Effects of salinity and clonal integration on the amphibious plant Paspalum paspaloides: growth, photosynthesis and tissue ion regulation

Aims Clonal integration can increase performance of clonal plants suffering from environmental stress, and clonal plants in many wetlands commonly face stress of flooding accompanied by salinity. However, few studies have tested roles of clonal integration in amphibious plants expanding from terrestrial to aquatic saline habitats. Methods Basal (older) ramets of clonal fragments of Paspalum paspaloides were grown in soil to simulate terrestrial habitats, whereas their apical (younger) ramets were placed at the surface of saline water containing 0, 50, 150 and 250 mmol l(-1) NaCl to mimic different salinity levels in aquatic habitats. Stolons connecting the apical and basal ramets were either intact (connected) to allow clonal integration or severed (disconnected) to prevent integration. Important Findings Increasing salinity level significantly decreased the growth of the apical ramets of P. paspaloides, and such effects on the leaf growth were much higher without than with stolon connection after 60-day treatment. Meanwhile, leaf and total mass ratios of the connected to the disconnected apical ramets were higher at high than at low saline treatments. Correspondingly, Fv/Fm and F/Fm of the apical ramets were higher with than without stolon connection in highly saline treatments. The results suggest that clonal integration can benefit the spread of apical ramets from terrestrial soil into saline water, and that the positive effects increase with increasing salinity. However, clonal integration did not significantly affect the growth of the whole fragments. Due to clonal integration, Na+ could be translocated from the apical to the basal ramets to alleviate ion toxicity in apical ramets. Our results suggest that clonal integration benefits the expansion of P. paspaloides from terrestrial to aquatic saline habitats via maintained photosynthetic capacities and changed biomass allocation pattern.