Cryptogams and dwarf evergreen shrubs are vulnerable to nitrogen addition in a boreal permafrost peatland of Northeast China

Abstract

AbstractAimBoreal peatlands are very sensitive to nitrogen (N) enrichment due to the low soil N availability. Our aim was to reveal how increased N availability altered plant composition in boreal permafrost peatlands with dense vascular plants (>50%).LocationGreater Khingan Mountains, Northeast China.MethodsA nitrogen addition experiment with four N addition levels (0, 3, 6, and 12 g N m−2 year−1) was conducted in a poor fen in the continuous permafrost zone with vascular plant coverage above 60%. Plant diversity, community composition, and above‐ground biomass were investigated after four, six, and eight years of N addition.ResultsNitrogen addition decreased species richness and diversity but enhanced total above‐ground biomass. Plant height determined the plants’ responses to N addition, and the magnitudes increased with N addition level and experimental duration. The relative coverage of high‐stature (>50 cm) species increased, but the relative coverage of low‐stature (<50 cm) species decreased with elevating N addition levels. When N addition proceeded, the relative coverage and above‐ground biomass of tall deciduous shrubs and nitrophilous grasses increased, whereas the relative coverage and above‐ground biomass of dwarf evergreen shrubs, mosses, and lichens declined. Regardless of N addition levels, cryptogams (i.e., mosses and lichens) and a dwarf evergreen shrub (Chamaedaphne calyculata) disappeared after eight‐year N addition.ConclusionsCryptogams and dwarf evergreen shrubs are highly vulnerable to increased N availability, and N enrichment‐induced biodiversity loss, especially the disappearance of cryptogams, will deteriorate ecosystem structure and function in boreal permafrost peatlands.