Growth and Transcriptional Changes in Poplar Under Different Nitrogen Sources

Abstract

Nitrogen greatly affects primary plant growth and development. The relationship between nitrogen availability and source and its effect on secondary growth is less well characterized. RNAseq has been used in various experiments to study changes in the plant transcriptome under experimental conditions. In this study, we first characterize the phenotypes of three tree species grown on varying nitrogen sources and levels. We then further characterize one of these three genotypes using RNAseq to identify differentially regulated genes under these varied conditions. Poplar trees were supplied with ammonium, nitrate, or ammonium nitrate. Ammonium nitrate was supplied under two concentrations. While there were few phenotypic changes in the three tree species assessed, each species had some changes in photosynthetic efficiency and biomass. Leaf weight was significantly different in two genotypes under high levels of ammonium nitrate. There was no change in height in any of the lines. Water use efficiency increased at higher N levels. Cell wall composition did not change across all genotypes for all treatments, with the exception of higher lignin in some high N conditions, contrary to previous studies. RNAseq revealed 8965 genes differentially regulated by a minimum of 1-fold with the largest changes seen in the nitrate and ammonium nitrate treatments. Assessment of the genes using MapMan showed that most genes belonged to stress response, nucleotide production, and photosynthesis reactions. The understanding of the relationship between nitrogen availability and secondary cell wall production is still limited. Here we show an unexpected result with increased lignin in high N treatments that may be development stage–specific. In addition, our results suggest that additional work in the area of understanding the impact of N on plant stress resistance is warranted.