施肥对台湾桤木-扁穗牛鞭草复合模式下桤木细根形态特征、生物量及组织碳氮含量的影响

细根具有良好的可塑性, 不同根序等级的细根会表现不同的策略来适应土壤资源有效性的改变, 了解各级细根对土壤资源有效性的可塑性反应对认识细根的养分和水分吸收规律、预测碳(C)在地下的分配特点具有重要意义。该文以四川省丹陵县台湾桤木(Alnus formosana)-扁穗牛鞭草(Hemarthria compressa)复合模式为研究对象, 采用施肥处理, 应用土柱法采样, 探讨了施肥对台湾桤木-扁穗牛鞭草模式土壤表层(0-10 cm)和亚表层(10-20 cm)台湾桤木1-5级细根的生物量、形态特征(直径、比根长)、全C和全氮(N)含量的影响。结果表明: (1)台湾桤木1-5级细根直径随根序的增大而增加, 施肥降低土壤表层台湾桤木各级细根直径而增加了土壤亚表层台湾桤木各级细根直径; 台湾桤木1-5级细根比根长则随根序的增加而减小, 施肥增加了台湾桤木各级细根的比根长, 且施肥极显著增加了表层和亚表层台湾桤木前三级细根的比根长(p < 0.01)。(2)台湾桤木1-5级细根生物量均随土层深度的增加而减小, 施肥减少了台湾桤木各个土层各级细根生物量, 且显著降低了台湾桤木前三级细根生物量占总生物量的比例(p < 0.05), 而增加了4、5级细根生物量。(3)台湾桤木3级细根全C最大, 1级根最小, 且土壤表层台湾桤木各级细根全C含量大于亚表层; 施肥降低了台湾桤木各级细根全C含量, 但影响并不显著(p > 0.05)。台湾桤木细根全N含量随根序的增加而降低, 且土壤表层1-5级细根全N含量均高于亚表层; 施肥极显著(p < 0.01)增加了土壤表层1级细根及亚表层1、2级细根的全N含量, 而对于3-5级细根全N含量则影响不显著(p > 0.05)。以上结果显示, 当土壤资源有效性变化时, 各级根序细根会作出不同的可塑性反应, 且施肥对各级细根的影响主要表现在低级根上。     

Tornado damage and initial recovery in three adjacent,lowland temperate forests in Missouri

Abstract. We surveyed tornado damage 14 months after disturbance in three adjacent forest sites in southeastern Missouri, USA: upland, an occasionally-flooded lowland and a frequently flooded swamp. We analysed three 0.09-ha plots in the swamp, and three 0.04-ha plots in the other sites and recorded the herbaceous-layer in five 1-m² quadrats per plot. Overall, 30 % of the individuals and 64 % of the basal area of these sites was blown down. However, mortality was less than structural damage: 20 % of the trees were dead 14 months post-disturbance, an intermediate level of mortality relative to other wind disturbances. Damage varied widely among species, sites and tree sizes, but large trees of all species were most likely to be damaged and least likely to resprout. While damage was greatest in the wettest site, we attribute the increase to larger tree sizes and lower density there, rather than to inherent rooting instability. This study suggests that different forest composition and structure may be sufficient to cause differential damage, without topographic effects. Herbaceous-layer response was more rapid than in a previously reported tornado windthrow in Pennsylvania, and was dominated by fast-growing, shade-intolerant forbs.     

Development of microsatellite markers for Euchresta japonica and E. formosana (Leguminosae)

We isolated 13 microsatellite loci from Euchresta japonica, an endangered shrub species that grows in warm-temperate forests in East Asia. Of these 13 loci, only one was codominant and polymorphic with five alleles. Cross-species amplification in a related species, E. formosana, detected nine of these loci, all of which were codominant and polymorphic with 2 to 9 alleles. These markers will facilitate further studies on the genetic characteristics of these two Euchresta species.     

Chlorophyll fluorescence measured using the Fraunhofer line-depth principle and relationship to photosynthetic rate in the field

Abstract. A field study was conducted to determine the relationship of solar-excited chlorophyll a fluorescence to net CO₂ assimilation rate in attached leaves. The Fraunhofer line-depth principle was used to measure fluorescence at 656.3 nm wavelength while leaves remained exposed to full sunlight and normal atmospheric pressures of CO₂ and O₂. Fluorescence induction kinetics were observed when leaves were exposed to sunlight after 10 min in darkness. Subsequently, fluorescence varied inversely with assimilation rate. In the C₄ Zea mays , fluorescence decreased from 2.5 to 0.8 mW m^-2 nm^-1 as CO₂ assimilation rate increased from 1 to 8 μmol m^-2 s^-1 (r²= 0.520). In the C₃ Liquidambar styraciflua and Pinus taeda , fluorescence decreased from 6 to 2 mW m^-2 nm^-1 as assimilation rate increased from 2 to 5 or 0 to 2 μmol m^-2 s^-1 (r²= 0.44 and 0.45. respectively). The Fraunhofer line-depth principle enables the simultaneous measurement of solar-excited fluorescence and CO₂ assimilation rate in individual leaves, but also at larger scales. Thus, it may contribute significantly to field studies of the relationship of fluorescence to photosynthesis.     

Transformation of sweetgum via microprojectile bombardment of nodule cultures

Summary A sweetgum (Liquidambar styraciflua) nodule culture system was developed and integrated with genetic transformation by microprojectile bombardment. Nodule cultures were established from seedling hypocotyls and proliferated in liquid medium containing 0.1 mg (0.45 μM) thidiazuron (TDZ) per 1 and 0.01 mg (0.045 μM) 2,4-dichlorophenoxyacetic acid (2,4-D) per 1. Shoots differentiated from the nodules in liquid media containing (per 1) 1 mg (4.4 μM) benzyladenine (BA), 0.5 mg (2.2 μM) BA, and 0.01 mg (0.054 μM) naphthaleneacetic acid (NAA), or 0.5 mg BA, 0.01 mg NAA, and 0.05 mg (0.23 μM) TDZ under the light. Differentiating shoots required 4 wk of dark treatment for further development on semisolid medium containing 1 mg BA per 1. Elongated shoots were harvested and the basal ends were soaked in a solution containing 10 mg (49.2 μM) indole-3-butyric acid (IBA) per 1 before being planted in potting mix for ex vitro rooting. Roots formed and leaves expanded in 2 wk. Sweetgum nodules were stably transformed by microprojectile bombardment with a 7.4-kb plasmid, pTRA 140, harboring CaMV 35S-HPH and CaMV 35S-GUS. Evidence that nodules growing in the presence of hygromycin B were stably transformed was provided by polymerase chain reaction analysis and β-glucuronidase activity. Sweetgum shoots differentiated in liquid medium in the presence of hygromycin B. Shoots transferred to solid medium lacking hygromycin B elongated and displayed β-glucuronidase activity in their expanding leaves and stems. Southern analysis confirmed the presence of the GUS gene in nodules and shoots. Transgenic shoots initiated roots and showed leaf expansion 2 wk after being planted in potting mix.     

Enhancing the productivity of hybrid yellow-poplar and hybrid sweetgum embryogenic cultures

Summary High-frequency embryogenesis systems were established for hybrid yellow-poplar (Liriodendron tulipifera×L. chinense) and hybrid sweetgum (Liquidambar styraciflua×L. formosana) by modifying a medium originally developed for embryogenic yellow-poplar cultures. Embryogenic cultures of both hybrids, consisting of proembryogenic masses (PEMs), were initiated from immature hybrid seeds on an induction-maintenance medium (IMM) supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D), benzyladenine (BA), and casein hydrolyzate (CH). For hybrid yellow-poplar, as many as 2100 germinable somatic embryos per 4000 cells or cell clumps were produced when PEMs were grown in liquid IMM lacking CH, at a pH that varied with genotype (3.5 or 5.6), followed by size fractionation and plating on semisolid embryo development medium (DM; IMM lacking 2,4-D and BA) without CH, but supplemented with 4.0 mgl⁻¹ (15 μM) abscisic acid. For hybrid sweetgum, up to 1650 germinable somatic embryos per 4000 cells or cell clumps were produced when PEMs were grown in liquid IMM without CH, but with 550 mgl⁻¹ l-glutamine, 510 mg l⁻¹ asparagine, and 170 mg l⁻¹ arginine at pH 5.6. Somatic embryos developed from cell clumps on DM without any plant growth regulators or other supplements. Hundreds of somatic embryos of both hybrids were germinated on DM without CH, transferred to potting mix, and hardened off in a humidifying chamber for transfer to the greenhouse.     

鄂东南低丘地区枫香林下枫香幼苗更新限制因子

深入理解幼苗更新的生态过程及其限制因子是植物种群保育和森林管理的基础。在鄂东南的低丘地区, 采用控制试验研究了限制枫香(Liquidambar formosana)幼苗在其自身林下更新的生态因子。由于枫香幼苗在马尾松(Pinus massoniana)林下偶尔更新良好, 在枫香林下几乎没有更新, 以马尾松林为对照, 设计了4个试验来检验: (1)低温和土壤湿度对枫香种子储藏过程中寿命的影响, (2)两种林型的土壤、凋落物对枫香种子越冬及存活的影响, (3)凋落物对枫香种子萌发是否具有化感作用, (4)林下的光强变化是否影响幼苗的存活。结果表明, 枫香种子在很低的温度下仍可以立即萌发, 这表明枫香种子没有休眠特性是影响枫香幼苗更新的重要因子; 土壤、凋落物和凋落物滤液对种子越冬后的存活没有影响, 不能解释“枫香林下没有枫香苗”的问题; 两种林型的主要凋落物滤液对枫香种子萌发没有抑制作用或促进作用; 一年生枫香幼苗遮阴试验的结果表明, 3%透光率下幼苗的死亡率接近90%。因此枫香林下弱的光环境和种子的低温萌发特性是影响枫香幼苗更新的重要因子。     

缺萼枫香叶挥发油的化学成分研究

以水蒸气蒸馏法提取缺萼枫香叶中的挥发油,首次以气相色谱-质谱联用技术对其化学成分进行分离、鉴定,共分离出44个成分,鉴定了其中的29个成分,占挥发油总量的81.04%,主要成分为n-棕榈酸(27.03%)和9,12,15-十八酸(13.35%)。     

Direct and indirect effects of elevated CO2 on leaf respiration in a forest ecosystem

We measured the short‐term direct and long‐term indirect effects of elevated CO₂ on leaf dark respiration of loblolly pine (Pinus taeda) and sweetgum (Liquidambar styraciflua) in an intact forest ecosystem. Trees were exposed to ambient or ambient + 200 µmol mol^?1 atmospheric CO₂ using free‐air carbon dioxide enrichment (FACE) technology. After correcting for measurement artefacts, a short‐term 200 µmol mol^?1 increase in CO₂ reduced leaf respiration by 7–14% for sweetgum and had essentially no effect on loblolly pine. This direct suppression of respiration was independent of the CO₂ concentration under which the trees were grown. Growth under elevated CO₂ did not appear to have any long‐term indirect effects on leaf maintenance respiration rates or the response of respiration to changes in temperature (Q₁₀, R₀). Also, we found no relationship between mass‐based respiration rates and leaf total nitrogen concentrations. Leaf construction costs were unaffected by growth CO₂ concentration, although leaf construction respiration decreased at elevated CO₂ in both species for leaves at the top of the canopy. We conclude that elevated CO₂ has little effect on leaf tissue respiration, and that the influence of elevated CO₂ on plant respiratory carbon flux is primarily through increased biomass.