开放式空气CO2增高对水稻物质生产与分配的影响

在大田栽培条件下,研究开放式空气CO2增加(FACE)200μmol·mol^-1的处理对水稻物质生产与分配的影响．结果表明,FACE处理使移栽至抽穗后20d的干物质积累量显著增加,使抽穗后20d至成熟期的干物质生产量显著减少,生物产量显著提高．移栽至抽穗期的干物质积累量增加是由于叶面积系数和净同化率共同提高所致;抽穗期至抽穗后20d的干物质积累量增加主要是由于叶面积系数的增加所致;抽穗后20d至成熟期的干物质生产量减少主要是由于净同化率的下降所造成．提高茎鞘占全株干物重的比例,降低叶片占全株干物重的比例,对穗占全株干物重的比例无显著影响,能显著提高水稻抽穗期茎鞘中可溶性糖、淀粉的含有率和含量,提高FACE处理的生物产量能极显著提高水稻产量(r＝0．7825)．     

Herbivore-induced changes in plant carbon allocation: assessment of below-ground C fluxes using carbon-14

Effects of above-ground herbivory on short-term plant carbon allocation were studied using maize (Zea mays) and a generalist lubber grasshopper (Romalea guttata). We hypothesized that above-ground herbivory stimulates current net carbon assimilate allocation to below-ground components, such as roots, root exudation and root and soil respiration. Maize plants 24 days old were grazed (c. 25–50% leaf area removed) by caging grasshoppers around individual plants and 18 h later pulse-labelled with¹⁴CO₂. During the next 8 h,¹⁴C assimilates were traced to shoots, roots, root plus soil respiration, root exudates, rhizosphere soil, and bulk soil using carbon-14 techniques. Significant positive relationships were observed between herbivory and carbon allocated to roots, root exudates, and root and soil respiration, and a significant negative relationship between herbivory and carbon allocated to shoots. No relationship was observed between herbivory and¹⁴C recovered from soil. While herbivory increased root and soil respiration, the peak time for¹⁴CO₂ evolved as respiration was not altered, thereby suggesting that herbivory only increases the magnitude of respiration, not patterns of translocation through time. Although there was a trend for lower photosynthetic rates of grazed plants than photosynthetic rates of ungrazed plants, no significant differences were observed among grazed and ungrazed plants. We conclude that above-ground herbivory can increase plant carbon fluxes below ground (roots, root exudates, and rhizosphere respiration), thus increasing resources (e.g., root exudates) available to soil organisms, especially microbial populations.     

Diel changes in the CO2 exchange rates of reproductive organs of the tropical tree Durio zibethinus

The daily variations in the in situ CO₂ exchange of the reproductive organs of Durio zibethinus trees, growing in an experimental field at University Putra Malaysia (UPM), were examined at different growth stages. Reproductive organs emerged on the leafless portions of branches inside the crown. The photon flux densities (PFD) in the chambers used for the measurements were less than 100 mol m^–2 s^–1 and were 40% of the PFD outside of the crown. The daytime net respiration rate and the nighttime dark respiration rate were higher at the time of flower initiation and during the mixed stages, when flower buds, flowers, and fruit coexist, than at the flower bud stage. The net respiration rate was lower than the daytime dark respiration rate at given temperatures, especially at the flower bud and fruit stages. Conversely, the net respiration rate was similar to the daytime dark respiration rate at the mixed stage. Photosynthetic CO₂ refixation reduced the daily respiratory loss by 17, 5, 0.3, and 24% at the flower bud, flower initiation, mixed, and fruit stages, respectively.     

Changes in alfalfa forage quality and stem carbohydrates induced by arbuscular mycorrhizal fungi and elevated atmospheric CO2

Alfalfa is a widely distributed forage legume whose leaves are high in protein content and whose stems are suitable for bioethanol production. However, alfalfa forage digestibility, quality and yield may vary under future climate change scenarios. This legume can establish double symbiosis with nitrogen‐fixing bacteria and arbuscular mycorrhizal fungi (AMF). The presence of AMF can modify the evolution of biomass production and partitioning during the vegetative growth of alfalfa. We hypothesised that mycorrhizal symbiosis may change the quantity and/or quality of carbohydrates and lignin in leaves and/or stems of alfalfa, with these changes being dependent on the atmospheric CO₂ concentration at which plants are grown. Results showed that mycorrhizal alfalfa plants exposed to elevated CO₂ had improved leaf, stem and root biomass, enhanced amount of hemicellulose and decreased concentration of lignin in cell walls of leaves as well as increased levels of glucose and fructose in stems compared with non‐mycorrhizal alfalfa. These results indicated improved forage quality (leaves) and enhanced potential for bioethanol conversion (stems) in mycorrhizal alfalfa cultivated under elevated CO₂. Moreover, the potential of stems for producing CH₄ reinforced their suitability for the conversion of biomass into bioethanol.     

The dynamics of photosynthetic acclimation to changes in light quanlity and quality in three Australian rainforest tree species

Photosynthetic acclimation was studied in seedlings of three subtropical rainforest species representing early (Omalanthus populifolius), middle (Duboisia myoporoides) and late (Acmena ingens) successional stages in forest development. Changes in the photosynthetic characteristics of pre-existing leaves were observed following the transfer of plants between deep shade (1–5% of photosynthetically active radiation (PAR), selectively filtered to produce a red/far-red (R/FR) ratio of 0.1) and open glasshouse (60% PAR and a R/FR ratio of 1.1–1.2), and vice versa. The extent and rate of response of the photosynthetic characteristics of each species to changes in light environment were recorded in this simulation of gap formation and canopy closure/overtopping. The light regimes to which plants were exposed produced significant levels of acclimation in all the photosynthetic parameters examined. Following transfer from high to low light, the light-saturated rate of photosynthesis was maintained near pre-transfer levels for 7 days, after which it decreased to levels which closely approximated those in leaves which had developed in low light. The decrease in photosynthetic capacity was associated with lower apparent quantum yields and stomatal conductances. Dark respiration was the parameter most sensitive to changes in light environment, and responded significantly during the first 4–7 days after transfer. Acclimation of photosynthetic capacity to increases in irradiance was significant in two of the three species studied, but was clearly limited in comparison with that of new leaves produced in the high light conditions. This limitation was most pronounced in the early-successional-stage species, O. populifolius. It is likely that structural characteristics of the leaves, imposed at the time of leaf expansion, are largely responsible for the limitations in photosynthetic acclimation to increases in irradiance.     

大气O3浓度升高和模拟N沉降对黄豆光合、生物量和非结构性碳水化合物积累及分配的影响

为探究全球气候变化带来的大气臭氧(O₃)浓度升高和氮(N沉降)对黄豆气体交换、生物量和非结构性碳水化合物(NSCs)积累及分配的影响, 利用开顶式气室(OTC)设置了2个O₃浓度(AA, 正常大气; AAO60, 正常大气+60 μg/m³O₃)和2个施N梯度(对照;施N)并开展了相关实验。研究结果表明： (1) N沉降处理后叶片净光合速率(Pn)和气孔导度(Gs)显著提高了96.21%和83.77%, 但是对黄豆各部位生物量的促进作用没有达到显著水平。N沉降处理后根系溶性糖和非结构性磷水化合物(NSCs)的比例显著下降了42.17%和38.95%, 而叶片淀粉分配比增加了41.55%, 豆粒和茎的可溶性糖含量分别提高了59.41%和95.29%。(2) O₃浓度升高处理后叶片Gs增加了94.89%, Pn降低了2.34%。叶片、茎、根和豆粒的生物量在O₃处理后分别显著降低了38.14%、56.25%、66.67%和25.49%。豆粒的可溶性糖和淀粉含量和总NSCs分别显著下降了21.94%和49.65%和30.55%。O₃浓度升高后根系中淀粉总量的比例的增加了56.21%。(3) O₃和N沉降处理二者共同处理在叶片净光合速率、蒸腾速率、豆粒、茎、根系NSCs组分均具有显著交互作用, 主要表现为拮抗作用。综上, 中度N沉降提高了叶片光合作用, 增加了对地上部分NSCs的分配而降低了对地下根系的分配;O₃浓度升高抑制了黄豆生长和NSCs积累, 但是相对增加了根系中淀粉总量的比例;N沉降一定程度上能够缓解O₃对光合和NSCs造成的损害, 但未见对生物量下降存在类似效应。     

植物水淹适应与碳水化合物的相关性

水淹会对陆生植物存活造成本质影响, 特别是完全水淹对陆生植物的影响更为明显。水淹对陆生植物最为主要的影响是氧气不足, 这主要是由氧气在水中的扩散速率较低引起的。同时, 在水淹胁迫下植物对光和CO₂的获取都会受到限制。所有这些因素都将引起植物生物量减少, 最终导致受淹植物死亡。碳水化合物是植物的能量来源, 与植物在水淹胁迫下存活与否有着密切联系。植物水淹适应性与碳水化合物的相关性主要体现在两大方面: 在生理形态层面, 植物通过伸长生长或抑制伸长生长、地上和地下部分碳水化合物的分配比例不同来应对水淹胁迫; 在另一个层面, 植物通过改变激素、酶和基因的表达, 调整碳水化合物的代谢方式, 从而适应水淹环境。该文结合国内外研究现状, 通过对植物在水淹胁迫下生理形态、激素、酶及基因表达诸方面的变化来认识水淹耐受性与碳水化合物的关系, 并就今后的研究方向提出几点建议。     

Release of resource constraints allows greater carbon allocation to secondary metabolites and storage in winter wheat

The atmospheric CO₂ concentration ([CO₂]) is rapidly increasing, and this may have substantial impact on how plants allocate metabolic resources. A thorough understanding of allocation priorities can be achieved by modifying [CO₂] over a large gradient, including low [CO₂], thereby altering plant carbon (C) availability. Such information is of critical importance for understanding plant responses to global environmental change. We quantified the percentage of daytime whole‐plant net assimilation (A) allocated to night‐time respiration (R), structural growth (SG), nonstructural carbohydrates (NSC) and secondary metabolites (SMs) during 8 weeks of vegetative growth in winter wheat (Triticum aestivum) growing at low, ambient and elevated [CO₂] (170, 390 and 680 ppm). R/A remained relatively constant over a large gradient of [CO₂]. However, with increasing C availability, the fraction of assimilation allocated to biomass (SG + NSC + SMs), in particular NSC and SMs, increased. At low [CO₂], biomass and NSC increased in leaves but decreased in stems and roots, which may help plants achieve a functional equilibrium, that is, overcome the most severe resource limitation. These results reveal that increasing C availability from rising [CO₂] releases allocation constraints, thereby allowing greater investment into long‐term survival in the form of NSC and SMs.     

大气二氧化碳浓度与温度升高对红桦幼苗养分积累和分配的影响

利用封闭式生长室,研究了CO2浓度升高(环境CO2 350 μmol·mol-1,EC)、温度升高(环境温度 2 ℃,ET)以及二者同时升高(ECT)对川西亚高山红桦幼苗养分积累和分配的影响.结果表明:经过一个生长季, EC处理下红桦幼苗单株N、P、K积累比对照分别增加44%、45%和11%(P《0.05),ET处理下分别增加37%、76%和9%(P《0.05),ECT处理下分别增加24%、88%和20% (P《0.05).EC处理使N向红桦幼苗叶中分配的比例降低11.68%(P《0.05),向枝、茎、根中分配的比例分别增加2.95%、3.39%和5.34%(P》0.05);ET处理使N向叶中分配的比例增加11.09%(P《0.05),向枝、茎、根中分配的比例分别降低0.69%、10.35%和0.05%(P》0.05).ECT处理下N的分配格局与EC处理相似.3种处理下P和K在红桦幼苗中的分配变化差异较大,CO2浓度和温度升高可能促进植物养分的积累,改变养分在植物各器官间的分配.     

Modulation of carbon and nitrogen allocation in Urtica dioica and Plantago major by elevated CO2: Impact of accumulation of nonstructural carbohydrates and ontogenetic drift

Doubling the atmospheric CO² concentration from 350 to 700 μ1 1^?1 increased the relative growth rate (RGR) of hydroponically grown Urtica dioica L. and Plantago major ssp. pleiosperma Pilger only for the first 10–14 days. Previous experiments with P. major led to the conclusion that RGR did not respond in proportion to the rate of photosynthesis. The present paper is focussed on the analysis of the impact of changes in leaf morphology, dry matter partitioning, dry matter chemical composition and ontogenetic drift on this discrepancy. Soon after the start of the treatment, carbohydrate concentrations were higher at elevated CO²: a reaction that was largely due to starch accumulation. An increase in the percentage of leaf dry matter and decreases in the specific leaf area (SLA) and the shoot nitrogen concentration were correlated with an increase in the total nonstructural carbohydrate concentration (TNC). A combination of accumulation of soluble sugars and starch and ontogenetic drift explains the decrease in SLA at the elevated CO² level. A similar ontogenetic effect of elevated CO² was observed on the specific root length (SRL). Other variables such as shoot nitrogen concentration and percentage leaf dry matter were not affected by correction of data for TNC levels. The net diurnal fluctuation of the carbohydrate pool in P. major was equal for both CO² concentrations, indicating that the growth response to elevated CO² may be ruled by variables other than photosynthesis, as for instance sink strength. Elevated CO² did not greatly influence the partitioning of nitrogen between soluble and insoluble, reduced N and nitrate, nor the allocation of dry matter between leaf. stem and root. The finding that the root to shoot ratio (R/S) was not affected by elevated CO² implies that, in order to maintain a balanced activity between roots and shoot, no shift in partitioning of dry matter upon doubling of the atmospheric CO² concentration is required. Our data on R/S are in good agreement with the response of R/S to high CO² predicted by models based on such a theorem.     

Soil and biomass carbon pools in model communities of tropical plants under elevated CO2

The experimental data presented here relate to the question of whether terrestrial ecosystems will sequester more C in their soils, litter and biomass as atmospheric CO₂ concentrations rise. Similar to our previous study with relatively fertile growth conditions (Körner and Arnone 1992), we constructed four rather nutrient-limited model communities of moist tropical plant species in greenhouses (approximately 7 m² each). Plant communities were composed of seven species (77 individuals per community) representing major taxonomic groups and various life forms found in the moist tropics. Two ecosystems were exposed to 340 l CO₂ l^–1 and two to 610 l l^–1 for 530 days of humid tropical growth conditions. In order to permit precise determination of C deposition in the soil, plant communities were initially established in C-free unwashed quartz sand. Soils were then amended with known amounts of organic matter (containing C and nutrients). Mineral nutrients were also supplied over the course of the experiment as timed-release full-balance fertilizer pellets. Soils represented by far the largest repositories for fixed C in all ecosystems. Almost 5 times more C (ca. 80% of net C fixation) was sequestered in the soil than in the biomass, but this did not differ between CO₂ treatments. In addition, at the whole-ecosystem level we found a remarkably small and statistically non-significant increase in C sequestration (+4%; the sum of C accretion in the soil, biomass, litter and necromass). Total community biomass more than quadrupled during the experiment, but at harvest was, on average, only 8% greater (i.e. 6% per year; n.s.) under elevated CO₂, mainly due to increased root biomass (+15%, P=0.12). Time courses of leaf area index of all ecosystems suggested that canopy expansion was approaching steady state by the time systems were harvested. Net primary productivity (NPP) of all ecosystems-i.e. annual accumulation of biomass, necromass, and leaf litter (but not plant-derived soil organic matter)-averaged 815 and 910 g m^–2 year^–1 at ambient and elevated CO₂, respectively. These NPPs are remarkably similar to those of many natural moist tropical forested ecosystems. At the same time net productivity of soil organic matter reached 7000 g dry matter equivalent per m² and year (i.e. 3500 g C m^–2 year^–1). Very slight yet statistically significant CO₂-induced shifts in the abundance of groups of species occurred by the end of the experiment, with one group of species (Elettaria cardamomum, Ficus benjamina, F. pumila, Epipremnum pinnatum) gaining slightly, and another group (Ctenanthe lubbersiana, Heliconia humilis, Cecropia peltata) losing. Our results show that: (1) enormous amounts of C can be deposited in the ground which are normally not accounted for in estimates of NPP and net ecosystem productivity; (2) any enhancement of C sequestration under elevated atmospheric CO₂ may be substantially smaller than is believed will occur (yet still very important), especially under growth conditions which permit close to natural NPP; and (3) species dominance in plant communities is likely to change under elevated CO₂, but that changes may occur rather slowly.     

CO2浓度升高对长白山三种树木幼苗叶碳水化合物和氮含量的影响

研究了持续 3个生长季高浓度CO2 处理的长白山主要树种红松、长白赤松和水曲柳幼苗叶 (片 )的蔗糖、果糖、可溶性总糖、淀粉及全氮含量变化 .结果表明 ,前两个生长季 70 0 μmol·mol-1CO2 处理 ,促进了水曲柳和长白赤松幼苗的淀粉累积 ,70 0和 5 0 0 μmol·mol-1CO2 却使红松幼苗的全N含量明显降低 .第三个生长季高浓度CO2 处理的第一周和第二周 ,红松和水曲柳幼苗的淀粉含量增加 ,全N含量降低 ,第八周时 ,水曲柳仍维持原来的变化趋势 .第三个生长季高浓度CO2 处理 ,并未使长白赤松的C、N含量有明显的增减 .CO2 浓度影响了碳水化合物在叶 (片 )中的积累形式     

ABA and GA3 increase carbon allocation in different organs of grapevine plants by inducing accumulation of non‐structural carbohydrates in leaves,enhancement of phloem area and expression of sugar transporters

Grape quality for winemaking depends on sugar accumulation and metabolism in berries. Abscisic acid (ABA) and gibberellins (GAs) have been reported to control sugar allocation in economically important crops, although the mechanisms involved are still unknown. The present study tested if ABA and gibberellin A₃ (GA₃) enhance carbon allocation in fruits of grapevines by modifying phloem loading, phloem area and expression of sugar transporters in leaves and berries. Pot‐grown Vitis vinifera cv. Malbec plants were sprayed with ABA and GA₃ solutions. The amount of soluble sugars in leaves and berries related to photosynthesis were examined at three points of berry growth: pre‐veraison, full veraison and post‐veraison. Starch levels and amylase activity in leaves, gene expression of sugar transporters in leaves and berries and phloem anatomy were examined at full veraison. Accumulation of glucose and fructose in berries was hastened in ABA‐treated plants at the stage of full veraison, which was correlated with enhancement of Vitis vinifera HEXOSE TRANSPORTER 2 (VvHT2) and Vitis vinifera HEXOSE TRANSPORTER 6 (VvHT6) gene expression, increases of phloem area and sucrose content in leaves. On the other hand, GA₃ increased the quantity of photoassimilates delivered to the stem thus increasing xylem growth. In conclusion, stimulation of sugar transport by ABA and GA₃ to berries and stems, respectively, was due to build‐up of non‐structural carbohydrates in leaves, modifications in phloem tissue and modulation in gene expression of sugar transporters.     

温度增高、CO2浓度升高、施氮对蒙古栎幼苗非结构碳水化合物积累及其分配的综合影响

蒙古栎(Quercus mongolica)是中国东北地区天然次生林重要组成树种, 研究该树种幼苗有机碳积累及碳库容对未来气候变化的响应, 可为预测未来气候变暖情景下蒙古栎林的天然更新及幼苗的培育提供科学参考。该文旨在探讨CO₂浓度和温度升高综合作用对蒙古栎幼苗非结构性碳水化合物(NSC)积累及其分配的影响。实验环境条件用人工气候箱控制, 控制条件如下: 1) CO₂浓度倍增(700 μmol·mol^-1), 温度升高4 ℃处理(HCHT); 2) CO₂浓度正常(400 μmol·mol^-1), 温度升高4 ℃处理(HT); 3) CO₂浓度和温度均正常, 即对照组(CK); 每个气候箱幼苗分别在3种氮素水平下生长: N2 (15 mmol·L^-1, 高氮), N1 (7.5 mmol·L^-1, 正常供氮)和N0 (不施氮), 一共为9个处理。研究结果表明, 1) HCHT共同作用对NSC积累无促进作用, 但改变了植物各器官中NSC的分配比例, 叶片中可溶性糖和淀粉的积累明显增加, HCHT下N2水平有利于NSC的积累。2) HT明显影响了蒙古栎一年生幼苗NCS的积累和分配。在N2水平下, HT明显促进NSC的积累, 并增加了在主根中的分配比例。3)植株各器官可溶性糖含量的动态变化因处理不同而异。主根淀粉含量随时间逐渐增加, 而细根淀粉含量随时间逐渐减少。在未来气候变暖的情况下, 土壤中大量的氮供给, 可能将促进蒙古栎幼苗的生长、增加其碳库容和抵御不良环境的能力, 进而提高其天然更新潜力。     

Individual and interactive effects of warming and nitrogen supply on CO2 fluxes and carbon allocation in subarctic grassland

Climate warming has been suggested to impact high latitude grasslands severely, potentially causing considerable carbon (C) losses from soil. Warming can also stimulate nitrogen (N) turnover, but it is largely unclear whether and how altered N availability impacts belowground C dynamics. Even less is known about the individual and interactive effects of warming and N availability on the fate of recently photosynthesized C in soil. On a 10-year geothermal warming gradient in Iceland, we studied the effects of soil warming and N addition on CO₂ fluxes and the fate of recently photosynthesized C through CO₂ flux measurements and a ¹³CO₂ pulse-labeling experiment. Under warming, ecosystem respiration exceeded maximum gross primary productivity, causing increased net CO₂ emissions. N addition treatments revealed that, surprisingly, the plants in the warmed soil were N limited, which constrained primary productivity and decreased recently assimilated C in shoots and roots. In soil, microbes were increasingly C limited under warming and increased microbial uptake of recent C. Soil respiration was increased by warming and was fueled by increased belowground inputs and turnover of recently photosynthesized C. Our findings suggest that a decade of warming seemed to have induced a N limitation in plants and a C limitation by soil microbes. This caused a decrease in net ecosystem CO₂ uptake and accelerated the respiratory release of photosynthesized C, which decreased the C sequestration potential of the grassland. Our study highlights the importance of belowground C allocation and C-N interactions in the C dynamics of subarctic ecosystems in a warmer world.     

Combined effects of elevated CO2 and soil drought on carbon and nitrogen allocation of the desert shrub Caragana intermedia

Impacts of either elevated CO₂ or drought stress on plant growth have been studied extensively, but interactive effects of these on plant carbon and nitrogen allocation is inadequately understood yet. In this study the response of the dominant desert shrub, Caragana intermedia Kuanget H.c.Fu, to the interaction of elevated CO₂ (700 ± 20 μmol mol⁻¹) and soil drought were determined in two large environmental growth chambers (18 m²). Elevated CO₂ increased the allocation of biomass and carbon into roots and the ratio of carbon to nitrogen (C:N) as well as the leaf soluble sugar content, but decreased the allocation of biomass and carbon into leaves, leaf nitrogen and leaf soluble protein concentrations. Elevated CO₂ significantly decreased the partitioning of nitrogen into leaves, but increased that into roots, especially under soil drought. Elevated CO₂ significantly decreased the carbon isotope discrimination (Δ) in leaves, but increased them in roots, and the ratio of Δ values between root and leaf, indicating an increased allocation into below-ground parts. It is concluded that stimulation of plant growth by CO₂ enrichment may be negated under soil drought, and under the future environment, elevated CO₂ may partially offset the negative effects of enhanced drought by regulating the partitioning of carbon and nitrogen.     

大气CO_2浓度升高对香蕉光合作用及光合碳循环过程中叶氮分配的影响

生长在高CO2 浓度 (70 0± 5 6 μl·L-1) 1周的香蕉叶片 ,其光合速率 (Pn ,μmol·m-2 ·s-1)为 5 .14± 0 .32 ,较生长在大气CO2 浓度 (35 6± 30lμl·L-1)的高 2 2 .1% ,而生长在较高CO2 浓度下 8周 ,叶片Pn较生长在大气CO2 浓度的低 18.1% ,表现香蕉叶片对较长期高CO2 浓度的驯化和光合作用抑制 .生长在高CO2 浓度的香蕉叶片有较低光下呼吸速率 (Rd) ,而不包括光下呼吸的CO2 补偿点则变幅较小 .最大羧化速率 (Vcmax)和电子传递速率 (J)分别较生长在大气CO2 浓度的低 30 .5 %和 14 .8% ,根据气体交换速率计算的表观量子产率 (α ,molCO2·mol-1光量子 ) ,生长在较高CO2 浓度下 8周的叶片为 0 .0 14± 0 .0 1,而生长在大气CO2 浓度下的为 0 .0 2 5±0 .0 0 5 .较高CO2 浓度下叶片的表观量子产率降低 44% .光能转换效率 (electrons·quanta-1)亦从 0 .2 0 3降低至0 .136 .生长在较高CO2 浓度下香蕉叶片的叶氮在Rubicos分配系数 (PR)、叶氮在生物力能学组分分配系数(PB)和叶氮在光捕组分的分配系数 (PL)均较生长在大气CO2 浓度低 ,表明在高CO2 浓度下较长期生长 (8周 )的香蕉叶片多个光合过程受抑制 ,光合活性明显降低 .     

The effects of chamber pressurization on soil-surface CO2 flux and the implications for NEE measurements under elevated CO2

Soil and ecosystem trace gas fluxes are commonly measured using the dynamic chamber technique. Although the chamber pressure anomalies associated with this method are known to be a source of error, their effects have not been fully characterized. In this study, we use results from soil gas-exchange experiments and a soil CO₂ transport model to characterize the effects of chamber pressure on soil CO₂ efflux in an annual California grassland. For greater than ambient chamber pressures, experimental data show that soil-surface CO₂ flux decreases as a nonlinear function of increasing chamber pressure; this decrease is larger for drier soils. In dry soil, a gauge pressure of 0.5 Pa reduced the measured soil CO₂ efflux by roughly 70% relative to the control measurement at ambient pressure. Results from the soil CO₂ transport model show that pressurizing the flux chamber above ambient pressure effectively flushes CO₂ from the soil by generating a downward flow of air through the soil air-filled pore space. This advective flow of air reduces the CO₂ concentration gradient across the soil–atmosphere interface, resulting in a smaller diffusive flux into the chamber head space. Simulations also show that the reduction in diffusive flux is a function of chamber pressure, soil moisture, soil texture, the depth distribution of soil CO₂ generation, and chamber diameter. These results highlight the need for caution in the interpretation of dynamic chamber trace gas flux measurements. A portion of the frequently observed increase in net ecosystem carbon uptake under elevated CO₂ may be an artifact resulting from the impact of chamber pressurization on soil CO₂ efflux.     

大气CO2浓度升高对香蕉光合作用及光合碳循环过程中叶氮分配的影响

生长在高CO₂浓度(700±5μl·L^-1)1周的香蕉叶片,其光合速率(Pn,μmol·m^-2·s^-1)为5.14±0.32,较生长在大气CO₂浓度(356±301μl·L^-1)的高22.1%,而生长在较高CO₂浓度下8周,叶片Pn较生长在大气CO₂浓度的低18.1%,表现香蕉叶片对较长期高CO₂浓度的驯化和光合作用抑制.生长在高CO₂浓度的香蕉叶片有较低光下呼吸速率(R_d),而不包括光下呼吸的CO₂补偿点则变幅较小.最大羧化速率(Vcmax)和电子传递速率(J)分别较生长在大气CO₂浓度的低30.5%和14.8%,根据气体交换速率计算的表观量子产率(α,mol CO₂·mol^-1光量子),生长在较高CO₂浓度下8周的叶片为0.014±0.01,而生长在大气CO₂浓度下的为0.025±0.005.较高CO₂浓度下叶片的表观量子产率降低44%.光能转换效率electrons·quanta^-1)亦从0.203降低至0.136.生长在较高CO₂浓度下香蕉叶片的叶氮在Rubicos分配系数(PR)、叶氮在生物力能学组分分配系数(P_B)和叶氮在光捕组分的分配系数(P_L)均较生长在大气CO₂浓度低,表明在高CO₂浓度下较长期生长(8周)的香蕉叶片多个光合过程受抑制,光合活性明显降低.