Photosynthesis and photoprotection in Quercus ilex resprouts after fire

Abstract

Plants that resprout after fires often have higher rates of photosynthesis than before a fire. To elucidate the mechanism of this response, we studied gas exchange and chlorophyll fluorescence in Quercus ilex L. plants growing on control (unburned) sites and on sites that had been burned the preceding summer. In early July, photosynthetic rates and stomatal conductance were similar in plants on unburned and burned plots, and in young and old foliage within unburned plots. At this time, photochemical efficiency of photosystem II (PSII), nonphotochemical quenching of chlorophyll fluorescence (NPQ), and the de-epoxidation of violaxanthin to zeaxanthin were also similar among leaves of different ages and treatments. In late July, photosynthetic rates and stomatal conductances were much greater in resprouts on the burned areas than in unburned plants. From early to late July, unburned plants showed an increase in NPQ and the de-epoxidation of violaxanthin to zeaxanthin, indicating increased photoprotection as a result of enhanced nonradiative dissipation of excess light energy. Plants on the burned plots did not show these changes. Leaves of all ages and treatments showed no substantial reduction in potential quantum yield of PSII (F(v)/F(m)) at midday or predawn, indicating that there was little or no photoinhibition. Leaf nitrogen and soluble protein contents varied with leaf age during July, but did not vary between treatments. We conclude that the primary effect of burning is an increase in water availability to resprouting plants that eliminates the need for photoprotection, at least in the short term. The decrease in photosynthetic rates of unburned leaves in late July was the result of reduced stomatal conductance. We suggest that lowered stomatal conductance is the primary limiting factor in Q. ilex leaves, governing the regulation of carboxylation activity and energy dissipation processes.

Effect of fungal infection on leaf gas-exchange and chlorophyll fluorescence in Quercus ilex

“…Mean values of midday potential quantum yield of PS II , (F v / F m ) were also similar for all kinds of treatment (0.7 ± 0.01) (figures 3g,h and figures 4g,h) and only slightly lower than reported pre-dawn values for this species (0.78) [17]. The lack of differences in F v / F m between inoculated and control plants denoted that light processing structures in PS II were not affected by infection.…”

“…After these measurements, leaves were wrapped in aluminium foil to measure dark-adapted fluorescence: F o , F m and F v / F m (potential quantum yield of PS II equivalent to (F m -F o ) / F m )). The adaptation time was at least 20 minutes, after which values of F v / F m reach about 95% of pre-dawn ones in Q ilex [17]. Data were corrected for changes in measuring light intensity induced by temperature changes in the Mini Pam.…”

“…Increased rates of gas-exchange and growth have been observed in resprouts after fire or clear-cut [14,15,26,36], due to increased water [13,17,30] and/or nitrogen [16,20] availability for smaller crowns. Quercus species are also often affected by fungal pathogens such as Cryphonectria parasitica (Murrill) Barr.…”

Morphological traits and water use strategies in seedlings of Mediterranean coexisting species

“…Species show different aboveground and belowground characteristics responsible for their survival, growth, and reproduction in different habitats. There is broad evidence supporting a correspondence between the various root system traits developed by species in drought-prone ecosystems and their performance (Davis et al 1999;Bell 2001;Verdaguer and Ojeda 2002), with important implications on the extent of fluctuations in water status of species (Fleck et al 1995(Fleck et al , 1998. In addition, it has been reported that the first summer rainless period after seedling establishment is a major limiting factor when seedling roots are not fully developed (Vallejo et al 1999;Pratt et al 2007).…”

Conductance mesophyllienne pour le CO2 et caractéristiques morphologiques des feuilles sous stress hydrique pendant la repousse de Quercus ilex L.

“…Resprouts after any of these events show decreased shoot/root ratios, which makes more water and nutrients available to the shoot than in the original plants and favours photosynthesis stimulation and rapid growth (Fleck et al, 1998). Q. ilex is exposed to multiple environmental stress factors such as drought, heat shock, chilling, nutrient deprivation and high light stress amongst others.…”