Dynamic Photosynthesis In Tomato Seedlings And Its Response To Environmental Factors In Protected Agriculture

In protected horticulture,leaves are often exposed to irradiance with dynamically changing quantity and quality at various temporal and spatial scales,due to changes in solar angle,cloud cover and shading from greenhouse construction and neighboring leaves or plants.Therefore,investigating how photosynthesis quickly responds and long-term adapts to the dynamic light condition,named dynamic photosynthesis,is important for plant light use efficiency.Red and blue light are two important light wavelengths in protected horticulture,and are major energy for photosynthesis,but their influences on dynamic photosynthesis are not clear.Investigating how to manipulate red:blue light ratio to improve dynamic photosynthesis is needed.Furthermore,soil salinization in protected horticulture in China is severe,and it is often accompanied by the dynamic light condition,but how soil salinization affects dynamic photosynthesis is not clear,neither.Therefore,in this thesis,tomato species were used,to systematically investigate how red:blue light ratios affect dynamic photosynthesis in a short-term and in a long-term,and to investigate how salt stress affects dynamic photosynthesis.The main results are as follows:1.Tomato seedlings were grown either in a greenhouse or in a climate room for 16-18 days.Photosynthetic induction in dark-adapted leaves was measured under the light intensity of 500μmol m^-2s^-1 with four different red:blue light ratios（100%red,100%blue,90%red+10%blue and 70%red+30%blue）.Photosynthetic induction rates in neither greenhouse grown leaves nor plant factory grown leaves,were affected by red:blue light ratio in incident light.Photosynthesis rate in all treatments increased slowly and reached 90%of final maximum photosynthesis after around 20 min.However,final maximum photosynthesis rate under monochromatic red light or under the combination of red and blue light were25%higher than that under monochromatic blue light.The increase rate of stomatal conductance was hardly affected by red:blue ratios in incident light,neither.2.Tomato seedlings were grown in a climate room under four different red:blue ratios(same as above with a light intensity of 400μmol m^-2 s^-1)to investigate how dynamic photosynthesis acclimates to red:blue ratios of growth light.Leaves grown under monochromatic red light showed decreased leaf thickness and nitrogen concentrations,with their steady-state photosynthetic capacity 18-22%lower than leaves grown under monochromatic blue light and the combination of red and blue light.However,photosynthetic induction rates(under 1000μmol m^-2 s^-1)were similar among the treatments.Leaves grown under monochromatic blue light had the highest（15%higher than other treatments）transient non-photochemical quenching during photosynthetic induction,suggesting the photoprotection capacity were enhanced.3.Tomato seedlings were grown in a climate room treated with either 0 mM,70 mM or 140 mM salt treatment for 7-9 days to investigate how dynamic photosynthesis responds to salt stress.Salt stress did not affect steady-state photosynthetic capacities in leaves,but slowed down their photosynthetic induction rates.The higher the salt concentration was,the severer its limitation was on photosynthetic induction.Salt stress slowed down photosynthetic induction rate via increasing both stomatal and biochemical limitation.During photosynthetic induction,salt stress did not downregulate PS II photosynthetic efficiency,instead,it enhanced non-photochemical quenching to protect photosynthetic apparatus from excess light.Under artificial fluctuating light intensity,reduction of stomatal conductance was also faster in salt-stressed leaves,resulting in a 12-42%decrease in carbon fixation compared to non-stressed leaves.In conclusion,regulating red:blue ratios can alter steady-state photosynthetic capacity but hardly change photosynthetic induction rate;however,when salt stress does not affect steady-state photosynthetic capacity,it can significantly decrease light use efficiency under dynamic light intensities.To improve light use efficiency in crops,both dynamic photosynthesis and steady-state photosynthetic capacity should be taken into consideration.