Annual ecosystem respiration of maize was primarily driven by crop growth and soil water conditions

In the context of global warming, carbon dioxide emissions have become a global concern. Cropland respiration is an important component of carbon dioxide emissions from terrestrial ecosystem. A large number of studies have investigated cropland respiration, although many controversies remain about its interannual variations and mechanisms. In this study, an eddy covariance instrument was used to observe carbon fluxes in a maize field for four consecutive years (2014-2017) in the arid region of Northwest China. The night-time respiration rates measured by eddy covariance were used to validate the accuracy of the Van't Hoff, Arrhenius, and Taylor models in estimating the respiration rate of a maize field. All three models performed well, although the Van't Hoff model had the highest accuracy. The three models were used to simultaneously estimate the respiration rate of the maize field throughout the growth season. The results showed that in the years 2014, 2015, 2016, and 2017, the annual respiration rates were 485, 1063, 711, and 651 g m(-2)y(-1), respectively. Surprisingly, the respiration rate in 2015 was markedly higher than that in the other three years, and the values were 119%, 49%, and 63% higher than the rates in 2014, 2016, and 2017, respectively. To interpret this observation, this article analyzed the relationships between the respiration rate in the maize field ecosystem and the maximum leaf area index, air temperature, soil surface temperature, and soil water content. The results show that at the interannual scale, the ecosystem respiration showed significant linear positive correlations with the maximum leaf area index and soil water content. The highest values for canopy area, net radiation, irrigation rate, and soil water content were observed in 2015; the crop biomass in 2015 was also greater than that in the other three years, which significantly increased the crop respiration and caused 2015 to have the highest respiration rate. The results showed that at the interannual scale, crop growth and soil surface water conditions were the critical determinants of respiration. This study provided a new perspective and a basis for an in-depth understanding of the mechanism of carbon dioxide emission in croplands.