Taxonomic scale-dependence of habitat niche partitioning and biotic neighbourhood on survival of tropical tree seedlings

In order to differentiate between mechanisms of species coexistence, we examined the relative importance of local biotic neighbourhood, abiotic habitat factors and species differences as factors influencing the survival of 2330 spatially mapped tropical tree seedlings of 15 species of Myristicaceae in two separate analyses in which individuals were identified first to species and then to genus. Using likelihood methods, we selected the most parsimonious candidate models as predictors of 3 year seedling survival in both sets of analyses. We found evidence for differential effects of abiotic niche and neighbourhood processes on individual survival between analyses at the genus and species levels. Niche partitioning (defined as an interaction of taxonomic identity and abiotic neighbourhood) was significant in analyses at the genus level, but did not differentiate among species in models of individual seedling survival. By contrast, conspecific and congeneric seedling and adult density were retained in the minimum adequate models of seedling survival at species and genus levels, respectively. We conclude that abiotic niche effects express differences in seedling survival among genera but not among species, and that, within genera, community and/or local variation in adult and seedling abundance drives variation in seedling survival. These data suggest that different mechanisms of coexistence among tropical tree taxa may function at different taxonomic or phylogenetic scales. This perspective helps to reconcile perceived differences of importance in the various non-mutually exclusive mechanisms of species coexistence in hyper-diverse tropical forests.     

水分对胡杨幼苗光合及生长特性的影响

采用盆栽控制实验方法对不同水分条件下胡杨幼苗的光合日变化以及生长特性进行分析研究.结果显示:(1)不同水分条件下胡杨幼苗的净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)和蒸腾速率(Tr)日变化曲线均呈单峰型,峰值时间均在12:00;当土壤含水量为21.6%～24.0%时,幼苗的水分利用效率(WUE)日变化曲线呈不明显的双峰型,峰值时间分别在8:00和18:00,其他处理均为单峰型,但峰值时段有差异;随着土壤含水量的减小,胡杨幼苗的Pn、Gs、Ci和Tr日均值逐渐降低,当土壤含水量为12.0%～19.2%时,幼苗的WUE日均值显著高于其他处理.(2)幼苗的株高、基径、各器官的生物量及总生物量均随土壤含水量的减小而降低,当土壤含水量为12.0%～19.2%时,幼苗地下生物量的降低程度大于地上生物量,且幼苗的根冠比也增大.研究表明,土壤含水量对胡杨幼苗的光合特性及其生长具有显著影响,当土壤含水量大于12.0%时,幼苗能够通过增大水分利用效率,改变根冠比提高抗旱性;当土壤含水量小于9.6%时,幼苗自我调节能力减弱,生长受到抑制.     

低温胁迫对广玉兰幼苗光合及叶绿素荧光特性的影响

以广玉兰幼苗为材料,对其进行0,-4℃、-8℃,-12℃和-16℃ 5个梯度低温处理,研究了广玉兰幼苗的光合作用与叶绿素荧光特性变化.结果表明:随着温度降低,广玉兰幼苗叶片的净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(G3)、叶肉细胞间隙CO2浓度(Ci)、叶绿素含量均逐步降低,最大光化学效率(Fv/Fm)、潜在光化学效率(Fv/F0)、最大量子产额(Yield)、光合电子传递速率(ETR)、光化学猝灭系数(qp)也均同时下降,而初始荧光(F0)、非光化学猝灭系数(qN)则逐步上升.可见,低温胁迫除导致光合作用的气孔抑制外,还直接损伤光合机构使PSⅡ反应中心失活,引起其光能原初捕捉能力和光能同化率减弱,增加了通过热辐射消耗的光能比例,最终导致广玉兰幼苗光合作用能力减弱.     

哀牢山湿性常绿阔叶林及不同类型次生植被的幼苗更新特征

采用"空间代替时间"的方法,对云南哀牢山徐家坝地区湿性常绿阔叶林及不同类型次生植被中木本植物幼苗的种类组成、数量及更新方式等进行了调查.结果表明:在所有调查样地中,共记录到木本植物幼苗46种,其中乔木31种、灌木15种.荒草地、滇山杨林、栎类萌生林、原生林4种不同植被类型的幼苗密度分别是(421.9±59.5)、(34.4±8.1)、(31.6±7.2)、(18.5±6.6)株·25 m-2.随着演替的进行,灌木的比例逐渐减小,乔木的比例则逐渐增加.在森林恢复演替过程中,处于演替初期的荒草地灌木萌生更新占优势,到了演替后期则以乔木萌生幼苗更新为主.随着群落演替进程的增加,幼苗密度逐渐减少,幼苗生活型和木本植物的幼苗更新方式均发生变化.     

外源一氧化氮对镉胁迫下黄瓜幼苗生长、活性氧代谢和光合特性的影响

镉是植物生长的非必需元素,它具有很大的生物毒性,与其它重金属相比,更易被植物吸收积累。通过采用营养液水培试验的方法,研究了外源一氧化氮（Nitric oxide,NO）对不同浓度Cd^2＋（100μmol L^-1．300μmol L^-1,500μmol L^-1）胁迫下黄瓜幼苗生长、叶片光合特性以及活性氧代谢的影响。结果表明：300μmol L^-1NO供体硝普钠（Sodium nitrop russide,SNP）能显著缓解镉胁迫时黄瓜植株造成的伤害,对300μmol L^-1 Cd^2＋处理的黄瓜幼苗缓解效果最好,可提高幼苗的生长量,增强幼苗叶片超氧物歧化酶（SOD）、过氧化物酶（POD）活性;提高了叶片叶绿素和脯氨酸（Pro）含量;降低了叶片内二醛（MDA）含量。     

SNP处理的辣椒幼苗对Cd^2＋胁迫的生理响应

采用溶液培养方法研究外源NO供体硝普钠（SNP）对Cd^2＋胁迫下辣椒幼苗生长和生理特性影响的结果表明：75μmol·L^-1SNP能在一定程度上缓解较高浓度Cd^2＋对辣椒幼苗生长、叶中Chla和Chlb含量以及根系活性的抑制作用,降低丙二醛（MDA）含量,增强超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、过氧化物酶（POD）的活性。     

Isolation and characterization of farnesyl diphosphate synthase from the cotton boll weevil,Anthonomus grandis

Farnesyl diphosphate synthase (FPPS) catalyzes the consecutive condensation of two molecules of isopentenyl diphosphate with dimethylallyl diphosphate to form farnesyl diphosphate (FPP). In insects, FPP is used for the synthesis of ubiquinones, dolicols, protein prenyl groups, and juvenile hormone. A full‐length cDNA of FPPS was cloned from the cotton boll weevil, Anthonomus grandis (AgFPPS). AgFPPS cDNA consists of 1,835 nucleotides and encodes a protein of 438 amino acids. The deduced amino acid sequence has high similarity to previously isolated insect FPPSs and other known FPPSs. Recombinant AgFPPS expressed in E. coli converted labeled isopentenyl diphosphate in the presence of dimethylallyl diphosphate to FPP. Southern blot analysis indicated the presence of a single copy gene. Using molecular modeling, the three‐dimensional structure of coleopteran FPPS was determined and compared to the X‐ray crystal structure of avian FPPS. The α‐helical fold is conserved in AgFPPS and the size of the active site cavity is consistent with the enzyme being a FPPS. © 2009 Wiley Periodicals, Inc.     

Influence of tannic acid and Cry1Ac toxin of Bacillus thuringiensis on larval survival, growth, and development of Helicoverpa armigera

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) causes huge economic losses in cotton production around the world. Tannin, one of the important secondary substances in cotton plants, can increase the δ‐endotoxin activity of Bacillus thuringiensis ssp. kurstaki. The mechanism of interaction between tannin and Bt toxin on H. armigera is unclear. We investigated the interaction between tannic acid and Cry1Ac toxin in H. armigera, and monitored survival, growth, and development during the larval period after treating the larvae with four concentrations of Cry1Ac toxin (0, 2, 8, and 14 μg^?1) alone or in combination with four concentrations of tannic acid (0, 0.5, 1, and 2 mg g^?1). Mortality of larvae treated with both tannic acid and Cry1Ac was higher than the mortality of larvae treated with tannic acid or Cry1Ac alone. Mortality was 47.5 and 51.5% in larvae treated with 14 μg g^?1 Cry1Ac alone or 2 mg g^?1 tannic acid alone, respectively. In contrast, larval mortality was 75% when treated with the mixture of 14 μg g^?1 Cry1Ac and 2 mg g^?1 tannic acid, suggesting that a mixture of the two enhanced the effectiveness of each one alone. The developmental time of larvae treated with the combination of tannic acid and Cry1Ac was significantly longer than when they were treated with Cry1Ac or tannic acid alone. Larval weight, pupal weight, and pupation rate were also significantly reduced in larvae treated with both toxins, compared with the larvae treated with either toxin alone. These results showed that the interactive effect of tannic acid and Cry1Ac on larval growth inhibition is additive, and that tannic acid improves Cry1Ac toxicity to insects. Tannic acid used in combination with B. thuringiensis might potentially reduce overall insecticide use, thus delaying development of insecticide resistance.     

Susceptibility of Tree Seedlings to Biotic and Abiotic Hazards in the Understory of a Moist Tropical Forest in Panama

We evaluated temporal patterns of seedling survival of eight Neotropical tree species generated under multiple abiotic and biotic hazards (vertebrates, disease, litterfall) in the forest understory on Barro Colorado Island, Panama. Seedlings were transplanted at first leaf expansion in low densities along a 6-km transect and damage and mortality were recorded for 1 yr. We also planted and monitored small and large artificial seedlings to estimate physical disturbance regimes. During 0–2 mo after transplant, vertebrate consumers of reserve cotyledons caused high mortality of real seedlings, but little damage to artificial seedlings. On real seedlings after 2 mo, disease became an important agent of mortality, despite a decrease in overall mortality rates. Damage by litterfall remained relatively low during the 1-yr study period. Survival ranks among species showed ontogenetic shifts over time, as species changed susceptibility to the mortality agents. Survival after 2 mo was positively correlated with stem toughness, not because species with tough stems were less likely to receive mechanical damage, but because they survived better after receiving mechanical damage. Within each transplant station, artificial seedlings were not good predictors of litterfall damage experienced by real seedlings. Forest-wide litterfall damage level, however, was similar for both real and artificial seedlings ( ca 10%/yr), a moderate level compared to other tropical forests. In conclusion, species traits including biomechanical traits interact to create complex temporal patterns of first year seedling survival, resulting in ontogenetic shifts that largely reflect changes in the relative importance of vertebrate consumers relative to other hazards.     

<Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated co-transformation of multiple genes in upland cotton

Two cotton genotypes, Simian 3 (SM 3) and WC, were co-transformed using a mixture of four Agrobacterium tumefaciens cultures of strain LBA4404, each carrying a plasmid harboring the following genes, Bt + sck (for Bacillus thuringenesis protein and modified Cowpea trypsin inhibitor), bar (for glufosinate), keratin, and fibroin. The frequency of callus induction, embryogenesis, and plant regeneration were notably different between the two genotypes. However, there were no differences between the two genotypes for number of plantlets carrying multiple gene copies of different gene combinations as well as transformation frequency for different gene combinations. PCR analysis indicated that more than 80% of plantlets carried the nptII gene for kanamycin resistance. Overall, the co-transformation frequency of two or more genes was about 35%. Southern blot analysis confirmed integration of target genes into the cotton genome, and the number of copies of the transgene(s) varied from one to four. Multiple transgene expression was confirmed by RT-PCR analysis in some transgenic lines. Further analysis of T₁ plants demonstrated that multiple transgenes were inherited and expressed in progenies. Fei-Fei Li and Shen-Jie Wu are joint first authors.