1,721,040 research outputs found
Le condizioni luminose che favoriscono la rinnovazione dell'abete bianco nel Parco Nazionale del Pollino
No full textCaratteristiche e prospettive di impiego della tecnica dei minirizotroni nello studio degli apparati radicali di alberi forestali: primi risultati di applicazione della tecnica in pinete di Pinus halepensis Mill.
No full textLandsat TM imagery and NDVI differencing for vegetation change detection: assessing natural expansion of forests in Basilicata, southern Italy
Full text linkThe NDVI (Normalized Difference Vegetation Index) differencing method using Landsat Thematic Mapping images was implemented to assess natural expansion of forests in the Basilicata region (southern Italy) for the period 1984 through 2010. Two Landsat TM (Thematic Mapper) images (1984-2010) were georeferenced and geographically corrected using the first order polynomial transformation, and the nearest neighbour method for resampling. The images were radiometrically corrected using the dark object subtraction model. The pre-processed Landsat TM images were used to calculate NDVI, and subsequently for NDVI differencing. Finally, a threshold for vegetation change detection was identified by visual analysis of Landsat TM RGB band composition, and ratios and visual comparison of digital aerial orthophotos. The methodology was validated using ground-truth observations over the study area. The applied method showed 91.8% accuracy in detection of natural forest expansion. During the examined period, total regional forest cover increased by 19.7% (70 154 ha), consistent with National Forest Inventory data (1984- 2005). The observed forest expansion was also examined in relationship with landscape physical characteristics and distribution of vegetation types in the Basilicata region. Surprisingly, considerable forest expansion also occurred on degraded soils in drought-prone Mediterranean areas
Contribution of diffusional and non-diffusional limitations to midday depression of photosynthesis in Arbutus unedo L.
No full textIt is still unknown whether the midday depression of photosynthesis under severe water stress, frequently observed in plants growing in a Mediterranean-type climate, is primarily a consequence of diffusional or non-diffusional limitations. We carried out combined measurements of gas exchanges and chlorophyll fluorescence in field-grown Arbutus unedo L. trees during late spring and mid summer, and a quantitative limitation analysis was performed to distinguish between the different limitations to photosynthesis, i.e., diffusional [D L = stomatal (S L) + mesophyll (MCL)] and non-diffusional (carboxylation capacity and electron transport, B L) limitations. Light-saturated assimilation at ambient CO2 (A max), stomatal conductance to water vapour (g sw) and maximum carboxylation rate (V cmax C i) showed a marked midday depression during both periods. The total limitations tended to increase during the day and were remarkably similar in June and July (50 and 48%, respectively); on a daily basis, D L was similar to B L (about 23%) in June; whereas, in July the former was predominant (38 and 4%, respectively). We concluded that the midday depression in photosynthesis was largely caused by diffusional limitations, with non-diffusional limitations playing a smaller role. Although stomatal closure was the main diffusional limitation, the decline in mesophyll conductance was not negligible during the hottest and driest period
Hydraulic limitations and water-use efficiency in Pinus pinaster along a chronosequence
No full textHydraulic constraints to water transport and water-use efficiency were studied in a Pinus pinaster Ait. chronosequence in Italy, consisting of four even-aged stands ranging from young (10 years old) to mature (75 years old), to explore the mechanisms involved in the decline of stand productivity as tree grow taller. Leaf-specific transpiration was estimated from sapflow rates measured by the heat dissipation technique, leaf-specific hydraulic conductance was computed from the slope of the relationship between transpiration and leaf water potential, long-term water-use efficiency was estimated from carbon isotope discrimination (Δ13C) in xylem cores, and photosynthetic capacity was assessed from CO2 assimilation/CO2 intercellular concentration curves. Leaf-specific transpiration decreased with stand development, suggesting a reduction in stomatal conductance, and a negative relationship was found between leaf-specific hydraulic conductance and tree height, suggesting a role of hydraulic constraints in the decline of current annual increment. Minimum daily leaf water potential did not change with stand height, suggesting that homeostasis in leaf water potential is achieved through a reduction in leaf transpiration. The Δ13C values increased with stand development, indicating a decline of water-use efficiency. Leaf level stomatal conductance was higher in the younger stand; no significant difference in maximum carboxylation rate was found among stands
Variation in nitrogen supply changes the water use efficiency of Pseudotsuga menziesii and Populus x euroamericana; a comparison of three different approaches to determine water-use efficiency
No full textWe studied the effects of three nitrogen (N) supply
rates (low, intermediate and high) on Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings and poplar clone “I-214” (Populus × euroamericana (Dole) Guinier) cuttings growing in mini-stands. Our specific objectives were to: (1) evaluate the effects ofNsupply onwater-use efficiency (WUE) and biomass production; (2) determine if N affects WUE through control of carbon assimilation rates or through
stomatal control of water loss; and (3) compare three methods of estimating WUE: one short-term method (WUEi, based on gas exchange measurements) and two long-term methods (WUET, based on the ratio between biomass production and transpired water, and Δ, based on leaf carbon isotope discrimination tested as a proxy of WUE). In both species, biomass production, WUEi andWUET increased with increasing Nsupply, but there was no effect of N supply on either transpiration or stomatal conductance and Δ was negatively related to leaf N concentration. Plots of Δ versus both WUEi and WUET revealed negative trends, but the regression betweenWUEi and Δ was significant only for Douglas-fir, and the regression between WUET and Δ was significant only for poplar. Thus, the mechanisms underlying the response of WUE to N supply were mainly related to a positive effect of N supply on photosynthetic rates. The data confirm that carbon isotope discrimination
may be a useful proxy of WUE. The finding that N
availability enhances both biomass production and WUE may
have practical implications in regions where these factors impose constraints on forest productivity
Differential climate-growth relationships in Abies alba Mill. and Fagus sylvatica L. in Mediterranean mountain forests
No full textAnalisi delle relazioni azoto-fotosintesi e azoto-efficienza di uso dell'acqua in Pseudotsuga menziesii e Populus euroamericana
No full textPhotosynthesis-nitrogen relationships: interpretation of different patterns between Pseudotsuga menziesii and Populus x euroamericana in a mini-stand experiment
No full textWe compared photosynthesis–nitrogen relationships of one broad-leaved (poplar; Populus × euroamericana (Dole) Guinier) and one conifer (Douglas-fir; Pseudotsuga menziesii (Mirb.) Franco) species. Plants were grown in large pots to allow free root development and were kept well watered. We determined effects of low, intermediate and high nitrogen supply rates on area-based leaf nitrogen (Na) and chlorophyll concentrations, leaf mass per area (LMA), light-saturated photosynthesis (Amax), maximum carboxylation (Vcmax) and electron transport rate (Jmax), photosynthetic nitrogen-use efficiency (PNUE), and proportions of leaf N in active Rubisco (PR), bioenergetic pools (PB) and the light-harvesting complex (PLH). Nitrogen supply significantly affected leaf Na. Leaf mass per area did not differ between species and was unaffected by the N treatments. In both species, there was a positive correlation between leaf Na and chlorophyll concentration, and between leaf Na and the photosynthetic parameters Amax, Jmax and Vcmax. At comparable leaf Na, however, poplar showed twofold higher PNUE and a threefold steeper slope of the Amax– nitrogen relationship than Douglas-fir. Leaf Na was negatively correlated with PNUE in Douglas-fir but not in poplar. Leaf Na was also negatively correlated with PR, PB and PLH in Douglas-fir, whereas in poplar, a negative correlation was found only for PLH. Parameter PR was significantly higher in poplar than in Douglas-fir. The ratio of CO2 concentration in the intercellular space to that in ambient air was higher in poplar than in Douglas-fir. Overall, our data suggest that differences in the photosynthesis–nitrogen relationship and PNUE between Douglas-fir and poplar primarily reflect a different investment of N to active Rubisco, and possibly a different constraint to CO2 diffusion
Growth patterns of Pinus sylvestris across Europe: a functional analysis using the HYDRALL model
No full textThe variability of Pinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestrisPinus sylvestris growth over two geographic transects across Europe has been explored through a process-based forest growth model (HYDRALL: HYDRaulic constraints on ALLocation) which accounts for the effects of environmental conditions not only on short-term gas exchanges, but also on allocation and tree structure. The model has been validated against both eddy-covariance and growth data under contrasting environmental conditions. Forest growth was found to be reduced by low temperatures (-50%) and water stress (-37%) at the opposite extremes of the natural range of the species. Application of a functional model made it possible to partition growth reductions between individual processes. Gross primary production was severely affected by low temperatures and short vegetative periods at the northern extreme of the specific range (-53%), and by low air and soil humidity at the southern limit (-26%). The ratio between net and gross primary production was found to be rather constant across the temperate region, only increasing in the boreal zone in response to low temperatures (+20%). Under dry conditions, on the contrary, a substantial proportion of the reduction in aboveground productivity was attributed to the need to allocate increasing amounts of resources to fine root production and maintenance (+16%). Both short and long-term responses should be considered in the prediction of climate change impact on forests
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