Abstract
Climate change is steering tree breeding programs towards the development of families and genotypes that will be adapted and more resilient to changing environments. Making genotype–phenotype–environment connections is central to these predictions and it requires the evaluation of functional traits such as photosynthetic rates that can be linked to environmental variables. However, the ability to rapidly measure photosynthetic parameters has always been limiting. The estimation of V c,max and J max using CO2 response curves has traditionally been time consuming, taking anywhere from 30 min to more than an hour, thereby drastically limiting the number of trees that can be assessed per day. Technological advancements have led to the development of a new generation of portable photosynthesis measurement systems offering greater chamber environmental control and automated sampling and, as a result, the proposal of a new, faster, method (RACiR) for measuring V c,maxand J max. This method was developed using poplar trees and involves measuring photosynthetic responses to CO2 over a range of CO2 concentrations changing at a constant rate. The goal of the present study was to adapt the RACiR method for use on conifers whose measurement usually requires much larger leaf chambers. We demonstrate that the RACiR method can be used to estimate V c,max and J max in conifers and provide recommendations to enhance the method. The use our method in conifers will substantially reduce measurement time, thus greatly improving genotype evaluation and selection capabilities based on photosynthetic traits. This study led to the developpement of an R package (RapidACi, https://github.com/ManuelLamothe/RapidACi) that facilitates the correction of multiple RACiR files and the post-measurement correction of leaf areas.
Highlights
Climate change is steering tree breeding programs towards the development of families and genotypes that will be adapted and more resilient to the warming climate and thereby ensure the health and productivity of forests (Aitken and Bemmels, 2015)
Vc,max, the maximum rate of ribulose-1,5-bisphosphate carboxylation (Rubisco) and Jmax, the maximum rate of electron transport, are two such parameters (Long and Bernacchi, 2003). These two parameters are incorporated into Earth System Models (Rogers, 2014) and can be used as “ground truthing” parameters for the development of phenotyping and forest health monitoring platforms using unmanned aerial vehicles (UAVs) and other types of mobile systems in combination with spectral measurements (Dash et al, 2017, Thompson et al, 2018), which is another incentive for the development of a method to obtain reliable estimates rapidly
Three Empty Chamber Response Curve (ECRC) were generated per day in an attempt to determine how often an empty chamber response curve needed to be generated to correct the raw RACiR curve measurements
Summary
Climate change is steering tree breeding programs towards the development of families and genotypes that will be adapted and more resilient to the warming climate and thereby ensure the health and productivity of forests (Aitken and Bemmels, 2015). Vc,max, the maximum rate of ribulose-1,5-bisphosphate carboxylation (Rubisco) and Jmax, the maximum rate of electron transport, are two such parameters (Long and Bernacchi, 2003). These two parameters are incorporated into Earth System Models (Rogers, 2014) and can be used as “ground truthing” parameters for the development of phenotyping and forest health monitoring platforms using unmanned aerial vehicles (UAVs) and other types of mobile systems in combination with spectral measurements (Dash et al, 2017, Thompson et al, 2018), which is another incentive for the development of a method to obtain reliable estimates rapidly. Estimates of Vc,max and Jmax are obtained through the measurement and modelling of photosynthetic response to CO2 concentration (A–Ci curves), which until recently could take anywhere from 30 min to more than 60 min per curve (depending on the number of CO2 concentrations measured and the system used), thereby greatly limiting the number of measurements that can be made daily
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