(1) In this experiment, the tolerance of Spiraea Jinshan and Spiraea Jin Yan to low light was studied, and the independent variable was light intensity. The experimental group used shading nets to control the light transmittance of different groups, and the control group should be natural light. Before 16: 00, the photosynthetic rate was higher than the respiration rate, so the maximum organic matter accumulation was 16.

(2) According to the curve analysis, when the light transmittance is 20% ~ 25%, the photosynthetic rate of the two Spiraea species only peaks once a day.

(3) From the curves of two kinds of Spiraea restoration treatments in Figure 1, it can be seen that Spiraea Jin Yan is more tolerant to low light, because the photosynthetic rate of Spiraea Jin Yan after restoration treatment under the condition of 20% ~ 25% light transmittance reaches the maximum at 8 o'clock low light.

(4) There is a "trough" around12, because the stomata are closed and the intercellular CO2 is insufficient, which affects the fixation of CO2 in the dark reaction and the decrease of C3.

So the answer is: (1) natural light (or: no shade at all)? 16:00

(2) 20% ~ 25% light transmittance? Photoreaction of granular or thylakoid membranes

(3) The photosynthetic rate of Spiraea Jin Yan with light transmittance of 20% ~ 25% reached the maximum under the condition of low light after restoration.

(4) carbon dioxide C3