HYDRAULIC ARCHITECTURE OF SUGARCANE IN RELATION TO PATTERNS OF WATER-USE DURING PLANT DEVELOPMENT

Hydraulic conductance was measured on leaf and stem segments excised from sugarcane plants at different stages of development. Maximum transpiration rates and leaf water potential (PSI(L)) associated with maximum transpiration were also measured in intact plants as a function of plant size. Leaf specific hydraulic conductivity (L(sc)) and transpiration on a unit leaf area basis (E) were maximal in plants with approximately 0.2m2 leaf area and decreased with increasing plant size. These changes in E and L(sc) were nearly parallel, which prevented PSI(L) in larger plants from decreasing to levels associated with substantial loss in xylem conductivity caused by embolism formation. Coordination of changes in E and leaf hydraulic properties was not mediated by declining leaf water status, since PSI(L) increased with plant size. Hydraulic constrictions were present at nodes and in the node-leaf sheath-leaf blade pathway. This pattern of constrictions is in accord with the idea of plant segmentation into regions differing in water transport efficiency and would tend to confine embolisms to the relatively expendable leaves at terminal positions in the pathway, thereby preserving water transport through the stem.