The Categorisation of Non-Categorical Colours: A Novel Paradigm in Colour Perception

In this paper, we investigate a new paradigm for studying the development of the colour ‘signal’ by having observers discriminate and categorize the same set of controlled and calibrated cardinal coloured stimuli. Notably, in both tasks, each observer was free to decide whether two pairs of colors were the same or belonged to the same category. The use of the same stimulus set for both tasks provides, we argue, an incremental behavioural measure of colour processing from detection through discrimination to categorisation. The measured data spaces are different for the two tasks, and furthermore the categorisation data is unique to each observer. In addition, we develop a model which assumes that the principal difference between the tasks is the degree of similarity between the stimuli which has different constraints for the categorisation task compared to the discrimination task. This approach not only makes sense of the current (and associated) data but links the processes of discrimination and categorisation in a novel way and, by implication, expands upon the previous research linking categorisation to other tasks not limited to colour perception.     

A Molecular Comparison of Plumage and Soil Bacteria Across Biogeographic,Ecological, and Taxonomic Scales

We used molecular methods to determine the microbial community of soil and avian plumage across biogeographic, ecological, and taxonomic scales. A total of 17 soil and 116 feather samples were collected from five avian species across multiple habitat types within one Neotropical and one temperate locality. Hypotheses regarding patterns of microbial composition relative to acquisition and dispersal of plumage bacteria in the ecosystem were tested by comparing microbial communities within and between soil and plumage. Samples from the plumage of American Redstarts (Setophaga ruticilla) were collected across both habitat types and geographic scales for intraspecific comparisons. The microbial diversity in avian plumage was moderately diverse and was dominated by Pseudomonas species. Despite a highly significant individual bird effect on microbial composition of the plumage, we detected significant biogeographic and type of habitat effects. Pseudomonas species were more abundant on the temperate site when all avian species were included in the analysis, and Bacillus subtilis and Xanthomonas groups were more abundant on the Neotropical site for redstarts alone. However, 16S rDNA sequence libraries were not significantly different between Jamaican and Maryland redstarts. Biogeographic and habitat effects were significant and more pronounced for soil samples indicating lower dispersal of soil microbiota. We detected a significant difference between soil and plumage microbial communities suggesting that soil plays a small role in plumage bacterial acquisition. Our results suggest bacterial communities on the plumage of birds are dynamic and may change at different stages in a bird’s annual cycle.     

Seasonal Changes in the Photosynthetic Rate in Apple Trees : A Comparison between Fruiting and Nonfruiting Trees

Seasonal changes in photosynthesis of apple trees (Malus domestica Borkh.) were monitored to examine the effect of source-sink interactions on photosynthesis and photorespiration. Elevated photosynthetic rates were observed during two periods of the growing season and correlated with the fruiting process. The first period of increased photosynthetic rates was during the bloom period, when spur leaves on flowering shoots exhibited up to 25% higher photosynthetic rates than vegetative spur leaves on a leaf area basis. CO₂ assimilation rates were also higher in fruiting trees than nonfruiting trees during the period of rapid fruit growth from July to September. Photorespiration, dark respiration, leaf resistance, and transpiration exhibited no seasonal changes which correlated to the presence or absence of fruit. These data represent the first comprehensive examination of the effects of flowering/fruit formation on photosynthesis and photorespiration in perennial plants.     

Seasonal Changes in Reproductive Tolerance, Spacing, and Social Organization in Meadow Voles: A Microtine Model

Current theory and supporting data regarding population regulationand cycling in microtine rodents needs to be reviewed in lightof a new, season-sensitive model of social behavior for meadowvoles, Microtus pennsylvanicus. The finding of a clear socialimperative among meadow voles during most of the fall, winterand spring conflicts with the prediction of high levels of socialintolerance in the higher density populations commonly existinglate in the year. The general rarity of adult dispersal, exceptduring periods of declining densityin winter and early spring,and the contact-seeking nature of this dispersal,are generallycontradictory to predictions based on "intrinsic’ theories.Finally,published data on meadow vole reproduction, recruitmentand dispersal, and hence demography, are probably biased asa result of effects produced by the spread of rodent pheromonesby investigators, prolonged entrapment of individual voles,and inappropriate behavioral measures in the field.     

Most and Least Preferred Colours Differ According to Object Context: New Insights from an Unrestricted Colour Range

Humans like some colours and dislike others, but which particular colours and why remains to be understood. Empirical studies on colour preferences generally targeted most preferred colours, but rarely least preferred (disliked) colours. In addition, findings are often based on general colour preferences leaving open the question whether results generalise to specific objects. Here, 88 participants selected the colours they preferred most and least for three context conditions (general, interior walls, t-shirt) using a high-precision colour picker. Participants also indicated whether they associated their colour choice to a valenced object or concept. The chosen colours varied widely between individuals and contexts and so did the reasons for their choices. Consistent patterns also emerged, as most preferred colours in general were more chromatic, while for walls they were lighter and for t-shirts they were darker and less chromatic compared to least preferred colours. This meant that general colour preferences could not explain object specific colour preferences. Measures of the selection process further revealed that, compared to most preferred colours, least preferred colours were chosen more quickly and were less often linked to valenced objects or concepts. The high intra- and inter-individual variability in this and previous reports furthers our understanding that colour preferences are determined by subjective experiences and that most and least preferred colours are not processed equally.     

Viral OTU Deubiquitinases: A Structural and Functional Comparison

Recent studies have revealed that proteases encoded by three very diverse RNA virus groups share structural similarity with enzymes of the Ovarian Tumor (OTU) superfamily of deubiquitinases (DUBs). The publication of the latest of these reports in quick succession prevented proper recognition and discussion of the shared features of these viral enzymes. Here we provide a brief structural and functional comparison of these virus-encoded OTU DUBs. Interestingly, although their shared structural features and substrate specificity tentatively place them within the same protease superfamily, they also show interesting differences that trigger speculation as to their origins.The covalent attachment of ubiquitin (Ub) to protein substrates, i.e., ubiquitination, plays a pivotal regulatory role in numerous cellular processes [1]–[5]. Ubiquitination can be reversed by deubiquitinases (DUBs) [6] and, not surprisingly, various virus groups encode such DUBs to influence ubiquitin-mediated host cell processes [7]–[21]. Some of these viral DUBs resemble proteases belonging to the Ovarian Tumor (OTU) superfamily [22]–[28]. Makarova et al. previously identified OTU proteases as a novel superfamily of cysteine proteases from different organisms [29], and their bioinformatics-based analysis included several of the viral enzymes discussed here. Recently reported structures of these viral DUBs include the OTU domains of the nairoviruses Crimean-Congo hemorrhagic fever virus (CCHFV) [22]–[24] and Dugbe virus (DUGV) [25], the papain-like protease (PLP2) domain of the arterivirus equine arteritis virus (EAV) [26], and the protease (PRO) domain of the tymovirus turnip yellow mosaic virus (TYMV) (Figure 1A–1D) [27], [28]. These viruses are strikingly diverse, considering that nairoviruses are mammalian negative-strand RNA viruses, while the mammalian arteriviruses and plant tymoviruses belong to separate orders of positive-strand RNA viruses.Open in a separate windowFigure 1Viral and eukaryotic OTU domain structures and viral protein context.Crystal structures of (A) CCHFV OTU (3PT2) [23], (B) DUGV OTU (4HXD) [25], (C) EAV PLP2 (4IUM) [26], (D) TYMV PRO (4A5U) [27], [28], (E) yeast OTU1 (3BY4) [57], and (F) human OTUD3 (4BOU) [46]. The β-hairpin motifs of CCHFV OTU and DUGV OTU are indicated in boxes in panels A and B, respectively, and the zinc-finger motif of EAV PLP2 is boxed in panel C. Active sites are indicated with arrows. The CCHFV OTU, DUGV OTU, EAV PLP2, and yeast OTU1 domains were crystallized in complex with Ub, which has been removed for clarity. Structure images were generated using PyMol [60]. (G) Schematic representation of the CCHFV large (L) protein [61], [62]. A similar organization is found in the DUGV L protein, but is not depicted. The OTU domain resides in the N-terminal region of this protein and is not involved in autoproteolytic cleavage events [48]. (H) Schematic representation of the EAV polyprotein 1ab [63]. PLP2 resides in nonstructural protein 2 (nsp2) and is responsible for the cleavage between nsp2 and nsp3 [51]. (I) Schematic representation of the TYMV ORF1 polyprotein [50]. PRO resides in the N-terminal product of this polyprotein and is responsible for two internal cleavages [49], [50]. Key replicative enzymes are indicated in G, H, and I. Colored arrowheads denote cleavage sites for the indicated protease domains. HEL, helicase; PLP, papain-like protease; RdRp, RNA-dependent RNA polymerase; SP, serine protease.Ubiquitination often involves the formation of polyubiquitin chains [1], which can target the ubiquitinated substrate to the proteasome for degradation [2] or modulate its protein–protein interactions, as in the activation of innate immune signaling pathways [3], [4]. Interestingly, several cellular OTU DUBs were found to negatively regulate innate immunity [30]–[33]. Likewise, both nairovirus OTU and arterivirus PLP2 were recently shown to inhibit innate immune responses by targeting ubiquitinated signaling factors [7]–[9], [26], [34], [35]. In contrast to eukaryotic OTU DUBs, both of these viral proteases were found to also deconjugate the Ub-like protein interferon-stimulated gene 15 (ISG15) [7], [36], which inhibits viral replication via a mechanism that is currently poorly understood [37]. Interestingly, coronaviruses (which, together with the arteriviruses, belong to the nidovirus order) also encode papain-like proteases targeting both Ub and ISG15 that were shown to inhibit innate immunity [11]–[13], [38]–[42] but belong to the ubiquitin-specific protease (USP) class of DUBs [6], [43], [44]. The presence of functionally similar, yet structurally different proteases in distantly related virus families highlights the potential benefits to the virus of harboring such enzymes.The proteasomal degradation pathway is an important cellular route to dispose of viral proteins, as exemplified by the turnover of the TYMV polymerase [45]. Moreover, the degradation of this protein is specifically counteracted by the deubiquitinase activity of TYMV PRO, which thus promotes virus replication [10]. The functional characterization of viral OTU DUBs remains incomplete and future studies will likely reveal additional roles in replication and virus–host interplay.Polyubiquitin chains can adopt a number of different configurations, depending on the type of covalent linkage present within the polymer [1]. A distal Ub molecule can be linked via its C-terminus to one of seven internal lysine residues present in a proximal Ub molecule via an isopeptide bond. Alternatively, in the case of linear chains, the C-terminus of the distal Ub is covalently linked to the N-terminal methionine residue of the proximal Ub via a peptide bond. While human OTU proteases often show a distinct preference for one or two isopeptide linkage types [46], nairovirus OTUs and TYMV PRO appear to be more promiscuous in their substrate preference [22], [25]. However, like most human OTU proteases, they seem unable to cleave linear polyubiquitin chains in vitro [22], [25], [46]. Arterivirus PLP2 has not been extensively studied in this respect.It is important to note that many positive-strand RNA viruses, including arteriviruses and tymoviruses, encode polyproteins that are post-translationally cleaved by internal protease domains [47]. Thus, while CCHFV OTU is not involved in viral protein cleavage and its activity seems dispensable for replication (Figure 1G) [48], both arterivirus PLP2 and tymovirus PRO are critically required for viral replication due to their primary role in polyprotein maturation (Figure 1H, 1I) [49]–[53]. Interestingly, while both EAV PLP2 and TYMV PRO can process peptide bonds in cis and in trans [50], [51], PRO does not cleave peptide bonds in linear polyubiquitin chains in vitro [25]. To date, activity of EAV PLP2 towards linear polyubiquitin chains has not been reported.Based on mutagenesis of putative catalytic residues, arterivirus PLP2 and tymovirus PRO were initially generally classified as papain-like cysteine proteases [51], [54], [55]. Now that crystal structures of these proteases are available, it is possible to search the DALI server [56] in order to identify structurally similar domains. Using the 3-dimensional coordinates of TYMV PRO, the most recently solved structure of a viral OTU protease, such a query identifies structural similarity with eukaryotic OTU DUBs as well as the nairovirus OTU domains and EAV PLP2 ([57] further highlights their similarities (Figure 2A–2C), and these comparisons together clearly position them within the OTU DUB superfamily. Sequence comparisons alone were insufficient to demonstrate this conclusively, as the similarity of viral OTU domains to each other and to eukaryotic OTU proteases is very limited and mostly restricted to the areas surrounding the active site residues [29].Open in a separate windowFigure 2Superpositions of the viral OTU proteases with yeast OTU1 and one another.Superpositions of yeast OTU1 (3BY4) [57] with (A) CCHFV OTU (3PT2) [23], RMSD: 1.8 Å over 112 residues, (B) EAV PLP2 (4IUM) [26], RMSD: 2.8 Å over 69 residues, and (C) TYMV PRO (4A5U) [27], [28], RMSD: 1.4 Å over 76 residues. Superpositions of the yeast OTU1-Ub complex with (D) the CCHFV OTU-Ub complex and (E) the EAV PLP2-Ub complex, highlighting the difference in the orientation of Ub between the two viral OTU domains versus the eukaryotic yeast OTU1 domain. The Ub that is complexed with yeast OTU1 is depicted in yellow, while the Ub complexed with CCHFV OTU or EAV PLP2 is depicted in orange. (F) Superposition of EAV PLP2 and TYMV PRO, RMSD: 2.5 Å over 53 residues. (G) Close-up of the active site region (boxed) of the superposition depicted in F. Side chains of the catalytic cysteine (Cys270 and Cys783 for EAV PLP2 and TYMV PRO, respectively) and histidine (His332 and His869 for EAV PLP2 and TYMV PRO, respectively) residues are shown as sticks, as well as the active site Asn263 for EAV PLP2. The backbone amide group of Asp267 likely contributes to the formation of the oxyanion hole in the active site of EAV PLP2, yet a functionally equivalent residue is absent in TYMV PRO. The Gly266 and Gly268 residues flanking Asp267 in EAV PLP2 are depicted as sticks as well, for clarity. Note the alternative orientation of the active site cysteine residue of TYMV PRO which, unlike EAV PLP2, was not determined in covalent complex with an Ub suicide substrate. All alignments were generated using the PDBeFOLD server [64], and thus the reported RMSD values differ from those reported in [60]. RMSD, root-mean-square deviation.

Table 1

Three-dimensional structural alignment of viral OTU domains against selected structures in the Protein Data Bank using the DALI server [56].

Costs and Benefits of Subadult Plumage in Mute Swans: Testing Hypotheses for the Evolution of Delayed Plumage Maturation

In some avian species, young birds capable of reproducing diminish their prospects of doing so by molting into a subadult plumage that accurately signals their subadult status. Several hypotheses have been proposed to explain the evolution of delayed plumage maturation, but testing them usually has involved interspecific comparisons that are hard to interpret. Mute swans (Cygnus olor) exhibit two phenotypes that differ in whether the birds have a gray subadult plumage (SAP phenotype) or molt immediately into an all white adult plumage (AP phenotype). The AP phenotype results from a recessive allele on the X chromosome; both phenotypes occur in the same population and even in the same brood. We compared costs and benefits of both phenotypes in mute swans on the Chesapeake Bay in 1972-1980 and on Long Island Sound in 1982-1989. Swans with the SAP phenotype had higher survival rates from hatching to fledging than AP swans. In the fall, when AP cygnets began to molt into their white plumage, their parents often attacked and drove them off while allowing SAP cygnets from the same brood to remain on their territories for several more months. SAP males had higher survival rates during their first 2 yr of life than AP males, but AP swans bred at a younger age than SAP swans. The only proposed hypothesis for the evolution of delayed plumage maturation that can explain its occurrence in mute swans is the status-signaling hypothesis. This hypothesis argues that males with subadult plumage honestly advertise their age and subordinate status while AP swans are cheaters and engaging in dishonest communication. SAP males acquire a longer period of parental care, suffer less aggression from older birds, and increase their survival but forgo the opportunity to breed at an early age. This is a unique example of how a single gene resulted in either honest or dishonest communication, changed a bird's relationship with its parents and potential mates, and altered the bird's chances to survive and to reproduce.     

Correlated Changes in Body Melanisation and Mating Traits of Drosophila melanogaster: A Seasonal Analysis

Altitudinal localities of the northern India are associated with high seasonal changes. Drosophila melanogaster flies are darker during the winter season as compared to the autumn season. We tested the hypothesis whether there are altitudinal clines for mating related traits. We observed negative cline for mating latency and positive for copulation period along altitude in D. melanogaster. We further tested if seasonally varying body melanisation is correlated with mating propensity in D. melanogaster. Thus, we examined the D. melanogaster flies collected during autumn and winter season for changes in body melanisation and mating-related traits. Flies from the winter season show high melanisation, copulation duration and fecundity/day as compared to the autumn season flies. By contrast mating latency is longer during autumn as compared to winter season. Based on within- and between-population analysis, body melanisation shows positive correlation with copulation duration and fecundity/day, while negative correlation with mating latency. Within-population analyses show no correlation between body size and ovariole number with body melanisation. Thus, our data suggest that seasonal changes in body melanisation are correlated with mating latency, copulation duration and fecundity/day, but no correlation with body size and ovariole numbers. Further, we observed that seasonal changes in these clines, although have some component of plasticity, have strong genetic basis as the seasonal and population differences were maintained for various traits after 8 generations in the laboratory.     

Social Environment Affects Acquisition and Color of Structural Nuptial Plumage in a Sexually Dimorphic Tropical Passerine

Structural colors result from the physical interaction of light with organic materials of differing refractive indexes organized at nanoscale dimensions to produce significant interference effects. Because color properties emerge from these finely organized nanostructures, the production of structural coloration could respond to environmental factors and be developmentally more plastic than expected, functioning as an indicator of individual quality. However, there are many unknown factors concerning the function and mechanisms regulating structural coloration, especially relative to social environment. We hypothesized that social environment, in the form of competitive settings, can influence the developmental pathways involving production of feather structural coloration. We experimentally assessed the impact of social environment upon body condition, molt and spectral properties of two types of structural color that compose the nuptial plumage in blue-black grassquits: black iridescent plumage and white underwing patches. We manipulated male social environment during nine months by keeping individuals in three treatments: (1) pairs; (2) all-male groups; and (3) male-female mixed groups. All morphological characters and spectral plumage measures varied significantly through time, but only acquisition of nuptial plumage coverage and nuptial plumage color were influenced by social environment. Compared with males in the paired treatment, those in treatments with multiple males molted into nuptial plumage faster and earlier, and their plumage was more UV-purple-shifted. Our results provide experimental evidence that social context strongly influences development and expression of structural plumage. These results emphasize the importance of long-term experimental studies to identify the phenotypic consequences of social dynamics relative to ornament expression.     

Plumage Colouration,Age, Testosterone and Dominance in Male Red Bishops (Euplectes orix): A Laboratory Experiment

Visual signals such as plumage characteristics in birds often play a key role in the establishment of dominance in contests by acting as a badge of status that can be used to assess individual fighting ability. We studied the role of plumage colouration in males of the red bishop (Euplectes orix), a sexually dimorphic and polygynous weaverbird species occurring in sub‐Saharan Africa and breeding in dense colonies around water. Males are highly territorial and often engage in competition over limited resources such as breeding sites and potential mates. By experimentally staging male–male contests over a limited food source, we wanted to determine whether the orange–red breeding plumage in this species serves as a dominance signal between individuals, with males with redder plumage being dominant over those with duller plumage. In the first set of experiments, we staged contests between unfamiliar and unmanipulated males. The setup of the second set of experiments was identical to the first, with the exception that those males with the lowest chroma and hue values had their plumage experimentally reddened within the range of the natural variation. In addition to plumage colouration, we incorporated testosterone levels, body condition and age into the analysis of factors contributing to contest outcome. Our results show a consistent and strong age effect in both sets of experiments, which seems to be independent of plumage colouration, testosterone and body condition. This suggests that in the red bishop, the outcome of male–male competitions over limited resources is determined by age‐related acquired experience rather than by status signalling through plumage colouration.     

Seasonal Changes in the Newt,Trituroides hongkongensis,Testis. I. A Histological and Histochemical Study

The testis of the newt, Trituroides hongkongensis is found to be made up of a chain of lobes each being divided into spermatogenetic zones which display seasonal cycles. Seasonal changes in the histology of the testis are studied. Lobule boundary cells are found present at the same time of the year when the secondary sex character, a lateral blue line along the tail, is best expressed. Both 5-ene-3β- and 17β-HSD activities have been located in the lobule boundary cells which are suggested to be steroidogenic and their secretion may probably be responsible for the maintenance of the secondary sex character. The Sertoli cell, which originates from the follicle cell, shows accumulation of cholesterol-positive lipid at certain stages of development but its capability in hormone production is uncertain.     

Parental Effort in Relation to Structural Plumage Coloration in the Mountain Bluebird (Sialia currucoides)

Indicator models of sexual selection suggest that costly ornaments signal reliable information regarding an individual's quality to potential mates. In species that produce altricial offspring, the amount of parental care provided by both males and females can impact reproductive success. The Good Parent Hypothesis proposes that ornamentation in biparental species can act as an honest signal of parental ability to potential mates. We tested this hypothesis using the mountain bluebird (Sialia currucoides), a sexually dichromatic, socially monogamous species in which both sexes have structurally based ornamental plumage coloration. A male's plumage color predicted neither the rate at which it provisioned nestlings nor brood growth rate. The same was true for females. We also found no indication of assortative mating by color or body condition. Feeding rates within pairs were positively correlated, which we suggest may be due to pairs responding similarly to the perceived needs of nestlings or to local area prey availability. In sum, our results do not support the Good Parent Hypothesis as an explanation for the evolution of ornamental plumage color in mountain bluebirds. We suggest alternative hypotheses for the evolution of ornamental plumage color in this species.     

Plumage colour in nestling blue tits: sexual dichromatism,condition dependence and genetic effects

Sexual-selection theory assumes that there are costs associated with ornamental plumage coloration. While pigment-based ornaments have repeatedly been shown to be condition dependent, this has been more difficult to demonstrate for structural colours. We present evidence for condition dependence of both types of plumage colour in nestling blue tits (Parus caeruleus). Using reflectance spectrometry, we show that blue tit nestlings are sexually dichromatic, with males having more chromatic (more 'saturated') and ultraviolet (UV)-shifted tail coloration and more chromatic yellow breast coloration. The sexual dimorphism in nestling tail coloration is qualitatively similar to that of chick-feeding adults from the same population. By contrast, the breast plumage of adult birds is not sexually dichromatic in terms of chroma. In nestlings, the chroma of both tail and breast feathers is positively associated with condition (body mass on day 14). The UV/blue hue of the tail feathers is influenced by paternally inherited genes, as indicated by a maternal half-sibling comparison. We conclude that the expression of both carotenoid-based and structural coloration seems to be condition dependent in blue tit nestlings, and that there are additional genetic effects on the hue of the UV/blue tail feathers. The signalling or other functions of sexual dichromatism in nestlings remain obscure. Our study shows that nestling blue tits are suitable model organisms for the study of ontogenetic costs and heritability of both carotenoid-based and structural colour in birds.     

Long-term Changes and Seasonal Development of Phytoplankton in a Strongly Stratified,Hypertrophic Lake

Changes in the phytoplankton community of the hypertrophic, sharply stratified Lake Verevi have been studied over eight decades. Due to irregular discharge of urban wastewater, the trophic state of the lake has changed from moderately eutrophic to hypertrophic. We found that the trophic state in summer increased in the 1980s and remained at a hypertrophic level since then. Planktothrix agardhii was recorded first in the 1950s and became the dominant species in the 1980s, forming biomass maxima under the ice and in the metalimnion during the vegetation period. In summer 1989, P. agardhii contributed almost 100% of the phytoplankton biomass. Generally, the highest biomass values occurred in the metalimnion. In spring, when P. agardhii was less numerous, diatoms and cryptophytes prevailed. In springs 2000 and 2001 different diatoms dominated – Synedra acus var. angustissima (18.6 g m⁻³) and Cyclostephanos dubius (9.2 g m⁻³), respectively. In recent years, the spring overturn has been absent. In the conditions of strong thermal stratification sharp vertical gradients of light and nutrients caused a large number of vertically narrow niches in the water column. During a typical summer stage, the epilimnion, dominated by small flagellated chrysophytes, is nearly mesotrophic, and water transparency may reach 4 m. The lower part of the water column is hypertrophic with different species of cryptophytes and euglenophytes. A characteristic feature is the higher diversity of Chlorococcales. Often, species could form their peaks of biomass in very narrow layers, e.g. in August 2001 Ceratium hirundinella (18.6 g m⁻³) was found at a depth of 5 m (the lower part of the metalimnion with hypoxic conditions), Cryptomonas spp. (56 g m⁻³) at 6 m (with traces of oxygen and a relatively high content of dissolved organic matter) and euglenophytes (0.6 g m⁻³) at 7 m and deeper (without oxygen and a high content of dissolved organic matter).     

沙冬青几种光合特性的季节性变化的研究(英)

研究了沙冬青（Ammopiptanthusmongolicus（Maxim．）Chegf．）几种光合特性的季节性变化。在气温升高时,沙冬青净光合速率（Pn）、气孔导度（Gs）和气孔限制值（Ls）均呈现下降趋势,而胞间CO2浓度（Ci）却呈上升趋势。根据Farquhar和Sharkey提出的关于区分气孔限制的两个标准,结果表明Pn的下降可能是非气孔限制因素导致。研究还证明,Rubisco大亚基的相对含量以及光化学活性与Pn的季节性变化相关,表明CO2同化的季节性变化主要取决于上述两种因素的变化。