Effect of Medium- and Long-Term Fertilization on Needles and Roots Gene Expression of Adult Norway Spruce (Picea abies) Trees.

In 1987 a long-term experiment on nutrient optimization was started in the Flakaliden research park in northern Sweden. Every year since, the plots have been treated every second day between June and mid-August with a dilute complete liquid fertilizer in combination with irrigation, at a rate of 75-100 kg N ha-1 per year. An additional treatment with liquid fertilizer was started in 2007 on plots that had been irrigated from the beginning. In 2012, one-year-old needles and root samples were collected at four different time points: late spring, early and late summer and early autumn. At the time of sampling, the trees were treated for five and 25 years.

In order to evaluate the effect of medium- and long-term fertilization in both tissues, RNA was extracted and sequenced. Our results suggest that after five years of annual fertilization, there was no detectable effect of altered soil nutrient availability on the needle or root transcriptomes. However, after 25 years of annual fertilization, there were a large number of differentially expressed genes in both, needles and roots. When GO enrichment analysis was conducted, the results show an up-regulation of the carbohydrate catabolism during spring, a strong down-regulation of photosynthetic process and light response during spring and early-summer in needles. Also, a strong up-regulation of nitrogen response during summer, an up-regulation on oxidative stress response in early autumn and a down-regulation on the defense response to fungus were found in roots.

Finally, our results lead us to think that long-term fertilization is required to have a real effect at transcriptomic levels in adults Norway spruce trees. In this sense, a long-term alteration in the nitrogen status has a negative effect in the photosynthetic machinery at the beginning of the growing season, while has a positive effect on nitrogen and iron uptake and carbon metabolic process.

Acknowledgments: PhD funded by CONICYT BECAS CHILE 72160239, Santiago, Chile.