5.1 Root infection rate of donor/recipient of P. massoniana seedlings under different nitrogen levels
Without receiving CK inoculation, the donor/recipient seedlings had a 0% mycorrhizal infestation rate (Table 2). Donor/recipient with N had a considerably higher rate of mycorrhizal infection than those without N (P < 0.05). The application of N6 nitrogen, which was 47.73% higher than N0, resulted in the greatest mycorrhizal infestation of donor seedlings; N4 nitrogen, which was 65.91% higher than N0, resulted in the greatest mycorrhizal infestation of recipient seedlings.
Table 2
Mycorrhizal infection of donor and recipient Pinus massoniana seedlings under different nitrogen levels
|
CK
|
Sm
|
Treatment
|
Mycorrhizal infection of donor plant (%)
|
Mycorrhizal infection of receiver plant (%)
|
Mycorrhizal infection of donor plant (%)
|
Mycorrhizal infection of receiver plant (%)
|
N0
|
0
|
0
|
31.61 ± 3.27 c
|
26.17 ± 0.96 c
|
N2
|
0
|
0
|
38.42 ± 0.81 b
|
31.10 ± 1.83 b
|
N4
|
0
|
0
|
44.48 ± 1.16 a
|
43.42 ± 1.46 a
|
N6
|
0
|
0
|
46.69 ± 1.23 a
|
41.33 ± 2.61 a
|
Note: N0、N2、N4、N6 were 0、2、4、6 g/L, respectively, nitrogen levels treatment; CK was not inoculated, Sm was inoculated; The data were mean ± standard deviation (n = 3); Different lowercase letters indicate significant difference among different nitrogen concentrations of the same strain (P < 0.05). The same below. |
5.2 Effect of common mycorrhizal network on biomass of P. massoniana seedlings under different nitrogen application levels
The biomass of the roots, stems, and leaves in the donor seedlings (Table 3) under CK treatment increased initially before decreasing as N application increased. This trend peaked at N4, where it was 1.42-, 3.02-, and 2.62-fold higher than that of N0, respectively (P < 0.05). There was no significant difference between N2 and N0 (P > 0.05), but the root-top ratio gradually dropped with increasing N application and was considerably lower (P < 0.05) than N0 at N4 and N6 applications. As nitrogen application increased under the Sm treatment, root biomass grew as well. It peaked with N6 nitrogen application, which was 2.62 times greater than that of N0 and significantly different from other nitrogen application rates (P < 0.05). With an increase in N application rate, the biomass of leaves and stems grew initially, then dropped, reaching a maximum value at N4 application, 2.44 and 2.60 times, respectively, that of N0 (P < 0.05). With an increase in the nitrogen application rate, the root-top ratio of seedlings inoculated with Sm changed from rising to falling to rising; the minimum at N4 was significantly different from that at N0 (P < 0.05), and the maximum at N6 was the highest (P < 0.05), but there was no significantly different from that at N0 (P > 0.05). With an increase in nitrogen application rate, the mycorrhizal dependency likewise displayed a rise-fall-rise pattern, with N6 application yielding the maximum value. However, there was no statistically significant difference observed between the nitrogen application rates (P > 0.05). Except for the root biomass treated with N0, the biomass of the Sm-inoculated stems, leaves, and roots was greater than that of CK at the same nitrogen administration rate.
Table 3
The biomass of Pinus massoniana seedling’s donor
Treatment
|
N level (g/L)
|
Biomass (g)
|
Root shoot ratio
|
RMD (%)
|
Root
|
Stem
|
Leaf
|
CK
|
N0
|
0.15 ± 0.01 Ab
|
0.06 ± 0.02 Ab
|
0.14 ± 0.05 Ab
|
0.80 ± 0.26 Aa
|
-
|
|
N2
|
0.15 ± 0.02 Ab
|
0.07 ± 0.01 Bb
|
0.14 ± 0.01 Bb
|
0.72 ± 0.12 Aa
|
-
|
|
N4
|
0.21 ± 0.03 Aa
|
0.19 ± 0.04 Ba
|
0.37 ± 0.02 Ba
|
0.38 ± 0.03 Ab
|
-
|
|
N6
|
0.13 ± 0.00 Bb
|
0.11 ± 0.05 Ab
|
0.29 ± 0.08 Ba
|
0.37 ± 0.13 Ab
|
-
|
Sm
|
N0
|
0.15 ± 0.05 Ac
|
0.12 ± 0.02 Ac
|
0.31 ± 0.12 Ac
|
0.34 ± 0.02 Ba
|
32.36 ± 29.25 a
|
|
N2
|
0.22 ± 0.02 Ab
|
0.16 ± 0.02 Ac
|
0.49 ± 0.05 Ab
|
0.35 ± 0.05 Aa
|
57.80 ± 3.24 a
|
|
N4
|
0.25 ± 0.03 Ab
|
0.30 ± 0.02 Aa
|
0.80 ± 0.09 Aa
|
0.23 ± 0.05 Bb
|
41.99 ± 8.25 a
|
|
N6
|
0.39 ± 0.00 Aa
|
0.24 ± 0.04 Ab
|
0.76 ± 0.06 Aa
|
0.39 ± 0.04 Aa
|
61.86 ± 10.26 a
|
Table 4
The biomass of Pinus massoniana seedling’s recipient
Treatment
|
N level
(g/L)
|
Biomass (g)
|
Root shoot ratio
|
RMD (%)
|
Root
|
Stem
|
Leaf
|
CK
|
N0
|
0.09 ± 0.01 Bb
|
0.07 ± 0.01 Ac
|
0.13 ± 0.02 Bc
|
0.49 ± 0.03 Aab
|
-
|
|
N2
|
0.11 ± 0.02 Aab
|
0.07 ± 0.02 Ac
|
0.10 ± 0.03 Bc
|
0.65 ± 0.23 Aa
|
-
|
|
N4
|
0.13 ± 0.00 Aa
|
0.16 ± 0.01 Ba
|
0.40 ± 0.02 Aa
|
0.24 ± 0.01 Ac
|
-
|
|
N6
|
0.13 ± 0.01 Ba
|
0.11 ± 0.02 Bb
|
0.22 ± 0.02 Bb
|
0.41 ± 0.02 Abc
|
-
|
Sm
|
N0
|
0.21 ± 0.01 Aab
|
0.13 ± 0.03 Ab
|
0.31 ± 0.04 Ab
|
0.47 ± 0.05 Aa
|
55.31 ± 9.10 a
|
|
N2
|
0.16 ± 0.02 Ab
|
0.15 ± 0.02 Ab
|
0.27 ± 0.04 Ab
|
0.39 ± 0.06 Aa
|
50.91 ± 6.90 a
|
|
N4
|
0.27 ± 0.05 Aa
|
0.31 ± 0.00 Aa
|
0.67 ± 0.27 Aa
|
0.29 ± 0.13 Aa
|
42.54 ± 10.81 a
|
|
N6
|
0.23 ± 0.03 Aab
|
0.17 ± 0.04 Ab
|
0.44 ± 0.08 Aab
|
0.38 ± 0.10 Aa
|
44.45 ± 1.57 a
|
When the nitrogen application rate was increased under the CK treatment, the biomass of the roots increased while the biomass of the stems first increased, then decreased as the nitrogen application rate increased, reaching its maximum value at N4 application, which was 143.64% higher than that of N0 with a significant difference (table.4, P < 0.05). The biomass of the root and leaf under the Sm treatment declined as the rate of nitrogen delivery increased, peaking at N4 application, which was 111.94% and 26.81% higher than that of N0, respectively. When nitrogen application increased, stem biomass first increased, then declined, and finally achieved its maximum value at N4 application, which was 137.24% more than that of N0 with a significant difference (P < 0.05). Sm inoculation could raise the dry matter weight of the recipient seedlings' roots, stems, and leaves at the same nitrogen administration rate as CK, but the root-top ratio did not differ significantly (P > 0.05).
5.3 Effects of common mycorrhizal network on roots, stems, and leaves nutrients of P. massoniana seedlings under different nitrogen application levels
5.3.1 Total nitrogen in roots, stems, and leaves of donor/recipient of P. massoniana seedlings
The total nitrogen content of donor and recipient seedlings' roots under CK treatment peaked at N4 application (Fig. 3A, B), which was 32.29% (P < 0.05) and 11.10% (P > 0.05) greater than that of N0, respectively. The total nitrogen in the receiver seedlings' roots reached its maximum at N4 application, 11.26% higher than that of N0 (P > 0.05), whereas the total nitrogen in the donor seedlings' roots was lower than that of N0 (P > 0.05) under the Sm treatment. The total nitrogen of recipient seedlings was higher than that of N0 (Fig. 3D) only at N2 application, and the total nitrogen of donor/recipient seedlings reached the minimal value at N4 application. In stems, the total nitrogen of donor seedlings treated with CK and Sm was lower than that of N0 (Fig. 3C). The total nitrogen in the leaves of donor seedlings in CK and Sm increased initially, but as the nitrogen application rate grew, it dropped (Fig. 3E). The maximal nitrogen application rate in the CK treatment was 103.42% higher than in the N0 treatment (P < 0.05). Total nitrogen was at its greatest under the Sm treatment at N2 application, 5.97% greater than at N0 (P > 0.05). When the nitrogen application rate was increased, the total nitrogen in the leaves of seedlings treated with CK and Sm changed in a fall-rise-fall pattern (Fig. 3F). At the N4 application rate, the total nitrogen reached its maximum value, which was 17.05% and 3.54% greater than that of N0, respectively (P < 0.05). While the total nitrogen of stems was not significantly different from CK (P > 0.05), and the total nitrogen of leaves was significantly higher at N0 and N2 application rates than CK (P < 0.05), Sm inoculation could increase the total nitrogen of donor/recipient seedlings at the same nitrogen application rate and with a significant difference at N2 application (P < 0.05).
5.3.2 Total phosphorus in roots, stems, and leaves of donor/recipient of P. massoniana seedlings
Under CK treatment, donor/recipient seedlings' total phosphorus content changed in a fall-rise-fall manner as the rate of nitrogen application increased (Fig. 4A, B). It peaked at the N4 application, when it was 60.27% and 131.45% higher than N0, respectively (P < 0.05). Total phosphorus in donor seedling stems grew initially, then dropped as nitrogen application increased. It reached its maximum value at N4 application, which was 171.72% greater than N0 application (Fig. 4C, D, P < 0.05). Total phosphorus in recipient seedling stems first declined, then grew as nitrogen treatment rate increased (Fig. 4D). Total phosphorus reached its maximum value at N6 application, 9.10% more than that of N0 (P < 0.05). In the donor/recipient seedlings, overall total phosphorus increased initially, then decreased as the nitrogen application rate increased (Fig. 4E, F). Total phosphorus reached its maximum value under N4 application, which was 284.68% and 269.51% higher than that of N0, respectively (P < 0.05).
Under Sm treatment, the total phosphorus in the recipient's roots and stems and the donor seedling's roots and stems changed fall-rise-fall as the nitrogen application rate increased (Fig. 4), peaking at the N4 application. By 0.36% (P > 0.05), 41.42% (P < 0.05), 39.99% (P < 0.05), 32.35% (P < 0.05), and 49.31% (P < 0.05), it was more than N0, in that order. When the rate of nitrogen treatment was raised, the total phosphorus in the recipient seedlings' leaves declined initially, increased, and reached its maximum value at the N6 application (Fig. 4F), which was 29.91% higher than that of N0 (P < 0.05). Overall, at the N4 treatment, the seedlings inoculated with Sm exhibited the greatest effect on total phosphorus uptake and use.
5.3.3 Total potassium of donor/recipient of P. massoniana seedlings
The total potassium of donor seedlings under CK treatment changed in a fall-rise-fall pattern as the rate of nitrogen application increased. It peaked at the application of N4, which was 11.55% greater than that of N0 (Fig. 5A, B, P < 0.05). Total potassium in the recipient seedlings' roots first rose, then fell as the amount of nitrogen applied increased. It reached its maximum value when N4 was applied, 18.53% more than N0 (Fig. 5C, D). With an increase in the nitrogen application rate, the total potassium of the donor and recipient seedlings changed overall in a fall-rise-fall pattern. It peaked at the N4 application, when it was 36.06% and 49.76% greater than the N0 application, respectively (Fig. 5E, F, P < 0.05).
Total potassium in the donor seedlings' roots, stems, and leaves increased initially under the Sm treatment, then decreased as the rate of nitrogen application increased (Fig. 5). The highest value was reached at the N4 application, which was 9.78% (P < 0.05), 9.02% (P > 0.05), and 28.46% (P < 0.05) higher than that of N0, among other values. When the rate of nitrogen application was increased, the total potassium in the recipient seedlings' roots and leaves changed in a fall-rise-fall pattern (Fig. 5B, F). In contrast, the total potassium in the stems first increased, then decreased (Fig. 5D), and finally reached its maximum at the N4 application. In comparison to N0, the total potassium content of the roots, stems, and leaves was 10.71% (P < 0.05), 64.29% (P < 0.05), and 21.04% (P > 0.05), respectively. Sm inoculation increased the total potassium in the roots, stems, and leaves of donor seedlings when compared to CK, and this difference was significant at the N4 application (P < 0.05). However, there was no significant difference in the total potassium in the roots, stems, and leaves of recipient seedlings inoculated with Sm when compared to CK (P > 0.05).
5.4 Effects of common mycorrhizal network on nitrogen uptake and distribution in roots, stems, and leaves of P. massoniana seedlings under different nitrogen application levels
5.4.1 Nitrogen uptake and mycelial contribution rate in roots, stems, and leaves of donor/recipient of P. massoniana seedlings
Table 5, P < 0.05, indicates that during the CK treatment, the nitrogen uptake of the donor's roots and leaves increased initially, then decreased as nitrogen application increased. Meanwhile, the stems exhibited a fall-rise-fall pattern, peaking at N4 application. The nitrogen uptake of the donor's roots, stems, and leaves was 1.90 times, 1.93 times, and 5.54 times that of N0. The recipient's roots and leaves under CK treatment exhibited a fall-rise-fall pattern as nitrogen application increased, whereas the stems increased initially before decreasing and reaching a maximum at N4 application. The nitrogen uptake of the roots, stems, and leaves was 1.55-, 1.94-, and 3.73-fold greater than that of N0, respectively (P < 0.05). Under the Sm treatment, the donor's stems and leaves absorbed more nitrogen as the amount of nitrogen applied rose. At the N6 application, the maximum amount of nitrogen absorbed was 2.59 times greater than at the N0 application (P < 0.05). The uptake of nitrogen by stems and leaves had an initial increase, followed by a reduction as the nitrogen application rate was raised. The greatest value was attained at the N4 application, where the uptake of nitrogen was 2.23 and 1.93 times higher than that of N0 (P < 0.05). When the rate of nitrogen administration was increased, the recipient seedlings' roots and leaves absorbed less nitrogen, yet the stem initially expanded and later dropped. At the N4 treatment, the maximal nitrogen uptake by the roots, stems, and leaves was 1.41-fold (P > 0.05), 2.14-fold (P < 0.05), and 2.24-fold (P < 0.05), respectively. When donor/recipient seedlings were inoculated with Sm at the same nitrogen delivery rate as CK, the roots, stems, and leaves of the former could absorb more nitrogen.
Table 5
The nitrogen uptake of roots, stems, leaves of Pinus massoniana seedling’s donor/recipient
|
|
N uptake (mg/pot )
|
N level
|
Inoculation treatment
|
Donor
|
Recipient
|
(g/L)
|
Root
|
Stem
|
Leaf
|
Root
|
Stem
|
Leaf
|
N0
|
CK
|
0.89 ± 0.06 Ab
|
0.35 ± 0.16 Ab
|
0.36 ± 0.10Ac
|
0.63 ± 0.12 Bb
|
0.21 ± 0.06 Ab
|
0.51 ± 0.04Bc
|
Sm
|
1.33 ± 0.44 Ac
|
0.61 ± 0.07 Ab
|
1.85 ± 0.61Ab
|
1.45 ± 0.09 Aab
|
0.41 ± 0.09 Ab
|
1.97 ± 0.29Ab
|
N2
|
CK
|
0.95 ± 0.22 Bb
|
0.29 ± 0.04 Bb
|
0.50 ± 0.02Bc
|
0.59 ± 0.11 Ab
|
0.29 ± 0.09 Aab
|
0.37 ± 0.13Bc
|
Sm
|
1.86 ± 0.14 Abc
|
0.65 ± 0.14 Ab
|
3.16 ± 0.51 Aa
|
1.18 ± 0.19 Ab
|
0.48 ± 0.05 Ab
|
1.61 ± 0.19Ab
|
N4
|
CK
|
1.69 ± 0.39 Aa
|
0.68 ± 0.11 Ba
|
1.98 ± 0.31 Ba
|
0.98 ± 0.07 Ba
|
0.40 ± 0.04 Ba
|
1.90 ± 0.14 Aa
|
Sm
|
2.17 ± 0.55 Ab
|
1.18 ± 0.08 Aa
|
4.12 ± 0.58 Aa
|
2.04 ± 0.38 Aa
|
0.88 ± 0.20 Aa
|
4.39 ± 2.03 Aa
|
N6
|
CK
|
0.98 ± 0.02 Bb
|
0.54 ± 0.22 Aab
|
1.27 ± 0.40 Ab
|
0.89 ± 0.15 Aa
|
0.36 ± 0.06 Aa
|
0.98 ± 0.01 Bb
|
Sm
|
3.43 ± 0.08 Aa
|
1.05 ± 0.33 Aa
|
3.57 ± 0.87 Aa
|
1.62 ± 0.58 Aab
|
0.51 ± 0.11 Ab
|
2.32 ± 0.54 Ab
|
The mycelial contribution rate was affected differently by varied nitrogen applications during Sm treatment (Table 6). With an increase in nitrogen treatment, donor seedlings' mycelial contribution rate changed in a rise-fall-rise pattern. The mycelial contribution rate peaked at the N2 application, when it was 27.47% greater than at N0, N6 followed suit, with an 18.38% higher rate than at N0 (P > 0.05). Mycelial contribution rate was the lowest with N4 application, and N0 was 1.29 times more than N4 (P < 0.05). The mycelial contribution rate in the recipient seedlings gradually decreased as the nitrogen application increased; it peaked at N0 and decreased at N6, but there was no discernible difference in the mycelium contribution rate between the various nitrogen application levels (P > 0.05).
Table 6
Contribution rate of ectomycorrhizal fungal hyphae under different nitrogen levels
|
Inoculation treatment
|
Donor
|
Recipient
|
N level (g/L)
|
Mycelial contribution rate(%)
|
Mycelial contribution rate(%)
|
N0
|
CK
|
-
|
-
|
Sm
|
54.27 ± 17.33 ab
|
64.48 ± 5.85 a
|
N2
|
CK
|
-
|
-
|
Sm
|
69.17 ± 5.21 a
|
61.75 ± 5.97 a
|
N4
|
CK
|
-
|
-
|
Sm
|
41.94 ± 5.90 c
|
53.2 ± 12.29 a
|
N6
|
CK
|
-
|
-
|
Sm
|
64.24 ± 11.81 a
|
49.28 ± 4.50 a
|
5.4.2 Effects of common mycorrhizal network on 15N uptake, utilization, and transfer rate in roots, stems, and leaves of donor/recipient of P. massoniana seedlings under different nitrogen application rates
Under CK treatment, donor seedlings' roots absorbed more 15N initially, but as the rate of nitrogen application rose, it declined and finally peaked at N4 application. With an increase in nitrogen treatment rate, stem and leaf 15N uptake increased and peaked at N6 application (Table 7). Under the CK treatment, the recipient seedlings' roots and leaves absorbed more 15N initially. However, when the rate of nitrogen supply increased, this absorption reduced and peaked at the application of N4. With an increase in nitrogen application rate, stems absorbed more 15N; this uptake peaked at N6 application. Under Sm treatment, the rate at which donor seedlings' roots, stems, and leaves absorbed 15N increased as nitrogen was applied, peaking at N6 application. As the rate of nitrogen application increased, the 15N uptake of the recipient seedlings' stems changed in a rise-fall-rise pattern, peaking at the N6 application; in contrast, the 15N uptake of the leaves increased initially, then declined, peaking at the N4 application. With the exception of N2, Sm seedlings absorbed more 15N in their roots, stems, and leaves than CK seedlings did.
Table 7
The 15N uptake of roots, stems, leaves of Pinus massoniana seedling’s donor/recipient
|
|
15N uptake (µg/pot)
|
N level
|
Inoculation treatment
|
Donor
|
Recipient
|
(g/L)
|
Root
|
Stem
|
Leaf
|
Root
|
Stem
|
Leaf
|
N0
|
CK
|
0.30 ± 0.00 Ab
|
0.07 ± 0.06 Ab
|
0.00 ± 0.00 Bb
|
0.17 ± 0.06 Bd
|
0.00 ± 0.00 Ac
|
0.10 ± 0.00 Ac
|
Sm
|
0.73 ± 0.25 Ad
|
0.23 ± 0.06 Ab
|
1.57 ± 0.50 Ab
|
1.00 ± 0.10 Ab
|
0.10 ± 0.00 Ac
|
0.17 ± 0.06 Ab
|
N2
|
CK
|
175.27 ± 40.91 Aa
|
23.90 ± 3.12 Ab
|
43.77 ± 1.33 Bb
|
2.50 ± 0.46 Aa
|
0.40 ± 0.10 Bb
|
0.30 ± 0.10 Ab
|
Sm
|
113.83 ± 8.57 Ac
|
21.80 ± 4.78 Ab
|
84.40 ± 13.62 Ab
|
1.23 ± 0.15 Ab
|
1.23 ± 0.15 Aa
|
0.20 ± 0.00 Ab
|
N4
|
CK
|
230.67 ± 53.33 Aa
|
56.93 ± 9.38 Ba
|
159.97 ± 24.69 Ba
|
1.97 ± 0.15 Bb
|
0.47 ± 0.06 Bb
|
0.63 ± 0.06 Aa
|
Sm
|
260.60 ± 65.52 Ab
|
85.63 ± 5.78 Aa
|
283.63 ± 39.86 Aa
|
3.37 ± 0.60 Aa
|
1.13 ± 0.23 Aa
|
4.90 ± 2.25 Aa
|
N6
|
CK
|
221.57 ± 4.60 Ba
|
71.40 ± 29.75 Aa
|
161.50 ± 50.64 Aa
|
0.77 ± 0.15 Bc
|
0.90 ± 0.17 Aa
|
0.60 ± 0.00 Ba
|
Sm
|
466.53 ± 10.35 Aa
|
92.57 ± 29.05 Aa
|
328.37 ± 79.92 Aa
|
5.10 ± 1.80 Aa
|
0.40 ± 0.10 Bb
|
1.43 ± 0.31 Ab
|
The donor/recipient seedlings under CK treatment have the highest 15N utilization rate at the N2 application. With a significant difference from other conditions (Table 8, P < 0.05), the donor/recipient seedlings' 15N utilization rate is maximum with Sm treatment at the N4 application. When nitrogen levels were N0 and N2, the 15N transfer rate of CK was higher than that of Sm; however, there was no significant difference (P < 0.05) between the 15N transfer rates of Sm and CK when nitrogen levels were N4 and N6. The nitrogen rate of N0, under the same inoculation treatment, resulted in the highest 15N transfer rate and was significantly higher than that of the other treatments (P < 0.05). However, the total 15N uptake rate was very low, and the utilization rate of 15N was 0. This could be because the natural abundance of the donor and recipient did not differ significantly from the total 15N uptake rate. N2 application under CK treatment had a greater 15N transfer rate than N4 and N6, whereas N4 application with Sm treatment had a higher 15N transfer rate than N2 and N6 (P > 0.05).
Table 8
The 15N utilization and transfer rate of P. massoniana seedling’s donor/recipient
|
Inoculation treatment
|
Donor
|
Recipient
|
|
N level
(g/L)
|
15N utilization (%)
|
15N utilization (%)
|
Transfer rate
(%)
|
N0
|
CK
|
0.00 ± 0.00 c
|
0.00 ± 0.00 d
|
46.26 ± 4.44 Aa
|
Sm
|
0.00 ± 0.00 c
|
0.00 ± 0.00 c
|
34.22 ± 7.66 Aa
|
N2
|
CK
|
2.02 ± 0.36 Aa
|
0.03 ± 0.00 Aa
|
1.33 ± 0.18 Ab
|
Sm
|
1.83 ± 0.10 Ab
|
0.02 ± 0.00 Ab
|
1.21 ± 0.14 Ab
|
N4
|
CK
|
1.86 ± 0.35 Ba
|
0.01 ± 0.00 Bb
|
0.69 ± 0.08 Ab
|
Sm
|
2.62 ± 0.23 Aa
|
0.04 ± 0.01 Aa
|
1.49 ± 0.42 Ab
|
N6
|
CK
|
1.26 ± 0.22 Ab
|
0.01 ± 0.00 Bc
|
0.51 ± 0.13 Ab
|
Sm
|
2.47 ± 0.33 Aa
|
0.02 ± 0.00 Ab
|
0.79 ± 0.28 Ab
|
5.4.3 Effect of common mycorrhizal network on the 15N allocation rate in roots, stems, and leaves of donor/recipient of P. massoniana seedlings under different nitrogen application levels
Figure 6A illustrates this. At the N0 application, the donor of P. massoniana seedlings under CK treatment had the greatest 15N allocation rate in the roots, at 74.8%, followed by 15.37% in the stems; with Sm treatment, the highest value was in the leaves, at 62.47%, followed by 28.17% in the roots. With the exception of N4 treatment, when Sm seedlings' 15N allocation rate was slightly higher in the root (41.13%), CK and Sm seedlings' 15N allocation rate was highest in the roots (45.21%) and lowest in the leaves (41.13%) during N2, N4, and N6 application.
The recipient seedlings (Fig. 6B) had the highest 15N allocation rate in their roots, followed by their leaves, under the CK and Sm treatment at the N0 application. The 15N allocation rates of the CK and Sm treatments were root > stem > leaf at the N2 application. Under CK treatment, the maximum rate of 15N allocation at N4 application was 63.83% in roots, followed by 20.42% in leaves; under Sm treatment, leaves (50.59) were greater than roots (37.01%) and stems (12.40%). When N6 was applied, the stems had the highest 15N allocation rate under the CK treatment (39.28%), followed by the roots (33.69%), and the roots had the highest 15N allocation rate under the Sm treatment (72.66%), followed by the leaves (21.38%).
5.5 Principal component and correlation analysis
5.5.1 Principal components and correlation analysis of donor
In order to perform principal component analysis of the seedlings treated with different nitrogen concentrations of Sm and CK, 26 indexes were selected from the donor seedlings, including infection rate, root-stem-leaf biomass, root-top ratio, root-stem-leaf nutrient NPK content, root-stem-leaf nitrogen uptake, mycelial contribution rate, root-stem-leaf 15N uptake, 15N utilization rate, 15N transfer rate, and root-stem-leaf 15N allocation rate (Table 9). The first three main components had cumulative contribution rates of 80.088% with eigenvalues larger than 1.
Table 9
Principal component analysis of indexes of donor seedlings of P. massoniana treated with different nitrogen concentrations
Number
|
Initial feature root
|
Feature roots
|
Eigenvalue
|
Contribution rate/%
|
Cumulative contribution rate/%
|
Eigenvalue
|
Contribution rate/%
|
Cumulative contribution rate/%
|
1
|
13.095
|
50.365
|
50.365
|
13.095
|
50.365
|
50.365
|
2
|
4.830
|
18.576
|
68.941
|
4.830
|
18.576
|
68.941
|
3
|
2.898
|
11.147
|
80.088
|
2.898
|
11.147
|
80.088
|
4
|
1.381
|
5.310
|
85.398
|
|
|
|
5
|
1.256
|
4.831
|
90.229
|
|
|
|
6
|
0.831
|
3.197
|
93.425
|
|
|
|
7
|
0.471
|
1.813
|
95.238
|
|
|
|
8
|
0.314
|
1.207
|
96.445
|
|
|
|
9
|
0.263
|
1.013
|
97.457
|
|
|
|
10
|
0.227
|
0.874
|
98.331
|
|
|
|
11
|
0.173
|
0.666
|
98.997
|
|
|
|
12
|
0.081
|
0.31
|
99.307
|
|
|
|
13
|
0.067
|
0.258
|
99.565
|
|
|
|
The first primary component's contribution rate was 50.365%. The donor seedlings' biomass, nitrogen uptake through their roots, stems, and leaves, as well as the rate at which nitrogen is absorbed and allocated by their stems and leaves, all show positive trends and high loads.
The second primary component's contribution rate was 18.575%. There is a positive sign and high load for the total K in roots, total K in leaves, total K in roots, and 15N uptake in roots.
The third primary component's contribution rate was 11.146%. The mycelial contribution rate, infection rate, and total P in the roots, stems, and leaves all show substantial loads and good signs.
The PCA analysis (Fig. 7A) showed that the Sm treatment was primarily dispersed in PC1 and PC2's positive region, whereas the CK treatment was primarily distributed in PC1 and PC2's negative region. It is evident that the donor seedlings' development under Sm treatment outperformed that of CK, suggesting that mycorrhiza promotes growth. Additionally, it can be observed that Sm-N0 is primarily dispersed in the positive region of PC1, Sm-N6 is primarily distributed in the positive region of PC2, and Sm-N4 and Sm-N2 are primarily distributed in the positive regions of PC1 and PC2 (Fig. 7B). Of these, there was a substantial correlation between Sm-N4 and the biomass of the stem, nitrogen intake, and mycelial infection rate. Sm-N4 and Sm-N6 treatment had a significant effect on the biomass and nitrogen uptake of donor seedlings, as evidenced by the high correlations found between them and the 15N uptake of the root, stem, and leaf as well as the 15N allocation rate. Additionally, the complete score showed that at N4, donor seedling development and nutrient absorption, transfer, and distribution under Sm treatment were at their greatest (Table 10).
Table 10
Scores of different nitrogen concentration treatment factors of donor seedlings of P. massoniana
|
F1
|
F2
|
F3
|
F
|
Order
|
Sm-N4
|
4.9237
|
1.4157
|
-0.7426
|
5.5969
|
1
|
Sm-N6
|
5.0581
|
-2.2912
|
2.6259
|
5.3927
|
2
|
Sm-N2
|
0.9149
|
2.0572
|
0.6134
|
3.5855
|
3
|
Sm-N0
|
-1.7264
|
3.6711
|
0.3444
|
2.2892
|
4
|
CK-N4
|
1.1312
|
-0.0253
|
-3.0236
|
-1.9177
|
5
|
CK-N0
|
-5.6890
|
0.2430
|
1.8541
|
-3.5919
|
6
|
CK-N6
|
-1.0463
|
-2.6558
|
-0.8741
|
-4.5762
|
7
|
CK-N2
|
-3.5663
|
-2.4147
|
-0.7974
|
-6.7785
|
8
|
5.5.2 Principal components and correlation analysis of recipient
In order to perform principal component analysis of the seedlings treated with different nitrogen concentrations of Sm and CK, 26 indexes were selected from the donor seedlings, including infection rate, root-stem-leaf biomass, root-top ratio, root-stem-leaf nutrient NPK content, root-stem-leaf nitrogen uptake, mycelial contribution rate, root-stem-leaf 15N uptake, 15N utilization rate, 15N transfer rate, and root-stem-leaf 15N allocation rate (Table 11). The first four main components had cumulative contribution rates of 78.587% with eigenvalues that were all greater than 1.
Table 11
Principal component analysis of indexes of recipient seedlings of P. massoniana treated with different nitrogen concentrations
Number
|
Initial feature root
|
Feature roots
|
Eigenvalue
|
Contribution rate/%
|
Cumulative contribution rate/%
|
Eigenvalue
|
Contribution rate/%
|
Cumulative contribution rate/%
|
1
|
11.961
|
46.002
|
46.002
|
11.961
|
46.002
|
46.002
|
2
|
3.672
|
14.122
|
60.124
|
3.672
|
14.122
|
60.124
|
3
|
2.744
|
10.555
|
70.680
|
2.745
|
10.555
|
70.680
|
4
|
2.056
|
7.906
|
78.586
|
2.056
|
7.906
|
78.586
|
5
|
1.687
|
6.487
|
85.073
|
|
|
|
6
|
1.049
|
4.034
|
89.107
|
|
|
|
7
|
0.794
|
3.055
|
92.162
|
|
|
|
8
|
0.684
|
2.631
|
94.793
|
|
|
|
9
|
0.447
|
1.718
|
96.511
|
|
|
|
10
|
0.328
|
1.262
|
97.773
|
|
|
|
11
|
0.218
|
0.839
|
98.612
|
|
|
|
12
|
0.145
|
0.556
|
99.168
|
|
|
|
13
|
0.067
|
0.258
|
99.565
|
|
|
|
The first primary component's contribution proportion was 46.002%. There was a positive sign and high load in the root-stem-leaf biomass, nitrogen uptake, 15N uptake, allocation and utilization rates, and infection rate.
The second primary component's contribution proportion amounted to 14.122%. The root-top ratio, mycelial contribution rate, and total P content in roots and stems were all positive and heavily loaded.
The third primary component's contribution percentage was 10.555%. There was a positive sign and high load for the 15N transfer rate, total N content in roots, stems, and leaves, mycelial contribution rate, and 15N allocation rate in stems.
The fourth primary component's contribution proportion is 7.906%. Roots and stems have a positive sign and a high load for the absorption and allocation rate of 15N.
The PCA analysis (Fig. 8A) shows that the Sm treatment was primarily dispersed in PC1 and PC2's positive region, whereas the CK treatment was primarily distributed in PC1 and PC2's negative region. As can be observed, the recipient seedlings' development under Sm treatment outperformed that of CK, suggesting that P. massoniana seedlings could create a shared mycorrhizal network and that mycorrhiza was beneficial to the recipient seedlings' growth. The distribution of Sm-N6 and Sm-N2 is primarily found in the positive regions of PC1 and PC2, whereas the distribution of Sm-N0 and Sm-N4 is primarily found in the positive regions of PC1 and PC2, respectively (Fig. 8B). The results showed that Sm-N6 treatment had the greatest effect on recipient seedlings' biomass and nitrogen uptake. Of them, the biomass of the root, stem, and leaf, nitrogen uptake, mycelial infection rate, and contribution rate of recipient seedlings were strongly correlated with Sm-N6 and Sm-N4. The complete score also showed that at N4, recipient seedlings under Sm treatment had the best growth, nutrient absorption, transfer, and distribution (Table 12).
Table 12
Scores of different nitrogen concentration treatment factors of recipient seedlings of P. massoniana
|
F1
|
F2
|
F3
|
F
|
Order
|
Sm-N4
|
4.9237
|
1.4157
|
-0.7426
|
5.5969
|
1
|
Sm-N6
|
5.0581
|
-2.2912
|
2.6259
|
5.3927
|
2
|
Sm-N2
|
0.9149
|
2.0572
|
0.6134
|
3.5855
|
3
|
Sm-N0
|
-1.7264
|
3.6711
|
0.3444
|
2.2892
|
4
|
CK-N4
|
1.1312
|
-0.0253
|
-3.0236
|
-1.9177
|
5
|
CK-N0
|
-5.6890
|
0.2430
|
1.8541
|
-3.5919
|
6
|
CK-N6
|
-1.0463
|
-2.6558
|
-0.8741
|
-4.5762
|
7
|
CK-N2
|
-3.5663
|
-2.4147
|
-0.7974
|
-6.7785
|
8
|
The biomass of roots and stems, as well as the uptake of N by roots, stems, and leaves, showed a strong positive connection with the mycorrhizal infection rate (P < 0.01, Fig. 9). The biomass, nitrogen uptake, and 15N uptake of roots, stems, and leaves were also strongly positively associated (P < 0.01), as were the total K, total N, and total P of donor/recipient seedlings. Furthermore, a noteworthy positive association was seen between the rate of 15N absorption and allocation in the roots of recipient and donor seedlings, as well as the nitrogen intake and biomass of the roots, stems, and leaves (P < 0.01).