Abstract
Abstract. 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 NH3/NH4+ 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 NH4+ concentrations of the 8 most abundant species (Lolium perenne, Phleum pratense, Festuca pratensis, Lolium multiflorum, Poa pratensis, Dactylis glomerata, Holcus lanatus, Bromus mollis) were used to calculate stomatal NH3 compensation points. Apoplastic NH4+ concentrations differed considerably among the species, ranging from 13 to 117 μM, with highest values in Festuca pratensis. Also apoplastic pH values varied, from pH 6.0 in Phleum pratense to 6.9 in Dactylis glomerata. The observed differences in apoplastic NH4+ and pH resulted in a large span of predicted values for the stomatal NH3 compensation point which ranged between 0.20 and 6.57 nmol mol−1. Three species (Lolium perenne, Festuca pratensis and Dactylis glomerata) had sufficiently high NH3 compensation point and abundance to contribute to the bi-directional NH3 fluxes recorded over the whole field. The other 5 grass species had NH3 compensation points considerably below the atmospheric NH3 concentration and were thus not likely to contribute to NH3 emission but only to NH3 uptake from the atmosphere. Evaluated across species, leaf bulk-tissue NH4+ concentrations correlated well (r2=0.902) with stomatal NH3 compensation points calculated on the basis of the apoplastic bioassay. This suggests that leaf tissue NH4+ concentrations combined with data for the frequency distribution of the corresponding species can be used for predicting the NH3 exchange potential of a mixed grass sward.
Highlights
The diversity of species in grasslands depends on a range of management and environmental factors (Cleland et al, 2006; Klimek et al, 2007; Pywell et al, 2007)
The field site consisted of nine grass species, dominated by Lolium perenne and followed by Phleum pratense, Festuca pratensis and Lolium multiflorum (Fig. 1)
Bromus mollis shown that the proportion of cultivated species like Lolium perenne increases with the amount of fertilization but decline with age of the sward (Whitehead, 1995)
Summary
The diversity of species in grasslands depends on a range of management and environmental factors (Cleland et al, 2006; Klimek et al, 2007; Pywell et al, 2007). The initial composition of the seed mixture sown determines the proportion of different species in grasslands (Bullock et al, 2007), while in the longer term other management factors such as cutting frequency (Pontes et al, 2007; Critchley et al, 2007), fertilization (Hill and Carey, 1997; Oelmann et al, 2007) and liming (Silvertown et al, 2006) become important. Species diversity is usually reduced with increasing amounts of N fertilization (Clark et al, 2007; Harpole et al, 2007). With increasing age of the sward, the proportion of perennial ryegrass and other cultivated species will decline, and the number of indigenous species will increase (Hopkins, 1986; Critchley et al, 2002)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
