Abstract: To understand the interaction of root and shoot and their response to drought, root-shoot interaction
in soybean is studied for water stress resistance. Response of PSII properties and biomass production to water stress
in leaves under different root-shoot interactions, grafted plants between drought-tolerant cultivar Liaodou 14 and
drought-sensitive cultivar Liaodou 21 were grown in pots. Physiological traits and dry mass of each tissue were mea⁃
sured at 13 d after drought treatment (50% of soil water in field) during podding stage. Under water stress, self-graft⁃
ed Liaodou 21 showed significant decrease in SPAD value, leaf area, photochemical quantum yield of PSII system (Y
(II)), quantum yield of regulated energy dissipation (Y(NPQ)), maximal rate of electron transfer (ETRmax), minimal
saturated light intensity (Ik). But a significant increase was found in the non-regulatory energy heat dissipation (Y
(NO)) of self-grafted Liaodou 21. As scions, Liaodou 14 always had higher SPAD value, Y (II), Y (NPQ), ETRmax and
Ik, which resulted in greater biomass, when compared to Liaodou 21 scions. In addition, grafting Liaodou 21 scion
onto Liaodou 14 rootstocks had higher root activity, which could significantly increase leaf area, Y (II), Y (NPQ),
ETRmax and Ik under water stress, and resulted greater pod mass. These results indicated that PSII performance and
biomass production were mainly determined by leaves features in shoot, but also affected by physiological activity of
roots especially under drought.

Key words:  , soybean；water stress；PSⅡ performance；biomass production；grafting