Document: TER-3-33-10

The role of soil amino acids in the structure and functioning of upland grassland swards in Great Britain.

NETTLETON, T.K.* ¹, W.D.DAVIES ² and J.S.RODWELL ²

University of Alaska, Fairbanks, AK 99775 ¹
Lancaster University, Lancaster, Great Britain, LA1 4YQ ²

Abstract:
The agriculturally important grasslands that constitute the upland of Britain generally occur on nutrient poor soils where soil nitrogen mineralization cannot provide all of the nitrogen requirements for plants. Understanding the role which organic forms of nitrogen, such as amino acids, play in determining the structure and function of upland swards is vital for UK agricultural management. To assess the importance of soil amino acids to upland grasslands we documented the temporal and spatial patterns of soil amino acids and the role of amino acids in nitrate uptake, growth, and competitive interactions of key species. We examined soil amino acid content from five upland sites throughout Britain representing three levels of fertilization. We also investigated nitrate uptake in key species in the presence of amino acids, and examined the growth and competition of grassland sward species in the presence of amino acids by treating potted plants with nitrate and/or amino acids. Amino acids tended to decrease as fertility of the soil increased. This pattern correlated with the level of microbial activity at these sites, where high microbial activity indicates high concentrations of total free amino acids. There was a gradual increase in total free amino acid concentrations from January-March with the highest amino acid content found in the late spring months (April and May) followed by a drop-off through the summer months. As little as 4M of arginine or glycine significantly decreased the nitrate uptake ability of Lolium perenne, a graminoid which dominates improved grassland swards in the uplands. In contrast, 10M of arginine or glycine significantly increased the nitrate uptake ability of Holcus lanatus, a species that dominates semi-improved pastures. Arginine significantly reduced the growth rate and competitive ability of L. perenne, while having no significant effect on H. lanatus. The crucial role that amino acids play in determining species composition of upland grassland swards is quite clear. Some species flourish in the presence of amino acids while others decline, and it is possible that the amount of soil amino acids in pastures and grasslands can be used as a predictor of future species composition.

Keywords: soil amino acids, upland grasslands, nitrate uptake, Lolium perenne, Holcus lanatus

This abstract is being presented at: 8:00 AM in session:
Oral Session #61: Plant Responses to Nutrients.