Water translocation between ramets of strawberry during soil drying and its effects on photosynthetic performance

To explore the mechanisms underlying water regulation in clonal plants and its effects on carbon assimilation under water stress, we studied the responses of water status, gas exchange and abscisic acid (ABA) contents to water stress in leaves of pairs of strawberry ramets that consist of mother and daughter ramets. There was a greater decrease in photosynthetic rates (Pn) and stomatal conductance (Gs) in the disconnected mother ramets than the connected mother ramets upon exposure to water stress, indicating that water stress in mother ramets was alleviated by water translocation from the well-watered daughter ramets. Conversely, the connected mother ramets displayed enhanced symptoms of water stress when the connected daughter ramets were exposed to water deficit. The mother ramets had lower water potential (ψw) due to their stronger osmotic adjustment than in well-watered daughter ramets; this resulted in water flow from the connected daughter ramets to mother ramets, thus alleviating water stress of mother ramets. During soil drying, there was a striking increase in ABA concentrations in leaves of the disconnected mother ramets, whereas leaf bulk ABA was much lower in the connected and water-stressed mother ramets than that in the drought-affected mother ramets in the disconnected group. In this study, though Gs was linearly correlated with leaf bulk ABA and ψw, Gs in water-stressed mother ramets in disconnected group exhibited less sensitivity to the variation in leaf bulk ABA and ψw than that in connected and water-stressed mother ramets. Taken together, these results indicate that: (1) the flux of water translocation between the connected ramets is determined by a water potential gradient; (2) water translocation between connected ramets helps to keep sensitivity of Gs to ABA and ψw in drought-affected ramets, thereby benefit to effectively maintain the homeostasis of leaf water status and (3) the improvements in Pn in water-stressed ramets due to water translocation from well-watered ramets suggest the advantages of physiological integration in clonal plants in environments with heterogeneous water distribution