Abstract
The development of technology, like the widely-used off-the-shelf portable photosynthesis systems, for the quantification of leaf gas exchange rates and chlorophyll fluorescence offered photosynthesis research a massive boost. Gas exchange parameters in such photosynthesis systems are calculated as gas exchange rates per unit leaf area. In small chambers (<10 cm2), the leaf area used by the system for these calculations is actually the internal gasket area (AG), provided that the leaf covers the entire AG. In this study, we present two inexpensive and non-destructive techniques that can be used to easily quantify the enclosed leaf area (AL) of plant species with leaves of surface area much smaller than the AG, such as that of cereal crops. The AL of the cereal crop species studied has been measured using a standard image-based approach (iAL) and estimated using a leaf width-based approach (wAL). iAL and wAL did not show any significant differences between them in maize, barley, hard and soft wheat. Similar results were obtained when the wAL was tested in comparison with iAL in different positions along the leaf in all species studied. The quantification of AL and the subsequent correction of leaf gas exchange parameters for AL provided a precise quantification of net photosynthesis and stomatal conductance especially with decreasing AL. This study provides two practical, inexpensive and non-destructive solutions to researchers dealing with photosynthesis measurements on small-leaf plant species. The image-based technique can be widely used for quantifying AL in many plant species despite their leaf shape. The leaf width-based technique can be securely used for quantifying AL in cereal crop species such as maize, wheat and barley along the leaf. Both techniques can be used for a wide range of gasket shapes and sizes with minor technique-specific adjustments.
Highlights
The process of photosynthesis is the key source of energy for life on earth (Zhu et al, 2008; Niinemets et al, 2017)
A strong linear relation (Y = 1.006X, R2 = 0.997) was developed between image-based measured leaf area (iAL) and leaf width-based measured leaf area (wAL) when the data points from all the species used in this study were included (Figure 3E)
Similar results were obtained when the wAL was tested in comparison with iAL along the monocotyledonous leaf in all species studied (Figure 4)
Summary
The process of photosynthesis is the key source of energy for life on earth (Zhu et al, 2008; Niinemets et al, 2017). Potential pitfalls of these off-the-shelf systems and ways to avoid them were displayed in literature to support a more precise quantification of photosynthetic parameters (e.g., Long and Bernacchi, 2003), for instance, the diffusional leakages of CO2 and H2O through the clamp-on leaf chambers (Flexas et al, 2007; Rodeghiero et al, 2007; Kitao et al, 2017), the air pressure changes in the leaf chamber (Jahnke and Pieruschka, 2006), the chamber response time (Weiss et al, 2009) and the overestimation of dark respiration rates because of the leaf chamber gasket shade effect (Pons and Welschen, 2002) were found to be contributing to errors when not considered in the estimation of leaf gas exchange parameters The LI-6400 portable photosynthesis system (LI-COR Biosciences, Lincoln, NE, USA) has been used in a large proportion of these studies (Figure 1A) for a wide range of applications, e.g., for the in vivo quantification of planar leaf photosynthetic parameters in different plant species with different leaf shapes (Savvides et al, 2012; Velez-Ramirez et al, 2014; Kaiser et al, 2016; Zait et al, 2017) grown/adapted in different environments (Velez-Ramirez et al, 2014; Kaiser et al, 2016; Rabert et al, 2017), or even for gas exchange of different plant structures (Apple et al, 2000; Savvides et al, 2013, 2014).
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