Photosynthetic rate Pn, transpiration rate tr, intercellular carbon dioxide concentration Ci and stomatal conductance cond are all photosynthetic physiological and ecological indicators. I have also done experiments on photosynthesis in my master's thesis, so I know something about it. It is strange that I can use leaves to distinguish species, because our research rarely involves these, but we can discuss them a little.

These four indicators, Pn/Tr/Ci/Cond, show the dynamic changes in different time periods of the day. Undoubtedly, Pn has the greatest influence on plant photosynthesis, with a peak at 8- 10 in the morning, a trough at around 2 pm, and then a rising process. But even if there are different dynamic changes in a day, photosynthetic rate is undoubtedly the main factor affecting crop growth and the key to distinguish different crops. This should be affirmative. For example, the photosynthetic rate of peanuts is 10.

μ

Mol/(m2 s), the photosynthetic rate of cassava is about 15.

μ

Molar/(m2 sec).

Generally speaking, the transpiration rate tr is greatly influenced by leaves and light, because different leaf selection or withering degree will lead to great differences in transpiration; The intercellular carbon dioxide concentration Ci is greatly influenced by the field carbon dioxide concentration Ca, so it is difficult to distinguish species, and so is the stomatal conductance, which is greatly influenced by the temperature and light in the environment.

Therefore, considering comprehensively, photosynthetic rate Pn is the best indicator if we must choose to distinguish plant species, but generally speaking, under certain conditions, like an experimental field, transpiration rate Tr, intercellular carbon dioxide concentration and stomatal conductance of different plants can still reflect some quantitative differences, or come from different trends in a day.