Contribution of different grass species to plant-atmosphere ammonia exchange in intensively managed grassland

• Main Authors: M. Mattsson, B. Herrmann, S. Jones, A. Neftel, M. A. Sutton, J. K. Schjoerring
• Format: Article
• Language: English
• Published: Copernicus Publications 2009-01-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/6/59/2009/bg-6-59-2009.pdf

Species diversity in grasslands usually declines with increasing input of nitrogen from fertilizers or atmospheric deposition. Conversely, species diversity may also impact the build-up of soil and plant nitrogen pools. One important pool is NH<sub>3</sub>/NH<sub>4</sub><sup>+</sup> which also can be exchanged between plant leaves and the atmosphere. Limited information is available on how plant-atmosphere ammonia exchange is related to species diversity in grasslands. We have here investigated grass species abundance and different foliar nitrogen pools in 4-year-old intensively managed grassland. Apoplastic pH and NH<sub>4</sub><sup>+</sup> concentrations of the 8 most abundant species (<i>Lolium perenne, Phleum pratense, Festuca pratensis, Lolium multiflorum, Poa pratensis, Dactylis glomerata, Holcus lanatus, Bromus mollis</i>) were used to calculate stomatal NH<sub>3</sub> compensation points. Apoplastic NH<sub>4</sub><sup>+</sup> concentrations differed considerably among the species, ranging from 13 to 117 μM, with highest values in <i>Festuca pratensis</i>. Also apoplastic pH values varied, from pH 6.0 in <i>Phleum pratense</i> to 6.9 in <i>Dactylis glomerata</i>. The observed differences in apoplastic NH<sub>4</sub><sup>+</sup> and pH resulted in a large span of predicted values for the stomatal NH<sub>3</sub> compensation point which ranged between 0.20 and 6.57 nmol mol<sup>−1</sup>. Three species (<i>Lolium perenne, Festuca pratensis</i> and <i>Dactylis glomerata</i>) had sufficiently high NH<sub>3</sub> compensation point and abundance to contribute to the bi-directional NH<sub>3</sub> fluxes recorded over the whole field. The other 5 grass species had NH<sub>3</sub> compensation points considerably below the atmospheric NH<sub>3</sub> concentration and were thus not likely to contribute to NH<sub>3</sub> emission but only to NH<sub>3</sub> uptake from the atmosphere. Evaluated across species, leaf bulk-tissue NH<sub>4</sub><sup>+</sup> concentrations correlated well (<i>r</i><sup>2</sup>=0.902) with stomatal NH<sub>3</sub> compensation points calculated on the basis of the apoplastic bioassay. This suggests that leaf tissue NH<sub>4</sub><sup>+</sup> concentrations combined with data for the frequency distribution of the corresponding species can be used for predicting the NH<sub>3</sub> exchange potential of a mixed grass sward.