Effects of drought and shade on nitrogen cycling in the leaves and canopy of Mediterranean Quercus seedlings

Abstract

Listen

Translate article

Nitrogen (N) withdrawn from leaves before abscission can help to supply N requirements in plants of nutrient poor habitats. Besides N shortage, Mediterranean Quercus seedlings must face water and light stresses. However, there is little information on the influence of these stresses in the nitrogen resorption efficiency (NRE) at leaf level, and none at canopy level. We tested in two separated experiments how changes in water and light availability affect NRE and its components at both levels in seedlings of two evergreen oaks [Quercus coccifera L. and Quercus ilex subsp. ballota (Desf.) Samp] and in a semi-deciduous one (Quercus faginea Lam.). In the summer drought experiment seedlings were left to dehydrate to −2.5 and to −0.5 MPa (water stress and control, respectively) before watering. In the light experiment seedlings were grown at 100, 20 and 5% of full sunlight. The leaf abscission pattern was monitored and N content, N loss and NRE were calculated in the two peaks of leaf abscission (spring and late summer). After one year of treatments summer drought had little effect on N resorption and its components at both leaf and canopy levels. Moderate shade increased NRE at leaf level in Q. faginea but this response vanished at canopy level. N loss at the leaf level was unaffected. Deep shade decreased N lost at the canopy level in spring but increased it in late summer. N resorption and N losses at the canopy level were lower at late summer than in spring, due to fewer leaves falling. This study highlights the importance of the scale on the study of nitrogen dynamics (leaf vs. whole canopy), as the scaling factor (amount of leaf shedding) also responds to environmental factors, either enhancing or reversing the effects found at leaf level.