Acclimation to irradiance in seedlings of three tropical rain forest Garcinia species after simulated gap formation

We investigated the acclimation of seedlings of three tropical rain forest sub-canopy Garcinia species (G. xanthochymus, G. cowa, and G. bracteata) after transfer from 4.5 (LI) to 40 % (HI) sunlight and 12.5 (MI) sunlight to HI (LH₁ and LH₂ denoting transfer from LI to HI and MI to HI transfer, respectively). The changes of chlorophyll (Chl) fluorescence, net photosynthetic rate (P _N), dark respiration rate (R _D), Chl content per unit area (Chl_area), leaf mass per unit area (LMA), and seedling mortality were monitored over two months after transfer. These parameters together with leaf anatomy of transferred and control seedlings (kept in LI, MI, and HI) were also examined after two months. No seedlings died during the two months. F_v/F_m, P _N, and Chl_area of the transferred seedlings decreased in the first 3 to 12 d. LH₁ leaves showed larger reduction in F_v/F_m (>23 % vs. <16 %) and slower recovery of F_v/F_m than LH₂ leaves. P _N started to recover after about one week of I transfer and approached higher values in all G. cowa seedlings and G. xanthochymus LH₁ seedlings than those before the transfer. However, P _N of G. bracteata seedlings approached the values before transfer. The final P _N values in leaves of transferred G. xanthochymus and G. cowa seedlings approached that of leaves kept in HI, while the final P _N values of transferred leaves of G. bracteata were significantly lower than that of leaves grown under HI (p<0.05). R _D of G. xanthochymus LH₁ seedlings and all G. cowa seedlings increased and approached the value of the seedlings in HI. The final Chl_area of both G. xanthochymus and G. cowa approached the values before transfer, but that of G. bracteata did not recover to the level before transfer. The final Chl_area of all transferred seedlings was not significantly different from that of seedlings in HI except that G. cowa LH₁ seedlings had higher Chl_area than that in HI. LMA decreased within 2 d and then increased continuously until about 30 d and approached the value under HI. Spongy/palisade mesophyll ratio decreased after transfer because of the increase in palisade thickness. Leaf thickness did not change, so LMA increase of transferred seedlings was mainly due to the increase of leaf density. Thus the mature leaves under LI and MI of G. xanthochymus and G. cowa are able to acclimate to HI by leaf physiological and anatomical adjustment, while G. bracteata had limited ability to acclimate to HI.     

Life-history characters and phylogeny are correlated with extinction risk in the Australian angiosperms

Aim To determine whether life‐history characters that affect population persistence (e.g. habit and life span) and those that influence reproductive success (e.g. sexual system and fruit type) are non‐randomly correlated with extinction risk (i.e. threat category) in the Australian flora (c. 19,000 species, of which c. 14% is threatened). To identify patterns that present useful conservation directions. To understand patterns of extinction risk in the Australian flora at a broad scale. Location Continental Australia. Methods A country‐wide exploration of four life‐history characters in the Australian flora (n = 18,822 species) was undertaken using reference texts, expert opinion, herbarium records and field work. For each character and threat‐category combination, a G‐test (using a log‐linear model) was performed to test the null hypothesis that the two factors were independent in their effects on count. A generalized linear model (GLM) with a logit link and binomial error distribution was constructed with the proportion of taxa in each extinction risk category as the response variable and the habit, sex and fruit‐type characters as explanatory terms. In a separate approach, we investigated patterns across the threat categories of non‐endangered extant, endangered, and extinct using a multinomial model. We examined whether or not species‐poor genera were more likely to contain threatened or extinct species than species‐rich genera. A GLM with a binomial error distribution and logit link function was constructed to obtain a weighted regression on the proportion of species listed as extinct or endangered within a genus versus the log of the size of the genus. We also used a supertree analysis and character tracing to investigate the role of phylogeny on extinction risk. Results We found that the Australian flora is primarily composed of bisexual shrubs with dry‐dehiscent fruits. Dioecious breeding systems (separate female and male flowers on separate plants) in many floras are the predominant unisexual system, but in Australia there are unexpectedly high levels of monoecy (separate female and male flowers on the same plant). Within the extinct data set of 31 species we detected a significant departure from that expected for habit but not for life span, sexual system or fruit type. There are significantly fewer trees on the extinct list than expected. This may reflect the greater resilience of trees than of other growth habits to extinction processes as well as the observation time‐frame. Within the endangered data set of 450 species we found significant differences in the representation of the observed characters from that expected within sex systems and fruit types. We show that, depending on the life form, unisexual breeding systems can be significantly and positively associated with endangered species compared with non‐threatened species. For example, there are more monoecious species than expected by chance among the tree species listed as endangered but fewer among the herbaceous life forms. Threat category was found to be non‐randomly clustered in some clades. Main conclusions Life‐history characters in certain combinations are predictive of extinction risk. Phylogeny is also an important component of extinction risk. We suggest that specific life‐history characters could be used for conservation planning and as an early warning sign for detecting vulnerability in lists of species.     

Importance of short-term dynamics in carbon isotope ratios of ecosystem respiration (delta13C(R)) in a Mediterranean oak woodland and linkage to environmental factors

Temporal dynamics in carbon isotope ratios of ecosystem respiration (delta13C(R)) were evaluated on hourly, daily and annual timescales in a Mediterranean woodland. Emphasis was given to the periods of transition from wet to dry season and vice versa, when the system turns from a net carbon sink to a source. The constancy of nocturnal delta13C(R) was tested. The relationship between delta13C(R) (determined through Keeling plots) and environmental factors was evaluated through time-lag analysis. Delta13C(R) exhibited high annual variation (> 7). During the transition periods, delta13C(R) correlated significantly with factors influencing photosynthetic discrimination, soil respiration, and whole-canopy conductance. Time-lags differed between below- and above-ground variables, and between seasons. A shift in regression parameters with environmental factors indicated seasonal differences in ecosystem responsiveness (e.g. temperature acclimation). Delta13C(R) exhibited substantial nocturnal enrichment (> 4) from dusk to dawn. These data indicate pronounced short-term dynamics in delta13C(R) at hourly to daily timescales and a modulated response to environmental drivers. Substantial short-term changes in nocturnal delta13C(R) may have important implications for the sampling protocols of nocturnal Keeling plots.     

Stoichiometry and large-scale patterns of leaf carbon and nitrogen in the grassland biomes of China

Nitrogen (N) and carbon–nitrogen (C:N) ratio are key foliar traits with great ecological importance, but their patterns across biomes have only recently been explored. We conducted a systematic census of foliar C, N and C:N ratio for 213 species, from 41 families over 199 research sites across the grassland biomes of China following the same protocol, to explore how different environmental conditions and species composition affect leaf N and C:N stoichiometry. Leaf C:N stoichiometry is stable in three distinct climatic regions in Inner Mongolia, the Tibetan Plateau, and Xinjiang Autonomous Region, despite considerable variations among co-existing species and among different vegetation types. Our results also show that life form and genus identity explain more than 70% of total variations of foliar N and C:N ratio, while mean growing season temperature and growing season precipitation explained only less than 3%. This suggests that, at the biome scale, temperature affects leaf N mainly through a change in plant species composition rather than via temperature itself. When our data were pooled with a global dataset, the previously observed positive correlation between leaf N and mean annual temperature (MAT) at very low MATs, disappeared. Thus, our data do not support the previously proposed biogeochemical hypothesis that low temperature limitations on mineralization of organic matter and N availability in soils lead to low leaf N in cold environments.     

Root Morphology and Anchorage of Six Native Tree Species from a Tropical Montane Forest and an Elfin Forest in Ecuador

Root architecture of tree species was investigated at two different altitudes in tropical forests in Ecuador. Increasing altitude was accompanied by higher wind speeds and more shallow soils, while slope angles of both sites were comparable (20–50°). Three tree species typical for the montane forest at 1900 m (Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae), Clethra revoluta (Ruiz & Pav.) Spreng. (Clethraceae), Vismia tomentosa Ruiz & Pav. (Clusiaceae)) and for the elfin forest at 3000 m (Weinmannia loxensis Harling (Cunoniaceae), Clusia spec. (Clusiacaea) Styrax foveolaria Perkins (Styraceae)) were examined. At 1900 m, 92% of the trees grew upright, in comparison to 52% at 3000 m. At 3000 m, 48% of the trees were inclined, lying or even partly uprooted. At this altitude, all trees with tap roots or with shoots connected by coarse rhizomes, 83% of the trees with stilt roots, and 50% of the trees in which stems or roots were supported by other trees grew upright, suggesting that these characteristics were relevant for tree stability. Root system morphology differed markedly between altitudes. In contrast to 1900 m, where 20% of structural roots originated in the deeper mineral soil, root origin at 3000 m was restricted to the forest floor. The mean ratio of root cross sectional area to tree height decreased significantly from 6.1 × 10⁻³ m² m⁻¹ at 1900 m to 3.2 × 10⁻³ m² m⁻¹ at 3000 m. The extent of root asymmetry increased significantly from 0.29 at 1900 m to 0.62 at 3000 m. This was accompanied by a significantly lower number of dominant roots at 3000 m (2.3 compared to 3.8 at 1900 m). In conclusion, native tree species growing in tropical montane and elfin forests show a variety of root traits that improve tree stability. Root system asymmetry is less important for tree stability where anchorage is provided by a deep and solid root–soil plate. When deep rooting is impeded, root traits improving the horizontal extension of the root–soil plate are more pronounced or occur more frequently. Furthermore, mutual mechanical support of roots and stems of neighboring trees seems to be an appropriate mechanism to provide anchorage in soils with low bulk density and in environments with high wind speeds.     

Use of isotope ratio mass spectrometry to detect doping with oral testosterone undecanoate: inter-individual variability of 13C/12C ratio

The metabolic effect of multiple oral testosterone undecanoate (TU) doses over 4 weeks was assessed in seven voluntary men. The protocol was designed to detect accumulation of the substance by choosing the appropriate spot urines collections time and to study the urinary clearance of the substance after weeks of treatment. Urines were analysed by a new GC/C/isotope ratio mass spectrometry (IRMS) method to establish the delta(13)C-values of testosterone metabolites (androsterone and etiocholanolone) together with an endogenous reference compound (16(5alpha)-androsten-3alpha-ol). The significant differences in inter-individual metabolism following TU intake was illustrated by large variations in delta(13)C-values of both T metabolites (maximum Deltadelta(13)C-values = 5.5 per thousand), as well as by very stable longitudinal T/E profiles and carbon isotopic ratios in the first hours following administration. According to T/E ratios and delta(13)C-values, the washout period after 80 mg TU intake was less than 48 h for all subjects and no accumulation phenomenon was observed upon chronic oral administration.     

Physiological and Optical Responses of the Harmful Dinoflagellate Heterocapsa circularisquama to a Range of Salinity

The responses of division rate, cell volume, cellular carbon (C) and nitrogen (N), cellular pigments and optical characteristics to changes in salinity were examined in the dinoflagellate Heterocapsa circularisquama. The physiological and optical characteristics of H. circularisquama were significantly affected by changes in salinity. When cells were exposed to different salinities, they exhibited physiological acclimation by adjusting their cellular properties associated with growth. This could be a beneficial tactic for ensuring proliferation and limiting damages induced by adverse environmental factors. The results of this study could be essential for assisting in the development of growth models for H. circularisquama.     

Evolution of host specificity in fleas: is it directional and irreversible?

Evolutionary trends in the evolution of host specificity have been the focus of much discussion but little rigorous empirical testing. On the one hand, specialization is often presumed to lead irreversibly into evolutionary dead ends and little diversification; this would mean that generalists might evolve into specialists, but not vice versa. On the other hand, low host specificity may limit the risk of extinction and provide more immediate fitness benefits to parasites, such that selection may favour evolution toward a generalist strategy. Here, we test for directionality in the evolution of host specificity using a large data set and phylogenetic information on 297 species of fleas parasitic on small mammals. The analyses determined whether host specificity, measured both as the number of host species exploited and their taxonomic diversity, was related to clade rank of the flea species, or the number of branching events between an extant species and the root of the phylogenetic tree (i.e., the total path length from the root of the tree to the species). Based on regression analyses, we found positive relationships between the number of host species used and clade rank across all 297 species, as well as within one (Hystrichopsyllidae) of four large families and one of seven large genera investigated separately; in addition, we found a positive relationship between the taxonomic diversity of host species used and clade rank in another of the seven genera. These results suggest a slight evolutionary trend of decreasing host specificity. Using a much more conservative likelihood ratio test, however, a random walk, or null model, of evolution could not be discarded in favour of the directional trends in all cases mentioned above. Still, these results suggest that host specificity may have tended to decrease in many flea lineages, a process that could have been driven by the benefits of exploiting a wide range of host species.     

Heme coordination states of unfolded ferrous cytochrome C

The structural changes of ferrous Cyt-c that are induced by binding to SDS micelles, phospholipid vesicles, DeTAB, and GuHCl as well as by high temperatures and changes in the pH have been studied by RR and UV-Vis absorption spectroscopies. Four species have been identified in which the native methionine-80 ligand is removed from the heme iron. This coordination site is either occupied by a histidine (His-33 or His-26) to form a 6cLS configuration, which is the prevailing species in GuHCl at pH 7.0 and ambient temperature, or remains vacant to yield a 5cHS configuration. The three identified 5cHS species differ with respect to the hydrogen-bond interactions of the proximal histidine ligand (His-18) and include a nonhydrogen-bonded, a hydrogen-bonded, and a deprotonated imidazole ring. These structural motifs have been found irrespective of the unfolding conditions used. An unambiguous spectroscopic distinction of these 5cHS species is possible on the basis of the Fe-N(imidazole) stretching vibrations, the RR bands in the region between 1300 and 1650 cm(-1), and the electronic transitions in the Soret- and Q-band regions. In acid and neutral solutions, the species with a hydrogen-bonded and a nonhydrogen-bonded His-18 prevail, whereas in alkaline solutions a configuration with a deprotonated His-18 ligand is also observed. Upon lowering the pH or increasing the temperature in GuHCl solutions, the structure on the proximal side of the heme is perturbed, resulting in a loss of the hydrogen-bond interactions of the His-18 ligand. Conversely, the hydrogen-bonded His-18 of ferrous Cyt-c is stabilized by electrostatic interactions which increase in strength from phospholipid vesicles to SDS micelles. The results here suggest that unfolding of Cyt-c is initiated by the rupture of the Fe-Met-80 bond and structural reorganizations on the distal side of the heme pocket, whereas the proximal part is only affected in a later stage of the denaturation process.     

Antimicrobial peptides temporins B and L induce formation of tubular lipid protrusions from supported phospholipid bilayers

The binding of the antimicrobial peptides temporins B and L to supported lipid bilayer (SLB) model membranes composed of phosphatidylcholine and phosphatidylglycerol (4:1, mol/mol) caused the formation of fibrillar protrusions, visible by fluorescent microscopy of both a fluorescent lipid analog and a labeled peptide. Multicolor imaging at low peptide-to-lipid ratios (P/L < approximately 1:5) revealed an initial in-plane segregation of membrane-bound peptide and partial exclusion of lipid from the peptide-enriched areas. Subsequently, at higher P/L numerous flexible lipid fibrils were seen growing from the areas enriched in lipid. The fibrils have diameters <250 nm and lengths of up to approximately 1 mm. Fibril formation reduces the in-plane heterogeneity and results in a relatively even redistribution of bound peptide over the planar bilayer and the fibrils. Physical properties of the lipid fibrils suggest that they have a tubular structure. Our data demonstrate that the peptide-lipid interactions alone can provide a driving force for the spontaneous membrane shape transformations leading to tubule outgrowth and elongation. Further experiments revealed the importance of positive curvature strain in the tubulation process as well as the sufficient positive charge on the peptide (>/=+2). The observed membrane transformations could provide a simplified in vitro model for morphogenesis of intracellular tubular structures and intercellular connections.