Photoinhibition and recovery in tropical plant species: response to disturbance

Abstract

Disturbance or rainforest is often followed by mass mortality of understorey seedlings. Transitions of shade grown plants to full sunlight can cause reductions in the efficiency with which light is used in photosynthesis, called photoinhibition. In order to assess the influence of photoinhibition on mortality and growth after rainforest disturbance this study examined photoinhibition in both simulated and real forest disturbances in northern Papua New Guinea. In an experiment simulating rainforest disturbance, exposure of shade-grown plants to full sunlight resulted in abrupt decreases in the chlorophyll fluorescence parameter F /F that is characteristic of photoinhibition. However, in the well-watered plants used in these experiments there were no fatalities during 3 weeks after exposure to full sunlight. Thus, it is unlikely that photoinhibition, alone, is responsible for seedling fatalities after rainforest disturbances, but more likely that fatalities are due to photoinhibition in conjunction with other environmental stress. There were differences between the response of species to the simulated disturbance that concurred with their preferred habitats. For example, species form the genus Barringtonia, which is commonly found in shaded understorey environments, underwent greater reductions in F /F and were slower to recover than species that usually inhabit high solar radiation environments. The extent of photoinhibition and the rate of recovery appeared to be dependent on avoidance of direct solar radiation by altering leaf angles and on increasing maximum photosynthetic rates. A field survey of photoinhibition in man-made rainforest gaps corroborated the findings of the simulated disturbance experiment showing that plant species commonly found in shaded environments showed a greater degree of photoinhibition in forest gaps at midday than those species which are classified as species that benefit from gaps or specialist gap inhabitors.

Photosynthesis and carbon gain under contrasting light levels in seedlings of a pioneer and a climax tree from a Brazilian Semideciduous Tropical Forest

“…Apparent quantum yield and F v /F m ratio at midday of both plants studied were very low when compared to rainforest climax species and did not show a complete recover at pre-dawn (Thompson et al 1992, Langenheim et al 1984, Lovelock et al 1994, Zipperlen & Press 1996, Barker et al 1997, Scholes et al 1997. However, with the exception of similar light levels in the studies of Langenheim et al (1984) and Ishida et al (1999), daily and maximum PFD under HL in our experiment were much higher than the high light treatments of those studies.…”

“…Under high radiation these species supposedly do not cope efficiently with more radiation than the capacity of photosynthetic utilisation. Thus, these species would be more sensitive to photoinhibition than pioneer species (Lovelock et al 1994).…”

Do mature shade leaves of tropical tree seedlings acclimate to high sunlight and UV radiation?

“…In leaves of G. hirsutum, the capacity of photosynthetic CO2 assimilation was increased. Acclimative responses of CO2 assimilation were also reported for a tropical understorey herb, Alocasia macrorrhiza (L.) G.Don subjected to simulated gap conditions (Mulkey and Pearcy 1992) and for plants of three tropical rain forest species grown in the shade and transferred to full sunlight (Lovelock et al 1994). Shade-grown seedlings of Anacardium excelsum (Bertero and Balb.)…”

“…Moreover, increases in xanthophyll-cycle pool size, midday deepoxidation levels and photosynthetic capacity were observed in leaves of shade-grown tree seedlings of four dipterocarp species (from the south-east Asian rain forest) exposed to full solar irradiance (Bungard et al 2000). The high initial susceptibility of PSII to photoinhibition in shade leaves was reduced upon high-light treatments (Mulkey and Pearcy 1992;Lovelock et al 1994;Bungard et al 2000;Kolb et al 2001). Changes in chloroplast structure and levels of chloroplast proteins were found upon high-light acclimation of mature leaves of the tropical epiphytic species, Guzmania monostachia (L.) Rusby ex Mez (MaxweUeia/.…”

Canopy conundrums: building on the Biosphere 2 experience to scale measurements of inner and outer canopy photoprotection from the leaf to the landscape

“…We will not deal with 'external photoprotection' in which changes in leaf angle with time scales of minutes (Ludlow and Björkman 1984;Lovelock et al 1994), or with slower changes (days to weeks) in leaf surface reflective properties (Robinson and Osmond 1994), both of which substantially reduce absorption of light and engagement of the photoprotective processes described below. Nor will we deal with 'internal photoprotection' based on chloroplast movements that achieve the same end (Brugnoli and Björkman 1992).…”