The first fossils that show the presence of vascular tissue date to the Silurian period, about million years ago. The simplest arrangement of conductive cells shows a pattern of xylem at the center surrounded by phloem.
Together, xylem and phloem tissues form the vascular system of plants. Xylem is the tissue responsible for supporting the plant as well as for the storage and long-distance transport of water and nutrients, including the transfer of water-soluble growth factors from the organs of synthesis to the target organs. The tissue consists of vessel elements, conducting cells, known as tracheids, and supportive filler tissue, called parenchyma.
These cells are joined end-to-end to form long tubes. Vessels and tracheids are dead at maturity. Phloem consists of living cells arranged end to end. Unlike xylem, phloem vessels contain cytoplasm, and this goes through holes from one cell to the next.
Phloem transports sucrose and amino acids up and down the plant. This is called translocation. The study showed that important understanding of whole tree functions can be gained by dimensional analysis across tree axes.
Sapwood turnover to heartwood seems to have an important functional role in affecting the scaling relations for xylem and phloem hydraulic conductances and nitrogen allocation. Xylem and phloem tissues are clearly a larger sink of nitrogen than the foliage as trees grow in height becoming an important and an often overlooked factor in the forest nitrogen cycle particularly in the nitrogen limited boreal forest where the slow nitrogen turnover rate is often the reason for growth limitation.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We thank Jouko Laasasenaho for sharing his data and Kourosh Kabiri for analysis of pine nitrogen content.
Anfodillo, T. Convergent tapering of xylem conduits in different woody species. New Phytol. Bergh, B. The effect of water and nutrient availability on the productivity of Norway spruce in northern and southern Sweden. CrossRef Full Text. Berninger, F.
Effects of tree size and position on pipe model ratios in Scots pine. Brown, J. Toward a metabolic theory of ecology. Ecology 85, — Cernusak, L.
Large variation in whole-plant water-use efficiency among tropical tree species. Chapin, F. Plant responses to multiple environmental factors. Bioscience 37, 49— De Schepper, V. Development and verification of a water and sugar transport model using measured stem diameter variations.
Evans, J. Photosynthetic acclimation and nitrogen partitioning within a lucerne canopy. Stability through time and comparison with a theoretical optimum. Plant Physiol. Ewers, F. Secondary growth in needle leaves of pinus longaeva bristlecone pine and other conifers: quantitative data. Field, C. Allocating leaf nitrogen for the maximization of carbon gain: leaf age as a control on the allocation program.
Oecologia 56, — Hacke, U. Trends in wood density and structure are linked to prevention of xylem implosion by negative pressure. Oecologia , — Hari, P. Annual pattern of photosynthesis in Scots pine in the boreal zone. Tree Physiol.
Helmisaari, H. Nutrient cycling in Pinus sylvestris stands in eastern Finland. Plant Soil. Hirose, T. Maximizing daily canopy photosynthesis with respect to the leaf nitrogen allocation pattern in the canopy. Oecologia 72, — Hoffmann, C. Tree-crown biomass estimation in forest species of the Ural and of Kazakhstan. Hollinger, D. Optimality and nitrogen allocation in a tree canopy. A physiological model of softwood cambial growth.
Linking phloem function to structure: analysis with a coupled xylem—phloem transport model. A carbon cost-gain model explains the observed patterns of xylem safety and efficiency. Plant Cell Environ. Huber, B. Ilomaki, S. Crown rise due to competition drives biomass allocation in silver birch Betula pendula L. Jensen, K. Interface 8, — Universality of phloem transport in seed plants. Jones, H. Stomatal control of xylem embolism. Kantola, A.
Crown development in Norway spruce Picea Abies [L. Trees 18, — Kaufmann, M. The relationship of leaf area and foliage biomass to sapwood conducting area in four subalpine forest tree species. Korhonen, J. Nitrogen balance of a boreal Scots pine forest. Biogeosciences 10, — Kull, O. Acclimation of photosynthesis in canopies: models and limitations. Lusk, C. Photosynthetic differences contribute to competitive advantage of evergreen angiosperm trees over evergreen conifers in productive habitats.
MacCurdy, E. The Notebooks of Leonardo Da Vinci. Definitive edition in one volume. Implications of the pipe model theory on dry matter partitioning and height growth of trees. The quarter-power scaling model does not imply size-invariant hydraulic resistance in plants.
Martinez-Vilalta, J. Hydraulic adjustment of Scots pine across Europe. Tree height and age-related decline in growth in Scots pine Pinus sylvestris L.
McCulloh, K. Water transport in plants obeys Murray's law. Nature , — McDowell, N. Environmental sensitivity of gas exchange in different-sized trees. Oecologia , 9— J, and Ryan, M. An investigation of hydraulic limitation and compensation in large, old Douglas-fir trees. G, Barnard, H. The relationship between tree height and leaf area: sapwood area ratio. Oecologia , 12— Meerts, P. Mineral nutrient concentrations in sapwood and heartwood: a literature review.
Melcher, P. Vulnerability of xylem vessels to cavitation in sugar maple. Scaling from individual vessels to whole branches. Mencuccini, M. Meinzer, T. Dawson, and B. Mooney, H. Solbrig, S. Jain, G. Johnson, and P. Role of foliar nitrogen in light harvesting and shade tolerance of four temperate deciduous woody species. Nikinmaa, E. Analyses of the growth of Scots pine; matching structure with function.
AFF , The xylem transports water and minerals from the roots up the plant stem and into the leaves. In a mature flowering plant or tree, most of the cells that make up the xylem are specialised cells called vessels. Transport in the xylem is a physical process.
It does not require energy. The phloem moves food substances that the plant has produced by photosynthesis to where they are needed for processes such as:. Transport in the phloem is therefore both up and down the stem.
0コメント