Influence of nitrogen supply and growth irradiance on photoinhibition and recovery in Heuchera americana (Saxifragaceae)

Abstract

Prior work demonstrated that Heuchera americana, an evergreen herb inhabiting the deciduous forest understory in the southeastern United States, has a 3‐4‐fold greater photosynthetic capacity under the low‐temperature, strong‐light, open canopies of winter compared to the high‐temperature, weak‐light, closed canopies of summer. Moreover, despite the reductions in soil nitrogen, the chilling temperatures, and the increased quantum flux associated with winter, chronic photoinhibition was not observed in this species at this time of the year. We were interested in the photosynthetic acclimation and photoinhibition characteristics of this species when grown under contrasting light and nitrogen regimes. Newly expanded shade‐acclimated leaves of forest‐grown plants exposed to strong light varying in intensity and duration at 25°C showed a reduction in Fv/Fm (the ratio of variable to maximum room temperature chlorophyll fluorescence measured after dark adaptation), which was correlated with a decline in øa (the intrinsic quantum yield of CO2‐saturated O2 evolution on an absorbed light basis). Plants grown in the glasshouse under contrasting light (high and low light; HL and LL, respectively) and nitrogen supply (high and low nitrogen; HN and LN, respectively) regimes showed that photosynthetic acclimation to HL was impaired in LN regimes. The HL‐LN plants also had the lowest values of Fv/Fm and of ø on both incident and absorbed light bases and had 50% less chlorophyll (per unit area) compared to plants from other growth regimes. Controlled exposure to bright light at low temperatures (2‐3°C) for 3 h resulted in a sharp decrease in Fv/Fm (and rise in Fo, the minimum fluorescence yield) in all plants. Shade‐grown plants from both N regimes were highly susceptible to chronic photoinhibition, as indicated by a greater reduction in Fv/Fm and incomplete recovery after 18 h in weak light at 25°C. The HL‐HN plants were the least susceptible to chronic photoinhibition, having the smallest decrease in Fv/Fm with near full recovery within 6 h. The decline in Fv/Fm in HL‐LN plants was comparable to that of shade‐acclimated plants, but recovered fully within 6 h. Low‐N plants from both light regimes displayed greater increases in Fo which did not return to pretreatment levels after 18 h of recovery. These studies indicate that HL‐LN plants were sensitive to chronic photoinhibition and, at the same time, had a high capacity for dynamic photoinhibition. Experimental garden studies showed that H. americana grown in an open field in summer were photoinhibited and did not fully recover overnight or during extended periods of weak light. These results are discussed in relation to the photosynthetic acclimation of H. americana under natural conditions.

Nitrite–dependent nitric oxide production pathway: implications for involvement of active nitrogen species in photoinhibitionin vivo

“…Thus, it has been widely appreciated that a high nitrogen supply improves the acclimation capacity of photosynthesis against strong light (Castro et al 1995;Evans 1989;Ferrar & Osmond 1986;Hikosaka & Terashima 1995;Ramalho et al 1997;Skillman & Osmond 1998). The ¢nding of NR-dependent NO production o¡ers the new prospect that the nitrate assimilation pathway may be an alternative source of oxidative stress in plant cells.…”

“…Numerous studies indicate that photoinhibition can be distinguished into two qualitatively distinct classes on the basis of their relaxation time, i.e. dynamic photoinhibition and chronic photoinhibition (Castro et al 1995;Osmond 1994;Skillman & Osmond 1998).…”

Low leaf‐level response to light and nutrients in Mediterranean evergreen oaks: a conservative resource‐use strategy?

“…This opposite pattern could be due to the two main but opposing functions of carotenoids in photosynthetic tissues ; to increase light harvesting by acting as accessory pigments, and to protect photosynthetic units against high irradiance by dissipating excess energy as heat and quenching triplet excited chlorophyll and singlet oxygen (Codgell, 1988 ;Havaux et al, 1998). Thus, the increased carotenoid content of nutrient-limited plants in the sun could reflect enhanced photoprotection (Skillman & Osmond, 1998), whereas the increased carotenoid content in enriched plants in the shade could reflect enhanced light harvesting.…”

“…However, light environment interacted with nutrient availability in determining carotenoid content and composition. Since N supply affects both the sensitivity to photoinhibition and the production of photoprotective compounds (Ferrar & Osmond, 1986 ;Demmig-Adams & Adams, 1996 ;Skillman & Osmond, 1998), we expected that nutrient availability affected photoprotection via the VAZ. But the effect of nutrient availability on VAZ was significant only in the sun, since shade plants of both oak species had similar VAZ contents regardless of the nutrient treatment.…”

“…Our objectives were as follows : to study the leaf-level response of these two oak species to nutrients and light, plus the corresponding interactions, with regard to a large number (37) of morphological and physiological variables ; to validate a plasticity index ((maximum value -minimum)\ maximum) in combination with the significance of the difference among the means, as a simple method to assess both the extent and the significance of plant responsiveness to environment for variables with very different units and ranges of variation ; to explore the adaptive value of high versus low responsiveness in relatively harsh environments such as Mediterranean-type ecosystems. On the basis of what could be expected from the abundant literature on plant response to light and nutrients (Lambers et al, 1998 ;Berendse et al, 1999 ;Pearcy, 1999), we tested three specific hypotheses : (1) according to the postulate that species from harsh environments are less plastic than those from more favourable environments (Lortie & Aarssen, 1996 ;Valladares et al, 2000), the responsiveness of the two evergreen oaks should be low compared with that of evergreen woody plants from other more favourable biomes ; (2) since the ecological distribution of a species might be partly determined by the plasticity of its individual members (Sultan, 1995), Q. coccifera, should be less plastic than Q. ilex ; (3) as photoprotection via carotenoids interacts with both the light environment and the nutrient supply (Demmig-Adams & Adams, 1996 ;Skillman & Osmond, 1998), plants at low-nutrient supply should exhibit larger xanthophyll-cycle pools than at highnutrient supply, especially under conditions of high light intensities.…”