Reproduction and seedling establishment of Picea glauca across the northernmost forest‐tundra region in Canada

The northern boundary of boreal forest and the ranges of tree species are expected to shift northward in response to climate warming, which will result in a decrease in the albedo of areas currently covered by tundra vegetation, an increase in terrestrial carbon sequestration, and an alteration of biodiversity in the current Low Arctic. Central to the prediction of forest expansion is an increase in the reproductive capacity and establishment of individual trees. We assessed cone production, seed viability, and transplanted seedling success of Picea glauca (Moench.) Voss. (white spruce) in the early 1990s and again in the late 2000s at four forest stand sites and eight tree island sites (clonal populations beyond present treeline) in the Mackenzie Delta region of the Northwest Territories, Canada. Over the past 20 years, average temperatures in this region have increased by 0.9 °C. This area has the northernmost forest‐tundra ecotone in North America and is one of the few circumpolar regions where the northern limit of conifer trees reaches the Arctic Ocean. We found that cone production and seed viability did not change between the two periods of examination and that both variables decreased northward across the forest‐tundra ecotone. Nevertheless, white spruce individuals at the northern limit of the forest‐tundra ecotone produced viable seeds. Furthermore, transplanted seedlings were able to survive in the northernmost sites for 15 years, but there were no signs of natural regeneration. These results indicate that if climatic conditions continue to ameliorate, reproductive output will likely increase, but seedling establishment and forest expansion within the forest‐tundra of this region is unlikely to occur without the availability of suitable recruitment sites. Processes that affect the availability of recruitment sites are likely to be important elsewhere in the circumpolar ecotone, and should be incorporated into models and predictions of climate change and its effects on the northern forest‐tundra ecotone.     

胺鲜酯对高产夏玉米产量及叶片光合羧化酶和保护酶活性的影响

采用田间小区试验,以高产玉米新品种登海661为材料,研究了拔节期叶面喷施10、20和40 mg·L^-1的胺鲜酯（DA-6）对玉米叶片光合羧化酶、保护酶活性和产量的影响.结果表明：喷施胺鲜酯各处理玉米分别比对照（含有表面活性剂和水）增产10.0%(10 mg·L^-1)、8.9%(20 mg·L^-1)和9.4%(40 mg·L^-1),增产效果显著,但各浓度间差异不显著.胺鲜酯处理后,花后玉米的叶面积指数、光合速率、RuBP羧化酶和PEP羧化酶活性均显著上升(P＜0.05),且对光合速率、RuBP羧化酶和PEP羧化酶活性的影响随着处理浓度的增加而提高;与对照相比,胺鲜酯处理后吐丝期、灌浆期、乳熟期和蜡熟期叶片SOD、CAT、POD和GSTs活性及可溶性蛋白质含量显著提高(P＜0.05),MDA含量显著降低(P＜0.05),其中CAT活性随着处理浓度的增加呈上升趋势,其余生理指标各浓度间无显著性差异.     

青冈常绿阔叶林氮的生物循环

对分布于浙江建德的青冈常绿阔叶林N的生物循环进行了研究.群落各代表种类的N浓度在0.49%～1.64%之间,其中下木层、草本层和藤本植物中N的浓度远大于乔木层和亚乔木层的种类;乔木层和亚乔木层4种器官中N的浓度基本为叶＞枝＞根＞干,其他层次的种类则为地上部分＞地下部分.乔木层青冈不同器官中N浓度的高低顺序为花序＞嫩叶＞老叶＞嫩枝＞老枝＞细根＞树干、粗根.各器官中N浓度的季节变化不是很大,其根、枝和叶中的N浓度均在秋季(10月份)最高;下木层青冈各部位N浓度在1月份最高.不同径级青冈中N浓度变化无明显规律.N元素在不同类型凋落物中的浓度范围为0.74%～2.30%,降水和穿透水中的N浓度分别为0.000038%和0.00009%,N在死地被层中的浓度为1.94%,土壤中N的浓度为0.59%.N在植物群落中现存量为1025.28 kg/hm2,死地被层中积累量为224.88 kg/hm2,土壤(A0～B层)中储存量为55151kg/hm2.群落中N的存留量为119.47 kg/(hm2·a);归还量为84.13 kg/(hm2·a),其中通过凋落物的为78.49kg/(hm2·a),通过穿透水的为5.64 kg/(hm2·a);吸收量为203.60 kg/(hm2·a).降水输入了4.88 kg/(hm2·a)的N.     

Factors limiting the recruitment of Quercus schottkyana,a dominant evergreen oak in SW China

Quercus schottkyana is a dominant species of oak in the Asian evergreen broad-leaved forests in southwestern China but seedlings are uncommon and recruitment is rare. Annual acorn production by Q. schottkyana is variable and the acorns are exposed to a series of mortality risks. Understanding the factors that limit recruitment of the oak requires knowledge of the oak's life cycle from acorn production to germination and seedling establishment. In this study, we first tested the effects of acorn density on establishment of seedlings by placing batches of acorns at different densities throughout the study area. Second, we tested the effects of herbivores on seedling survival by erecting fences around both natural and transplanted seedling populations. Our results show that even though the rate of seedling establishment increases as acorn density increases (for 32-8000 acorns·m^-2), survival rates of seedlings in the field were generally low (0-0.6%). We show that seedling recruitment of Q. schottkyana is mainly limited to the acorn stage where 88% of the acorns died from the combined effects of desiccation and predation by weevils (Curculio) and bark beetles (Coccotrypes sp.). Herbivory results in the death of some seedlings and consequently also affects the recruitment of seedlings of Q. schottkyana.     

ABA和NaCl对碱蓬多胺和脯氨酸代谢的影响

比较了 5 0 μmol/L的ABA和 4 0 0mmol/L的NaCl对碱蓬植株内脯氨酸 (Pro)和多胺 (PAs)含量和代谢关键酶活性的影响。结果表明 :ABA处理能诱导碱蓬植株吡咯啉 5 羧酸合成酶 (P5CS)、鸟氨酸脱羧酶(ODC)、多胺氧化酶 (PAO)和脯氨酸脱氢酶 (ProDH)活性上升 ,Pro和游离多胺含量增加。ABA NaCl处理促进碱蓬植株体内Pro和PA的积累。与NaCl处理相比 ,ABA NaCl处理后碱蓬植株P5CS活性显著上升 ,ProDH活性变化不明显 ,ODC活性极显著上升 ,PAO和转谷酰胺酶 (TGase)活性上升 ,从而使Pro和游离多胺含量均显著上升 ,游离态多胺 (Spd PAx) /Put提高 ,结合态多胺总量上升。ABA NaCl处理对碱蓬植株体内Pro和PAs合成的促进与其对生长速率的促进效应相一致     

Causes and Consequences of Invasive Plants in Wetlands: Opportunities,Opportunists, and Outcomes

Wetlands seem to be especially vulnerable to invasions. Even though ≤6% of the earth's land mass is wetland, 24% (8 of 33) of the world's most invasive plants are wetland species. Furthermore, many wetland invaders form monotypes, which alter habitat structure, lower biodiversity (both number and “quality” of species), change nutrient cycling and productivity (often increasing it), and modify food webs. Wetlands are landscape sinks, which accumulate debris, sediments, water, and nutrients, all of which facilitate invasions by creating canopy gaps or accelerating the growth of opportunistic plant species. These and other disturbances to wetlands, such as propagule influx, salt influx, and hydroperiod alteration, create opportunities that are well matched by wetland opportunists. No single hypothesis or plant attribute explains all wetland invasions, but the propensity for wetlands to become dominated by invasive monotypes is arguably an effect of the cumulative impacts associated with landscape sinks, including import of hydrophytes that exhibit efficient growth (high plant volume per unit biomass).     

Biotic disturbance in expanding subarctic forests along the eastern coast of Hudson Bay

* The past and present occurrence of insect disturbance on white spruce (Picea glauca) trees was evaluated at their northern range limit on the eastern coast of Hudson Bay, and its effects on tree growth and population dynamics studied. * Three sites were sampled along an altitudinal gradient. Ring-width chronologies and stem analysis were used to evaluate tree growth. The occurrence of holes in the bark, of resin pockets and blue-stain fungi, and ring-width evidence for growth releases were used to assess the impact of bark beetle. * The white spruce population was established at these sites in the 17th century. Since their establishment, the spruce trees have developed a tree growth form, except at the uppermost site, where severe growth suppression occurred in the 19th century. Bark beetle and blue-stain fungi occurred with different timing and intensity. Their highest occurrence, associated with high mortality rates, was at the lowest site in the late 20th century. In the uppermost sites, biotic disturbance has occurred since the 18th century, associated with evidence for mechanical disturbance. * The simultaneous arrival of white spruce in the area resulted in a synchronous onset of spruce beetle activity driven by tree ageing. Unfavourable climatic conditions affected tree growth severely in the most exposed sites.     

Morphological, anatomical and chemical characterization of white spruce ( Picea glauca ‘Conica’) differently aged needles and hypotheses on their influence on Oligonychus ununguis infestation

Our investigations suggest that the usually observed avoidance by O. ununguis of current year’s twigs of P. glauca ‘Conica’ as a place for feeding and development may be connected with their morphological and anatomical structure as well their biochemical composition. Needles of the current year’s twigs were covered with a thicker layer of wax and formed more extensive epidermis cell walls, in comparison with needles of 1-year-old twigs. Young needles also showed lower concentration of reducing sugars and soluble proteins, which might additionally reduce their nutritional suitability for mite development. Differences were also found between the 1-year-old growth and current growth in contribution of essential oils and a range of other compounds. Further analyses of the effect of these compounds on mite behavior may provide additional explanation of the feeding preferences of the mite.

粉绿铁线莲挥发油成分分析

利用气相色谱－质谱联用技术对青海粉绿铁线莲的挥发油成分进行了研究,共鉴定出59种组分,其中主要成分为十六酸乙酯,9,12,15－十八三烯酸乙酯,亚油酸乙酯,十九烷,正二十五烷,正二十六烷,6,10,14－三甲基－2－十五烷酮,双（2－乙基己基）邻苯二甲酸酯,十八烷酸乙酯,N－苯基－萘胺等,其中十六酸乙酯的含量最高,占挥发油成分总量的24．06％,检出成分占挥发油总量的87．8％。