Response Of Stomatal Conductance Research Articles

Intact leaf gas exchange provides a robust method for measuring the kinetics of stomatal conductance responses to abscisic acid and other small molecules in Arabidopsis and grasses

BackgroundGuard cells perceive external and internal stimuli and regulate stomatal conductance in plants. With the use of gas exchange analyzers, time-resolved stomatal conductance responses to light intensity, [CO2] concentration and relative humidity changes can be measured. This is more difficult to achieve when measuring stomatal responses to small soluble molecules such as the plant hormone abscisic acid (ABA) or the bacterial peptide flagellin 22 (flg22), in particular when investigating mutants with response phenotypes.ResultsA method to evaluate the dynamic effects of small molecules on stomatal conductance in a time-resolved fashion using gas exchange analyzers is presented here. ABA-induced stomatal closure was investigated by adding ABA to the transpiration stream of intact leaves placed in a microcentrifuge tube containing water. Strong ABA responses were resolved in time- and in a dose-dependent manner in wild-type Arabidopsis leaves, whereas the same response was not observed in leaves of the ABA-insensitive mutant open stomata 1-3 (ost1-3). Moreover, when leaves of the Plasma membrane Intrinsic Protein (PIP) aquaporin quadruple mutant pip1;1 pip1;2 pip2;1 pip2;2 were tested, robust wild-type-like responses to ABA were observed. When the bacterial peptide flg22 was added to the transpiration stream of intact wild-type leaves, a strong flg22-induced stomatal closure effect was observed. Finally, the proposed technique was further developed and optimized for evaluation of stomatal conductance responses to small molecules in leaves of grasses using the reference plant Brachypodium distachyon.ConclusionsDue to the variable size of stomata in Arabidopsis and the limited dynamic response of stomata in isolated epidermal strips, evaluation of the effect of small molecules on stomatal physiology has been challenging and has led in some cases to inconsistent results. Moreover, potential signals from the mesophyll are missing when using epidermal peels to evaluate stomatal aperture responses. Here we propose a less invasive technique which allows for time-resolved measurements of stomatal conductance responses to small molecules optimized for both Arabidopsis and Brachypodium distachyon leaves.

The Response of Plant Photosynthesis and Stomatal Conductance to Fine Particulate Matter (PM2.5) based on Leaf Factors Analyzing

The effects of particles on the photosynthesis of vegetation, which is a sink for fine particulate matter (PM2.5) deposition, are still not well understood. Here, we carried out indoor measurements to evaluate the variation dynamics of net photosynthetic rate and stomatal conductance of four plant species with different leaf characteristics under different PM2.5 levels. Then tree leaves were sampled and the groove proportion, leaf trichome density, stomatal density and stomatal size were quantitatively studied by scanning electron microscopy (SEM). The stomatal conductance of the 4 species had a close positive correlation with photosynthetic rate. Net photosynthetic rate and stomatal conductance declined over time at elevated PM2.5, and the rate of the decline became more rapid with higher concentration of PM2.5. The inhibiting effect might be caused by the closure of the stomata and the decrease of stomatal conductance, which was proved by the reduction of the stomatal size of under the condition of PM2.5 pollution. Leaf trichome and groove seemed to show a protective role for plants from PM2.5 exposure and be responsible for the difference of photosynthetic rate and stomatal conductance under the condition of PM2.5 pollution. The higher groove proportion and the presence of trichomes on the leaf surface in Neolitsea aurata and Lindera kwangtungensis absorbed some particulate matters and buffered the effect of PM2.5 pollution on stomata.

Photosynthetic Characteristics of Individual Strawberry (Fragaria ×ananassa Duch.) Leaves under Short-distance Lightning with Blue, Green, and Red LED Lights

To clarify the response of net photosynthetic rate (Pn), stomatal conductance (gS), transpiration rate (Tr), and leaf intercellular CO2 concentration (Ci) to irradiance on the adaxial and abaxial sides of mature and young strawberry leaves using blue, green, and red light-emitting diodes (LEDs), irradiation from a short distance was investigated using ‘Tochiotome’. Light–photosynthetic response curves of the adaxial side of mature leaves were not different among LED treatments. However, those of the adaxial side of young leaves irradiated with red LEDs were less than those of other LED treatments. Pn of the abaxial side of mature leaves was 42% to 71% of the abaxial side. In young leaves, Pn of the abaxial side was 17% to 68% of the adaxial side. Moreover, light–transpiration response curves were different with LED treatments. Ci and Tr under blue and green LEDs were greater than those under red LEDs. This indicates that blue and green lights affected the stomatal opening. In contrast, red LEDs decreased Ci more than other LED treatments. In addition, reactions of the adaxial side of young leaves under blue and red LEDs were seen not only in ‘Tochiotome’, but also in ‘Sachinoka’ and ‘Eran’, which indicates that the photosynthetic reactions of blue light and red light are common characteristics of the strawberry. Therefore, red LEDs promoted the photochemical reaction and activated the CO2 fixation system. Based on the results of this study of short-distance lighting with LEDs in strawberry production, irradiance of the abaxial side of leaves by blue or green LEDs might improve more assimilates in young leaves compared with red LEDs to increase strawberry yield.

Radiometric Method for Determining Canopy Stomatal Conductance in Controlled Environments

Canopy stomatal conductance is a key physiological factor controlling transpiration from plant canopies, but it is extremely difficult to determine in field environments. The objective of this study was to develop a radiometric method for calculating canopy stomatal conductance for two plant species—wheat and soybean from direct measurements of bulk surface conductance to water vapor and the canopy aerodynamic conductance in controlled-environment chambers. The chamber provides constant net radiation, temperature, humidity, and ventilation rate to the plant canopy. In this method, stepwise changes in chamber CO2 alter canopy temperature, latent heat, and sensible heat fluxes simultaneously. Sensible heat and the radiometric canopy-to-air temperature difference are computed from direct measurements of net radiation, canopy transpiration, photosynthesis, radiometric temperature, and air temperature. The canopy aerodynamic conductance to the transfer of water vapor is then determined from a plot of sensible heat versus radiometric canopy-to-air temperature difference. Finally, canopy stomatal conductance is calculated from canopy surface and aerodynamic conductances. The canopy aerodynamic conductance was 5.5 mol m−2 s−1 in wheat and 2.5 mol m−2 s−1 in soybean canopies. At 400 umol mol−1 of CO2 and 86 kPa atmospheric pressure, canopy stomatal conductances were 2.1 mol m−2 s−1 for wheat and 1.1 mol m−2 s−1 for soybean, comparable to canopy stomatal conductances reported in field studies. This method measures canopy aerodynamic conductance in controlled-environment chambers where the log-wind profile approximation does not apply and provides an improved technique for measuring canopy-level responses of canopy stomatal conductance and the decoupling coefficient. The method was used to determine the response of canopy stomatal conductance to increased CO2 concentration and to determine the sensitivity of canopy transpiration to changes in canopy stomatal conductance. These responses are useful for improving the prediction of ecosystem-level water fluxes in response to climatic variables.

Dynamic leaf energy balance: deriving stomatal conductance from thermal imaging in a dynamic environment.

In spite of the significant progress made in recent years, the use of thermography to derive biologically relevant traits remains a challenge under fluctuating conditions. The aim of this study was to rethink the current method to process thermograms and derive temporal responses of stomatal conductance (gsw) using dynamic energy balance equations. Time-series thermograms provided the basis for a spatial and temporal characterization of gsw responses in wheat (Triticum aestivum). A leaf replica with a known conductance was used to validate the approach and to test the ability of our model to be used with any material and under any environmental conditions. The results highlighted the importance of the co-ordinated stomatal responses that run parallel to the leaf blade despite their patchy distribution. The diversity and asymmetry of the temporal response of gsw observed after a step increase and step decrease in light intensity can be interpreted as a strategy to maximize photosynthesis per unit of water loss and avoid heat stress in response to light flecks in a natural environment. This study removes a major bottleneck for plant phenotyping platforms and will pave the way to further developments in our understanding of stomatal behaviour.

Stomatal conductance responses to evaporative demand conferred by rice drought-yield quantitative trait locus qDTY12.1.

Rice quantitative trait locus (QTL) qDTY12.1 is a major-effect drought yield QTL that was identified from a cross of Vandana (recipient parent) and Way Rarem (donor parent) through breeding efforts to improve rice yield under upland drought stress conditions. The two main physiological effects previously observed to be related to the presence of qDTY12.1 were (i) increased lateral root growth, and (ii) increased transpiration efficiency. Since relatively more progress has thus far been made on characterising the lateral root growth response related to qDTY12.1, the present study focussed on characterising how qDTY12.1 confers higher transpiration efficiency under upland drought stress in the Vandana background. In a series of field experiments in which stomatal conductance was measured across different times of day in four qDTY12.1 near isogenic lines (NILs), the NILs and Way Rarem showed consistently higher stomatal conductance than Vandana under conditions of low vapour pressure deficit (VPD) and low photosynthetically active radiation (PAR), and consistently lower stomatal conductance than Vandana under high VPD and high PAR. Leaf δ18O was higher in the qDTY12.1 NIL than in Vandana, and although this trend was previously observed for leaf δ13C it appeared to be more consistent across measurement dates and treatments for leaf δ18O. The qDTY12.1 NILs and Way Rarem tended to show greater large vein to small vein interveinal distance and mesophyll area than Vandana, also consistent across treatments. In terms of aquaporin-related plant hydraulics, variation among NILs in terms of aquaporin inhibition of root hydraulic conductivity (Lpr) was observed, with the highest-yielding NIL showing a lack of Lpr inhibition similar to Way Rarem. The results reported here suggest that the effects of qDTY12.1 are in response not only to soil moisture, but also to atmospheric conditions. An interaction among multiple mechanisms including leaf anatomy and aquaporin function appear to confer the transpiration efficiency effect of qDTY12.1.

Contrasting responses of stomatal conductance and photosynthetic capacity to warming and elevated CO2 in the tropical tree species Alchornea glandulosa under heatwave conditions

Factorial experiments of combined warming and elevated CO2 are rarely performed but essential for our understanding of plant physiological responses to climate change. Studies of tropical species are particularly lacking, hence we grew juvenile trees of Alchornea glandulosa under conditions of elevated temperature (+1.5 °C, eT) and elevated CO2 (+400ppm, eC) in a factorial open top chamber experiment. We addressed three questions: i) To what extent does stomatal conductance (gs) reduce with eT and eC treatments?; ii) Is there an interactive effect of eT and eC on gs?; iii) Does reduced gs as a result of eT and/or eC cause an increase in leaf temperature?; iv) Do the photosynthetic temperature optima (Topt) and temperature response of photosynthetic capacities (Vcmax, Jmax) shift with higher growth temperatures? The experiment was performed during an anomalously hot period, including a heatwave during the acclimation period. Our key findings are that: 1) the eT treatment reduced gs more than the eC treatment, 2) reduced gs caused an increase in leaf temperatures, and 3) net photosynthesis and photosynthetic capacities showed very high temperature tolerances with no evidence for acclimation to the eT treatment. Our results suggest that A. glandulosa may be able to cope with increases in air temperatures, however reductions in gs may cause higher leaf temperatures beyond those induced by an air temperature rise over the coming century.

Transpiration Response of Cotton to Vapor Pressure Deficit and Its Relationship With Stomatal Traits.

Many studies have demonstrated that the cotton in warm environments is vulnerable to water-limitations thus reducing the yield. A number of plant traits have been recommended to ameliorate the effects of water deficits on plant growth and yield. Limitation on maximum transpiration rate (TR) under high vapor pressure deficit (VPD), usually occurs during midday, is often considered as a water conservation trait. The genotypes with this trait are desirable in high VPD environments where water deficits commonly develop in the later part of the growing season. Our objective of the study was to find the genotypic variation for the trait limited TR under high VPD and also to study leaf temperature, water potential, photosynthesis, and stomatal conductance responses. Also, our objective was also to study the structural changes in the stomatal traits when exposed to long term high VPD conditions and involvement in such responses. In the present study, 17 cotton genotypes were studied for their (TR) response to various VPD environments under well irrigated conditions. Out of 17, eight genotypes limited TR after approximately 2 kPa VPD and rest of them increased their TR with increased VPD. Five selected genotypes with different TR response to increasing VPD were further studied for gas exchange and stomatal properties. All genotypes, irrespective of exhibiting limited TR at high VPD, reduced stomatal conductance, photosynthesis and water potential at high VPD of 3.3 kPa. The genotypes with limited TR modified their stomatal traits mostly on the adaxial surface with frequent and small stomata under high VPD. The genotypes with limited TR also exhibited an increase in epidermal cell expansion and stomatal index at contrasting VPD gradients to effectively balance the liquid and vapor phase conductance to limit TR at high VPD.

Stomatal Conductance Responses of Acacia caven to Seasonal Patterns of Water Availability at Different Soil Depths in a Mediterranean Savanna

Soil water availability controls plant productivity in seasonally dry ecosystems, although plant water use at different soil depths and times is, to the best of our knowledge, not clearly understood. Environmental variables at the canopy level and the soil volumetric water content (VWC) at five different soil depths were continuously recorded for three years (2011–2014) in an Acacia caven savanna site in central Chile. Stomatal conductance ( g s ) was measured every hour during daytime for 42 days distributed across the study period. Values of g s were weakly controlled by photosynthetically active radiation, vapor pressure deficit, and leaf temperature when considering the whole series. The variance proportion being explained increased from 5% to 20% if the whole series was partitioned into a dry and a wet season. According to the above, A. caven exhibited a more anisohydric behavior than previously thought. When we added the VWC in the root zone, to the g s atmospheric variables model, R2 increased to 47% when separately considering the dry and wet seasons. However, we did not find a differentiated use of water in the root zone, but instead a joint activity of the radicular system within the top 100 cm of the soil controlling g s .

The role of environmental factors in ozone uptake of Pinus mugo Turra

Montane forests in the High Tatra Mountains are exposed to high ambient ozone (O 3 ) concentrations that may adversely affect the physiological processes and health of plants. This study presents the modelled results of the phytotoxic ozone dose (POD) for dwarf mountain pine ( P. mugo ) in 2016. POD metrics were calculated using the deposition model DO 3 SE, with O 3 concentration and meteorological data measured in three altitudinal zones. In addition, maximal stomatal conductance (G max ) derived from gasometric field measurement in local conditions was included in the model. Field measurements confirmed the robust performance of the DO 3 SE model for stomatal conductance (G sto ). The site-specific stomatal conductance response model was largely congruent with average values estimated by DO 3 SE, though differences in temporal G sto distribution were observed. We determined a moderate limitation of O 3 uptake due to environmental factors (f ENVI ) such as air temperature and relative humidity, solar radiation, and soil water availability. It appears that G max is more relevant for annual POD than f ENVI in the temperate mountain forest. The results indicate a high level of POD and O 3 uptake by P. mugo in the High Tatra Mountains, which corresponds with the O 3 -induced visible injury symptoms observed. We also identified visible O 3 injury in P. mugo needles, which was more prevalent among the two-year old needles than younger individuals.

Starch biosynthesis by AGPase, but not starch degradation by BAM1/3 and SEX1, is rate-limiting for CO2 -regulated stomatal movements under short-day conditions.

Starch in guard cells functions in osmoregulation during stomatal movements. Starch metabolism is controlled by the circadian clock. We investigated the role of starch metabolism in stomatal responses to CO2 under different photoperiodic conditions. Guard cell starch levels correlate with low/high [CO2 ] exposure. Starch biosynthesis-deficient AGPase (ADG1) mutants but, unexpectedly, not the starch degradation-deficient BAM1, BAM3, and SEX1 mutants alone, are rate-limiting for stomatal conductance responses to [CO2 ]-shifts. Interestingly, AGPase is rate-limiting solely under short- but not long-day conditions. These findings suggest a model of enhanced AGPase activity in guard cells under short days such that starch biosynthesis becomes rate-limiting for CO2 -induced stomatal closing.

New insights into the cellular mechanisms of plant growth at elevated atmospheric carbon dioxide concentrations.

Rising atmospheric carbon dioxide concentration ([CO2 ]) significantly influences plant growth, development, and biomass. Increased photosynthesis rate, together with lower stomatal conductance, has been identified as the key factors that stimulate plant growth at elevated [CO2 ] (e[CO2 ]). However, variations in photosynthesis and stomatal conductance alone cannot fully explain the dynamic changes in plant growth. Stimulation of photosynthesis at e[CO2 ] is always associated with post-photosynthetic secondary metabolic processes that include carbon and nitrogen metabolism, cell cycle functions, and hormonal regulation. Most studies have focused on photosynthesis and stomatal conductance in response to e[CO2 ], despite the emerging evidence of e[CO2 ]'s role in moderating secondary metabolism in plants. In this review, we briefly discuss the effects of e[CO2 ] on photosynthesis and stomatal conductance and then focus on the changes in other cellular mechanisms and growth processes at e[CO2 ] in relation to plant growth and development. Finally, knowledge gaps in understanding plant growth responses to e[CO2 ] have been identified with the aim of improving crop productivity under a CO2 rich atmosphere.

The Responses of Plant Leaf CO2/H2O Exchange and Water Use Efficiency to Drought: A Meta-Analysis

Persistent drought severely inhibits plant growth and productivity, which negatively affects terrestrial primary productivity worldwide. Therefore, it is important to investigate the impacts of drought on plant leaf CO2/H2O exchange and water use efficiency. This study assessed the responses of net photosynthesis (Pn), stomatal conductance (Gs), transpiration (Tr), and instantaneous water use efficiency (WUE) to drought based on a worldwide meta-analysis of 112 published studies. The results demonstrated that drought decreased Pn, Tr, and Gs significantly and differently among different moderators. C4 plants had smaller Pn reduction than C3 plants, which gives C4 plants an advantage in Pn. But their WUE decreased under drought conditions, indicating a great flexibility in C4 WUE. Annual herbs sacrificed WUE (−6.2%) to maintain efficient Pn. Perennial herbs took a different strategy in response to drought with an increased WUE (25.1%). Deciduous tree species displayed a greater increase in WUE than conifers and evergreen species. Additionally, Gs had a significant correlation with Pn and Tr, but an insignificant correlation with WUE, which could be because WUE is affected by other factors (e.g., air flow, CO2 concentration, and relative humidity). These findings have significant implications for understanding the worldwide effects of drought on plant leaf CO2/H2O exchange and water use efficiency.

Increasing stomatal conductance in response to rising atmospheric CO2.

Background and Aims Studies have indicated that plant stomatal conductance (g(s)) decreases in response to elevated atmospheric CO2, a phenomenon of significance for the global hydrological cycle. ...

Increasing stomatal conductance in response to rising atmospheric CO2.

Studies have indicated that plant stomatal conductance (gs) decreases in response to elevated atmospheric CO2, a phenomenon of significance for the global hydrological cycle. However, gs increases across certain CO2 ranges have been predicted by optimization models. The aim of this work was to demonstrate that under certain environmental conditions, gs can increase in response to elevated CO2. Using (1) an extensive, up-to-date synthesis of gs responses in free air CO2 enrichment (FACE)experiments, (2) in situ measurements across four biomes showing dynamic gs responses to a CO2 rise of ~50 ppm (characterizing the change in this greenhouse gas over the past three decades) and (3) a photosynthesis-stomatal conductance model, it is demonstrated that gs can in some cases increase in response to increasing atmospheric CO2. Field observations are corroborated by an extensive synthesis of gs responses in FACE experiments showing that 11.8 % of gs responses under experimentally elevated CO2 are positive. They are further supported by a strong data-model fit (r2 = 0.607) using a stomatal optimization model applied to the field gs dataset. A parameter space identified in the Farquhar-Ball-Berry photosynthesis-stomatal conductance model confirms field observations of increasing gs under elevated CO2 in hot dry conditions. Contrary to the general assumption, positive gs responses to elevated CO2, although relatively rare, are a feature of woody taxa adapted to warm, low-humidity conditions, and this response is also demonstrated in global simulations using the Community Land Model (CLM4). The results contradict the over-simplistic notion that global vegetation always responds with decreasing gs to elevated CO2, a finding that has important implications for predicting future vegetation feedbacks on the hydrological cycle at the regional level.

Acclimation to Fluctuating Light Impacts the Rapidity of Response and Diurnal Rhythm of Stomatal Conductance.

Plant acclimation to growth light environment has been studied extensively; however, the majority of these studies have focused on light intensity and photo-acclimation, with few studies exploring the impact of dynamic growth light on stomatal acclimation and behavior. To assess the impact of growth light regime on stomatal acclimation, we grew Arabidopsis (Arabidopsis thaliana) plants in three different lighting regimes (with the same average daily intensity), fluctuating with a fixed pattern of light, fluctuating with a randomized pattern of light (sinusoidal), and nonfluctuating (square wave), to assess the effect of light regime dynamics on gas exchange. We demonstrated that gs (stomatal conductance to water vapor) acclimation is influenced by both intensity and light pattern, modifying the stomatal kinetics at different times of the day and resulting in differences in the rapidity and magnitude of the gs response. We also describe and quantify the response to an internal signal that uncouples variation in A and gs over the majority of the diurnal period and represents 25% of the total diurnal gs This gs response can be characterized by a Gaussian element and when incorporated into the widely used Ball-Berry model greatly improved the prediction of gs in a dynamic environment. From these findings, we conclude that acclimation of gs to growth light could be an important strategy for maintaining carbon fixation and overall plant water status and should be considered when inferring responses in the field from laboratory-based experiments.

Non-convergent transpiration and stomatal conductance response of a dominant desert species in central Asia to climate drivers at leaf, branch and whole plant scales

Non-convergent transpiration and stomatal conductance response of a dominant desert species in central Asia to climate drivers at leaf, branch and whole plant scales

Physiological acclimation dampens initial effects of elevated temperature and atmospheric CO2 concentration in mature boreal Norway spruce.

Physiological processes of terrestrial plants regulate the land-atmosphere exchange of carbon, water, and energy, yet few studies have explored the acclimation responses of mature boreal conifer trees to climate change. Here we explored the acclimation responses of photosynthesis, respiration, and stomatal conductance to elevated temperature and/or CO2 concentration ([CO2 ]) in a 3-year field experiment with mature boreal Norway spruce. We found that elevated [CO2 ] decreased photosynthetic carboxylation capacity (-23% at 25°C) and increased shoot respiration (+64% at 15°C), while warming had no significant effects. Shoot respiration, but not photosynthetic capacity, exhibited seasonal acclimation. Stomatal conductance at light saturation and a vapour pressure deficit of 1kPa was unaffected by elevated [CO2 ] but significantly decreased (-27%) by warming, and the ratio of intercellular to ambient [CO2 ] was enhanced (+17%) by elevated [CO2 ] and decreased (-12%) by warming. Many of these responses differ from those typically observed in temperate tree species. Our results show that long-term physiological acclimation dampens the initial stimulation of plant net carbon assimilation to elevated [CO2 ], and of plant water use to warming. Models that do not account for these responses may thus overestimate the impacts of climate change on future boreal vegetation-atmosphere interactions.

Dissecting the rootstock control of scion transpiration using model-assisted analyses in grapevine.

How rootstocks contribute to the control of scion transpiration under drought is poorly understood. We investigated the role of root characteristics, hydraulic conductance and chemical signals (abscisic acid, ABA) in the response of stomatal conductance (gs) and transpiration (E) to drought in Cabernet Sauvignon (Vitis vinifera) grafted onto drought-sensitive (Vitis riparia) and drought-tolerant (Vitis berlandieri × Vitis rupestris 110R) rootstocks. All combinations showed a concomitant reduction in gs and E, and an increase in xylem sap ABA concentration during the drought cycle. Cabernet Sauvignon grafted onto 110R exhibited higher gs and E under well-watered and moderate water deficit, but all combinations converged as water deficit increased. These results were integrated into three permutations of a whole-plant transpiration model that couples both chemical (i.e., ABA) and hydraulic signals in the modelling of stomatal control. Model comparisons revealed that both hydraulic and chemical signals were important for rootstock-specific stomatal regulation. Moreover, model parameter comparison and sensitivity analysis highlighted two major parameters differentiating the rootstocks: (i) ABA biosynthetic activity and (ii) the hydraulic conductance between the rhizosphere and soil-root interface determined by root system architecture. These differences in root architecture, specifically a higher root length area in 110R, likely explain its higher E and gs observed at low and moderate water deficit.

Rice Cultivation under Changing Climate with Mitigation Practices: A Mini Review

Assessments of the impact of climate change on rice production in Asia that comprehensively consider the uncertainty would therefore be very valuable for predicting future food security in this region. With the increase in daily maximum temperature averaged over flowering period above about 36℃, rice yield generally declined because of spikelet sterility induced by high temperatures. Methane emission from the rice fields is estimated to be globally 37 Tg yr-1 by IPCC while N2O emission is much lower as the total N2O emission from overall cultivated area was put at 1.8-5.3 Tg yr-1.Reduction of stomatal conductance due to elevated CO2 has been commonly observed in rice. However, the response of stomatal conductance to elevated CO2 varies considerably in response to various environmental factors. The response of stomatal conductance to elevated CO2 varied widely among times of day, growth stages, and years. Cultural and soil disturbances, pre-flooding and post-harvest drying contribute about 15% of the seasonal methane emission.