US EPA

2484825 

Journal Article 

Effects of chronic nitrogen additions on understory species in a red pine plantation 

Rainey, SM; Nadelhoffer, KJ; Silver, WL; Downs, MR 

1999 

Yes 

Ecological Applications
ISSN: 1051-0761
EISSN: 1939-5582 

9 

3 

949-957 

WOS:000081972600016 

Two plots in a red pine stand at the Harvard Forest, Massachusetts, have been fertilized for 7 yr with 5 g.m(-2).yr(-1) or 15 g.m(-2).yr(-1) of N and compared to an unfertilized control to study the effects of chronic N additions on nutrient cycling, plants, and soil. Movement of added N into soils and plant biomass was tracked using additions of an N-15 label to the 5 g.m(-2).yr(-1) and control plots for two of these years. We present data on changes in the understory plant community of these plots. We measured aboveground biomass, density, N and other elemental concentrations, and N-15 tracer recoveries to catalogue the effects of the N additions on this community. Nitrogen contents increased while biomass and nutrient cation concentrations decreased in some species. Percent recoveries of N-15 tracers were small but detectable. The natural abundances of N-15 also increased in a fertilized treatment without tracer additions. Though this forest has not yet reached N saturation by some definitions, it is possible that the understory is already saturated with N, Understory species may be useful indicators for N saturation through their increasing N content, decreasing nutrient concentrations, and increasing delta(15)N in tissues. 

ground flora; Harvard Forest; N cycle; N deposition; N-15 labeling; N-15 natural abundance; N saturation; Pinus resinosa; red pine; temperate forests