Flavonoid Responses in Wheat Grown at Elevated CO2: Green Versus Senescent Leaves

We compared flavonoids in green, mature, and senescing flag leaves of wheat grown under ambient (AC - 370 mol mol^-1) and elevated (EC - 550 mol mol^-1) concentrations of CO₂ in a FACE (Free Air CO₂ Enrichment) system. The concentrations of flag leaf flavonoids (e.g., isoorientin and tricin) decreased to one third in mature leaves, and the majoritary isoorientin almost disappeared in senescing leaves. Flavonoid concentrations increased in green well-developed flag leaves under EC (46 % isoorientin and 55 % tricin), whereas the differences disappeared in mature and senescing flag leaves. Predictions of changes in litter phenolic concentrations and their effects on decomposition rates under EC based on changes in green leaves need to be revised.     

Stereoselectivity of Pseudomonas cepacia lipase toward secondary alcohols: a quantitative model

The lipase from Pseudomonas cepacia represents a widely applied catalyst for highly enantioselective resolution of chiral secondary alcohols. While its stereopreference is determined predominantly by the substrate structure, stereoselectivity depends on atomic details of interactions between substrate and lipase. Thirty secondary alcohols with published E values using P. cepacia lipase in hydrolysis or esterification reactions were selected, and models of their octanoic acid esters were docked to the open conformation of P. cepacia lipase. The two enantiomers of 27 substrates bound preferentially in either of two binding modes: the fast-reacting enantiomer in a productive mode and the slow-reacting enantiomer in a nonproductive mode. Nonproductive mode of fast-reacting enantiomers was prohibited by repulsive interactions. For the slow-reacting enantiomers in the productive binding mode, the substrate pushes the active site histidine away from its proper orientation, and the distance d(H(N epsilon) - O(alc)) between the histidine side chain and the alcohol oxygen increases, d(H(N epsilon) - O(alc)) was correlated to experimentally observed enantioselectivity: in substrates for which P. cepacia lipase has high enantioselectivity (E > 100), d(H(N epsilon) - O(alc)) is >2.2 A for slow-reacting enantiomers, thus preventing efficient catalysis of this enantiomer. In substrates of low enantioselectivity (E < 20), the distance d(H(N epsilon) - O(alc)) is less than 2.0 A, and slow- and fast-reacting enantiomers are catalyzed at similar rates. For substrates of medium enantioselectivity (20 < E < 100), d(H(N epsilon) - O(alc)) is around 2.1 A. This simple model can be applied to predict enantioselectivity of P. cepacia lipase toward a broad range of secondary alcohols.     

The pi-helix translates structure into function

A search for the occurrence of the rare pi-helix was performed with Iditis from the Oxford Molecular Group upon the Protein Data Bank. In 8 of the 10 confirmed crystal structures that harbor the pi-helix, its unique conformation has been linked directly to the formation or stabilization of a specific binding site within the protein. In the discussion to follow, the role for each of these eight pi-helices will be addressed in regard to protein function. It is clear upon closer examination that the conformation of the pi-helix has evolved to provide unique structural features within a variety of proteins.     

Leaf litter inhabiting beetles as surrogates for establishing priorities for conservation of selected tropical montane cloud forests in Honduras, Central America (Coleoptera; Staphylinidae, Curculionidae)

Thirteen tropical montane cloud forests (TMCFs) in Honduras and adjacent El Salvador were evaluated for species diversity and endemism in leaf litter inhabiting Curculionidae (weevils) and Staphylinidae in June and August of 1994. Totals of 26,891 specimens representing 293 species of Curculionidae, and 7349 specimens representing 224 species of Staphylinidae, were collected. Regional endemism was high with 173 species (58.7% of total) of Curculionidae and 126 species (56.3% of total) of Staphylinidae, restricted to single sites. Measures of diversity (number of observed species [Sobs]; number of endemic species) and estimates of biodiversity (Chao 2, first and second order Jackknife and Bootstrap richness estimators) are given for each site for Curculionidae and Staphylinidae. Priority-areas analyses based on Sobs (Greedy), Sobs, Chao 2, number of endemic species, site complementarity and higher taxonomic diversity (Curculionidae only) are presented. Weak or lack of correlation was noted between site area and site diversity for either Curculionidae or Staphylinidae. The optimum sequence for site conservation was determined based on Sobs (Greedy). Four sites are identified as the highest conservation priorities; Parque Nacional Montecristo, P.N. La Muralla, P.N. Santa Barbara and P.N. Comayagua. Identification as high priority sites supports their designation as Parques Nacionales rather than the less diverse Reservas Biologias or Reservas Vidas Silvestres. While closely approximating performance of Sobs (Greedy), no one of Sobs, number of endemics, Chao 2 or site complementarity give results equivalent to the optimum sequence based on Sobs (Greedy) and the latter is concluded to be the best method for establishing conservation priorities in TMCF. Results of the analyses based on one of Curculionidae or Staphylinidae differ in the ordering of site priorities based on each of Sobs, Chao 2 or number of endemics at each site, with at best, weak positive correlations between results based on each taxon. Data from other taxa are necessary to determine if one of Curculionidae or Staphylinidae emerges as the better surrogate for general patterns of biodiversity in TMCF. Conservation strategies in Central America should emphasize the importance of TMCF particularly in view of high regional endemism. In formulating these strategies, consideration needs to be given to the preservation of many small regional preserves rather than fewer larger preserves. Data from inventories of other taxa should be included where available and all biological data should be integrated with social and cultural issues of regional importance.     

次生栎林蒸腾强度与生态因子的关系

采用多元回归分析和灰色关联分析方法,探讨下蜀次生栎林蒸腾强度与生态因子的相关关系。研究认为用二次工咕次多项式回归方程和指数回归方程拟合更能反映各生态因子在整个生长季中与蒸腾强度关系的性质。影响蒸腾强度的主要生态因子是温度和净辐射;其次是空气相对湿度和土壤热流通量;风速和土壤含水率的影响很小。灰色关联分析与多元回归分析的结论一致。研究结果为进一步阐明次生栎林的结构和功能提供了理论基础。     

西双版纳人工林林窗光照剖线分布特征

以林窗北缘为中心,研究了西双版纳地区橡胶林林窗及周边Ｎ－Ｓ样带上光照水平梯度分布。结果表明：林窗的发生导致光照明显增加,从林内到林窗中央,光强呈明显增大趋势,上午雾末消退时,相对光照强度水平梯度变化曲线峰值出现于林窗中央,午后雾消退后,林窗边缘为相对光强梯度变化最甚的地段,峰值由林窗中央向林窗北缘移进。林窗边缘,林窗中央及林内光照强度日变化曲线均为不对称的单峰型,但峰值出现和振幅不同。在太阳高度角     

Fish Communities in Central Amazonian White- and Blackwater Floodplains

In Amazonian floodplains, the flood cycle of the river is becoming the dominant seasonal factor, and fish communities are found to fluctuate greatly over the year. During inundation, fish migrate into floodplain forests to feed on fruits and seeds, in an area more than 300000km² in size. To document patterns of species diversity, distribution, abundance and temporal dynamics and in order to describe the ecological importance of the inundated forest, floodplain fish were captured using variously sized gill nets in white and black water areas inside and outside the floodplain forests during low, rising, high and falling water level in 1990 and 1991. Dominance varies to some extent in white water between floodplain forest (0.06) and open water (0.11) while it is unchanged in black water (0.04). Black water fish communities were more diverse. Most abundant among white water fish were Liposarcus pardalis, Pygocentrus nattereri, and Pellona flavipinnis, for example, or Plagioscion squamsissimus, Serrasalmus rhombeus, and Serrasalmus manueli in black water. Among the most abundant white water fish, Colossoma macropomum, Mylossoma duriventre and Osteoglossum bicirrhosum occurred almost exclusively in inundated forests. Of the black water species there were a large number of species which were captured only in inundated forest, such as Geophagus cf. altifrons, Hoplias malabaricus, Osteoglossum bicirrhosum and Uaru amphiacanthoides. Catches varied with sample site, water level and direction of water level change. The average CPUE in white and black water was 190 and 41g fishm^–2 and day, respectively, with maximum yields at low water and minimum yields at high water. Comparing rising and falling water levels, a significantly higher quantity of fishes was captured at falling water level. In black water, fish catches from the floodplain forest exceeded the open water catch by 183 to 550%, depending on season. Differences in respect of white water are smaller (106–281%). Fish communities in the area under investigation seem to be stochastically assembled, with significant differences between white and black water only. Many fishes move into the floodplain forest not only to feed but probably also for other reasons – to seek shelter, for example.     

Evaluation of major genetic loci contributing to inbreeding depression for survival and early growth in a selfed family of Pinus taeda

The magnitude of fitness effects at genetic loci causing inbreeding depression at various life stages has been an important question in plant evolution. We used genetic mapping in a selfed family of loblolly pine (Pinus taeda L.) to gain insights on inbreeding depression for early growth and viability. Two quantitative trait loci (QTLs) were identified that explain much of the phenotypic variation in height growth through age 3 and may account for more than 13% inbreeding depression in this family. One of these QTLs maps to the location of cad-nl, a lignin biosynthesis mutation. Both QTLs show evidence of overdominance, although evidence for true versus pseudo-overdominance is inconclusive. Evidence of directional dominance for height growth was noted throughout the genome, suggesting that additional loci may contribute to inbreeding depression. A chlorophyll-deficiency mutation, spf did not appear to be associated with growth effects, but had significant effects on survival through age 3. Previously identified embryonic viability loci had little or no overall effect on germination, survival, or growth. Our results challenge, at least in part, the prevailing hypothesis that inbreeding depression for growth is due to alleles of small effect. However, our data support predictions that loci affecting inbreeding depression are largely stage specific.     

Responses of N fluxes and pools to elevated atmospheric CO2 in model forest ecosystems with acidic and calcareous soils

The objectives of this study were to estimate how soil type, elevated N deposition (0.7 vs. 7 g N m^–2y^–1) and tree species influence the potential effects of elevated CO₂ (370 vs. 570 mol CO₂ mol^–1) on N pools and fluxes in forest soils. Model spruce-beech forest ecosystems were established on a nutrient-rich calcareous sand and on a nutrient-poor acidic loam in large open-top chambers. In the fourth year of treatment, we measured N concentrations in the soil solution at different depths, estimated N accumulation by ion exchange resin (IER) bags, and quantified N export in drainage water, denitrification, and net N uptake by trees. Under elevated CO₂, concentrations of N in the soil solution were significantly reduced. In the nutrient-rich calcareous sand, CO₂ enrichment decreased N concentrations in the soil solution at all depths (–45 to –100%). In the nutrient-poor acidic loam, the negative CO₂ effect was restricted to the uppermost 5 cm of the soil. Increasing the N deposition stimulated the negative impact of CO₂ enrichment on soil solution N in the acidic loam at 5 cm depth from –20% at low N inputs to –70% at high N inputs. In the nutrient-rich calcareous sand, N additions did not influence the CO₂ effect on soil solution N. Accumulation of N by IER bags, which were installed under individual trees, was decreased at high CO₂ levels under spruce in both soil types. Under beech, this decrease occurred only in the calcareous sand. N accumulation by IER bags was negatively correlated with current-years foliage biomass, suggesting that the reduction of soil N availability indices was related to a CO₂-induced growth enhancement. However, the net N uptake by trees was not significantly increased by elevated CO₂. Thus, we suppose that the reduced N concentrations in the soil solution at elevated CO₂ concentrations were rather caused by an increased N immobilisation in the soil. Denitrification was not influenced by atmospheric CO₂ concentrations. CO₂ enrichment decreased nitrate leaching in drainage by 65%, which suggests that rising atmospheric CO₂ potentially increases the N retention capacity of forest ecosystems.     

High abscission rates of damaged expanding leaves: field evidence from seedlings of a Bornean rain forest tree

Herbivore damage is known to cause the premature loss of mature leaves. However, the effects of herbivory on abscission during the early stages of leaf development remain unexplored, even though herbivores frequently prefer unlignified, immature leaves. In a field experiment, we removed 50% of the tissue from leaves at various stages of development on seedlings of Shorea hopeifolia (Dipterocarpaceae), a dominant rain forest tree in Indonesian Borneo. Four weeks following simulated herbivory, >88% of unlignified expanding leaves had been abscised, compared to only 20% of fully expanded, unlignified leaves and 0% of recently lignified, mature leaves. In a separate experiment over 9 wk, simulated herbivory did not increase abscission rates of mature leaves, even when 75% of leaf tissue was removed. Because most (58%) of S. hopeifolia seedlings under natural conditions had lost 1% or less of the tissue from their mature leaves, herbivore damage probably has little effect on the abscission of mature leaves. In contrast, the tendency for damaged expanding leaves to abscise may explain why 49% of S. hopeifolia seedlings had already lost their youngest leaf. If similar patterns occur in other species, herbivore attacks on developing leaves may contribute substantially to both leaf loss and the cumulative impact of herbivory on the growth and survival of whole plants.