Abstract: In order to reveal the effects of high temperature and high humidity interaction on photosynthetic characteristics of tomato leaves, a L₉ (3-3) orthogonal test with tomato cv. ‘Jinfen 5’ was carried out in artificial climate chamber. To measure the photosynthetic parameters and fluorescence dynamic parameters of different treatments, three levels of influencing factors were set: Temperature of 35 ℃ (daytime)/18 ℃ (nighttime), 38 ℃/18 ℃, 41 ℃/18 ℃), relative air humidity of daytime (50%±5%, 70%±5%, 90%±5%), treatment days (3, 6, 9 d), and 28 ℃/18 ℃, 45%-55% as a control (CK). The results showed that the net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), water use efficiency (WUE), PSII maximum quantum efficiency (F_v/F_m), photochemical quenching coefficient (q_P) and electron transfer rate (ETR) were significantly lower than the CK, while the intercellular CO₂ concentration (C_i) was the lowest in the 38 ℃/18 ℃, 70% air humidity treatment, stomatal limitation (L_s) was the lowest in the 38 ℃/18 ℃, 90% air humidity treatment. Compared to the CK, leafP_n under temperatures of 38 ℃/18 ℃, 35 ℃/18 ℃, 41 ℃/18 ℃, and humidity of 70%, 50%, 90% decreased by 30.1%, 21.4%, 51.9%, 31.2%, 31.4% and 38.6%, respectively. No obvious differences in these indicators were observed among the treatment durations of 3 days, 6 days and 9 days. High temperature was the main stress factor affecting the P_n of tomato(P<0.05), and high humidity was a second stress factor; the interaction of high temperature and high humidity had a significant effect onP_n (P<0.01). This study confirmed that when the maximum air temperature rises above 38 ℃, appropriate increase in air relative humidity to 65%-75% can effectively reduce the heat stress on tomato damage.

Key words: soil moisture dynamic, probability density function, stochastic simulation, Gurbantunggut Desert., fixed dune