Submitted to: Photosynthesis Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/8/1996
Publication Date: N/A
Citation: Interpretive Summary: In previous research, we showed that increasing soybean leaf density can increase photosynthesis if the more dense leaf does not also become more wrinkled or have a more uneven leaf surface. Most leaves with higher density were also found to have greater surface wrinkling. The currently used method to evaluate leaf density requires a known area of leaf to be cut, dried and weighed. This is a time consuming process and prevents the evaluation of large populations that will be necessary to identify the needed types. The objective of this research was to establish a faster and easier method to determine leaf density. We evaluated a simple commercial device that measures reflectance of a specific wave-length of light from the leaf surface. With this device we can evaluate a plant in a few seconds. In this research we found that the leaf reflectance value was closely related to the physical measurements of leaf density and was also closely related to the actual chlorophyll concentration in the leaf. Using this method we will be able to evaluate large numbers of plants to select those with high density and low rugosity. This enhanced selection process can be used to try to improve photosynthetic rate and ultimately soybean yield.
Technical Abstract: Increasing specific leaf weight (SLW) may improve leaf apparent photosynthesis (AP) in soybean [Glycine max (L.) Merr.] but screening for SLW and AP is laborious. The objectives of this study were i) to determine the time course of leaf reflectance, SLW, and chlorophyll concentration in experimental lines selected for differences in SLW and ii) to evaluate the potential use of leaf reflectance as a rapid estimator of SLW, AP, and chlorophyll concentration in leaves of soybean. In 1991 and 1992, sixteen experimental lines representing extremes in SLW were grown at Urbana, IL and West Lafayette, IN with three replications at each location. Leaf reflectance, SLW and AP were measured at the R2, R4 and R5 growth stages. In 1992, SLW, leaf reflectance, and chlorophyll concentration were measured weekly. Seasonal patterns of leaf reflectance, SLW, and chlorophyll concentration were very similar through R5. After R5, SLW continued to increase but leaf reflectance and chlorophyll concentration declined. Leaf reflectance and SLW were highly correlated at the R2, R4, and R5 stages at both locations and in both years. However, AP and leaf reflectance were correlated only at the R4 growth stage at Urbana in 1992. Leaf reflectance readings separated the high- and the low-SLW classes but were inconsistent at ranking individual lines and may only be useful as an initial screening tool in large populations.