3.1. Seed Germination
Among the species, northern red oak displayed the highest germination success, measured as percent of seeds germinated, across all treatments with an average of 95% compared to an average of 69% for chestnut oak and 62% for red maple (
Table 1). Most of the northern red oak germinated during the second week after being sown whereas chestnut oak germinated mainly during the third and the fourth week.
All treatments produced significantly higher germination success rates (84.7%–100.0%) compared to the control (75.7%) for northern red oak. TMn and SMn treatments produced 100% germination success for northern red oak. The HS treatment produced the second highest success at 96%. The NMn treatment produced the lowest germination success rate of all treatments (84.7%), but was still significantly higher than the control.
Only the TMn and HS treatments produced significantly higher germination success compared to the control (71.7%) for chestnut oak at 80.3% and 84.3%, respectively. However, both the SMn and NMn treatments seemed to have a suppressing effect on chestnut oak germination as the germination success was significantly lower at 58.3% and 54.7%, respectively
Only the HS treatment produced higher germination success (79.0%) compared to the control (72.0%) for red maple. All Mn treatments resulted in lower germination success, with the TMn and NMn treatments producing significantly lower success at 57.0% and 41.0%, respectively. The SMn treatment produced lower but non-significant germination success compared to the control at 71.0%.
In summary, these results revealed that Mn treatments improved northern red oak seed germination, as northern red oak had a 100% germination success with the TMn and SMn treatments. The application of Mn appeared to have no or a suppressing effect on red maple germination. However, there was a mixed effect on chestnut oak germination as the TMn treatment improved germination while the NMn and SMn treatments appeared to have a suppressing effect.
3.2. Morphology and Biomass of Seedlings
All fertilization treatments had a significant effect (
p < 0.05) on seedling height, diameter, and leaf number of northern red oak, and a significant effect on chestnut oak, and red maple seedling height when compared to the control (
Table 2). The greatest seedling height growth of northern red oak was 24.89 ± 0.69 cm (mean ± SE) with the NMn treatment; for chestnut oak was 18.10 ± 1.28 cm with the SMn fertilizer treatment; and for red maple was 8.9 ± 0.12 cm with the TMn treatment.
When compared to the control, all Mn treatments significantly increased the height growth of northern red oak from 151% to 158%, whereas the HS treatment increased height growth significantly by 119%. For chestnut oak, all Mn treatments likewise increased height growth significantly from 139% to 177%. While the HS treatment significantly increased the height growth of chestnut oak, it increased by only 54%. All treatments had a significant but less of an effect on red maple compared to the oaks, where the Mn treatments increased red maple seedling height growth from 43% to 60%, while the HS treatment increased the height growth by only 30%.
All treatments significantly increased the basal diameter growth of northern red oak compared to the control, with no significant differences among treatments (
Table 2). There was an average increase among all treatments of 51.5% with the TMn treatment producing the greatest increase of 55.0%. For chestnut oak only the NMn and SMn treatments significantly increased basal diameter growth compared to the control, producing increases of 63.4% and 46.6%, respectively. Non-significant increases of 7.1% and 35.8% were produced by the HS and TMn treatments, respectively.
All treatments had less of an impact on red maple basal diameter growth compared to the oak species with an overall average increase of 19.8% (
Table 2). Only the TMn significantly increased the basal diameter growth with an increase of 34.6%. Although not significant, the NMn and SMn treatments caused a greater increase in basal diameter growth then the HS treatment.
If we quantify the overall seedling size as the basal diameter squared times the seedling height, we found that the treatments, particularly the Mn treatments, increased the overall oak seedling size to a greater extent than red maple. Even though the red maple seedlings were inherently smaller, greater gains were made by the oak seedlings (
Figure 1). The Mn treatments increased the overall seedling size more than the HS treatment. The TMn treatment produced the greatest increase in size of red maple with a 191.6% increase, but this treatment increased the overall size of northern red oak and chestnut oak by 503.7% and 339.5%, respectively. The greatest increase in overall seedling size for northern red oak occurred with the SMn treatment at 507.2%, and for chestnut oak occurred with the NMn treatment at 601.2%.
Treatments used in this study had a significant effect on northern red oak biomass, except for the stem and leaf biomass (
Table 3). The TMn treatment produced the greatest biomass increase for northern red oak whether you consider the whole plant or root, which were 12.09 ± 0.02 g and 5.52 ± 0.30 g, respectively.
Similarly, treatments caused significant increase in the whole seedling biomass and the biomass of the seedling components for chestnut oak. The greatest biomass increase occurred with the NMn treatment for the whole plant (4.15 ± 0.56 g), root (1.17 ± 0.24 g), stem (1.09 ± 0.18 g), and foliage (1.89 ± 0.16 g).
The overall response of the red maple seedling biomass was of a lesser magnitude than that of the oaks, with only the foliage biomass displaying a significant increase. The TMn treatment produced the greatest foliar biomass increase (0.32 ± 0.03 g) as well as the greatest total seedling biomass increase (0.61 ± 0.02 g).
Compared to the control, the TMn treatment produced the largest increase in total and root biomass for northern red oak of 123.1% and 110%, respectively. The NMn treatment caused the largest stem increase for northern red oak of 151.2% while the HS treatment resulted in the largest foliage increase at 139.6%. For chestnut oak, the NMn treatment caused the largest increase for root, stem, and foliage with increases of 67.1%, 303.7%, and 397.4%, respectively. TMn treatment caused the largest increases in total, stem, and foliage for red maple at 369.2%, 300.0%, and 966.7%, respectively. The SMn treatment caused a comparable increase of stem biomass for red maple as the TMn treatment, and the SMn treatment caused the largest root biomass increase of 183.3%. Except for the foliage biomass of northern red oak, the Mn treatments produced the greatest biomass gains in the different seedling components as well as the total biomass.
The Mn fertilizer improved the oak and maple biomass compared with the control and the N, P, and K additions with the HS treatment. The HS treatment increased the total seedling biomass for northern red oak, chestnut oak, and red maple by 4.92 g, 0.21 g, and 0.19 g, respectively, compared to the control. However, the average increases in total biomass for the Mn treatments were 5.35 g, 1.88 g, and 0.46 g for northern red oak, chestnut oak, and red maple, respectively, compared to the control. These treatments caused a redistribution of biomass among the seedling components. The root system and foliage biomass comprised 52% and 28%, respectively, for chestnut oak in the control. The HS treatment changed this distribution to 40% and 40% for the root system and foliage, respectively. The Mn treatments caused this distribution to become more heavily to foliage as the average distribution percentage was 29% and 46% for the root system and foliage, respectively.
A similar trend was observed for northern red oak as the distribution of dry biomass for the root system and foliage in the control was 48% and 28%, respectively. The HS treatment changed the distribution of root and foliage biomass to 37% and 36%, respectively. The average redistribution of the root and foliage biomass in the Mn treatments was 37% and 45%, respectively.
3.3. Plant Element Concentrations
Northern red oak accumulated higher concentrations of elements in the foliage compared to the stem and root (
Table 4). The elements N and P were significantly higher in all seedling components across all treatments when compared to the control. The elements K and Fe in the roots were significantly higher than the control in the Mn treatments and SMn treatments, respectively. However, there were no significant differences of Mg concentrations in all the northern red oak seedling components, and no significant differences of K (except SMn treatment in stem) and Mn concentrations in foliage and stem components across all treatments.
The TMn treatment produced the highest concentration of N in northern red oak foliage (2.36 ± 0.02 mg g−1) and the highest concentration of N and K in the root component (1.18 ± 0.10 mg g−1 and 7.79 ± 0.30 mg g−1, respectively). The SMn treatment produced the highest concentration of Fe (0.07 ± 0.00 mg g−1) in the root component.
The highest concentrations of N, K, Mg, and Mn accumulated in the foliage of chestnut oak while the highest concentrations of P and Fe accumulated in the roots (
Table 5). The concentrations of P in the chestnut oak foliage, stem, and root components were significantly different among all treatments compared to the control. The concentrations of N, K, Fe, and Mn in the root component were likewise significantly different among all treatments. The HS treatment produced the highest concentrations of N (2.68 ± 0.18 mg g
−1) in the foliage. The highest concentrations of K (16.35 ± 1.94 mg g
−1) and Fe (0.12 ± 0.01 mg g
−1) were found in the root component of the SMn and NMn treatments, respectively.
The concentrations of N, P, K, and Mg, in the red maple seedling were significantly higher in all treatments compared to the control (
Table 6). The concentrations of Fe were significantly higher than the control in only the Mn treatments, but the concentrations of Mn were not significantly different from the control in all treatments.
The HS treatment resulted in the highest concentrations of N and P in chestnut oak compared to other treatments, and the highest accumulation was in the root system for both elements (42% and 40%, respectively). The TMn and SMn treatments produced the highest concentration of total N and P, respectively, in northern red oak. The highest accumulation of N from the TMn treatment occurred in the foliage (54%) while the highest accumulation of P from the SMn treatment occurred in the root system (36%). The SMn treatment produced the highest total concentrations of K for both oak species, with the highest accumulation in the roots (44%) for chestnut oak and in the foliage (45%) for northern red oak.
The northern red oak had the greatest foliage N concentration (2.36%), and the greatest total N concentration (4.35%) with the TMn treatment. The TMn treatment also produced the largest root biomass (46% of the total biomass) of all the treatments. However, the HS treatment produced the highest foliar N concentration (2.68%) and total N concentration (7.08%) for chestnut oak, but the lowest root biomass, even lower than the control. The NMn treatment, which produced the greatest amount of root biomass (47%) more than the HS treatment) for chestnut oak, had only 11% less foliar N than the HS treatment.