Nitrogen storage and seasonal nitrogen cycling in Populus: bridging molecular physiology and ecophysiology.

While both annual and perennial plants store nitrogen resources during the growing season, seasonal N cycling is a hallmark of the perennial habit. In Populus the vegetative storage proteins BSP, WIN4 and PNI288 all play a role in N storage during active growth, whereas BSP is the major form of reduced N storage during winter dormancy. In this review we explore cellular and molecular events implicated in seasonal N cycling in Populus, as well as environmental cues that modulate both the phenology of seasonal N cycling, and the efficiency and proficiency of autumn N resorption. We highlight recent advances that have been made using Populus genomics resources to address processes germane to seasonal N cycling. Genetic and genetological studies are enabling us to connect our understanding of seasonal N cycling at molecular and cellular levels with that at ecophysiological levels. With the genomics resources and foundational knowledge that are now in place, Populus researchers are poised to build an integrative understanding of seasonal N cycling that spans from genomes to ecosystems.