Nutrient relations of dwarf <Emphasis Type="Italic">Rhizophora mangle</Emphasis> L. mangroves on peat in eastern Puerto Rico

Dwarf mangroves on peat substrate growing in eastern Puerto Rico (Los Machos, Ceiba State Forest) were analyzed for element concentration, leaf sap osmolality, and isotopic signatures of C and N in leaves and substrate. Mangrove communities behind the fringe presented poor structural development with maximum height below 1.5 m, lacked a main stem, and produced horizontal stems from which rhizophores developed. This growth form departs from other dwarf mangrove sites in Belize, Panama, and Florida. The dwarf mangroves were not stressed by salinity but by the low P availability reflected in low P concentrations in adult and senescent leaves. Low P availability was associated with reduced remobilization of N and accumulation of K in senescent leaves, contrasting with the behavior of this cation in terrestrial plants. Remobilization of N and P before leaf abscission on a weight basis indicated complete resorption of these nutrients. On an area basis, resorption was complete for P but not for N. Sulfur accumulated markedly with leaf age, reaching values up to 400%, compared with relatively modest accumulation of Na (40%) in the same leaves. This suggests a more effective rejection of Na than sulfate at the root level. Dwarf mangrove leaves had more positive δ¹³C values, which were not related to salinity, but possibly to drought during the dry season due to reduced flooding, and/or reduced hydraulic conductance under P limitation. Negative leaf δ¹⁵N values were associated with low leaf P concentrations. Comparison with other R. mangle communities showed that P concentration in adult leaves below 13 mmol kg⁻¹ is associated with negative δ¹⁵N values, whereas leaves with P concentrations above 30 mmol kg⁻¹ in non-polluted environments had positive δ¹⁵N values.     

Novel ecosystems: theoretical and management aspects of the new ecological world order

We explore the issues relevant to those types of ecosystems containing new combinations of species that arise through human action, environmental change, and the impacts of the deliberate and inadvertent introduction of species from other regions. Novel ecosystems (also termed 'emerging ecosystems') result when species occur in combinations and relative abundances that have not occurred previously within a given biome. Key characteristics are novelty, in the form of new species combinations and the potential for changes in ecosystem functioning, and human agency, in that these ecosystems are the result of deliberate or inadvertent human action. As more of the Earth becomes transformed by human actions, novel ecosystems increase in importance, but are relatively little studied. Either the degradation or invasion of native or 'wild' ecosystems or the abandonment of intensively managed systems can result in the formation of these novel systems. Important considerations are whether these new systems are persistent and what values they may have. It is likely that it may be very difficult or costly to return such systems to their previous state, and hence consideration needs to be given to developing appropriate management goals and approaches.     

Nutrient limitation in a tropical saline lake: a microcosm experiment

There is increasing evidence that nitrogen limitation is of widespread occurrence in tropical lakes. Nonetheless, data on the deep tropical Lake Alchichica (Mexico) show that dissolved inorganic nitrogen (DIN) to soluble reactive phosphorus (SRP) ratio fluctuates widely. To elucidate further the role of nitrogen and phosphorus limitation on the phytoplankton growth in tropical saline lakes, we present the results of a series of nutrient enrichment experiments with natural assemblages of Lake Alchichica phytoplankton conducted monthly for a year. Our assays indicate that phosphorus and nitrogen alternate in limiting Lake Alchichica phytoplankton biomass. Phosphorous limited phytoplankton growth most (41.7%) of the time, followed by nitrogen (33.3% of the time), and both nutrients for the rest of the time (25.0%). This alternation in nitrogen and phosphorus responsible for phytoplankton growth limitation in Lake Alchichica is attributed to the combination of natural conditions (e.g., young volcanic terrain rich in phosphorus) that would favor nitrogen limitation and anthropogenic impacts (e.g., agricultural nitrogen fertilization) which would cause phosphorus limitation. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Interactions between lithology and biology drive the long-term response of stream chemistry to major hurricanes in a tropical landscape

Humid tropical forests play a dominant role in many global biogeochemical cycles, yet long-term records of tropical stream chemistry and its response to disturbance events such as severe storms and droughts are rare. Here we document the long-term variability in chemistry of two streams in the Luquillo Mountains, Puerto Rico over a period of 27 years. Our two focal study watersheds, the Río Icacos and Quebrada Sonadora, both drain several hundred hectares of tropical wet forests, and each received direct hits from Hurricanes Hugo (1989) and Georges (1998). They differ primarily in lithology (granitic vs. volcaniclastic) and elevation. Changes in major cations, anions, silica, and dissolved organic carbon were minimal over the study period, but the concentrations of nitrate show a strong response to hurricane disturbance and the longest time to recovery. Potassium also showed a large, although less consistent, response to disturbance. In the granitic terrain, nitrate concentrations exceeded long-term pre-hurricane background levels for over a decade, but were elevated in the volcaniclastic terrain for only 1–2 years. Lithology appears to be the primary driver explaining the different response trajectories of the two watersheds. In the granitic terrain, which showed slow recovery to pre-hurricane conditions, the quartz diorite bedrock weathers to produce coarser soils, deeper groundwater flow paths, and riparian zones with sharp spatial variation in redox conditions and very high nitrogen levels immediately adjacent to the stream. Groundwater flow paths are shallow and the levels of N in streamside groundwater are much lower in the volcaniclastic terrain. The recovery of vegetation following hurricane disturbance appears similar in the two watersheds, suggesting that the extent of structural damage to canopy trees determines the magnitude of NO₃ increases, but that the duration of elevated concentrations in stream water is a function of lithology.     

BRD4 Short Isoform Interacts with RRP1B,SIPA1 and Components of the LINC Complex at the Inner Face of the Nuclear Membrane

Recent studies suggest that BET inhibitors are effective anti-cancer therapeutics. Here we show that BET inhibitors are effective against murine primary mammary tumors, but not pulmonary metastases. BRD4, a target of BET inhibitors, encodes two isoforms with opposite effects on tumor progression. To gain insights into why BET inhibition was ineffective against metastases the pro-metastatic short isoform of BRD4 was characterized using mass spectrometry and cellular fractionation. Our data show that the pro-metastatic short isoform interacts with the LINC complex and the metastasis-associated proteins RRP1B and SIPA1 at the inner face of the nuclear membrane. Furthermore, histone binding arrays revealed that the short isoform has a broader acetylated histone binding pattern relative to the long isoform. These differential biochemical and nuclear localization properties revealed in our study provide novel insights into the opposing roles of BRD4 isoforms in metastatic breast cancer progression.     

Aniracetam Does Not Alter Cognitive and Affective Behavior in Adult C57BL/6J Mice

There is a growing community of individuals who self-administer the nootropic aniracetam for its purported cognitive enhancing effects. Aniracetam is believed to be therapeutically useful for enhancing cognition, alleviating anxiety, and treating various neurodegenerative conditions. Physiologically, aniracetam enhances both glutamatergic neurotransmission and long-term potentiation. Previous studies of aniracetam have demonstrated the cognition-restoring effects of acute administration in different models of disease. No previous studies have explored the effects of aniracetam in healthy subjects. We investigated whether daily 50 mg/kg oral administration improves cognitive performance in naïve C57BL/6J mice in a variety of aspects of cognitive behavior. We measured spatial learning in the Morris water maze test; associative learning in the fear conditioning test; motor learning in the accelerating rotarod test; and odor discrimination. We also measured locomotion in the open field test, anxiety through the elevated plus maze test and by measuring time in the center of the open field test. We measured repetitive behavior through the marble burying test. We detected no significant differences between the naive, placebo, and experimental groups across all measures. Despite several studies demonstrating efficacy in impaired subjects, our findings suggest that aniracetam does not alter behavior in normal healthy mice. This study is timely in light of the growing community of healthy humans self-administering nootropic drugs.     

Trace Fear Conditioning in Mice

In this experiment we present a technique to measure learning and memory. In the trace fear conditioning protocol presented here there are five pairings between a neutral stimulus and an unconditioned stimulus. There is a 20 sec trace period that separates each conditioning trial. On the following day freezing is measured during presentation of the conditioned stimulus (CS) and trace period. On the third day there is an 8 min test to measure contextual memory. The representative results are from mice that were presented with the aversive unconditioned stimulus (shock) compared to mice that received the tone presentations without the unconditioned stimulus. Trace fear conditioning has been successfully used to detect subtle learning and memory deficits and enhancements in mice that are not found with other fear conditioning methods. This type of fear conditioning is believed to be dependent upon connections between the medial prefrontal cortex and the hippocampus. One current controversy is whether this method is believed to be amygdala-independent. Therefore, other fear conditioning testing is needed to examine amygdala-dependent learning and memory effects, such as through the delay fear conditioning.