Species ecology determines the role of nitrogen nutrition on the frost tolerance of pine seedlings

Abstract

Frost determines the evolution and distribution of plants in temperate and cold regions. Several environmental factors can influencefrost acclimation of woody plants but the magnitude and direction of the effect of nitrogen (N) availability is controversial.We studied the effect of N availability on root and shoot frost tolerance in mid-fall and in winter in seedlings of four pines of contrastingecology: Pinus nigra J.F. Arnold, P. pinaster Ait., P. pinea L. and P. halepensis Mill.. Organ N and soluble sugar concentration,and timing of cessation of shoot elongation were measured to assess the physiological mechanisms underlying frostacclimation. Nitrogen was supplied at high and low rates only during the pre-hardening period and at a moderate N rate duringhardening in the fall. Shoot frost tolerance increased over winter while root frost tolerance did not change in any species. PrehardeningN availability affected the frost tolerance of both roots and shoots, although the effect was species-specific: high Nreduced the overall root and shoot frost tolerance in P. pinea and P. halepensis, and increased the frost tolerance in P. nigra, buthad no effect in P. pinaster. Nitrogen supply in the fall consistently increased frost tolerance in all species