Abstract
AbstractNitrate is a limiting resource in heathland acid soils. Nitrate levels increase in heathland soils after Pteridium aquilinum invasions, and this species is assumed to biologically control nitrogen cycle processes, thus increasing nitrate availability. We compared how P. aquilinum (bracken) and Erica cinerea (bell heather) modify processes driving nitrate availability along a soil pH gradient in a Natura 2000 reserve facing bracken invasion. Soil nitrate and ammonium concentrations, substrate‐induced respiration (SIR), denitrification and nitrification enzyme activities (DEA and NEA, respectively), root procyanidin concentrations, and denitrification inhibition by procyanidins were measured on five sites under P. aquilinum and E. cinerea stands. NEA and nitrate levels were higher, and ammonium levels and SIR lower, for P. aquilinum in the most acid soils. Procyanidins from both species induced the same level of denitrification inhibition, soil nitrate being correlated with root procyanidin concentration for both species. Soil nitrate correlated with NEA only for P. aquilinum. Our results show that both species increased procyanidin production in the most acid soils, thereby reducing denitrification and decreasing nitrate loss, this process being more efficient for E. cinerea. However, P. aquilinum additionally increased nitrification, and this double control on nitrification and denitrification was very efficient to increase soil nitrate availability in the most acid soils. This may participate to the success of P. aquilinum invasions in heathlands. This shows that approaches for bracken control in heathlands should better account for belowground processes and, more generally, that biological denitrification inhibition by plants may be a widespread phenomenon influencing soil N dynamics in N‐poor environments.
Highlights
Nitrogen (N) is a major factor that limits plant growth in many terrestrial ecosystems (Vitousek and Howarth 1991, LeBauer and Treseder 2008)
Our results suggest that changes in soil NO3À and NH4+ concentrations are driven by several controls acting on nitrification and denitrification depending on the plant species and that P. aquilinum has developed a biocontrol strategy of these N cycle processes, which is more efficient than the strategy developed by E. cinerea to enhance soil NO3À availability
When applied at the same concentrations and tested on Pseudomonas brassicacearum, procyanidins extracted from roots of both species did not differ in biological denitrification inhibition (BDI) efficiency. These results suggest that E. cinerea inhibits denitrification more than P. aquilinum, mainly because of a higher procyanidin production, which is consistent with the lower Denitrifying enzyme activity (DEA)/substrate-induced respiration (SIR) ratio observed for this species
Summary
Nitrogen (N) is a major factor that limits plant growth in many terrestrial ecosystems (Vitousek and Howarth 1991, LeBauer and Treseder 2008). The N used by plants is mainly in the form of amino acids, NO3À, and NH4+ (Boudsocq et al 2012), and the competition between roots and microorganisms for these N forms is intense (Hodge et al 2000, Kuzyakov and Xu 2013). Et al 2006, Le Roux et al 2013), sometimes through the release of specific compounds by roots (Subbarao et al 2009, DeLuca et al 2013, Dietz et al 2013, Bardon et al 2014, Srikanthasamy et al 2018).
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