A. Virzo De Santo

TRACE METAL BIOMONITORING IN THE SOIL AND THE LEAVES OF QUERCUS ILEX IN THE URBAN AREA OF NAPLES

The concentrations of Pb, Cu, Fe, and Mn were analyzed in surface deposit and tissue ofQuercus ilex leaves from several sites of the urban area of Naples, exposed to different degrees of air pollution. These included some major roads with heavy traffic loads, squares, and three urban parks. The soil from the trunk base area ofQ. ilex trees in the same sites was also analyzed for total and available metal contents. Pb, Cu, and Fe contents in the surface deposit and leaf tissue were significantly higher (p<0.01) in leaves from roadside sites than in leaves from parks; significant correlations were found between deposit- and tissue-contents of Pb, Cu, and Fe. Mn content in leaves from roadside sites and in leaves from parks were similar and Mn content in the leaf deposit was irrelevant. Significant differences (p<0.001) in both total and available Pb and Cu soil content were found between sampling sites. Also for available Fe and Mn soil content differences among sites were relevant, although the highest values were measured in soil from urban parks. A positive correlation between leaf and soil metal content was found only for Pb, thus suggesting that trace metal contents of leaves directly depend on atmospheric depositions. Seasonal variations of Pb, Cu, and Fe were pronounced at a polluted site, whereas no relevant seasonal variation was observed at a control site; moreover, metal accumulation was high at the polluted site. Mn content and seasonal dynamics were comparable at control and polluted sites.

Seasonal changes in photosynthetic activity and photochemical efficiency of the Mediterranean shrub Phillyrea angustifolia L

Abstract This research aimed to investigate the physiological strategies that allow Phillyrea angustifolia, a sclerophyllous shrub widespread in the Mediterranean maquis, to cope successfully with the most stressful conditions of the Mediterranean climate i.e. summer drought and winter cold. Gas exchange and chlorophyll a fluorescence measurements as well as pigment content determinations were performed periodically throughout one whole year (spring 2004–spring 2005) on plants growing outdoor in the Botanical Garden of the Naples University. In June and July 2004 and in February 2005 the light-saturated net photosynthetic rate (P N) and stomatal conductance (gH2O) were lower compared to May and October 2004. Carboxylation rate (v c) was negatively affected by summer drought and low temperature. The quantum yield (ΦPSII) and maximum photochemical efficiency of PSII (F v/F m) significantly declined in February. All monitored parameters increased after each stressful period. The highest carotenoid content was detected in July whereas total pigment content was lower both in July and in February as compared to May and October, respectively. The photosynthetic apparatus of P. angustifolia is able to cope with summer drought and winter cold by different strategies: in summer, efficient stomatal control reduces water loss whereas in winter, PSII efficiency is down-regulated to avoid irreversible damage.

CAM, Transpiration, and Adaptive Mechanisms to Xeric Environments in the Succulent Cucurbitaceae

Xerosicyos danguyi Humbert and Seyrigia humbertii Keraudren are highly specialized members of the Cucurbitaceae and show adaptive features involving form, structure, and function which improve water economy and allow life in xeric environments. Both species exhibit succulence. Outdoor experiments demonstrated very low daily transpiration rates, relatively large nocturnal water loss, and malate accumulation, that is, the occurrence of crassulacean acid metabolism, which constitutes a high degree of physiological adaptation to drought.

Relationship between CAM and Succulence in Some Species of Vitaceae and Piperaceae

Crassulacean acid metabolism (CAM) and succulence were compared in two species of Peperomia (Piperaceae) and six species of Cissus and Cyphostemma (Vitaceae) The species include thin-leaved plants, leaf succulents, and stem succulents Succulence at the organ or the cellular level (mesophyll succulence [Sm]) does not appear to be causally related to CAM Peperomia, with high Sm, shows low CAM activity, while Cyphostemma, with relatively low Sm, exhibits very high CAM activity Overnight accumulation of malic acid as high as 332 μeq/g fresh weight was measured in the nonsucculent, thin leaves of Cissus sp, while only 50 μeq of malic acid per gram fresh weight accumulated in the succulent, photosynthesizing stem of the same plant In the thin-leaved species of Cissus, CAM does not appear to be related to drought adaptation Succulence in the CAM species Cissus may be a new acquisition that has allowed the genus to spread from the wet tropics to arid environments We suggest that CAM and succulence are often associated in drought-adapted plants because both characters have been selected for in arid environments

Photosynthesis and photoprotective strategies in Laurus nobilis L. and Quercus ilex L. under summer drought and winter cold

Abstract Photosynthesis and photoprotective mechanisms were investigated in the field on Laurus nobilis L. and Quercus ilex L. leaves exposed to summer drought (July) and winter cold (February) conditions compared with no-stress conditions (May). In July, net photosynthetic rate (A) and stomatal conductance (g s) decreased significantly compared with May in both species; conversely the highest ETR/A ratio and no difference in non-photochemical quenching (NPQ) was observed. In February A, g s and ETR/A declined compared with May but the highest NPQ were found in both species. Our data suggest that during summer, an increase of photochemical alternative pathways to carbon reduction, were able to effectively protect the photosynthetic apparatus under drought. In winter, the thermal dissipation of excess absorbed light constitutes the main safety valve for the photosynthetic apparatus.

Gas exchange and leaf metabolism of irrigated maize at different growth stages

Abstract Net ecosystem exchange (NEE), leaf gas exchange and biochemical traits were investigated in an irrigated maize crop grown under Mediterranean conditions. Sub-optimal irrigation water supply determined a drought stress during the early vegetative growth stage (45–49 days after swing) that decreased NEE. Drought, in the late vegetative stage, also caused a reduction of leaf gas exchange. In the latter period, proline, glycine and serine, as well as sucrose leaf contents increased, while starch, proteins and glucose contents decreased. In the early reproductive stage, the crop experienced a longer dry spell that induced a reduction in canopy as well as in leaf gas exchanges, while protein and free amino acid contents decreased with respect to the late vegetative stage. Both ecophysiological and biochemical data demonstrate a good capacity of cultivar Pioneer PR32D99 to endure the environmental stress, related to Mediterranean summer drought, leading to an elevated dry matter yield at harvest. Photosynthetic apparatus appeared fairly resistant to soil water shortage due likely to the increased leaf content of organic solutes, such as amino acids and soluble sugars.

Ecosystem carbon fluxes of a ryegrass and clover fodder crop in a Mediterranean environment

A mixture of ryegrass (Lolium italicum A. Braun) and clover (Trifolium alexandrinum L.) was sown in Eboli (Salerno, Southern Italy) in September 2007. Crop growth, leaf and canopy gas exchange and ecophysiological traits were monitored throughout the growth cycle. The gross primary production (GPP) was not affected by air temperature (Tair); on the contrary the ecosystem respiration (Reco) decreased as Tair decreased while net ecosystem CO2 exchange (NEE) increased. When was normalized with leaf area index (LAI), GPP decreased with Tair, a likely response to cold that down-regulated canopy photosynthesis in order to optimize the light use at low winter temperatures. Net photosynthetic rates (PN), the effective quantum yield of PSII (ΦPSII) and photosynthetic pigment content were higher in clover than ryegrass, in relation to the higher leaf N content. The lower ΦPSII in ryegrass was linked to lower photochemical quenching coefficient (qP) values, due to a reduced number of reaction centres, in agreement with the lowest Chl a content. This behaviour can be considered as an adaptive strategy to cold to avoid photooxidative damage at low temperature rather than an impairment of PSII complexes.

Crassulacean acid metabolism in Sedum dasyphyllum L.

Abstract Crassulacean Acid Metabolism (CAM) in Sedum dasyphyllum L. (Crassulaceae) was analysed by studying four ecotypes collected in sites at different altitudes in the Campania region (Italy), and grown in well‐watered conditions at the Botanical Garden of Naples. During the growth season, from winter to late spring, the overall malate content at dusk and at dawn declined strongly, thus showing a negative correlation with photoperiod. Overnight malate accumulation occurred even in plants kept in well‐watered conditions, but its extent varied with time and among the ecotypes. It was not related to photoperiod but to the daily temperature excursion which, when below a certain value, could prevent CAM activity. The specific activity of the enzymes involved in CAM also showed a seasonal pattern with a significant increase for phosphoenolpyruvate carboxylase, but a decrease for NAD‐dependent malate dehydrogenase and NADP‐dependent malic enzyme, at least in two ecotypes. Because phosphoenolpyruvate carboxyki...

Asymbiotic nitrogen fixation in the litter and surface soil of a Pinus laricio Poiret forest (Sila, Calabria, Italy)

Abstract Nitrogen fixation was measured in a Corsican pine (Pinus laricio Poiret) forest in Calabria (Southern Italy). Acetylene reduction activity (ARA) and CO2 production levels were determined by incubation of litter and superficial (0–5 cm) soil layer samples in the field, at monthly intervals. ARA variations were not correlated to those of substrate moisture, air temperature and microbial respiration. In fact N2 fixation presented phases of different intensity which irregularly followed each other. Both litter and soil showed similar rates of N2 fixation. Based on a C2H2:N2 ratio of 3:1 0.8 Kg N ha–1 y–1 in each layer are fixed in the Pinus laricio forest, thus contributing to the N status of the soil in this nutrient–poor forest.

Daily malate fluctuations in Sedum dasyphyllum L.

Abstract Sedum dasyphyllum L. leaves of well-watered plants kept outdoors and under controlled conditions show diurnal malic acid fluctuations. In well-watered plants growing outdoors the malate accumulation undergoes seasonal variations and seems to be inhibited by short photoperiod and/or by low temperature. The seasonal variations of CAM activity correspond to seasonal variations of mesophyll succulence. Water stress markedly depressed CAM activity. In fact, plants of S. dasyphyllum show, under controlled conditions, a decrease of malate accumulation as relative water content decreases. Recovery from water stress is fairly slow. Water potential quickly increases during rewatering and exceeds the original value after few days, suggesting a consumption of osmotic compounds during the water stress period.