Application of Five Light-Response Models in the Photosynthesis of Populus × Euramericana cv. ‘Zhonglin46’ Leaves

Abstract

The light-response curve of photosynthesis is an important tool used to study plant ecophysiology and can provide a scientific basis for the response of plant photosynthetic characteristics to environmental factors. At present, there are five common light-response models of photosynthesis. To gain deeper insight into the applicability of different light-response models of photosynthesis and the photosynthetic physiological characteristics of Populus euramericana cv. 'Zhonglin46', two typical light-response curves of photosynthesis in P. euramericana cv. 'Zhonglin46' leaves, one under drought stress and the other under control conditions, were measured using a CIRAS-2 portable photosynthesis system. The light-response data were divided into two groups: one set of data was used to fit light-response curves, and the other set of data was used to test them. The accuracy of the fitting and the predictions of the different models were evaluated by mean square error and mean absolute error. The results showed that the light-response curves of P. euramericana cv. 'Zhonglin46' under drought stress matched the light-saturated inhibition type and that those under the control condition matched the approaching light-saturation type. The two new models (i.e., the modified rectangular hyperbola model and modified exponential model) fit the two light-response curves and their characteristic parameters well, and the fitting results of the two models were similar. Conversely, the three traditional models (i.e., the rectangular hyperbola model, nonrectangular hyperbola model, and exponential model) did not fit the two light-response curves well; in particular, they overestimated the maximum net photosynthetic rate, underestimated the light saturation point (LSP), and did not fit the net photosynthetic rate during the light-saturated stage. The LSP calculated by the "linear method" combined with the traditional models was significantly lower than the measured values; additionally, the appropriate value of the proportional coefficient was difficult to determine, and the assumed value (empirical value) could easily lead to unreliable results by the "coefficient method". The "estimation method" based on the measured light-response data was still a relatively accurate, simple, and practical way to determine LSP. In addition, the nonrectangular hyperbolic model also had good accuracy and applicability in fitting the approaching light saturation curve on the basis of the "estimation method" to determine LSP.

Drought Effects on Photosynthesis and Implications of Photoassimilate Distribution in 11C-Labeled Leaves in the African Tropical Tree Species Maesopsis eminii Engl.

“…14 CO 2 autoradiographs of Nicotiana tabacum L., an active loader with high export rates, also showed elevated tracer amounts in the major veins, with a lower evenly distributed amount of tracer in the mesophyll, measured one hour after labeling [84]. The active phloem loading strategy has been linked to (i) an increased carbon export from leaves to sinks (e.g., shoots and roots) [32,40,85]; (ii) an improved efficiency of sugar transport [58]; and (iii) an increased growth potential [40]. Active transport is less common in woody tree species, but not unique [83].…”

“…Light response curves were fitted based on the non-rectangular hyperbola model ( [58]; Equation (1)):…”

“…In addition, the light compensation point (I c ) (Equation (2); Fang et al [58]) and the light saturation point (L s ) at 70% P n,max (δ = P n /P n,max = 0.7) (Equation (3); Wang et al [49]) were calculated for each measurement day:…”

“…Simulated courses were integrated to obtain day-and nighttime as well as total carbon exchange rates (Figure 3). Albeit a simplified approach because fluxes are projected from specific light response curves instead of [58] to obtain average model parameters from which an average light response curve per measurement day was developed. Net photosynthesis (P n , µmol CO 2 m −2 s −1 ) increases with increasing light intensity (I, µmol m −2 s −1 ).…”

Comparison of the Photosynthetic Capacity of Phragmites australis in Five Habitats in Saline‒Alkaline Wetlands

“…The physiological characteristics of photosynthetic carbon fixation in plants are mainly studied in terms of the effects of water (water level), salt [ 5 ], and heavy metal stress [ 6 ] on photosynthesis and fluorescence in plants. Combined with the plant community characteristics and growth characteristics, models are used to fit the photosynthetic carbon fixation process [ 7 , 8 ]. For example, the tolerance to flooding of four species, including P. australis , has been compared using isotopic techniques.…”