Effects of simulated nitrogen deposition on the ecophysiological responses of Populus beijingensis and P. cathayana under intra- and interspecific competition

Abstract

Aims N deposition has become a major driver of a decline in species richness and biodiversity loss. We aim to discover whether N deposition could affect competitive relationships between poplars to predict threats posed by the introduction of exotic hybrids to native relative species.Methods Intra-and interspeci c competition was investigated for an introduced hybrid poplar (Populus beijingensis) and the native paternal species P. cathayana under two N deposition regimes (with and without N deposition).Results Under control conditions, P. cathayana grown under either of the competition modes showed consistently greater above-ground biomass, root-to-shoot ratio (R/S), photosynthetic capacity, higher activities of N-assimilation enzymes in leaves, and preference for N-NO 3 than corresponding P. beijingensis.Interspeci c competition increased the leaf area (LA), speci c leaf area (SLA), R/S, and photosynthetic nitrogen use e ciency (P NUE ) in P. cathayana, but decreased P NUE in P. beijingensis compared to the values under monoculture. Thus, P. cathayana can gain a competitive advantage over P. beijingensis at low N availability. In contrast, under N deposition, P. beijingensis grown in a mixture showed more positive responses in growth, higher plasticity in biomass allocation, more exible ne root traits, and the shift for N-NO 3 preference when compared with P. cathayana, which resulted in relatively higher values in LA, SLA, and biomass accumulation in P. beijingensis.Conclusions Our results suggest that N deposition could reverse competitive relationships between the poplars, and exotic P. beijingensis has the potential to outcompete and displace native P. cathayana under growing N deposition.