Preferences for Different Nitrogen Forms by Coexisting Plant Species and Soil Microbes

Abstract

The growing awareness that plants might use a variety of nitrogen (N) forms, both organic and inorganic, has raised questions about the role of resource partitioning in plant communities. It has been proposed that coexisting plant species might be able to partition a limited N pool, thereby avoiding competition for resources, through the uptake of different chemical forms of N. In this study, we used in situ stable isotope labeling techniques to assess whether coexisting plant species of a temperate grassland (England, UK) display preferences for different chemical forms of N, including inorganic N and a range of amino acids of varying complexity. We also tested whether plants and soil microbes differ in their preference for different N forms, thereby relaxing competition for this limiting resource. We examined preferential uptake of a range of 13C15N-labeled amino acids (glycine, serine, and phenylalanine) and 15N-labeled inorganic N by coexisting grass species and soil microbes in the field. Our data show that while coexisting plant species simultaneously take up a variety of N forms, including inorganic N and amino acids, they all showed a preference for inorganic N over organic N and for simple over the more complex amino acids. Soil microbes outcompeted plants for added N after 50 hours, but in the long-term (33 days) the proportion of added 15N contained in the plant pool increased for all N forms except for phenylalanine, while the proportion in the microbial biomass declined relative to the first harvest. These findings suggest that in the longer-term plants become more effective competitors for added 15N. This might be due to microbial turnover releasing 15N back into the plant-soil system or to the mineralization and subsequent plant uptake of 15N transferred initially to the organic matter pool. We found no evidence that soil microbes preferentially utilize any of the N forms added, despite previous studies showing that microbial preferences for N forms vary over time. Our data suggest that coexisting plants can outcompete microbes for a variety of N forms, but that such plant species show similar preferences for inorganic over organic N.

Nitrogen uptake strategies of edaphically specialized Bornean tree species

“…Error bars are ± 1 SE; there were no statistically significant differences in uptake rates of the two N forms for any species (Table 2) N-form use by Hawaiian plant species (Houlton et al 2007) and Jamaican tree species (Brearley 2013). Plasticity in the use of different N forms may be adaptive if it allows for more effective competition for N resources at the root-level, where availability of different forms can fluctuate on small spatial and temporal scales due to variation in, e.g., mineralization rates, soil moisture, and differential diffusion (Nye 1977;Owen and Jones 2001;Miller and Cramer 2004), as well as competition with neighboring plants and microorganisms (Schimel and Bennett 2004;Harrison et al 2007;Miller et al 2007). Variation among tree species in the capacity to take up differentially available inorganic N forms is thus unlikely to be a dominant mechanism influencing their distributions across soil types in this Bornean rain forest.…”

Potential for biological nitrification inhibition to reduce nitrification and N2O emissions in pasture crop–livestock systems

“…Nature has shown that by routing reactive N through multiple pathways and restricting the flow through nitrification path, N can be cycled more effectively with limited leakage into the environment (Vitousek and Matson, 1984;Cooper, 1986;White, 1991;Northup et al, 1995;Stelzer and Bowman, 1998;Harrison et al, 2007;Ashton et al, 2010;Smolander et al, 2012). As nitrification and denitrification are the two primary biological drivers for the production of NO 3 2 , N 2 O and NO (i.e.…”

Stable nitrogen isotope patterns of trees and soils altered by long-term nitrogen and phosphorus addition to a lowland tropical rainforest

“…For example, plant d 15 N values reflected a community-wide switch between two mineral N sources along a precipitation gradient in Hawaii (Houlton et al 2006;Schuur and Matson 2001) and among spatially distinct N sources in litter and mineral soils of French Guiana (Schimann et al 2008). Experimental additions of 15 N-enriched tracers have shown that plants prefer mineral over organic forms of N, even in N limited ecosystems (Harrison et al 2007;Ashton et al 2008), and that local adaptations to growth conditions in part determine N uptake rates and preferences for ammonium versus nitrate (Wang and Macko 2011;Andersen and Turner 2013).…”