نتایج جستجو برای: pit seeding
تعداد نتایج: 17959 فیلتر نتایج به سال:
The pit membrane in bordered pits of conifer tracheids is characterized by a porous margo and central thickening (torus), which is traditionally considered to function as an impermeable safety valve against air-seeding. However, electron microscopy based on 33 conifer species, including five families and 19 genera, reveals that pores occur in the torus of 13 of the species studied. The pores ha...
Despite renewed interest in the nature of limitations on maximum tree height, the mechanisms governing ultimate and species-specific height limits are not yet understood, but they likely involve water transport dynamics. Tall trees experience increased risk of xylem embolism from air-seeding because tension in their water column increases with height because of path-length resistance and gravit...
Bordered pits play an important role in permitting water flow among adjacent tracheary elements in flowering plants. Variation in the bordered pit structure is suggested to be adaptive in optimally balancing the conflict between hydraulic efficiency (conductivity) and safety from air entry at the pit membrane (air seeding). The possible function of vestured pits, which are bordered pits with pr...
Water transport in plants is based on a metastable system as the xylem "works" at negative water potentials (ψ). At critically low ψ, water columns can break and cause embolism. According to the air-seeding hypothesis, this occurs by air entry via the pits. We studied the formation of embolism in dehydrating xylem sections of Juniperus virginiana (Cupressaceae), which were monitored microscopic...
Cavitation resistance is a key parameter to understand tree drought tolerance but little is known about the mechanisms of air entry into xylem conduits. For conifers three mechanisms have been proposed: (1) a rupture of pit margo microfibrils, (2) a displacement of the pit torus from its normal sealing position over the pit aperture, and (3) a rupture of an air-water menisci in a pore of the pi...
The mechanism of water-stress-induced xyletn embolism was studied in three species of conifers: Abies balsamca (L.) Mill., Picea rtibens Sarg. and ./uniperus virginiana L. Each species showed a characteristic relationship between xylem tension and the loss of hydraulic conductivity by air etnbolistn. Abies balsamea and Picea rubens began to etnbolize at tensions between 2 and 3 MPa and were com...
Selecting the appropriate rangeland improvement method is a challenging task for range managers because it requires consideration of various criteria. This study was aimed to evaluate various restoration and reclamation practices in the rangelands of Semirom-Isfahan using Multi-Criteria Decision Making (MCDM) methods. Grazing management, water point development, pit seeding, exclosure, water ...
The hypothesis that greater safety from cavitation by airseeding through inter-vessel pits comes at the cost of less porous pit membranes with greater flow resistance was tested . Sixteen vessel-bearing species were compared: 11 from the Rosaceae, four from other angiosperm families, and one fern. Unexpectedly, there was no relationship between pit resistance (and hence the prevailing membrane ...
The biological and mechanical measures adapted to crucial renewable resources (water, vegetation and soil) and sustaining agriculture and soil fertility. However, local inhabitants’ participation is the main challengeable issue, particularly maintaining the constructed watershed management projects. The objectives of this research were to evaluate the watershed management measures which constru...
INTRODUCTION Histological diagnosis of malignant mesothelioma requires an invasive procedure such as CT-guided needle biopsy, thoracoscopy, video-assisted thorascopic surgery (VATs) or thoracotomy. These invasive procedures encourage tumour cell seeding at the intervention site and patients can develop tumour nodules within the chest wall. In an effort to prevent nodules developing, it has been...
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