to nonshaded plants (Fig. 1A). Average plant leaf area also showed a similar quadradic response to shading, as did total leaf area (data not presented), but with greater average leaf area in plants with 33% or 56% shading, and reduced leaf area at 98% shading, compared to nonshaded plants (Fig. 1B). Average plant SLW declined with shading, showing a quadratic response curve (Fig. 1C). Shoot, root, lateral root, and plant DW were similar with 0%, 33%, or 56% shading, but declined with 81% or 98% shading, resulting in a quadratic response curve to shading (Fig. 2A, B, and C). Total shoot DW was greater in plants with 33% shading compared to nonshaded plants (Fig. 2A). Root to shoot ratio of control plants was reduced with shading of 33%, 56%, or 81% compared to nonshaded plants, but increased in plants with 98% shading, showing a quadratic response curve (Fig. 2D).
shoot DW, root DW, lateral root DW, and total plant DW. Leaf number and average SLW were similar in control and Cu(OH)2-treated plants (Fig 1A and B). Cupric hydroxide treated plants had decreased average leaf area at 33% shading, compared to nontreated plants (Fig. 1C). Although not significant, there was a trend toward a reduction in shoot DW in Cu(OH)2 treated plants at 0% or 33% shading compared to nontreated plants (Fig. 2A). Root DW and lateral root DW were reduced in Cu(OH)2-treated plants at 0% shading compared to nontreated plants (Fig. 2B). Total plant DW was reduced in Cu(OH)2-treated plants at 0% shading compared to nontreated plants (Fig. 2B). Root to shoot ratio was similar in Cu(OH)2-treated and nontreated plants (Fig. 2D).
Leaf chl a, b, p, and total chl concentration was not affected by shading of plants that did not have containers treated with Cu(OH)₂; however, chl a to b ratio showed a negative linear response to increasing shading (Fig. 3). In contrast, Cu(OH)₂-treated plants showed a negative linear response to shading on leaf chl a, b, p, and total chl concentration (Fig. 3). Leaf chl a, b, p, and total chl concentration in Cu(OH)₂-treated plants were all lower than non-treated plants under 33%, 56%, or 81% shading (Fig. 3).
Plants in containers treated with Cu(OH) 2 also showed a similar quadratic response to shading to that of nontreated plants in terms of leaf number, average leaf area, total leaf area, average plant SLW,
Fig. 2. Effect of shading and treatment of containers with (open symbols) and without (closed symbols) cupric hydroxide [Cu(OH) 2] on biomass production by pawpaw seedlings grown in the greenhouse. (A) Shoot DW of plants with (y = 2.670 + 0.049x - 0.001x^2, R^2 = 0.98, P = 0.001) and without Cu(OH) 2(y = 3.409 + 0.046x - 0.001x^2, R^2 = 0.96, P = 0.001), (B) total root DW in plants with (y = 2.842 + 0.028x - 0.001x^2, R^2 = 0.98, P = 0.001) and without Cu(OH) 2(y = 3.207 - 0.002x - 0.001x^2, R^2 = 0.96, P = 0.003), and for lateral root DW for plants with (y = 0.549 + 0.006x - 0.001x^2, R^2 = 0.97, P < 0.001) and without Cu(OH) 2 (y = 0.710 - 0.001x - 0.001x^2 R^2 = 0.98, P < 0.007), (C) total plant DW in plants with (y = 5.512 + 0.770x - 0.001x^2, R^2 = 0.96, P = 0.001) and without Cu(OH) 2(y = 6.616 + 0.043x - 0.001x^2, R^2 = 0.96, P = 0.001), and (D) root to shoot ratio in plants with and without Cu(OH) 2(y = 1.016 - 0.019x + 0.001x^2, R^2 = 0.57, P = 0.004). Each symbol is the mean of two blocks ± SE.*Indicates that means were significantly different between Cu(OH) 2 treated and nontreated plants using an unpaired t test (P < 0.05, n = 2).
OUTDOOR STUDY (EXPT. 2). Incident light levels were reduced by 28%, 51%, 81%, and 98% for the 30%, 55%, 80%, and 95% shade fabric treatments, respectively (Table 1). Red to far-red light ratio was the same for all treatments; however, UV irradiance declined with increased shading (Table 1). Average daily air temperature was higher in the 95% shade treatment, than in the other shade treatments. Incident light levels (PPF) were about 10% higher outdoors than in the greenhouse and UV light levels were ≈2-fold higher outdoors than in the greenhouse. Air temperature was ≈5 °C higher in the greenhouse than outdoors.
In plants grown outdoors, leaf number showed a quadratic response to increasing shade level, with plants showing increased leaf number at 28%, 51%, or 81% shading over nonshaded plants (Fig. 4A). Plants in the 98% shade level produced the fewest leaves. Plants were taller under 28%, 51%, or 81% shading than in nonshaded plants (unpaired t test, P < 0.05, n = 2, Fig. 4A). Leaf area was greater at 28%, 51%, or 81% shading than in nonshaded plants; plants at 95% shading had reduced leaf area compared to nonshaded plants (unpaired t test, P < 0.05, n = 2; Fig. 4B). Average plant SLW declined with shading, showing a quadratic response curve (Fig. 4C). Total shoot, root, and plant DW increased under 28%, 51%, or 81% shading, but declined with 98% shading, resulting in a quadratic response curve to shading (Fig. 5A, B, and C). Root to shoot ratio was reduced only at 81% shading when compared to nonshaded plants (Fig. 5D). Seedlings showed a positive quadratic response to shading for leaf chl a, p, and total chl concentration (Fig. 6A). Leaf chl b concentration increased with 28%, 51%, or 81% shading (Fig. 6A). In contrast to plants grown in the greenhouse, there was a positive linear response in chl a to b ratio with increased shading outdoors (Fig. 6B).
About 4 weeks after the seedlings were placed outdoors, nonshaded seedlings in one block were completely defoliated by caterpil
Shade (%)
16
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