In order to explore the relationship between photosynthetic index and the variation of CO2 concentration in the rhizosphere of cotton soils with different salinity contents

four different salinity treatments (CK:0%

F1:0.2%

F2:0.4%

F3:0.6%) were set

and the variation of soil CO2 concentration and photosynthetic characteristics of cotton under two soil texture (sandy soil and loam soil) were studied in barrel cultivated cotton. The results showed that with the development of cotton growth period

the CO2 concentration of the two soil textures both increased first and then decreased

and the peak values appeared at the flowering and boll stage

and the maximum CO2 concentration was 17 061.95 μmol/mol in loam and 17 572.00 μmol/mol in sandy soil. Under the salt treatments

the soil CO2 concentration of the two soil textures both increased with the increasing of soil depth. The average value of soil CO2 concentration at 50 cm soil depth was 13 540.32 μmol/mol

which was nearly two times that of the surface layer at 10 cm depth. With the increasing of salinity content

the difference of CO2 concentration between the two texture soils was significant

both of them showed a downward trend

and the CO2 concentration of loam soil was significantly higher than that of sandy soil. The interaction between salinity content and soil texture had extremely significant effects on net photosynthetic rate (Pn) of cotton (P<0.01). Under the same soil texture condition

Pn of cotton showed a downward trend with the increasing of salinity content at different growth stages

and reached the minimum value in F3 treatment

but the effect of low salinity content on cotton photosynthesis index was not significant (P>0.05). Under the same salinity treatment

there was significant difference in Pn of cotton between different soil textures

showing loam > sandy soil. There was a close correlation between CO2 concentration of two soil textures and cotton net photosynthetic rate under different salinity treatments

and cotton Pn could explain 81.2% of the variation of CO2 concentration in rhizosphere soil

which indicated that salinity content and soil texture type affected soil CO2 concentration through cotton net photosynthetic rate. The results could provide a theoretical reference for the growth environment of crop.