In the spring of each year (1972-1974) air-dry grains of two inbred lines of Z. mays (7275-13-1 and 106) were exposed for 17 h to a low level (25 kHz) of ultrasound and subsequently planted in the field together with untreated controls and grown to maturity. In the fall of each year the ears of each group were harvested and the number of broken stalks, the yield and weight of grains and grain parts and the alcohol-soluble amino acid complement of the grain parts were determined. Broken stalks and yields were unaffected, however the embryos from the treated groups retained more moisture than their respective controls, dry weights were also significantly increased. The alcohol-soluble amino acid composition of the embryos was markedly changed, levels of proline were severely depressed in the embryos of both lines and generally increased in the endosperms. Sonication resulted in an overall decrease of up to 40% in totalled alcohol-soluble amino acids in the grains of 7275-13-1.

No abstract

Outside of tropical and arid regions, plant productivity is limited by the availability of soil N.Ironically, these are the regions where N-fixing plants are restricted to early successional habitats. The energy cost of N fixation has been used to explain the paucity of N-fixing plants in late-successional ecosystems, and models predict reduced light and increased soil N availability will reduce N-fixing plant success. The lack of success of N-fixing plants has also been explained by their greater need for some elements, especially phosphorus. We examined the effect of N and P fertilizer over four years on N fixation in Alnus alnobetula spp. crispa in a mature Pinus banksiana forest in the southern boreal forest, and an adjacent site where wildfire had removed the tree canopy. We also monitored N fixation throughout two growing seasons examined the effect of artificial shading on photosynthesis. The addition of N or P fertilizer resulted in a 60% decrease in plant nodule nitrogenase activity. N fertilizer also reduced the proportion of cells in the root nodules containing N-fixing vesicles in the forest site. Shrubs in the forest had the highest photosynthetic rate when measured on a leaf mass basis, indicating an increased carbon capture efficiency compared with shrubs in the open. Over the course of two growing seasons, soil temperature had a positive effect on specific nitrogenase activity, and soil in the open site was warmer than soil in the forest in the spring. However, as soil moisture decreased, temperature was a weaker predictor of nitrogenase activity. Although all shrubs consistently acquired most of their N from fixation, shrubs in the forest derived more than shrubs in the open, which were more water limited. Overall, these results show that N-fixing plants may benefit from being in the understory for improved water balance in this region of the boreal forest. As such, light availability may not be the primary factor limiting the abundance of N-fixing shrubs.