Castanea sativa Mill: Reponse of water stress. Application of the chlorophyll fluorescence technique

Castanea sativa Mill.: RESPONSE OF WATER STRESS. APPLICATION OF THE CHLOROPHYLL FLUORESCENCE TECHNIQUE Svetla BRATANOVA-DONCHEVA1 & Maurice METHY2 Central Laboratory of General Ecology - BAS, [email protected] 2 Centre d`Ecologie Fonctionnelle et Evolutive – CNRS

1

ABSTRACT Bratanova-Doncheva S. & Methy M. (2004). Castanea sativa Mill.: response of water stress. application of the chlorophyll fluorescence technique. Proceedings of the 2nd Congress of Ecologists of the Republic of Macedonia with International Participation, 25-29.10.2003, Ohrid. Special issues of Macedonian Ecological Society, Vol. 6, Skopje. The drought tolerance of the plant is: the maintain of high photochemical PSII efficiency with good limitation of water loses via the stomates and with efficacy PSII regulation in the presence of high light radiation. The Castanea sativa Mill. presented a high capacity of PSII to ignore the chronical photodamages and to restore very effectively the optimal photochemical efficiency - this is a very important component of the drought strategy of this species. Key words: drought tolerance strategy, water stress, water predawn potential, maximal photochemical efficiency, actual photochemical efficiency, non photochemical quenching of fluorescence, chlorophyll fluorescence, Castanea sativa Mill.

Introduction Chestnut forests in the South West parts in Bulgaria with Mediterranean influence are submitted to rather mild climate with not enough precipitation. The climatic characteristics include a pronounced bi-seasonality with dry and hot summers and moist and cool autumns and winters. And they suffer at irregular intervals from marked periods of drought and it is very possible to be at least partly responsible for occurrence of dieback. The drought probably also had marked effects on chestnut growth and productivity. They suffered greatly from water shortage during the summer. Response to water stress The physiological events and mechanisms involved in water stress tolerance are still insufficiently understood. Efficiencies of soil water extraction and water transport pathways in the trees probably play a major role and differ significantly among species. Stomatal regulation of leaf gas exchange during water shortage has been well documented for drought-adapted species growing under Mediterranean or semi-arid environment (Tenhunen et al. 1987). Stomatal closure contributes to reduce water losses during the period of limited water availability and high evaporative demand. But in addition, the ability to keep a photosynthetic activity during the drought period and to maintain significant rate of CO2 assimilation has

an important role in the plant strategy to drought tolerance. The drought tolerance of the plant could be defined with: the maintain of high photochemical PSII efficiency with good limitation of water loses via the stomata and with efficacy PSII regulation in the presence of high light radiation. Results obtained in vivo with the chlorophyll fluorescence measurements and oxygen evolution of leaf disks revealed that the photosynthetic apparatus may be rather resistant to leaf water deficits (Kraiser 1987; Cornic et al. 1989; Epron & Dreyer 1992). But under natural conditions many other factors interact with the soil water depletion and promote damage to Photosystem II, like as high temperatures and high irradiance. Increased sensitivity to high irradiance and protection mechanisms against these injuries has been reported during water deficits under controlled conditions (Cornic et al. 1989; Epron & Dreyer 1990; Methy et al. 1996; BratanovaDontcheva et al. 1998). Chlorophyll fluorescence technique The chlorophyll fluorescence technique actually in ecophysiology is a tool for better understands the plant response to stress. This non-destructive and rapid technique gives quickly the estimation of the photosynthesis in vivo and presents possibilities to assess not only the actual photochemical efficiency of the plant and its capacity but also to enter in the details in the biochemical part of the photochemical reactions and to help to understand the different ways of energy

Proceedings of the 2nd Congress of Ecologists of Macedonia

43

Svetla BRATANOVA-DONCHEVA & Maurice METHY usage (Krause&Weis 1991; Von Caemmerer & Farquhar 1981; Schreiber & Berger 1987; Epron et al. 1992; Bratanova-Dontcheva 1995). Today the chlorophyll fluorescence was evoluted as a very useful and rich of information probe for analysis of the photosynthetic electron transport in dependence of the different stress factors (Briantais et al. 1986; Schreiber & Berger 1987; Krauze & Weis 1991). Chlorophyll fluorescence has been used successfully for analyzing PSII activity in vivo with (Epron et al. 1992; Bratanova-Dontcheva et al. 1998) or without (Janda et al. 1994; Jefferies 1994; Methy et al. 1996) further net CO2 assimilation measurements. Maximal and actual photochemical efficiencies of PSII can be assessed (Genty et al. 1989). Sharkey et al. (1988) showed that electron transport estimated by fluorescence was directly comparable (nearly 1:1) with electron transport estimated by CO2 assimilation, assuming that only 4 electrons transported by PSII are used for CO2 fixed. The chestnut tree prefers the north expositions and the expositions with north component. It prefers also the high level of humidity atmospheric, but what about the drought of soil. These results are part of large project, which the main aim is the assessment of the actual state of the chestnut ecosystems in the South West part of Bulgaria in the global change conditions. Aim of the study The objective of this study was to estimate the sensitivity of photosynthetic apparatus to water stress of Castanea sativa Mill. in vivo and to precise the protection mechanisms, which are the main components of the drought protection strategy of this species.

Material and methods Plant material, experimental design The experiments were carried out in Montpellier, France (43°36’ N, 3°53’E; 55 m elevation), on 25, 3-

years old individuals of Castanea sativa Mill. in 8-l pots filled with a mixture of compost (53%), mould (21%) and loam (26%). In the beginning of the experiment the plants ware irrigated twice a week. Withholding of water supply in the beginning of the growth period imposed drought. Predawn leaf water potential, monitored by means of a Scholander pressure chamber, was used as an index of drought intensity. This parameter was assessed on 3 leaves on the upper part of them. Chlorophyll fluorescence measurements The saturation pulse method associated with the pulseamplitude-modulation technique (Schreiber et al., 1986; Schreiber & Bilger, 1987; Epron & Dreyer, 1992; Methy et al., 1996; Bratanova-Dontcheva et al., 1995; 1998 etc) was used for chlorophyll fluorescence measurements (fluorometer PAM 2000, Walz, Germany). Initial fluorescence Fo was determined by applying a weak modulated measuring light (0,1 µmol.m-2.s-1, 655 nm) at a frequency of 600 Hz on the adaxial surface of dark-adapted leaves. Leaf clips (PEA/LC, Hansatech, UK) were used for the dark adaptation (30 min) in the daytime. Maximal fluorescence Fm in dark-adapted state was assessed with pulses of 800 ms high intensity (>15 000 µmol.m-2.s1 ) white light (