Abstract
Chlorophyll meters are widely used to guide nitrogen (N) management by monitoring leaf N status in agricultural systems, but the effects of environmental factors and leaf characteristics on leaf N estimations are still unclear. In the present study, we estimated the relationships among SPAD readings, chlorophyll content and leaf N content per leaf area for seven species grown in multiple environments. There were similar relationships between SPAD readings and chlorophyll content per leaf area for the species groups, but the relationship between chlorophyll content and leaf N content per leaf area, and the relationship between SPAD readings and leaf N content per leaf area varied widely among the species groups. A significant impact of light-dependent chloroplast movement on SPAD readings was observed under low leaf N supplementation in both rice and soybean but not under high N supplementation. Furthermore, the allocation of leaf N to chlorophyll was strongly influenced by short-term changes in growth light. We demonstrate that the relationship between SPAD readings and leaf N content per leaf area is profoundly affected by environmental factors and leaf features of crop species, which should be accounted for when using a chlorophyll meter to guide N management in agricultural systems.
Highlights
The relationship between SPAD readings and chlorophyll content per leaf area has been found to vary widely among species, in some cases even within a same species[18,19,20]. This variability is presumed to be due to variability of measurement conditions[21] and to structural differences aomg the leaves that cause different light reflection and/or scattering effects. These results suggest that the relationship between SPAD readings and chlorophyll content per leaf area remains to be stablished
There was a close relationship between SPAD value and chlorophyll content per leaf area in both the monocot and dicot groups (Fig. 1)
The relationship between SPAD readings and chlorophyll content per leaf area was fitted as a linear regression[11,12]
Summary
The relationship between SPAD readings and chlorophyll content per leaf area has been found to vary widely among species, in some cases even within a same species[18,19,20] This variability is presumed to be due to variability of measurement conditions[21] and to structural differences aomg the leaves that cause different light reflection and/or scattering effects. These results suggest that the relationship between SPAD readings and chlorophyll content per leaf area remains to be stablished. The objectives of this study were as follows: (1) to estimate the variations in SPAD readings and chlorophyll content per leaf area among species; (2) to identify the impacts of leaf features and light conditions on the relationships between SPAD values and chlorophyll content and leaf N content; and (3) to clarify the risks of relying on SPAD readings for N management
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