B Quantification of gene copy numbers b With respect to quantification of gene copy numbers, one additional reference should be included. With respect to N fertilization, the experimental setup should be adjusted as follows: Through the course of the experiment, plants were regularly fertilized with N ( B 80 kg N ha b SP B -1 b sp B as urea at month 6, and 160 kg N ha b SP B -1 b sp B as (NH b SB B 4 b sb B ) b SB B 2 b sb B SO b SB B 4 b sb B at month 12 b ) to stimulate soil nitrification potential. [Extracted from the article]