Omission and Resupply of Nitrogen Affect Physiological and Enzymatic Activities and the Gene Expression of Eucalypt Clones

ABSTRACT: The mineral nutrient uptake of plants in the field occurs in pulses, due to variations in the substance concentrations at the root surface. The fluctuations in nutrient supply probably induce changes in the plant, which are to date unknown for Eucalyptus. This study evaluated these changes in plant growth, nutritional status, photosynthesis, and gene expression, which can serve as biomarkers of the nitrogen status, of four eucalypt clones exposed to N omission and resupply. A greenhouse experiment with four Eucalyptus clones was installed, and after initial growth exposed to N omission for 21 d, followed by N resupply in nutrient solution for 14 d. Nitrogen omission decreased the total N and photosynthetic pigments, net photosynthesis and photochemical dissipation, and increased enzyme activity especially in leaves and the gene expression in leaves and roots. Nitrogen resupply decreased these variations, indicating recovery. The total N concentration was highly and significantly correlated with net photosynthesis, enzyme activity, expression of genes GS2;1 and Gln1;3 in the leaves and AMT1;2 in the roots, contents of chlorophyll a and b, and photochemical energy dissipation. The enzymes GS and NR in the leaves and the genes AMT1;2, GS2;1 and Gln1;3 proved to be sensitive N indicators

Induced flooding as environmental filter for riparian tree species

The waterlogging of commonly non-flooded soils acts as a filtering for plant communities. River impoundments can flood a large area never flooded before, changing the local conditions and affecting seeds and growing plants. Therefore, the recruitment process in the regenerating community on these new formed margins may be inhibited. Lists containing plant species indicated for restoration of periodically flooded habitats have been published but the germination and initial development behavior of these species are poorly known. We hypothesize that species indicated to restore flooded habitats (FH) are faster to germinate and their seedling also develop better than species from non-flooded habitats (NH) under waterlogging conditions. Seeds of species from flooded and non-flooded habitats were submitted to treatments of flooding (F) and non-flooding (N) for 90 days, and germination was daily registered. Seedlings of Psidium guajava and Handroanthus serratifolius were submitted to flooding and morphophysiological parameters were measured. Species from both groups had similar patterns of germination, and for most species flooding led to a faster germination. In general, the number of germinated seeds was smaller under flooding. P. guajava seedlings presented decreasing growth and photosynthesis under flooding and H. serratifolius seedlings presented chlorosis, foliar abscission, negative net photosynthetic rate, and root-rotting. Flooding was harmful for plants of both groups, but was worse for seeds and seedlings from NH species. The outcomes show that the use of plant species in restoration programs of dams and reservoir margins must take into account if it will be used seeds or seedlings, since the success and sustainability of this action will depend on the fast and well development of the plants