Cypress seedling height and height growth rhythm
The seedling height of the cypress clones appeared to be different after Ca2+ was added to the 2 soils. In the fertile soil, seedling height of cypress did not differ significantly among the Ca2+ treatments. In the infertile soil, there were significant differences in seedling height among the Ca2+ treatments (P < 0.01). The treatment with 3 g·kg− 1 Ca2+ significantly promoted seedling height growth, resulting in 34.22% and 32.19% increases in seedling height for clones C1 and C2, respectively, compared with the 0 g·kg− 1 Ca2+ treatment. By contrast, seedling height showed a decrease following the addition of 6 g·kg− 1 Ca2+.
In both soil conditions, seedling height exhibited a “slow-fast-slow” growth process (Fig. 1). In the fertile soil, the fast-growing period for seedling height began at 61 and 69 days under the 3 g·kg− 1 and 6 g·kg− 1 Ca2+ treatments, respectively; the beginning date was delayed by 5 and 13 days, while the duration of the fast-growing period was shortened by 9 and 14 days, respectively, compared with that of 0 g·kg− 1 Ca2+ treatment (Table 2). In the infertile soil, the fast-growing period for seedling height began at 76 days after the addition of 3 g·kg− 1 Ca2+; the beginning date was advanced by 5 days, while the duration of the fast-growing period was prolonged by 6 days, compared with that of 0 g·kg− 1 Ca2+ treatment. By contrast, the fast-growing period for seedling height began at 82 days after the addition of 6 g·kg− 1 Ca2+; the beginning date was delayed by 1 day, while the duration of the fast-growing period was prolonged by 4 days compared with that of control group (0 g·kg− 1 Ca2+ treatment).
Table 1
Physical and chemical properties of potted soil
Nutrient elements
|
Total N
(g•kg-1)
|
Total P
(g•kg-1)
|
Hydrolytic N
(mg•kg-1)
|
Available K
(mg•kg-1)
|
Available P
(mg•kg-1)
|
Organic matter
(g•kg-1)
|
Exchange Ca
(mg•kg-1)
|
Exchange Mg
(mg•kg-1)
|
pH value
|
Average content
|
0.75±0.09
|
0.32±0.05
|
53.5±4.70
|
18.5±1.12
|
0.99±0.14
|
15.8±1.89
|
128±12.5
|
9.24±0.85
|
4.65±0.21
|
Table 2
Parameters of fitting curve of height growth of C. funebres under different Ca2+ treatments
Nutrient environment | Ca2+ treatment | k | a | b | R2 | t1 | t2 |
Fertile soil conditions | 0 g•kg− 1 | 31.61 | 14.04 | 0.024 | 0.9814 | 56 | 176 |
3 g•kg− 1 | 30.84 | 16.33 | 0.024 | 0.9834 | 61 | 172 |
6 g•kg− 1 | 33.51 | 21.17 | 0.025 | 0.9892 | 69 | 175 |
Infertile soil conditions | 0 g•kg− 1 | 15.32 | 35.61 | 0.027 | 0.9846 | 81 | 177 |
3 g•kg− 1 | 19.40 | 27.05 | 0.026 | 0.9854 | 76 | 178 |
6 g•kg− 1 | 14.12 | 32.85 | 0.026 | 0.9848 | 82 | 182 |
Dry biomass
In the fertile soil, Ca2+ addition had no significant effects on dry matter accumulation in the roots, stems or leaves of cypress clones C1 and C2. Both clones had significantly higher root-shoot ratios under the 0 g·kg− 1 Ca2+ treatment than under the other treatments. In the infertile soil, Ca2+ addition had significant effects on dry biomass in the roots, stems, leaves and whole plants of C1 and C2 seedlings (P < 0.05). The highest dry biomass of various organs was always obtained from plants under the 3 g·kg− 1 Ca2+ treatment. In terms of the root-shoot ratio, C1 had the highest ratio under the 6 g·kg− 1 Ca2+ treatment, and C2 had the highest ratio under the 3 g·kg− 1 Ca2+ treatment (Fig. 2).
Root growth and development
In the infertile soil, root length, root surface area and root volume of the diameter classes D1–D4 (except for D5) differed significantly among the Ca2+ treatments. The addition of 3 g·kg− 1 Ca2+ significantly promoted root development of classes D1–D4 in clone C1, and the resulting root lengths were 1.16-, 1.17-, 1.15- and 1.30-fold that under the 0 g·kg− 1 Ca2+ treatment, respectively; the root lengths of classes D1–D4 in clone C2 were 1.15-, 1.36-, 1.29- and 1.06-fold that under the 0 g·kg− 1 Ca2+ treatment, respectively (Fig. 3d). The corresponding root surface area and root volume also showed similar variation, with a 1.05–1.35-fold increase (Fig. 3e,f). When the concentration of Ca2+ added was 6 g·kg− 1, root length, root surface area, and root volume of classes D1–D4 all decreased compared with those under the 0 g·kg− 1 Ca2+ treatment. The sum of the root length of classes D1–D3 accounted for 97.1%, 98.7% and 98.3% of total root length across the three Ca2+ treatments (0, 3, and 6 g·kg− 1), respectively; among these, the root length of class D1 accounted for 63.26%, 66.32% and 60.53% of total root length, respectively.
In the fertile soil, root length, root surface area and root volume of the diameter classes D1–D5 all significantly decreased in clone C2 following Ca2+ addition (Fig. 3a,b,c). By contrast, Ca2+ addition had no significant effects on root length, root surface area or root volume in clone C1. The sum of the root lengths of classes D1–D3 accounted for 96.6%, 97.1%, and 97.0% of total root length across the three Ca2+ treatments (0, 3, and 6 g·kg− 1), respectively; among these, the root length of class D1 accounted for 59.34%, 55.22%, and 52.18% of total root length, respectively.
N, P and Ca accumulation efficiencies
In the two soils, accumulation efficiencies of N, P and Ca all differed significantly among the Ca2+ treatments. In the fertile soil, N accumulation efficiency for both clones exhibited a downward trend with increasing Ca2+ concentration, and the highest N accumulation efficiency was achieved under the 0 g·kg− 1 Ca2+ treatment. The P use efficiency for clone C1 was the highest under the 3 g·kg− 1 Ca2+ treatment, while that of clone C2 was the highest under the 6 g·kg− 1 Ca2+ treatment. Both clones achieved their highest Ca accumulationefficiency under the 6 g·kg− 1 Ca2+ treatment. In the infertile soil, both C1 and C2 achieved their highest N, P, and Ca accumulation efficiencies under the 3 g·kg− 1 Ca2+ treatment (Fig. 4).
Clone effect
In the fertile soil, the mean seedling height of clone C1 was 56.45 cm, and the mean dry biomasses of its roots, stems and leaves were 5.53, 5.97 and 10.46 g, respectively; these mean values were 30%, 87%, 86% and 64% higher than those for clone C2, respectively. The lengths of total roots (D1–D5) for clone C1 were 26.5%, 108.0% and 67.4% longer than those for clone C2 across the three Ca2+ treatments (0, 3 and 6 g·kg− 1), respectively. Root surface area and root volume for C1 were also significantly higher than those for C2. N and Ca accumulation efficiencies differed significantly between clones. In terms of N, the accumulation efficiencies for C1 were 3.04%, 13.52% and 10.64% higher than those for C2 across the three Ca2+ treatments (0, 3 and 6 g·kg− 1), respectively. In terms of Ca, the accumulation efficiencies for C1 were 16.94%, 6.84% and 10.39% higher than those for C2 across the three Ca2+ treatments, respectively. However, no significant difference was detected in P accumulation efficiency between clones.
In the infertile soil, the mean seedling height of clone C1 was 38.38 cm, and the mean dry biomasses of its roots, stems and leaves were 3.58, 2.23 and 4.50 g, respectively; these mean values were 15.71%, 10.05% and 3.12% higher than those of clone C2. Root length, root surface area and root volume of D1, D2 and D3 differed significantly between clones, but no significant differences were detected in D4 and D5 between clones. Root lengths of D1, D2 and D3 in clone C1 were 11.5%, 7.0% and 25.1% higher than those in clone C2 across the 3 Ca2+ treatments (0, 3 and 6 g·kg− 1), respectively. Similar trends were observed for root surface area and root volume. C1 achieved significantly higher N accumulation efficiency than did C2, while P and Ca accumulation efficiencies did not differ significantly between clones.