In most plant communities, the net effect of nitrogen enrichment is an increase in plant productivity. However, nitrogen enrichment also has been shown to decrease species richness and to acidify soils, each of which may diminish the long-term impact of nutrient enrichment on productivity. Here we use a long-term (20 year) grassland plant diversity by nitrogen enrichment experiment in Minnesota, United States (a subexperiment within the BioCON experiment) to quantify the net impacts of nitrogen enrichment on productivity, including its potential indirect effects on productivity via changes in species richness and soil pH over an experimental diversity gradient. Overall, we found that nitrogen enrichment led to an immediate positive increment in productivity, but that this effect became nonsignificant over later years of the experiment, with the difference in productivity between fertilized and unfertilized plots decreasing in proportion to nitrogen addition-dependent declines in soil pH and losses of plant diversity. The net effect of nitrogen enrichment on productivity could have been 14.5% more on average over 20 years in monocultures if not for nitrogen-induced decreases in pH and about 28.5% more on average over 20 years in 16 species communities if not for nitrogen-induced species richness losses. Together, these results suggest that the positive effects of nutrient enrichment on biomass production can diminish in their magnitude over time, especially because of soil acidification in low diversity communities and especially because of plant diversity loss in initially high diversity communities.
Bibliographical noteFunding Information:
We thank Kally Worm, Dan Bahauddin, Susan Barrott, and many summer interns for their assistance with this research. This work was supported by grants from the US National Science Foundation, including the Long-Term Ecological Research (LTER) program (DEB-1831944), the Major Research Instrumentation program (DBI-1725683), and the Long-Term Research in Biology program (DEB-1753859). Further support was provided by the Cedar Creek Ecosystem Science Reserve and the University of Minnesota.
We thank Kally Worm, Dan Bahauddin, Susan Barrott, and many summer interns for their assistance with this research. This work was supported by grants from the US National Science Foundation, including the Long‐Term Ecological Research (LTER) program (DEB‐1831944), the Major Research Instrumentation program (DBI‐1725683), and the Long‐Term Research in Biology program (DEB‐1753859). Further support was provided by the Cedar Creek Ecosystem Science Reserve and the University of Minnesota.
© 2020 John Wiley & Sons Ltd
- indirect effects
- long-term experiment
- nitrogen enrichment
- soil pH
- species diversity