Alleviation Of Pyroligneous And Geniposide On Cotton Seedlings Alkaline Stress

China has a large area of saline-alkali land,and developing cotton planting technology in such lands is one of the important strategy to ensure the sustainable development of cotton production.Using HM3097（Gossypium hirsutum L.）as the experimental material,present study was conducted to investigate the mechanism of impairment caused by Na₂CO₃（0,5 m M,10 m M,15 m M,20 m M）stress on cotton seedlings,and explored the efficacy of foliar-applied pyroligneous(0,1 m L L^-1,2 m L L^-1,3 m L L^-1,4 m L L^-1)or geniposide(0,2.5 mg L^-1,5 mg L^-1,7.5 mg L^-1,10.0 mg L^-1)in mitigating Na₂CO₃（15m M）stress in cotton seedlings,and provide scientific basis for cotton planting technology in saline-alkali soil.The main results are as follows:1.Na₂CO₃ stress inhibited the growth of cotton seedlings.On the 25th day after transplanting,the plant height,stem diameter,leaf area,and root surface area of cotton seedlings decreased,while the root-shoot ratio increased.As result of gradual increase of Na₂CO₃ concentration,the root length,root volume,and dry weight of roots,stems,and leaves of seedlings first increased and then decreased.However,Na₂CO₃ stress led to,an increase in malondialdehyde（MDA）content,reactive oxygen species（O₂^-,H₂O₂）,Na⁺content,osmoprotectants（soluble sugars,soluble proteins,free proline）accumulation,and antioxidant enzyme（SOD,POD,CAT）activity in cotton seedling leaves,but resulted in a decline of K⁺/Na⁺content.On other hand,the Ca²⁺content,chlorophyll content,chlorophyll a/b ratio,net photosynthetic rate（Pn）,stomatal conductance（Gs）,and transpiration rate（Tr）first increased and then gradually decreased with soaring level of alkaline stress.Mild stress of Na₂CO₃（5 m M）can promote the root growth of cotton seedlings.2.Foliar application of pyroligneous or geniposide mitigated the Na₂CO₃（15 m M）stress in cotton seedlings.Foliar-applied pyroligneous(3 m L L^-1)or geniposide(7.5 mg L^-1)improved leaf chlorophyll content,chlorophyll a/b ratio,Pn,Gs,Tr,osmoprotectants content,antioxidant enzymes activity,K⁺,Ca²⁺content,and K⁺/Na⁺of cotton seedlings under Na₂CO₃ stress.Contrary,foliar spray of pyroligneous or geniposide decreased the MDA content,reactive oxygen species,and Na⁺content in cotton seedlings,and enhanced plant growth in terms of better plant height,stem diameter,leaf area,root length,root surface area,root volume,and dry biomass of roots,stems,and leaves.It can be seen that Na₂CO₃-induced stress causes oxidative damage,osmotic stress,and ionic toxicity which affects enzyme catalysis,photosynthesis,and other metabolic processes and ultimately inhibits the growth of cotton seedlings.Foliar-applied pyroligneous(3 m L L^-1)or geniposide(7.5 mg L^-1)attenuated the inhibitory effects of alkaline stress on cotton seedling growth by scavenging oxidative damage and ion toxicity and improving osmoregulation,antioxidants activity,and photosynthetic capacity.