| Taking Larix kaempferi Carr., Larix olgensis Herry., Larix kaempferi×L. olgensis and Larix olgensis×L.kaempferi as study object, the thesis gived exploration research of breeding for high photosynthetic efficiency of larch. It consisted of the following parts:In order to investigate the differences on photosynthesis physiologic characteristics of young Larix kaempferi, L.olgensis, L.kaempferi×L.olgensis and L.olgensis×L.kaempferi, Characteristics of photosynthetic rate and other physiological indexes were measured on 5 days in larch comparing and assessing forest at Dagujia,Qingyuan,Liaoning province. The results were as follows: the diurnal changes of net photosynthetic rate (Pn) of Larch showed double-peak curves, daily highest Pn appeared between 8:00～9:00, daily lowest Pn appeared at 14:00, if there was secondary peak, it appeared at 15:00. CO2 absorption presented maximum at 7:00-10:00. The sequence of daily mean values of Pn was L.olgensis×L.kaempferi>L.kaempferi×L. olgensis>L.olgensis>L.kaempferi. The diurnal changes of transpiration (Tr) rate showed double-peak curves, the lowest value appeared at 7:00 and the highest value appeared between 9:00～10:00. The secondary peak appeared after lower point at 11:00. The sequence of daily mean values of Tr was L.olgensis > L.olgensis×L.kaempferi >L.kaempferi×L.olgensis>L.kaempferi. The diurnal changes of water use efficiency (WUE) showed single-peak curve or L pattern, hybrids had high WUE than L. kaempferi and L. olgensis before 9:00 but had no differences after 9:00. The diurnal changes of stomatal conductance showed single-peak curve. Larch had obvious phenomena in midday depression of photosynthesis. The decline in apparent quantum yield was not the main reason for the decline of net photosynthetic rate. We concluded that stomatal limitation is the dominant cause of the midday depression of photosynthesis according the change tendency of Pn, stomatal limiting value, intercellular CO2 concentration.In order to compare the photosynthetic efficiency of L.kaempferi, L. olgensis, L.kaempferi×L.olgensis and L. olgensis×L. kaempferi, light response curse and CO2 response curse were measured. The results were as follows: Compared with L.kaempferi×L.olgensis, the maximum net photosynthetic rate, light saturation point , light compensation point (LCP), apparent quantum yield (AQY), dark respiration rate (Rd), photosynthetic capacity,CO2 saturation point and CO2 compensation point (Γ) of L.kaempferi was superior, but the carboxylation efficiency (CE), photorespiration rate (Rp) of two showed no differences. Compared with L.olgensis×L.kaempferi, the AQY,Γof L.olgensis was superior but Rd of L. olgensis was inferior, and CE, Rp, LCP of the two showed no differences. Compared with L.kaempferi×L.olgensis, CE, Rp,Γof L.kaempferi×L. olgensis was a litter superior, but AQY, Rd, LCP of the two showed no differences.In order to make sure maternal and paternal effects on photosynthetic characters of L. kaempferi×L.olgensis hybrids, light response curse and CO2 response curse of 6 L. kaempferi×L.olgensis families, including poly-crossed and full-sib families, and 3 corresponding open-pollinated female parent families were analyzed. Result indicated that there were significant differences in AQY, Rd, CE, and very significant differences in LCP,Γamong poly-crossed families, while only Rd exerted very significant differences among full-sib hybrid families who shared the same mother. Maternal effect played a more important role than paternal effect.In order to study the relationship between photosynthetic characteristics and growth of Larch, height growth, daily mean values of net photosynthetic rate (Pn), phenophase, morphological traits, dark respiration rate of young L. kaempferi , L. olgensis , L. kaempferi×L. olgensis and L. olgensis×L. kaempferi were measured. Results showed that although the daily mean of Pn of L.kaempferi 85 was the lowest, the advantage of phenophase, morphological traits and dark respiration rate helped it had the fasest growth. Although Rd of L. olgensis 4C was the lowest, the disadvantage of phenophase, morphological traits and the daily mean of Pn helped it had the slowest growth. The daily mean values of Pn were not valuable to predict growth. It was conclueded that selecting parents with high photosynthetic efficiency should take into account of growth performance.
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