The Growth response of slash pine (Pinus elliottii) to climate in the Georgia Coastal Plain

We examined tree-ring growth in a naturally seeded old-growth slash pine (Pinus elliottii Engelm. var. elliottii) stand in coastal Georgia to develop growth-climate models and reconstruct past climatic conditions during the mid and late 1800s. We generated earlywood, latewood, and annual ring chronologies dating to 1818, based on 40 cores collected from 22 trees at the Wormsloe State Historic Site near Savannah, Georgia, with 28 cores dating before 1900. We used correlation and response function analysis to relate tree-ring growth to climatic variables and El Niño/Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) indices. Water availability (represented by PDSI and secondarily, precipitation) was the most important factor determining growth for all three series, with latewood and September PDSI showing the strongest relationship. Like other species in the southeastern United States, moisture in the late winter and spring was crucial for earlywood development, while latewood and annual growth was enhanced in cooler, wetter summers, particularly with hurricanes bringing rainfall late in the growing season. Earlywood growth was greater following +ENSO (winter) phases and −NAO (winter) phases – for both indices, times when the northern Georgia coast is often relatively cool and wet. A verified split-calibration regression model based on latewood ring growth showed temporal stability and accounted for 27% of the variation in the observed September PDSI record from 1895 to 2009 (mean reduction in error = 0.21 and coefficient of efficiency = 0.05). During the instrument record, the timing of reconstructed and observed dry and moist periods matched closely; prior to that, reconstructed PDSI values indicated drought from the early 1840s to late 1850s – a period of unusually low latewood growth.     

滇西北玉龙雪山不同海拔云南松(Pinus yunnanensis)径向生长对气候因子的响应

云南松(Pinus yunnanensis)是重要的造林树种,在我国西南地区广泛分布。研究不同海拔云南松径向生长对气候变化的响应,有助于了解气候变化背景下云南松的敏感性和适应性。在滇西北丽江玉龙雪山不同海拔采集了云南松树木年轮样品,采用传统的树木年轮方法制作了不同海拔云南松树轮宽度标准化年表,并分析了不同海拔云南松径向生长与气候因子的相关性。结果表明:1)低海拔样点云南松具有较快的年平均生长速率。2)不同海拔云南松对气候因子的响应模式一致,树轮宽度与当年5—6月的降水量、帕尔默干旱指数(PDSI)和相对湿度呈正相关,与同期温度呈负相关。3)不同海拔的云南松径向生长对气象因子的响应程度不一样,即低海拔样点云南松树轮宽度与当年5月份的干旱指数、相对湿度、降水量相关系数较高;而高海拔样点的云南松树轮宽度与5—6月的降水、相对湿度、干旱指数的相关系数较低。研究表明春末夏初的水分条件是玉龙雪山云南松径向生长的主要限制因子,且低海拔地区云南松生长受水分限制更为严重,区域气候变暖和干旱化趋势可能对低海拔地区云南松的生长产生持续的负面效应。研究结果可为探讨气候变化下云南松的适宜分布区、以及云南松人工林的经营和可持续管理提供参考。     

Evaluating the temperature sensitivity of radial growth patterns from whitebark pine in the western Canadian Cordillera

We present a network of thirteen annual ring-width chronologies from high elevation whitebark pine (Pinus albicaulis Engelm.) sites in the western Canadian Cordillera in order to assess the dendroclimatic potential of this long-lived tree species. The temperature signal within the chronologies is complex and strongly influenced by diverging trends in the summer temperature and ring-width records from across the region. A first differences transformation of the tree-ring and temperature records illustrates a loss of frequency coherence in growth response to summer temperatures following reduced radial growth in the 1950s. Prior to reduced growth, we note a positive association with summer temperatures for both first differenced (r_d = 0.60) and traditional (r = 0.50) records. Following reduced growth, the association at first differences is maintained (r_d = 0.49) whereas there is a change in the lower frequency component of tree growth response to summer temperatures (r = ?0.34). We suggest the cause of this reduced temperature sensitivity is related to the interaction between diurnal temperature and cloud cover patterns, the hydrological regime of snowpack, and site conditions which have been amenable to the initiation of moisture stress during the latter half of the 20th century. Reduced radial growth is coincident with the arrival of white pine blister rust (Cronatium ribicola J.C. Fisch. ex Raben) into the study region which suggests this infestation may be related to the observed reduction in radial growth. Whitebark pine has considerable potential for the field of dendroclimatology. Unfortunately, the decline of the species due to the combined effects of climate change, white pine blister rust, mountain pine beetle (Dendroctonus ponderosae Hopk.), and forest fire exclusion practices indicate this potential may remain unfulfilled.     

Reconstruction of heat index based on tree-ring width records of western Himalaya in India

To study climate variability/change, the tree-ring width index chronologies of two species (Cedrus deodara and Pinus roxburghii) of the western Himalaya was determined. The first principal component (PC1) prepared using the three-site tree-ring width chronologies of the western Himalaya was found to be negatively correlated with the heat index and positively with the Palmer Drought Severity Index (PDSI) and moisture index from February to May as representative of the regional climate. The correlation coefficient of PC1 with the heat index, PDSI, and moisture index for the period 1901–1988 was estimated to be −0.60, 0.37, and 0.59, respectively, which were highly significant at 0.1% level. The result shows that increasing the heat index may enhance transpiration and evaporation over the western Himalaya, which may cause insufficient moisture at the root zone of the trees. Based on the tree-ring data, the heat index of spring season (February–May) was reconstructed back to AD 1839. The reconstructed heat index showed the longest warm periods during 1952–1963 and 1966–1976 in the 20th century.     

Climate-growth relationships for Rocky Mountain juniper (Juniperus scopulorum Sarg.) on the volcanic badlands of western New Mexico,USA

We sampled Rocky Mountain junipers (RMJ) to produce a multi-century tree-ring chronology from a relict lava flow, the Paxton Springs Malpais (PAX), in the Zuni Mountains of western New Mexico. Our objective was to assess crossdating potential for RMJ growing on the volcanic badlands of the region, investigate potential relationships between climate and RMJ growth, and investigate temporal variability in relationships identified between climate and RMJ growing at our site. We hypothesized that, similar to other drought stressed-conifers growing on the lava flows, RMJ responds to climate factors that influence and indicate moisture availability. We found a high average mean sensitivity value (0.53), which indicated the PAX chronology exhibited enough annual variability to capture fluctuations in environmental conditions. The average interseries correlation (0.74) indicated confident crossdating and a significant association of annual growth among trees within the stand. The positive correlation between the PAX chronology and total precipitation for the local water year was significant (r = 0.53; P < 0.001). Significant positive correlations also were identified between monthly PDSI, monthly total precipitation, and RMJ radial growth. Analyses of temporal stability indicated that the positive relationship between RMJ growth at the PAX site and monthly PDSI was the most stable relationship during the period of analysis (1895–2007). More importantly, we identified a unique inverse relationship between radial growth and monthly mean temperature during periods of the preceding year and current growing year, the first such finding of a strong temperature response for a low-mid elevation tree species in the American Southwest. Our results confirm that RMJ samples collected on the Paxton Springs Malpais are sensitive to climate factors that affect moisture availability, further suggesting that RMJ may be suitable for use in dendroclimatic research at additional locations across the broad distribution of the species.     

Process-based modeling of tree-ring formation and its relationships with climate on the Tibetan Plateau

Response of climate warming on tree-ring formation has attracted much attention during recent years. However, most studies are based on statistical analysis, lacking understanding of tree-physiological processes, especially in the mountainous regions of the Tibetan Plateau (TP). Herein, we firstly use an updated new version of the tree-ring process-based Vaganov-Shashkin model (VS-oscilloscope) to simulate tree-ring formation and its relationships with climate factors during the past six decades. Our analyses covered 341 sampled trees growing within elevations ranging from 2750 to 4575 m a.s.l. at five sampling sites across the TP. Simulated tree-ring width series are significantly (p < 0.01) correlated with actual tree-ring width chronologies during their common interval periods. Starting dates of tree-ring formation are determined by temperature at all five sampling sites. After the initiation of tree stem cambial activity, soil moisture content has a significant effect on tree radial growth. Ending dates of cambial activity are driven by temperature over the whole study region. Simulated results indicate differences between wide and narrow tree-rings are mostly induced by soil moisture content, especially during the first half of the growing season, when effects from temperature variations are minor. Interestingly, we detected significantly (p < 0.001) increased relative growth rates due to higher soil moisture content after the year 1985 at the five sampling sites. However, the variability of mean relative growth rates due to temperature is negligible before and after that. Based on the successful application of VS-oscilloscope modeling on the high-elevation tree stands on the TP, our study provides a new perspective on tree radial growth process and their varying relationships to climate factors during the past six decades.     

气候变暖抑制西藏拉萨河大果圆柏树木生长

西藏拉萨河作为雅鲁藏布江最大的支流,近几十年气温已显著上升,将可能从不同的程度上影响流域内植被的生长动态。以拉萨河流域主要分布的树种—大果圆柏(Sabina tibetica)为研究对象,采用树木年轮学的方法对大果圆柏进行了年轮采样和处理,建立了树木年表,探讨了大果圆柏过去的生长动态特征,并用相关分析、偏相关分析和滑动相关分析的方法分析了不同气候因子与树木年轮宽度指数的关系。研究结果表明,大果圆柏树木年轮宽度指数与前一年6—10月和当年3—7月的降水、相对湿度和帕默尔干旱指数(PDSI)呈显著的正相关关系,而与前一年6—9月和当年3—8月的平均温度和平均最高温度以及当年5—7月的平均最低温度均呈显著的负相关关系,表明了气候变暖引起的干旱胁迫是导致近几十年来大果圆柏树木径向生长下降的主要原因。在未来气候变暖背景下,拉萨河大果圆柏林将可能出现生长下降,甚至死亡的现象,将潜在驱动区域森林减少。     

Common tree growth anomalies over the northeastern Tibetan Plateau during the last six centuries: implications for regional moisture change

The world's hydrological cycle is believed to intensify with global warming, yet current climate models have only a limited ability to assess moisture responses at regional scales. Tree-ring records are a valuable source of information for understanding long-term, regional-scale moisture changes, particularly for large regions such as the Tibetan Plateau (TP), where the observational data are short and sparse. Here, we present a new ring-width chronology developed from Qilian Juniper ( Sabina przewalskii ) wood at two sites on the northeastern TP. This chronology, combined with others from the same region, demonstrates that tree growth anomalies are linked to regional late spring to early summer moisture availability. Although late monsoon season precipitation in the study area decreased during recent decades, tree growth continued to increase due to persistent moisture availability in the early monsoon season. Comparison with global sea surface temperatures (SSTs) indicates that early (late) monsoon season precipitation is closely related to tropical Pacific (Indian Ocean) SSTs, suggesting a possible seasonal shift in the dominant moisture source area for monsoonal precipitation over the northeastern TP. It is further shown that there is a very high degree of coherency regarding low-frequency tree growth anomalies over the northeastern TP during the last six centuries. The most prominent drought epoch occurred during ca. 1450–1500, which may have been caused by a significant decrease in the thermal gradient between the Eurasian continent and the tropical oceans. A persistent tree growth increase since the 1880s is coincident with global warming, suggesting an intensified early monsoon season moisture regime in the study area.     

Abies spectabilis shows stable growth relations to temperature,but changing response to moisture conditions along an elevation gradient in the central Himalaya

A better understanding of growth-climate responses of high-elevation tree species across their distribution range is essential to devise an appropriate forest management and conservation strategies against adverse impacts of climate change. The present study evaluates how radial growth of Himalayan fir (Abies spectabilis D. Don) and its relation to climate varies with elevation in the Manaslu Mountain range in the central Himalaya. We developed tree-ring width chronologies of Himalayan fir from three elevational belts at the species’upper distribution limit (3750−3900 m), in the middle range (3500−3600 m), and at the lower distribution limit (3200−3300 m), and analyzed their associations with climatic factors. Tree growth of Himalayan fir varied synchronously across elevational belts, with recent growth increases observed at all elevations. Across the elevation gradient, radial growth correlated positively (negatively) with temperature (precipitation and standardized precipitation-evapotranspiration index, SPEI-03) during the summer (July to September) season. However, the importance of summer (July to September) temperatures on radial growth decreased with elevation, whereas correlations with winter (previous November to current January) temperatures increased. Correlations with spring precipitation and SPEI-03 changed from positive to negative from low to high elevations. Moving correlation analysis revealed a persistent response of tree growth to May and August temperatures. However, growth response to spring moisture availability has strongly increased in recent decades, indicating that intensified spring drought may reduce growth rates of Himalayan fir at lower elevations. Under sufficient moisture conditions, increasing summer temperature might be beneficial for fir trees growing at all elevations, while trees growing at the upper treeline will take additional benefit from winter warming.     

Polymorphisms of the NOS3 gene and risk of myocardial infarction in the Tunisian population

Controversial results regarding the association of eNOS gene (NOS3) polymorphisms with myocardial infarction (MI) have been reported. This study investigated the relationship of the −786T>C (rs2070744), 894G>T (rs1799983) and 4a4b polymorphisms of the NOS3 gene with the presence of MI in the Tunisian population. In addition, we also examined the association of NOS3 gene haplotypes with MI in Tunisian subjects.A total of 303 patients with MI and 225 controls were included in the study. The 894G>T and −786T>C single nucleotide polymorphisms were analyzed by PCR-RFLP, and 4a4b polymorphism just for PCR.There was significant linkage disequilibrium between the three NOS3 polymorphisms (p < 0.0001). The genotype distribution and allele frequency of NOS3 4a4b, but not −786T>C and 894G>T, polymorphism was significantly different between MI patients and controls. The univariate logistic regression analysis showed a significant association of the 4a4b polymorphism and MI according to co-dominant, dominant and recessive models (co-dominant model OR: 4.38, 95%CI: 1.24–15.41; p = 0.021, dominant model OR: 1.66, 95%CI: 1.14–2.42); p = 0.007, and recessive model OR: 3.85, 95%CI: 1.10–13.47; p = 0.035). The multivariate analysis, adjusted for traditional cardiovascular risk factors, revealed that the NOS3 4a4a genotype was an independent predisposing factor to MI, according to the models considered. In addition, a haplotype 7 (C-T-4a), (OR = 12.05, p = 0.010) was a risk factor of MI after controlling for classical risk factors.These finding suggest that the 4a4b polymorphism of the NOS3 gene was associated with MI in Tunisian patients.     

Spatio-temporal growth variability of three Pinus species of Northeast Himalaya with relation to climate

This research aimed to evaluate spatio-temporal growth variability of three Pinus species viz. Pinus kesiya (Khasi pine), Pinus merkusii (Merkus pine) and Pinus wallichiana (Blue pine) along with the existence of species differentiation among the taxa in northeast India. Several statistical analyses were used, namely Pearson correlation and multivariate approaches involving UPGMA Cluster Analysis; ordination methods by Principal Component Analysis (PCA) and Non-metric multidimensional scaling (NMDS) on tree-ring width chronologies from 13 sites. The tree growth-climate relationships were assessed with both correlation and bootstrap response function using regional climate datasets of each sampling site prepared by averaging the nearest grid points of 0.5 × 0.5° of CRU TS-2.1 climate dataset. Pronounced species differentiation in the growth pattern among the three Pinus taxa was inferred. The observed spatio-temporal variability revealed inter-species tree growth variations were not uniform suggesting no common factor influenced the radial tree growth in this region, which may be related to anthropogenic impact or non-climatic factors. The tree growth-climate relationship showed that climatic factors limiting the radial growth of Pine are mostly similar for intra-species but diverse in inter-species. This study is extremely relevant in terms of species and site selection for the long-term climate reconstruction and forest management in the Northeast Himalaya.     

Effects of water potential on mycelial growth,sclerotial production,and germination of Rhizoctonia solani from potato

The effects of osmotic and matric potential on mycelial growth, sclerotial production and germination of isolates of Rhizoctonia solani [anastomosis groups (AGs) 2-1 and 3] from potato were studied on potato dextrose agar (PDA) adjusted osmotically with sodium chloride, potassium chloride, glycerol, and matrically with polyethylene glycol (PEG) 6000. All isolates from AGs 2-1 and AG-3 exhibited fastest mycelial growth on unamended PDA (−0.4 MPa), and growth generally declined with decreasing osmotic and matric potentials. Growth ceased between −3.5 and −4.0 MPa on osmotically adjusted media, and at −2.0 MPa on matrically adjusted media, with slight differences between isolates and osmotica. Sclerotium yield declined with decreasing osmotic potential, and formation by AG 2-1 and AG-3 isolates ceased between −1.5 and −3.0 MPa and −2.5 and −3.5 MPa, respectively. On matrically adjusted media, sclerotial formation by AG 2-1 isolates ceased at −0.8 MPa, whereas formation by AG-3 isolates ceased at the lower matric potential of −1.5 MPa. Sclerotial germination also declined with decreasing osmotic and matric potential, with total inhibition occurring over the range −3.0 to −4.0 MPa on osmotically adjusted media, and at −2.0 MPa on matrically adjusted media. In soil, mycelial growth and sclerotial germination of AG-3 isolates declined with decreasing total water potential, with a minimum potential of −6.3 MPa permitting both growth and germination. The relevance of these results to the behaviour of R. solani AGs in soil and their pathogenicity on potato is discussed.     

Ring widths of Rhododendron shrubs reveal a persistent winter warming in the central Himalaya

Himalayan Mountains provide unique opportunities for the extension of shrub-ring based dendroclimatology beyond the upper tree limit. However, little is known about limiting climate factors of shrub growth under harsh environmental conditions. We established a new ring-width chronology of a Himalayan shrub rhododendron (Rhododendron campanulatum D. Don) at the upper Krummholz treeline in the Mt. Gaurishankar massif, central Himalaya, Nepal. Bootstrapped correlation analysis showed positive relationships between radial growth and temperatures of all months from previous November to current October. Correlations were the highest with winter (December-February) minimum temperature (r = 0.781, p < 0.001), indicating that radial growth of R. campanulatum is strongly sensitive to winter minimum temperature. The linear regression model explained 61 % of the actual winter minimum temperature variance during the calibration period 1960–2013. Periods of low and high minimum winter temperatures in the central Himalaya were consistent with cool and warm episodes found by other regional winter temperature reconstructions from the Himalayas and the Tibetan Plateau. Spatial correlation analysis with land surface temperatures revealed the spatial representativeness of our reconstruction for a larger geographical territory over the Himalayas and the Tibetan Plateau. Furthermore, winter temperature in the central Himalaya is teleconnected with the December-February India-Burma trough. The persistent increasing winter temperature in recent decades in the central Himalaya coincides with continental-scale warming. Alpine vegetation in humid regions of the Himalayas may benefit from winter warming via an earlier start and extension of the growing season, as long as moisture availability is sufficient.     

Effects of lambing season,sex and birth type on growth performance in Norduz lambs

The aim of this study was to evaluate effects of two production systems (spring and winter), sex and birth type on growth performance in Norduz lambs. Data were collected using 103 and 140 lambs born during the winter and spring, respectively. Lambs born in the winter were heavier (P < 0.01) than those born in the spring at birth, 90 and 180 days of age by 0.5, 1.6 and 1.7 kg, respectively. Ram lambs were heavier (P < 0.01) than ewe lambs at birth, 90 and 180 days of age by 0.5, 1.0 and 2.3 kg, respectively, while lambs born as singles were heavier (P < 0.01) than lambs born as twins at birth, 90 and 180 days of age by 0.9, 1.6 and 2.3 kg, respectively. Lambs born in the winter recorded a higher (P < 0.01) pre-weaning ADG (15 g/day) than spring-born lambs, while ram lambs recorded a higher (P < 0.01) pre-weaning ADG (11 g/day) than ewe lambs. The effect of birth type was not significant on pre-weaning ADG. The influence of lambing season and sex were also not significant on post-weaning ADG. Lambs born as singles recorded a higher (P < 0.01) post-weaning ADG (16 g/day) than lambs born as twins. Results suggest the winter season to give rise to heavier lambs at weaning and post-weaning and suggest lambs born in different seasons to have distinctly different growth patterns. The data also confirm that the influence of sex and type of birth on growth to be very important and to be take into account sheep production.     

Intra-annual radial growth of Schrenk spruce (Picea schrenkiana Fisch. et Mey) and its response to climate on the northern slopes of the Tianshan Mountains

Schrenk spruce (Picea schrenkiana Fisch. et Mey.) is widely distributed in the Tianshan Mountains. In this study, four Schrenk spruce trees were continuously monitored with dendrometers from 27 April to 30 September 2014 on the northern slopes of the Tianshan Mountains in northwest China. The goal of this monitoring study was to determine the main growing season of Schrenk spruce and to analyze intra-annual radial growth variability and its relation to daily meteorological factors. Our studies have shown that the critical growing season of Schrenk spruce is from late May to late July and that the rapid growth stage is from mid-June to early July. Meanwhile, in the growing season, changes in the radial growth of Schrenk spruce were negatively correlated with daily temperature, evaporation, sunshine hours and vapor pressure deficit (VPD), and were positively correlated with precipitation and relative humidity (RH). The correlation coefficient between radial growth and RH can be as high as 0.750 (Pearson, p < 0.0001, n = 60). Dates in which precipitation occurred corresponded to periods of rapid growth. The results of the climate-growth analysis show that changes in radial growth reflect the effect of water stress on tree growth, whether or not the changes are positively or negatively correlated with the above climatic factors. This indicates that moisture plays a major role in the growth of Schrenk spruce. We suggest that precipitation between late May to late June is a limiting factor for radial growth of Schrenk spruce on the northern slopes of the Tianshan Mountains.     

Gradual expansion of moisture sensitive Abies spectabilis forest in the Trans-Himalayan zone of central Nepal associated with climate change

Population structure and tree recruitment dynamics in the natural treeline ecotone of high mountains are strong indicators of vegetation responses to climate. Here, we examined recruitment dynamics of Abies spectabilis across the treeline ecotone (3439–3638 m asl) of Chimang Lekh of Annapurna Conservation Area in the Trans-Himalayan zone of central Nepal. Dendrochronological techniques were used to establish stand age structure by ring counts of adults, and by terminal bud scar count for seedlings and saplings. The results showed abundant seedling recruitment, higher regenerative inertia and colonization with a consistent range shift of the A. spectabilis treeline. The upward expansion of this sub-alpine treeline was found to be driven by a strong dependence of seedling recruitment and radial growth on snowmelt and precipitation as temperatures rise. The radial growth of A. spectabilis at the alpine timberline ecotone (ATE) and closed timberline forest (CTF) showed sensitivity to spring season (March–May) climate. Tree ring indices of CTF showed a strong positive correlation with spring and annual precipitation, and a significant negative correlation with spring and annual temperature, however, moisture sensitivity was less strong at ATE than CTF.     

Climatic potential of δ18O of Abies spectabilis from the Nepal Himalaya

A 50-year tree-ring δ¹⁸O chronology of Abies spectabilis growing close to the tree line (3850 m asl) in the Nepal Himalaya is established to explore its dendroclimatic potential. Response function analysis with ambient climatic records revealed that tree-ring δ¹⁸O is primarily governed by rainfall during the monsoon season (June–September), and the regression model accounts for 35% of the variance in rainfall. Extreme dry years identified in instrumental weather data are detected in the δ¹⁸O chronology. Further, tree-ring δ¹⁸O is much more sensitive to rainfall fluctuations than other tree-ring parameters such as width and density typically used in dendroclimatology. Correlation analyses with Niño 3.4 SST reveal time-dependent behavior of ENSO–monsoon relationships.     

5种干旱指数在吉林省农业干旱评估中的适用性

干旱是对吉林省农业生产影响最大的气象灾害,干旱指数能够表征农业旱情,但不存在普遍适用的干旱指数,开展干旱指数在吉林省农业干旱评估中的适用性研究具有重要的现实意义.基于1961-2014年吉林省的逐日气象数据、土壤水分资料和历史旱情统计信息,选取典型干旱年和典型干旱区,评估了降水量距平百分率(PA)、相对湿润度指数(MI)、作物水分亏缺距平指数(CWDIa)、帕默尔干旱指数(PDSI)和气象干旱综合指数(MCI)共5种干旱指数在吉林省农业干旱评估中的适用性.结果表明:对于1997和2007年两个典型旱年,MI对农业旱情的评价结果与旱情记录较一致,PA和MCI次之.对于吉林省典型旱区(西部通榆、中部梨树、东部和龙),MI和PDSI对农业旱情的评估较好.在农作物生长季,PA较适用于评价4、7和8月的旱情,MI较适用于评价4、5和9月的旱情,CWDIa只适用于评价5月的旱情,PDSI对6-9月的旱情均有一定的指示作用,MCI适用于5-8月的农业干旱过程评估.从农业干旱发生范围来看,MI、PDSI和MCI较适用于评估吉林省西部旱情,PDSI较适用于评价吉林省中部旱情,PA、PDSI和MCI较适用于评估吉林省东部旱情.     

CO2 fertilization and enhanced drought resistance in Greek firs from Cephalonia Island,Greece

Growth–climate relationships were investigated in Greek firs from Ainos Mountain on the island of Cephalonia in western Greece, using dendrochronology. The goal was to test whether tree growth is sensitive to moisture stress, whether such sensitivity has been stable through time, and whether changes in growth–moisture relationships support an influence of atmospheric CO₂ on growth. Regressions of tree‐ring indices (ad 1820–2007) with instrumental temperature, precipitation, and Palmer Drought Severity Index (PDSI) indicate that growth is fundamentally limited by growing‐season moisture in late spring/early summer, most critically during June. However, this simple picture obscures a pattern of sharply evolving growth–climate relationships during the 20th century. Correlations between growth and June temperature, precipitation, and PDSI were significantly greater in the early 20th century but later degraded and disappeared. By the late 20th–early 21st century, there remains no statistically significant relationship between moisture and growth implying markedly enhanced resistance to drought. Moreover, growth experienced a net increase over the last half‐century culminating with a sharp spike in ad 1988–1990. This recent growth acceleration is evident in the raw ring‐width data prior to standardization, ruling out artifacts from statistical detrending. The vanishing relationship with moisture and parallel enhancement of growth are all the more notable because they occurred against a climatic backdrop of increasing aridity. The results are most consistent with a significant CO₂ fertilization effect operating through restricted stomatal conductance and improved water‐use efficiency. If this interpretation is correct, atmospheric CO₂ is now overcompensating for growth declines anticipated from drier climate, suggesting its effect is unusually strong and likely to be detectable in other up‐to‐date tree‐ring chronologies from the Mediterranean.     

Soil and tree chemistry reflected the cumulative impact of acid deposition in Pinus banksiana and Populus tremuloides stands in the Athabasca oil sands region in western Canada

The spatial variability of soil chemistry and Ca/Al ratios of soil solution and fine roots were investigated in jack pine (Pinus banksiana) and trembling aspen (Populus tremuloides, aspen) stands to assess the impact of chronic acid deposition on boreal forest ecosystems in the Athabasca oil sands region (AOSR) in Alberta, Canada. Available SO₄²⁻ (as the sum of soluble and adsorbed SO₄²⁻) accumulated in the soil near tree boles of both species, reflecting the influence of canopy intercepted SO₄²⁻. In jack pine stands, pH and soluble base cation concentrations decreased towards tree boles due to increased SO₄²⁻ leaching; the reverse was found in aspen stands due to deposition of base cations leached from the canopy. As a result, Ca/Al ratios in the soluble fraction in soils near jack pine boles were 5–20 times lower than that near aspen boles. The Ca/Al ratio did not reach the critical limits of 1.0 for soil solution (ranged from 1.0 to 4.1) or 0.5 for fine roots (0.7–7.9) in the studied watersheds. However, Alⁿ⁺ concentrations in the soil solution ranged from 0.2 to 4.1 mg L⁻¹ in NE7 and from 0.1 to 8.5 mg L⁻¹ in SM8 that can inhibit the growth of white spruce (Picea glauca) seedlings that commonly succeed aspen in upland sites in the AOSR. We suggest that the spatial variation caused by tree canopies/stems will affect forest regeneration and the effect of acid deposition on forest succession in the AOSR should be further studied.