Effects of mesophyll water potential on photosynthesis in Gramineae plants: with special reference to phylogeny of subfamilies

We selected several species from six Gramineae subfamilies and examined relationships between the photosynthetic rate and mesophyll water potential (ΨL). We used the oxygen electrode method originally devised by Ishii et al. and modified by Ishihara et al. Namely, we used a liquid -phase oxygen electrode and measured the O2 evolution rate

Effects of mesophyll water potential on photosynthesis in Cyperaceae plants: with special reference to phylogeny of tribes and decarboxylation sub-types

We examined the photosynthetic rates under water stress conditions in 43 Japanese Cyperaceae species using the same method used for Gramineae plants. Compared with Gramineae, the difference between C4 and C3 species was more distinct in Cyperaceae. Moreover, C4 Cyperaceae species were very susceptible to water stress like Panicoideae C4 species. These species belong to the NADP-ME subtype. It appears that the sensitivity of photosynthesis to water stress would be different depending on the decarboxylation sub-types

Photosynthetic Characteristics of an Amphibious C4 Plant, Eleocharis retroflexa ssp. chaetaria

Eleocharis retroflexa (Poir.) Urban ssp. chaetaria (Roem. & Schult.) T. Koyama, an amphibious leafless sedge, grows not only under terrestrial conditions but also under completely submerged aquatic conditions. We investigated the photosynthetic traits and structural features of the culms, which are the photosynthetic organs, in the terrestrial and submerged forms of this species and compared them with those of other amphibious species of Eleocharis which are known to change the photosynthetic modes. The culms of the terrestrial form had Kranz anatomy with well-developed Kranz (bundle sheath) cells and high levels of C4 enzyme activity typical of the NAD-malic enzyme (NAD-ME) subtype of C4 metabolism. They also had a δ 13C value typical of C4 plants, indicating that the terrestrial form fixes carbon through the C4 pathway. The culms of the submerged form had not only a Kranz-like anatomy but also revealed anatomical traits typical of leaves of submerged aquatic plants. The activities of the C4 enzymes in the submerged form were lower than those in the terrestrial form, but were still in the range typical of G4 plants, 14C pulse-12C chase experiments with the submerged form indicated that almost all of the fixed 14C was incorporated into G4 compounds, and subsequently the raioactivity was transferred into C3 compounds and sucrose. The submerged form showed no diurnal fluctuation in malate level. These data demonstrate that a C4 metabolism is operative even in the submerged form. This unique amphibious C4 plant provides an intriguing example of the physiological and ecological adaptability of C4plants

Studies on Matter Production in Sweet Potato Plants : 2. Changes of Gross and Net Photosyntheses, Dark Respiration and Solar Energy Utilization with Growth under Field Conditions

To make clear the variation of the CO, balance of sweet potatoes (Ipomoea batatas (L.) Lam.) with growth under field conditions, canopy photosynthesis and dark respiration were measured on the same materials used in the previous paper. Canopy photosynthesis was measured using chamber method. Dark respiration in population was calculated based on the dark respiratory rates and dry weight of each plant part during the growth period. Diurnal change of canopy photosynthesis at matured stage closely correlated with that of solar radiation. The response of gross photosynthetic rate to light intensity changed with LA1 increase from a saturated curve to a non-saturated one. Its highest value was 32.4g DW/m^2/day at the end of August. Dark respiratory rates differed with each plant part and with growth stage. The amount of gross photosynthesis (Pg) and of dark respiration (R) per day, and net production (Pn=Pg-R) increased with LA1 increase, reaching a maximum in August, and then decreased gradually until November. Pn/Pg and R/Pg ratios differed with growth stage, and were 60-70 % in the former and 30-40s in the latter during the main growth period. Pn calculated CO, balance almost corresponded to CGR measured in the field. Efficiency of solar energy utilization (Eu) also differed with each growth stage. Eu based on Pg, Pn and CGR were 1.95 %, 1.25 % and 1.35 % in mean value during the growth period, respectively

Relationship between Canopy Architecture and Crop Production with Reference to Light and CO_2 Environment : III. Relations between Canopy Architecture and Construction Factors for CO_2 Diffusion in Some Crop Stands

It is clear that a canopy architecture affects the CO_2 diffusion in a foliage. The CO_2 diffusion coefficient is expressed by D = U・i・l_m where D is diffusion coefficient, U is wind speed, i is relative turbulence intensity and I, is mixing length. In this paper we show the relation of canopy architecture with attenuation coefficient (β) of wind speed (U) in the canopy and drag coefficient (C_d) as one of the construction factors of β. The results are summarized as follows ; From the profiles of the wind speed above and within the canopies of barnyard millet, upland rice, paddy rice, wheat, soybean and short and tall types of grain sorghum, the attenuation coefficients (β) of wind speed and drag coefficients (C_d) of leaves in these canopies were obtained. The β obtained from the wind profile in the canopy can be expressed as β ∝ F_L・C_d where F_L is leaf area index. Though C_d of the horizontal foliage was smaller than that of vertical foliage, β of the soybean canopy was larger than paddy and upland rice vertical foliages compared on the same F_L. This resulted from the soybean canopy having large leaf area density (LAD) in upper layers of the foliage. The β of the tall type of grain sorghum was smaller than that of the short type. This resulted from the small C_d of the tall grain sorghum canopy. As mentioned above, it was found that the attenuation coefficient (β) of wind speed was affected by not only leaf inclination but also vertical distribution of leaf area and canopy height.群落構造はC0_2拡散に強く関係している.群落内のC0_2拡散係数は風速,相対乱流強度および混合距離の積で表わされる.拡散係数はこれらのうち風速に特に支配される傾向が強い.本報では群落構造と風速の減衰係数,およびその構成要素の一つである抵抗係数との関係を調べた.1)栽培ヒエ,陸稲,小麦,大豆,グレインソルガムの短稈系統と長稈系統および水稲個体群について,風速の観測を行い,風速の減衰係数および葉身の風に対する抵抗係数を求めた.2)高さ方向に対する風速分布から求めた減衰係数βは葉面積指数と対抗係数の積で表わされた.減衰係数は葉面積密度が植被の上層で高い大豆で大きく,植被の下層で高い陸稲が小さかった.草高が等しく,葉面積密度の垂直分布が紡垂型をしている個体群(グレインソルガムの短稈系統,水稲)では,両者の中間であった.3)積算葉面積に対する風速分布から求めた減衰係数β\u27は大豆個体群で小さく,陸稲及び水稲個体群で大きかった.グレインソルガムの長稈系統でもβ\u27は小さい傾向があった.4)減衰係数β\u27は抵抗係数と関係しており,大豆とグレインソルガムの長稈系統の個体群において抵抗係数は小さかった.5)以上の結果から,葉面積密度と抵抗係数の小さいグレインソルガムの長稈系統の個体群においてCO_2拡散係数が大きいことが示唆された

Response Differences of Photosynthesis, Transpiration and Water Use Efficiency to Light Intensity in C₃ and C₄ Crop Species

To make clear the response differences of photosynthesis，transpiration and water use efficiency to light intensity in C₃ and C₄ crops belonging to Gramineae，the CO₂ exchange and transpiration rates were measured with the attached leaves. Also，water use efficiency， leaf conductance and intercellular CO₂ concentration were calculated based on these measured data. The response of photosynhetic and transpiration rates to light intensity were simultaneously measured using the open system assimilation chamber method provided with a by-pass to dehydrate the water transpired by the leaves. In each crop，light intensity was changed in 9 steps from 110 klx to total darkness. During the measuring，temperature and relative humidity in the chamber were maintained at 30±O.5℃ and 64.3±1.24%，respectively. The results obtained were as follows : 1) Light saturation point，maximum photosynthetic rate and initial slope in the photosynthetic light response curve of C₄ crops were higher compared with those of C₃ crops. 2) The response of the transpiration and water use efficiency to light intensity in both crops saturated at 30 Klx and 10 klx，respectively. The transpiration of C₄ crops was three fourths that of C₃ crops. On the other hand，the water use efficiency of C₄ crops was about twice that of C₃ crops. 3) Leaf conductance and intercellular CO₂ concentration of C₃ crops were larger than those of C₄ crops. 4) There were，in the case of the present experiment，high positive correlations between transpiration and photosynthetic rates in each of the crops. 5) The relations of water use efficiency and intercellular CO₂ concentration with leaf conductance in all crops under high light intensity showed a high negative correlation for water use efficiency and a high positive correlation for intercellular CO₂ concentrations. 6) The higher water use efficiency of C₄ crops was mainly caused by restricting the loss of water vapour from leaves with the smaller Ieaf conductance than those of C₃ crops. 7) Under such small Ieaf conductance，it is considered that the C₄ crops maintain their high photosynthetic rate by means of the high carboxylation efficiency and of the large CO₂ gradient (from the atmosphere to the inside leaves)

Studies on Matter Production in Sweet Potato Plants : 2. Changes of Gross and Net Photosyntheses, Dark Respiration and Solar Energy Utilization with Growth under Field Conditions

To make clear the variation of the CO, balance of sweet potatoes (Ipomoea batatas (L.) Lam.) with growth under field conditions, canopy photosynthesis and dark respiration were measured on the same materials used in the previous paper. Canopy photosynthesis was measured using chamber method. Dark respiration in population was calculated based on the dark respiratory rates and dry weight of each plant part during the growth period. Diurnal change of canopy photosynthesis at matured stage closely correlated with that of solar radiation. The response of gross photosynthetic rate to light intensity changed with LA1 increase from a saturated curve to a non-saturated one. Its highest value was 32.4g DW/m^2/day at the end of August. Dark respiratory rates differed with each plant part and with growth stage. The amount of gross photosynthesis (Pg) and of dark respiration (R) per day, and net production (Pn=Pg-R) increased with LA1 increase, reaching a maximum in August, and then decreased gradually until November. Pn/Pg and R/Pg ratios differed with growth stage, and were 60-70 % in the former and 30-40s in the latter during the main growth period. Pn calculated CO, balance almost corresponded to CGR measured in the field. Efficiency of solar energy utilization (Eu) also differed with each growth stage. Eu based on Pg, Pn and CGR were 1.95 %, 1.25 % and 1.35 % in mean value during the growth period, respectively

Relationship between Canopy Architecture and Crop Production with Reference to Light and CO, Environments : I. Light Intensity on Both Upper and Lower Surfaces of Leaves in Rice and Soybean Canopies

In our previous paper it was reported that the rice plant population had higher utilization and conversion efficiencies than the soybean plant population, In this paper, these results are studied from the viewpoint of the differences between rice and soybean stands in inclination angle of a leaf, and light intensity on both surface of a leaf within a canopy. Azimuth angles of the normal on the upper surface of rice leaves were distributed uniformly in all direction, but those of soybean leaves were mostly oriented to the south at noon and to the west in late afternoon. The inclination angles of rice leaves to the horizontal were large at upper layers and it decreased gradually to the lower layers within a stand. Though inclination angles of soybean leaves at the top layer were slightly larger, those at other layers were smaller. The light intensity incident on the upper surface of rice leaves was somewhat equal throughout the canopy but that of soybean leaves was divided into two groups of high and low intensity. Also, the lower surfaces of rice leaves had received more light energy than those of soybean. Since the photosynthetic rates of leaves with radiation on both surfaces were larger than those with radiation on the upper surface only, the photosynthesis of rice leaves favoured.水稲個体群と大豆個体群による物質生産･太陽光利用の違いを本報では個葉の空間配置,圃場条件下での葉の表･裏面の受光量の違いならびに葉の表･裏面を光照射した場合の個葉光合成速度の増加等から説明することを試みた.1)水稲の葉面の方位角にはほとんど偏りはなかったが,大豆では正午に南向,午後は西向のものが多かった.2)葉身の傾斜角は水稲および大豆個体群でともに,上位葉は立ち型の葉が多い傾向があった.しかしながら,水稲は下層から上層に行くにしたがって,しだいに傾斜角が大きくなるという整然とした傾向があったのに対して,大豆では上層葉の傾斜角のみが大きかった.3)水稲個体群では大豆個体群に比べて,多くの葉はより平均的な強さの光を受けていた.水稲では大豆よりも裏面受光量が多かった.4)個葉光合成速度は葉の片面のみを照射するよりも,同じ強さの光を葉の向軸側と背軸側に分けて照射した方が,水稲と大豆でともに高かかった

Relationship between Canopy Architecture and Crop Production with Reference to Light and CO, Environments : II. CO, Diffusion Coefficient and Canopy Photosynthesis of Rice and Soybean Populations

The characteristics of CO, diffusion within canopies of rice and soybean were investigated by the heat balance method. There were differences between CO, profiles within rice and soybean stands. The minimum CO, concentration within the rice stand appeared in the lower layer but that within the soybean appeared in the upper layer of the canopy. And in spite of the rice stand having larger leaf area index than soybean, CO_2 source activity in lower layer of rice canopy was smaller than that of snybean stand. These differences might be resulted because light extinction coefficient of rice stand was so small that rice leaves could recieve more light energy than those of soybean and then leaf photosynthesis at the lower layer of the rice was higher than soybean stand. Canopy photosynthetic rates at noon were 8.8g CO_2, /m^2h in rice and 6.8g CO_2 /m^2h in soybean stands.水稲個体群と大豆個体群におけるCO_2拡散の特徴を熱収支法で調べた.1)草高がほぼ等しい水稲と大豆個体群の植被面のCO_2拡散係数はほぼ等しかった.しかしながら,水稲個体群ではLAIが大きかったので,CO_2拡散係数の減衰係数は大豆個体群よりも大きくなった.2)群落内のCO_2プロファイルの特徴は水稲と大豆では異なり,水稲個体群ではCO_2濃度の極小値が群落の下層にあるのに対して,大豆個体群では上層にあった.また,水稲個体群ではLAIが大きいにもかかわらず,群落の下層におけるC0_2のsourceとしての働きは大豆個体群よりも小さかった.これは水稲では光の消散係数が小さく,下層でも光合成作用が行われていることが主な理由と考えられた.3)群落光合成速度は日中の最も光合成が盛んに行われている時で,水稲個体群で8.8gCO_2/m^2h,大豆個体群で6.8gCO_2/m^2hであった