Responses of Scots pine (Pinus sylvestris) seedlings grown in different nutrient regimes to changing root zone temperature in spring

We examined effects of nutrient availability and changing root zone temperature (RZT) on growth, gas exchange and plasma membrane H(+)-ATPase (PM-ATPase) activity of roots of 1-year-old Scots pine (Pinus sylvestris L.) seedlings during spring flushing. The 6-week growth-chamber experiment was carried out in hydroponic cultures that supplied the seedlings with low (0.5 mM N) or high (3 mM N) nutrient concentration and two rates of increase in RZT were simulated: slow warming (SW-treatment) and fast warming (FW-treatment). Air temperature, humidity, and light conditions were similar in all treatments. Growth of roots and shoots was retarded at low RZT, and fresh mass increment of roots was closely correlated with RZT sum. High nutrient availability increased nitrogen concentrations of needles and stems, but only at RZTs >13 degrees C. Low RZT and low availability of nutrients suppressed gas exchange of the seedlings. Real PM-ATPase activity was highly dependent on RZT. At high RZTs, real PM-ATPase activity was affected by nutrient availability but this effect was related to root growth. We conclude that, under conditions of high nutrient availability, Scots pine seedlings can compensate for the suppressive effects of long-term exposure to low RZT by rapidly accelerating growth, gas exchange and root metabolism, but only when RZT has increased above a threshold value, which was 13 degrees C in this study.     

Effects of temperature and nutrient availability on plasma membrane lipid composition in Scots pine roots during growth initiation

We studied the effects of root zone temperature (RZT) and nutrient availability on free sterols and phospholipids in the plasma membrane (PM) and on PM-ATPase activity in roots of 1-year-old Scots pine (Pinus sylvestris L.) seedlings during growth initiation in the spring. Seedlings were grown for 6 weeks in hydroponic cultures with low (0.5 mM N; LN) or high (3 mM N; HN) nutrient availability. The root zone was subjected to slow warming (SW) and fast warming (FW) treatments while maintaining similar air temperatures in both treatments. Decreases in the amount of phospholipids and in the phospholipid/free sterol ratio, an increase in the degree of saturation of phospholipid fatty acids and changes in free sterol composition were observed during root growth initiation. Changes in lipid composition of the PM associated with the cold deacclimation process were detected at RZTs above 9 degrees C. Nutrient availability affected the lipid composition of the PM only when RZT was increased slowly. When RZT increased from 4 to 6 degrees C in the SW treatment, the degree of saturation of phospholipid fatty acids decreased, especially in HN seedlings. The sitosterol/stigmasterol ratio remained higher in HN seedlings than in LN seedlings. After an RZT of 9 degrees C had been reached in the SW treatment, HN caused increases in the saturation of phospholipid fatty acids and root PM-ATPase activity, and a decrease in the phospholipid/free sterol ratio. Possible effects of changes in PM lipid composition on root growth and PM-ATPase activity are discussed.     

Root-zone temperatures affect phenology of bud break, flower cluster development, shoot extension growth and gas exchange of 'Braeburn' (Malus domestica) apple trees

We investigated the effects of root-zone temperature on bud break, flowering, shoot growth and gas exchange of potted mature apple (Malus domestica (Borkh.)) trees with undisturbed roots. Soil respiration was also determined. Potted 'Braeburn' apple trees on M.9 rootstock were grown for 70 days in a constant day/night temperature regime (25/18 degrees C) and one of three constant root-zone temperatures (7, 15 and 25 degrees C). Both the proportion and timing of bud break were significantly enhanced as root-zone temperature increased. Rate of floral cluster opening was also markedly increased with increasing root-zone temperature. Shoot length increased but shoot girth growth declined as root-zone temperatures increased. Soil respiration and leaf photosynthesis generally increased as root-zone temperatures increased. Results indicate that apple trees growing in regions where root zone temperatures are < or = 15 degrees C have delayed bud break and up to 20% fewer clusters than apple trees exposed to root zone temperatures of > or = 15 degrees C. The effect of root-zone temperature on shoot performance may be mediated through the mobilization of root reserves, although the role of phytohormones cannot be discounted. Variation in leaf photosynthesis across the temperature treatments was inadequately explained by stomatal conductance. Given that root growth increases with increasing temperature, changes in sink activity induced by the root-zone temperature treatments provide a possible explanation for the non-stomatal effect on photosynthesis. Irrespective of underlying mechanisms, root-zone temperatures influence bud break and flowering in apple trees.     

Patterns of photosynthesis and starch allocation in seedlings of four bottomland hardwood tree species subjected to flooding

Effects of short-term (32 days) flooding on photosynthesis, stomatal conductance, relative growth rate and tissue starch concentrations of flood-intolerant Quercus alba L. (white oak), bottomland Quercus nigra L. (water oak), bottomland Fraxinus pennsylvanica Marshall. (green ash) and flood-tolerant Nyssa aquatica L. (water tupelo) seedlings were studied under controlled conditions. Net photosynthetic rates of flooded N. aquatica seedlings were reduced by 25% throughout the 32-day flooding period. Net photosynthetic rates of flooded Q. alba seedlings fell rapidly to 25% of those of the control seedlings by Day 4 of the flooding treatment and to 5% by Day 16. In F. pennsylvanica and Q. nigra, net photosynthetic rates were reduced to 50% of control values by Day 8 but remained at approximately 30 and 23%, respectively, of control values by Day 32. Leaves of flooded Q. alba seedlings accumulated approximately twice as much starch as leaves of non-flooded control plants, whereas root starch concentrations decreased to 67% of those of control plants by the end of the 32-day flooding treatment. In contrast, flooding caused only a small increase in leaf starch concentrations of N. aquatica plants, but it increased root starch concentrations to 119% of those of the control plants by the end of the experiment. The co-occurring bottomland species, Fraxinus pennsylvanica and Q. nigra, differed from each other in their patterns of stomatal conductance and root starch concentrations. We conclude that the maintenance of low leaf starch concentrations, and high pre-flood root tissue starch concentrations are important characteristics allowing flood-tolerant species to survive in flooded soils.     

Root growth potential as an indicator of drought stress history

Container-grown quiescent Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) seedlings were air dried to plant water potentials of -0.2, -2.2 or -3.8 MPa (unstressed, moderate, and severe stress treatments, respectively). Trees from each treatment were either placed in root mist chambers held at 10, 20, or 28 degrees C for 28 days and root growth potential (RGP) and plant water potential (PWP) measured weekly, or potted in a 1/1 mix of peat and vermiculite, watered only once, and height growth and survival recorded after 10 weeks in an unheated greenhouse. Root growth potential of unstressed trees was greater than that of moderately stressed trees at all temperatures. Root growth potential of severely stressed trees was zero. Predawn plant water potentials of unstressed and moderately stressed trees were initially high, fell to -0.5 to -0.8 MPa, and then increased. Predawn plant water potential of severely stressed trees declined continuously over the 28-day experiment. Survival and height growth of the severely stressed trees were reduced compared to the unstressed and moderately stressed trees. Among the root growth potential measurements, RGP measured after 7 days at 10 degrees C was most sensitive to drought stress history and revealed differences in vigor that were not apparent from the survival and height growth data.     

A comparison of wetland tree growth response to hydrologic regime in Louisiana and South Carolina

Numerous investigations have examined the growth of wetland tree species under a variety of hydrologic conditions. Most studies have compared flooded versus non-flooded conditions in greenhouses or in one to a few field sites near each other or within the same region. Comparisons of wetland tree growth among widely separated areas of the country are rare. This study compared the diameter growth of Nyssa sylvatica var. biflora, Nyssa aquatica, and Taxodium distichum trees from Louisiana (Gulf Coastal Plain) and South Carolina (Atlantic Coastal Plain). In both regions, individual trees were distributed along a gradient of hydrologic regimes from infrequent to permanent flooding. Nyssa sylvatica var. biflora was restricted to periodically flooded sites in both regions. Within these sites, this species showed little response to differences in mean water depth. In contrast, significant differences among hydrologic regimes were detected for N. aquatica in both regions. In Louisiana, patterns of growth response did not correlate with the gradient of hydrologic regimes, but in South Carolina maximum growth was inversely related to mean water levels during the growing season. Maximum growth of T. distichum trees was observed at sites with shallow, permanent flooding in both regions.     

Growth, shoot phenology and physiology of diverse seed sources of black spruce: II. 23-year-old field trees

Four sources of 23-year-old black spruce (Picea mariana (Mill.) B.S.P.) from a provenance test at the Petawawa National Forestry Institute (46 degrees N, 77 degrees 30' W) were assessed for height growth, shoot phenology and seasonal gas exchange. The provenances were designated 7000 (Yukon, 63 degrees 34' N, 135 degrees 55' W), 6979 (Alberta 52 degrees 22' N, 115 degrees 15' W), 6908 (Ontario, 48 degrees 59' N, 80 degrees 38' W) and 6901 (Ontario, 45 degrees 10' N, 77 degrees 10' W). Trees of southern provenances (6901 and 6908) were considerably taller, and broke bud and ceased growth later than trees of northern provenances (6979 and 7000). In early spring, trees of northern provenances had higher net photosynthetic rates (P(n)) than trees of southern provenances (6908 and 6901). During midsummer, trees of Provenance 7000 generally had the highest P(n) as a result of low rates of shoot dark respiration (R(d)). Trees of northern provenances displayed an earlier autumn decline in P(n) than trees of southern provenances. Provenance differences in growth, shoot phenology and physiology agreed well with results from a greenhouse study of seedlings from the same provenances. We conclude that the poor growth performance of trees of northern provenances in Ontario was associated with: (1) a short period of shoot growth, (2) a high rate of dry matter partitioning to roots, (3) low rates of late-season P(n) in response to decreasing photoperiod, and possibly, (4) a high rate of root R(d).     

Streamside trees: responses of male, female and hybrid cottonwoods to flooding

Cottonwoods, riparian poplars, are dioecious and prior studies have indicated that female poplars and willows can be more abundant than males in low-elevation zones, which are occasionally flooded. We investigated the response to flooding of clonal saplings of 12 male and 9 female narrowleaf cottonwoods (Populus angustifolia) grown for 15 weeks in a greenhouse, along with three females of a co-occurring native hybrid (Populus?×?jackii?=?Populus deltoides?×?Populus balsamifera). Three water-level treatments were provided, with substrate inundation as the flood treatment. In the non-flooded condition, the hybrids produced about four-fold more dry weight (DW) than the narrowleaf cottonwoods (P??P. angustifolia male?>?P.?×?jackii female. This indicates that narrowleaf cottonwoods are relatively flood tolerant and suggests that females are more flood tolerant than males. We propose the concept of 'strategic positioning', whereby the seed-producing females could be better adapted to naturally flooded, low-elevation streamside zones where seedling recruitment generally occurs.     

Flood tolerance of four tropical tree species

Many seasonally flooded habitats in the tropics are dominated by one or a few tree species. We tested the hypothesis that the inability to tolerate flooding restricts most species from becoming established in flood-prone habitats. We compared morphological and physiological responses to flooding in seedlings of Prioria copaifera Griseb., a species that forms monodominant stands in seasonally flooded habitats, and in three species confined to flood-free sites; namely, Calophyllum longifolium Willd., Virola surinamensis Aubl. and Gustavia superba (H.B.K.) Berg. Flooding reduced photosynthesis at Day 45 in all species by 10-30%. By Day 90, photosynthesis returned to the control rate in Prioria, but not in the other species. Flooding reduced stomatal conductance by 25-35% in all species except Calophyllum, and it reduced leaf area growth by 44% in Virola, but not in the other species. All species survived 90 days of flooding without mortality, leaf chlorosis, leaf necrosis, or leaf abscission. Flooding reduced root:shoot ratio significantly in Gustavia and Calophyllum, but not in the other species, and it reduced maximum root depth by 29% in Prioria, but by 61% or more in the species from flood-free habitats.     

Physiological, morphological and anatomical responses of Fraxinus mandshurica seedlings to flooding

Two-year-old Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings were flooded to 8 cm above soil level for 70 days. The flooding treatment altered the growth, morphology, stem anatomy and ethylene production of the seedlings. Although flooding did not affect height growth, it stimulated diameter growth of the submerged stems by increasing both the number and size of wood fibers produced; however, the thickness of the cell walls of the wood fibers was reduced by flooding. In response to the flooding treatment, the seedlings formed abundant hyperhydric tissues, originating from the vicinity of lenticels on the surface of the flooded stems, and adventitious roots, which grew through the hyperhydric tissues. Aerenchyma tissues were observed in the bark of the adventitious roots. The flooding treatment did not affect dry weight increment of leaves and stems, but it reduced the total dry weight increment of the root system even though it promoted adventitious root formation. Flooding also enhanced ethylene production in the submerged portions of stems. The potential roles of flood-induced ethylene in cambial growth and adventitious root formation in flooded plants are discussed.     

Responses of black spruce (Picea mariana) and tamarack (Larix laricina) to flooding and ethylene

Black spruce (Picea mariana (Mill.) BSP) and tamarack (Larix laricina (Du Roi) K. Koch) are the predominant tree species in the boreal peatlands of Alberta, Canada, where low nutrient availability, low soil temperature and a high water table limit their growth. Effects of flooding for 28 days on morphological and physiological responses were investigated in greenhouse-grown black spruce and tamarack seedlings in a growth chamber. Flooding reduced root hydraulic conductance, net assimilation rate and stomatal conductance, and increased water-use efficiency (WUE) and needle electrolyte leakage in both species. Although flooded black spruce seedlings maintained higher net assimilation rates and stomatal conductance than flooded tamarack seedlings, flooded tamarack seedlings were able to maintain higher root hydraulic conductance than flooded black spruce seedlings. Needles of flooded black spruce developed tip necrosis and electrolyte leakage after 14 days of flooding, and these symptoms were subsequently more prominent than in needles of flooded tamarack seedlings. Flooded tamarack seedlings exhibited no visible injury symptoms and developed hypertrophied lenticels at their stem base. Application of exogenous ethylene resulted in a significant reduction in net assimilation, stomatal conductance and root respiration, whereas root hydraulic conductivity increased in both species. Thus, although flooded black spruce seedlings maintained a higher stomatal conductance and net assimilation rate than tamarack seedlings, black spruce did not cope with the deleterious effects of prolonged soil flooding and exogenous ethylene as well as tamarack.     

Coarse and fine root respiration in aspen (Populus tremuloides)

Coarse and fine root respiration rates of aspen (Populus tremuloides Michx.) were measured at 5, 15 and 25 degrees C. Coarse roots ranged from 0.65 to 4.45 cm in diameter, whereas fine roots were less than 5 mm in diameter. To discriminate between maintenance and growth respiration, root respiration rates were measured during aboveground growing periods and dormant periods. An additional measurement of coarse root respiration was made during spring leaf flush, to evaluate the effect of mobilization of resources for leaf expansion on root respiration. Fine roots respired at much higher rates than coarse roots, with a mean rate at 15 degrees C of 1290 micromol CO2 m-3 s-1 during the growing period, and 660 micromol CO2 m-3 s-1 during the dormant period. The temperature response of fine root respiration rate was nonlinear: mean Q10 was 3.90 for measurements made at 5-15 degrees C and 2.19 for measurements made at 15-25 degrees C. Coarse root respiration rates measured at 15 degrees C in late fall (dormant season) were higher (370 micromol CO2 m-3 s-1) than rates from roots collected at leaf flush and early summer (200 micromol CO2 m-3 s-1). The higher respiration rates in late fall, which were accompanied by decreased total nonstructural carbohydrate (TNC) concentrations, suggest that respiration rates in late fall included growth expenditures, reflecting recent radial growth. Neither bud flush nor shoot growth of the trees caused an increase in coarse root respiration or a decrease in TNC concentrations, suggesting a limited role of coarse roots as reserve storage organs for spring shoot growth, and a lack of synchronization between above- and belowground growth. Pooling the data from the coarse and fine roots showed a positive correlation between nitrogen concentration and respiration rate.     

Estimation of genetic variances in flood tolerance of poplar and selection of resistant F1 generations

Five Aigeiros section poplar clones were adopted as parents to produce five full-sib families through cross-breeding. Morphological, ecophysiological, and growth characteristics of the five parents and their 15 superior F1 generations were investigated during 45 days of flooding followed by a 10-day recovery period. Cuttings were subjected to two treatments: watered (control) and flooded to 10 cm above the soil surface. Results showed that flooded cuttings showed significant reduction in growth of height, root-collar diameter and leaf area, and root and total biomass yield. All 20 clones formed hypertrophied lenticels and adventitious roots by day 6–14 of flooding. In flooded cuttings, net photosynthesis, stomatal conductance, transpiration, and chlorophyll fluorescence were decreased significantly compared with the control. After flooding ended, all plants recovered rapidly. Generally, progenies showed higher growth of height, root-collar diameter, root biomass and leaf area than their parents both under flooding and control conditions, showing that heterosis existed in F1 generations, regardless of flooding. However heterosis was lower under flooding conditions than in the control. Under flooding, the highest heterosis of higher-parent in height and root-collar diameter were 68.63 and 20.83%, respectively. Variability of flood tolerance among progenies was clear in growth of height and root-collar diameter. Selection criteria for parents in cross-breeding were different between control and flooding. Relative effect values of the specific combining ability (SCA) and relative effect values of the general combining ability (GCA) of parents were more important than their flood tolerance. Progenies with a higher level of flood tolerance could be obtained, even from parents intolerant to flooding. In terms of breeding, height growth would be most important characteristic to measure in flooding conditions, and root-collar diameter growth was also very useful. Based on all measured values, the tested 20 clones were classified into three groups using hierarchical cluster analysis. Clones Lu, E4, E9, E29, A2, A8, A9, B1, B3, B4, and D8, were flood-tolerant. Clones Lf, Ha, Lm, D1, D7, F9, and F21 were moderately flood-tolerant. Clones Sm and F13 were flood-susceptible.     

Acclimation of loblolly pine (Pinus taeda) seedlings to high temperatures

To determine the extent to which loblolly pine seedlings (Pinus taeda L.) acclimate to high temperatures, seedlings from three provenances-southeastern Texas (mean annual temperature 20.3 degrees C), southwestern Arkansas (mean annual temperature 16.2 degrees C) and Chesapeake, Maryland (mean annual temperature 12.8 degrees C)-were grown at constant temperatures of 25, 30, 35 or 40 degrees C in growth chambers. After two months, only 14% of the seedlings in the 40 degrees C treatment survived, so the treatment was dropped from the experiment. Provenance and family differences were not significant for most measured variables. Total biomass was similar in the 25 and 30 degrees C treatments, and less in the 35 degrees C treatment. Foliage biomass was higher, and root biomass lower, in the 30 degrees C treatment compared with the 25 degrees C treatment. Net photosynthesis and dark respiration of all seedlings were measured at 25, 30 and 35 degrees C. Both net photosynthesis and dark respiration exhibited acclimation to the temperature at which the seedlings were grown. For each temperature treatment, the highest rate of net photosynthesis was measured at the growth temperature. Dark respiration rates increased with increasing measurement temperature, but the basal rate of respiration, measured at 25 degrees C, decreased from 0.617 &mgr;mol m(-2) s(-1) in the 25 degrees C treatment to 0.348 &mgr;mol m(-2) s(-1) in the 35 degrees C treatment, resulting in less carbon loss in the higher temperature treatments than if the seedlings had not acclimated to the growth conditions. Temperature acclimation, particularly of dark respiration, may explain why total biomass of seedlings grown at 30 degrees C was similar to that of seedlings grown at 25 degrees C.     

Soil temperature and plant growth stage influence nitrogen uptake and amino acid concentration of apple during early spring growth

In spring, nitrogen (N) uptake by apple roots begins about 3 weeks after bud break. We used 1-year-old 'Fuji' Malus domestica Borkh on M26 bare-root apple trees to determine whether the onset of N uptake in spring is dependent solely on the growth stage of the plant or is a function of soil temperature. Five times during early season growth, N uptake and total amino acid concentration were measured in trees growing at aboveground day/night temperatures of 23/15 degrees C and belowground temperatures of 8, 12, 16 or 20 degrees C. We used (15NH4)(15NO3) to measure total N uptake and rate of uptake and found that both were significantly influenced by both soil temperature and plant growth stage. Rate of uptake of 15N increased with increasing soil temperature and changed with plant growth stage. Before bud break, 15N was not detected in trees growing in the 8 degrees C soil treatment, whereas 15N uptake increased with increasing soil temperatures between 12 and 20 degrees C. Ten days after bud break, 15N was still not detected in trees growing in the 8 degrees C soil treatment, although total 15N uptake and uptake rate continued to increase with increasing soil temperatures between 12 and 20 degrees C. Twenty-one days after bud break, trees in all temperature treatments were able to acquire 15N from the soil, although the amount of uptake increased with increasing soil temperature. Distribution of 15N in trees changed as plants grew. Most of the 15N absorbed by trees before bud break (approximately 5% of 15N supplied per tree) remained in the roots. Forty-six days after bud break, approximately one-third of the 15N absorbed by the trees in the 12-20 degrees C soil temperature treatments remained in the roots, whereas the shank, stem and new growth contained about two-thirds of the 15N taken up by the roots. Total amino acid concentration and distribution of amino acids in trees changed with plant growth stage, but only the amino acid concentration in new growth and roots was affected by soil temperature. We conclude that a combination of low soil temperature and plant developmental stage influences the ability of apple trees to take up and use N from the soil in the spring. Thus, early fertilizer application in the spring when soil temperatures are low or when the aboveground portion of the tree is not actively growing may be ineffective in promoting N uptake.     

Influence of controlled water supply on shoot and root development of young peach trees

Three controlled water supply treatments were applied to 1-year-old peach trees grown in root observation boxes. The treatments were: I(0), growth medium maintained at 50% field capacity; I(1), water supplied when daily net tree stem diameter change was negative or zero for 1 day; I(3) as for I(1) except that water was applied after net daily stem diameter change was negative or zero for 3 consecutive days. Trees in treatment I(0) had the greatest mean daily first-order shoot growth rates, and trees in treatment I(3) had the lowest shoot growth rates. Because leaf production rate (apparent plastochron) of first-order shoots was unaffected by treatment, differences in shoot length were due to differences in internode extension and not to the number of internodes. Trees in treatment I(0) had a greater number of second-order shoot axes than trees in treatment I(1) or I(3). Furthermore, an increase in the rate of growth of the first-order shoot axis was associated with an increased tendency for branching (i.e., the development of sylleptic second-order shoots). Increased leaf length was also associated with more frequent watering. Trees in treatment I(0) had the greatest root lengths and dry weights, and this was attributed to a greater number of first-and second-order (lateral) root axes compared with trees in the I(1) and I(3) treatments. The extension rate and apical diameter of first-order roots were reduced by the I(3) treatment. The density of second-order roots along primary root axes was not affected by any of the treatments.     

Fraxinus americana Roots Respond to Subsurface Feeding of Mycorrhizal Inoculum and Nitrogen Fertilizer

Abstract

Ball and burlap Fraxinus americana (Autumn purple ash) trees were evaluated for their response to subsurface feeding of mycorrhizal inoculum with root biostimulant (mycorrhiza Roots) and nitrogen fertilizer (Coron 28-0-0) on difficult sites in the Colorado front range. Two root ingrowth cores were installed around each of twelve trees following planting in fall 1998 and excavated in fall 1999. Inoculation with mycorrhiza Roots alone resulted in sigificantly increased dry root weights and mycorrhizal colonization percentage on treated purple ash trees (p ≤ 0.05). Mycorrhiza Roots with Coron also significantly increased dry root weights and mycorrhizal colonization percentage on treated ash (p ≤ 0.05). Increases in root growth were dramatic. Purple ash trees treated with mycorrhiza Roots and Coron had greater than 3.5 times the dry root weights in excavated root ingrowth cores compared controls. Trees treated with mycorrhiza Roots alone had greater than 3 times the dry weights compared to controls. Trees treated with mycorrhiza Roots alone had more than 12 times higher mycorrhi-zal colonization percentage compared to controls. Control trees were poorly colonized by mycorrhizal fungi. This study indicates that subsurface feeding of purple ash ball and burlap trees following outplanting with mycorrhizal inoculum and root biostimulant can greatly improve root growth and mycorrhizal colonization.     

Effects of flooding depth on growth,morphology and photosynthesis in <Emphasis Type="Italic">Alnus japonica</Emphasis> species

The present study deals with effects of flooding depth on growth, morphology and photosynthesis in Alnus japonica species thorough one field study and two controlled experiments. In the field study performed in Kushiro Mire, Hokkaido Island, Japan, tree heights and stem diameters decreased with an increase in water depth accompanied with the reduction of soil redox potential. In contrast, the rate of multiple stems per individual tree increased. In the controlled experiments for seedlings flooding suppressed the shoot elongation and biomass increment in roots. However, diameter increment around water levels, epicormic shoot development and adventitious root formation were enhanced in flooded seedlings. The photosynthetic rate and stomatal conductance of flooded seedlings also were lowered with an increase in flooding depth. The recovery of the reduced photosynthetic rate and stomatal conductance occurred simultaneously with the advancement of adventitious root formation in the flooded seedlings. These results indicate the importance of a series of morphological changes occurring on stems around water levels in flood tolerance in A. japonica species.     

Remobilization and uptake of N by newly planted apple (Malus domestica) trees in response to irrigation method and timing of N application

Environmentally sound management of N in apple orchards requires that N supply meets demand. In 1997, newly planted apple trees (Malus domestica Borkh. var. Golden Delicious on M.9 rootstock) received daily applications of N for six weeks as Ca(15NO3)(2) through a drip irrigation system at a concentration of 112 mg l(-1) at 2-8, 5-11 or 8-14 weeks after planting. Irrigation water was applied either to meet estimated evaporative demand or at a fixed rate. In 1997, trees were harvested at 5, 8, 11 and 14 weeks after planting; and in 1998 at 3 weeks after full bloom. The amount of fertilizer N recovered was similar in trees in both irrigation treatments, but efficiency of fertilizer use was greater for trees receiving demand-controlled irrigation than fixed-rate irrigation. This was attributed to lower N inputs, greater retention time in the root zone and less N leaching in the demand-controlled irrigation treatments compared with fixed-rate irrigation treatments. Less fertilizer N was recovered by trees receiving an early application of N than a later application of N and this was related to the timing of N supply with respect to tree demand. Demand for root-supplied N was low until 11 weeks after planting, because early shoot and root growth was supported by N remobilized from woody tissue, which involved 55% of the total tree N content at planting. Rapid development of roots > 1 mm in diameter occurred between 11 and 14 weeks after planting, after remobilization ended, and was greater for trees receiving an early application of N than for trees receiving a later application of N. Late-season tree N demand was supplied by native soil N, and uptake and background soil solution N concentrations were higher for trees receiving demand-supplied irrigation compared with fixed-rate irrigation. Total annual N uptake by roots was unaffected by treatments and averaged 6-8 g tree(-1). Nitrogen applications in 1997 affected growth and N partitioning in 1998. Trees receiving early applications of N had more flowers, spur leaves and bourse shoots than trees receiving later applications of N. Consequently, more N was remobilized into fruits in trees receiving early applications of N compared with fruits in trees receiving later applications of N. Demand for N in the young apple trees was low. Early season demand was met by remobilization from woody tissues and the timing of demand for root-supplied N probably depends on whether flowering occurs. Method of N delivery affected the efficiency of N use. We conclude that N demand can be met at soil solution N concentrations of around 20 mg l(-1).     

Studies on the Health of Beech Trees in Surrey, England: Relationship between Winter Canopy Assessment by Roloff's Method and Twig Analysis

Trees and saplings of all sizes (total 229) were studied atthree amenity sites in Surrey representing mixed woodland, beechhigh forest and open parkland. Roloff's winter assessment ofthe twig pattern of growth demonstrated an underlying differencebetween the sites, which was consistent with an associationbetween greater deterioration and more exposure to climate extremesand pollutants. Trees showed deterioration with age but prematureageing was seen in 35–50-year-old parkland trees. Withinthe woodland the more exposed trees had worse scores. Quantitative twig analysis was carried out on twigs from theupper canopy of 19 trees and saplings. In the most severelysuppressed trees yearly growth declined from the 1976 drought.Subsidiary shoot development was markedly reduced in such treesand there were high numbers of distorted and acute angled shoots.The latter two characteristics increased with age with younghealthy trees having very few of these types of shoots, buttwo 35-year-old trees in open parkland showed premature ageingwith larger numbers of such shoots. Twig analysis defined categories of twig pattern according toage and deterioration levels. There was generally good correlationbetween these categories and the Roloff twig canopy score beforeanalysis or with canopy scores of similar sized neighbours.Objective criteria suggested for future studies were: (1) measurementof annual primary shoot growth; (2) total secondary shoot lengthrelative to a standard primary shoot length; (3) mean numberof subsidiary shoots per year; and (4) proportion of shootsgrowing at 40° or less.