title: Differential nitrogen cycling in semiarid sub-shrubs with contrasting leaf habit.
abstract: Nitrogen (N) is, after water, the most limiting resource in semiarid ecosystems. However, knowledge on the N cycling ability of semiarid woody plants is still very rudimentary. This study analyzed the seasonal change in the N concentrations and pools of the leaves and woody organs of two species of semiarid sub-shrubs with contrasting leaf habit. The ability of both species to uptake, remobilize and recycle N, plus the main storage organ for N during summer drought were evaluated. We combined an observational approach in the field with experimental (15)N labelling of adult individuals grown in sand culture. Seasonal patterns of N concentrations were different between species and organs and foliar N concentrations of the summer deciduous Lepidium subulatum were almost double those of the evergreen Linum suffruticosum. L. subulatum up took ca. 60% more external N than the evergreen and it also had a higher N resorption efficiency and proficiency. Contrastingly, L. suffruticosum relied more on internal N remobilization for shoot growth. Differently to temperate species, the evergreen stored N preferentially in the main stem and old trunks, while the summer deciduous stored it in the foliage and young stems. The higher ability of L. subulatum to uptake external N can be related to its ability to perform opportunistic growth and exploit the sporadic pulses of N typical of semiarid ecosystems. Such ability may also explain its high foliar N concentrations and its preferential storage of N in leaves and young stems. Finally, L. suffruticosum had a lower ability to recycle N during leaf senescence. These strategies contrast with those of evergreen and deciduous species from temperate and boreal areas, highlighting the need of further studies on semiarid and arid plants.
authors.affiliation: Instituto Pirenaico de Ecología (IPE-CSIC), Avda. Nuestra Señora de la Victoria, Jaca, Huesca, Spain.
authors.forename: Sara
authors.initials: S
authors.lastname: Palacio
authors.affiliation: Instituto Pirenaico de Ecología (IPE-CSIC), Avda. Montañana, Zaragoza, Spain.
authors.forename: Melchor
authors.initials: M
authors.lastname: Maestro
authors.affiliation: Instituto Pirenaico de Ecología (IPE-CSIC), Avda. Montañana, Zaragoza, Spain.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Montserrat-Martí
mesh_terms: D000704:Analysis of Variance; D029686:Lepidium / Q000378:metabolism*; D058458:Nitrogen Cycle; D010641:Phenotype; D018515:Plant Leaves / Q000378:metabolism*; D018520:Plant Shoots / Q000378:metabolism; D012621:Seasons