Lower Radiation Use Efficiency Research Articles

Physiological contributors to yield in advanced cotton breeding lines

AbstractCotton (Gossypium hirsutum L.) yield can be expressed as the product of intercepted photosynthetically active radiation (IPAR), radiation use efficiency (RUE), and harvest index (HI). Studies comparing genetic diversity in functional yield drivers for the progeny of elite breeding lines are limited or non‐existent. A field study was conducted during the 2020 and 2021 growing seasons to characterize crop development and to evaluate yield and underlying yield drivers in 16 advanced breeding lines (F7 generation). Significant breeding line differences existed for lint yield, cutout date, reproductive, vegetative, and total biomass, RUE, and HI but not for IPAR. The lint yield for the lowest yielding lines was 24% lower than the highest yielding line with a lint yield of 1706 kg ha−1. Differences in RUE were not associated with single‐leaf photosynthetic rates. HI positively contributed to lint yield gain for most lines evaluated, whereas RUE was negatively correlated with lint yield for the majority of breeding lines evaluated. However, in the two highest‐yielding lines, two different strategies of yield maximization were identified. One line exhibited the earliest cutout date, reduced biomass production, low RUE, and the highest HI values, whereas the other line had the latest cutout date and produced the highest total biomass, highest RUE, and a low to intermediate HI. Breeding lines used in the current study achieved high yields by differentially manipulating underlying physiological components such as RUE, biomass accumulation, or dry matter allocation to fiber. Our work provides future direction for efforts aimed at maximizing yield through the selection for functional yield drivers.

Quantifying physiological determinants of potential yield in mungbean (Vigna radiata (L.) Wilczek)

A comprehensive understanding of key drivers of grain yield is essential to identify opportunities to improve productivity in mungbean ( Vigna radiata (L.) Wilczek). The objective of this study was to assess and quantify physiological factors underpinning yield of mungbean grown in non-water-limiting conditions. Two field experiments, employing three genotypes (Jade-AU, Opal-AU and Satin II) and four canopy density treatments were conducted in the summer growing season (Jan-Mar) of 2019 and 2020 at Gatton campus, The University of Queensland, Australia. Crop leaf area dynamics, radiation interception, extinction coefficient ( k ), radiation use efficiency (RUE), total dry matter (TDM) (above ground dry matter) and grain yield (GY) were measured. Leaf area index (LAI), influenced by the canopy density treatments, was the key driver of differences in radiation interception. The variation in intercepted radiation resulted in differences in TDM and GY across canopy density treatments. Genotypes did not differ significantly and partitioned more than 90% of TDM to pod development. The radiation extinction coefficient, k , was stable and estimated to be 0.68, while average RUE was calculated as 1.3 g MJ -1 . Variations in GY were strongly associated with grain number, which was related to intercepted radiation per unit of accumulated temperature around flowering. Using this quantification of the physiology of crop growth and yield in mungbean to form a simple crop model, simulations suggested that median potential yields of 1.88–2.48 tonnes ha −1 were possible in NE Australian production environments, with greater yield associated with spring sowing. Understanding the physiological basis of the very low RUE in mungbean was considered a key avenue to improve potential yield. This study has provided a quantitative framework for potential yield that will enable more comprehensive modelling of crop adaptation in mungbean. • This study highlights the importance of identifying key physiological determinants of yield for increasing productivity in mungbean. • Leaf area index differences in response to varying canopy density treatments was the key driver of differences in radiation interception and biomass. • Radiation use efficiency for current commercial mungbean was found to be 1.3 g MJ −1 . • Intercepted radiation per unit of accumulated temperature between flowering and maturity was significantly associated with grain number. • Simulations of potential yield indicated 2.5 tonnes ha −1 was attainable in NE Australia and higher yield occurred in spring planting.

Physiological activity and biomass production in crop canopy under a tropical environment in soybean cultivars with temperate and tropical origins

In order to explore the plant factors facilitating better adaptation of soybean to high temperatures, genotypic variability till the beginning of seed filling (R5) were examined with reference to biomass production, relative transpiration activity and relevant plant factors under a tropical environment. Twenty-nine (in 2014 and 2015) and 20 (in 2016) soybean cultivars of temperate (Japan and USA) and tropical (Indonesia-old, Indonesia-modern, and Others) origin were grown in Serang, Banten (2014 and 2015; Experiment 1) and in Bogor, West Java (2016; Experiment 2), Indonesia. In Experiment 1, aboveground biomass at R5 (TDWR5) of the temperate cultivars was one-third to one-fourth of that of the tropical cultivars. This was associated with less than half the amount of the cumulative intercepted radiation to R5 (CIRR5) due to their shorter growth duration and lower value of the mean fraction of canopy light interception till R5 (mean FVE-R5). In addition, the radiation use efficiency (RUE) at R5 of the temperate cultivars was also as low as 0.54gMJ−1, as compared to 0.87gMJ−1 in the tropical cultivars. The value of canopy temperature minus air temperature (CTd), as an indicator of relative transpiration activity, of temperate cultivars was markedly larger than that of the tropical cultivars, indicating lower transpiration activity in temperate cultivars, which was associated with the low RUE. In Experiment 2, greater activity of transpiration in tropical cultivars was attributed to their higher stomatal conductance (gs) and greater stomatal density (Nstoma) of upper leaves than that in those from the temperate regions. These results indicate that low biomass production in temperate cultivars occurs not only due to the cumulative intercepted radiation in the canopy but also due to low RUE and that the low RUE in temperate cultivars is associated with low gas exchange activity, in which leaf morphological traits are involved. Within temperate cultivars, US cultivars tended to perform better than the Japanese cultivars with respect to gas exchange activity.

Radiation use efficiency and biomass partitioning to storage roots in fodder beet crops

Abstract Intercepted photosynthetic active radiation (IPAR), radiation use efficiency (RUE) and partitioning of dry matter (DM) to storage roots (proot, %) were quantified for fodder beet crops subjected to contrasting water (irrigated or rain-fed) and nitrogen (N; 0, 25, 50, 100 and 200 kg/ha) supply conditions in Canterbury, New Zealand. The objectives were to enhance the understanding of physiological processes controlling fodder beet response to abiotic stresses and also to estimate parameters for biophysical models that simulate crop growth. Data from three field experiments showed a wide range of fodder beet yield (14–29 t DM/ha) in response to water and N stress. These yield differences were mostly explained by the treatments effect on IPAR (650–1050 MJ PAR/ha), with relatively smaller responses in RUE and proot. For unconstrained (fully irrigated; ≥100 kg N/ha) growth conditions, maximum values were 3.6 g DM/MJ PAR for RUE and 78% for proot for total biomass at final harvest. The RUE for the rain-fed, 0 kg N/ha crops was reduced by up to 25%, while proot was only marginally reduced (∼3% in rain-fed crops) compared with crops under unconstrained growth conditions. While the RUE responded linearly to additional N supply in irrigated crops, rain-fed crops showed a more consistent decline in RUE across N fertiliser rates with 65–70% of unstressed values. High RUE values were observed across a wide range of crop N status (Nitrogen Nutrition Index [NNI] from 0.8 to 1.6) in irrigated crops. In contrast, RUE in rain-fed was low at high NNI estimates because of high N concentration in a smaller canopy area. The lower RUE in rain-fed crops was aligned with reduced leaf photosynthetic rates (Pnleaf) although there was a high variability in Pnleaf measurements. These results give a first quantification of IPAR, RUE, proot and Pnleaf in fodder beet. They provide insights on the relative sensitivity of fodder beet to water and N stresses. These results are valuable for the interpretation of crop responses and for setting parameters for biophysical models to simulate fodder beet growth.

Maximum Plant Uptakes for Water, Nutrients, and Oxygen Are Not Always Met by Irrigation Rate and Distribution in Water-based Cultivation Systems.

Growing on rooting media other than soils in situ -i.e., substrate-based growing- allows for higher yields than soil-based growing as transport rates of water, nutrients, and oxygen in substrate surpass those in soil. Possibly water-based growing allows for even higher yields as transport rates of water and nutrients in water surpass those in substrate, even though the transport of oxygen may be more complex. Transport rates can only limit growth when they are below a rate corresponding to maximum plant uptake. Our first objective was to compare Chrysanthemum growth performance for three water-based growing systems with different irrigation. We compared; multi-point irrigation into a pond (DeepFlow); one-point irrigation resulting in a thin film of running water (NutrientFlow) and multi-point irrigation as droplets through air (Aeroponic). Second objective was to compare press pots as propagation medium with nutrient solution as propagation medium. The comparison included DeepFlow water-rooted cuttings with either the stem 1 cm into the nutrient solution or with the stem 1 cm above the nutrient solution. Measurements included fresh weight, dry weight, length, water supply, nutrient supply, and oxygen levels. To account for differences in radiation sum received, crop performance was evaluated with Radiation Use Efficiency (RUE) expressed as dry weight over sum of Photosynthetically Active Radiation. The reference, DeepFlow with substrate-based propagation, showed the highest RUE, even while the oxygen supply provided by irrigation was potentially growth limiting. DeepFlow with water-based propagation showed 15–17% lower RUEs than the reference. NutrientFlow showed 8% lower RUE than the reference, in combination with potentially limiting irrigation supply of nutrients and oxygen. Aeroponic showed RUE levels similar to the reference and Aeroponic had non-limiting irrigation supply of water, nutrients, and oxygen. Water-based propagation affected the subsequent cultivation in the DeepFlow negatively compared to substrate-based propagation. Water-based propagation resulted in frequent transient discolorations after transplanting in all cultivation systems, indicating a factor, other than irrigation supply of water, nutrients, and oxygen, influencing plant uptake. Plant uptake rates for water, nutrients, and oxygen are offered as a more fundamental way to compare and improve growing systems.

Biomass productivity and radiation utilisation of innovative cropping systems for biorefinery

In order to supply future biorefineries there is a need to sustainably intensify the biomass production on current agricultural land. The aim of this work was to determine biomass yield and associated radiation utilisation for novel perennial grasses and annual crops in rotations optimised for biomass production, and compare their performance with traditional cropping systems commonly used in northern European agriculture. Measurements of biomass yield from 2012 to 2015 at two Danish sites differing in soil type and climatic conditions were conducted in three main cropping systems: i) optimised rotation of annual crops (maize, beet, hemp/oat, triticale, winter rye and winter rapeseed), ii) perennial crops intensively fertilised (festulolium, reed canary, cocksfoot and tall fescue), low-fertilised (miscanthus) or unfertilised (grass-legume mixtures) and iii) traditional systems (continuous monocultures of maize and triticale, and a rotation of spring barley−winter barley−winter rapeseed).The results showed that on sandy loam soil, the highest biomass yield (mean of three years following the establishing year) was achieved by festulolium (20.4Mgha−1), followed by tall fescue (18.5Mgha−1), optimised rotation (16.7Mgha−1), reed canary (15.9Mgha−1) and cocksfoot (15.2Mgha−1). On coarse sandy soil, the highest biomass was achieved by tall fescue (17.7Mgha−1), followed by cocksfoot (15.9Mgha−1), reed canary (14.3Mgha−1) and optimised rotation (13.9Mgha−1). The biomass yield of traditional cropping systems varied between 11 and 18Mgha−1, with continuous maize being the most productive. Although traditional maize produced similar or higher biomass yields than the novel cropping systems, the novel systems are expected to reduce environmental impact and have positive effects on biodiversity.The fraction of intercepted photosynthetically active radiation (fIpar), the accumulated intercepted photosynthetically active radiation (Ipar) and the radiation use efficiency (RUE) were determined from canopy radiations measured biweekly for three years. These results showed a higher annual Ipar (800–1200MJm−2) but lower RUE (1.0–2.0gMJ−1) for the most productive perennial crops than for the most productive annual crops such as maize and beet (Ipar=600–750MJm−2, RUE=2.3–3.0gMJ−1), with variations depending on crop species, management actions and prevailing meteorological conditions. The lower aboveground RUE of perennial crops than of annual crops indicates differences in photosynthesis efficiencies and partitioning of assimilates to non-harvested plant parts and calls for further breeding of the perennial crops to improve their RUE.

Biomass production and yield of soybean grown under converted paddy fields with excess water during the early growth stage

Soybean production in converted paddy fields is generally impacted by excess soil water condition which typically occurs during the early stage of vegetative growth in Japan. This study attempted to identify how the excess water stress in this stage affects light components involved in crop production processes (biomass accumulation and seed yield). The Enrei cultivar was grown in three experiments under optimum soil moisture throughout the season (Opt) and with excess water at only the early vegetative growth stage (Ex-Wt). The excess water was imposed from 11 to 15 days after emergence (DAE) by water stagnation between ridged rows or raising the water table by sub-soil irrigation. Biomass accumulation was analyzed based on periodical harvesting and its relationship with the light components such as intercepted radiation (IR), radiation use efficiency (RUE) and light extinction coefficient (K). In all experiments, Ex-Wt produced fewer yields than Opt by 25–31%. The accumulation of total dry weight (TDW) before beginning of seed filling (R5) was less in Ex-Wt by 24–51%, while the harvest index was changed only slightly. In the Ex-Wt fields, the restricted leaf area resulted in 13–27% less intercepted radiation (cum IR) and exhibited a 13–33% lower RUE from emergence to R5. On average, the difference in yield between conditions was lesser in the dense planting than the sparse planting, and a similar trend was seen for cum IR. Thus, dense planting would ameliorate yield reduction to a limited extent. The results suggest that a 2-week period of excess water would reduce yield by reducing TDW, attributed to reduction in less cum IR and low RUE, even if the water condition is maintained at a preferable level for the remaining time.

Physiological Traits Contributing to Differential Canopy Wilting in Soybean under Drought

ABSTRACTDelayed wilting is observed in a few unusual soybean [Glycine max (L.) Merr.] genotypes, but the reasons and importance of this trait for conferring agronomic drought tolerance are poorly understood. We hypothesized that soybean genotypes with delayed wilting conserve soil moisture by restricting transpiration and that this would be reflected in decreased radiation use efficiency (RUE) and/or improved water use efficiency (WUE). Water conserved when soil moisture was plentiful would be available later in the season when drought is usually more severe. Irrigated field experiments in eight environments compared RUE of genotypes known to wilt differently during drought. In addition, we measured stomatal conductance, carbon isotope discrimination (CID), volumetric soil‐moisture content, stomatal density, and canopy temperature depression. In six of the eight environments, slow‐wilting genotypes generally had lower RUE than fast‐wilting genotypes, which is consistent with our hypothesis. Three of four slow‐wilting genotypes had higher soil moisture immediately before irrigation than fast‐wilting genotypes, which is also consistent with the hypothesis. Genotypic differences in CID (a proxy for WUE) were present but were not consistently related with slow wilting. No genotypic differences were detected in stomatal conductance or canopy temperature. These results suggest that multiple mechanisms involving RUE and WUE could result in soil‐water conservation in these diverse genotypes.

Radiation Use Efficiency in Dual Winter Cereal–Forage Production Systems

Winter cereal production systems in the northern USA are inefficient with respect to the capture of photosynthetically active radiation (PAR) during the year. Our objectives were to determine radiation use efficiency (RUE) in winter wheat (Triticum aestivum L.) and triticale (× Triticosecale Wittmack) at low (67–125 plants m−2), medium (116–170 plants m−2), and high (205–332 plants m−2) plant densities and RUE of interseeded red clover (Trifolium pratense L.) during two growth periods after cereal harvest. During the linear phase of cereal growth (GS 30–80), RUE averaged across plant density was 3.50 g MJ−1 for wheat and 3.21 for triticale in 2004 and 3.37 for wheat in 2006. In 2006, triticale RUE was similar at the low and medium plant density (3.28 g MJ−1) but lower at the high plant density (2.84 g MJ−1). Red clover RUE following wheat and triticale differed by growth period and exhibited varying levels of plant density dependence within growth period. Following wheat at the high plant density, RUE ranged from 1.40 to 1.97 g MJ−1 across years and growth periods. Following cereal harvest in mid‐July until early October, red clover interseeded in wheat intercepted on average 65% (2004) and 35% (2006) of incident PAR. The wheat–red clover system was more robust than triticale–red clover for grain RUE and intercepting PAR after cereal harvest.

Model-assisted physiological analysis of Phyllo, a rice architectural mutant.

Studies of phenotype of knockout mutants can provide new insights into physiological, phenological and architectural feedbacks in the plant system. Phyllo, a mutant of Nippon Bare rice (Oryza sativa L.) producing small leaves in rapid succession, was isolated during multiplication of a T-DNA insertion library. Phyllo phenotype was compared with the wild type (WT) during vegetative development in hydroponics culture using a wide range of physiological and biometric measurements. These were integrated with the help of the functional-structural model EcoMeristem, explicitly designed to study interactions between morphogenesis and carbon assimilation. Although the phenotype of the mutant was caused by a single recessive gene, it differed in many ways from the WT, suggesting a pleiotropic effect of this mutation. Phyllochron was 25 (1-4 leaf stage) to 38% (>>4 leaf stage) shorter but showed normal transition from juvenile to adult phase after leaf 4. Leaf size also increased steadily with leaf position as in WT. The mutant had reduced leaf blade length : width and blade : sheath length ratios, particularly during the transition from heterotrophic to autotrophic growth. During the same period, root : shoot dry weight ratio was significantly diminished. Specific leaf area (SLA) was strongly increased in the mutant but showed normal descending patterns with leaf position. Probably related to high SLA, the mutant had much lower light-saturated leaf photosynthetic rates and lower radiation use efficiency (RUE) than the WT. Leaf extension rates were strongly reduced in absolute terms but were high in relative terms (normalised by final leaf length). The application of the EcoMeristem model to these data indicated that the mutant was severely deficient in assimilate, resulting from low RUE and high organ initiation rate causing high assimilate demand. This was particularly pronounced during the heterotrophic-autotrophic transition, probably causing shorter leaf blades relative to sheaths, as well as a temporary reduction of assimilate partitioning to roots. The model accurately simulated the mutant's high leaf mortality and absence of tillering. The simulated assimilate shortage was supported by observed reductions in starch storage in sheaths. Soluble sugar concentrations differed between mutant and WT in roots but not in shoots. Specifically, the hexose : sucrose ratio was 50% lower in the roots of the mutant, possibly indicating low invertase activity. Furthermore, two OsCIN genes coding for cell wall invertases were not expressed in roots, and others were expressed weakly. This was interpreted as natural silencing via sugar signalling. In summary, the authors attributed the majority of observed allometric and metabolic modifications in the mutant to an extreme assimilate shortage caused by hastened shoot organogenesis and inefficient leaf morphology.

Growth analysis of broccoli in relation to fertilizer nitrogen application

SummarySix field experiments with different planting dates over three years in the South of Norway were used to analyse biomass production of broccoli. N was applied at rates of 0, 120, and 240 kg ha–1. Mineralized N levels in soil before planting differed among the experiments. Crop biomass, leaf area index (LAI), and accumulated intercepted photosynthetically active radiation (PAR) increased with enhanced N rate. So did also radiation use efficiency (RUE), but not significantly from 120 to 240 kg ha–1. Thus, crop biomass increased to the highest N rate rather by more intercepted radiation than by enhanced RUE. RUE reached saturation level when the sum of applied N and Nmin in soil before planting was about 200 kg ha–1. There was a strong effect of N application on early plantings, when low temperature and possibly oversaturation of light were the most likely reasons for low LAI, RUE, and RGR at low or no N application. The plant N concentration decreased with increasing biomass over time. Of two alternative relationships of critical N concentration (Nc) suggested by Greenwood et al., the linear one, which gave the higher estimates, fitted better. Both equations were evaluated on the correspondence between a relative N concentration N/Nc = 1 and maximum relative values for: biomass, LAI, accumulated intercepted PAR, and RUE. However, a curvilinear function for Nc might produce a higher correlation over the whole range of plant N concentrations. RUE and accumulated intercepted PAR approached a saturation level at a lower relative N concentration than did biomass and LAI, suggesting that N was more limiting for biomass production than for PAR interception and RUE at N rates below the highest application rate. Incident radiation was fully intercepted at a low LAI, resulting in a low RUE.

Effect of plant density and initial crown size on growth, development and yield in strawberry cultivars Elsanta and Bolero

SummaryThe effects of density (plant spacing) and initial plant size on vegetative growth, flowering and fruiting were studied in the strawberry cultivars Elsanta and Bolero in their first and second years of cropping. The influence of these factors on light use and dry-matter partitioning was investigated. The size of planting material in ‘Elsanta’ and ‘Bolero’ slightly affected plant growth and yield, but this effect was not consistent and radiation use efficiency (RUE) and harvest index were unaltered. Plant spacing did not significantly affect the early stages of crop growth, but was important in determining growth and yield later in the season, this effect being more significant in the second year of cropping. Plant growth and yield per plant increased as plant spacing increased from 20 to 30 cm in both ‘Elsanta’ and ‘Bolero’, but the highest harvest index and yield per square metre were obtained at the closest spacing. Increased plant spacing also resulted in a greater leaf area and leaf area index. However, light was used less efficiently resulting in a lower RUE and lower harvest index (HI).

Radiation-use efficiency in flue-cured tobacco ( Nicotiana tabacum L.): response to nitrogen supply, climatic variability and sink limitations

A field experiment was conducted during 1998 and 1999 with the aim of investigating radiation-use efficiency (RUE) in flue-cured tobacco and its response to nitrogen (N) supply. Three levels of N supply, named as N0, N40, N80, in kg ha −1, were applied to an irrigated crop with pests effectively controlled. Leaf area index (LAI), and aboveground biomass partitioned in leaves and stems, were sampled weekly during the growing seasons. A canopy extinction coefficient ( k) of 0.44 was estimated on the basis of daily values of photosynthetically active solar radiation (PAR) measured above and underneath the canopy in 1999. This value was used for calculating radiation intercepted throughout the growing season for both years. RUE results were characterized by considerable seasonal variations after the removal of inflorescence (topping). However, in 1998 RUE was not significantly influenced by the rate of N fertilization. RUE for the vegetative phase ranged from 2.31 g MJ −1 for the treatment N0 to 2.48 g MJ −1 for the treatment N80 ( P>0.05). After topping, RUE decreased dramatically to 0.74 g MJ −1 for N0 and 0.95 g MJ −1 for N80 ( P>0.05). Since specific leaf nitrogen (SLN) increased during the maturation phase, it is likely that the abrupt RUE reduction reflected sink limitations imposed by topping. Surprisingly, an opposite trend for N response was observed in 1999. RUE for the vegetative phase was 2.02 g MJ −1 for the treatment N0 and decreased to 1.74 g MJ −1 for the treatment N80 ( P<0.05). After topping, RUE ranged from 1.24 g MJ −1 for the treatment N0 to 0.71 g MJ −1 for the treatment N80, although this difference was not statistically significant ( P>0.05). The low pre-anthesis RUE of 1999 was attributed to soil water logging occurred during early crop establishment. It seems likely that higher RUE observed for the treatment N0 was due to variability of water logging conditions within the field rather than to the N treatment. Overall, these variable results provide information on factors affecting RUE. The RUE concept helped to elucidate situations in which the efficient use of solar resources was impaired, especially the important role played by sink limitations.

Effects of nitrogen pre-treatment of transplants from in vitro produced potato plantlets on transplant growth and yield in the field

In vitro propagated potato plantlets, cultivars Gloria and Spunta, were pre-treated with 10 or 40 mg nitrogen per plant before transplanting to the field to determine after-effects of nitrogen on field performance of these transplants in two experiments. Yield, ground cover (GC), accumulated intercepted radiation (AIR), radiation use efficiency (RUE) and harvest index (HI) were assessed. Spunta had higher GC, AIR, total dry matter and tuber fresh and dry weights but lower RUE and HI than Gloria at final harvest. Nitrogen pre-treatment had no clear effect on plant growth at the end of the transplant production phase or during early field growth. Later, higher nitrogen pre-treatment resulted in a slightly higher GC and AIR. In one experiment this resulted in a significantly higher yield. Pre-treatment did not affect HI at the end of the season. Nitrogen pre-treatment can improve seasonal light interception of plantlets of transplant crops from early cultivars.

Estimating Gross Photosynthesis Using Satellite and Ancillary Data: Approach and Preliminary Results

Observations by space-borne sensors can provide photosynthetically active radiation (PAR) intercepted by a canopy (IPAR), which, together with radiation use efficiency (RUE), can be used to estimate carbon assimilation by terrestrial plant communities. Evaluation of biological and environmental factors determining variability of RUE for daily total gross photosynthesis within and among species suggests a biophysically based approach for estimating daily total gross photosynthesis using satellite and ancillary data. Calculations have been done using leaf photosynthesis and canopy characteristics derived from field measurements for six cultivated herbaceous and 12 uncultivated (herbaceous and needle leaf and broadleaf woody) species, and mixed species stands of temperate deciduous forest and tropical moist and dry forests. These data are for 65 canopies, divided about equally between cultivated and uncultivated species, and the leaf area index varies between 0.6 and 9.5. A model for instantaneous canopy photosynthesis, considering sunlit and shaded leaves, variation of maximum rate of leaf photosynthesis within the canopy, and a solution of the radiative transfer equation for propagation of direct and diffuse PAR, is numerically integrated in space (angular variation of radiances and depth within the canopy) and time (diurnal variation) to obtain daily total gross photosynthesis and IPAR for varied incident irradiances. The results show that the maximum rate of leaf photosynthesis and magnitudes of direct and diffuse irradiance incident on the canopy are the major factors determining RUE for unstressed conditions. Also, while woody species on the average have lower RUE, they are found to utilize diffuse radiation more efficiently than cultivated species. Comparison of calculated RUE with observations for 10 cultivated species in varied environment gave differences of −23% to +11% for individual species, but aggregately they have almost equal coefficient of variation (∼25%) and their averages differ by −6% (underestimation). Monthly and annual gross photosynthesis determined using satellite and ancillary data are obtained for rain forest (in Brazil), boreal forest (in Canada), and cropland (in the United States). Annual photosynthesis calculated using satellite data for the three biomes differed from that determined from field measurements by −29% to +15%, averaging to +6%. The above error estimates for RUE and photosynthesis are obtained without calibrating any model parameter.

Nitrogen Stress Effects on Growth and Nitrogen Accumulation by Field‐Grown Tomato

There are few growth studies evaluating within‐season effects of N on vegetative growth and N accumulation of tomato (Lycopersicon esculentum Mill.). Growth analysis of field‐grown tomato for a number of Florida locations and management systems is presented here. Severe N stress resulted in fewer and smaller, but thicker, leaves. With increasing N, average leaf area index (LAI) increased from ≈0.75 to ≈3, but radiation use efficiency (RUE) typically increased less then 30%. Lower RUE under N‐limited conditions reflected a decrease in N concentration of the most recently matured leaves from 40 mg g−1 to as little as 15 mg g−1. Over the life of well‐fertilized crops, leaf N concentrations dropped from 55 to 65 mg g−1 during initial growth to 20 to 35 mg g−1 at final harvest. Corresponding N concentrations for fruit and for stems were 30 to 35 mg g−1 and 15 to 25 mg g−1. Severe N stress affected leaf and stem N concentrations most drastically, whereas N in fruits was less variable. With lower N supply (N &lt; 180 kg ha−1) under careful management, nitrogen use efficiency (NUE) for field‐grown tomato was ≈0.4 Mg fresh fruit (kg N)−1 and average crop N accumulation increased from 37 to 210 kg N ha−1 as N fertilization increased from 0 to 333 kg N ha−1. As a fraction of the fertilizer N applied N fertilizer recovery ranged from 0.36 to 0.74 and 0.61 to 0.96 for drip‐irrigated and subirrigated crops, respectively.

Atmospheric carbon dioxide and fertilizer nitrogen effects on radiation interception by rice 1

In order to predict the potential impacts of global change, it is important to understand the impact of increasing global atmospheric [CO2] on the growth and yield of crop plants. The objectives of this study were to determine the interaction of N fertilization rates and atmospheric [CO2] on radiation interception and radiation-use efficiency of rice (Oryza sativa L. cv. IR72) grown under tropical field conditions. Rice plants were grown inside open top chambers in a lowland rice field at the International Rice Research Institute in the Philippines at ambient (about 350 μmol mol-1) or elevated (about 600 μmol mol-1 during the 1993 wet season and 700 μmol mol-1 during the 1994 dry season) in combination with three levels of applied N (0, 50 or 100 kg N ha-1 in the wet season; 0, 90 or 200 kg N ha-1 in the dry season). Light interception was not directly affected by [CO2], but elevated [CO2] indirectly increased light interception through increasing total absorbed N. Plant N requirement for radiation interception was similar for rice grown under ambient [CO2] or elevated [CO2] treatments. The conversion efficiency of intercepted radiation to dry matter, radiation-use efficiency (RUE), was about 35% greater at elevated [CO2] than at ambient [CO2]. The relationship between leaf N and RUE was curvilinear. At ambient [CO2], RUE was fairly stable across levels of leaf N, but leaf N less than about 2.5% resulted in lower RUE for plants grown with elevated [CO2] than for plant grown at ambient [CO2]. Decreased leaf N with increased [CO2], therefore decreased RUE of rice plants grown at elevated [CO2]. When predicting responses of rice to elevated [CO2], RUE should be adjusted with a decrease in leaf N.

Radiation interception and radiation use efficiency of near-isogenic wheat lines with different height

Three near isogenic lines of spring wheat grown to determine whether Rht dwarfing alleles alter radiation interception. A field study (involving two sowing dates in two growing seasons) with lines containing different allelic dosage of Rht1 and Rht2 (i.e. dwarf, DD; semi-dwarf, SD and tall SH), was conducted without water and nutritional deficiencies. Dwarfing genes did not modify the timing of occurrence of phenological events. Above-ground biomass at anthesis was reduced by 22% in the DD line in relation of the rest of the lines. However, at maturity accumulated biomass of the DD and SH lines were not significant different. Dwarfing genes increased the light attenuation coefficient (k, with values of 0.48, 0.62 and 0.78 for the SH, SD and the DD line respectively). A similar trend was followed to the leaf thickness (estimated by the specific leaf weight, SLW). Despite the differences observed among the lines, both in k and SLW values, they did not differ significantly in the proportion of incoming radiation intercepted by the canopy, nor in the cumulative intercepted radiation during the pre and post-anthesis periods. Radiation use efficiency (RUE) differed significantly among the lines. While RUE during pre-anthesis was the lowest in the DD line, from anthesis to maturity the lines with Rht alleles showed higher RUE values than the SH line. The low pre-anthesis RUE in the DD lines could be associated with (i) poor canopy architecture due to reductions in leaf sheath and internode lengths and/or (ii) reduced canopy CO2 exchange rate. Post-anthesis RUE was lower than that recorded pre-anthesis in all lines. But the magnitude of the reduction was inversely related to the doses of the Rht alleles. Post-anthesis RUE appeared to be closely and positively associated with the number of grains set per unit biomass at anthesis. This relationship suggests a regulatory effect of the sink size on the efficiency of the crop to convert radiation into biomass during this period.

Variation among clonal lines of potato in response to irrigation regimes in an isohyperthermic environment

Potato ( Solanum spp.) tuber yields are limited under hot tropical environments. Three field experiments were conducted in the Philippines to determine the yields of 27 diverse clonal lines with variations in moisture supply. Differences among lines in yield were interpreted in terms of intercepted radiation ( R i) and radiation-use efficiency (RUE). The effects of irrigation regimes on these functions were associated with the maturity classification of the clonal lines. Relative reduction in tuber yield was less for early lines (15%) than for the medium- or late-maturing lines (30–35%). Low moisture supply significantly reduced tuber and total plant dry matter (DM) but not harvest index (HI). The reduction in total plant and tuber DM was attributed to low R i due to the restricted canopy size and accelerated senescence of the canopy and to small RUE tuber. The low RUE tuber (0.30–1.04 g MJ −1), particularly for late, unadapted, lines, was associated with late tuber formation and low HI. The results indicated that a favorable balance between time to tuber formation and achievement of a relatively large and long-lived canopy is important for satisfactory yields under moisture-limiting conditions in hot tropical environments.