Elevated CO2 and temperature effect on canopy development and seed yield of sunflower (Helianthus anus L)

Climate is one of the main determinants of agricultural production. Throughout the world there is significant concern about the effects of climate change and its variability on agricultural production. The Intergovernmental Panel on Climate Change (IPCC) has predicted that the present atmospheric CO2 (aCO2) concentration (>400 ppm) may increase up to 660 ppm and 790 ppm in 2060 and 2090, respectively (IPCC, 2007 and 2014). This is expected to raise global temperatures due to the CO2 capacity to absorb infrared light and possibly change the precipitation patterns. Studies have shown a significant effect of change in climatic factors on the average crop yield (Seo and Mendelsohn, 2008). Sunflower being C3 crop responded significantly and positively with increased CO2 and temperature than C4 plants. The present study was conducted with an objective to identify the potential sunflower hybrid under elevated/ enhanced carbon dioxide and temperature concentration over aCO2. Experimental Setup

Climate is one of the main determinants of agricultural production. Throughout the world there is significant concern about the effects of climate change and its variability on agricultural production. The Intergovernmental Panel on Climate Change (IPCC) has predicted that the present atmospheric CO 2 (aCO 2 ) concentration (>400 ppm) may increase up to 660 ppm and 790 ppm in 2060 and 2090, respectively (IPCC, 2007 and2014). This is expected to raise global temperatures due to the CO 2 capacity to absorb infrared light and possibly change the precipitation patterns. Studies have shown a significant effect of change in climatic factors on the average crop yield (Seo and Mendelsohn, 2008). Sunflower being C 3 crop responded significantly and positively with increased CO 2 and temperature than C 4 plants. The present study was conducted with an objective to identify the potential sunflower hybrid under elevated/ enhanced carbon dioxide and temperature concentration over aCO 2 .

Experimental Setup
Controlled set of experiment was carried out to study the response of sunflower genotypes to elevated CO 2 (eCO 2 ) and temperature regimes under Open Top Chambers (OTC) at Center for Agro-climatic studies belongs to University of Agricultural Sciences, Raichur Karnataka during Kharif 2016. Four sunflower genotypes RSFH-1, KBSH-44, DRSH-1 and PAC-37904 were selected for the study. In each OTC and open field condition all hybrids were planted at 5.55 plants/m 2 . Different set of treatments comprised of eCO 2 @ 550 ± 25ppm, eCO 2 @ 550 ± 25ppm with 2ᴼC rise in temperature, aCO 2 @390 ± 25ppm with 2ᴼC rise in temperature, Reference open top chamber and reference plot in open field condition. Prevailed temperature, rainfall, relative humidity and sunshine hours were collected throughout the season. Collected data were analyzed by using Fisher's method of covariance at significance level of 5% as completely randomized design.

Crop period and weather condition
Daily maximum and minimum temperature, relative humidity, evaporation, rainfall was found optimum for crop growth. However distribution of rainfall during the experimental period was erratic for plants outside OTC. Even though experiment was conducted in controlled condition but open field plot was significantly influenced by prevailed weather. Experiment was irrigated both in inside and outside OTC's. The region is characterized by tropical high temperature during cropping period.

Plant height
Elevated CO 2 and temperature levels brought about significant difference in the height of sunflower across different hybrids. The RFSH-1 and KBSH-44 hybrids recorded taller plants (16.88 and 16.63 cm) in 550 ppm CO 2 treatment. Rate of increased plant height was observed between 45 to 60 days after sowing. Greater difference in plant height at 75 DAS was observed in DRSH-1 (8.5%) and PAC 37904 (7.0%). Irrespective of the CO 2 and temperature treatments dwarf plants were observed in PAC-37904 (Table  1). At CO 2 550 ppm, plant height much higher than CO 2 @550 ppm + 2 o C temperature rise. Whereas, plants grown in CO 2 @ 390 ppm with increased temperature was taller than rest of the treatments. This might be due to effect of eCO 2 and temperature levels which favoured cell elongation resulted in taller plants. Similar results on increased plant height under eCO 2 were reported by Das et al. (2020). Similar response of sunflower plant height among hybrids and eCO 2 and temperature rise was observed throughout the growing period.

Leaves per plant
Sunflower plant growth has primarily indicated by development of individual leaves. Elevated CO 2 generally Vol. 23, No. 2 resulted in increased biomass accumulation in leaves, stem and total. All the sunflower hybrids exhibited greater number of leaves per plant in the eCO 2 and temperature treatments.  (Table 1).
Jyothi Lakshmi et al. (2017) also reported eCO 2 has enhanced number and dry weight of leaves per plant as compared to aCO 2 .

Days to 50% flowering
The days to 50 per cent flowering in sunflower was recorded in all the genotypes under climate change treatments. Less number of days was taken for 50 per cent flowering by all genotypes under eCO 2 and temperature treatments. However, the genotypes RFSH-1 and PAC-37904 took least days (52.0 and 53.0 days respectively) for 50 per cent flowering under elevated climate change treatments. On contrary, these two genotypes took more days for 50 per cent flowering in the reference plot.

Days to maturity
The physiological maturity of a plant is an important factor in determining the yield of the plant. Early maturity was showed by all the genotypes grown under eCO 2 and temperature conditions, while, they showed late maturity in the aCO 2 and temperature conditions. The genotypes PAC-37904 and DRSH-1 matured very early at 82 and 84 days respectively, followed by RFSH-1 (88.0 days) and KBSH-44 (92.0 days) at eCO 2 and temperature conditions. However, more number of days for maturity were taken by the genotypes KBSH-44 (97.0 days) and followed by other three genotypes (92.0 days) in the aCO 2 and temperature treatments.

Yield attributes
The Head diameter of sunflower was taken at maturity under different climatic conditions. The genotypes showed more head diameter in the eCO 2 and temperature treatments when compared to ambient treatments. More head diameter was recorded by the genotypes DRSH-1 (19.75) and RFSH-1 (19.22) followed by  and  genotypes in the 550 ppm CO 2 with normal temperature treatment. Meanwhile, smaller heads with diameters 15.03 and 17.43 were recorded by  and PAC-37904 genotypes in the reference plot respectively (Table 3). Similar results in biomass and yield differences due to CO 2 concentration was reported by Jyothi Lakshmi et al. (2017).
Seed yield per plant of different genotypes were taken under different climatic conditions. More yield was recorded by DRSH-1 (26.55 g/plant) and RFSH-1 (25.98 g/ plant) under 550 ppm CO 2 with normal temperature treatment followed by 550 ppm with 2°C rise in temperature treatment in which the genotypes PAC-37904 and KBSH-44 recorded yield of 24.98 and 24.28 g/plant respectively. However, fewer yields were recorded under ambient treatments irrespective of the genotypes. The genotypes KBSH-44 and RFSH-1 recorded least seed yield of 22.98 and 23.08 g/plant in the ambient treatments (Table 3). Elevated CO 2 caused increase in crop growth and yield due to increased photosynthesis, decreased photorespiration (C 3 crops) and decreased stomatal conductance. Increase in CO 2 negates negative effect of rise in temperature up to certain degree. Under rain fed conditions, in spite of higher CGR, harvestable yield of sunflower will be reduced due to reduction in harvest index (Koocheki et al.,