Agricultural System Models in Field Research and Technology Transfer, 2002
CHAPTER 4 Experience with On-Farm Applications of GLYCIM/GUICS Dennis J. Timlin, Yakov Pachepsky,... more CHAPTER 4 Experience with On-Farm Applications of GLYCIM/GUICS Dennis J. Timlin, Yakov Pachepsky, Frank D. Whisler, and Vangimalla R. Reddy CONTENTS Introduction 55 On-Farm Testing of GLYCIM 57 Field Sampling Protocol 58 Modifications to GLYCIM Based on On-...
The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled e... more The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled environment chambers by measuring condensate draining from cooling coils in a constant humidity en- vironment. This provides a direct measure of evapotranspiration (ET). However, in growth chambers with soilbins, this does not give in- formation on soil water status or root activity. The objective of
Background and Aims High-temperature environments with >30 C during flowering reduce boll retenti... more Background and Aims High-temperature environments with >30 C during flowering reduce boll retention and yield in cotton. Therefore, identification of cotton cultivars with high-temperature tolerance would be beneficial in both current and future climates.
Maize (Zea mays L.) hybrids varying in drought tolerance were treated with water stress in contro... more Maize (Zea mays L.) hybrids varying in drought tolerance were treated with water stress in controlled environments. Experiments were performed during vegetative growth and water was withheld for 19 days beginning 17 days after sowing. Genotypic comparisons used measured changes of leaf water potential or results were expressed by time of treatment. Total dry matter of the drought tolerant hybrid on the final harvest was 53% less than that of the intermediate and susceptible maize hybrids when plants were water sufficient. This showed that maize hybrids selected for extreme drought tolerance possessed a dwarf phenotype that affected soil water contents and leaf water potentials. Changes of shoot and root growth, leaf water potential, net photosynthesis and stomatal conductance in response to the time of water stress treatment were diminished when comparing the drought tolerant to the intermediate or susceptible maize hybrids. Genotypic differences were observed in 26 of 40 total foliar metabolites during water stress treatments. Hierarchical clustering revealed that the tolerant maize hybrid initiated the accumulation of stress related metabolites at higher leaf water potentials than either the susceptible or intermediate hybrids. Opposite results occurred when changes of metabolites in maize leaves were expressed temporally. The above results demonstrated that genotypic differences were readily observed by comparing maize hybrids differing in drought tolerance based on either time of treatment or measured leaf water potential. Current findings provided new and potentially important insights into the mechanisms of drought tolerance in maize.
Plant reproduction is highly vulnerable to global climate change components such as carbon dioxid... more Plant reproduction is highly vulnerable to global climate change components such as carbon dioxide concentration ([CO 2 ]), temperature (T), and ultraviolet-B (UV-B) radiation. The objectives of this study were to determine the effects of season-long exposure to treatments of [CO 2 ] at 360 (control) and 720 lmol mol 21 (1CO 2 ), temperature at 30/22 8C (control) and 38/30 8C (1T) and UV-B radiation 0 (control) and 10 kJ m 22 d 21 (1UV-B) on flower and pollen morphology, pollen production, germination, and tube lengths of six soybean genotypes (D 88-5320, D 90-9216, Stalwart III, PI 471938, DG 5630RR, and DP 4933RR) in sunlit, controlled environment chambers. The control treatment had 360 lmol mol 21 [CO 2 ] at 30/22 8C and 0 kJ UV-B. Plants grown either at 1UV-B or 1T, alone or in combination, produced smaller flowers with shorter standard petal and staminal column lengths. Flowers so produced had less pollen with poor pollen germination and shorter tube lengths. Pollen produced by the flowers of these plants appeared shrivelled without apertures and with disturbed exine ornamentation even at 1CO 2 conditions. The damaging effects of 1T and 1UV-B were not ameliorated by 1CO 2 conditions. Based on the total stress response index (TSRI), pooled individual component responses over all the treatments, the genotypes were classified as tolerant (DG 5630RR, D 88-5320: TSRI >2790), intermediate (D 90-9216, PI 471938: TSRI <2790 to >21026), and sensitive (Stalwart III, DP 4933RR: TSRI <21026). The differences in sensitivity identified among genotypes imply the options for selecting genotypes with tolerance to environmental stresses projected to occur in the future climates.
The effects of CO 2 enrichment on the growth and physiology of maize were investigated at the mol... more The effects of CO 2 enrichment on the growth and physiology of maize were investigated at the molecular, biochemical, leaf, and canopy levels. Maize plants were grown in sunlit soil-plant-atmosphere research (SPAR) chambers at ambient (370 lmol mol À1 ) or elevated (750 lmol mol À1 ) atmospheric carbon dioxide concentration (C a ) under wellwatered and fertilized conditions. Canopy gas exchange rates and leaf temperatures were monitored continuously during the growing season. CO 2 enrichment did not enhance the growth or canopy photosynthesis of maize plants. However, canopy evapotranspiration rates decreased by 22% and daytime leaf temperatures were increased about 1 1C in response to CO 2 enrichment. Leaf carboxylation efficiency and leaf nitrogen concentration also decreased at elevated C a . Transcription profiling using maize cDNA microarrays revealed that approximately 5% of tested genes responded to CO 2 enrichment. Of the altered transcripts, several were known to encode proteins involved in stomatal development or photosynthesis. For the majority of the altered transcripts, however, it was difficult to link their functions with specific physiological factors partly because many of these genes encoded unknown proteins. We conclude that maize did not exhibit enhanced growth or photosynthesis in response to CO 2 enrichment but a number of molecular and physiological processes including those involved in stomatal relations were affected by growth in elevated C a .
An experiment was conducted under outdoor pot-culture conditions to determine effects of nitrogen... more An experiment was conducted under outdoor pot-culture conditions to determine effects of nitrogen (N) deficiency on sorghum growth, physiology, and leaf hyperspectral reflectance properties. Sorghum (cv. DK 44C) was seeded in 360 twelve-litre pots filled with fine sand. All pots were irrigated with half-strength Hoagland's nutrient solution from emergence to 25 days after sowing (DAS). Thereafter, pots were separated into three identical groups and the following treatments were initiated: (1) the control (100% N) continued receiving the half-strength nutrient solution; (2) reduced N to 20% of the control (20% N); and (3) withheld N from the solution (0% N). Photosynthetic rate (Pn), chlorophyll (Chl) and N concentrations, and hyperspectral reflectance of the uppermost, fully expanded leaves were determined at 3-to 4-day-interval from 21 to 58 DAS during the N treatments. Plants were harvested 58 DAS to determine effects of N deficiency on leaf area (LA), biomass accumulation, and partitioning. Nitrogen deficiency significantly reduced LA, leaf Chl content and Pn, resulting in lower biomass production. Decreased leaf Pn due to N deficiency was mainly associated with lower stomatal conductance rather than carboxylation capacity of leaf chemistry. Among plant components of dry weights, leaf dry weight had the greatest and root dry weight had the smallest decrease under N deficiency. Nitrogen-deficit stress mainly increased leaf reflectance at 555 (R 555 ) and 715 nm (R 715 ) and caused a red-edge shift to shorter wavelength. Leaf N and Chl concentrations were linearly correlated with not only the reflectance ratios of R 405 /R 715 (r 2 = 0.68 * * * ) and R 1075 /R 735 (r 2 = 0.64 * * * ), respectively, but also the first derivatives of the reflectance (dR/dλ) in red edge centered 730 or 740 nm (r 2 = 0.73-0.82 * * * ). These specific reflectance ratios or dR/dλ may be used for rapid and non-destructive estimation of sorghum leaf Chl and plant N status. Published by Elsevier B.V.
Global atmospheric carbon dioxide concentrations (C a ) are rising. As a consequence, recent clim... more Global atmospheric carbon dioxide concentrations (C a ) are rising. As a consequence, recent climate models have projected that global surface air temperature may increase 1.4-5.8 • C with the doubling of C a by the end of the century. Because, changes in C a and temperature are likely to occur concomitantly, it is important to evaluate how the temperature dependence of key physiological processes are affected by rising C a in major crop plants including maize (Zea mays L.), a globally important grain crop with C 4 photosynthetic pathway. We investigated the temperature responses of photosynthesis, growth, and development of maize plants grown at five temperature regimes ranging from 19/13 to 38.5/32.5 • C under current (370 mol mol −1 ) and doubled (750 mol mol −1 ) C a throughout the vegetative stages using sunlit controlled environmental chambers in order to test if the temperature dependence of these processes was altered by elevated C a . Leaf and canopy photosynthetic rates, C 4 enzyme activities, leaf appearance rates, above ground biomass accumulation and leaf area were measured. We then applied temperature response functions (e.g., Arrhenius and Beta distribution models) to fit the measured data in order to provide parameter estimates of the temperature dependence for modeling photosynthesis and development at current and elevated C a in maize. Biomass, leaf area, leaf appearance rate, and photosynthesis measured at growth C a was not changed in response to CO 2 enrichment. Carboxylation efficiency and the activities of C 4 enzymes were reduced with CO 2 enrichment indicating possible photosynthetic acclimation of the C 4 cycle. All measured parameters responded to growth temperatures. Leaf appearance rate and leaf photosynthesis showed curvilinear response with optimal temperatures near 32 and 34 • C, respectively. Total above ground biomass and leaf area were negatively correlated with growth temperature. The dependence of leaf appearance rate, biomass, leaf area, leaf and canopy photosynthesis, and C 4 enzyme activities on growth temperatures was comparable between current and elevated C a . The results of this study suggest that the temperature effects on growth, development, and photosynthesis may remain unchanged in elevated C a compared with current C a in maize. Published by Elsevier B.V.
Quantitative knowledge of infiltration processes and the mechanisms that control water movement i... more Quantitative knowledge of infiltration processes and the mechanisms that control water movement in soil is necessary to properly manage water and chemical use in agricultural fields. The objective of this study was to compare the soil water content dynamics in row ...
A gronomy J our n al • Volume 10 0 , I s sue 3 • 2 0 0 8 711 ABSTRACT Reductions in potato (Solan... more A gronomy J our n al • Volume 10 0 , I s sue 3 • 2 0 0 8 711 ABSTRACT Reductions in potato (Solanum tuberosum L.) canopy growth are observed with mild water stress. Potato growth is enhanced by elevated atmospheric carbon dioxide ([CO 2 ]), but interactions of [CO 2 ] and water stress on canopy formation and dry matter partitioning have not been studied. Two soil-plant-atmosphere research (SPAR) experiments were conducted at 370 or 740 μmol mol -1 [CO 2 ] and six diff erent irrigations from 10 to 100% of the daily water uptake of the control. Increases in plant length from 23 to 111 cm at 60 d aft er emergence (DAE), leaf appearance duration from 38 to 71 d, leaf appearance rate from 0.5 to 0.93 leaves d -1 , individual leaf area from 50 to 175 cm 2 , and lateral branch elongation were observed as irrigation increased. Values were generally smaller for elevated [CO 2 ] plants under water stress. Biomass increased with irrigation from 73 to 346 g plant -2 . Th e percentage allocated to the canopy increased with irrigation from 50 to 80% in ambient and 30 to 80% in elevated [CO 2 ]. Despite decreased canopy size, elevated [CO 2 ] plants produced similar total biomass, but higher yield, at most irrigations. Reduced canopy mass in elevated [CO 2 ] plants was attributed to suppressed lateral branch development due to an interactive eff ect of [CO 2 ] and water stress on tuber sink strength. Th ese results indicate that water stress predicted by climate change models will be mediated somewhat under [CO 2 ] enrichment.
Mature potato (Solanum tuberosum L. cv. Kennebec) canopies are composed of leaves originating fro... more Mature potato (Solanum tuberosum L. cv. Kennebec) canopies are composed of leaves originating from main-and axillary-stem branches. Canopy leaf distribution and its corresponding contribution to wholecanopy photosynthetic rates have not been quantified. An experiment using SPAR (Soil-Plant-Atmosphere-Research) chambers maintained at 16-h day/night thermoperiods of 14/10, 17/12, 20/15, 23/18, 28/23, and 34/29°C was conducted. Mature canopies were divided into three horizontal layers of equal depth. Canopies were defoliated at each layer, from the ground upward, on successive days. Response curves for photosynthetic rate vs. irradiance were obtained after each defoliation. Leaf area within each layer followed a quadratic relationship with temperature. The largest areas were between 16.6 and 22.1°C. Main-stem leaves accounted for .50% of the total leaf area at temperatures ,22°C, while the proportion of axillary-stem leaf area in each layer increased with temperature. Canopy maximum gross photosynthetic rates, A MAX , before harvest ranged from 9.5 to 34.8 mmol CO 2 m 22 s 21 (production-area basis) and were higher at 14/10, 17/12, and 20/15°C temperatures than at 23/18, 28/23, and 34/29°C. These values were largely related to the quantity of leaf area in each chamber. The value of A MAX and canopy light use efficiency declined as successive canopy layers were removed, primarily due to decreases in canopy light interception. These results indicate that the relative proportion of main-or axillary-stem leaves are not as important for potato canopy modeling considerations as is the need to simulate the correct quantity of leaf area.
Plants continue to grow and generate new organs in symmetric patterns throughout their lives. Thi... more Plants continue to grow and generate new organs in symmetric patterns throughout their lives. This development requires an interconnected regulation of genes, hormones, and anisotropic growth, which in part is guided by environmental cues. Recently, several studies have used a combination of experiments and mathematical modeling to elucidate the mechanisms behind different growth and molecular patterns in plants. The computational models were used to investigate the often non-intuitive consequences of different hypotheses, and the in silico simulations of the models inspired further experimentation.
The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled e... more The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled environment chambers by measuring condensate draining from cooling coils in a constant humidity environment. This provides a direct measure of evapotranspiration (ET). However, in growth chambers with soilbins, this does not give information on soil water status or root activity. The objective of this study was to compare ET measurements from the condensate system with ET calculated from measurements of water content by TDR. Data from an irrigation 3 carbon dioxide (CO 2 ) study on potato (Solanum tuberosum L.) were used for this study. The soil water contents in the growth chamber soilbins were monitored once an hour at five vertical depths with three measurement locations per depth using an automated TDR system. The correspondence between daily ET rates for the two systems was good. Maximum daily ET rates were near 6.1 to 7.1 mm cm 22 d 21 (7-8 L d 21 on a chamber basis) and differences were on the order to 0.89 to 1.8 mm cm 22 d 21 (1-2 L d 21 ). At the higher daily ET rates, the daily values from the two methods were closer. The correspondence between hourly measurements of ET measured from the condensate system and calculated from TDR water contents was poor due to instrument and soil variability. A significant source of error was vertical variation in water content in the soil between horizontally placed TDR probes, especially during irrigation events. Evapotranspiration estimates from TDR measurements were much more robust for calculation of water use over a period of time. Data from the condensate system were most useful for quantification of diurnal transpiration rates and were better correlated with radiation.
to photoperiod. It is widely accepted that the early phase of soybean development is not influenc... more to photoperiod. It is widely accepted that the early phase of soybean development is not influenced by photope-To accurately model the flowering process in soybean, it is essential riod and can therefore be described as a juvenile phase to identify photoperiod-sensitive and photoperiod-insensitive phases (Shanmugasundaram and Tsou, 1978; Hodges and of development. Despite extensive studies, there remains some disagreement about when soybean plants first become sensitive to photo- French, 1985; Ellis et al., 1992). The juvenile phase deperiod. The length of the juvenile phase from emergence has been scribed in this study is the length of photoperiod-insensifound to differ for the same cultivar. This experiment tested the Abbreviations: DAE, days after emergence. Published in Agron. J. 90:389-392 (1998).
a b s t r a c t CO 2 has been predicted to increase in the future, and thus leading to possible c... more a b s t r a c t CO 2 has been predicted to increase in the future, and thus leading to possible changes in precipitation patterns. The objectives of this study were to investigate water use and canopy level photosynthesis of corn plants, and to quantify water use efficiency in corn plants under two different CO 2 levels combined with four different water stress levels. Corn plants were planted in sunlit plant growth chambers and a day/night temperature of (28/18 • C) was applied. From 21 days after emergence (DAE), the eight treatments including two levels of carbon dioxide concentrations (400 and 800 mol mol −1 ) and four levels of water stress (well-watered control, "mild", "moderate", and "severe" water stress) treatments at each CO 2 level were imposed. Height, number of leaves, leaf lengths, and growth stages of corn plants were monitored from nine plants twice a week. Corn plants were separately collected, dried, and analyzed for the biomass accumulation at 21 and 60 DAE. Soil water contents were monitored by a time domain reflectometry (TDR) system (15 probes per chamber). The "breaking points" (changes from high to low rates of soil water uptake) were observed in the bottom of soil depth for the water stressed conditions, and the "breaking points" under ambient CO 2 appeared 6-9 days earlier than under elevated CO 2 . Although approximately 20-49% less water was applied for the elevated CO 2 treatments than for ambient CO 2 from 21 DAE, higher soil water contents were recorded under elevated CO 2 than under ambient CO 2 . However, corn growth variables such as height, leaf area, and biomass accumulation were not significantly different in CO 2 or water stressed treatments. This result may be explained by considering that significant differences in canopy level gross photosynthesis among the water stress treatments was observed only toward the end of the experiment. The higher soil water contents observed under elevated CO 2 resulted mainly from less water use than under ambient CO 2. WUE (above ground biomass per water use since 21 DAE) at the final harvest was consistently higher and varied with a smaller range under elevated CO 2 than under ambient CO 2 . This study suggests that less water will be required for corn under high-CO 2 environment in the future than at present.
Outdoor growth chambers allow plants to be grown under sunlight while other environmental variabl... more Outdoor growth chambers allow plants to be grown under sunlight while other environmental variables such as air temperature and CO 2 concentration are controlled. Photosynthetically active radiation (PAR) inside these sunlit chambers could differ from ambient levels due to attenuations and reflections by the glazing materials. This study identified diurnal patterns and distribution of PAR inside various types of sunlit growth chambers, including soil-plant-atmosphere-research (SPAR) units using single-point and line quantum sensors. In comparison with the ambient levels, higher PAR was measured when reflections from the adjacent walls overlapped at specific locations in the SPAR unit. Within the crop growing area located in the northern part of a SPAR unit, daily integrals of PAR were between 93% and 105% of the ambient PAR on a clear day. A gradient in daily PAR existed, increasing from south to north inside the chamber. On a cloudy day, PAR within the crop growing area was between 92% and 95% of ambient PAR. A mathematical model was developed to predict incident PAR inside sunlit chambers. This model accounted for solar geometry, direct and diffuse radiations, chamber geometry, and the optical properties of the glazing material. The model was capable of simulating the diurnal patterns of PAR inside various types of sunlit chambers. The model predicted that the mean daily PAR inside sunlit chambers of acrylic sheets would usually be within 5% of the ambient PAR. Spatial distribution of the predicted daily PAR ranged from 75% to 120% of ambient levels inside various types of sunlit chambers including SPAR and open-top chambers. Published by Elsevier B.V.
Experiments were conducted in outdoor, naturally sunlit, soil-plant-atmosphere research (SPAR) ch... more Experiments were conducted in outdoor, naturally sunlit, soil-plant-atmosphere research (SPAR) chambers using plants grown in pots. Drought treatments were imposed on potato plants (Solanum tuberosum cv. Kennebec) beginning 10 days after tuber initiation. A total of 23 out of 37 foliar metabolites were affected by drought when measured 11 days after initiating water stress treatments. Compounds that accumulated in response to drought were hexoses, polyols, branched chain amino acids (BCAAs) and aromatic amino acids, such as proline. Conversely, leaf starch, alanine, aspartate and several organic acids involved in respiratory metabolism decreased with drought. Depending upon harvest date, a maximum of 12 and 17 foliar metabolites also responded to either CO2 enrichment or diurnal treatments, respectively. In addition, about 20% of the measured metabolites in potato leaflets were simultaneously affected by drought, CO2 enrichment and diurnal factors combined. This group contained BCAAs, hexoses, leaf starch and malate. Polyols and proline accumulated in response to water stress but did not vary diurnally. Water stress also amplified diurnal variations of hexoses and starch in comparison to control samples. Consequently, specific drought responsive metabolites in potato leaflets were dramatically affected by daily changes of photosynthetic carbon metabolism.
Agricultural System Models in Field Research and Technology Transfer, 2002
CHAPTER 4 Experience with On-Farm Applications of GLYCIM/GUICS Dennis J. Timlin, Yakov Pachepsky,... more CHAPTER 4 Experience with On-Farm Applications of GLYCIM/GUICS Dennis J. Timlin, Yakov Pachepsky, Frank D. Whisler, and Vangimalla R. Reddy CONTENTS Introduction 55 On-Farm Testing of GLYCIM 57 Field Sampling Protocol 58 Modifications to GLYCIM Based on On-...
The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled e... more The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled environment chambers by measuring condensate draining from cooling coils in a constant humidity en- vironment. This provides a direct measure of evapotranspiration (ET). However, in growth chambers with soilbins, this does not give in- formation on soil water status or root activity. The objective of
Background and Aims High-temperature environments with >30 C during flowering reduce boll retenti... more Background and Aims High-temperature environments with >30 C during flowering reduce boll retention and yield in cotton. Therefore, identification of cotton cultivars with high-temperature tolerance would be beneficial in both current and future climates.
Maize (Zea mays L.) hybrids varying in drought tolerance were treated with water stress in contro... more Maize (Zea mays L.) hybrids varying in drought tolerance were treated with water stress in controlled environments. Experiments were performed during vegetative growth and water was withheld for 19 days beginning 17 days after sowing. Genotypic comparisons used measured changes of leaf water potential or results were expressed by time of treatment. Total dry matter of the drought tolerant hybrid on the final harvest was 53% less than that of the intermediate and susceptible maize hybrids when plants were water sufficient. This showed that maize hybrids selected for extreme drought tolerance possessed a dwarf phenotype that affected soil water contents and leaf water potentials. Changes of shoot and root growth, leaf water potential, net photosynthesis and stomatal conductance in response to the time of water stress treatment were diminished when comparing the drought tolerant to the intermediate or susceptible maize hybrids. Genotypic differences were observed in 26 of 40 total foliar metabolites during water stress treatments. Hierarchical clustering revealed that the tolerant maize hybrid initiated the accumulation of stress related metabolites at higher leaf water potentials than either the susceptible or intermediate hybrids. Opposite results occurred when changes of metabolites in maize leaves were expressed temporally. The above results demonstrated that genotypic differences were readily observed by comparing maize hybrids differing in drought tolerance based on either time of treatment or measured leaf water potential. Current findings provided new and potentially important insights into the mechanisms of drought tolerance in maize.
Plant reproduction is highly vulnerable to global climate change components such as carbon dioxid... more Plant reproduction is highly vulnerable to global climate change components such as carbon dioxide concentration ([CO 2 ]), temperature (T), and ultraviolet-B (UV-B) radiation. The objectives of this study were to determine the effects of season-long exposure to treatments of [CO 2 ] at 360 (control) and 720 lmol mol 21 (1CO 2 ), temperature at 30/22 8C (control) and 38/30 8C (1T) and UV-B radiation 0 (control) and 10 kJ m 22 d 21 (1UV-B) on flower and pollen morphology, pollen production, germination, and tube lengths of six soybean genotypes (D 88-5320, D 90-9216, Stalwart III, PI 471938, DG 5630RR, and DP 4933RR) in sunlit, controlled environment chambers. The control treatment had 360 lmol mol 21 [CO 2 ] at 30/22 8C and 0 kJ UV-B. Plants grown either at 1UV-B or 1T, alone or in combination, produced smaller flowers with shorter standard petal and staminal column lengths. Flowers so produced had less pollen with poor pollen germination and shorter tube lengths. Pollen produced by the flowers of these plants appeared shrivelled without apertures and with disturbed exine ornamentation even at 1CO 2 conditions. The damaging effects of 1T and 1UV-B were not ameliorated by 1CO 2 conditions. Based on the total stress response index (TSRI), pooled individual component responses over all the treatments, the genotypes were classified as tolerant (DG 5630RR, D 88-5320: TSRI >2790), intermediate (D 90-9216, PI 471938: TSRI <2790 to >21026), and sensitive (Stalwart III, DP 4933RR: TSRI <21026). The differences in sensitivity identified among genotypes imply the options for selecting genotypes with tolerance to environmental stresses projected to occur in the future climates.
The effects of CO 2 enrichment on the growth and physiology of maize were investigated at the mol... more The effects of CO 2 enrichment on the growth and physiology of maize were investigated at the molecular, biochemical, leaf, and canopy levels. Maize plants were grown in sunlit soil-plant-atmosphere research (SPAR) chambers at ambient (370 lmol mol À1 ) or elevated (750 lmol mol À1 ) atmospheric carbon dioxide concentration (C a ) under wellwatered and fertilized conditions. Canopy gas exchange rates and leaf temperatures were monitored continuously during the growing season. CO 2 enrichment did not enhance the growth or canopy photosynthesis of maize plants. However, canopy evapotranspiration rates decreased by 22% and daytime leaf temperatures were increased about 1 1C in response to CO 2 enrichment. Leaf carboxylation efficiency and leaf nitrogen concentration also decreased at elevated C a . Transcription profiling using maize cDNA microarrays revealed that approximately 5% of tested genes responded to CO 2 enrichment. Of the altered transcripts, several were known to encode proteins involved in stomatal development or photosynthesis. For the majority of the altered transcripts, however, it was difficult to link their functions with specific physiological factors partly because many of these genes encoded unknown proteins. We conclude that maize did not exhibit enhanced growth or photosynthesis in response to CO 2 enrichment but a number of molecular and physiological processes including those involved in stomatal relations were affected by growth in elevated C a .
An experiment was conducted under outdoor pot-culture conditions to determine effects of nitrogen... more An experiment was conducted under outdoor pot-culture conditions to determine effects of nitrogen (N) deficiency on sorghum growth, physiology, and leaf hyperspectral reflectance properties. Sorghum (cv. DK 44C) was seeded in 360 twelve-litre pots filled with fine sand. All pots were irrigated with half-strength Hoagland's nutrient solution from emergence to 25 days after sowing (DAS). Thereafter, pots were separated into three identical groups and the following treatments were initiated: (1) the control (100% N) continued receiving the half-strength nutrient solution; (2) reduced N to 20% of the control (20% N); and (3) withheld N from the solution (0% N). Photosynthetic rate (Pn), chlorophyll (Chl) and N concentrations, and hyperspectral reflectance of the uppermost, fully expanded leaves were determined at 3-to 4-day-interval from 21 to 58 DAS during the N treatments. Plants were harvested 58 DAS to determine effects of N deficiency on leaf area (LA), biomass accumulation, and partitioning. Nitrogen deficiency significantly reduced LA, leaf Chl content and Pn, resulting in lower biomass production. Decreased leaf Pn due to N deficiency was mainly associated with lower stomatal conductance rather than carboxylation capacity of leaf chemistry. Among plant components of dry weights, leaf dry weight had the greatest and root dry weight had the smallest decrease under N deficiency. Nitrogen-deficit stress mainly increased leaf reflectance at 555 (R 555 ) and 715 nm (R 715 ) and caused a red-edge shift to shorter wavelength. Leaf N and Chl concentrations were linearly correlated with not only the reflectance ratios of R 405 /R 715 (r 2 = 0.68 * * * ) and R 1075 /R 735 (r 2 = 0.64 * * * ), respectively, but also the first derivatives of the reflectance (dR/dλ) in red edge centered 730 or 740 nm (r 2 = 0.73-0.82 * * * ). These specific reflectance ratios or dR/dλ may be used for rapid and non-destructive estimation of sorghum leaf Chl and plant N status. Published by Elsevier B.V.
Global atmospheric carbon dioxide concentrations (C a ) are rising. As a consequence, recent clim... more Global atmospheric carbon dioxide concentrations (C a ) are rising. As a consequence, recent climate models have projected that global surface air temperature may increase 1.4-5.8 • C with the doubling of C a by the end of the century. Because, changes in C a and temperature are likely to occur concomitantly, it is important to evaluate how the temperature dependence of key physiological processes are affected by rising C a in major crop plants including maize (Zea mays L.), a globally important grain crop with C 4 photosynthetic pathway. We investigated the temperature responses of photosynthesis, growth, and development of maize plants grown at five temperature regimes ranging from 19/13 to 38.5/32.5 • C under current (370 mol mol −1 ) and doubled (750 mol mol −1 ) C a throughout the vegetative stages using sunlit controlled environmental chambers in order to test if the temperature dependence of these processes was altered by elevated C a . Leaf and canopy photosynthetic rates, C 4 enzyme activities, leaf appearance rates, above ground biomass accumulation and leaf area were measured. We then applied temperature response functions (e.g., Arrhenius and Beta distribution models) to fit the measured data in order to provide parameter estimates of the temperature dependence for modeling photosynthesis and development at current and elevated C a in maize. Biomass, leaf area, leaf appearance rate, and photosynthesis measured at growth C a was not changed in response to CO 2 enrichment. Carboxylation efficiency and the activities of C 4 enzymes were reduced with CO 2 enrichment indicating possible photosynthetic acclimation of the C 4 cycle. All measured parameters responded to growth temperatures. Leaf appearance rate and leaf photosynthesis showed curvilinear response with optimal temperatures near 32 and 34 • C, respectively. Total above ground biomass and leaf area were negatively correlated with growth temperature. The dependence of leaf appearance rate, biomass, leaf area, leaf and canopy photosynthesis, and C 4 enzyme activities on growth temperatures was comparable between current and elevated C a . The results of this study suggest that the temperature effects on growth, development, and photosynthesis may remain unchanged in elevated C a compared with current C a in maize. Published by Elsevier B.V.
Quantitative knowledge of infiltration processes and the mechanisms that control water movement i... more Quantitative knowledge of infiltration processes and the mechanisms that control water movement in soil is necessary to properly manage water and chemical use in agricultural fields. The objective of this study was to compare the soil water content dynamics in row ...
A gronomy J our n al • Volume 10 0 , I s sue 3 • 2 0 0 8 711 ABSTRACT Reductions in potato (Solan... more A gronomy J our n al • Volume 10 0 , I s sue 3 • 2 0 0 8 711 ABSTRACT Reductions in potato (Solanum tuberosum L.) canopy growth are observed with mild water stress. Potato growth is enhanced by elevated atmospheric carbon dioxide ([CO 2 ]), but interactions of [CO 2 ] and water stress on canopy formation and dry matter partitioning have not been studied. Two soil-plant-atmosphere research (SPAR) experiments were conducted at 370 or 740 μmol mol -1 [CO 2 ] and six diff erent irrigations from 10 to 100% of the daily water uptake of the control. Increases in plant length from 23 to 111 cm at 60 d aft er emergence (DAE), leaf appearance duration from 38 to 71 d, leaf appearance rate from 0.5 to 0.93 leaves d -1 , individual leaf area from 50 to 175 cm 2 , and lateral branch elongation were observed as irrigation increased. Values were generally smaller for elevated [CO 2 ] plants under water stress. Biomass increased with irrigation from 73 to 346 g plant -2 . Th e percentage allocated to the canopy increased with irrigation from 50 to 80% in ambient and 30 to 80% in elevated [CO 2 ]. Despite decreased canopy size, elevated [CO 2 ] plants produced similar total biomass, but higher yield, at most irrigations. Reduced canopy mass in elevated [CO 2 ] plants was attributed to suppressed lateral branch development due to an interactive eff ect of [CO 2 ] and water stress on tuber sink strength. Th ese results indicate that water stress predicted by climate change models will be mediated somewhat under [CO 2 ] enrichment.
Mature potato (Solanum tuberosum L. cv. Kennebec) canopies are composed of leaves originating fro... more Mature potato (Solanum tuberosum L. cv. Kennebec) canopies are composed of leaves originating from main-and axillary-stem branches. Canopy leaf distribution and its corresponding contribution to wholecanopy photosynthetic rates have not been quantified. An experiment using SPAR (Soil-Plant-Atmosphere-Research) chambers maintained at 16-h day/night thermoperiods of 14/10, 17/12, 20/15, 23/18, 28/23, and 34/29°C was conducted. Mature canopies were divided into three horizontal layers of equal depth. Canopies were defoliated at each layer, from the ground upward, on successive days. Response curves for photosynthetic rate vs. irradiance were obtained after each defoliation. Leaf area within each layer followed a quadratic relationship with temperature. The largest areas were between 16.6 and 22.1°C. Main-stem leaves accounted for .50% of the total leaf area at temperatures ,22°C, while the proportion of axillary-stem leaf area in each layer increased with temperature. Canopy maximum gross photosynthetic rates, A MAX , before harvest ranged from 9.5 to 34.8 mmol CO 2 m 22 s 21 (production-area basis) and were higher at 14/10, 17/12, and 20/15°C temperatures than at 23/18, 28/23, and 34/29°C. These values were largely related to the quantity of leaf area in each chamber. The value of A MAX and canopy light use efficiency declined as successive canopy layers were removed, primarily due to decreases in canopy light interception. These results indicate that the relative proportion of main-or axillary-stem leaves are not as important for potato canopy modeling considerations as is the need to simulate the correct quantity of leaf area.
Plants continue to grow and generate new organs in symmetric patterns throughout their lives. Thi... more Plants continue to grow and generate new organs in symmetric patterns throughout their lives. This development requires an interconnected regulation of genes, hormones, and anisotropic growth, which in part is guided by environmental cues. Recently, several studies have used a combination of experiments and mathematical modeling to elucidate the mechanisms behind different growth and molecular patterns in plants. The computational models were used to investigate the often non-intuitive consequences of different hypotheses, and the in silico simulations of the models inspired further experimentation.
The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled e... more The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled environment chambers by measuring condensate draining from cooling coils in a constant humidity environment. This provides a direct measure of evapotranspiration (ET). However, in growth chambers with soilbins, this does not give information on soil water status or root activity. The objective of this study was to compare ET measurements from the condensate system with ET calculated from measurements of water content by TDR. Data from an irrigation 3 carbon dioxide (CO 2 ) study on potato (Solanum tuberosum L.) were used for this study. The soil water contents in the growth chamber soilbins were monitored once an hour at five vertical depths with three measurement locations per depth using an automated TDR system. The correspondence between daily ET rates for the two systems was good. Maximum daily ET rates were near 6.1 to 7.1 mm cm 22 d 21 (7-8 L d 21 on a chamber basis) and differences were on the order to 0.89 to 1.8 mm cm 22 d 21 (1-2 L d 21 ). At the higher daily ET rates, the daily values from the two methods were closer. The correspondence between hourly measurements of ET measured from the condensate system and calculated from TDR water contents was poor due to instrument and soil variability. A significant source of error was vertical variation in water content in the soil between horizontally placed TDR probes, especially during irrigation events. Evapotranspiration estimates from TDR measurements were much more robust for calculation of water use over a period of time. Data from the condensate system were most useful for quantification of diurnal transpiration rates and were better correlated with radiation.
to photoperiod. It is widely accepted that the early phase of soybean development is not influenc... more to photoperiod. It is widely accepted that the early phase of soybean development is not influenced by photope-To accurately model the flowering process in soybean, it is essential riod and can therefore be described as a juvenile phase to identify photoperiod-sensitive and photoperiod-insensitive phases (Shanmugasundaram and Tsou, 1978; Hodges and of development. Despite extensive studies, there remains some disagreement about when soybean plants first become sensitive to photo- French, 1985; Ellis et al., 1992). The juvenile phase deperiod. The length of the juvenile phase from emergence has been scribed in this study is the length of photoperiod-insensifound to differ for the same cultivar. This experiment tested the Abbreviations: DAE, days after emergence. Published in Agron. J. 90:389-392 (1998).
a b s t r a c t CO 2 has been predicted to increase in the future, and thus leading to possible c... more a b s t r a c t CO 2 has been predicted to increase in the future, and thus leading to possible changes in precipitation patterns. The objectives of this study were to investigate water use and canopy level photosynthesis of corn plants, and to quantify water use efficiency in corn plants under two different CO 2 levels combined with four different water stress levels. Corn plants were planted in sunlit plant growth chambers and a day/night temperature of (28/18 • C) was applied. From 21 days after emergence (DAE), the eight treatments including two levels of carbon dioxide concentrations (400 and 800 mol mol −1 ) and four levels of water stress (well-watered control, "mild", "moderate", and "severe" water stress) treatments at each CO 2 level were imposed. Height, number of leaves, leaf lengths, and growth stages of corn plants were monitored from nine plants twice a week. Corn plants were separately collected, dried, and analyzed for the biomass accumulation at 21 and 60 DAE. Soil water contents were monitored by a time domain reflectometry (TDR) system (15 probes per chamber). The "breaking points" (changes from high to low rates of soil water uptake) were observed in the bottom of soil depth for the water stressed conditions, and the "breaking points" under ambient CO 2 appeared 6-9 days earlier than under elevated CO 2 . Although approximately 20-49% less water was applied for the elevated CO 2 treatments than for ambient CO 2 from 21 DAE, higher soil water contents were recorded under elevated CO 2 than under ambient CO 2 . However, corn growth variables such as height, leaf area, and biomass accumulation were not significantly different in CO 2 or water stressed treatments. This result may be explained by considering that significant differences in canopy level gross photosynthesis among the water stress treatments was observed only toward the end of the experiment. The higher soil water contents observed under elevated CO 2 resulted mainly from less water use than under ambient CO 2. WUE (above ground biomass per water use since 21 DAE) at the final harvest was consistently higher and varied with a smaller range under elevated CO 2 than under ambient CO 2 . This study suggests that less water will be required for corn under high-CO 2 environment in the future than at present.
Outdoor growth chambers allow plants to be grown under sunlight while other environmental variabl... more Outdoor growth chambers allow plants to be grown under sunlight while other environmental variables such as air temperature and CO 2 concentration are controlled. Photosynthetically active radiation (PAR) inside these sunlit chambers could differ from ambient levels due to attenuations and reflections by the glazing materials. This study identified diurnal patterns and distribution of PAR inside various types of sunlit growth chambers, including soil-plant-atmosphere-research (SPAR) units using single-point and line quantum sensors. In comparison with the ambient levels, higher PAR was measured when reflections from the adjacent walls overlapped at specific locations in the SPAR unit. Within the crop growing area located in the northern part of a SPAR unit, daily integrals of PAR were between 93% and 105% of the ambient PAR on a clear day. A gradient in daily PAR existed, increasing from south to north inside the chamber. On a cloudy day, PAR within the crop growing area was between 92% and 95% of ambient PAR. A mathematical model was developed to predict incident PAR inside sunlit chambers. This model accounted for solar geometry, direct and diffuse radiations, chamber geometry, and the optical properties of the glazing material. The model was capable of simulating the diurnal patterns of PAR inside various types of sunlit chambers. The model predicted that the mean daily PAR inside sunlit chambers of acrylic sheets would usually be within 5% of the ambient PAR. Spatial distribution of the predicted daily PAR ranged from 75% to 120% of ambient levels inside various types of sunlit chambers including SPAR and open-top chambers. Published by Elsevier B.V.
Experiments were conducted in outdoor, naturally sunlit, soil-plant-atmosphere research (SPAR) ch... more Experiments were conducted in outdoor, naturally sunlit, soil-plant-atmosphere research (SPAR) chambers using plants grown in pots. Drought treatments were imposed on potato plants (Solanum tuberosum cv. Kennebec) beginning 10 days after tuber initiation. A total of 23 out of 37 foliar metabolites were affected by drought when measured 11 days after initiating water stress treatments. Compounds that accumulated in response to drought were hexoses, polyols, branched chain amino acids (BCAAs) and aromatic amino acids, such as proline. Conversely, leaf starch, alanine, aspartate and several organic acids involved in respiratory metabolism decreased with drought. Depending upon harvest date, a maximum of 12 and 17 foliar metabolites also responded to either CO2 enrichment or diurnal treatments, respectively. In addition, about 20% of the measured metabolites in potato leaflets were simultaneously affected by drought, CO2 enrichment and diurnal factors combined. This group contained BCAAs, hexoses, leaf starch and malate. Polyols and proline accumulated in response to water stress but did not vary diurnally. Water stress also amplified diurnal variations of hexoses and starch in comparison to control samples. Consequently, specific drought responsive metabolites in potato leaflets were dramatically affected by daily changes of photosynthetic carbon metabolism.
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