Abstract:

The continuous expansion of soil salinization in coastal areas necessitates the selection and breeding of woody plants with both salt tolerance and ornamental value. This practice is vital for utilizing saline soil resources and enhancing the ecosystem. To elucidate the response mechanism to salt stress, we analyzed the effects of varying concentrations of salt stress on calcium components and osmotic substances in Cornus hongkongensis subsp. tonkinensis seedlings. The results can serve as a theoretical foundation for promoting and cultivating ornamental dogwood in coastal areas. The study involved the hydroponic cultivation of seedlings with four gradient concentrations of sea salt [0 (CK), 0.20% (T1), 0.30% (T2), and 0.45% (T3)]. The degree of salt damage index (ISD) in salinized seedlings increased with both the rising salt concentration and the extension of stress duration. After 5 days of salt stress, the ISD and survival rate in salinized seedlings showed no significance. Salinized seedlings exposed to T1, T2, and T3 exhibited ISD of 47.80%, 52.00%, and 71.20% after 30 days of salt stress, and the corresponding survival rates were 82.60%, 84.00%, and 56.00%. During short- term saline stress (5 d), the Ca²⁺ concentration in the guard cells of leaves exposed to T1, T2, and T3 increased, reaching 13.98%, 22.54%, and 17.33% above CK, separately. Simultaneously, the width-to-length ratios of pore in T1, T2, and T3 were lower than that in CK by 23.60%, 25.98%, and 36.05%, respectively. Thereof, the Ca²⁺ concentration in the guard cells of leaves exposed to T3 increased strikingly with the extension of stress duration. After 30 days of salt stress, the mass fractions of water-soluble calcium, oxalate calcium, and pectin-bound calcium in T3 significantly decreased to the values of 4.99, 7.12, and 4.04 mg·g^?1, respectively. Additionally, as the salt concentration increased, there was obvious fragmentation of calcium oxalate crystals in mesophyll cells. The area proportion of calcium oxalate crystals in mesophyll cells exposed to T1, T2, and T3 fell by 43.10%, 15.25%, and 69.90% above CK, separately. The content of soluble protein (SP), soluble sugar (SS), and proline (Pro) in the leaves of T3 treatment increased by 20.04 %, 15.38%, and 19.74% compared to CK, respectively. The results indicate that C. hongkongensis subsp. tonkinensis exhibits tolerance to 0.45% salt stress for 30 days. The salt tolerance of C. hongkongensis subsp. tonkinensis seedlings are believed to be achieved through an increase in both the Ca²⁺ content and soluble protein content. In addition, the release of Ca²⁺ through the decomposition of calcium oxalate may be an effective strategy to mitigate the damage caused by salt stress in dogwoods.

Key words: salt stress, calcium component, calcium oxalate, osmotic substances

摘要：

随着滨海地区土壤盐渍化程度不断扩大，选育耐盐性和观赏价值并存的木本植物进行引种栽培，将有利于盐渍土壤资源的利用和生态系统的改善。东京四照花（Cornus hongkongensis subsp. tonkinensis）作为观赏型苗木，从幼苗的钙组分与渗透物质方面探讨其盐胁迫响应机制，为其在滨海地区推广种植提供理论依据。设置4种质量分数梯度的盐浓度：0（CK）、0.20%（T1）、0.30%（T2）和0.45%（T3），水培法培养幼苗。盐处理幼苗的盐害等级（I_SD）随着盐分浓度的升高和胁迫时间的延长而增加。盐胁迫5 d时，各处理组的幼苗I_SD和成活率未有明显变化；盐胁迫30 d时，T1、T2和T3处理组的I_SD分别为47.80%、52.00%和71.20%，对应的成活率分别为82.60%、84.00%和56.00%。胁迫初期（5 d），T1、T2和T3保卫细胞中Ca²⁺浓度较CK分别增加了13.98%、22.54%和17.33%。同时，T1、T2和T3的气孔孔径的宽长比（W/L）比CK分别减少了23.60%、25.98%和36.05%。其中，仅T3处理保卫细胞中Ca²⁺浓度随胁迫时间延长而显著升高。胁迫至30 d，T3处理下的水溶性钙（H₂O-Ca）、草酸钙（HCl-Ca）、果胶酸钙（NaCl-Ca）质量分数分别降低至4.99、7.12、4.04 mg?g^?1。同时，随着盐浓度的升高，草酸钙晶体在叶肉细胞中破碎化程度明显。与CK相比，T1、T2和T3草酸钙晶体在叶肉细胞中面积占比分别显著降低了43.10%、15.25%、69.90%。T3处理下的可溶性蛋白（SP）、可溶性糖（SS）和脯氨酸（Pro）含量较CK分别增加了20.04 %、15.38%和19.74%。东京四照花短期（30 d）可承受0.45%的盐胁迫。幼苗通过提高Ca²⁺浓度，促进可溶性蛋白的合成来提高其耐盐性。此外，草酸钙降解释放出的Ca²⁺可能是缓解盐胁迫对东京四照花幼苗损伤的有效策略。

关键词: 盐胁迫, 钙组分, 草酸钙, 渗透物质