Free-air exposure systems to scale up ozone research to mature trees

Because seedlings and mature trees do not necessarily respond similarly to O(3) stress, it is critically important that exposure systems be developed that allow exposure of seedlings through to mature trees. Here we describe three different O(3) Free-Air Exposure Systems that have been used successfully for exposure at all growth stages. These systems of spatially uniform O(3) release have been shown to provide reliable O(3) exposure with minimal, if any, impact on the microclimate. This methodology offers a welcome alternative to chamber studies which had severe space constraints precluding stand or community-level studies and substantial chamber effects on the microclimate and, hence physiological tree performance.     

Spatial heterogeneity in the determinants of woody plant invasion of lowland heath

Questions: 1. What is the scale and extent of spatial variability in factors affecting Betula invasion of heaths? 2. How much effect does each factor have on within‐patch patterns of invasion? 3. How can this understanding aid in managing Betula invasions? Location: Lowland heath of southern England. Methods: Determinants of Betula (both B. pubescens and B. pendula) invasion: biomass density, necromass density, mean vegetation height, P‐availability, soil water content and total Betula seed bank density, were measured at two sites on a 5‐ha sampling grid. Spatial pattern was assessed using geostatistics. Contributions of each determinant to within‐site heterogeneity in predicted Betula seedling densities were estimated by varying variables over their full and interquartile ranges in a statistical model derived from experimental data. Results: Salient spatial trends were revealed: strong autocorrelation over distances of < 50 m for soil factors and more extensive autocorrelation (0 to > 150 m) in vegetation variables and Betula seed bank densities. The latter resulted in single across‐site gradients, the former small, distinct patches. All patterns were overlain with variance that was present at distances of < 17.6 m. Variables displaying spatial pattern also accounted for within‐site heterogeneity in predicted Betula seedling densities but their relative contribution to this varied between sites. Conclusions: Identifiable spatial autocorrelation in factors controlling patch‐scale invasion patterns allows managers to target invasion prone patches, potentially reducing management intensities. Furthermore, management effort may be optimised by spatially de‐coupling Betula seed from safe‐sites. This plan may adaptable to the management of other weeds and open‐land ecosystems.     

黄龙山白桦桦木醇与桦木酸含量研究

为了阐明黄龙山白桦不同生境、不同径级、不同器官桦木醇与桦木酸含量,系统采集了陕北黄土高原黄龙山林场阳坡、阴坡、林缘、孤立木4种生境下的白桦不同径级植株的树皮、树枝和树叶样品,采用超声波辅助提取法提取样品,用高效液相色谱法测定了不同生境、不同径级白桦各器官桦木醇、桦木酸含量。结果表明：（1）不同生境下白桦各器官桦木醇、桦木酸含量均存在显著差异（P＜0.05）,白桦树皮中桦木醇与桦木酸含量、白桦树枝中桦木酸含量在4种生境下均表现为阴坡＞孤立木＞林缘＞阳坡,白桦树叶中桦木醇与桦木酸含量及树枝中桦木醇含量均表现为阴坡＞林缘＞孤立木＞阳坡,总体来看阴坡生境下白桦各器官桦木醇与桦木酸含量都是最高的。（2）在白桦各器官中,桦木醇、桦木酸含量均表现为树皮＞树枝＞树叶。（3）不同生境下白桦各器官桦木醇、桦木酸含量随着胸径的增大均先增大后减小,均在第Ⅱ径级即胸径10.1~20 cm达到最大。研究认为,阴坡生境有利于白桦各器官积累桦木醇、桦木酸;白桦各器官中桦木醇含量较高,桦木酸含量比较低,而以桦木酸为原料的生物制剂已进入临床应用阶段,因此,以桦木醇为原料制取桦木酸是解决桦木酸在天然植物中含量低、提取困难的有效途径;对白桦各器官的采收应注意把握时机,于白桦生长到胸径10.1~20 cm时为最佳采收期。     

The contribution of trees to ecosystem methane emissions in a temperate forested wetland

Wetland‐adapted trees are known to transport soil‐produced methane (CH₄), an important greenhouse gas to the atmosphere, yet seasonal variations and controls on the magnitude of tree‐mediated CH₄ emissions remain unknown for mature forests. We examined the spatial and temporal variability in stem CH₄ emissions in situ and their controls in two wetland‐adapted tree species (Alnus glutinosa and Betula pubescens) located in a temperate forested wetland. Soil and herbaceous plant‐mediated CH₄ emissions from hollows and hummocks also were measured, thus enabling an estimate of contributions from each pathway to total ecosystem flux. Stem CH₄ emissions varied significantly between the two tree species, with Alnus glutinosa displaying minimal seasonal variations, while substantial seasonal variations were observed in Betula pubescens. Trees from each species emitted similar quantities of CH₄ from their stems regardless of whether they were situated in hollows or hummocks. Soil temperature and pore‐water CH₄ concentrations best explained annual variability in stem emissions, while wood‐specific density and pore‐water CH₄ concentrations best accounted for between‐species variations in stem CH₄ emission. Our study demonstrates that tree‐mediated CH₄ emissions contribute up to 27% of seasonal ecosystem CH₄ flux in temperate forested wetland, with the largest relative contributions occurring in spring and winter. Tree‐mediated CH₄ emissions currently are not included in trace gas budgets of forested wetland. Further work is required to quantify and integrate this transport pathway into CH₄ inventories and process‐based models.     

Antioxidant and anticancer activity of extract from Betula platyphylla var. japonica

The antioxidant and anticancer properties of a medicinal plant, Betula platyphylla var. japonica were investigated. The total methanol extract of B. platyphylla var. japonica had protective effects against hydrogen peroxide (H2O2) in the Chinese hamster lung fibroblast (V79-4) cell line and induced apoptotic cell death in human promyelocytic leukemia (HL-60) cells, a cancer cell line. B. platyphylla var. japonica extract significantly increased cell viability against H2O2. The extract also showed high 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (IC50 2.4 microg/ml) and lipid peroxidation inhibitory activity (IC50 below 4.0 microg/ml). Furthermore, B. platyphylla var. japonica extract reduced the number of V79-4 cells arrested in G2/M in response to H2O2 treatment and increased the activities of several cellular antioxidant enzymes, including superoxide dismutase, catalase and glutathione peroxidase. Treatment with B. platyphylla var. japonica extract induced cytotoxicity and apoptosis in HL-60 cells, as shown by nucleosomal DNA fragmentation, increases in the subdiploid cell population, and fluorescence microscopy. B. platyphylla var. japonica extract gradually increased the expression of pro-apoptotic Bax and led to the activation of caspase-3 and cleavage of PARP. These findings suggest that B. platyphylla var. japonica exhibits potential antioxidant and anticancer properties.     

The effects of understorey dwarf bamboo (Sasa kurilensis) removal on soil fertility in a Betula ermanii forest of northern Japan

We investigated the changes in soil microbial biomass C (MBC), microbial biomass N (MBN) and N mineralization in Sasa kurilensis-present (SP) and S. kurilensis-removed (SR) stands in a Betula ermanii forest. The mean levels of MBC and MBN were significantly higher in the SR stand than in the SP, which may have positively influenced the N-mineralization rate as depicted by a significant positive correlation between these variables and the N-mineralization rate. N immobilization and subsequent N release along with decreased use of available soil N due to S. kurilensis removal may have ensured greater N availability in the SR stand.     

Reproducibility of vegetation cover estimates in south‐central Alaska forests

Abstract. Reproducibility of vegetation measurements is critical for large‐scale or long‐term studies, where numerous observers collect data, but past studies have questioned repro‐ducibility of some techniques. Five methods of evaluating understory composition were appraised for reproducibility among six observers in two forest types in south‐central Alaska: ocular estimates in quadrats, overall community species rank and cover estimates, nested rooted frequency, horizontal‐vertical profiles, and pin drop (systematic points). One forest type was selected to represent structure of coastal communities, another to represent structure of interior Alaska communities. Three general methods of evaluating reproducibility were considered: standard deviations (precision among observers), components of variance (percentage of total variance attributable to observers), and analysis of variance (significance of observer variance). Observer variances were generally similar among techniques and significant in most cases. No technique stood out as being more reproducible than others. Features of techniques other than reproducibility may be more important when selecting a technique. Management decisions based on vegetation cover data should consider the observer errors involved as well as biological significance.     

以光合效率度量天然白桦种群生态位初探

生态位常被理解为“一个生物单位 (个体、种群或物种 )生存条件或适应性的总集合体[3 ,5] 。过去常用于动物种群生态学研究 ,Ｗｈｉｔｔａｋｅｒ首次将生态位理论应用于森林生态学研究[5] 。目前 ,国内外对生态位的研究主要集中在以下方面 :①把生态位与资源利用谱等同起来 ;②生态位占据与竞争联系在一起 ;③生态位是多维空间内具有一定功能的 ,为一个种或种群所占有的功能单位 ,亦即符合该种适合性的小区。这就涉及到“功能单位”的应有宽度及其计测标准和方法 ;④各种有机体均有其在自然群落中的地位、功能作用或某种生活方式 ,它们之间…