C. Arena

Organic matter, nutrient content and biological activity in burned and unburned soils of a Mediterranean maquis area of southern Italy

Experimental fires were performed during the summer-drought period in a Mediterranean maquis in the Castel Volturno Nature Reserve in south-western Italy. The two different fuel loads applied (4 kg m−2 and 2 kg m−2) resulted in complete and partial combustion of the vegetation, respectively. Soil organic matter content (SOM), total and available element concentrations (K, Mg, Na, Mn, Fe, Cu, Pb, Cd), microbial carbon, respiration, metabolic quotient (qCO2), and the coefficient of endogenous mineralization (CEM) were measured at intervals in the dry and wet seasons over a period of about 3 years, in burned and adjacent unburned soils. Soil samples (0–5 cm depth) were collected under the cover of Phillyrea angustifolia L., a dominant species in the study area. Both fires induced long-lasting increases in SOM. As indicated by the increase in CEM, part of the accumulated SOM was mineralized in the first 3 months after fire whereas part of the accumulated SOM was instead stable. Both fires increased the total and available fractions of nutrients and trace elements. During the first 3 months after fire, microbial biomass and qCO2 were higher in the burned soils, which were richer in nutrients, but were characterized by harsher environmental conditions compared to unburned soils.

Paraheliotropism in Robinia pseudoacacia L.: an efficient strategy to optimise photosynthetic performance under natural environmental conditions

We assessed the contribution of leaf movements to PSII photoprotection against high light and temperature in Robinia pseudoacacia. Gas exchange and chlorophyll a fluorescence measurements were performed during the day at 10:00, 12:00, 15:00 and 18:00 hours on leaves where paraheliotropic movements were restrained (restrained leaves, RL) and on control unrestrained leaves (UL). RL showed a strong decrease of net photosynthesis (A(n)), stomatal conductance (g(sH2O)), quantum yield of electron transport (PhiPSII), percentage of photosynthesis inhibited by O2 (IPO) and photochemical quenching (q(P)) in the course of the day, whereas, a significant increase in C(i)/C(a) and NPQ was observed. Contrary to RL, UL had higher photosynthetic performance that was maintained at elevated levels throughout the day. In the late afternoon, A(n), g(sH2O), PhiPSII and q(P) of RL showed a tendency to recovery, as compared to 15:00 hours, even if the values remained lower than those measured at 10:00 hours and in UL. In addition, contrary to UL, no recovery was found in F(v)/F(m) at the end of the study period in RL. Data presented suggest that in R. pseudoacacia, leaf movements, by reducing light interception, represent an efficient, fast and reversible strategy to overcome environmental stresses such as high light and temperature. Moreover, paraheliotropism was able to protect photosystems, avoiding photoinhibitory damage, leading to a carbon gain for the plant.

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.

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.

Impact of the invasive tree black locust on soil properties of Mediterranean stone pine-holm oak forests

Background and aimsInvasion by N2-fixing species may alter biogeochemical processes. We hypothesized that the grade of invasion by the N2-fixer black locust (Robinia pseudoacacia L.) could be related to the distribution and pools of carbon (C) and nitrogen (N) along the profile of two Mediterranean mixed forests of stone pine (Pinus pinea L.) and holm oak (Quercus ilex L.).MethodsA low-invaded (LIN) and a high-invaded (HIN) mixed forest were studied. We assessed: N concentration in green and in senescent leaves; C and N pools along the soil profile; seasonal changes of soluble C and N fractions, and microbial activity.ResultsCompared to coexisting holm oak and stone pine, black locust had higher N content in green and in senescent leaves. In the mineral soil: N stocks were similar in LIN and HIN; water soluble C and microbial activity, were lower in HIN compared to LIN; water soluble N showed seasonal changes consistent with tree growth activity in both HIN and LIN. In the organic layer of HIN, C and N stocks were about twofold larger than expected on the basis of stand density.ConclusionBlack locust increased C and N stocks in the upper organic layers that are more vulnerable to disturbance. However, it did not increase N stocks in the mineral soil.

Photosynthetic response of Quercus ilex L. plants grown on compost and exposed to increasing photon flux densities and elevated CO2

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 (PN) 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 PN 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.

Assessment of Eco-Physiological Performance of Quercus ilex L. Leaves in Urban Area by an Integrated Approach

Plant physiological performance may be endangered in contaminated urban areas. Metal and polycyclic aromatic hydrocarbon (PAH) content in Quercus ilex leaves mainly reflects air pollution, being for these pollutants traceable the translocation from soil. In this work, in a field study, the responses at structural and functional level of Q. ilex leaves to metal and PAH pollution were assessed by an integrated approach. At this purpose, morphological (functional traits), biochemical (pigment content, antioxidant capacity, and PARP activity), and physiological (partitioning of absorbed light in the photosynthetic process) analyses were performed in leaves collected at urban parks and roadsides. Compared to the leaves of the urban parks, those sampled at the roadsides showed higher metal and PAH accumulation. The most contaminated leaves showed smaller leaf sizes and lower relative water and pigment content, as well as a lower photochemistry. In this circumstance, the excess of absorbed light at PSII was mainly dissipated via non-regulated than heat processes. On the basis of the biochemical analyses, the occurrence of DNA damages in contaminated Q. ilex leaves may be hypothesized.

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.

Suitability of two types of organic wastes for the growth of sclerophyllous shrubs on limestone debris: a mesocosm trial.

This study investigated whether overlaying organic wastes directly on limestone debris allowed the growth of sclerophyllous shrubs; the aim was to explore the feasibility of rehabilitation of sites destroyed by quarrying activity. In an open air mesocosm experiment two types of organic material were compared: compost from municipal wastes (C) and a mixture of compost and poultry manure added with wheat husk (C-PW). Mesocosms were pots (1m diameter, 60cm height) containing limestone debris covered by the organic material. Seven mesocosms with C and seven mesocosms with C-PW were planted with sclerophyllous shrubs (Laurus nobilis L., Phillyrea angustifolia L. and Quercus ilex L.). The substrates were characterised in terms of chemical and physical parameters, microbial activity and biomass, and total and active fungal biomass. Shrub photosynthetic performance and growth were evaluated. Over the whole experimental period, organic matter mineralization was higher in C-PW. Microbial biomass and respiration were higher in C-PW than in C but after one year no statistically significant difference between the two substrates occurred. Fungal mycelium was a minor fraction of the microbial community in both types of substrates and decreased dramatically after setting up the mesocosms. The metabolic quotient was higher in C suggesting more stressful conditions as compared to C-PW. Both substrates allowed shrub growth; however photosynthetic rates and the increase of plant size were higher on C-PW than on C. The results demonstrated that, as compared to only compost, the mixture of compost and poultry manure added with wheat husk is a substrate more suitable to both microbial processes and plant growth. Therefore a plan to revegetate quarries based on the use of organic wastes as a substrate for sclerophyllous shrubs could be feasible and, what is more, helpful to mitigate the environmental impact of organic wastes disposal.

Growth and gas exchange response to water shortage of a maize crop on different soil types

The effect of water shortage on growth and gas exchange of maize grown on sandy soil (SS) and clay soil was studied. The lower soil water content in the SS during vegetative growth stages did not affect plant height, above-ground biomass, and leaf area index (LAI). LAI reduction was observed on the SS during the reproductive stage due to early leaf senescence. Canopy and leaf gas exchanges, measured by eddy correlation technique and by a portable photosynthetic system, respectively, were affected by water stress and a greater reduction in net photosynthetic rate (AN) and stomatal conductance (gs) was observed on SS. Chlorophyll and carotenoids content was not affected by water shortage in either condition. Results support two main conclusions: (1) leaf photosynthetic capacity was unaffected by water stress, and (2) maize effectively endured water shortage during the vegetative growth stage.