3.1 Nutrient concentration and accumulation in wheat plants
3.1.1 Effect of CWRA on PNC and PNA
As shown in Figure 2, the leaves N concentrations subjected to diverse treatments had certain differences across different growth stages. The water retention agent treatments were significantly better than CK under the N level, and the performances were basically the same in the two-year experiments. In 2019-2020, T2 wheat plants had the highest N concentration in the whole growth period. T2 and T3 at 20 days after anthesis were significantly higher than those of other treatments; at harvest stage, the N concentration of wheat plants in all treatments showed T2>T3>T4>T1>CK. In 2020-2021, there were no significant differences between T2 and T3 in the three sampling dates from 0d to 20d after anthesis. The N concentration of T2 at 30 days after anthesis was significantly higher than other treatments. At the harvest stage, all treatments were significantly higher than CK, and T2 was 13.69% higher than CK, particularly.
With the development of wheat growth, the PNA in each treatment showed a gradually upward tendency. The rate of increase was relatively slow from the anthesis stage to 10 days after anthesis and then fast from 20 days to 40 days after anthesis. The trends in the two-year experiments were basically the same. In the two-year experiments, after flowering the N accumulation of T2 was significantly higher than other treatments, and the level of wheat plants in each treatment was T2>T3>T4>T1>CK. In summary, application of WRA under the conditions of our experiment promoted N accumulation in saline winter wheat plants after flowering, with T2 promoting the most obvious effect.
3.1.2 Effect of CWRA on PPC and PPA
The P concentration in wheat plants treated with WRA was significantly higher than without added, and PPC decreased as the wheat matured, the performances were basically the same in the two-year treatments.
Unlike PPC, PPA has been on an increasing trend throughout the after anthesis period in all treatments. And the rate of increase in P accumulation was significantly faster in the T2 treatment than in the other treatments after 20 days after anthesis.
3.1.3 Effect of CWRA on PKC and PKA
K concentrations of plants in the WRA treatments were generally significantly higher than in the CK treatment, and experimental results were essentially the same in both years (Figure 4). With the development of the wheat growth period, the K accumulation in each treatment showed a gradually rising trend. Although there was little difference in PKC between the T2 and T3 treatments, PKA differed considerably, especially at 40 days after anthesis. At the harvest stage (40 days post-anthsis), the PKC of T3 was 14.51% higher than CK, and T2 was 14.19% higher than CK; the PKA of T2 was 42.57% higher than CK, T3 was 35.70% higher than CK.
saline-alkali soil
3.2.1 Effect of CWRA on the relative expression of the Ammonium transporter gene TaAMT1.1 in flag leaves
As shown in Figure 5, the expression of the TaAMT1.1 gene was the highest at the anthesis stage, and then decreased. Later, the expression of TaAMT1.1 increased with the progress of grouting, and decreased after the completion of grouting. Significant differences were observed among the treatments, especially values under WRA treatment were significantly higher than those under CK treatment. Among these treatments, the relative gene expression under the T2 treatment was the highest during the whole reproductive period.
3.2.2 Effect of CWRA on the relative expression of the Glutamine synthetase gene TaGS1 in flag leaves
The relative expression of the TaGS1 gene for glutamine synthetase in wheat flag leaves changed with increasing days to flowering, as shown in Figure 6. The expression of TaGS1 increased after anthesis, and decreased after grouting. The relative expression of TaGS1 was significantly increased from the anthesis stage to 21 days after anthesis in each treatment with WRA compared with CK. At 14 days after anthesis, the relative gene expression in T2 and T3 was significantly higher than CK, and the relative gene expression in T2 and T3 was 2.76 times and 2.34 times that in CK, respectively.
3.2.3 Effect of CWRA on the P transporter gene TaPHT2;1 in flag leaves
Significant differences in TaPHT2;1, the flag leaf P transporter protein gene of winter wheat in saline soils, were observed under different treatment conditions (Fig. 7). Compared with CK, the relative expression of the applied water retention agent was significantly increased, and the relative expression of the T2 P transporter gene TaPHT2;1 was the largest. The expression reached a maximum at the late filling stage, and then began to decrease with leaf senescence.
3.4 Effect of CWRA on yield and yield components of winter wheat in saline-alkali soil
The field test results were as shown in Table 4. In our study, different treatments had little impact on the NFT and NGS, and there was no significant difference in the two-year tests. The GY of the water retention agent treatments was significantly higher than that of the blank handling. T2 had the highest yield, followed by T3. There was no significant difference between T1 and T4, and the performance was consistent in the two-year tests.
In 2019-2020, the W1000 of T2 and T3 was significantly higher than that of the other treatments, but there was no significant difference between T2 and T3. The GY of T2 was 14.4% higher than CK, T3 was 11.2% higher than CK. In 2020-2021, the W1000 of T2 was significantly higher than other treatments. The GY of T2 was 13.3% higher than CK, and the T3 was 9.82% higher than CK. In summary, the application of the water retention agent under our test conditions increased the GY by increasing the W1000 of wheat. The WUE of the treatment with the water retention agent was significantly improved, and the WUE of T2 was the highest, which increased by 14.41% and 13.24% compared with CK in the two years.
Table 4 Effects of CWRA on yield and yield components of winter wheat in saline-alkali soil.
Year
|
Treatment
|
NFT
(104 ha-1)
|
NGS
(plants)
|
W1000
(g)
|
GY
(kg ha-1)
|
WUE
(kg ha-1 mm-1)
|
2019-2020
|
CK
|
449a
|
35.15a
|
39.71c
|
6257d
|
1.26d
|
T1
|
446a
|
34.98a
|
40.71bc
|
6403c
|
1.29c
|
T2
|
451a
|
35.07a
|
45.52a
|
7161a
|
1.45a
|
T3
|
456a
|
35.16a
|
44.17a
|
6959b
|
1.41b
|
T4
|
455a
|
35.10a
|
41.28b
|
6502c
|
1.31c
|
2020-2021
|
CK
|
450a
|
35.00a
|
40.39d
|
6364d
|
1.15d
|
T1
|
453a
|
35.11a
|
41.32c
|
6503c
|
1.17c
|
T2
|
451a
|
35.08a
|
45.78a
|
7210a
|
1.30a
|
T3
|
453a
|
35.05a
|
44.33b
|
6989b
|
1.26b
|
T4
|
449a
|
35.18a
|
41.37c
|
6517c
|
1.18c
|
Note: Different letters represent the significant difference in the mean values of different treatments of the same measurement item (P<0.05, Duncan’s new multiple range method). Hereinafter the same.
The results of the pot test are shown in Table 5. The effects of different treatments on the NFT and NGS of saline-alkali winter wheat were small, and there was no significant difference within the two years. The GY of the treatment with the water retention agent was significantly higher than other treatments, which was manifested as T2> T3> T4>T1>CK, and the performance was consistent for two years. Among them, the GY of T2 was 29.03% and 29.64% higher than CK in the two years. The W1000 of T2 increased by 22.74% and 22.84%, respectively, compared with CK in the two years. In summary, the application of the water retention agent under this test condition increased the GY by increasing the W1000 of wheat.
Table 5 Effects of CWRA on yield and component factors of winter wheat in saline-alkali soil.
Year
|
Treatment
|
NFT
|
NGS
|
W1000(g)
|
GY(g/pot)
|
2019-2020
|
CK
|
12.12a
|
33.93a
|
35.84e
|
14.64e
|
T1
|
12.18a
|
34.13a
|
38.09d
|
16.00d
|
T2
|
12.83a
|
34.15a
|
43.99a
|
18.89a
|
T3
|
12.71a
|
34.30a
|
41.59b
|
17.89b
|
T4
|
12.59a
|
34.25a
|
40.06c
|
17.25c
|
2020-2021
|
CK
|
11.79a
|
33.25a
|
34.10e
|
13.90e
|
T1
|
11.76a
|
33.36a
|
36.31d
|
15.25d
|
T2
|
12.51a
|
33.33a
|
41.89a
|
18.02a
|
T3
|
12.36a
|
33.30a
|
39.20b
|
16.46b
|
T4
|
12.28a
|
33.42a
|
38.77c
|
16.28c
|
The correlation analysis of wheat yield and plant nutrient indexes at the harvest stage were shown in Table 6. The yield was highly significantly positively correlated with plant dry weight, N, P and K.
Table 6 Correlation analysis between yield and each index.
|
GY
|
Dry weight
|
Plant N
|
Plant P
|
Plant K
|
GY
|
1
|
|
|
|
|
Dry weight
|
0.950**
|
1
|
|
|
|
Plant height
|
0.715*
|
0.641*
|
|
|
|
Plant N
|
0.912**
|
0.965**
|
1
|
|
|
Plant P
|
0.559*
|
0.694*
|
0.804**
|
1
|
|
Plant K
|
0.808**
|
0.907**
|
0.921**
|
0.897**
|
1
|
Note: ** and * indicate significant correlations at P<0.01 and P<0.05 levels, respectively.