Forest waste biochar enhances growth and antioxidant defence in Sonneratia caseolaris seedlings grown under salinity stress / Nur Sa’adah Abdul Halim

Nur Sa’adah, Abdul Halim (2024) Forest waste biochar enhances growth and antioxidant defence in Sonneratia caseolaris seedlings grown under salinity stress / Nur Sa’adah Abdul Halim. PhD thesis, Universiti Malaya.

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Abstract

Mangrove forests are well inundated by seawater that is particularly high in salinity which limits propagule germination, seedling growth, survival rate and reproduction of mangrove trees. Continual loss of mangroves will bring detrimental impacts on the ecosystem and humans. Therefore, mangrove conservation is now a priority, and this involves enormous efforts to rehabilitate the forest. Recently, biochar, which is a product from thermal degradation of organic biomass under low- oxygen condition known as pyrolysis process has a great ability in adsorbing salt ions has received numerous applications. Application of biochar as a soil amendment can assist to mitigate the adverse impacts of salinity stress. Thus, this study was aimed to elucidate the effect of forestry waste biomass biochar on Sonneratia caseolaris under salinity stress in mangrove nursery by optimizing the production of biochar from different sources of forestry waste biomass and, to determine the effects of biochar application as soil amendments on plant growth, soil properties and nutrient uptake as well as the antioxidant defense mechanism in plants. Biochar was produced from forestry sources of Gigantochloa levis, Melaleuca cajuputi, Bruguiera parviflora and Sonneratia caseolaris. The materials were pyrolyzed at 300 ℃, 450 ℃ and 600 ℃ for 2 hours. Proximate analysis and ultimate analyses were done followed with physical and chemical analyses of the biochar before undergoing the sodium adsorption study. From the study, the fixed carbon was observed to increase from 11.75% to 70.62% (Bruguiera parviflora) and 9.04% to 72.92% (Gigantochloa levis) upon carbonization of the raw materials. These values correlated with the increasing C content of the samples, which also resulted in lower H/C value. It was found that biochar aromaticity and stability increased with increasing temperature. Additionally, Field Emission Scanning Electron Microscopy (FESEM) elucidated that higher pyrolysis temperature increased the porosity and surface area. The pH was observed to increase from 4.51 to 9.83. (B. parviflora) and 5.36 to 7.98 (G. levis). In Langmuir isotherm, biochar can adsorb exchangeable Na content up to 121.95 mg/g and (B. parviflora) and 49.15 mg/g (G. levis). These two biochar types were further studied at different application in incubation study for 35 days and application as soil amendment in Sonneratia caseolaris seedlings through a six-month study period at Kampung Sijangkang Mangrove Recreational Park, Telok Panglima Garang, Selangor. Five treatments were evaluated in this study: control (T1), 10% of B. parviflora biochar (T2), 20% of B. parviflora biochar (T3), 10% of G. levis biochar (T4), and 20% of G. levis biochar (T5). From the incubation study, both B. parviflora biochar and G. levis biochar can significantly increase the pH value of mangrove soil, while significantly reducing the EC of mangrove soil. Meanwhile, these two biochars can also significantly increase the SOM of mangrove soil. On the other hand, mangrove soil SAR has a strong positive correlation with Na+ content, a negative correlation with Ca2+ content, and almost no relationship with Mg2+ content. In nursery study, application of 20% of B. parviflora biochar (T3) were observed to give the highest plant height, stem diameter, biomass dry weight, root fresh weight, length of entire plant, length of primary root, and also possess low ROS (H2O2, OH-, MDA) and DPPH meanwhile high in (chlorophyll a, carotenoid, CAT, APX, DHAR, and FRAP potential) which signifies a good impact for the growth of the seedlings. These demonstrate the potential of the treatment as soil amendments to not only improve soil properties, but also improve Sonneratia caseolaris plants’ tolerance towards salinity stress. Other than that, numerus metabolites with antioxidant potential were induced in T3 compared to other treatments, which were shown to elicit notable responses in terms of metabolite production. To sum up, B. parviflora biochar gave the best quality of biochar and can improve the growth of mangrove plant seedlings where it can adsorb salinity, improve root growth and development, as well as scavenging the ROS, v improve enzymatic and non-enzymatic activities, which help to protect the seedlings from oxidative and salinity stress. In conclusion, this research demonstrates the positive impacts of biochar application as soil amendment on the growth performance, physiological features, and biochemical properties of Sonneratia caseolaris when cultivated in high salinity mangrove area.

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