Comparative response of seedlings of selected native dry tropical and alien invasive species to CO2 enrichment

Aims Global climate change and ongoing plant invasion are the two prominent ecological issues threatening biodiversity world wide. Among invasive species, Lantana camara and Hyptis suaveolens are the two most important invaders in the dry deciduous forest in India. We monitored the growth of these two invasive species and seedlings of four native dry deciduous species (Acacia catechu, Bauhinia variegata, Dalbergia latifolia and Tectona grandis) under ambient (375–395 μ mol mol^-1) and elevated CO₂ (700–750 μ mol mol^-1) to study the differential growth response of invasive and native seedlings.Methods Seedlings of all the species were exposed to ambient and elevated CO₂. After 60 days of exposure, seedlings were harvested and all the growth-related parameters like plant height; biomass of root, stem and leaves; total seedling biomass; R/S ratio; allocation parameters; net assimilation rate (NAR) and relative growth rate (RGR) were determined.Important findings Biomass, RGR and NAR of all the species increased under elevated CO₂ but the increase was higher in invasive species and they formed larger seedlings than natives. Therefore under the CO₂ -enriched future atmosphere, competitive hierarchies could change and may interfere with the species composition of the invaded area.     

Effects of enhanced UV-B radiation and nitrogen deposition on the growth of invasive plant Triadica sebifera

Aims Exotic plant invasions are important components of global change, threatening both the stability and function of invaded ecosystems. Shifts in competitive ability of invasive plants versus their native congeners have been documented. Enhanced UV-B radiation and nitrogen (N) deposition might interact with soil biota communities impacting the invasion process of exotic plant species. To understand the potential effects by UV-B and N with soil biota on plant growth would enhance our understanding of the mechanisms in plant invasions in the context of global change.
Methods We conducted a full-factorial pot experiment in the native range (China) of Triadica sebifera invading US to investigate how UV-B radiation, N and soil biota together determined their seedling growth.
Important findings The results showed that UV-B radiation, N and soil sterilization together impacted the growth of T. sebifera seedlings. UV-B radiation induced changes in biomass allocation with larger leaf biomass observed in response to UV-B radiation. In addition, N increased aboveground biomass and decreased root biomass simultaneously. Soil biota imposed positive effects on growth of T. sebifera, and the addition of N amplified these positive effects. The negative effects by UV-B radiation on growth of T. sebifera showed no response to N addition. Plant height, leaf biomass and total biomass of the invasive T. sebifera populations out- performed those of the native ones. In addition, invasive T. sebifera populations weakened the dependence of root/shoot ratio and root biomass on local soil microorganisms than native populations, but enhanced that of leaf area ratio.     

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.     

AMF colonization and community of a temperate invader and co-occurring natives grown under different CO2 concentrations for 3 years

连续3年不同CO₂浓度下一种温带外来入侵植物和两种共存本地植物丛枝菌根真菌群落及侵染率 大气CO₂浓度升高等全球变化过程不仅能促进外来植物入侵,也能改变土壤丛枝菌根真菌(AMF)的群落结构,但我们并不清楚大气CO₂浓度升高促进外来植物入侵是否与其对外来入侵植物和 本地植物AMF共生的影响有关。为回答这一问题,我们在环境和倍增CO₂浓度下连续3年栽培一年生外来入侵植物瘤突苍耳(Xanthium strumarium)与两种共存的一年生本地近缘植物,比较了AMF侵染率、土 壤养分和土壤AMF群落组成的差异。研究结果表明,大气CO₂浓度升高只在少数情况下提高根系AMF侵染率,并且瘤突苍耳AMF侵染率的提高并不比本地种多。在环境CO₂浓度下,栽培第一年瘤突苍耳的AMF侵染侵染率显著高于两种本地植物;而栽培第二年和第三年与两种本地植物的差异不显著,因为两种本地植物的AMF侵染率随种植时间的增加而增加,而瘤突苍耳AMF侵染率受种植时间的影响较小。物种、CO₂浓度和种植时间对AMF侵染率的影响与它们对土壤养分和AMF群落的影响有关,土壤养分对AMF侵染率的影响可能比AMF群落组成的影响更大,因为后者也受土壤养分的影响。上述结果表明,与本地植物相比,入侵植物能更快地与AMF形成共生关系,有利于其适应和入侵新生境;在探究全球变化如大气CO₂浓度升高等对外来植物入侵的影响时,需要考虑AMF的影响和时间效应。     

UV-B has larger negative impacts on invasive populations of Triadica sebifera but ozone impacts do not vary

Aims Abiotic stresses may interact with each other to determine impacts on plants so that their combined impact is less than or more than additive. Increasing UV-B radiation and surface ozone (O 3) are two major components of global change that may have such interactive impacts. Moreover, invasive and native populations of plants may respond differently to stresses as they can vary in primary and secondary metabolism.Methods Here, we conducted a factorial field experiment with open-top chambers assigned to an ozone treatment (ambient, 100 ppb, or 150 ppb) and UV-B treatment (ambient or increased 20%). We grew seedlings of native and invasive populations of Triadica sebifera in these chambers for one growing season.Important findings Invasive plants grew faster than native plants in ambient UV-B but they did not differ significantly in elevated UV-B. Litter production of invasive plants was especially sensitive to UV-B in a way that increased with UV-B for native plants but decreased for invasive plants which may be important for nutrient cycling. In ambient UV-B, total mass decreased as ozone increased. Total mass was lower with elevated UV-B but there was no additional impact of increasing ozone. Leaf area did not decrease with UV-B so SLA and LAR were lowest at ambient ozone levels. These results suggest that the effects of ozone will depend on UV-B conditions perhaps due to changes in foliar traits. The traits that allow invasive populations of plants to be successful invaders may make them especially sensitive to UV-B which may reduce their success in future climatic conditions.     

土壤微生物对不同种源乌桕生长的影响

【背景】土壤微生物对植物成功入侵具有重要影响,研究中国本地土壤微生物对美国入侵种乌桕的净生长效应有利于进一步理解乌桕成功入侵的机理。【方法】以本地和入侵2个种源多个种群的乌桕为试验材料,通过对土壤进行灭菌处理,研究土壤微生物对不同种源乌桕幼苗生长的影响。【结果】土壤微生物对入侵种乌桕具有正效应,与本地种相比,入侵种乌桕幼苗总生物量、相对生长速度、根冠比以及总叶面积、叶面积比、比叶面积等生物学指标在新鲜土壤中均表现出明显优势。种源和土壤处理间存在交互效应的指标显示土壤微生物去除对入侵种乌桕的抑制作用更为明显。这一结果与土壤自然天敌逃逸假说相背,入侵种乌桕在一定程度上具有较本地种更强的土壤微生物利用能力,在非根际土壤微生物的作用下入侵种乌桕具有较强的生长能力和明显的竞争优势。【结论与意义】本研究证实土壤微生物可能对乌桕成功入侵具有不可忽略的作用。由于该试验在乌桕起源地进行,结合在乌桕入侵地进行的研究有助于进一步分析土壤微生物对入侵的贡献作用;研究土壤微生物与入侵植物的互作关系有助于对入侵物种进行准确预测和有效控制,减少生物入侵对生态系统功能的破坏。     

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.     

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.     

CO2 enrichment accelerates successional development of an understory plant community

Aims Rising concentrations of atmospheric carbon dioxide ([CO₂]) may influence forest successional development and species composition of understory plant communities by altering biomass production of plant species of functional groups. Here, we describe how elevated [CO₂] (eCO₂) affects aboveground biomass within the understory community of a temperate deciduous forest at the Oak Ridge National Laboratory sweetgum (Liquidambar styraciflua) free-air carbon dioxide enrichment (FACE) facility in eastern Tennessee, USA. We asked if (i) CO₂ enrichment affected total understory biomass and (ii) whether total biomass responses could be explained by changes in understory species composition or changes in relative abundance of functional groups through time.Materials and Methods The FACE experiment started in 1998 with three rings receiving ambient [CO₂] (aCO₂) and two rings receiving eCO₂. From 2001 to 2003, we estimated species-specific, woody versus herbaceous and total aboveground biomass by harvesting four 1 × 0.5-m subplots within the established understory plant community in each FACE plot. In 2008, we estimated herbaceous biomass as previously but used allometric relationships to estimate woody biomass across two 5 × 5-m quadrats in each FACE plot.Important findings Across years, aboveground biomass of the understory community was on average 25% greater in eCO₂ than in aCO₂ plots. We could not detect differences in plant species composition between aCO₂ and eCO₂ treatments. However, we did observe shifts in the relative abundance of plant functional groups, which reflect important structural changes in the understory community. In 2001–03, little of the understory biomass was in woody species; herbaceous species made up 94% of the total understory biomass across [CO₂] treatments. Through time, woody species increased in importance, mostly in eCO₂, and in 2008, the contribution of herbaceous species to total understory biomass was 61% in aCO₂ and only 33% in eCO₂ treatments. Our results suggest that rising atmospheric [CO₂] could accelerate successional development and have longer term impact on forest dynamics.     

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.     

高CO2浓度对长白山阔叶红松林主要树种的影响

组成长白山阔叶红松林的主要树种红松、云杉、落叶松、大青杨、白桦、椴树、水曲柳和色木的幼树,盆栽于模拟自然光照和人工调节CO₂浓度为700μl·L^-1、400μl·L^-1的气室内两个生长季,以生长在400μl·L^-1下的幼树为对照组,在各自生长条件下测定,高CO₂浓度下生长的红松、云杉、落叶松、大青杨、白桦、椴树、水曲柳和色木的高生长比对照组的幼树提高10%～40%.高CO₂浓度的幼树与对照CO₂下的幼树相比各树种蒸腾速率升降不一,但水分利用效率均有不同程度的提高,不同树种的可溶性糖和叶绿素含量对高CO₂浓度反应不一,反映出幼树对高CO₂浓度适应的复杂性.长期高CO₂浓度环境下生长的阔叶树对CO₂变化反应较针叶树敏感,供试树种均发生光合驯化现象.     

Temporal and spatial variations of stem CO2 efflux of three species in subtropical China

Aims Although stem CO₂ efflux is critical to ecosystem carbon and energy balance and its feedback to future climate change, little information is available on stem CO₂ efflux and its responses to temperature, especially in subtropical China. This study aims to (i) evaluate the temporal and spatial variations of stem CO₂ efflux of three species, including oak (Quercus acutissima Carr.), masson pine (Pinus massoniana Lamb.) and loblolly pine (Pinus taeda Linn.) in subtropical China and (ii) analyze the temperature sensitivity of stem CO₂ efflux in the three species based on 2-year field measurements.Methods We measured stem CO₂ efflux and stem temperature (at 3 cm depth) of the three species using the horizontally oriented soil chamber technique from September 2008 to August 2010. We also conducted a 24-h measurement to examine the diurnal variation of stem CO₂ efflux in three consecutive days in April 2009.Important findings The temporal dynamics of stem CO₂ efflux followed the change of the stem temperature in a 3-cm depth with a bell-shaped curve in the three species. Stem temperature explained 77–85% of the seasonal variations of stem CO₂ efflux over the entire study period in the three species. The temperature sensitivity (Q 10) of stem CO₂ efflux was obviously different among the three species with higher Q 10 value found in oak (2.24) and lower values in the coniferous species (1.76 and 1.63). Our results also showed that the Q 10 values of stem CO₂ efflux in all the three species were lower in the growing season than that in the non-growing season, indicating that the growth and maintenance respiration had different temperature responses. Moreover, we found that the temperature-normalized stem CO₂ efflux (R 10) changed greatly between the growing and non-growing seasons in oak and masson pine, but not in loblolly pine. Additionally, we also found that in the non-growing season, the principal factor responsible for the spatial variation of stem CO₂ efflux among the 15 sampling trees was sapwood volume, whereas in the growing season, stem CO₂ efflux was closely related to annual dry-matter production in the three subtropical species.     

N availability does not modify plant-mediated responses of Trichoplusia ni to elevated CO2

Aims Elevated CO₂ and increased N availability can alter a variety of plant physiological processes leading to changes in the nutritional quality of leaf tissue for herbivores. Numerous experiments have examined the responses of herbivores to environmental change; however the potential effects of simultaneous change in multiple factors on leaf-chewing insect herbivores are less well understood. The plant-mediated effects of elevated CO₂ and high N on the performance of a generalist leaf-chewing insect herbivore, Trichoplusia ni, were investigated.Methods Newly hatched T. ni larvae were introduced to Amaranthus viridis and Polygonum persicaria plants grown under ambient and elevated CO₂ and low and high N conditions. Insect performance was assessed by measuring larvae weight after ten days of feeding. Plant photosynthesis, biomass, leaf area and specific leaf weight were measured to determine the effects of elevated CO₂, N and insect feeding on plant performance.Important findings Elevated CO₂ did not have strong effects on plant or insect performance, only affecting a few responses under low or high N conditions, but not both. Growth under high nitrogen improved almost all measures of plant performance. Trichoplusia ni performed significantly better on Amaranthus viridis (C 4) compared to Polygonum persicaria (C 3), despite similar leaf C:N ratios in both species. The performance of T. ni caterpillars was only improved by the high nitrogen treatment when they were feeding on P. persicaria, the host they performed poorly on. The only interactions between N and CO₂ affecting plant performance were seen for leaf photosynthesis of P. persicaria and leaf area of A. viridis. Contrary to the predictions, there were no significant CO₂ by N interactions affecting T. ni performance.     

The role of light,soil and human factors on the probability of occurrence of an invasive and three native plant species in coastal transitions of coastal Mississippi,USA

Aims Understanding relationships between the distributions of species and their surrounding environment provides a basis for forecasting how species will respond to future environmental changes. In this study, we examined the effects of environmental factors and human developmental features associated with disturbances on probability of occurrence of juveniles of invasive Triadica sebifera and three native plant species, Baccharis halimifolia, Ilex vomitoria and Morella cerifera within a typical coastal transition in coastal Mississippi, USA.Methods We recorded presence of juveniles of focal species and measured environmental factors (soil salinity, canopy openness, soil texture and soil carbon to nitrogen ratio) along an 11.3 km transect located at Grand Bay National Estuarine Research Reserve. Further, we documented anthropogenic features and associated activities as a proxy for human disturbance.Important findings With the exception of I. vomitoria, all other species occurrences were significantly influenced by an interaction between soil salinity and canopy openness. The occurrence of I. vomitoria sharply decreased with salinity. B. halimifolia occurrence peaked at moderate levels of salinity and low to moderate levels of canopy openness. Occurrences of M. cerifera and the invasive T. sebifera were highest at low levels of salinity and canopy openness. These results indicate that salinity is a strong driver that limits distribution of juvenile native and invasive species in coastal transitions. Logistic regression confirmed the positive effects of anthropogenic disturbances on T. sebifera and I. vomitoria occurrence. It appears that while soil salinity is likely to drive retreat of the seaward boundaries of woody plant species distributions, increased human developments along the coast likely enhance the inland spread of species, in particular the invasive T. sebifera by increasing disturbances and facilitating dispersal. Results from this study can offer insight for the development of T. sebifera management and preventive measures for further spread along coastal areas of the southeastern USA.     

CO2浓度升高和氮沉降对南亚热带主要乡土树种及群落生物量的影响

选取荷木、海南红豆、肖蒲桃、红鳞蒲桃和红锥5种南亚热带乡土树种构建混交群落,通过5年人为提高CO₂浓度和氮输入试验,研究碳-氮交互作用对南亚热带主要乡土树种及群落的生物量积累与分配的影响.结果表明：CO₂浓度升高及氮沉降对植物生物量的积累和分配的影响因树种不同而有显著差异.CO₂浓度升高和氮沉降对豆科植物生物量积累相对提高了49.3%和71.0%,且促进了阳生植物生物量的积累;氮沉降能显著提高偏阴生植物生物量积累,但在CO₂浓度升高条件下,其生物量积累低于对照.CO₂浓度升高抑制了阳生植物地下生物量的分配,但促进偏阴生植物地下生物量的分配.CO₂浓度升高、氮沉降以及碳-氮交互作用对南亚热带植物群落生物量积累均具有促进作用;CO₂浓度升高促进群落地下生物量积累,氮沉降显著提高其地上部分生物量分配.在全球变化背景下,南亚热带林业固碳树种适宜选用海南红豆和红锥.     

阴晴天条件下高CO_2浓度对杂交稻光合作用影响的FACE研究

光和二氧化碳(CO_2)是绿色植物光合作用的两个基本条件.为了明确不同光照条件下,高CO_2浓度对不同杂交水稻光合特性的影响,2017年利用稻田大型FACE平台,以‘Y两优900’和‘甬优538’为供试材料,设置环境CO_2和高CO_2浓度(增200μmol·mol^-1)两个水平,分别在拔节期和灌浆期同时测定阴、晴天气条件下顶部全展叶光合特性参数.结果表明:高CO_2浓度使不同天气情况下两品种叶片的净同化率(P_n)均呈增加趋势,其中晴天条件下的增幅(31%)大于阴天(25%),拔节期的增幅(37%)大于灌浆期(21%),CO_2与天气、CO_2与生育期均存在显著的互作效应.叶片水分利用效率(WUE)对高CO_2浓度的响应趋势与P_n一致.高CO_2浓度环境下叶片气孔导度(g_s)、蒸腾速率(T_r)均呈下降趋势,晴天条件下的降幅略大于阴天.与晴天相比,阴天条件下叶片P_n、g_s、T_r、WUE和L_s平均分别下降41%、18%、41%、26%和27%,差异均达显著或极显著水平.相关分析表明,晴天P_n、g_s、T_r均与阴天时的参数呈极显著正相关关系.表明阴天使水稻生育中、后期叶片光合参数及其对高CO_2浓度的响应均大幅降低,且两品种表现一致.评估未来水稻产量潜力需要考虑天气条件.     

阴晴天条件下高CO2浓度对杂交稻光合作用影响的FACE研究

光和二氧化碳(CO₂)是绿色植物光合作用的两个基本条件.为了明确不同光照条件下,高CO₂浓度对不同杂交水稻光合特性的影响,2017年利用稻田大型FACE平台,以‘Y两优900’和‘甬优538’为供试材料,设置环境CO₂和高CO₂浓度(增200 μmol·mol^-1)两个水平,分别在拔节期和灌浆期同时测定阴、晴天气条件下顶部全展叶光合特性参数.结果表明: 高CO₂浓度使不同天气情况下两品种叶片的净同化率(P_n)均呈增加趋势,其中晴天条件下的增幅(31%)大于阴天(25%),拔节期的增幅(37%)大于灌浆期(21%),CO₂与天气、CO₂与生育期均存在显著的互作效应.叶片水分利用效率(WUE)对高CO₂浓度的响应趋势与P_n一致.高CO₂浓度环境下叶片气孔导度(g_s)、蒸腾速率(T_r)均呈下降趋势,晴天条件下的降幅略大于阴天.与晴天相比,阴天条件下叶片P_n、g_s、T_r、WUE和L_s平均分别下降41%、18%、41%、26%和27%,差异均达显著或极显著水平.相关分析表明,晴天P_n、g_s、T_r均与阴天时的参数呈极显著正相关关系.表明阴天使水稻生育中、后期叶片光合参数及其对高CO₂浓度的响应均大幅降低,且两品种表现一致.评估未来水稻产量潜力需要考虑天气条件.     

Influence of elevated CO2 and ozone concentrations on late blight resistance and growth of potato plants

Potato plants (Solanum tuberosum L. cv. Indira) with high susceptibility to the late blight pathogen Phytophthora infestans were exposed for 4 weeks to two different CO₂ concentrations (400/700 ppm) combined with ambient and double ambient ozone concentrations (first experiment) and with 1/5 ambient and ambient ozone concentrations (second experiment) in climate chambers. Leaves of the potato plants were then inoculated with Phytophthora infestans zoospores. Plants from the “high CO₂” variant showed a significantly increased resistance to the pathogen, verified by visual evaluation and quantitative real-time PCR, whereas plants treated with double ambient ozone were slightly more susceptible. An increase in the constitutive activities of the PR-proteins β-1,3-glucanase and osmotin in leaves of plants exposed to 700 ppm CO₂ correlated with the increase in resistance at this CO₂-concentration. Biomass parameters were barely affected by the elevated CO₂-concentration but decreased with increasing ozone concentrations. Biochemical analyses revealed that the content of starch as well as the content of soluble sugars in leaves were highest at the double ambient ozone/700 ppm CO₂ variants pointing to an ozone-induced inhibition of assimilate allocation from leaves to tubers. Leaf C/N-ratio increased at elevated CO₂-concentrations due to a decrease in N-content. The effect of the ozone- and CO₂-induced biochemical changes on the resistance response of potato towards Phytophthora infestans is discussed.     

全球变化主要过程对海滨生态系统生物入侵的影响

作为海陆交错带的海滨生态系统是海洋与陆地的过渡带, 是承受全球变化及其引起海平面上升等影响最为前沿、最为重要的缓冲带, 同时又是人类活动极为频繁和强烈的地带, 因此海滨生态系统是生物入侵的高发区之一。本文在分析海滨生态系统生物入侵现状的基础上, 分析了CO₂升高、海平面上升和富营养化等全球变化过程对海滨生态系统生物入侵的影响: CO₂浓度上升改变了入侵种的竞争态势, 海平面上升调整了入侵种的空间分布格局, 而富营养化为外来入侵种的进一步拓展提供了动力。为了深入揭示全球变化对海滨生态系统生物入侵过程的潜在影响, 很有必要在阐明单因子作用机制与过程的基础上加强与其他组分的交互作用研究, 以及中、长时间尺度上的动态分析。与此同时, 生物入侵导致的海滨生态系统变化对全球变化相关过程的反馈作用研究也具有极其重要的意义。     

Mycorrhizal associations of an invasive tree are enhanced by both genetic and environmental mechanisms

Biotic interactions involving exotic plants in their introduced ranges may differ from those of co‐occurring plant species and from interactions in their native ranges. When interactions are less negative, or more positive compared to native plant species, this may increase invasion success, and differences among ranges may cause changes in exotic plant traits. Here, we investigated arbuscular mycorrhizae (AM) associated with Triadica sebifera seedlings from populations in native (China) and introduced ranges (US) and with seedlings from US and China species within three co‐occurring genera (Liquidambar, Ulmus, Celtis) grown in multiple common gardens in both ranges. No general pattern of higher or lower AM colonization was found in the introduced range for China and US Celtis, Liquidambar, or Ulmus species. However, AM colonization was significantly higher for Triadica than for other genera, particularly in the introduced range, suggesting AM may improve Triadica's invasion success. Triadica AM colonization was higher in US than China gardens, decreased with increasing soil nitrogen in China, but was independent of soil nitrogen in the US. This might reflect a different effect of soil fertility on this mutualism among ranges. Introduced Triadica populations had higher AM colonization than native populations, particularly in US gardens, implying a possible advantage from greater AM association in the introduced range. This is the first field study demonstrating post‐introduction changes in mycorrhizal colonization of an invasive species. It indicates that there are ecological and evolutionary components to the effect of positive interactions on plant invasions.