Interspecific Differences in Physiological and Biochemical Traits Drive the Water Stress Tolerance in Young Morus alba L. and Conocarpus erectus L. Saplings.

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.

Foliar Application of Salicylic Acid Improves Water Stress Tolerance in Conocarpus erectus L. and Populus deltoides L. Saplings: Evidence from Morphological, Physiological, and Biochemical Changes.

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.

Increased antioxidative enzyme activity mediates the phytoaccumulation potential of Pb in four agroforestry tree species: a case study under municipal and industrial wastewater irrigation.

Wastewater used as irrigation water is causing heavy metal accumulation in the agro-ecosystems. A greenhouse study was conducted to compare the phytoaccumulation ability of four agroforestry tree species under different wastewater treatments. Three-month-old potted seedlings of Morus alba, Acacia nilotica, Acacia ampliceps, and Azadirachta indica were irrigation with tap water (C), municipal wastewater (MWW), and industrial wastewater (IWW). Results showed that MWW had a positive and IWW had a negative impact on biomass production in all the species. Acacia ampliceps showed the highest increment (65%) and showed the lowest decrease (5%) in total biomass under both MWW and IWW treatment. Pb concentration was also found highest in the leaves, stem and roots of Azadirachta indica (108.5, 46.2, 180.5 mg kg-1, respectively) under IWW. Production of H2O2 was highest in IWW treatment with almost 148% increase observed in Azadirachta indica. Similarly, the production of antioxidative enzymes (Superoxide dismutase, Catalase and Peroxidase) was also highest in Azadirachta indica under IWW. Therefore, results suggest that along with high increment in total biomass, both Acacia ampliceps and Azadirachta indica showed high Pb concentration and an effective antioxidative defense mechanism and thus, can be used for planting in soils irrigated with MWW and IWW.

Assessment of European and hybrid aspen clones efficiency based on height growth and removal percentage of petroleum hydrocarbons-a field trial.

Soils polluted by organic or inorganic pollutants are an emerging global environmental issue due to their toxic effects. A phytoremediation experiment was conducted to evaluate the extraction potential of three European aspen clones (R2, R3, and R4) and seven hybrid aspen clones (14, 27, 34, 134, 172, 191, and 291) grown in soils polluted with hydrocarbons (includes polycyclic aromatic hydrocarbons (PAH) and total petroleum hydrocarbons (TPH)). Height growth, plant survival rates, and .hydrocarbon removal efficiencies were investigated over a 4-year period at a site in Somerharju, Luumaki Finland, to assess the remediation potential of the clones. Hydrocarbon content in the soil was determined by gas chromatography and mass spectrometry. The results revealed that hybrid aspen clones 14 and 34 and European aspen clone R3 achieved greater height growth (171, 171, and 114 cm, respectively) than the other clones in the study. Further, the greatest removals of PAH (90% at depth 10-50 cm) and (86% at depth 5-10 cm) were observed in plot G15 planted with clone R2. Furthermore, the greatest TPH removal rate at 5-10 cm depth (C22-C40, 97%; C10-C40, 96%; and C10-C21, 90%) was observed in plot 117 with clone 134. However, other clones demonstrated an ability to grow in soils with elevated levels of TPH and PAH, which indicates their tolerance to hydrocarbons and their potential capacity for phytoremediation of hydrocarbon-polluted soils. Our study suggests that European aspen and hybrid aspen clones could be used for the remediation of soils polluted with PAH and TPH.

Phytoaccumulation of Zn, Pb, and Cd in Conocarpus lancifolius irrigated with wastewater: does physiological response influence heavy metal uptake?

Conocarpus lancifolius is a fast-growing and drought tolerant tree species with phytoremediation potential in arid environments. The present study was conducted to evaluate the phytoaccumulation potential under wastewater treatment. The experiment was performed in a greenhouse where 3-month-old seedlings were irrigated with industrial wastewater and growth, biomass and physiological parameters were measured. Concentrations of zinc (Zn), lead (Pb), and cadmium (Cd) in leaves, shoots, and roots along with translocation and tolerance index were also determined. The results showed that under wastewater treatment total biomass increased from 24.2 to 31.5 g, net CO2 assimilation rate increased from 9.93 to 13.3 µmol m-2 s-1, and water use efficiency increased from 1.7 to 2.42. Similarly, heavy metals (Zn, Pb, and Cd) accumulation in stem, leaves, and roots increased significantly under wastewater treatment where the highest concentration of Zn, Pb and Cd was found in roots followed by leaves and stem, respectively. Tolerance index was found >1, and translocation factor of all heavy metals was found >1. The study revealed that phytoaccumulation potential of C. lancifolius was mainly driven by improved net CO2 assimilation rate and water use efficiency.