A. Bonito

Relationship between acorn size and seedling morphological and physiological traits of Quercus ilex L. from different climates

Effects of Quercus ilex acorn size on seedling morphological and physiological traits were analysed. The study was carried out with five populations from different geographical areas and covering an aridity gradient. Seedling morphological traits (height and total leaf area) were analyzed during the first growing year. Physiological traits (net photosynthesis, stomatal conductance, leaf transpiration, and intrinsic water-use efficiency) were analysed at different air temperatures during spring, summer, and winter months, and in response to water stress. There were significant correlations among the considered acorn (volume, fresh mass) and seedling traits. Differences in growth and physiological traits among the considered populations were found. The larger differences in the growth parameters were observed during the first growing season, and they could be justified by the significant differences among acorn size. On the contrary, the physiological response to air temperature and aridity was more related to the geographical origin of the considered populations than to acorn size. Q. ilex acorn and seedling traits more tolerant to drought might have a high potential for vegetation recovery in afforestation projects and restoration programmes particularly under water-limited environments or in degraded areas.

Leaf traits variation during leaf expansion in Quercus ilex L.

The morphological, anatomical and physiological variations of leaf traits were analysed during Quercus ilex L. leaf expansion. The leaf water content (LWC), leaf area relative growth rate (RGRl) and leaf dry mass relative growth rate (RGRm) were the highest (76±2 %, 0.413 cm2 cm−2 d−1, 0.709 mg mg−1 d−1, respectively) at the beginning of the leaf expansion process (7 days after bud break). Leaf expansion lasted 84±2 days when air temperature ranged from 13.3±0.8 to 27.6±0.9 °C. The net photosynthetic rate (PN), stomatal conductance (gs), and chlorophyll content per fresh mass (Chl) increased during leaf expansion, having the highest values [12.62±1.64 µmol (CO2) m−2 s−1, 0.090 mol (H2O) m−2 s−1, and 1.03±0.08 mg g−1, respectively] 56 days after bud break. Chl was directly correlated with leaf dry mass (DM) and PN. The thickness of palisade parenchyma contributed to the total leaf thickness (263.1±1.5 µm) by 47 %, spongy layer thickness 38 %, adaxial epidermis and cuticle thickness 9 %, and abaxial epidermis and cuticle thickness 6 %. Variation in leaf size during leaf expansion might be attributed to a combination of cells density and length, and it is confirmed by the significant (p<0.001) correlations among these traits. Q. ilex leaves reached 90 % of their definitive structure before the most severe drought period (beginning of June — end of August). The high leaf mass area (LMA, 15.1±0.6 mg cm−2) at full leaf expansion was indicative of compact leaves (2028±100 cells mm−2). Air temperature increasing might shorten the favourable period for leaf expansion, thus changing the final amount of biomass per unit leaf area of Q. ilex.

Environmental induced variations in leaf dark respiration and net photosynthesis of Quercus ilex L.

The relationships between dark respiration rate (RD) and net photosynthetic rate (PN) in Quercus ilex L. shrubs growing at the Botanical Garden in Rome were analysed. Correlation analysis of the data sets collected in the year 2006 confirmed the dependence among the considered leaf traits, in particular, RD was significantly (p<0.05) correlated with PN (r = 0.40). RD and PN increased from March to May [1.40±0.10 and 10.1±1.8 µmol(CO2) m−2 s−1 mean values of the period, respectively], when air temperature was in the range 14.8–25.2 °C, underlining the highest metabolic activity in the period of the maximum vegetative activity that favoured biomass accumulation. On the contrary, the highest RD [1.60±0.02 µmol(CO2) m−2 s−1], associated to the lowest PN rates (44 % of the maximum) and carbon use efficiency (CUE) in July underlined the mobilization of stored material during drought stress by a higher air temperature (32.7 °C).

Growth analysis of a reestablished population versus a natural population of Bidens cernua L.

Abstract A reintroduction experiment of Bidens cernua L., a species included in the Red List of Italian Flora, was carried out at Lake Posta Fibreno (Lazio, central Italy). There were no significant differences in the length of the phenological phases between the reestablished population (Pr) and the natural one (Pn). The length of the phenological cycle, from seedling emergence to the end of the fruiting phase, was 207 ± 3 days. The relative growth rate in height (RGRH) and relative growth rate in mass (RGRm) were significantly (p < 0.05) higher for Pr (0.047 ± 0.001 cm cm−1 d−1 and 0.057 ± 0.001 g g−1 d−1, respectively) than for Pn (0.045 ± 0.001 cm cm−1 d−1 and 0.055 ± 0.001 g g−1 d−1, respectively). There were significant (p < 0.05) differences for plant height (H) and total leaf area per plant (TLA) between Pr and Pn, the latter having the lower values. Total plant dry mass (PDM) was significantly higher for Pr, and the above‐ground/below‐ground dry mass ratio was 6.7 ± 0.4 and 4.7 ± 0.2 for Pr and Pn, respectively. On the whole, results demonstrate that the Pr of B. cernua has the potential to develop in a manner that is demographically similar to the Pn present in the Posta Fibreno Lake protected area. Abbreviations: H, plant height; LA, mean leaf area; LM, leaf dry mass; PCA, principal component analysis; PDM, total plant dry mass; Pn, natural population; Pr, reestablished population; RGRH, relative growth rate in plant height; RGRm, relative growth rate in plant dry mass; SLA, specific leaf area; TLA, total leaf area per plant