The changes in water-use efficiency and stoma density of Leymus chinensis along Northeast China Transect

Leymus chinensis is a keystone species in the temperate zone grassland of China. Along the NECT (Northeast China Transect) in 2001, water-use efficiency of L. chinensis was analyzed with δ¹³C, and changes in the stoma density of its leaves were observed and computed under a microscope. Results showed that the ecological plasticity modulation of the stoma density of L. chinensis and its water-use efficiency were two important mechanisms for its broad ecological adaptability. From east to west along the NECT, the δ¹³C of the species varied from -27.49‰ to -23.57‰, consisting with the reduction of annual precipitation, soil water and annual average temperature, but increased with the increase of the elevation of sampling sites. The stoma density increased from 96.9/mm² to 169.5/mm², indicating that the water-use efficiency for the species was improved along the gradient. The linear coefficient between the two parameters was significant (R² = 0.7338). The results of a stepwise regression analysis showed that the soil water was the first marked factor for determining the stoma density, and the next was the annual precipitation, which suggested that the water factors were the primary ecological factors influencing the stoma density of L. chinensis. The findings in this study showed that the responses of the stoma density and the water-use efficiency for L. chinensis to environmental changes were very complicated. They may be the outcome operated synthetically by all environmental factors in the long-term adaptation to different ecological environments, including human activity, for L. chinensis.     

中国东北样带关键种羊草水分利用效率与气孔密度

沿中国东北样带,从长春到阿巴嘎旗,大约每个经度设1个样地,共10个样地,研究了草原段关键种羊草的水分利用效率、叶片下表面气孔密度和气孔大小的变化,以及它们与年降水量、年均温度、土壤水分和海拔的关系．结果表明：自东向西,随年降水量、年均温度、土壤水分的降低和海拔的升高,羊草水分利用效率有明显增强的趋势,而气孔密度有明显增大的趋势,气孔大小没有明显变化规律并主要与取样时刻开张状态有关,说明羊草气孔数量的增多有利用提高水分利用效率．逐步回归分析结果表明,土壤水分是决定羊草气孔密度变化的第一显著因子,其次是年降水量,说明水分条件是羊草气孔密度变化的主要生态因子．从数据分布散点图、温度和放牧干扰作用的复杂性以及受土壤和地形条件特殊性影响样地的分析表明,羊草水分利用效率和气孔密度对环境变化的响应是非常复杂的,是包括植被利用方式与强度在内的环境因子综合作用的结果,也是羊草长期适应各样地环境的结果．     

中国东北样带关键种羊草水分利用效率与气孔密度

沿中国东北样带, 从长春到阿巴嘎旗, 大约每个经度设1个样地, 共10个样地, 研究了草原段关键种羊草的水分利用效率、叶片下表面气孔密度和气孔大小的变化, 以及它们与年降水量、年均温度、土壤水分和海拔的关系. 结果表明: 自东向西, 随年降水量、年均温度、土壤水分的降低和海拔的升高, 羊草水分利用效率有明显增强的趋势,而气孔密度有明显增大的趋势, 气孔大小没有明显变化规律并主要与取样时刻开张状态有关, 说明羊草气孔数量的增多有利用提高水分利用效率. 逐步回归分析结果表明, 土壤水分是决定羊草气孔密度变化的第一显著因子, 其次是年降水量, 说明水分条件是羊草气孔密度变化的主要生态因子. 从数据分布散点图、温度和放牧干扰作用的复杂性以及受土壤和地形条件特殊性影响样地的分析表明, 羊草水分利用效率和气孔密度对环境变化的响应是非常复杂的, 是包括植被利用方式与强度在内的环境因子综合作用的结果, 也是羊草长期适应各样地环境的结果.     

Climate-driven changes in shoot density and shoot biomass in Leymus chinensis (Poaceae) on the North-east China Transect (NECT)

Aim Climate‐driven changes affecting ecosystem primary production have been well documented for many vegetation types, while the effects of climate on plant populations remains unclear. Herein, we address the relationships between climatic variables and shoot density, reproductive allocation and shoot biomass in Leymus chinensis on a large‐scale climatic gradient in 2000. Location Nine sites experiencing similar light regimes, but differing in longitude, precipitation and altitude were selected on the North‐east China Transect (NECT) from 115° to 124°E, around a latitude of 43.5°N. Methods Densities of total, vegetative and reproductive shoots and of shoot biomass were measured twice over the growing season in each site. Climatic data were taken from the climate database of the Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences and from the local weather stations throughout the NECT. Results Densities of total, vegetative and reproductive shoots increased significantly from the west to the east and from dry to moist along the NECT, and were strongly correlated with annual precipitation (r² = 0.934, 0.943 and 0.863, respectively) and an aridity index (r² = 0.809, 0.816 and 0.744, respectively). The average total shoot density at the east end (470/m²) was about three times that at the west (160/m²). Reproductive allocation and shoot biomass for both vegetative and reproductive shoots increased with precipitation and declined with the aridity index along the NECT. There were positive correlations between shoot biomass and annual precipitation for vegetative shoots (P < 0.05, R² = 0.604) and March precipitation for reproductive shoots (P < 0.05, R² = 0.533), respectively. Main conclusions These findings suggest that L. chinensis adjusts to decreasing precipitation/increasing aridity by alterations in shoot density, reproductive allocation and shoot biomass along the drought gradient of the NECT.     

Change of tree diversity on Northeast China Transect (NECT)

Analysis of information from about 287 sample plots on Northeast China Transect (NECT) indicated that between 1986 and 1994 at latitude 43.48° N to 43.55° N and longitude 124.93° E to 131.28° E, the relative abundance of different tree species changed differently. The change of relative abundance for the moisture-sensitive tree species, such as Quercus mongolica and Larix olgensis, was helpful to detect climate change. Use of GIS software and the and _w indices of tree diversity on NECT showed that the areas of high and medium tree diversity decreased, respectively, while the area of low tree diversity increased. The heterogeneity of habitats along the NECT increased with climate change and local human activities.     

Caloric content of plant species and its role in a Leymus chinensis steppe community of Inner Mongolia, China

The caloric contents of 42 species and their composition in a Leymus chinensis steppe community of Inner Mongolia, China were determined and analyzed based on the field experiment for 11 years. The caloric content (x ± SD) of aboveground parts of plant species varied from (13156 ± 1141) J·g^?1 (ash contained) to (18141 ± 527) J·g^?1. The average caloric content of all species was (16899 ± 840) J·g^?1 and the inter-specific CV (coefficient of variation) was 4.9%. Of all the species, Caragana microphylla had the highest caloric content (18142 J·g^?1). Grasses had a higher average caloric content ((17425 ± 291) J·g^?1) than forbs ((16734 ± 844)J·g^?1). When the herbaceous species were classified into subgroups according to life-form and growth-form, the order of average caloric contents, from high to low, was: tall grasses ((17717 ± 92) J·g^?1) > legume ((17228 ± 433) J·g^?1) > short grasses ((17250 ± 218) J·g^?1) > remaining forbs ((16784 ± 529) J·g^?1) > subshrubs ((16719 ± 69) J·g^?1) > annuals and biennials ((15911 ± 1759) J·g^?1). There was a positive correlation (P < 0.05) between the caloric contents of 42 species and their relative biomass in the community. When all species were classified into 3 groups according to their composition in the community, the average caloric contents, weighed by the species relative biomass, followed the order: dominant (17740 J·g^?1) > companion (17244 J·g^?1) > incidental (16653 J·g^?1). The plants with high caloric contents were more competitive, which allowed them to gain a dominant status, whereas the competitive abilities of plants with low caloric contents were generally weak. The latter made up the companion or incidental species in a steppe community.     

氮沉降强度和频率对羊草叶绿素含量的影响

氮沉降强度和沉降频率是决定其对陆地生态系统影响的重要决定因素。我们结合当前世界上各地区的氮沉降状况,设计了包括9个氮沉降梯度的长期控制实验,并将氮沉降分为两种沉降频率（一年2次和每月1次）、草原管理方式分为封育和割草两种。本文主要基于上述实验平台的优势植物（羊草）叶片叶绿素含量来探讨氮沉降方式（强度和频度）和草原管理方式（封育和打草）对草地生态系统结构和功能的影响。实验结果表明：1）氮沉降显著增加了植物叶片叶绿素含量（P < 0.001）;2）每月一次模拟氮沉降处理的植物叶绿素含量显著低于一年两次氮沉降的处理（P = 0.026）;3）在相同的氮沉降强度处理下,打草地相对于封育草地具有更高的叶绿素含量（P = 0.012）;4）羊草叶绿素含量与其叶片氮浓度显著正相关（P < 0.001）;5）羊草叶绿素含量与该植株高度极显著正相关（P < 0.001）。根据上述结果我们可以看出一年一次或一年两次的模拟氮沉降（类似于施肥处理或低频率的氮素添加实验）可能会夸大真实氮沉降对草地生态系统结构和功能的影响,今后在外推类似实验结论时应更加谨慎。此外,氮沉降下打草管理有利于增加了植物叶片叶绿素含量,可提高植物的光合作用,因此在未来氮沉降加剧状况下,打草可以保持或提高内蒙古草地生产力,有利于该地区草地的可持续利用。     

中国东北样带羊草群落C3和C4植物功能群生物量及其对环境变化的响应

在全球动态植被模型的发展中,受限于人力、物力和财力使得在物种水平上的研究变得既不可能也无必要。植物功能群的划分是从生态学的,而不是系统发育的角度来相互比较地对待不同地区的植物,从而削减了植被变化研究中植物分类群的数量,已成为研究植被变化及生物多样性对生态系统功能作用的重要单位。植物的不同光合途径（C3、C4和CAM）从叶片组织结构到生理功能,从生态适应到地理分布均表现出对不同水、热、光环境的响应,是理想的植物功能群分类。为此,分析了中国东北样带以羊草（Leymus chinensis）为建群种或共建种的草原群落植物光合类型功能群生物量及其与群落初级生产力和环境变化的关系。结果表明：（1）C4植物生物量具有明显的变化规律,且对环境变化的响应显著,其变异性较高,更能反映样地问环境变化的差异;（2）C4与C3植物变化具有明显的互补性,并且多数C4植物常在逆境中起到更大作用,如干旱化、盐碱化和放牧干扰;（3）C4植物种类少,在所有调查样方中仅出现7种,占总出现种类的9．72％。这些特点说明C4植物可以考虑作为评估和预测我国温带草原植被及其生态系统变化的重要植物功能群。     

The Complexity and Diversity of Typical Plant Communities Along the Northeast China Transect (NECT)

This study examine the notion of plant community complexity in a broad sense and develop a new measure based on the average length L(S) (L(S)=∑ qj=1p jl j ) of the communication-theoretical parsimonious code required to describe the community (S). Total complexity may be differentiated into organized and unorganized complexity. The author refers to Shannon-Wiener entropy H(S) (H(S)=-∑ qj=1 p j log 2 p j ) and Renyi entropy H 12 (S) (H α(S)=11-αlog 2∑ qj=1 p α j , where α =12) as “disorder-based complexity", L(S) as “total complexity" and the difference Δ(S)=L(S)-H(S) and Δ 12 (S)=L(S)-H 12 (S) as “structural complexity". The complexity and diversity of typical plant communities along the NECT (Northeast China Transect) were discussed. The results suggest that structural complexity is higher in the lightly grazed grassland than the heavily grazed grassland. Clearly, structural complexity and disorder-based diversity are not substitutes for one another and should be considered as autonomous, equally important properties. Δ 12(S) measures a community complexity distinct form the disorder-based complexity H 12 (S) .     

中国东北样带（NECT）植物群落复杂性与多样性研究

在更广的意义上考虑群落复杂性的概念,将群落总复杂性分离为基于无序的复杂性和结构复杂性,并以群落的两个原始数据－群落组分（例如种群）数和各组分个体的比例分布为基础,用描述群落的最小剩余码的平均码长Ｌ（Ｓ）＝ｑ／∑／ｊ＝１ｐｊｌｊ（其中ｌｊ为物种Ｓ的相对多度的Ｈｕｆｆｍａｎ码字长度,ｑ是物种数,ｐｊ满ｑ／∑／ｊ＝１ｐｊ＝１）测度群落总复杂性,用Ｓｈａｎｎｏｎ－Ｗｉｅｎｅｒ熵Ｈ（Ｓ）＝－ｑ／∑／ｊ＝１ｐ     

中国东北样带土壤氮的分布特征及其对气候变化的响应

根据2001年中国东北样带土壤全氮和有效氮的实测数据,结合CO₂浓度倍增与不同土壤湿度的模拟试验数据,对土壤全氮和有效氮的梯度分布、影响因子分析及其对气候变化的响应进行研究.结果表明,样带土壤表层全氮和有效氮的梯度分布与土壤有机碳的分布基本一致:沿经度呈现东高西低的趋势,局部由于土壤退化而出现低谷.土壤全氮的剖面分布和土壤有机碳相似,而土壤有效氮则有所不同.样带土壤全氮和有效氮与土壤pH、有机碳、全磷、全硫、全锌、土壤活性碳、有效磷、有效钾、有效锰、有效锌、土壤容重、田间持水量、土壤总孔度等因子均呈显著或极显著的相关关系.样带土壤全氮和有效氮与降雨量之间呈极显著的正相关关系(r=0.682,P＜0.001和0.688,P＜0.001).短期培养试验中,CO₂浓度倍增和不同土壤湿度下土壤全氮和有效氮的变异较小(变异系数分别是5.55%和3.84%),但可反映一定的变化趋势.     

三种利用方式对羊草草原土壤氨氧化细菌群落结构的影响

本文以内蒙古呼伦贝尔羊草草原为研究对象,利用聚合酶链式反应－变性梯度凝胶电泳(PCR－DGGE)技术及扩增产物序列分析方法比较研究了刈割、放牧和围栏封育三种利用方式对羊草草原土壤氨氧化细菌多样性和系统发育的影响,结果表明：羊草草原土壤中氨氧化细菌的优势类群为亚硝化螺旋菌属和亚硝化单孢菌属的细菌,分别占氨氧化细菌总数的72.4%和28.6%,Cluster 4和Cluster 6在各个样地中均为优势类群但所占比例不同,放牧样地中氨氧化细菌的多样性最高,逐步回归分析的结果表明,影响多样性指数的关键理化因子是土壤硝态氮含量。放牧样地中脲酶活性和硝化率都显著高于其他两种利用方式,其中,脲酶活性与土壤硝态氮和全磷含量表现出极显著的相关性,与速效磷含量表现出显著相关性;而硝化率仅与硝态氮含量表现出显著相关性。不同利用方式土壤氨氧化细菌群落与土壤理化因子的典范对应分析结果表明铵态氮的含量对氨氧化细菌群落的影响显著。     

Quickly identifying tree species susceptible to extinction: a case study of seven tree species at Northeast China Transect

Quickly predicting which species are most susceptible to extirpation in a defined area is important for conservation and environmental monitoring. We hypothesised that the susceptibility of tree species to extinction in an area could be inferred by the spatial and temporal dynamics of its populations. Here we use change in population size, population spatial variability, spatial autocorrelation, spatial cohesion, crash rate, and recovery rate to characterise the relative susceptibility to extirpation for seven tree species along the Northeast China Transect from 1986 to 1994. Betula dahurica Pall. and Populus davidiana Dode. were found to have a higher susceptibility to loss than Pinus koraiensis Siebold et Zucc., Betula costata Trautv., and Larix olgensis A. Henry in this area during this time period. The same methods could be useful to monitor and predict the susceptibility of species extinction at a larger regional scale.     

Application of Discriminant Analysis in Distinguishing Plant Photosynthetic Types-A Case Study in Northeast China Transect (NECT) Area

Discriminant analysis is an important method in multivariate statistic analysis to distinguish whatever type an individual should belong to. Based on the field actual photosynthetic data obtained from the research platform--Northeast China Transect (NECT), the concept and principle of discriminant analysis were used to distinguish the different plant photosynthetic types. A number of indices related to plant photosynthetic rate measured by a LCA4 photosynthesis system were selected to build the discriminant model. In this case study, 15 plant species from C4 plant functional groups and 51 from C3 plant functional groups were selected to build a discriminant model. The rate of accuracy, of returned classification using methods of squared Mahalanobis distances from group centroids and posterior probabilities, reached to 98.48 %. With the help of this model, any plants' photosynthetic types could be distinguished simply by using their four related parameters, viz., photosynthetic rate, transpiration, stomatal conductance and the temperature difference between leaf surface and atmosphere.     

Morphological responses of Leymus chinensis (Poaceae) to the large-scale climatic gradient along the North-east China Transect (NECT)

A field experiment was conducted to examine the morphological variations of Leymus chinensis along the climatic gradient of the North‐east China Transect (NECT), from 115° to 125° E, in the vicinity of 43.5° N, in north‐eastern China. Ten sites selected for plant sampling along the gradient have approximately uniform theoretical radiation, but differ in precipitation and geographical elevation. The results of analyses showed that vegetative and reproductive shoot heights, flag leaf lengths and widths and seed numbers per inflorescence increased from the west to the east with precipitation, but decreased with aridity. Leaf lengths and widths for most leaf types from 115° to 124° E exhibited little variations. Significant correlations of plant heights, flag leaf lengths and widths and seed numbers per inflorescence with large‐scale climatic variables (e.g. annual precipitation, aridity) and geographical variation (longitude) found in this study indicated that climatic factors have significant effects on some morphological traits of L. chinensis along the NECT.     

Using spatial analysis to monitor tree diversity at a large scale: a case study in Northeast China Transect

Aims Monitoring and assessing diversity change at a large scale is important for any meaningful biodiversity conservation and management. Spatial analysis techniques can provide information about different aspects of diversity distribution including change. We applied some common spatial analysis methods and additive partitioning of species diversity in the Northeast China Transect as a case study to show how to characterize the distribution and change of tree diversity in this area from different perspectives.Methods The field data were collected from the permanent plots conducted every 4 km. The additive partitioning of species diversity was used to characterize the diversity of tree species at different scales. Moran's I was used for identifying the spatial scale of autocorrelation, lacunarity was studied for diversity patch contagion and dispersion and spectral entropy was used for assessing the overall spatial distribution.Important findings Data collected from 1986 to 1994 indicate that the change of α diversity was not significant in the study area, but the change of β diversity was significant. The percentage of α diversity in total diversity (γ) increased from 14.2 to 17.2%, and the percentage of β diversity decreased from 85.8 to 82.8%. For both α and β diversities, the scale of spatial autocorrelation decreased at the scale of 25–40 km and increased around 15–20 and 200 km. The lacunarity of α diversity decreased significantly and there was a sudden change at the scale of 56–68 km, but the lacunarity of β diversity increased across scales. The spectral entropy decreased slightly in α diversity and remained similar for β diversity. By using spatial analysis, we can monitor the diversity change over a large area and also assess the effectiveness of the current conservation strategies.     

不同群落中米氏冰草和羊草的年龄结构动态

米氏冰草和羊草都是根茎型禾草,是典型的无性系植物。采取单位面积挖掘取样法,对呼伦贝尔沙地植被次生演替过程中的米氏冰草和羊草种群分株年龄结构进行调查。结果表明,在单生和混合群落中,米氏冰草分株分别由3和4个年龄级组成,羊草均由2个年龄级组成;米氏冰草分株数量和生物量年龄结构变化基本一致,即随着生长年限的延长,呈减少低龄级和增加高龄级比例的趋势,使单生群落中始终为增长型,但接近于稳定型,混生群落中由增长型变为稳定型。羊草分株数量和生物量年龄结构在连续2a均为明显的增长型。羊草各龄级平均单株生产力均高于米氏冰草,平均是米氏冰草的5.2倍。米氏冰草和羊草种群分株年龄结构的变化,蕴含着米氏冰草种群的优势地位将被羊草种群取代的趋势。     

中国东北样带树种（属）的空间特性及变化

对中国东北样带上１６个树种（属）在１９８６年与１９９４年景观水平的地理分布、出现频率、优势度及空间相关性等空间特性的分析得出,红松（Ｐｉｎｕｓ ｋｏｒａｉｅｎｓｉｓ Ｓｌｅｂ．ｅｔ Ｚｕｃｃ．）与花曲柳（Ｆｒａｘｉｎｕｓ ｒｈｙｎｃｈｏｐｈｙｌｌａ Ｈｅｍｓｌ．）分别是向西和向东扩展最快;种群的分布边界形态与该边界的移动有密切关系;红松、山杨（Ｐｏｐｕｌｕｓ ｄａｖｉｄｉａｎａ Ｄｏｄｅ．）、黄檗     

中国东北样带树种(属)的空间特性及变化

The 16 tree species on Northeast China Transect (NECT) were analyzed from the change of geographical distribution, frequency and dominance pattern and the spatial correlation at landscape scale in 1986 and 1994. Pinus koraiensis Sieb. et Zucc. and Fraxinus rhynchophylla Hemsl. had spread rapidly towards west and east, respectively. The frontier form of species had close relation with its movement. The patch size of Pinus koraiensis, Populus davidiana Dode., Phellodendron amurense Rupr., Juglans mandshurica Maxim., Fraxinus mandshurica Rupr., Betula dahurica Pall., Picea koraiensis Nakai, Abies nephrolepis Maxim. and Larix olgeusis var. koreana Nakai decreased, however, Quercus mongolica Fisch., Betula costata Trautv., Acer mono Maxim., Tilia spp., Ulmus spp., Betula platyphylla Suk. and Fraxinus rhynchophylla increased. The frequency pattern of Populus davidiana, Betula platyphylla, Fraxinus rhynchophylla and Betula dahurica changed significantly. The dominance pattern of Populus davidiana, Tilia spp., Juglans mandshurica, Betula platyphylla, Betula dahurica and Abies nephrolepis changed significantly. The spatial correlation between Quercus mongolica and Betula dahurica, Betula costata and Picea spp., Betula costata and Abies nephrolepis, Picea spp. and Abies nephrolepis declined, however, the spatial correlation between Larix spp. and Betula platyphylla, Acer mono and Ulmus spp. increased.     

Effects of different land use patterns on nifH genetic diversity of soil nitrogen-fixing microbial communities in Leymus Chinensis steppe

Biological nitrogen fixation through prokaryotic microbe is an important source of nitrogen been input into many natural ecosystems. In this study the active diazotrophic community was investigated in the three treatments of mowed, grazed and enclosed Leymus chinensis steppes in Hulunbeier grassland of Inner Mongolia by using approaches of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR–DGGE) and sequence analysis. The community structure and diversity of the bacterial groups from the different samples was further analyzed by using different techniques, such as statistical analysis and diversity index evaluation of the band patterns etc. The results showed that grazing activity significantly reduced the number of species and quantities of nitrogen-fixing microorganisms, as well as the nifH gene diversity. However, enclosed plots had the lowest diversity of nifH gene. While the highest one found in mowing plots. A total of 30 sequences representing 25 different sequence types were recovered from the DGGE gels after phylogenetic constructions. The results also revealed that most sequences were coming from Alphaproteobacteria of Proteobacteria, and characterized by sequences of members of Rhodobacter, Bradyrhizobium, Mesorhizobium, Rhodopseudomonas, Xanthomonas, Azospirillum, Gluconacetobacter, Methylobacterium and Methylocystis. Symbiotic nitrogen-fixers existed in grazing, mowing and enclosed plots accounted for 21.4%, 47.3% and 31.3% respectively in their dominant nitrogen-fixing bacteria. The result of principal components analysis showed that the influence of different land use patterns on nitrogen-fixing microbial communities composition can be ordered as grazing plots > enclosed plots > mowing plots. Nitrogen-fixing microbial communities in L. chinensis steppe were significantly (P < 0.05) influenced by the levels of nitrate nitrogen, total phosphorus, available phosphorus contents and pH value when canonical correspondence analysis was employed to identify relationship between nifH gene and soil physicochemical factors under different land use patterns. The result obtained from correlation analysis showed that there was a significant (P < 0.05) negative relationship between the nitrate nitrogen and the total phosphorus content, furthermore, the available phosphorus content was strongly correlated (P < 0.01) with the pH value.