Abstract
This study is to test the effects of Bt gene introduction on the foliar water/nitrogen use efficiency in cotton. We measured leaf stomatal conductance, photosynthetic rate, and transpiration rate under light saturation condition at different stages of a conventional cultivar (zhongmian no. 16) and its counterpart Bt cultivar (zhongmian no. 30) that were cultured on three levels of fertilization, based on which leaf instantaneous water use efficiency was derived. Leaf nitrogen concentration was measured to calculate leaf photosynthetic nitrogen use efficiency, and leaf δ13C was used to characterize long term water use efficiency. Bt cultivar was found to have lower stomatal conductance, net photosynthetic rates and transpiration rates, but higher instantaneous and long time water use efficiency. In addition, foliar nitrogen concentration was found to be higher but net photosynthetic rate was lower in the mature leaves of Bt cultivar, which led to lower photosynthetic nitrogen use efficiency. This might result from the significant decrease of photosynthetic rate due to the decrease of stomatal conductance. In conclusion, our findings show that the introduction of Bt gene should significantly increase foliar water use efficiency but decrease leaf nitrogen use efficiency in cotton under no selective pressure.
Highlights
As the most important commercial crop in China, cotton is the main consumer of agricultural water[2]
Leaves are the organ completing the processes of both water transpiration and CO2 sequestration; the ratio of photosynthetic rate to transpiration rate is often used to characterize instantaneous water use efficiency (IWUE)
Carbon isotope composition (δ13C) has been widely used to characterize the long term water use efficiency (LWUE) because it is associated with the ratio of CO2 partial pressure within the leaves (Pi) to the CO2 partial pressure outside the leaves (Pamb)
Summary
Three fertilizer levels were set up as 50%, 100% and 150% of regular level according local peasant’s experience. The factorial experiment consists of two factors (cultivar and fertilizer level) that had two and three levels, respectively, forming six treatments in total. At FPS, 3 individuals from each treatment were randomly selected and one flag leaf of each individual was used to measure photosynthetic parameters including net photosynthetic rate (Pn, μmolCO2·m−2·s−1), transpiration rate (E, μmolH2O·m−2·s−1) and stomatal conductance (Gs, molH2O·m−2·s−1). At BBOS and BOPS, we randomly selected one flag leave on each tagged individual to perform measurements. For each tagged individual, different leaves were measured at different stages since it is hardly possible to keep all leaves alive during the whole growing season.
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