桔梗苗期生长发育对盐胁迫的响应及耐盐阈值分析

Response of Platycodon grandiflorus Seedling Growth and Development to Salt Stress and Analysis of Salt Tolerance Threshold

摘要: 为了探究苗期桔梗生长发育对滨海盐渍土复合盐胁迫的响应，明确其耐盐阈值及适应性生理机制，本研究以滨海原生盐渍土为基质，通过梯度配比设置土壤实际含盐量为0.11% (CK)、0.21%、0.32%和0.40%的土壤处理，开展45天盆栽胁迫试验，系统测定桔梗幼苗的生长及生理指标，并建立回归模型。结果表明，盐胁迫显著抑制桔梗幼苗株高、地上部与地下部生物量(P < 0.05)。低盐胁迫下地下部鲜质量和根冠比分别较CK显著提升25.0%和8.9% (P < 0.05)，但盐分 ≥ 0.32%时，生长抑制效应显著加剧。盐胁迫下桔梗苗期总叶绿素含量随盐浓度升高显著下降(P < 0.05)，叶片质膜透性、丙二醛(MDA)和脯氨酸(Pro)含量显著上升(P < 0.05)，可溶性蛋白含量在0.32%盐浓度下达到峰值，较CK提升35.1%，随后显著下降。相关性分析显示，地上部干质量与土壤含盐量呈极显著负相关，可作为桔梗耐盐性评价的核心指标。基于二次回归模型，以地上干质量降幅25%为适宜种植临界值，降幅50%为临界标准，确定桔梗幼苗在滨海复合盐渍土中适宜种植临界含盐量为0.20%，耐盐阈值为0.29%。本研究结果可为滨海盐碱地桔梗规范化栽培提供理论依据与技术参数。

Abstract: To explore the response of Platycodon grandiflorus seedling growth and development to compound salt stress in coastal saline soil, and to clarify its salt tolerance threshold and adaptive physiological mechanism, a 45-day pot experiment was conducted using natural coastal saline soil as the growth substrate. Four soil salt content treatments (0.11% for CK, 0.21%, 0.32% and 0.40%) were established via gradient mixing. Growth and physiological indicators of Platycodon grandiflorus seedlings were determined systematically, and a quadratic regression model was constructed. The results showed that salt stress significantly inhibited the plant height, aboveground and underground biomass of Platycodon grandiflorus seedlings (P < 0.05). Under low salt stress, underground fresh weight and root-shoot ratio increased significantly by 25.0% and 8.9% compared with CK (P < 0.05). Growth inhibition was markedly aggravated when soil salt content was ≥0.32%. The total chlorophyll content of Platycodon grandiflorus seedlings decreased significantly with the increase of salt concentration under salt stress (P < 0.05), while the leaf plasma membrane permeability, malondialdehyde (MDA) and proline (Pro) contents increased significantly (P < 0.05). Soluble protein content reached the maximum at the salt concentration of 0.32%, being 35.1% higher than CK, followed by a significant decline. Correlation analysis showed that aboveground dry weight was extremely significantly negatively correlated with soil salt content, which could be used as the core index for the evaluation of Platycodon grandiflorus salt tolerance. Based on the quadratic regression model, taking a 25% decrease in aboveground dry weight as the critical limit for suitable cultivation and a 50% decrease as the salt tolerance critical standard, the critical soil salinity for suitable cultivation and salt tolerance threshold of Platycodon grandiflorus seedlings in coastal composite saline soil were determined as 0.20% and 0.29%, respectively. The results of this study can provide a theoretical basis and technical parameters for the standardized cultivation of Platycodon grandiflorus in coastal saline-alkali land.