Effects of soil amendments on growth performance, physiological and biochemical properties of Melastoma malabathricum L. grown on tropical acidic soil / Lili Syahani Rusli

Lili Syahani , Rusli (2024) Effects of soil amendments on growth performance, physiological and biochemical properties of Melastoma malabathricum L. grown on tropical acidic soil / Lili Syahani Rusli. PhD thesis, Universiti Malaya.

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Abstract

Soil acidity, primarily caused by the leaching of basic cation, acid deposition and the decomposition of organic matter led to a decrease in soil pH. Growth under an abiotic stress environment, particularly on low soil pH, typically decreases the growth performance of a plant. Among the plant species, Melastoma malabathricum L., or sendudok has adapted to thrive in tropical acidic soil conditions and it successfully stabilizes the problematic soil, prevents landslides, and enhances the aesthetic values of the landscape. However, its adaptation to low pH and fertility resulted in a lower growth rate and shallow root profile. To ameliorate this downside, soil amendments can be applied. Organic wastes from the food waste and palm oil industries can be turned into compost and biochar and used as soil amendments to enhance the soil quality and growth performance of plants grown on infertile acidic soil. Thus, this study aimed to elucidate the effect of soil amendments on growth and nutrient uptake through a six-month study period at the Rimba Ilmu glasshouse, Universiti Malaya. Eight treatments were evaluated in this study; control (Q), palm kernel biochar (B), a combination of liming and palm kernel biochar (BL), a combination of food waste compost and palm kernel biochar (BC), a combination of liming, food waste compost and palm kernel biochar (BCL), food waste compost (C), liming (L) and a combination of liming and compost (CL). The best two treatments, PK biochar (B) and FW compost (C) were further evaluated in terms of plant’s cellular antioxidant, oxidative stress indicators and the distribution of metabolites. Treatment with B showed the best growth in terms of M. malabathricum L. height, stem diameter, leaf area index, root length and root length density. In physiological performance, treatment C recorded a significantly higher rate of photosynthesis and relative chlorophyll content by 16% and 154%, respectively in comparison to the control. For soil analysis, both treatments B and C showed comparable results. Treatment C and B also showed improved H2O2 level in all parts of the plant. The enzymatic antioxidants activities and non-enzymatic antioxidants were also higher in treatment C. In addition, the same treatment exhibited the highest total anthocyanin content (leaves; 36.1 x 10-2 ± 0.034 mg/g DW and root extract; 8.9 x 10-2 ± 0.020 mg/g DW), total phenolic content (stem extract; 4930.956 ± 16.025 mg GAE/g DE) and total flavonoid content (stem extract; 209.984 ± 0.572 mg QE/g DE). The M. malabathricum L. plants that were grown without soil amendment, (Q) recorded the highest number of metabolites (leaves; 57 and root extract; 40) followed by treatment C (leaves; 46 and root extract; 31) and treatment B (leaves; 26 and root extract; 31). The findings of this study indicate that the PK biochar, followed by FW compost substantially enhanced the growth and physiological characteristics of M. malabathricum L., resulting in taller plants, larger stem diameters, increased root length and density, and enhanced chlorophyll content and photosynthesis. The soil analysis revealed that the use of PK biochar and FW compost retained nutrients, enhanced soil pH, and increased water retention, but lime had a higher nutrient absorption rate. Concerning oxidative stress indicators, the treatment with FW compost and PK biochar enhanced the plant's antioxidant defense system against oxidative damage by increasing the activities of antioxidant enzymes such as SOD and APX, as well as the synthesis of antioxidant metabolites such as chlorophylls, carotenoid, ascorbic acid, anthocyanin, phenolic and flavonoid compounds, compared to control plants. These demonstrate the potential of both treatments as soil amendments to not only improve soil properties, but also improve M. malabathricum L. plants’ tolerance towards abiotic stress (soil acidity). In conclusion, this research demonstrates the positive impacts of food waste compost, followed by palm kernel biochar as soil supplements on the growth performance, physiological features, and biochemical properties of M. malabathricum L. when cultivated in acidic soil. The effect of these discoveries include boosting plant growth in environments where abiotic stress is present and improving the soil fertility.

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