The characteristics of ecosystem respiration and its components of a representative film-mulched and drip-irrigated cotton field in Northwest China

Abstract

Ecosystem respiration (Re) is the largest terrestrial carbon flux into the atmosphere; thus, investigating its characteristics is a prerequisite for understanding the global carbon balance. Croplands are important in regulating regional and global carbon cycles, given their unique role as humans’ food source. The widely used film-mulched and drip-irrigation (FMDI) for the water-saving purpose has clear benefits for promoting crop production, but the impact of FMDI on Re and its components remains rarely explored. The objective of this study is to evaluate the characteristics of Re and its above-ground autotrophic (Raa), below-ground autotrophic (Rab), and heterotrophic (Rh) components in an FMDI cotton field in an oasis of Northwest China. To achieve this, we measured Net Ecosystem Exchange (NEE) with the atmosphere using the eddy covariance from 2012 through 2016 and partitioned it into Gross Primary Productivity (GPP) and Re using the nighttime method; in 2016, we used chamber-based technique to measure Rh and total soil respiration (Rs), and used their relationships with soil temperature and moisture to construct continuous records to estimate the annual soil CO2 effluxes for the five years. Results showed that the mean annual Re was 1340 g C m−2 yr−1, with Raa, Rab, and Rh accounting for 24%, 24%, and 52%, respectively. Rs was the dominant part of Re compared with the Raa; Rh accounted for 68% of Rs, and Rab accounted for only 32% of Rs due to the low root ratio. Our results suggested that the unique soil temperature and moisture conditions generated by FMDI generally stimulate heterotrophic respiration more than autotrophic respiration. This study contributes important knowledge of Re and its components in the FMDI cotton field and helps better understand how FMDI may impact the regional carbon balance.