Effects of elevated carbon dioxide concentration and soil temperature on the growth and biomass responses of mountain maple (Acer spicatum) seedlings to light availability

Aims Some shade-tolerant understory tree species such as mountain maple (Acer spicatum L.) exhibit light-foraging growth habits. Changes in environmental conditions, such as the rise of carbon dioxide concentration ([CO₂]) in the atmosphere and soil warming, may affect the performance of these species under different light environments. We investigated how elevated [CO₂] and soil warming influence the growth and biomass responses of mountain maple seedlings to light availability.Methods The treatments were two levels of light (100% and 30% of the ambient light in the greenhouse), two [CO₂] (392 μmol mol^-1 (ambient) and 784 μmol mol^-1 (elevated)) and two soil temperatures (T soil) (17 and 22°C). After one growing season, we measured seedling height, root collar diameter, leaf biomass, stem biomass and root biomass.Important findings We found that under the ambient [CO₂], the high-light level increased seedlings height by 70% and 56% at the low T soil and high T soil, respectively. Under the elevated [CO₂], however, the high-light level increased seedling height by 52% and 13% at the low T soil and high T soil, respectively. The responses of biomasses to light generally followed the response patterns of height growth under both [CO₂] and T soil and the magnitude of biomass response to light was the lowest under the elevated [CO₂] and warmer T soil. The results suggest that the elevated [CO₂] and warmer T soil under the projected future climate may have negative impact on the colonization of open sites and forest canopy gaps by mountain maple.     

双季稻不同生育期净同化速率对大气CO2浓度和温度升高的响应

大气CO₂浓度和温度升高对水稻干物质积累的影响因不同栽培区域和不同稻作类型而异。目前,我国双季稻轮作系统干物质生产力对温度、CO₂浓度升高和二者交互作用的响应特征尚不明确。本研究以早稻‘两优287’和晚稻‘湘丰优9号’为供试材料,在湖北省荆州市利用开顶式气室(OTC)进行连续3年的大田原位模拟试验,设置大田(UC)、对照(CK,OTC控制大气温度和CO₂浓度)、增温2 ℃(ET)、CO₂浓度增加60 μmol·mol^-1(EC)、增温2 ℃+CO₂浓度增加60 μmol·mol^-1(ETEC)5个处理,研究温度和CO₂浓度升高对早稻和晚稻地上部生物量、叶面积和净同化速率的影响。结果表明: CO₂浓度和/或温度升高对早稻和晚稻移栽-拔节阶段净同化速率影响不显著,提高了拔节-齐穗阶段净同化速率,但降低了齐穗-成熟阶段净同化速率(除早稻对高CO₂浓度表现为正响应外)。CO₂浓度和/或温度升高促进了各生育期叶面积的增长,以ETEC处理叶面积指数最高(除成熟期外)。在齐穗期,温度和CO₂浓度升高协同促进了地上部干物质积累,ETEC处理早稻和晚稻地上部生物量比CK高10.3%～39.8%和23.6%～34.4%;在早稻成熟期,增温在一定程度上抵消了增加CO₂浓度对地上部干物质积累的促进作用,ETEC比EC地上部生物量降低3.2%～14.1%;而晚稻成熟期,增温和增加CO₂浓度表现为正向的交互作用,可进一步提高地上部生物量。回归分析表明,温度和CO₂浓度升高在双季稻营养生长阶段对植株净同化能力以正向作用为主,在生殖生长阶段增温表现为负向作用。由于生长特性、生育期跨度和温度资源配置的差异,CO₂浓度和温度升高可能提高我国双季稻轮作系统干物质生产力。     

红松幼苗对CO2浓度升高的生理生态反应

研究了用开顶箱控制CO₂浓度在500和700μmol·mol^-1左右时红松幼苗的生理生态反应.结果表明,高浓度CO₂(500、700μmol·mol^-1CO₂)和对照(对照开顶箱、裸地)条件下,红松幼苗的净光合速率与气孔导度之间的变化不同.红松幼苗在500μmol·mol^-1CO₂条件下,RuBPcase活性最高,呈现光合上调反应,日平均净光合速率最大,叶绿素及可溶性糖含量最高;而生长在700μmol·mol^-1CO₂的红松幼苗呈现光合下调反应,光合作用明显低于对照植株,其酶活性及物质含量均最低.     

The effects of elevated ozone and CO2 on growth and defense of native,exotic and invader trees

Aims Elevated ozone and CO₂ can differentially affect the performance of plant species. Variation among native, exotic and invader species in their growth and defense responses to CO₂ and ozone may shape CO₂ and ozone effects on invasions, perhaps in part also due to variation between native and invasive populations of invaders.Methods We manipulated ozone (control or 100 ppb) and CO₂ (ambient or 800 ppm) in a factorial greenhouse experiment in replicated chambers. We investigated growth and defense (tannins) of seedlings of Triadica sebifera from invasive (USA) and native (China) populations and pairs of US and China tree species within three genera (Celtis, Liquidambar and Platanus).Important findings Overall, ozone reduced growth in ambient CO₂ but elevated CO₂ limited this effect. T. sebifera plants from invasive populations had higher growth than those from native populations in control conditions or the combination of elevated CO₂ and ozone in which invasive populations had greater increases in growth. Their performances were similar in elevated CO₂ because native populations were more responsive and their performances were similar with elevated ozone because invasive populations were more susceptible. Compared to other species, T. sebifera had high growth rates but low levels of tannin production that were insensitive to variation in CO₂ or ozone. Both China and US Platanus plants reduced tannins with increased CO₂ and/or ozone and US Liquidambar plants increased tannins with the combination of elevated CO₂ and ozone. The growth results suggest that intraspecific variation in T. sebifera will reduce the effects of CO₂ or ozone alone on invasions but increase their combined effects. The tannin results suggest that defense responses to CO₂ and ozone will be variable across native and exotic species. The effects of CO₂ and ozone on growth and defense of native and exotic species indicate that the benefit or harm to species from these global change drivers is an idiosyncratic combination of species origin and genus.     

CO2浓度升高条件下长白赤松幼苗种植密度对净光合速率的影响

The effect of Pinus sylvestriformis seedlings density on net photosynthetic rate was studied under elevated CO₂. Atmospheric CO₂ concentration was controlled in OTC (Open Top Chamber). The results showed that elevated CO₂ not only made net photosynthetic rates (NPRs) of two Pinus sylvestriformis seedlings densities increased,but also mitigated their intra-specific competition. Meanwhile,the difference of seedling NPRs between100 and 400 plant·m^-2 under 500 μmol·mol^-1 air CO₂ concentration was less than that under 350 μmol·mol^-1 with the same PARlevels. When air CO₂ concentration reached 700 μmol·mol^-1, the NPRs of seedlings under both planting densities were close to each other with the same PARlevels. The intra-specific competition was minimized under air CO₂ concentration of 700 μmol·mol^-1.     

高CO2浓度、干旱及其互作对不同持绿型小麦幼苗的影响

以小麦持绿型品种‘烟农19'和非持绿型品种‘旱选3号'为试材,在开放式气室(OTC)内设置正常CO₂浓度(370 μmol·mol^-1)和高CO₂浓度(550 μmol·mol^-1),干旱(田间持水量的45%～55%)和灌溉(田间持水量的75%～85%),共4个环境处理,采用盆栽法研究高CO₂浓度、干旱及其互作对不同持绿型小麦幼苗生长性状、生物量积累和生理性状的影响。结果表明: 干旱显著抑制了小麦幼苗的生长发育;高CO₂浓度对小麦幼苗的生长发育有明显的促进作用,对分蘖数的影响更显著,干旱条件下高CO₂浓度使旱选3号和烟农19的分蘖数分别增加了61.0%和42.3%。两种水分条件下,高CO₂浓度显著增加了小麦幼苗的生物量,降低了幼苗叶片过氧化物酶和脯氨酸的含量。干旱条件下,高CO₂浓度表现出更好的“肥效作用”。此外,不同持绿型小麦品种对高CO₂浓度的响应存在差异,旱选3号对CO₂的响应更敏感。因此,在未来气候变化背景下,CO₂浓度升高时可以适当减少田间灌水量,合理利用水资源,还需注意选择适宜的品种。     

Water-use efficiency of four native trees under CO2 enrichment and N addition in subtropical model forest ecosystems

Aims We aimed to evaluate the changes in water-use efficiency (WUE) in native tree species in forests of subtropical China, and determine how coexisting species would be responding to increases in atmospheric carbon dioxide (CO₂) concentrations and nitrogen (N) deposition.Methods We used model forest ecosystems in open-top chambers to study the effects of elevated CO₂ (ca. 700 μmol mol^-1) alone and together with N addition (NH 4 NO 3 applied at 100kg N ha^-1 year^-1) on WUE of four native tree species (Schima superba, Ormosia pinnata, Castanopsis hystrix and Acmena acuminatissima) from 2006 to 2010.Important findings Our result indicated that all species increased their WUE when they were exposed to elevated CO₂. Although higher WUE was shown in faster-growing species (S. superba and O. pinnata) than that of slower-growing species (C. hystrix and Acmena acuminatissima), the increased extent of WUE induced by elevated CO₂ was higher in the slower-growing species than that of the faster-growing species (P < 0.01). The N treatment decreased WUE of S. superba, while the effects on other species were not significant. The interactions between elevated CO₂ and N addition increased intrinsic WUE of S. superba significantly (P < 0.001), however, it did not affect WUE of the other tree species significantly. We conclude that the responses of native tree species to elevated CO₂ and N addition are different in subtropical China. The species-specific effects of elevated CO₂ and N addition on WUE would have important implications on species composition in China's subtropics in response to global change.     

Changes in leaf nutrient traits and photosynthesis of four tree species: effects of elevated [CO2], N fertilization and canopy positions

Aims Leaf traits of trees exposed to elevated [CO₂] in association with other environmental factors are poorly understood in tropical and subtropical regions. Our goal was to investigate the impacts of elevated [CO₂] and N fertilization on leaf traits in southern China.Methods Four tree species, Schima superba Gardn. et Champ. (S. superba), Ormosia pinnata (Lour.) Merr (O. pinnata), Castanopsis hystrix AC. DC. (C. hystrix) and Acmena acuminatissima (Blume) Merr. et Perry (A. acuminatissima) were studied in a factorial combination of atmospheric [CO₂] (ambient at ~390 μmol mol ? 1 and elevated [CO₂] at ~700 μmol mol^-1) and N fertilization (ambient and ambient + 100 kg N ha^-1 yr^-1) in open-top chambers in southern China for 5 years. Leaf mass per unit leaf area (LMA), leaf nutrient concentration and photosynthesis (A sat) were measured.Important findings Results indicated that leaf traits and photosynthesis were affected differently by elevated [CO₂] and N fertilization among species. Elevated [CO₂] decreased LMA in all species, while N fertilization did not affect LMA. Leaf mass-based N concentration (N M) was significantly greater in O. pinnata and C. hystrix grown in elevated [CO₂] but was lower in S. superba. Leaf mass-based P concentration (P M) was significantly greater in C. hystrix and A. acuminatissima exposed to elevated [CO₂] but was lower in S. superba. N fertilization significantly increased P M in O. pinnata but decreased P M in S. superba. Photosynthetic stimulation in O. pinnata, C. hystrix and A. acuminatissima was sustained after 5 years of CO₂ fumigation. N fertilization did not modify the effects of elevated [CO₂] on photosynthesis. Leaf traits (N M, N A, P M, P A) and light-saturated photosynthesis were decreased from the upper to lower canopy. Canopy position did not alter the responses of leaf traits and photosynthesis to elevated [CO₂]. Results suggest that photosynthetic stimulation by elevated [CO₂] in native species in subtropical regions may be sustained in the long term.     

Traits of an invasive grass conferring an early growth advantage over native grasses

Aims Invasive species often have higher relative growth rates (RGR) than their native counterparts. Nutrient use efficiency, total leaf area and specific leaf area (SLA) are traits that may confer RGR differences between natives and invasives, but trait differences are less prominent when the invasive species belongs to the same plant functional type as the dominant native species. Here, we test if traits displayed soon after germination confer an early size advantage. Specifically, we predicted that invasive species seedlings grow faster than the natives because they lack trade-offs that more strongly constrain the growth of native species.Methods We quantified plant morphological and physiological traits and RGR during early seedling growth at high and low nutrient levels in three dominant perennial native C₄ grasses: Panicum virgatum L. (switchgrass), Schizachyrium scoparium (Michx.) Nash (little bluestem) and Andropogon gerardii Vitman (big bluestem); and a perennial C₄ exotic invasive grass, Sorghum halepense (L.) Pers. (Johnsongrass).Important findings After 2 weeks of growth, Johnsongrass seedlings had greater biomass, SLA and photosynthetic nitrogen use efficiency, but lower leaf N concentrations (% leaf N) and root:shoot ratio than natives. As growth continued, Johnsongrass more quickly produced larger and thicker leaves than the natives, which dampened the growth advantage past the first 2 to 3 weeks of growth. Investment in carbon gain appears to be the best explanation for the early growth advantage of Johnsongrass. In natives, growth was constrained by an apparent trade-off between allocation to root biomass, which reduced SLA, and production of leaves with high N content, which increased carbon gain. In Johnsongrass, root:shoot ratio did not interact with other traits, and % leaf N was decoupled from RGR as a result of a trade-off between the positive indirect association of % leaf N with RGR and the negative direct association of % leaf N with RGR.     

水稻叶片光合作用对开放式空气CO2浓度增高(FACE)的响应与适应

利用便携式光合气体分析系统(LI-6400),比较测定了高CO₂浓度(FACE,free-airCO₂enrichment)和普通空气CO₂浓度下生长的水稻叶片的净光合速率、水分利用率、表观量子效率和RuBP羧化效率等光合参数.在各自生长CO₂浓度(380vs580μmol·mol^-1)下测定时,高CO₂浓度(580μmol·mol^-1)下生长的水稻叶片的净光合速率、碳同化的表观量子效率和水分利用率明显高于普通空气(380μmol·mol^-1)下生长的水稻叶片.但是,随着FACE处理时间的延长,高CO₂浓度对净光合速率的促进作用逐渐减小.在相同CO₂浓度下测定时,FACE条件下生长的水稻叶片净光合速率和羧化效率明显比普通空气下生长的对照低.尽管高CO₂浓度下生长的水稻叶片的气孔导度明显低于普通空气中生长的水稻叶片,但两者胞间CO₂浓度差异不显著,因此高CO₂浓度下生长的水稻叶片光合下调似乎不是由气孔导度降低造成的.     

大气CO2增加对土壤脲酶、磷酸酶活性的影响

The response of soil urease and phosphatase activities at different rice growth stages to free air CO₂ enrichment (FACE) was studied. The results showed that comparing with the ambient atmospheric CO₂ concentration (370μmol·mol^-1), FACE (570μmol·mol^-1) significantly increased the urease activity of 0～5cm soil layer at the vigorous growth stage of rice, whole that of 5～10cm layer had no significant change during the whole growing season. Phosphatase activity of 0～5cm and 5～10cm soil layers significantly increased, and the peak increment was at the vigorous growth stage of rice.     

日光温室冬季增施CO2对切花红掌光合作用及生长发育的影响

针对切花红掌日光温室冬季生产时CO₂亏缺严重的现象,以不增施CO₂为对照,研究了增施700、1000、1300 μmol·mol^-1浓度CO₂对切花红掌‘火焰’光合特性和生长发育的影响.结果表明: 增施60 d CO₂,红掌叶片的净光合速率、胞间CO₂浓度和水分利用效率均显著提高,且以1000 μmol·mol^-1处理的增幅最大;而气孔导度则较对照显著下降.增施CO₂后,红掌叶片的可溶性糖、淀粉和可溶性蛋白含量均较对照显著增加,佛焰苞大小、色泽、花茎长度等切花品质参数,以及叶片发育质量参数和花茎生长速率均有不同程度的提高,且均以1000 μmol·mol^-1浓度最佳.增施1000 μmol·mol^-1的CO₂可以有效促进日光温室切花红掌的冬季生产.     

日光温室冬季增施CO2对切花红掌光合作用及生长发育的影响

针对切花红掌日光温室冬季生产时CO₂亏缺严重的现象,以不增施CO₂为对照,研究了增施700、1000、1300 μmol·mol^-1浓度CO₂对切花红掌‘火焰’光合特性和生长发育的影响.结果表明: 增施60 d CO₂,红掌叶片的净光合速率、胞间CO₂浓度和水分利用效率均显著提高,且以1000 μmol·mol^-1处理的增幅最大;而气孔导度则较对照显著下降.增施CO₂后,红掌叶片的可溶性糖、淀粉和可溶性蛋白含量均较对照显著增加,佛焰苞大小、色泽、花茎长度等切花品质参数,以及叶片发育质量参数和花茎生长速率均有不同程度的提高,且均以1000 μmol·mol^-1浓度最佳.增施1000 μmol·mol^-1的CO₂可以有效促进日光温室切花红掌的冬季生产.     

Variation in growth stimulation by elevated carbon dioxide in seedlings of some C3 crop and weed species

Seven C₃ crop and three C₃ weed species were grown from seed at 360 and at 700 cm³ m^–3 carbon dioxide concentrations in a controlled environment chamber to compare dry mass, relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR) and photosynthetic acclimation at ambient and elevated carbon dioxide. The dry mass at the final harvest at elevated carbon dioxide relative to that at ambient carbon dioxide was highly correlated with the RGR at the lower carbon dioxide concentration. This relationship could be quite common, because it does not require that species differ in the response of RGR or photosynthesis to elevated carbon dioxide, and holds even when species differ moderately in these responses. RGR was also measured for a limited period at the end of the experiment to determine relationships with leaf gas exchange measured at this time. Relative increases in RGR at elevated carbon dioxide at this time were more highly correlated with the relative increase in NAR at elevated carbon dioxide than with the response of LAR. The amount of acclimation of photosynthesis was a good predictor of the relative increase in NAR at elevated carbon dioxide, and the long-term increase in photosynthesis in the growth environment. No differences between crops and weeds or between cool and warm climate species were found in the responses of growth or photosynthetic acclimation to elevated carbon dioxide.     

CO2浓度增加对半干旱区春小麦生产和水分利用效率的影响

为了解CO₂浓度升高条件下春小麦生产和水分利用效率(WUE)的响应特征,在典型半干旱区定西,利用开顶式气室(OTC)试验平台开展了CO₂浓度增加模拟试验.试验设对照(390 μmol·mol^-1)、480 μmol·mol^-1和570 μmol·mol^-1 3个CO₂浓度.结果表明: CO₂浓度升高使春小麦冠层空气温度小幅上升,10 cm深处的土壤环境温度下降;CO₂浓度增加对春小麦各器官生物量和总生物量都有明显促进作用,在480和570 μmol·mol^-1浓度下,地上干物质量平均增长20.6%和41.5%,总干物质量平均增长19.3%和39.6%.生物量增加主要是由茎叶干物质量增加所致,与生育中期物质生产能力明显增强有关;在两种CO₂浓度处理下,植株根冠比分别降低7.3%和11.8%,CO₂浓度增加对春小麦地上部分干物质积累的贡献大于地下部分;CO₂浓度升高主要通过影响穗粒数来影响最终产量,在480和570 μmol·mol^-1浓度下,小麦产量分别增加了8.9%和19.9%;大气CO₂浓度升高对春小麦光合作用影响的长期效应不明显,随CO₂浓度升高,光合速率显著提高,蒸腾速率降低,蒸发蒸腾量减小.随CO₂浓度升高,叶片、群体和产量3个水平的WUE都增加,其中群体水平的WUE增幅最大,产量水平的WUE增幅最小.     

CO2浓度升高、增温和冬小麦种植对土壤酶活性的影响

研究农田土壤酶活性对CO₂浓度升高和增温的响应,可为气候变化背景下农田生态系统养分管理提供科学依据。本研究在人工模拟气候室进行盆栽控制试验,设置了4种气候情景,分别为对照(CK,CO₂浓度400 μmol·mol^-1+正常环境温度)、CO₂浓度升高(ECO₂,CO₂浓度800 μmol·mol^-1+正常环境温度)、增温(ET,CO₂浓度400 μmol·mol^-1+增温4 ℃)及CO₂浓度和温度均升高(ECO₂+T,CO₂浓度800 μmol·mol^-1+增温4 ℃),研究有、无冬小麦生长下β--葡萄糖苷酶(βG)、β-N-乙酰葡糖苷酶(NAG)、碱性磷酸单脂酶(ALP)和多酚氧化酶(PPO)4种土壤酶活性在冬小麦拔节期(JS)、开花期(AS)、灌浆期(FS)和成熟期(MS)对CO₂浓度升高和增温的响应。结果表明:无冬小麦生长下,ECO₂与CK间4种土壤酶活性差异不显著,而ET和ECO₂+T处理对4种土壤酶活性有显著抑制作用。有冬小麦生长条件下,与CK相比,ECO₂和ECO₂+T处理对4种土壤酶活性均无显著影响;ET处理对土壤ALP和PPO活性有显著影响;ECO₂+T与ET间4种土壤酶活性有显著差异,与ET相比,ECO₂+T处理的土壤βG活性在JS期显著增加,NAG活性在JS期显著降低,ALP活性在AS和FS期显著增加,PPO活性在JS期显著降低,而在AS期显著增加。CO₂浓度升高与增温的交互作用在有、无冬小麦生长下均对土壤NAG和ALP活性有显著影响;无冬小麦生长下,增温和试验时段的交互作用对4种土壤酶活性有显著影响,而在有冬小麦生长下,增温和生育期的交互作用仅对ALP和PPO活性有显著影响;CO₂浓度升高、增温与试验时段的交互作用在无冬小麦生长下对土壤βG、ALP和PPO活性有显著影响,而在有冬小麦生长下CO₂浓度升高、增温与生育期对土壤NAG、ALP和PPO活性有显著影响。冬小麦生长对土壤βG、NAG和ALP活性在前两个生育期(JS+AS期)表现为显著抑制作用,在后两个生育期(FS+MS期)表现为显著促进作用,对土壤PPO活性在全生育期均表现为显著抑制作用。总体上,CO₂浓度升高对冬小麦土壤酶活性的影响不显著,而CO₂浓度与温度均升高对冬小麦土壤酶活性的影响在不同生育期因土壤酶种类不同而不同;此外,有、无冬小麦条件下4种土壤酶活性对CO₂浓度升高与增温的交互作用响应程度不一。     

CO2浓度增加对半干旱区春小麦生产和水分利用效率的影响

为了解CO₂浓度升高条件下春小麦生产和水分利用效率(WUE)的响应特征,在典型半干旱区定西,利用开顶式气室(OTC)试验平台开展了CO₂浓度增加模拟试验.试验设对照(390 μmol·mol^-1)、480 μmol·mol^-1和570 μmol·mol^-1 3个CO₂浓度.结果表明: CO₂浓度升高使春小麦冠层空气温度小幅上升,10 cm深处的土壤环境温度下降;CO₂浓度增加对春小麦各器官生物量和总生物量都有明显促进作用,在480和570 μmol·mol^-1浓度下,地上干物质量平均增长20.6%和41.5%,总干物质量平均增长19.3%和39.6%.生物量增加主要是由茎叶干物质量增加所致,与生育中期物质生产能力明显增强有关;在两种CO₂浓度处理下,植株根冠比分别降低7.3%和11.8%,CO₂浓度增加对春小麦地上部分干物质积累的贡献大于地下部分;CO₂浓度升高主要通过影响穗粒数来影响最终产量,在480和570 μmol·mol^-1浓度下,小麦产量分别增加了8.9%和19.9%;大气CO₂浓度升高对春小麦光合作用影响的长期效应不明显,随CO₂浓度升高,光合速率显著提高,蒸腾速率降低,蒸发蒸腾量减小.随CO₂浓度升高,叶片、群体和产量3个水平的WUE都增加,其中群体水平的WUE增幅最大,产量水平的WUE增幅最小.     

Carbon dioxide exchange and biomass productivity of the herbaceous layer of a managed tropical humid savanna ecosystem in western Kenya

Aims Humid savannas, as a result of high precipitation amounts, are highly productive. They are also hotspots for land use change and potential sources of carbon dioxide (CO₂) due to the large soil carbon (C) stocks. Understanding how ecosystem CO₂ exchange is influenced by changes arising from agricultural land use is vital in future management of these ecosystems and in responding to the ongoing shifts in management and climate. The aim of this study was to identify how ecosystem CO₂ exchange and biomass productivity of the herbaceous layer of a humid savanna in Kenya respond to current management practices.Methods We used flux chambers to quantify CO₂ fluxes, while monthly harvests were undertaken to determine biomass development of the herbaceous layer of three sites that were (i) fenced to exclude livestock grazing, (ii) subjected to grazing by livestock and (iii) abandoned after being cultivated for maize production and also open to grazing by livestock.Important findings The peak aboveground biomass ranged between 380 and 1449g m ?2 and biomass production was significantly (P < 0.05) lower in the grazed and abandoned plots. The maximum gross primary production (GPP) and net ecosystem CO₂ exchange (NEE) ranged between 21.8±1.3 to 32.5±2.7 and ?9.6±0.7 to^-17.9±4.8 μmol m ?2 s^-1, respectively. Seasonal NEE fluctuations ranged between 10 and 21 μmol m ?2 s^-1, while spatial (among sites) differences ranged between 2 and 10 μmol m ?2 s^-1. Ecosystem respiration (R eco) fluctuated between 5 and 10 μmol m ?2 s^-1 during the growing season. R eco was, however, not significantly different among the sites. Unlike in other similar ecosystems where ecosystem respiration is determined by the ambient temperature, we did not find any relationship between R eco and temperature in this savanna. Instead, soil moisture accounted for 38–88% of the spatial and seasonal fluctuations in ecosystem CO₂ fluxes and aboveground biomass production. Management influenced the maximum GPP and NEE rates through modification of soil moisture, plant species composition and aboveground biomass. We concluded that soil moisture is the key determinant of ecosystem CO₂ exchange and productivity in this tropical savanna. Management, however, significantly modifies C fluxes and productivity through its influence on soil moisture, plant species composition and aboveground green biomass and should be taken into consideration in future similar studies.     

大气CO2浓度升高对水稻秸秆化学组成的影响

水稻秸秆是生物能源生产的潜在材料,大气二氧化碳(CO2)浓度升高改变水稻秸秆的量和质,从而改变其生物能源的生产潜力.本试验水稻秸秆来自中国自由大气CO2富集平台(FACE),选取FACE平台(试验组CO2浓度控制在570μmol·mol^-1左右,比对照组高200μmol·mol-1)3种水稻品种‘武运粳27’、‘Y两优900’和‘日本晴N16’,通过对秸秆化学组成进行分析,探讨CO2浓度升高对水稻秸秆质量的影响.结果表明:大气CO2浓度升高显著提高了水稻秸秆C含量和C/N;增加了秸秆中非结构碳水化合物含量;CO2浓度升高使武运粳27、Y两优900和N16秸秆中释放的总糖分别增加8.8%、6.7%和9.9%;CO2浓度升高显著提高N16秸秆生物量,但对其他两种水稻秸秆生物量没有显著影响;N16的总糖产量在CO2浓度升高下增加最显著,达到19.2%.表明CO2浓度升高可以改善水稻秸秆质和量,从而提高生物燃料利用潜能.     

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.