Research Progress and Prospect on the Influencing Factors of Photosynthesis in Higher Plants

Yilong HOU

Abstract Photosynthesis plays an important role in organic synthesis， solar energy storage， and environmental protection. Photosynthesis is of great theoretical and practical significance. In this paper， the main factors affecting photosynthesis of higher plants， including light， water， temperature， CO2， mineral elements and plant genotypes， were briefly reviewed and summarized， and the development prospect of photosynthesis was prospected.

Key words Higher plants; Photosynthesis; Photosynthetic rate; Illumination intensity

Green plants absorb solar energy， convert carbon dioxide and water into photosynthetic products， and release oxygen at the same time. The above process is photosynthesis， which has a huge effect on the entire biological world. The first is that photosynthesis can transform inorganic matter into organic matter， which can be directly or indirectly used as production and daily necessities for humans and animals such as food; and the second is that photosynthesis can convert light energy into chemical energy， which is accumulated in the formed organic compounds， which is the energy needed to improve the survival of organisms; and the third is that photosynthesis can maintain the relative balance of oxygen and carbon dioxide in the atmosphere and form the ozone layer， which protects the entire earth environment and allows living things to survive. At present， human beings are faced with five major issues： food， energy， resources， environment and population. The solution of these issues is closely related to photosynthesis.

Photosynthesis is a process unique to most plants， but this process is affected by many factors. Therefore， it is very important to understand the factors that affect plant photosynthesis， promote photosynthesis， increase photosynthesis rate， effectively use solar energy， and increase crop yield and quality.

The Effect of Light

Photosynthesis is a photochemical reaction， and the light environment is one of the important factors affecting photosynthesis. Within a certain range， the photosynthetic rate increases with the increase of light intensity. In the dark， photosynthesis ceases. When the light intensity exceeds the amount that can be used by the light and the system， the photosynthetic function decreases and light inhibition occurs. Photosynthetic capacity is also affected by the intensity of photosynthesis in a day， resulting in a single-peak or double-peak curve of photosynthetic rate. Light quality also affects the photosynthetic efficiency of plants. Generally speaking， the photosynthesis rate is the fastest under orange and red light， followed by blue and purple light， and green light is the worst.

Under field conditions， Zhang et al.[1]measured the light response curves of 12 soybean varieties during the blooming period. Their study found that different soybean varieties responded differently to light intensity， but the trends were the same. When the light intensity was lower， the net photosynthetic rate of soybean leaves increased with the increase of light intensity. When the light intensity exceeded a certain range， the net photosynthetic rate of soybean leaves increased slowly and tended to decrease.

Zhang et al.[2]used LED light source to set three red and blue light ratios and two light intensities [50 and 80 μmol/（m2·s）]， and carried out a test on 2-year-old American ginseng for the effects on chlorophyll content and net photosynthetic rate. The net photosynthetic rate of American ginseng increased with the increase of light intensity and gradually became saturated， and the light intensity of 800 μmol/（m2·s） was the light saturation point. In the case of a large proportion of red light， the photosynthetic rate was relatively large. Fan et al.[3]used Chinese cabbage as an experimental material and designed such 5 treatments as monochromatic yellow light， monochromatic green light， monochromatic blue light and monochromatic red light and control， and studied the effect of different light quality on the photosynthetic rate of Chinese cabbage. According to the research， the net photosynthetic rate of Chinese cabbage leaves varied significantly under different light qualities， and the maximum value was 8 times the minimum. The net photosynthetic rate of Chinese cabbage was the highest under blue light， which was significantly higher than those of other light qualities. Red light took the second place， and green light and yellow light were the lowest.

Light is the main influencing factor of photosynthesis. Too low or too high light intensity will damage photosynthetic organs， reduce photosynthetic capacity， and affect plant growth and development. The research of Wu et al.[4]proved this point. They studied the photoinhibition and photoprotection mechanism of peanut variety ‘Baisha 106 in the process of photosynthesis recovery under natural light by means of shading. The photoinhibition or photodamage continued to increase in the 0-5 d after the shading was released. It is believed that the production of active oxygen is the main cause of photodamage， and heat dissipation and the removal of active oxygen play an important protective role in photosynthetic restoration. The study by Du et al.[5]also showed that too much light would reduce the net photosynthetic rate. They used green bamboo as the experimental material and designed three light treatments， namely 100% natural light [1 357 μmol/（m2·s）]， 70% light [925 μmol/（m2·s）]and 30% light [376 μmol/（m2·s）]. The net photosynthetic rate of green bamboo under 70% light was the largest， and significantly better than those of 100% light and 30% light， which also showed that green bamboo has good adaptability to weaker light， but excessive light will damage its photosynthetic capacity. Ren et al.[6]measured the leaf photosynthesis-CO2 response curves of two tree species， Quercus variabilis and Robinia pseudoacacia in the sunny leaves under light conditions and shaded leaves on the back side. The study found that the maximum net photosynthetic rate of the shaded leaves of Q. variabilis was 31.3% lower than that of the sunny leaves， indicating that the photosynthetic capacity was stronger under high light intensity; and the maximum net photosynthetic rate of the shaded leaves of R. pseudoacacia was 23.5% higher than that of the sunny leaves， which might be because that R. pseudoacacia was more adapted to weaker light intensity， and when the light intensity was too high， the photosynthetic capacity would be inhibited instead. Quan et al.[7]used two varieties of Porphyra chinensis as materials to study their photosynthetic and respiration characteristics under different treatment time and light intensities. The results showed that the photosynthetic oxygen production rates of the two varieties of P. haitanensis increased first and then decreased with the increase of light intensity， and both reached the highest at 2 800 lx and the lowest at 3 800 lx， indicating that the light was too strong and photoinhibition occurred， making the photosynthetic capacity decrease instead of increasing.

The Effect of CO2

CO2 is a raw material for photosynthesis and has a great impact on photosynthesis. Within a certain range， the photosynthetic rate is positively correlated with the CO2 concentration.

Yuan et al.[8]used the OTC （open-top champer） system to study the effect of increased CO2 concentration on pepper photosynthesis. The CO2 concentration of the control gas chamber was 360-400 μmol/mol， and the CO2 concentration of the treatment gas chamber was the CO2 concentration of the control gas chamber plus 200 μmol/mol. The results of the experiment found that the increase of atmospheric CO2 concentration significantly increased the net photosynthetic rate of leaves， and the chlorophyll content also increased significantly， which was beneficial to the growth and development of pepper.

Jing et al.[9]set up two levels of environmental CO2 and high-concentration CO2 （increase by 200 μmol/mol） and measured the photosynthetic characteristic parameters such as the net photosynthetic rate of the top full-spreading leaves under cloudy and sunny conditions at the jointing stage and the filling stage， with ‘Y Xiyou 900 and ‘Yongyou 538 rice as test materials， using a large-scale FACE platform for rice fields. The results showed that under both cloudy and sunny weather conditions， the net photosynthetic rates of the two varieties showed an increasing trend under the high CO2 concentration， and there were significant interaction effects between CO2 and weather， and CO2 and growth period.

Zhang et al.[1]used 12 soybean varieties from different sources as materials under field conditions， and measured the carbon dioxide response curve during the full bloom period. The results showed that different soybean varieties responded differently to carbon dioxide， but the trends were the same. When the carbon dioxide concentration was in a certain range， the net photosynthetic rate of soybean leaves increased with the increase of carbon dioxide concentration. When the carbon dioxide concentration exceeded 1 000 μmol/mol， the net photosynthetic rate of soybean varieties from different sources had a decreasing trend.

Wang et al.[10]studied the gas exchange parameters of 8 crops （soybean， sweet potato， peanut， rice， cotton， maize， sorghum and millet） under the condition of doubled CO2 concentration （natural CO2 concentration 375 μmol/mol， CO2 concentration doubled 750 mol/mol）. The results showed that the doubled CO2 concentration improved the photosynthetic rate and reduced the transpiration rate， thereby improving water use efficiency， and the increase in photosynthetic rate contributed more; and C3 crops had larger increases in photosynthetic rate and water use efficiency than C4 crops， and the increase in the photosynthetic rate of C3 crops contributed more to water use efficiency than C4 crops. Also in the case of a doubled CO2 concentration， Liu et al.[11]on Dendrobium chrysotoxum， Zhang et al.[12]on soybeans obtained results very similar to those of Wang et al. On D. chrysotoxum， the high concentration of CO2 improved the net photosynthetic rate， intercellular CO2 concentration and water use efficiency. On soybeans， the treatment of doubling the CO2 concentration improved the content of chlorophyll， anthocyanin and carotenoids， and improved all of photosynthetic rate， Rubsico activity， stomatal conductance and PS II function.

Regarding the reports of CO2 fertilization on cucumbers， in general， CO2 fertilization can promote photosynthesis， inhibit respiration and reduce transpiration， and is conducive to cucumber growth and yield formation， while improving product quality and enhancing resistance[13-14].

The effect of temperature

The dark reaction in photosynthesis is a biochemical reaction catalyzed by enzymes. Temperature directly affects the activity of enzymes， so temperature affects photosynthesis. According to the research of Yuan et al.[15]， the chlorophyll content of the leaves of three cotton varieties （HLY， XYM68， TS16） from the seedling stage to the full bloom stage increased with the increase of temperature， and the net photosynthetic rate was also on the rise. In the peak boll-bearing stage， due to the drop in temperature， the chlorophyll content of the leaves showed a downward state， and the net photosynthetic rate also showed a downward trend.

Yin et al.[16]used tomato seedlings as experimental materials to study the responses of the photosynthetic gas exchange parameters， chlorophyll fluorescence parameters， PSII reaction center， relative expression of PSII core protein coding genes， and active oxygen metabolism to 12 h stress of different high temperatures （25， 30， 35， 40 ℃）， hoping to provide a reference basis for tomato cultivation in the high-temperature season. The results showed that with the increase of temperature， the photosynthetic carbon assimilation ability of tomato seedling leaves increased first and then was inhibited. The weakening of photosynthesis of tomato seedling leaves under the high-temperature stress of 30 and 35 ℃ was mainly due to stomatal factors， while at 40 ℃， it was limited by both stomatal and non-stomata factors. Under high temperature stress， the activity of PSII reaction center in tomato seedling leaves decreased， PSⅡ electron transfer was blocked， and photosynthesis was seriously affected.

Yang et al.[17]simulated the effects of relative low temperature （average daily temperature 16.5 ℃）， normal temperature （average daily temperature 23.5 ℃） and relatively high temperature （average daily temperature 30.5 ℃） on tobacco growth and photosynthesis through an artificial climate chamber. The results showed that relatively low and high temperature treatments resulted in lower net photosynthetic rate， PSⅡ maximum photochemical quantum efficiency， PSⅡ actual photochemical quantum efficiency， and RuBP carboxylase activity than the normal temperature treatment. Long-term higher or lower temperature will inhibit the growth and development of tobacco， which may be because it inhibits the activity of the photosynthetic apparatus of tobacco leaves to a certain extent and damages the reaction center， thereby reducing the photosynthesis of tobacco and inhibiting the growth of tobacco plants， and the long-term average daily temperature of 23.5 ℃ is conducive to tobacco growth and photosynthesis.

Shi et al.[18]treated Nymphoides peltatum rhizomes used as an experimental material at three temperatures （28， 30， 32℃） indoors， and measured the light response curve and CO2 response curve of N. peltatum under the three temperature treatments. At the three temperatures， the photosynthetic capacity of N. peltatum showed an order of 30 ℃>32 ℃>28 ℃. At a temperature lower than 30 ℃， with the increase of temperature， the photosynthetic capacity of N. peltatum increased significantly， which promoted the growth of plants; and when the temperature exceeded 30 ℃， the photosynthetic efficiency decreased and the growth of plants was inhibited. Within a suitable temperature range （<30 ℃）， a small increase in temperature （2 ℃） produced a significant accumulated temperature effect （200 ℃·d）， which promoted the growth of N. peltatum.

Jin et al.[19]simulate the temperature conditions in Jiangchuan， Yunnan， Zunyi， Guizhou， and Xiang County， Henan through an artificial climate chamber and treated ‘Yunyan 87 used as a material at the tobacco transplanting-rosette， rosette-budding and maturation stages， so as to study the effects of different growth temperatures on tobacco leaf photosynthesis rate， plastid pigment content， metabolism-related enzyme activity and related gene expression. In general， different growth temperatures had different effects on the photosynthetic rate， plastid pigment content， metabolism-related enzyme activity and gene expression of tobacco leaves at different growth stages. Compared with other growth periods， the temperature at maturation stage had the greatest effects on the photosynthetic rate， chlorophyll content and carotenoid content of tobacco leaves. Xiang County， Henan Province， which has relatively high growth temperature conditions， is more conducive to the progress of tobacco photosynthesis and the accumulation of plastid pigments.

Temperature has a great influence on photosynthesis of chestnut. In a suitable temperature range （28.5-30.5 ℃）， the photosynthetic rate of chestnut accelerated with the increase of temperature.

Yilong HOU et al. Research Progress and Prospect on the Influencing Factors of Photosynthesis in Higher Plants

The Effect of Mineral Element

As the structural substance of chlorophyll， mineral elements participate in the process of photosynthetic electron transport and water splitting， or participate in the transportation and transformation of photosynthetic products. Therefore， mineral elements directly or indirectly affect photosynthesis.

Selenium is a trace element necessary for life activities， and the role of selenium as a plant fertilizer has attracted increasing attention. For example， selenium can improve photosynthesis， and can affect the structure and function of chloroplasts， as well as the enzymes and proteins related to the photosystem; and the application of selenium can enhance the resistance of crops to various adversities. Experiments have proved that when plants are under stress from the outside world， they will produce a large amount of free radicals and damage the chloroplast membrane structure. Glutathione peroxidase can remove a large number of free radicals caused by adversity in higher plants[20]. The selenium atom is located in the active center of the free radical scavenging enzyme GSH-Px molecule， thus ensuring the integrity of the chloroplast membrane structure.

Under the continuous cropping stress caused by continuous planting， the chloroplasts of soybeans swell， and the grana disappear， and even turned into lutein， while the application of selenium can keep the soybean chloroplast membrane structure intact. The application of low-concentration selenium can not only alleviate the peroxidation damage of chloroplast membrane caused by soybean continuous cropping stress， but also significantly increase the contents of Mg， Fe， and Mn in soybean leaves that are directly related to the structure and function of chloroplasts[21]. In addition， Filek et al.[22]found that cadmium pollution stress caused the degradation of the chloroplast membrane of rape seedlings. When 2 μmol/L selenium was applied， the submicroscopic structure of damaged chloroplasts was rebuilt， the chloroplasts became larger， and the unsaturation of fatty acids and the fluidity of cell membranes increased.

The synthesis of chlorophyll is a series of enzymatic reactions. Metal elements such as Fe， Mn， Cu and Zn are important enzyme active centers involved in the process of chlorophyll biosynthesis. In the physiological concentration range， selenium can promote the absorption of P， K， Ca， Mg， Mn， Zn， Mo and other elements by plants[23]. The promotion of chlorophyll synthesis may be achieved by promoting the absorption of mineral elements related to chlorophyll synthesis.

Studies have shown that as plant growth regulators， light rare earths such as lanthanum and cerium can promote the absorption and utilization of trace elements such as iron， manganese， zinc， copper and chlorine by crops， promote leaf growth， increase leaf chlorophyll content， and enhance photosynthesis， as well as enhancing the ability of crops to resist diseases， droughts and floods， ultimately achieving the effects of increasing yield， improving quality and reducing disease. Ruan et al. used "Fuji" apples as test materials to study the effects of spraying rare earth compound foliar fertilizers at concentrations of 0.01， 0.10， and 1.00 mg/L during the growing season on apple leaf photosynthesis and fruit quality. The results showed that 0.01-1.00 mg/L rare earth compound foliar fertilizer treatments increased the chlorophyll content， net photosynthetic rate， and PSII photochemical electron transfer efficiency of apple leaves to varying degrees; and at the same time， it alleviated the effect of the "photosynthetic lunch break" of the leaves. It shows that spraying rare earth compound foliar fertilizer can significantly increase leaf chlorophyll content and leaf photosynthetic energy conversion efficiency， and ultimately improve fruit quality.

Wei et al.[24]conducted water-nitrogen coupling experiments on maize in oasis irrigation areas， and showed that water-nitrogen coupling enhanced maize photosynthesis and increased the growth rate of dry matter， which was expressed as under the condition of certain irrigation amount， the net photosynthetic rate of high nitrogen level was higher than that of medium nitrogen level and no nitrogen application.

Mushroom residue is the waste of the culture medium left after cultivating various edible fungi. It is rich in a large number of nutrients such as nitrogen， phosphorus， potassium and other nutrients required for the growth of crops， medium nutrients such as calcium， magnesium and sulfur， and micronutrients such as copper， zinc and iron. Wu et al.[25]used waste fungus residue from Pleurotus ostreatus planting to study the effects of returning the fungus residue to the field on photosynthesis， chlorophyll content and fruit quality of the citrus variety ‘Bendizao. The results showed that the application of mushroom residues increased the chlorophyll content of the spring shoot leaves of ‘Bendizao， which showed an overall increasing trend as the amount of mushroom residues increased. Continuous application of mushroom residues for 2 years effectively increased the net photosynthetic rate of the spring shoot leaves of ‘Bendizao， which increased with the increase in the amount of mushroom residues. Zhao et al.[26]also proved that the application of mushroom residues increased photosynthesis and increased yield， and the effect was significant.

Fungi and plant root cells symbiotically form mycorrhiza. Fungi obtain nutrients from plant root cells， and simultaneously expand the root absorption area and absorption capacity， which is conducive to the absorption of water and minerals by the roots， especially the absorption of phosphorus. Zhang et al.[27]found that inoculation with Arbuscular mycorrhizas （AM） increased plant height， leaf area and biomass of Cyclobalanopsis glauca， while improving photosynthesis and water use efficiency. He et al.[28]and Han et al.[29]both believed that AM helped to increase the net photosynthetic rates and growth of Broussonetia papyrifera and Coleus blumei. Sun et al.[30]proved on Lavandula angustifolia that the inoculation of single AM strain and mixed inoculation of two strains increased chlorophyll content， net photosynthetic rate and biomass， and the mixed inoculation had the greatest effect.

The effect of moisture

Water is one of the raw materials for photosynthesis， and photosynthetic products need to be dissolved in water for transportation. Therefore， the amount of water in the soil and plants will also affect the photosynthetic capacity of plants.

Ma et al.[31]conducted a study on the effects of light and soil moisture on the photosynthesis of Armeniaca sibirica and Atriplex canescens. The study found that for A. sibirica， in the range of soil water content of 8.57%-19.08%， soil water content was positively correlated with net photosynthetic rate， and when the soil water content exceeded 19.08%， the net photosynthetic rate decreased. For A. canescens， in the range of soil water content from 5.64% to 17.89%， the soil water content was positively correlated with the net photosynthetic rate， and when the soil water content exceeded 17.89%， the net photosynthetic rate decreased. The reason is that the tested plants were under water stress， and the stomatal conductance of the two tree species was reduced， resulting in the formation of a protective mechanism. With different soil water content， the net photosynthetic rates of A. sibirica and A. canescens tended to increase gradually with the increase of light intensity. When the light intensity reached about 1 500 μmol/（m2·s）， the net photosynthetic rates of A. sibirica and A. canescens reached the maximums.

Zhang et al.[32]used 1-year-old seedlings of Malus hupehensis as experimental materials to study the effects of waterlogging stress on the growth and photosynthesis of M. hupehensis. The results showed that in the early flooding stage （0-15 d）， the growth of the seedling height of M. hupehensis was not significantly inhibited， but in the late flooding stage （15-35 d）， the inhibition was significantly increased and resulted in a final seedling height 10.7% of the control. The net photosynthetic rate， stomatal conductance and stomatal limit values during flooding were significantly lower than conventional management. The relative mass fraction of chlorophyll was significantly lower than the control.

Li et al.[33]measured and analyzed the effects of different soil moisture on the light response process of the photosynthesis of Vitex negundo L. as a test material. The results showed that the photosynthetic rate of V. negundo increased rapidly under the light intensity of 0-600 μmol/（m2·s）， especially under the light intensity of 0-200 μmol/（m2·s）， it increased basically linearly; when it increased to the maximum photosynthetic rate， the increase gradually slowed down， but had been maintained at a higher level; when the light intensity was 600-1 200 μmol/（m2·s）， the photosynthetic rate slowly increased with the increase of light intensity; and when the light intensity was greater than 1 200 μmol/（m2·s）， the photosynthetic rate of V. negundo was in a stable state， and it could be considered that 1 200 μmol/（m2·s） was the light saturation point of V. negundo， and the corresponding photosynthetic rate was the maximum photosynthetic rate. The net photosynthetic rate in the photosynthetically active radiation range of 600-1 400 μmol/（m2·s） could be maintained at a high level， indicating that the photosynthesis of V. negundo has a wide range of adaptation and utilization of photosynthetic active radiation. With the increase of relative water content， the net photosynthetic rate of V. negundo increased rapidly， but when the relative water content was 57.7%， the photosynthetic rate began to decrease. It can be seen that the relative water content has a relatively obvious threshold response to the net photosynthetic rate of V. negundo. When the relative water content was in the range of 39.6%-57.7%， the net photosynthetic rate of V. negundo leaves was maintained at a high level， indicating that the relative water content within this range had a relatively stable effect on the net photosynthetic rate of V. negundo.

The effect of genotype

Studies have found that the photosynthetic capacities of different varieties （genotypes） of the same plant are not the same in response to light intensity， and there are even greater differences. Quan et al.[7]also found that the photosynthetic rate of Dongtou native nori was always significantly higher than the photosynthetic rate of Zhedong No. 1 under different light conditions when studying the photosynthetic characteristics of Porphyra chinensis， showing differences between genotypes.

In order to screen for varieties with strong drought resistance， Zheng et al.[34]used 5 cotton lines 16N2， 16N3， 16N4， 16N5 and Yuanmian 6 as test materials， and measured the net photosynthetic rate and other photosynthetic indexes of cotton at the boll stage under drought stress and normal irrigation. The results showed that the net photosynthetic rate and other photosynthetic indicators of 16N3 were significantly higher than other varieties， indicating that there are differences in photosynthetic capacity between varieties.

Song et al.[35]conducted a comparative experiment on the photosynthesis characteristics of 5 varieties of buckberry. It was found that there were certain differences in the net photosynthetic rate and other photosynthetic characteristics between different varieties. Among them， the net photosynthetic rates of ‘Brigitta and ‘Misty were significantly higher than the other three varieties， and they belong to the varieties with high photosynthetic capacity and can be used as a backup parent in breeding.

The study of Yuan et al.[15]on cotton showed that the net photosynthetic rate and chlorophyll content of the three tested lines （HLY， XYM68， TS16） were significantly different in the four phenological phases measured. Among them， HLY had the highest leaf net photosynthetic rate and chlorophyll content， followed by XYM68， and TS16 was the lowest， and there were also differences between genotypes.

In order to explore the photosynthesis characteristics of Cerasus humilis， Zhang et al.[36]used 5 C. humilis varieties as materials and local wild plum as a control to determine the leaf photosynthesis indicators. The results showed that the daily changes in the net photosynthetic rates of the five C. humilis leaves showed the characteristic of a double-peak curve， and they all had different degrees of photosynthetic "midday break". The net photosynthetic rates of the other four varieties except Nongda 7 were higher than that of wild species， and Nongda 5 and Nongda 3 had better photosynthesis performance and had obvious advantages in photosynthesis.

In order to screen high temperature-tolerant varieties， Gong et al.[37]carried out a study on the differences in photosynthetic characteristics， yield characteristics and quality characteristics between different cotton varieties under high temperature stress， and analyzed the effects of high temperature stress on cotton photosynthetic characteristics. The photosynthetic characteristics and yield traits of the tested varieties were significantly different after high temperature stress. Under high temperature stress， the photosynthetic capacities of Zhongmiansuo 35， Xiangmian 11， and Emian 10 were relatively stronger， and the yield traits were relatively high. They had stronger high temperature tolerance， and the selected materials can be used as germplasm resources for high temperature breeding.

Prospects

The research on photosynthesis of higher plants has always been a concern of scientists in the field of botany， and many results have been achieved， but from the perspective of theory and practice， it needs to be further improved. First， we should carry out the development of high photosynthetic efficiency preparations. In view of the various factors that affect plant photosynthesis， comprehensive （complex） research on various factors can be conducted to develop high photosynthetic efficiency preparations suitable for different crops or universally applicable to main crops. The preparations should contain favorable factors that can promote photosynthesis， and can achieve the purposes of improving leaf quality， delaying leaf senescence and falling， increasing leaf chlorophyll content， enhancing photosynthesis， increasing photosynthetic rate， and improving crop yield and quality. We are conducting relevant research. Second， we should carry out research on photosynthesis in local environments. Artificial adjustment of some factors that affect photosynthesis can improve photosynthetic efficiency to a certain extent， such as increasing light intensity， prolonging light time， increasing CO2 concentration， etc.， but in natural environments， it is very difficult to manually adjust the above factors on a large scale， or it is even impossible to achieve. However， in a local environment， in a small area， such as greenhouses， it is completely possible to carry out relevant manual adjustments， and it should even be encouraged. Strengthening the research of photosynthesis in local environments can not only enrich and improve the theory of photosynthesis， but also promote the improvement of crop cultivation techniques in local environments， such as greenhouses， laying the foundation for high yield and quality. Third， we should carry out research on the physiological functions of photorespiration. Photorespiration can significantly weaken photosynthesis and reduce crop yields. What are the physiological functions of photorespiration. It has not been studied clearly yet. Therefore， carrying out research on the physiological functions of photorespiration and clarifying the significance of photorespiration is of great significance for rationally promoting photosynthesis. Fourth， we should carry out research on the molecular mechanism of photosynthesis. Revealing the mechanism of photosynthesis at the molecular level， such as the cloning and transformation of photosynthesis-related genes， will help improve photosynthetic efficiency. Fifth， carrying out photosynthesis synthetic biology research， such as constructing a new photosynthetic system that does not exist in nature， and expanding the photosynthetic system to use multiple energy channels， will provide huge potential for expanding food and energy production channels. Sixth， carrying out research on the differences in the photosynthetic capacity between genotypes of the main crop species can lay a foundation for the selection and reserve of high photosynthetic efficiency resources and the breeding for high photosynthetic capacity.

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