Spatial variation and controlling factors of temperature sensitivity of soil respiration in forest ecosystems across China

土壤呼吸的温度敏感性(Q₁₀)是陆地碳循环与气候系统间相互作用的关键参数。尽管已有大量关于不同类型森林Q₁₀季节和年际变化规律的研究, 但是对Q₁₀在区域尺度的空间变异特征及其影响因素仍认识不足, 已有结果缺乏一致结论。该研究通过整合已发表论文, 构建了中国森林生态系统年尺度Q₁₀数据集, 共包含399条记录、5种森林类型(落叶阔叶林(DBF)、落叶针叶林(DNF)、常绿阔叶林(EBF)、常绿针叶林(ENF)、混交林(MF))。分析了不同森林类型Q₁₀的空间变异特征及其与地理、气候和土壤因素的关系。结果显示, 1) Q₁₀介于1.09到6.24之间, 平均值(±标准误差)为2.37 (± 0.04), 且在不同森林类型之间无显著差异; 2)当考虑所有森林类型时, Q₁₀随纬度、海拔、土壤有机碳含量(SOC)和土壤全氮含量(TN)的增加而增大, 随经度、年平均气温(MAT)、平均年降水量(MAP)的增加而减小。气候(MAT、MAP)和土壤(SOC、TN)因素间存在相互作用, 共同解释了33%的Q₁₀空间变异, 其中MAT和SOC是Q₁₀空间变异的主要驱动因素; 3)不同类型森林Q₁₀对气候和土壤因素的响应存在差异。在DNF中Q₁₀随MAP的增加而减小, 而其他类型森林中Q₁₀与MAP无显著相关性; 在EBF、DBF、ENF中Q₁₀随TN的增加而增大, 但Q₁₀对TN的敏感性在EBF中最高, 在ENF中最低。这些结果表明, 尽管Q₁₀有一定的集中分布趋势, 但仍有较大范围的空间变异, 在进行碳收支估算时应注意尺度问题。Q₁₀的主要驱动因素和Q₁₀对环境因素的响应随森林类型而变化, 在气候变化情景下, 不同森林类型间Q₁₀可能发生分异。因此, 未来的碳循环-气候模型还应考虑不同类型森林碳循环关键参数对气候变化的响应差异。     

Associations between litterfall dynamics and micro-climate in forests of Putuoshan Island,Zhejiang, China

Aims Seasonal litterfall production plays an important role in the carbon and nutrient cycling in forest ecosystems. This study examines the effects of micro-environmental factors on seasonal litterfall dynamics in the forests of Putuoshan Island, Zhejiang Province of eastern China.
Methods The study covers five forest types, including Liquidambar formosana forest, Cinnamomum japonicum and Machilus thunbergii forest, Pinus massoniana forest, Cyclobalanopsis glauca forest, and Distylium gracile forest, in Putuoshan Island. We collected micro-meteorological data, and measured monthly litterfall in stands of the five forest types over one year. Redundancy analysis (RDA) was performed to determine the effects of micro-climatic factors on litterfall production．
Important findings The average annual litterfall production ranged from 3.45 to 5.36 t·hm^-2·a^-1 across five types of forests, albeit no effect of forest types on the litterfall production. The partitioning of litterfall components differed among the five forest types. The seasonal litterfall production exhibited two contrasting patterns, i.e. double climax curve and triple peaks, and varied significantly among the five forest types. Moreover, the peak in the litterfall production mostly occurred in the windy months of the year, such as in April, July and December, which was consistent with the dynamics of wind speed. RDA results showed that components of litterfall production in different months were controlled by different micro-climatic factors. The total, leaves, fruits, and miscellaneous litterfall productions were directly and positively affected by air temperature. Twig litterfall production was positively affected by the overstory wind velocity. Flower litterfall production was negatively affected by air humidity. In summary, forest types had no effects on litterfall production. However, variations in litterfall productions were explained by air temperature, air humidity, and overstory wind velocity in the forests studied.     

Characteristics of water and carbon fluxes during growing season in three typical arid ecosystems in central Asia

亚洲中部干旱区地处欧亚大陆腹地, 干旱少雨, 生态环境十分脆弱, 研究该地区大气与地表之间的能量和物质交换对干旱区水资源利用和生态环境保护具有重要意义。该文分析了亚洲中部干旱区荒漠与草地生态系统能量、水汽和CO₂通量的日变化及季节变化特征, 探究了水汽和CO₂通量对主要环境因子的响应。通过分析亚洲中部干旱区3个站点的涡度相关资料发现: 亚洲中部干旱区荒漠和草地生态系统在生长季(4-10月)能量、水汽通量、净CO₂通量和总初级生产力的日变化呈“单峰型”, 而荒漠生态系统呼吸日变化相对稳定; 草地生态系统白天的潜热通量占净辐射通量的比例明显高于荒漠生态系统; 草地生态系统在5-8月呈现较强的碳汇, 而荒漠生态系统表现为弱碳汇。亚洲中部干旱区草地和荒漠生态系统水汽通量和总初级生产力对降水、净辐射通量或光合有效辐射、饱和水汽压差、气温均表现出明显的敏感性。     

Effluxes of nitrous oxide,methane and carbon dioxide and their responses to increasing nitrogen deposition in the Gurbantünggüt Desert of Xinjiang,China

Aims Desert soils play an important role in the exchange of major greenhouse gas (GHG) between atmosphere and soil. However, many uncertainties existed in understanding of desert soil role, especially in efflux evaluation under a changing environment. Methods We conducted plot-based field study in center of the Gurbantünggüt Desert, Xinjiang, and applied six rates of simulated nitrogen (N) deposition on the plots, i.e. 0 (N0), 0.5 (N0.5), 1.0 (N1), 3.0 (N3), 6.0 (N6) and 24.0 (N24) g·m^-2·a^-1. The exchange rates of N₂O, CH₄ and CO₂ during two growing seasons were measured for two years after N applications. Important findings The average efflux of two growing seasons from control plots (N0) were 4.8 μg·m^-2·h^-1, -30.5 μg·m^-2·h^-1 and 46.7 mg·m^-2·h^-1 for N₂O, CH₄ and CO_2, respectively. The effluxes varied significantly among seasons. N0, N0.5 and N1 showed similar exchange of N₂O in spring and summer, which was relatively higher than in autumn, while the rates of N₂O in N6 and N24 were controled by time points of N applications. The uptake of CH₄ was relatively higher in both spring and summer, and lower in autumn. Emission of CO₂ changed minor from spring to summer, and greatly decreased in autumn in the first measured year. In the second year, the emission patterns were changed by rates of N added. N additions generally stimulated the emission of N₂O, while the effects varied in different seasons and years. In addition, no obvious trends were found in the emission factor of N₂O. The uptake of CH₄ was not significantly affected by N additions. N additions did not change CO₂ emissions in the first year, while high N significantly reduced the CO₂ emissions in spring and summer of the second year, without affected in autumn. Structure equation model analysis on the factors suggested that N₂O, CH₄ and CO₂ were dominantly affected by the N application rates, soil temperature or moisture and plant density, respectively. Over the growing seasons, both the net efflux and the global warming potential caused by N additions were small.     

Exploring the influence of soil types underneath the canopy in winter wheat leaf area index remote estimating

Aims Remote sensing is an effective and nondestructive way to retrieve leaf area index (LAI) from plot, regional and global range. Soil background is one of the confounding factors limiting remotely estimating LAI. And soil type contains a large proportion of soil background information, which can influence the optical properties of vegetation canopy and soil. However, our knowledge on the effects stemmed from soil types underneath the canopy on LAI remote estimating have been in shortage. Thus, this study aims to explore the influences of soil types underneath the canopy on winter wheat LAI remote estimating. Methods We analyzed the sensitivity variation of eight spectral indices, named normalized difference vegetation index (NDVI), modified soil-adjusted vegetation index (MSAVI), modified chlorophyll absorption ratio index 2 (MCARI₂), red edge inflection point (REIP), red edge amplitude (Dr), red edge area (SDr), red edge symmetry (RES), normalized difference spectral index (NDSI), to LAI in different soil types, and then we identified some spectral intervals or parameters that were insensitive to soil type variations underneath the canopy. We also compared the accuracy of two commonly used regression models, partial least squares regression (PLSR) and random forest regression (RFR), in estimating LAI for different soil types. We also explored the problems arising from applying the regression model developed in single soil type area to complex soil types area in retrieving LAI. Important findings This paper demonstrates the effects of soil types underneath the canopy on LAI retrieving. 1) The sensitivity of spectral indices to LAI is significantly different due to the soil type variation, but REIP has the least effects from soil type variation among the eight spectral indices. Meanwhile, the band selection algorithm of lambda-by-lambda not only chooses the most sensitive spectral interval for LAI, but also provides a feasible way to construct the spectral index that exhibits strong resistances to the effects of soil types underneath the canopy. 2) The accuracy of LAI estimation by regression models differs under soil type considered or not. So we suggest that in small scale researches, especially in a field scale, the ability of regression models in explaining variables is the priority consideration, while the PLSR is superior to RFR in this respect. Under the premise of unknown priori knowledge of land surfaces, the RFR is more suitable for retrieving LAI than PLSR, but land surface priori knowledge is still necessary. These findings provide the theoretical basis and methods for developing remotely sensing estimating LAI models adapted to various land surfaces. Further analysis is needed in applying the findings in more crop types, cultivars and growth stages.     

Study on the current population and habitat of the wild Chinese alligator ( Al ligator sinensis )

A survey of wild Chinese Alligator was conducted from July to August 1999 and from August to September 2000 by direct counting after dark (20 z00pm) using headlamps or a 12v portable spotlight. At each site visited , the authors mapped the ponds using laser rangefinder and compass , characterized the physical nature of the ponds and vegetation , and conducted interviews with local residents. The location of all sites was recorded using a hand2held GPS. There are 26 sites in 5 counties that were surveyed where wild Chinese Alligators still exist in Anhui province , including 13 designated conservation sites of the National Chinese Alligator Reserve. The current wild alligator populations mainly exist in the best type of habitat , which totals 17.4 ha with estimated populations of 50.7 % in 1999 and 40.0 % in 2000. This can be compared with the other two types of habitat , which total 22. 0 ha and 19. 0 ha , with their estimated population numbers of 24.0 % in 1999 and 30.9 % in 2000 , and 25.3 % in 1999 and 29.1 % in 2000 respectively. The average ecological densities of the alligators in the two years were 1.3 ind. / ha and 1.8 ind. / ha , with an estimated population of 145 individuals. However , the population has been evidently divided into 18 isolated small local populations with different numbers of individuals. We suggest that habitat should be restored and captive-reared alligators should be reint roduced into the area to rebuild a viable population.     

华北地区主要灌丛群落物种组成及系统发育结构特征

灌丛在中国北方广泛分布, 研究其物种组成特征及构建机制对植被恢复有重要意义。群落系统发育结构能有效反映群落组成的生态过程, 对揭示群落构建机制具有重要作用。该研究利用华北地区自然植物群落资源综合考察数据库的灌丛数据, 分析了中国华北地区主要灌丛群落的分布情况、物种组成及其系统发育结构特征。同时, 结合WorldClim数据库中的气候因子利用逐步回归和一般线性模型分析了气温和降水对灌丛不同垂直结构层物种系统发育结构特征的影响。经统计, 共调查木本植物75科207属570种; 草本植物99科491属1 221种。按植被型和群系类型分类后, 共有5种植被型, 195个群系, 其中分布最多的群系类型为虎榛子(Ostryopsis davidiana)灌丛、荆条(Vitex negundo var. heterophylla)灌丛、荆条+酸枣(Ziziphus jujuba)灌丛和沙棘(Hippophae rhamnoides)灌丛。整体上, 草本层的物种丰富度高于灌木层。草本层的系统发育结构表现为发散模式, 而灌木层的系统发育结构表现为聚集模式, 且不同植被型灌丛的系统发育结构不同。气候因子的变化对灌木层和草本层系统发育结构都表现出了明显的影响, 但对灌木层的影响要强于对草本层的影响, 且气候因子和植被型、群系类型都有明显的交互作用。分析结果表明, 区域尺度上气温和降水的变化会影响灌丛群落不同结构层的系统发育结构特征, 且对不同的植被型和群系类型的影响不同。     

Construction of CO2-response model of electron transport rate in C4 crop and its application

准确估算光合电子流对CO₂响应的变化趋势对深入了解光合过程具有重要意义。该研究在植物光合作用对CO₂响应新模型(模型I)的基础上构建了电子传递速率(J)对CO₂的响应模型(模型II), 并对用LI-6400-40便携式光合仪测量的玉米(Zea mays)和千穗谷(Amaranthus hypochondriacus)的数据进行了拟合。结果表明, 模型II可以很好地拟合玉米和千穗谷叶片J对CO₂浓度的响应曲线(J-C_a曲线), 得到玉米和千穗谷的最大电子传递速率分别为262.41和393.07 mmol·m ^-2·s ^-1, 与估算值相符合。在此基础上, 对光合电子流分配到其他路径进行了探讨。结果显示, 380 mmol·mol ^-1 CO₂浓度下玉米和千穗谷碳同化所需的电子流为247.92和285.16 mmol·m ^-2·s ^-1, 分配到其他途径的光合电子流为14.49和107.91 mmol·m ^-2·s ^-1(考虑植物CO₂的回收利用)。比较两种植物的其他途径光合电子流分配值发现, 两者相差6倍之多。分析认为这与千穗谷和玉米的催化脱羧反应酶种类以及脱羧反应发生的部位不同密切相关。该发现为人们研究C₄植物中烟酰胺腺嘌呤二核苷磷酸苹果酸酶型和烟酰胺腺嘌呤二核苷酸苹果酸酶型两种亚型之间的差异提供了一个新的视角。此外, 构建的电子传递速率对CO₂的响应模型为人们研究C₄植物的光合电子流的变化规律提供了一个可供选择的数学工具。     

Responses of soil respiration with biocrust cover to water and temperature in the southeastern edge of Tengger Desert,Northwest China

Aims Soil respiration of the lands covered by biocrusts is an important component in the carbon cycle of arid, semi-arid and dry-subhumid ecosystems (drylands hereafter), and one of the key processes in the carbon cycle of drylands. However, the responses of the rate of soil respiration with biocrusts to water and temperature are uncertain in the investigations of the effects of experimental warming and precipitation patterns on CO₂ fluxes in biocrust dominated ecosystems. The objectives of this study were to investigate the relationships of carbon release from the biocrust-soil systems with water and temperature in drylands. Methods Intact soil columns with two types of biocrusts, including moss and algae-lichen crusts, were collected in a natural vegetation area in the southeastern fringe of the Tengger Desert. Open top chambers were used to simulate climate warming, and the soil respiration rate was measured under warming and non-warming treatments using an automated soil respiration system (LI-8150). Important findings Over the whole observational period (from April 2016 to July 2016), soil respiration rates varied from -0.16 to 4.69 μmol·m^-2·s^-1 for the moss crust-covered soils and from -0.21 to 5.72 μmol·m^-2·s^-1 for the algae-lichen crust-covered soils, respectively, under different rainfall events (the precipitations between 0.3-30.0 mm). The mean soil respiration rate of the moss crust-covered soils is 1.09 μmol·m^-2·s^-1, which is higher than that of the algae-lichen crust-covered soils of 0.94 μmol·m^-2·s^-1. The soil respiration rate of the two types of biocrust-covered soils showed different dynamics and spatial heterogeneities with rainfall events, and were positively correlated with precipitation. The mean soil respiration rate of the biocrust-covered soils without warming was 1.24 μmol·m^-2·s^-1, significantly higher than that with warming treatments of 0.79 μmol·m^-2·s^-1 (p < 0.05). By increasing the evaporation of soil moisture, the simulated warming impeded soil respiration. In most cases, soil temperature and soil respiration rate displayed a similar single-peak curve during the diel cycle. Our results show an approximately two hours’ lag between soil temperature at 5 cm depth and the soil respiration rate of the biocrust-covered soils during the diel cycle.     

《中国植被志》研编内容与规范

植被志是基于植被(或植物群落)调查资料, 全面记叙植被的外貌、物种组成、结构和功能, 以及地理分布和生境条件等特征, 并对同类植被进行归纳和总结的志书。《中国植被志》是第一部对中国植被进行全面记述的志书, 预计完成约48卷110册。在借鉴《中国植被》(1980)(简称“80方案”)植被分类基本原则的基础上,《中国植被志》将对中国植被分类系统的高级分类单位(植被型组、植被型和植被亚型)进行归纳和总结, 对中级和低级分类单位(群系组、群系、亚群系, 群丛组、群丛)进行详细描述。植被高级分类单位的描述具有概括性质, 是在中国植被分类系统中级和低级分类单位描述的基础上, 对其在全球和中国境内的地理分布、自然环境、群落外貌、植被类型及多样性、优势种或共优势种、生物多样性保育价值以及资源现状等进行概述, 并对“80方案”相关内容进行修订和拓展, 将提供对中国植被基本特征客观、准确的记述。在植被中级和低级分类单位中, 群系组描述的内容包括地理分布、自然环境、群落外貌、植被类型以及价值与保育等内容; 群系描述的主要内容包括地理分布、自然环境、生态特征、物种组成、群落结构、群丛组和群丛的分类与描述、优势种的生物学特性、生物量与生产力、植被动态与演替以及价值与保育等方面。作为植被志研编的核心内容, 群丛组和群丛的分类与描述主要基于植被调查资料, 采用数量分类方法, 根据群落结构和物种组成的差异划分出不同的植被类型, 并对其基本特征进行定量描述和归纳。其中, 群落的层片结构、特定植被分类单元的特征种或特征种组的筛选与甄别是植被类型划分的关键环节; 而群落外貌, 群落结构, 物种组成, 各类物种的生长习性、生境的偏适性等是群丛组和群丛描述与归纳的重点内容。该文提出了中国植被中级和低级分类单位的命名方案, 其特点在于植被类型的科学名称中同时体现了植被分类单元特征种或优势种的名称及其所属的高级植被分类单位(植被型组或植被型)的名称, 兼顾了植被名称的规范性与实用性。《中国植被志》的研编工作由文献整编、群落调查、数据分析与整理、文本撰写等环节组成。该文对植被样方的调查与收集, 文献收集与整编, 气候、土壤、地形等相关数据的来源及其整理方法, 植被分类方法, 植被命名, 植被分类单元描述的内容, 植被志章节编写大纲、体裁及撰写等多个规范进行了详细的阐述或示例。     

全球森林土壤微生物生物量碳氮磷化学计量的季节动态

土壤微生物生物量在森林生态系统中充当具有生物活性的养分积累和储存库。土壤微生物转化有机质为植物提供可利用养分, 与植物的相互作用维系着陆地生态系统的生态功能。同时, 土壤微生物也与植物争夺营养元素, 在季节交替过程和植物的生长周期中呈现出复杂的互利-竞争关系。综合全球数据对温带、亚热带和热带森林土壤微生物生物量碳(C)、氮(N)、磷(P)含量及其化学计量比值的季节动态进行分析, 发现温带和亚热带森林的土壤微生物生物量C、N、P含量均呈现夏季低、冬季高的格局。热带森林四季的土壤微生物生物量C、N、P含量都低于温带和亚热带森林, 且热带森林土壤微生物生物量C含量、N含量在秋季相对最低, 土壤微生物生物量P含量四季都相对恒定。温带森林的土壤微生物生物量C:N在春季显著高于其他两个森林类型; 热带森林的土壤微生物生物量C:N在秋季显著高于其他2个森林类型。温带森林土壤微生物生物量N:P和C:P在四季都保持相对恒定, 而热带森林土壤微生物生物量N:P和C:P在夏季高于其他3个季节。阔叶树的土壤微生物生物量C含量、N含量、N:P、C:P在四季都显著高于针叶树; 而针叶树的土壤微生物生物量P含量在四季都显著高于阔叶树。在春季和冬季时, 土壤微生物生物量C:N在阔叶树和针叶树之间都没有显著差异; 但是在夏季和秋季, 针叶树的土壤微生物生物量C:N显著高于阔叶树。对于土壤微生物生物量的变化来说, 森林类型是主要的显著影响因子, 季节不是显著影响因子, 暗示土壤微生物生物量的季节波动是随着植物其内在固有的周期变化而变化。植物和土壤微生物密切作用表现出来的对养分的不同步吸收是保留养分和维持生态功能的一种权衡机制。     

Main plant communities and characteristics of Kalamaili Ungulate Nature Reserve in east Junggar Basin

The main vegetation types of Kalamaili Nature Reserve in east Junggar Basin were investigated in this paper, and based on the data from 54 plot samples, the characteristics of the main desert plant communities from the main vegetation types were quantitatively described. And the results showed that, the vegetation in this reserve can be divided in to 9 major desert plant community types were recognized: Form. Haloxylon ammodendron, Form. Krascheninnikovia ceratoides, Form. Atraphaxis spinosa, Form. Reaumuria songarica, Form. Artemisia songarica, Form. Convolvulus tragacanthoides, Form. Anabasis salsa, Form. Stipa glareosa and Form. Seriphidium terrae-albae, and then, 16 associations were divided from these 9 major community types.     

青海森林生态系统中灌木层和土壤生态化学计量特征

灌木层作为森林生态系统的重要组成部分, 了解其生态化学计量特征将有助于揭示森林生态系统物质周转和养分循环等生态功能。该研究选取青海省7种主要优势林分——白桦(Betula platyphylla)林、毛白杨(Populus tomentosa)林、红桦(Betula albosinensis)林、青扦(Picea wilsonii)林、山杨(Populus davidiana)林、圆柏(Sabina chinensis)林、云杉(Picea asperata)林为研究对象, 采用野外取样和室内实验分析相结合的方法, 研究了不同林分林下灌木层不同器官(叶、枝干、根)及其表层(0-10 cm)土壤的碳(C)、氮(N)、磷(P)含量及其相关性。结果表明: 7种林分间灌木(叶、枝干、根) P含量、C:P均没有明显差异性; 山杨林、圆柏林、云杉林的林下灌木(叶、枝干、根) N含量、N:P高于白桦林、毛白杨林、红桦林和青扦林, C:N则相反。圆柏林的林下灌木生长受P限制, 其余6种林分的林下灌木生长受N限制。7种林分间土壤有机碳(SOC)和总氮(TN)含量呈现出明显差异性, 而总磷(TP)含量则差异不明显。相关性分析表明, 林下灌木(叶、枝干、根) N含量、C:N、N:P与土壤TN含量、C:N、N:P呈极显著相关性, 而P含量、C:P与土壤TP含量呈显著相关性。冗余分析表明, 林下灌木层植被C、N、P含量及生态化学计量特征受到土壤化学计量特征及各环境因子的共同影响, 其中土壤C:N、海拔、年平均气温、年降水量为主要影响因子。     

鄂西南亚高山不同覆被类型泥炭藓沼泽湿地甲烷排放特征及其环境影响因子

沼泽湿地是大气甲烷(CH₄)的重要来源, 但有关亚热带亚高山沼泽湿地CH₄排放的研究却鲜有报道, 特别是对不同覆被类型泥炭藓沼泽湿地CH₄排放量的精确估算及其与环境因子的关系尚不清楚。该研究选择鄂西南亚高山泥炭藓沼泽湿地为研究区域, 于2018年11月-2019年10月间, 使用静态箱-气相色谱仪法原位测定3种覆被类型泥炭藓沼泽湿地CH₄通量, 同步记录大气和地下5 cm土壤的温度以及地下水位变化。结果表明: (1)光照下, 裸露地(B)、泥炭藓(Sphagnum paluster)(S)、金发藓(Polytrichum commune)(P) 3种覆被类型泥炭藓沼泽湿地CH₄-C通量全年变化范围分别为: 0.012-1.372、0.022-1.474、0.027-3.385 mg·m^-2·h^-1; 遮光处理下, B、S、P 3种覆被类型泥炭藓沼泽湿地CH₄-C通量的全年变化范围分别为: 0.012-1.372、0.009-1.839、0.017-2.484 mg·m^-2·h^-1, 均为CH₄排放源。同时, 光照条件下不同覆被泥炭藓沼泽湿地CH₄排放量略大于黑暗条件, 但差异不明显。(2)不同覆被类型泥炭藓沼泽湿地CH₄排放存在明显的季节变化规律, 即: 夏季>秋季>春季>冬季, 其中夏季CH₄排放量显著大于其他季节, 占全年的57%-84%。该研究发现泥炭藓沼泽湿地CH₄通量均与气温和地下5 cm土壤温度极显著相关, 且CH₄排放量随温度升高呈指数增加, 表明温度是影响泥炭藓沼泽湿地CH₄排放时间变化的主要环境因子。(3) 3种覆被类型泥炭藓沼泽湿地的年平均和年累计CH₄排放量均依次为: P > S > B, P显著大于B。该研究发现植被类型与泥炭藓沼泽湿地CH₄排放量存在显著相关性, 表明覆被类型是影响泥炭藓沼泽湿地CH₄排放量空间变异的主要因子。(4) 3种覆被类型泥炭藓沼泽湿地CH₄排放量均与地下水位变化不相关。该研究进一步丰富了泥炭藓沼泽湿地CH₄排放规律, 同时也为区域碳循环提供了详实的基础数据。     

Soil inorganic carbon stock in alpine grasslands on the Qinghai-Xizang Plateau: An updated evaluation using deep cores

Aims To estimate the size and spatial patterns of 3-m-deep soil inorganic carbon (SIC) stock across alpine grasslands on the Qinghai-Xizang Plateau.Methods We conducted a comprehensive investigation and collected soil samples from 342 3-m-deep cores and 177 50-cm-deep pits across the study area. Using Kriging interpolation, we interpolated site-level observations to the regional level. The distribution of SIC density was then overlaid with the regional vegetation map at a scale of 1:1000000 to calculate SIC stock of the alpine steppe and alpine meadow. Kruskal-Wallis tests were further conducted to examine the differences of SIC density between the two grassland types and among soil depths with 50 cm-depth intervals.Important findings The total SIC stock at depths of 50 cm, 1 m, 2 m and 3 m were estimated at 8.26, 17.82, 36.33 and 54.29 Pg C, with SIC density being 7.22, 15.58, 31.76 and 47.46 kg C·m^-2, respectively. SIC density exhibited large spatial variability, with an increasing trend from the southeastern to the northwestern plateau. Much larger SIC stock was observed in the alpine steppe than alpine meadow, with the former accounting for 63%-66% of the total stock at depths of 50 cm, 1 m, 2 m and 3 m. A large amount of SIC stock was found in deep soils (1-3 m), amounting to approximately 2 times as much carbon stored in the top 1-m-deep soil layer. The vertical distributions of SIC density differed between the two grassland types. The highest proportions of SIC occurred in the upper 50 cm layer for the alpine steppe while the highest proportions occurred in 100-150 cm layer for the alpine meadow. These results highlight that a large amount of SIC is stored in deep soil layers, which should be considered in evaluating terrestrial carbon balance under global change scenario.     

Classification of plant associations based on a 20 hm2 dynamics plot of evergreen broad- leaved forest in Mt. Tiantong,Zhejiang, China

为获取能够代表浙江天童山的森林植被典型群丛类型, 同时也为植被分类中如何发现过渡类型和确定典型类型提供参考, 该研究利用天童20 hm ²森林大样地资料, 运用双向指示种分析(TWINSPAN)与除趋势对应分析(DCA), 剔除过渡群落, 进行群丛划分。结果表明, 去除过渡地段后更利于研究区域典型群丛类型的确定。大样地的植被类型可划分为宜昌荚蒾-厚皮香/港柯+云山青冈群丛(Viburnum erosum-Ternstroemia gymnanthera/Lithocarpus harlandii + Cyclobalanopsis sessilifolia Ass.); 虎皮楠-柯/木荷+米槠群丛(Daphniphyllum oldhami-Lithocarpus glaber/Schima superba + Castanopsis carlesii Ass.); 红毒茴-紫楠/南酸枣+薄叶润楠群丛(Illicium lanceolatum-Phoebe sheareri/Choerospondias axillaries + Machilus leptophylla Ass.)。DCA排序同时能反映各群丛类型分布与环境的相关关系, 结果显示, 海拔和凹凸度对群丛分布有较大影响, 坡度和坡向对群丛分布影响较小。     

Forest net primary productivity dynamics and driving forces in Jiangxi Province,China

Aims Subtropical forest ecosystem has great carbon sequestration capacity. Net primary productivity (NPP) plays a critical role in forest carbon cycle and is affected by a number of factors, including climate change, atmospheric composition, forest disturbance intensity and frequency, and forest age, etc. However, the contribution of these factors to the temporal-spatial dynamics of NPP is still not clear. Quantifying the main driving forces on the temporal-spatial dynamics of NPP for subtropical forest ecosystems is a critical foundation for understanding their carbon cycle.
Methods We utilized multi-sources dataset, including observed meteorological data, inversed annual maximum leaf area index (LAI), referenced NPP (simulated by Boreal Ecosystem Productivity Simulator (BEPS) model), forest age and forest types, land cover, digital elevation model (DEM), soil texture, CO₂ concentration and nitrogen deposition. We used the InTEC (integrated terrestrial ecosystem carbon-budget) model to simulate the NPP dynamics for forest ecosystems in Jiangxi Province during the period of 1901-2010. The effects of climate change, forest age, CO₂ concentration and nitrogen (N) deposition on forest NPP from 1970 to 2010 were discussed through designed scenarios.
Important findings (1) Validations by flux measurements and forest inventory data indicated that the InTEC model was able to capture the interannual and spatial variations of forest NPP. (2) The average forest NPP was 47.7 Tg C·a^-1 (± 4.2 Tg C·a^-1) during 1901-2010. The NPP in the 1970s, 1980s, 1990s and 2000s was 50.7, 48.8, 45.4, and 55.2 Tg C·a^-1, respectively. As forest regrows, NPP significantly increased for forests in Jiangxi Province in the 2000s, and exceed that in the 1970s for more than 60% of the forest area. (3) During 1970-2010, under the scenarios of disturbance and non-disturbance, the forest NPP were underestimated by 7.3 Tg C·a^-1 (14.5%) and overestimated by 3.6 Tg C·a^-1 (7.1%) compared to the scenarios of all disturbance and non-disturbance factors, respectively. Compared to the average NPP during 1970-2010, climate change decreased NPP by -2.0 Tg C·a^-1 (-4.7%), N deposition increased NPP by 4.5 Tg C·a^-1 (10.4%), CO₂ concentration change, and the integrated fertilization of CO₂ and N deposition increased NPP by 4.4 Tg C·a^-1 (10.3%) and 9.4 Tg C·a^-1 (21.8%), respectively.     

Effects of litter removal and addition on ecosystem carbon fluxes in a typical steppe

为揭示凋落物去除和添加处理对草原生态系统碳通量的影响, 2013和2014年连续两年在成熟群落围封样地进行凋落物去除实验、在退化群落放牧样地进行凋落物添加实验, 并运用静态箱法探讨碳通量变化规律并分析其主要影响因子。结果表明: 两种群落的净生态系统CO₂交换(NEE)有明显的季节性变化。对成熟群落而言, 去除50%凋落物显著增加了NEE, 去除100%凋落物显著降低了NEE, 而对生态系统总初级生产力(GEP)和生态系统呼吸(ER)均无显著影响; 对退化群落而言, 凋落物添加显著增加了GEP和NEE, 而对ER无显著影响。两种群落的GEP与10 cm土壤温度显著正相关, 但NEE和GEP的变化规律与土壤温度相反, 与10 cm土壤湿度相同。由此可见, 凋落物去除和添加处理对生态系统碳通量的影响主要是改变土壤湿度和地上生物量,而不是改变土壤温度。该研究为合理利用凋落物改善草地生态系统管理和促进草地恢复提供了理论依据。     

Impacts of elevated carbon dioxide concentration on terrestrial ecosystems: problems and prospective

理解生态系统对过去、现在和未来CO₂浓度变化的响应,对于在生态进化的时间尺度上认识和预测全球变化的后果至关重要。过去三十多年来CO₂浓度升高相关的科学问题主要集中在对植物生长和生产力的影响, 碳氮周转, 生态系统渐进式氮限制(PNL)形成, 与其他胁迫因子(O₃污染、氮沉降、升温、干旱)之间的交互作用等方面。尽管生态学家在数据累积、基础理论上取得了一定进展, 但是仍然存在较大不确定性和大量未知有待解决。该文探究了近30年来CO₂浓度升高对陆地生态系统影响研究的国际研究进展、重点领域及热点, 回顾了CO₂浓度升高对植物影响的模拟实验研究发展, 重点论述了CO₂浓度升高对粮食产量及品质、碳固定、水分利用效率、生态系统氮利用和土壤微生物响应等国际前沿动态研究中存在的主要问题与不足, 在此基础上展望了未来研究中值得关注的前沿研究方向。     

Alpine grassland water use efficiency based on annual precipitation,growing season precipitation and growing season evapotranspiration

Water use efficiency (WUE) is an important parameter to understand the coupling between the water, and carbon cycles of terrestrial ecosystems. Previous studies on the grassland ecosystem WUE on the Qinghai-Xizang Plateau mainly based on annual precipitation (AP). However, vegetation water use mainly occurs in growing season. Therefore, we aimed to explore the differences of ecosystem WUE between alpine meadow and alpine steppe, and the relationships between ecosystem WUE and environmental factors from 2000 to 2010, using annual precipitation use efficiency (PUE_a), growing season precipitation use efficiency (PUE_gs), growing season water use efficiency (WUE_gs) based on AP, growing season precipitation (GSP) and growing season evapotranspiration (ET_gs ) respectively. Combining satellite-derived above-ground net primary productivity (ANPP), satellite-derived evapotranspiration and meteorological data from 2000 to 2010, we calculated PUE_a (ANPP / AP), PUE_gs (ANPP / GSP) and WUE_gs (ANPP / ET_gs) to find the differences of PUE_a, PUE_gs and WUE_gs between alpine meadow and alpine steppe. Moreover, we explored the relationships between PUE_a, PUE_gs or WUE_gs and precipitation (or evapotranspiration) or air temperature. We found that (1) the PUE_a and PUE_gs of alpine meadow were higher than that of alpine steppe, but there were no significant difference between WUE_gs of the two grassland types, indicating that there may be similar intrinsic water use efficiencies of the two grassland types. (2) The inter-annual variation of PUE_a and PUE_gs were similar while WUE_gs showed a larger fluctuation, implying that ET-based WUE_gs was more sensitive than precipitation-based PUE_a and PUE_gs, therefore WUE_gs is a better indicator of ecosystem water use efficiency than PUE_a or PUE_gs. (3) The PUE_a, PUE_gs and WUE_gs were negatively correlated with AP, GSP and ET_gs respectively, reflecting a consistency of the three water use efficiency measurements. In the alpine steppe, only WUE_gs was observed positively correlated with air temperature among the three measurements, but in the alpine meadow, no significant relationships between water use efficiency and air temperature was detected, suggesting that the WUE_gs of alpine steppe was more sensitive to air temperature than that of alpine meadow.