Comparison of Trunk and Branch Sap Flow with Canopy Transpiration in Pecan

Trunk and branch sap flow were compared with canopy transpirationin a 5-year-old pecan tree (Carya illinoensis ‘Wichita’).Total trunk sap flow, measured by a heat balance trunk flowgauge, was 122.8 kg over a 24 h period, corresponding closelyto the 113.4 kg of canopy transpiration measured by a largeprecision weighing lysimeter. Branches, less than half the diameterof the main trunk, had a total sap flow an order of magnitudeless than the total flow in the trunk. Sap flow in a branchwith a northern exposure was 41% less than that with a southernexposure. When sap flow was normalized per unit tree or branchleaf area, peak sap flow in the south branch matched that inthe main trunk. Tree transpiration and the sap flow in trunkand branches began concurrently, indicating little dynamic waterstorage in the trunk above the gauge. The hydraulic conductanceof the entire tree was 8 to 14 x 10^–14 m s^–1 Pa^–1,similar to values found for a number of woody and herbaceousspecies. Key words: Sap flow, Carya illinoensis, transpiration, lysimeter, trunk flow gauge     

金龙鱼(Scleropages:Osteoglossomorpha)化石的首次发现

金龙鱼化石的鳞片和骨骼碎片在过去时有报道,但鉴定并非十分可靠,因为在骨舌鱼科鱼类中这些鳞片和骨骼十分相似.首次记述了保存完美的金龙鱼化石,标本产于湖南湘乡下湾铺组和湖北松滋洋溪组,确立为骨舌鱼科金龙鱼属一新种:中华金龙鱼Scleropages sinensis sp.nov..新种与现生金龙鱼(Scleropages)在头部骨骼、尾骨骼、各鳍的形状和位置以及具有网状鳞片等方面极为相似,因而归入该属.然而,新种在以下特征上不同于金龙鱼的现生种:鼻骨无纹饰,鼻骨上的感觉管显露于沟内,感觉管联合不经过顶骨,翼耳骨侧向加厚,眶前骨上的感觉孔大,眼眶后的眶下骨不完全覆盖前鳃盖骨上支,其宽高比例为0.75而非现生种的1-1.2,前鳃盖骨后下角变尖,鳃盖骨后下缘凹形、下端变尖,匙骨背突长大,脊椎46-48,椎体横突短小,胸鳍十分长大,上下两端的尾鳍条和内部鳍条等长.亚洲的现生种发现于各种河流和小溪中,比较喜欢水草茂盛的静水环境,一般游弋于表层水中,以鱼虾、昆虫等为食,新种中华金龙鱼也应该有相似的生长环境和食性.新种似具有性二形性,雄鱼体形略纤细,头部略大,口裂更深.中华金龙鱼化石的发现,说明金龙鱼属(Scleropages)和骨舌鱼属(Osteoglossum)在早始新世以前就已经分化,这对解释骨舌鱼类的跨洋分布具有十分重要的意义.     

Vertical partitioning of CO2 production within a temperate forest soil

The major driving factors of soil CO₂ production – substrate supply, temperature, and water content – vary vertically within the soil profile, with the greatest temporal variations of these factors usually near the soil surface. Several studies have demonstrated that wetting and drying of the organic horizon contributes to temporal variation in summertime soil CO₂ efflux in forests, but this contribution is difficult to quantify. The objectives of this study were to partition CO₂ production vertically in a mixed hardwood stand of the Harvard Forest, Massachusetts, USA, and then to use that partitioning to evaluate how the relative contributions of CO₂ production by genetic soil horizon vary seasonally and interannually. We measured surface CO₂ efflux and vertical soil profiles of CO₂ concentration, temperature, water content, and soil physical characteristics. These data were applied to a model of effective diffusivity to estimate CO₂ flux at the top of each genetic soil horizon and the production within each horizon. A sensitivity analysis revealed sources of uncertainty when applying a diffusivity model to a rocky soil with large spatial heterogeneity, especially estimates of bulk density and volumetric water content and matching measurements of profiles and surface fluxes. We conservatively estimate that the O horizon contributed 40–48% of the total annual soil CO₂ efflux. Although the temperature sensitivity of CO₂ production varied across soil horizons, the partitioning of CO₂ production by horizon did not improve the overall prediction of surface CO₂ effluxes based on temperature functions. However, vertical partitioning revealed that water content covaried with CO₂ production only in the O horizon. Large interannual variations in estimates of O horizon CO₂ production indicate that this layer could be an important transient interannual source or sink of ecosystem C.     

Foraging behaviour and habitat partitioning of two sympatric cormorants in Patagonia, Argentina

Radiotelemetry was used to assess the distribution and diving behaviour of Rock Shags Phalacrocorax magellanicus and Red-legged Cormorants Phalacrocorax gaimardi breeding in sympatry, and Rock Shags breeding in isolation. When breeding in sympatry there was little overlap in the foraging locations of the two species, with the highest densities of each species separated by 10 km. Red-legged Cormorants fed significantly closer to the breeding colony than did Rock Shags and undertook shorter foraging trips, making almost twice as many foraging trips per day as Rock Shags. Rock Shags breeding in isolation had a shorter foraging range than the birds breeding in sympatry with Red-legged Cormorants and foraging trip duration was significantly shorter. However, the number of feeding trips per day was similar between areas of sympatry and allopatry. Differences in the foraging ecology of Rock Shags in areas of sympatry and allopatry may be due to interspecific competition, which forces niche differentiation. The distance between foraging sites, the speed of movement of the prey, a species tendency to move into prey-depleted areas and the length of the breeding season (during which the birds are constrained to be in the same area) may play critical roles in determining the extent to which differential area use by competitors is a strategy that benefits both parties.     

Biochemical Analysis of a Mutant Tetrahymena Lacking Outer Dynein Arms

ABSTRACT. Tetrahymena thermophila mutants homozygous for the oad mutation become nonmotile when grown at the restrictive temperature, and axonemes isolated from nonmotile mutants lack approximately 90% of their outer dynein arms. Electrophoretic analyses of axonemes isolated from nonmotile mutants ( oad axonemes) indicate they contain significantly fewer of the 22 S dynein heavy chains that axonemes isolated from wild-type cells (wild-type axonemes) contain. The 22 S dynein heavy chains that remain in axonemes isolated from nonmotile, oad mutants are assembled into 22 S dynein particles that exhibit wild-type levels of ATPase activity. Two-dimensional gel electrophoresis of oad axonemes show that they are deficient in no proteins other than those proteins thought to be components of 22 S dynein. This report is the first formal proof that outer dynein arms in Tetrahymena cilia are composed of 22 S dynein.     

The Titrimetric Assay of OH- and HCO3- Excreted by Ricinus Cultivated on NO3--containing Nutrient Media: The Influence of Ionic Strength, End Point pH and CO2 Supersaturation

Allen, S. and Allen, C. R. 1987. The titrimetric assay of OH^–and excreted by Ricinus cultivatedon -containing nutrient media: the influence of ionic strength, end point pH and CO² supersaturation.–J. exp. Bot. 38: 607–617. When spent -containing nutrient media were titrated to the starting pH of 6.5 the titre wasequivalent to 50%orless of the base (i.e. ) excreted. Calculation of the total amount of baseexcreted could only be made from data obtained by titrationto pH 4–5. An accurate calculation of the amount of baserequired the inclusion of activity coefficients, estimated fromionic strength, in the calculations. Spent nutrient media contained from four to ten times the concentrationof CO₂ predicted from equilibrium values. It is probable that is very slow. Key words: Ricinus, nitrate-N nutrient medium, base excretion, ionic activity coefficients, carbon dioxide supersaturation     

Variation in leaf respiration in relation to growth and photosynthesis of Lolium

Six Lolium genotypes with contrasting apparent photorespiration and CO_a compensation concentration, [C0₂]_c, were compared for net photosynthesis, dark respiration, leaf starch accumulation, rate of leaf expansion and shoot regrowth. Plants were grown in day/night temperatures of 15/10 and 25/20 ^oC. There were significant (P < 0–05) differences between the genotypes in all these parameters. At 25/20 ^oC apparent photorespiration was correlated with [CO₂]_c. Correlation coefficients, pooled from both temperature regimes, revealed that genotypes with high rates of net photosynthesis accumulated more leaf starch during light periods than genotypes with slow photosynthesis, but rates of leaf expansion and dry matter increase were only correlated, negatively, with dark respiration. Apparent photorespiration was negatively correlated with dark respiration. These findings suggest that attributes related to photorespiration such as [CO₂]_c and O₂ uptake from CO₂-free air in the light are unlikely to be useful selection criteria for growth of C₃ grasses, that net photosynthesis was probably not limiting growth and that maintenance respiration may have been an important determinant of genotypic differences in growth rate. Selections for slow and fast rates of dark respiration of mature leaves were therefore made at 8 and at 25 ^oC from within two different populations of L. perenne, S.23. This characteristic showed repeatabilities (broad-sense heritability) of from 0–41 to o-66. Six independent comparisons of simulated swards of the slow- and fast-respiring selections were made under periodic cutting regimes, either in a growth room at 25 ^oC or in a glasshouse from August to May. Growth of all plots of slow-respiring genotypes was consistently more rapid than that of the fast-respiring, at 25 ^oC in the growth room, and during autumn and spring in the glasshouse. There was no difference in winter growth. The implications of these results for the use of gas exchange measurements as selection criteria in plant breeding programmes are discussed.     

Microsatellite loci for distinguishing spotted owls (Strix occidentalis), barred owls (Strix varia), and their hybrids

We identified four diagnostic microsatellite loci that distinguish spotted owls (Strix occidentalis), barred owls (Strix varia), F₁ hybrids and backcrosses. Thirty‐four out of 52 loci tested (65.4%) successfully amplified, and four of these loci (11.8%) had allele sizes that did not overlap between spotted and barred owls. The probability of correctly identifying a backcross with these four loci is 0.875. Genotyping potential hybrid owls with these markers revealed that field identifications were often wrong. Given the difficulty of identifying hybrids in the field, these markers will be useful for hybrid identification, law enforcement and spotted owl conservation.     

Effects of potato leafroll virus on the crop processes leading to tuber yield in potato cultivars which differ in tolerance of infection

The effects of infection with potato leafroll virus (PLRV) on the four crop processes leading to tuber fresh weight yield were examined in field plots of four cultivars (Montana, Pentland Crown, Maris Piper and King Edward) differing in tolerance to infection. Averaged across cultivars, infection decreased yield by 50%. This decrease was equally due to less light (total solar radiation) being intercepted, a lower efficiency with which intercepted light was converted into dry weight, and a smaller proportion of dry weight being partitioned to tubers. Dry matter content of the tubers was also diminished but to a lesser extent. The main difference between the cultivars in their response to infection was in the partitioning of dry weight. In Montana and Pentland Crown, harvest index was decreased by 15% in infected plants, whereas in the less tolerant cultivars, Maris Piper and King Edward, it was decreased by 25%. The decline in photosynthetic performance of Montana, a cultivar with slightly earlier maturity than the other three, was delayed in PLRV-infected plants. Effects on number of daughter tubers essentially reflected those on yield to the extent that average tuber weight did not change in Maris Piper, was one third less in King Edward, and the change was intermediate in Montana and Pentland Crown.     

HARD PATERNALISM,FAIRNESS AND CLINICAL RESEARCH: WHY NOT?

Jansen and Wall suggest a new way of defending hard paternalism in clinical research. They argue that non‐therapeutic research exposing people to more than minimal risk should be banned on egalitarian grounds: in preventing poor decision‐makers from making bad decisions, we will promote equality of welfare. We argue that their proposal is flawed for four reasons. First, the idea of poor decision‐makers is much more problematic than Jansen and Wall allow. Second, pace Jansen and Wall, it may be practicable for regulators to uncover the values that a potential research participant holds when agreeing to enter a research project, so their claim that we must ban such research projects for all if we are to ban them for poor decision‐makers looks to be unmotivated. Third, there seem to be cases where the liberty to enter the sort of research project Jansen and Wall discuss is morally weighty, and arguably should outweigh concerns of egalitarian distribution. Fourth, banning certain types of research, which seem on the face of it to offer an unfavourable risk‐benefit ratio, would have unwelcome consequences for all clinical research, which Jansen and Wall do not recognize.