title: Decreasing, not increasing, leaf area will raise crop yields under global atmospheric change.
abstract: Without new innovations, present rates of increase in yields of food crops globally are inadequate to meet the projected rising food demand for 2050 and beyond. A prevailing response of crops to rising [CO2] is an increase in leaf area. This is especially marked in soybean, the world's fourth largest food crop in terms of seed production, and the most important vegetable protein source. Is this increase in leaf area beneficial, with respect to increasing yield, or is it detrimental? It is shown from theory and experiment using open-air whole-season elevation of atmospheric [CO2] that it is detrimental not only under future conditions of elevated [CO2] but also under today's [CO2]. A mechanistic biophysical and biochemical model of canopy carbon exchange and microclimate (MLCan) was parameterized for a modern US Midwest soybean cultivar. Model simulations showed that soybean crops grown under current and elevated (550 [ppm]) [CO2] overinvest in leaves, and this is predicted to decrease productivity and seed yield 8% and 10%, respectively. This prediction was tested in replicated field trials in which a proportion of emerging leaves was removed prior to expansion, so lowering investment in leaves. The experiment was conducted under open-air conditions for current and future elevated [CO2] within the Soybean Free Air Concentration Enrichment facility (SoyFACE) in central Illinois. This treatment resulted in a statistically significant 8% yield increase. This is the first direct proof that a modern crop cultivar produces more leaf than is optimal for yield under today's and future [CO2] and that reducing leaf area would give higher yields. Breeding or bioengineering for lower leaf area could, therefore, contribute very significantly to meeting future demand for staple food crops given that an 8% yield increase across the USA alone would amount to 6.5 million metric tons annually.
authors.affiliation: The Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana Champaign, Urbana, IL, USA.
authors.forename: Venkatraman
authors.initials: V
authors.lastname: Srinivasan
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois Urbana Champaign, Urbana, IL, USA.|Department of Atmospheric Sciences, University of Illinois Urbana Champaign, Urbana, IL, USA.
authors.forename: Praveen
authors.identifier: 0000-0002-4787-0308
authors.initials: P
authors.lastname: Kumar
authors.affiliation: The Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana Champaign, Urbana, IL, USA.|Department of Crop Sciences, University of Illinois Urbana Champaign, Urbana, IL, USA.|Department of Plant Biology, University of Illinois Urbana Champaign, Urbana, IL, USA.|Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Long
mesh_terms: D002245:Carbon Dioxide; D018556:Crops, Agricultural; D007087:Illinois; D010788:Photosynthesis; D018515:Plant Leaves; D013025:Glycine max
chemical_list: D002245:Carbon Dioxide
keywords: climate change; crop bioengineering; ecohydrology; food security; plant breeding; rising CO2