A. munitus under KRD conditions shows a decreasing trend
The results revealed significant differences (p < 0.05) in stem number, stem length, middle lateral branch length and leaf length between the EG and CK plants of A. munitus (Table 1). No significant differences were observed for the other indicators. LSD indicated no significant difference in below-ground biomass, however CK averaged approximately one-third higher than EG, EG tubers tended to be shorter but greater in diameter (Fig. 2A, B). Overall, EG growth was inhibited, especially above ground, and was weaker than that in the CK treatment.
Table 1
Agronomic traits of A. munitus plants grown in different regionsa and b indicate significant differences at the 0.05 level (p < 0.05); A and B indicate significant differences at the 0.01 level (p < 0.01). The values are the means ± standard deviations
Trait | Unit | Control check | Experiment group |
Number of stems | each | 5.33 ± 0.82 A | 3.67 ± 0.52 B |
Basal stem thickness | mm | 3.05 ± 0.46 a | 2.98 ± 0.53 a |
Stems length | cm | 141.66 ± 16.8 a | 114.05 ± 21.0 b |
Lateral branch length | cm | 21.97 ± 2.84 A | 16.85 ± 1.88 B |
Leafy shoot length | mm | 6.76 ± 0.87 A | 5.18 ± 0.61 B |
Above-ground biomass | g | 42.30 ± 10.19 a | 34.88 ± 6.64 a |
Underground biomass | g | 245.53 ± 62.67 a | 186.76 ± 30.11 a |
Biochemical responses of A. munitus leafy shoots to KRD
The stomatal density in the EG treatment was significantly greater than that in the CK treatment (Fig. 3), averaging 471.26 mm− 2. Compared to those in the CK treatment, the photosynthetic pigment content in the EG treatment was markedly lower; however, the carotenoid-to-chlorophyll ratio differed highly significantly between the groups (Table 2). Similarly, the leaf SOD, POD, and CAT activities in the EG treatment were 1.4, 1.6 and 1.7 times greater than those in the CK treatment, respectively. Osmoregulatory substances showed similar increasing trends in the EG compared to the CK. These results suggest that A. munitus individuals experience some degree of stress under KRD conditions.
Table 2
Biochemical indicators of plants in different environments. A and B indicate significant differences at the 0.01 level (p < 0.01). The values are the means ± standard deviations. FW: fresh weight
Trait | Unit | Control check | Experiment group |
Stomata density | Pcs/mm2 | 375.43 ± 45.92 B | 471.26 ± 103.52 A |
Chlorophyll a | mg/g FW | 1.81 ± 0.03 A | 1.43 ± 0.04 B |
Chlorophyll b | mg/g FW | 0.72 ± 0.058 A | 0.52 ± 0.033 B |
Carotenoid | mg/g FW | 0.41 ± 0.002 A | 0.37 ± 0.004 B |
Carotenoids/chlorophyll | ×10− 2 | 16.27 ± 0.12 B | 18.83 ± 0.49 A |
The medicinal components of A. munitus are not affected by KRD
Total saponins, polysaccharides and total amino acids are the main medicinal components of A. munitus tubers. The results showed that the polysaccharide content was significantly greater (p < 0.05) in the EG tubers than in the CK tubers, while no significant differences were observed for the other components (Fig. 4). These findings indicate that A. munitus plants can accumulate medicinal components normally when planted in KRD areas, which is even slightly higher than what is observed in the CK treatment.
Correlation analysis and principal component analysis of agronomic traits in A. munitus Correlation analysis revealed strong associations between most agronomic traits, except for basal stem thickness, which was less correlated with the other indicators (Fig. 5). After removing the basal stem thickness, the remaining traits were subjected to principal component analysis. The first two principal components had eigenvalues above 1 (5.248 and 1.424) and accounted for 83.400% of the total variance (Table 3). Thus, these two components represent the majority of the information from the eight agronomic traits. Leafy shoot length and tuber diameter had the highest eigenvector values for the first and second principal components (Table 4). Therefore, the principal components included leafy shoot length and tuber diameter.
Table 3
Principal component analysis of the agronomic traits of A. munitus
Components | Eigenvalue | Contribution rate | Cumulative contribution rate |
1 | 5.248 | 65.594 | 65.594 |
2 | 1.424 | 17.806 | 83.400 |
3 | 0.513 | 6.411 | 89.811 |
4 | 0.343 | 4.289 | 94.100 |
5 | 0.258 | 3.221 | 97.320 |
6 | 0.119 | 1.485 | 98.806 |
7 | 0.077 | 0.968 | 99.773 |
8 | 0.018 | 0.227 | 100.000 |
Table 4
Principal component analysis eigenvectors and contributions of agronomic traits
Agronomic trait | Eigenvector |
Principal Component 1 | Principal Component 2 |
Number of stems | 0.867 | -0.198 |
Stems length | 0.782 | 0.321 |
Lateral branch length | 0.851 | 0.160 |
Leafy shoot length | 0.976 | -0.010 |
Above-ground biomass | 0.793 | 0.540 |
Underground biomass | 0.951 | 0.083 |
Tuber length | 0.821 | -0.228 |
Tuber diameter | -0.025 | 0.951 |
Table 5
Effect of A. munitus planting on the physical properties of KRD soils. a and b indicate significant differences at the 0.05 level (p < 0.05); A and B indicate significant differences at the 0.01 level (p < 0.01). The values are the means ± standard
Trait | Unit | Soil control | Soil near A. munitus |
pH | | 7.37 ± 0.05 A | 7.21 ± 0.06 B |
soil water content | % | 24.50 ± 1.10 B | 30.76 ± 0.97 A |
soil bulk density | % | 0.93 ± 0.02 b | 1.02 ± 0.04 a |
soil total porosity | % | 59.81 ± 4.24 B | 62.15 ± 0.92 A |
soil capillary porosity | % | 54.83 ± 1.48 b | 58.78 ± 0.89 a |
soil noncapillary porosity | % | 2.64 ± 0.21 B | 3.37 ± 0.12 A |
Table 6
Effect of A. munitus planting on the soil nutrient content of KRD soils. a and b indicate significant differences at the 0.05 level (p < 0.05), and A and B indicate significant differences at the 0.01 level (p < 0.01). The values are the means ± standard deviations
Trait | Unit | Soil control | Soil near A. munitus |
Soil organic matter | % | 5.80 ± 0.23 B | 8.09 ± 0.40 A |
Total nitrogen | g/kg | 3.15 ± 0.17 B | 4.04 ± 0.21 A |
Total phosphorus | g/kg | 0.85 ± 0.04 a | 0.72 ± 0.05 b |
Total potassium | g/kg | 12.82 ± 0.12 a | 11.07 ± 0.54 b |
Alkali-hydro nitrogen | g/kg | 243.87 ± 10.04 B | 317.72 ± 13.14 A |
Available phosphorus | mg/kg | 6.26 ± 0.75 A | 2.32 ± 0.19 B |
Available potassium | mg/kg | 119.33 ± 10.02 a | 94.33 ± 6.43 b |
A. munitus Planting Changes the Soil Physical Properties in the KRD Area
The KRD test site was weakly alkaline. Planting A. munitus significantly reduced the SA pH by 0.16 units on average compared to that in SC (p < 0.01). Additionally, SA had an extremely significantly higher SWC versus SC (p < 0.01), at more than 31%. SBD, SP, SCP and SNP all differed significantly between SA and SC to varying degrees. These results demonstrated that A. munitus strongly affects the basic physical properties of KRD soils.
Planting A. munitus altered the KRD soil nutrient content
The KRD soil nutrient levels varied according to fertility grade. SOM and TN were enriched (Class I), AK was moderate (Class III), and AP was depleted (Class IV), indicating that the site was relatively deficient in P and K. Planting A. munitus significantly increased SOM, TN and AN in SA versus SC (p < 0.05). TP and AP differed significantly between SA and SC, with SC having 2.7 times greater AP. TK and AK were also significantly greater in the SC treatment than in the SA treatment (p < 0.05). Taken together, these findings demonstrated that A. munitus planting depletes soil P and K, especially P. Overall, A. munitus decreased the KRD soil pH but increased the SWC, SBD, SP, SOM, TN and AN while decreasing P and K. These data indicate that planting A. munitus significantly alters basic physicochemical properties of KRD soil, largely in beneficial ways.