Chiara Cascio

Chlorophyll a fluorescence analysis along a vertical gradient of the crown in a poplar (Oxford clone) subjected to ozone and water stress

An experiment in open-top chambers was carried out in summer 2008 at Curno (Northern Italy) in order to study the effects of ozone and mild water stress on poplar cuttings (Oxford clone). In this experiment direct fluorescence parameters (JIP-test) were measured in leaves from different sections of the crown (L: lower; M: medium; U: upper parts of the crown). The parameters considered were calculated at the different steps of the fluorescence transient, and include maximum quantum yield efficiency in the dark-adapted state (F(v)/F(M)); the L-band, at 100 ∝ s, that expresses the stability of the tripartite system reaction centre-harvesting light complex-core antenna; the K-band, at 300 ∝ s, that expresses the efficiency of the oxygen-evolving complex; the J-phase, at 2 ms, that expresses the efficiency with which a trapped exciton can move an electron into the electron transport chain from Q(A)(-) to the intersystem electron acceptors; the IP-phase, which expresses the efficiency of electron transport around the photosystem 1 (PSI) to reduce the final acceptors of the electron transport chain, i.e., ferredoxin and NADP; and finally the performance index total (PItot) for energy conservation from photons absorbed by PSII to the reduction flux of PSI end acceptors. The main results are: (i) different dynamics were observed between leaves in the lower section, whose PItot decreased over time, and those in the upper sections in which it increased, with a dynamic connected to the leaf age; (ii) ozone depressed all the considered fluorescence parameters in basal leaves of well-watered plants, while it had little or no damaging effect on medium-level or upper-section leaves; (iii) PItot and IP-phase increased in upper leaves of plants subjected to ozone stress, as well as the net photosynthesis; (iv) water stress increased PItot of leaves in all levels of the crown. The results suggest that ozone-damaged poplar plants compensate, at least partially, for the loss of photosynthesis with higher photosynthetic rates in young leaves (in the upper section of the crown), more efficient to fix carbon.

Short and long term photosynthetic adjustments in sun and shade leaves of Fagus sylvatica L., investigated by fluorescence transient (FT) analysis

Abstract Fluorescence transient (FT) analysis (fast kinetics) was carried out on sun and shade leaves of beech seedlings in an experimental field at Curno (North Italy), during the 2008 growing season (June–August). The aim of the research was to determine: (1) morphology in sun leaves as long term acclimation to high light; (2) short term responses to high light, i.e. during the course of the day; (3) evolution of responses during the growing season and the ageing process. Sun leaves differ from shade leaves by their lower trapping capacity (expressed by the ratio FV/FM) and higher capacity to reduce end acceptors beyond PSI (expressed by phase I–P of the FT). These features were assessed at pre-dawn, when the entire plant is fully dark-adapted. Short term responses (differences between midday and pre-dawn assessments) occur especially in sun leaves, indicating that the photosynthetic machinery reacts to the high excitation pressure by increasing photochemical and non-photochemical de-excitation processes. Other responses concern the inactivation of the oxygen evolving system and a stability loss of the tripartite system reaction centre (RC) – harvesting light complex – core antenna, expressed by the onset of K and L-bands at midday. Sun leaves are well acclimated to high light from a structural and functional point of view, however, the irradiance at midday provokes conditions of instability in the photosynthetic machinery, possibly through reactive oxygen species (ROS) production at both PSII and PSI sides. The temporal patterns across the growing season indicate the progression of senescence processes, that are more pronounced in sun leaves which present a permanent (chronic) condition of photoinhibition. Differences between sun and shade leaves decrease over time.

Responses to ozone on Populus "Oxford" clone in an open top chamber experiment assessed before sunrise and in full sunlight

The effects of ambient levels of ozone and summer drought were assessed on a poplar clone (Populus maximowiczii Henry X P. × berolinensis Dippel — Oxford clone) in an open top chamber experiment carried out at the Curno facilities (Northern Italy). Chlorophyll (Chl) a fluorescence parameters (from both modulated and direct fluorescence) were assessed at different hours of the day (predawn, morning, midday, afternoon, and evening), from June to August 2008. This paper compares the results from predawn (PD, before sunrise) and afternoon (AN, in full sunlight) measurements, in order to evaluate the role of high sunlight as a factor influencing responses to ozone stress. Sunlight affected the maximum quantum yield of primary photochemistry (decrease of Fv/Fm) thus indicating photoinhibition. The effective quantum yield (ΦPSII) and the photochemical quenching (qP) were enhanced in the afternoon with respect to the predawn, whereas the nonphotochemical quenching (NPQ) was reduced. The effect of ozone was detected with fluorescence on well watered plants in the first week of July, before the onset of visible symptoms. As far as Fv/Fm are concerned, the differences between ozone-treated and control plants were statistically significant in the predawn, but not in the afternoon. Ozone exerted only minor effects on drought exposed plants because of the reduced stomatal ozone uptake, but effects on the IP phase of the fluorescence transient were observed also in drought-stressed plants.

The JIP test: a tool to screen the capacity of plant adaptation to climate change

Abstract Adaptation and acclimation are strategies that forests enact to cope with climate change. They consist of genotypic and phenotypic adjustments that allow plants to grow and reproduce successfully in a stressful environment. Both these aspects can be actively promoted by reforestation programmes. The key phases are: (1) selection of the most suitable provenances and genotypes; (2) adoption of adequate cultural techniques in nursery; and (3) monitoring of the plantations. Physiological techniques may be useful to assist all the phases of this process. Among these, chlorophyll fluorescence-based techniques, such as the JIP test, are relevant to monitor the stress conditions and the effectiveness of the cultural practices. JIP test is a non-destructive, non-invasive, informative, very fast and inexpensive technique, and can be used to support the cultural decision.

Response to Ozone of Fagus sylvatica L. Seedlings Under Competition, in an Open-Top Chamber Experiment: A Chlorophyll Fluorescence Analysis

This study was carried out within an open-top chamber facility in Southern Switzerland. The experiment was performed in the year 2004 and consisted in small populations of Fagus sylvatica L. seedlings growing in pure culture and under the competition of Viburnum lantana L. seedlings, in sub-plots in four non filtered (NF, i.e. treated with ambient air) and four charcoal-filtered chambers (CF, i.e. treated with air containing 50% of ambient air ozone). Chlorophyll a fluorescence of the PS II was measured once a month from June to September 2004. PS II efficiency and performances tended to decrease over time in the NF chambers as compared to CF ones, in the Fagus sylvatica plants growing without competition. On the other hand, the presence of Viburnum lantana (which grows faster than Fagus sylvatica) seemed to protect the photosynthesis machinery of the Fagus sylvatica plants growing under competition.

Variability of Photosynthetic Performances in Tree Seedlings Under Ozone and Water Stress

Analysis of the variability in photosynthetic properties and responses (within and among individuals) is important in assessing the impact of stress factors in plant population and communities, as well as in supporting remote sensing techniques. Photosynthesis parameters, namely the Performance Index (PIABS), assessed by direct fluorescence techniques, were measured during an open-top chamber experiment at Curno (North Italy) in 2005. This experiment consisted in treatments of seedlings belonging to different tree species, in non filtered (NF, i.e. treated with ambient air) and charcoal-filtered (CF, i.e. treated with air with 50% of ambient air ozone) air, in watered (W) and not watered (D) conditions. The variability of PIABS was tested by means of the coefficient of variation (CV% = standard deviation/mean expressed as percent). CV% changed over time: it is higher at the beginning of the season and lower in the central months of the summer. CV% was usually higher in stressful conditions and correlated negatively with PIABS. This finding indicates that moderate stress factors act selectively on different individuals, and individual differences within population are enhanced.