Foliar nitrogen uptake in simulated wet deposition in Abies religiosa

To evaluate foliar absorption of inorganic nitrogen by simulated wet deposition in Abies religiosa, a greenhouse factorial experiment was established with three-year old seedlings using a randomized design. Eight treatments resulted from the combination of N form (NO3- or NH4+), dose (high or low) and runoff to the substrate (with and without). N-15 was used to evaluate N absorption. Plants were harvested and current year foliage, foliage >1 year old, twigs, stem and roots were separated. The form of N and dose had significant effects (p=0.001) in all plant components, showing higher recovery with NO3- as source and at a high dose. Runoff increased recovery in twigs, stem and roots. Current-year foliage showed the highest N absorption. N absorption by the whole plant was nine and three times higher with NO3- than with NH4+ for foliage >1 year and roots, respectively. N absorption was higher in the stem than in other plant components, whereas foliage >1 year was the least sensitive component to N absorption. The average amount of N recovered per plant was 1.8mg N. Aboveground N-NO3- recovery reached 57%, probably because the plants were not exposed to rainfall that could wash NO3- from the canopy. The results suggest a high potential of N absorption by the foliage and branches of A. religiosa. The initial symptoms of N saturation documented in the Valley of Mexico may worsen if air pollution remains uncontrolled. The effects of N deposition may occur via foliage before soil N is affected.