近20年来西南地区植被净初级生产力时空变化与影响因素及其对生态工程响应

植被净初级生产力（NPP）是研究陆地生态系统中物质和能量转换的重要指标，NPP的空间分布与区域气候、植被生长以及人类活动等因素息息相关，其变化能反映植被群落的生产能力，是生态系统功能和结构变化的重要表征。近20年来，中国西南地区植被NPP呈现增长趋势。然而，目前对NPP时空变化格局及潜在原因尚不清楚。因此，利用2001-2018年间MODIS-NPP、岩性、气候、土地利用、造林面积和石漠化治理情况等数据，对西南地区植被NPP的时空变化趋势及其成因进行了分析。结果发现：（1）2001-2018年间，中国西南地区植被NPP总体呈增长趋势，突变分析结果显示，2012-2018年间NPP的增长速度（5.13 gC m^-2a^-1）比2001-2011年更快（1.78 gC m^-2a^-1），在两个时段，岩溶区NPP增长速度都高于非岩溶区；（2）对西南地区植被NPP变化与气候因子的相关分析结果显示，2001-2011年与2012-2018年两个时间段内NPP与温度的平均相关性（R=0.19，0.26）要高于NPP与降水的平均相关性（R=0.07，0.05），表明西南地区植被NPP更容易受到温度的影响；（3）对两个时期土地利用变化下NPP总量的变化情况的研究结果显示，2001-2011年期间城市用地面积增加使得NPP总量下降，而2012-2018年未利用地面积增长造成了NPP总量下降；（4）2001-2018年西南地区累计造林面积与NPP存在显著正相关性（R=0.7，P<0.05），说明"退耕还林"工程实施促进了西南地区NPP增长。对石漠化面积统计结果表明，2011年后石漠化面积显著减少，这与NPP的突变点一致，表明石漠化治理对西南地区NPP增长有重要促进作用。     

基于全球净初级生产力的能源足迹计算方法

净初级生产力是当前生态足迹改进研究的重要突破口。针对传统能源足迹存在着忽略多数土地的碳吸收贡献、碳吸收能力界定不清等不足,提出了基于全球平均净初级生产力的能源足迹计算方法。结果表明:单位质量能源的生态足迹空间构成中,前3位依次为海洋、林地和草地,分别占28.32%、27.25%、21.77%。单位空间占用面积的能源热值由高至低依次为电力、气态、液态和固态能源,分别达2.11×106—9.76×107、108—116、88—99、68—72 GJ/hm2。对各类能源生态影响的判断均较传统方法乐观,这是综合考虑全球各类土地和水体碳吸收贡献的结果。基于全球净初级生产力的能源足迹反映了能源消费的空间占用平均水平,有助于提高评价结果的真实性与准确性。     

汉江流域植被净初级生产力时空格局及成因

运用MOD17A3-NPP等数据,分析汉江流域植被NPP的时空格局及其形成演变机理,为区域生态环境管治提供科学理论依据。运用GIS空间分析法、线性拟合法研究流域NPP的时空格局,结合相关系数法、土地利用程度指数等方法探析成因。结果显示:(1)汉江流域植被NPP多年平均值为439 g C m~(-2)a~(-1),整体呈微小的波动上升趋势,年增长幅度为3.11 g C m~(-2)a~(-1)。植被NPP集中分布在300—600 g C m~(-2)a~(-1),占全域面积的83.65%。(2)从流域空间上看,多年平均NPP呈上游中游下游,各子流域内部差异呈上游中游下游。高值区集中分布在汉中,十堰、襄樊和荆门平均NPP呈下降趋势的所占面积最大。(3)垂直景观上植被NPP的空间分布往往受水热综合作用的影响,汉江流域降水是植被NPP累积的主要制约因素。(4)垂直方向上NPP呈规律性变化:高程上表现为"陡升-下降-缓升-陡降,坡向上为阳坡半阳坡半阴坡阴坡。(5)浅山丘陵区NPP变化主要受土地利用方式的影响,高山区NPP变化受气候变化的影响。汉江流域植被NPP稳定,中下游平原区植被NPP略有下降;气候和地形特征决定了植被NPP的空间分布特征,气候变化和人类活动对植被NPP的变化有重要影响。     

Carbon dynamics,net primary productivity and human‐appropriated net primary productivity across a forest–cocoa farm landscape in West Africa

Terrestrial net primary productivity (NPP) is an important metric of ecosystem functioning; however, there are little empirical data on the NPP of human‐modified ecosystems, particularly smallholder, perennial crops like cocoa (Theobroma cacao), which are extensive across the tropics. Human‐appropriated NPP (HANPP) is a measure of the proportion of a natural system's NPP that has either been reduced through land‐use change or harvested directly and, previously, has been calculated to estimate the scale of the human impact on the biosphere. Additionally, human modification can create shifts in NPP allocation and decomposition, with concomitant impacts on the carbon cycle. This study presents the results of 3 years of intensive monitoring of forest and smallholder cocoa farms across disturbance, management intensity, distance from forest and farm age gradients. We measured among the highest reported NPP values in tropical forest, 17.57 ± 2.1 and 17.7 ± 1.6 Mg C ha^?1 year^?1 for intact and logged forest, respectively; however, the average NPP of cocoa farms was still higher, 18.8 ± 2.5 Mg C ha^?1 year^?1, which we found was driven by cocoa pod production. We found a dramatic shift in litterfall residence times, where cocoa leaves decomposed more slowly than forest leaves and shade tree litterfall decomposed considerably faster, indicating significant changes in rates of nutrient cycling. The average HANPP value for all cocoa farms was 2.1 ± 1.1 Mg C ha^?1 year^?1; however, depending on the density of shade trees, it ranged from ?4.6 to 5.2 Mg C ha^?1 year^?1. Therefore, rather than being related to cocoa yield, HANPP was reduced by maintaining higher shade levels. Across our monitored farms, 18.9% of farm NPP was harvested (i.e., whole cocoa pods) and only 1.1% (i.e., cocoa beans) was removed from the system, suggesting that the scale of HANPP in smallholder cocoa agroforestry systems is relatively small.     

The relationships between net primary productivity, human population density and species conservation

Aim In this study, I determine the relationships between net primary productivity (NPP), human population density, species richness and land use. I also examine the implications of human settlement patterns for species conservation. Location Australia. Methods I document the associations between NPP, human population density and the species richness of birds, butterflies and mammals using correlations and spatial regressions. I also assess changes in land‐use with NPP and population density, focussing particularly on protected areas. An initial exploration into the implications of the NPP‐population density relationship for regional conservation strategies is provided. Results Human population density increases with NPP suggesting that available energy may be a key driving force of human settlement patterns. The species richness of each taxonomic group and geographically restricted species also increases with NPP leading to substantial overlap between species diversity and populated regions. The percentage of land designated as minimal use decreases considerably with increasing human population density and NPP, while intensive agriculture is confined entirely to areas of high NPP. There are strong negative relationships between the size of Australia's National Parks and human population density and NPP. Small parks are often surrounded by relatively dense settlements, but have high average NPP, while large parks are mostly isolated and characterized by low productivity. There are no areas in the highest quartile of NPP that also occur in the most sparsely populated regions, presenting challenges for conservation strategies wanting to protect productive areas under the least threat of human development. Main conclusions Human population density and species richness respond similarly to variation in NPP, leading to spatial congruence between human settlements and productive, species rich regions. Planning strategies are required that minimize the potential threat posed by human development to diverse ecosystems and maximize the underlying productivity of protected areas. Reducing the level of threat may require stabilizing the size of the human population, while capturing larger areas of relatively high productivity in the conservation reserve system would lead to greater protection of local diversity.     

盘锦湿地净初级生产力时空分布特征

主要采用中巴地球资源卫星(CBERS)、合成孔径雷达(SAR)和数字高程模型(DEM)数据,通过主成分变换融合算法、分类回归树CART算法和混合像元分解模型结合神经网络算法,进行了盘锦湿地土地覆盖类型分类。充分考虑湿地生态系统的典型特征,将盐分胁迫因子作为估算湿地耐盐植被净初级生产力(NPP)的环境影响因子之一,构建了基于光能利用率和遥感数据的湿地植被净初级生产力模型。分析了盘锦湿地植被NPP的时空分布特征,并研究了盘锦湿地植被NPP对气温和降水的响应特征。结果表明:2009年盘锦市植被净初级生产力介于0—1175 gC·m-·2a-1之间,平均值为553 gC·m-·2a-1。盘锦市植被NPP空间分布规律呈东北向西南逐渐递增的趋势。在湿地植被分类类型中,芦苇的单位面积平均NPP最高,达到1016 gC·m-·2a-1。2004—2009年盘锦植被单位面积平均NPP值在缓慢上升,湿地已呈现缓慢恢复的趋势。总体上气温对盘锦湿地主要植被类型芦苇月平均NPP的影响要强于降水。2004—2009年降水对盘锦地区植被年平均NPP的影响强于气温。     

The Energetic Metabolism of the European Union and the United States: Decadal Energy Input Time-Series with an Emphasis on Biomass

This article presents an assessment of energy inputs of the European Union (the 15 countries before the 2004 enlargement, abbreviated EU‐15) for the period 1970–2001 and the United States for 1980–2000. The data are based on an energy flow analysis (EFA) that evaluates socioeconomic energy flows in a way that is conceptually consistent with current materials flow analysis (MFA) methods. EFA allows assessment of the total amount of energy required by a national economy; it yields measures of the size of economic systems in biophysical units. In contrast to conventional energy balances, which only include technically used energy, EFA also accounts for socioeconomic inputs of biomass; that is, it also considers food, feed, wood and other materials of biological origin. The energy flow accounts presented in this article do not include embodied energy. Energy flow analyses are relevant for comparisons across modes of subsistence (e.g., agrarian and industrial society) and also to detect interrelations between energy utilization and land use. In the EU‐15, domestic energy consumption (DEC = apparent consumption = domestic extraction plus import minus export) grew from 60 exajoules per year (1 EJ = 10¹⁸ J) in 1970 to 79 EJ/yr in 2001, thus exceeding its territory's net primary production (NPP, a measure of the energy throughput of ecosystems). In the United States, DEC increased from 102 EJ/yr in 1980 to 125 EJ/yr in 2000 and was thus slightly smaller than its NPP. Taken together, the EU‐15 and the United States accounted for about 38% of global technical energy use, 31% of humanity's energetic metabolism, but only 10% of global terrestrial NPP and 11% of world population in the early 1990s. Per capita DEC of the United States is more than twice that of the EU‐15. Calculated according to EFA methods, energy input in the EU and the United States was between one‐fifth and one‐third above the corresponding value reported in conventional energy balances. The article discusses implications of these results for sustainability, as well as future research needs.     

水热波动和土地覆盖变化对东北地区植被NPP的相对影响

研究水热波动和土地覆盖变化对植被净初级生产力（Net Primary Productivity,NPP）的影响对于估算陆地碳循环及其驱动机制具有重要意义。利用MODIS遥感影像获得的时间序列NPP和土地覆盖产品,结合气象观测数据（气温和降水）,采用相关分析、回归分析和空间分析相结合的方法,研究2000-2015年东北地区植被NPP的时空变化特征,并定量评估水热波动和土地覆盖变化对该地区植被NPP的相对影响。研究结果表明,2000-2015年东北地区植被NPP呈波动上升趋势,从2000年的369.24 g C m^-2 a^-1增加到2015年的453.84 g C m^-2 a^-1,平均值是412.10 g C m^-2 a^-1,年际增加速率为4.54 g C m^-2 a^-1。近16年来东北地区年均植被NPP空间上呈现南高北低、东高西低的分布格局,整体变化趋势以增加为主,其中轻微增加面积占该地区总面积的45.9%。不同土地覆盖类型的年均NPP差异明显,其中灌木最高为400.34 g C m^-2 a^-1,草地最低为300.49 g C m^-2 a^-1。东北地区植被NPP与气温的相关性不明显,而与降水量主要表现为正效应。水热波动对该地区不同土地覆盖类型NPP总量变化的贡献大于土地覆盖变化的贡献,其中对森林和农田的贡献最大,均达到70%以上。     

基于变异系数的植被NPP人为影响定量研究——以石羊河流域为例

人类活动是NPP变化的重要影响因子,定量计算NPP人为影响值具有较重要的意义。提出基于变异系数法的NPP人为影响模型,对其基本概念、理论基础、计算流程等进行了阐述,并以石羊河流域为研究区,分析该流域NPP人为影响分布规律。研究结果表明:(1)该模型基于一种间接计算的思想回避了人为作用的复杂过程,模型理论科学,以变异系数为参数,所需参数少,技术可行,计算结果为NPP值,易于定量评价。(2)2000—2010年期间,石羊河流域人类活动对植被NPP的影响广泛而严重,年均影响值大于40g C m~(-2)a~(-1)的面积占96.21%,影响程度严重以上占26.94%。NPP人为正负影响均较大,正影响年均为1.63×106g C m~(-2)a~(-1),负影响年均为1.21×106g C m~(-2)a~(-1),年均净增加4.20×105g C m~(-2)a~(-1);正向平均影响强度为136.84 g C m~(-2)a~(-1),负向平均影响强度为100.32 g C m~(-2)a~(-1),全流域表现为正影响。(3)凉州区是人为影响最为剧烈的地区,表现为强烈正影响;其次是天祝县,为强烈负影响;接下来是民勤县,表现为正影响;其它县区依次是永昌、古浪、肃南和金昌。(4)2000—2010期间,NPP人为影响值变化较大,人为活动减弱面积占53.90%,增加占46.10%;影响值正向减弱8.12×105g C m~(-2)a~(-1),负向减弱8.07×105g C m~(-2)a~(-1),正向增强8.02×105g C m~(-2)a~(-1),负向增强3.94×105g C m~(-2)a~(-1),人为活动影响净减少4.25×105g C m~(-2)a~(-1),人为作用总体呈减弱趋势。     

土地利用转变与海拔高度协同作用黄土高原植被固碳变化特征

全球固碳释碳问题一直是近年来关乎民生的热点话题,区域碳源/碳汇对生态环境的重要性不言而喻。基于CASA模型估算黄土高原1990—2015年植被净初级生产力的年际变化,并分析土地利用变化、海拔高度及两者协同作用对其综合影响,结果表明：(1)黄土高原1990—2015年植被NPP与植被固碳总体呈增加趋势,年均NPP增速2.74 gC m^-2 a^-1,年均固碳增速1.13 TgC/a,研究区林地年均NPP(619.5 gC m^-2 a^-1)远超其他用地类型,固碳效果理想;(2)黄土高原年均NPP随高程的增加先降低后升高,年总NPP和固碳量随高程增加变化趋势相反;(3)研究区土地利用转变类型中退耕还林的植被固碳效果最好;而林地变为耕地或草地均不能达到固碳目的,此外,更推荐在研究区海拔低于1500 m变草为耕,海拔高于1500 m退耕还草,海拔高于3000 m变耕、草为林。以期为区域尺度的生态环境建设提供一定的参考和科学依据。     

Land use intensification increasingly drives the spatiotemporal patterns of the global human appropriation of net primary production in the last century

Land use has greatly transformed Earth's surface. While spatial reconstructions of how the extent of land cover and land-use types have changed during the last century are available, much less information exists about changes in land-use intensity. In particular, global reconstructions that consistently cover land-use intensity across land-use types and ecosystems are missing. We, therefore, lack understanding of how changes in land-use intensity interfere with the natural processes in land systems. To address this research gap, we map land-cover and land-use intensity changes between 1910 and 2010 for 9 points in time. We rely on the indicator framework of human appropriation of net primary production (HANPP) to quantify and map land-use-induced alterations of the carbon flows in ecosystems. We find that, while at the global aggregate level HANPP growth slowed down during the century, the spatial dynamics of changes in HANPP were increasing, with the highest change rates observed in the most recent past. Across all biomes, the importance of changes in land-use areas has declined, with the exception of the tropical biomes. In contrast, increases in land-use intensity became the most important driver of HANPP across all biomes and settings. We conducted uncertainty analyses by modulating input data and assumptions, which indicate that the spatial patterns of land use and potential net primary production are the most critical factors, while spatial allocation rules and uncertainties in overall harvest values play a smaller role. Highlighting the increasing role of land-use intensity compared to changes in the areal extent of land uses, our study supports calls for better integration of the intensity dimension into global analyses and models. On top of that, we provide important empirical input for further analyses of the sustainability of the global land system.     

近30年来黄河三角洲植被净初级生产力时空特征及主要影响因素

我国拥有丰富的海岸带蓝色碳汇,准确把握海岸带蓝碳生态系统净初级生产力(NPP)状况,辨识不同人为干扰下蓝碳生态系统NPP的时空分布特征具有重要意义。以黄河三角洲为研究区,以近30a(1987年、1995年、2005年、2016—2017年)为时间尺度,通过遥感手段和现场调查,对黄河三角洲NPP时空变化特征及其主要影响因素进行研究。结果显示:(1)近30年来研究区NPP均值和总量呈现先下降又略微增长的特征,2016—2017年度NPP平均值为294.38g C m~(-2)a~(-1),总量为710.05Gg C/a,表现出显著的季节差异。(2)研究区NPP在各行政区、保护区和地表覆盖类型中均表现出了明显的空间分异性;2016—2017年度NPP分区结果显示,不同分区面积由大到小依次为中生产力区(49.5%)、低生产力区(38.3%)和高生产力区(12.1%)。(3)研究区NPP的时空分异性是地表覆盖类型和植被生长状况共同影响的结果,海陆交互作用、开发利用活动和近年来的生态建设是NPP时空变化的主要影响因素。(4)湿地植被和农田是研究区碳汇的主要贡献者,20世纪90年代以来二者NPP均值逐渐上升,在2016—2016年度分别达570.28g C m~(-2)a~(-1)和335.92g C m~(-2)a~(-1);近30年来,湿地植被NPP总量逐渐减少,农田NPP总量则逐渐增加。湿地植被是海岸带蓝碳的典型载体,农田作为位于滨海地区、由湿地植被转化而来、本身具有较高固碳能力和潜力的碳汇类型,可作为海岸带蓝碳的重要补充。     

定量评价人类活动对净初级生产力的影响

以人类活动为主导的城市扩张和土地覆被变化对城市生态环境产生了重要影响,并与气候变化共同影响植被净初级生产力(NPP),但目前从时空尺度上脱离气候干扰仅以人类活动为主导因素来定量分析其对植被NPP影响的研究尚不充分.本研究以广州市为研究区,利用CASA模型估算2001—2013年实际净初级生产力(NPP_act),结合CHIKUGO模型估算得到的潜在净初级生产力(NPP_p)计算因土地覆被变化导致的NPP损失(NPP_lulc),并建立相对贡献指数(RCI)定量分析和评价在城市扩张过程中人类活动对NPP的影响.结果表明:2001—2013年间,广州总体及其5片区NPP_act和NPP_lulc分别呈减少和增加趋势,并存在明显的空间差异性;RCI呈明显增加趋势,东北片区RCI值最低,为0.31,表明气候变化是其NPP变化的主要原因,其他4个片区的RCI值均高于0.5,说明4个片区人为干扰严重,人类活动是其NPP减少的主导因素;广州市及其5片区的RCI变化斜率均大于0,人类活动对植被的干扰逐年增强,北部片区RCI变化斜率值最大(0.693),人为干扰增加趋势最明显.     

2008—2018年伊犁河流域植被净初级生产力时空分异特征

基于MODIS数据和改进的光能利用率模型(CASA模型)对2008—2018年伊犁河流域植被净初级生产力(NPP)进行估算,通过一元线性回归趋势分析、变异系数、Hurst指数等方法对其时空分异特征进行分析。结论如下：(1)时间特征上,伊犁河流域植被NPP呈现波动上升趋势,年内植被NPP呈现出“单峰型”特点,该流域四季植被NPP大小关系为：夏季>春季>秋季>冬季;(2)空间特征上,伊犁河流域植被NPP呈现东北低西南高,沿天山山脉呈环状分布,各植被类型NPP的大小为：林地(624.13 g C m^-2 a^-1)>耕地(575.04 g C m^-2 a^-1)>草地(270.57 g C m^-2 a^-1)>裸地(114.26 g C m^-2 a^-1)。该流域植被NPP在海拔、经纬度方面均呈现不同的变化特征。(3)空间稳定性上,伊犁河流域植被NPP存在明显的空间差异性,各变异程度...     

基于MODIS序列的北京市土地利用变化对净初级生产力的影响

了解土地利用变化对区域净初级生产力(NPP)的影响,对于综合理解区域植被的固碳能力及其与土地利用变化的关系,以及维持区域生态安全均具有重要意义。以北京市为例,基于2000—2012年MODIS NPP遥感影像和土地利用类型数据,利用同期Landsat TM影像(分辨率30 m)对MODIS NPP数据进行降尺度计算的基础上,分析北京市区域NPP的时空分布特征,探讨土地利用变化对植被固碳能力的影响。结果表明:研究期内Landsat NDVI与NPP数据的线性关系显著(R~2为0.22—0.68,P0.01),基于该线性关系可实现对MODIS NPP的降尺度重计算。土地利用面积分配和景观格局的变化均显著影响NPP。13年间,北京市林地和草地面积增加而耕地面积迅速减少,NPP总量由123万t C增长至190万t C,其中66%的NPP由林地贡献,其次为耕地(26%),草地最低(8%)。2000—2006年,面积变化促进了NPP的增加,贡献率为34%;而2006—2012年,面积变化则抑制区域NPP的增加,贡献率降低至27%。同时,研究区域内斑块聚集度的降低,斑块密度及丰富度的增加均有利于其NPP的增加。提高研究区植被固碳能力,需要在维持区域当前植被数量和质量的基础上,增加区域景观的异质性和多样性。     

我国西南喀斯特地区2001—2018年植被净初级生产力时空演变

植被净初级生产力（Net primary productivity,NPP）是陆地生态系统碳循环的重要指标,定量评价NPP的变化规律是碳循环机理的主要研究内容之一。以我国西南地区为研究区域,基于土地覆盖和NPP产品分析了2001-2018年西南地区NPP的时空变化特征,利用土地转移矩阵和统计分析方法,定量描述了土地覆盖类型变化导致的NPP变化量,对NPP变化的主要原因进行分析。结果表明：（1）2001-2018年,西南地区NPP均值呈波动上升趋势。（2） NPP变化趋势在空间分布上呈南高北低,NPP呈增长趋势主要集中在四川的中东部、重庆、贵州西部和云南东部;NPP呈减少趋势出现在云南、四川中西部和贵州东部。（3）森林、草地和耕地转灌丛以及灌丛转森林是对NPP变化量影响较大的土地覆盖类型转变,土地类型转变导致的NPP净增量为20.643 TgC。（4）降水与NPP相关性低,气温与NPP有一定相关性,植被叶面积指数与NPP有显著相关关系,表明气候因子对NPP的影响较小,植被生长密度对NPP有显著影响。退耕还林还草等生态工程实施,导致耕地面积减少和森林面积大量增加,是西南地区NPP上升的主导因素,因此生态工程的实施是西南地区NPP增加的重要影响因素。研究可为生态工程实施背景下NPP的变化机理研究提供参考。     

南方丘陵山地带植被净第一性生产力时空动态特征

基于MODIS数据并结合气象资料和植被参数,利用修正过最大光能利用率的CASA(Carnegie-Ames-Stanford Approach)模型,对国家生态安全屏障区的"两屏三带"之一南方丘陵山地带2000—2010年的植被净第一性生产力(NPP)进行模拟,并对其时空分布格局进行了分析。研究结果表明:(1)研究区2000—2010年期间年NPP的变化范围为406.0—485.6 g C m-2a-1,年平均NPP为445.7 g C m-2a-1,高于全国平均水平;NPP年际上升趋势不显著(P=0.39),平均增加值为2.28 g C m-2a-1;(2)NPP空间分布特征与植被类型具有较好的一致性,单位面积NPP以混交林覆盖区最高(501.0 g C m-2a-1),草地覆盖区NPP最低(390.7 g C m-2a-1);(3)植被NPP的时空变化与气温、降雨和太阳辐射等自然因素的变化有直接关系,而社会、经济、政策等人为因素通过改变土地利用方式来间接影响。     

东亚地区夏季干旱、强台风事件与松树枯萎病的关系

松树枯萎病的发生和流行给东亚的日本、中国和韩国带来了不小的损失,引起许多国家的重视. 本文应用实地观测和气象数据分析等方法,研究了东亚地区松树枯萎病的发生和流行特点,以及与灾害气象事件之间的关系.结果表明: 在日本、中国和韩国,持续的夏季干旱少雨和强台风等极端气象事件能够诱发松树枯萎.在极端干热的环境中,松树常出现能量代谢失调, 以至于受胁迫的松树整株枯萎;而在低温多雨的年份,松树枯萎少,甚至没有发生枯死现象.在松材线虫及其媒介昆虫侵染之前,松树的活力业已下降.松树枯萎病似乎应该局限在台风频发和持续干热的地区.在自然环境优越、少有台风和干热事件出现且没有不当扩大松树栽培范围的地区,松树枯萎病大面积发生的可能性不大.     

广西植被净初级生产力(NPP)时空演变及主要影响因素分析

利用2001-2010年EOS/MODIS17A3卫星遥感资料,对广西植被净初级生产力(NPP)时空特征及其影响因素进行分析.结果表明：(1)NPP 表现出明显的年际变化,2005年植被年均 NPP 最小为625 gC??m-2??a-1,2003年最大,为714 gC??m-2??a-1,十年间广西植被年NPP平均值为662 gC??m-2??a-1;(2)不同植被类型NPP有较大差异,森林、灌木、农作物的NPP 平均值分别为834、614、517 gC??m-2??a-1;(3)十年间广西区年均NPP为显著下降趋势,且年均气温和降水对NPP时间变化作用显著,而日照时数对 NPP 时间变化的作用不显著;(4)广西区NPP空间格局形成主要影响因素为坡度,其次为经度,再次为地貌特征、纬度和降水;(5)非喀斯特区域北热带季雨林、南亚热带季雨林化/季雨化常绿阔叶林年均 NPP 大于喀斯特地区,相反,喀斯特地区中亚热带常绿阔叶林,农作物年均NPP大于非喀斯特地区.整体而言,广西非喀斯特地区植被NPP为683 gC??m-2??a-1,喀斯特地区植被NPP为620 gC??m-2??a-1.     

Asymmetry in above‐ and belowground productivity responses to N addition in a semi‐arid temperate steppe

Nitrogen (N) enrichment often increases aboveground net primary productivity (ANPP) of the ecosystem, but it is unclear if belowground net primary productivity (BNPP) track responses of ANPP. Moreover, the frequency of N inputs may affect primary productivity but is rarely studied. To assess the response patterns of above‐ and belowground productivity to rates of N addition under different addition frequencies, we manipulated the rate (0–50 g N m^?2 year^?1) and frequency (twice vs. monthly additions per year) of NH₄NO₃ inputs for six consecutive years in a temperate grassland in northern China and measured ANPP and BNPP from 2012 to 2014. In the low range of N addition rates, BNPP showed the greatest negative response and ANPP showed the greatest positive responses with increases in N addition (<10 g N m^?2 year^?1). As N addition increased beyond 10 g N m^?2 year^?1, increases in ANPP dampened and decreases in BNPP ceased altogether. The response pattern of net primary productivity (combined above‐ and belowground; NPP) corresponded more closely to ANPP than to BNPP. The N effects on BNPP and BNPP/NPP (f_BNPP) were not dependent on N addition frequency in the range of N additions typically associated with N deposition. BNPP was more sensitive to N addition frequency than ANPP, especially at low rates of N addition. Our findings provide new insights into how plants regulate carbon allocation to different organs with increasing N rates and changing addition frequencies. These root response patterns, if incorporated into Earth system models, may improve the predictive power of C dynamics in dryland ecosystems in the face of global atmospheric N deposition.