The OJIP fast fluorescence rise characterizes Graptophyllum species and their stress responses

Causes for rarity in plants are poorly understood. Graptophyllum reticulatum is an endangered endemic species, and it has three close relatives with different conservation status: the vulnerable G. ilicifolium, the rare G. excelsum, and the common G. spinigerum. Applied to the chlorophyll a fluorescence transient of leaves, the JIP test provides a Performance Index (PI) which quantifies the main steps in photosystem II (PSII) photochemistry including light energy absorption, excitation energy trapping, and conversion of excitation energy into electron flow. The PI is calculated from three components which depend on the reaction center density, the trapping efficiency, and the electron transport efficiency. PI was measured in the natural habitats of the four species and under artificially imposed environmental stresses in the glasshouse to determine whether conservation status was related to stress resilience. The results showed that soil type is unlikely to restrict the endangered G. reticulatum, vulnerable G. ilicifolium, or rare G. excelsum because PI was similar in plants grown in diverse soils in the glasshouse. Photoinhibition is likely to restrict the endangered G. reticulatum to shade habitats because PI was significantly reduced when plants were exposed to more than 15% ambient light in controlled experiments. Water availability may determine the location and distribution of the vulnerable G. ilicifolium and common G. spinigerum because PI was reduced more than 60% when plants were exposed to water stress. While the characteristics of their natural habitats correspond to and explain the physiological responses, there was no obvious relationship between conservation status and environmental resilience. PI can be used to monitor vigor and health of populations of plants in the natural habitat. In cultivation experiments PI responds to key environmental variables that affect the distribution of species with conservation significance

Seasonal, diurnal and vertical variation of chlorophyll fluorescence on **Phyllostachys humilis** in Ireland

In recent years, temperate bamboo species have been introduced in Europe not only as an ornamental plant, but also as a new biomass crop. To measure adaptation stress of bamboo to the climate of Western Europe, chlorophyll fluorescence was measured on a diurnal and seasonal basis in Ballyboughal, Co. Dublin, Ireland. Measurements were attained on the leaves of each node of Phyllostachys humilis. The most frequently used parameter in chlorophyll fluorescence is the photosynthetic efficiency (Fv/Fm). A seasonal dip - as well as a larger variation - of Fv/Fm in spring compared to the rest of the year was observed. Over the year, the upper leaves of the plant perform better than the bottom leaves. These findings were linked to environmental factors such as light intensity, air temperature and precipitation, as increased light intensities, decreasing air temperatures and their interactions, also with precipitation levels have an effect on the photosynthetic efficiency (Fv/Fm) in these plants