Canopy Light Extinction Coefficient Research Articles

Factors influencing the variation in canopy light extinction coefficient (k) among pisifera parents of two oil palm origins

Summary The canopy light extinction coefficient (k) is defined as the exponential decline in the amount of light passing through the leaf layers as a function of leaf area index (LAI). This definition is standard in oil palm breeding trials and models of canopy photosynthesis, where k is sometimes assumed to have a fixed value. The present experiment aims to validate the alleged constancy of k. Therefore, k was inferred from the fractional transmission of photosynthetically active radiation (PAR) and LAI, as obtained from dura x pisifera test crosses of Nigeria and Ghana pisifera origins. The palms were planted at two densities (135 and 160 palms ha−1) in North Sumatra in 2010. At the age of 7.5 years after planting, the area of newly opened leaves approached a maximum. Transmission of PAR remained very low and was only weakly related to k. By contrast, LAI exerted a strong negative effect on k, which generated, under both densities, considerable differences in k between both origins and among pisifera within an origin. The assumption of applying a fixed k value for a certain genotype or palm density, as obtained during leaf expansion at closed canopy, may therefore not be realistic. The present study suggests that the relationship of k with LAI over time merits further investigation, starting just before canopy closure.

Growing-season carbon budget of alpine meadow ecosystem in the Qinghai Lake Basin: a continued carbon sink through this century according to the Biome-BGC model

BackgroundThe alpine meadow is one of the most important ecosystems in the Qinghai-Tibet Plateau (QTP), and critically sensitive to climate change and human activities. Thus, it is crucial to precisely reveal the current state and predict future trends in the carbon budget of the alpine meadow ecosystem. The objective of this study was to explore the applicability of the Biome-BGC model (BBGC) in the Qinghai Lake Basin (QLB), identify the key parameters affecting the variation of net ecosystem exchange (NEE), and further predict the future trends in carbon budget in the QLB.ResultsThe alpine meadow mainly acted as carbon sink during the growing season. For the eco-physiological factors, the YEL (Yearday to end litterfall), YSNG (Yearday to start new growth), CLEC (Canopy light extinction coefficient), FRC:LC (New fine root C: new leaf C), SLA (Canopy average specific leaf area), C:Nleaf (C:N of leaves), and FLNR (Fraction of leaf N in Rubisco) were confirmed to be the top seven parameters affecting carbon budget of the alpine meadow. For the meteorological factors, the sensitivity of NEE to precipitation was greater than that to vapor pressure deficit (VPD), and it was greater to radiation than to air temperature. Moreover, the combined effect of two different meteorological factors on NEE was higher than the individual effect of each one. In the future, warming and wetting would enhance the carbon sink capacity of the alpine meadow during the growing season, but extreme warming (over 3.84 ℃) would reduce NEE (about 2.9%) in the SSP5-8.5 scenario.ConclusionOverall, the alpine meadow ecosystem in the QLB generally performs as a carbon sink at present and in the future. It is of great significance for the achievement of the goal of carbon neutrality and the management of alpine ecosystems.

Incorporating dynamic schemes of canopy light extinction coefficient improves transpiration model performance for fruit plantations

The light extinction coefficient (C) describes the efficiency of light interception by a plant canopy, and is a key parameter commonly used to partition radiant energy between a vegetation canopy and the soil surface in several important transpiration models. The C has been observed to vary considerably in the field, but is often parametrized as a fixed constant value, resulting in large potential uncertainty in transpiration estimation. We hypothesized that C changes with leaf area index (LAI) and environments, and that accurate characterization of the C variation pattern would improve transpiration modelling. To test these hypotheses, the relationships between measured C and potential influencing factors were explored for three different fruit plantations in different climate zones in China. Based on these relationships, a new method was proposed to capture C dynamics that considered both LAI and environmental factors. Additionally, 16 C schemes (15 dynamic C schemes and one fixed C scheme) were individually embedded in the Penman-Monteith model, and comprehensive comparisons were made to determine the most effective C scheme for simulating transpiration based on a Bayesian framework. Results showed that C displayed clear variations across all sites, and that there were significant relationships of C with LAI and environmental factors. Compared with the model using a fixed C scheme, the model using the best dynamic C scheme significantly improved model performance by increasing estimation accuracy and decreasing model uncertainty. Specifically, the average coefficients of determination (R2) increased from 0.35 to 0.76, 0.82 to 0.85, and 0.90 to 0.93 for the orange orchard, the jujube orchard, and the grape greenhouse, respectively. Additionally, the average mean relative errors (MRE) decreased by 54.99%, 26.62%, and 13.95%, respectively, and the average uncertainty band widths (B) decreased by 46.81%, 21.74%, and 11.43%, respectively. Model performance improvement was more significant at sites with more serious environmental stresses. The results of our study emphasize the necessity for considering dynamic C patterns in water consumption estimation, particularly for regions facing severe abiotic stresses that are likely to occur in many regions under future climate conditions.

Sensitivity Analysis of Biome-BGC for Gross Primary Production of a Rubber Plantation Ecosystem: A Case Study of Hainan Island, China.

Accurate monitoring of forest carbon flux and its long-term response to meteorological factors is important. To accomplish this task, the model parameters need to be optimized with respect to in situ observations. In the present study, the extended Fourier amplitude sensitivity test (eFAST) method was used to optimize the sensitive ecophysiological parameters of the Biome BioGeochemical Cycles model. The model simulation was integrated from 2010 to 2020. The results showed that using the eFAST method quantitatively improved the model output. For instance, the R2 increased from 0.53 to 0.72. Moreover, the root-mean-square error was reduced from 1.62 to 1.14 gC·m-2·d-1. In addition, it was reported that the carbon flux outputs of the model were highly sensitive to various parameters, such as the canopy average specific leaf area and canopy light extinction coefficient. Moreover, long-term meteorological factor analysis showed that rainfall dominated the trend of gross primary production (GPP) of the study area, while extreme temperatures restricted the GPP. In conclusion, the eFAST method can be used in future studies. Furthermore, eFAST could be applied to other biomes in response to different climatic conditions.

Sensitivity analysis of Biome-BGCMuSo for gross and net primary productivity of typical forests in China

Process-based models are widely used to simulate forest productivity, but complex parameterization and calibration challenge the application and development of these models. Sensitivity analysis of numerous parameters is an essential step in model calibration and carbon flux simulation. However, parameters are not dependent on each other, and the results of sensitivity analysis usually vary due to different forest types and regions. Hence, global and representative sensitivity analysis would provide reliable information for simple calibration. To determine the contributions of input parameters to gross primary productivity (GPP) and net primary productivity (NPP), regression analysis and extended Fourier amplitude sensitivity testing (EFAST) were conducted for Biome-BGCMuSo to calculate the sensitivity index of the parameters at four observation sites under climate gradient from ChinaFLUX. Generally, GPP and NPP were highly sensitive to C:Nleaf (C:N of leaves), Wint (canopy water interception coefficient), k (canopy light extinction coefficient), FLNR (fraction of leaf N in Rubisco), MRpern (coefficient of linear relationship between tissue N and maintenance respiration), VPDf (vapor pressure deficit complete conductance reduction), and SLA1 (canopy average specific leaf area in phenological phase 1) at all observation sites. Various sensitive parameters occurred at four observation sites within different climate zones. GPP and NPP were particularly sensitive to FLNR, SLA1 and Wint, and C:Nleaf in temperate, alpine and subtropical zones, respectively. The results indicated that sensitivity parameters of China's forest ecosystems change with climate gradient. We found that parameter calibration should be performed according to plant functional type (PFT), and more attention needs to be paid to the differences in climate and environment. These findings contribute to determining the target parameters in field experiments and model calibration.

Genetic control of leaf angle in sorghum and its effect on light interception.

Developing sorghum genotypes adapted to different light environments requires understanding of a plant's ability to capture light, determined through leaf angle specifically. This study dissected the genetic basis of leaf angle in 3 year field trials at two sites, using a sorghum diversity panel (729 accessions). A wide range of variation in leaf angle with medium heritability was observed. Leaf angle explained 36% variation in canopy light extinction coefficient, highlighting the extent to which variation in leaf angle influences light interception at the whole-canopy level. This study also found that the sorghum races of Guinea and Durra consistently having the largest and smallest leaf angle, respectively, highlighting the potential role of leaf angle in adaptation to distinct environments. The genome-wide association study detected 33 quantitative trait loci (QTLs) associated with leaf angle. Strong synteny was observed with previously detected leaf angle QTLs in maize (70%) and rice (40%) within 10 cM, among which the overlap was significantly enriched according to χ2 tests, suggesting a highly consistent genetic control in grasses. A priori leaf angle candidate genes identified in maize and rice were found to be enriched within a 1-cM window around the sorghum leaf angle QTLs. Additionally, protein domain analysis identified the WD40 protein domain as being enriched within a 1-cM window around the QTLs. These outcomes show that there is sufficient heritability and natural variation in the angle of upper leaves in sorghum which may be exploited to change light interception and optimize crop canopies for different contexts.

Beetroot (Beta vulgaris L.) growth and response to N supply – a case study

ABSTRACT There is need for information on the general crop physiology and nitrogen (N) fertiliser responses of beetroot in New Zealand. We investigated the responses to N of beetroot grown in a silt loam near Hastings, Hawke’s Bay. Four fertiliser treatments (0, 160, 320 or 480 kg N ha−1) were applied as urea, split evenly over four application times. The canopy light extinction coefficient averaged 0.64. Radiation use efficiency averaged 1.05 g MJ−1 for the treatments that received N fertiliser. Maximum yield occurred at an N fertiliser rate around 320 kg N ha−1. Published recommendations suggest only 225 kg N ha−1 would have been needed. This underestimation would have led to a yield penalty of only about 6%, but decreased the risk of significant mineral being N left in the soil. We discuss approaches to account for N supply from the soil when forecasting residual mineral N and N leaching risk.

Radiative behavior and canopy light extinction coefficient in a savanna urban area

The knowledge of the radiative characteristics of an area is essential to understanding the flows of matter and energy. The value of the Light Extinction Coefficient (K) is a parameter that describes the efficiency of the interception of light in a given canopy, being required, as input, for several SWAP (Soil-Water-Atmosphere-Plant) models, which allow the characterization of the interactive properties among soil, plant and atmosphere concerning these exchanges of matter and energy. This study aimed to obtain the light extinction coefficient (K) for a savanna fragment located in the urban area of Cuiabá. The used data correspond to one measurement each month, totaling twelve measurements in 30 points during the period from October 2014 to September 2015. The measured variables were the LAI (Leaf Area Index), the photosynthetically active incident radiation (PARinc) and the transmitted radiation (PARtrans), and the calculated ones were the zenith angle (Zh) and the extinction coefficient (K). Was observed an annual variability for the light extinction coefficient between 0.49 and 0.69. There are seasonal changes that interfere with the canopy geometry and the position of the study area in relation to the solar radiation incidence, concluding that the K variability is predominantly temporal.

Variation of parameters in a Flux-Based Ecosystem Model across 12 sites of terrestrial ecosystems in the conterminous USA

Terrestrial ecosystem models have been extensively used in global change research. When a model calibrated with site-specific parameters is applied to another site, how and why the parameters have to be adjusted again in order to fit data well are pervasive yet underexplored issues. In this exploratory study, we examined how and why model parameters of a Flux-Based Ecosystem Model (FBEM) varied across different sites. Parameters were estimated from data at 12 eddy-covariance towers in the conterminous USA using the conditional inversion method. Results showed that optimized values of these parameters varied across sites. For example, the estimated coefficients in the Leuning model, gl and D0, exhibited high cross-site variation, but the ratio of internal to air CO2 concentration (fCi) and canopy light extinction coefficient (kn) varied little among these sites. Parameters greatly varied with ecosystem types at adjacent sites where climate conditions were similar. Five parameters (activation energy of carboxylation, EKc; activation energy of oxygenation, EVm; ecosystem respiration, Reco0; temperature sensitivity of respiration, Q10; and stomatal conductance coefficient, D0) were highly correlated with mean annual temperature and precipitation across sites, which were distributed in different climate regions of conterminous US. Our results indicate that individual parameters vary to different degrees across sites and parameter variation can be related to different biological factors (e.g., ecosystem types) and environmental conditions (e.g., temperature and precipitation). It is essential to further examine magnitudes of and mechanisms underlying the parameter variation in ecosystem models so as to improve model prediction.

On the angular dependency of canopy gap fractions in pine, spruce and birch stands

The angular profiles of canopy gap fraction curves are influenced by canopy structure, and are commonly expected to vary with stand- and crown-level variables such as tree pattern, crown shape and leaf orientation. In this study, measurements of canopy structure, gap fractions and effective LAI in 986 plots of Scots pine, Norway spruce and Silver birch stands in Finland were used to assess how similar the angular canopy gap fraction profiles are for common boreal tree species. The profiles were characterized with help of the shape function ψ(θ), defined as the normalized value of the canopy light extinction coefficient at zenith angle (θ). Variation in ψ(θ) would be induced not only by a non-spherical leaf orientation, but also by differences in the directional clumping indices, such as could result from species-specific differences in crown shape. Our results showed that there is wide variation in the shape of ψ in the individual plots of the three different species. The species-specific mean curves ψ(θ), however, showed relatively small variation with θ, except for a sudden drop at large zenith angles, and the shape of the curves was similar for the different tree species. Results indicate that differences in crown shape of the study species do not significantly affect the angular profiles of canopy gap fraction.

A meta-analysis of the canopy light extinction coefficient in terrestrial ecosystems

The canopy light extinction coefficient (K) is a key factor in affecting ecosystem carbon, water, and energy processes. However, K is assumed as a constant in most biogeochemical models owing to lack of in-site measurements at diverse terrestrial ecosystems. In this study, by compiling data of K measured at 88 terrestrial ecosystems, we investigated the spatiotemporal variations of this index across main ecosystem types, including grassland, cropland, shrubland, broadleaf forest, and needleleaf forest. Our results indicated that the average K of all biome types during whole growing season was 0.56. However, this value in the peak growing season was 0.49, indicating a certain degree of seasonal variation. In addition, large variations in K exist within and among the plant functional types. Cropland had the highest value of K (0.62), followed by broadleaf forest (0.59), shrubland (0.56), grassland (0.50), and needleleaf forest (0.45). No significant spatial correlation was found between K and the major environmental factors, i.e., mean annual precipitation, mean annual temperature, and leaf area index (LAI). Intra-annually, significant negative correlations between K and seasonal changes in LAI were found in the natural ecosystems. In cropland, however, the temporal relationship was site-specific. The ecosystem type specific values of K and its temporal relationship with LAI observed in this study may contribute to improved modeling of global biogeochemical cycles.

SENSITIVITY ANALYSIS OF BIOME-BGC MODEL FOR DRY TROPICAL FORESTS OF VINDHYAN HIGHLANDS, INDIA

Abstract. A process-based model BIOME-BGC was run for sensitivity analysis to see the effect of ecophysiological parameters on net primary production (NPP) of dry tropical forest of India. The sensitivity test reveals that the forest NPP was highly sensitive to the following ecophysiological parameters: Canopy light extinction coefficient (k), Canopy average specific leaf area (SLA), New stem C : New leaf C (SC:LC), Maximum stomatal conductance (gs,max), C:N of fine roots (C:Nfr), All-sided to projected leaf area ratio and Canopy water interception coefficient (Wint). Therefore, these parameters need more precision and attention during estimation and observation in the field studies.

Radiation interception and use by maize/peanut intercrop canopy

The efficient use of solar radiation is one of the major criteria for obtaining a yield advantage through intercropping. Although various combinations of crops have been reported for intercropping systems, the maize/peanut association has yet to be analysed. This report presents the radiation-use efficiency ( ɛ) results of a maize/peanut intercrop study. The experiment constituted three treatments: sole crops of maize and peanut, and a maize/peanut intercrop. The canopy light extinction coefficient ( k) of peanut was reduced while intercropped with maize. The mean ɛ of intercropped peanut (2.13 g(DW) MJ −1) was 79% higher than that of peanut stands alone. The ɛ of combined intercropped stands (3.03 g(DW) MJ −1) was more than two-fold that of sole peanut, but slightly lower than that of maize stands alone (3.27 g(DW) MJ −1). The harvest index (HI) of intercropped peanut was about 13% lower than that of peanut grown alone, but produced 46% of the pods of the latter (299 g m −2), the parameter that represents the true output of this intercropping system. These results suggest that a maize/peanut intercropping would help to increase production through the efficient utilisation of solar energy. A simple model was developed to isolate the daily radiation interception of each of the canopies of the intercrop partners in separate strata, taking into account the alteration of the k of the understorey. The model may also be applicable in agroforestry systems.

Light-use efficiency of native and hybrid poplar genotypes at high levels of intracanopy competition

In southern Wisconsin, U.S.A., tree growth and associated canopy traits were compared among five native and hybrid genotypes of poplar (Populus spp.) in replicated, monoclonal stands planted at a 1 × 1 m spacing. The overall objective of this study was to assess clonal suitability to cultural conditions entailing high levels of intracanopy competition (such as high-density plantations or long rotations) and to identify selection criteria suitable to such conditions. Two of the clones were Populus deltoides Bartr., two were P. deltoides × Populus nigra L. (DN) crosses, and the fifth was a P. nigra × Populus maximowiczii A. Henry (NM) cross. In the third year after establishment, variation in aboveground biomass gain (ANBG) was analyzed in relation to canopy light interception (IPAR) and canopy light-use efficiency (LUE) during a 31-day period when growing conditions were most favorable (late June through late July). ANBG in this interval varied by twofold among genotypes (2.76–5.78 Mg·ha–1), and it was highest in the two P. deltoides clones, followed by the NM and DN hybrids, respectively. Across genotypes, ANBG was unrelated to IPAR, which varied by only 5%. Instead, it was strongly and positively related (r2 = 0.99) to the twofold variation in LUE (1.06–2.22 g·MJ–1). Among measured canopy traits, the best predictor of LUE (r2 = 0.88) was an additive combination of factors associated to the optimization of canopy photosynthesis: LUE was negatively related to both the canopy light-extinction coefficient and compensation irradiance at the canopy base. We infer from these findings that poplar genotypes can vary considerably in LUE and, correspondingly, in the extent to which photosynthesis is optimized in dense canopies. Furthermore, the low LUE among hybrid genotypes at this level of intracanopy competition may reflect a bias in "tree improvement" efforts towards maximizing biomass production under conditions of relatively low competition.

Description of development, light interception and growth of sunflower at two sowing dates and two densities

The relationship between dry matter production and solar radiation interception by plant canopies is well known for several crops including sunflower. The effects of temperature environment on sunflower development have also been subject of much research. However, under seasonal rainfall, management strategies, such as the choice of sowing dates and of plant densities may change crop responses to temperature and radiation, preventing the use of standard relationships. The object of this work is to study the influence of two sowing dates on crop development and two plant densities on light interception and growth of sunflower crops grown on stored soil water in the semi-arid Mediterranean region of southern Portugal. The cultivar “Florassol” was sown at Évora, Portugal on 13 March 1997 (S1) and on 5 May 1997 (S2) and in each sowing date at the densities of 11.4 plants m −2 (D 1) and 4 plants m −2 (D 2). Leaf number, leaf area and above-ground dry matter were measured weekly throughout the crop cycle. Meteorological parameters and canopy light transmission were measured continuously. Crop development was slower in S1 than in S2 because of cooler temperatures during crop cycle in S1 but thermal requirements for each development phase were similar. Temperature, though affecting the duration of phenological phases, did not affect maximum leaf area per plant, which was similar for the same plant density in both sowing dates. For the first sowing, significant differences in dry matter production and light interception were found between the two densities. Crop dry matter production and solar radiation interception were smaller in D 2 than in D 1 owing to a greater leaf area index in D 1, although leaf area and above-ground dry mass per plant were higher in the lower density (D 2). Leaf number, canopy light extinction coefficient and the radiation use efficiency were similar in both densities.

Potential Yield in Carrots (Daucus carota L.): Theory, Test, and an Application

There is little published information on the physiological behaviour of carrots at the crop level. Here we derive and test a simple model for the potential yield of carrot crops. The model calculates green leaf area index (L) using a daily time step. Dry matter production is related linearly to light interception, calculated fromL and canopy light extinction coefficient (k). Two stages of growth are distinguished. In stage 1, leaf expansion on each plant is unaffected by neighbouring plants. Stage 2 commences when L reaches a critical value and the plants start to interact. Compared to stage 1, stage 2 has slower leaf expansion and a k which varies with plant density. Dry matter partitioning between shoots and the storage root depends on L. We calibrated the model for two processing cultivars, ‘Chantenay Red Core’ and ‘Red Hot’, using data from a 1997–98 plant density experiment in Hawke's Bay, New Zealand. The model accounted for 72% of the observed variation in root size and 79% of the variation in yield. We tested the model against results from two experiments in 1995–96 and 1996–97. In both experiments the same two cultivars were sown at three different sowing times. Overall, the model accounted for 72% of the observed variation in root size and 66% of the variation in yield, showing that it is portable to other environments. Finally, we applied the model to interpret the effects of sowing date in these two experiments. Previous attempts were confounded by variation in plants m−2with sowing date. The model allowed us to separate the effects of these factors, and indicated that early sowing substantially benefited yield.

Effect of Radiation Environment on Radiation Use Efficiency and Growth of Sunflower

The level of incident radiation and the proportion of radiation that is diffuse affects radiation use efficiency (RUE) in crops. However, the degree of this effect, and its importance to growth and yield of sunflower (Helianthus annuus L.) have not been established. A field experiment was conducted to investigate the effects of radiation environment on RUE, growth, and yield of sunflower. A fully irrigated crop was sown on an alluvial‐prairie soil (Fluventic Haplustoll) and was exposed to three distinct radiation environments. In two treatments, the level of incident radiation was reduced by 14 and 20% by suspending two different types of polyethylene plastic films well above the crop. In addition to the reductions in incident radiation, the proportion of radiation that was diffuse was increased by about 14% in these treatments. Lower incident radiation and increased proportion of diffuse radiation had no effect on total biomass, phenology, leaf area, and the canopy light extinction coefficient (k = 0.89). However, yield was reduced in shaded treatments due to smaller grain size and lower harvest index. Although crop RUE measured over the entire crop cycle (1.25 g/MJ) did not differ significantly among treatments, there was a trend where RUE compensated for less intercepted incident radiation. Theoretical derivations of the response of RUE to different levels of incident radiation supported this finding. Shaded sunflower crops have the ability to produce biomass similar to unshaded crops by increasing RUE, but have lower harvest indices.

The growth, development and yield of onion (Allium cepaL.) in response to temperature and CO2

SummaryStands of two cultivars (cv. Hysam and Sito) of onion (Allium cepa L.) were grown in the field within polyethylene-covered tunnels along which a temperature gradient was imposed. Pairs of tunnels were maintained at either 374 or 532 µmol mol−1 CO2. The rates of progress from transplanting to bulbing, and from bulbing to harvest maturity, were positive linear functions of mean temperature for each cultivar. At a given temperature, the time of bulbing was earlier, but the duration of bulb growth longer, at elevated compared with normal CO2. Canopy architecture was not affected by CO2, temperature or cultivar; an estimate of 0.25 for the canopy light extinction coefficient was common to all treatment combinations. Radiation use efficiency was greater at elevated compared with normal CO2 in the period up to bulbing, but was the same at both CO2 concentrations during subsequent bulb growth. Total crop dry weight at bulbing was increased by 32–44% due to elevated CO2. Bulb yields at harvest maturity declined with progressively warmer temperatures and to a greater extent in cv. Sito than cv. Hysam. Enrichment with CO2 increased bulb yields by 29–37% and by 35–51% in cvs Hysam and Sito, respectively. From comparison of the temperature rise needed to offset entirely the yield increases of each cultivar due to elevated CO2, it is concluded that current estimates of climate change should be beneficial for bulb onion production, particularly for long-season cultivars.

Effects of CO 2, temperature and their interaction on the growth, development and yield of cauliflower ( Brassica oleracea L. botrytis)

Stands of summer cauliflower were grown within polyethylene-covered tunnels along which a temperature gradient was imposed. Two tunnels were maintained at either normal or elevated CO 2 concentrations. At the last harvest (88 days from transplanting) no interaction between CO 2 and temperature on total biomass was detected. The total dry weight of plants grown at 531 μmol mol −1 CO 2 was 34% greater than those grown at 328 μmol mol −1 CO 2, whereas a 1 °C rise reduced dry weight by 6%. From serial harvests the radiation conversion coefficient was 2.01 g MJ −1 and 1.42 g MJ −1 at 531 μmol mol −1 CO 2and 328 μmol mol −1 CO 2, respectively, but was not greatly affected by differences in temperature. No effect of either CO 2 or temperature on the canopy light extinction coefficient was detected. The rate of progress towards curd initiation increased to a maximum at 15.5 °C, and declined thereafter. Provided the effect of temperature was accounted for, CO 2 enrichment did not affect the time of curd initiation. From serial harvests after curd initiation, the logarithm of curd weight or diameter were negative linear functions of mean temperature from initiation. Increases in curd weight and diameter at 531 compared with 328 μmol mol −1 CO 2 were greater at warmer temperatures (27% at 13 °C compared with 47% at 15 °C, 57 days after initiation). Effects of CO 2 on curd diameter were less than those on curd dry weight because the curd dry matter content was greater at 531 compared with 328 μmol mol −1 CO 2. Thus, the effects of elevated CO 2 concentrations on fresh weight based yield parameters of cauliflower were less than the increase in total dry matter production.

Variation Analysis of Efficiency of Intercepted Radiation Conversion in the Accumulation of Dry Matter by Soybean.

Field experiments were conducted in 1989 on a converted paddy field at Shiga Agricultural Experiment Station (Azuchi, Shiga Prefec.), and in 1990 on an upland field at Shiga Prefectural Junior College (Kusatsu, Shiga Prefec.), in order to investigate stability of efficiency of intercepted photosynthetically active radiation conversion in the accumulation of dry matter (EPAR) by soybean and determine factors which might affect EPAR. In 1989, cultivar 'Enrei' was sown on 3 different dates in various planting patterns, and in 1990, cultivar 'Tamahomare' was grown at various plant population densities. The intercepted PAR and the top dry matter accumulation were in quite close relationship. But it was not always linear over the whole growth duration. EPAR increased in the early growth stage, then, approximately after the canopy closure, it was kept relatively stable or increased slightly until early grain filling period when EPAR began to decline. This time course of EPAR was considered to be resulted primarily from the change of crop photosynthetic activity. But in addition to that, the greater portion of light-saturated leaves at the early stage and the increasing maintenance respiration at the late growth stage also might cause lower EPAR at those stages respectively. Since almost all EPAR values calculated for the period through which those were observed to be stable, were within a small range, from 2.1 to 2.3gMJ-1 in 1989 and from 2.4 to 2.5gMJ-1 in 1990, respectively, due to sowing dates and planting patterns, it was concluded that the ability of dry matter production of soybean crop was not affected considerably by those conditions. Within the small variation of EPAR caused by different planting patterns in 1989, EPAR showed no correlation with N content per unit leaf area, while it showed relatively clear correlation (r=-0.651) with canopy light extinction coefficient KPAR.