Soil <scp><scp>CO₂</scp></scp> 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

Abstract

Abstract In shrub willow biomass crop ( SWBC ) production systems, the soil CO 2 efflux (F c ) component in the carbon cycle remains poorly understood. This study assesses (i) differences of F c rates among the 5‐, 12‐, 14‐, and 19‐year‐old SWBC s 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 F c rates; (iii) root respiration contributions to total F c ; and (iv) climatic variables affecting F c . During the growing season (May to September), F c 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), F c rates revealed no statistically significant differences across different ages ( P = 0.305) and treatment interaction with age ( P = 0.097). F c rates differed significantly ( P &lt; 0.001) among different times of the day and times of the year. F c rates, between 00 and 1059 h, between 1100 and 1659 h, and between 1700 and 2400 h displayed consistency from May to November; however, F c rates in these three time intervals showed significant differences ( P &lt; 0.0001). In December, F c rates remained constant over 24 h. F c rates demonstrated higher temporal and spatial variations among willow age classes than between regrowth and removal treatments. Temporal and spatial variations of F c were higher during the dormant season than during the growing season. The proportion of root respiration to total F c ranged from 18 to 33% across age classes. F c rates showed strong association with soil and air temperatures, and relative humidity.