Study On The Photosynthetic Characteristics And Response To Drought Stress On Photosynthesis Characteristics Of P. Cornutum (L.) Gaertn And P. Dolabratum Maxim

Puionium Gaertn which belongs to Cruciferae, is distributed in sandy soil of Mongolia altiplano. It is a kind of vegetable with officinal, hygienical, feeding and sand-fixation functions. Two of its species, P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. Study on the photosynthetic characteristics and response to drought stress on photosynthesis characteristics of P. cornutum(L.)Gaertn and P.dolabratum Maxim. The results showed that:(1)The light compensation point and the light saturation point were 46.55μmol·m^-2·s^-1 and 1325μmol·m^-2·s^-1 respectively in P.cornutum(L.) Gaertn. while the light compensation point and the light saturation point were 47.50μmol·m^-2·s^-1and 1212.5μmol·m^-2·s^-1 respectively in P.dolatum Maxim.var.dolabratum, indicating that the available range of light intensity in P.cornutum(L.) Gaertn. was wider than in P.dolatum Maxim.var.dolabratum. The maximum photosynthetic rate and apparent quantum yield of P.cornutum(L.) Gaertn. higher than that of P.dolatum Maxim.var.dolabratum. The dark resp iration rate of P.cornutum(L.) Gaertn. lower than that of P.dolatum Maxim.var.dolabratum. The Quantum use efficiency are 0.0413 and 0.0515,respectively, The Quantum use efficiency of P.cornutum(L.) Gaertn. Is higher than that of P.dolatum Maxim.var.dolabratum. The content of chlorophyll was comparatively high and chlorophyll ratio was low, which guaranteed obvious light adaptation capacity.(2)Photosynthetic daily change showed a twin-peak curve with the"photosynthetic noon break"phenomenon. The reason that resulting in photosynthetic midday depression is stomatal limitation. P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. net photosynthetic rate had significantly positive correlationship with environmental temperature under less than 1599μmol·m^-2·s^-1 of photosynthetic active radiation; it with air relative humidity was not a significantly negative related; and it had positively correlated with stomatal conductance degrees, the value of stomatal limitation, transpiration rate, water use efficiency; and it with intercellular CO2 concentration was significantly negative correlated.(3) In the stress process, P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. relative water content of seedling leaves show a decreased trend, P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. decreased by 8.7% and 6.8%; P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum.seedlings Leaf and root water potential showed a decreased trend, P.cornutum(L.) Gaertn. leaves and roots were lower than the water potential of P.dolatum Maxim.var.dolabratum..(4) In different drought stress treatments, P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. seedlings decreased biomass ratio, root biomass and the ratio of root and shoot increased ,there is significant difference with control. However, in mild stress, P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. seedling leaf biomass per plant increased significantly, changes in root biomass per plant was significant.(5) With the drought strengthed ,the content of Chla, Chlb, Car content of P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum were decreased; Chla/b ratio increased significantly; Car/Chl ratio have no significantly chang in the medium and moderate drought,but showed evidently increased in serious drought stress In different stress conditions, The content of Chla, Chlb and Car of the P.dolatum Maxim.var.dolabratum. seedlings were higher than P.cornutum(L.) Gaertn. seedlings.The Chla/b ratio of P.dolatum Maxim.var.dolabratum. was higher than P.cornutum(L.) Gaertn., but Car / Chl ratio of P.dolatum Maxim was significantly lower than P.cornutum(L.) Gaertn..(6) Under the slight stress, Maximum photosynthetic rate, apparent quantum efficiency, dark respiration rate of P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. was higher than the control, P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. seedlings had a increased light compensation point and a decreased light saturation point, but under serious drought stress,these indexes decreased. Under in slight drought stress, quantum use efficiency of P.cornutum(L.) Gaertn.was the highest, followed by the control, moderate and severe; P.dolatum Maxim.var.dolabratum. was also similar trend. Under slight drought stress, net photosynthetic rate, transpiration rate, water use efficiency, stomatal conductance, intercellular CO2 concentration of P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum.were higher than the control, but with drought stress increasing, the leaf net photosynthetic rate, transpiration rate, water use efficiency, stomatal conductance dedreased, but the value of intercellular CO2 concentration increased slightly.(7) Under drought stress, changes in net photosynthetic rate, transpiration rate diurnal variation, changes in stomatal conductance of P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. seedling leaves showed a typical double-peak curve; changes of water use efficiency and stomatal limitation value were a decreased curve; the changes of intercellular CO2 concentration was a "W" curve. Under slight drought stress compared with the control,medium and serious drought stress they decreased, and decreased evidently in serious stress.(8) Under drought stress, the resons why net photosynthetic rate of P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum.decreased were :under the slight stress, P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum. seedling leaf photosynthetic rate had opposite chages with intercellular CO2 changes, and stomatal limitation value of increased ,these result showed the decreasedof net photosynthetic rate owed to stomatal limitation in the slight stress; On the other hand,under the medium and serious stress, leaf photosynthetic rate of P.cornutum(L.) Gaertn. and P.dolatum Maxim.var.dolabratum.seedlings decreased significantly, while the intercellular CO2 concentration has increased, and stomatal limitation value decrease,these result showed the decreasedof net photosynthetic rate owed to non-stomatal limitation under the medium and serious stress.