1,721,124 research outputs found
Nitrification in tree canopies. In: Forest Conditions - ICP Forests 2017 Executive Report (invited contribution)
No full textN/
Age-related decline in stand productivity: The role of structural acclimation under hydraulic constraints
No full textThe decline in above-ground net primary productivity (P-a) that is usually observed in forest stands has been variously attributed to respiration, nutrient or hydraulic limitations. A novel model is proposed to explain the phenomenon and the co-occurring changes in the balance between foliage, conducting sapwood and fine roots. The model is based on the hypothesis that a functional homeostasis in water transport is maintained irrespective of age: hydraulic resistances through the plant must be finely tuned to transpiration rates so as to avoid extremely negative water potentials that could result in diffuse xylem embolism and foliage dieback, in agreement with experimental evidence. As the plant grows taller, allocation is predicted to shift from foliage to transport tissues, most notably to fine roots. Higher respiration and fine root turnover would result in the observed decline in P-a. The predictions of the model have been compared with experimental data from a chronosequence of Pinus sylvestris stands. The observed reduction in P-a is conveniently explained by concurrent modifications in leaf area index and plant structure. Changes in allometry and shoot hydraulic conductance with age are successfully predicted by the principle of functional homeostasis
The distribution of resistances along the hydraulic pathway is controlled by the tapering of xylem conduits
No full textDespite on abundance of information on the anatomical and hydraulic features of the xylem transport system, there is still a lack of evidence on how the former may affect the latter. We carried out a comparative analysis of hydraulic and anatomical data to test the actual role of conduit tapering in controlling the distribution of hydraulic resistance along the longitudinal axis of a branch. We measured the total hydraulic resistance (R) of the main axis of 9 sycamore branches by measuring the water flow at the top apex. We repeated the measurements for reduced branch lengths. The scaling of R with the distance from the apex (L) was then compared with that predicted by a theoretical model built upon the actual conduit tapering of the analyzed branches. R scaled against L with a scaling exponent (d) that was always <1.0 (from 0.29 to 0.64). The scaling exponents from the actual measurements were not significantly different from those estimated by the model. The results highlight the essential role played by the tapering of xylem conduits in controlling the distribution of hydraulic resistances along a branch or stem. Conduit tapering is likely to be the most effective strategy to minimize the effect of height on the whole-tree hydraulic resistance. Finally, the results implied that vessel furcation was unlikely to occur in the branches of sycamore
Genetic relationship among cultivated and wild olives revealed by AFLP markers
No full textThe cultivated and wild forms of olive represent one of the widest and well preserved genetic system among fruit crops. In fact over 2000 varieties of olive are still under cultivation and wild olives represent an important component of the Mediterranean maquis. To date the level and distribution of the entire variability, especially at molecular level, were never evaluated. The study of olive diversity could instead represent a powerful tool to monitor the presence within the wild germplasm of agronomically interesting traits, to explore strategies for the introgression of such traits into the cultivated genotypes and to understand the potentiality of new gene combinations. Our study compared wild olives coming from different sites with some widely cultivated varieties. The within and between groups variability was tested and it was possible to observe that varieties and wilds clustered separately. Two types of wild olives were recognized: one showing a higher relatedness with the cultivars and a second one with a molecular profile clearly different from both cultivated and other wild plants. The samples coming from Sicily, Sardinia and Corsica belonged to the first type while the wild plants collected in Apulia showed a higher range of variability and, for some of them, the belonging to the 'oleaster' form of Olea europaea was hypothesized
PRIMI RISULTATI NELLA TRASFORMAZIONE GENETICA DELL’OLIVO MEDIANTE L’IMPIEGO DI AGROBATTERI.
No full textSi è cercato di individuare le migliori condizioni per trasformare tessuti di cultivar di olivo mediante Agrobacterium timefaciens ingegnerizzato, contenente il gene reporter GUSint o i geni rol A,B,C /ORFs 10.11.12) del T-DNA dell'Agrobacterium rhizogenes 1855 ed entrambi il gene per la resistenza alla kanamicina NPTII. L'espressione del gene GUS è stata rilevata su callo e piccioli fogliari con l'esame istologico, mediante colorazione con XGLUC, evidenziando, in entrambi i casi, trasformazioni chimeriche
Sanio's Laws revisited. Size-dependent changes in the xylem architecture of trees
No full textEarly observations led Sanio [Wissen. Bot., 8, (1872) 401] to state that xylem conduit
diameters and lengths in a coniferous tree increase from the apex down to a height below
which they begin to decrease towards the tree base. Sanios law of vertical tapering has
been repeatedly tested with contradictory results and the debate over the scaling of
conduit diameters with distance from the apex has not been settled. The debate has
recently acquired new vigour, as an accurate knowledge of the vertical changes in wood
anatomy has been shown to be crucial to scaling metabolic properties to plant and
ecosystem levels. Contrary to Sanios hypothesis, a well known model (MST, metabolic
scaling theory) assumes that xylem conduits monotonically increase in diameter with
distance from the apex following a power law. This has been proposed to explain the
three-fourth power scaling between size and metabolism seen across plants. Here, we (i)
summarized available data on conduit tapering in trees and (ii) propose a new numerical
model that could explain the observed patterns. Data from 101 datasets grouped into 48
independent profiles supported the notions that phylogenetic group (angiosperms versus
gymnosperms) and tree size strongly affected the vertical tapering of conduit diameter.
For both angiosperms and gymnosperms, within-tree tapering also varied with distance
from the apex. The model (based on the concept that optimal conduit tapering occurs
when the difference between photosynthetic gains and wall construction costs is
maximal) successfully predicted all three major empirical patterns. Our results are
consistent with Sanios law only for large trees and reject the MST assumptions that
vertical tapering in conduit diameter is universal and independent of rank number
Sanio's laws revisited. Size-dependent changes in the xylem architecture of trees
No full textEarly observations led Sanio [Wissen. Bot., 8, (1872) 401] to state that xylem conduit
diameters and lengths in a coniferous tree increase from the apex down to a height below
which they begin to decrease towards the tree base. Sanios law of vertical tapering has
been repeatedly tested with contradictory results and the debate over the scaling of
conduit diameters with distance from the apex has not been settled. The debate has
recently acquired new vigour, as an accurate knowledge of the vertical changes in wood
anatomy has been shown to be crucial to scaling metabolic properties to plant and
ecosystem levels. Contrary to Sanios hypothesis, a well known model (MST, metabolic
scaling theory) assumes that xylem conduits monotonically increase in diameter with
distance from the apex following a power law. This has been proposed to explain the
three-fourth power scaling between size and metabolism seen across plants. Here, we (i)
summarized available data on conduit tapering in trees and (ii) propose a new numerical
model that could explain the observed patterns. Data from 101 datasets grouped into 48
independent profiles supported the notions that phylogenetic group (angiosperms versus
gymnosperms) and tree size strongly affected the vertical tapering of conduit diameter.
For both angiosperms and gymnosperms, within-tree tapering also varied with distance
from the apex. The model (based on the concept that optimal conduit tapering occurs
when the difference between photosynthetic gains and wall construction costs is
maximal) successfully predicted all three major empirical patterns. Our results are
consistent with Sanios law only for large trees and reject the MST assumptions that
vertical tapering in conduit diameter is universal and independent of rank number
Tapering of xylem conduits and hydraulic limitations in sycamore (Acer pseudoplatanus) trees
No full textVertical conduit tapering is proposed as an effective mechanism to almost eliminate the increase in hydraulic resistance with increased height. Despite this potential role, very little is known about its changes during ontogeny. Here, conduit tapering and stem morphology of young/small and old/tall individuals of Acer pseudoplatanus in the field, as well as 3-yr-old grafted trees from both age classes, were analysed. The distribution of hydraulic resistance along stems was also determined in a subsample of trees. Substantial conduit tapering was found in small trees (field-grown and grafted from both age classes), whereas values were lower in tall trees, indicating that tapering was a size-related, not an age-related process. Apical conduit diameters were larger in tall trees and were inversely correlated with the degree of tapering. Hydraulic resistance increased less than linearly with distance from the apex. Its scaling against distance was indistinguishable from that predicted from anatomical measurements. Conduit tapering was an effective but partial mechanism of compensation for the increase in hydraulic resistance with tree height. Size-related changes in tapering and in apical conduit diameters may be explained by the combined need to reduce the build-up of hydraulic resistance while minimizing the carbon costs of building vessel walls
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