Responses of Soil Respiration to Biotic and Abiotic Drivers in a Temperate Cropland

To investigate the temporal dynamics of CO2 efflux from the soil surface in a temperate cropland and to quantify the effects of soil temperature, soil water content, N fertilization and plant growth on soil carbon dioxide efflux (R-s) field and lab experiments were performed. The field experiment was conducted in a cropland site with a conventional farming system in Central Hungary. The temporal changes of R-s were estimated using a closed chamber IRGA system about bi-weekly/monthly between November 2017-November 2019 in 10 positions. The measured average soil CO2 efflux values ranged from 0.06 +/- 0.007 to 7.04 +/- 0.44 mu mol CO2 m(-2) s(-1) Soil respiration model including soil temperature (T-s), soil water content (SWC) and the incorporation of VIgreen (plant growth and functioning) gave a higher goodness-of-fit value (r(2) = 0.54) than the simple temperature response. According to our field results, different variables including T-s, SWC and VIgreen play a principal role in the carbon cycle of the investigated cropland. We further investigated the effects of the main drivers in a laboratory experiment with the same soil. Closed chamber technique was used for measuring the emission of carbon dioxide by a Picarro G1101-i gas analyzer. We also introduced a fertilization experiment: three different N treatments were applied (N0, N75 and N150) with different levels of soil water content on the soil planted with maize and bare soil. According to our laboratory results, the cumulative CO2 efflux from soil was found to have a positive correlation with plant growth and with N fertilizer rate: as higher plant biomass and more N added, more CO2 was emitted, whereas, the cumulative emissions values from planted soil were around two times higher than in bare soil in all treatments. Significant positive correlations were found between CO2 efflux and SWC indicating that the soil water content was the main factor limiting the rate of the CO2 emission from soil in both planted and bare soil, in which the cumulative CO2 efflux was increased with the increase in soil water content, and it was almost three times higher in planted soils at higher soil moisture level than in the bare soil. We can conclude that the effects of plant presence and soil moisture on soil respiration had similar magnitude; however, the effect of N addition was small.