability in WD was better explained by PATOT and FA, which were highly correlated. Angiosperms with a higher P50 (less negative) had a higher amount of PATOT and total amount of nonstructural carbohydrates. Instead, in gymnosperms, P50 vs PATOT was not significant. The correlation between PATOT and P50 might have a biological meaning and also suggests that the causality of the commonly observed relationship of WD vs P50 is indirect and dependent on the parenchyma fraction. Our study suggests that angiosperms have a potential active embolism reversal capacity in which parenchyma has an important role, while in gymnosperms this might not be the case