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Photosynthesis occurs in chloroplasts, which contain chlorophyll and the enzymes needed to fix carbon dioxide into sugars. Other organelles carry out different, equally essential jobs in the cell.
Transpiration is the evaporation of water from leaf surfaces, chiefly through stomata, and accounts for the great majority of a tree's water loss. It also generates the pull that lifts water through the xylem.
Xylem is the water-conducting tissue; its tracheids and vessel elements form continuous tubes running from the roots to the leaves. The other tissues listed serve transport of sugars, storage, or packing.
Leaf arrangement is named by how many leaves attach at each node: one is alternate, two facing each other is opposite, and three or more is whorled. Fascicled leaves are clustered in bundles rather than paired across the stem.
Gymnosperms are seed plants whose seeds sit on the scales of cones rather than inside an ovary; pines are typical examples. Maples, oaks and basswoods are angiosperms that flower and enclose their seeds in fruit.
Fine roots concentrate in the shallow, well-aerated upper soil where oxygen, water and nutrients are plentiful, and they often extend far beyond the drip line. Deep or saturated soil holds too little oxygen to support much root activity.
The vascular cambium is a lateral meristem that produces secondary xylem on its inner face and secondary phloem on its outer face. Because far more xylem is made, the woody cylinder builds up inward year after year.
Each year of secondary growth typically consists of one band of earlywood and one band of latewood, which together count as a single annual ring. Extra rings can appear after drought or defoliation, but one per year is the rule.
Guard cells lose turgor as water stress develops, which closes the stomatal pore and sharply reduces transpirational loss. The trade-off is reduced carbon dioxide uptake, so photosynthesis declines at the same time.
Auxin moving down from the terminal bud inhibits lateral buds, concentrating growth in the leader; this is apical dominance. Removing the terminal bud lowers the auxin supply below it and releases lateral shoots, which is why heading cuts stimulate branching.
Wall 1 forms fastest and is the weakest: existing xylem elements are plugged with tyloses and gums, slowing decay organisms moving up and down the stem. Later walls involve changes in living cells, denser latewood, and finally a new barrier zone.
Rays are ribbons of parenchyma cells running radially, moving water, minerals and carbohydrates between xylem and phloem and storing starch. They also take part in compartmentalizing wounds.
Monocots have one cotyledon, parallel leaf veins, and vascular bundles scattered across the stem rather than arranged in a ring, so they normally lack true secondary growth. Nearly all trees are dicots, which show net venation and a vascular cambium.
Fungal hyphae reach far beyond the root surface, greatly enlarging the absorbing area for water and nutrients, especially phosphorus. The tree repays the fungus with sugars from photosynthesis.
Phloem sap moves from sources such as mature leaves to sinks such as growing shoots, roots or developing fruit, so its direction changes with the location of the sink and the season. Xylem flow is essentially one-way from roots to leaves.
A pinnately compound leaf has leaflets attached along both sides of the rachis, while a palmately compound leaf has leaflets meeting at one point. Terms such as alternate, opposite and whorled describe how whole leaves attach to the stem.
An excurrent crown keeps a strong central leader running through the tree, giving a conical outline as in many conifers. In a decurrent crown the leader is overtopped and the crown spreads into several large scaffold limbs.
Palisade mesophyll cells are packed with chloroplasts and stand in columns near the upper surface, where light reaches them with least interference. The spongy mesophyll below is specialized mainly for gas movement.
Shade leaves maximize light capture with a broad, thin blade and fewer palisade layers, while sun leaves are smaller, thicker and more heavily cutinized to limit water loss and tolerate high light. Both types are fully green and photosynthetic.
Lenticels are loose masses of cells in the periderm that allow oxygen and carbon dioxide to diffuse in and out, since corky bark is otherwise nearly impermeable. They appear as raised dots or slits on young twigs and branches.
The endodermis is the innermost layer of the root cortex, and its Casparian strip blocks movement through cell walls, forcing water and minerals through membranes where selective uptake can occur. This lets the root regulate what reaches the xylem.
Hardwoods form tension wood on the upper side of a leaning stem, and its gelatinous fibers contract to pull the stem upward. Conifers respond differently, forming compression wood on the lower side that pushes the stem upright.
Ring-porous woods concentrate wide vessels in the earlywood, creating a visible band each year. Diffuse-porous woods such as maple and birch have vessels of similar size spread through the ring, and non-porous woods such as pines conduct through tracheids and lack vessels altogether.
Chlorophyll a and b absorb mainly red and blue-violet wavelengths and reflect green, which is why healthy foliage looks green. Green light is therefore used relatively poorly in photosynthesis.
Conifer wood consists almost entirely of tracheids, elongated cells with tapered ends that conduct water through pits and also bear mechanical load. Vessel elements are the wider conducting cells of hardwoods, while sieve tubes and companion cells belong to the phloem.
Soil separates are ranked by particle size: sand is the largest, followed by silt, then clay. Large particles create large pore spaces, so water moves through sand quickly and it holds little water. Clay particles are tiny and pack tightly, giving slow drainage and high water retention.
The majority of landscape trees perform well in slightly acid to neutral soil, roughly pH 5.5 to 7.0. In this range most essential nutrients remain soluble and available while toxic elements such as aluminum stay insoluble. Strongly acid or strongly alkaline soils commonly produce deficiencies.
Cation exchange capacity comes from negatively charged surfaces that hold nutrient cations. Clay minerals and humus have very large surface areas and abundant charge sites, so they supply nearly all of the exchange capacity. Sand, silt and gravel have little surface charge.
Compaction squeezes soil particles together, reducing pore space and raising bulk density. High bulk density, together with slow infiltration and hard resistance to a penetrometer, is the standard field indicator. Earthworms, crumb structure and deep litter indicate well-aerated, uncompacted soil.
Roots need oxygen for respiration, and gas exchange in saturated soil is extremely slow because diffusion through water is about ten thousand times slower than through air. Oxygen is consumed faster than it is replaced, so roots suffocate and die. Anaerobic microbes also produce toxic compounds such as hydrogen sulfide.
Plant-available water is the water held between field capacity and permanent wilting point. Medium-textured soils such as silt loam retain a large share of their water at tensions roots can overcome. Sands drain too freely, while clays hold much water so tightly that roots cannot extract it.
Core aeration creates macropores that let water enter the profile, and compost improves aggregation and pore continuity. Together they raise infiltration capacity so rainfall soaks in rather than running off. Bare soil and frequent light watering do not restore structure.
A 2 to 4 inch layer conserves moisture, moderates temperature and suppresses weeds while still allowing oxygen to diffuse into the soil. Deeper layers can restrict gas exchange and keep the root zone too wet. Mulch should also be pulled back from direct contact with the trunk.
Fertilizer grades are always stated in the order nitrogen, available phosphate and soluble potash, expressed as percentages by weight. The first number is therefore the nitrogen content, here 20 percent. The second number refers to phosphate (P2O5), not elemental phosphorus.
Organic matter acts like a sponge and carries negative charge sites, so it increases both water retention and cation exchange capacity in coarse soils. It also binds sand grains into aggregates, improving structure. It does not eliminate the need for irrigation, but it reduces how often water must be applied.
The A horizon is the surface mineral layer where litter accumulates and decomposes, giving it the darkest color and highest organic matter content. The E horizon is a pale leached layer, the C horizon is weathered parent material, and the R horizon is unweathered bedrock.
Mycorrhizal fungi form associations with fine roots and spread hyphae far beyond the root surface, greatly extending the volume of soil explored for water and nutrients, especially phosphorus. They are beneficial symbionts, not pathogens, and they require well-aerated soil. Nitrogen fixation in woody plants is performed by bacteria in root nodules, not by mycorrhizae.
Gravity cannot pull water out of the bottom of a container, so a saturated zone always sits above the drainage holes. Its height depends on the pore size of the mix: finer mixes hold a taller saturated layer. Frequent watering therefore keeps the lower root ball wet regardless of what drains out.
Fine roots concentrate in the shallow, well-aerated, organic-rich surface soil, usually within the upper foot or two. Roots also spread well beyond the dripline, often two to three times the canopy radius. Deep rooting occurs but represents a small fraction of the total.
Deep, infrequent irrigation wets the full root zone and then allows the upper soil to dry, which favors roots growing deeper where moisture persists. Shallow or very frequent applications keep water near the surface and promote shallow rooting. Wetting depth is what determines rooting depth.
The original root ball dries faster than the surrounding backfill soil and must be soaked directly until roots grow outward. Water should be applied slowly to the root ball, and frequency adjusted to rainfall and soil type. Daily light sprinkling wets only the surface.
Air excavation loosens compacted soil while separating it from roots, so the operator can see and avoid tearing them. Radial trenches also create channels for air, water and new roots. Mechanical tillage indiscriminately cuts roots and often recompacts the soil.
Salts accumulate at the leaf margins, where water evaporates, and chloride or sodium reaches toxic levels there first. The result is tip and marginal scorch that appears on older leaves before younger ones. Interveinal yellowing on new growth is more typical of iron deficiency.
A silt fence placed along the downslope perimeter slows sheet flow and traps sediment before it leaves the site. It should be installed before grading and keyed into the soil. Watering or tilling loose soil does not stop sediment transport.
A representative sample is built from many small cores taken randomly across the area to the same depth, then mixed in a clean bucket. A subsample of that mixture is submitted to the laboratory. Single spot samples reflect only local conditions and give misleading results.
Clay particles are microscopic and pack closely, so the resulting pores are tiny and conduct water very slowly. Capillary forces also hold water tightly in those small pores. As a result, clay soils can be saturated for long periods even though they store a lot of water.
Iron is immobile in the plant, so deficiency appears first on the youngest leaves as interveinal chlorosis while the veins remain green. It is common in alkaline or poorly drained soils where iron becomes insoluble. Uniform yellowing of older leaves suggests a mobile nutrient such as nitrogen.
Sodium chloride raises the osmotic potential of the soil solution, so roots must work against a steeper gradient and can lose water to the soil. The result is drought-like stress, marginal scorch and sometimes outright root death. Sodium also degrades soil structure and displaces other cations from exchange sites.
The backfill should be the soil removed from the hole, loosened but otherwise unamended, so that water moves uniformly between the root ball and surrounding soil. Radically different backfill textures create a bathtub effect that traps water. Compost is better used as mulch on the surface.
Saturated soil lacks oxygen, so fine roots die and living roots cannot absorb water efficiently. The plant then shows drought symptoms even though water is abundant. A percolation test or drainage check should be done before further irrigation is added.