Morfofisiología del género Rhizophora en la Reserva Natural Isla Juan Venado, Pacífico de Nicaragua

Los manglares son ecosistemas únicos que crecen en aguas salobres en las fronteras de los litorales tropicales; representan un enorme valor científico, ecológico, económico y cultural. En Nicaragua representan una gran fuente de recursos económicos para las poblaciones locales. Las especies más afectadas por la tala son Rizophora mangle L, Rhizophora harrisonii y Rizhophora racemosa G. Mey. Debido a que estas especies presentan características fenotípicas similares su separación como especie es difícil. Por lo que el objetivo de este trabajo fue diferenciar morfofisiológicamente las tres especies del género Rhizophora. Para llevar a cabo este estudio se utilizaron muestras foliares de las especies R. mangle, R. harrisonii Leechm y R. racemosa provenientes de la Isla Juan Venado. Se realizaron comparaciones morfológicas y análisis de pigmentos y tocoferoles. La actividad de los sistemas fotoprotectores, resultaron ser muy variables intraespecíficamente. El contenido total de tocoferoles fue muy diferente entre las tres especies siendo R. racemosa la de máxima concentración y R. harrisonii la de menor. El papel del g-tocoferol en la tolerancia a la salinidad podría ser responsable de las diferencias interespecificas.    La distinta composición en tocoferoles podría ser utilizada como parámetro bioquímico de distinción interespecífica.

Freezing induces an increase in leaf spectral transmittance of forest understorey and alpine forbs

Evergreen plants growing at high latitudes or high elevations may experience freezing events in their photosynthetic tissues. Freezing events can have physical and physiological effects on the leaves which alter leaf optical properties affecting remote and proximal sensing parameters. We froze leaves of six alpine plant species (Soldanella alpina, Ranunculus kuepferi, Luzula nutans, Gentiana acaulis, Geum montanum, and Centaurea uniflora) and three evergreen forest understorey species (Hepatica nobilis, Fragaria vesca and Oxalis acetosella), and assessed their spectral transmittance and optically measured pigments, as well as photochemical efficiency of photosystem II (PS_II) as an indicator of freezing damage. Upon freezing, leaves of all the species transmitted more photosynthetically active radiation (PAR) and some species had increased ultraviolet-A (UV-A) transmittance. These differences were less pronounced in alpine than in understorey species, which may be related to higher chlorophyll degradation, visible as reduced leaf chlorophyll content upon freezing in the latter species. Among these understorey forbs, the thin leaves of O. acetosella displayed the largest reduction in chlorophyll (-79%). This study provides insights into how freezing changes the leaf optical properties of wild plants which could be used to set a baseline for upscaling optical reflectance data from remote sensing. Changes in leaf transmittance may also serve to indicate photosynthetic sufficiency and physiological tolerance of freezing events, but experimental research is required to establish this functional association.

Patterns of spatio-temporal distribution of winter chronic photoinhibition in leaves of three evergreen Mediterranean species with contrasting acclimation responses

High irradiance and relatively low temperature, which characterize Mediterranean winters, cause chilling stress in plants. Downregulation of photosynthetic efficiency is a mechanism that allows plants to survive these conditions. This study aims to address whether this process shows a regular spatial pattern across leaf surface or not. Three species (Buxus sempervirens, Cistus albidus and Arctostaphylos uva-ursi) with contrasting responses to winter stress were studied. During 7 days, macro and micro Fv/Fm spatial patterns were monitored by the use of chlorophyll fluorescence imaging techniques. In the field, the strongest photoinhibition was found in B. sempervirens, while there was almost no chronic photoinhibition in C. albidus. In leaves of the first species, Fv/Fm decreased from base to tip while in C. albidus it was uniform over the leaf lamina. An intermediate behavior is shown by A. uva-ursi leaves. Spatial heterogeneity distribution of Fv/Fm was found inside the leaves, resulting in greater Fv/Fm values in the inner layers than in the outer ones. Neither xanthophyll-linked downregulation of Fv/Fm nor protein remobilization were the reasons for such spatial patterns since pigment composition and nitrogen content did not reveal tip-base differences. During recovery from winter, photoinhibition changes occurred in Fv/Fm, pigments and chloroplast ultrastructure. This work shows for the first time that irrespective of physiological mechanisms responsible for development of winter photoinhibition, there is an acclimation response with strong spatio-temporal variability at leaf level in some species. This observation should be taken into account when modeling or scaling up photosynthetic responses.