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Many studies across a range of ecosystems have shown that decomposition in mixed litter is not predictable from single-species results due to synergistic or antagonistic interactions. Some studies also reveal that species composition and relative abundance may be more important than just richness in driving non-additive effects. Most studies on litter decomposition in Mediterranean maquis, an high-diversity shrubby ecosystem, have dealt exclusively with single species. In this study we investigated, at the individual-litter level, as well as at the litter-mixture level, the effect of litter mixing on decomposition of 3-species litter assemblages with different relative abundance of the component litters; we set up two types of litter assemblages that reflected the heterogeneity of bush cover in the inner maquis and at the edge maquis/gaps, as related to the leaf traits, i. e. sclerophylly vs mesophylly. We measured mass loss, decay of lignin, cellulose and ADSS (acid detergent soluble substances) and fungal mycelium ingrowth. The results show that over a 403-day incubation period, the decomposition of individual litters in mixtures deviated from that of monospecific litters and had different directions. In litter mixtures of the sclerophylls Phillyrea angustifolia and Pistacea lentiscus with the mesophyll Cistus, decomposition was lower than expected (antagonistic effect); in the mixtures of litters with similar physical structure (Ph. angustifolia and P. lentiscus with Quercus ilex) decomposition was faster than expected (synergistic effect). When considering the different decomposition phases, both negative and positive effects occurred in Quercus mixtures depending on the phase of decomposition. In both types of 3-species litter assemblages the greatest effect occurred in uneven mixtures rather than in even mixtures. Our results show that species composition drives the direction whilst the decomposability and the relative abundance drive the magnitude of non-additive effects of litter mixing on decomposition.

In natural conditions, litters shed from different species become mixed with each other, and decompose together. Most studies deal with decomposition of individual species; few studies investigate the influence of litter mixing on decomposition and nutrient dynamics; the results are contradictory as positive, negative, or no effect, of litter mixing have been observed. In this study we test the hypothesis: i) that litter mixing in the Mediterranean maquis, a nutrient poor, high diversity ecosystem, produces non-additive effects on nutrient dynamics; ii) that the effects vary with the composition in species of the mixture and with the relative amount of the species component the mixture. Two types of 3-species mixtures were set up; one contained three sclerophylls, Phillyrea angustifolia, Pistacia lentiscus and Quercus ilex; the other contained the first two species with the mesophyll Cistus. Litterbags, containing monospecific litters and even and uneven mixtures, were incubated under natural condition in situ; even mixtures had the 3 species in equal proportion, whereas uneven mixtures had one of the species as dominant (50%) and the other two species in equal proportion (25%:25%). Litterbags were retrieved after 92, 188 and 403 days; litters from the mixtures were separately analyzed for mass loss and content of nitrogen (N), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn). Results indicate that mixing influences the dynamics of N, Mn, Ca, Mg, Fe, Cu and Zn, but scarcely affects the dynamics of K and Na. The comparison of observed to expected values for changes of nutrients in litterbags indicates the occurrence of non-additive effects of litter mixing on movements of N, Fe, Cu, and Zn to or from the litterbags containing the mixtures. The effects depend on the composition in species of the mixture, whereas the relative amount of the species component the mixture is not relevant.

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.

The Mediterranean area of Southern Italy is characterized by different natural plant covers that mainly reflect different successional stages (i.e. low maquis, high maquis, Quercus ilex wood) and managed areas with introduced plant species (such as Pinus species). Soil properties could be affected by plant cover types as well as by plant species. Our objective was to determine the relationships of plant cover types and plant species with the chemical and biological characteristics of the soil. In four neighbouring areas with different plant cover types (low maquis, pure high maquis, high maquis with pines and pinewood, with pines planted by foresters in both cases), soil samples were collected under different plant species in order to evaluate the effect of plant cover types and plant species on soil properties. Soil samples were analyzed for nutrient content, microbial biomass, soil potential respiration and enzymatic activity (phosphatase, arylsulphatase, β-glucosidase and hydrolase activities) as well as for pH, water holding capacity (WHC) and cation exchange capacity (CEC). Application of cluster analysis and principal component analysis to the data revealed that the plant cover type was the key factor influencing soil properties more than plant species. In fact, the largest differences were observed between pure high maquis soils and all other soils, with pure high maquis soils generally showing the highest values of WHC, CEC, nutrient content, organic and microbial C, soil respiration, phosphatase, arylsulphatase and β-glucosidase activities. The significantly lower values of these variables in the low maquis relative to the pure high maquis probably reflect the effect of ecological succession on soil. The high maquis with pine, differing from the pure high maquis only for the presence or absence of pine, showed values of soil physical, chemical and biological characteristics similar to those found in the low maquis, thus suggesting that the presence of pine retards soil development. © 2004 Elsevier Ltd. All rights reserved.

We studied late-stages decomposition of four types of coniferous needle and three types of deciduous leaf litter at two sites, one nutrient-poor boreal and one nutrient-rich temperate. The late stage was identified by that reached by litters at the onset of net loss of lignin mass, i.e. at about 1 year after the incubation when the highest amount of lignin had been detected; the study extended over the following 2 year period. Decomposition rates were significantly lower at the boreal than at the temperate site and did not differ between needle litter and leaf litter. In the boreal forest: (1) mass-loss was positively correlated with N and Mn release, (2) Mn concentration at the start of the late stage was positively correlated with lignin decay, (3) Ca concentration was negatively correlated to litter mass loss and lignin decay. In the temperate forest neither lignin, N, Mn, and Ca concentration at the start of the late stage, nor their dynamics were related to litter decomposition rates and lignin decay. In leaf litter mass-loss and lignin decay were positively correlated with N and Ca release and with Ca concentration. In needle litter mass-loss was positively correlated to Mn release and N concentration negatively with lignin decay. We concluded that Ca, N and Mn have different roles in controlling lignin decay depending on type of litter and site conditions. © 2008 Springer Science+Business Media B.V.

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), ana 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 snowing 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 carboxykinase activity was not detected, S. dasyphyllum could be placed in the group of malic enzyme CAM species. None of the activities were correlated to overnight malate accumulation, but, like overall malate content, to photoperiod, at least in two ecotypes. No statistically significant changes in the day/night activities of phosphoenolpyruvate carboxylase and NADP-dependent malic enzyme were detected. Overnight malate accumulation ana phosphoenolpyruvate carboxylase activity were higher in leaves from flowering stems than in those from vegetative ones, suggesting that CAM activity can also contribute to the reproductive success of the species in its habitat, where water can be limited when flowering and seed ripening occur. © 1999 Taylor & Francis Group, LLC.

The dynamics of nutrients (N, P, K, Ca, Mg) in decomposing beech and fir litters was studied. N, P, Mg and Ca content increased in all litters, whereas K content decreased. Nutrient content correlated to mass loss with a few exceptions for K and P. Final N, K, Mg and Ca content was higher the lower the initial content and the higher the initial C/nutrient ratio was. Final P content correlated neither with initial P content nor with initial C/P ratio. All litters lost K very quickly, mainly by leaching. P was lost initially by leaching, although at a lower rate than K, and later by mineralization. Mg, Ca and N showed alternate phases of accumulation and release. Mg losses by leaching occurred only in litters with high initial Mg content; in litters with low initial Mg content, Mg losses occurred by mineralization. Ca and N were lost only by mineralization. A mobility series K>P>Mg>Ca=N is suggested.

Gas exchange and chlorophyll a fluorescence measurements were performed simultaneously on leaves of Phillyrea angustifolia L. to assess the effects of heat stress (30 min at 40 °C) on photosynthesis and photosystem II (PSII) photochemical efficiency of plants grown at ambient CO2 and exposed to an elevated CO2 concentration (800 µmol·mol–1) and 300 µmol photons·m–2·s–1. No significant difference was found in the heat-induced decreases of net photosynthesis (PN), quantum yield of PSII electron transport (ΦPSII), and maximum PSII photochemical efficiency (Fv/Fm) between plants exposed to ambient and elevated CO2 concentrations, showing that elevated CO2 was not able to reduce the potential for photoinhibition at high temperatures under moderate light conditions. The heat-induced decrease of PN was higher than that of ΦPSII indicating that reductive power was more utilized in non-assimilatory processes than in CO2 fixation at both CO2 treatments. This result suggested that impairment of the Calvin cycle rather than electron transport inhibition was the main cause of the limitation in CO2 fixation.

The dynamics of Mn, Zn, Fe, Cu, Pb, and Cd during litter decomposition was studied to understand how litter and soil metal concentrations influence the accumulation and/or the release of metals. Three types of leaf litters (green and brown leaves of Populus tremula L., green leaves of Betula pubescens Ehrh.) and four types of needle litters (green and brown needles of Pinus sylvestris L., brown needles of Pinus contorta L. and Pinus pinea L.), differing in heavy metal concentrations were incubated at two unpolluted coniferous forest sites: a temperate silver fir (Abies alba Mill.) forest at site Monte Taburno, southern Italy, and a boreal Scots pine (Pinus sylvestris L.) forest at site Jadraas, Sweden. Compared to the Scots pine forest, the humic surface horizon of the silver fir forest had a higher pH, higher concentrations of available Cu and Cd, and lower Fe concentration. After a period of about 900 days, all litter types were more decomposed at M. Taburno than at Jadraas. Zn, Fe, Pb and Cd concentrations in leaf and needle litters increased at both sites; Cu concentrations increased only in the silver fir forest; Mn concentration decreased in the litter richest in Mn and increased in the litters poorest in Mn. Litter decomposition in an early phase (0 up to 528/565 days) was significantly and positively correlated to initial Cu and Cd concentrations in litter. In a late phase (528/565 up to 918/929 days), decomposition was correlated significantly and negatively with litter Zn and Cu, and significantly and positively with litter Mn concentration at the start (528/565 days) of the period. At both sites, increases in absolute amounts of Fe, Cd, and Pb were observed in all litters; however, P. pinea, which showed the highest initial concentration of Pb, released Pb during decomposition. All litters released Cu at Jadraas and accumulated Cu at M. Taburno. Zn was released at both sites from all leaf litters and from the needle litter of P. contorta. Mn was released at both sites from all litters, except the litter of P. tremula, which accumulated Mn at Jadraas. The results indicate that heavy metal accumulation or release may depend on the gradient of metal concentration between litter and soil, on the pH of the soil, and on the capacity of litter to bind metal; atmospheric deposition could account at least partly for the increase of absolute amounts of Pb, Fe, and Cu at M. Taburno.

Quercus ilex plants grown on two different substrates, sand soil (C) and compost (CG), were exposed to photosynthetic photon flux densities (PPFD) at 390 and 800 µmol(CO2) mol−1 (C390 and C800). At C800 both C and CG plants showed a significant increase of net photosynthetic rate (P N) and electron transport rate (ETR) in response to PPFD increase as compared to C390. In addition, at C800 lower non-photochemical quenching (NPQ) values were observed. The differences between C390 and C800 were related to PPFD. The higher P N and ETR and the lower dissipative processes found in CG plants at both CO2 concentrations as compared to C plants suggest that substrate influences significantly photosynthetic response of Q. ilex plants. Moreover, short-term exposures at elevated CO2 decreased nitrate photo-assimilation in leaves independently from substrate of growth.

Litter quality is an important determinant of soil organic matter formation. Changes of organic components were investigated along decomposition of black locust (Robinia pseudoacacia L.) leaf litter and black pine (Pinus nigra Arn.) needle litter in the native adjacent coeval forest stands. To this purpose, data from proximate analyses were compared with those from CPMAS 13C NMR. Newly shed leaf litter of black locust had significantly higher concentrations of ADSS (acid detergent soluble substances) as well as lower concentrations of cellulose and AUR (acid unhydrolyzable residues that include lignin) and higher AUR-to-Cellulose ratio than that of black pine. The 13C CPMAS NMR spectra of newly shed leaf litter of black locust and black pine revealed that O-Alkyl-C components (including cellulose and hemicelluloses) accounted, respectively, for 53.8% and 61.4% of the total area of the spectra. All other C fractions were relatively more abundant in black locust than in black pine. Within individual sampling periods, relationships between residual litter mass and concentrations of ADSS, cellulose and AUR were examined, as were relationships between residual litter C and NMR fractions. Four periods were defined based on the slopes of the decomposition curve, with the length of period I defined by the start of a net decrease of AUR. Proximate analyses and NMR data showed changes in chemical composition over the decomposition process, as well as changes in decay rates of the residues, following different paths in the two litters. ADSS decayed faster in black locust litter; in contrast cellulose and AUR decayed faster in that of black pine. AUR concentration increased in both litters during decomposition; however, compared to black pine, the remaining litter of black locust was richer in AUR, despite the lower initial concentration, and had a higher AUR-to-Cellulose ratio. Phenol-C and Aryl-C decayed faster in black locust litter, while Alkyl-C decayed faster in that of black pine. In both litters, mass loss in periods was negatively correlated to concentration of AUR at the start of the periods. C loss in periods was negatively correlated to the concentration at the start of the periods of MC-to-PC (an index of lignin content) in black locust litter and positively correlated to Alkyl-C and O-Alkyl-C in that of black pine. Phenol-C, O-Alkyl-C and Aryl-C were the most decomposable C fractions in black locust. O-Alkyl-C and Alkyl-C were the most decomposable C fractions in black pine. Limit value was lower in black pine than in black locust. Consequently the different pattern of litter decomposition can affect the size of C sequestration in the forest floor and the quality of accumulated organic carbon.

Plants in Mediterranean environments can adopt photoprotective mechanisms to cope with winter temperatures, thus avoiding photoinhibition. An increase in global temperature is expected in the future as a consequence of climate change. The aims of this work were (i) to analyse anatomy and photochemical activity in winter leaves of Cistus incanus L., to identify characters having a potential role in photoprotection under natural winter conditions, and (ii) to evaluate the effect of higher temperature on such traits. Leaves from plants grown in a greenhouse (indoor) were compared with those from plants grown outdoors on the basis of anatomical and photochemical traits, including indexes evaluating the exposure of chloroplasts at the cell surface. Leaves developed outdoors were characterized by anatomical traits related to the optimization of light harvesting and to gas-exchange control. Such traits were accompanied by a higher pigment content and an increase in the thermal dissipation of excess absorbed light. Indoor leaves showed physiological and morphoanatomical adjustments addressed to invest more of absorbed light in photochemistry. Overall, our analysis showed that (i) photoprotection in C. incanus relies on adaptive traits at both the morphoanatomical and physiological level and (ii) C. incanus leaves seem to be able to acclimatize to warmer winters.

The objective of this investigation was to assess the changes in chemical composition (lignin, cellulose, hemicelluloses, non-structural compounds, N, and ash) of decomposing litter. Standard Pinus sylvestris needle litter, originating from southern Sweden, was incubated in litterbags at 15 sites selected from the Netherlands to south Spain. The changes in chemical composition of this litter were determined using near infrared reflectance spectroscopy. The hypothesis was that standard (chemically uniform) litter decomposing under a range of climates would show different dynamics of accumulation and loss of C-fractions, N, and ash, relative to mass loss. It was shown that, for a given mass-loss value (10, 20, 30, 40, or 50%), the proportion of lignin, cellulose, hemicelluloses, non-structural compounds, N, and ash in the decomposing pine needles differed between sites. Lignin concentration in the litter residue at 50% mass loss ranged from approximately 26 to 43%, cellulose from 19 to 27%, hemicelluloses from 7 to 11%, non-structural compounds from 19 to 25%, N from 0.7 to 1.3%, and ash content from 1.4 to 10.1%. Lignin concentrations showed the highest range of variation. Lignin concentrations during decomposition were positively related to moisture factors as significant correlations were found with actual evapotranspiration and were improved in multiple regressions by the mean annual precipitation or the water surplus. Cellulose was degraded further at sites with high precipitation whereas hemicellulose degradation was related to temperature. This leads to the conclusion that the remaining organic matter produced by standard litter decomposition within the studied climatic range of variations tended to be more recalcitrant under wet and warm climatic conditions than under cold or dry climate.

We synthesized available data for decomposition of pine (Pinus) needle litter in pine forests to determine the litter chemical characteristics and climate factors that explained variation in the limit value, i. e. the level of accumulated mass loss at which the decomposition process either continues at a very low rate or possibly stops. Our data base included 56 separate studies on decomposition of pine needle litter, spanning Scots pine, lodgepole pine, Aleppo pine, stone pine and white pine, mainly incubated at the site of collection. Studies had 5 to 19 samplings, on average 10, and the decomposition was followed to a mass loss ranging from 47 to 83%, on average 67%. The periods from 3.0 to 5.4 years, on average 3.9 years, were of sufficient duration to allow estimates of limit values of decomposition. We used a linear mixed model with regression effects to relate limit values to potential explanatory variables, namely the sites' long-term mean annual temperature (MAT) and mean annual precipitation (MAP) and to substrate-chemistry factors. Regarding the latter, we explored two models; one that included initial concentrations of water solubles, lignin, N, P, K, Ca, Mg, and Mn and one that included only lignin, N, Ca, and Mn to focus on those nutrients known to influence lignin degradation. Using backward elimination significant explanatory variables were determined. For litter decomposed in its site of origin we found the limit value to depend mainly on the initial concentration of Mn, with higher Mn concentrations resulting in higher accumulated mass loss. Thus, litter with higher Mn reached a higher limit value and left a smaller stable fraction. This is likely due to the fact that Mn is an essential component of ligninolytic enzymes important for degrading litter in the later stages of decomposition. Manganese has received little attention in decomposition studies to date. Given its significance in this synthesis, the role of Mn in influencing variation in the late stages of decomposition among ecosystems and among litters of other genera besides Pinus deserves further attention. © 2010 Springer Science+Business Media B.V.

The final (limit) values for litter decomposition were estimated and, by extrapolating a linear relationship between accumulated litter mass loss and litter N concentration, the N concentration at the limit value (Nlimit) was estimated. The values for Nlimit were compared with those of the A01 layer (Nhumus) and of newly shed litter (Ninit). No difference was found between the A01 and A02 layers when their N concentrations were compared with the values for Nlimit. There was a highly significant linear relationship between Nlimit and Ninit (R2 = 0.769 and p < 0.001). Likewise, there was a highly significant linear relationship between Nhumus and Ninit. When these two linear relationships were compared, there was no significant difference in slope, while there was a significant difference in the intercepts of 6.76 and 7.25 mg·g-1 for Nhumus and Ninit, respectively. Thus, for a given site in our investigation, the estimated value for N concentration in humus would be 6.8% lower than the measured one.

The present study investigates the impact of fire (low and high severity) on soil fungal abundance and microbial efficiency in C assimilation and mineralisation in a Mediterranean maquis area of Southern Italy over 2 years after fire. In burned and control soils total and active fungal mycelium, microbial biomass C, percentage of microbial biomass C present as fungal C, metabolic quotient (qCO2) and coefficient of endogenous mineralisation (CEM) were assayed together with several chemical properties of soil (i.e. pH and contents of organic C, total and mineral N, available K, Mg, Mn and water). Fire significantly decreased the fungal mycelium, whereas it stimulated microbial growth probably through the enhancement of bacterial growth because of the increase in organic C and nutrient contents in burned plots. This shift in microbial community composition might explain the observed reduction in soil microbial efficiency of C assimilation (high qCO2) and the increase in C mineralisation rate (CEM) in the first 84 days after fire. Therefore, fire might increase CO2 input to the atmosphere not only during combustion phase but also in the post-fire period. © 2007 Springer-Verlag.

Summary The effects of high irradiance (700 and 1400 μmol photons m −2 s −1 ) on the regulation of photochemistry in leaves and stems of the CAM plant Cissus quinquangularis Chiov. were investigated by chlorophyll a fluorescence parameters. Significant decreases in F o , F m and F v were observed in the leaf and in the stem tissues with increasing light intensity and exposure time. F v /F m , the PS II photochemical efficiency, decreased at an higher extent in stems and leaves at 1400 μmol photons m −2 s −1 . Non-photochemical quenching increased with the intensity and duration of light exposure, being higher in leaves than in stems. Upon high-light stress, a slighter reduction in quantum yield of the PS II electron transport was observed in the stem than in the leaf tissue. A significant decrease of photochemical quenching was observed in leaves but not in stems, thus suggesting a different strategy in the regulation of photochemistry in leaves and stems of C. quinquangularis plants exposed to high-light stress.

The fungal mycelium ingrowth and the rates of mass loss and respiration of needle litter of Pinus pinea, Pinus laricio, Pinus sylvestris, and Abies alba were investigated, in three coniferous forests, over a 3-year period by means of a composite set of incubations. In the early stages, the fungal flora of the decomposing needles was dominated by dematiaceous hyphomycetes and coelomycetes. Basidiomycetes reached a peak after 6 months on pine needles, but were absent from the N-rich needles of A. alba. Soil fungi (Penicillium, Trichoderma, Absidia, Mucor sp. pl.) became most frequent in later stages. At the end of the study period, the total mycelium amount showed the lowest values in all pine needles incubated in the P. laricio forest and the highest ones in P. pinea needles incubated in the P. pinea forest. In all data sets, as in data for boreal forests examined for comparison, the concentration of litter fungal mycelium versus litter mass loss followed a common exponential model. However, in later stages, the amount of litter fungal mycelium was very close to that of the humus at the incubation site, thus supporting the hypothesis of a logistic growth pattern. Respiration rates of decomposing litters varied with season and decreased with litter age to values close to those of the humus at the incubation site. Respiration of water-saturated litter was negatively correlated with the total mycelium concentration, and this was consistent with the observation that in far-decomposed litter only a minor fraction of the total mycelium is alive. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Significant differences in the chemical composition of falling needle litter were found among various pine species. A comparison between the needle litter of northern species (Scots pine and lodgepole pine) and that of 17 other, southern species combined showed that concentrations of N, P, Mg, K, and lignin were significantly lower in the northern group. In contrast, the Mn concentration was significantly higher in this northern group. Along a transect from the Barents Sea (69°45′N) to the Carpathian Mountains (49°53′N), concentrations of N, P, S, and K in Scots pine litter fall increased significantly. The best-fit regression models described asymptotic curves, suggesting that concentrations of these major nutrients approach their maximum values at sites with high values for actual evapotranspiration (AET). Low values were found in the north. By contrast, Mn concentrations, increased with latitude and decreased with increasing AET. High covariation among concentrations of the major nutrients (N, P, S, and K) can be attributed to their being major constituents of structural compounds. Analysis of various regression models relating the chemical composition of needle litter fall to latitude and AET, together with a factor analysis, suggested that concentrations of N, P, S, and K were related mainly to climatic conditions, whereas those of Mg and Mn were related more to site-specific properties such as soil fertility. A high level of predictability was found for concentrations of N, P, S, and K using multiple regression, with values for R2adjbetween 0.63 and 0.93. Key words: litter fall, chemical composition, interspecific variability, geographical variability, climate, soil fertility.

Decomposition of oak (Quercus ilex) leaves containing different concentrations of Fe, Zn, Cu, Cr, Ni and Pb was measured in laboratory microcosms. The leaves were collected from a polluted site inside the city of Naples and from a control site away from the city. Soil was sampled from the upper A horizon (0–5 cm) at both sites and analyzed for respiration, microbial biomass and abundance of fungal mycelia. The soils from the two sites differed significantly in heavy metals concentrations. The accumulated mass loss reached an asymptotic value after four months both for the control and polluted litters. However, control and polluted litters significantly differed in accumulated mass loss, that was respectively 40 % and 29 % of the initial weight, after 10 months. Moreover decomposition rates appeared to be strongly influenced by metal contamination in the early stages, while in later stages, they did not differ significantly. Litter respiration appeared to be inhibited by metal contamination and showed pattern and rates consistent with those found for litter decomposition. Fungal mycelia were significantly less abundant both in litter and soil from the polluted site than from the control site. Metabolic activity (both as soil respiration and degree of mineralization) was lower in the polluted soil. Soil respiration and amount of soil mycelia correlated negatively with soil Pb, Zn and Cr concentration.

Summary The composition of the photosynthetic pigments (chlorophylls and carotenoids) was investigated in leaf and stem tissue of the CAM species Cissus quinquangularis Chiov. grown at a sun-exposed site in the summer 1993. Significant differences were not found between leaves and stems concerning the level of chlorophyll a and b and the total carotenoids. In addition most individual carotenoids also ranged within similar values for leaf and stem tissue. The sum of the xanthophyll cycle carotenoids violaxantin, antheraxanthin and zeaxanthin was, however, significantly higher in the stem as compared to the leaf tissue. At low-light conditions or after a 12 h dark period the stem tissue always exhibited a significantly higher zeaxanthin content than that found in the leaf. There were no significant differences concerning the ratios of prenylpigments, except for the ratio chlorophyll a/ carotene, which was significantly lower in the leaf (18.8) as compared to the stem (23.1). The pigment ratios of the CAM-plant Cissus quinquangularis are, however, somewhat different from C3-plants. The performance of the violaxanthin/zeaxanthin cycle was investigated in leaf and stem tissue by giving a 1 h high-light treatment (1400 μmolm-2·s-1) after a 12-hour dark period. The results indicate that the violaxanthin/zeaxanthin cycle, which is assumed to be involved in the protection of photosynthetic apparatus against excess light energy, is active in the leaf as well as in the stem tissue. The photoconversion of violaxanthin to zeaxanthin, however, proceeded in all samples from different Cissus plants to a significantly higher extent in leaf than in stem tissue. Correspondingly, upon high-light treatment, the deepoxidation state DEPS of the violaxanthin/zeaxanthin cycle carotenoids increased 3.2 times in leaf and only 2.4 times in stem tissue.

In plants, the decline of poly(ADP-ribosyl)ation activity is involved in energy homeostasis and stress tolerance. By reducing stress-induced poly(ADP-ribosyl)ation activity, NAD(+) breakdown is inhibited preventing high energy consumption. Under these conditions, plants preserve their energy homeostasis without an overactivation of mitochondrial respiration, thus avoiding the production of reactive oxygen species. Therefore, plants with lowered poly(ADP-ribosyl)ation activity appear tolerant to multiple stresses. In this study, the evergreen species Cistus incanus L. was used as a model because of its capacity to overcome successfully the environmental constraints of the Mediterranean climate. The aim of the present work was to characterize and assess the role of poly(ADP-ribosyl)ation in C. incanus plants kept under different temperature in greenhouse (GH), outdoor during winter (WO) and outdoor during spring (SO). Data showed that in C. incanus polyADPribose metabolism occurs. The enzyme responsible for poly(ADP-ribose) chains synthesis is a poly(ADP-ribose)polymerase of about 80 kDa, lacking "zinc finger" N-terminal domain and able to automodify. The lowest PARP activity, as well as the lowest quantum yield of PSII linear electron transport (Φ(PSII)) and photochemical quenching (q(P)), was found in WO plants. Instead, in SO plants the recovery of photochemical activity associated to a poly(ADP-ribose)polymerase activity increase of about 50%, as compared to GH plants, was observed. Taking into account both biochemical and eco-physiological responses, a possible explanation for the poly(ADP-ribosyl)ation deficiency in WO plants has been hypothesized.

The contribute of paraheliotropism in PSII photoprotection at high light and temperature was assessed by gas exchange and chlorophyll fluorescence. Measurements were performed at 10:00, 12:00, 15:00 and 18:00 on blocked leaves (BL) and on control unblocked leaves (UL) of R. pseudoacacia. In BL at midday as well as at 15:00 and 18:00, An, gCO2, ΦPSII, IPO and F'q/F'v declined compared to 10:00 whereas Ci/Ca ratio and qN increased significantly. Differently from BL, UL maintained an higher An, IPO and ΦPSII as well as a lower qN throughout the day. At 18:00, An, gCO2, ΦPSII and F'q/F'v of BL recovered as compared to 15:00 even if the values remained lower than 10:00 and UL. Moreover, conversely to UL, a significant decrease of Fv/Fm was observed in the evening. Data suggest that in R. pseudoacacia leaf movements represent an efficient strategy to face the photoinhibition at no cost for plant in terms of An reduction.

Lignin decomposition in litter of beech leaves and fir needles as related to litter N concentration and litter mass loss was studied for 7 y in two forests at Mount Taburno (41°05′N., 12°07′E.; Campania Apennines). Both types of litter showed a pattern of decomposition characterized by two stages with significantly decreasing decomposition rates. Litter N concentration did not appear to influence the rate of litter decomposition in either the early or the late stage of the process. On the contrary mass loss rates of litter were influenced by lignin concentrations at the beginning of the late stage: the lower the lignin concentration the higher was mass loss rate. Both in beech and fir litter lignin degradation started immediately during incubation. Lignin degradation throughout the study was less in fir needles than in beech leaves with lignin losses of 60-67% and 73-87% of initial amount, respectively. Both in beech and fir litter, lignin loss rate was negatively correlated to the initial N concentration. Lignin loss rate of both beech and fir litter was correlated to litter mass loss rate during the early as well as during the late phase of decomposition. Different dynamics of lignin decomposition between the two species were observed with a higher lignin decomposition rate in the early stage than in the late stage in beech litter, and rates of lignin decomposition increasing from early to late phase in fir litter. Copyright © 1996 Elsevier Science Ltd. All rights reserved.

We used long-term litter decomposition data to estimate final decomposition levels using an asymptotic function. The estimated final limit values for decomposition were compared with available chemical data for the different litter types. A total of 41 limit values were estimated from as many different decomposition studies, and 20 different litter types were incubated in eight different forest systems. The limit values estimated varied with litter type. They ranged from about 35 to about 100% decomposition and were linearly related to the initial litter concentrations of N, Mn, and Ca in the newly shed litter. For these three nutrients, there are causal relationships to lignin degradation and to the lignin-degrading microbial community. Using all available data, we made simple and multiple linear regressions and obtained a negative linear relationship between limit value and initial N concentration ([Formula: see text]; n = 41; p 2 values, indicating that the models were good. Thus for all sites and litter types, N, Mn, and Ca combined gave an [Formula: see text] value of 0.640 with n = 25 (p

The decomposition dynamics of needle litter of Stone pine (Pinus pinea), Corsican pine (Pinus laricio), Scots pine (Pinus sylvestris) and Silver fir (Abies alba) were investigated in a comparative study including five coniferous forest sites. Initial chemical composition, mass-loss rates, and the water-holding capacities of the litters were determined in the early stages of decomposition. Water-holding capacity differed among the fresh litters but increased in linear proportion to litter mass both over each species and over all species combined in a linear regression (r = 0.708; n = 45; P < 0.001). At the early decomposition stages the daily mass-loss rate of Scots pine needles in two dry sites was positively related to (1) the measured litter water content at sampling (r = 0.727; n = 16; P < 0.0025), (2) mean daily precipitation in the period of measurement (r =0.909; n = 16; P < 0.0001). These models could explain water as a rate-limiting factor to the extent of 49 and 81% respectively. A significant linear relationship was also found between decay rate during a moist period and accumulated mass loss (r = 0.771; n = 8; P < 0.05) which has been suggested to be due to the increase of litter water-holding capacity with increasing accumulated mass loss. Three types of decay curve are described and the pattern of decomposition at dry sites has been found to be influenced by moisture variations more than by litter quality. © 1993.

The concentrations of four macroelements (C, N, P, S) and eight trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) were measured in the leaves and roots of the emergent plant, Phragmites communis Trin., and in the shoots and roots of the submersed Najas marina L., taken from Lake Averno (Naples, Italy). Phragmites communis leaves showed higher concentrations of carbon, nitrogen and phosphorus than roots, while the roots exhibited significantly higher concentrations of sulphur and trace metals. Najas marina roots also showed higher concentrations of sulphur and trace metals than shoots, but these differences were less marked than in Phragmites communis except for sulphur. Sulphur was the only macronutrient to show the highest concentrations in the roots. Phragmites communis roots had higher values of Cr, Cu, Fe, Mn and Ni than Najas marina roots. By contrast, Cd, Cr, Fe, Ni, Pb and Zn concentrations were higher in Najas marina shoots than in Phragmites communis leaves. Phragmites communis, available through the year, showing high capability to accumulate trace metals in the roots, appears a good monitor of lake contamination, better than Najas marina.

Plants of Mediterranean-type ecosystems are exposed to climatic conditions that may limit carbon metabolism resulting in limitation of productivity and growth. During springtime, photosynthetic activity and plant growth are promoted, while they are constrained by aridity in summer and by low temperatures in winter. To overcome such stressful conditions, Mediterranean species have developed strategies expressed by phenological, physiological and structural modifications. Among the various woody species of the Mediterranean maquis in Southern Italy, Cistus incanus L. shows its phenology and cambial activity strictly related to the annual fluctuations of the environmental conditions. In this study, several structural, functional and eco-physiological characteristics were investigated on plants of C. incanus sampled during the autumn development in the Castevolturno Nature Reserve (NA, Italy). Anatomical and cytological features of leaves and twigs were analysed through light and fluorescence microscopy, mainly focusing on traits associated to a) regulation of water relations and b) protection of tissues from excessive irradiation and permanent injuries due to drought and predation. Efficiency and safety of the vascular system were evaluated on the basis of a detailed analysis of the xylem cell types. As regards eco-physiological behaviour, simultaneous measurements of gas exchange and chlorophyll fluorescence were conducted on fully expanded leaves at midday under saturating light intensity. The following parameters were analyzed: net photosynthesis (PN), stomatal conductance (gtH2O), water use efficiency (A/E) and quantum yield of PSII electron transport (Fe). All data were interpreted under ecological and functional perspectives.

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. © Taylor & Francis Group, LLC.

The genus Cissus (Vitaceae) is found throughout both the wet and arid tropics of the world. Surveys of δ 13C values for plants collected in their natural habitats, as well as studies in controlled conditions (Schutte et al. 1967; Milburn et al. 1968; Virzo De Santo et al. 1978, 1980, 1983, 1987a; Ting et al. 1983; Olivares et al. 1984) suggest that CAM is a widespread feature in the genus Cissus that might have facilitated the spread of the genus from the wet into the arid tropics.

The internal parenchyma of the leaf and rhizome in 36 species of Sansevieria is made of dead cells and living cells arranged in a regular pattern. Intercellular spaces are lacking. The walls of dead cells consist of an inner amorphous layer positive to the fluorescence test for callose, a middle suberin‐like layer and an outer fibrillar layer. In about half of the species examined, the inner layer forms distinctive thickenings. Detached leaves of Sansevieria lose water very slowly, and are able to recover it quickly. The pattern of leaf dehydration appears to be related to leaf morphology, whereas no relation is evident between the pattern of leaf rehydration and leaf morphology. Neither leaf dehydration nor leaf rehydration pattern is affected by the presence of wall thickenings in the dead parenchyma cells. The fresh weight per unit volume of both turgid and droughted leaves is nearly 1, denoting that the dead cells are filled with water and do not undergo substantial cavitation during drought. The data indicate that the dead parenchyma cells of Sansevieria are a specialized water‐storing system. Copyright © 1989, Wiley Blackwell. All rights reserved

Crassulacean acid metabolism (CAM) and succulence were compared in two species of Peperomia (Piperaceae) and six species of Cissus and Cyphostenz ma (Vitaceae). The species include thin-leaved plants, leaf succulents, and stem succulents. Succulence at the organ or the cellular level mesophylll succulence [Sm]) does not appear to be causally related to CAM. Peperomia, with high Sm, shows low CAM activity, while Cypizostenima, 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.

Leaf necroses, chlorophyll destruction and sulphur accumulation followed from SO2 fumigation of Mentha piperita L. and Arabidopsis thaliana L. A SO2 dependent decrease in the cell sap pH occurred in both species, but A. thaliana showed a less effective buffering capacity as compared with M. piperita. Exposure to SO2 resulted in a decreased N content in H. piperita and in an increased N content in A. thaliana. M. piperita appeared to be able to remove SO2 from the air bringing about a pollutant sink.

Physiological adaptations to « aerial » life in the genus Tillandsia.—Ten « atmospheric » Tillandsia species, with different degree of adaptation to drought, were investigated to verify the occurrence of CAM and to determine their daily transpiration pattern. Most of the species were collected during the Botanical Expeditions of the Accademia dei Lincei in Latin America in 1969 and 1971. All species had been maintained in the greenhouse of the Naples Botanical Garden during the winter months and in the open air during the warmer months, previous to experiments. The diurnal cycle of transpiration, the malic acid content and cell sap pH of the leaves were studied under outdoor conditions. Curves of malic acid and pH variations typical of CAM have been obtained for all the examined species. Moreover, the transpiration data indicate that stomata are open at night. The rates of transpiration appear to be extremely low. The highest transpiration rates refer to the species of the relatively moister habi...

Ecological aspects of C3, C4 and CAM photosynthetic pathways. - Three different photosynthetic CO2 fixation pathways are known to occur in higher plants. However all three pathways ultimately depend on the Calvin-Benson cycle for carbon reduction. The oxygenase activity of RuBP carboxilase is responsible for photorespiratory CO2 release. Both C4 and CAM pathways behave as a CO2 concentrating mechanism which prevent photorespiration. The CO2-concentrating mechanism in C4 plants is based on intracellular symplastic transport of C4 dicarboxylic acids from mesophyll-cells to the adjacent bundle-sheath cells. On the contrary in CAM plants the CO2-concentrating mechanism is based on the intracellular transport of malic acid into and out of the vacuole. The C4 photosynthetic pathway as compared to the C3 pathway permits higher rates of CO2 fixation in high light and high temperature environments at low costs in terms of water loss, given the stability of the photosynthetic apparatus under such condition...

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.

Stem chlorenchymatous cells from well‐watered and water‐stressed plants of Cissus quadrangularis L. were examined to evaluate the effect of drying on cell structure and metabolism. At a stem relative water content as low as 52‐58%, cellular integrity was maintained, but some qualitative and quantitative alterations occurred. Chlorophyll coment was higher in stressed plants, and the intact photosynthetic apparatus exhibited an increased degree of thylakoid stacking paralleled by a lower chlorophyll a/h ratio. Overnight malate accumulation was very low. Starch was retained but its day/night fluctuation was practically suppressed. Plastosomes were smaller and fewer, and the range of their daily fluctuation was very reduced. Vacuoles underwent fragmentation and accumulated osmiophilic deposits. The maintenance of the cellular integrity accounts for the ability of C. quadrangularis to recover rapidly from water stress. Copyright © 1984, Wiley Blackwell. All rights reserved

Pattern and magnitude of stem gas exchange were studied under controlled conditions on two CAM species of the genus Cissus differing in morphological features. In the cactus-like liana Cissus quadrangularis, at water vapour deficit of the air (VPD) lower than 400 mPa Pa-1 during daytime, under 24/16°C and 27/16°C temperature regime, CO2 uptake occurred during daytime and nighttime but night fixation was responsible for 74 and 77% respectively of the CO2 fixed during the whole diurnal cycle; the contribution of night fixation increased up to 84% at VPD of 590 mPa Pa-1 under 27/15°C. In Cissus sp., a slightly succulent xerophytic liana with mesophytic deciduous leaves, at 27°C day temperature and VPD of 520-540 mPa Pa-1, under both 12 and 16°C night temperature, CO2 uptake occurred exclusively during the night; however at lower day temperatures (18-20°C) and lower VPD (169-269 mPa Pa-1) substantial CO2 uptake was observed in the light. Transpiration was higher in Cissus sp. than in Cissus quadrangularis under all of the conditions applied; moreover night transpiration in Cissus sp. contributed more to total day transpiration as compared with Cissus quadrangularis. The results support the opinion that the nocturnal gas exchange has a preeminent role in Cissus sp. as compared with Cissus quadrangularis. Indeed under conditions which enhance evaporative demand even well-watered plants of Cissus sp. resort totally to night fixation. In contrast Cissus quadrangularis which shows a larger resistance to water loss and possesses an abundant water storing parenchyma as compared with Cissus sp. resorts totally to night CO2 fixation only under drought stress. © 1987 Martinus Nijhoff Publishers.

Cissus quadrangularis, Vitacea, has a succulent stem and shows Crassulacean Acid Metabolism (CAM). Environmental control of CAM is shown with respect to water supply, day temperature, and light intensity. C. quadrangularis, under moderate drought, has a high capacity for dark CO2 fixation and high efficiency of water use (nocturnal transpiration ratio = 8). Severely droughted plants of C. quadrangularis still show dark CO2 fixation although at a reduced rate, which allows a maintenance level metabolism. On the other hand, high temperature and light intensity promote CAM activity in well-watered plants resulting in luxuriant and fast growth. Data indicate that under natural conditions CAM should effectively contribute to the successful adaptation of C. quadrangularis to its environment. © 1980 Oxford University Press.

In order to apply state-of-the-art molecular breeding techniques in fibre crop it is necessary to have a good knowledge of major polymer biosynthesis gene sequences and their expression pattern. Polymerase chain reaction was employed to isolate sequences of the major genes for lignin and cellulose biosynthesis in a kenaf cultivar. CeSA, 4cl, c4h, cad, and ccr gene primers were designed according to their conservative regions; partial sequences of lignin and cellulose biosynthesis genes were obtained. One actin II gene sequence was also isolated from the kenaf genome as a housekeeping gene to be employed in qPCR analysis. Expression levels of genes c4h, cad and CeSA in bark and core from plants harvested at three different growth stages were evaluated. Using qPCR analyses it was found that the expression levels of the two biosynthesis lignin genes in bark tissues increased during plant growth, while a negative trend was recorded in core tissues. In both bark and core, the quantity of lignin was positively correlated to plant growth while cellulose content decreased.