The Journal of Agricultural Sciences - Sri Lanka Vol. 17, No 1, January 2022. Pp 148-160 http://doi.org/10.4038/jas.v17i1.9616 Influence of Canopy Architecture on the Light Interception, Photosynthetic and Biomass Productivity in Irrigated Elite Sri Lankan Rice Varieties A.N.M. Mubarak*, Musthapha Mufeeth, M.R. Roshana and A.D.N.T. Kumara Received: 02nd March 2021 / Accepted: 06th November 2021 ABSTRACT Purpose: Canopy light interception and extinction play a crucial role in determining crop yield. Developing new rice varieties with improved canopy architecture along with modified intrinsic photosynthetic mechanisms will ensure the global food security. However, a comprehensive understanding of local rice varieties addressing on such avenues have not been reported. Hence, our pioneering experiments were carried out to elucidate such underlying properties among locally developed two elite rice varieties viz; At-362 and Bg 94-1 grown in the Ampara district of Sri Lanka. Research Method: The field experiment was carried out at the Agro Tech Park, Malwatta (7°20'N and 81°44'E altitude 16.0 m above sea level) between October 2019 to January 2020 implemented with Randomized Complete Block Design with four replicates. The Photosynthetically Active Radiation (PAR) distribution on the above and below canopy level was measured during the pre and post-anthesis stages. Then leaf stomatal conductance, chlorophyll fluorescence parameters and the chlorophyll content were also measured. At harvest, the final biomass produced were compared. Findings: The result revealed that variety At-362 had a higher Leaf Area Index (LAI) of 2.64 at pre anthesis and tend to decline at the latter part of their growth cycle. The striking feature was the extinction coefficient (k) seems to be much lower (0.47) in the At-362 variety than the Bg 94-1 (0.60) depicting that the former has produced vertical leaves (erect-leaf type) while the latter tends to produce horizontal leaf plans in the canopy. Hence, light attenuation was high and eventually, the bottom canopy layer received much lower PAR. Furthermore, LAI had a strong negative correlation with understory PAR indicating that the canopy architecture with an improved light interception will lead to permit more light penetration and utilization through the improved quantum yield efficiencies than the horizontal canopies. Hence significantly (p<0.05) improved above-ground biomass and panicle weight were observed in At-362. Originality/value: This experiment depicts that rice yield could be further improved through introgression of canopy architectural features along with improved photosynthetic traits. Keywords: Canopy architecture, extinction coefficient, leaf area index, rice INTRODUCTION Rice (Oryza sativa L.) belongs to the Poaceae consumption was around 122 kg per person/year family, is one of the most important cereal crops in 2017 (Food and Agriculture Organization, and acts as the primary source of staple food for 2017) which contributes 45 % of the total calories. more than half of the global population. Asian continent contributes approximately 90% of the world’s rice production and is a staple meal * Department of Biosystems Technology, Faculty of Technology, for 2.7 billion people worldwide (Food and South Eastern University of Sri Lanka, University Park, Oluvil # 32360, Sri Lanka Agriculture Organization, 2018). Rice is a major anmubarak@seu.ac.lk portion of the Sri Lankan diets and the per capita https://orcid.org/0000-0002-1703-8609 148 Open Access Article The Journal of Agricultural Sciences - Sri Lanka, 2022, Vol. 17 No 1 According to the national statistics, 1,116,933 ha simplified canopy light distribution model has of land were under paddy cultivation and the 3 led to develop other models viz canopy multi- ½ month varieties were the most popular among layer models (Monteith, 1965), the spherical farmers and account for 77 % adaptation. Among leaf angle distribution model to describe those, the irrigated rice variety, At-362 contributes canopy photosynthesis and crop Radiation Use 198,001 ha (17.73%), while the Bg 94-1 was Efficiency (de Pury and Farquhar, 1997) and 3D cultivated in 37,658 ha (3.37%) respectively plant architecture model (Roupsard et al., 2008). (DOA, 2020). In terms of rice production, Ampara district is one of the popular rice growing The leaf area and the Leaf Area Index (LAI) can regions in Sri Lanka and a total of 136,036 ha be viewed as one of the main components in of paddy was cultivated predominantly with the assessing the above mentioned crop models. LAI At-362 and Bg-94-1 (DOA 2020) owing to their is the ratio of the total, onside leaf surface area improved agronomic and yield characteristics. of the canopy and the ground area corresponding At-362 produces red long grains with an average to below canopy. Measuring LAI is vital for both plant height of 66.3 ± 1.2 cm, whereas Bg 94-1 is farmers and plant scientist to monitor the growth a white long grain characterized with an average and the wellbeing of the plants (Murchie et al., plant height of 56.58 ± 1.7 cm (Begum et al., 2009). Several methods have been developed to 2018; Department of Agriculture (DOA), 2020). measure LAI including the direct contact method, passive optical method and active remote sensing Crop yield is predominantly determined by the methods. Directed techniques are relatively ability of capturing of resources by the canopies laborious and time-consuming and destructive (e.g., light, water, and nutrients), the ability for sampling is not necessarily feasible in small conversion of resources into biomass and the plot experiment. Sampling in indirect leaf area extent of partitioning of biomass into harvesTable measurement such as using ceptometer (non- 0product (Wu et.al ., 2015). Particularly for destructive passive optical method) is widely rice, the optimized solar radiation, temperature, used in analyzing LAI and is widely recognized a balanced fertilizer, and water availability are in the scientific communities and have been important at pre and post anthesis stages to applied in large fields (Pokovai and Fodor, 2019). ensure increased final biomass and grain yield According to the previous findings, the variation production (Fageria, 2007; Khalifa, 2009). in crop productivity and growth is closely linked to the amount of intercepted radiation, primarily As such, photosynthetically active radiation determined by the leaf area index (LAI) (Ewert, (PAR) is a critical natural resource, essentially 2004; Ahmad et al., 2009). controls crop production. The amount of daily irradiance (light intensity, duration and quality) Considering those facts, crop modellers have affects rice yield and quality (Ho et al., 2013). proposed that upright leaves, large panicles and The light extinction properties have been well fewer tillers with a deeper root system are the documented in many crop varieties (Azam- ideal structures for rice (Virk, Khush and Peng, Ali and Squire, 2002). The first mathematical 2004). Deeper canopy layers lead to uniformity model was proposed by Monsi and Saeki (1953) of light within the canopy setting and confer on canopy photosynthesis in response to light maximal net photosynthesis (Normile, 1999; attenuation. They demonstrated that under a Falster and Westoby, 2003). Canopy architectural given light climate, stand structures develop to traits include; plant height, number of leaves and maximize canopy photosynthesis. Leaf structure, tillers and leaf traits such as length, width and orientation, and leaf area are the key determinants LAI, are inherently linked to the resulting light of canopy architecture (Hirose, 2005). This robust environment and since the photosynthetic rate is and effective model shows that light attenuation strongly light-dependent (Burgess et al., 2017). is almost exponential in randomly distributed In cereal crops, improvement of leaf-level and crop canopies and further, the common form of canopy photosynthesis hold a great potential the Beer-Lambert equation for light extinction to increase biomass and yield (Murchie et al., was incorporated (Goudriaan, 1977). Hence, this 2009; Song et al., 2016). There by, determining 149 A.N.M. Mubarak, Musthapha Mufeeth, M.R. Roshana and A.D.N.T. Kumara the leaf-level functions considering the role of Experimental Design stomatal physiologies, density, and distribution are paramount as they are closely associated with The field experiment was laid out in randomized gas diffusion into the leaf tissues that determines complete block design to minimize the soil the rates of photosynthesis and transpiration rates fertility variation. Two commercially popular (Lawson and Mathews, 2020). A recent study rice varieties namely At-362 and Bg 94-1 were confirmed that modification of stomatal densities planted with four replicates in each plot sizes of leads to improve leaf-level photosynthesis 5m x 5m. (Yu et al., 2016). However, links between canopy architectural traits and photosynthetic productivity are poorly understood for the field Field Measurements grown rice varieties in Sri Lanka. In recent studies, it has been found that the irrigated rice Plant physiological parameters were carried out variety, At-362 produced superior biomass and to quantify the traits during the pre and post- grain yield than the Bg 94-1 (Begum et al., 2018), anthesis stages of rice varieties. The pre-anthesis though a comprehensive understanding for such measurements were focused at 50-55 days after observation has not been reported. As such, this field planting while the post-anthesis at 70-75 study hypothesized that elite rice varieties might days. Leaf stomatal conductance was measured have altered light interception and extinction on 10 randomly selected plants per treatment properties that may lead to vary in biomass at the widest part of flag leaves employing leaf production. porometers (SC-1, Decagon Devices Inc, USA). Before taking measurements, the instrument was Therefore, the present study was carried out to calibrated each time according to instructions explore the relationship between light extinction, given by the manufacturer under a different set photosynthetic and biomass characteristics of At- of environmental conditions to ensure accurate 362 and Bg 94-1 locally developed irrigated rice measurements. varieties in Sri Lanka. A ceptometer (LP- 80, AccuPAR, Meter Group Inc, USA) was used to measure the above (I0) and below canopy (I) photosynthetically active MATERIALS AND METHODS radiation (PAR). Before the field measurements, The field trial was carried out between October the parameters such as the latitudes (7.3°N), 2019 to January 2020 at the Agro Tech Park, longitudes (81.7°E) were manually fed to the Malwatta (7°20'N and 81°44'E altitude 16.0 m instrument and the leaf distribution was set at above sea level) managed by the South Eastern 1.00. Then the calibration was performed as per University, located in the Ampara district of Sri the manufacturer’s instruction on an hourly basis. Lanka. Agro-ecologically, this experimental site The external PAR sensor was used to measure is classified under the dry zones (DL 2b, Natural the above canopy light intensity, while the below resource management centre, Department of canopy light levels were taken at 5 cm above Agriculture, 2017) characterized with sandy the ground level using the ceptometer probes loam soils which typically receive an annual (Pokovai and Fodor, 2019). Here, at least 8-10 rainfall of 1600mm, predominantly through the measurements per plot were made during the north-east monsoon (October-December). To cloudless clear sky to minimize the proportion explore the climatic data for this experimental of diffuse radiation into the plant canopy. Each site, nine-year meteorological data were PAR values were measured by placing the probe collected (between 2010 and 2018) from the parallel and perpendicular positions to the crop 2 regional meteorological station (Pottuvil) of rows, by which scanning approximately 0.6 m the Department of Meteorology of Sri Lanka. of canopies. Subsequently, calculated the mean monthly Based on the ceptometer readings, the Leaf Area rainfall (RF), temperature and relative humidity Index (LAI) was estimated based on the ratio (RH) received at the experimental site. of two PAR levels. Moreover, light extinction 150 The Journal of Agricultural Sciences - Sri Lanka, 2022, Vol. 17 No 1 coefficients (k) for radiation was calculated by RESULTS AND DISCUSSION employing equation (1) as previously described by Monsi and Saeki (1953). Here the L represents Based on the meteorological data (2010- the LAI of a particular crop canopy. 2018), the annual mean rainfall received at the experimental site was 1,525.6 ± 33.4 mm I / Io = e −kL whereby it was distributed unevenly among the months. Typically, rainfall increases at the onset Then to find the k values for each rice crop of September, then reaches peak in December. canopies, graphs were plotted with ln (I/Io) Thereafter, a sharp decline was seen until April, against LAI which determines the architecture then mild rainfall (75.0 mm) received in May of crop canopies (Azam-Ali and Squire, 2002). (two peaks). This was true for the year 2019/2020 Then the fraction of radiation intercepted by cultivation as our field trials were carried out the crop canopy (f) was calculated from the between October to January (typically Maha knowledge of L (equation 2). season) that assured sufficient precipitation was f =1− e(−kL) received through the North-Eastern monsoon (Annexure 1). Before the initiation of the trial, the Moreover, the morphological characteristics tillage operations were performed in September including the dimensions (length and width) of with the aid of irrigation water received through five flag leaves (FL) and the penultimate leaves local agricultural tanks. (leaf positioned just below the FL) per treatment were recorded. Then the actual leaf area of those The mean air temperatures were calculated leaves was measured using a handheld leaf area from the minimum and maximum temperatures meter (LI-3100C, Lincoln, USA). Subsequently, from meteorological data. The annual mean the amount of chlorophyll presented in the temperature for the experimental site was flag leaves was quantified using SPAD meters 30.3 ± 0.5 0C, here the highest temperatures (SPAD 502 plus Chlorophyll Meter, Spectrum were recorded between May to July while the technologies Inc, USA). Following this, temperature slightly declined towards October. the quantum yield was measured using the Hence, comparably reduced rates of evaporation chlorophyll fluorescence technique (FluroPen from soil and transpiration from the plant FP-100 Photon Systems Instruments, Czech canopies are expected during the crop vegetative Republic) in both the light- and the dark-adapted and reproductive growth. flag leaves. At harvest, the biomass production was compared Light penetration through the crop canopy by employing a quadrate of 0.5 m × 0.5 m to collect plant samples from the field (0.25 m2). During the field measurement at the pre anthesis Then they were separated into panicle and straw stage, the mean above canopy PAR of At-362 parts before the samples were placed in a dry and Bg 94-1 were 2197.6 ± 27.7 μmolm-2s-1 oven at 80°C until constant dry weights were and 1770.8 ± 42.8 μmolm-2s-1 (Table 01). Here, obtained. From those readings, the above-ground the variety At-362 received a significantly (F1,59 dry matter (AGDM) and harvest index were = 10.879; p = 0.002) lower amount of PAR at calculated. The data generated from the above ground levels (574.8 ± 39.9 μmolm-2s-1) than the experiments were analyzed using SAS (version Bg 94-1. Hence, the present results indicated 9.1.3) software package. Prior to this, the data that the extinction of light levels significantly mentioned here met the assumption of constant (F1,59 = 52.155; p = 0.0001) vary between the rice variance and normal distribution of residuals. canopies. Then the ANOVA was performed to test the differences between varieties at a 5 % significant This implies that 73.4% of light had been -2 -1 level. Further, a correlation matrix was used to diminished (1613 ± 29.7 μmolm s ) and utilized investigate the relationships between ln (I/Io) by the canopy in the former, while in the latter and LAI. was 67.5% (Table 01). However, this scenario 151 A.N.M. Mubarak, Musthapha Mufeeth, M.R. Roshana and A.D.N.T. Kumara has significantly changed in the post-anthesis while the latter counterpart tends to possess leaf stage which had a reduced amount of light, as blades with the horizontal plan. light had been absorbed by the At-362 canopy (40.4 %) and Bg 94-1(41.4% ) respectively, Theoretically, a low k indicates that much though, insignificant changes were seen at this radiation can reach the bottom of the canopy. stage. When compared the LAI, variety At-362 Conversely, a high k represents little radiation that produced significantly (F = 6.783; p = 0.01) can be penetrated the understory of the canopy. 1,59 higher LAI of 2.64 at pre anthesis stage while Theoretically, k is dependent on the leaf inclined in the counterpart Bg 94-1 variety produced angle (α) and solar zenith angle (θ) (Campbell, much lower (2.20). With canopy age, the LAI 1986). This scenario was much pronounced had substantially reduced in both varieties at at the post-anthesis stage at 70 days after field post anthesis stage, a lower LAI was noticed. planting. Both varieties had displayed lower According to Beer-Lambert’s light extinction k-values (0.13 and 0.20 respectively) indicating theory, the attenuation of light depends on the that leaves inclined further vertically when the arrangement of canopy architecture. A crop with crop canopies at their latter stages. Moreover, narrow and erect leaves tends to have lower Zhang et al. (2014) found that horizontal leaves k-values than a crop with more horizontally commonly possess a k-value of 0.7–1.0, whereas displayed leaf arrangement (Azam-Ali and vertically inclined leaves give 0.3–0.5. Squire, 2002). Our findings are in line with the study of San- To find out of k-values of each crop strands, oh et al., (2006) who found the k value of rice graphs were constructed which showed a linear in the ranges of 0.5 – 0.7, conversely, a higher k negative relationship between the natural log indicates that only a little radiation can penetrate scale of radiation transmission (ln (I/Io)) and the understory of the canopy (Chang et al., 2019). LAI at pre and post-anthesis stage (Fig 1a & b). Further, the PAR absorption rate of the canopy The extinction coefficient (k) value of At 362 was is impacted by leaf orientation, sun elevation in relatively smaller (kAt = 0.48) while, the variety the sky (Nobel, Forseth and Long, 1992). Thus, Bg 94-1 remained at increased values (k = 0.59). the increased k value have knock-on effects by Bg This evidence depicts that the former rice variety creating mutual shading in the corresponding leaf possessed vertically arranged leaves (erect type), when flatter canopy architecture has prevailed. Table 01: Amount of light (PAR) received at above and below canopy levels, PAR extinction and LAI characteristics at pre and post-anthesis stages of At-362 and Bg 94-1 rice cultivars Variety Measuring -2 -1 Amount of PAR % of PAR Stage PAR levels (μmolm s ) extinction (μmolm-2s-1 ) extinction LAI Above canopy Below canopy Pre-anthesis 1770.8 ± 42.8 672.5 ± 29.71 1195.9 ± 65.2 67.5% 2.22 ± 0.13 Bg 94-1 Post-anthesis 1953.5 ± 26.9 1144.9 ± 16.3 808.6 ± 34.5 41.4% 2.00 ± 0.08 Pre-anthesis 2197.6 ± 27.7 574.8 ± 39.9* 1613.3 ± 29.7* 73.4%* 2.64 ± 0.11* At-362 Post-anthesis 2032.1 ± 42.4 1230.8 ± 19.3 820.7 ± 44.3 40.4% 1.95 ± 0.05 The symbol (*) indicates significant differences between pre and post anthesis stages of rice cultivars (p-value < 0.05). The values correspond to the means of each parameter ± SE. 152 The Journal of Agricultural Sciences - Sri Lanka, 2022, Vol. 17 No 1 Figure 01a: Relationship between canopy In(I/ Figure 01b: Relationship between canopy In(I/ I0) and LAI at pre-anthesis stage I0) and LAI at post-anthesis stage of Bg 94-1 and At 302 rice varieties. of Bg 94-1 and At 302 rice varieties. Furthermore, the fractional interception of The measurements on leaf dimensions were radiation intercepted by the crop canopy (f) was performed (Table 02) and revealed that the At- estimated. It was found in Bg 94-1 (fBg at pre- 362 variety had produced a larger flag leaf length anthesis stage = 0.73, fBg at post-anthesis stage of 33.51 ± 0.80 cm and width (11.20 ± 0.30 mm) = 0.33) while similar values were observed in and confirmed these produced increased leaf At 362 (fAt at pre-anthesis = 0.72, fAt at post- size than the Bg 94-1 variety. When compared anthesis = 0.21). However, it was interesting the leaf area using LI-3000C porTable 0leaf area to note that k values of At-362 were lower, as a meter, it was revealed that the At-362 possessed a result the occurrence of light interception within significantly (F1,39 = 5.639; p = 0.024) increased the canopy tent to absorb more due to its erected flag-leaf area (33.66 ± 2.11 cm2) than the leaf nature. Pradhan et al. (2018) propose that counterpart. Though, as it was outlined earlier, when intercepted radiation is higher, that had the k-value for At-362 was lower and thus implies directly increased the photosynthetic rates when an erect type leaves with greater leaf areas appear other plant growth factors remain in optimal to provide an increased photosynthesis surface. conditions, it will eventually improve the above- Conversely, the penultimate leaf traits in both ground biomass production. rice varieties remained the same, as this shows an important role of flag leaves at a flowering To explore how canopy architecture influences stage that can convert photosynthates into useful photosynthesis and light interception at the biomass production. whole canopy level, the correlation between the LAI and PARBelow was carried out and found The trial further compared the chlorophyll strong correlation at both stages of the tested rice contents among the flag leaves, both rice varieties varieties (Fig.2). This indicates the importance had increased chlorophyll content (>37.0 SPAD of maintaining the higher leaf canopies with the values) but no significant difference was seen arrangement of the leaves. Our finding is in line among them (Table 03), implying that both with previous work where the total canopy light rice varieties had sufficient Nitrogen nutrients interception is negatively correlated to measure to synthesize chlorophyll molecules and other LAI at both growth stages (Burgess et al., 2017). photosynthetic related proteins as to perform Increasing LAI within a canopy could increase light-dependent and independent reactions the PAR interception by crop in a productive successfully in the chloroplasts. Here, the supply manner, while this becomes true when the leaf of a sufficient amount of nitrogen will ensure arrangement on the main culm and the plan area the persistence of enzyme rubisco for catalyzing are arranged in optimum positions to enhance carbon acceptor molecule in the Calvin cycle light penetration further deeper into the canopy. (Taiz et al., 2015). 153 A.N.M. Mubarak, Musthapha Mufeeth, M.R. Roshana and A.D.N.T. Kumara Figure 02: Relationship between leaf area index (LAI) and below canopy PAR (PARBelow) (a) Pre-anthesis of Bg 94-1 (b) Post-anthesis of Bg 94-1 (c) Pre-anthesis of At-362 (d) Post- anthesis of At-362. The r indicates the relationship between LAI and PARBelow. The R2 indicate the portion of the total variability that is explained by the fitted linear model. Table 02: Leaf morphological traits and the actual leaf area of At-362 and Bg 94-1 varieties Rice cultivar Leaf morphological traits At-362 Bg 94-1 Flag leaf area (cm2) 33.66 ± 2.11* 23.26 ± 1.88 Penultimate leaf area (cm2) 32.18 ± 1.52 27.56 ± 2.04 Flag leaf length (cm) 33.51 ± 0.80 32.56 ± 1.59 Flag leaf width (mm) 11.20 ± 0.30 10.75 ± 0.42 Penultimate leaf length (cm) 39.40 ± 0.89 37.39 ± 1.41 Penultimate leaf width (mm) 9.55 ± 0.34 9.30 ± 0.36 The symbol (*) indicates significant differences between rice cultivars (p value < 0.05). The values correspond to the means of each parameter ± SEM, (n=20). 154 The Journal of Agricultural Sciences - Sri Lanka, 2022, Vol. 17 No 1 Table 03: Quantum yield, leaf chlorophyll content and stomatal conductance of At-362 and Bg 94-1 varieties Rice cultivar Measured parameter n At-362 Bg 94-1 Quantum Yield 0.68 ± 0.01* 0.65 ± 0.01 20 Chlorophyll content (SPAD value) 37.81 ± 0.94 37.19 ± 2.02 20 Stomatal conductance (μmol m-2 s-1) at pre-anthesis 2229.7 ± 102.5* 2632.7± 59.2 40 Stomatal conductance (μmol m-2 s-1) at post-anthesis 723.2 ± 20.2* 2436.9 ± 93.6 40 The symbol (*) indicates significant differences between rice cultivars (p-value < 0.05). The values correspond to the means of each parameter ± SE. Moreover, when compared the quantum yield The flag leaf stomatal conductance (gs) of At- (Qy) in flag leaves, the variety At-362 had 362 displayed significantly lower than Bg 94-1 displayed significantly (F1,59 = 8.447; p = 0.005) at both pre anthesis stage (F1,79 =16.254; p = higher Qy than the Bg 94-1 indicating that the At- 0.000) and post anthesis stage (F1,79 =411.701; 362 had possessed an improved photosynthetic p = 0.000) (Table 03). The lower stomatal efficiency to capture the light photons then to conductance featured in cereal crops may indicate convert them to useful photosynthetic products the drought tolerance characteristics (Lawson as glucose. Hou et al. (2017) claim that the ratio and Mathews, 2020), thereby At-362 variety of the number of photons emitted to the number might possess inherently superior morphological of photons absorbed and considered as a measure and photosynthetic properties than the Bg 94-1 of photosystem II efficiency (PS II). Thus, the variety. At-362 can intercept lighter quantum, which can serve as the driving force to the light-dependent At harvest, the mean above-ground biomass photosynthetic reactions and the subsequent per unit land area (AGDM) was measured light-independent reactions that involve in the by considering their shoot weight. The mean Calvin-Benson cycles. This observations are AGDM for At-362 was significantly higher particularly important to PS II embedded in the (F1,37 = 21.463; p = 0.000) and produced 1302.3 -2 thylakoid membrane where the absorbed photons ± 153.5 gm whereas the Bg 94-1 variety had -2 are utilized for the splitting of water molecules 897.8 ± 61.5 gm (Figure 03.a). This confirms which essentially produces the H+ ions to the improved canopy architectural traits along initiate ion gradient within the thylakoid lumen with photosynthetic characteristic had led of chloroplasts (Taiz et al., 2015; Hou et al., to display an increased capacity for biomass 2017). This phenomenon may be further useful production. This confirms the previous study that in the production of sufficient ATPs and NADPs , the variety At-362 produced with significantly generated in the former stage and be useful in higher biomass and panicle weight than the Bg the Calvin and Benson cycle. Here, the initiating 94-1 (Begum et al., 2018). The harvest index was molecule RuBP accepts CO in the presence of compared by measuring the ratio between panicle 2 catalyst Rubisco enzymes to follow the remainder weight and AGDM per unit land area from the process that may lead to a substantial sucrose trials. When compared, the harvest index of production. Once a sufficient amount of sucrose both varieties had displayed above 0.51, which is produced in the day time, while in the dark, confirms that both varieties are well improved it triggers efficient carbohydrate metabolism for commercial cultivation, typically for the dry within the cytosols (Murchie et al., 2009; Taiz zone in Sri Lanka. However, when the 100-grain et al., 2015) so as the larger amount of starch is weight was analyzed, no significant differences stored in the sinks (spikelet) that certainly will were observed. This reveals that At-362 could improve biomass and grain yield. have produced more grains per panicle than the other variety. 155 A.N.M. Mubarak, Musthapha Mufeeth, M.R. Roshana and A.D.N.T. Kumara Figure 03: Dry matter production in two rice varieties. (a) Above-ground dry biomass (AGDM) and panicle dry weight (n = 22) (b) Dry weight of 100 grains of two varieties (n = 5). Error bars indicate the standard error of the mean. The symbol (*) indicates significant differences between rice cultivars (p-value <0.05). Thereby, rice yield can be increased by size and weight of panicle characteristics, and employing cultivars with superior morphological the ability of efficient dry matter partitioning and physiological characteristics while within the canopy. The source size particularly maintaining an optimal cultural practice in the the LAI, productive tiller numbers have a direct cropping fields. This ensures the plant growth impact on the sink size viz; spikelet numbers and development of aerial and underground per panicle, chiefly determined by canopy light parts through which efficient utilization of solar distribution, availability of water, and the supply radiation, water and nutrients can take place (Wu of required nutrients (Singh et al., 2003; Assuero et al., 1998; Miah et al., 2004). Moreover, the and Tognetti, 2010). Considering the above facts, conversion of solar radiation into useful biomass the crops grown in the present field trial had the production also dependents on the contribution optimum growth condition, thus the variations of canopy architecture, leaf-level photosynthesis in the morphology, physiology and biomass and minimizing photo-oxidative stress exerted are attributed due to their genetic inheritance by individual leaves (Murchie et al., 2009). It characters. has been reported the canopy architectures and the harvesting index for most cereals have been plateaued and novel avenues have been suggested CONCLUSIONS by altering the photosynthesis properties of leaves and the canopies (Sheehy et al., 2008). Based on Canopy architecture primarily determines the this expectations, numerous experiments have amount of light (PAR) interception and extinction been conducted to alter the conventional C3 by crops that permits optimized photosynthesis photosynthesis mechanisms possess within rice and biomass production. Here, we showed the plants through mutational treatments (Nagoor, crop canopy architecture can be identified based 2013), by altering the leaf vein counts (Smillie et on the light extinction coefficient (k), in fact, lower al., 2012; Feldman et al., 2017) and even through k-values depict the upright leaf architecture (At- genetic modification. However, most of the 362) and an increased k represents the horizontally previous attempts in converting C3 rice plants into arranged leaves (Bg 94-1). Furthermore, this an efficient C4 photosynthetic mechanism remain study showed that photosynthetic performance a challenge owing to the complex anatomical and is determined by the factors other than canopy physiological modifications that are required. architectural traits, and an increased quantum yield with optimized stomatal conductance for Overall, the biomass and the harvest index in rice rice enhances carbon gain. This observation has crops give rise from the dry matter accumulation, some profound implications for the improvement yield components particularly the number, of canopy photosynthesis and resource use 156 The Journal of Agricultural Sciences - Sri Lanka, 2022, Vol. 17 No 1 efficiency in crops. First, that farmers in the ACKNOWLEDGEMENT dry zone areas are advised to use upright leaf architecture with improved rice varieties (such The authors wish to thank the farm supervisor as At-362) to ascertain productivity even though Mr. Y. B. Mohamed Kamil for his valuable crops are exposed to harsh environmental support throughout this field trial at AgroTech temperature. Second, the present study explores Park Malwatta, Department of Biosystems the future avenues of employing state-of-the- Technology, Faculty of Technology, South art technologies aided with the ceptometers, Eastern University of Sri Lanka. Further, we chlorophyll fluorescence technologies, thank to technical officers and lab attendants porometers and instantaneous chlorophyll of Department of Biosystems Technology who measurements will elucidate the underlying provided the valuable support for the laboratory morpho and physiological mechanisms within analysis of this study. plant canopies and identifies rice plants confers with improved canopies and a cellular level photosynthetic process to ensure sustainable food production. REFERENCES Ahmad, A., Iqbal, S., Ahmad, S., Khaliq, T., Nasim, W., Husnain, Z., Hussain, A., Zia-Ul-Haq, M. and Hoogenboom, G. 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