Hydraulic conductance of Acacia phyllodes (foliage) is driven by primary nerve (vein) conductance and density

We determined effects of venation traits on hydraulic conductance of phyllodes (foliage), using an array of Acacia s.str. species with diverse phyllode morphologies as the source of variation. Measurements were made on phyllodes from 44 species, grown in common gardens but originating from different positions along a precipitation gradient. K_phyllode varied 18-fold and was positively correlated with primary nerve hydraulic conductance, and with primary nerve (vein) density but not with minor nerve density, in contrast with previous studies of true leaves in other dicotyledons. Phyllodes with higher primary nerve density also had greater mass per area (PMA) and larger bundle sheath extensions (BSEs) from their minor nerves. We suggest that higher primary nerve conductivity and density may decrease the distance travelled in the high-resistance extra-xylem pathways of the phyllode. Further, larger BSEs may increase the area available for dispersion of water from the xylem to the extra-xylem tissue. High PMA phyllodes were more common in acacias from areas receiving lower annual precipitation. Maximizing efficient water movement through phyllodes may be more important where rainfall is meagre and infrequent, explaining relationships between nerve patterns and the climates of origin in Australian phyllodinous Acacia. In this study, we found that transformation of tomato plants with the codA gene improved tolerance to Hydraulic conductance was studied in relation to venation traits in morphologically diverse phyllodes of 44 species of Acacia that had been grown in common gardens but varied in origins along a precipitation gradient in Australia. As in leaves, hydraulic conductance of phyllodes was correlated with primary nerve density. However, unlike leaves, hydraulic conductance of phyllodes was not correlated with minor nerve density, possibly because the conductive role of bundle sheath extensions superseded that of minor nerves. Phyllodes with higher hydraulic conductance had higher mass per area and were more common in species originating from drier areas.