Canopy Structure And Leaf Senescence In Different Genotypes Of Foxtail Millet During Grain Filling

Foxtail millet is the main corp in arid and semi-arid of northern China because it is drought resistance, barren endurance and high water use efficiency. Drought is the main factor which influences the yeild and quality of foxtail millet.The effects of drought stress on different genotypes of foxtail millet are diverse. Optimal canopy structure could improve canopy internal ventilation and illumination and increase crop yield. The photosynthetic capacity of top three leaves significantly affect the yield formation during filling period. Antioxidant enzymes are able to scavenge active oxygen, delay leaf senescence, and maintain physiological functions of leaves. Therefore, investigating activated oxygen metabolism and canopy structure in different drought-resistance types of foxtail millet, could improve water usage efficiency and yield of foxtail millet.This study employed different drought-resistant types of foxtail millet as materials, linking field experiments and laboratory analysis to investgate activated oxygen metabolism, photosynthetic performance and canopy structure. Then, prediction models of chlorophyll content and leaf area index were established. The study reached the following main results.(1) Under drought conditions, there are significant differences in metabolic senescence in different genotypes of foxtail millet. The chlorophyll content, soluble protein content, SOD activity, POD activity and CAT activity of drought-resistant and high-yeild(DRHY) type were significantly higher than drought-resistant and low-yeild(DRLY) type and drought-sensitive(DS) type. Compared with top second leaf and top third leaf, the antioxidant enzyme activity were higher and cell membrane lipid peroxidation were lower in the flag leaf. the activity of top three leaves were ordered as follow, the flag leaf>top second leaf>top third leaf. Compared with top second leaf and top third leaf, the antioxidant enzyme activity were higher and cell membrane lipid peroxidation were lower in the flag leaf. The activity of top three leaves were ordered as follow, the flag leaf>top second leaf>top third leaf. The leaves of DRHY type foxtail millet senescence slowly, which is the basis for high yield.(2) Under drought conditions, there are significant differences in yield in different genotypes of foxtail millet. The average yield of DRHY was the highest. It was 6937.53 kg·hm-2. The average yield of DRLY was in the middle. It was 5940.01 kg·hm-2. The average yield of DS was the lowest, it was 5194.98 kg·hm-2. Correlation analysis showed that chlorophyll content in flag leaf, soluble protein content, SOD activity, POD activity were positively correlated with yield, GPS and 1000-grain weight. O-2 content and MDA content were significantly negatively correlated with yield, GPS and 1000-grain weight. The result showed that active oxygen metabolism and millet production are closely linked. When the antioxidant of leaves was stronger, the metabolism was faster, and the yield was higher.(3) Under drought conditions, the temperture of DRHY type was low. The average relative canopy temperture was-1.44°C. The temperture of DRLY was higher. The average relative canopy temperture was 0.21°C. The temperture of drought-sensitive and high-yield(DSHY) and drought-sensitive and low-yield(DSLY) were the highest. The relative canopy temperture was 1.08°C and 2.12°C, respectively.(4) Average PAR in canopy decaied down from the top. The attenuation of PAR is rapid in the upper canopy and slow down in the middle and lower canopy. Upper 1/3 region of canopy was the variation region. 75% PAR was absorbed in this region. The PAR absorption of DRHY type was stronger. PAR transmittance at 2/3 region of DRHY type was 21.83%, 42.99% and 62.10% lower than DRLY, DSHY and DSLY, respectively.(5) The correlation between spectrum of foxtail millet canopy and chlorophyll content and LAI was studied. The result showed that the chlorophyll content was significant correlated with spectrums of the wavelength 499-577 nm, 577-597 nm, 597-622 nm and 623-659 nm. Correlation coefficient was 0.760-0.856. The LAI was significant correlated with spectrums of the wavelength 517-620 nm and 697-726 nm. Correlation coefficient was 0.7-0.771. based on the correlation analysis, prediction models of chlorophyll content and leaf area index were established.