ABSTRACT
Cedrus deodara is the central conifer plant affected by ozone and nitrogen pollutants among forest species worldwide. The growth of C. deodara depends upon the ectomycorrhizal (ECM) association, which is usually disturbed by these factors. This study aims to understand how these factors affect plants at physiological and biochemical levels. Three fungal strain consortiums were inoculated with two-year-old C. deodara seedlings. The stresses of 100 kg N h-1and 100 ppb O3 were applied for six months to study their impact on chlorophyll and antioxidant enzymes (SOD, CAT, and APX). The results showed that C2 (Consortium of Cedrus deodara) positively impacted the growth of selected plant species. The high photosynthesis rate was determined by enhanced chlorophyll content, and C2-treated plants showed high chlorophyll content. Relatively, chlorophyll a and b contents increased significantly in the seedlings treated with Ethylenediurea (EDU) alone and with ozone stress. In addition, a significant difference was observed between EDU and O3-treated plants (14% EDU400-O3 and 23% EDU600-O3) and the control. Overall, antioxidant activities were higher in the treated samples than in the control. The order of SOD activity was C2 (448 U/gFW) and lowest (354.7 U/gFW) in control. APX also showed higher activity in treated plants in C1 ≥ C2 ≥ C3+O3, whereas CAT activity was the highest in C2 treatments. Ozone and nitrogen-stressed plants showed higher activities than EDU-treated plants compared to non-treated ones. Our findings highlight the importance of understanding the signaling effects of numerous precursors. Moreover, an extended investigation of seedlings developing into trees must be conducted to verify the potential of ectomycorrhizal strains associated with C. deodara and comprehend EDU's role as a direct molecular scavenger of reactive toxicants.
ABSTRACT
Cedrus deodara is economically and ethnobotanically an important forest tree and is shown to be at decline in Northern areas of Pakistan in recent years mainly due to high concentration of Nitrogen in forests. Ectomycorrhizal (ECM) association forming fungi enables the forest trees to develop optimally by absorbing water from the rhizosphere through their absorptive hyphae and by making available the nutrients by mobilization of N and P from the organic substrates. This study was conducted to identify the ECM strains from C. deodara rhizosphere and to analyse the impact of high N load on the C. deodara seedlings to establish N critical load value for coniferous forests of Pakistan. Six new fungal strains were identified from the rhizosphere of C. deodara and were registered at GenBank (NCBI) as Emmia latemarginata strain ACE1, Aspergillus terreus strain ACE2, Purpureocillium lilacinum strain ACE3, Talaromyces pinophilus strain ACE4, A. fumigatus strain ACE5 and T. pinophilus strain ACE6 with accession numbers MH145426, MH145427, MH145428, MH145429, MH145430 and MH547115. Four out of six isolated strains were inoculated with seedlings of C. deodara singly and in consortium (CN) in combination with nitrogen load of 0 (C), 25 (T1), 50 (T2), 100 kg N ha-1 yr-1 (T3). Agronomic, physiological and gene expression studies for ExpansinA4 (EXPA4) and Cystatins (Cys) were made to analyse the impact of fungal strains in relation to high N stress. This study suggests a positive impact of T1 (25 kg N ha-1 yr-1) Nitrogen load and a negative impact of T3 (100 kg N ha-1 yr-1) on growth parameters and expression patterns of EXPA4 and Cys genes. Peroxidase (POX) activity decreased in the order ACE5 > ACE2 > C > ACE3 > ACE1 > CN. However, the results of Superoxide dismutase (SOD) showed decreasing trend in the order ACE5 > C > CN > ACE1 > ACE2 > ACE3. Strain ACE3 was shown to have a positive impact on the seedlings in terms of growth, physiology and expression of genes. Present study suggests that newly identified fungal strains showing positive impact on the growth and physiology of C. deodara could be used for the propagation of this economically important plant in Pakistan after pathogenicity test.
