中国东部温带植被生长季节的空间外推估计

利用地面植物物候和遥感归一化差值植被指数（NDVI）数据,以及一种物候-遥感外推方法,实现植被生长季节从少数站点到较多站点的空间外推。结果表明：（1）在1982～1993年期间,中国东部温带地区植被生长季节多年平均起讫日期的空间格局与春季和秋季平均气温的空间格局相关显著;（2）在不同纬度带和整个研究区域,植被生长季节结束日期呈显著推迟的趋势,而开始日期则呈不显著提前的趋势,这与欧洲和北美地区植被生长季节开始日期显著提前而结束日期不显著推迟的变化趋势完全不同;（3）北部纬度带的植被生长季节平均每年延长1．4～3．6d,全区的植被生长季节平均每年延长1．4d,与同期北半球和欧亚大陆植被生长季节延长的趋势数值相近;（4）植被生长季节结束日期的显著推迟与晚春至夏季的区域性降温有关,而植被生长季节开始日期的不显著提前则与晚冬至春季气温趋势的不稳定变化有关;（5）在年际变化方面,植被生长季节开始和结束日期分别与2～4月份平均气温和5～6月份平均气温呈负相关关系。     

Trends and temperature response in the phenology of crops in Germany

The phenology of 78 agricultural and horticultural events from a national survey in Germany spanning the years 1951–2004 is examined. The majority of events are significantly earlier now than 53 years ago, with a mean advance of 1.1–1.3 days per decade. The mean trends for 'true phases', such as emergence and flowering, of annual and perennial crops are not significantly different, although more trends (78% vs. 46%) are significant for annual crops. We attempt to remove the influence of technological advance or altered farming practices on phenology by detrending the respective time series by linear regression of date (day number) on year. Subsequently, we estimate responses to mean monthly and seasonal temperature by correlation and regression in two ways; with and without removing the year trend first. Nearly all (97%) correlation coefficients are negative, suggesting earlier events in warmer years. Between 82% and 94% of the coefficients with seasonal spring and summer temperatures are significant. The conservative estimate (detrended) of mean temperature response against mean March–May temperature (−3.73 days °C⁻¹) is significantly less than the full estimate (−4.31 days °C⁻¹), the 'true' size of phenological temperature response may lie in between. Perennial crops exhibited a significantly higher temperature response to mean spring temperature than the annual crops.     

Near-zero recent carbon accumulation in a bog with high nitrogen deposition in SW Sweden

We present data on the accumulation of carbon and nitrogen into an open oceanic ombrotrophic bog, SW Sweden, with high levels of anthropogenic nitrogen deposition. The aim was to investigate if this peatland currently acts as a sink for atmospheric carbon. Peat cores were sampled from the top peat layer in five different vegetation types. Small pines were used to date the cores. The cores bulk density and carbon and nitrogen content were determined. A vegetation-classified satellite image was used to estimate the areal extent of the vegetation types and to scale up these results to bog level. The rate of current carbon input into the upper oxic acrotelm was 290 g m⁻² yr⁻¹, and there were no significant differences in accumulation rates among the vegetation types. This organic matter input to the acrotelm was almost completely decomposed before it was deposited for storage in the deeper peat layers (the catotelm) and only a small fraction (≪1%) or 0.012 g m⁻² yr⁻¹ of the carbon would be left, assuming a residence time of 100 years in the acrotelm. Nitrogen accumulation rates differed between the vegetation classes, and the average input via primary production varied from 5.33 to 16.8 g m⁻² yr⁻¹. Current nitrogen input rates into the catotelm are much lower, 0–0.059 g m⁻² yr⁻¹, with the highest accumulation rates in lawn-dominated communities. We suggest that one of the main causes of the low carbon input rates is the high level of nitrogen deposition, which enhances decomposition and changes the vegetation from peat-forming Sphagnum -dominance to dominance by dwarf shrubs and graminoids.     

Changes in topsoil carbon stock in the Tibetan grasslands between the 1980s and 2004

Climate warming is likely inducing carbon loss from soils of northern ecosystems, but little evidence comes from large-scale observations. Here we used data from a repeated soil survey and remote sensing vegetation index to explore changes in soil organic carbon (SOC) stock on the Tibetan Plateau during the past two decades. Our results showed that SOC stock in the top 30 cm depth in alpine grasslands on the plateau amounted to 4.4 Pg C (1 Pg=10¹⁵ g), with an overall average of 3.9 kg C m⁻². SOC changes during 1980s–2004 were estimated at −0.6 g C m⁻² yr⁻¹, ranging from −36.5 to 35.8 g C m⁻² yr⁻¹ at 95% confidence, indicating that SOC stock in the Tibetan alpine grasslands remained relatively stable over the sampling periods. Our findings are nonconsistent with previous reports of loss of soil C in grassland ecosystems due to the accelerated decomposition with warming. In the case of the alpine grasslands on the Tibetan Plateau studied here, we speculate that increased rates of decomposition as soils warmed during the last two decades may have been compensated by increased soil C inputs due to increased grass productivity. These results suggest that soil C stock in terrestrial ecosystems may respond differently to climate change depending on ecosystem type, regional climate pattern, and intensity of human disturbance.     

Population dynamics and production of the pelagic amphipod Hyalella montezuma in a thermally constant system

SUMMARY. 1. The population dynamics and annual production of the multivoltine. pelagic amphipod Hyalella montezuma were studied over a 3-year period in the thermally constant environment of Montezuma Well. Arizona.
2. H. montezuma showed two maxima which coincided with spring and autumn phytoplankton maxima. Juveniles comprised over 85% of the population in the pelagic zone compared to 37% in the littoral vegetation and there were significantly more females in the littoral vegetation. It appears that juvenile and adult H. montezuma show different habitat preferences.
3. Total annual mean production for H. montezuma calculated by the size frequency method and adjusted for multiple generations, was 357 kg ha⁻¹ yr⁻¹, which is higher than single-species production estimates reported for most zoobenthic amphipods and multivoltine planktonic crustaceans. Average energy production for H. montezuma was 4640 kJ ha⁻¹ yr⁻¹ in the pelagic zone and 1072 kJ ha⁻¹ yr⁻¹ in the littoral vegetation.
4. Average cohort P / ratios for H. montezuma were higher in the pelagic zone (5.5) than in the litttoral vegetation (3.7). Juveniles had higher cohort P ratios than adults in the pelagic zone, while the reverse relationship was true in the littoral vegetation. We propose that different size-selective predators may contribute to the differences in P ratios for juveniles and adults in these two habitats.     

European phenological response to climate change matches the warming pattern

Global climate change impacts can already be tracked in many physical and biological systems; in particular, terrestrial ecosystems provide a consistent picture of observed changes. One of the preferred indicators is phenology, the science of natural recurring events, as their recorded dates provide a high-temporal resolution of ongoing changes. Thus, numerous analyses have demonstrated an earlier onset of spring events for mid and higher latitudes and a lengthening of the growing season. However, published single-site or single-species studies are particularly open to suspicion of being biased towards predominantly reporting climate change-induced impacts. No comprehensive study or meta-analysis has so far examined the possible lack of evidence for changes or shifts at sites where no temperature change is observed. We used an enormous systematic phenological network data set of more than 125 000 observational series of 542 plant and 19 animal species in 21 European countries (1971–2000). Our results showed that 78% of all leafing, flowering and fruiting records advanced (30% significantly) and only 3% were significantly delayed, whereas the signal of leaf colouring/fall is ambiguous. We conclude that previously published results of phenological changes were not biased by reporting or publication predisposition: the average advance of spring/summer was 2.5 days decade⁻¹ in Europe. Our analysis of 254 mean national time series undoubtedly demonstrates that species' phenology is responsive to temperature of the preceding months (mean advance of spring/summer by 2.5 days°C⁻¹, delay of leaf colouring and fall by 1.0 day°C⁻¹). The pattern of observed change in spring efficiently matches measured national warming across 19 European countries (correlation coefficient r =−0.69, P <0.001).     

1982—2012年新疆植被NDVI的动态变化及其对气候变化和人类活动的响应

植被在调节陆地碳平衡、气候系统中发挥了重要作用,并在生态系统服务功能提供方面占据主导地位,因此,监测植被生长变化意义重大.基于AVHRR GIMMS NDVI和MODIS NDVI数据集,在区域、像元两个空间尺度,研究了中国典型干旱区新疆1982—2012年间植被生长的动态变化,探讨了气候变化和人类活动对植被生长的影响.结果表明: 区域尺度,1982—2012年生长季植被NDVI呈极显著增加趋势(4.09×10^-4·a^-1);NDVI变化趋势存在明显阶段性,1998年前后分别呈极显著增加(10×10^-4·a^-1)和显著减少(-3×10^-4·a^-1);生长季NDVI变化趋势的逆转主要发生在夏季,其次是秋季,而春季不存在逆转.像元尺度上,农业区NDVI增加趋势显著;NDVI变化呈两极分化现象,剧烈变化区域多随时段长度延长而增加,尤其是显著减少区域范围快速扩张,导致区域尺度NDVI增加的停滞或放缓.研究区域植被生长受水热条件、人类活动共同控制.春、秋季的气温发挥主导作用,而夏季主要受到降水量的影响.大量施肥、灌溉面积增加等生产活动提高了农田植被覆盖,种植结构、灌溉方式等的改变降低了春季农田NDVI值,载畜量的增加则降低了部分草地的NDVI.     

Carbon mitigation by the energy crop, Miscanthus

Biomass crops mitigate carbon emissions by both fossil fuel substitution and sequestration of carbon in the soil. We grew Miscanthus x giganteus for 16 years at a site in southern Ireland to (i) compare methods of propagation, (ii) compare response to fertilizer application and quantify nutrient offtakes, (iii) measure long-term annual biomass yields, (iv) estimate carbon sequestration to the soil and (v) quantify the carbon mitigation by the crop. There was no significant difference in the yield between plants established from rhizome cuttings or by micro-propagation. Annual off-takes of N and P were easily met by soil reserves, but soil K reserves were low in unfertilized plots. Potassium deficiency was associated with lower harvestable yield. Yields increased for 5 years following establishment but after 10 years showed some decline which could not be accounted for by the climate driven growth model MISCANMOD. Measured yields were normalized to estimate both autumn (at first frost) and spring harvests (15 March of the subsequent year). Average autumn and spring yields over the 15 harvest years were 13.4±1.1 and 9.0±0.7 t DW ha⁻¹ yr⁻¹ respectively. Below ground biomass in February 2002 was 20.6±4.6 t DW ha⁻¹. Miscanthus derived soil organic carbon sequestration detected by a change in ¹³C signal was 8.9±2.4 t C ha⁻¹ over 15 years. We estimate total carbon mitigation by this crop over 15 years ranged from 5.2 to 7.2 t C ha⁻¹ yr⁻¹ depending on the harvest time.     

Convergence in the relationship of CO2 and N2O exchanges between soil and atmosphere within terrestrial ecosystems

Ecosystem CO₂ and N₂O exchanges between soils and the atmosphere play an important role in climate warming and global carbon and nitrogen cycling; however, it is still not clear whether the fluxes of these two greenhouse gases are correlated at the ecosystem scale. We collected 143 pairs of ecosystem CO₂ and N₂O exchanges between soils and the atmosphere measured simultaneously in eight ecosystems around the world and developed relationships between soil CO₂ and N₂O fluxes. Significant linear regressions of soil CO₂ and N₂O fluxes were found for all eight ecosystems; the highest slope occurred in rice paddies and the lowest in temperate grasslands. We also found the dominant role of growing season on the relationship of annual CO₂ and N₂O fluxes. No significant relationship between soil CO₂ and N₂O fluxes was found across all eight ecosystem types. The estimated annual global N₂O emission based on our findings is 13.31 Tg N yr⁻¹ with a range of 8.19–18.43 Tg N yr⁻¹ for 1980–2000, of which cropland contributes nearly 30%. Our findings demonstrated that stoichiometric relationships may work on ecological functions at the ecosystem level. The relationship of soil N₂O and CO₂ fluxes developed here could be helpful in biogeochemical modeling and large-scale estimations of soil CO₂ and N₂O fluxes.     

Climate-induced changes in high elevation stream nitrate dynamics

Mountain terrestrial and aquatic ecosystems are responsive to external drivers of change, especially climate change and atmospheric deposition of nitrogen (N). We explored the consequences of a temperature-warming trend on stream nitrate in an alpine and subalpine watershed in the Colorado Front Range that has long been the recipient of elevated atmospheric N deposition. Mean annual stream nitrate concentrations since 2000 are higher by 50% than an earlier monitoring period of 1991–1999. Mean annual N export increased by 28% from 2.03 kg N ha⁻¹ yr⁻¹ before 2000 to 2.84 kg N ha⁻¹ yr⁻¹ in Loch Vale watershed since 2000. The substantial increase in N export comes as a surprise, since mean wet atmospheric N deposition from 1991 to 2006 (3.06 kg N ha⁻¹ yr⁻¹) did not increase. There has been a period of below average precipitation from 2000 to 2006 and a steady increase in summer and fall temperatures of 0.12 °C yr⁻¹ in both seasons since 1991. Nitrate concentrations, as well as the weathering products calcium and sulfate, were higher for the period 2000–2006 in rock glacier meltwater at the top of the watershed above the influence of alpine and subalpine vegetation and soils. We conclude the observed recent N increases in Loch Vale are the result of warmer summer and fall mean temperatures that are melting ice in glaciers and rock glaciers. This, in turn, has exposed sediments from which N produced by nitrification can be flushed. We suggest a water quality threshold may have been crossed around 2000. The phenomenon observed in Loch Vale may be indicative of N release from ice features such as rock glaciers worldwide as mountain glaciers retreat.     

1982—2009年基于卫星数据的北半球中高纬地区植被春季物候动态及其与气候的关系

深入认识北半球植被物候在全球变暖背景下的动态变化特征,对于评估和预测生态系统结构和功能对气候变化的响应有重要的指示作用.遥感技术是获取北半球植被春季物候的最重要方法,但是由于物候提取算法的差异,目前还存在较大的不确定性.本文利用5种方法,基于卫星获取的归一化植被指数估算了北半球中高纬地区1982—2009年植被春季物候开始日期,分析了该日期的多年动态变化的时空特征,并探讨了气候变化对春季物候变化的影响.结果表明: 研究区植被春季物候开始日期呈现提前趋势,研究期间提前(4.0±0.8) d,其中,欧亚大陆提前速率为(0.22±0.04) d·a^-1,显著高于北美大陆的变化速率(0.03±0.02 d·a^-1);不同植被类型的变化趋势不同,5种方法都显示草地表现为显著提前趋势,而林地的提前趋势不显著.区域平均的植被春季物候开始日期的年际波动主要受春季温度的变化所驱动(r² =0.61,P<0.001), 温度每上升1 ℃,可以导致春季物候提前(3.2±0.5) d,而春季降水影响不显著(P>0.05).     

Antagonistic effects of growing season and autumn temperatures on the timing of leaf coloration in winter deciduous trees

Autumn phenology remains a relatively neglected aspect in climate change research, which hinders an accurate assessment of the global carbon cycle and its sensitivity to climate change. Leaf coloration, a key indicator of the growing season end, is thought to be triggered mainly by high or low temperature and drought. However, how the control of leaf coloration is split between temperature and drought is not known for many species. Moreover, whether growing season and autumn temperatures interact in influencing the timing of leaf coloration is not clear. Here, we revealed major climate drivers of leaf coloration dates and their interactions using 154 phenological datasets for four winter deciduous tree species at 89 stations, and the corresponding daily mean/minimum air temperature and precipitation data across China's temperate zone from 1981 to 2012. Results show that temperature is more decisive than drought in causing leaf coloration, and the growing season mean temperature plays a more important role than the autumn mean minimum temperature. Higher growing season temperature and lower autumn minimum temperature would induce earlier leaf coloration date. Moreover, the mean temperature over the growing season correlates positively with the autumn minimum temperature. This implies that growing season mean temperature may offset the requirement of autumn minimum temperature in triggering leaf coloration. Our findings deepen the understanding of leaf coloration mechanisms in winter deciduous trees and suggest that leaf life‐span control depended on growing season mean temperature and autumn low temperature control and their interaction are major environmental cues. In the context of climate change, whether leaf coloration date advances or is delayed may depend on intensity of the offset effect of growing season temperature on autumn low temperature.     

Latitudinal trends in Spartina alterniflora productivity and the response of coastal marshes to global change

Marshes worldwide are actively degrading in response to increased sea level rise rates and reduced sediment delivery, though the growth rate of vegetation plays a critical role in determining their stability. We have compiled 56 measurements of aboveground annual productivity for Spartina alterniflora , the dominant macrophyte in North American coastal wetlands. Our compilation indicates a significant latitudinal gradient in productivity, which we interpret to be determined primarily by temperature and/or the length of growing season. Simple linear regression yields a 27 g m⁻² yr⁻¹ increase in productivity with an increase of mean annual temperature by 1 °C. If temperatures warm 2–4 °C over the next century, then marsh productivity may increase by 10–40%, though physiological research suggests that increases in the north could potentially be offset by some decreases in the south. This increase in productivity is roughly equivalent to estimates of marsh lost due to future sea level change. If a warming-induced stimulation of vegetation growth will enhance vertical accretion and limit erosion, then the combined effects of global change may be to increase the total productivity and ecosystem services of tidal wetlands, at least in northern latitudes.     

Spatial and temporal variation of phenological growing season and climate change impacts in temperate eastern China

Using phenological and normalized difference vegetation index (NDVI) data from 1982 to 1993 at seven sample stations in temperate eastern China, we calculated the cumulative frequency of leaf unfolding and leaf coloration dates for deciduous species every 5 days throughout the study period. Then, we determined the growing season beginning and end dates by computing times when 50% of the species had undergone leaf unfolding and leaf coloration for each station year. Next, we used these beginning and end dates of the growing season as time markers to determine corresponding threshold NDVI values on NDVI curves for the pixels overlaying phenological stations. Based on a cluster analysis, we determined extrapolation areas for each phenological station in every year, and then implemented the spatial extrapolation of growing season parameters from the seven sample stations to all possible meteorological stations in the study area. Results show that spatial patterns of growing season beginning and end dates correlate significantly with spatial patterns of mean air temperatures in spring and autumn, respectively. Contrasting with results from similar studies in Europe and North America, our study suggests that there is a significant delay in leaf coloration dates, along with a less pronounced advance of leaf unfolding dates in different latitudinal zones and the whole area from 1982 to 1993. The growing season has been extended by 1.4–3.6 days per year in the northern zones and by 1.4 days per year across the entire study area on average. The apparent delay in growing season end dates is associated with regional cooling from late spring to summer, while the insignificant advancement in beginning dates corresponds to inconsistent temperature trend changes from late winter to spring. On an interannual basis, growing season beginning and end dates correlate negatively with mean air temperatures from February to April and from May to June, respectively.     

Migration of anadromous brown trout Salmo trutta in a Norwegian river

1. Upstream and downstream migrating anadromous brown trout Salmo trutta were monitored daily in fish traps in the River Imsa in south-western Norway for 24 years, from 1976 to 1999. One-third of the fish descended to sea during spring (February–June) and two-thirds during autumn (September–January).
2. In spring, high water temperature appeared to influence the downstream descent. Large brown trout (> 30 cm, chiefly two or more sea sojourns) descended earlier and appeared less dependent on high water temperature than smaller and younger fish. The spring water flow was generally low and of little importance for the descent.
3. In autumn, the daily number of descending brown trout correlated positively with flow and negatively with water temperature.
4. Brown trout ascended from the sea between April and December, but more than 70% ascended between August and October. The number of ascending trout increased significantly with both decreasing temperature and flow during the autumn. This response to flow appeared to be the result of the autumn discharge which is generally high and most fish ascended at an intermediate flow of 7.5–10 m³ s⁻¹ (which is low for the season).
5. In a river like the Imsa with low spring and high autumn flows, water temperature appears to be the main environmental factor influencing the timing and rate of spring descent, while both water temperature and flow seemed to influence the timing and rate of the autumn descent and ascent. These relationships make sea trout migrations susceptible to variation in climate and human impacts of the flow regime in rivers.     

Trends in phenological phases in Europe between 1951 and 1996

Increases in air temperature due to the anthropogenic greenhouse effect can be detected easily in the phenological data of Europe within the last four decades because spring phenological events are particularly sensitive to temperature. Our new analysis of observational data from the International Phenological Gardens in Europe for the 1959–1996 period revealed that spring events, such as leaf unfolding, have advanced on average by 6.3 days (–0.21 day/year), whereas autumn events, such as leaf colouring, have been delayed on average by 4.5 days (+0.15 day/year). Thus, the average annual growing season has lengthened on average by 10.8 days since the early 1960s. For autumn events, differences between mean trends of species could not be detected, but for spring events there were differences between species, with the higher trends for leaf unfolding and flowering of shrubs indicating that changes in events occurring in the early spring are more distinct. These observed trends in plant phenological events in the International Phenological Gardens and results of other phenological studies in Europe, summarised in this study, are consistent with AVHRR satellite measurements of the normalized difference vegetation index from 1981 to 1991 and with an analysis of long-term measurements of the annual cycle of CO₂ concentration in Hawaii and Alaska, also indicating a global lengthening of the growing season. Received: 21 October 1999 / Accepted: 2 March 2000     

Dynamic social system in Nubian ibex: can a second mating season develop in response to arid climate?

We studied a population of Nubian ibex Capra ibex nubiana in the eastern extreme of its range, the hyper-arid central desert of the Sultanate of Oman. Long-term data were collected from January 1983 to December 1997 by direct observation, as well as VHF telemetry on 12 animals (eight from 1987 to 1990; four from 1994 to 1996). We recorded 884 sightings: 40.4% of single animals and 59.6% of groups. Although no significant monthly variation of group size (Jarman's Typical Group Size) was found, there were distinct peaks in March (4.0 ind. group⁻¹) and September (5.1 ind. group⁻¹). Groups of males and females formed especially in March and November, and female–kid groups in February and July–August. Our data may suggest two mating periods: the first one in autumn (similar to the rut of ibex in temperate mountain areas), with kids born in spring/early summer, after winter–spring rainfall, and the second one in spring, with kids born in late summer/autumn, before winter–spring rainfalls. We suggest that the second rutting period may have evolved as a micro-evolutionary process, with the local population adapting to hyper-arid environment constraints. The spring mating season may favour only females in prime conditions, who can afford a pregnancy in the local severe summers and will deliver kids when plant greening begins, in the autumn, whereas the autumn (original) mating season may be afforded by any female, but kids will be born in an unfavourable period, before the summer drought.     

Seasonal Response of Grasslands to Climate Change on the Tibetan Plateau

Background

Monitoring vegetation dynamics and their responses to climate change has been the subject of considerable research. This paper aims to detect change trends in grassland activity on the Tibetan Plateau between 1982 and 2006 and relate these to changes in climate.

Methodology/Principal Findings

Grassland activity was analyzed by evaluating remotely sensed Normalized Difference Vegetation Index (NDVI) data collected at 15-day intervals between 1982 and 2006. The timings of vegetation stages (start of green-up, beginning of the growing season, plant maturity, start of senescence and end of the growing season) were assessed using the NDVI ratio method. Mean NDVI values were determined for major vegetation stages (green-up, fast growth, maturity and senescence). All vegetation variables were linked with datasets of monthly temperature and precipitation, and correlations between variables were established using Partial Least Squares regression. Most parts of the Tibetan Plateau showed significantly increasing temperatures, as well as clear advances in late season phenological stages by several weeks. Rainfall trends and significant long-term changes in early season phenology occurred on small parts of the plateau. Vegetation activity increased significantly for all vegetation stages. Most of these changes were related to increasing temperatures during the growing season and in some cases during the previous winter. Precipitation effects appeared less pronounced. Warming thus appears to have shortened the growing season, while increasing vegetation activity.

Conclusions/Significance

Shortening of the growing season despite a longer thermally favorable period implies that vegetation on the Tibetan Plateau is unable to exploit additional thermal resources availed by climate change. Ecosystem composition may no longer be well attuned to the local temperature regime, which has changed rapidly over the past three decades. This apparent lag of the vegetation assemblage behind changes in climate should be taken into account when projecting the impacts of climate change on ecosystem processes.     

黄土高原植被物候变化及其对季节性气候变化的响应

受气候变化影响,全球范围内植被物候发生了显著变化,而目前针对不同植被分区类型下（荒漠草原区、典型草原区、森林草原区、落叶栎林区、落叶栎林亚区）植被物候变化及其对季节性气候变化响应的研究尚少。因此基于MODIS遥感归一化差值植被指数（MODIS NDVI：MOD13Q1）数据、中国植被区划数据及135个气象站点插值数据,利用Sen''s斜率估计、Hurst指数和高阶偏相关分析等方法,研究黄土高原2001-2018年植被物侯变化及其对季节性气候变化的响应。结果表明：（1）黄土高原植被生长季始期（SOS,Start of Growing Season）主要集中在第96-144天,子植被分区由西北向东南方向,逐渐呈现提前趋势,71.0%的像元植被SOS整体提前0-2 d/10a （α=0.05）,且在未来一段时间66%的像元植被SOS继续呈现提前趋势;植被生长季末期（EOS,End of Growing Season）主要集中在第288-304天,各子植被分区植被EOS变化基本保持一致,87.6％的像元植被EOS整体延迟0-3 d/10a （α=0.05）,且在未来一段时间有80%的像元植被EOS继续呈现推迟趋势。（2）黄土高原植被SOS主要受各季节温度的影响;当年春季降水导致植被SOS提前,主要分布在黄土高原中部;上年夏季和上年秋季降水增加会导致植被SOS推迟;当年春季、上年秋季和年初冬季的温度升高均会导致植被SOS提前;各子植被分区植被SOS对不同季节降水的响应存在差异,而对不同季节温度的响应具有一致性。（3）黄土高原植被EOS主要受各季节降水和秋季温度的影响;不同季节降水增加均会导致大部分植被EOS推迟;当年秋季温度导致整体区域植被EOS推迟,且各子植被区植被EOS对当年秋季温度响应具有一致性。该研究可为大尺度植被物候影响因素提供新的认识,也为植被适应未来气候变化提供借鉴。     

Phenological responses of <Emphasis Type="Italic">Ulmus pumila</Emphasis> (Siberian Elm) to climate change in the temperate zone of China

Using Ulmus pumila (Siberian Elm) leaf unfolding and leaf fall phenological data from 46 stations in the temperate zone of China for the period 1986–2005, we detected linear trends in both start and end dates and length of the growing season. Moreover, we defined the optimum length period during which daily mean temperature affects the growing season start and end dates most markedly at each station in order to more precisely and rationally identify responses of the growing season to temperature. On average, the growing season start date advanced significantly at a rate of −4.0 days per decade, whereas the growing season end date was delayed significantly at a rate of 2.2 days per decade and the growing season length was prolonged significantly at a rate of 6.5 days per decade across the temperate zone of China. Thus, the growing season extension was induced mainly by the advancement of the start date. At individual stations, linear trends of the start date correlate negatively with linear trends of spring temperature during the optimum length period, namely, the quicker the spring temperature increased at a station, the quicker the start date advanced. With respect to growing season response to interannual temperature variation, a 1°C increase in spring temperature during the optimum length period may induce an advancement of 2.8 days in the start date of the growing season, whereas a 1°C increase in autumn temperature during the optimum length period may cause a delay of 2.1 days in the end date of the growing season, and a 1°C increase in annual mean temperature may result in a lengthening of the growing season of 9 days across the temperate zone of China. Therefore, the response of the start date to temperature is more sensitive than the response of the end date. At individual stations, the sensitivity of growing season response to temperature depends obviously on local thermal conditions, namely, either the negative response of the start date or the positive response of the end date and growing season length to temperature was stronger at warmer locations than at colder locations. Thus, future regional climate warming may enhance the sensitivity of plant phenological response to temperature, especially in colder regions.