Effects of Free-air CO2 Enrichment on Root Characteristics and C:N Ratio of Rice at the Heading Stage

A hydroponics experiment was conducted to investigate the rice root growth in FACE （free-air carbon dioxide enrichment）. The root biomass, root volume, ratio of root/shoot, number of adventitious roots and root diameter significantly increased under FACE conditions, while the CO2 enrichment decreased the N concentration in rice roots without any change in the C content, leading to an increase in root C：N ratio. Moreover, the elevated CO2 resulted in a remarkable decrease of root activity, expressed as per unit root dry weight, which might be responsible for decreased N concentration in roots.

Responses of soil enzymes to long-term CO_2 enrichment in forest ecosystems of Changbai Mountains

A study was conducted to determine the responses of soil enzymes （invertase, polyphenol oxidase, catalase, and dehydrogenase） to long-term CO2 enrichment at the Research Station of Changbai Mountain Forest Ecosystems, Chinese Academy of Sciences （42°24＇N, 128°28＇E; 738 m in elevation） in the northeast China during 1999-2006. Three treatments of the CO2 enrichment, designed as 500 μmol·mol-1 CO2 open-top chamber （OTC）, ambient control chamber and unchambered field （approx. 370 μmol·mol^-1CO2）, were conducted with Pinus koraiensis and Pinus sylvestriformis tree species. Soil sampling was made and analyzed separately in spring, summer and autumn in 2006 after the soil enzymes were exposed to elevated CO2 concentration （500 μmol·mol^-1） for eight growing seasons. Results showed that, at elevated CO2 concentration （500 μmol·mol^-1）, the activities of invertase （except for the summer samples of P. koraiensis） presented a remarkable decline in all growing seasons, while the activities of dehydrogenase had an increase but only part of the results was remarkable; the activities of polyphenol oxidase in P. sylvestriformis rhizosphere showed a remarkable decrease; the catalase activities increased in spring, while in turn were decline in other seasons. This study also revealed that the soil enzyme activities are significantly correlated with the tree species under the CO2 enhancement.

Effect of CO_2 Enrichment on the Growth and Nutrient Uptake of Tomato Seedlings

Exposing tomato seedlings to elevated CO2 concentrations may have potentially profound impacts on the tomato yield and quality. A growth chamber experiment was designed to estimate how different nutrient concentrations influenced the effect of elevated CO2 on the growth and nutrient uptake of tomato seedlings. Tomato (Hezuo 906) was grown in pots placed in controlled growth chambers and was subjected to ambient or elevated CO2 (360 or 720μL L-1) and four nutrient solutions of different strengths (1/2-, 1/4-, 1/8-, and 1/16-strength Japan Yamazaki nutrient solutions) in a completely randomized design. The results indicated that some agricultural characteristics of the tomato seedlings such as the plant height, stem thickness, total dry and fresh weights of the leaves, stems and roots, the G value (G value = total plant dry weight/seedling age), and the seedling vigor index (seedling vigor index = stem thickness/(plant height×total plant dry weight) increased with the elevated CO2, and the increases were strongly dependent on the nutrient solution concentrations, being greater with higher nutrient solution concentrations. The elevated CO2 did not alter the ratio of root to shoot. The total N, P, K, and C absorbed from all the solutions except P in the 1/8- and 1/16-strength nutrient solutions increased in the elevated CO2 treatment. These results demonstrate that the nutrient demands of the tomato seedlings increased at elevated CO2 concentrations.

Four years of free-air CO_2 enrichment enhance soil C concentrations in a Chinese wheat field

Elevated atmospheric CO2 can influence soil C dynamics in agroecosystems. The effects of free-air CO2 enrichment （FACE） and N fertilization on soil organic C （Corg）, dissolved organic C （DOC）, microbial biomass C （Cmic） and soil basal respiration （SBR） were investigated in a Chinese wheat field after expose to elevated CO2 for four full years. The results indicated that elevated CO2 has stimulative effects on soil C concentrations regardless of N fertilization. Following the elevated CO2, the concentrations of Corg and SBR were increased at wheat jointing stage, and those of DOC and Cmic were enhanced obviously across the wheat jointing stage and the fallow period after wheat harvest. On the other hand, N fertilization did not significantly affect the content of soil C. Significant correlations were found among DOC, Cmic, and SBR in this study.

Effect of CO_2 enrichment on competition between Skeletonema costatum and Heterosigma akashiwo

We investigated the effect of CO2 enrichment and initial inoculum density on competition between Skeletonema costatum and Heterosigma akashiwo,two common algae seen in algal blooms.The initial inoculum density(0.2×104,0.4×104,0.8×104 cells/ml) had a significant effect on population growth and competition between H.akashiwo and S.costatum.The time required for population growth to reach the exponential growth phase and stationary phase decreased significantly as the initial density increased.When the two species were cultured together,S.costatum tended to outcompete H.akashiwo,especially when present at higher initial ratios.CO_2 enrichment(5 000μl/L CO_2) increased the maximum population density and carrying capacity of H.akashiwo but decreased these measures for S.costatum.Thus,CO_2 enrichment favored the growth of H.akashiwo over S.costatum.

Effects of Culture Media and Light Intensity on in vitro Growth of Oncidium under CO_2 Enrichment Condition

The effects of culture media and light intensity on in vitro growth of Oncidium 慉loha Iwanga were investigated under CO2 enrichment condition. Height, fresh and dry weight of the Oncidium seedlings were measured, and the leaf number per plant, shoot number per plant, leaf width and leaf chlorophyll content were also investigated. The results were as follows: 1) The seedling height, fresh and dry weight, leaf number per plant, leaf width and leaf chlorophyll content of the shoots growing on MS complete culture medium were higher than those on 1/2MS, VW and 1/2VW media. The root number per plant and ratio of dry matter of the seedlings cultured on 1/2MS and 1/2VW media were higher than those on MS and VW; 2) The seedling height, fresh weight, dry weight, dry matter ratio and leaf chlorophyll content, leaf length, leaf width, root length, leaf number per plant, root number per plant of seedlings of Oncidium growing under 4 500 lx and 1 700 lx were higher than those under 750 lx. However, there was no significant difference in those growth parameters mentioned above while dealing with 4 500 lx and 1 700 lx except for the seedling height. Nevertheless, the leaf color of plants under 4 500 lx was lighter and the leaves of the lower parts became yellowish in comparison with those growing under 1 700 lx.

Effects of free-air CO_2 enrichment on adventitious root development of rice under low and normal soil nitrogen levels

Free air CO2 enrichment(FACE) and nitrogen(N) have marked effects on rice root growth,and numerical simulation can explain these effects. To further define the effects of FACE on root growth of rice, an experiment was performed, using the hybrid indica cultivar Xianyou63. The effects of increasing atmospheric CO2 concentration [CO2], 200 μmol mol-1higher than ambient, on the growth of rice adventitious roots were evaluated, with two levels of N: low(LN, 125 kg ha-1) and normal(NN, 250 kg ha-1). The results showed a significant increase in both adventitious root number(ARN) and adventitious root length(ARL) under FACE treatment. The application of nitrogen also increased ARN and ARL, but these increases were smaller than that under FACE treatment. On the basis of the FACE experiment, numerical models for rice adventitious root number and length were constructed with time as the driving factor. The models illustrated the dynamic development of rice adventitious root number and length after transplanting, regulated either by atmospheric [CO2] or by N application.The simulation result was supported by statistical tests comparing experimental data from different years, and the model yields realistic predictions of root growth. These results suggest that the models have strong predictive potential under conditions of atmospheric [CO2] rises in the future.

二氧化碳、施氮量和移栽密度对汕优63产量形成的影响--FACE研究

大气二氧化碳(CO2)浓度升高使水稻产量增加,但这种影响是否因不同栽培条件而异尚不清楚。2011年利用中国稻田FACE(Free Air CO2Enrichment)系统平台,以敏感水稻品种汕优63为供试材料,二氧化碳设环境CO2浓度(Ambient)和高CO2浓度(Ambient+200μmol·mol-1),施氮量设低氮(15 g·m-2)和高氮(25 g·m-2),移栽密度设低密度(16穴·m-2)和高密度(24穴·m-2),研究了不同栽培条件下大气CO2浓度升高对杂交水稻产量形成的影响。结果表明:高浓度CO2对水稻抽穗期和成熟期没有影响,但使结实期株高显著增高(+7%);使单位面积穗数(+8%)和每穗颖花数(+19%)明显增多,进而使单位面积颖花量大幅增加(+29%)。高浓度CO2条件下穗数增多主要与最高分蘖数明显增加有关,而分蘖成穗率显著下降;穗型增大主要由单茎干重而非单位干重形成的颖花数增加所致。高浓度CO2环境下水稻结实能力呈增加趋势,其中平均粒重的增幅达显著水平。大气CO2浓度升高使水稻籽粒产量平均增加36%,其中在低氮低密度、低氮高密度、高氮低密度和高氮高密度条件下分别增加43%、46%、34%、23%。增施氮肥或增加移栽密度使水稻产量略有下降,但均未达显著水平。以上结果表明,高浓度CO2环境下杂交水稻因库容量增大导致产量大幅增加,调整施氮水平和移栽密度可在一定程度上改变这种肥料效应。

开放式空气中CO_2浓度增高(FACE)对水稻生长和发育的影响

人类活动导致的大气和气候变化将极大地改变作物的生长环境,其中最大的一个变化就是大气二氧化碳(CO2)浓度的迅速上升:从工业革命前的平均270μmol/mol上升到目前的381μmol/mol,到2050年至少超过550μmol/mol。FACE(Free-air CO2 enrichment,开放式空气中CO2浓度增高)试验是目前评估未来高浓度CO2对作物生长和产量实际影响的最佳方法。水稻无疑是人类最重要的食物来源,迄今为止人类利用FACE技术开展水稻响应和适应的研究已有10a(19982008年)的历史。以生长发育为主线,首次系统综述了10a水稻FACE试验在该领域的研究成果,总结了FACE情形下高浓度CO2(模拟本世纪中叶大气CO2浓度)对主要供试水稻品种(小区面积大于4m2)光合作用、生育进程、地上部生长、地下部生长、物质分配、籽粒灌浆、产量构成以及倒伏性状等影响的研究进展,比较了FACE与非FACE研究之间以及中国和日本FACE研究(世界上唯一的两个大型水稻FACE研究)之间的异同点。根据研究进展以及当前的技术水平,文章最后提出了该领域的3个优先课题:(1)FACE情形下杂交稻生产力响应高于预期的生物学机制;(2)FACE情形下CO2与主要栽培措施的互作效应;(3)FACE情形下CO2与主要空气污染物臭氧的互作效应。这些响应的机理性解析将有助于从根本上减少人类预测未来粮食安全的不确定性,进而更加有效地制订出应对全球变化的适应策略。

Effect of CO_2 Elevation on Root Growth and Its Relationship with Indole Acetic Acid and Ethylene in Tomato Seedlings

A hydroponic experiment was carried out to study the effect of elevated carbon dioxide(CO2) on root growth of tomato seedlings.Compared with the control(350 μL L-1),CO2 enrichment(800 μL L-1) significantly increased the dry matter of both shoot and root,the ratio of root to shoot,total root length,root surface area,root diameter,root volume,and root tip numbers,which are important for forming a strong root system.The elevated CO2 treatment also significantly improved root hair development and elongation,thus enhancing nutrient uptake.Increased indole acetic acid concentration in plant tissues and ethylene release in the elevated CO2 treatment might have resulted in root growth enhancement and root hair development and elongation.

Effects of elevated CO_2 concentration on growth and water usage of tomato seedlings under different ammonium/nitrate ratios

Increasing atmospheric CO2 concentration is generally expected to enhance photosynthesis and growth of agricultural C3 vegetable crops, and therefore results in an increase in crop yield. However, little is known about the combined effect of elevated CO2 and N species on plant growth and development. Two growth-chamber experiments were conducted to determine the effects of NH4^＋/NO3^- ratio and elevated CO2 concentration on the physiological development and water use of tomato seedlings. Tomato was grown for 45 d in containers with nutrient solutions varying in NH4^＋/NO3^- ratios and CO2 concentrations in growth chambers. Results showed that plant height, stem thickness, total dry weight, dry weight of the leaves, stems and roots, G value （total plant dry weight/seedling days）, chlorophyll content, photosynthetic rate, leaf-level and whole plant-level water use efficiency and cumulative water consumption of tomato seedlings were increased with increasing proportion of NO3- in nutrient solutions in the elevated CO2 treatment. Plant biomass, plant height, stem thickness and photosynthetic rate were 67%, 22%, 24% and 55% higher at elevated CO2 concentration than at ambient CO2 concentration, depending on the values of NH4^＋/NO3^- ratio. These results indicated that elevating CO2 concentration did not mitigate the adverse effects of 100% NH4^＋-N （in nutrient solution） on the tomato seedlings. At both CO2 levels, NH4^＋/NO3^- ratios of nutrient solutions strongly influenced almost every measure of plant performance, and nitrate-fed plants attained a greater biomass production, as compared to ammonium-fed plants. These phenomena seem to be related to the coordinated regulation of photosynthetic rate and cumulative water consumption of tomato seedlings.

A possible mechanism of mineral responses to elevated atmospheric CO_2 in rice grains

Increasing attentions have been paid to mineral concentration decrease in milled rice grains caused by CO2 enrichment, but the mechanisms still remain unclear. Therefore, mineral （Ca, Mg, Fe, Zn and Mn） translocation in plant-soil system with a FACE （Free-air CO2 enrichment） experiment were investigated in Eastern China after 4-yr operation. Results mainly showed that： （1） elevated CO2 significantly increased the biomass of stem and panicle by 21.9 and 24.0%, respectively, but did not affect the leaf biomass. （2） Elevated CO2 significantly increased the contents of Ca, Mg, Fe, Zn, and Mn in panicle by 61.2, 28.9, 87.0, 36.7, and 66.0%, respectively, and in stem by 13.2, 21.3, 47.2, 91.8, and 25.2%, respectively, but did not affect them in leaf. （3） Elevated CO2 had positive effects on the weight ratio of mineral/biomass in stem and panicle. Our results suggest that elevated CO2 can favor the translocation of Ca, Mg, Fe, Zn, and Mn from soil to stem and panicle. The CO2-led mineral decline in milled rice grains may mainly attribute to the CO2-1ed unbalanced stimulations on the translocations of minerals and carbohydrates from vegetative parts （e.g., leaf, stem, branch and husk） to the grains.

Microbial Activity in a Temperate Forest Soil as Affected by Elevated Atmospheric CO_2

Microorganisms play a key role in the response of soil ecosystems to the rising atmospheric carbon dioxide （CO2） as they mineralize organic matter and drive nutrient cycling. To assess the effects of elevated CO2 on soil microbial C and N immobilization and on soil enzyme activities, in years 8 （2006） and 9 （2007） of an open-top chamber experiment that begun in spring of 1999, soil was sampled in summer, and microbial biomass and enzyme activity related to the carbon （C）, nitrogen （N） and phosphorus （P） cycling were measured. Although no effects on microbial biomass C were detected, changes in microbial biomass N and metabolic activity involving C, N and P were observed under elevated CO2. Invertase and .dehydrogenase activities were significantly enhanced by different degrees of elevated CO2. Nitrifying enzyme activity was significantly （P 〈 0.01） increased in the August 2006 samples that received the elevated COs treatment, as compared to the samples that received the ambient treatment. Denitrifying enzyme activity was significantly （P 〈 0.04） decreased by elevated COs treatments in the August 2006 and June 2007 （P 〈 0.09） samples, β-N-acetylglucosaminidase activity was increased under elevated CO2 by 7% and 25% in June and August 2006, respectively, compared to those under ambient CO2. The results of June 2006 samples showed that acid phosphatase activity was significantly enhanced under elevated CO2. Overall, these results suggested that elevated CO2 might cause changes in the belowground C, N and P cycling in temperate forest soils.

Interactive effects of elevated carbon dioxide and nitrogen availability on fruit quality of cucumber (Cucumis sativus L.)

Elevated CO2 and high N promote the yield of vegetables interactively, whilst their interactive effects on fruit quality of cucumber （Cucumis sativus L.） are unclear. We studied the effects of three CO2 concentrations （400 IJmOl mol^-1 （ambient）, 625 pmol mol^-1 （moderate） and 1 200 pmol mol^-1（high）） and nitrate levels （2 mmol L^-1 （low）, 7 mmol L^-1 （moderate） and 14 mmol L^-1 （high）） on fruit quality of cucumber in open top chambers. Compared with ambient CO2, high CO2 increased the concentrations of fructose and glucose in fruits and maintained the titratable acidity, resulting in the greater ratio of sugar to acid in moderate N, whilst it had no significant effects on these parameters in high N. Moderate and high CO2 had no significant effect on starch concentration and decreased dietary fiber concentration by 13 and 18%, nitrate by 31 and 84% and crude protein by 19 and 20% averagely, without interactions with N levels. The decreases in amino acids under high CO2 were similar, ranging from 10-18%, except for tyrosine （50%）. High CO2 also increased the concentrations of P, K, Ca and Mg but decreased the concentrations of Fe and Zn in low N, whilst high CO2 maintained the concentrations of P, K, Ca, Mg, Fe, Mn, Cu and Zn in moderate and high N. In conclusion, high CO2 and moderate N availability can be the best combination for improving the fruit quality of cucumber. The fruit enlargement, carbon transformation and N assimilation are probably the main processes affecting fruit quality under CO2 enrichment.

Modeling Methane Emissions from Paddy Rice Fields under Elevated Atmospheric Carbon Dioxide Conditions

Abstract Methane （CH4） emissions from paddy rice fields substantially contribute to the dramatic increase of this greenhouse gas in the atmosphere. Due to great concern about climate change, it is necessary to predict the effects of the dramatic increase in atmospheric carbon dioxide （CO2） on CH4 emissions from paddy rice fields. CH4MOD 1.0 is the most widely validated model for simulating CH4 emissions from paddy rice fields exposed to ambient CO2 （hereinafter referred to as aCO2）. We upgraded the model to CH4MOD 2.0 by： （a） modifying the description of the influences of soil Eh and the water regime on CH4 production; （b） adding new features to reflect the regulatory effects of atmospheric CO2 upon methanogenic substrates, soil Eh during drainages, and vascular CH4 transport; and （c） adding a new feature to simulate the influences of nitrogen （N） addition rates on methanogenic substrates under elevated CO2 （hereinafter referred to as eCO2） condition. Validation with 109 observation cases under aC02 condition showed that CHaMOD 2.0 possessed a minor systematic bias in the prediction of seasonally accumulated methane emissions （SAM）. Validation with observations in free-air CO2 enrichment （FACE） experiments in temperate and subtropical climates showed that CH4MOD 2.0 successfully simulated the effects of eCO2 upon SAM from paddy rice fields incorporated with various levels of previous crop residues and/or N fertilizer. Our results imply that CH4MOD 2.0 provides a potential approach for estimating of the effects of elevated atmospheric CO2 upon CHa emissions from regional or global paddy rice fields with various management practices in a changing climate.

Lipid accumulation and CO_2 utilization of two marine oil-rich microalgal strains in response to CO_2 aeration

Biological CO2 sequestration by microalgae is a promising and environmentally friendly technology applied to sequester CO2. The characteristics of neutral lipid accumulation by two marine oil-rich microalgal strains,namely, Isochrysis galbana and Nannochloropsis sp., through CO2 enrichment cultivation were investigated in this study. The optimum culture conditions of the two microalgal strains are 10% CO2 and f medium. The maximum biomass productivity, total lipid content, maximum lipid productivity, carbon content, and CO2 fixation ability of the two microalgal strains were obtained. The corresponding parameters of the two strains were as follows：（（142.42±4.58） g/（m^2·d）,（149.92±1.80） g/（m^2·d））,（（39.95±0.77）%,（37.91±0.58）%）,（（84.47±1.56） g/（m^2·d）,（89.90±1.98） g/（m^2·d））,（（45.98±1.75）%,（46.88±2.01）%）, and（（33.74±1.65） g/（m^2·d）,（34.08±1.32） g/（m^2·d））. Results indicated that the two marine microalgal strains with high CO2 fixation ability are potential strains for marine biodiesel development coupled with CO2 emission reduction.

The effects of enriched C0_(2) and enhanced UV-B radiation on ultrastructure of Dunaliella salina, singly and in combination

The effects of ambient CO2/ambient UV-B, enriched CO2/ambient UV-B, ambient CO2/enhanced UV-B, and enriched CO2/enhanced UV-B on the ultrastructure of Dunaliella salina were investigated. （1） The ultrastructure of D..salina cell in the control experiment showed that the arrangement of thylakoid lamellae was regular, and there were many large starch grains among the thylakoid lamellae. A prominent well-developed pyrenoid was found in the middle of the chloroplast. Nucleus envelope and nucleolus were clearly observed. The Golgi apparatus accompanied by numerous vesicles with a compact arrangement of cisternae and the peripheral tips of the cisternae were swollen to a size comparable to that of some of the associated vesicles. （2） The ultrastructure of D. salina cell in enriched CO2 showed that the arrangement of thylakoid was regular and the lamellae were vivid. Developed pyrenoids were found in the low-CO2-grown cells, but not in the high-CO2-grown cells. The mitochondria cristae were vivid. The arrangement of Golgi apparatus was compact. （3） The ultrastructure of D. salina cell in enhanced UV-B showed that the thylakoid was dissolved and the cells had a less developed pyrenoid or no detectable pyrenoid. Part of the nucleus envelope was dissolved. The number ofmitochondria was increased and some mitochondria cristae were disintegrated. The starch grains were broken apart into many small starch grains. The Golgi apparatus with a loose arrangement ofcistemae and the peripheral tips of the Golgi cistemae were not especially swollen, with several large associated vesicles. （4） The ultrastructure of D. salina cell in the enriched CO2/enhanced UV-B showed that part of the thylakoid and nucleus envelopes of some cells were dissolved. The pyrenoid was larger than that of the enhanced UV-B. There were many mitochondria between stroma and chloroplast membrane, but mitochondria cristae were partly dissolved. Many small starch grains were accumulated in cells. The starch sheath was broken into several discontinuous starch grains with different sizes. The arrangement of Golgi apparatus was loose. Above all, although the enriched CO2 can alleviate the damage induced by the UV-B radiation, the effects of experimental UV-B radiation were larger than the effects of actual UV-B radiation, the damage induced by the UV-B radiation was so severe, therefore, CO2 enrichment could not restore the ultrastructure to the control level.

Responses of Irrigated Winter Wheat Yield in North China to Increased Temperature and Elevated CO2Concentration

North China is one of the main regions of irrigated winter wheat production in China. Climate warming is apparent in this region, especially during the growing season of winter wheat. To understand how the yield of irrigated winter wheat in North China might be affected by climate warming and CO2 concentration enrichment in future, a set of manipulative field experiments was conducted in a site in the North China Plain under increased temperature and elevated CO2 concentration by using open top chambers and infrared radiator heaters. The results indicated that an average temperature increase of 1.7℃ in the growing season with CO2 concentration of 560 μmol mol-1 did not reduce the yield of irrigated winter wheat. The thousand- kernel weight of winter wheat did not change significantly despite improvement in the filling rate, because the increased temperature shortened the duration of grain filling. The number of effective panicles and the grain number per ear of winter wheat did not show significant changes. There was a large increase in the shoot biomass because of the increase in stem number and plant height. Consequently, under the prescribed scenario of asymmetric temperature increases and elevated CO2 concentration, the yield of irrigated winter wheat in North China is not likely to change significantly, but the harvest index of winter wheat is likely to be greatly reduced.

Effect of Elevated CO2 on the Growth and Macronutrient （N, P and K） Uptake of Annual Wormwood （Artemisia annua L.）

Annual wormwood(Artemisia annua L.) is the only viable source of artemisinin,an antimalarial drug.There is a pressing need to optimize production per cultivated area of this important medicinal plant;however,the effect of increasing atmospheric carbon dioxide(CO_2) concentration on its growth is still unclear.Therefore,a pot experiment was conducted in a free-air CO2 enrichment(FACE) facility in Yangzhou City,China.Two A.annua varieties,one wild and one cultivated,were grown under ambient(374μmol mol^(-1)) and elevated(577 μmol mol^(-1)) CO_2 levels to determine the dry matter accumulation and macronutrient uptake of aerial parts.The results showed that stem and leaf yields of both A.annua varieties increased significantly under elevated CO_2 due to the enhanced photosynthesis rate.Although nitrogen(N),phosphorus(P),and potassium(K) concentrations in leaves and stems of both varieties decreased under elevated CO_2,total shoot N,P,and K uptake of the two varieties were enhanced and the ratios among the concentrations of these nutrients(N:P,N:K,and P:K) were not affected by elevated CO_2.Overall,our results provided the evidence that elevated CO_2 increased biomass and shoot macronutrient uptake of two A.annua varieties.

Photoautotrophic Growth and Net Photosynthetic Rate of Sweet Potato Plantlets In Vitro as Affected by the Number of Air Exchanges of the Vessel and Type of Supporting Material

To produce high-quality sweet potato plantlets rapidly at low production costs, single nodal leafy cuttings of sweet potato （Ipomoea batatas （L.） Lam.） plantlets were cultured in vitro for 14 days on sugarand phytohormone-free Murashige and Skoog （MS） liquid medium, at a photosynthetic photon flux （PPF） of 200 μmol.m^-2.s^-1 and a CO2 concentration （v/v） of 1.8×10^-3. A factorial experiment was conducted with two levels of the number of air exchanges of the vessel （NAE）, 8.7-12.2 h^-1 and 〉12.2 h^-1, and two types of supporting material, vermiculite and Florialite （a porous material）. The control treatment consisted of a pho- tomixotrophic culture using a sugar- and NAA-containing agar MS medium with an NAE of 2.4 h^-1. PPF and CO2 concentrations were the same as the photoautotrophic treatments. In comparison with the control treatment, the photoautotrophic treatments with NAE of 8.7-12.2 h^-1 （MF treatment） and ≥12.2 h^-1 （HF treatment） were, respectively, 2.2 and 2.8 times in dry weight, and 3.7 and 4.2 times in net photosynthetic rate, when Florialite was used. The survival percentages of the plantlets in the field were, respectively, 86% and 97% in the MF and HF treatments, and 35% and 46% higher than that in the control treatment. The plantlets cultured with Florialite showed greater growth, compared with those cultured with vermiculite. Photoautotrophic micropropagation system with high NAE and the use of porous supporting material can produce high-quality plantlets and make it possible to reduce production costs.