Dynamics,productivity and species richness of tropical rainforests along elevational and edaphic gradients on Mount Kinabalu,Borneo

We studied the dynamics of nine tropical rainforests on Mount Kinabalu, Borneo, at four elevations (700, 1,700, 2,700 and 3,100 m) on various edaphic conditions for four 2-year periods over 8 years (1995–2003), and examined the relationships with above-ground productivity. Mean growth rate of stem diameter, basal area turnover rate and estimated recruitment rate (using growth rate and size distribution) correlated with productivity among the nine forests in all periods. These rates based on growth rates of surviving stems appeared to be good measures of stand turnover. However, observed recruitment rate and mortality (and turnover rate as mean of these rates) based on direct observation of recruits and deaths did not correlate with productivity in some periods. These rates may not be useful as measures of stand turnover given small sample size and short census interval because they were highly influenced by stochastic fluctuation. A severe drought associated with the 1997–1998 El Niño event inflated mortality and depressed mean growth rate, recruitment rate and basal area turnover rate, but had little effect on the correlations between these rates (except mortality) and productivity. Across broad elevational and edaphic gradients on Mount Kinabalu, forest turnover, productivity and species richness correlated with each other, but the causal interpretation is difficult given the different histories and species pools among forests at different elevations.     

Impairment of hippocampal long-term depression and defective spatial learning and memory in p35 mice

Cdk5 (cyclin-dependent kinase 5) activity is dependent upon association with one of two neuron-specific activators, p35 or p39. Genetic deletion of Cdk5 causes perinatal lethality with severe defects in corticogenesis and neuronal positioning. p35(-/-) mice are viable with milder histological abnormalities. Although substantial evidence implicates Cdk5 in synaptic plasticity, its role in learning and memory has not been evaluated using mutant mouse models. We report here that p35(-/-) mice have deficiencies in spatial learning and memory. Close examination of hippocampal circuitry revealed subtle histological defects in CA1 pyramidal cells. Furthermore, p35(-/-) mice exhibit impaired long-term depression and depotentiation of long-term potentiation in the Schaeffer collateral CA1 pathway. Moreover, the Cdk5-dependent phosphorylation state of protein phosphatase inhibitor-1 was increased in 4-week-old mice due to increased levels of p39, which co-localized with inhibitor-1 and Cdk5 in the cytoplasm. These results demonstrate that p35-dependent Cdk5 activity is important to learning and synaptic plasticity. Deletion of p35 may shift the substrate specificity of Cdk5 due to compensatory expression of p39.     

DNA-fiber EPR study of the orientation of Cu(II) complexes of 1,10-phenanthroline and its derivatives bound to DNA: mono(phenanthroline)-copper(II) and its ternary complexes with amino acids

The orientation of mono(1,10-phenanthroline)copper(II), [Cu(phen)]2+, and the ternary complexes with amino acids, [Cu(phen)X(aa)]n+, where X(aa) stands for an alpha-amino acid, has been investigated by electron paramagnetic resonance (EPR) spectra of the complexes on DNA fibers. It has been revealed that these complexes bind to DNA with several different binding modes. The observation of a species whose g axis is almost parallel to the DNA double helical axis has suggested that the phenanthroline moiety intercalates to DNA. An absence of the intercalated species for the corresponding 2,2'-bipyridine complex has shown that the three-fused aromatic rings in phenanthroline are critical for the intercalative binding of the complexes. The intercalative binding was promoted by 5,6-dimethyl groups on the phenanthroline ring, whereas it was disturbed by 2,9-dimethyl groups, indicating that the planarity of the coordination sphere is important for the intercalative binding. In all cases, the amount of the non-intercalated species was larger than that of the intercalated one. The amino acids in the ternary complexes of glycine, leucine, serine, threonine, cysteine, methionine, and asparagine were partly substituted with some coordinating groups in DNA, whereas the ternary complexes of lysine, arginine, and glutamine remained intact on DNA.     

Environmental Control of Root Exudation of Low-Molecular Weight Organic Acids in Tropical Rainforests

The availability of phosphorus (P) can limit net primary production (NPP) in tropical rainforests growing on highly weathered soils. Although it is well known that plant roots release organic acids to acquire P from P-deficient soils, the importance of organic acid exudation in P-limited tropical rainforests has rarely been verified. Study sites were located in two tropical montane rainforests (a P-deficient older soil and a P-rich younger soil) and a tropical lowland rainforest on Mt. Kinabalu, Borneo to analyze environmental control of organic acid exudation with respect to soil P availability, tree genus, and NPP. We quantified root exudation of oxalic, citric, and malic acids using in situ methods in which live fine roots were placed in syringes containing nutrient solution. Exudation rates of organic acids were greatest in the P-deficient soil in the tropical montane rainforest. The carbon (C) fluxes of organic acid exudation in the P-deficient soil (0.7?mol?C?m^?2?month^?1) represented 16.6% of the aboveground NPP, which was greater than those in the P-rich soil (3.1%) and in the lowland rainforest (4.7%), which exhibited higher NPP. The exudation rates of organic acids increased with increasing root surface area and tip number. A shift in vegetation composition toward dominance by tree species exhibiting a larger root surface area might contribute to the higher organic acid exudation observed in P-deficient soil. Our results quantitatively showed that tree roots can release greater quantities of organic acids in response to P deficiency in tropical rainforests.     

Effects of selective logging on tree species diversity and composition of Bornean tropical rain forests at different spatial scales

Reduced-impact logging (RIL) is known to be beneficial in biodiversity conservation, but its effects on tree diversity remain unknown. Pattern of tree diversity following disturbance usually varies with spatial scale of sampling (i.e., plot size). We examined the impacts of RIL on species richness and community composition of tree species at different spatial scales, and the scale (plot size) dependency of the two metrics; species richness versus community similarity. One 2-ha and three to four 0.2-ha plots were established in each of primary, RIL, and conventionally logged (CL) forest in Sabah, Malaysia. Species richness (the number of species per unit number of stems) was higher in the RIL than in the CL forest at both scales. The relationship between species richness and logging intensity varied with plot size. Species richness was greater in the RIL than in the primary forest at the 2-ha scale, while it was similar between the two forests at 0.2-ha scale. Similarly, species richness in the CL forest demonstrated a greater value at the 2-ha scale than at the 0.2-ha scale. Greater species richness in the two logged forests at the 2-ha scale is attributable to a greater probability of encountering the species-rich, small patches that are distributed heterogeneously. Community composition of the RIL forest more resembled that of the primary forest than that of the CL forest, regardless of plot size. Accordingly, species richness is a scale-dependent metric, while community similarity is a more robust metric to indicate the response of tree assemblage to anthropogenic disturbance.     

Comparative study of additive basal area of conifers in forest ecosystems along elevational gradients

We examined the basal area of two life forms (conifers vs. broadleaf trees) along elevational gradients on Yakushima Island, Japan and on two series of geological substrate on Mount Kinabalu, Borneo. On Yakushima, total stand basal area abruptly increased from 700 to 1,050 m in accordance with the high dominance of conifers, indicating the presence of additive basal area of conifers in conifer–broadleaf mixed forests at higher elevations (1,050–1,300 m). Along two substrate series on Kinabalu, some forests at higher elevations (1,860–3,080 m) showed relatively high dominance of conifers, but conifer basal area did not appear to be additive. Conifers were emergents above the canopy of broadleaf trees in mixed forests on Yakushima, but two life forms usually coexisted in the single-story canopy in mixed forests on Kinabalu. Litterfall rate as a surrogate of productivity decreased with decreasing temperature along elevation on both the sites, but the rate of decrease was slower on Yakushima, where mixed forests at higher elevations showed relatively high rates. Thus, we suggest that additive basal area of conifers was linked to their emergent status, and that it enhanced productivity by complementary use of light by two life forms that occupy different stories. On Yakushima, typhoons are a major disturbance, but do not severely limit the height growth of conifers, allowing the development of two-story mixed forests. On Kinabalu, a major disturbance is El Niño-driven drought, and hydraulic limitation to tree height may explain the non-additive and non-emergent nature of conifers.     

Importance of natural licks for the mammals in Bornean inland tropical rain forests

An intensive camera-trapping study and a nutrient analysis were carried out to understand how natural licks are important for mammals in inland tropical rain forests where soil cations are usually depleted. Using camera traps, we investigated the fauna, food habits, and the frequency of visitation by species at five natural licks in the Deramakot forest reserve, Sabah, Malaysia. All food-habit types of mammals (carnivore, herbivore-frugivore, insectivore, and omnivore), which included 29 (78.4%) of 37 species known in Deramakot, were recorded at the natural licks. The sambar deer, followed by the bearded pig, the lesser mouse-deer, the Malay badger, and the orangutan were the most commonly recorded species and represented 77.5% in terms of the frequency of appearance in all photographs taken throughout the year. These results indicated that, although the proportion of species recorded at the natural licks relative to the whole mammalian fauna of the forest was high, the frequency of visitation greatly varied among the species, and only a few species dominated. The frequency of visitation seemed to reflect both the density of species and the demand for the minerals, because some endangered, low-density species were more frequently recorded by cameras than expected—for example, the orangutan which was one of the top five species among natural-lick users. The natural licks with greater concentrations of minerals in seepage soil water were significantly preferred by the sambar deer and the bearded pig than those with lower concentrations of minerals. This result suggests that the chemical properties of soil water in natural licks determine the frequency of visitation of these herbivorous species that have strong demand for minerals.     

Primary succession of Hawaiian montane rain forest on a chronosequence of eight lava flows

Abstract. The primary-successional sere of a Hawaiian montane rain forest was inferred from an age sequence of eight closely located ‘a’ ā flows (clinker type lava); 8, 50, 140, ca. 300, ca. 400, ca. 1400, ca. 3000 and ca. 9000 yr, on a windward slope of Mauna Loa, Hawaii. All study sites (0.2 ha each) were at 1120 — 1250 m a.s.l. with 4000 mm mean annual rainfall. The 400-yr, 1400-yr, and 9000-yr flows had younger volcanic ash deposits, while the others were pure lava. Comparisons of tree size and foliar nutrients suggested that ash increased the availability of nitrogen, and subsequently standing biomass. An Unweighted Pair Group Cluster Analysis on the samples (flows) using quantitative vascular species composition revealed that clusters were correlated with age regardless of the substrate types (pure lava vs. ash), and an indirect ordination on the samples suggested that the sequence of sample scores along axis 1 was perfectly correlated with the age sequence. Although ash deposits increased biomass, they did not affect the sequence of the successional sere. Both pubescent and glabrous varieties of Metrosideros polymorpha (Myrtaceae) dominated upper canopy layers on all flows ≥ 50 yr and ≤ 1400 yr, but the pubescent variety was replaced by the glabrous on the flows ≥ 3000 yr. Lower layers were dominated initially by a matted fern, Dicranopteris linearis, up to 300 yr, and subsequently by tree ferns, Cibotium spp., to 9000 yr. The cover of Cibotium declined slightly after 3000 yr, while other native herb and shrub species increased. A ‘climax’ stage in the conventional sense was apparently not reached on the observed age gradient, because the sere changed continuously in biomass and species; this divergent successional phenomenon may be unique to Hawaii where the flora is naturally impoverished and disharmonic due to its geographic isolation in contrast to more diverse and harmonic floras in continents.     

Regulation of Hippocampal and Behavioral Excitability by Cyclin-Dependent Kinase 5

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine kinase that has been implicated in learning, synaptic plasticity, neurotransmission, and numerous neurological disorders. We previously showed that conditional loss of Cdk5 in adult mice enhanced hippocampal learning and plasticity via modulation of calpain-mediated N-methyl-D-aspartic acid receptor (NMDAR) degradation. In the present study, we characterize the enhanced synaptic plasticity and examine the effects of long-term Cdk5 loss on hippocampal excitability in adult mice. Field excitatory post-synaptic potentials (fEPSPs) from the Schaffer collateral CA1 subregion of the hippocampus (SC/CA1) reveal that loss of Cdk5 altered theta burst topography and enhanced post-tetanic potentiation. Since Cdk5 governs NMDAR NR2B subunit levels, we investigated the effects of long-term Cdk5 knockout on hippocampal neuronal excitability by measuring NMDAR-mediated fEPSP magnitudes and population-spike thresholds. Long-term loss of Cdk5 led to increased Mg²⁺-sensitive potentials and a lower threshold for epileptiform activity and seizures. Biochemical analyses were performed to better understand the role of Cdk5 in seizures. Induced-seizures in wild-type animals led to elevated amounts of p25, the Cdk5-activating cofactor. Long-term, but not acute, loss of Cdk5 led to decreased p25 levels, suggesting that Cdk5/p25 may be activated as a homeostatic mechanism to attenuate epileptiform activity. These findings indicate that Cdk5 regulates synaptic plasticity, controls neuronal and behavioral stimulus-induced excitability and may be a novel pharmacological target for cognitive and anticonvulsant therapies.