青藏高原沼泽湿地植被NDVI时空变化及其对气候变化的响应

基于2000—2017年逐旬MODIS NDVI数据和逐月气温、降水数据,分析了青藏高原不同类型沼泽湿地植被生长季NDVI时空变化特征及其对气候变化的响应。研究结果表明：青藏高原沼泽植被生长季多年平均NDVI自西北向东南逐渐增加;沼泽植被生长季平均NDVI在2000—2017年总体呈现显著上升趋势 (0.010/10a) ,生长季NDVI呈上升趋势的面积占整个研究区面积的78.25%。青藏高原沼泽植被生长季NDVI与降水量总体上呈现弱的相关性,表明降水并不是影响该地区沼泽植被生长的主要因素。青藏高原沼泽植被生长主要受气温影响,气温升高能明显促进沼泽植被的生长。此外,首次发现白天和夜晚温度升高对青藏高原沼泽植被生长具有不对称性影响,其中夜晚增温对沼泽植被生长的促进效果更加显著。在全球白天和夜晚不对称增温的背景下,白天和夜晚温度对青藏高原沼泽植被的不对称影响应当引起重视,尤其是在利用模型模拟未来气候变化对该地区沼泽植被影响时。     

黄土高原草地净初级生产力时空动态及其影响因素

利用光能利用效率模型(Carnegie-Ames-Stanford approach,CASA)模拟2000-2015年黄土高原草地净初级生产力(NPP),分析黄土高原草地NPP的时空动态、NPP变化稳定性和持续性特征,从植被类型、地形因素、气候变化和人类活动4个方面探讨黄土高原草地NPP的影响因素.结果表明:黄土高原草地NPP的平均值为202.93 g C·m^-2·a^-1,其年际变化特征呈现显著增加的趋势,平均年增加速率为2.43 g C·m^-2·a^-1;分布具有明显的空间异质性,大体呈南高北低的状态.黄土高原草地NPP呈增加趋势的区域占总草地面积的91.2%,主要分布在陕西省的大部分地区、甘肃陇东及陇中地区和青海等地.草地NPP变化较为稳定的区域主要集中在鄂尔多斯的南部地区、陕北地区和甘肃等地.大部分地区草地NPP未来的变化趋势与过去一致,且陕西省的大部分地区以及甘肃省的陇中及陇东地区的草地NPP将呈现持续显著增加的趋势.坡面草地的平均NPP值最高,为703.37 g C·m^-2·a^-1;而高山亚高山草地NPP平均值最低,为57.28 g C·m^-2·a^-1.高海拔地区的草地NPP较高,而平原及丘陵地带草地NPP相对较低.研究期间黄土高原降水量的增加对草地NPP的增加具有明显的促进作用;人类活动诸如过度放牧状况的改善以及退耕还草等政策的实施对黄土高原草地NPP的增加也具有重要作用.     

基于 NDVI 的新疆和静县草地植被覆盖动态变化及其与气温降水的关系

以新疆和静县为研究区, 以 2000、2005、2010 和 2015 年 Landsat 影像及 2000～2015 年 MODIS-NDVI 16d 合成产品为主要数据源, 运用 ArcGIS 叠加分析功能, 分级估算 4 个不同时期草地植被覆盖度动态变化特征, 结合气温和降水数据, 利用 NDVI 偏差, 采用趋势线分析方法, 研究区草地植被覆盖变化对温度和降水的响应。研究结果表明:(1)2000—2015 年, 研究区植被覆盖表现为退化, 退化面积为 13763.48 km2, 占研究区面积 49.42%, 较植被覆盖度增加面积多出 12611.65 km2, 是植被覆盖度增加面积的 11.95 倍。(2)2000—2015 年, 研究区植被 NDVI 呈现下降趋势, 年平均气温和 NDVI 的相关系数为–0.32, 呈现负相关, 年平均降水量和 NDVI 的相关系数为 0.76, 呈现正相关。(3)研究区 NDVI 值年内变化呈现单峰型, 夏季 NDVI 值平均每 10a 增长约–3.6%, 秋季 NDVI 值平均每 10a 增长约–1.6%, 春季 NDVI 值平均每 10a 增长约 0.1%;植被 NDVI 值和月平均气温的相关系数为 0.801(n=144); 植被 NDVI 值与月平均降水量相关系数为 0.832(n=144), 均超过 p<0.01 的检验。     

鄱阳湖生态经济区成立前后NDVI时空动态变化及其驱动因素

鄱阳湖生态经济区是中部地区正在加速形成的增长极之一,研究其植被变化特征可以为鄱阳湖生态经济区更合理的调控经济发展与生态保护提供支持。本研究基于2000-2017年MODIS NDVI,采用最小二乘法斜率探讨生态经济区成立前后NDVI时空变化特征,并借助相关性分析定量化研究气候因素和人为因素对NDVI变化的驱动作用。结果表明:生态经济区成立前(2000-2008年)和成立后(2009-2017年),区域植被覆盖整体均呈现增长趋势。生态经济区成立前NDVI变化趋势为0.05210 a^-1(P<0.05),成立后NDVI变化趋势为0.02510 a^-1(P<0.05),成立后NDVI增长出现放缓现象;空间上,成立前植被发生退化的区域主要分布在地级市和省会周围;成立后,省会和中心城市周围植被退化现象进一步加剧,同时湖区周围、区域北部以及南部农耕区植被也出现退化现象;在影响因素方面,在全区域尺度上,气候因素是NDVI变化的主导因素,气温对NDVI影响大于降水;在NDVI显著变化的区域,人类活动则是影响NDVI变化的主要因素;生态经济区成立前,城市化进程的加快是引起区域植被退化的主要人为活动因素,而生态经济区成立后,农耕区和湖区植被退化、非农建设用地占用其他类型土地、农村宅基地占用草地是区域植被退化的重要人为活动因素。     

内蒙古大青山国家级自然保护区植被归一化指数时空变化及其与环境因子的关系

选取2000—2020年MODIS影像的归一化指数(NDVI)数据及同期的气象数据,采用趋势分析、变异系数、相关分析等方法,从海拔、坡度和坡向的角度分析了内蒙古大青山国家级自然保护区生长季NDVI的时空变化特征,并进一步探讨了NDVI时空变化与气候因子的相关性。结果表明：(1)2000—2020年,内蒙古大青山国家级自然保护区植被总体覆盖状况良好且呈增长趋势,增长速率为0.058/10a;(2)保护区NDVI空间分布呈现出西部低、东部高的从西到东逐渐增加的特征。保护区生长季NDVI均值随着海拔的升高而明显增加,随着坡度的增加呈缓慢增加趋势,在不同坡向上,生长季NDVI均值大小依次为阴坡>半阴坡>半阳坡>阳坡;(3)从NDVI变化趋势分析来看,2000—2020年大青山自然保护区植被覆盖改善的面积占总面积的61.75%,其中,显著改善、极显著改善面积分别占总面积的41.13%、20.62%,基本保持不变的面积占总面积的38.17%,退化面积占总面积的0.07%。在空间分布上,NDVI显著、极显著增加的区域主要分布在保护区西部和东部,中部以变化不显著为主。保护区各功能区N...     

近20年来中国植被活动在增强

为阐明近20年来中国植被覆盖变化的整体状况, 利用归一化植被指数(NDVI)作为植被活动的指标, 使用第3代NOAA-AVHRR/NDVI时间序列数据, 研究了1982~1999年间中国地区NDVI的变化. 为消除地表非植被因素的影响, 参考国际惯例, 定义年NDVI≥0.1的地区为有植被覆盖地区(简称植被地区), NDVI < 0.1的地区为植被稀少地区. 结果表明, 18年来, 我国大多数地区的NDVI都呈现不同程度的增加趋势, 表明我国的植被活动在增强. 与80年代初相比, 90年代末植被地区的面积增加3.5%, 植被稀少地区的面积下降了18.1%. 全国平均年NDVI增加了7.4%. 生长季节的延长和生长加速是我国NDVI增加的主要原因, 而温度上升和夏季降水量的增加以及农业活动的加强可能是其主要的驱动因子. 我国NDVI变化趋势显示了较大的空间异质性: 东部沿海地区呈下降趋势或变化不明显; 农业产区和西部地区增加显著. 这种空间异质性是由于城市化过程、农业生产活动、区域气候特征以及植被对气候变化的区域响应等综合因素作用的结果.     

2000-2010年黄河流域植被覆盖的时空变化

黄河流域位于干旱、半干旱和半湿润地区,生态环境脆弱,近年来,在气候变化和人类活动影响下,植被覆盖状况发生了变化。因此需要对黄河流域植被覆盖的变化进行监测,进而掌握流域植被的动态变化特征。在此背景下,利用2000-2010年的250 m分辨率的MOD13Q1数据来研究黄河流域植被覆盖区域的NDVI时空变化特征。采用Theil-Sen Median趋势分析和Mann-Kendall检验来研究NDVI的变化趋势特征,通过对Theil-Sen Median趋势分析和Mann-Kendall检验的结果和Hurst指数的结果的叠加,来研究NDVI的可持续特征。研究表明：1）从空间分布上看,黄河流域NDVI呈现出西部和东南部高,北部低的特征;2）从时间变化特征上看,2000-2010年植被覆盖区域年均NDVI均值在0.3-0.4之间波动,其中2000-2004年NDVI波动较大,但自2005年以来NDVI呈现快速增长的趋势;3）从变化趋势上看,2000-2010年黄河流域植被改善的区域远远大于退化的区域,改善的区域占植被覆盖区域总面积的62.9%,退化的区域占27.7%,9.4%的区域NDVI稳定不变;4）从可持续性来看,86.0%的植被覆盖区域NDVI呈现正向可持续性,即NDVI的可持续性较强;由变化趋势与Hurst指数的耦合信息得出,持续改善的面积占植被覆盖区域总面积的53.7%,持续稳定不变的区域占7.8%,持续退化的区域占24.5%,另外14.0%的区域未来变化趋势无法确定,持续退化和未来变化趋势无法确定区域的植被变化状况需要研究人员继续关注。     

青藏高原植被覆盖时空变化及其对气候因子的响应

研究青藏高原植被覆盖时空分布特征对加深气候变化的认识及生态环境保护具有重要的生态价值和现实意义。利用2000—2016年MODIS NDVI 1km/月分辨率数据以及气象观测数据,采用最大合成法、趋势性分析以及相关分析方法,探讨了不同时间尺度青藏高原地区NDVI的分布特征及其与降水、气温的关系。结果表明:(1)青藏高原东南部植被状况明显好于西北部,植被覆盖的分布格局与区域水热条件的时空分布保持了较好的一致性;近17年来青藏高原植被覆盖改善的地区要比退化的地区面积大,严重退化的区域主要位于青藏高原西南部;青藏高原NDVI值在2000—2016年呈幅度较小的增加趋势。(2)除夏季降水量外,研究时段内其他季节降水量均呈增加趋势;气温均呈增加趋势,尤其以春季增加最为显著,整体上青藏高原气候呈现"暖湿化"趋势。总体上年降水量与年最大合成NDVI呈较好的正相关;年平均气温与年最大合成NDVI在高原东南部呈正相关,西南部呈负相关。降水量和热量条件均是高原植被生长的影响因素,降水与植被覆盖的影响较气温密切。     

1982-2016年东北黑土区植被NDVI动态及其对气候变化的响应

植被是陆地生态系统的重要组成部分,在调节气候、水土保持等方面具有重要作用,因此,监测植被生长变化并探讨其与气候变化之间的关系,在全球变化研究中具有重要意义。基于MODIS NDVI和GIMMS NDVI数据集,并通过一致性检验,在区域和像元两个空间尺度上,利用一元线性回归模型,研究东北黑土区1982-2016年植被生长动态,分析植被生长对气温和降水量的响应程度。结果表明：区域尺度上,1982-2016年东北黑土区植被生长季NDVI变化分为3个阶段（先增加继而减少最后再增加）,区域植被的生长在气温、降水量的共同作用下,呈现出明显季节差异;像元尺度上,1982-2016年东北黑土区NDVI总体趋势为改善状态,主要改善植被类型为草原、森林和农业植被,鹤岗市、绥化市和长春市改善面积较大;多年平均NDVI值与同期气温和降水量具有一定的相关关系,平原地区植被NDVI与气温主要呈显著正相关关系,植被类型主要为耕地;平原地区边缘和山地地区的植被NDVI与降水量以显著正相关关系为主,主要植被类型为森林和草地。     

人类活动对山西省不同地表覆盖类型NDVI时空变化的影响

植被是影响生态环境质量的重要因子，阐明不同地表覆盖类型植被特征对人类活动的响应对制定有针对性的植被管理和恢复措施具有重要指导意义。本研究基于MOD13Q1数据，采用残差分析方法，分析了2000—2020年山西省不同地表覆盖类型人类活动对NDVI的影响。结果表明：山西省生长季NDVI最大值时空分布模式差异明显，呈现出由西北向东南逐渐增加的趋势，2000—2020年平均NDVI年增长率为0.0069;人类活动对山西省NDVI变化影响贡献率的方向和强度均呈现显著的时空差异，2000—2004年为负面影响，而2005年以后则转变为明显正向影响；2000—2020年人类活动对NDVI变化影响贡献率呈显著增加的趋势，年增长率为0.0055;人类活动对NDVI变化影响的趋势及显著程度存在空间差异，并呈现西高东低的趋势，其中产生正、负影响的区域面积分别占93.62%和6.38%;人类活动对农田、森林、草地NDVI的变化以积极影响为主，且影响的程度呈增加趋势，年均增长率分别为0.0065、0.0061和0.0047;人类活动对NDVI正负影响的均值表现为建设用地>农田>草地>森林。     

Galactolipid synthesis in chromoplasts in vitro

Isolated chromoplasts from Narcissus pseudonarcissus flowers contain: a fatty acid synthesizing system; acyl-CoA synthetase (EC 6.2.1.3); glycero-phosphate acyltransferase (EC 2.3.1.15); acylglycero-phosphate acyltransferase; phosphatidate phosphatase (EC 3.1.3.4); diacylglycerol galactosyltransferase (EC 2.4.1.46); and diacylgalactosylglycerol galactosyltransferase, i.e. all enzymatic activities necessary for the synthesis of diacylgalactosylglycerol and diacylgalabiosylglycerol from acetate, HCO _- ³ , sn-glycerol 3-phosphate, and UDP-d-galactose. Diacylgalactosylglycerol and diacylgalabiosylglycerol, however, are synthesized from these precursors to only a very low extent in an in vitro system. This is attributed to a specificity of diacylglycerol galactosyltransferase for highly unsaturated diacylglycerols. Specificities of acyltransferase reactions were also found.     

Peroxisomes in Rice Coleoptiles Grown in Air and in Anoxia

Rice coleoptiles grow under anoxia. When the ultrastructure of anoxic coleoptile cells was examined, it was seen that most organelles maintain their integrity, with the exception of peroxisomes (unspecialized type). The lack of O₂ greatly reduced the number of these organelles and altered the ultrastructure of the remaining ones. To examine the effect of O₂ on peroxisome development in more detail, coleoptiles grown in air were transferred to N₂ and anoxic coleoptiles were transferred to oxygen. Marker enzyme activity was measured in entire coleoptiles as well as in the isolated organelles. As expected, anoxia greatly depressed enzyme activity when imposed from the beginning of the germination process, while it had a lesser effect when imposed for only two days on aerobic seedlings. When coleoptiles were grown constantly under N₂, the density of the organelles was 1.216 g/cm³, while the corresponding aerobic organelles showed a buoyant density of 1.241 g/cm³. When transferred to air the anoxic peroxisomes reached the intermediate density of 1.227 g/cm³. The results confirm the particular sensitivity of rice peroxisomes to O₂ availability.     

A comparison of in vitro with in vivo flowering in Gentian

Young nodal explants of Gentiana triflora Pall. var. axillariflora were cultured in a woody plant medium (WPM) supplemented with B5 vitamins, sucrose (3%) and kinetin (2.0 μM). A novel observation was made in that in vitro flowering occurred following development of the axillary bud of the cultures. A comparison was made between in vitro and in vivo flowers. Although smaller in size, the in vitro flowers were morphologically comparable to the in vivo ones. Flowers from both sources were semi-opened or not opened. The colour of the in vitro flowers was paler than those in vivo. Stigma development was generally poor in both in vitro and in vivo flowers. Pollen viability was over 90% in both types of flowers. About 11% and 34% of pollen from in vitro and in vivo flowers, respectively, germinated on WPM containing 100 g l⁻¹ sucrose solidified with 10 g l⁻¹ agar. Hand pollination of stigma could raise viable seed production in in vivo-flowering plants from 0.3 o/o (i.e. without aided pollination) to 3% but none in in vitro-flowering plants where only seed-like structures, probably unfertilised ovules, were found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fumonisins in Maize in Relation to Climate,Planting Time and Hybrids in Two Agroecological Zones in Zambia

Field experiments in the high rainfall zone (HRZ) and the medium rainfall zone (MRZ) in Zambia were designed to determine the natural occurrence of fumonisins (FB_1–2) in Zambian maize hybrids, accumulation of FB_1–2 resulting from artificial inoculation with Fusarium verticillioides and effects of climate and planting time on FB_1–2 in maize. Combined FB_1–2 concentrations varied from 0 to 13,050 ng/g, with an overall mean of 666 ng/g. Maize from the HRZ had low incidences of FB_1–2-positive samples (mean 41%) which contained FB_1–2 below 500 ng/g. In the MRZ, higher incidences (mean 97%) and concentrations (40% of samples >1,000 ng/g) were recorded in two out of three years. There was no correlation between mean location FB_1–2 concentrations in individual years and precipitation, number of rain days or monthly precipitation. Postponing the planting time with 10 or 20 days did not significantly affect FB_1–2 concentration, but it reduced the yields in some years.     

Climate-driven changes in biomass allocation in pines

Future increases in air temperature resulting from human activities may increase the water vapour pressure deficit (VPD) of the atmosphere. Understanding the responses of trees to spatial variation in VPD can strengthen our ability to predict how trees will respond to temporal changes in this important variable. Using published values, we tested the theoretical prediction that conifers decrease their investment in photosynthetic tissue (leaves) relative to water‐conducting tissue in the stem (sapwood) as VPD increases. The ratio of leaf/sapwood area (A_L/A_S) decreased significantly with increasing VPD in Pinus species but not in Abies, Pseudotsuga, Tsuga and Picea, and the average A_L/A_S was significantly lower for pines than other conifers (pines: 0.17 m² cm^?2; nonpines: 0.44 m² cm^?2). Thus, pines adjusted to increasing aridity by altering above‐ground morphology while nonpine conifers did not. The average water potential causing a 50% loss of hydraulic conductivity was ?3.28 MPa for pines and ?4.52 MPa for nonpine conifers, suggesting that pines are more vulnerable to xylem embolism than other conifers. For Pinus ponderosa the decrease in A_L/A_S with high VPD increases the capacity to provide water to foliage without escalating the risk of xylem embolism. Low A_L/A_S and plasticity in this variable may enhance drought tolerance in pines. However, lower A_L/A_S with increasing VPD and an associated shift in biomass allocation from foliage to stems suggests that pines may expend more photosynthate constructing and supporting structural mass and carry less leaf area as the climate warms.     

Seasonal variation in photosynthesis in six woody species with different leaf phenology in a valley savanna in southwestern China

During 2003–2005, we examined the effect of seasonal drought on water status, gas exchange, δ¹³C, chlorophyll fluorescence and spectral reflectance in six woody species in a valley savanna near the Yuanjiang River (the upper Red River) in southwestern China. Three different phenological types of these woody species were compared, i.e., an evergreen species, Cyclobalanopsis helferiana, two winter-deciduous (WD) species, Buchanania latifolia and Symplocos racemosa, and three drought-deciduous (DD) species, Terminthia paniculata, Wendlandia tinctoria and Woodfordia fruticosa. We aimed to test the following three hypotheses: (1) the evergreen and WD species employ a drought avoidance strategy, whereas DD species employ a drought tolerance strategy; (2) the evergreen and WD species have a more economical water use strategy than the DD species and (3) the evergreen and WD species have a stronger photoprotection capacity through thermal dissipation than the DD species. At the end of a prolonged drought, the predawn leaf water potential (Ψ_pd) in C. helferiana and S. racemosa dropped to ca. −0.8 MPa, whereas the Ψ_pd in B. latifolia remained close to zero and DD species were leafless. In the rainy seasons, maximal photosynthetic rates of the evergreen (18.4 μmol m⁻² s⁻¹) and W. fruticosa (18.0 μmol m⁻² s⁻¹) were higher than those of the other four species (12.2−13.8 μmol m⁻² s⁻¹). The evergreen and WD species responded to drought by closing stomata and thus maintained a constant relative water content (RWC), which is a typical drought avoidance strategy; however, it is at the expense of carbon gain. DD species maintained a high photosynthetic capacity with a decrease in both stomatal conductance and RWC until the driest period, and then shifted from the drought tolerance strategy to the avoidance mechanism by shoot dieback. There was no significant difference in the means of δ¹³C across the phenological groups. The evergreen and WD species had stronger heat dissipation than the DD species in dry seasons. All species increased leaf spectral reflectance, probably because of degradation of chlorophyll as indicated by the leaf reflectance index, which should reduce light harvesting. All species showed a strong increase in the ratio of red to green spectral reflectance of leaves during dry seasons, indicating the accumulation of anthocyanin, which may contribute to screening sunlight and scavenging reactive oxygen species. Different responses to drought of savanna woody species with different leaf phenologies may facilitate the partitioning of resource use and hence their co-existence.     

Variation in Aggressiveness Components in the Hemileia vastatrix Population in Brazil

The Pucciniomycete fungus Hemileia vastatrix causes leaf rust on coffee trees. The pathogen is responsible for considerable yield losses in susceptible coffee cultivars if appropriate management strategies are not implemented. Rapid spread and epidemics of rust fungi are usually associated with the emergence of new races of the pathogen that overcome resistance or with the emergence of more aggressive populations of the pathogen. In Brazil, coffee production is dominated by susceptible cultivars of Coffea arabica and Coffea canephora. We assessed aggressiveness in 46 populations of H. vastatrix from Minas Gerais and Espírito Santo, two of the most important coffee‐producing states in Brazil. We observed a significant difference in the incubation period between the populations from Minas Gerais and Espírito Santo when 183 single‐pustule isolates were inoculated onto Catuaí Vermelho IAC 44, a susceptible C. arabica cultivar. Variation in aggressiveness components was observed between and within localities. Isolates with longer incubation periods also tended to have longer latent periods, although there was only a low correlation between these two aggressiveness components (r² = 0.34, P = 2.2 × 10^?16). Low‐sporulating isolates also had significantly longer incubation and latent periods. The H. vastatrix population from Minas Gerais and Espírito Santo is structured by the formation of groups of individuals with differential level of aggressiveness. Our results indicate that the variation in aggressiveness of the Brazilian H. vastatrix population may be associated with the geographic coffee‐producing areas.