Effects of different sand burial depths on the emergence process of X. spinosum seeds
Different sand burial depths have substantial effects on the initial emergence time of X. spinosum and the peak time of emergence. At a sand depth of 1 cm, the initial emergence time was shortest at about 5 days, whereas at 9 cm sand burial depth, the time required for seedlings to be unearthed was longest at about 22 days. In the 3–9 cm treatment group, the deeper the sand burial depth, the longer the time needed for seedling emergence.
The emergence peak time was about 1–2 days after the first emergence time, and had a value of 1 day after the first emergence time when the sand burial depth was 1 cm, whereas the other treatment groups reached the emergence peak after 2 days (Table 1).
Table 1
Effect of sand burial depth on the emergence process of X. spinosum seeds (mean ± SE)
Sand burial depth (cm) | Seeding emergence initiation time (d) | Seeding emergence peak time (d) |
1 | 5 ± 0.05d | 6 ± 0.10d |
2 | 8 ± 0.13ab | 10 ± 0.47ab |
3 | 6 ± 0.15c | 8 ± 0.14c |
5 | 8 ± 0.22b | 10 ± 0.52b |
7 | 11 ± 0.55a | 13 ± 0.22a |
9 | 22 ± 0.51a | 22 ± 0.00a |
Different lowercase letters indicate significant differences among the different sand burial depths of X. spinosum by using one-way ANOVA from LSD tests (P < 0.05). |
Figure 1 shows that the emergence rate of X. spinosum seeds decreased with the increase of sand burial depth. The emergence rate was fastest at 1 cm sand burial depth, with values of 14.5% and 62% on the 5 days and 10 days after sowing, respectively, and reached 68% after sowing for 20 days. Subsequently, the emergence rate only increased slowly, with the highest emergence rate value of 71.5%. The emergence of seedlings was slowest at 9 cm depth, and they emerged for the first time at 22 days after sowing, with an emergence rate of only 4.75%, and maximum of only 12.25%. The emergence rate of 7 cm depth was 3.75% at 11 days and 17.15% at 13 days, and the highest emergence rate was only 44.25%. There was no significant difference between the emergence rates of 1, 2, 3 and 5 cm after 20 days.
Relationship between seedling height and sowing days at different sand burial depths
Figure 2 shows that the seedling height of X. spinosum was substantially affected by different sand burial depth. As sand burial depth increased, the seedling height gradually decreased. The seedling height at 1-cm burial depth was significantly higher than that at other sand burial depths (P < 0.05). From the 15th day, the seed height under 1-, 2-,3-,5- and 7-cm sand burial depth began to change significantly, and continued to the end of the experimental period. Compared with 1-, 2-,3- and 5-cm sand burial depth, the depth of 7 cm and 9 cm were significantly inhibited within 10-20 days after sowing. The heights at burial depths of 7 and 9 cm were not recorded until 15 and 24 days after sowing, respectively. At the end of the experiment, 36 days after sowing, the height of seedlings at 1 cm sand burial depth was the highest at 5.8 cm, and the height of seedlings at 9 cm sand burial depth was the lowest at 1.67 cm.
Morphological characteristics of X. spinosum seedlings at different sand burial depths
Figure 3A shows that the main root length and plant height were significantly affected by sand burial depth (main root length, F = 48.5, P < 0.001; plant height, F = 105.5, P < 0.001, respectively). The length of the main root at 9-cm burial depth was significantly higher than that in other treatment groups (P < 0.001), at 13.6 m, and the minimum length of main root in at 5 cm sand burial depth was 9.3 cm. There was no significant difference in root length at sand burial depths of 1, 2 and 3 cm (P > 0.05), with an average value of 10.0 cm for these depths.
As sand burial depth increased, plant height gradually decreased (Fig. 3A). At 1-cm sand burial depth, the plant height was significantly higher than that of other treatment groups (P = 0.002), at 7.1 cm, and the minimum plant height at 9 cm was 2.9 cm. There was no significant difference in plant height between 2- and 3-cm sand burial depth (P = 0.749).
The number of leaves and leaf area was also significantly affected by sand burial depth (number of leaves, F = 97.4, P < 0.001; leaf area, F = 103.7, P < 0.001, respectively) (Fig. 3B). There was no significant difference in leaf number and leaf area at 1-, 2- and 3-cm sand burial depth (P > 0.05), but they were significantly higher than those at 5-, 7- and 9-cm sand burial depth (P < 0.05). From 5 cm, the number and area of leaves decreased with sand burial depth. At 5 cm sand burial depth, the number of leaves per X. spinosum seedling was about 9, and the leaf area was 11.8 cm2, but at 9-cm depth, the number of leaves per X. spinosum seedling was only about 5, and the leaf area was only 2.1 cm2.
(A, main root length and plant height of X. spinosum at different sand burial depths; B, the number of leaves and leaf area of X. spinosum at different sand burial depths)
Different lowercase letters indicate significant differences among the different sand burial depths of X. spinosum by using one-way ANOVA from LSD tests (P < 0.05).
Biomass accumulation of X. spinosum seedlings at different sand burial depths
The biomass accumulation of X. spinosum seedlings was significantly affected by sand burial depth (root biomass, F = 81.0, P < 0.001; stem biomass, F = 95.8, P < 0.001; leaf biomass, F = 92.2, P < 0.001; reproductive component, F = 3.4, P = 0.005; total biomass, F = 63.0, P < 0.001, respectively) (Table 2). With the increase of sand burial depth, the root biomass gradually increased, and the root biomass at 9-cm sand burial depth was significantly higher than that at other sand burial depths (P < 0.001) at 0.2854 g, which is about twice of the root biomass at 1-cm sand burial depth. There was no significant difference between the root biomass at 1- and 2-cm sand burial depth (P = 0.698), there was significant difference between the root biomass at 2- and 3-cm burial depth(P = 0.006), and there was no significant difference between the root biomass at 5- and 7-cm burial depth (P = 0.816).
As sand burial depth increased, the stem biomass gradually decreased. The stem biomass at 1-cm burial depth was significantly higher than that at other sand burial depths (P < 0.001), at 0.1849 g, which was about 4.5 times the stem biomass at 9-cm sand burial depth (0.0408 g).
As sand burial depth increased, the leaf biomass showed a decreasing trend. The leaf biomass (0.6109 g) at 1-cm sand burial depth was significantly higher than that at 9-cm sand burial depth (0.1097 g) (P < 0.001). There was no significant difference in leaf biomass at sand burial depths of 1-, 2-, 3- and 5-cm (P > 0.05).
There was no significant difference among reproductive components at sand burial depths of 1-, 2-, 3- and 5-cm (P > 0.05). At 9-cm sand burial depth, there was no reproductive component.
The total biomass and leaf biomass both showed an overall decreasing trend with sand burial depth. The total biomass (0.9933 g) at 1-cm sand burial depth was significantly higher than that at 9-cm sand burial depth (0.4359 g) (P < 0.001), which was about twice as high. There was no significant difference in total biomass at 2-, 3- and 5-cm sand burial depths (P > 0.05).
Table 2
Biomass accumulation of X. spinosum seedlings at different sand burial depths (mean ± SE)
Different depths(cm) | Root biomass (g) | Stem biomass (g) | Leaf biomass (g) | Reproductive component(g) | Total biomass (g) |
1 | 0.1329 ± 0.0047d | 0.1849 ± 0.0055a | 0.6109 ± 0.0185a | 0.0336 ± 0.0021a | 0.9933 ± 0.0258a |
2 | 0.1360 ± 0.0049d | 0.1545 ± 0.0058b | 0.5341 ± 0.0190b | 0.0374 ± 0.0090a | 0.8855 ± 0.0300b |
3 | 0.1608 ± 0.0047c | 0.1411 ± 0.0055bc | 0.5817 ± 0.0202ab | 0.0345 ± 0.0017a | 0.9459 ± 0.0293ab |
5 | 0.2041 ± 0.0050b | 0.1326 ± 0.0068c | 0.5338 ± 0.0275b | 0.0390 ± 0.0055a | 0.9363 ± 0.0379ab |
7 | 0.2060 ± 0.0063b | 0.0625 ± 0.0027d | 0.2483 ± 0.0103c | 0.0173 ± 0.0057b | 0.5213 ± 0.0168c |
9 | 0.2854 ± 0.0110a | 0.0408 ± 0.0028e | 0.1097 ± 0.0121d | 0.0000 ± 0.0000c | 0.4359 ± 0.0185c |
Different lowercase letters indicate significant differences among the different sand burial depths of X. spinosum by using one-way ANOVA from LSD tests (P < 0.05). |
Biomass distribution of X. spinosum seedlings at different sand burial depths
The biomass allocation of X. spinosum seedlings was significantly affected by sand burial depth (root biomass ratio, F = 387.4, P < 0.001; stem biomass ratio, F = 60.7, P < 0.001; leaf biomass ratio, F = 160.1, P < 0.001; root to shoot ratio, F = 91.6, P < 0.001, respectively) (Table 3). With the increase of sand burial depth, the root biomass ratio gradually increased, and the root biomass ratio at 9-cm sand burial depth was significantly higher than that at other sand burial depths (P < 0.05). However, as sand burial depth increased, the stem biomass decreased gradually, and the stem biomass at 1 cm sand burial depth was significantly higher than that at other sand burial depths (P < 0.05). As sand burial depth increased, the leaf biomass ratio showed a decreasing trend. The biomass ratio of leaves at 1-, 2- and 3-cm sand burial depth was significantly higher than that at 9-cm sand burial depth (P < 0.05). The root to shoot ratio increased gradually with the increase of sand burial depth, among which the root to shoot ratio at 9-cm sand burial depth was significantly higher than that at other burial depths (P < 0.05), and there was no significant difference between root to shoot ratios at 1-, 2-, 3- and 5-cm sand burial depth (P > 0.05).
Table 3
Biomass distribution of X. spinosum seedlings at different sand burial depths (mean ± SE)
Sand burial depth (cm) | Root biomass ratio | Stem biomass ratio | Leaf biomass ratio | Root to shoot ratio |
1 | 0.1359± 0.0046e | 0.1881 ± 0.0044a | 0.6115 ± 0.0078a | 0.1600 ± 0.0069c |
2 | 0.1572 ± 0.0050de | 0.1764 ± 0.0051b | 0.6022 ± 0.0095a | 0.1896 ± 0.0076c |
3 | 0.1754 ± 0.0048d | 0.1493 ± 0.0031cd | 0.6106 ± 0.0062a | 0.2160 ± 0.0073c |
5 | 0.2336 ± 0.0073c | 0.1406 ± 0.0048d | 0.5553 ± 0.0110b | 0.3142 ± 0.0133c |
7 | 0.4033 ± 0.0101b | 0.1195 ± 0.0031e | 0.4693 ± 0.0082c | 0.7113 ± 0.0313b |
9 | 0.6753 ± 0.0251a | 0.0918 ± 0.0051f | 0.2329 ± 0.0212d | 3.1712 ± 0.3780a |
Different lowercase letters indicate significant differences among the different sand burial depths of X. spinosum by using one-way ANOVA from LSD tests (P < 0.05). |