Photoinhibition of photosynthesis under natural conditions in ivy (Hedera helix L.) growing in an understory of deciduous trees |
| |
Authors: | Walter Oberhuber Helmut Bauer |
| |
Affiliation: | (1) Institut für Botanik der Universität, Sternwartestrasse 15, A-6020 Innsbruck, Austria |
| |
Abstract: | We investigated to what extent south-exposed leaves (E-leaves) of the evergreen ivy (Hedera helix L.) growing in the shadow of two deciduous trees suffered from photoinhibition of photosynthesis when leaf-shedding started in autumn. Since air temperatures drop concomitantly with increase in light levels, changes in photosynthetic parameters (apparent quantum yield, i and maximal photosynthetic capacity of O2 evolution, Pmax; chlorophyll-a fluorescence at room temperature) as well as pigment composition were compared with those in north-exposed leaves of the same clone (N-leaves; photosynthetic photon flux density PPFD< 100 mol · m–2 · s–2) and phenotypic sun leaves (S-leaves; PPFD up to 2000 mol · m–2 · s–1).In leaves exposed to drastic light changes during winter (E-leaves) strong photoinhibition of photosynthesis could be observed as soon as the incident PPFD increased in autumn. In contrast, in N-leaves the ratio of variable fluorescence to maximum fluorescence (FV/FMm) and i did not decline appreciably prior to severe frosts (up to -12° C) in January. At this time, i was reduced to a similar extent in all leaves, from about 0.073 mol O2 · mol–1 photons before stress to about 0.020. Changes in i were linearly correlated with changes in fv/fm (r = 0.955). The strong reduction in FV/FM on exposure to stress was caused by quenching in FM. The initial fluorescence (F0), however, was also quenched in all leaves. The diminished fluorescence yield was accompanied by an increase in zeaxanthin content. These effects indicate that winter stress in ivy primarily induces an increase in non-radiative energy-dissipation followed by photoinhibitory damage of PSII. Although a pronounced photooxidative bleaching of chloroplast pigments occurred in January (especially in E-leaves), photosynthetic parameters recovered completely in spring. Thus, the reduction in potential photosynthetic yield in winter may be up to three times greater in leaves subjected to increasing light levels than in leaves not exposed to a changing light environment.Abbreviations and Symbols F0, FM initial and maximal fluorescence yield when all PSII centres are open and closed - FV variable fluorescence (FM-F0) - Pmax maximal photosynthetic capacity at 1000 umol · m–2 · s–1 PPFD and CO2 saturation - PPFD photosynthetic photon flux density - i apparent quantum yield of photosynthetic O2 evolution - E-leaves, N-leaves shade leaves exposed, not exposed to drastic light changes during winter - S-leaves sun leaves from an open ivy standDedicated to Professor Otto Härtel on the occasion of his 80th birthdayThis work was supported by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung. |
| |
Keywords: | Chlorophyll fluorescence Hedera Photoinhibition of photosynthesis Photosynthesis (photoinhibition) Winter stress Xanthophyll cycle |
本文献已被 SpringerLink 等数据库收录! |
|