Soil CO2 effluxes, temporal and spatial variations, and root respiration in shrub willow biomass crops fields along a 19‐year chronosequence as affected by regrowth and removal treatments

In shrub willow biomass crop (SWBC) production systems, the soil CO2 efflux (Fc) component in the carbon cycle remains poorly understood. This study assesses (i) differences of Fc rates among the 5‐, 12‐, 14‐, and 19‐year‐old SWBCs with two treatments: continuous production (regrowth) willow fields that were harvested and allowed to regrow, and willow fields that were harvested, killed, and then stools and roots were ground into the soil (removal); (ii) temporal and spatial variations of Fc rates; (iii) root respiration contributions to total Fc; and (iv) climatic variables affecting Fc. During the growing season (May to September), Fc rates showed no statistically significant differences across different ages (P = 0.664), and between treatments (P = 0.351); however, there was an interaction between age and treatment (P = 0.001). Similarly, during the dormant season (October to April), Fc rates revealed no statistically significant differences across different ages (P = 0.305) and treatment interaction with age (P = 0.097). Fc rates differed significantly (P