The Kyoto protocol and the agreement reached at Bonn requires an assessment of the net carbon balance at different scales, ranging from projects and nations to continents. In the following we give an overview about the biological control of net carbon fluxes. Depending on the processes under consideration, these range from gross primary productivity, GPP (photosynthesis), and net primary productivity, NPP (plant growth), to net ecosystem productivity, NEP (CO₂ assimilation minus heterotrophic respiration), and net biome productivity, NBP, including non-respiratory losses, such as by harvest and fire. We give an overview about the quantification of these processes based on Europe and Siberia. The Kyoto commitment is focused on the woody component of NPP, which is in the order of 1 to 2 t C ha^-1 year^-1. But, if all respiratory and non-respiratory losses are considered, the NBP decreases to less than 0.5 t C ha^-1 year^-1. Given the uncertainty of the assessments, and the difference between NPP and NBP it appears questionable to include biological sinks into the carbon accounting of fossil fuel emissions.

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2段階の栽植密度条件でジャガイモ2品種 (メークイン, デジマ) を栽培し, 生育時期別に遮光処理が生育, 収量および硝酸還元酵素 (NR) 活性に及ぼす影響について検討した.遮光処理は無処理 (100%, C区) , 弱遮光 (48%遮光, S1区) , および強遮光 (76%遮光, S2区) として寒冷紗を用いて行った.生育時期を三つの時段階 (1期: 萌芽から塊茎形成期, II期: 塊茎形成期から塊茎発達期, III期: 塊茎発達期から成熟期) に区分し, それぞれのステージに遮光処理を行った.すべての遮光処理区, および密植区で草丈は高くなり, 葉面積指数は密植区で増加した.初期の遮光区では塊茎形成期が遅延した.遮光程度が強くなるほど乾物生産, 上イモ収量および全塊茎重が低下した.収量の低下程度はII期のS2区で最大 (41%) , III期のSl区で最小 (15%) であった.品種, 栽植密度, 全生育段階を含めた平均値でみると, C区に比べ, 弱遮光区で19%, 強遮光区で30%の減収となった.葉のNR活性は遮光処理区で抑制され, C区に比べ, 平均値で弱遮光区は16%, 強遮光区は25%低下した.両処理条件での光強度に対する収量およびNR活性の減少係数はそれぞれ0.40, 0.33であった.以上の結果は光強度の低下が収量およびNR活性の低下と直接関連していることを示唆している.本研究より, II期が塊茎収量に対する光の影響の最も大きな時期であり, NR活性および収量低下に直接関連しているものと結論した.

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近年, 機能水の一つである電解陰極水に, 活性酸素除去能力があるという実験結果が発表された.そこで本研究では, 活性酸素が介在して生じる光合成の光阻害が, 電解陰極水によって抑制されうるかどうかを評価することを目的に実験を行った.水耕栽培したホウレンソウおよびサツマイモ苗に電解陰極水を与え, 光阻害が発生しやすい強光および低温条件下に一定時間おいた後, 光阻害の発生の指標となるクロロフィル蛍光のパラメータ, φ_PSIIおよびF_v/F_mを測定した.電解陰極水を灌水, 葉面へのスプレーまたはシャワーにより与えたホウレンソウとサツマイモのφ_PSIIは, いずれもストレス条件下で低下した.また, 電解陰極水を用いたサツマイモの遊離細胞けん濁液を強光に暴露したときのφ_PSIIも同様に低下した.これらの結果から, 電解陰極水は低温・強光ストレスによる光阻害の抑制の効果はないことが示唆された.

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8年生のカキ4品種を供試して樹体の生育, 光合成速度の時期別変化および休眠覚醒時期について調査し, 温暖な気候条件に対する適応性について検討した.夏季における光合成速度は, ‘平核無’と‘刀根早生’で高い値で推移したが, ‘富有’では常に低い値で推移した.休眠覚醒時期は‘平核無’と‘刀根早生’では11月下旬頃にあると思われたが, ‘西村早生’と‘富有’では12月頃と思われた.生育期間中の主幹の肥大量は‘刀根早生’と‘西村早生’で大きい値を示したが, ‘富有’では最も小さい値であった.以上のことから, 夏期における光合成速度が低く推移する品種では樹体の生育が劣り, また休眠覚醒に必要な低温要求量が高い品種では温暖地での経済栽培には適さないと考えられた.

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種々のタイプおよび濃度のサイトカイニンを添加したMS固形培地で嵯峨ギク葉片から不定芽を誘導したところ, 不定芽誘導に対する最適培地および形成率が品種間で大きく異なった.‘小倉錦’では, ウレア型サイトカイニンであるTDZを2.5×10^-5 M添加した培地で82.2%と最も高い不定芽形成率が得られ, 続いて‘嵯峨の秋’でウレア型サイトカイニンであるCPPUを2.5×10^-6 M添加した培地で56.7%, ‘嵯峨の雪’でプリン型サイトカイニンであるBAを2.5×10^-6 M添加した培地で12.2%, および‘嵯峨の春’で5.0×10^-6MTDZ添加培地での1.3%の順であった.一方, ‘嵯峨の春’を除くいずれの品種もホルモンフリーの培地で容易に発根できたが, ‘嵯峨の春’で得られた不定芽からは発根せず, 再分化植物体を得ることができなかった.以上の結果から, 嵯峨ギク品種群内において葉片からの不定芽形成能に大きな品種間差異が存在することが明らかとなった.また, キク品種ではこれまでに極めて報告の少ないTDZあるいはCPPU等のウレア型サイトカイニンが不定芽形成に有効であることが示唆された.

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An accurate irrigation control system needs to be developed in order to improve the stability of high Brix tomato production under the moderate water stress by restricted root-zone hydroponics. In this paper, applicability of a simple evapolimeter devised to control irrigation based on evaporation rate (Ep) was investigated. The evaporimeter is composed of a combshaped water tank, which is assembled with polyvinyl chloride pipes (φ20 mm), and an evaporating disk made of φ200 mm non-woven fabric sheet. In this evaporimeter, Ep is evaluated as the difference of water levels in the water tank measured by an ultra sonic level sensor with the precision of 0.1 mm. The irrigation control system attached with this evaporimeter starts irrigation when the cumulative evaporation (ΣEp) exceeds the irrigation point (IP) of ΣEp during the irrigation period in the day and thus the higher IPs result in longer intervals of irrigation per ΣEp. Transpiration rate of tomato plants at the 6th leaf stage was more closely correlated with Ep than with photosynthetic photon flux density. A high positive correlation between the amount of irrigation and cumulative evapotranspiration was evident on a daily basis, except the early stages of cultivation. In tomato production with this irrigation control system, more than 9% Brix fruits were successfully harvested when the IP was adjusted to an appropriate level to optimize the water stress of plants.

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A simple irrigation control system with a fabric sensor was developed for high-Brix tomato production in the restricted root-zone hydroponics. The fabric sensor is composed of a L-shape acrylic unit (LAU) with a non-woven fabric (NWF, thickness: 2 mm, width: 20 mm) and an electrode unit (EU) . The vertical part of NWF in LAU is in contact with a pair of electrodes of EU, and the horizontal part of the NWF is placed under the rooting substrate in the bed. In this irrigation control system, electrification between the electrodes of fabric sensor is detected by a float-less level switch (FLS) . When water content in the substrate is high, the electrodes are charged with electricity because the NWF absorbs ionic water by capillarity. An irrigation pump starts working when the substrate becomes too dry to maintain the electric current in the electrodes. Water content in the substrate at the beginning of irrigation (IP) increased with increasing the height of placement of EU (HEU) and variable resistance (VR) between the electrodes as well as with decreasing the electric conductivity of nutrient solution (EC_n) . Using the irrigation control system, the amount of irrigation changed automatically in response to substrate water content, which was affected by solar radiation and plant growing stage. Tomato fruits with Brix values higher than 9% were produced by using this irrigation control system under appropriate conditions of HEU, VR and EC_n to optimize the water stress level of the plants.

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Multiplication ratios (average number of harvestable propagules per stock plant) and electric energy consumption per harvestable propagule (single nodal cutting with an unfolded leaf, SNC) as affected by two propagation methods, propagation method using SNC only as propagules and propagation method using both SNC and stock plant base with an unfolded leaf (SPB) as propagules were investigated for sweetpotato (Ipomoea batatas (L.) Lam.) vegetative propagation in a closed transplant production system. Total number of harvestable propagules and electric energy consumption per harvestable propagule n multiplication cycles after the start of propagation (P (n) and E_p (n), respectively) were simulated for the two propagation methods, based on the results of the experiment : multiplication ratios were 1.8 and 3.7 for SNC and SPB, respectively, when a multiplication cycle was 12 d. P (10) were 89 to 197 times greater in the propagation method using both SNC and SPB than in the propagation method using SNC only. E (n) five or more multiplication cycles after the start of propagation in the propagation method using both SNC and SPB were reduced by 40% compared with those in the propagation method using SNC only. Results show that propagation method using both SNC and SPB as propagules in the system reduces the electricity cost and shortens the multiplication period.

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We investigated the effect of dim light on the growth and photosynthetic ability of cabbage plug-transplants stored for 14 d at l0°C. Transplants stored in darkness were elongated succulently by etiolation, and their leaf chlorophyll content and photosynthetic rate decreased. Both intermittent and continuous lighting at a photosynthetic photon flux density (PPFD) of 10 μmol m^-2 s^-1 suppressed the succulent elongation. Longer photoperiod resulted in greater shoot elongation accompanied by dry matter deposition. The leaf chlorophyll content and photosynthetic rate in all lighting conditions remained higher than those in darkness. The photosynthetic rate in intermittent lighting was higher than that in continuous lighting. In intermittent lighting with a 1-h light/23-h dark cycle, the succulent elongation and the reduction of photosynthetic rate were suppressed to some extent at a PPFD from 0.5 to 10 μmol m^-2 s^-1. These results suggest that intermittent dim light could be used for preserving the quality of cabbage plug-transplants during low-temperature storage.

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Effects of NaCl addition to the nutrient solution on the activities of acid and neutral invertases (AI and NI) (EC 3.2.1.26) and sucrose synthase (SS) (EC 2.4.1.13) of cucumber (Cucumis sativus L. cv. Asomidori No. 5) fruits were studied. In spring of 1992, cucumber plants were grown with solution culture in a greenhouse. The aeration rate of the solution was kept low. Sixty millimolar NaCl was added to the solution when 10th leaf was expanding. In control fruits, AT activity was fairly constant until 7 d after anthesis. On the day of anthesis, AT activity at 60 mM NaCl tended to be higher than control. At 60 mM NaCl, AT activity tended to be higher in the proximal half than in the distal half of a fruit. In control fruits, SS activity declined as fruits grew. SS activity tended to be lower in fruit at 60 mM NaCl. The developmental changes in the activities of AT and SS tended to be different between pollinated and parthenocarpic fruit. The activity of NI was much lower than those of AT and SS.

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