Abstract:

In view of the problem that the seedling and production of protected tomato often suffer from high daytime temperature in summer,this paper aimed to study the simple and effective technology and regulation mechanism of high temperature resistance of tomato seedlings. Tomato seeds were treated with cold plasma（CP）of 25,50,75,100,125,150,175 and 200 W respectively for 10 s,the seeds without CP treatment were used as control,these seeds were cultured in a controllable temperature glass greenhouse in summer. When the temperature was lower than 35 ℃,there was no ventilation to reduce the temperature. When the temperature was higher than 35 ℃,the temperature was controlled by ventilation or wet curtain. The temperature is controlled between 32 ℃ to 35 ℃ to create a daytime sub-high temperature environment for seedling growth. The growth indexes of seedlings were analyzed,and the diurnal variations of water and gas exchange parameters and chlorophyll fluorescence parameters were measured under control and optimal CP treatment（75 W）. The results showed that the plant height,stem diameter,shoot dry weight,root dry weight,root-shoot ratio and seedling index of the seedlings were firstly increased and then decreased with the increase of CP treatment power,and reached the highest values in CP treatments from 25 to 75 W. The growth quality of tomato seedlings showed the best level at 75 W CP treatment. In control,excepting the intercellular CO₂ concentration（C_i）,the net photosynthetic rate（P_n）,transpiration rate（T_r）,stomatal conductance（G_s）,stomatal limiting value（L_s）and water use efficiency（WUE）were firstly decreased and then increased in daytime,which arrived at the highest（lowest）values in the sub-high temperature（34.9-35.3 ℃）at noon（12:00 to 14:00）in summer. When compared with control,CP treatment increased midday P_n,T_r,G_s,L_s,and decreased C_i,and showed a higher WUE in daytime. Meanwhile,CP treatment significantly increased the maximum fluorescence（F_m）,potential photochemical activity（F_v/F_o）,maximum photochemical efficiency（F_v/F_m）,excitation energy capture efficiency（F_v′/F_m′）,actual photochemical efficiency（Φ_PSⅡ）,photochemical quenching coefficient（q_P）,chlorophyll fluorescence decay rate（R_fd）,excitation energy distribution coefficient of PSⅠ（α）and the share（P）of absorbed light energy used for photochemical reactions when compared with control treatment. The minimum fluorescence（F_o）,non photochemical quenching coefficient（NPQ）,relative limiting value of photosynthetic function（L_PFD）,excitation energy pressure of PSⅡ（1-q_P）,excitation energy distribution coefficient of PSⅡ（β）,imbalance of excitation energy distribution between PSⅠand PSⅡ（β/α-1）,share of thermal dissipation of antenna（D）and the share of non photochemical dissipation（E_x）were decreased. The results showed that CP treatment could reasonably regulate leaf water and air exchange and light energy utilization,and promote the healthy growth of tomato seedlings under daytime sub-high temperature environment in summer.

Key words: tomato, cold plasma, seed treatment, sub-high temperature, photosynthesis