Can hydrochar and pyrochar affect nitrogen uptake and biomass allocation in poplars?
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Positive effects of pyrochar on soil nutrient availability and plant growth are widely reported in literature. However, few studies have reported effects of hydrochars on plant nutrition. A pot trial was conducted over a period of 2 years to investigate the effect of a pyrochar (AGT) and a hydrochar (HTC) on poplar (Populus × generosa, clone AF8) growth, biomass allocation and nitrogen (N) uptake with special emphasis on the quantification (using an isotopic mass balance approach) of char-derived nitrogen (CDN) absorbed by plants. We found that both pyrochar and hydrochar positively affected above-ground biomass productivity in the first year, and biomass and nitrogen (N) allocation over the 2 years by reducing the allocation of resources to fine roots. By the end of the experiment, even though the total N uptake was not affected by char, the CDN was more than 24% of the total N absorbed by HTC-treated plants compared to a negligible amount absorbed by AGT-treated ones. Finally, char did not affect nitrogen use efficiency (NUE) in the first year of growth, but by the end of the experiment, NUE was higher in the above-ground biomass of HTC-treated than in AGT- and control poplars.