RESPONSES OF PHOTOSYNTHESIS TO CHANGING LIGHT INTENSITIES IN LEAVES OF TOMATO PLANTS GROWN WITH DIFFERENT FERTILIZATIONS

A more sensitive response of leaf photosynthesis to changing densities of photosynthetic photon flux (PPF) may show a higher physiological activity in both aspects of stomatal opening and CO₂ fixation.
In the present study, comparing leaves of tomato plants fertilized with chemical fertilizers, photosynthesis was more sensitive to changing PPF in organically fertilized tomato leaves.
The sensitivity of photosynthetic rate (P_N) to changing PPF was tested by a phenomenon of photosynthetic hysteresis.
When P_N is measured by changing PPF from low to high and then reversing PPF from high to low, the curve of the reversed cycle is usually higher than the first cycle, and consequently an area appears between the two curves.
This phenomenon is called photosynthetic hysteresis.
The light response curve was modeled as
P_N = P_C (1 – e^–Ki) – R_D,
where P_C was photosynthetic capacity, K was a constant, i was PPF and R_D was dark respiration.
The hysteresis (HP) was calculated as (formula available in full text) where i_L and i_H were PPF started from low to high, and from high to low, respectively. H_P was the relative value of the area surrounded by the two PPF response curves within the range from a (0 µmol m^-2 s^-1) to b (2000 µmol m^-2 s^-1). Compared with chemically fertilized tomato plants, organically fertilized tomato plants showed a lower H_P, suggesting less constraint existing in the photosynthetic system, which might be due to more sensitive stomatal conductance and more activated enzymes by abundance of micronutrients.
Discussions were made in association with fruit yield and quality.

VI International Symposium on Light in Horticulture

H.L. Xu, Q.C. Xu, F.F. Qin, F.L. Du

hysteresis, light, organic fertilizer, photosynthesis, tomato

https://doi.org/10.17660/ActaHortic.2011.907.54