Abstract:

Flood-tolerant Populus deltoides cv.Lux ex I-69/55 and flood-susceptible Populus simonii were adopted as materials in the present study to investigate the influences of soil flooding on ultrastructure and photosynthetic capacity of leaves.Results showed that flooding affected ultrastructure and photosynthetic capacity of leaves adversely,especially with the aggravation and prolonging of flooding treatment.After eight-day flooding,slight decrease of netphotosynthetic rate (P_n),potential efficiency of primary conversion of light energy of PSⅡ (P_n，F_v/F_m),and chlorophyll content occurred in both clones,as well as some destructions in ultrastructure of leaves,including starch grain disappeared sharply,osmophore slowly increased,swelled thylakoid and slightly distorted grana layers.Significant differences were observed between the two clones at day 15,instead of day eight.High P_n，F_v/F_m and chlorophyll content were observed in P.deltoides cv.Lux ex I-69/55 due to its relatively intact ultrastructure of leaves.Whereas,serious decline in P_n，F_v/F_m and chlorophyll content occurred in P.simonii,accompanied with severe destructions in ultrastructure of leaves,including occurrences of plasmolysis,chloroplast swelled and its envelope disappeared,swelled thylakoid,grana layers distorted and decomposed,as well as decreased mitochondria cristaes and exuded inclusion.Mitochondria was more flood-tolerant than chloroplast.Destruction of ultrastructure of leaves,especially of photosynthetic organs,which was identical to declines of P_n，F_v/F_m and chlorophyll content,were important reasons in decline of photosynthetic capacity.Flood tolerance of ultrastructure differed significantly in different poplar clones.Under flooding,flood-tolerant poplar clones had more stable ultrastructure of leaves than intolerant ones,including slighter and slower destruction.Stability of ultrastructure of leaves was positively related to flood-tolerance,which could be adopted as a cytology reference to identify flood tolerance of poplar clones.

Key words: poplar, flooding, ultrastructure, photosynthetic rate, chlorophyll fluorescence