Experimental whole‐lake increase of dissolved organic carbon concentration produces unexpected increase in crustacean zooplankton density

The observed pattern of lake browning, or increased terrestrial dissolved organic carbon (DOC) concentration, across the northern hemisphere has amplified the importance of understanding how consumer productivity varies with DOC concentration. Results from comparative studies suggest these increased DOC concentrations may reduce crustacean zooplankton productivity due to reductions in resource quality and volume of suitable habitat. Although these spatial comparisons provide an expectation for the response of zooplankton productivity as DOC concentration increases, we still have an incomplete understanding of how zooplankton respond to temporal increases in DOC concentration within a single system. As such, we used a whole‐lake manipulation, in which DOC concentration was increased from 8 to 11 mg L^?1 in one basin of a manipulated lake, to test the hypothesis that crustacean zooplankton production should subsequently decrease. In contrast to the spatially derived expectation of sharp DOC‐mediated decline, we observed a small increase in zooplankton densities in response to our experimental increase in DOC concentration of the treatment basin. This was due to significant increases in gross primary production and resource quality (lower seston carbon‐to‐phosphorus ratio; C:P). These results demonstrate that temporal changes in lake characteristics due to increased DOC may impact zooplankton in ways that differ from those observed in spatial surveys. We also identified significant interannual variability across our study region, which highlights potential difficulty in detecting temporal responses of organism abundances to gradual environmental change (e.g., browning).     

Trophic structure of a coastal fish community determined with diet and stable isotope analyses

A combination of dietary guild analysis and nitrogen (δ¹⁵N) and carbon (δ¹³C) stable‐isotope analysis was used to assess the trophic structure of the fish community in Rhode Island and Block Island Sounds, an area off southern New England identified for offshore wind energy development. In the autumn of 2009, 2010 and 2011, stomach and tissue samples were taken from 20 fish and invertebrate species for analysis of diet composition and δ¹⁵N and δ¹³C signatures. The food chain in Rhode Island and Block Island Sounds comprises approximately four trophic levels within which the fish community is divided into distinct dietary guilds, including planktivores, benthivores, crustacivores and piscivores. Within these guilds, inter‐species isotopic and dietary overlap is high, suggesting that resource partitioning or competitive interactions play a major role in structuring the fish community. Carbon isotopes indicate that most fishes are supported by pelagic phytoplankton, although there is evidence that benthic production also plays a role, particularly for obligate benthivores such as skates Leucoraja spp. This type of analysis is useful for developing an ecosystem‐based approach to management, as it identifies species that act as direct links to basal resources as well as species groups that share trophic roles.     

Predatory — prey relationships in subtropical zooplankton: water mite against cladocerans in an Argentine lake

Summary In a small lake in northern Argentina pelagic water mite Piona sp. had the maximum of population density in January following with a five-day delay after the peak of zooplankton dominant — Daphnia laevis. The mite density was highly predicted by the previous variations of Daphnia density during 4 months of observation (December–March). Daphnia density was a negative delayed function of the predator density but only in December–January when Piona was abundant. During that period Daphnia death rate, d was also correlated with the mite density (r ²=0.80, P<0.005). In laboratory experiments water mites killed 1–7 Daphnia · predator^-1 · hour^-1 in a broad range of prey density. Another zooplankton component, Diaphanosoma birgei, was consumed at the same rates. The mite hardly consumed any copepods. In the pelagium during 24 hours the mite was more associated with Daphnia, than with Diaphanosoma, probably, because of the coincidence in photoreactions with Daphnia. Piona contribution to the death rates of its prey estimated by using the data on functional and numerical responses as well as by means of Edmondson-Paloheimo model, could reach 53% for Daphnia and 40% for Diaphanosoma. A computer experiment on the reconstruction of prey dynamics after subtraction of predator influence showed that the mite could have caused a depression in Daphnia numbers observed in the lake, but the declines in Diaphanosoma population were caused by other factors. After the removal of mite pressure model Daphnia population increased its average density 10-fold. Experiments on Piona feeding revealed a strong effect of interference among predators. This was eliminated by putting one mite per experimental vessel, which led to a 20-fold increase in predation rate. The effect explains the low feeding rates of Piona obtained by the previous authors who ignored the possibility of interference.     

The rivers of North East Scotland: physicochemical characteristics

Multivariate analysis of spatial variation in 15 physicochemical characteristics grouped the seven major north-east rivers into two sets — highland and lowland rivers. The highland rivers formed a continuum that could be further divided into rivers with low concentrations of dissolved materials including the Spey and Dee (full highland rivers), and a more variable group with higher concentrations of dissolved materials including the Don, Deveron and Lossie (intermediate highland rivers) emphasising the diversity of river types classically described as highland. The Lossie was differentiated from the other intermediate highland rivers by lower oxygen concentration and pH. The major differences in physicochemistry between rivers were consistent with differences in catchment geology, soil type, climate, and land use. The large amounts of dissolved material and high nutrient status of the lowland Ythan and Ugie rivers reflected the high proportion of their catchments under agriculture, and the acidity of the Lossie reflected the high proportion of its catchment under forest. The small amounts of dissolved material in the Spey and Dee were attributable to the high proportion of slow weathering acidic rocks and acid soils in their catchments, and to the high volume flows of these rivers relative to the others. The amounts of dissolved material were greater in summer during low base flows and were accomparied by an increase in phosphate concentration in the lowland rivers. Oxygen saturation increased in summer in the Ythan and the Don, presumably as a result of greater photosynthetic activity. Marked declines in silica were thought to result from significant diatom growth in the highland and intermediate highland rivers, particularly the Don, during summer.     

Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits

We explored potential of morphological and anatomical leaf traits for predicting ecophysiological key functions in subtropical trees. We asked whether the ecophysiological parameters stomatal conductance and xylem cavitation vulnerability could be predicted from microscopy leaf traits. We investigated 21 deciduous and 19 evergreen subtropical tree species, using individuals of the same age and from the same environment in the Biodiversity‐Ecosystem Functioning experiment at Jiangxi (BEF‐China). Information‐theoretic linear model selection was used to identify the best combination of morphological and anatomical predictors for ecophysiological functions. Leaf anatomy and morphology strongly depended on leaf habit. Evergreen species tended to have thicker leaves, thicker spongy and palisade mesophyll, more palisade mesophyll layers and a thicker subepidermis. Over 50% of all evergreen species had leaves with multi‐layered palisade parenchyma, while only one deciduous species (Koelreuteria bipinnata) had this. Interactions with leaf habit were also included in best multi‐predictor models for stomatal conductance (g_s) and xylem cavitation vulnerability. In addition, maximum g_s was positively related to log ratio of palisade to spongy mesophyll thickness. Vapour pressure deficit (vpd) for maximum g_s increased with the log ratio of palisade to spongy mesophyll thickness in species having leaves with papillae. In contrast, maximum specific hydraulic conductivity and xylem pressure at which 50% loss of maximum specific xylem hydraulic conductivity occurred (Ψ₅₀) were best predicted by leaf habit and density of spongy parenchyma. Evergreen species had lower Ψ₅₀ values and lower maximum xylem hydraulic conductivities. As hydraulic leaf and wood characteristics were reflected in structural leaf traits, there is high potential for identifying further linkages between morphological and anatomical leaf traits and ecophysiological responses.     

Skin colour in north Indian populations

The skin colour of six endogamous groups of north India has been studied reflectometrically. The percentage reflectance at upper arm and forchead of 650 adult males (20–25 years) is described and discussed using 601 (425 nm), 605 (545 nm) and 609 (685 nm) filters of the “EEL” spectrophotometer. The inter-group heterogeneity is revealed by variance-ratio test. The t-test has been applied to study inter-group differences in pigmentation. Some correspondence has been found in skin colour with caste hierarchy, which holds only when the populations living in the same region are compared. These differences are assigned to adaptive adjustments superimposed by caste endogamy and assortative mating for skin colour.     

华南南亚热带植被第一性生产量的影响因素及预测模型

讨论植被类型、降雨、湿度、土壤条件对华南南亚热带植被第一性生产量的影响。比较各种预测第一性生产量的气候模型,为更好地预测和提高华南南亚热带植被第一性生产量提供依据。     

Late Pliocene vegetation and climate of Zhangcun region,Shanxi, North China

To understand the Neogene climatic changes in eastern Asia and evaluate the intercontinental climatic differences, we have quantitatively reconstructed the vegetation successions and climatic changes in the late Pliocene Zhangcun area based on the palynological data and explored the regional climatic differences between central Europe and eastern Asia. The late Pliocene palynological assemblage of Zhangcun, Shanxi was composed of 63 palynomorphs, belonging to 50 families, covering angiosperms (90.2%), gymnosperms (9.7%), ferns (0.09%), and other elements (0.02%). Four periods of vegetation succession over time were recognized. In period 1, a needle‐ and broad‐leaved mixed forest prevailed with a cool and dry climate. Period 2 was characterized by an expansion of forest with a warmer and wetter climate. The number of conifers increased and that of herbs decreased in period 3, and the climate became cool and dry. In period 4, the forest was dominated by conifers and reflecting a cooler climate. The data of seven climatic parameters in general and four periods estimated by the Coexistence Approach suggested that (1) The late Pliocene temperatures and precipitations were higher than today. (2) The Neogene climate of both Central Europe and North China exhibited a general cooling and drying trend although the mean annual temperature dropped by ca. 1 °C in North China, vs. ca. 7 °C in Central Europe from the middle Miocene to the late Pliocene. (3) The decline of the mean maximum monthly precipitation might signal a weakening of the summer monsoon. (4) The decline of both the mean coldest monthly temperature and the mean minimum monthly precipitation might be linked to the strengthening of the winter monsoon in eastern Asia. (5) The rapid uplift of the Tibetan Plateau strengthened the climatic cooling and drying during the late Pliocene of the Zhangcun region.     

Morpho-environmental characterization of the genus Baldellia Parl. (Alismataceae) in the Iberian Peninsula,Balearic islands and North Morocco

Abstract

The genus Baldellia Parl. has always been a complex taxon. Three species and three subspecies have been proposed for the Iberian Peninsula. The morphological variation of this genus in the Iberian Peninsula, Balearic islands and northern Morocco, and its thermo-pluviometric and altitudinal correlation are the focus of this contribution. Twenty-eight morphological variables were examined and subjected to a multivariate statistical analysis. The three morphotypes observed (Form 1, which includes B. ranunculoides subsp. repens and B. alpestris; Form 2, which includes B. ranunculoides and Form 3 – for the new combination B. ranunculoides subsp. ranunculoides var. tangerina (Pau) J. Rocha, A. Crespí, M. García-Barriuso, R. Almeida, J. Honrado, comb. nova proposed here for the first time) seem to represent different reproductive strategies. Morphological variables related with the presence or absence of stolons and the architecture of the inflorescence; the size and number of fruits are the most discriminating variables. Form 1 represents the asexual morphotype; Forms 2 and 3 correspond to morphotypes for which sexual reproduction is preferential. The environmental approach revealed that the asexual form (Form 1) grows in temperate, in more humid conditions, and within a broad altitudinal range. In contrast, the two sexual forms are more common in warmer and drier conditions, and occur over a narrower interval of altitudes.     

祁连山北坡灌木群落数量分类与排序

植物群落的空间分布格局是异质生境条件下物种种间相互作用的结果,其分异规律及其与环境因子的关系研究有助于认识植物的生态适应性。本文基于祁连山北坡28个样地的调查数据,采用双向指示种分析法(TWINSPAN)和典范对应分析(CCA)法探讨了灌木群落的空间分布与环境因子间相互关系。结果表明:(1)TWINSPAN分类将祁连山北坡灌木植被划分为盐爪爪+珍珠猪毛菜(Ass.Kalidium foliatum+Lyonia ovalifolia)、灌木亚菊+合头草(Ass.Ajania fruticulosa+Sympegma regelii)、合头草+茵陈蒿(Ass.Sympegma regelii+Artemisia capillaries)、珍珠猪毛菜+多根葱(Ass.Lyonia ovalifolia+Allium polyrhizum)、甘蒙锦鸡儿+针茅(Ass.Caragana opulens+Stipa capillata)、鬼箭锦鸡儿+高山柳(Ass.Caragana jubata+Salix cupularis)和金露梅+珠芽蓼(Ass.Dosiphora fruticosa+Polygonum viviparum)等7个群丛类型;(2)CCA排序结果表明,海拔和土壤全盐量是影响祁连山北坡灌木群落分布的主要环境因子,有机质、土壤含水量、土壤容重和p H值是次要因子,速效磷和速效钾对植物群落的影响较弱。