Changes In Leaf Structure And Photosynthetic Characteristics Of Rice Cultivars Breeding Of Different Years

Breed improvement in yield potential has increased radiation conversion efficiency in modern indica rice varieties.Yet,the underlying leaf morphological and physiological mechanisms have not been established.Here we investigated the variation in leaf anatomy and photosynthetic physiology along with the breeding progress using indica and japonica varieties released from 1930s to 2000s.Twenty indica varieties were divided into four breeding groups,namely 1930s-1950s,1960s-1970s,1980s-1990s and 2000s.And twelve japonica varieties were separated into six breeding groups,namely 1950s,1960s,1970s,1980s,1990s and 2000s.In the field experiment of 2016,leaf anatomy and leaf nitrogen?N?content were measured.In addition,the operational stomatal conductance(g_op)and leaf temperature were measured in the field experiment of 2017.Simultaneously,pot experiment was conducted to meaure the photosynthetic traits in2017,such as light saturated photosynthetic rate(A_sat),g_op,specific leaf weight?SLW?and specific leaf N content?SLN?and etc.The main results are as following:?1?In comparison to the old varieties,new indica varieties had longer,wider and erect leaves.Moreover,the flag leaf of new indica varieties had higher N content,and senescenced slower.Leaf N content in the japonica varieties even increased during the grain filling period,indicating the japonica varieites had better stay-green trait.?2?Stomatal density significantly increased along with the breeding progress,which were 213?243?243 and 294 mm^-2in 7^thleaf,513?589?603 and 696 mm^-2in flag leaf for the four breeding groups,respectively.Compared to the varieties in 1930s-1950s,stomatal density was increased by 14%,14%and 38%in 7^thleaf,and 15%,17%and 36%in flag leaf for the varieites released in 1960s-1970s,1980s-1990s and 2000s,respectively.Stomatal size was not significantly changed,while the anatomical maximum stomatal conductance(g_max)was significantly increased similar to the trend of stomatal density.There was no significant change in both stomatal density and size for the japonica varieites along with the breeding progress.Genetic improment significantly increased the vein size and the bundle sheath cell number in indica varieties,but not in japonica varieties.Significant correlation was observed between the vein area and stomatal density for indica varieties.?3?Breed improvement significantly increased g_op,which resulted in significant decrease in leaf temperature of the new varieties(?T_l-a).There was a significant and negative correlation between g_opand?T_l-a,indicating that leaf temperature decreased as the increase in stomatal conductance.Breed improvement significantly increased A_satin flag leaf,which was significantly correlated with g_op.The present study found that genetic improvement significantly increased stomatal density and vein area in indica varieties,which led to higher g_maxand g_op.The higher operational stomatal conductance in new indica varieties decreased the leaf temperature,while increased the photosynthetic rate.In conclusion,the present study provided the leaf anatomical and eco-physiological mechanisms underlying the improvement in RUE during genetic improvement.These results will be beneficial to the future crop breeding to improve yields in a warming climate.