Theodore T. Kozlowski

The Physiological Ecology of Woody Plants

How Woody Plants Grow. Physiological and Environmental Requirements for Tree Growth. Establishment and Growth of Tree Stands.Radiation. Temperature. Soil Properties and Mineral Nutrition. Water Stress. Soil Aeration, Compaction, And Flooding. Air Pollution. Carbon Dioxide. Fire. Wind. Cultural Practices. Each Chapter Includes References. Index.

Acclimation and Adaptive Responses of Woody Plants to Environmental Stresses

AbstractThe predominant emphasis on harmful effects of environmental stresses on growth of woody plants has obscured some very beneficial effects of such stresses. Slowly increasing stresses may induce physiological adjustment that protects plants from the growth inhibition and/or injury that follow when environmental stresses are abruptly imposed. In addition, short exposures of woody plants to extreme environmental conditions at critical times in their development often improve growth. Furthermore, maintaining harvested seedlings and plant products at very low temperatures extends their longevity. Drought tolerance: Seedlings previously exposed to water stress often undergo less inhibition of growth and other processes following transplanting than do seedlings not previously exposed to such stress. Controlled wetting and drying cycles often promote early budset, dormancy, and drought tolerance. In many species increased drought tolerance following such cycles is associated with osmotic adjustment that involves accumulation of osmotically active substances. Maintenance of leaf turgor often is linked to osmotic adjustment. A reduction in osmotic volume at full turgor also results in reduced osmotic potential, even in the absence of solute accumulation. Changes in tissue elasticity may be important for turgor maintenance and drought tolerance of plants that do not adjust osmotically.Water deficits and nutrient deficiencies promote greater relative allocation of photosynthate to root growth, ultimately resulting in plants that have higher root:shoot ratios and greater capacity to absorb water and minerals relative to the shoots that must be supported.At the molecular level, plants respond to water stress by synthesis of certain new proteins and increased levels of synthesis of some proteins produced under well-watered conditions. Evidence has been obtained for enhanced synthesis under water stress of water-channel proteins and other proteins that may protect membranes and other important macromolecules from damage and denaturation as cells dehydrate. Flood tolerance: Both artificial and natural flooding sometimes benefit woody plants. Flooding of orchard soils has been an essential management practice for centuries to increase fruit yields and improve fruit quality. Also, annual advances and recessions of floods are crucial for maintaining valuable riparian forests. Intermittent flooding protects bottomland forests by increasing groundwater supplies, transporting sediments necessary for creating favorable seedbeds, and regulating decomposition of organic matter. Major adaptations for flood tolerance of some woody plants include high capacity for producing adventitious roots that compensate physiologically for decay of original roots under soil anaerobiosis, facilitation of oxygen uptake through stomata and newly formed lenticels, and metabolic adjustments. Halophytes can adapt to saline water by salt tolerance, salt avoidance, or both. Cold hardiness: Environmental stresses that inhibit plant growth, including low temperature, drought, short days, and combinations of these, induce cold hardening and hardiness in many species. Cold hardiness develops in two stages: at temperatures between 10° and 20°C in the autumn, when carbohydrates and lipids accumulate; and at subsequent freezing temperatures. The sum of many biochemical processes determines the degree of cold tolerance. Some of these processes are hormone dependent and induced by short days; others that are linked to activity of enzyme systems are temperature dependent. Short days are important for development of cold hardiness in species that set buds or respond strongly to photoperiod. Nursery managers often expose tree seedlings to moderate water stress at or near the end of the growing season. This accelerates budset, induces early dormancy, and increases cold hardiness. Pollution tolerance: Absorption of gaseous air pollutants varies with resistance to flow along the pollutant’s diffusion path. Hence, the amount of pollutant absorbed by leaves depends on stomatal aperture, stomatal size, and stomatal frequency. Pollution tolerance is increased when drought, dry air, or flooding of soil close stomatal pores. Heat tolerance: Exposure to sublethal high temperature can increase the thermotolerance of plants. Potential mechanisms of response include synthesis of heat-shock proteins and isoprene and antioxidant production to protect the photosynthetic apparatus and cellular metabolism. Breaking of dormancy: Seed dormancy can be broken by cold or heat. Embryo dormancy is broken by prolonged exposure of most seeds to temperatures of 1° to 15°C. The efficiency of treatment depends on interactions between temperature and seed moisture content. Germination can be postponed by partially dehydrating seeds or altering the temperature during seed stratification. Seed-coat dormancy can be broken by fires that rupture seed coats or melt seedcoat waxes, hence promoting water uptake. Seeds with both embryo dormancy and seed-coat dormancy may require exposure to both high and low temperatures to break dormancy. Exposure to smoke itself can also serve as a germination cue in breaking seed dormancy in some species.Bud dormancy of temperate-zone trees is broken by winter cold. The specific chilling requirement varies widely with species and genotype, type of bud (e.g., vegetative or floral bud), depth of dormancy, temperature, duration of chilling, stage of plant development, and daylength. Interruption of a cold regime by high temperature may negate the effect of sustained chilling or breaking of bud dormancy. Near-lethal heat stress may release buds from both endodormancy and ecodormancy. Pollen shedding: Dehiscence of anthers and release of pollen result from dehydration of walls of anther sacs. Both seasonal and diurnal pollen shedding are commonly associated with shrinkage and rupture of anther walls by low relative humidity. Pollen shedding typically is maximal near midday (low relative humidity) and low at night (high relative humidity). Pollen shedding is low or negligible during rainy periods. Seed dispersal: Gymnosperm cones typically dehydrate before opening. The cones open and shed seeds because of differential shrinkage between the adaxial and abaxial tissues of cone scales. Once opened, cones may close and reopen with changes in relative humidity. Both dehydration and heat are necessary for seed dispersal from serotinous (late-to-open) cones. Seeds are stored in serotinous cones because resinous bonds of scales prevent cone opening. After fire melts the resinous material, the cone scales can open on drying. Fires also stimulate germination of seeds of some species. Some heath plants require fire to open their serotinous follicles and shed seeds. Fire destroys the resin at the valves of follicles, and the valves then reflex to release the seeds. Following fire the follicles of some species require alternate wetting and drying for efficient seed dispersal. Stimulation of reproductive growth: Vegetative and reproductive growth of woody plants are negatively correlated. A heavy crop of fruits, cones, and seeds is associated with reduced vegetative growth in the same or following year (or even years). Subjecting trees to drought during early stages of fruit development to inhibit vegetative growth, followed by normal irrigation, sometimes favors reproductive growth. Short periods of drought at critical times not only induce formation of flower buds but also break dormancy of flower buds in some species. Water deficits may induce flowering directly or by inhibiting shoot flushing, thereby limiting the capacity of young leaves to inhibit floral induction. Postharvest water stress often results in abundant return bloom over that in well-irrigated plants. Fruit yields of some species are not reduced or are increased by withholding irrigation during the period of shoot elongation. In several species, osmotic adjustment occurs during deficit irrigation. In other species, increased fruit growth by imposed drought is not associated largely with osmotic adjustment and maintenance of leaf turgor. Seedling storage: Tree seedlings typically are stored at temperatures just above or below freezing. Growth and survival of cold-stored seedlings depend on such factors as: date of lifting from the nursery; species and genotype; storage temperature, humidity, and illumination; duration of storage; and handling of planting stock after storage. Seedlings to be stored over winter should be lifted from the nursery as late as possible. Dehydration of seedlings before, during, and after storage adversely affects growth of outplanted seedlings. Long-term storage of seedlings may result in depletion of stored carbohydrates by respiration and decrease of root growth potential. Although many seedlings are stored in darkness, a daily photoperiod during cold storage may stimulate subsequent growth and increase survival of outplanted seedlings. For some species, rapid thawing may decrease respiratory consumption of carbohydrates (over slowly thawed seedlings) and decrease development of molds. Pollen storage: Preservation of pollen is necessary for insurance against poor flowering years, for gene conservation, and for physiological and biochemical studies. Storage temperature and pollen moisture content largely determine longevity of stored pollen. Pollen can be stored successfully for many years in deep freezers at temperatures near −15°C or in liquid nitrogen (−196°C). Cryopreservation of pollen with a high moisture content is difficult because ice crystals may destroy the cells. Pollens of many species do not survive at temperatures below −40°C if their moisture contents exceed 20–30%. Pollen generally is air dried, vacuum dried, or freeze dried before it is stored. To preserve the germination capacity of stored pollen, rehydration at high humidity often is necessary. Seed storage:

Carbohydrate sources and sinks in woody plants

Each perennial woody plant is a highly integrated system of competing carbohydrate sinks (utilization sites). Internal competition for carbohydrates is shown by changes in rates of carbohydrate movement from sources to sinks and reversals in direction of carbohydrate transport as the relative sink strengths of various organs change. Most carbohydrates are produced in foliage leaves but some are synthesized in cotyledons, hypocotyls, buds, twigs, stems, flowers, fruits, and strobili. Although the bulk of the carbohydrate pool moves to sinks through the phloem, some carbohydrates are obtained by sinks from the xylem sap. Sugars are actively accumulated in the phloem and move passively to sinks along a concentration gradient. The dry weight of a mature woody plant represents only a small proportion of the photosynthate it produced. This discrepancy results not only from consumption of plant tissues by herbivores and shedding of plant parts, but also from depletion of carbohydrates by respiration, leaching, exudation, secretion, translocation to other plants through root grafts and mycorrhizae and losses to parasites. Large spatial and temporal variations occur in the use of reserve- and currently produced carbohydrates in metabolism and growth of shoots, stems, roots, and reproductive structures. A portion of the carbohydrate pool is diverted for production of chemicals involved in defense against fungi, herbivores, and competing plants. Woody plants accumulate carbohydrates during periods of excess production and deplete carbohydrates when the rate of utilization exceeds the rate of production. Stored carbohydrates play an important role in metabolism, growth, defense, cold hardiness, and postponement or prevention of plant mortality.ZusammenfassungJede mehrjährige Holzpflanze stellt ein komplexes System von miteinander konkurrierenden Kohlenhydratverbrauchsorten (sinks) dar. Interne Konkurrenz um Kohlenhydrate zeigt sich in Veränderungen der Kohlenhydrattransportraten vom Produktionsort (source) zum Verbrauchsort (sink) und in Richtungsänderungen des Kohlenhydrattransportes, wenn der relative Kohlenhydratverbrauch einzelner Organe sich ändert. Die meisten Kohlenhydrate werden in Laubblättern produziert, einige jedoch werden in Keimblättern, Hypokotylen, Knospen, Zweigen, Stengeln, Blüten, Früchten und Blütenachsen synthetisiert. Obwohl sich der größte Teil des Kohlenhydratpools im Phloem zu den Verbrauchsorten bewegt, werden jedoch einige Kohlenhydrate dem Xylem entnommen. Zucker werden aktiv im Phloem akkumuliert und bewegen sich entlang eines Konzentrationsgefälles passiv zum Verbrauchsort. Das Trockengewicht einer ausgewachsenen Holzpflanze stellt nur einen geringen Teil der photosynthetischen Produktion dar. Diese Diskrepanz beruht nicht nur auf dem Verbrauch von pflanzlichem Gewebe durch Herbivore und Abwurf von Pflanzenteilen, sondern auch auf der Abschöpfung von Kohlenhydraten durch Atmung, Auswaschung, Ausscheidung, Translokation in andere Pflanzenteile durch Wurzelpfropfe und Verluste an Parasiten. Große räumliche und zeitliche Veränderungen zeigen sich beim Verbrauch von gespeicherten und laufend produzierten Kohlenhydraten im Stoffwechsel und Wachstum von Keimlingen, Sproßachsen, Wurzeln und reproduktiven Organen. Ein Teil des Kohlenhydratpools wird in die Produktion von Abwehrstoffen gegen Pilze, Herbivoren und konkurrierende Pflanzen umgelenkt. Holzpflanzen akkumulieren Kohlenhydrate in Zeiten der Überproduktion, die wieder abgebaut werden, wenn die Verbrauchstrate die Produktionstrate übersteigt. Speicherkohlenhydrate spielen eine wichtige Rolle im Stoffwechsel, Wachstum, Abwehr, Kälteresistenz, und in der Verzögerung oder Vermeidung von Pflanzentod.

Soil compaction and growth of woody plants.

Abstract Although soil compaction in the field may benefit or inhibit the growth of plants, the harmful effects are much more common. This paper emphasizes the deleterious effects of predominantly high levels of soil compaction on plant growth and yield. High levels of soil compaction are common in heavily used recreation areas, construction sites, urban areas, timber harvesting sites, fruit orchards, agroforestry systems and tree nurseries. Compaction can occur naturally by settling or slumping of soil or may be induced by tillage tools, heavy machinery, pedestrian traffic, trampling by animals and fire. Compaction typically alters soil structure and hydrology by increasing soil bulk density; breaking down soil aggregates; decreasing soil porosity, aeration and infiltration capacity; and by increasing soil strength, water runoff and soil erosion. Appreciable compaction of soil leads to physiological dysfunctions in plants. Often, but not always, reduced water absorption and leaf water deficits develop. S...

Plant Responses to Flooding of Soil

Flooding of soil rapidly depletes soil oxygen and alters plant metabolism, thereby inhibiting growth. Reduced growth is preceded by stomatal closure; reduced photosynthesis, carbohydrate translocation, and mineral absorption; as well as altered hormone balance. Flood tolerance varies widely among plant species, cultivars, and ecotypes and is associated with both morphological and physiological adaptations. (Accepted for publication 22 July 1983)

Food relations of woody plants

SYNTHESIS OF FOODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 Photosynthetic Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 Photosynthetic Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 Carbohydrate Stability and Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

PHYSIOLOGICAL-ECOLOGICAL IMPACTS OF FLOODING ON RIPARIAN FOREST ECOSYSTEMS

Riparian forest ecosystems are important for their high productivity of biomass, their biodiversity, and ecological services including control of floods and erosion, removal of nutrients from agricultural runoff, alleviation of pollution effects, and as habitats for birds and mammals. Intermittent cycles of flooding by meandering streams followed by soil drainage are essential for regeneration, optimal growth, preservation of biodiversity, and sustainability of these valuable ecosystems. The straightening of river channels and disruption of intermittent river flow by dams lead to decreases in downstream forest productivity and ecological services, reflecting arrested forest regeneration, suppression of tree growth, and early tree mortality. These responses result from inadequate seed supplies and poor seedbeds, as well as deficiencies of ground water and mineral nutrients. Water deficits in downstream forest trees induce dysfunctions in photosynthesis and mineral nutrition, which lead to growth inhibition and plant mortality. Very few bottomland forest species can withstand extended soil inundation. Hence, prolonged upstream flooding by interruption of river flow is followed by massive losses of biomass as a result of poor seed germination, arrested plant growth, and accelerated mortality of trees. The adverse impacts of flooding on upstream forests are associated with physiological dysfunctions induced by soil anaerobiosis. These include changes in respiration, photosynthesis, protein synthesis, mineral nutrition, and hormone relations, together with increased exposure to a variety of phytotoxic compounds. There is urgent need for developing more integrated and holistic flood-management policies that will recognize the need for protecting and restoring valuable riparian forests while also meeting other flood-control objectives.

Shoot growth in woody plants

Introduction ..................................................................................................................................................................... 335 Variability of Shoot Elongation ............................................................................................................... 336 Initiation of Shoot Growth .......................................................................................................................... 341 Length of Growing Season ........................................................................................................................... 342 Tree Age and Shoot Growth ........................................................................................................ 344 Variations in Length of Growing Season ........................................................................ 345 Effect of Competition and Cultural Conditions on Shoot Growth ............ 347 Laminas, Proleptic and Sylleptic Shoots ........................................................................... 348 Multinodal Buds and Shoot Growth Characteristics ............................................. 350 Apical Dominance .................................................................................................................................................. 351 The Mechanism of Apical Dominance .............................................................................. 354 Geographic Variation in Shoot Growth .......................................................................................... 359 Variation in Time of Bud Break ................................................................................................ 362 Variation in Amount and Duration of Shoot Growth .......................................... 363 Altitudinal Effects ....................................................................................................................................... 367 Photoperiodic Effects ................................................................................................................................. 368 Thermoperiodic Effects ........................................................................................................................... 371 Predetermination and Control of Shoot Growth .................................................................. 372 Influence of Site and Other Factors ...................................................................................................... 377 Literature Cited ......................................................................................................................................................... 379

Effects of flooding on Eucalyptus camaldulensis and Eucalyptus globulus seedlings

SummaryFlooding for up to 40 days induced morphological changes and reduced growth of 6-week-old Eucalyptus camaldulensis and Eucalyptus globulus seedlings. However, the specific responses to flooding varied markedly between these species and with duration of flooding. Both species produced abundant adventitious roots that originated near the tap root and original lateral roots, but only E. camaldulensis produced adventitious roots on submerged portions of the stem. Flooding induced leaf epinasty and reduced total dry weight increment of seedling of both species but growth of E. globulus was reduced more. In both species dry weight increment of shoots was reduced more than dry weight increment of roots, reflecting compensatory growth of adventitious roots. Adaptation to flooding appeared to be greater in E. camaldulensis than in E. globulus. the importance of formation of adventitious roots in flooding tolerance is emphasized.

Effects of flooding, tilting of stems, and ethrel application on growth, stem anatomy, and ethylene production of acer platanoides seedlings

Flooding of soil, tilting of stems, and application of ethrel to stems variously influenced growth, stem anatomy and ethylene production of 12‐month‐old Acer platanoides L. seedlings. Flooding greatly suppressed height growth, stem diameter growth, and the rate of dry weight increase of leaves, stems, and roots, with root growth suppressed most. Flooding also increased bark thickness above the level of submergence, reduced the xylem increment, and stimulated ethylene production of stems and ACC accumulation in the roots. Tilting of stems inhibited height growth somewhat, increased diameter growth and fiber production on the upper side of the leaning stem, increased ethylene production somewhat on both the upper and lower side of the stem, and induced formation of tension wood on the upper side of the stem. Tilting did not affect dry weight increase of leaves, stems, or roots. Application of ethrel to upright stems increased xylem increment around the stem; in tilted, ethrel‐treated seedlings xylem increme...