Differences In Net Photosynthesis Research Articles

Quality Green Tea (Camellia sinensis L.) Clones Marked through Novel Traits

Tea clones and seed varieties released from Tocklai Tea Research Institutes are suitable primarily for manufacturing black tea (CTC/orthodox) while green tea manufactured from these clones are poor in quality. This led to identifying germplasm suitable for manufacturing green tea of high quality. Physiological parameters on net photosynthesis, transpiration, stomatal conductance, water-use efficiency, leaf temperature, and carboxylation efficiency of six selected germplasm (DH 1 and 2, DH 3 and 4, DH 5 and 6, DL 13, DL 25, and DL 39) were measured in first flush, second flush, rain flush, and autumn flush. Seasonal Yield, biochemical (L-theanine to total polyphenol ratio), and taster’s score were compared among seasons. Two protocols were used for green tea manufacturing, i.e., roasting and steaming. Significant differences in net photosynthesis (pn), stomatal conductance (gs), carboxylation efficiency (ci/ca), and yield were observed between flushes. Among the six test clones, the L-theanine to total polyphenol ratio found was highest in DH 5 and 6 in the roasting method. Structural and cluster analysis revealed that the DH clones genotypically occupied the same position as that of the popular green tea clone Longjing 43 of China and Yabukita of Japan, indicating suitability of these germplasm to develop new green tea clones. Clones DH 5 and 6 are suitable for green tea manufacturing and they can be released to the industry as new green tea clones. As far as manufacturing protocol is concerned, the roasting method of tea manufacturing was found superior over steaming.

Changes induced by plastic film mulches on soil temperature and their relevance in growth and fruit yield of pickling cucumber

ABSTRACTPurpose: The aim of this study was to realize whether soil mulching, with different plastic mulch colors, is a suitable practice for the culture of pickling cucumber.Materials and Methods: The crop was cultured or not with black, silver/black, white/black, and aluminum/black plastic films, treatments were evaluated in randomized complete block design, to determine their effect on soil temperature, gas exchange, nutrient concentration, growth, and fruit yield.Results and Conclusions: Black, silver/black, and aluminum/black plastic mulches were higher (p ≤ 0.05) in plant height, leaf area, and shoot dry weight than bare soil at 15 days after sowing, whose results were similar than using white/black film. Maximum, minimum, and mean soil temperatures were higher with all plastic mulches except for aluminum/black, in which the maximum soil temperature was similar to the one in bare soil. There was no difference in net photosynthesis and there was very little difference in nutrient concentration between plants in plastic mulches and plants in bare soil; however, early and total yield showed a higher (p ≤ 0.05) yield in all plastic mulches, and lower with bare soil and white/black plastic mulch. Our results confirm that soil mulching impacts the pickling cucumber yield. We suggest a carefull selection of the color plastic mulch.

Drought stress ecophysiology of shrub and grass functional groups on opposing slope aspects of a temperate grassland valley

Plant functional groups with contrasting growth strategies co-occur in semiarid ecosystems. In the northern Great Plains, woody shrubs and grasses interact competitively, with shrubs prevalent on mesic hillslopes. To understand topographic influences on physiological drought acclimation, we measured seasonal photosynthetic water use in C3 shrubs ( Artemisia cana Pursh and Rhus trilobata Nutt.) and grasses ( Agropyron cristatum (L.) Gaertn. and Stipa viridula Trin.) on north- and south-facing slopes. Relationships between abiotic controls and photosynthesis were similar on both aspects, indicating an absence of long-term photosynthetic acclimation to xeric, south-facing conditions. Acclimatory differences were observed between functional groups. Soil moisture depletion lowered intercellular:atmospheric CO2 ratio (Ci/Ca) and increased intrinsic water-use efficiency (WUEi = Amax/gs) in shrubs, but not grasses. Consequently, between-slope differences in net photosynthesis (Amax) and stomatal conductance (gs) occurred only in shrubs, with lower values on the south-facing slope. Shrubs also exhibited between-slope differences in the photochemical reflectance index, suggesting drought-related photoprotection. The deuterium:hydrogen ratios of stem water showed that deep water use facilitated late summer growth in shrubs. Consistent with plant distribution, cumulative water use and photosynthesis were higher in shrubs than in grasses on the north-facing slope, but higher in grasses than in shrubs on the south-facing slope. This shows that topographic effects on leaf photosynthetic gas exchange are mediated by physiological acclimation strategy and water source use.

Interactive responses of Quercus suber L. seedlings to light and mild water stress: effects on morphology and gas exchange traits

• The combined effect of water stress and light on seedlings of forest species is a key factor to determine the best silvicultural and afforestation practices in the Mediterranean area. • The aims of this work was (1) to determine the optimal light level for the early development of cork oak seedlings under mild water stress and (2) to test if the combined effect of water stress and light followed the trade-off, the facilitation or the orthogonal hypothesis. • Shade reduced instantaneous photosynthetic rates and water use efficiency in cork oak. However, seedlings grown under moderate shade (15% of full sunlight) were capable to accumulate similar amount of biomass than those grown under more illuminated environments by increasing their specific leaf area. Absolute differences in net photosynthesis between light treatments were higher in well watered than in water stressed seedlings. However, the impact of both factors on overall growth was orthogonal. • We concluded that cork oak development is impaired under deep shade (5% of full sunlight) but it can be optimal under moderate shade (15% of full sunlight) even under moderate water stress. Implications of these patterns on regeneration, cultivation and afforestation of cork oak are discussed.

Tobacco aquaporin NtAQP1 is involved in mesophyll conductance to CO2in vivo

Leaf mesophyll conductance to CO(2) (g(m)) has been recognized to be finite and variable, rapidly adapting to environmental conditions. The physiological basis for fast changes in g(m) is poorly understood, but current reports suggest the involvement of protein-facilitated CO(2) diffusion across cell membranes. A good candidate for this could be the Nicotiana tabacum L. aquaporin NtAQP1, which was shown to increase membrane permeability to CO(2) in Xenopus oocytes. The objective of the present work was to evaluate its effect on the in vivo mesophyll conductance to CO(2), using plants either deficient in or overexpressing NtAQP1. Antisense plants deficient in NtAQP1 (AS) and NtAQP1 overexpressing tobacco plants (O) were compared with their respective wild-type (WT) genotypes (CAS and CO). Plants grown under optimum conditions showed different photosynthetic rates at saturating light, with a decrease of 13% in AS and an increase of 20% in O, compared with their respective controls. CO(2) response curves of photosynthesis also showed significant differences among genotypes. However, in vitro analysis demonstrated that these differences could not be attributed to alterations in Rubisco activity or ribulose-1,5-bisphosphate content. Analyses of chlorophyll fluorescence and on-line (13)C discrimination indicated that the observed differences in net photosynthesis (A(N)) among genotypes were due to different leaf mesophyll conductances to CO(2), which was estimated to be 30% lower in AS and 20% higher in O compared with their respective WT. These results provide evidence for the in vivo involvement of aquaporin NtAQP1 in mesophyll conductance to CO(2).

Carbon sink limitation and frost tolerance control performance of the tree Kageneckia angustifolia D. Don (Rosaceae) at the treeline in central Chile

The decrease in temperature with increasing elevation may determine the altitudinal tree distribution in different ways: affecting survival through freezing temperatures, by a negative carbon balance produced by lower photosynthetic rates, or by limiting growth activity. Here we assessed the relative importance of these direct and indirect effects of altitudinal decrease in temperature in determining the treeline in central Chile (33°S) dominated by Kageneckia angustifolia. We selected two altitudes (2000 and 2200 m a.s.l.) along the treeline ecotone. At each elevation, leaf non-structural carbohydrates (NSC) and gas exchange parameters were measured on five individuals during the growing season. We also determined the cold resistance of K.␣angustifolia, by measuring temperatures that cause 50% seedling mortality (LT50) and ice nucleation (IN). No differences in net photosynthesis were found between altitudes. Although no differences were detected on NSC concentration on a dry matter basis between 2000 and 2200 m, when NSC concentration was expressed on a leaf area basis, higher contents were found at the higher elevation. Thus, carbon sink limitations may occur at the K. angustifolia’s upper altitudinal limit. For seedlings derived from seeds collected at the 2200 m, LT50 of cold-acclimated and non-acclimated plants were −9.5 and −7 °C, respectively. However, temperatures as low as −10 °C can frequently occur at this altitude during the end of winter. Therefore, low temperature injury of seedlings seems also be involved in the treeline formation in this species. Hence, a confluence of global (carbon sink limitation) and regional (freezing tolerance) mechanisms explains the treeline formation in the Mediterranean-type climate zone of central Chile.

Heat Stress Responses of Four Herbaceous Ornamentals Differing in Heat Tolerance

The demand for new and/or improved herbaceous annuals and perennials continues to increase, making information on production and viability of these plants a necessity. In Louisiana and the Southern U.S., one of the greatest impediments to production of marketable herbaceous plants and their longevity is high temperature. Herbaceous plants have various stages of vegetative growth and flowering; high temperatures during these developmental stages can have a tremendous impact on plant metabolism, and thus plant growth and development. The goal of this research was to better understand the differences between heat tolerant (HT) and heat sensitive (HS) species and cultivars at various high temperatures in terms of whole plant growth, flowering, photosynthesis, carbohydrate content, electrolyte leakage, chlorophyll content and plant small heat shock proteins (HSP) expression levels. Salvia splendens Vista Series (HT), Sizzler series (HS); Viola witrokiana `Crystal Bowl Purple' (HT), `Majestic Giant Red Blotch' (HS), F1 Nature Series (HT) and F1 Iona Series (HS); Gaillardia × grandiflora `Goblin' (HT) and Coreopsis grandiflora `Early Sunrise' (HS) were grown from seed in growth chambers under 25/18 °C (day/night) cycles. Plants at 4, 6, and 8 weeks after germination were subjected to different high temperature treatments of 25 (control), 30, 35, 40, and 45 °C for 3 h. Results show that there was a significant difference in net photosynthesis, electrolyte leakage, soluble carbohydrate content and HSP levels between HT and HS cultivars. Effects of high temperature on plant growth, chlorophyll content, and number of days to flower, flower size, and marketable quality were also significantly different.

Effect of Flower Bud Removal on Carbon Dioxide Exchange Rates of Cotton

Numerous fruit removal studies have demonstrated that reproductive sink removal enhances cotton (Gossypium hirsutum L.) vegetative growth and development. Few studies, however, have examined changes in CO2 exchange rates accompanying fruit removal. The objective of this study was to establish the effect of early season flower bud removal on whole plant CO2 exchange rates of cotton. The effect of flower bud removal on the CO2 exchange rates of cotton was investigated in a 31-day study conducted in a controlled environment. Differences in net photosynthesis, dark respiration, daily carbon gain, and carbon use efficiency were not observed in this study with flower bud removal. However, the rate of increase (or decrease in dark respiration) for these parameters was greater with flower bud removal with their maxima occurring later in the study period. All selected photosynthetic parameters also increased steadily with time for both treatments.

Diurnal fluctuations of gas exchange and water potential in different stand structures of Pinus ponderosa

Leaf-level gas exchange and leaf water potential (Ψleaf) measurements were made over a diurnal time-course in multi-aged and even-aged stand structures of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) in central Oregon (June) and western Montana (July) to test for differences in physiological performance due to stand structure. Total site occupancy was similar between the geographic regions as measured by basal area, leaf area index, and stand density index. No differences in net photosynthesis (A net), stomatal conductance (g s), transpiration (E), instantaneous water use efficiency (WUE) or Ψleaf were observed in June in Oregon. As a whole, even-aged plots appeared to be more water-stressed than multi-aged plots that were able to maintain higher rates of E in July in Montana. There were no differences in WUE between multi-aged and even-aged stand structures in Montana, but because both A net and E tended to be less in even-aged trees, overall productivity and efficiency of foliage may be less than in multi-aged stand structures. It is concluded that under environmental conditions that are not limited by water, patterns in gas exchange and water use are unaffected by stand structure. The data from this study further suggest that water-limiting conditions found later in the growing season may influence diurnal gas exchange patterns in a way that could result in lower productivity in even-aged stand structures.

Effects of Spraying Ozonated Water on the Severity of Powdery Mildew Infection on Cucumber Leaves

Effects of spraying ozonated water on the severity of powdery mildew infection, visible disorder/injury occurrence, and net photosynthesis in cucumbers were investigated. The severity in the ozonated water treatment was contained to almost the same level throughout the 14-day period of the experiment, while the severity steadily increased in the non-treated control and distilled water treatment. Neither visible disorder/injury on the leaves nor a large difference in net photosynthesis between before and after spraying the ozonated water was observed. The results indicate that ozonated water can be at least a partial alternative to agricultural chemical fungicides for powdery mildew on cucumber leaves.

Relationship between intercepted radiation, net photosynthesis, respiration, and rate of stem volume growth of Pinus taeda and Pinus elliottii stands of different densities

Intercepted radiation, net photosynthesis, foliar respiration, stem respiration, and foliar nitrogen concentrations were measured to determine how changes in physiology that occur with increasing stand density affect the rate of stem volume growth. Intensively managed Pinus taeda L. (loblolly pine) and Pinus elliottii Engelm. (slash pine) stands in their third and fourth growing seasons planted at densities of 740, 2220, and 3700 trees ha −1 on the lower coastal plain of the southeastern United States were sampled. During the third growing season, stem volume growth was not proportional to stocking density with smaller increases in stem volume growth occurring as stand density is increased. The proportion of radiation intercepted by the canopies during the period of maximum leaf area was linearly related to the rate of stem volume growth. Stem respiration was greater for the trees planted at 740 trees ha −1 than for trees at the other densities on a stem surface area basis, but not on a stem volume basis. Foliar respiration and net photosynthesis were not different between the trees growing at different densities even though foliar nitrogen concentration decreased with increasing stocking density. One difference between the species was that the specific leaf area (m 2 kg −1 of leaf) of P. elliottii was significantly lower than P. taeda, with the result that area-based comparisons of foliar gas exchange were similar between P. taeda and P. elliottii, but on a mass basis, P. elliottii gas exchange was lower than P. taeda. For both species, specific leaf area increased with increasing stocking density. These results indicate that differences in net photosynthesis or respiration rates among stocking densities, or between species, were minimal and did not explain differences in stand growth rates. Instead, growth was well correlated with intercepted radiation and trees in the different density treatments appeared to modify their leaf morphology to improve canopy light interception.

Effects of mycorrhizal colonization and elevated atmospheric carbon dioxide on carbon fixation and below-ground carbon partitioning in Plantago lanceolata

Plantago lanceolata with or without the mycorrhizal fungus Glomus mosseae were grown over a 100 d period under ambient (380 ± 50 µmol mol-1) and elevated (600 ± 150 Émol mol-1) atmospheric CO2 conditions. To achieve similar growth, non-mycorrhizal plants received phosphorus in solution whereas mycorrhizal plants were supplied with bonemeal. Measures of plant growth, photosynthesis and carbon input to the soil were obtained. Elevated CO2 stimulated plant growth to the same extent in mycorrhizal and non-mycorrhizal plants, but had no effect on the partitioning of carbon between shoots and roots or on shoot tissue phosphorus concentration. Mycorrhizal colonization was low, but unaffected by CO2 treatment. Net photosynthesis was stimulated both by mycorrhizal colonization and elevated CO2, and there was a more than additive effect of the two treatments on net photosynthesis. Colonization by mycorrhizal fungi inhibited acclimation, in terms of net carbon assimilation, of plants to elevated CO2. 13C natural abundance techniques were used to measure carbon input into the soil, although the results were not conclusive. Direct measurements of below-ground root biomass showed that elevated CO2 did stimulate carbon flow below-ground and this was higher in mycorrhizal than non-mycorrhizal plants. For the four treatment combinations, the observed relative differences in amount of below-ground carbon were compared with those expected from the differences in net photosynthesis. A considerable amount of the extra carbon fixed both as a result of mycorrhizal colonization and growth in elevated CO2 did not reveal itself as increased plant biomass. As there was no evidence for a substantial increase in soil organic matter, most of this extra carbon must have been respired by the mycorrhizal fungus and the roots or by the the plants as dark-respiration. The need for detailed studies in this area is emphasized.

Effects of mycorrhizal colonization and elevated atmospheric carbon dioxide on carbon fixation and below-ground carbon partitioning in Plantago lanceolata

Plantago lanceolata with or without the mycorrhizal fungus Glomus mosseae were grown over a 100 d period under ambient (380±50 μmol mol -1 ) and elevated (600 ± 150 μmol mol -1 ) atmospheric CO 2 conditions. To achieve similar growth, non-mycorrhizal plants received phosphorus in solution whereas mycorrhizal plants were supplied with bonemeal. Measures of plant growth, photosynthesis and carbon input to the soil were obtained. Elevated CO 2 stimulated plant growth to the same extent in mycorrhizal and non-mycorrhizal plants, but had no effect on the partitioning of carbon between shoots and roots or on shoot tissue phosphorus concentration. Mycorrhizal colonization was low, but unaffected by CO 2 treatment. Net photosynthesis was stimulated both by mycorrhizal colonization and elevated CO 2 , and there was a more than additive effect of the two treatments on net photosynthesis. Colonization by mycorrhizal fungi inhibited acclimation, in terms of net carbon assimilation, of plants to elevated CO 2 . 13 C natural abundance techniques were used to measure carbon input into the soil, although the results were not conclusive. Direct measurements of below-ground root biomass showed that elevated CO 2 did stimulate carbon flow below-ground and this was higher in mycorrhizal than non-mycorrhizal plants. For the four treatment combinations, the observed relative differences in amount of below-ground carbon were compared with those expected from the differences in net photosynthesis. A considerable amount of the extra carbon fixed both as a result of mycorrhizal colonization and growth in elevated CO 2 did not reveal itself as increased plant biomass. As there was no evidence for a substantial increase in soil organic matter, most of this extra carbon must have been respired by the mycorrhizal fungus and the roots or by the the plants as dark-respiration. The need for detailed studies in this area is emphasized.

Photosynthesis and stomatal conductance of Juncus effusus in a temperate wetland ecosystem

Net photosynthesis and stomatal conductance of the emergent macrophyte Juncus effusus L. was measured in six plots in the Talladega Wetland Ecosystem (Hale County, AL) over diel and annual periods to evaluate the effects of water table fluctuations on photosynthesis and water losses. Half of the plots were in the areas where sediments remained saturated annually (stable water table) and the remaining plots were in the areas where water table heights fluctuated and sediments (upper 20 cm) did not remain continuously saturated. Annual patterns of average net photosynthesis were similar among all sample plots at the wetland ( p > 0.05; repeated measures ANOVA), which suggested that no differences in net photosynthesis resulted from the observed differences in sediment saturation. A marked seasonal pattern of net photosynthesis occurred with the greatest average photosynthesis during winter, summer (1997), and spring (11.0, 10.2, and 9.03 μmol CO 2 m −2 s −1, respectively) compared to autumn and summer (1996) (6.64 and 5.93 μmol CO 2 m −2 s −1, respectively). Average apparent photosynthetic efficiency of J. effusus was 1.43% and varied seasonally with the highest values in winter (1.86%) followed by spring (1.69%), autumn (1.34%), and summer (0.80 and 1.13%; 1996 and 1997, respectively). Although significant differences ( p < 0.05) in stomatal conductance occurred among sample plots within the wetland, no correlation was found between stomatal conductance and sample plot location or sediment saturation within the wetland. Seasonally, greater transpiration by J. effusus occurred during the summer (1996) and autumn months (0.43 and 0.28 mol H 2O m −2 s −1, respectively) compared to winter, spring, and summer (1997) (0.22, 0.20, and 0.16 mol H 2O m −2 s −1, respectively). Seasonal measurements of diel photosynthesis and stomatal conductance showed that daily net photosynthesis was variable among sample plots and among the seasons at the wetland, with maximum photosynthesis from 1000 to 1400 hours. Diel measurements of stomatal conductance showed significantly higher transpirative water loss during evening hours compared to high light periods.

Carbon balance of young birch trees grown in ambient and elevated atmospheric CO2 concentrations

AbstractWe constructed a carbon budget for young birch trees grown in ambient and elevated CO2 concentrations over their fourth year of growth. The annual total of net leaf photosynthesis was 110% more in elevated CO2 than in ambient CO2. However, the trees in elevated CO2 grew only 59% more biomass than the trees in ambient CO2 over the year. Modelling studies showed that larger loss of carbon from fine‐root production and growth of the root‐associated mycorrhiza by the trees in elevated CO2 probably accounted for all the remaining difference in net photosynthesis between the two treatments. Our modelling also showed that the fraction of net photosynthate consumed by respiration of nonleaf tissue was similar in the two CO2 treatments, and was 26% and 24% for trees in ambient and elevated CO2, respectively.Trees in elevated CO2 had 43% more leaves, and produced 110% more net photosynthate than trees in ambient CO2, even though the maximum rate of carboxylation per unit leaf nitrogen decreased by 21%. Sensitivity studies showed that down‐regulation reduced the annual net photosynthetic production of the trees in elevated CO2 by only 6%. Direct effects of higher CO2 on photosynthesis and greater leaf area of the trees in elevated CO2 increased the net photosynthesis of the trees by 68% and 60%, respectively; and together accounted for most of the difference in net photosynthesis between the two treatments.

Family variation in photosynthesis of 22-year-old black spruce: a test of two models of physiological response to water stress

Gas exchange and water potential were measured in 22-year-old black spruce (Piceamariana (Mill.) BSP) trees from four full-sib families on two sites (one drier and one wetter) at the Petawawa National Forestry Institute, Ontario. Based on an observed genotype × environment interaction and earlier work with seedlings, a hypothesis was formed that at high soil moisture availability, no genetic differences in net photosynthesis (Pn) would exist and as soil moisture decreases, genetic differences in Pn would increase. From results of initial research with mature trees we formed an alternative hypothesis that genetic differences in Pn are constantly maintained under an array of soil moisture conditions. The two models were rigorously tested over a range of soil moisture conditions using two physiological measurement crews who switched sites throughout the day. Second-year foliage Pn of mature black spruce was more affected by nonstomatal limitations than by stomatal limitations. Progeny of one female had 12.5% and 7.4% higher Pn than progeny of another female on the dry and wet site, respectively. Genetic variation in Pn was consistent over a range of soil water potential. Thus, the first hypothesis was rejected in favor of the alternative hypothesis. Genetic variation in Pn appeared to be due to differential response to vapor pressure deficit. Suggestions as to how to reconcile the observed genotype × environment interaction in growth with the genetic differences in Pn are discussed.

Gas Exchange Rates for Selected Red Maple Cultivars Grown in Alabama

Abstract The objective of this study was to develop a rapid screening technique to characterize selected red maple (Acer rubrum L.) cultivars based on their gas exchange capacities. Evaluations were conducted in Alabama under ambient conditions on an established, irrigated field trial. In preliminary evaluations 9 red maple cultivars (‘Autumn Flame’, ‘Fairview Flam’, ‘Franksred’, ‘Karpick’, ‘Northwood’, ‘October Glory’, ‘Redskin’, ‘Schlesingeri’, and ‘Tilford’) and 3 Freeman maple (Acer x freemanii E. Murray) selections (‘Autumn Blaze’, ‘Morgan’, and ‘Scarsen’) were observed for differences in net photosynthesis (Pn), transpiration (E), and stomatal conductance (Cs). Based on these results, 4 cultivars of A. rubrum were selected and evaluated intensively over 2 years. Throughout the study, growth rates for the 4 selections failed to correspond with gas exchange observations.

Design and testing of twig chambers for ozone fumigation and gas exchange measurements in mature trees

SynopsisA twig chamber system was developed for the exposure of mature trees to ozone (O3) under field conditions. The fumigation system allowed the exact control of O3 concentrations in the chambers, the measurement of O3 uptake as well as gas exchange measurements under ambient and controlled conditions during and after O3 fumigation. Because of differences in individual twigs the system should provide the exposure of replicates to different O3 treatments. Tests showed that temperature, humidity and O3 concentrations inside the chambers were comparable with diurnal courses observed in the field. Comparative gas exchange measurements indicated that there were no differences in net photosynthesis and conductance of twigs outside the chambers and twigs which remained within the chambers for 23 weeks receiving ambient air.

Comparative Flood Tolerance of Birch Rootstock

The potential for enhancing flood tolerance of birches by using better adapted rootstock was evaluated. Survival, growth, and physiological responses were compared among flooded and nonflooded container-grown Japanese birch (Betula platyphylla var. japonica Hara. `Whitespire') trees grafted onto each of four rootstock: paper birch (B. papyrifera Marsh), European birch (B.pendula Roth.), river birch (B. nigra L.), and `Whitespire' Japanese birch. Separate studies were conducted in Fall 1991 and Spring 1992. Results showed no consistent differences in net photosynthesis (Pn) or survival among nonflooded plants regardless of rootstock or season, nor, were any symptoms of graft incompatibility evident. Flooding the root system for as long as 44 days revealed considerable differences among the four rootstock, with similar trends for fall and spring. Plants on river birch rootstock typically had one of the highest P rates and stomatal conductance (g,) and, in certain cases, greater mean shoot growth rates and survival of plants subjected to prolonged flooding. Although plants with European birch rootstock had survival rates similar to those of plants with river birch rootstock, plants on European birch rootstock had lower Pn under prolonged flooding, fewer late-formed roots, lower root-tip density after flooding, more abscissed leaves, and greater inhibition of shoot growth of plants flooded the previous fall. Paper and Japanese birch rootstock were most sensitive to flooding and had the lowest survival rate after flooding. However, plants on paper birch rootstock were the only plants whose Pn did not increase significantly when flooding ended; they had the most abscissed leaves during spring flooding and the greatest inhibition of shoot growth in the spring after flooding the previous fall. The four rootstock ranked from most to least flood tolerant were river &gt; European &gt; Japanese &gt; paper.

Modeling the Influence of Postdirected Sethoxydim on Corn Yields

AbstractPostdirected sethoxydim 2‐[1‐(ethoxyimino)butyl]‐5‐[2‐(ethylthio) propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one, used to control monocot weeds, is known to reduce corn (Zea mays L.) yields. The objective was to develop an integrative model combining a growing plant with the effect of sethoxydim. CERES‐Maize (version 1.0) was modified to respond to herbicide‐induced grain yield reductions by incorporating a herbicide stress factor and the stress duration into calculation of the daily biomass production. Herbicide stress was defined as the difference in net photosynthesis between treated and nontreated plants. A seasonal herbicide stress factor (0–1) was determined from field measurements of treated and nontreated corn yields as a function of sethoxydim concentration (110 and 220 g a.i. ha−1) for all application dates. This factor was modified to reflect the period of the herbicide stress duration by scaling it to the fraction of time the sethoxydim was active. Field experiments were conducted using four corn hybrids (Pioneer 3475, 3379, 3377, and 3183). Data from 1988 field experiments were used to calibrate the genetic inputs for each hybrid and develop a herbicide stress relationship. The data collected in 1989 were used to validate the modifications made to CERES‐Maize. Overall, the model predicted that sethoxydim use would reduce corn yields, and this trend was consistent with independently measured field data. Based on the ratio of treated to nontreated yields for simulations and measurements, the model predictions underestimated the sethoxydim effect for the hybrids 3475, 3379, and 3183.