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The present programme “Influence of elevated CO 2 on zinc dynamics in rice (Oryza sativa L.)” was undertaken in the Department of Plant Physiology, College of Agriculture, Vellayani during 2018-2020 with the objective of assessing the impact of elevated CO2 on growth, development and nutritional quality of rice in relation to modifications in Zn dynamics.

The extent of variation in growth, physiological, biochemical parameters and parameters related to Zn dynamics were assessed in two rice genotypes, Uma (MO16) and Njavara-golden yellow. Plants were maintained under three CO2 conditions i.e., OTC (Open Top Chamber) (500 ppm), Polyhouse (420 ppm) and open field condition (390 ppm) with four zinc enrichment treatments (D1- Foliar spray (ZnSO4 0.5% at panicle initiation and grain filling stage); D2-AMF (3g of AMF inoculum /cavity of protrays); D3-Seed treatment: seed priming with 6.4% ZnSO4 for 36 hrs; D4-control) with the aim to improve the zinc status of rice plants. The experiments were laid out in CRD with 24 treatment combinations and three replications.

The study indicated that upon exposure to 500ppm CO2, highest values were recorded in plant height, no. of tillers, root weight and straw yield in the case of both varieties. The treatment with 0.5% ZnSO4 foliar spray (D1) recorded highest plant height (102cm), no. of tillers (34) and straw yield, (35g/plant) in Uma and in Njavara the same treatment resulted in highest plant height (130cm), no. of tillers (32) and straw yield (46.8g/plant). AMF treatment (D2) has recorded highest root weight both in Uma (26.7g/plant) and Njavara (20.4g/plant). The no. of days to 50% flowering was increased under OTC (85 days in Uma and 71 days in Njavara) and Polyhouse (80 days in Uma 69 days in Njavara) as against 72 days in Uma and 61days in Njavara under open field condition.

Physiological and biochemical parameters recorded at active tillering and grain filling stage had shown that OTC condition resulted in highest total chlorophyll content (2.33 mg g-1 fresh weight), photosynthetic rate (27 µmol CO 2 m -2s-1) and total reducing sugars (1.9 mg g-1) at active tillering stage. The same trend was observed in grain filling stage also but to a lesser extent in total chlorophyll content (1.805 mg g-1 fresh weight) and photosynthetic rate (17.6 µmol CO 2 m -2s-1) whereas the total reducing sugars (6.3 mg g-1) was increased to a greater extent. However the photosynthetic rate and total chlorophyll content were decreased at grain filling stage in all the three CO2 conditions. Lowest total soluble protein was recorded under OTC in active tillering stage (0.8 mg g-1) and grain filling stage (7.1 mg g-1). All the Zinc treatments had significant influence on all the above parameters and foliar spray with 0.5% ZnSO4 resulted in maximum enhancement. The transpiration rate and stomatal conductance which was decreased under eCO2 did not show significant difference upon application of Zn treatments in both the varieties.

Yield attributes and Zn content in grain and bran could not be recorded as there was no grain development in plants under OTC due to high temperature. The parameters related to zinc dynamics were analyzed in leaf and shoot under all the conditions. Decreasing levels of zinc in leaf and shoot with increasing levels of CO2 was evident in both the varieties of rice in the present study in untreated plants. Though all the zinc treatments were having positive influence on Zinc status, foliar application of 0.5% ZnSO4 was found to be the most effective one followed by seed treatment and AMF. The zinc content in leaf was highest in D1 with 25.8 μg g-1 in Uma and 26.1μg g-1 in Njavara. Similarly, the zinc content in shoot was also recorded highest in D1 with 25.4 μg g-1 in Uma and 26 μg g-1 in Njavara followed by D3 and D2.

In the present study, increasing concentration of CO2 was found to enhance growth and development in rice variety Uma and Njavara by inducing increased photosynthetic rate, chlorophyll and reducing sugars content but at the same time it had a negative influence on Zinc content leaf and shoot tissue which was decreased due to the accumulation of more no. of carbohydrates which has diluted the Zn concentration in the leaf and shoot tissue in the untreated plants. Supplement of zinc through different treatments has elevated the zinc content in the leaf and shoot tissue in all the three different CO2 conditions.

These results offer a small slice of the broad implications for the impact of higher CO2 on nutrition and health. Taken together, CO2 induced nutritional declines could produce a major headwind on progress towards alleviating malnutrition and deserves attention and concerted action.


The information generated will help farmers to raise quality produce with the help of low cost technologies, to make paddy cultivation more profitable and can also be an answer to the serious health crisis and malnutrition faced globally in this changing climatic scenario.