湘南典型次生林粗木质残体生物量、碳储量和养分特征

对九龙江森林公园次生常绿阔叶林粗木质残体(CWD)进行量化研究,了解亚热带典型次生林CWD的本底数据。以九龙江森林公园典型天然次生林中的6个20m×20m的标准样地为对象,调查并分析样地内不同分解等级CWD的生物量、碳储量和养分特征变化。九龙江森林公园亚热带典型次生林的CWD储量在2.8—30.4t/hm~2之间,碳储量在6.10—6.75t/hm~2之间,大量营养元素(N、P、K、 Ca、 Mg)含量相对稳定,化学计量变化不显著,微量营养元素中Pb与Cd元素含量随着分解等级的增加而增加。九龙江森林公园亚热带典型次生林的CWD储量在亚热带常绿阔叶林中处于中等水平,CWD主要以分解中后期的倒木为主,反映出该次生林处于中幼龄林阶段,具有较高的碳储量,养分含量相对稳定,并表现出Pb与Cd在CWD中积累的现象,在中度分解和重度分解的CWD中Pb含量分别增加了62.65%和69.88%,Cd含量则分别增加了33.33%和100%,其内在机理有待进一步深入研究。研究结果有助于进一步了解CWD如何参与森林生态系统养分循环、重金属积累等生态过程,比较不同林分干扰历史下CWD储量、分布及养分特征的异质性...     

表施和混施污泥对团花根系生长的影响

林地利用被认为是污泥资源化利用的重要方式,但施用污泥对林木根系生长的影响报道较少。本研究通过根箱试验,分析表施和混施10%污泥对速生树种团花不同土层根系形态、土壤pH值和电导率动态变化及根系重金属含量的影响,并拟合土壤pH值、电导率和根系重金属含量与根长的关系。结果表明: 与不施污泥(对照)相比,混施污泥显著抑制了团花根长、根表面积和根体积增长,混施污泥120和240 d后,0～20 cm土层总根长分别为不施污泥的76.9%和67.4%;表施污泥对团花根长和根表面积的影响不显著,但显著提高了根体积。混施污泥显著提高了土壤pH值和电导率及根系重金属含量,混施污泥0～20和20～40 cm土层根系镉含量分别是不施污泥的11.5和10.0倍。线性回归拟合分析显示,不同处理0～20 cm土层的电导率与根长均呈显著负相关;表施和混施污泥根系镉含量与根长呈极显著负相关。上述结果表明,混施污泥抑制了团花根系生长,这可能是由于混施污泥提高了土壤电导率和根系镉含量所致,而表施污泥对团花根系生长的作用不明显。     

天童山阔叶木本植物叶片大小与叶脉密度及单位叶脉长度细胞壁干质量的关系

叶片大小是植物生态策略中的一个关键性状, 而叶脉是叶内主要的支撑和输导结构, 对叶片的生长发育具有重要的影响。该研究以天童山38种阔叶木本植物为研究对象, 以叶片面积、干质量和周长表征叶片大小, 采用标准化主轴估计(SMA)方法和系统发育独立比较(PIC)分析主脉密度、细脉密度和总叶脉密度, 以及各级叶脉单位长度的细胞壁干质量与叶片大小之间的关系, 拟从叶片内部结构和资源分配策略的角度探明叶片大小与叶脉结构之间的变化关系及生态学意义。研究结果显示: (1)叶片大小与主脉密度极显著负相关, 细脉密度以及总叶脉密度与叶片大小关系不显著, 表明叶片越小, 主脉密度越高, 而细脉密度与叶片大小无关; (2)单位主脉长度的细胞壁干质量与叶片大小极显著正相关, 单位细脉和总叶脉长度的细胞壁干质量与叶片大小的相关性均不显著, 表明随着叶片的增大, 单位主脉长度的细胞壁干质量显著增加, 而细脉的细胞壁干质量与叶片大小无关; (3)主脉密度与单位主脉长度的细胞壁干质量之间是斜率显著大于-1的负异速生长关系, 表明主脉密度随单位主脉长度的细胞壁干质量增加而显著下降, 两者之间存在权衡关系, 而单位细脉长度的细胞壁干质量与细脉密度关系不显著。上述结果表明, 与大叶片相比, 小叶中通常具有较高的主脉密度, 这不仅是叶片发育过程中叶形变化调控的结果, 也是单位叶脉长度的细胞壁干质量调控的结果, 单位叶脉长度的细胞壁干质量是导致叶片大小与主、细脉密度之间不同变化关系的直接因素。该研究结果为我们理解全球范围内叶片大小变化的生物地理分布模式以及植物对环境的适应策略提供了参考。     

古尔班通古特沙漠固定沙丘上白梭梭和梭梭的空间分布及种间关联性

为了探讨沙漠中固沙灌木种群共存和演替机制, 本文基于古尔班通古特沙漠东南缘固定沙丘上白梭梭(Haloxylon persicum)和梭梭(H. ammodendron)种群的地理位置和生长发育阶段信息(幼株、营养株、生殖株和死株), 采用点格局分析方法(g(r)函数)及Monte-Carlo随机模拟检验和零模型选取的方法, 分析了固沙灌木白梭梭和梭梭种群不同生长发育阶段在0-20 m尺度内的空间分布格局及种间关联性。结果表明: (1)两个种群在研究尺度范围内呈聚集分布, 随着尺度的增大, 其聚集强度逐渐减弱; (2)两个种群整体上呈负关联关系, 尺度越大负关联关系越显著; (3)白梭梭种群生长发育阶段相差越大, 个体间正关联关系越显著; 梭梭种群生长发育阶段越接近, 个体间正关联关系越显著; (4)两个种群中龄级较大的个体(如营养株、生殖株和死株)会对对方种群中龄级较小的幼株产生一定的抑制作用; 同时, 随着两个种群中个体的成长, 双方受到的抑制作用逐渐减弱, 主要表现为正关联和无关联。总体而言, 古尔班通古特沙漠固定沙丘白梭梭和梭梭种群的分布格局整体上为聚集分布, 随龄级增加聚集性减弱, 受生境异质性和扩散限制的影响明显。种间关系多为负相关, 种内不同生长发育阶段之间均为正关联关系。     

Regional Estimate of Nitric Oxide Emissions Following Woody Encroachment: Linking Imaging Spectroscopy and Field Studies

Woody encroachment, a spatially explicit process of land-cover change, is known to affect the biophysical and biogeochemical properties of ecosystems. However, little information is available on the impacts of woody encroachment on N oxide emissions from savanna regions. We combined hyperspectral remote sensing and field measurements to quantify spatial patterns and estimate regional fluxes of soil N oxide emissions as they covary with vegetation cover and soil type across a semiarid rangeland in north Texas. Soil nitric oxide (NO) emissions were highly correlated with Prosopis canopy cover, allowing the extrapolation of NO fluxes from hyperspectral observations of woody cover. NO emissions were highly variable, ranging from 0 to 550 kg NO-N km^–2 y^–1 across the region, with the lowest emissions from shallow clay soils and highest from deeper upland clay loams. An estimate of annual NO emissions based on remotely derived Prosopis cover, temperature, and precipitation was 160 kg NO-N km^–2 y^–1, almost twice that of the value derived from traditional averaging of field measurements. We conclude that relationships between NO emissions and remotely sensed structure and composition are advantageous for quantifying NO emissions at the regional scale. This study also provides new insight into the role of woody encroachment on biogeochemical processes that are highly variable and otherwise difficult to measure at the regional scale.     

森林粗死木质残体的概念及其分类

森林粗死木残体 (Coarse woody debris,CWD)在不同的文献中有不同的定义 ,没有通用而确切的概念用来描述 CWD,对研究结果的比较造成了很大障碍。 2 0世纪 90年代以来 ,随着景观生态学的发展 ,以及对 CWD生态功能的深入研究 ,国外的森林管理和研究机构 (例如 USDA Forest Service和 L TER)为了把 CWD放在区域以及景观尺度上进行比较 ,对 CWD的概念等进行了统一 ,将其直径标准由原来的≥ 2 .5 cm调整到≥ 10 cm,但是我国在此方面还没有与国际接轨 ,仍采用旧标准 (≥ 2 .5 cm ) ,这样的研究结果难于和国外进行比较 ,不利于我国 CWD的长期深入研究。另外 ,有关 CWD的分类一直以来也没有形成一个完整的分类系统 ,我国也缺少 CWD分类方法的介绍。鉴于以上情况 ,综合国内外近年来在 CWD方面的研究动态 ,综述了 CWD的概念和分类情况 ,并初步提出较综合的 CWD概念及其分类系统 ,以供相关研究者讨论和参考 ,为我国的 CWD研究起到推动作用     

北方森林土壤呼吸和木质残体分解释放出的CO2通量

北方森林因其面积大、土壤碳储量高以及对全球暖化响应敏感而在全球碳平衡和气候系统中起着至关重要的作用。土壤呼吸和木质残体分解释放出的 CO2 通量是北方森林生态系统输入大气圈的最主要的碳源。量化这个通量并深刻理解其中的机理过程 ,是评价和预测北方森林在全球变化中的作用必不可少的内容。综述了北方森林生态系统土壤呼吸和木质残体分解释放出的 CO2 通量随生态系统类型及环境条件而变化的一般格局以及自养呼吸和异氧呼吸在土壤表面 CO2 通量中的相对贡献 ;分析了影响北方森林土壤呼吸的主要生物物理因子 ;讨论了该领域研究存在的问题和今后的研究方向 ;并强调木质残体分解释放出的 CO2 通量虽然在以往的森林生态系统碳平衡研究中常被忽略 ,但在火灾频繁的北方森林中不容忽视     

Beringia as a glacial refugium for boreal trees and shrubs: new perspectives from mapped pollen data

Aim Beringia, far north‐eastern Siberia and north‐western North America, was largely unglaciated during the Pleistocene. Although this region has long been considered an ice‐age refugium for arctic herbs and shrubs, little is known about its role as a refugium for boreal trees and shrubs during the last glacial maximum (LGM, c. 28,000–15,000 calibrated years before present). We examine mapped patterns of pollen percentages to infer whether six boreal tree and shrub taxa (Populus, Larix, Picea, Pinus, Betula, Alnus/Duschekia) survived the harsh glacial conditions within Beringia. Methods Extensive networks of pollen records have the potential to reveal distinctive temporal–spatial patterns that discriminate between local‐ and long‐distance sources of pollen. We assembled pollen records for 149 lake, peat and alluvial sites from the Palaeoenvironmental Arctic Sciences database, plotting pollen percentages at 1000‐year time intervals from 21,000 to 6000 calibrated years before present. Pollen percentages are interpreted with an understanding of modern pollen representation and potential sources of long‐distance pollen during the glacial maximum. Inferences from pollen data are supplemented by published radiocarbon dates of identified macrofossils, where available. Results Pollen maps for individual taxa show unique temporal‐spatial patterns, but the data for each taxon argue more strongly for survival within Beringia than for immigration from outside regions. The first increase of Populus pollen percentages in the western Brooks Ranges is evidence that Populus trees survived the LGM in central Beringia. Both pollen and macrofossil evidence support Larix survival in western Beringia (WB), but data for Larix in eastern Beringia (EB) are unclear. Given the similar distances of WB and EB to glacial‐age boreal forests in temperate latitudes of Asia and North America, the widespread presence of Picea pollen in EB and Pinus pollen in WB indicates that Picea and Pinus survived within these respective regions. Betula pollen is broadly distributed but highly variable in glacial‐maximum samples, suggesting that Betula trees or shrubs survived in restricted populations throughout Beringia. Alnus/Duschekia percentages show complex patterns, but generally support a glacial refugium in WB. Main conclusions Our interpretations have several implications, including: (1) the rapid post‐glacial migration rate reported for Picea in western Canada may be over estimated, (2) the expansion of trees and shrubs within Beringia should have been nearly contemporaneous with climatic change, (3) boreal trees and shrubs are capable of surviving long periods in relatively small populations (at the lower limit of detection in pollen data) and (4) long‐distance migration may not have been the predominant mode of vegetation response to climatic change in Beringia.     

Forest Restoration in Urbanizing Landscapes: Interactions Between Land Uses and Exotic Shrubs

Preventing and controlling exotic plants remains a key challenge in any ecological restoration, and most efforts are currently aimed at local scales. We combined local‐ and landscape‐scale approaches to identify factors that were most closely associated with invasion of riparian forests by exotic shrubs (Amur honeysuckle [Lonicera maackii] and Tatarian honeysuckle [L. tatarica]) in Ohio, U.S.A. Twenty sites were selected in mature riparian forests along a rural–urban gradient (<1–47% urban land cover). Within each site, we measured percent cover of Lonicera spp. and native trees and shrubs, percent canopy cover, and facing edge aspect. We then developed 10 a priori models based on local‐ and landscape‐level variables that we hypothesized would influence percent cover of Lonicera spp. within 25 m of the forest edge. To determine which of these models best fit the data, we used an information‐theoretic approach and Akaike's information criterion. Percent cover of Lonicera was best explained by the proportion of urban land cover within 1 km of riparian forests. In particular, percent cover of Lonicera was greater in forests within more urban landscapes than in forests within rural landscapes. Results suggest that surrounding land uses influence invasion by exotic shrubs, and explicit consideration of land uses may improve our ability to predict or limit invasion. Moreover, identifying land uses that increase the risk of invasion may inform restoration efforts.