Chlorophyll fluorescence, stress and survival in populations of Mediterranean grassland species

Abstract

Abstract. Photosynthetic stress in response to a natural episode of frost and seasonal drought was assessed in a ‘dehesa’ grassland of SW Spain with a portable fluorimeter. Chlorophyll fluorescence characteristics of dark‐adapted leaves of 11 abundant species of Mediterranean grassland were measured over the course of a growing season from November 1992 to July 1993. Concomitant changes in population size were estimated from censuses of permanent quadrats. There was a general decline in the photochemical efficiency (Fv/Fm) during the growing season and this was particularly evident late in the growing season (spring and early summer) when ambient temperatures were increasing rapidly and rainfall was low; it coincided with the period of most intense mortality for most species. A frost in early March (‐ 5 °C), when photosynthetically active radiation was relatively high, resulted in a small decrease in Fv/Fm that was consistent across many species. The mechanisms of protection in species of Mediterranean grassland appear to be sufficiently effective to avoid damage to PSII for most of the year. For most species there was little evidence of photosystem II damage, as initial fluorescence (F0) usually did not increase. Many of the effects observed were due to a reduction in Fm and thus were consistent with non‐photochemical quenching. This could be adaptive in protecting PSII from damage in species that show little evidence of stress. The sharp increase in stress toward the end of the life cycle coincided with the fall in net population size.

Local population differentiation in Bromus tectorum L. in relation to habitat-specific selection regimes

“…A fluorescence meter emits light at 680 nm and after 10 s of exposure, a reading is taken to measure the 695 nm light energy being re-emitted by the plant (Fv/Fm). This provides a relative measure of vigor because photosystem II quantum efficiency is a reliable indicator of plant stress (Figueroa et al 1997). For analysis, Fv/Fm values were regressed on time for each seed source-salinity combination.…”

Can gypsophytes distinguish different types of gypsum habitats?

“…High F 0 values are only recorded in July, with maximum records at 14:00, that is, coincidentally with the lowest T m values, particularly in the case of Helianthemum squamatum and, to a lesser extent, in the case of Gypsophila struthium. This would indicate some damage in the plant photosystems induced by exposure to light (Figueroa et al, 1997). However, this damage is by no means long-lasting, since the F v /F m values return to normal levels during the night in the three species.…”

“…The recording of chlorophyll fluorescence values is a useful method for checking PSII photosynthetic efficiency and, therefore, the plant photosynthetic response to environmen-tal disruptions (Figueroa et al, 1997). With the introduction of easy-to-handle, portable fluorimeters capable of providing a large amount of data with only a minimum of experience and time on the part of the researcher, and without damaging the plants, it is nowadays relatively easy to record in the field the fluorescence kinetic values induced by quick exposure to actinic light in leaves previously adapted to darkness.…”

Plant stress activated by chlorine from disinfectants prepared on the base of sodium hypochlorite

“…The measurement of chlorophyll content and fluorescence has become established as a sensitive method for assessing the efficiency of PSII photosynthetically, as well as its role in environmental perturbations of photosynthesis. Some researchers have reported that chlorophyll content might estimate the influence of environmental stress on growth because these parameters were closely correlated with the rate of carbon exchange (Figueroa et al 1997;Guo and Li 2000).…”