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Temperature Influence on Potato Leaf and Branch Distribution and on Canopy Photosynthetic Rate

USDA-ARS Crop Systems and Global Change Lab., 10300 Baltimore Ave., Beltsville, MD 20705

View larger version (42K): [in a new window]   Fig. 1. Schematic representation of a hypothetical potato plant shown with main (M), basal (B), and apical (A) stems. For harvesting purposes, the canopy was divided into three horizontal sections (top, middle, and bottom), each 1/3 the height of the main stem plus the longest apical-stem [A(1)] branches.

View larger version (33K): [in a new window]   Fig. 2. Pooled harvest components vs. average 24-h temperature (°C): (A) total and tuber dry mass; (B) branch and leaf dry mass; (C) total and main-, basal-, and apical-stem branch dry mass; (D) total and main-, basal-, and apical-stem leaf area; and fraction of total branch (E) dry mass or (F) leaf area from main-, basal-, and apical-stem branches or leaves. Symbols are observed data, lines are trend lines estimated with the coefficients in Table 3; observed data for branch and leaf components not shown to improve clarity.

View larger version (26K): [in a new window]   Fig. 3. Leaf area vs. observed average 24-h temperature at different canopy layers: (A) total leaf area; (B) main-stem leaf area; (C) basal-stem leaf area; and (D) apical-stem leaf area. Symbols are observed data, lines are trend lines estimated with regression coefficients in Table 5; observed data from individual canopy layers not shown to improve clarity. Common regression coefficients were obtained for the top and middle layers in (A) and the bottom and middle layers in (B).

View larger version (20K): [in a new window]   Fig. 4. Fraction of leaf area per canopy layer attributed to stem type vs. observed average 24-h temperature: (A) bottom layer; (B) middle layer; and (C) top layer. Symbols are observed data, lines are trend lines estimated with the regression coefficients in Table 5.

View larger version (37K): [in a new window]   Fig. 5. Measured data (symbols) and simulated (lines) values (using Eq. [3] and parameters in Table 6) of canopy gross photosynthetic rate (AG) vs. irradiance at successive harvest dates. Alternative units: 1 J PAR = 4.57 µmol (Thimijan and Heins, 1983).