Dynamics of novel forests of Castilla elastica in Puerto Rico: from species to ecosystems

Novel forests (NFs)—forests that contain a combination of introduced and native species—are a consequence of intense anthropogenic disturbances and the natural resilience of disturbed ecosystems. The extent to which NFs have similar forest function as comparable native secondary forests is a matter of debate in the scientific community. Little is known about the performance of individual species in those forests. This study focuses on the functional attributes of Castilla elastica NFs in Puerto Rico and on the differences between introduced and native species growing side by side in these forests. Rates of processes measured here were later compared with data from literature about NSFs. I hypothesize that juvenile plants of C. elastica in NFs have higher survival rate than those of native species and that C. elastica trees have faster biomass fluxes than native trees. To test the hypotheses, I measured survival rates of juvenile plants and tree growth and characterized the aboveground litter fluxes and storage. Although juvenile plants of native species displayed higher survival rates than those of C. elastica (53% vs. 28%), the latter was dominant in the understory (96%). Stand biomass growth rate was 2.0 ± 0.4 (average ± one standard deviation) Mg·ha⁻¹·year⁻¹ for the whole forest, and Guarea guidonia, a native species, exhibited the highest tree growth. Total litter fall was 9.6 ± 0.5 Mg·ha⁻¹·year⁻¹, and mean litter standing stock was 4.4 ± 0.1 Mg·ha⁻¹. Castilla elastica litter fall decomposed twice as fast as that of native species (5.8 ± 1.1 vs. 3.03 ± 1 k·year⁻¹). Literature comparisons show that the present NFs differ in some rates of processes from NSFs. This study brings unique and detailed supporting data about the ecological dynamics under mature novel forest stands. Further comprehensive studies about NFs are important to strengthen the body of knowledge about the wide range of variation of emerging tropical ecosystems. Due to the large increase in the area covered by NFs, greater attention is needed to understand their functioning, delivery of ecological services and management requirements.     

Dosage and duration effects of nitrogen additions on ectomycorrhizal sporocarp production and functioning: an example from two N‐limited boreal forests

1. Although it is well known that nitrogen (N) additions strongly affect ectomycorrhizal (EM) fungal community composition, less is known about how different N application rates and duration of N additions affect the functional role EM fungi play in the forest N cycle.
2. We measured EM sporocarp abundance and species richness as well as determined the δ¹⁵N in EM sporocarps and tree foliage in two Pinus sylvestris forests characterized by short- and long-term N addition histories and multiple N addition treatments. After 20 and 39 years of N additions, two of the long-term N addition treatments were terminated, thereby providing a unique opportunity to examine the temporal recovery of EM sporocarps after cessation of high N loading.
3. In general, increasing N availability significantly reduced EM sporocarp production, species richness, and the amount of N retained in EM sporocarps. However, these general responses were strongly dependent on the application rate and duration of N additions. The annual addition of 20 kg·N·ha⁻¹ for the past 6 years resulted in a slight increase in the production and retention of N in EM sporocarps, whereas the addition of 100 kg·N·ha⁻¹·yr⁻¹ during the same period nearly eliminated EM sporocarps. In contrast, long-term additions of N at rates of ca. 35 or 70 kg·N·ha⁻¹·yr⁻¹ for the past 40 years did not eliminate tree carbon allocation to EM sporocarps, although there was a decrease in the abundance and a shift in the dominant EM sporocarp taxa. Despite no immediate recovery, EM sporocarp abundance and species richness approached those of the control 20 years after terminating N additions in the most heavily fertilized treatment, suggesting a recovery of carbon allocation to EM sporocarps after cessation of high N loading.
4. Our results provide evidence for a tight coupling between tree carbon allocation to and N retention in EM sporocarps and moreover highlight the potential use of δ¹⁵N in EM sporocarps as a relative index of EM fungal sink strength for N. However, nitrogen additions at high dosage rates or over long time periods appear to disrupt this feedback, which could have important ramifications on carbon and nitrogen dynamics in these forested ecosystems.

     

Stability of thioester intermediates in ubiquitin‐like modifications

Ubiquitin-like modifications are important mechanisms in cellular regulation, and are carried out through several steps with reaction intermediates being thioester conjugates of ubiquitin-like proteins with E1, E2, and sometimes E3. Despite their importance, a thorough characterization of the intrinsic stability of these thioester intermediates has been lacking. In this study, we investigated the intrinsic stability by using a model compound and the Ubc9∼SUMO-1 thioester conjugate. The Ubc9∼SUMO-1 thioester intermediate has a half life of approximately 3.6 h (hydrolysis rate k = 5.33 ± 2.8 ×10⁻⁵ s⁻¹), and the stability decreased slightly under denaturing conditions (k = 12.5 ± 1.8 × 10⁻⁵ s⁻¹), indicating a moderate effect of the three-dimensional structural context on the stability of these intermediates. Binding to active and inactive E3, (RanBP2) also has only a moderate effect on the hydrolysis rate (13.8 ± 0.8 × 10⁻⁵ s⁻¹ for active E3 versus 7.38 ± 0.7 × 10⁻⁵ s⁻¹ for inactive E3). The intrinsically high stability of these intermediates suggests that unwanted thioester intermediates may be eliminated enzymatically, such as by thioesterases, to regulate their intracellular abundance and trafficking in the control of ubiquitin-like modifications.     

Cryopreservation at −20 and −70 °C of Pleurotus ostreatus on Grains

Alternative substrates for cryopreservation at −20 °C have been little explored for basidiomycetes and could bring new possibilities of lower cost cryopreservation. Nevertheless, freezing temperatures between −15 and −60 °C are very challenging because they frequently result in cryoinjuries. The objective of this study was to evaluate substrates associated to cryoprotective agents for Pleurotus ostreatus cryopreservation at −20 or −70 °C in order to develop alternative techniques for basidiomycete cryopreservation. P. ostreatus was grown on potato dextrose agar or whole grains of oat, wheat, rice or millet and transferred to cryovials with cryoprotective solution with 1 % dimethyl sulfoxide, 5 % glycerol, 10 % saccharose, 4 % glucose, 6 % polyethylene glycol-6000 or 5 % malt extract. The mycelium in the cryovials were cryopreserved at −20 or −70 °C and recovered for evaluation of the mycelial growth viability after 1 and 3 years. Both substrates and cryoprotectants affect the viability of the mycelial growth cryopreserved at −20 or −70 °C; wheat grains combined with cryoprotectants such as saccharose or glucose are effective for keeping mycelium viable after cryopreservation at −20 °C for 1 or 3 years; for cryopreservation at −70 °C after 1 or 3 years, any substrate combined with any cryoprotectant is effective for preserving the mycelium viable, except for millet grains with polyethylene glycol after 3 years; semi-permeable cryoprotective agents such as saccharose and glucose are the most effective for cryopreservation at −20 or −70 °C for at least 3 years.     

Specificity of RSG-1.2 peptide binding to RRE-IIB RNA element of HIV-1 over Rev peptide is mainly enthalpic in origin

Rev is an essential HIV-1 regulatory protein which binds to the Rev responsive element (RRE) present within the env gene of HIV-1 RNA genome. This binding facilitates the transport of the RNA to the cytoplasm, which in turn triggers the switch between viral latency and active viral replication. Essential components of this complex have been localized to a minimal arginine rich Rev peptide and stem IIB region of RRE. A synthetic peptide known as RSG-1.2 binds with high binding affinity and specificity to the RRE-IIB than the Rev peptide, however the thermodynamic basis of this specificity has not yet been addressed. The present study aims to probe the thermodynamic origin of this specificity of RSG-1.2 over Rev Peptide for RRE-IIB. The temperature dependent melting studies show that RSG-1.2 binding stabilizes the RRE structure significantly (ΔT _m = 4.3°C), in contrast to Rev binding. Interestingly the thermodynamic signatures of the binding have also been found to be different for both the peptides. At pH 7.5, RSG-1.2 binds RRE-IIB with a K_a = 16.2±0.6×10⁷ M⁻¹ where enthalpic change ΔH = −13.9±0.1 kcal/mol is the main driving force with limited unfavorable contribution from entropic change TΔS = −2.8±0.1 kcal/mol. A large part of ΔH may be due to specific stacking between U72 and Arg15. In contrast binding of Rev (K_a = 3.1±0.4×10⁷ M⁻¹) is driven mainly by entropy (ΔH = 0 kcal/mol and TΔS = 10.2±0.2 kcal/mol) which arises from major conformational changes in the RNA upon binding.     

Skeletal muscle myofibrillar and sarcoplasmic protein synthesis rates are affected differently by altitude-induced hypoxia in native lowlanders

As a consequence to hypobaric hypoxic exposure skeletal muscle atrophy is often reported. The underlying mechanism has been suggested to involve a decrease in protein synthesis in order to conserve O₂. With the aim to challenge this hypothesis, we applied a primed, constant infusion of 1-¹³C-leucine in nine healthy male subjects at sea level and subsequently at high-altitude (4559 m) after 7–9 days of acclimatization. Physical activity levels and food and energy intake were controlled prior to the two experimental conditions with the aim to standardize these confounding factors. Blood samples and expired breath samples were collected hourly during the 4 hour trial and vastus lateralis muscle biopsies obtained at 1 and 4 hours after tracer priming in the overnight fasted state. Myofibrillar protein synthesis rate was doubled; 0.041±0.018 at sea-level to 0.080±0.018%⋅hr⁻¹ (p<0.05) when acclimatized to high altitude. The sarcoplasmic protein synthesis rate was in contrast unaffected by altitude exposure; 0.052±0.019 at sea-level to 0.059±0.010%⋅hr⁻¹ (p>0.05). Trends to increments in whole body protein kinetics were seen: Degradation rate elevated from 2.51±0.21 at sea level to 2.73±0.13 µmol⋅kg⁻¹⋅min⁻¹ (p = 0.05) at high altitude and synthesis rate similar; 2.24±0.20 at sea level and 2.43±0.13 µmol⋅kg⁻¹⋅min⁻¹ (p>0.05) at altitude. We conclude that whole body amino acid flux is increased due to an elevated protein turnover rate. Resting skeletal muscle myocontractile protein synthesis rate was concomitantly elevated by high-altitude induced hypoxia, whereas the sarcoplasmic protein synthesis rate was unaffected by hypoxia. These changed responses may lead to divergent adaptation over the course of prolonged exposure.     

Temporal changes of soil physic‐chemical properties at different soil depths during larch afforestation by multivariate analysis of covariance

Soil physic-chemical properties differ at different depths; however, differences in afforestation-induced temporal changes at different soil depths are seldom reported. By examining 19 parameters, the temporal changes and their interactions with soil depth in a large chronosequence dataset (159 plots; 636 profiles; 2544 samples) of larch plantations were checked by multivariate analysis of covariance (MANCOVA). No linear temporal changes were found in 9 parameters (N, K, N:P, available forms of N, P, K and ratios of N: available N, P: available P and K: available K), while marked linear changes were found in the rest 10 parameters. Four of them showed divergent temporal changes between surface and deep soils. At surface soils, changing rates were 262.1 g·kg⁻¹·year⁻¹ for SOM, 438.9 mg·g⁻¹·year⁻¹ for C:P, 5.3 mg·g⁻¹·year⁻¹ for C:K, and −3.23 mg·cm⁻³·year⁻¹ for bulk density, while contrary tendencies were found in deeper soils. These divergences resulted in much moderated or no changes in the overall 80-cm soil profile. The other six parameters showed significant temporal changes for overall 0–80-cm soil profile (P: −4.10 mg·kg⁻¹·year⁻¹; pH: −0.0061 unit·year⁻¹; C:N: 167.1 mg·g⁻¹·year⁻¹; K:P: 371.5 mg·g⁻¹ year⁻¹; N:K: −0.242 mg·g⁻¹·year⁻¹; EC: 0.169 μS·cm⁻¹·year⁻¹), but without significant differences at different soil depths (P > 0.05). Our findings highlight the importance of deep soils in studying physic-chemical changes of soil properties, and the temporal changes occurred in both surface and deep soils should be fully considered for forest management and soil nutrient balance.     

Is the simple auger coring method reliable for below-ground standing biomass estimation in Eucalyptus forest plantations?

Background and Aims

Despite their importance for plant production, estimations of below-ground biomass and its distribution in the soil are still difficult and time consuming, and no single reliable methodology is available for different root types. To identify the best method for root biomass estimations, four different methods, with labour requirements, were tested at the same location.

Methods

The four methods, applied in a 6-year-old Eucalyptus plantation in Congo, were based on different soil sampling volumes: auger (8 cm in diameter), monolith (25 × 25 cm quadrate), half Voronoi trench (1·5 m³) and a full Voronoi trench (3 m³), chosen as the reference method.

Key Results

With the reference method (0–1m deep), fine-root biomass (FRB, diameter <2 mm) was estimated at 1·8 t ha⁻¹, medium-root biomass (MRB diameter 2–10 mm) at 2·0 t ha⁻¹, coarse-root biomass (CRB, diameter >10 mm) at 5·6 t ha⁻¹ and stump biomass at 6·8 t ha⁻¹. Total below-ground biomass was estimated at 16·2 t ha⁻¹ (root : shoot ratio equal to 0·23) for this 800 tree ha⁻¹ eucalypt plantation density. The density of FRB was very high (0·56 t ha⁻¹) in the top soil horizon (0–3 cm layer) and decreased greatly (0·3 t ha⁻¹) with depth (50–100 cm). Without labour requirement considerations, no significant differences were found between the four methods for FRB and MRB; however, CRB was better estimated by the half and full Voronoi trenches. When labour requirements were considered, the most effective method was auger coring for FRB, whereas the half and full Voronoi trenches were the most appropriate methods for MRB and CRB, respectively.

Conclusions

As CRB combined with stumps amounted to 78 % of total below-ground biomass, a full Voronoi trench is strongly recommended when estimating total standing root biomass. Conversely, for FRB estimation, auger coring is recommended with a design pattern accounting for the spatial variability of fine-root distribution.     

High rates of growth recorded for hawksbill sea turtles in Anegada,British Virgin Islands

Management of species of conservation concern requires knowledge of demographic parameters, such as rates of recruitment, survival, and growth. In the Caribbean, hawksbill turtles (Eretmochelys imbricata) have been historically exploited in huge numbers to satisfy trade in their shells and meat. In the present study, we estimated growth rate of juvenile hawksbill turtles around Anegada, British Virgin Islands, using capture–mark–recapture of 59 turtles over periods of up to 649 days. Turtles were recaptured up to six times, having moved up to 5.9 km from the release location. Across all sizes, turtles grew at an average rate of 9.3 cm year⁻¹ (range 2.3–20.3 cm year⁻¹), and gained mass at an average of 3.9 kg year⁻¹ (range 850 g–16.1 kg year⁻¹). Carapace length was a significant predictor of growth rate and mass gain, but there was no relationship between either variable and sea surface temperature. These are among the fastest rates of growth reported for this species, with seven turtles growing at a rate that would increase their body size by more than half per year (51–69% increase in body length). This study also demonstrates the importance of shallow water reef systems for the developmental habitat for juvenile hawksbill turtles. Although growth rates for posthatching turtles in the pelagic, and turtles larger than 61 cm, are not known for this population, the implications of this study are that Caribbean hawksbill turtles in some areas may reach body sizes suggesting sexual maturity in less time than previously considered.     

Carbon stocks and fluxes in tropical lowland dipterocarp rainforests in Sabah, Malaysian Borneo

Deforestation in the tropics is an important source of carbon C release to the atmosphere. To provide a sound scientific base for efforts taken to reduce emissions from deforestation and degradation (REDD+) good estimates of C stocks and fluxes are important. We present components of the C balance for selectively logged lowland tropical dipterocarp rainforest in the Malua Forest Reserve of Sabah, Malaysian Borneo. Total organic C in this area was 167.9 Mg C ha⁻¹±3.8 (SD), including: Total aboveground (TAGC: 55%; 91.9 Mg C ha⁻¹±2.9 SEM) and belowground carbon in trees (TBGC: 10%; 16.5 Mg C ha⁻¹±0.5 SEM), deadwood (8%; 13.2 Mg C ha⁻¹±3.5 SEM) and soil organic matter (SOM: 24%; 39.6 Mg C ha⁻¹±0.9 SEM), understory vegetation (3%; 5.1 Mg C ha⁻¹±1.7 SEM), standing litter (<1%; 0.7 Mg C ha⁻¹±0.1 SEM) and fine root biomass (<1%; 0.9 Mg C ha⁻¹±0.1 SEM). Fluxes included litterfall, a proxy for leaf net primary productivity (4.9 Mg C ha⁻¹ yr⁻¹±0.1 SEM), and soil respiration, a measure for heterotrophic ecosystem respiration (28.6 Mg C ha⁻¹ yr⁻¹±1.2 SEM). The missing estimates necessary to close the C balance are wood net primary productivity and autotrophic respiration.Twenty-two years after logging TAGC stocks were 28% lower compared to unlogged forest (128 Mg C ha⁻¹±13.4 SEM); a combined weighted average mean reduction due to selective logging of −57.8 Mg C ha⁻¹ (with 95% CI −75.5 to −40.2). Based on the findings we conclude that selective logging decreased the dipterocarp stock by 55–66%. Silvicultural treatments may have the potential to accelerate the recovery of dipterocarp C stocks to pre-logging levels.     

Effect of heat treatment around the fruit set region on growth and yield of watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai]

The present experiment was aimed to study the effect of imposing modulated temperature treatments 14 °C and 18 °C, around the fruiting region of watermelon plants, and to estimate the economic feasibility of the temperature treatments based on energy consumption for heating. Watermelon cultivar ‘Sambok-gul’ was selected and sown on perlite beds in a plastic house under controlled conditions at Watermelon Farm, Jeongeup-Jeonbuk, longitude 35° 31′ 47.51N, 126° 48′48.84E, altitude 37 m during the early spring season (2010–2011). The findings revealed that the temperature treatment at 18 °C caused significant increase in weight (2.0 kg plant⁻¹), fruit weight (8.3 kg plant⁻¹), soluble solid content (11.5 %), and fruit set rate (96.5 %) at harvest stage. Higher contents of Ca²⁺ and Mg²⁺ ions were observed in the 1st upper leaf of the fruit set node (79.3 mg L⁻¹) and the 1st lower leaf of the fruit set node (12.0 mg L⁻¹), respectively at 14 °C. The power consumption and extra costs of the temperature treatment 18 °C were suggested as affordable and in range of a farmer’s budget (41.14 USD/22 days). Hence, it was concluded that modulating temperature treatments could be utilized successfully to optimize the temperature range for enhancing the fruit yield and quality in the winter watermelon crops.     

Decadal Changes in the World's Coastal Latitudinal Temperature Gradients

Most of the world''s living marine resources inhabit coastal environments, where average thermal conditions change predictably with latitude. These coastal latitudinal temperature gradients (CLTG) coincide with important ecological clines,e.g., in marine species diversity or adaptive genetic variations, but how tightly thermal and ecological gradients are linked remains unclear. A first step is to consistently characterize the world''s CLTGs. We extracted coastal cells from a global 1°×1° dataset of weekly sea surface temperatures (SST, 1982–2012) to quantify spatial and temporal variability of the world''s 11 major CLTGs. Gradient strength, i.e., the slope of the linear mean-SST/latitude relationship, varied 3-fold between the steepest (North-American Atlantic and Asian Pacific gradients: −0.91°C and −0.68°C lat⁻¹, respectively) and weakest CLTGs (African Indian Ocean and the South- and North-American Pacific gradients: −0.28, −0.29, −0.32°C lat⁻¹, respectively). Analyzing CLTG strength by year revealed that seven gradients have weakened by 3–10% over the past three decades due to increased warming at high compared to low latitudes. Almost the entire South-American Pacific gradient (6–47°S), however, has considerably cooled over the study period (−0.3 to −1.7°C, 31 years), and the substantial weakening of the North-American Atlantic gradient (−10%) was due to warming at high latitudes (42–60°N, +0.8 to +1.6°C,31 years) and significant mid-latitude cooling (Florida to Cape Hatteras 26–35°N, −0.5 to −2.2°C, 31 years). Average SST trends rarely resulted from uniform shifts throughout the year; instead individual seasonal warming or cooling patterns elicited the observed changes in annual means. This is consistent with our finding of increased seasonality (i.e., summer-winter SST amplitude) in three quarters of all coastal cells (331 of 433). Our study highlights the regionally variable footprint of global climate change, while emphasizing ecological implications of changing CLTGs, which are likely driving observed spatial and temporal clines in coastal marine life.     

Recent Changes in Glacial Area and Volume on Tuanjiefeng Peak Region of Qilian Mountains,China

Glaciers'' runoff in the Qilian Mountains serves as a critical water resource in the northern sections of the Gansu province, the northeastern sections of the Qinghai province, and the northeastern fringe of the Tibetan Plateau. Changes in the glacial area and volume around the highest peak of the Qilian Mountains, i.e., Tuanjiefeng Peak, were estimated using multi-temporal remote-sensing images and digital elevation models, and all possible sources of uncertainty were considered in detail. The total glacier area decreased by 16.1±6.34 km² (9.9±3.9%) during 1966 to 2010. The average annual glacier shrinkage was −0.15% a⁻¹ from 1966 to 1995, −0.61% a⁻¹ from 1995 to 2000, −0.20% a⁻¹ from 2000 to 2006, and −0.45% a⁻¹ from 2006 to 2010. A comparison of glacier surface elevations using digital elevation models derived from topographic maps in 1966 and from the Shuttle Radar Topography Mission in 1999 suggests that 65% of the grid cells has decreased, thereby indicating that the glacier thickness has declined. The average change in glacier thickness was −7.3±1.5 m (−0.21±0.04 m·a⁻¹) from 1966 to 1999. Glaciers with northeastern aspects thinned by 8.3±1.4 m from 1966 to 1999, i.e., almost twice as much as those with southwestern aspects (4.3±1.3 m). The ice volume decreased by 11.72±2.38×10⁸ m³ from 1966 to 1999, which was about 17.4% more than the value calculated from the statistical relationship between glacier area and volume. The relationship between glacier area change and elevation zone indicates that glacier change is not only dominated by climate change but also affected by glacier dynamics, which are related to local topography. The varied response of a single glacier to climate change indicates that the glacier area change scheme used in some models must be improved.     

Increasing pCO2 correlates with low concentrations of intracellular dimethylsulfoniopropionate in the sea anemone Anemonia viridis

Marine anthozoans maintain a mutualistic symbiosis with dinoflagellates that are prolific producers of the algal secondary metabolite dimethylsulfoniopropionate (DMSP), the precursor of the climate-cooling trace gas dimethyl sulfide (DMS). Surprisingly, little is known about the physiological role of DMSP in anthozoans and the environmental factors that regulate its production. Here, we assessed the potential functional role of DMSP as an antioxidant and determined how future increases in seawater pCO₂ may affect DMSP concentrations in the anemone Anemonia viridis along a natural pCO₂ gradient at the island of Vulcano, Italy. There was no significant difference in zooxanthellae genotype and characteristics (density of zooxanthellae, and chlorophyll a) as well as protein concentrations between anemones from three stations along the gradient, V1 (3232 μatm CO₂), V2 (682 μatm) and control (463 μatm), which indicated that A. viridis can acclimate to various seawater pCO₂. In contrast, DMSP concentrations in anemones from stations V1 (33.23 ± 8.30 fmol cell⁻¹) and V2 (34.78 ± 8.69 fmol cell⁻¹) were about 35% lower than concentrations in tentacles from the control station (51.85 ± 12.96 fmol cell⁻¹). Furthermore, low tissue concentrations of DMSP coincided with low activities of the antioxidant enzyme superoxide dismutase (SOD). Superoxide dismutase activity for both host (7.84 ± 1.37 U·mg⁻¹ protein) and zooxanthellae (2.84 ± 0.41 U·mg⁻¹ protein) at V1 was 40% lower than at the control station (host: 13.19 ± 1.42; zooxanthellae: 4.72 ± 0.57 U·mg⁻¹ protein). Our results provide insight into coastal DMSP production under predicted environmental change and support the function of DMSP as an antioxidant in symbiotic anthozoans.     

Cytotoxicity and genotoxicity of zingiberene on different neuron cell lines in vitro

The main objective of this study is to investigate the cytotoxic, genotoxic and antioxidant properties of zingiberene (ZBN) in an in vitro rat brain cell culture study. The cytotoxic effect was determined against the rat neuron and N2a neuroblastoma (N2a-NB) cell lines using the 3,(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, while the antioxidant activity was assessed using the total antioxidant capacity (TAC) and total oxidative stress (TOS) assays. The effects on DNA damage were also evaluated in this study by the single cell gel electrophoresis assay. The results indicated that ZBN has an anti-proliferative activity suppressing the proliferation of N2a-NB cells at concentrations over 50 mg L⁻¹ and neuron cells at concentrations over 150 mg L⁻¹. In addition, ZBN treatments at higher doses (≤50 mg L⁻¹) led to increases of TOS levels in N2a-NB cell cultures. However 25 mg L⁻¹ of ZBN treatment caused increases of TAC levels in cultured neuron and N2a-NB cell cultures while ZBN at doses of 10–400 mg L⁻¹ did not increase the number of total damage score in both cell lines. This study clearly indicates that ZBN has a significant potential to be used as a natural anticancer agent in cultured N2a-NBs.     

Floral thermogenesis of three species of Hydnora (Hydnoraceae) in Africa

Background and Aims

Floral thermogenesis occurs in at least 12 families of ancient seed plants. Some species show very high rates of respiration through the alternative pathway, and some are thermoregulatory, with increasing respiration at decreasing ambient temperature. This study assesses the intensity and regulation of respiration in three species of African Hydnora that represent the Hydnoraceae, an unusual family of holoparasitic plants from arid environments.

Methods

Long-term respirometry (CO₂ production) and thermometry were carried out on intact flowers of H. africana, H. abyssinica and H. esculenta in the field, and short-term measurements were made on floral parts during the protogynous flowering sequence.

Key Results

For H. africana, there was no temperature elevation in either the osmophores or the gynoecial chamber in any phase, and mass-specific respiration rates of the flower parts were low (maximum 8·3 nmol CO₂ g⁻¹ s⁻¹ in osmophore tissue). Respiration tracked ambient and floral temperatures, eliminating the possibility of the inverse relationship expected in thermoregulatory flowers. Hydnora abyssinica flowers had higher respiration (maximum 27·5 nmol g⁻¹ s⁻¹ in the osmophores) and a slight elevation of osmophore temperature (maximum 2·8 °C) in the female stage. Respiration by gynoecial tissue was similar to that of osmophores in both species, but there was no measurable elevation of gynoecial chamber temperature. Gynoecial chamber temperature of H. esculenta could reach 3·8 °C above ambient, but there are no respiration data available. Antheral tissue respiration was maximal in the male phase (4·8 nmol g⁻¹ s⁻¹ in H. africana and 10·3 nmol g⁻¹ s⁻¹ in H. abyssinica), but it did not raise the antheral ring temperature, which showed that thermogenesis is not a by-product of pollen maturation or release.

Conclusions

The exceptionally low thermogenesis in Hydnora appears to be associated with scent production and possibly gynoecial development, but has little direct benefit to beetle pollinators.Key words: Pollination biology, Hydnora, thermogenesis, respiration rate, temperature, flowers, insects     

Effects of coral reef benthic primary producers on dissolved organic carbon and microbial activity

Benthic primary producers in marine ecosystems may significantly alter biogeochemical cycling and microbial processes in their surrounding environment. To examine these interactions, we studied dissolved organic matter release by dominant benthic taxa and subsequent microbial remineralization in the lagoonal reefs of Moorea, French Polynesia. Rates of photosynthesis, respiration, and dissolved organic carbon (DOC) release were assessed for several common benthic reef organisms from the backreef habitat. We assessed microbial community response to dissolved exudates of each benthic producer by measuring bacterioplankton growth, respiration, and DOC drawdown in two-day dark dilution culture incubations. Experiments were conducted for six benthic producers: three species of macroalgae (each representing a different algal phylum: Turbinaria ornata – Ochrophyta; Amansia rhodantha – Rhodophyta; Halimeda opuntia – Chlorophyta), a mixed assemblage of turf algae, a species of crustose coralline algae (Hydrolithon reinboldii) and a dominant hermatypic coral (Porites lobata). Our results show that all five types of algae, but not the coral, exuded significant amounts of labile DOC into their surrounding environment. In general, primary producers with the highest rates of photosynthesis released the most DOC and yielded the greatest bacterioplankton growth; turf algae produced nearly twice as much DOC per unit surface area than the other benthic producers (14.0±2.8 µmol h⁻¹ dm⁻²), stimulating rapid bacterioplankton growth (0.044±0.002 log10 cells h⁻¹) and concomitant oxygen drawdown (0.16±0.05 µmol L⁻¹ h⁻¹ dm⁻²). Our results demonstrate that benthic reef algae can release a significant fraction of their photosynthetically-fixed carbon as DOC, these release rates vary by species, and this DOC is available to and consumed by reef associated microbes. These data provide compelling evidence that benthic primary producers differentially influence reef microbial dynamics and biogeochemical parameters (i.e., DOC and oxygen availability, bacterial abundance and metabolism) in coral reef communities.     

Cholesterol absorption status and fasting plasma cholesterol are modulated by the microsomal triacylglycerol transfer protein −493 G/T polymorphism and the usual diet in women

An important inter-individual variability in cholesterol absorption has been reported. It could result from polymorphisms in genes coding for proteins involved in the absorption process and in interaction with dietary intakes. To assess whether the extent of cholesterol absorption or synthesis is modified in adult women according to the −493 G/T polymorphism in the microsomal triglyceride transfer protein gene (MTP) and/or the habitual diet. Cholestanol and sitosterol, as well as desmosterol and lathosterol, surrogate markers of cholesterol absorption or synthesis, respectively, were analyzed in the fasting plasma of 69 middle-aged women under a Western-type diet (WD) and after 3 months on a low-saturated fat, low-cholesterol/Mediterranean-type diet (LFLCD). Genotypes for MTP −493G/T polymorphism were determined. Under an usual WD, subjects homozygous for the MTP −493 T allele exhibited higher (P < 0.05) fasting serum concentrations of cholestanol (199.0 ± 30.0 vs. 133 ± 7.4 × 10² mmol/mol cholesterol) and lathosterol (188.7 ± 21.8 vs. 147.6 ± 9.1 × 10² mmol/mol cholesterol), as well as total cholesterol (7.32 ± 0.22 vs. 6.63 ± 0.12 mmol/l) compared to G carrier subjects. After 3 months on a LFLCD, level of absorption markers decreased in TT subjects with no change in synthesis ones, leading to values comparable to those measured in G carriers. The lowering of plasma total and LDL cholesterol due to dietary change was 2.4- and 2.3-fold greater in TT women than in G carriers. The polymorphism −493G/T in MTP modulates the level of cholesterol absorption but not synthesis in women under a WD, an effect abolished under a prudent LFLCD.     

The fate of assimilated carbon during drought: impacts on respiration in Amazon rainforests

Interannual variations in CO₂ exchange across Amazonia, as deduced from atmospheric inversions, correlate with El Niño occurrence. They are thought to result from changes in net ecosystem exchange and fire incidence that are both related to drought intensity. Alterations to net ecosystem production (NEP) are caused by changes in gross primary production (GPP) and ecosystem respiration (R_eco). Here, we analyse observations of the components of R_eco (leaves, live and dead woody tissue, and soil) to provide first estimates of changes in R_eco during short-term (seasonal to interannual) moisture limitation. Although photosynthesis declines if moisture availability is limiting, leaf dark respiration is generally maintained, potentially acclimating upwards in the longer term. If leaf area is lost, then short-term canopy-scale respiratory effluxes from wood and leaves are likely to decline. Using a moderate short-term drying scenario where soil moisture limitation leads to a loss of 0.5 m² m⁻² yr⁻¹ in leaf area index, we estimate a reduction in respiratory CO₂ efflux from leaves and live woody tissue of 1.0 (±0.4) t C ha⁻¹ yr⁻¹. Necromass decomposition declines during drought, but mortality increases; the median mortality increase following a strong El Niño is 1.1% (n=46 tropical rainforest plots) and yields an estimated net short-term increase in necromass CO₂ efflux of 0.13–0.18 t C ha⁻¹ yr⁻¹. Soil respiration is strongly sensitive to moisture limitation over the short term, but not to associated temperature increases. This effect is underestimated in many models but can lead to estimated reductions in CO₂ efflux of 2.0 (±0.5) t C ha⁻¹ yr⁻¹. Thus, the majority of short-term respiratory responses to drought point to a decline in R_eco, an outcome that contradicts recent regional-scale modelling of NEP. NEP varies with both GPP and R_eco but robust moisture response functions are clearly needed to improve quantification of the role of R_eco in influencing regional-scale CO₂ emissions from Amazonia.