西南桦速生单株选择

采用方差分析、遗传参数分析和聚类分析方法,在福建省华安县引种实验林进行西南桦(Betula alnoides Buch.-Ham.ex D. Don)速生单株选择,从25个种源中筛选出8个优良种源,树高平均遗传增益为10.4%.对8个种源中69个家系进行聚类分析,选择出13个速生家系,树高的平均遗传增益为29.4%.运用K快速聚类法从95个单株中筛选出14株速生单株,其遗传增益为118.01%,增产效果显著,在闽南一带可用作无性繁殖材料,以加速西南桦引种造林良种化进程.     

Effects of fire on the vegetation of a lowland heathland in North-western Italy

This study focuses on the effect of fire on lowland heathlands at the extreme southern edge of their European distribution (Vauda Nature Reserve, NW Italy). Forty-nine plots (50 m radius) were surveyed between 1999 and 2006. Each year, fire occurrences were recorded and per cent cover of four vegetation types (grassland, heath, low shrubland, and tall shrubland) was estimated in each plot. Vascular plant species richness was also recorded in 255, 1 m² quadrats. After a fire, grassland vegetation expanded, but then declined rapidly as heath and shrubland recovered: 7 years after a fire, tall shrubland encroached on to more than 40% of the plots, and grassland declined from 50% to 20% cover. Between 1999 and 2006, Betula pendula shrubland greatly expanded, while grassland decreased over most of the Reserve, even where fire frequency was high. Tall shrubland had low plant diversity and was dominated by widespread species of lower conservation value. By contrast, early successional vegetation (grassland and low shrubland) had higher richness and more narrowly distributed species, indication that the development of tall shrubland causes significant species loss in the heathland. Italian lowland heathlands are characterized by high rates of shrubland encroachment that threatens both habitat and species diversity. Burning frequencies of once in 3–6 years seem appropriate in this habitat, but burning alone might not suffice without actions to increase herbivore grazing.     

Long‐term experimental manipulation of climate alters the ectomycorrhizal community of Betula nana in Arctic tundra

Climate warming is leading to shrub expansion in Arctic tundra. Shrubs form ectomycorrhizal (ECM) associations with soil fungi that are central to ecosystem carbon balance as determinants of plant community structure and as decomposers of soil organic matter. To assess potential climate change impacts on ECM communities, we analysed fungal internal transcribed spacer sequences from ECM root tips of the dominant tundra shrub Betula nana growing in treatments plots that had received long‐term warming by greenhouses and/or fertilization as part of the Arctic Long‐Term Ecological Research experiment at Toolik Lake Alaska, USA. We demonstrate opposing effects of long‐term warming and fertilization treatments on ECM fungal diversity; with warming increasing and fertilization reducing the diversity of ECM communities. We show that warming leads to a significant increase in high biomass fungi with proteolytic capacity, especially Cortinarius spp., and a reduction of fungi with high affinities for labile N, especially Russula spp. In contrast, fertilization treatments led to relatively small changes in the composition of the ECM community, but increased the abundance of saprotrophs. Our data suggest that warming profoundly alters nutrient cycling in tundra, and may facilitate the expansion of B. nana through the formation of mycorrhizal networks of larger size.     

大兴安岭森林草原过渡带白桦及主要草本植物生态位关系的研究

以白桦、日阴菅及其它主要草本植物的个体数量为指标,分析了各植物种群在土壤有机质,速效P和pH值3个资源维上的生态位宽度和生态位重叠及其在不同海拔条件下的变化规律。日阴菅生态位宽度随海拔升高而增大,其余植物种类在有机质资源维上的生态位宽度,大都是以中等海拔（800m)的样带最宽,而在速效P资源维上,又以中等海拔的样带为最窄,由于高海拔及相应低气温在某种程度上限制了植物种群在土壤有机质和速效P的利用,主要植物种对之间在这两个资源维上的生态位重叠以高海拔（950m)样带为最小,在土壤pH值资源维上,溪荪与其它主要植物种间的生态位重叠皆以低海拔（650m)样带为最小,可能是其特殊的环境组合迫使溪荪发生了生态位移动,大多数种对在土壤有机质,速效P和pH值3个资源维上都以海拔800m的样带生态位重叠最大。     

西南桦人工林与山地雨林的群落学特征比较

人类活动对生态系统的影响是当今生态学的研究热点之一,但对在退化生态系统上进行人工造林对地带性植被群落学特征的影响研究尚较欠缺。本文根据组成群落的植物生态学特征能对其生态环境做出准确的反应这一规则,通过样地调查法分析了林龄为12年的西南桦（Betula alnoides）人工群落的区系组成和基本的群落学特征,并与当地的地带性植被——山地雨林的区系组成和群落学特征进行了比较,从而探讨人工造林对当地天然生态系统的影响。结果发现,与天然群落相比,人类活动（人工种植西南桦林）对生态系统的植物物种的生活型谱、物种叶型谱、区系成分、物种多样性等方面的群落学特征影响不大;即使在这些方面有或多或少的差异,可能也是小环境的异质性造成的。但是人工种植西南桦林对群落的季相外貌、群落的结构、物种组成、物种丰富度以及生物量等方面有较大的影响。进行综合分析后得出结论：虽然人工造林可以缩短植被自然恢复的时间以及具有显著的经济价值,但与地带性植被相比,还是有较大的生态学差异。建议为了当地经济的发展,有必要适当发展一定面积的人工林,但规模应适度。     

Seedling establishment in relation to microhabitat variation in a windthrow gap in a boreal Pinus sylvestris forest

Abstract. The characteristics of microhabitats of established Pinus sylvestris and Betula seedlings were studied in a small windthrow gap in a mature P. sylvestris-dominated forest in the Petkeljärvi National Park in eastern Finland. Seedlings were strongly clustered in disturbed microhabitats, particularly uprooting pits and mounds, formed by tree falls. They covered 3% of the 0.3.ha study area consisting of the gap and some of the forest edge. Although Betula occurred only as scattered individuals in the dominant canopy layer of the forest, it accounted for 30% of the seedlings found in the study area. Betula regeneration was almost completely restricted to pits and mounds, where 91% of the seedlings were found. Uprooting spots were also the most important regeneration microhabitats for Pinus, where 60% of the seedlings grew, even though the seedlings were found in other substrates as well, particularly on sufficiently decomposed coarse wood. Undisturbed field- and bottom-layer vegetation had effectively hindered tree seedling establishment, which emphasises the role of soil disturbance for regeneration. While the establishment of seedlings was found to be clearly determined by the availability of favourable regeneration microhabitats, the early growth of seedlings was affected by a complex interaction of environmental variables, including the type of microhabitat, radiation environment and interferences caused by competing seedlings and adjacent trees. In the most important regeneration microhabitats, i.e. in uprooting pits and on mounds, the distributions of the local elevations of Pinus and Betula seedlings were different. Pinus seedlings occurred closer to ground level, i.e. on the fringes of pits and lower on mounds, while Betula seedlings grew deeper in pits and higher on mounds. The position of the Betula seedlings indicate that they may have a competitive advantage over Pinus seedlings in the dense seedling groups occurring in uprooting spots. We suggest that this initial difference in Pinus and Betula establishment may affect the subsequent within-gap tree species succession and can, in part, explain the general occurrence of Betula in conifer-dominated boreal forests.     

小叶桦花序生长物候及其生态适应意义

小叶桦(Betula microphylla)是一种典型的荒漠和山地乔木植物,在中国仅分布于新疆。为了明确小叶桦花序生长物候规律及发育特征,该研究对小叶桦进行了花序物候观测,分析其生长规律及果实结籽情况。结果显示:小叶桦雄花序为越年生殖器官,物候周期为345d,其中营养生长期154d、休眠期158d、开花生长期33d;雌花序与果序为当年生殖器官,物候期为105d,其中雌花序生长期24d、果序生长期90d。虽然雄花序比雌花序的生长周期明显较长,但开花授粉均在4月中下旬,雄花序散粉期和雌花序可授粉期之间具有较高的同步性和协调性,表现出集中开花授粉模式,同时这种开花模式在自然条件下,果序的结籽数和结籽率分别为220和76.7%,种子库中具有活力的种子约每平米4万粒,表明小叶桦在荒漠极端环境中能顺利完成有性生殖过程。     

青藏高原东缘林线交错带糙皮桦幼苗光合特性对模拟增温的短期响应

采用开顶式生长室(OTC)模拟增温对植被影响的研究方法, 研究了青藏高原东缘林线交错带糙皮桦(Betula utilis)光合特性对模拟增温的响应。结果表明: 与对照样地相比, OTC内日平均气温(1.2 m)在植物生长季中增加2.9 ℃, 5 cm土壤温度增加0.4 ℃。增温使糙皮桦幼苗叶片的净光合速率(P_n)、蒸腾速率(T_r)和气孔导度(G_s)分别增加17.4%、21.4%和33.9%, 但对糙皮桦幼苗叶片的水分利用率(WUE)却没有明显影响, 而对糙皮桦的叶氮浓度却表现为显著的负效应。同时, 增温能显著增加糙皮桦幼苗的最大同化速率(P_nmax) (+19.6%)、暗呼吸速率(R_d) (+14.3%)、表观量子效率(AQY) (+7.9%), 但对其光补偿点(LCP)和光饱和点(LSP)却没有明显的影响。此外, 增温使糙皮桦幼苗叶片的最大羧化速率(V_cmax)和电子传递速率(J)分别增加了12.3%和11.7%, 而磷酸丙糖利用率(TPU)和CO₂补偿点(CCP)对增温却并不敏感。该研究表明, 模拟增温对林线糙皮桦光合生理总体上表现为正效应, 这有可能帮助该物种对未来气候变化更快更好地适应。     

赛黑桦不同半同胞家系种子活力比较

种子活力能够预测幼苗的生长势和适应性,可作为评价采种母树的重要指标。赛黑桦作为东北林区木质坚硬的树种之一,关于其种子活力研究尚未见报道。比较不同家系赛黑桦种子活力,对赛黑桦采种母树进行初步评价,可为赛黑桦优良家系的选择提供参考。本研究以赛黑桦蛟河、集安和珲春3个采种地共30个半同胞家系为试材,对采种地及家系间种子千粒重、发芽率、发芽势、发芽指数、活力指数、出苗率和幼苗健壮率等7个性状进行了方差分析、遗传力估算、多重比较、相关性分析,并利用主成分分析法对参试家系进行了综合评价。结果表明,赛黑桦种子活力指数和幼苗健壮率在不同采种地间的差异达到了显著或极显著水平;7个性状在不同家系间的差异均达到显著或极显著水平;除出苗率和幼苗健壮率外,各性状的家系遗传力均高于0.68;7个性状间均呈现显著或极显著的正相关;采用主成分分析法选择JH6、JA1、JA7、JH10、JH3、HC1和HC10等7个家系为优良家系,这些家系的种子千粒重、发芽率、发芽势、发芽指数、活力指数、出苗率和幼苗健壮率的平均值分别比总平均值高3.87%、30.29%、30.22%、31.99%、58.22%、11.88%和30.60%。初步认为这些优良家系的母树是赛黑桦采种的首选母树。     

广西区西南桦天然居群遗传多样性的研究

 以采自广西区11个西南桦(Betula alnoides)天然居群的种子培育出的幼苗为材料,取其嫩叶开展21种酶系统的水平切片淀粉凝胶电泳实验,运用作者改进的Tris-马来酸提取缓冲液 (含30%PVP 40 000和1%2-巯基乙醇),筛选出AMP(氨基肽酶Aminopeptidase)、FBA(果糖二磷酸酶Fructose-bisphosphate aldolase)、GDH(谷氨酸脱氢酶Glutamate dehydrogenase)、G6PD(6-磷酸葡萄糖脱氢酶Glucose-6-phosphate dehydrogenase)、IDH(异柠檬酸脱氢酶Isocitrate dehydrogenase)、MDH(苹果酸脱氢酶Malate dehydrogenase)、PGD(6-磷酸葡萄糖酸脱氢酶Phosphogluconate dehydrogenase)、PGI(磷酸葡萄糖异构酶Phosphoglucoisomerase)、PGM(磷酸葡萄糖变位酶Phosphoglucomutase)和SKD(莽草酸脱氢酶Shikimate dehydrogenase)等10种酶,获得了清晰且可重复的酶谱。通过谱带遗传分析确定了15个位点,其中有6个单态位点,9个多态位点 (0.95标准),具40个等位基因。在居群水平上,西南桦的多态位点百分数 (P) 为55.2%,平均每个位点的等位基因数 (A) 为2.00,平均预期杂合度 (He) 为0.204。均超过Hamrick (1992)等提出的远交风媒木本植物的平均值(53.0%,184%和0154),表明西南桦的遗传变异水平高。在11个西南桦居群内,实际杂合度 (Ho)均高于预期杂合度,出现杂合子过量,可能存在利于杂合子的自然选择。西南桦遗传多样性与地理位置相关不显著。居群2 (靖西地州)、5 (平果海城)、9 (田林者苗) 包含绝大部分的等位基因,而且具较高的遗传多样性,应加以保护和管理,作为其基因资源就地保存的基地。本研究解决了以西南桦嫩叶为材料进行等位酶分析的关键技术,为进一步开展西南桦乃至桦木属树种的遗传结构和遗传多样性等提供了技术基础;同时掌握了西南桦天然居群的遗传多样性现状,为其有效保护和合理经营以及西南桦的遗传改良提供了理论依据。