Visible Symptoms Of Damage Research Articles

Effects of mineral fertilization (NPK) on combined high temperature and ozone damage in rice

BackgroundIncreasing concern has recently been highlighted regarding crop damage due to extreme weather events caused by global warming and the increased production of ground-level ozone. Several studies have investigated rice growth in response to fertilization conditions under various environmental stress conditions; however, studies on growth development in response to fertilization conditions under combined high-temperature/ozone treatment conditions are scarce. In this study, we aimed investigate the growth and physiological development of rice under combined high temperature and ozone treatment conditions and to reveal the damage-mitigation effects of NPK fertilization treatments.ResultsThe plants were treated with varying levels of NPK [N2 (N-P-K: 9.0-4.5-4.0 kg/a), P2 (4.5-9.0-4.0 kg/a), K2 (4.5-4.5-8.0 kg/a), and control (4.5-4.5-4.0 kg/10a).] under combined high-temperature (35 ℃) and ozone (150 pb) treatment conditions. Analysis of the growth metrics, including plant height, leaf age, dry weight, and the plant height/leaf age (PH/L) ratio were revealed that combined high-temperature/ozone treatment promoted the phenological development indicated by increasing leaf age but decreased the plant height and dry weight indicating its negative effect on quantitative growth. The effects of this combined high-temperature/ozone treatment on growth were alleviated by NPK fertilization, particularly in K2 treatment but worsened in N2 treatment. Visible damage symptoms in rice leaves induced by exposure to the combined stressors was also alleviated by the K2 treatment. At the physiological level, K2 treatment reduced the expression of OsF3H2, which is associated with antioxidant activity, suggesting that potassium improved stress tolerance. Additionally, expression of genes related to abscisic acid (ABA) metabolism showed increased OsNECD (ABA synthesis) and decreased OsCYP707A3 (ABA degradation) in the K2 treatment, promoting a stronger adaptive stress response. Stomatal conductance measurements indicated a slight increase under K2 treatment, reflecting enhanced regulation of stomatal function during stress.ConclusionThe study highlights the potential of potassium fertilization to mitigate combined high-temperature and ozone stress in rice, suggesting it as a strategy to improve crop resilience and optimize fertilization. The findings offer insights into fertilization treatments and can guide future research on stress tolerance in crops.

Black germ of wheat in the conditions of the Krasnoyarsk forest-steppe

Black germ is a ubiquitous disease of wheat, which, without particularly affecting crop yields, can affect the parameters of the technological evaluation of grain. Until now, there is no consensus on the nature of the occurrence of this disease. In our study, we studied the relationship between the visible symptoms of damage by a black germ and infection of seeds of spring soft wheat samples with fungi of the genera Alternaria and Biporalis in the conditions of the Krasnoyarsk forest-steppe. The phytopathological analysis of asymptomatic and black-embryonic grains revealed in the latter a significant excess of infestation with p. Alternaria fungi in two out of ten samples. There were no differences in seed infection with p. Biporalis micromycetes between the variants. Only in one sample, the germination of seeds with manifested symptoms of the disease was lower than in visually healthy ones. The percentage of germination of other varieties and lines in both variants did not differ statistically significantly.

Performance of RR soybean submitted to postemergence application of glyphosate with a foliar elicitor product

ABSTRACT With the advent of glyphosate-resistant soybean, postemergence applications of the herbicide have become routine. In this way, problems related to the selectivity of glyphosate have been shown to be increasingly intense, due to the use of increased dosages and applications of the herbicide at unrecommended moments. In order to evaluate the agronomic performance of soybean plants subjected to the postemergence application of glyphosate – both in isolation and together with Crop+ – at different stages and dosage levels, a randomized block design experiment was carried out with two adjacent checks and four repetitions. The treatments consisted of: glyphosate (1296 g·ha-1); glyphosate + Crop+ (1296 + 0.25 g or L·ha-1); glyphosate + Crop+ (1296 + 0.5 g or L·ha-1); glyphosate (2592 g·ha-1); glyphosate + Crop+ (2592 + 0.25 g or L·ha-1); glyphosate + Crop+ (2592 + 0.5 g or L·ha-1); 2 × glyphosate (2 × 1296 g·ha-1); 2 × glyphosate + Crop+ (2 × 1296 + 0.25 g or L·ha-1); 2 × glyphosate + Crop+ (2 × 1296 + 0.5 g or L·ha-1) and Crop+ (0.5 g·ha-1). The phytotoxicity, soil plant analysis development (SPAD) index, height, stand, mass of 100 grains, and yield of the soybean plants were evaluated. The use of Crop+ on soybean plants led to an increase in the SPAD index; the use of Crop+ in association with glyphosate made possible the attenuation of visible symptoms of damage, preventing reductions in crop yield.

Two New Species of the GenusLeipothrixKeifer, 1966 (Acari: Eriophyidae: Phyllocoptinae) From China

Two new species of the genus Leipothrix Keifer, 1966 from China are described and illustrated. These species are Leipothrix pilosae sp. nov. , from Bidens pilosa L. (Compositae), and Leipothrix sarcandrae sp. nov. , from Sarcandra glabra (Thunb.) Nakai (Chloranthaceae). Both the new species described herein were found to be vagrant on their host plants without visible damage symptoms observed.

Losses of leaf area owing to herbivory and early senescence in three tree species along a winter temperature gradient.

In temperate climates, evergreen leaves have to survive throughout low temperature winter periods. Freezing and chilling injuries can lead to accelerated senescence of part of the leaf surface, which contributes to a reduction of the lifespan of the photosynthetic machinery and of leaf lifetime carbon gain. Low temperatures are also associated with changes in foliar chemistry and morphology that affect consumption by herbivores. Therefore, the severity of foliar area losses caused by accelerated senescence and herbivory can change along winter temperature gradients. The aim of this study is to analyse such responses in the leaves of three evergreen species (Quercus ilex, Q. suber and Pinus pinaster) along a climatic gradient. The leaves of all three species presented increased leaf mass per area (LMA) and higher concentrations of structural carbohydrates in cooler areas. Only the two oak species showed visible symptoms of damage caused by herbivory, this being less intense at the coldest sites. The leaves of all three species presented chlorotic and necrotic spots that increased in size with leaf age. The foliar surface affected by chlorosis and necrosis was larger at the sites with the coldest winters. Therefore, the effects of the winter cold on the lifespan of the photosynthetic machinery were contradictory: losses of leaf area due to accelerated senescence increased, but there was a decrease in losses caused by herbivory. The final consequences for carbon assimilation strongly depend on the exact timing of the appearance of the damage resulting from low temperature and grazing by herbivores.

Effect of imazapyr treated maize on Striga infestation and time of intercropping cowpea in Samaru, Nigeria

Two field experiments were conducted at the research farm of Institute for Agricultural Research (IAR) Samaru, Zaria during the 2011 cropping season, with the aim of determining the effect of imazapyr treated maize on Striga infestation and time of intercropping cowpea in Samaru, northern guinea savannah of Nigeria. There were two sets of experiments: the first experiment consisted of Six (6) hybrids (AS1128-1, AS1128-2, AS1128-3, AS1128-4, AS1128-6 and AS1128-8) of imazapyr resistant (IR) maize seeds treated with imazapyr chemical and intercropped with cowpea at 2, 4 and 6 weeks after sowing (WAS) of maize. The second experiment consisted of the same Six (6) hybrids of IR maize seeds but untreated and also intercropped with cowpea at 2, 4 and 6 WAS of maize. The experiments were laid out in a split plot design with time of intercropping cowpea as main plot and hybrid maize varieties as sub plot, and replicated three times. The cowpea variety used for the trial was IT97K-499-35. Among the treated IR-maize hybrids, only AS1128-1, AS1128-2, AS1128-3 and AS1128-4 germinated while for the untreated, all the six hybrids germinated. The grain yields per hectare of all the treated maize hybrids did not significantly differed whereas grain yields per hectare of the untreated maize hybrids AS1128-1, AS1128-2, AS1128-3 and AS1128-4 were significantly higher than the hybrid AS1128-8. The treated IR maize hybrids exerted 100% control of Striga while the untreated supported Striga emergence. There was no visible damage symptoms observed on the cowpea intercropped with treated maize at all times of intercropping. It is therefore concluded that the IR-maize hybrids ASII28-1, ASII28-2, ASII28-3 and ASII28-4 should be used in the treated forms for the control of Striga. Moreover, the intercropping of cowpea with imazapyr treated maize can be carried out starting from 2 WAS of maize.Key words: Intercropping, imazapyr resistant maize (IR-maize), cowpea, Striga.

Tolerance of <i>Urochloa brizantha</i> cv. MG5 to Mn Toxicity

Available information of the effects of manganese nutrition on the forage genus Urochloa is scarce. In the context, this study aims to evaluate the tolerance of Urochloa brizantha cv. MG5 to Mn toxicity. The experiment was conducted in a greenhouse at the University of the State of Sao Paulo (UNESP) in the city of Jaboticabal, SP. Plants were cultivated in vases (3.5 L) filled with soil according to a completely randomized experimental design comprising of five levels of Mn (0, 15, 30, 60 and 120 mg?dm?3) and four replications and cut in two periods: one is 42 days after sowing and the other is 30 days after the first one. Samples from both cuts were evaluated as to plant height, number of leaves and tillers, dry weight, Mn content and accumulation, and the green index was determined in the last cut. Manganese addition to soil caused an increase in chlorophyll content at the dosage of 68 mg?dm?3 observed in the second plant cut. Dosages of Mn above 15 mg?dm?3 did not induce increases in nutrient accumulation and in the number of leaves in the first and second cuts of the grass, and tillers in the first cut. The highest concentrations of manganese in the shoots did not produce visual symptoms of damage or a decrease in forage productivity demonstrating that Urochloa brizantha cv. MG5 has high tolerance to manganese toxicity.

A new eriophyoid mite genus and species, Gymnaceria cupuassu (Acari: Eriophyidae), described from the cupuaçu tree in Brazil

A new eriophyoid mite genus and species, Gymnaceria cupuassu n. sp. et n. gen. (Acari: Eriophyidae: Eriophyinae: Ace-riini), is described from young fruits and other plant parts of the cupuaçu tree, Theobroma grandiflorum (Willd. Ex Spreng.) K. Schum. (Sterculiaceae), from the State of Bahia, northeastern Brazil. No visible damage symptoms were observed.

Antioxidant and photosynthetic response of a purple-leaved and a green-leaved cultivar of sweet basil (Ocimum basilicum) to boron excess

Boron (B) toxicity induces oxidative stress and alterations in the photosynthetic process. The occurrence of visible symptoms depends on plant species and even on cultivar. However, limited information is available concerning antioxidant responses to B toxicity; therefore a study was carried out to assess the role of antioxidants in hydroponically grown sweet basil submitted to B excess. Two cultivars were compared: the purple-leaved ‘Red Rubin’ that shown scarce symptoms of B-induced toxicity and the green-leaved ‘Tigullio’ in which they were evident.Sweet basil plants were grown in “floating raft system” for 20 days with 0.2 (control), 2 and 20mgL−1 of B in the nutrient solution. At the end of treatments visible symptoms of damage were evaluated and some parameters were measured: growth, leaf B accumulation, gas exchange and chlorophyll fluorescence, pigment, phenols and malondialdehyde (MDA) concentrations, total non-enzymatic antioxidant ability, antioxidant molecules and enzymes.B excess negatively affected growth and photosynthesis in both cultivars but differential mechanisms were recorded. ‘Tigullio’ exhibited a larger B accumulation in leaves as compared to ‘Red Rubin’. Moreover, in ‘Red Rubin’ plants a greater constitutive content of ascorbic acid, glutathione, anthocyanins and, consequently, a stronger antioxidant ability than ‘Tigullio’ were recorded. MDA test confirmed that the extent of oxidative stress was larger in ‘Tigullio’ than in ‘Red Rubin’. A general stimulation of antioxidant enzymes occurred by increasing B concentration in the growth medium. Notable, anthocyanins were likely involved in the B tolerance shown by ‘Red Rubin’ in consideration of their antioxidant properties and because of the role of these compounds in photoprotection. This paper represents a contribution to understanding the role of antioxidant compounds in plant tolerance to B toxicity.

Potential of Native Plant Species From the Industrial Complex of Camaçari (BA, Brazil) as Accumulators of Chemical Elements Contained in Air Pollution

The present study aimed to assess the potential of plant species Anacardium occidentale L., Miconia albicans (Sw.) Triana and Byrsonima sericea DC. as bioaccumulators of aluminum (Al), arsenic (As), copper (Cu), nickel (Ni), zinc (Zn) and sulphur (S), coming from industrial emission from the Industrial Complex of Camaçari (ICC). Element concentrations were measured in the leaves of three adult individuals per species. The data showed that M. albicans is an accumulator species of Al, Cu and S. Moreover, this specie showed visible damage symptoms on the leaves such as chloroses and necroses, which may be attributed to air pollution. On the other hand, the accumulation of the elements was lower in the leaves of A. occidentale and B. sericea. In general, Zn concentrations were similar in all species. As and Ni concentrations in the species were below detection limit. The results indicate that M. albicans may potentially be employed in biomonitoring studies in this region.

New eriophyoid mites (Acari: Prostigmata: Eriophyoidea) from banana and heliconia in Northeastern Brazil—two new genera and three new species

A new genus and new species of the mite family Eriophyidae (Phyllocoptinae), namely Cothrix erugata n. sp. et n. gen., is described from Heliconia stricta Huber (Heliconiaceae). In addition, one new genus and two new species of Diptilomiopidae, namely Rhyncadicrus asperulus n. sp. et n. gen. from banana, Musa acuminata Colla x Musa balbisiana Colla (genomic group AAB) (Musaceae) and Catarhinus granatus n. sp. from Heliconia bihai L., are described and illustrated. The mites were collected in the State of Pernambuco, Northeastern Brazil. All were vagrants on the lower leaf surfaces of their host plants and no visible damage symptoms were observed.

Screening USDA-ARS Wheat Germplasm for Bird Cherry-Oat Aphid Tolerance

The bird cherry-oat aphid (Rhopalosiphum padi L.) can cause significant yield reduction in wheat (Triticum aestivum L.) without causing aboveground visual damage symptoms. This lack of obvious aboveground symptom development makes it difficult to use standard aphid tolerance testing protocols, which are very effective in testing wheat for tolerance to other aphids. This study utilized an alternative screening method, using clear germination pouches, to assess the effects on both root and shoot development following aphid feeding as a way to deduce aphid feeding tolerance. Over 4,000 wheat accessions from the USDA-ARS National Small Grains Collection were evaluated. Qualitative ratings were determined by comparing wheat accession infested with bird cherry-oat aphids against the control (noninfested treatment). Following the infestation treatment, 17 accessions showed no dramatic decreases in root and shoot growth. Accessions identified are of considerable interest to those wheat breeding programs where bird cherry-oat aphid tolerance is an objective.

Determination of the rate of 18F-labeled water movement to the leaf and its association with water relations in acid soil-tolerant rice varieties

The visual symptoms of damage by acid sulfate soil look quite similar to those due to soil moisture deficit. The present paper is to confirm if acid soil-tolerance is associated with drought tolerance in terms of leaf water potential, transpiration, and dry matter production. Seedlings of seven acid soil-tolerant (acid-tolerant), and three acid soil-intolerant varieties (acid-intolerant) were subjected to low pH conditions (pH 3.8) for 48 hours. The rate of water uptake was determined continuously by measuring radioactivity in the collar part (target area) of rice leaves exposed to 18F-labeled water (18F-water) using a Positron Emitting Tracer Imaging System (PETIS). The PETIS measurement showed that the radioactivity in the target position of leaves of acid-tolerant varieties increased faster than that of the intolerant varieties after the 18F-water was applied into the vial. In the plants subjected to low pH conditions, the transpiration rate (Tr) and leaf water potential (Ψ) decreased in both acid-tolerant and intolerant varieties. However, the extent of reduction was less in the acid-tolerant varieties than in the intolerant ones. Moreover, the dry matter production rate of the acid-tolerant varieties was significantly higher than that of the acid-intolerant ones in the low pH conditions. This study clearly shows that 18F-water uptake in a leaf was higher, and water relations were also better maintained in the acid-tolerant varieties compared with intolerant ones, resulting in higher growth rate in the acid-tolerant varieties, when plants were exposed to the acid solution conditions. We conclude that acid soil-tolerance is closely associated with leaf water relations in rice plants.

Physiological responses of wheat and barley to Russian wheat aphid, Diuraphis noxia (Mordvilko) and bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae)

Although aphids are among the most injurious of all agronomic insect pests, much remains unknown about how their feeding alters plant physiology. Two experiments were conducted to examine the physiological responses of wheat, Triticum aestivum L. and barley, Hordeum vulgare L. to injury by Diuraphis noxia (Mordvilko) and Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Gas-exchange parameters, chlorophyll fluorescence, and chlorophyll content were examined at 3, 6, and 9 days post-infestation on control and aphid (D. noxia and R. padi) infested treatments. In general, chlorophyll content and chlorophyll fluorescence parameters (non-variable minimal fluorescence, maximal fluorescence, and variable fluorescence) were not significantly affected by either aphid species. Photochemical and non-photochemical quenching coefficients were significantly impacted by both aphid species, suggesting that aphid feeding may influence the photoprotective xanthophyll cycle altering the thylakoid membrane pH gradient. Feeding by both aphid species resulted in an increase in electron transport rate, but at different time periods. Wheat plants infested with D. noxia had accelerated declines in photosynthetic capacity when compared to R. padi-infested and control plants. These plants exhibited decreased values for Amax, which was accompanied by decreased values for Vcmax and Jmax Neither aphid species negatively affected the photosynthetic capacity of the barley plants until day 9. At this time, aphid-infested plants had decreased values for Amax which was accompanied by decreased values in Jmax. Although R. padi feeding does not typically result in visual damage symptoms as previously demonstrated, clearly this aphid does have an impact on the gas-exchange and chlorophyll fluorescence of its host plants.

Ozone effects on high light-induced photoinhibition in Phaseolus vulgaris

In this study the response to photoinhibition of photosynthesis and subsequent recovery was examined in plants of Phaseolus vulgaris L. cultivar ‘Pinto’ exposed to charcoal-filtered air or to ozone (O 3) at 150 nL L −1 either for 3 h, or for 5 h. The responses were analysed using chlorophyll fluorescence imaging and by conventional fluorometry. Compared to control plants maintained in charcoal-filtered air, in plants exposed for 3 h to O 3 and then subjected to high light treatment, the results show an increased tolerance to photoinhibition. Plants exposed to the same O 3 concentration but for the longer 5-h period, were not tolerant to the photoinhibition treatment and, instead showed visible symptoms of damage (chlorosis and necrosis) clearly attributable to the longer O 3 exposure. Here the detrimental effects of O 3 aggravated the effects of the high light photoinhibitory treatment. The leaves exposed to the shorter O 3 treatment (150 nL L −1 for 3 h) developed an ability to counteract the negative effects of a high light exposure probably because the O 3 had activated an antioxidant system able to protect the photosynthetic machinery.

β-1,3-Glucanase gene expression as a molecular marker for postharvest physiological disorders in citrus fruit and its hormonal regulation

The aim of this work was to understand whether a CrglcQ gene, encoding an acidic class III β-1,3-glucanase isolated from citrus flavedo, may serve as a biochemical marker for the development of postharvest physiological disorders; and whether this gene is regulated by ethylene and abscisic acid (ABA). We have examined the changes in the accumulation of the CrGlcQ mRNA in the flavedo of ‘Navelate’ oranges, a variety prone to develop brown non-depressed areas in response to chilling, and in the flavedo of its ABA-deficient mutant ‘Pinalate’, a variety tolerant to chilling but very susceptible to non-chilling peel pitting, during fruit storage at chilling (2 °C) and non-chilling temperatures (12 °C). The levels of the CrGlcQ transcript increased transiently in fruit exposed to postharvest conditions favoring both chilling and non-chilling peel disorders, such an increase being evident even in the fruit of the ABA-deficient mutant ‘Pinalate’ in which ABA does not increase in response to stress conditions. Such increases paralleled those in ethylene production and preceded the appearance of visible symptoms of damage. Moreover, we examined changes in gene expression in ‘Fortune’ mandarins held under water stress conditions (20 °C and 55–60% RH) that did not cause any peel damage, and found that the increase in ABA was not mirrored by the changes in CrglcQ mRNA accumulation. The results revealed that changes in CrglcQ gene expression are linked to the development of postharvest peel disorder, in spite of being induced by different environmental conditions, and indicated that this gene might be regulated by ethylene but not by the ABA.

Copper toxicity and bioaccumulation in Chinese cabbage (Brassica pekinensis Rupr.)

Copper is among the major heavy metal contaminants in the environment with various anthropogenic and natural sources. Human health risk from heavy metal bioaccumulation in vegetables has been a subject of growing concern in recent years. To investigate Cu phytotoxic effects and bioaccumulation in the popular vegetable Chinese cabbage (Brassica pekinensis Rupr) as well as the implications for human health due to Cu in the vegetable supply, seed germination and pot culture experiments with this vegetable were carried out. Six levels (0, 0.008, 0.031, 0.125, 0.5, and 2.0 mM/L) and 3 levels (0, 0.2, and 1.0 mM/kg) of Cu treatments were performed for the seed germination and pot culture experiments, respectively. The LC(50) of Cu for seed germination of Chinese cabbage was 0.348 mM/L. In the pot culture experiments, Cu treatments significantly increased electrolyte leakage and peroxidase activity of shoot tissues, demonstrating Cu phytotoxicity to the plants. On the other hand, Cu treatments significantly stimulated, instead of reduced, chlorophyll content. Cu treatments did not show a significant effect on shoot biomass. Compared to the control, Cu treatments significantly elevated the Cu content of the shoots-9.9, 42.5, and 119.0 mg/kg (DW) of Cu were detected in the 0, 0.2, and 1.0 mM/kg treatments, respectively. These results showed that although the plants accumulated an elevated copper content and suffered damage to some extent under Cu treatment, they looked healthy. It was suggested that Chinese cabbage with an elevated Cu content and without showing visible symptoms of damage possibly could cause a risk to human health from the transfer of the metal in food.

Recovery of Norway spruce (Picea abies) seedlings from repeated drought as affected by boron nutrition

The effects of two boron (B) levels on growth, shoot water potential, gas exchange and nutrient accumulation in Norway spruce [Picea abies (L.) Karst.] seedlings were studied in a growth room experiment lasting 22 weeks which included well-watered control seedlings and seedlings exposed to one (8 days) or two (6+8 days) periods of drought and a rewatering period (8 days) at the end of the experiment. The effects of B and drought were monitored during drought and recovery. Needle B concentrations were 6 mg kg−1 (−B treatment) and 34 mg kg−1 (+B treatment) at the end of the experiment. The −B seedlings showed visible symptoms of damage in the upper shoot after repeated drought and had reduced height growth, root dry mass, allocation of biomass to roots and formation of root tips and mycorrhizas and reduced needle P, Ca, and Mg concentrations and contents. In contrast, 15N uptake, shoot water potential and gas exchange were not markedly affected by B. It can be concluded that the visible symptoms of damage at low B were probably related to reduced B transport due to repeated drought. In contrast, the effects of low B on growth, particularly of the roots, and on nutrient uptake can be regarded as early effects which occur before any influence on shoot water potential or gas exchange. The positive effects of B on root biomass and nutrient accumulation are of particular importance regarding the establishment of young seedlings in the field.

Ecophysiological adaptations of black spruce ( Picea mariana ) and tamarack ( Larix laricina ) seedlings to flooding

Black spruce (Picea mariana (Mill.) B.S.P.) and tamarack (Larix laricina (Du Roi) K. Koch) are the predominant tree species in boreal peatlands. The effects of 34 days of flooding on morphological and physiolog- ical responses were investigated in the greenhouse for black spruce and tamarack seedlings in their second growing season (18 months old). Flooding resulted in reduced root hydraulic conductance, net assimilation rate and stomatal conductance and increased needle electro- lyte leakage in both species. Flooded tamarack seedlings maintained a higher net assimilation rate and stomatal conductance compared to flooded black spruce. Flooded tamarack seedlings were also able to maintain higher root hydraulic conductance compared to flooded black spruce seedlings at a comparable time period of flooding. Root respiration declined in both species under flooding. Sugar concentration increased in shoots while decreasing in roots in both species under flooding. Needles of flooded black spruce appeared necrotic and electrolyte leakage increased over time with flooding and remained signif- icantly higher than in flooded tamarack seedlings. No visible damage symptoms were observed in flooded tamarack seedlings. Flooded tamarack seedlings devel- oped adventitious roots beginning 16 days after the start of flooding treatment. Adventitious roots exhibited significantly higher root hydraulic conductivity than similarly sized flooded tamarack roots. Flooded black spruce lacked any such morphological adaptation. These results suggest that tamarack is better able to adjust both morphologically and physiologically to prolonged soil flooding than black spruce seedlings.

Recovery of Net Photosynthetic Rate after SO<sub>2</sub> Fumigation in Quercus acutissima, Pinus densiflora, Populus alba×glandulosa, and Acanthopanax sessiliflorus

After SO2 fumigation, Quercus acutissima and Pinus densiflora maintained high net photosynthetic rate (P N) and did not show visible symptoms of damage. In contrast, Populus alba×glandulosa and Acanthopanax sessiliflorus had significantly reduced P N and showed visible necrosis.