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Fertilization effects on species density and primary productivity in herbaceous plant communities
Author(s) -
Gough Laura,
Osenberg Craig W.,
Gross Katherine L.,
Collins Scott L.
Publication year - 2000
Publication title -
oikos
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.672
H-Index - 179
eISSN - 1600-0706
pISSN - 0030-1299
DOI - 10.1034/j.1600-0706.2000.890302.x
Subject(s) - species richness , productivity , primary production , plant community , ecology , tundra , biology , context (archaeology) , graminoid , human fertilization , arctic , ecosystem , agronomy , paleontology , macroeconomics , economics
Fertilization experiments in plant communities are often interpreted in the context of a hump‐shaped relationship between species richness and productivity. We analyze results of fertilization experiments from seven terrestrial plant communities representing a productivity gradient (arctic and alpine tundra, two old‐field habitats, desert, short‐ and tall‐grass prairie) to determine if the response of species richness to experimentally increased productivity is consistent with the hump‐shaped curve. In this analysis, we compared ratios of the mean response in nitrogen‐fertilized plots to the mean in control plots for aboveground net primary productivity (ANPP) and species density ( D ; number of species per plot of fixed unit area). In general, ANPP increased and plant species density decreased following nitrogen addition, although considerable variation characterized the magnitude of response. We also analyzed a subset of the data limited to the longest running studies at each site (≥4 yr), and found that adding 9 to 13 g N m −2 yr −1 (the consistent amount used at all sites) increased ANPP in all communities by approximately 50% over control levels and reduced species density by approximately 30%. The magnitude of response of ANPP and species density to fertilization was independent of initial community productivity. There was as much variation in the magnitude of response among communities within sites as among sites, suggesting community‐specific mechanisms of response. Based on these results, we argue that even long‐term fertilization experiments are not good predictors of the relationship between species richness and productivity because they are relatively small‐scale perturbations whereas the pattern of species richness over natural productivity gradients is influenced by long‐term ecological and evolutionary processes.