Abstract
Accurately predicting the crown photosynthesis of trees is necessary for better understanding the C circle in terrestrial ecosystem. However, modeling crown for individual tree is still challenging with the complex crown structure and changeable environmental conditions. This study was conducted to explore model in modeling the photosynthesis light response curve of the tree crown of young Larix principis-rupprechtii Mayr. Plantation. The rectangular hyperbolic model (RHM), non-rectangular hyperbolic model (NRHM), exponential model (EM) and modified rectangular hyperbolic model (MRHM) were used to model the photosynthetic light response curves. The fitting accuracy of these models was tested by comparing determinants coefficients (R2), mean square errors (MSE) and Akaike information criterion (AIC). The results showed that the mean value of R2 of MRHM (R2 = 0.9687) was the highest, whereas MSE value (MSE = 0.0748) and AIC value (AIC = -39.21) were the lowest. The order of fitting accuracy of the four models for Pn-PAR response curve was as follows: MRHM > EM > NRHM > RHM. In addition, the light saturation point (LSP) obtained by MRHM was slightly lower than the observed values, whereas the maximum net photosynthetic rates (Pmax) modeled by the four models were close to the measured values. Therefore, MRHM was superior to other three models in describing the photosynthetic response curve, the accurate values were that the quantum efficiency (α), maximum net photosynthetic rate (Pmax), light saturation point (LSP), light compensation point (LCP) and respiration rate (Rd) were 0.06, 6.06 μmol·m-2s-1, 802.68 μmol·m-2s-1, 10.76 μmol·m-2s-1 and 0.60 μmol·m-2s-1. Moreover, the photosynthetic response parameters values among different layers were also significant. Our findings have critical implications for parameter calibration of photosynthetic models and thus robust prediction of photosynthetic response in forests.
Highlights
As the largest carbon flux in global carbon (C) cycling, photosynthesis can assimilate CO2 from the atmosphere and dedicating to climate change mitigation
The results showed that light response curves (Pn—photosynthetically active radiation (PAR)) fitted by nonrectangular hyperbola model (NRHM), exponential model (EM) and modified rectangular hyperbola model (MRHM) from different layers were of similar tendency, while rectangular hyperbola model (RHM) were difficult to implement because the curves increased gradually with no extreme
The fitting results showed the fitting photosynthetic rate (Pn) values of the four models were very close to the measured values when the PAR was low (PAR
Summary
As the largest carbon flux in global carbon (C) cycling, photosynthesis can assimilate CO2 from the atmosphere and dedicating to climate change mitigation. In the contrary, owing to the addition of two adjusting factors (β and γ) into this model, which made the model highly advantageous in fitting the photo-inhibition and light saturation stages [20, 26], the MRHM can directly produce Pmax and LSP, and overcome the limitation of above three models, the accuracy were higher and the results were suitable for fitting Pn-PAR curve and photosynthetic parameters under various environmental conditions [20, 24, 26, 27], it has been successfully applied in simulating light-response curves of many plants, such as Keteleeria calcarea [28], Pinu stabulaeformis Carr. In the contrary, owing to the addition of two adjusting factors (β and γ) into this model, which made the model highly advantageous in fitting the photo-inhibition and light saturation stages [20, 26], the MRHM can directly produce Pmax and LSP, and overcome the limitation of above three models, the accuracy were higher and the results were suitable for fitting Pn-PAR curve and photosynthetic parameters under various environmental conditions [20, 24, 26, 27], it has been successfully applied in simulating light-response curves of many plants, such as Keteleeria calcarea [28], Pinu stabulaeformis Carr. [29], Pinus koraiensis [30], Betula utilis [31]
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