The influence of secondary senescence processes within the culm of a pseudoviviparous grass (Poa alpina var. vivipara L.) on the supply of water to propagules

An anatomical investigation of the culm of pseudoviviparous alpine meadow g rass (Poa alpina var. vivipara L.) revealed that transpiration flow, as del imited by Lucifer Yellow tracer dye, was maintained despite advanced senesc ence (as evidenced by loss of chlorophyll and chloroplasts), with leafy spi kelets driving transpiration flow. Transpiration flow was not hindered by c avitation or tylosis in older culms, the low frequencies of these senescenc e processes being bypassed via nodal plexi. Despite this, water content of plantlets declined over time and water stress became apparent, suggesting t hat water supply via the determinate culm was not sufficient for the increa sing transpirational demand of indeterminate plantlets. The implications of declining water content on the biomechanical properties of the culm, and c oncomitant limitations on the pseudoviviparous reproductive strategy, are d iscussed. Nomenclature of grass follows Hubbard.