Heat Tolerance Study Of Kosteletzkya Virginica (L.) Presl

This study tries to explore the damage effects of different high temperature treatments on thephotosynthetic characteristics of Kosteletzkya virginica（L.） Presl and to search for the criticaltolerant temperature of Kosteletzkya virginica under high temperature stress. Furthermore, wesearched the recovery mechanism of Kosteletzkya virginica after high temperature stress. In theend, Kosteletzkya virginica was treated with high temperature and high salinity stress at the sametime in order to explore the cross-resistance of high temperature and salinity in Kosteletzkyavirginica. The main results were as follows:1. Critical high temperature to Kosteletzkya virginicaUnder high temperature stress, Kosteletzkya virginic showed a low photosynthetic oxygenevolution rate and a low net photosynthetic rate. Stomatal conductance decreased withtreatment temperature, but began to rise above 45℃. Under 42℃, the decrease ofphotosynthetic rate of Kosteletzkya virginica was mainly due to stomatal limitation factors, andthen changed to non-stomatal limitation factors because of the damage of photosyntheticapparatus and the mesophyll limitations after 48℃.High temperature treatments suppressedΦPSⅡof Kosteletzkya virginica and leaded to lowactual photochemical efficiency.The high temperature leaded to a higher Fo. We can indicate from the Arrhenius’s diagramthat the critical temperature for Fo change was at 44.9℃.As the treatment temperature rised, K phase began to appear under 45℃treatment. Hightemperature stress decreased theΦ_PoandΦ_Eowhile increasedΦ_Doof Kosteletzkya virginica.Kosteletzkya virginica protected against high temperature damage by increasing heat dissipation.Under high temperature stress, the density of active reaction centers per excited cross-section（RC/CSo） of Kosteletzkya virginica decreased. Accompanied with the decline of the energyabsorbed and captured by per unit leaf area used in electronic transfer, the energy absorbed andcaptured by per excited cross-section used in electronic transfer was increased. The heatdissipation was increased at both per unit leaf area and per excited cross-section bases.PIABSshowed a significant decreasing trend with the increase of treating temperature,especially at 42℃, 45℃and 48℃.Above all, 45℃was the critical temperature for the high temperature tolerance ofKosteletzkya virginica.2. The recovery of Kosteletzkya virginica after high temperature stress.After high temperature treatment with Kosteletzkya virginica, the recovery of net photosynthetic rate （Pn） was consistent with photosynthetic oxygen evolution in 48 hours. TheKosteletzkya virginica could return to the level before in 48 hours after 42℃treatment.Recovery to normal levels in 48h at 45℃，and no recovery after 48℃treatment.The Fo didn’t increase with 42℃treatment. 45℃treatment increase Fo but it could return tothe normal level in 8 hours under light conditions rather than in dark conditions. However, after48℃treatment, the Fo ofKosteletzkya virginica under light still increased gradually, andpresented a significant trend of increase after 8, 24, 48hours treatment. On the contrary, the Fo ofKosteletzkya virginica under dark conditions didn’t show obvious variation after heat treatment.With the treatments of 42℃under light conditions,Kosteletzkya virginica could return to anormal level within 8 hours, which showed that the high temperature didn’t exert serious damageto the PSⅡ. With the treatments of 45℃under light conditions,Kosteletzkya virginica couldrecover to normal gradually within 48 hours.Φ_Po、Φ_Eo、RC/CSm、ABS/CSm、TRo/CSm、ETo/CSm decreased at first and then increased, which suggested that 45℃did damaged PSⅡby leading to decomposition but PSⅡcould reconstruct under light conditions. The PSⅡdidn’tshow significant recovery under dark conditions which indicated that the light condition wasnecessary for the recovery and synthesis of PSⅡ. With the treatments of 48℃, bothligh anddark conditions didn’t show significant recovery in PSⅡ, which implied that high temperatureexceeding 48℃s eriously damaged PSⅡand destroyed its recovery capability.3. The cross-resistance to salt stress and high temperature in Kosteletzkya virginica.As the treatment temperature increased, the Wk of Kosteletzkya virginica without salttreatment rised. However, Wk with 200 mmol·L-1NaCl treatment was much lower than thatwithout NaCl treatment. TheΦ_Poof Kosteletzkya virginica under salt treated was much higherthan that without salt treatment at 45℃andeven at 48℃. TheΦ_Eo, RC/CSm、PIABSand Pn ofKosteletzkya virginica showed the similar trend in salt and high temperature treatment, whileΦ_Dowas just the opposite, implying that pre-salt treatment can alleviate the injury of the PSⅡdonorside caused by high temperature. Increase electron transfer and thus reduce heat dissipation.Furthermore, salt-treatment helped to mitigate the reduction of active reaction centers andprevents the further decrease of PIABS. All the indices suggested salt treatment increased heatresistance in Kosteletzkya virginica. And there was considerable cross-resistance to salt stressand high temperature in Kosteletzkya virginica.