模拟氮沉降对北京东灵山辽东栎林树木生长的影响

传统的元素限制模型认为氮是温带森林生长的限制元素, 不过该结论更多是从地上生物量以及群落水平进行阐述, 忽视了不同物种以及不同径级树木对外源氮的响应差异。辽东栎(Quercus wutaishanica)林是华北地区常见的森林类型, 该研究以北京东灵山辽东栎林为研究对象, 通过设置3个氮添加水平的实验, 即对照CK (0 kg·hm ^-2·a ^-1), N50 (50 kg·hm ^-2·a ^-1)和N100 (100 kg·hm ^-2·a ^-1), 模拟氮沉降对群落和物种水平以及不同径级树木生长的影响。经过7年氮添加, 实验结果显示: 物种水平上, 氮添加明显促进了优势树种辽东栎的生长; 群落水平上, 树木生长随氮浓度增加有不断上升趋势, 但统计学差异不显著; 氮添加显著抑制了辽东栎以及群落内小径级(3-10 cm)树木生长, 中(10-20 cm)、大径级(>20 cm)树木生长随氮沉降水平增加呈上升趋势, 但统计学差异不显著。表明氮是辽东栎以及温带森林树木生长的限制元素; 不同径级的辽东栎和群落内其他植物对氮添加响应不一致, 氮添加抑制了小径级树木生长, 中、大径级树木生长对氮添加响应不明显。     

Tree mineral nutrition is deteriorating in Europe

The response of forest ecosystems to increased atmospheric CO₂ is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂ emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.     

华北低丘山区栓皮栎生态系统氧同位素日变化及蒸散定量区分

利用稳定同位素技术对华北低丘山区栓皮栎生态系统氧同位素日变化及蒸散定量区分进行研究,为华北低丘山区森林生态系统水汽交换研究提供基础。试验采用离轴积分腔输出光谱技术(OA-ICOS)连续测定生态系统不同高度水汽浓度和δ18O值,同时采用真空提取和液态水同位素分析仪测定枝条和土壤的δ18O值。结果显示,4个晴天中大气水汽浓度日变化复杂,变化趋势差异大,而δ18O日变化均成高-低-高的"V"型变化,最小值出现在12:00—18:00。Keeling方程在10:00—12:00的相关系数R2均大于0.71,方程达到极显著水平,表明此时段蒸腾速率较高,满足植物蒸腾的同位素稳定态假设。利用Keeling方程估算的栓皮栎生态系统δET值有相似的低-高-低日变化,与大气的δv值变化趋势相反。同位素分割结果显示栓皮栎生态系统中蒸腾占蒸散比例日变化呈现低-高-低的趋势,10:00—14:00蒸腾占蒸散比例达到90%以上,尽管6:00—10:00和14:00—18:00的蒸腾占蒸散比例下降,但平均值仍高达69.38%,表明华北低丘山区栓皮栎生态系统的蒸散主要来源于植物蒸腾。     

13种栎属植物叶片的气孔特征及其相关性分析和分类学意义

以13种栎属(Quercus Linn.)植物〔包括产自辽宁省的槲栎组(Sect. Quercus)8种和麻栎组(Sect. Aegilops)2种以及引自北美洲的沼生栎组(Sect. Erythobalanus)2种和引自波兰的白栎组(Sect. Lepidabalanus)1种〕为试材,观察了这些种类叶片的气孔形态,并分析了气孔器和气孔的形态参数,还对各形态参数间的相关性进行了分析;在此基础上,对13种栎属植物进行了聚类分析。结果表明：栎属植物叶片的气孔仅分布于下表皮;气孔器排列属无规则型;气孔保卫细胞呈肾形,内壁加厚;气孔下陷,呈椭圆形或狭长椭圆形。供试种类的气孔和气孔器的形态参数差异明显,变异系数差异较大;气孔器的长轴长度、短轴长度和面积分别为18.24~27.46μm、14.63~23.18μm和221.56~501.70μm2,变异系数分别为7.73%~15.90%、7.10%~17.44%和14.13%~32.73%,气孔器指数为0.73~0.85;气孔的长轴长度、短轴长度、面积和密度分别为8.69~15.41μm、1.94~8.49μm、15.15~104.93μm2和462.32~984.44 mm-2,变异系数分别为12.03%~22.17%、13.65%~34.10%、27.95%~54.13%和8.10%~16.99%,气孔指数为0.22~0.57;总体上,按照多数气孔器和气孔参数从大至小的变化趋势依次排序为沼生栎组、白栎组、麻栎组、槲栎组。相关性分析结果表明：供试种类的气孔密度与气孔器和气孔的长轴及短轴长度均呈极显著(P<0.01)负相关;气孔器面积与气孔器指数和气孔指数分别呈极显著和显著(P<0.05)正相关;气孔面积与气孔器和气孔的长轴和短轴长度、气孔器指数和气孔指数呈极显著正相关,但与气孔密度呈显著负相关。聚类分析结果表明：在欧氏距离10处可将13种栎属植物分为3类,第Ⅰ类包含槲栎组的8种,第Ⅱ类包含麻栎组和白栎组的3种,第Ⅲ类包含沼生栎组的2种。研究结果显示：栎属植物叶片的气孔特征具有一定的稳定性,可作为栎属植物组间分类及亲缘关系分析的依据之一。     

秦岭南坡锐齿栎次生林空间结构特征分析

该研究采用坐标定位方法对秦岭南坡不同坡向锐齿栎次生林样地内胸径DBH≥5cm的乔木进行调查,记录树种名称、坐标、胸径、高度、冠幅、生长状况等因子,运用角尺度、大小比数和混交度3个指数分析不同坡向锐齿栎次生林的空间结构,探寻不同坡向锐齿栎林空间结构的形成和差异。结果显示:(1)调查样地内物种多样性丰富,锐齿栎重要值最大,长势良好,占据主要生态空间。(2)两种坡向中,角尺度取值为0.5的个体数均过半,表明随机分布是锐齿栎次生林的主要分布方式。(3)优势木、亚优势木、中庸木、劣态木和绝对劣态木所占比重均为20%左右,表明林木大小差异不明显,在空间结构单元中,林木较稳定,阳坡优势木个体数高于阴坡。(4)两种坡向中,混交度取值大于0.5林木个体分别为84%和73%,表明多数林木个体处于中度、强度和极强度混交状态。研究表明,秦岭南坡锐齿栎次生林聚集度不高、混交良好、分化程度较高,锐齿栎种群优势度明显,林分整体暂时处于相对稳定状态。     

A new positive relationship between pCO2 and stomatal frequency in Quercus guyavifolia (Fagaceae): a potential proxy for palaeo-CO2 levels

Background and Aims The inverse relationship between atmospheric CO₂ partial pressure (pCO₂) and stomatal frequency in many species of plants has been widely used to estimate palaeoatmospheric CO₂ (palaeo-CO₂) levels; however, the results obtained have been quite variable. This study attempts to find a potential new proxy for palaeo-CO₂ levels by analysing stomatal frequency in Quercus guyavifolia (Q. guajavifolia, Fagaceae), an extant dominant species of sclerophyllous forests in the Himalayas with abundant fossil relatives.Methods Stomatal frequency was analysed for extant samples of Q. guyavifolia collected from17 field sites at altitudes ranging between 2493 and 4497 m. Herbarium specimens collected between 1926 and 2011 were also examined. Correlations of pCO₂–stomatal frequency were determined using samples from both sources, and these were then applied to Q. preguyavaefolia fossils in order to estimate palaeo-CO₂ concentrations for two late-Pliocene floras in south-western China.Key Results In contrast to the negative correlations detected for most other species that have been studied, a positive correlation between pCO₂ and stomatal frequency was determined in Q. guyavifolia sampled from both extant field collections and historical herbarium specimens. Palaeo-CO₂ concentrations were estimated to be approx. 180–240 ppm in the late Pliocene, which is consistent with most other previous estimates.Conclusions A new positive relationship between pCO₂ and stomatal frequency in Q. guyavifolia is presented, which can be applied to the fossils closely related to this species that are widely distributed in the late-Cenozoic strata in order to estimate palaeo-CO₂ concentrations. The results show that it is valid to use a positive relationship to estimate palaeo-CO₂ concentrations, and the study adds to the variety of stomatal density/index relationships that available for estimating pCO₂. The physiological mechanisms underlying this positive response are unclear, however, and require further research.     

云居山栓皮栎群落特征及多样性研究

栓皮栎群落是我国暖温带和亚热带落叶阔叶林的重要森林群落类型之一,也是赣北珍稀森林群落之一,在森林演替和植物资源利用中占有重要的地位。通过对江西云居山栓皮栎(Quercus variabilis)群落进行实地调查,采用区系分析、生活型谱分析、物种多样性和双向聚类等方法对其群落特征进行了研究,发现云居山自然保护区栓皮栎群落结构简单,层次明显,多样性程度不高。物种调查及区系研究结果显示,云居山栓皮栎群落维管束植物共计43科56属70种,植物区系主要以泛热带、东亚及北美间断、北温带分布为主,表现出从温带区系向热带区系过渡的特征;生活型谱以高位芽植物为主(占70%),其他生活型相对较少,反映出中亚热带森林以高位芽植物为主的特点。群落物种丰富度、多样性指数均为乔木层小于灌木层和草本层,均匀度指数分析表明,乔木层为聚集分布、灌木层和草本层为均匀分布。双向聚类分析表明,调查的5个样地均为栓皮栎群落,以乔木层物种多度可将5个样地分为3类,组成群落的24个主要物种可分为10类。     

Fire history of a prairie/forest boundary: more than 250 years of frequent fire in a North American tallgrass prairie

Questions: Most modern fire‐prone landscapes have experienced disruptions of their historic fire regimes. Are the primary tallgrass prairies of the Flint Hills reflective of a history of continuous fire occurrence? Did fire frequency, severity, size and seasonality change in connection with changes in land use? Has fire occurrence been related to drought conditions? Location: Edges of Cross Timbers forest stands at the Tallgrass Prairie Preserve (TGPP) in the Flint Hills of Osage County, Oklahoma, USA. Methods: Cross‐sections of 76 Quercus stellata were collected from Cross Timbers stands at or near the grassland edge in the TGPP. Dendrochronological methods were used to identify years of formation for tree rings and fire scars. Superposed epoch analysis was used to evaluate the effect of drought conditions on fire occurrence. Results: Fires were recorded in 46.6% of the years between 1729 and 2005. In 41 cross‐sections at one site, the mean fire interval between 1759 and 2003 was 2.59 years, with fire interval decreasing from a mean fire interval of 3.76 years in the early part of the record to 2.13 years in modern times. No extended periods without fire were recorded in the study area. Drought conditions had no significant effect on fire occurrence. Conclusions: In contrast with many fire‐prone landscapes worldwide, the prairies of the Flint Hills have experienced no recent fire suppression or exclusion. Changes in fire frequency mark transitions in land use, primarily from being traditionally used by Native Americans to being managed for cattle production.