Biological inhibition of denitrification (BDI): an early plant strategy for Fallopia x bohemica seedling development

Background and aims: The successful plant Fallopia x bohemica presents interesting capacities for the control of soil nitrogen cycle at the adult stage, named the biological denitrification inhibition (BDI). BDI strategy allows the plant, through the production of secondary metabolites (procyanidins), to compete with denitrifying microbial community and to divert, to its benefit, the nitrate from soil. This study aims to analyze whether seedlings of F. x bohemica, can implement BDI at the seedling stage. We also determined whether soil nitrogen availability influence the implementation of BDI and seedling growth.

Methods: We sowed achenes of F. x bohemica in soils representing a nitrogen gradient (6 treatments) and harvested seedlings after twenty and forty days of growth. The denitrification and related microbial communities (i.e., functional gene abundances of nirK and nirS), soil parameters (nitrate content and humidity) and plant performances (biomass, growth and root morphology) were determined.

Key results: On soil without nitrogen addition, BDI was observed after twenty days of growth, whereas a stimulation of denitrification was found after forty days. The increase of soil N content had few effects on activity and structure of soil denitrifying community and on the plant biomasses or the relative growth rates. Correlations between plant and microbial parameters were observed after 20 days of growth reflecting early and strong chemical interactions between plants and denitrifying community, which decreased with plant growth after 40 days.

Conclusions: This study shows that an early in the first weeks of growth, and then to a change to a root conservative strategy after 40 days. This switch to a conservative strategies involved resource storage, an altered allocation to aboveground and belowground parts and an investment in fine roots. It now seems clear that this storage strategy starts very young with an early BDI establishment, allowing this clonal plant exceptional storage and multiplication capacities.