中国Holdridge生命地带平均中心的时空分布及其偏移趋势

在分析目前生态地理模型及其实现方法的基础上 ,提出基于 ARC/ INFO与 VC 综合集成的先插值再运行模型的全新研究方法和技术路线 ,克服了以前模型实现过程中所存在的局限性。利用中国 1 96 2～ 2 0 0 2年 735个站点逐日温度与降水量观测数据 ,通过对 Holdridge生命地带模型和生命地带平均中心模型进行模拟运算后获得中国 Holdridge生命地带类型平均中心时空分布图及 2 0世纪 6 0、70、80与 90年代平均中心偏移趋势图。从生命地带类型平均中心时空分布及其偏移趋势分析研究中发现 ,生命地带类型平均中心的时空分布及其偏移趋势与相关气候因子的变化趋势相对应 ,并能够很好地与我国土地覆被类型实际的空间分布及其变化情况相符 ;各种生命地带类型平均面积的变化规律与相应的气候因子的变化趋势 (尤其是降水量、温度 )存在着一定相关性。另外 ,通过对我国生命地带类型平均面积比例大小进行排序分析发现与我国土地覆被类型的实际情况能够很好吻合     

Study on Climate Vegetation Classification for Global Change in China

The study on climate-vegetation relationship is the basis for determining the re sponse of terrestrial ecosystem to global change. By means of quantitative analysis on climate-vegetation interaction, vegetation types and their distribution pattern could be corresponded with certain climatic types in a series of mathematical forms. Thus, the climate could be used to predict vegetation types and their distribution, the same is in reverse. Potential evapotranspiration rate is a comprehensive climatological index which combines temperature with precipitation, and could be used to evaluate the effect of climate on vegetation. In this respect, Holdridge life zone system has been drawing much attention and widely applied internationally owing to its simplicity. It is especially used in the assessment of sensibility of terrestrial ecosystems and their distribution in accordance with climate change and in prediction of the changing pattern of vegetation under doubled CO2 condition. However, Prentice (1990) pointed out that the accurancy of Holdridge life zone system is less than 40 % when it is used at global scale. The reason may be that the potential evapotranspiration calculated by Thornthwaite method, which is used in Holdridge life zone system, reflects the potential evapotranspiration from small evaporated area, while climate-vegetation classification is based on the regional scale. The authors try to establish a new climate-vegetation classification system based on the regional potential evapotranspiration. According to the following formula: where E designates regional actual evapotranspiration: Ep local potential evapotran-spiration: Epo, regional potential evapotranspiration. Ed can be calculated from Penman model or other models. E can be calculated from the following model: E=r · Rn (r2+Rn2+r · Rn) / (2) (r+Rn) · (r2+Rn2)where r designates precipitation (mm); Rn, net radiation (mm). Thus, Ep0 can be easily obtained. It is used as the regional thermal index (RTI) of climate-vegetation classification,and can be expressed as: RTl = Epo (3) Moisture index is another index of climate-veggetation classification. Usually, it can be expressed as the ratio between potential evapotranspiration and precipitation. However, this ratio can not reflect soil moisture, which is important for plant. The ratio between regional actual evapotranspiration and regional potential evapotranspiration is associated not only with climatic condition but also with soil moisture. So it can be used as the moisture index of climate-vegetation classification, and is defined as regional moisture index (RMI): RMI = E/Epo (5) Based on the average climatological data of 30 years from 647 meteorological observation stations in China. It was found that RTl could well reflect a regional thermal level. The values of RTI were less than 360 mm in cold temperate zone, 360～650 mm in temperate zone, 650～380 mm in warm temperate zone, 780～1100 mm in subtropical zone. And more than 1100 mm in tropical zone. RMI also reflects a regional moisture level very well. The values of RMI was less than 0.4 in desert area, 0.4～0.7 in grassland area and more than 0.7 in forest area. Thus, the climate-vegetation classification in China is established on the basis of the two indices: RTI and RMI. According to this model, the changing patterns of vegetation zones in China are given under the conditions of mean annual temperature in creasing by 2℃ and 4℃ and mean annual precipitation increasing by 20%. The results showed that the areas of forest and grassland would decrease, the vegetation zones would move northward and upward, and the area of desert would increase. The results also indicate that the Tibetan Plateau is an area highly sensitive to global change. It could be considered as an indicative or forewarning area for global change , and therefore, an area of great siginificance for monitoring and research. The possible beneficial effect of global change on China terrestrial ecosystems is that the plantation boundary will move northwards and upwards; and the disadvantageous effect is the expansion of desertification and the increase of instability in climatic conditions.     

Land use impacts on freshwater regulation, erosion regulation, and water purification: a spatial approach for a global scale level

Purpose

Rarely considered in environmental assessment methods, potential land use impacts on a series of ecosystem services must be accounted for in widely used decision-making tools such as life cycle assessment (LCA). The main goal of this study is to provide an operational life cycle impact assessment characterization method that addresses land use impacts at a global scale by developing spatially differentiated characterization factors (CFs) and assessing the extent of their spatial variability using different regionalization levels.

Methods

The proposed method follows the recommendations of previous work and falls within the framework and principles for land use impact assessment established by the United Nations Environment Programme/Society of Environmental Toxicology and Chemistry Life Cycle Initiative. Based on the spatial approach suggested by Saad et al. (Int J Life Cycle Assess 16: 198–211, 2011), the intended impact pathways that are modeled pertain to impacts on ecosystem services damage potential and focus on three major ecosystem services: (1) erosion regulation potential, (2) freshwater regulation potential, and (3) water purification potential. Spatially-differentiated CFs were calculated for each biogeographic region of all three regionalization scale (Holdridge life regions, Holdridge life zones, and terrestrial biomes) along with a nonspatial world average level. In addition, seven land use types were assessed considering both land occupation and land transformation interventions.

Results and discussion

A comprehensive analysis of the results indicates that, when compared to all resolution schemes, the world generic averaged CF can deviate for various ecosystem types. In the case of groundwater recharge potential impacts, this range varied up to factors of 7, 4.7, and 3 when using the Holdridge life zones, the Holdridge regions, and the terrestrial biomes regionalization levels, respectively. This validates the importance of introducing a regionalized assessment and highlights how a finer scale increases the level of detail and consequently the discriminating power across several biogeographic regions, which could not have been captured using a coarser scale. In practice, the implementation of such regionalized CFs suggests that an LCA practitioner must identify the ecosystem in which land occupation or transformation activities occur in addition to the traditional inventory data required—namely, the land use activity and the inventory flow.

Conclusions

The variability of CFs across all three regionalization levels provides an indication of the uncertainty linked to nonspatial CFs. Among other assumptions and value choices made throughout the study, the use of ecological borders over political boundaries was deemed more relevant to the interpretation of environmental issues related to specific functional ecosystem behaviors.     

A biogeochemistry‐based dynamic vegetation model and its application along a moisture gradient in the continental United States

Abstract. We develop and evaluate a large‐scale dynamic vegetation model, TEM‐LPJ, which considers interactions among water, light and nitrogen in simulating ecosystem function and structure. We parameterized the model for three plant functional types (PFTs): a temperate deciduous forest, a temperate coniferous forest, and a temperate C₃ grassland. Model parameters were determined using data from forest stands at the Harvard Forest in Massachusetts. Applications of the model reasonably simulated stand development over 120 yr for Populus tremuloides in Wisconsin and for Pinus elliottii in Florida. Our evaluation of tree‐grass interactions simulated by the model indicated that competition for light led to dominance by the deciduous forest PFT in moist regions of eastern United States and that water competition led to dominance by the grass PFT in dry regions of the central United States. Along a moisture transect at 41.5° N in the eastern United States, simulations by TEM‐LPJ reproduced the composition of potential temperate deciduous forest, temperate savanna, and C3 grassland located along the transect.     

Effect of climate change over the past half century on the distribution,extent and NPP of ecosystems of Inner Mongolia

The response of natural vegetation to climate change is of global concern. In this research, changes in the spatial pattern of major terrestrial ecosystems from 1956 to 2006 in Inner Mongolia of China were analyzed with the Holdridge Life Zone (HLZ) model in a GIS environment, and net primary production (NPP) of natural vegetation was evaluated with the Synthetic model, to determine the effect of climate change on the ecosystem. The results showed that climate warming and drying strongly influenced ecosystems. Decreased precipitation and the subsequent increase in temperature and potential evapotranspiration caused a severe water deficiency, and hence decreased ecosystem productivity. Climate change also influenced the spatial distribution of HLZs. In particular, new HLZs began to appear, such as Warm temperate desert scrub in 1981 and Warm temperate thorn steppe in 2001. The relative area of desert (Cool temperate desert scrub, Warm temperate thorn steppe, Warm temperate desert scrub, Cool temperate desert and Warm temperate desert) increased by 50.2% over the last half century, whereas the relative area of forest (Boreal moist forest and Cool moist forest) decreased by 36.5%. Furthermore, the area of Cool temperate steppe has continuously decreased at a rate of 5.7% per decade; if the current rate of decrease continues, this HLZ could disappear in 173 years. The HLZs had a large shift range with the mean center of the relative life zones of desert shifting northeast, resulting a decrease in the steppe and forest area and an increase in the desert area. In general, a strong effect of climate change on ecosystems was indicated. Therefore, the important role of climate change must be integrated into rehabilitation strategies of ecosystem degradation of Inner Mongolia.     

基于地形因素的新疆荒漠植被-气候模型应用研究

本研究在新疆荒漠植被型分类的基础上,用植被与气候Holdridge生命带模型进行荒漠植被型的模拟,并用Kappa检验系数进行结果检验,模拟结果很差(0.19),将地形作为模拟模型具体考虑的一个因素,对重新分类的气候区进行二次植被模拟。二次模拟结果Kappa检验系数平均值为0.45,二次模拟整体荒漠植被型模拟结果的Kappa检验系数为0.64,极大地提高了模型模拟的准确度。模型模拟准确度的提高在于将影响新疆水分分配的地形因素作为改进Holdridge生命带模型的参数,该参数的引入为提高Holdridge生命带模型的准确度提供了新的思路,也为较准确地模拟新疆地区的植被提供了新途径。     

全球不同气候带陆地植被净初级生产力变化趋势与可持续性

分析全球不同气候带陆地植被净初级生产力(NPP)的变化趋势与可持续性,对于估算全球陆地生态系统的结构、功能和碳源(汇)具有重要意义。运用Mann-Kendall突变检验、Theil-Sen斜率估计、Hurst指数分析全球不同气候带陆地NPP的变化趋势与可持续性。结果表明：(1)全球陆地NPP有明显的地域分异规律,呈现低纬高、高纬低,沿海高、内陆低的特点。约48.79%陆地生态系统的植被NPP得到了改善,其中显著改善的面积占全球陆地生态系统的8.45%,主要分布在北美洲北部和中部、亚马逊河流域西部、刚果盆地、欧洲南部、印度半岛西北部、中国黄土高原;轻微改善的面积占全球陆地生态系统的40.34%,主要分布在南美洲中南部、亚洲东部和澳大利亚大陆东部。(2)各气候带NPP变化趋势和突变点表现为：热带、亚热带、极地带的NPP呈不显著下降趋势(R²=0.111,P=0.176;R²=0.144,P=0.120;R²=0.002,P=0.854),热带无明显突变点,亚热带突变点为2015年,极地带突变点为2005年;干旱气候带的NPP...     

Tree‐mycorrhizal associations detected remotely from canopy spectral properties

A central challenge in global ecology is the identification of key functional processes in ecosystems that scale, but do not require, data for individual species across landscapes. Given that nearly all tree species form symbiotic relationships with one of two types of mycorrhizal fungi – arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi – and that AM‐ and ECM‐dominated forests often have distinct nutrient economies, the detection and mapping of mycorrhizae over large areas could provide valuable insights about fundamental ecosystem processes such as nutrient cycling, species interactions, and overall forest productivity. We explored remotely sensed tree canopy spectral properties to detect underlying mycorrhizal association across a gradient of AM‐ and ECM‐dominated forest plots. Statistical mining of reflectance and reflectance derivatives across moderate/high‐resolution Landsat data revealed distinctly unique phenological signals that differentiated AM and ECM associations. This approach was trained and validated against measurements of tree species and mycorrhizal association across ~130 000 trees throughout the temperate United States. We were able to predict 77% of the variation in mycorrhizal association distribution within the forest plots (P < 0.001). The implications for this work move us toward mapping mycorrhizal association globally and advancing our understanding of biogeochemical cycling and other ecosystem processes.     

Sensitivity of primary production to precipitation across the United States

Primary production, a key regulator of the global carbon cycle, is highly responsive to variations in climate. Yet, a detailed, continental‐scale risk assessment of climate‐related impacts on primary production is lacking. We combined 16 years of MODIS NDVI data, a remotely sensed proxy for primary production, with observations from 1218 climate stations to derive values of ecosystem sensitivity to precipitation and aridity. For the first time, we produced an empirically‐derived map of ecosystem sensitivity to climate across the conterminous United States. Over this 16‐year period, annual primary production values were most sensitive to precipitation and aridity in dryland and grassland ecosystems. Century‐long trends measured at the climate stations showed intensifying aridity and climatic variability in many of these sensitive regions. Dryland ecosystems in the western US may be particularly vulnerable to reductions in primary production and consequent degradation of ecosystem services as climate change and variability increase in the future.     

Determinants of soil organic carbon sequestration and its contribution to ecosystem carbon sinks of planted forests

The area of forest established through afforestation/reforestation has been increasing on a global scale, which is particularly important as these planted forests attenuate climate change by sequestering carbon. However, the determinants of soil organic carbon (SOC) sequestration and their contribution to the ecosystem carbon sink of planted forests remain uncertain. By using globally distributed data extracted from 154 peer‐reviewed publications and a total of 355 sampling points, we investigated above‐ground biomass carbon (ABC) sequestration and SOC sequestration across three different climatic zones (tropical, warm temperate, and cold temperate) through correlation analysis, regression models, and structural equation modeling (SEM). We found that the proportion of SOC sequestration in the ecosystem C sequestration averaged 14.1% globally, being the highest (27.0%) in the warm temperate and the lowest (10.7%) in the tropical climatic zones. The proportion was mainly affected by latitude. The sink rate of ABC (R_ABC) in tropical climates (2.48 Mg C ha^?1 year^?1) and the sink rate of SOC (R_SOC) in warm temperate climates (0.96 Mg C ha^?1 year^?1) were higher than other climatic zones. The main determinants of R_SOC were the number of frost‐free days, latitude, mean annual precipitation (MAP), and SOC density (SOCD) at the initial observation; however, these variables depended on the climatic zone. According to the SEM, frost‐free period, mean annual temperature (MAT) and MAP are the dominant driving factors affecting R_SOC in Chinese plantations. MAT has a positive effect on R_SOC, and global warming may increase R_SOC of temperate plantations in China. Our findings highlight the determinants of SOC sequestration and quantitatively reveal the substantial global contribution of SOC sequestration to ecosystem carbon sink provided by planted forests. Our results help managers identify and control key factors to increase carbon sequestration in forest ecosystems.     

On the difference in the net ecosystem exchange of CO2 between deciduous and evergreen forests in the southeastern United States

The southeastern United States is experiencing a rapid regional increase in the ratio of pine to deciduous forest ecosystems at the same time it is experiencing changes in climate. This study is focused on exploring how these shifts will affect the carbon sink capacity of southeastern US forests, which we show here are among the strongest carbon sinks in the continental United States. Using eight‐year‐long eddy covariance records collected above a hardwood deciduous forest (HW) and a pine plantation (PP) co‐located in North Carolina, USA, we show that the net ecosystem exchange of CO₂ (NEE) was more variable in PP, contributing to variability in the difference in NEE between the two sites (ΔNEE) at a range of timescales, including the interannual timescale. Because the variability in evapotranspiration (ET) was nearly identical across the two sites over a range of timescales, the factors that determined the variability in ΔNEE were dominated by those that tend to decouple NEE from ET. One such factor was water use efficiency, which changed dramatically in response to drought and also tended to increase monotonically in nondrought years (P < 0.001 in PP). Factors that vary over seasonal timescales were strong determinants of the NEE in the HW site; however, seasonality was less important in the PP site, where significant amounts of carbon were assimilated outside of the active season, representing an important advantage of evergreen trees in warm, temperate climates. Additional variability in the fluxes at long‐time scales may be attributable to slowly evolving factors, including canopy structure and increases in dormant season air temperature. Taken together, study results suggest that the carbon sink in the southeastern United States may become more variable in the future, owing to a predicted increase in drought frequency and an increase in the fractional cover of southern pines.     

Total ecosystem carbon stocks at the marine‐terrestrial interface: Blue carbon of the Pacific Northwest Coast,United States

The coastal ecosystems of temperate North America provide a variety of ecosystem services including high rates of carbon sequestration. Yet, little data exist for the carbon stocks of major tidal wetland types in the Pacific Northwest, United States. We quantified the total ecosystem carbon stocks (TECS) in seagrass, emergent marshes, and forested tidal wetlands, occurring along increasing elevation and decreasing salinity gradients. The TECS included the total aboveground carbon stocks and the entire soil profile (to as deep as 3 m). TECS significantly increased along the elevation and salinity gradients: 217 ± 60 Mg C/ha for seagrass (low elevation/high salinity), 417 ± 70 Mg C/ha for low marsh, 551 ± 47 Mg C/ha for high marsh, and 1,064 ± 38 Mg C/ha for tidal forest (high elevation/low salinity). Soil carbon stocks accounted for >98% of TECS in the seagrass and marsh communities and 78% in the tidal forest. Soils in the 0–100 cm portion of the profile accounted for only 48%–53% of the TECS in seagrasses and marshes and 34% of the TECS in tidal forests. Thus, the commonly applied limit defining TECS to a 100 cm depth would greatly underestimate both carbon stocks and potential greenhouse gas emissions from land‐use conversion. The large carbon stocks coupled with other ecosystem services suggest value in the conservation and restoration of temperate zone tidal wetlands through climate change mitigation strategies. However, the findings suggest that long‐term sea‐level rise effects such as tidal inundation and increased porewater salinity will likely decrease ecosystem carbon stocks in the absence of upslope wetland migration buffer zones.     

基于IBIS模型的1960-2006年中国陆地生态系统碳收支格局研究

定量评估区域陆地生态系统碳收支是生态系统与全球变化科学研究的重要科学问题之一。利用集成生物圈模型（IBIS）对中国陆地生态系统历史时期（1960-2006年）气候及CO₂浓度变化条件下碳收支时空变异特征和发展趋势进行了模拟分析。结果表明,1960-2006年间,中国陆地生态系统净初级生产力（NPP）总量水平约为2.46 GtC/a,总体呈上升趋势,在东南及西南地区最高,其次是长白山及大小兴安岭地区,西北内陆地区的净初级生产力水平最低;1960-2006年间,中国陆地生态系统净生态系统生产力（NEP）总量水平约为0.11 GtC/a,总体呈上升趋势,绝大部分区域表现为碳汇效应,大兴安岭、小兴安岭、长白山、东南地区及西南部分地区碳汇效应较强,西北内陆区表现出弱碳源效应,温带湿润区、高原温带区和高原寒带区碳汇效应呈显著上升趋势;中国11个气候区,NPP与降水均为正相关,除了中温带湿润区、寒温带湿润区、高原温带和高原寒带外,降水是限制植被生长的主要因子。除了高原寒带外,NEP同样表现出与降水的更强相关性,与气温的相关性较弱。经验证,IBIS模型对于中国陆地生态系统碳收支的模拟结果合理,可以为科学预测生态系统的固碳潜力和制定区域碳管理政策提供科学依据。     

4个常用的气候-植被分类模型对中国植被分布模拟的比较研究

 应用KAPPA一致性检验方法,比较研究了4个常用的气候植被分类模型：Penman模型、Holdridge生命地带系统、Kira模型和Thornthwaite模型对中国植被分布模拟的一致性和适用性。结果表明：这4个常用的气候 植被分类模型对中国植被区划一级分类的植被地理分布模拟效果较好。其中,Holdridge生命地带系统的KAPPA值达到0.57,模拟效果优于其它三者。但对特定地区,如青藏高原的植被地理分布,所有模型均需改进或引入新的影响因子才能较好地模拟二级植被区划的植被地理分布。1)Penman模型对温带草原和青藏高原的植被地理分布模拟的KAPPA值超过0.50,是4个模型中对青藏高原植被地理分布模拟效果最好的。2)Thornthwaite模型对热带雨林、季雨林植被地理分布模拟的KAPPA值达到0.40,可以弥补Holdridge生命地带系统对热带植被地理分布模拟精度的不足。3) Holdridge生命地带系统对中国植被地理分布模拟的效果最佳,但对西部季雨林、雨林区域(52)、西部草原亚区域(63)、青藏高原温性荒漠地带(86)和温性草原地带(84)的模拟程度不理想。4)Kira模型对亚热带常绿阔叶林植被地理分布的模拟效果可与Holdridge生命地带系统相媲美;对低海拔和湿润、湿润地区植被地理分布的模拟效果尚可,但在温带荒漠区与青藏高原区植被地理分布的模拟效果与实际相差较远。     

Critical land change information enhances the understanding of carbon balance in the United States

Large‐scale terrestrial carbon (C) estimating studies using methods such as atmospheric inversion, biogeochemical modeling, and field inventories have produced different results. The goal of this study was to integrate fine‐scale processes including land use and land cover change into a large‐scale ecosystem framework. We analyzed the terrestrial C budget of the conterminous United States from 1971 to 2015 at 1‐km resolution using an enhanced dynamic global vegetation model and comprehensive land cover change data. Effects of atmospheric CO₂ fertilization, nitrogen deposition, climate, wildland fire, harvest, and land use/land cover change (LUCC) were considered. We estimate annual C losses from cropland harvest, forest clearcut and thinning, fire, and LUCC were 436.8, 117.9, 10.5, and 10.4 TgC/year, respectively. C stored in ecosystems increased from 119,494 to 127,157 TgC between 1971 and 2015, indicating a mean annual net C sink of 170.3 TgC/year. Although ecosystem net primary production increased by approximately 12.3 TgC/year, most of it was offset by increased C loss from harvest and natural disturbance and increased ecosystem respiration related to forest aging. As a result, the strength of the overall ecosystem C sink did not increase over time. Our modeled results indicate the conterminous US C sink was about 30% smaller than previous modeling studies, but converged more closely with inventory data.     

Spatial distribution of young forests and carbon fluxes within recent disturbances in Russia

Forest stand age plays a major role in regulating carbon fluxes in boreal and temperate ecosystems. Young boreal forests represent a relatively small but persistent source of carbon to the atmosphere over 30 years after disturbance, while temperate forests switch from a substantial source over the first 10 years to a notable sink until they reach maturity. Russian forests are the largest contiguous forest belt in the world that accounts for 17% of the global forest cover; however, despite its critical role in controlling global carbon cycle, little is known about spatial patterns of young forest distribution across Russia as a whole, particularly before the year 2000. Here, we present a map of young (0–27 years of age) forests, where 12‐ to 27‐year‐old forests were modeled from the single‐date 500 m satellite record and augmented with the 0‐ to 11‐year‐old forest map aggregated from the 30 m resolution contemporary record between 2001 and 2012. The map captures the distribution of forests with the overall accuracy exceeding 85% within three largest bioclimatic vegetation zones (northern, middle, and southern taiga), although mapping accuracy for disturbed classes was generally low (the highest of 31% for user's and producer's accuracy for the 12–27 age class and the maximum of 74% for user's and 32% for producer's accuracy for the 0–11 age class). The results show that 75.5 ± 17.6 Mha (roughly 9%) of Russian forests were younger than 30 years of age at the end of 2012. The majority of these 47 ± 4.7 Mha (62%) were distributed across the middle taiga bioclimatic zone. Based on the published estimates of net ecosystem production (NEP) and the produced map of young forests, this study estimates that young Russian forests represent a total sink of carbon at the rate of 1.26 Tg C yr^?1.     

Accounting for ecosystem alteration doubles estimates of conservation risk in the conterminous United States

Previous national and global conservation assessments have relied on habitat conversion data to quantify conservation risk. However, in addition to habitat conversion to crop production or urban uses, ecosystem alteration (e.g., from logging, conversion to plantations, biological invasion, or fire suppression) is a large source of conservation risk. We add data quantifying ecosystem alteration on unconverted lands to arrive at a more accurate depiction of conservation risk for the conterminous United States. We quantify ecosystem alteration using a recent national assessment based on remote sensing of current vegetation compared with modeled reference natural vegetation conditions. Highly altered (but not converted) ecosystems comprise 23% of the conterminous United States, such that the number of critically endangered ecoregions in the United States is 156% higher than when calculated using habitat conversion data alone. Increased attention to natural resource management will be essential to address widespread ecosystem alteration and reduce conservation risk.     

基于Holdridge和CCA分析的中国生态地理分区的比较

在前人工作基础上,对中国自然地理要素与生态地理区域的关系进行了综合分析,采用全国地形、土壤、气候、植被及遥感植被指数等数据,综合分析中国范围生态地理区域的分异规律,制订了生态地理分区的初步方案,并建立了相应的地理信息系统.基于Holdridge模型和CCA分析划分中国生态地理分区,建立了分区的指标体系,得到中国生态分区的大致界线,初步总结了各生态地理分区的地形、植被、气候等综合自然地理特征,完成对中国区域生态地理分区的划分.基于CCA分析的生态地理的分区,不仅结合自然区划和生态地理两种方法,而且加入了生态群落和遥感数据的综合应用.结果显示,由于受到模型适用性及数据误差的原因,基于CCA分析的结果比Holdridge模型的结果更合理一些.     

High‐density linkage map reveals QTL underlying growth traits in AP13×VS16 biparental population of switchgrass

Switchgrass (Panicum virgatum L.), a native warm‐season perennial grass, is being considered as a feedstock for biofuel production in the United States. To expedite its genetic improvement and enhance genetic gain per selection cycle, application of marker‐assisted selection is indispensable. A high‐density linkage map was constructed in a pseudo‐F₁ testcross mapping population of AP13×VS16, consisting of 349 progenies. A total of 8,757 single nucleotide polymorphism (SNP) markers generated through genotype‐by‐sequencing (GBS) were used to construct the linkage map. The total map length spans up to 2,540.2 cM with the marker density of one marker in every 0.25–0.34 cM. Spring green‐up (SG), days to flowering (FL), and the vegetative growth period (VP) data were analyzed and used for quantitative trait loci (QTL) mapping. The population showed significant variations and exhibited transgressive segregation for SG, FL, and VP. QTL analyses were performed using trait mean of each year and location along with BLUP (best linear unbiased prediction) values of the traits. A total of 35, 37, and 34 QTL for SG, FL, and VP, respectively, were identified. Phenotypic variability explained by each QTL ranged from 11.29% to 27.85%. The additive genetic effects of individual QTL ranged from ?1.81 to 2.40, ?6.12 to 7.58, and ?16.01 to 6.38 for SG, FL, and VP, respectively. Comparing major QTL regions in the switchgrass genome, 20 candidate genes were identified which were reported to be involved in growth‐, development‐, and flowering‐related traits in switchgrass.     

Effects of forest clearing and succession on the carbon and nitrogen content of soils in Puerto Rico and US Virgin Islands

Soil samples from mature and secondary forests and agricultural sites in three subtropical life zones of Puerto Rico and the US Virgin Islands were collected to determine the effects of forest conversion to agriculture and succession on soil organic carbon (C) and nitrogen (N) contents. Site characteristics that may affect soil C and N (slope, elevation, aspect, and texture) were as uniform as possible. Carbon contents (to 50 cm depth or bedrock) of cultivated sites, as a percent of corresponding mature forests, were lower in the wet (44%) and moist (31%) than in the dry (86%) life zones whereas N contents were relatively high regardless of life zone (60–130% of the mature forests). Conversion of forests to pasture resulted in less soil C and N loss than conversion to crops. The time for recovery of soil C and N during succession was approximately the same in all three life zones, about 40–50 yr for C about 15–20 yr for N. However, the rate of recovery of soil C was faster in the wet and moist life zone, whereas N appeared to recover faster in the dry life zone. Evidence for loss of soil C during cultivation and gain during succession to soil depths of 50–100 cm is presented.