Determination of the most effective design for the measurement of photosynthetic light-response curves for planted Larix olgensis trees

Abstract

A photosynthetic light-response (PLR) curve is a mathematical description of a single biochemical process and has been widely applied in many eco-physiological models. To date, many PLR measurement designs have been suggested, although their differences have rarely been explored, and the most effective design has not been determined. In this study, we measured three types of PLR curves (High, Middle and Low) from planted Larix olgensis trees by setting 31 photosynthetically active radiation (PAR) gradients. More than 530 million designs with different combinations of PAR gradients from 5 to 30 measured points were conducted to fit each of the three types of PLR curves. The influence of different PLR measurement designs on the goodness of fit of the PLR curves and the accuracy of the estimated photosynthetic indicators were analysed, and the optimal design was determined. The results showed that the measurement designs with fewer PAR gradients generally resulted in worse predicted accuracy for the photosynthetic indicators. However, the accuracy increased and remained stable when more than ten measurement points were used for the PAR gradients. The mean percent error (M%E) of the estimated maximum net photosynthetic rate (P max) and dark respiratory rate (R d) for the designs with less than ten measurement points were, on average, 16.4 times and 20.1 times greater than those for the designs with more than ten measurement points. For a single tree, a unique PLR curve design generally reduced the accuracy of the predicted photosynthetic indicators. Thus, three optimal measurement designs were provided for the three PLR curve types, in which the root mean square error (RMSE) values reduced by an average of 8.3% and the coefficient of determination (R 2) values increased by 0.3%. The optimal design for the High PLR curve type should shift more towards high-intensity PAR values, which is in contrast to the optimal design for the Low PLR curve type, which should shift more towards low-intensity PAR values. The photosynthetic light-response (PLR) curve reflects the instantaneous response of the net photosynthetic rate (P n) to different gradients of photosynthetically active radiation (PAR). It can provide measures of many photosynthetic indicators, such as the maximum P n (P max), dark respiration rate (R d), apparent quantum yield (AQY), light compensation point (LCP) and light saturated point (LSP), for analysing plant photosynthetic activity 1. In addition, it is also a basic element for modelling the photosynthesis 2-4 and primary productivity 5-7 of vegetation and forests. In recent studies, the application of the PLR model has been expanded from a single leaf to larger scales by linking some leaf functional traits and environmental conditions, such as the leaf mass

Effects of photosynthetic models on the calculation results of photosynthetic response parameters in young Larix principis-rupprechtii Mayr. plantation

“…According to the previous studies, for trees, the upper limit of the P n -PAR curves was significantly different within different crown whorls in the vertical direction [ 32 – 34 ]. Thus, we divided the crowns of three sample trees respectively into three vertical layers with the trisection of crown depth (the distance from the top of the tree to the base of its live crown, CD), and each layer was divided into two parts in horizontal direction (sunny and shaded) ( Fig 2 ) [ 35 ].…”

Photosynthetic CO2response characteristics in canopy ofLarix principis-rupprechtiiMayr. tree and practicability of three Models

“…According to previous studies [26][27], the crowns of five sample trees were divided respectively into three vertical layers (upper layer (UP), middle layer (MD), and lower layer (LW)) of equal divisions with the trisection of crown depth (the distance from the top of the tree to the bottom of its live canopy), and each layer was further divided into four orientations-east, south, west and north (Fig. 1) [28].…”