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.