川西亚高山箭竹群落枯枝落叶层生物化学特性

对川西亚高山3个不同箭竹群落枯枝落叶层现存量及生物化学特性作了初步研究,结果表明(1)枯枝落叶层贮量箭竹-冷云杉林(46.3×103kg/hm 2)＞箭竹-桦木-冷云杉林(25.8×103kg/hm2)＞箭竹-桦木林(6.5×103kg/hm2).(2)各林型枯枝落叶层营养元素贮量(kg/hm2)箭竹-冷云杉林为N 553.14,P 54.63,K 164.75,Ca 606.12,Mg 125.78,箭竹-桦木-冷云杉林为N269.45,P 23.61,K 96.31,Ca 367.04,Mg 79.08,箭竹-桦木林为N 68.69,P 7.73,K 27.64,Ca 21.66,Mg11.45;各元素贮量分布规律箭竹-冷云杉林和箭竹-桦木-冷云杉林为Ca＞N＞K＞Mg＞P,箭竹-桦木林则是N＞K＞Ca＞Mg＞P.(3)箭竹-冷云杉林和箭竹-桦木-冷云杉林枯枝落叶层有机质(如有机碳、粗蛋白、粗脂肪、粗纤维、无氮浸出物等)含量分布格局均为未分解凋落物层(L)＞半分解层(F)＞腐殖质层(H),有机质贮量分布格局为H层＞F层＞L层,箭竹-桦木林各亚层有机质含量及贮量均为L-F层＞H层;箭竹-桦木林、箭竹-桦木-冷云杉林和箭竹-冷云杉林枯枝落叶层有机质平均分解率分别为38.15%、23.54%、19.14%.(4)各林型枯枝落叶层微生物(细菌、真菌、放线菌)数量、酶(酸性磷酸酶、蛋白酶、蔗糖酶、过氧化氢酶和多酚氧化酶)活性箭竹-冷云杉林与箭竹-桦木-冷云杉林均为F层＞L层＞H层,箭竹-桦木林为H层＞L-F层.结果表明随着箭竹-桦木林向箭竹-桦木-冷云杉林及箭竹-冷云杉林恢复演替,林下枯枝落叶层微生物数量、酶活性逐渐降低,凋落物平均分解率降低,凋落物、有机质及营养元素逐渐积累,养分循环速率逐渐降低.     

Relationships between photosynthetic activity and silica accumulation with ages of leaf in Sasa veitchii (Poaceae, Bambusoideae)

BACKGROUND AND AIMS: Bamboos have long-lived, evergreen leaves that continue to accumulate silica throughout their life. Silica accumulation has been suggested to suppress their photosynthetic activity. However, nitrogen content per unit leaf area (N(area)), an important determinant of maximum photosynthetic capacity per unit leaf area (P(max)), decreases as leaves age and senescence. In many species, P(max) decreases in parallel with the leaf nitrogen content. It is hypothesized that if silica accumulation affects photosynthesis, then P(max) would decrease faster than N(area), leading to a decrease in photosynthetic rate per unit leaf nitrogen (photosynthetic nitrogen use efficiency, PNUE) with increasing silica content in leaves. METHODS: The hypothesis was tested in leaves of Sasa veitchii, which have a life span of 2 years and accumulate silica up to 41 % of dry mass. Seasonal changes in P(max), stomatal conductance, N(area) and silica content were measured for leaves of different ages. KEY RESULTS: Although P(max) and PNUE were negatively related with silica content across leaves of different ages, the relationship between PNUE and silica differed depending on leaf age. In second-year leaves, PNUE was almost constant although there was a large increase in silica content, suggesting that leaf nitrogen was a primary factor determining the variation in P(max) and that silica accumulation did not affect photosynthesis. PNUE was strongly and negatively correlated with silica content in third-year leaves, suggesting that silica accumulation affected photosynthesis of older leaves. CONCLUSIONS: Silica accumulation in long-lived leaves of bamboo did not affect photosynthesis when the silica concentration of a leaf was less than 25 % of dry mass. Silica may be actively transported to epidermal cells rather than chlorenchyma cells, avoiding inhibition of CO2 diffusion from the intercellular space to chloroplasts. However, in older leaves with a larger silica content, silica was also deposited in chlorenchyma cells, which may relate to the decrease in PNUE.     

The ecological changes of Echuya afromontane bamboo forest, Uganda

Echuya forest reserve was gazetted in 1939 and was then mainly a bamboo forest with very few hardwood trees. However, the current ecological situation shows that hardwood trees are replacing bamboo. This study analysed the current ecological situation in relationship to past ecological changes and influences. Line transects were laid systematically at 1000 m intervals across the forest in order to describe the current vegetation variation. Echuya forest has changed in size and composition from 1954 to the present. The area occupied by pure bamboo has decreased from 20.5% to 12.5%, bamboo–hard wood mixture decreased from 48.2% to 26.2% and pure hardwood stands increased from 16% to 51%. It can be suggested that the exclusion of fire, herbivores and human activities after reservation of Echuya have gradually led to the conversion of the grassland–bamboo ecosystem into a hardwood forest ecosystem. Macaranga kilimandscharia Pax. is the major colonizing hardwood tree species. Most of the gaps are covered with heavy loads of Mimulopsis species climbers, which suppress bamboo growth.     

Functional morphology of the pectoral fins in bamboo sharks, Chiloscyllium plagiosum: benthic vs. pelagic station-holding

Bamboo sharks (Chiloscyllium plagiosum) are primarily benthic and use their relatively flexible pectoral and pelvic fins to rest on and move about the substrate. We examined the morphology of the pectoral fins and investigated their locomotory function to determine if pectoral fin function during both benthic station-holding and pelagic swimming differs from fin function described previously in leopard sharks, Triakis semifasciata. We used three-dimensional kinematics and digital particle image velocimetry (DPIV) to quantify pectoral fin function in five white-spotted bamboo sharks, C. plagiosum, during four behaviors: holding station on the substrate, steady horizontal swimming, and rising and sinking during swimming. During benthic station-holding in current flow, bamboo sharks decrease body angle and adjust pectoral fin angle to shed a clockwise fluid vortex. This vortex generates negative lift more than eight times that produced during open water vertical maneuvering and also results in an upstream flow that pushes against the posterior surface of the pectoral fin to oppose drag. In contrast, there is no evidence of significant lift force in the wake of the pectoral fin during steady horizontal swimming. The pectoral fin is held concave downward and at a negative dihedral angle during steady horizontal swimming, promoting maneuverability rather than stability, although this negative dihedral angle is much less than that observed previously in sturgeon and leopard sharks. During sinking, the pectoral fins are held concave upward and shed a clockwise vortex with a negative lift force, while in rising the pectoral fin is held concave downward and sheds a counterclockwise vortex with a positive lift force. Bamboo sharks appear to sacrifice maneuverability for stability when locomoting in the water column and use their relatively flexible fins to generate strong negative lift forces when holding position on the substrate and to enhance stability when swimming in the water column.     

Effects of understory dwarf bamboo on soil water and the growth of overstory trees in a dense secondary <Emphasis Type="Italic">Betula ermanii</Emphasis> forest,northern Japan

The effects of understory dwarf bamboo (Sasa kurilensis) on soil water and the growth of overstory trees were studied in a dense secondary forest of Betula ermanii in northern Japan. Four plots were established in a Betula ermanii forest with Sasa kurilensis in the understory. The Sasa was removed in two of the plots. The annual increment of the trunk diameter for each tree was measured in the first two years from the commencement of the experiment. Soil water potential was similar in the plots following significant rainfall, but was found to be greater in the plot without Sasa between rainfall events. This suggests that the removal of Sasa slows the reduction of soil water after rainfall. The relative growth rate of the trunk diameter of Betula ermanii increased with tree size in all of the plots because taller trees strongly suppressed smaller ones in the dense forest. The growth rates of Betula ermanii were higher in the plots without Sasa. However, the difference in growth rates between all of the plots tended to be smaller in smaller size classes, possibly because smaller trees were strongly suppressed by larger ones, irrespective of the presence/absence of Sasa. Therefore, the removal of Sasa increased soil water and encouraged the growth of larger Betula ermanii in dense forest during the first two years after the Sasa was removed. The present study suggests that Sasa can reduce the growth of larger Betula ermanii in dense forest by limiting available soil water to these trees.     

四个竹秆变异毛竹变型的全基因组序列分析

毛竹是我国重要的经济竹种,在长期栽培适应过程中产生了丰富的变异。为揭示毛竹竹秆变异变型的全基因组突变类型,以黄皮毛竹、金丝毛竹、绿皮花毛竹和花毛竹4个毛竹变型为实验材料,采用高通量重测序技术获得全基因组序列,进行单核苷多态性(SNP)、小片段插入缺失(InDel)和结构变异(SV)检测和注释,并将变异基因进行功能注释。结果表明:花毛竹基因组检测得到的基因变异数最多,为12 555个; 金丝毛竹样品变异位点数最少,为11 923个; 4个样品都有7 000多个变异基因得到功能注释。GO注释分类包括细胞组件、分子功能和生物过程三个基因功能分类体系的56个功能组。在细胞组件方面,叶绿素合成相关基因有2 431个; 在生物过程方面,参与类胡萝卜素合成过程的基因有75个,参与花青素合成过程中的调控以及紫外光下组织中花青素积累的相关基因有80个。COG分类表明参与复制、重组和修复的基因数为369个,信号转导机制的基因数为291个,转录的相关基因为222个。通过KEGG数据库系统地分析变异基因参与的黄酮类、类胡萝卜素等物质代谢合成途径。深入研究这些差异基因的调控途径,从DNA水平上解释竹秆的变异机制,可为深入研究毛竹种内丰富的多态性和遗传变异提供数据支持,阐析不同变异类型的基因家族、功能基因等遗传基础。     

毛竹扩张对常绿阔叶林土壤微生物群落的影响

毛竹具有独特的生理生态学特征,会不断地向邻近的生态系统扩张。这一现象会造成生态系统退化、土壤理化性质和微生物群落结构改变等问题,引起了人们的高度关注。然而,目前关于毛竹扩张对微生物群落结构的影响研究甚少。以安吉灵峰寺林场的长期定位试验为平台,在4条毛竹扩张样带上依次设置常绿阔叶林(BLF)、竹-阔混交林(MEF)和毛竹林(PEF)样地,测定不同林型的土壤理化性质以及微生物群落特征。结果表明: 随着毛竹的扩张,土壤pH值显著上升,毛竹林土壤pH值分别比竹-阔混交林和常绿阔叶林高0.37和0.32,而有机碳、铵态氮、硝态氮含量显著降低;除丛枝菌根真菌外,其他主要微生物类群都有下降的趋势,且微生物多样性和丰富度显著降低。毛竹扩张对土壤碳输入及养分的改变是影响地下微生物群落生物量及结构的重要因素,其中土壤有机碳、铵态氮含量是影响土壤微生物群落变化的主要因子。     

Moso bamboo and Japanese cedar seedlings differently affected soil N2O emissions

毛竹和日本柳杉幼苗对土壤氧化亚氮排放的影响及微生物机制 毛竹(Phyllostachys edulis)向日本柳杉(Cryptomeria japonica)林的扩张现象越发普遍,其扩张对大 气重要温室气体氧化亚氮(N₂O)排放的影响也引起了更多的关注,而其微生物机制尚不明确。本研究通过添加微生物抑制剂链霉素和扑海因分别抑制细菌和真菌活性,连续观测土壤N₂O排放速率以及相关土壤养分和植物生物量。研究结果表明：(i)毛竹土壤N₂O的排放速率显著高于日本柳杉;与对照相比,细菌抑制剂、真菌抑制剂及其交互作用均对N₂O排放速率具有显著抑制效应,但三者之间无显著差异;(ii)毛竹生物量显著高于日本柳杉;(iii)日本柳杉土壤有机质、全氮和铵态氮显著高于毛竹土壤,日本柳杉土壤pH和全磷显著低于毛竹土壤。真菌抑制剂降低了土壤有机质含量,细菌抑制剂降低了土壤硝态氮含量。真菌抑制剂与物种在影响土壤pH、全磷和铵态氮方面具有显著交互作用。细菌抑制剂与物种在影响土壤全氮方面有显著交互作用。综上所述,毛竹和日本柳杉在生长过程中土壤N₂O排放速率不同,毛竹幼苗土壤N₂O排放及生物量均高于日本柳杉。细菌抑制剂和真菌抑制剂对N₂O的排放速率均具有一定抑制作用。因而,在全球气候变化背景下,应进一步深入了解森林生态系统物种组成和变化对N₂O排放的影响,以有效评估毛竹扩张等导致的生物多样性变化对全球N₂O排放的贡献。     

Interactions among dwarf bamboo,litter and consumption by small vertebrates place multiple constraints on the establishment of native tree seedlings in a Japanese agricultural landscape

Aims Faunal assemblage alterations due to anthropogenic impacts have changed herbivore–vegetation relationships in various ecosystems, but the influences of small vertebrates on revegetation processes remain unclear. In a peri-urban agricultural landscape in eastern Japan that lacks large ungulates but supports small generalist herbivores, fewer native seedlings have become established in thickets dominated by native dwarf bamboo,Pleioblastus chino(Franch. et Sav.) Makino. The mechanisms limiting tree seedling establishment are unknown. Our aim here was to evaluate the influence of interactions among the dwarf bamboo, its litter cover and small vertebrate herbivores on the microsite conditions governing the establishment of native tree seedlings from different successional stages in an old field in temperate Japan.     

Multivariate path analysis of the relationships between seedling regeneration and environmental factors beneath a dwarf bamboo understory

Seedling emergence and establishment are fragile processes that determine the direction and structure of forest succession and regeneration. However, seedling emergence and establishment are easily affected by biotic and abiotic (environmental) factors. A dense and expanding understory of dwarf bamboo is one such important factor that can seriously hinder the seedling regeneration. We conducted a field experiment to investigate the emergence and establishment of canopy tree seedlings under artificially controlled densities of dwarf bamboo. We found that understory dwarf bamboo obstructed seedling emergence but reduced the death of seedlings. Although understory dwarf bamboo reduced the median retention time of seedlings, dense bamboo increased the mean survival time of seedlings. Our results suggest that understory dwarf bamboo has multiple selectivities for tree seedling emergence and establishment: high‐density dwarf bamboo was beneficial to evergreen species but lower‐density of bamboo was conducive to the survival of deciduous species, it means the dwarf bamboo potentially alters successional trajectories of forest communities. Path analysis revealed that the most important factors affecting tree seedling emergence and death were the abundance of seeds in the seed bank and the density of emerged seedlings, and that the soil temperature promoted seedling emergence but increased seedling death, the thickness of litter limited seedling emergence, and the leaf area index of the bamboo canopy limited seedling death. The present study suggests that dwarf bamboo can directly alter the microenvironment, significantly reducing light levels and soil temperature but increasing the thickness of litter and soil humus, thereby indirectly impacting the regeneration of tree seedlings. Our results indicate that various factors affected seedling emergence, and there were complex indirect relationships among these factors. In general, biological factors had a stronger influence on tree seedling regeneration than environmental factors.