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Title:   Author  item
                                            KOESTER, R - University Of Illinoisitem
                                            NOHL, B - University Of Illinoisitem
                                            DIERS, B - University Of Illinoisitem
                                            Ainsworth, Elizabeth

                                                         - *Lisa*
  Submitted to: Plant Cell and Environment
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/1/2015
                                    Publication  Date: 2/1/2016
                                    Citation: Koester, R.P., Nohl, B.M., Diers, B.W., Ainsworth, E.A. 2016. Has photosynthetic capacity increased with 80 years of soybean breeding? An examination of historical soybean cultivars. Plant Cell and Environment. 39:1058-1067.Interpretive Summary: Soybean yields have increased substantially throughout the past century due to improvements in genetics and farming practices. Previously we showed that breeding for increased seed yield has improved the efficiencies by which soybean canopies capture light energy, convert that energy into carbohydrate and parition fixed carbon to seeds. In this study we investigated how photosynthesis and respiration have changed with breeding in 24 soybean cultivars released from 1923 to 2007. The results showed that photosynthesis was greater in more modern soybean lines when soil water content and stomatal conductance was high. Respiration rates have not changed in the 24 soybean cultivars studied. This study provides a comprehensive analysis of how photosynthesis has been affected by breeding for seed yield improvement in U.S. soybean germplasm, and offers insight into the need for different strategies for improving photosynthesis in the future.
                                Technical Abstract: Crop biomass production is a function of the efficiencies with which sunlight can be intercepted by the canopy and then converted into biomass. Conversion efficiency is below the theoretical limit and has been identified as a target for improvement to enhance crop biomass and yield. Higher conversion efficiency of modern soybean [Glycine max (L.) Merr.] cultivars was documented in “common garden” field trials with historical cultivars, and this study explored the physiological basis for this observation. In replicated field trials conducted over three successive years, diurnal leaf gas-exchange and photosynthetic CO2 response curves were measured in 24 soybean cultivars with year of release dates (YOR) from 1923 to 2007. We found that maximum photosynthetic capacity and nighttime respiration rate has not changed with cultivar release date. However, daily carbon gain was significantly greater in more recently released cultivars when stomatal conductance was high. Previous work has shown that modern soybean cultivars yield more than old cultivars in all environments, but gains are greater in high-yielding environments. This study provides a physiological explanation for that observation in that under conditions of ample soil moisture, stomatal conductance was greater in modern cultivars, supporting greater daily C gain.


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