Abstract: External stresses affect the plant growth and metabolism in a number of ways, especially the photosynthesis (P_n). As P_n is an important factor affecting productivity, the study on its mechanism is still a hot issue in the field of plant physiology and ecology. P_n, however, is mainly restricted by stomatal or non-stomatal factors, and it has not been determined yet. This paper mainly discussed the methods for calculating the stomatal and non-stomatal limit values (L_s and C_i (sub-stomatal CO₂ concentration)/gs (the stomatal conductance)), stomatal and non-stomatal limitations under different stresses and the effects on P_n: ① We summarized the methods for calculating the (relative) L_s and C_i/g_s values, which could be the basis for judging the main restriction factors; ② We classified the external stresses and summarized the achievements from the aspects of manual controlling conditions (water, salt-alkali and multi-factor stresses) and natural conditions of the previous studies; ③ We analyzed the impact ways of stomatal and non-stomatal factors on P_n. The features of the L_s and C_i/g_s, values and the mechanisms of one species at different growth and development stages and in different habitats (hydrothermal, salty, nutrient, and artificial and natural conditions) were explored and discussed, and this will be the key trend and direction for researching.

Key words: plant leaves, photosynthesis, stomatal limitation, non-stomatal limitation, water stress, research summary