Reforestation efforts are being challenged as water stress is hampering the sapling growth and survival in arid to semiarid regions. A controlled experiment was conducted to evaluate the effect of foliar application of salicylic acid (SA) on water stress tolerance of Conocarpus erectus and Populus deltoides. Saplings were watered at 90%, 60%, and 30% of field capacity (FC), and half of the saplings under 60% and 30% FC were sprayed with 1.0 mM SA. Results indicated that dry weight production decreased significantly in Populus deltoides under both water deficit conditions, and leaf gas exchange parameters decreased significantly in both the species under both soil water deficit conditions. Foliar application of SA resulted in a significant increase in leaf gas exchange parameters, and compatible solutes, thereby increasing the dry weight production in both of the species under soil water deficit. Oxidative stress (hydrogen peroxide and superoxide anions) increased under soil water deficit and decreased after the foliar application of SA and was parallel to the increased antioxidant enzymes activity (superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase). Therefore, it can be concluded that foliar application of 1.0 mM SA can significantly improve the water stress tolerance in both species, however, positive impacts of SA application were higher in Conocarpus erectus due to improved photosynthetic capacity and increased antioxidant enzyme activity.

Low water availability predicted under climate change is a major abiotic factor limiting plants growth and productivity. In this study a greenhouse experiment was conducted on three important tree species of arid environment: Conocarpus erectus (CE), Acacia modesta (AM), and Salix tetrasperma (ST). Young saplings were subjected to control (C), medium (MWD) and severe soil water deficit (SWD) treatments and response was evaluated. Results showed that in all the three species leaf, stem and root dry weight production remained similar to C under MWD treatment but decreased significantly under SWD. The highest decrease in total dry weight was noticed in ST and the lowest was evidenced in AM under SWD. Root:shoot ratio increased significantly in both CE and AM under MWD and SWD. Furthermore, chlorophyll content decreased while proline content increased significantly in both MWD and SWD treatments. The production of oxidants (hydrogen peroxide and superoxide anions) and antioxidants (superoxide dismutase, catalase, peroxidase and ascorbate peroxidase) increased significantly under both MWD and SWD treatments and were the highest in AM in both MWD and SWD treatments. Therefore, we may conclude that all the three species can tolerate medium water stress due to increased root production and an effective antioxidant defense mechanism.

Fruit tree culture is at the brink of disaster in arid to semi-arid regions due to low water availability. A pot experiment was carried out to analyze whether foliar application of salicylic acid (SA) can improve water stress tolerance in Syzygiumcumini. Saplings were subjected to control (CK, 90% of field capacity, FC), medium stress (MS, 60% of FC) and high stress (HS, 30% of FC) along with foliar application of 0.5 and 1.0 mM of SA. Results showed that soil water deficit significantly decreased leaf, stem and total dry weight, leaf gas exchange attributes and chlorophyll a, b. However, root dry weight and root/shoot ratio increased under MS and HS, respectively. Contrarily, foliar application of SA significantly improved chlorophyll a, b, leaf gas exchange attributes, and dry weight production under soil water deficit. Concentration of oxidants like hydrogen peroxide and superoxide radicals, along with malondialdehyde and electrolyte leakage increased under soil water deficit; however, decreased in plants sprayed with SA due to the increase in the concentration of antioxidant enzymes like superoxide dismutase, peroxidase, catalase and ascorbate peroxidase. Results suggest that the foliar application of SA can help improve water stress tolerance in Syzygiumcumini saplings; however, validation of the results under field conditions is necessary.

Morus alba L. is a multipurpose and fast-growing tree species. However, its growth and productivity are susceptible to water stress. Therefore, a study was conducted to check the effectiveness of foliar application of salicylic acid (SA) in improving the water stress tolerance of M. alba. A pot experiment was conducted and the morphological, physiological and biochemical attributes of young M. alba saplings were assessed under control (CK, 90% of field capacity (FC)), moderate (MS, 60% of FC) and high soil water deficits (HS, 30% of FC), along with MS and HS + foliar application of SA 0.5 and 1.0 mM (MS + 0.5; HS + 0.5; MS + 1.0, and HS+1.0, respectively). Results demonstrated that the highest decrease in plant growth, leaf, stems and roots’ dry biomass, chlorophyll a, b, carotenoid contents and leaf gas exchange parameters was observed under HS, whereas the lowest decrease was evidenced for HS + 1.0 mM SA. Electrolyte leakage, malondialdehyde contents, hydrogen peroxide and superoxide radicals significantly increased under HS, while the lowest increase was evidenced for HS + 1.0 mM SA. The highest increase in proline content, total soluble sugar, total phenolic content, soluble protein and superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase was also found under HS + 1.0 mM SA. Based on the results, it can be concluded that foliar application of SA can help improve the water deficit tolerance of Morus alba saplings, especially under high soil water deficit.

Phytoremediation is a green technology; however, very few species of arid environments have been identified as hyperaccumulators and fast growers. Therefore, a greenhouse experiment was performed to evidence the phytoaccumulation potential of Conocarpus erectus, Syzygium cumini, Populus deltoides and Morus alba at the sapling stage. Six-month-old plant saplings were subjected to control (CK; 0 µM) and cadmium treatments (Cd; CdCl₂; 200 µM). The results depicted that plant growth, dry biomass production (leaf and stem) and chl a, b and carotenoid contents decreased significantly in all four species under Cd treatment; however, the lowest decrease was evidenced in Conocarpus erectus. The concentration of hydrogen peroxide and superoxide radical increased significantly in all four species, with the highest increase observed in Morus alba. Osmolytes production, antioxidant enzymes activity (superoxide dismutase, peroxidase, catalase and ascorbate peroxidase) and Cd accumulation in the leaves, stem and root increased significantly in all four species under Cd treatment, with the highest increase observed in Conocarpus erectus. The translocation factor was >1 in Conocarpus erectus, Syzyngoim cumini and Populus deltoides and was <1 in Morus alba. The study revealed a better Cd tolerance in Conocarpus erectus, which was driven by the effective osmolyte balance and antioxidant enzymes mechanism.

Mitigating climate change requires the identification of tree species that can tolerate water stress with fewer negative impacts on plant productivity. Therefore, the study aimed to evaluate the water stress tolerance of young saplings of C. erectus and M. alba under three soil water deficit treatments (control, CK, 90% field capacity, FC, medium stress MS, 60% FC and high stress, HS, 30% FC) under controlled conditions. Results showed that leaf and stem dry weight decreased significantly in both species under MS and HS. However, root dry weight and root/shoot ratio increased, and total dry weight remained similar to CK under MS in C. erectus saplings. Stomatal conductance, CO₂ assimilation rate decreased, and intrinsic water use efficiency increased significantly in both species under MS and HS treatments. The concentration of hydrogen peroxide, superoxide radical, malondialdehyde and electrolyte leakage increased in both the species under soil water deficit but was highest in M. alba. The concentration of antioxidative enzymes like superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase also increased in both species under MS and HS but was highest in C. erectus. Therefore, results suggest that C. erectus saplings depicted a better tolerance to MS due to an effective antioxidative enzyme system.