The effects of soil fertilizer on amino acids in the floral nectar of corncockle, Agrostemma githago (Caryophyllaceae)

Plants of the meadow annual Agrostemma githago (Caryophyllaceae) were grown in 1-m2 field plots prepared with three fertilizer treatments as follows: (a) "low", no fertilizer, (b) "medium", 75 g of slow release fertilizer granules, (c) "high", 175 g of granular treatment. After sowing in spring the plants were left until flowering in late summer. Nectar was extracted using 5-μl glass microcapillary tubes. The material was frozen and sampled at a later date. The samples were analysed by high performance liquid chromatography (HPLC) using the AccQtag (Waters Corp.) system. Analysis showed that the total concentration of amino acids increased significantly with increasing fertilizer treatment (P < 0.05). Of the amino acids present glutamine showed a large and significant increase (P < 0.01), proline showed an increase (P < 0.05) and γ-amino butyric acid (GABA) showed a decrease (P < 0.05). No others showed a significant change. It is interesting to note that a common biosynthetic pathway (from α-ketoglutarate) links the amino acids that altered in concentration. Due to these changes the relative abundance of about half of the amino acids in the nectar was significantly altered. Glutamine showed a significant increase (P < 0.001) in percentage of the total with most of the remaining amino acids declining in relative abundance. The results show that, in contradiction to earlier work, soil conditions can affect the amino acid complement of nectar. This may have implications for plant-insect interactions, as local populations of pollinators may benefit from the increased amino acid content of the nectar and preferentially visit plants growing in high nutrient conditions