Mechanisms of nitrate accumulation under resource-independent plant competition.

点击翻译按钮获取中文摘要

Resource-independent weed competition is an important stress factor that not only affects early development of crop seedlings but also exerts long-lasting effects even after weed removal resulting in significant reductions in yield potential. These effects result from the central importance of far-red light reflected from neighbouring weeds that inactivate phytochrome photoreceptors. Recently, we found a direct link between increasing duration of weed presence and decreases in photosynthetic efficiency, CO2 assimilation, and yield potential, which could not be recovered if weed presence extended to reproductive stages. Photosynthesis and respiration, however, more than any other physiological processes are integrated with nitrogen assimilation. Therefore, the knowledge of the effects of neighbouring weeds on nitrate assimilation in major crop plants is pivotal to making progress in the development of weed management strategies and nitrogen fertilizer application under weed stress. Our laboratory has shown that nitrate accumulation in the model plant Arabidopsis and maize is an early response to neighbouring weeds and simulated far-red light. This response appears to be due to reduced activity of a major enzyme in the nitrate assimilation pathway. Despite establishing this link, we cannot exclude the possibility of the involvement of nitrate transporters and in this proposal this possibility will be investigated by conducting high throughput sequencing. Further, nitrate accumulation in Arabidopsis in response to neighbouring weeds appears to be independent of phytochrome B photoreceptor inactivation. We hypothesize that nitrate accumulation in maize under resource-independent competition may cause nitrate limitation or inadequate nitrate utilization, which if maintained for some time after weed removal, affects early development and subsequent performance of maize. Therefore, two major objectives of our proposal are (1) to elucidate the molecular mechanisms of nitrate accumulation in response to resource-independent competition under controlled environment using maize mutants deficient in phytochrome B photoreceptor and (2) extend our research to field conditions and determine the relationship between the increasing duration of weed presence and nitrate accumulation and subsequent performance of maize following weed removal. The new information generated as the outcome of this research are appropriate for training of highly qualified personnel in photobiology and weed research and open up avenues for research on new far-red light actions that are independent of phytochrome inactivation. In addition, the new information can be transferred to field biologist and farmers to devise weed control plans prior to critical periods for weed control and mitigate not only the impact of resource-independent weed competition on major crop plants but also the impact of excess nitrate on the environment.