Host Plant Modulated Physio-Biochemical Process Enhances Adaptive Response of Sandalwood (<i>Santalum album</i> L.) under Salinity Stress

Salinity is one of the most significant abiotic stress that affects the growth and development of high-value tree species, including sandalwood, which can also be managed effectively on saline soils with the help of suitable host species. Therefore, the current investigation was conducted to understand the physiological processes and antioxidant mechanisms in sandalwood along the different salinity gradients to explore the host species that could support sandalwood growth in salt-affected agro-ecosystems. Sandalwood seedlings were grown with ten diverse host species with saline water irrigation gradients (EC_iw~3, 6, and 9 dS m⁻¹) and control (EC_iw~0.82 dS m⁻¹). Experimental findings indicate a decline in the chlorophyll content (13–33%), relative water content (3–23%), photosynthetic (27–61%) and transpiration rate (23–66%), water and osmotic potential (up to 137%), and ion dynamics (up to 61%) with increasing salinity levels. Conversely, the carotenoid content (23–43%), antioxidant activity (up to 285%), and membrane injury (82–205%) were enhanced with increasing salinity stress. Specifically, among the hosts, <i>Dalbergia sissoo</i> and <i>Melia dubia</i> showed a minimum reduction in chlorophyll content, relative water content, and plant water relation and gas exchange parameters of sandalwood plants. Surprisingly, most of the host tree species maintained K⁺/Na⁺ of sandalwood up to moderate water salinity of EC_iw~6 dS m⁻¹; however, a further increase in water salinity decreased the K⁺/Na⁺ ratio of sandalwood by many-fold. Salinity stress also enhanced the antioxidative enzyme activity, although the maximum increase was noted with host plants <i>M. dubia</i>, followed by <i>D. sissoo</i> and <i>Azadirachta indica</i>. Overall, the investigation concluded that sandalwood with the host <i>D. sissoo</i> can be successfully grown in nurseries using saline irrigation water and, with the host <i>M. dubia,</i> it can be grown using good quality irrigation water.