A. Alfani

Temporal and spatial variation in C, N, S and trace element contents in the leaves of Quercus ilex within the urban area of Naples.

This paper presents a comparative analysis of the concentrations of C, N and S and several trace elements (Fe, Mn, Na, Zn, Cu, V, Pb, Ni, Cr, Cd) in leaves of Quercus ilex, an evergreen oak, collected in the urban area of Naples in 1989 and 1996. The samplings were carried out from 25 urban sites (roads with different traffic flows as well as urban and suburban parks) and from two remote areas as controls. Relative to 1989, the values measured in 1996 denote a strong decrement of S, Fe, Na, Pb, and Cr, with the exception of S in control sites. By contrast, C, N and Cd contents were higher in 1996 than in 1989. Cu and Ni showed a conspicuous increment in control sites as well as in urban sites facing the sea and in the parks, while in all the other urban sites these elements decreased remarkably. No significant difference was found in the leaf contents of Mn, Zn and V measured in 1989 relative to 1996. Both in 1989 and 1996 the contents of N, S, Fe, Na, Cu, Pb, V, Ni, Cr and Cd were significantly higher in leaves from urban sites than in the controls, reflecting the high degree of contamination of the urban area. Concentration factors expressed as the ratio of road/control values for most of the elements were still very high in leaves collected in 1996, though remarkably lower than in 1989.

Fungal mycelium and decomposition of needle litter in three contrasting coniferous forests

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.

Nutrient dynamics in decaying leaves of Fagus sylvatica L. and needles of Abies alba Mill.

Abstractu2002The 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.

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.

Gas exchange of two CAM species of the genus Cissus (vitaceae) differing in morphological features

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.

Adaptability ofMentha piperita l. to irradiance. Growth, specific leaf area and levels of chlorophyll, protein and mineral nutrients as affected by shading

Height growth ofMentha piperita L. is better at 44% than 100% daylight. At 14% daylight, growth is limited, probably by lack of photosynthate, and no flowering occurs. Specific leaf area and protein content increase significantly with the decrease of irradiance. Shade leaves contain more chlorophyll and potassium than sun leaves. Sun leaves show higher levels of calcium because of their more xeromorphic structure. Transfer experiments between light and shade indicate thatM. piperita responds very effectively to irradiance also in a late stage of the life cycle with changes of specific leaf area and chlorophyll content.

Responses of Mentha piperita L. and Arabidopsis thaliana L. to fumigation with SO2 at different concentrations

Abstract 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.

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.