The effect of exogenous CaCl2 on photosystem I and II (PSI and PSII) activities, cyclic electron flow (CEF), and proton motive force of tomato leaves under low night temperature (LNT) was investigated. LNT stress decreased the net photosynthetic rate (Pn), effective quantum yield of PSII [Y(II)], and photochemical quenching (qP), whereas CaCl2 pretreatment improved Pn, Y(II), and qP under LNT stress. LNT stress significantly increased the non-regulatory quantum yield of energy dissipation [Y(NO)], whereas CaCl2 alleviated this increase. Exogenous Ca2+ enhanced stimulation of CEF by LNT stress. Inhibition of oxidized PQ pools caused by LNT stress was alleviated by CaCl2 pretreatment. LNT stress reduced zeaxanthin formation and ATPase activity, but CaCl2 pretreatment reversed both of these effects. LNT stress caused excess formation of a proton gradient across the thylakoid membrane, whereas CaCl2 pretreatment decreased the said factor under LNT. Thus, our results showed that photoinhibition of LNT-stressed plants could be alleviated by CaCl2 pretreatment. Our findings further revealed that this alleviation was mediated in part by improvements in carbon fixation capacity, PQ pools, linear and cyclic electron transports, xanthophyll cycles, and ATPase activity.

High temperature and high light intensity is a common environment posing a great risk to organisms. This study aimed to elucidate the effects of sub-high temperature and high light intensity stress (HH, 35°C, 1000 μmol⋅m-2⋅s-1) and recovery on the photosynthetic mechanism, photoinhibiton of photosystem II (PSII) and photosystem I (PSI), and reactive oxygen (ROS) metabolism of tomato seedlings. The results showed that with prolonged stress time, net photosynthetic rate (Pn), Rubisco activity, maximal photochemistry efficiency (Fv/Fm), efficient quantum yield and electron transport of PSII [Y(II) and ETR(II)] and PSI [Y(I) and ETR(I)] decreased significantly whereas yield of non-regulated and regulated energy dissipation of PSII [Y(NO) and Y(NPQ)] increased sharply. The donor side limitation of PSI [Y(ND)] increased but the acceptor side limitation of PSI [Y(NA)] decreased. Content of malondialdehyde (MDA) and hydrogen peroxide (H2O2) were increased while activity of superoxide dismutase (SOD) and peroxidase (POD) were significantly inhibited compared with control. HH exposure affected photosynthetic carbon assimilation, multiple sites in PSII and PSI, ROS accumulation and elimination of Solanum lycopersicum L.

Soil-related obstacles resulting from continuous monoculture have limited the sustainable development of the tomato industry in China. An experiment on tomatoes with seven continuous monoculture treatments (the 1st, 3rd, 5th, 7th, 9th, 11th, and 13th crops, respectively) was conducted in a solar greenhouse, to investigate the influence of monoculture on soil quality. Most soil quality indicators first increased and then decreased with increasing continuous monoculture crops, and significant differences among crops were observed. Indicators at the 13th crop were significantly lower than those at the other crops in terms of average well color development (AWCD), substrate richness (S), the Shannon diversity index (H), and the McIntosh index (U) of the soil microbial community (SMC), soil urease (UR), and neutral phosphatase (N-PHO) activities, and available nitrogen (AN) and potassium (AK). However, fungal abundance (FUN) at the 13th crop was significantly higher than that at the other crops. As principal component analysis (PCA) revealed, SMC functional diversity at the 1st, 11th, and 13th crops were similar, and were obviously distinguished from those at the other crops. Moreover, the tomato yield was significantly and positively correlated with soil-available potassium and SMC functional diversity indexes. Our findings indicated that short-term continuous monoculture, e.g., for fewer than seven or nine crops, was beneficial for soil quality improvement. However, continuous monoculture for greater than 11 crops had adverse effects on soil enzyme activities, soil microbial abundances, soil chemical properties, soil SMC functional diversity, and the tomato yield, particularly at the 13th crop.