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Intracanopy CO2 and light interactions on Humulus lupulus L. net canopy carbon gain under current and future atmospheric CO2 concentrations
Agricultural and Forest Meteorology  (IF5.734),  Pub Date : 2021-09-08, DOI: 10.1016/j.agrformet.2021.108621
William L. Bauerle

Photosynthetic light response curves were measured in four cultivars of Humulus lupulus L. (hop) at CO2 concentrations of 415, 500, 600, and 700 μmol CO2 mol−1. Short-term elevated CO2 increased net photosynthesis (An), light-saturated rates of photosynthesis, and quantum yield and decreased the light compensation point and leaf respiration. To illustrate the effects on canopy carbon gain, we used a rigorously validated physiologically-explicit canopy process model (MAESTRA). The cultivar-specific leaf-level physiological response parameters at 415, 500, 600, and 700 μmol CO2 mol−1 were extrapolated throughout the canopy to reproduce the cultivar-specific carbon gain under current and future atmospheric CO2 conditions. Under sub optimal light conditions, the initial CO2 increase of 415 to 500 μmol CO2 mol−1 resulted in the highest relative carbon gain increase (∼18%), whereas enrichment from 500 to 600 and 600 to 700 μmol CO2 mol−1 resulted in an additional carbon uptake of ∼16% and ∼12%. Ratios of An to increased CO2 indicated that shaded leaves benefit more from elevated CO2 than light saturated leaves. Estimated daily canopy carbon uptake increased ∼24% from 415 to 500 µmol mol−1 CO2. Daily carbon uptake increased by ∼17% from 500 to 600 µmol mol−1 CO2 and ∼18% from 600 to 700 µmol mol−1. Thus, in comparison to leaves exposed to direct sunlight, hop canopy carbon gain in shaded diffuse light lower canopy layers may contribute a greater proportion of total canopy carbon in future atmospheric CO2 conditions.