Nutrient content, osmolytes accumulation and antioxidative enzyme activities of sandalwood under drought and salt stresses

Sandalwood (<i>Santalum album L</i>.) has potential to grow into various types of soil under arid as well as semi-arid regions. To find out the sustainable host plant species for sandalwood grown under stress, an RBD experiment was conducted on sandalwood grown without a host and with five selected hosts (<i>Alternanthera</i> sp., <i>Azadirachata indica</i>, <i>Dalbergia sissoo</i>, <i>Melia dubia</i>, and <i>Aquilaria malaccensis</i>) based on prior studies. After 6 weeks of establishment, individual and combine water and salinity stresses were applied and maintained for up to 180 days to investigate their impact on the nutrient content, concentration of osmolytes, and activities of antioxidative enzymes in sandalwood. Haustoria formation showed significant reduction under individual and combined water deficit and salinity stress. Sandalwood grown with <i>Dalbergia sissoo</i> and <i>Melia dubia</i> showed relatively higher nutrients content such as N, P, Ca, Mg, Zn, Fe, and S, which were dramatically reduced under individual and combined water deficit and salinity stress. Osmolytes concentration (proline, soluble sugars, and soluble proteins) increased with intensified stress and sandalwood accumulated higher osmolytes when grown with <i>Dalbergia sissoo</i> and <i>Melia dubia</i>. The activities of antioxidant enzymes showed a significant increase under water deficit, salinity, and combined stress compared to the control, but sandalwood grown with <i>Dalbergia sissoo</i> and <i>Melia dubia</i> exhibited higher activities. Results signify the importance of hosts i.e. <i>Dalbergia sissoo</i> and <i>Melia dubia</i> which provide suitable growth and nutrition to growing sandalwood by maintaining ion homeostasis, ROS balance, and nutrient content under water deficit, salinity, and interactive stress. Results highlighted the significance of <i>D. sissoo</i> and <i>M. dubia,</i> which may be good long-lasting host species for sandalwood production in sub-tropical climates to adapt to changing environmental conditions.

檀香（Santalum album L.）可在干旱及半干旱区域的多种土壤类型中生长。为筛选出胁迫环境下檀香的可持续寄主植物，本研究基于前期研究，针对无寄主及5种选定寄主（莲子草属（Alternanthera sp.）、印楝（Azadirachata indica）、印度黄檀（Dalbergia sissoo）、麻楝（Melia dubia）、马来沉香（Aquilaria malaccensis））伴生的檀香开展随机区组试验（Randomized Block Design，RBD）。定植6周后，施加单独及复合的水分与盐胁迫，并持续处理180天，以探究胁迫对檀香养分含量、渗透调节物质浓度及抗氧化酶活性的影响。研究结果显示，吸器的形成在单独及复合水分亏缺与盐胁迫下显著降低。与印度黄檀和麻楝伴生的檀香，其氮（N）、磷（P）、钙（Ca）、镁（Mg）、锌（Zn）、铁（Fe）及硫（S）等养分含量相对更高，但在单独及复合水分亏缺与盐胁迫下会显著下降。渗透调节物质（脯氨酸、可溶性糖及可溶性蛋白）的浓度随胁迫加剧而升高，且与印度黄檀和麻楝伴生的檀香积累的渗透调节物质更多。与对照组相比，水分亏缺、盐胁迫及复合胁迫下抗氧化酶活性显著升高，而与印度黄檀和麻楝伴生的檀香抗氧化酶活性更高。结果表明，印度黄檀与麻楝这两种寄主可通过维持离子稳态、活性氧（Reactive Oxygen Species，ROS）平衡及养分含量，为檀香生长提供适宜的环境与营养，在水分亏缺、盐胁迫及交互胁迫下发挥积极作用。本研究凸显了印度黄檀与麻楝的应用价值，二者可作为亚热带气候下檀香规模化种植的长效优良寄主，以适应不断变化的环境条件。