Allometry of acetylene reduction and nodule growth of Robinia pseudoacacia families subjected to varied root zone nitrate concentrations

The effects of nitrate (NO(3) (-)) on acetylene reduction and growth were examined in nodulated seedlings from three open-pollinated families of black locust (Robinia pseudoacacia L.) grown in sand culture. In the first study, nine-week-old seedlings were supplied with 0.0, 0.5, 1.0, 5.0 or 15.0 mM NO(3) (-), for two weeks during which acetylene reduction and biomass were measured five times. In the second study, eight-week-old seedlings were supplied with 0.0, 1.0 or 5.0 mM NO(3) (-) for 51 days during which acetylene reduction and biomass were measured six times. Results were analyzed with and without adjustments for seedling size. In the first study, 15.0 mM NO(3) (-) significantly decreased total acetylene reduction but lower concentrations did not. In seedlings given 15.0 mM NO(3) (-), both nitrogenase activity and nodule biomass were reduced. Inhibition of nitrogenase activity by NO(3) (-) was reversible. In the second study, both the 1.0 and 5.0 mM NO(3) (-) treatments increased plant growth compared to the control (0.0 mM). At the end of the 51-day treatment period, total acetylene reduction and nodule biomass were greatest in the 1.0 mM NO(3) (-) treatment and least in the 5.0 mM NO(3) (-) treatment. However, when adjusted for seedling size, total acetylene reduction and nodule biomass were similar in the 0.0 and 1.0 mM NO(3) (-) treatments. The greater total acetylene reduction and nodule biomass of seedlings grown with 1.0 mM NO(3) (-) resulted from increased seedling size due to fertilization. After adjustment for plant size, total acetylene reduction, nodule biomass and nitrogenase activity were significantly lower in the 5.0 mM NO(3) (-) treatment compared with the control or 1.0 mM NO(3) (-) treatment. Adjustment for seedling size, by means of allometric principles, appears necessary to interpret treatment effects on total acetylene reduction and its components, nodule biomass and nitrogenase activity correctly.     

Responses of condensed tannins in poplar roots to fertilization and gypsy moth defoliation

We examined the effects of fertilization and gypsy moth defoliation on condensed tannin concentration (%CT) of hybrid poplar (Populus x canadensis cv 'Eugeneii') fine roots in the summers of 1997 and 1998. This factorial experiment included two defoliation treatments (defoliated and a foliated control) and fertilization treatments (100 kg nitrogen (N) ha(-1) and an unfertilized control). Gypsy moth (Lymantria dispar L.) populations were experimentally increased to obtain defoliation in the summers of 1996, 1997 and 1998; fertilization subplots were supplemented with NH4NO3 (100 kg N ha(-1)) in the spring of each year. Despite the severity of defoliation, the effects were small, and significant on only two sampling dates: in May 1997, when fine root %CT was 23% lower in the defoliated trees, and in November 1997, when trees in the defoliated unfertilized plots had 35% higher root %CT than trees in all other plots. Defoliation effects on root %CT did not follow the same seasonal pattern as defoliation effects on root starch content, N uptake capacity or leaf %CT. Regulation of root condensed tannin concentration appeared to be partially uncoupled from these traits. The small transient effects on root defense reflect the resilience of this early successional tree to severe early season defoliation.     

Consequences of resource limitation for recovery from repeated defoliation in Eucalyptus globulus Labilladière

Recovery following defoliation can be modified by co-occurring site resource limitations. The growth response of young Eucalyptus globulus saplings to two defoliation events was examined in an experimental plantation with combinations of low (-) or high (+) water (W) and nitrogen (N) resources. Artificial defoliation was applied at 3 and 9 months of age to remove ~40 and 55% of leaf area in the upper crown, respectively. At 18 months of age, height, stem diameter and leaf area were not significantly different between control and defoliated saplings, across all resource treatments. However, stem volume, bark volume and branch number were significantly increased in defoliated saplings, including a significant interaction with resource treatment. Total above-ground biomass of saplings in response to defoliation was significantly higher (almost double) than controls for the low water (N?+?W-) treatment only. Significantly increased foliar starch content (and a trend for increased soluble sugars) in the upper crown zone was found in the defoliated saplings of the N?+?W- treatment compared with the upper zone of control saplings. Foliar total non-structural carbohydrates were significantly correlated to stem biomass regardless of resource treatment or defoliation, and we suggest that foliar resources are most important for stem growth in E. globulus rather than stored carbon (C) from other tissues. After repeated defoliation and several months recovery, E. globulus saplings were generally not C limited in this study.     

Increased photosynthesis following partial defoliation of field-grown Eucalyptus globulus seedlings is not caused by increased leaf nitrogen

Increased photosynthetic rates following partial defoliation may arise from changes in leaf biochemistry, water relations or nutrient status. Twelve-month-old field-grown Eucalyptus globulus Labill. seedlings were pruned from below to reduce the green crown depth by 50 (D50) or 70% (D70). Photosynthetic responses to light and CO2 concentration were examined before and one, three and five weeks after partial defoliation. One week after defoliation, photosynthetic rates were greater in seedlings in the D50 (21 micromol m(-2) s(-1)) and D70 (23 micromol m(-2) s(-1)) treatments than in control seedlings (15 micromol m(-2) s(-1)); however, there was little difference in photosynthetic rates between partially defoliated seedlings and control seedlings after 5 weeks. An analysis of the sensitivity of photosynthesis to biochemical parameters revealed that the transient increase in photosynthetic rate in response to partial defoliation was largely a function of the maximum rate of carboxylation (85-87%) and the maximum rate of RuBP regeneration (55-60%) rather than stomatal conductance (12-13%). Nitrogen increased in leaves following partial defoliation (increases of 0.6 and 1.2 g m(-2) for D50 and D70, respectively), but was accumulated in a non-photosynthetic form (i.e., there was no increase in nitrogen concentration of Rubisco or chlorophyll). Increased photosynthetic rates immediately following partial defoliation were primarily a result of increased activity rather than amount of photosynthetic machinery. There was no evidence that phosphorus was responsible for the increase in photosynthetic rates after partial defoliation.     

Root system architecture and receptivity to mycorrhizal infection in seedlings of Cedrus atlantica as affected by nitrogen source and concentration

Effects of nitrogen (N) source and concentration on root system architecture and receptivity to mycorrhizal infection were studied in seedlings of Atlas cedar (Cedrus atlantica Manetti) grown in root observation boxes in a controlled-environment chamber. Nitrogen was supplied in a solution containing either NO3-; or NH4+ at a concentration of either 0.25 or 5.0 mM. Root extension was recorded twice weekly by tracing the roots growing in contact with the transparent face of the root observation box. Among treatments, lateral root production and branching density were greatest with 5.0 mM NO3-. Inoculation with mycelium of Tricholoma cedrorum Malencon was carried out 3 months after the start of the N treatments. The highest percentage of mycorrhizal roots, and the greatest amounts of living mycelium (estimated by the ergosterol assay) were observed in the NO3- treatments. Differences in root branching density among the N treatments were insufficient to explain the observed differences among treatments in the extent of mycorrhizal infection of seedlings.     

Absorption and assimilation of nitrate and ammonium ions by jack pine seedlings

Jack pine (Pinus banksiana Lamb.) seedlings were grown in a shaded or unshaded light regime with either NO(3) (-)- or NH(4) (+)-N as the sole N source. After three months, seedlings grown with NH(4) (+)-N were larger than seedlings grown with NO(3) (-)-N. Irradiance had a greater effect on growth of ammonium-fed seedlings than on growth of nitrate-fed seedlings.At all times from 6 to 24 h following incorporation of (15)N, soluble, insoluble, and total (15)N contents of shoots and roots were higher in ammonium-fed seedlings than in nitrate-fed seedlings. The pattern of (15)N accumulation in shoots was similar to that in roots. After 6 and 24 h of (15)N incorporation, unshaded, ammonium-fed seedlings had 8.8 and 2.8 times greater total (15)N contents, respectively, than unshaded, nitrate-fed seedlings. In response to shading, ammonium-fed seedlings increased their total uptake of (15)N per unit root weight, whereas nitrate-fed seedlings did not. No nitrate or (15)NO(3) (-) was detected in any plant tissue. Nitrate-fed plants had higher NH(4) (+), Asp, and Gln concentrations in needles and higher gamma-aminobutyric acid and Arg concentrations in stems. Accumulation of (15)N in roots was not affected by the pH of the (15)N solution or by the N source fed to the seedlings before the period of (15)N incorporation. Thus NO(3) (-) transport into roots, rather than its reduction or transport within the plant, seems to be the factor limiting the growth of jack pine supplied with NO(3) (-)-N as the sole N source.     

Carbon and nitrogen assimilation in red oaks (Quercus rubra L.) subject to defoliation and nitrogen stress

To examine how rates of net photosynthesis and N uptake of red oak seedlings respond to defoliation under contrasting conditions of N availability, nitrogen-deficient plants were grown in sand culture and subjected to partial defoliation and increased N availability under low light conditions. Both photosynthesis and N uptake rates were measured regularly before and after the treatments. Defoliation resulted in elevated rates of net photosynthesis in both low-N and high-N trees, but the high-N trees were able to maintain the high photosynthetic rates for a longer period of time. Nitrogen availability did not affect the photosynthetic rate of the undefoliated plants. Nitrogen uptake was not affected by the defoliation treatment, but was increased by increasing N availability in both the defoliated and undefoliated plants. Nitrogen uptake rates increased less than would be expected on the basis of N availability alone, but the uptake rates were apparently not limited by carbon supply in the short term. Suboptimal concentrations of N in plant tissues resulted in a strong sink for N even in the absence of refoliation.     

European larch and eastern white pine respond similarly during three years of partial defoliation

To test whether trees with different leaf life spans respond differently to defoliation, eastern white pine (Pinus strobus L.) and European larch (Larix decidua Mill.) trees (9 years old in 1991) were partially defoliated by hand between July 1 and 10 in 1989, 1990 and 1991. At the end of 1991, trees of both species had received either 0, 1, 2 or 3 years of defoliation. Trees that received only 1 year of defoliation were defoliated in 1989. Variables measured included photosynthesis, twig water potential, leaf mass per area and leaf nitrogen concentration. There were few significant responses to defoliation in any of the three years of treatment in either species, and only the current-year defoliation treatments caused significant responses. Both species had reduced photosynthetic rates and less negative twig water potentials in response to defoliation in 1989. In 1990 and 1991, the defoliation treatments had no significant effect on any of the parameters measured in European larch. In 1990, there was a significant reduction in foliar nitrogen concentration in eastern white pine in response to defoliation in 1990. In 1991, eastern white pine had significantly less negative twig water potentials in response to defoliation in 1991. Leaf mass per area was not affected by defoliation in either species. We conclude that, for European larch and eastern white pine, differences in leaf life span have no effect on leaf- and twig-level responses to defoliation.     

Influence of a high Mn supply on Norway spruce (Picea abies (L.) Karst.) seedlings in relation to the nitrogen source

Effects of 3, 25, 100, 200 and 800 microM Mn on biomass and pigment, starch and nitrate concentrations were studied in Norway spruce (Picea abies (L.) Karst.) seedlings grown with either NO(3) (-) or NH(4) (+) as the sole nitrogen source. After 77 days of exposure to 800 microM Mn, shoot growth had ceased in about 50% of the seedlings independently of the N source. Despite high Mn concentrations in roots and shoots of the Mn-treated seedlings, no visible symptoms of Mn toxicity were evident. The rate of root elongation was decreased by treatment with >/= 200 microM Mn when N was supplied as NO(3) (-), but not when it was supplied as NH(4) (+). This difference could be attributed to the higher Mn concentrations in root tips of the NO(3) (-)-grown seedlings compared with the NH(4) (+)-grown seedlings. In Mn-treated seedlings, the concentration of Mg, and to a lesser extent that of Ca, decreased. Depletion of these elements might account for the observed growth depression. Potassium concentrations were similar in the control and Mn-treated seedlings. Treatment of seedlings with 800 microM Mn for 50 days led to several physiological changes: starch accumulated, the concentrations of nitrate and phenolic compounds increased, pigment concentrations decreased, and in vivo nitrate reductase activity in roots was reduced.     

Effects of partial defoliation on carbon and nitrogen partitioning and photosynthetic carbon uptake by two-year-old cork oak (Quercus suber) saplings

At the end of the growing season in late July, 20-month-old cork oak (Quercus suber L.) saplings were partially defoliated (63% of leaf area) to evaluate their ability to recover leaf area after defoliation. At 18 and 127 days after defoliation, changes in starch and nitrogen pools were determined in leaves and perennial organs, and variations in photosynthetic carbon uptake were investigated. To determine the role of stored nitrogen in regrowth after defoliation, plant nitrogen was labeled in the previous winter by enriching the nutrient solution with 15N. Plants recovered the lost leaf area in 127 days. Although there was remobilization of starch and nitrogen from leaves and perennial organs, the availability of resources for growth in the following spring was not decreased by defoliation. On the contrary, starch concentration in coarse roots was higher in defoliated saplings than in control saplings, presumably as a result of the higher net CO2 exchange rate in newly developed leaves compared with pre-existing leaves.     

氮肥对盆栽欧洲水青冈生物量和营养分配的影响(英文)

调查了施加氮肥(15NH4和15NO3)处理后在两个连续生长季内欧洲水青冈(Fagus sylvatica L.)幼苗地上部分和地下部分的生物量和营养元素分配。盆栽欧洲水青冈幼苗培养于温室大棚内,培养土样取自相邻的三种林分:欧洲水青冈,挪威赤松,欧洲水青冈-赤松混交林。结果表明,氮肥(15N)处理对欧洲水青冈营养元素分配没有显著影响,施加氮素形式决定自身流入植物库的情况。欧洲水青獭收氮素主要以硝态氮的形式,因此,尽管植物体内保存的硝态氮和氨态氮并没有统计差异,但是叶片中硝态氮明显减少。施加硝态氮对欧洲水青冈氮素恢复的影响要大于施加氨态氮。与欧洲水青冈茎、粗根相比,优质根系对氮素(15N)固定是一个缓慢过程。表8图1参40。     

Beech regeneration of seed and root sucker origin: A comparison of morphology, growth, survival, and response to defoliation

American beech (Fagus grandifolia Ehrh.) reproduces sexually, and vegetatively by root suckers. Although many studies have investigated its regeneration response, most did not account for differences that may exist between its two modes of reproduction. This study was performed in an old-growth Acer - Fagus forest in southern Quebec, where beech bark disease had only a minor effect at the time of the study. We compared the density and frequency of occurrence of beech seedlings and root suckers (height < 30 cm), as well as their morphology, growth, survival, and response to experimental defoliation. Root suckers accounted for 13% of beech regeneration at our site. Density and frequency of occurrence were greater for seedlings than suckers, but did not vary with light availability, which was low at our study site (mean: 2.9%). Seedlings and suckers did not differ in leaf characteristics, but several differences were observed in terms of plant morphology, growth, and survival. Root suckers showed more lateral growth than height growth, and had a lower leaf area index than seedlings. Root suckers had both a greater growth in height and diameter, and a higher survivorship than seedlings (height and diameter growth were, respectively, five and two times greater for suckers than seedlings, and 74% of suckers survived more than 1 year, compared to 52% for seedlings). Defoliation treatments, which included levels of defoliation of 50% and 100% (1) did not affect current-year extension growth of seedlings and suckers; (2) did not affect seedling diameter growth, but had a negative impact on sucker diameter growth; and (3) affected survivorship for both origins, but had a much greater negative impact on seedling survivorship (none of the completely defoliated seedlings survived over one year, while 55% of the suckers did). This study showed that several differences exist between small beech seedlings and root suckers in traits that are important determinants of a species’ competitive ability. We therefore expect that variation in the relative importance of root suckering among sites might have several community-level implications.     

Defoliation and nitrogen effects on photosynthesis and growth of Eucalyptus globulus

Plant responses to defoliation are complex. We established a field experiment in a nine-month-old Eucalyptus globulus Labill. plantation to examine the effects of pattern (upper crown versus lower crown removal), frequency (single, double or triple defoliation within a 12-month period) and severity (25 versus 38% of leaf area removed) of defoliation and the effect of soil nitrogen (N) on photosynthetic processes and stem growth. The photosynthetic responses observed following defoliation could be attributed to changes in source:sink ratios. Light-saturated CO(2) uptake (A(max)) increased with increasing severity and frequency of defoliation irrespective of defoliation pattern. Seedlings defoliated in autumn did not exhibit increases in A(max) until the following spring, whereas there was no such delay in photosynthetic responses associated with spring defoliation. Application of N before defoliation allowed trees to compensate for the effect of defoliation on stem diameter growth, which could not be explained simply in terms of increases in A(max). The observed increases in stem diameter increment following N fertilization of defoliated trees suggested increases in leaf area development, and there were changes in the leaf area:leaf dry mass ratio that may have increased light absorption by the crown. Nitrogen fertilization also increased partitioning of dry mass to branches at the expense of main stems, suggesting that N supply was important in rebuilding crowns following a defoliation event.     

Physiological and phenological responses of oak seedlings to oak forest soil in the absence of trees

Established trees influence the growth and physiology of seedlings by altering above- and belowground conditions; however, tree influences on seedling physiology via belowground interactions are not well understood. We used soil transfers to an open field to examine the belowground influences of a Quercus ellipsoidalis E.J.Hill dominated forest on Q. ellipsoidalis seedling mycorrhizal infection, nutrient uptake, growth and photosynthesis over three years. After two years, seedlings planted with large quantities of forest soil (HF treatment) had greater leaf mass and foliar N concentrations than seedlings receiving smaller quantities of forest soil (LF) and control treatments. Mycorrhizal infection was greater in the HF treatment after one year compared with the LF and control treatments, with a positive correlation of foliar N and mycorrhizal infection in Year 2. There were marked effects of treatments on seedling spring phenology with HF seedlings breaking bud up to 17 days earlier than seedlings in the other treatments. The HF seedlings also had more rapid leaf expansion and larger leaves, and an increase in net photosynthetic rates. These results highlight complex linkages between above- and belowground physiology: forest soil had substantial effects on seedling physiology, including traits such as phenology that have previously been considered to be under aboveground control. Belowground influences of trees on conspecific seedlings may play a critical role in early seedling establishment.     

Photosynthetic responses of field-grown Pinus radiata trees to artificial and aphid-induced defoliation

The phloem-feeding aphid Essigella californica represents a potential threat to the productivity of Pinus radiata plantations in south-eastern Australia. Five- and nine-year-old field trials were used to characterize the effects of artificial and natural aphid-induced (E. californica) defoliation, respectively, on shoot photosynthesis and growth. Photosynthetic capacity (A(max)) was significantly greater following a 25% (D25) (13.8 μmol m(-2) s(-1)) and a 50% (D50) (15.9 μmol m(-2) s(-1)) single-event upper-crown artificial defoliation, 3 weeks after defoliation than in undefoliated control trees (12.9 μmol m(-2) s(-1)). This response was consistently observed for up to 11 weeks after the defoliation event; by Week 16, there was no difference in A(max) between control and defoliated trees. In the D50 treatment, this increased A(max) was not sufficient to fully compensate for the foliage loss as evidenced by the reduced diameter increment (by 15%) in defoliated trees 36 weeks after defoliation. In contrast, diameter increment of trees in the D25 treatment was unaffected by defoliation. The A(max) of trees experiencing upper-crown defoliation by natural and repeated E. californica infestations varied, depending on host genotype. Despite clear differences in defoliation levels between resistant and susceptible genotypes (17 vs. 35% of tree crown defoliated, respectively), growth of susceptible genotypes was not significantly different from that of resistant genotypes. The observed increases in A(max) in the lower crown of the canopy following attack suggested that susceptible genotypes were able to partly compensate for the loss of foliage by compensatory photosynthesis. The capacity of P. radiata to regulate photosynthesis in response to natural aphid-induced defoliation provides evidence that the impact of E. californica attack on stem growth will be less than expected, at least for up to 35% defoliation.     

Growth and mineral nutrition of Gmelina arborea Roxb. seedlings fertilized with four sources of nitrogen on a latosolic soil

The growth and mineral nutrition of Gmelina arborea Roxb. seedlings were investigated in response to four nitrogen-based fertilizers applied at 0, 2.5, 5.0 or 7.5 g N per plant. Nitrogen sources included NH(4)-N as ammonium sulfate, NO(3)-N as potassium nitrate, NH(4)NO(3)-N as calcium ammonium nitrate, and urea-N as urea. Seedlings fertilized with NH(4)NO(3)-N or urea-N had greater height, collar diameter, dry weight, net assimilation rate, and relative growth rate than seedlings fertilized with NH(4)-N or NO(3)-N. For all sources of nitrogen, increasing the amount of exogenously supplied N per plant promoted shoot growth more than root development, hence the root to shoot ratios of all fertilized seedlings were smaller than those of the unfertilized controls. Applications of NO(3)-N increased the nitrogen, potassium, and phosphorus concentrations of fertilized seedlings. Regardless of source, a nitrogen application of 2.5 g N per plant was apparently optimal for the growth of Gmelina seedlings on a latosolic soil.     

Effects of elevated nitrate and aluminum on the growth and nutrition of red spruce (Picea rubens) seedlings

Acidic deposition in high-elevation forests in the Appalachian Mountains of the eastern United States has been implicated in the decline of red spruce (Picea rubens Sarg.). Elevated soil acidity may increase soil Al availability and toxicity to roots. Enhanced soil solution NO(3) (-) concentrations, resulting from precipitation inputs and enhanced soil organic matter mineralization, may exacerbate Al toxicity by increasing root Al uptake. We exposed red spruce seedlings to 350, 500, 800 or 1400 micro M NO(3) (-) and 0 or 200 micro M Al in a factorial design in sand-nutrient solution culture to test if increased NO(3) (-) concentrations enhance Al uptake and toxicity. In addition to significant reductions in seedling growth parameters resulting from Al exposure, we found significant interactions between NO(3) (-) and Al for seedling height growth rate, needle weight, shoot weight and root weight. Differences in these parameters between Al treatments became more pronounced as solution NO(3) (-) concentration increased and reflected an Al-mediated inhibition of seedling response to increasing NO(3) (-) concentration. Solution NO(3) (-) concentrations above 500 micro M induced root nitrate reductase (NR) activity, whereas shoot NR activity increased in response to NO(3) (-) up to 500 micro M and declined above that concentration. In contrast, exposure to Al depressed NR activity of roots but tended to stimulate needle NR activity. Foliar N concentrations increased in seedlings grown in cultures containing between 350 and 500 micro M NO(3) (-), with no change above 500 micro M. Increasing concentrations of NO(3) (-) depressed foliar P concentrations, with reductions being greatest in seedlings exposed to 1400 micro M NO(3) (-). Exposure to Al increased foliar Ca, K and Al concentrations, decreased foliar P concentrations, and inhibited increases in foliar Mg concentration in response to increasing NO(3) (-). The consistent interactions between NO(3) (-) and Al for growth, root NR activity and foliar Mg concentration were the result of an inhibition of seedling response to NO(3) (-) mediated by Al in solution, rather than enhanced Al toxicity resulting from growth in the presence of elevated NO(3) (-) concentrations.     

Partial shoot removal increases net CO(2) assimilation and alters water relations of Citrus seedlings

Effects of defoliation on partial shoot removal by decapitation on seedling growth, water use and net gas exchange of remaining basal leaves, were examined in Citrus spp. Shoot and root growth rates were manipulated to test for effects of growth demands on net gas exchange. Partially defoliated plants had higher leaf pressure potentials, root conductivities and rates of water use than intact control plants. Shoot regrowth occurred at the expense of root loss. Basal leaves on defoliated plants consistently had higher rates of CO(2) assimilation (A) than leaves on intact plants. Stomatal conductance (g(s)) changed little after defoliation so the higher A of leaves on defoliated plants lowered the ratio of intercellular to ambient CO(2) concentration (C(i)/C(a)) in the mesophyll. In some cases, g(s) increased with A in defoliated plants but C(i)/C(a) was not affected. Stomatal conductance only limited A when intact seedlings were stressed by root confinement in small pots or when leaves were exposed to high vapor pressure deficits during gas exchange measurements. Increased carbon demand for shoot regrowth increased photosynthetic capacity and was more important than stomatal responses in determining A after partial shoot loss.     

Detection of dead or defoliated spruces using digital aerial data

The purpose of this study was to develop a method for detecting dead and defoliated spruces and defoliated stands in remote-sensing material using a semi-automatic pattern-recognition technique, spectral properties of trees, and different degrees of defoliation. The study material included two mapped defoliation stands in the municipality of Juupajoki (61°50′N, 24°18′E) in southern Finland. The ground truth data were collected during 1996–1997. The aerial color infrared (CIR) photographs, scaled to 1:5000, were taken on 28 June 1995 and on 19 June 1997. The degree of defoliation was visually estimated for every conifer in the defoliation stands. Individual trees in the digital aerial photographs were segmented using a robust segmentation method based on the recognition of tree crown patterns at a sub-pixel accuracy. The images were filtered with a Gaussian N×N smoothing operator, and local maxima above a threshold level were segmented using a directional derivate with some constraints. The segments were placed into defoliation classes using linear Fisher classification models, the parameters of which were estimated by cross-validation. Discriminant analysis was used to find variables for the segment classification. Defoliated tree segments and stands were classified satisfactorily. The accuracy of the pattern-recognition method proved adequate for detecting dead or heavily defoliated trees and heavily defoliated stands. The method described provides an interesting approach to using digital aerial data for automatically detecting severely defoliated spruce stands or individual trees.     

Interactive effects of water supply and defoliation on photosynthesis, plant water status and growth of Eucalyptus globulus Labill

Increased climatic variability, including extended periods of drought stress, may compromise on the health of forest ecosystems. The effects of defoliating pests on plantations may also impact on forest productivity. Interactions between climate signals and pest activity are poorly understood. In this study, we examined the combined effects of reduced water availability and defoliation on maximum photosynthetic rate (A(sat)), stomatal conductance (g(s)), plant water status and growth of Eucalyptus globulus Labill. Field-grown plants were subjected to two water-availability regimes, rain-fed (W-) and irrigated (W+). In the summer of the second year of growth, leaves from 75% of crown length removed from trees in both watering treatments and physiological responses within the canopies were examined. We hypothesized that defoliation would result in improved plant water status providing a mechanistic insight into leaf- and canopy-scale gas-exchange responses. Defoliated trees in the W+ treatment exhibited higher A(sat) and g(s) compared with non-defoliated trees, but these responses were not observed in the W- treatment. In contrast, at the whole-plant scale, maximum rates of transpiration (E(max)) and canopy conductance (G(Cmax)) and soil-to-leaf hydraulic conductance (K(P)) increased in both treatments following defoliation. As a result, plant water status was unaffected by defoliation and trees in the defoliated treatments exhibited homeostasis in this respect. Whole-plant soil-to-leaf hydraulic conductance was strongly correlated with leaf scale g(s) and A(sat) following the defoliation, providing a mechanistic insight into compensatory up-regulation of photosynthesis. Above-ground height and diameter growth were unaffected by defoliation in both water availability treatments, suggesting that plants use a range of responses to compensate for the impacts of defoliation.