Temperature sensitivity of soil respiration to elevated temperature and nitrogen availability

Abstract

Plastic film mulching (PFM) and nitrogen (N) fertilization are two important agricultural management methods that are used to enhance crop yields in semi-arid dryland agriculture. However, the impacts of PFM and N fertilization on the temperature sensitivity (Q₁₀) of soil respiration (R_t), particularly its heterotrophic (R_h) and autotrophic (R_a) components, remain unclear. To investigate this, a trenching experiment was carried out between 2019 and 2021 in a rainfed maize-cultivated cropland that had been under cultivation for 7 years. There were four treatments: no PFM and N fertilization (control), full PFM without N fertilization (PFM), 150 kg N ha^–1 fertilization without PFM (Nfer), and full PFM with 150 kg N ha^–1 fertilization (PFM+Nfer). PFM and N fertilization not only enhanced crop yield and root biomass but also increased soil total respiration (R_t) and its components, due to improved soil hydrothermal conditions with PFM and increased N availability with N fertilization. Soil hydrothermal conditions and root biomass were identified as the most important factors influencing R_h and R_a, respectively. The greater increase in R_a (84 %–212 %) compared to R_h (9 %–29 %) resulted in a decrease in the proportion of R_h in R_t decreasing from 81.2 % in the control to 58 % under the PFM+Nfer treatment. The R_h/R_t ratio decreased in all three treatments compared to the control (p < 0.05). The increase in R_h under PFM led to a decrease in soil organic carbon (SOC) by 17 %. Specifically, the soil labile C content (i.e. LFOC 44 %) decreased more under PFM and PFM+Nfer (p < 0.05) compared to control, but not under the Nfer treatment (p > 0.05). Plastic film mulching increased the Q₁₀ of R_h (p < 0.05) through decrease the content of soil labile C, whereas N fertilization had no effect (p > 0.05). Both PFM and N fertilization increased the Q₁₀ of R_a (p < 0.05) by increasing root biomass. The impact of R_a’s Q₁₀ (0.66) on R_t’s Q₁₀ is greater compared to R_h’s Q₁₀ (0.31). To our knowledge, this is the first long-term field study to examine the response of R_t components and their Q₁₀ to PFM and N fertilization. Our results highlight that soil labile C and root biomass are the determining factors for the Q₁₀ of R_h and R_a, respectively. We emphasize the importance of accurately modeling the temperature responses of R_h and R_a when predicting R_t under climate change scenarios.