Seasonal and diurnal trends in progressive isotope enrichment along needles in two pine species

The Craig–Gordon type (C–G) leaf water isotope enrichment models assume a homogeneous distribution of enriched water across the leaf surface, despite observations that Δ¹⁸O can become increasingly enriched from leaf base to tip. Datasets of this ‘progressive isotope enrichment’ are limited, precluding a comprehensive understanding of (a) the magnitude and variability of progressive isotope enrichment, and (b) how progressive enrichment impacts the accuracy of C–G leaf water model predictions. Here, we present observations of progressive enrichment in two conifer species that capture seasonal and diurnal variability in environmental conditions. We further examine which leaf water isotope models best capture the influence of progressive enrichment on bulk needle water Δ¹⁸O. Observed progressive enrichment was large and equal in magnitude across both species. The magnitude of this effect fluctuated seasonally in concert with vapour pressure deficit, but was static in the face of diurnal cycles in meteorological conditions. Despite large progressive enrichment, three variants of the C–G model reasonably successfully predicted bulk needle Δ¹⁸O. Our results thus suggest that the presence of progressive enrichment does not impact the predictive success of C–G models, and instead yields new insight regarding the physiological and anatomical mechanisms that cause progressive isotope enrichment.     

Effect of competition on stable carbon isotope ratios of two tussock grass species

Summary Previous studies have shown that plant carbon isotope composition varies when plants experience differences in water and nutrient availability. However, none have addressed the effect of root interactions, including competition for these soil resources, on carbon isotope ratios. We studied the effect of interspecific root interactions on the productivity and carbon isotope ratios of two Great Basin tussock grass species (Agropyron desertorum and Pseudoroegneria spicata). We compared grasses grown in mixture with sagebrush (Artemisia tridentara) to grasses in similar mixtures but where root interactions with sagebrush were limited by fiberglass partitions. During both years of the study, tussocks growing in competition with sagebrush produced tissue with more negative ¹³C values than grasses experiencing limited root interaction with sagebrush. The magnitude of this difference (0.5 to 0.9%) is similar to that found in other studies when soil fertility and moisture availability were altered.     

Ophiostomatoid fungi including two new fungal species associated with pine root-feeding beetles in northern Spain

Many bark beetles live in a symbiosis with ophiostomatoid fungi but very little is known regarding these fungi in Spain. In this study, we considered the fungi associated with nine bark beetle species and one weevil infesting two native tree species (Pinus sylvestris and Pinus nigra) and one non-native (Pinus radiata) in Cantabria (Northern Spain). This included examination of 239 bark beetles or their galleries. Isolations yielded a total of 110 cultures that included 11 fungal species (five species of Leptographium sensu lato including Leptographium absconditum sp. nov., five species of Ophiostoma sensu lato including Ophiostoma cantabriense sp. nov, and one species of Graphilbum). The most commonly encountered fungal associates of the bark beetles were Grosmannia olivacea, Leptographium procerum, and Ophiostoma canum. The aggressiveness of the collected fungal species was evaluated using inoculations on two-year-old P. radiata seedlings. Leptographium wingfieldii, Leptographium guttulatum, and Ophiostoma ips were the only species capable of causing significant lesions.     

Interspecific interactions between coexisting Siberian and Ezo salamander larvae examined by stable isotope analyses

Limnology - Hokkaido Island is inhabited by two salamander species, Siberian salamander (Salamandrella keyserlingii) and Ezo salamander (Hynobius retardatus), which were previously considered...     

Trophic relationships of two species of grebe on a prairie lake based on stable isotope analysis

Loch Leven, U.K., contains brown trout (Salmo trutta), eel (Anguilla anguilla), minnow (Phoxinus phoxinus), perch (Perca fluviatilis), pike (Esox lucius) and three-spined stickleback (Gasterosteus aculeatus), with brook lamprey (Lampetra planeri) and stone loach (Barbatula barbatula) also present in its tributaries. Arctic charr (Salvelinus alpinus), Atlantic salmon (Salmo salar) and flounder (Platichthys flesus) are now extinct. The brown trout population has supported a world-renowned recreational fishery for over a century, although a decline in fishery performance led to extensive stocking between 1983 and 2006, including with non-native rainbow trout (Oncorhynchus mykiss). This review combines historical information with contemporary gill-net and hydroacoustic surveys. In 2008, brown trout, perch and three-spined sticklebacks were abundant, but pike and stone loach were rare. The obstruction of migratory routes was probably responsible for the loss of Atlantic salmon and flounder, while a lowering of water level likely caused the extinction of Arctic charr and contributed to a reduction in pike abundance. Perch abundance has fluctuated markedly, being influenced by disease and eutrophication, although a reduction in nutrients and associated recovery of macrophytes are likely to have benefitted this species. Although the brown trout population has undoubtedly shown a long-term decline, individuals are currently in excellent condition.     

A single-substrate model to interpret intra-annual stable isotope signals in tree-ring cellulose

The carbon and oxygen stable isotope composition of wood cellulose ( δ ¹³C_cellulose and δ ¹⁸O_cellulose, respectively) reveal well-defined seasonal variations that contain valuable records of past climate, leaf gas exchange and carbon allocation dynamics within the trees. Here, we present a single-substrate model for wood growth to interpret seasonal isotopic signals collected in an even-aged maritime pine plantation growing in South-west France, where climate, soil and flux variables were also monitored. Observed seasonal patterns in δ ¹³C_cellulose and δ ¹⁸O_cellulose were different between years and individuals, and mostly captured by the model, suggesting that the single-substrate hypothesis is a good approximation for tree ring studies on Pinus pinaster , at least for the environmental conditions covered by this study. A sensitivity analysis revealed that the model was mostly affected by five isotopic discrimination factors and two leaf gas-exchange parameters. Modelled early wood signals were also very sensitive to the date when cell wall thickening begins ( t _wt). Our model could therefore be used to reconstruct t _wt time series and improve our understanding of how climate influences this key parameter of xylogenesis.     

Revisiting the fate of buds: size and position drive bud mortality and bursting in two coexisting Mediterranean Quercus species with contrasting leaf habit

Understanding the relationships between bud size and position and bud fate through time is crucial for identifying and subsequently modeling the mechanisms underlying tree architecture. However, there is a lack of information on how bud size drives crown architectural patterns in coexisting tree species. We studied bud demography in two coexisting Mediterranean oak species with contrasting leaf habit (Quercus ilex, evergreen; Q. faginea, deciduous). The main objective was to analyse the effect of bud size on the fate of buds with different positions along the shoot (apical, leaf axillary and scale-cataphyll axillary buds). The number, length and position of all buds and stems were recorded in marked branches during 4 years. Study species presented different strategies in bud production and lifespan. The evergreen species showed greater mortality rate than the deciduous one, which produced larger buds. Bud size and position were highly related since apical buds where longer than axillary ones and bud length declined basipetally along the stem. Apical buds had also higher chances of bursting than axillary ones. Within positions, longer buds presented a higher probability of bursting than shorter ones, although no absolute size threshold was found below which bud bursting was impaired. In Q. ilex, four-year-old buds were still viable and able to burst, whereas in Q. faginea practically all buds burst in their first year or died soon after. Such different bud longevities may indicate contrasting strategies in primary growth between both species. Q. ilex is able to accumulate viable buds for several ages, whereas Q. faginea seems to rely on the production of large current-year buds with high bursting probability under favourable environmental conditions.     

Vibrio species associated with mortality of sharks held in captivity

Two urease-positiveVibrio spp. were isolated from a brown shark (Carcharhinus plumbeus) that died in captivity at a national aquarium. Morphological, biochemical, and molecular genetic studies revealed one of the isolates to beV. damsela; the other isolate was unique and has been classified asV. carchariae sp. nov. BothV. damsela andV. carchariae were found to be virulent for spiny dogfish (Squalus acanthias), causing death in less than 18 hours after intraperitoneal injection of ca. 4×10⁶ cells.V. damsela was strongly cytotoxic for Y1 adrenal cell monolayers;V. carchariae exhibited weak cytotoxicity for Y1 cells.V. damsela contained cryptic plasmids and both isolates were urease positive.V. carchariae was able to utilize urea as sole source of carbon and nitrogen.     

Photosynthesis, water use efficiency and stable carbon isotope composition are associated with anatomical properties of leaf and xylem in six poplar species

Although fast‐growing Populus species consume a large amount of water for biomass production, there are considerable variations in water use efficiency (WUE) across different poplar species. To compare differences in growth, WUE and anatomical properties of leaf and xylem and to examine the relationship between photosynthesis/WUE and anatomical properties of leaf and xylem, cuttings of six poplar species were grown in a botanical garden. The growth performance, photosynthesis, intrinsic WUE (WUE_i), stable carbon isotope composition (δ¹³C) and anatomical properties of leaf and xylem were analysed in these poplar plants. Significant differences were found in growth, photosynthesis, WUE_i and anatomical properties among the examined species. Populus cathayana was the clone with the fastest growth and the lowest WUE_i/δ¹³C, whereas P. × euramericana had a considerable growth increment and the highest WUE_i/δ¹³C. Among the analysed poplar species, the highest total stomatal density in P. cathayana was correlated with its highest stomatal conductance (g_s) and lowest WUE_i/δ¹³C. Moreover, significant correlations were observed between WUE_i and abaxial stomatal density and stem vessel lumen area. These data suggest that photosynthesis, WUE_i and δ¹³C are associated with leaf and xylem anatomy and there are tradeoffs between growth and WUE_i. It is anticipated that some poplar species, e.g. P. × euramericana, are better candidates for water‐limited regions and others, e.g. P. cathayana, may be better for water‐abundant areas.     

Instar-dependent mortality rates of coexisting Daphnia species in Lake Vechten, The Netherlands

In Lake Vechten, population parameters were determined for twocoexisting Daphnia species, D.hyalina and D.cucullata, fromApril 23 to December 10, 1986. Daphnia hyalina is dominant inspring and D.cucullata in summer and autumn. Size frequencydistributions were converted into instar frequency distributionsby using experimental growth curves and field measurements onnewborn size and the size at first reproduction. A discreteevent computer model was used to calculate the instar mortalityrates. Relative importances of instar mortality rates for thepopulation mortality rate were calculated and discussed. Themortality of the juvenile stages was found to be more importantthan adult mortality during most of the sampling season, despiteegg mortality when egg-bearing females are killed. Only in Septemberand October was the mortality of adult instars more important.Correlation coefficients between differences in the rates ofincrease and differences in mean brood size and instar mortalitiesshow that the former are caused mainly by differences in juvenilemortality, the main factor determining the replacement of D.hyalinaby D.cucullata during early summer.     

基于碳、氮稳定同位素的厦门筼筜湖两种优势端足类食性分析

测定了厦门市筼筜湖(内、外湖)大型海藻群落两种优势端足类(强壮藻钩虾Ampitheoe valida和上野蜾蠃蜚Corophium uenoi)及其潜在食源的碳、氮稳定同位素比值(δ~(13)C和δ~(15)N),分析研究了这两种端足类摄食习性的空间变动特征。研究发现,端足类的潜在食源包括悬浮颗粒有机物(Particulate organic matter:POM),沉积有机物(Sedimentary organic matter:SOM),石莼(Ulva lactuca:Ulva)及其表面的附生生物(Epiphytes:Epi),它们的δ~(13)C和δ~(15)N值分别介于-24.0‰(POM)—-11.8‰(Ulva)和-1.7‰(POM)—4.7‰(Ulva)之间。其中,Ulva和POM的δ~(13)C值的内、外湖差异不显著;而外湖SOM和Epi的δ~(13)C值则明显高于内湖。采样区SOM有机质来源的空间差异是其δ~(13)C内、外湖差异的主要原因。除POM外,外湖有机碳源的δ~(15)N明显高于内湖,这与它们利用氮源的δ~(15)N的差异有关。潜在食源稳定同位素组成的空间差异,使得筼筜湖端足类的稳定同位素组成,尤其是δ~(15)N值表现出显著的空间变动特征(强壮藻钩虾和上野蜾蠃蜚δ~(15)N的内、外湖差异高达1.6‰和4.2‰,变幅约1个营养级),但2种端足类食性的空间差异却不尽相同:强壮藻钩虾的食性相对稳定,其δ~(13)C值介于Ulva和Epi之间,表明它主要从Ulva及其表面的Epi获取碳源;而上野蜾蠃蜚的食性内、外湖差异较大:内湖从石莼表面的Epi获取碳源,约20%是来自POM的贡献,而外湖则主要以Ulva及其表面的Epi为食。分析显示,筼筜湖内、外湖端足类δ~(15)N的空间差异并不是端足类的营养级发生了变化,而是由于端足类食源δ~(15)N的空间差异引起的,而不同端足类食性的内、外湖差异则可能与环境中饵料的丰度和生物量密切相关。     

Elevational changes in productivity of saplings relate to distribution of two congeneric tree species

Journal of Plant Research - Elevational changes in vegetation are associated with changes in environmental factors, an example of which is provided by the shade-tolerant Abies mariesii and less...     

Mother-offspring isotope fractionation in two species of placentatrophic sharks

Stable-isotope values of a scalloped hammerhead Sphyrna lewini and blacktip shark Carcharhinus limbatus and their respective embryos were analysed. Embryos of both species were enriched in δ(15) N compared to their mothers (0·82 and 0·88‰, respectively), but fractionation of δ(13) C varied. Embryonic S. lewini were enriched (1·00‰) in δ(13) C while C. limbatus were depleted (0·27‰) relative to their mothers.     

Habitat and diet variability of two coexisting tit species in central European forests

Capsule: Blue Tits and Great Tits occupied different habitats within forests in Central Europe but their nestlings shared a similar diet.

Aims: To quantify the differences in offspring diet and territory habitat between Great Tits Parus major and Eurasian Blue Tits Cyanistes caeruleus in two European forests, and to test whether the ecological niches of the two species overlap.

Methods: Research was conducted on Great Tits and Eurasian Blue Tits, breeding in nest boxes in two forests near Kraków, Poland, during years: 2009, 2011 and 2012. Nine days after hatching, food items were collected from offspring using neck-collars. Habitat parameters surrounding each nest box were quantified.

Results: Great Tit territories were in old Oak-Hornbeam forest, whereas Blue Tits often nested in mixed forest. There were no significant differences between the two bird species in the variation in their caterpillar diets for which both species were highly variable. Great Tits collected more caterpillars of Noctuidae per nest than did Blue Tits in 2009 and 2011 in Niepo?omice Forest; Blue Tits collected more Tortricidae in 2011 and more spiders every year. In Krzyszkowice Forest in 2012, tits fed their nestlings in different periods and did not differ in the proportion of caterpillars. Habitat affected diet differently in each species.

Conclusion: Although Great Tits and Blue Tits occupied different territories in each forest and year of research, the diets of both species’ nestlings contained similar species of invertebrates. The overlaps of the birds’ environmental needs are specific at a local scale.     

Contrasting genetic patterns between two coexisting Eleutherococcus species in northern China

Climate oscillations are the key factors to understand the patterns in modern biodiversity. East Asia harbors the most diverse temperate flora, largely because an extensive terrestrial ice cap was absent during repeated Pleistocene glaciation–interglacial cycles. Comparing the demographic histories of species that are codistributed and are close relatives may provide insight into how the process of climate change influences species ranges. In this study, we compared the spatial genetic structure and demographic histories of two coexisting Eleutherococcus species, Eleutherococcus senticosus and E. sessiliflorus. Both species are distributed in northern China, regions that are generally considered to be sensitive to climatic fluctuations. These regions once hosted temperate forest, but this temperate forest was replaced by tundra and taiga forest during the Last Glacial Maximum (LGM), according to pollen records. Using three chloroplast DNA fragments, we assessed the genetic structure of 20 and 9 natural populations of E. senticosus and E. sessiliflorus, respectively. Extremely contrasting genetic patterns were found between the two species; E. sessiliflorus had little genetic variation, whereas E. senticosus had considerably higher levels of genetic variation (15 haplotypes). We speculated that a recent severe bottleneck may have resulted in the extremely low genetic diversity in E. sessiliflorus. In E. senticosus, populations in Northeast China (NEC) harbored all of the haplotypes found in this species and included private haplotypes. The populations in NEC had higher levels of genetic diversity than did those from North China (NC). Therefore, we suggest that both the NC and NEC regions can sustain LGM refugia and that lineage admixture from multiple refugia took place after the LGM elevated the local genetic diversity in NEC. In NEC, multiple genetic hot spots were found in the Changbai Mountains and the Xiaoxing'an Range, which implied that multiple locations in NEC may sustain LGM refugia, even in the Xiaoxing'an Range.     

The environmental signals of stable carbon isotope in various tree-ring components of Pinus tabulaeformis

Chinese pine (Pinus tabulaeformis) trees were sampled in the Helan Mountain, northwest China. The stable carbon isotope (δ¹³C) values of whole wood, holocellulose and alpha-cellulose in tree rings over 30 years (1968–1997) were measured to study the δ¹³C response of different tree-ring components to past environmental change. There were obvious differences in the δ¹³C values of the three components. The Pearson correlation coefficient between the δ¹³C of alpha-cellulose and that of holocellulose was 0.547 (ρ < 0.01); between alpha-cellulose and whole wood, the coefficient was −0.126 (ρ > 0.10); between holocellulose and whole wood, the coefficient was −0.056. Correlation function analyses indicated that the δ¹³C content of tree-ring alpha-cellulose correlated strongly with the average temperature from June to August (r = 0.427, ρ < 0.05), more than that of holocellulose (0.324, ρ < 0.10) or total wood (−0.245, ρ > 0.10). Significant correlations were observed between δ¹³C of tree-ring alpha-cellulose and the precipitation from the current year’s February to July (r = −0.514, ρ < 0.01) that were much higher than that of holocellulose (−0.481, ρ < 0.05) or total wood (−0.249, ρ > 0.10). A significant correlation (−0.545, ρ < 0.01) was also found between the ring width and the δ¹³C residual chronologies. These results suggest that more past environmental information is retained in the δ¹³C of tree-ring alpha-cellulose. Thus, the δ¹³C of alpha-cellulose of tree rings is the most suitable among the studied parameters for reconstructing the past climatic conditions during the growing season. The δ¹³C values of other organic compounds in Pinus tabulaeformis xylem were affected by the external environment after carbon was fixed from the atmosphere.     

3种松树林林分改造树种的生长格局

对3 种松林下的黎蒴、白花油茶、竹节树苗木的生长进行了研究.3 种苗木的地径和冠幅生长量以及黎蒴和油茶的树高生长量排序为湿地松林分>有凋落物加勒比松林分>无凋落物加勒比松林分,而竹节树在有凋落物加勒比松林下的树高生长略大于湿地松林,二者显著大于无凋落物加勒比松林.无凋落物的加勒比松林因为去除地表凋落物后减少了养分的输入,土壤有机质和氮含量减少,导致苗木生长下降.总体来看,竹节树的地径和冠幅的生长量最大,黎蒴树高的生长量最大,二者是改造松林的优良树种,而油茶生长慢.     

Crown light environments of saplings of two species of rain forest emergent trees

Summary The crown light environments of saplings of two Costa Rican rain forest tree species were simultaneously compared. The species, Dipteryx panamensis (Pitt.) Record & Mell., a relatively shade-intolerant species, and Lecythis ampla Miers, a shade-tolerant species, have contrasting growth and branching patterns. Quantum sensors were placed throughout the crowns of saplings up to 2.5 m tall and quantum fluxes were recorded with microloggers for seven-day periods. The shade-intolerant species had total quantum flux densities 35% larger than those of the shade-tolerant species, but totals for both species were less than 2% of full sun. More than 90% of the quantum flux densities measured within the crowns of both species were less than 25 mol m^-2s^-1. Lateral light was an important component of daily quantum flux totals; for saplings of both species, the half-hour with the maximum average irradiance for the day frequently occurred in mid-morning or midafternoon. Despite dissimilar crown and leaf display, there was no difference in the overall variability of irradiance within the crowns of the two species. However, quantum fluxes received within the crowns differed substantially in both species. Within-crown locations differed significantly from day to day because of variation in weather conditions. Daily total quantum flux densities and totals expressed as a percent of full sun were significantly correlated with height growth over the previous 12 months.     

Different competitive potential in two coexisting mouse lemur species in northwestern Madagascar

Interspecific competition has been suggested to influence the biogeographic distribution patterns of species. A high competitive potential could entail species-specific advantages during resource acquisition that could translate into a higher potential for range expansion. We investigated whether differences in the competitive potential of the morphologically similar and partially sympatric gray mouse lemur (Microcebus murinus) and golden-brown mouse lemur (Microcebus ravelobensis) may help to explain differences in their geographic range sizes. We carried out encounter experiments with 14 pairs of captured female mouse lemurs of both species. The experimental dyads were tested in a two-cage arrangement, with individuals being separated from each other outside the experiments. Two days of habituation and four subsequent days of 1-h encounter experiments were conducted, before releasing the animals again in the wild. In general, the M. murinus individuals won significantly more conflicts than their partners. In eight of 14 tested pairs, there was a significant species bias in winning conflicts, and in 87.5% of these dyads, M. murinus was the "dyad winner". A high competitive potential did not depend on body mass. Furthermore, "dyad winners" spent more time feeding (P < 0.05) and were less spatially restricted than "dyad losers". To conclude, our results suggest that the widely distributed M. murinus may indeed have a higher competitive potential than the regional endemic M. ravelobensis, which may, among other possible factors, have enabled this species to expand geographically, despite the presence of other competing congeners.