Effects of elevated CO_2 concentration and nitrogen supply on biomass and active carbon of freshwater marsh after two growing seasons in Sanjiang Plain, Northeast China

An experiments were carried out with treatments differing in nitrogen supply （0, 5 and 15 g N/m^2） and CO2 levels （350 and 700 μmol/mol） using OTC （open top chamber） equipment to investigate the biomass of Calamagrostis angustifolia and soil active carbon contents after two years. The results showed that elevated CO2 concentration increased the biomass of C. angustifolia and the magnitude of response varied with each growth period. Elevated CO2 concentration has increased aboveground biomass by 16.7% and 17.6% during the jointing and heading periods and only 3.5% and 9.4% during dough and maturity periods. The increases in belowground biomass due to CO2 elevation was 26.5%, 34.0% and 28.7% during the heading, dough and maturity periods, respectively. The responses of biomass to enhanced CO2 concentrations are differed in N levels. Both the increase of aboveground biomass and belowground biomass were greater under high level of N supply （15 g N/m^2）. Elevated CO2 concentration also increased the allocation of biomass and carbon in root. Under elevated CO2 concentration, the average values of active carbon tended to increase. The increases of soil active soil contents followed the sequence of microbial biomass carbon （10.6%） 〉 dissolved organic carbon （7.5%） 〉 labile oxidable carbon （6.6%） 〉 carbohydrate carbon （4.1%）. Stepwise regressions indicated there were significant correlations between the soil active carbon contents and plant biomass. Particularly, microbial biomass carbon, labile oxidable carbon and carbohydrate carbon were found to be correlated with belowground biomass, while dissolved organic carbon has correlation with aboveground biomass. Therefore, increased biomass was regarded as the main driving force for the increase in soil active organic carbon under elevated CO2 concentration.

Soil and Root Respiration Under Elevated CO_2 Concentrations During Seedling Growth of Pinus sylvestris var.sylvestriformis

The objectives of this study were to investigate the effect of higher CO2 concentrations （500 and 700 μmol mol^-1） in atmosphere on total soil respiration and the contribution of root respiration to total soil respiration during seedling growth of Pinus sylvestris vat. sylvestriformis. During the four growing seasons （May-October） from 1999 to 2003, the seedlings were exposed to elevated concentrations of CO2 in open-top chambers. The total soil respiration and contribution of root respiration were measured using an LI-6400-09 soil CO2 flux chamber on June 15 and October 8, 2003. To separate root respiration from total soil respiration, three PVC cylinders were inserted approximately 30 cm deep into the soil in each chamber. There were marked diurnal changes in air and soil temperatures on June 15. Both the total soil respiration and the soil respiration without roots showed a strong diurnal pattern, increasing from before sunrise to about 14：00 in the afternoon and then decreasing before the next sunrise. No increase in the mean total soil respiration and mean soil respiration with roots severed was observed under the elevated CO2 treatments on June 15, 2003, as compared to the open field and control chamber with ambient CO2. However, on October 8, 2003, the total soil respiration and soil respiration with roots severed in the open field were lower than those in the control and elevated CO2 chambers. The mean contribution of root respiration measured on June 15, 2003, ranged from 8.3% to 30.5% and on October 8, 2003, from 20.6% to 48.6%.

Effect of elevated ambient CO_2 concentration on water use efficiency of Pinus sylvestriformis

Pinus Syvestfiformis is an important species as an indicator of global climate changes in Changbai Mountain, China. The water use efficiency (WUE) of this species (11 -year old ) was studied on response to elevated Co, concentration at 500±μLL' L-1 by directly injecting CO2 into the canopy under natural condition in 1998-1999. The results showed that the elevated Co, concentration reduced averagely stomatal opening, stomatal conductance and stomatal density to 78%, 80% and 87% respectively, as compared to normal ambient. The elevated Co, reduced the transpiration and enhances the water use efficiency (WUE) of plant.

Interactive Effects of Drought Stresses and Elevated CO_2 Concentration on Photochemistry Efficiency of Cucumber Seedlings

To reveal and quantify the interactive effects of drought stresses and elevated CO2 concentration [CO2] on photochemistry efficiency of cucumber seedlings, the portable chlorophyll meter was used to measure the chlorophyll content, and the Imaging-PAM was used to image the chlorophyll fluorescence parameters and rapid light response curves （RLC） of leaves in two adjacent greenhouses. The results showed that chlorophyll content of leaves was reduced significantly with drought stress aggravated. Minimal fluorescence （Fo） was increased while maximal quantum yield of PSII （Fv/Fm） decreased significantly by severe drought stress. The significant decrease of effective quantum yield of PSII （Y（Ⅱ）） accompanied by the significant increase of quantum yield of regulated energy dissipation （Y（NPQ）） was observed under severe drought stress condition, but there was no change of quantum yield of nonregulated energy dissipation （Y（NO））. We detected that the coefficient of photochemical quenching （qP） decreased, and non-photochemical quenching （NPQ） increased significantly under severe drought stress. Furthermore, we found that maximum apparent electron transport rate （ETRmax） and saturating photosynthetically active radiation （PPFDsat） decreased significantly with drought stress aggravated. However, elevated [CO2] significantly increased FvlFm, qP and PPFDsat, and decreased NPQ under all water conditions, although there were no significant effects on chlorophyll content, Fo, Y（Ⅱ）, Y（NPQ）, Y（NO） and ETRmax. Therefore, it is concluded that CO2-fertilized greenhouses or elevated atmospheric [CO2] in the future could be favorable for cucumber growth and development, and beneficial to alleviate the negative effects of drought stresses to a certain extent.

Global CO_(2) concentration change induced by“trigger-connectors”model,especially since about 24 Ma?A preliminary hypothesis

Background,aim,and scope The tectonic uplift of the Cenozoic Tibetan Plateau has produced a chain effect,which is an excellent location for Earth system science research,and its uplift process,mechanism and environmental effects are the hot spot and frontier of the current research.The“Tibetan Plateau uplift-weathering-CO_(2) concentration-global climate change”model was put forward by Raymo and Ruddiman to interpret the Late Cenozoic climate change.However,there are still some questions suspended,such as does the weathering of the Tibetan Plateau have the ability to control the global climate?How to explain the modern-like global CO_(2) concentration starting at about 24 Ma?Here,a short space was taken to present a brainstorm about the above questions on account of existing geological pieces of evidence.Materials and methods In this paper,we integrate the formation and evolution of the Yangtze River and Pearl River,the origin and development of the Asian inland aridification-monsoon system,the Cenozoic tectonic uplift process of the Tibetan Plateau,and the westerly winds to discuss and analyze the relationship between the Cenozoic CO_(2) concentration changes and the uplift of the Tibetan Plateau and why the CO_(2) concentration similar to the present was formed at about 24 Ma.Results Similar correspondence of the surface uplift history of Xizang,other global mountains,and the declining CO_(2) concentration could support the theory Tibetan Plateau weathering inf luences CO_(2) concentration.Starting from 24 Ma,the most important character was the uplift and erosion of Xizang and Himalaya,collaborating with Ocean Iron Fertilization(OIF)together as an entity to control the atmospheric CO_(2) concentration because the great Asian rivers,Asian monsoons,and westerlies connected Xizang and surrounded seas together through materials transportation.Discussion Paleogeographic reconstructions from 40 Ma to 20 Ma illustrate that the main topographic change occurred in the Andes,Cordillera orogenic belt,and Xizang.We comprise a comprehensive set of evidence from independent data,which correspond temporally with the tipping point(about 24 Ma)of the atmospheric CO_(2) and we noticed that modern-like Asia monsoon,inland aridity,Asian great rivers,and climate zone formed at about 24 Ma and also there are tectonic activities for the Andes and Rockies.We raised the possibility that the modern-like atmospheric CO_(2) concentration at about 24 Ma was caused by the above geological factors.Here the rivers,monsoon,and westerlies are termed as“connectors”.In addition,these Asian rivers originated from Xizang,the monsoon,and inner Asian aridification are strongly a function of the uplift and growth of Xizang,thus,Xizang here is named as“trigger”.The distinct character of“trigger-connectors”model is that this not only takes the monsoon,westerlies,and the global great rivers into consideration but also expands the range which inf luences atmospheric CO_(2) concentration,from local points to a vast area since about 24 Ma,such as from Tibetan Plateau to Asia,including surrounded seas,after about 24 Ma.However,because the opening of the Late Oligocene-Early Miocene Antarctic periphery straits is highly coincident with the onset of modern-like global atmospheric CO_(2) concentration,we are forced to consider that they also had a significant impact on the reduction of atmospheric CO_(2) concentrations at this time.Conclusions“Trigger-connectors”was put forward to explain the Cenozoic CO_(2) variation,especially modern-like global CO_(2) concentration since about 24 Ma.Recommendations and perspectives Here we use the“trigger-connectors”model to explain the formation of modern-like CO_(2) concentrations starting at about 24 Ma,but there are still some problems.The most important premise for the“trigger-connectors”model is the constructed Cenozoic CO_(2) concentration record is reliable,which is the foundation of our hypothesis.In the future,potential improvements should focus on topographic reconstructions of Xizang and the global mountains.Here we have concentrated on Xizang in the considered timeslices but still,pay less attention to other global orogenic belts.Collaborations with geologist experts in those regions could provide valuable feedback to evaluate their potential role of them in CO_(2) evolution.What is more,considerable progress may be achieved with the addition and consideration of more and new geological data.

Response of seedlings of different tree species to elevated CO_2 in Changbai Mountain

Eco-physiological responses of seedlings of eight species, Pinus koraiensis, Picea koraiensis, Larix olgensis, Populus ussuriensis, Betula platyphylla, Tilia amurensis, Traxinus mandshurica and Acer mono from broadleaved/Korean pine forest, to elevated CO2 were studied by using open-top chambers under natural sunlight in Changbai Mountain, China in two growing seasons (1998-1999). Two concentrations of CO2 were designed: elevated CO2 (700 祄olmol-1) and ambient CO2 (400 祄olmol-1). The study results showed that the height growth of the tree seedlings grown at elevated CO2 increased by about 10%-40% compared to those grown at ambient CO2. And the water using efficiency of seedlings also followed the same tendency. However, the responses of seedlings in transpiration and chlorophyll content to elevated CO2 varied with tree species. The broad-leaf tree species were more sensitive to the elevated CO2 than conifer tree species. All seedlings showed a photosynthetic acclimation to long-term elevated CO2.

RELATIONSHIPS OF STARCH CONCENTRATION WITH SPECIFIC LEAF WEIGHT AND MINERAL CONCENTRATIONS IN POTATO LEAVES UNDER VARIED CO_2 AND TEMPERATURE

Foliar concentrations of starch and major nutrients N, P, K, Ca, and Mg along with specific leaf weight (SLW) were determined in the potato (Solanun tuberosum L.) cvs "Denali", "Norland "'and "Russet Burbank" grown for 35 days under the CO2 concentrations of 500, 1 000, 1 500 and 2 000 mol mol-1 at both 16 and 20℃ air temperature. The starch concentration, pooled from the three cultivars, increased with increasing CO2 concentration at both 16 and 20℃,, and was consistently higher at 16℃ than at 20℃. The SLW (g m-2) was positively related to the foliar starch concentration on the basis of leaf area or dry weight. The concentrations of N, P, Ca, and Mg in leaves were negatively related to starch concentration under 14% starch on a dry weight basis. Above 14%, there was no significant relationship between nutrient and starch concentrations . The similar patterns were seen when the SLW and nutrient concentrations were expressed on a starch-free basis. In contrast, the leaf concentration of K was not closely related to the starch concentration. The results indicated that the changes in SLW and concentrations of N, P, Ca, and Mg in potato leaves only partially resulted from the changed starch concentration.

Stomatal response of Pinus sylvestriformis to elevated CO2 concentrations during the four years of exposure

Four-year-old Pinus sylvestriformis were exposed for four growing seasons in open top chambers to ambient CO2 concentration (approx. 350 μmol·mol-1) and high CO2 concentrations (500 and 700 μmol·mol-1) at Research Station of Changbai Mountain Forest Ecosystems, Chinese Academy of Sciences at Antu Town, Jilin Province, China (42oN, 128oE). Stomatal response to elevated CO2 concentrations was examined by stomatal conductance (gs), ratio of intercellular to ambient CO2 concentration (ci/ca) and stomatal number. Reciprocal transfer experiments of stomatal conductance showed that stomatal conductance in high-[CO2]-grown plants increased in comparison with ambient-[CO2]-grown plants when measured at their respective growth CO2 concentration and at the same measurement CO2 concentration (except a reduction in 700 μmol·mol-1 CO2 grown plants compared with plants on unchambered field when measured at growth CO2 concentration and 350 μmol·mol-1CO2). High-[CO2]-grown plants exhibited lower ci/ca ratios than ambient-[CO2]-grown plants when measured at their respective growth CO2 concentration. However, ci/ca ratios increased for plants grown in high CO2 concentrations compared with control plants when measured at the same CO2 concentration. There was no significant difference in stomatal number per unit long needle between elevated and ambient CO2. However, elevated CO2 concentrations reduced the total stomatal number of whole needle by the decline of stomatal line and changed the allocation pattern of stomata between upper and lower surface of needle.

Effects of elevated CO_2 on net photosynthetic rate of trees in Changbai Mountain

Net photosynthetic rates (NPRs) of four species seedlings, Pinus koraiensis, Ptrius Syvestriformis,Fraxinus mandshuthe and Phellodendron amurense, were measured at different CO2 concentrations and time respectively in Changbai Mountain during the growing season in 1999. The seedlings were cultivated in open-top chambers (OTCs), located outdoors and exposed to natural sunlight. The experimental objects were divided into four groups by tree species. CO2 concentrations in chambers were kept at 500 μL-L-1 and 700 μL-L-1 and contrast chamber and contrast field were set. The results showed that the effects of elevated CO2 on NPR of the trees strongly depended on tree species and time. NPRs of Pin us koreaipsis and Pinus syvestriformis seedfings increased with the rising of CO2 concentration, while that of Phellodron amurense and haus mandshurica increased at some time and decreased at another time.

Spatial variations in daily average CO_2 concentrations above wetland surface of Xianghai National Nature Reserve, China

Horizontal and vertical variations of daily average CO 2 concentration above the wetland surface were studied in Xianghai National Nature Reserve of China in August, 2000 The primary purpose was to study spatial distribution characteristics of CO 2 concentration on the four levels of height(0 1 m, 0 6 m, 1 2 m and 2 m) and compare the differences of CO 2 concentration under different land covers. Results showed that daily average CO 2 concentration above wetland surface in Xianghai National Natural Reserve was lower than that above other wetlands in northeast China as well as the worldwide average, suggesting that Xianghai wetland absorbed CO 2 in August and acted as “sink” of CO 2 The horizontal variations on the four levels of height along the latitude were distinct, and had the changing tendency of “decreasing after increasing” with the increase of height. The areas with obvious variations were consistent on different levels of height, and those with the highest variations appeared above surface of shore, sloping field, Typha wetland and Phragmites wetland; the vertical variations were greatly different, with the higher variations in Phragmites wetland and Typha wetland, and the lands near the shore and the sloping field with the lower variations. Spatial variations of daily average CO 2 concentrations above wetland surface were affected by surface qualities and land covers.

CO_2 CONCENTRATION AND FLUX NEAR GROUND IN MARSH OF THE SANJIANG PLAIN OF NORTHEAST CHINA

There is limited information available on CO2 concentration and flux over marsh. The objective of this work was to characterize CO2 concentration and flux within and above marsh plant (Cares lasiocarpa Ehrh. and C. pseudoucuaica F. Schm) canopy at heights 0. 5, 1. 0 and 1. 5 m.CO2 concentration was measured sequentially every 3 bars by using an infrared gas analyzer. Soil and air temperature, wind speed, net radiation and soil heat flux were also measured simultaneously. Extremely drily minimum and maximum CO2 concentration rangal from 250 to 754 μmd/mol for the 4-year work. The typical minimum and maximum values ranged from 314 to 464 μmol/mol at the height of marsh plant (about 0. 5 m) during the fruiting perioed and mature date. The seasonal changes in CO2 concentration show that the minimum CO2 concentration occurred in the fruiting period and mature date, and both of their minimum values were 314 μmol/mol. This illustrates that CO2 consumed by photosynthesis was stable during the period. The flux of CO2 can be thought as a turbulent diffusion phenomenon. By micrometeorological methods, the diurnal CO2 fluxes were measured in the flowering peried, fruiting period, early mature date, late mature date and yellow-ripe stage. Their values were -0. 18, 38. 15,24. 13, 10. 9 and 4. 91 μmol/mol respectively.

Effect of Different High CO_2 Concentrations on the Development of 2-cell Mouse Embryos in vitro

Objective To investigate effects of different high CO_2 concentrations on the development of 2-cell mouse embryos in vitro Methods At levels of 5% CO_2 (control group), 5.7% CO_2, 6.0% CO_2 and 15% CO_2, embryos were incubated in drops with CZB medium, respectively, and the drops were covered by paraffin oil which was treated with three-distilled water. In addition, at the level of 15% CO_2, there were another two groups, in which paraffin oil was treated with phosphate-buffered saline (PBS) solution or the drops were uncovered. The development of embryos in all stages was noted. Results The developmental rates of blastocysts in five experimental groups were significantly lower than that of the control group (P<0.01). At the level of 5.7% CO_2, the developmental rate of blastocysts was 4.3%, and those of other experimental groups were 0. At the levels of 5.7% and 6.0% CO_2, embryos were blocked in the 2-cell or the 4-cell stage, and no significant difference was showed between the two groups (P>0.05). At the level of 15% CO_2, 15% embryos developed in the 4-cell stage with irregular blastomere and degenerated quickly in the group which paraffin oil was treated with distilled water; 2.2% embryos developed in the 4-cell stage in the group which paraffin oil was treated with PBS and the rest stagnated in the 2-cell stage. Conclusions High CO_2 concentrations had toxic effect on the in vitro development of 2-cell mouse embryos, and was responsible for the inhibition of the embryos. It is important for the development of embryos in vitro to detect strictly CO_2 concentration.

Spatial Inhomogeneity of Atmospheric CO_(2) Concentration and Its Uncertainty in CMIP6 Earth System Models

This paper provides a systematic evaluation of the ability of 12 Earth System Models(ESMs)participating in the Coupled Model Intercomparison Project Phase 6(CMIP6)to simulate the spatial inhomogeneity of the atmospheric carbon dioxide(CO_(2))concentration.The multi-model ensemble mean(MME)can reasonably simulate the increasing trend of CO_(2) concentration from 1850 to 2014,compared with the observation data from the Scripps CO_(2) Program and CMIP6 prescribed data,and improves upon the CMIP5 MME CO_(2) concentration(which is overestimated after 1950).The growth rate of CO_(2) concentration in the northern hemisphere(NH)is higher than that in the southern hemisphere(SH),with the highest growth rate in the mid-latitudes of the NH.The MME can also reasonably simulate the seasonal amplitude of CO_(2) concentration,which is larger in the NH than in the SH and grows in amplitude after the 1950s(especially in the NH).Although the results of the MME are reasonable,there is a large spread among ESMs,and the difference between the ESMs increases with time.The MME results show that regions with relatively large CO_(2) concentrations(such as northern Russia,eastern China,Southeast Asia,the eastern United States,northern South America,and southern Africa)have greater seasonal variability and also exhibit a larger inter-model spread.Compared with CMIP5,the CMIP6 MME simulates an average spatial distribution of CO_(2) concentration that is much closer to the site observations,but the CMIP6-inter-model spread is larger.The inter-model differences of the annual means and seasonal cycles of atmospheric CO_(2) concentration are both attributed to the differences in natural sources and sinks of CO_(2) between the simulations.

室内人体呼吸代谢暴露对学生阅读效率影响的实验研究

高校教室是学生学习和生活的重要场所,其室内空气质量与学生健康及学习效率密切相关,而针对代谢污染暴露引起的健康影响量化研究还有待深化。本文以CO_(2)作为室内空气质量的表征参数,利用实验舱进行室内环境调控,通过主观舒适度评价、学习任务测试等方法,探讨不同工况(CO_(2)浓度分别为600 ppm、1000 ppm、1500 ppm、2000 ppm、2500 ppm、3000 ppm和4000 ppm)下人体代谢污染物对室内人员生理感知指标及各类型学习任务的影响关系。结果表明:第一,随着室内CO_(2)浓度升高,受试学生的热舒适度下降22.2%,其中人体的热感觉和病态建筑综合征(SBS)中各项生理反馈在室内CO_(2)浓度超过1500 ppm时发生显著变化;第二,CO_(2)浓度升高对校对任务速度的减缓影响更显著,而对文本阅读的影响主要表现在正确率上;第三,在高浓度工况下(4000 ppm)受试学生的综合阅读效率相比低浓度(1000 ppm)下降14.1%,而低于1500 ppm时维持更低的CO_(2)浓度对阅读效率的提高不会有明显收益。实验结果为教室空气质量调控和规范制定提供参考。

1979-2022年北极海冰变化及影响因素分析

海冰是海洋-大气交互系统的重要组成部分,是全球气候变化的指示器。深入分析海冰演变规律,探索全球气候变化与海冰范围之间的关联,对应对和减缓全球气候变化具有重要的理论意义。本文以北极海冰为研究对象,深入分析了1979-2022年北极海冰范围的季节、年际和年代际变化特征,并构建向量自回归模型(Vector AutoRegressive Model,VAR)检验全球平均气温、大气CO_(2)浓度与北极海冰范围之间的因果关系,并分析影响程度。结果表明:(1)北极海冰范围季节变化特征明显,一般在3月达到最大,9月达到最小,这主要与太阳辐射的年变化周期相关;(2)1979-2022年,北极海冰范围总体呈减小趋势,年变化量为5.3万km^(2);(3)北极海冰范围在年代际尺度上逐渐减小,2000-2009年,北极海冰范围较上一个十年减小最多(减少67万km^(2));(4)全球平均气温和大气CO_(2)浓度均对北极海冰范围变化造成了显著影响;(5)全球平均气温和大气CO_(2)浓度与北极海冰范围均有显著负相关关系,相关系数分别为-0.92和-0.95。

大兴安岭多年冻土区两种水体温室气体浓度动态与冬季储存特征

北方内陆水体是温室气体排放的热点,对量化区域碳收支起重要作用,但其排放的季节变化尚不清楚。观测了大兴安岭多年冻土区府库奇河及其改道形成的牛轭湖(演替晚期)冻结期冰层中储存的二氧化碳(CO_(2))和甲烷(CH_(4))浓度,并比较了两种水体中CO_(2)和CH_(4)浓度在三个不同时期(冻结期、非冻结期、春季融化)的差异。结果表明:两种水体CO_(2)和CH_(4)浓度季节变化存在差异。牛轭湖在冻结期水体中CO_(2)和CH_(4)浓度最高,有明显的冰下积累现象,其中CH_(4)浓度平均值为(2.21±0.54)μmo/L,分别是非冻结期和春季融化期水体CH_(4)浓度的5倍和14倍。河流水体中CO_(2)和CH_(4)浓度最高出现在春季融化期,显著高于非冻结期和冻结期(P<0.05)。水中CO_(2)和CH_(4)浓度受多种环境因子的影响,与可溶性有机碳(DOC)正相关(P<0.05),与溶解氧(DO)、水温为负相关(P<0.05)。冻结期冰层形成后,温室气体会以冰气泡的形式存储在冰层中,气泡的主要成分是CO_(2)和CH_(4),其中CO_(2)占90%以上。由于冰气泡中CO_(2)和CH_(4)浓度约为冰下水体浓度的1%—30%,忽略冰层中储存的温室气体将会增加北方水体碳排放的不确定性。研究明确了大兴安岭多年冻土区两种水体溶解性CO_(2)和CH_(4)的季节变化特征与冬季温室气体储存能力,为深入认知该区域水体碳循环过程提供重要数据支持。

北京地区办公建筑室内典型污染物日均浓度与工作时均浓度对比分析

以办公建筑为代表的具有明确作息规律的建筑中,以污染物浓度24 h平均值作为室内污染物评价指标的合理性尚不清楚。本文以北京某办公建筑为对象,利用为期1个月的室内CO_(2)和PM2.5浓度的实时监测数据,分析了24 h日均浓度和工作时均浓度(07:00—19:00)的关系。结果表明,对照我国GB/T 18883—2022,室内CO_(2)和PM2.5日均浓度的超标率小于2%,但工作时均浓度的超标率远高于日均浓度(1.25~20倍)。日均浓度与工作时均浓度之间存在较大偏差,PM2.5相对偏差的最大值为0.45,中位值为0.14;CO_(2)相对偏差的最大值为0.34,中位值为0.04。对照我国标准,室内CO_(2)的漏判率为100%,错罚率为0;室内PM2.5的漏判率为62.3%,错罚率为19.7%。错罚率和漏判率与所采用的评价标准密切相关,随着浓度标准的提高,即浓度限值减小,错罚率和漏判率均下降。因此,针对实际办公建筑的空气质量评价,应当同时关注污染物的工作时均浓度而非仅采用24 h日均浓度,并选择合适的评价标准和浓度限值。本文的研究结果为更加准确、有效地评价办公建筑的空气质量评价提供了新思路。

大气CO_(2)浓度升高背景下秸秆还田对小麦土壤氮矿化的影响

为探讨小麦土壤氮矿化对CO_(2)浓度升高、秸秆还田及其交互作用的响应,本研究利用人工控制气候室设置2种CO_(2)浓度处理CK(CO_(2)浓度为400μmol·mol^(−1))、EC(CO_(2)浓度为600μmol·mol^(−1)),3种秸秆处理:秸秆不还田(R)、秸秆掺入(I)、秸秆覆盖(M),测定小麦土壤理化性质、碳氮相关酶活性;通过为期35 d的室内培养试验,分析土壤硝态氮、铵态氮含量动态变化和净氮矿化速率等。结果表明,培养35 d后与秸秆不还田相比,两种秸秆还田方式均增加了土壤碳氮有效性,秸秆掺入和秸秆覆盖处理土壤净硝化速率在两种CO_(2)浓度处理下分别平均增加0.76和0.55 mg·kg^(-1)·d^(-1)。3种秸秆处理方式中,以秸秆掺入土壤净矿化速率最大;秸秆覆盖土壤净氨化速率较低,导致其净矿化速率低于秸秆掺入。与CK相比,CO_(2)浓度升高使土壤无机氮含量平均下降8.1%,土壤氮矿化量平均降低14.98 mg·kg^(-1)。与CK相比,CO_(2)浓度升高下秸秆还田使土壤无机氮含量增加74.2 mg·kg^(-1),主要是由于土壤硝态氮含量增加了73.8 mg·kg^(-1),导致土壤净硝化速率提高了0.57 mg·kg^(-1)·d^(-1);CO_(2)浓度升高下土壤净氨化速率整体下降,其中秸秆覆盖下降幅度较大,导致其净氮矿化速率低于CK。综上,CO_(2)浓度升高下秸秆还田增加了土壤氮的可利用性,其中秸秆覆盖提高了土壤氮固持能力,减少了氮素淋失,秸秆掺入增加了土壤氮矿化,可提供更多无机氮以供作物利用。本研究为未来气候变化背景下选择适宜秸秆还田措施以维持土壤供氮潜力提供了理论依据和技术支持。

大气CO_(2)浓度升高背景下优化施氮对淹水稻田CH4排放的影响

为探讨未来气候变化条件下,合理管理氮肥以充分协调水稻产量与温室气体排放量之间的矛盾,实现低碳排放并保持水稻产量,本研究探讨了大气CO_(2)浓度升高120μmol·mol^(-1)与氮肥减施40%对淹水稻田水稻生产及CH4排放的影响及机理。利用开顶式气室(OTC)组成的CO_(2)浓度自动调控平台设置4个处理,即环境CO_(2)浓度+施氮250 kg·hm^(-2)(CK)、大气CO_(2)浓度升高120μmol·mol^(-1)+施氮250 kg·hm^(-2)(C+)、环境CO_(2)浓度+施氮150 kg·hm^(-2)(N-)、大气CO_(2)浓度升高120μmol·mol^(-1)+施氮150 kg·hm^(-2)(C+N-),分析了稻田CH4累积排放量(CAC)、水稻生物量及产量、土壤理化性质及酶活性等指标。结果表明:与CK处理相比,C+处理使CAC/产量显著提高了16.93%,N-处理使CAC/产量显著降低了13.33%,C+N-处理使CAC/产量降低了7.89%,但不显著;N-处理在一定程度上削弱了C+处理对CAC、CAC/产量、水稻生物量、土壤可溶性有机碳含量的促进作用;逐步回归分析表明,基于可溶性有机碳和硝态氮含量及土壤脲酶活性的线性模型,可解释稻田CH4累积排放64%的变异。综上,在大气CO_(2)浓度升高条件下,氮肥减施可通过影响土壤碳、氮基质及土壤脲酶活性来调节稻田CH4排放。

高CO_2浓度对温带三种针叶树光合光响应特性的影响

将长白山地区阔叶红松林中主要针叶树种红松、红皮云杉和长白落叶松的幼苗 ,盆栽于模拟自然光照和人工调节CO2 浓度为 70 0和 40 0 μmol·mol-1的气室内两个生长季 ,在各自的生长环境条件下 ,利用CI 30 1PS便携式CO2 分析系统测定针叶的光合光响应曲线 .结果表明 ,不同树种及同一树种的不同CO2浓度处理间差异明显 .比较饱和净光合速率、暗呼吸、光补偿点、光饱和点、及光能利用率 (QUE)的变化可见 ,长白落叶松为阳性树种 ,其光合作用对高CO2 浓度的适应能力较好 ,红松树种次之 ,阴性树种红皮云杉光合作用对高CO2 浓度适应能力最差 .