Co-regulation of temperature and moisture in the irrigated agricultural ecosystem productivity

Agroecosystem photosynthesis is key to coping with global climate change. In farmland where human activities are highly involved, the interaction between environmental factors and their influences on gross primary pro-ductivity (GPP) are insufficiently understood. Particularly, the irrigation and mulching in water-saving agri-culture can alter the crop responses to environmental change. Based on eddy covariance measurements of maize fields under mulched drip irrigation (DM) and mulched border irrigation (BM) in arid areas of Northwest China from 2014 to 2018, we systematically studied the interaction between multiple environmental factors and their independent effects on GPP using structural equation modeling, partial correlation coefficient and decoupling analysis by bins. The top three factors exerting the largest total effects on the GPP were soil temperature (Ts), canopy temperature (Tc) and vapor pressure deficit (VPD), among which Ts (0.75) and Tc (0.66) had the largest total effect on GPP under DM and BM, respectively. The independent effects of Ts, soil water content (SWC) and VPD on GPP were different under the two irrigation methods. SWC after excluding the influence of Ts showed a negative effect on GPP under DM (-1.24 g Cm(-2)d(-1)), while a positive effect under BM (0.02 g Cm(-2)d(-1)). By contrast, SWC after excluding the influence of VPD showed a positive effect on GPP under DM (0.59 g Cm(-2)d(-1)), while a negative effect under BM (-0.05 g Cm(-2)d(-1)). Interestingly, higher Ts, lower SWC and higher VPD had the potential to increase GPP under the two irrigation methods. We also found that the total effects of irrigation and VPD as well as the indirect effects of environmental factors on GPP should not be ignored. Our study will provide important reference for dealing with the effect of high temperature and drought stress on agro-ecosystem GPP and evaluating the response of vegetation to environmental factors.

Automated summary

Agroecosystem photosynthesis is crucial for addressing global climate change. The interaction between environmental factors and their effects on gross primary productivity (GPP) in farmland, particularly in water-saving agriculture, remains insufficiently understood. This study on maize fields in Northwest China found that soil temperature, canopy temperature, and vapor pressure deficit had the greatest impact on GPP, and the effects of irrigation and mulching varied under different methods.