Autumn warming reduces the CO2 sink of a black spruce forest in interior Alaska based on a nine‐year eddy covariance measurement

Nine years (2003–2011) of carbon dioxide (CO₂) flux were measured at a black spruce forest in interior Alaska using the eddy covariance method. Seasonal and interannual variations in the gross primary productivity (GPP) and ecosystem respiration (RE) were associated primarily with air temperature: warmer conditions enhanced GPP and RE. Meanwhile, interannual variation in annual CO₂ balance was controlled predominantly by RE, and not GPP. During these 9 years of measurement, the annual CO₂ balance shifted from a CO₂ sink to a CO₂ source, with a 9‐year average near zero. The increase in autumn RE was associated with autumn warming and was mostly attributed to a shift in the annual CO₂ balance. The increase in autumn air temperature (0.22 °C yr^?1) during the 9 years of study was 15 times greater than the long‐term warming trend between 1905 and 2011 (0.015 °C yr^?1) due to decadal climate oscillation. This result indicates that most of the shifts in observed CO₂ fluxes were associated with decadal climate variability. Because the natural climate varies in a cycle of 10–30 years, a long‐term study covering at least one full cycle of decadal climate oscillation is important to quantify the CO₂ balance and its interaction with the climate.     

Growing-season precipitation since 1872 in the coastal area of subtropical southeast China reconstructed from tree rings and its relationship with the East Asian summer monsoon system

Tree rings from temperate zones of the world have provided abundant palaeo- ecological and paleo-hydroclimatic information. However, tree rings from subtropical to tropical regions remain relatively scarce, which greatly limit our fully understanding about the climate change issues. In the present work, tree-ring-width (TRW) measurements of Masson pine from Fujian province, the coastal area of subtropical southeast China were successfully crossdated and a TRW STD chronology was developed from 1854 to 2012. Significantly positive correlation was identified between the tree rings and April–November total precipitation (r = 0.71, p < 0.01). The reconstructed April–November precipitation exhibited two comparatively wet (1876–1886 and 1957–1962) and one comparatively dry (1986–2004) periods. An evident drying trend since 1959 was seen and it was mitigated after 1993. Most of the extreme low-precipitation years in the reconstruction were supported by the historical records. As revealed by the spatial correlation patterns, our precipitation reconstruction was also consistent with other hydroclimatic records along the coastal areas of southeast China, proving its ability to capture the large-scale hydrological signal in southeast China (mainly refers to the south of the middle-lower reaches of Yangtze River). The reconstructed precipitation showed significant correlation with the East Asian summer Monsoon (EASM) index. Moreover, it also indicated simultaneous variation with the monsoon precipitation in North China on a decadal scale, implying that growing season precipitation variations in both regions were influenced by the EASM strength. This work highlights the potential of using tree-ring width to reconstruct precipitation in subtropical southeast China, while the relevant issues about precipitation variation in this region is far from resolved.     

Tree-Ring Based May-July Temperature Reconstruction Since AD 1630 on the Western Loess Plateau,China

Tree-ring samples from Chinese Pine (Pinus tabulaeformis Carr.) collected at Mt. Shimen on the western Loess Plateau, China, were used to reconstruct the mean May–July temperature during AD 1630–2011. The regression model explained 48% of the adjusted variance in the instrumentally observed mean May–July temperature. The reconstruction revealed significant temperature variations at interannual to decadal scales. Cool periods observed in the reconstruction coincided with reduced solar activities. The reconstructed temperature matched well with two other tree-ring based temperature reconstructions conducted on the northern slope of the Qinling Mountains (on the southern margin of the Loess Plateau of China) for both annual and decadal scales. In addition, this study agreed well with several series derived from different proxies. This reconstruction improves upon the sparse network of high-resolution paleoclimatic records for the western Loess Plateau, China.     

Growth/climate response shift in a long subalpine spruce chronology

A new Norway spruce (Picea abies (L.) Karst.) tree-ring width chronology based on living and historic wood spanning the AD 1108–2003 period is developed. This composite record combines 208 high elevation samples from 3 Swiss subalpine valleys, i.e., Lötschental, Goms, and Engadine. To retain potential high- to low-frequency information in this dataset, individual spline detrending and the regional curve standardization are applied. For comparison, 22 high elevation and 6 low-elevation instrumental station records covering the greater Alpine area are used. Previous year August–September precipitation and current year May–July temperatures control spruce ring width back to ～1930. Decreasing (increasing) moving correlations with monthly mean temperatures (precipitation) indicate instable growth/climate response during the 1760–2002 period. Crucial June–August temperatures before ～1900 shift towards May-July temperature plus August precipitation sensitivity after ～1900. Numerous of comparable subalpine spruce chronologies confirm increased late-summer drought stress, coincidently with the recent warming trend. Comparison with regional-, and large-scale millennial-long temperature reconstructions reveal significant similarities prior to ～1900 (1300–1900 mean r=0.51); however, this study does not fully capture the commonly reported 20th century warming (1900–1980 mean r=?0.17). Due to instable growth/climate response of the new spruce chronology, further dendroclimatic reconstruction is not performed.     

Climate signal shift under the influence of prevailing climate warming – Evidence from Quercus liaotungensis on Dongling Mountain,Beijing, China

Increasing climate warming is inducing drought stress and resulting in forest growth decline in many places around the world. The recent climate of northern China has shown trends of both warming and drying. In this study, we obtained tree ring width chronology of Quercus liaotungensis Koidz. from Dongling Mountain, Beijing, China. We divided the temperature series of the study area into cooling (1940–1969) and warming intervals (1970–2016). The climate–tree growth response analysis showed that temperature exerted a limiting impact on the annual radial growth of Q. liaotungensis during the cooling period, whereas the influence of temperature was lower during the warming period. The moving correlation analysis showed that the influence of summer temperature decreased with the warming climate since the 1970s, and that the influence of winter and spring temperatures decreased since the 2000s. The correlation values between the chronology and precipitation decreased during the cooling period, whereas spring and early summer precipitation correlations began to increase in the 1970s and reached significance (p < 0.05) in the 1990s. Our results show that the positive influence of temperature on radial growth of Q. liaotungensis in the study area has weakened, whereas precipitation has become the dominant regulator with climate warming. These findings suggest that forest growth on Dongling Mountain will decline if climate warming continues in the future.     

Interannual variation in methane emissions from tropical wetlands triggered by repeated El Niño Southern Oscillation

Methane (CH₄) emissions from tropical wetlands contribute 60%–80% of global natural wetland CH₄ emissions. Decreased wetland CH₄ emissions can act as a negative feedback mechanism for future climate warming and vice versa. The impact of the El Niño–Southern Oscillation (ENSO) on CH₄ emissions from wetlands remains poorly quantified at both regional and global scales, and El Niño events are expected to become more severe based on climate models’ projections. We use a process‐based model of global wetland CH₄ emissions to investigate the impacts of the ENSO on CH₄ emissions in tropical wetlands for the period from 1950 to 2012. The results show that CH₄ emissions from tropical wetlands respond strongly to repeated ENSO events, with negative anomalies occurring during El Niño periods and with positive anomalies occurring during La Niña periods. An approximately 8‐month time lag was detected between tropical wetland CH₄ emissions and ENSO events, which was caused by the combined time lag effects of ENSO events on precipitation and temperature over tropical wetlands. The ENSO can explain 49% of interannual variations for tropical wetland CH₄ emissions. Furthermore, relative to neutral years, changes in temperature have much stronger effects on tropical wetland CH₄ emissions than the changes in precipitation during ENSO periods. The occurrence of several El Niño events contributed to a lower decadal mean growth rate in atmospheric CH₄ concentrations throughout the 1980s and 1990s and to stable atmospheric CH₄ concentrations from 1999 to 2006, resulting in negative feedback to global warming.     

Increased extreme drought events in south–central China since the last century：Evidence from oxygen isotope signatures preserved in tree ring cellulose

Tree-ring cellulose oxygen isotope ratios (δ¹⁸O) is a well-established proxy for hydroclimatic conditions in monsoon Asia. We reconstructed June–October relative humidity (RH_J–O) variations from 1808 to 2017, based on tree-ring cellulose δ¹⁸O data, which explain 46.2% of the actual RH variance in the Nanyue region, south–central China. Extreme wet events occurred frequently prior to the 1900s, but there have been more extreme dry events since the 1900s, apart from the late 1930s and early 1950s. Periodicity analysis revealed that the reconstructed RH_J–O records show obvious 15–30 years cycles from the 1830–1970s. The multi-decadal signals may reflect the effect of the Pacific Decadal Oscillation (PDO) on hydroclimate. In the positive PDO phase, there is drying in south–central China, which is related to a weaker East Asian summer monsoon (EASM) via the Pacific–Japan teleconnection. The decadal signal has weakened since the 1970s. In addition, the reconstructed RH_J–O record shows strong interannual variations, which may be related to the Central Pacific El Niño–Southern Oscillation (CP ENSO). During extreme CP El Niño events, there is a weaker EASM due to the Pacific–Japan teleconnection, and the study site experienced drought. Our reconstructed moisture record is characterized by a decreasing influence from the PDO and increasing influence from the CP ENSO in recent decades. Moreover, the frequency of CP ENSO events is projected to increase under anthropogenic warming. Consequently, more extreme droughts which are related to CP ENSO events may increase in the south–central China in near future.     

Interactive Effects of Warming and Increased Precipitation on Community Structure and Composition in an Annual Forb Dominated Desert Steppe

To better understand how warming, increased precipitation and their interactions influence community structure and composition, a field experiment simulating hydrothermal interactions was conducted at an annual forb dominated desert steppe in northern China over 2 years. Increased precipitation increased species richness while warming significantly decreased species richness, and their effects were additive rather than interactive. Although interannual variations in weather conditions may have a major affect on plant community composition on short term experiments, warming and precipitation treatments affected individual species and functional group composition. Warming caused C₄ grasses such as Cleistogenes squarrosa to increase while increased precipitation caused the proportions of non-perennial C₃ plants like Artemisia capillaris to decrease and perennial C₄ plants to increase.     

Annual precipitation in Liancheng, China, since 1777 AD derived from tree rings of Chinese pine (Pinus tabulaeformis Carr.)

Precipitation from the previous August to the current June over the last 232 years in Liancheng, China, was reconstructed by a transfer function based on the correlation between tree-ring widths and local meteorological data. The explained variance was 45.3 %, and fluctuations on both annual and decadal scales were captured. Wet periods with precipitation above the 232-year mean occurred from 1777 to 1785, 1802 to 1818, 1844 to 1861, 1889 to 1922 and 1939 to 1960. Dry periods (precipitation below the mean) occurred from 1786 to 1801, 1819 to 1843, 1862 to 1888 and 1923 to 1938. The reconstruction compares well with a tree-ring-based precipitation reconstruction at Mt. Xinglong; both of them showed the well-known severe drought in the late 1920s. The rainfall series also shows highly synchronous decreasing trends since the 1940s, suggesting that precipitation related to the East Asian summer monsoon at these two sites has decreased by large spatial and temporal (decadal) scales. Power spectrum analysis of the reconstruction showed remarkable 21.82-, 3.48-, 3.12-, 3.08- and 2.31-year cycles for the past 232 years; the 22-year cycle corresponds to the solar cycle and is expressed widely in tree ring/precipitation reconstructions on the China Loess Plateau. This may suggest a solar influence on the precipitation variations on the Loess Plateau, although the mechanisms are not well understood.     

中国东北地区近50年净生态系统生产力的时空动态

东北地区处于我国最高纬度地区,是全球气候变化最敏感的区域之一,研究东北地区净生态系统生产力对气候变化的响应,对阐明北半球中高纬度陆地生态系统碳源汇格局具有重要意义。基于CEVSA(Carbon Exchange between Vegetation,Soil and Atomasphere)模型,对1961—2010年东北地区净生态系统生产力NEP的时空格局及变化趋势进行分析,并探讨了气候变化与区域碳源汇的关系。结果表明:(1)1961—2010年,东北地区年NEP总量在-0.094PgC/a—0.117PgC/a之间波动,年平均0.026PgC/a,占全国NEP总量的15%—37%。过去50年东北区域NEP没有明显的线性变化趋势,20世纪80年代碳吸收量最高,20世纪90年代后碳吸收量开始下降。(2)东北地区NEP的空间分布呈现出东部高,西部和中部低,北部高,南部低的空间格局。过去50年来,碳源区向大气释放的碳量在减少,碳汇区从大气吸收的碳也在减少。(3)NEP的年际变化与温度呈负相关(r=-0.343,P0.05),与降水呈显著正相关(r=0.859,P0.01),东北地区NEP和年降水量的变化规律基本一致,即同期上升或达到最高值,温度和降水共同作用导致东北地区NEP的年际变化,而年降水量的变化对NEP年际变化起主要作用。在空间上,东北地区NEP与降水呈极显著正相关(P0.01)的面积占研究区域总面积的91.5%,与温度呈显著负相关(P0.05)的面积占31.6%,降水也是决定NEP空间分布的最主要因子。(4)升温伴随降水增加导致1961—1990年NEP呈增加趋势,而其后升温伴随降水减少则是近20年东北区域碳汇能力减弱的重要原因。     

基于SPEI指数的长江中下游流域干旱时空特征分析

基于长江中下游流域1961—2015年129个气象站点的逐日气温和降水数据,利用标准化降水蒸散指数(SPEI),对长江中下游流域近55年年尺度及各季节干旱变化趋势、站次比、强度和频率进行了分析,并探讨了干旱和区域气温、降水变化及ENSO的关系。结果表明:(1)在区域尺度,近55年长江中下游流域年尺度、春季和秋季呈干旱化趋势,春季干旱化趋势显著;夏季和冬季呈湿润化趋势。空间变化上,对于年尺度,汉江流域、中游干流区及洞庭湖流域以干旱化趋势为主,鄱阳湖流域、下游干流区和太湖流域以湿润化趋势为主;春季和秋季分别有96.90%和92.25%的站点呈干旱化趋势;夏季和冬季分别有82.95%和72.87%的站点呈湿润化趋势。(2)年尺度、春季和秋季干旱站次比及强度均呈增加趋势,春旱站次比与强度增加趋势显著;夏季和冬季干旱站次比和强度均呈下降趋势。(3)年尺度和春季干旱频率在21世纪初均达到最高,年尺度、春季和夏季干旱频率从20世纪90年代到21世纪初均呈增加趋势。(4)春、秋季干旱化趋势与降水量的减少及气温的上升相关,夏、冬季降水量的增加使得夏、冬季呈湿润化趋势。冬季SOI和次年春季干旱相关性极显著,冬季发生拉尼娜事件时,次年春季更易发生干旱。     

Multidecadal- to century-scale arid episodes on the northern Altiplano during the middle Holocene

We present reconstructions of multidecadal- to centennial-scale shifts in the hydrologic balance of the northern Altiplano during the middle Holocene using stable isotopic, geochemical, and sedimentologic evidence from Lake Titicaca sediments. Large downcore changes in the δ¹³C_org of bulk organic matter, previously shown to be a site-specific lake-level proxy, indicate that extended periods of lake-level regression occurred in response to sustained reductions in mean annual precipitation and/or increases in air temperature. Supporting evidence from a floating interval of finely-laminated sediments indicates that salinity and stratification were enhanced at Lake Titicaca during the middle Holocene. The age model used in this study is based on 7 AMS ¹⁴C age dates estimated from bulk decalcified sediment from a 60 cm sequence spanning 7200–5600 ¹⁴C cal yr BP. Simulations from a hydrological-energy balance model of the Titicaca Basin indicate that the ～ 38 m drop in lake level that preceded the maximum lowstand at ～ 6200 yr BP would require a significant decrease in mean annual precipitation of up to 50% and/or a significant increase in mean annual temperature of up to 8 °C. Today, the Altiplano is often affected by drought during periods of enhanced summertime westerly wind flow, which reduces the delivery of moisture from the east. This investigation supports the idea of sustained periods of enhanced westerly air flow during the mid-Holocene and provides additional submillennial-scale information about the timing and magnitude of regional drought. Results of our frequency-domain analysis of the floating lamination interval indicate significant power at a decadal periodicity (10–12 yr) associated with the Schwabe cycle of solar activity. Frequency domain analysis also reveals power in a 75 year time series of modern lake level. We suspect that solar influence on large-scale atmospheric circulation features results in changes to the moisture balance in the Titicaca basin over decadal and possibly century-scale time periods.     

川西亚高山林线岷江冷杉和红杉对气候变化的响应

为揭示川西亚高山林线优势树种岷江冷杉（Abies fargesii var.faxoniana）和红杉（Larix potaninii）径向生长对气候变化的响应差异。通过树木年轮生态学的方法,研究了岷江冷杉和红杉径向生长与年均温的分异现象、生长衰退以及应对严重干旱事件的抵抗力和恢复力稳定性,并结合限制岷江冷杉和红杉径向生长的主要气候因素进行了分析。结果表明：（1）温度是限制林线岷江冷杉径向生长的主要气候因素,而限制红杉径向生长的主要气候因素是降水;（2）岷江冷杉的径向生长与年平均温度的变化趋势一致,红杉在20世纪90年代后径向生长呈现出下降的趋势,与年均温的升高出现分异;（3）1800-2019年间,岷江冷杉出现生长衰退2次,红杉出现生长衰退5次,相同的时间内,红杉的衰退频率高于岷江冷杉;（4）岷江冷杉对严重干旱事件的恢复力相比升温前有所增强,抵抗力相比升温前下降明显,红杉对严重干旱事件的抵抗力和恢复力相比升温前均呈现出下降的趋势。可为川西亚高山林线的植被动态变化预测和历史区域气候重建提供参考。     

大兴安岭林区南、北部天然樟子松生长对气候变化的响应差异

利用树木年代学方法,建立大兴安岭林区南、北部樟子松(Pinus sylvestris var.mongolica)年轮宽度年表,探讨樟子松径向生长对气候变化的响应差异。结果表明,南部(阿尔山、海拉尔)树轮宽度主要与当年4—9月的平均标准化降水蒸散指数SPEI(Standardized Precipitation Evapotranspiration Index)极显著正相关(r=0.639,P0.01),而北部(漠河、塔河)树轮宽度主要与同时期的平均最低温极显著正相关(r=0.488,P0.01)。说明南部樟子松径向生长主要受当年4—9月的水分限制,北部主要受同期平均最低温调控。两个地区树木生长对降水的响应一致,对当年4—9月(6月除外)的温度响应相反。近几十年来随着温度显著升高(P0.01),南部树木生长对4—9月平均最高温的负响应不断增强,而北部树木对同时段平均最低温的正响应更加明显。同时,南部樟子松生长量快速下降(r=0.612,P0.001),而北部生长量显著增加(r=0.474,P0.001)。研究发现,高温加剧干旱胁迫是南部樟子松生长量下降的主要原因,而北部樟子松生长量增加是受到4—9月平均最低温和降水量的相互作用。如果持续变暖,未来樟子松分布区可能北移。     

Carbon, Water, and Energy Exchanges of a Hybrid Poplar Plantation During the First Five Years Following Planting

Eddy covariance was used to measure above-canopy exchanges of CO₂ and water vapor at an operational plantation of hybrid poplar (variety ??Walker??) established on marginal agricultural land in east central Alberta, Canada. Winter ecosystem respiration (R _e) rates were inferred from seasonal changes in the normalized respiration rate at 10°C (R ₁₀) for the growing season and observations of soil CO₂ concentration measured with solid-state probes. Over five consecutive growing seasons following planting, gross ecosystem production (GEP) increased each year, ranging from 21?g?C?m^?2?y^?1 in year 1 to 469?g?C?m^?2?y^?1 in year 5. During this period, the annual carbon balance shifted from a net source of greater than 330?g?C?m^?2 in year 1 to approximately C-neutral in year 5. Total carbon (C) release over 5?years likely exceeded 630?g?C?m^?2. Intra- and interannual variations in temperature and soil water availability greatly affected annual C balance each year. GEP and R _e were particularly sensitive to temperature during spring and to soil water availability in summer: year 5 was notable because a cold spring and accumulating drought caused growth and carbon uptake to fall well below their potential. Annual evapotranspiration (ET) increased slightly with leaf area, from 281?mm in year 1 to 323?mm in year 4, but in year 5 it declined, while exceeding total precipitation (P). This trend of increasing annual ET/P suggests that annual GEP could become increasingly water-limited in years with below normal precipitation, as the plantation achieves maximum leaf area. Measured canopy albedos did not change appreciably over three winters, suggesting that estimates of increased radiative forcing resulting from afforestation in high latitudes could be exaggerated in regions where fast-growing deciduous plantations are managed on short (~20-year) rotations.     

1801年以来河南尧山地区油松高温变化及影响机制

基于建立的河南尧山地区油松树轮宽度标准年表,分析了油松径向生长与该地区气温、降水等气候因子之间的关系以及气温升高前后树木生长与平均最高气温间的相关性,结果表明:4—7月平均最高气温与树轮年表的相关系数高达-0.64,是该地区油松径向生长的主要限制因子;气候变暖后树轮年表与9、10月份平均最高气温显著正相关,与2、3月降水显著正相关,与4—7月平均最高气温间的相关性较为稳定。因此,重建了尧山地区1801年来4—7月平均最高气温,其方差解释量达40%(调整自由度后为38.9%)。过去216年的高温重建历史中经历了6个较暖的时期:1801—1825,1845—1853,1876—1889,1922—1944,1957—1975,1996—2013年和5个较冷的时期:1826—1844,1854—1875,1890—1921,1945—1956,1978—1995年,其结果与过去伏牛山龙池曼地区5—7月温度重建序列具有很好的一致性。周期分析结果发现该地区4—7月平均最高气温变化存在着2—4年(ENSO周期)和35.23—48.47年的主要变化周期,小波分析发现在1920年前后气候由长周期变为短周期变化;空间相关分析显示重建的高温序列很好地代表了豫东平原地区的温度变化,同时也发现与北太平洋副热带高压850 hPa上空的温度有非常高的正相关关系,表明豫东高温的波动可能与北太平洋海气振荡有关,这一研究结果为山区森林管理及平原区农业生产提供基础服务数据。     

树轮宽度记录的额尔齐斯河上游地区过去291年的降水变化

利用采自额尔齐斯河上游6个采点的西伯利亚云杉(Picea obovata Ledeb)树轮样本建立了区域树轮宽度年表。与气候要素的相关分析表明,该地区树木径向生长主要受降水制约,区域树轮宽度年表与富蕴气象站上年7月至当年6月的降水总量相关显著。在此基础上建立了转换方程,重建了额尔齐斯河上游地区1722—2012年上年7月至当年6月的降水总量,方差解释量高达55.1%(调整自由度后为54.2%)。重建结果显示,该地区过去291年间存在9个降水偏多的时期和8个降水偏少的时期。降水重建序列还存在2.1a和3.2a的显著周期及2.3、21.6、24.3a的较显著周期,并且在1876—1877年及1983年前后发生了降水突变。空间相关分析表明,重建的上年7月至当年6月降水量对额尔齐斯河上游阿勒泰地区的降水量具有很好的空间代表性。此外,重建结果还与周边地区其他基于树轮资料重建的降水序列的干湿变化有较好的一致性。     

Interactive responses of old‐field plant growth and composition to warming and precipitation

As Earth's atmosphere accumulates carbon dioxide (CO₂) and other greenhouse gases, Earth's climate is expected to warm and precipitation patterns will likely change. The manner in which terrestrial ecosystems respond to climatic changes will in turn affect the rate of climate change. Here we describe responses of an old‐field herbaceous community to a factorial combination of four levels of warming (up to 4 °C) and three precipitation regimes (drought, ambient and rain addition) over 2 years. Warming suppressed total production, shoot production, and species richness, but only in the drought treatment. Root production did not respond to warming, but drought stimulated the growth of deeper (> 10 cm) roots by 121% in 1 year. Warming and precipitation treatments both affected functional group composition, with C₄ grasses and other annual and biennial species entering the C₃ perennial‐dominated community in ambient rainfall and rain addition treatments as well as in warmed treatments. Our results suggest that, in this mesic system, expected changes in temperature or large changes in precipitation alone can alter functional composition, but they have little effect on total herbaceous plant growth. However, drought limits the capacity of the entire system to withstand warming. The relative insensitivity of our study system to climate suggests that the herbaceous component of old‐field communities will not dramatically increase production in response to warming or precipitation change, and so it is unlikely to provide either substantial increases in forage production or a meaningful negative feedback to climate change later this century.     

石榴园西花蓟马种群动态及其与气象因素的关系

2007-2008年,对云南省建水石榴园西花蓟马种群动态进行了系统调查,并采用回归分析(逐步回归分析、通径分析)、主成分分析及灰色系统分析就气象因子对该虫种群动态的影响进行了系统分析。结果表明,西花蓟马在建水石榴园常年发生,冬季较低,夏季最高,成虫全年种群消长呈单峰型,高峰期为5月份。相关性分析结果表明,西花蓟马种群数量与月相对湿度间呈极显著正相关性(P<0.01),与月均气温和月最低气温间呈显著正相关性(P<0.05),与月最高气温、月均降雨量和月均蒸发量间无相关性(P>0.05)。回归分析结果表明,石榴园西花蓟马种群动态的决定因子中影响最大的气象因素是月最低气温,而月均气温和月相对湿度是影响种群数量变动的主要因素。主成分分析表明,月最低气温是主要成分,其累积方差贡献率达73.03%。灰色系统分析结果表明,影响石榴园6种蓟马种群动态最关键的因子是月相对湿度;年度间影响最大的是年总降雨量;石榴花期各蓟马的种群数量与气象因素间关联度最大的是月最低温;果期各种蓟马的种群数量与气象因素间关联度最大的是月均降雨量。     

Effects of elevated CO2, warming and precipitation change on plant growth,photosynthesis and peroxidation in dominant species from North China grassland

Warming, watering and elevated atmospheric CO₂-concentration effects have been extensively studied separately; however, their combined impact on plants is not well understood. In the current research, we examined plant growth and physiological responses of three dominant species from the Eurasian Steppe with different functional traits to a combination of elevated CO₂, high temperature, and four simulated precipitation patterns. Elevated CO₂ stimulated plant growth by 10.8–41.7 % for a C₃ leguminous shrub, Caragana microphylla, and by 33.2–52.3 % for a C₃ grass, Stipa grandis, across all temperature and watering treatments. Elevated CO₂, however, did not affect plant biomass of a C₄ grass, Cleistogenes squarrosa, under normal or increased precipitation, whereas a 20.0–69.7 % stimulation of growth occurred with elevated CO₂ under drought conditions. Plant growth was enhanced in the C₃ shrub and the C₄ grass by warming under normal precipitation, but declined drastically with severe drought. The effects of elevated CO₂ on leaf traits, biomass allocation and photosynthetic potential were remarkably species-dependent. Suppression of photosynthetic activity, and enhancement of cell peroxidation by a combination of warming and severe drought, were partly alleviated by elevated CO₂. The relationships between plant functional traits and physiological activities and their responses to climate change were discussed. The present results suggested that the response to CO₂ enrichment may strongly depend on the response of specific species under varying patterns of precipitation, with or without warming, highlighting that individual species and multifactor dependencies must be considered in a projection of terrestrial ecosystem response to climatic change.