Does repeated biochar incorporation induce further soil priming effect?

Purpose
Positive priming effect following the incorporation of biochar may partially reduce the biochar-induced soil carbon (C) sequestration. We hypothesize that repeated biochar incorporations induce further priming effect in the soil that was already amended with biochar.

Materials and methods
Two biochars prepared from Miscanthus giganteus at 350 and 700 °C, at a rate of 50 g C kg−1 soil, were added into the soil previously received each biochar separately with a pre-incubation of 1.5 years.

Results and discussion
The second addition of fresh biochar caused 108 and 26.9 μg CO2-C g−1 soil of soil C losses, which is the same order but less amount (about 72 and 56%) of C losses as the first biochar addition. This might be due to the depleted soil C after 1.5 years of incubation. Also, it might be attributed to the altered soil microbial community with lower proportions (%) of gram-positive bacteria, and higher proportions of fungi, actinobacteria and gram-negative bacterial phospholipid fatty acids (PLFAs) with repeated biochar addition.

Conclusions
Our research provided insights into the second addition of biochar-induced priming effects and responsible PLFAs.