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Citation. Dijkstra, F.; West, J.; Hobbie, S.; Reich, P.B. 2007. Dissolved inorganic and organic N leaching from a grassland field experiment: interactive effects of plant species richness, atmospheric (CO2) and N fertilization. Ecology 88:490-500.
Abstract. In nitrogen (N)-limited systems, the potential to sequester carbon depends on the balance
between N inputs and losses as well as on how efficiently N is used, yet little is known
about responses of these processes to changes in plant species richness, atmospheric CO2
concentration ([CO2]), and N deposition. We examined how plant species richness (1 or
16 species), elevated [CO2] (ambient or 560 ppm), and inorganic N addition (0 or 4
g·m−2·yr−1) affected ecosystem N losses, specifically leaching of dissolved inorganic N
(DIN) and organic N (DON) in a grassland field experiment in Minnesota, USA. We
observed greater DIN leaching below 60 cm soil depth in the monoculture plots (on
average 1.8 and 3.1 g N·m−2·yr−1 for ambient N and N-fertilized plots respectively) than
in the 16-species plots (0.2 g N·m−2·yr−1 for both ambient N and N-fertilized plots),
particularly when inorganic N was added. Most likely, loss of complementary resource
use and reduced biological N demand in the monoculture plots caused the increase in
DIN leaching relative to the high-diversity plots. Elevated [CO2] reduced DIN
concentrations under conditions when DIN concentrations were high (i.e., in N-fertilized
and monoculture plots). Contrary to the results for DIN, DON leaching was greater in the
16-species plots than in the monoculture plots (on average 0.4 g N·m−2·yr−1 in 16-species
plots and 0.2 g N·m−2·yr−1 in monoculture plots). In fact, DON dominated N leaching in the 16-species plots (64% of total N leaching as DON), suggesting that, even with high biological demand for N, substantial amounts of N can be lost as DON. We found no significant main effects of elevated [CO2] on DIN or DON leaching; however, elevated [CO2] reduced the positive effect of inorganic N addition on DON leaching, especially during the second year of observation. Our results suggest that plant species richness, elevated [CO2], and N deposition alter DIN loss primarily through changes in biological
N demand. DON losses can be as large as DIN loss but are more sensitive to organic matter production and turnover.
Key words: dissolved inorganic nitrogen, dissolved organic nitrogen, drainage, elevated CO2, grassland, leaching, lysimeter, nitrogen deposition, nitrogen loss, plant species richness.