Recovery of diurnal depression of leaf hydraulic conductance in a subtropical woody bamboo species: embolism refilling by nocturnal root pressure

Despite considerable investigations of diurnal water use characteristics in different plant functional groups, the research on daily water use strategies of woody bamboo grasses remains lacking. We studied the daily water use and gas exchange of Sinarundinaria nitida (Mitford) Nakai, an abundant subtropical bamboo species in Southwest China. We found that the stem relative water content (RWC) and stem hydraulic conductivity (K-s) of this bamboo species did not decrease significantly during the day, whereas the leaf RWC and leaf hydraulic conductance (K-leaf) showed a distinct decrease at midday, compared with the predawn values. Diurnal loss of K-leaf was coupled with a midday decline in stomatal conductance (g(s)) and CO2 assimilation. The positive root pressures in the different habitats were of sufficient magnitude to refill the embolisms in leaves. We concluded that (i) the studied bamboo species does not use stem water storage for daily transpiration; (ii) diurnal down-regulation in K-leaf and gs has the function to slow down potential water loss in stems and protect the stem hydraulic pathway from cavitation; (iii) since K-leaf did not recover during late afternoon, refilling of embolism in bamboo leaves probably fully depends on nocturnal root pressure. The embolism refilling mechanism by root pressure could be helpful for the growth and persistence of this woody monocot species.