Age and growth of Lutjanus kasmira (Forskål) in Hawaiian waters

The growth of Hawaiian taape, Lutjanus kasmira , was studied by examining otoliths and by analysing length-frequency distribution. Annual hyaline and opaque markings were visible in whole mounts of sagittae, which were verified by enumeration of daily increments with a scanning electron microscope (SEM) and through marginal increment analysis. The von Bertalanffy growth curve was fitted to the data, resulting in: where t. l . is total length (cm) and t is age (years). SEM observations revealed that the slowgrowth hyaline zones were composed of daily increments too small (0.4–0.8 μm) to be resolved optically. Thus, age estimates derived by numerically integrating otolith growth rate data obtained with a light microscope showed a negative bias, resulting in overestimation of growth rates. Parameter estimates obtained from three different types of length-frequency analysis were also unstable. This was due, at least in part, to differences in the size composition of fish sampled with different fishing gears and from different depths.
The growth rate registered in Hawaii falls within the reported growth coefficients of lutjanids, whereas it is one of the highest in the Pacific and clearly higher than a deep-water lutjanid species growth in Hawaii. Probably, this high growth rate may have been enhanced by the relative lack of competitors in the depauperate Hawaiian marine fish community.     

Evidence of linkage and association with body fatness and abdominal fat on chromosome 15q26

Objective: In the present study, we undertook a two‐step fine mapping of a 20‐megabase region around a quantitative trait locus previously reported on chromosome 15q26 for abdominal subcutaneous fat (ASF) in an extended sample of 707 subjects from 202 families from the Quebec Family Study. Research Methods and Procedure: First, 19 microsatellites (in addition to the 7 markers initially available on 15q24‐q26; total = 26) were genotyped and tested for linkage with abdominal total fat, abdominal visceral fat, and ASF assessed by computed tomography and with fat mass (FM) using variance component‐based approach on age‐ and sex‐adjusted phenotypes. Second, 16 single nucleotide polymorphisms (SNPs) were genotyped and tested for association using family‐based association tests. Results: After the fine mapping, the peak logarithm of odds ratio (LOD) score (marker D15S1004) increased from 2.79 to 3.26 for ASF and from 3.52 to 4.48 for FM, whereas for abdominal total fat, the peak linkage (marker D15S996) decreased from 2.22 to 1.53. No evidence of linkage was found for abdominal visceral fat. Overall, for genotyped SNPs, three variants located in the putative MCTP2 gene were significantly associated with FM and the three abdominal fat phenotypes (p ≤ 0.05). The major allele and genotype of rs1424695 were associated with higher adiposity values (p < 0.004). The same trend was found for the two other polymorphisms (p < 0.05). None of the other SNPs was associated with adiposity phenotypes. The linkage for FM became non‐significant (LOD = 0.84) after adjustment for the MCTP2 polymorphisms, whereas the one for ASF remained unchanged. Discussion: These results suggest that the MCTP2 gene, located on chromosome 15q26, influences adiposity. Other studies will be needed to investigate the function of the MCTP2 gene and its role in obesity.     

Speciation in Hawaiian angiosperm lineages: cause, consequence, and mode

The biota of Hawaiian Islands is derived entirely from long distance dispersal, often followed by in situ speciation. Species descended from each colonist constitute monophyletic lineages that have diverged to varying degrees under similar spatial and temporal constraints. We partitioned the Hawaiian angiosperm flora into lineages and assessed morphological, ecological, and biogeographic characteristics to examine their relationships to variation in species number (S). Lineages with external bird dispersal (through adhesion) were significantly more species-rich than those with abiotic dispersal, but only weakly more species-rich than lineages with internal bird dispersal (involving fleshy fruits). Pollination mode and growth form (woody vs. herbaceous) had no significant effect on S, in contrast to studies of angiosperm families. S relates positively to the geographic and ecological range size of whole lineages, but negatively to local abundance and mean range sizes of constituent species. Species-rich lineages represent a large proportion of major adaptive shifts, although this appears to be an artifact of having more species. Examination of 52 sister species pairs in numerous lineages provides evidence for allopatric (including peripheral isolates) and parapatric (ecological) modes, with 15 cases of each. Although postspeciational dispersal may obscure these modes in many of the remaining cases, instances of sympatric and hybrid speciation are also discussed. Because speciation is both a consequence and a cause of ecological and biogeographic traits, speciation mode may be integral to relationships between traits. We discuss the role of speciation in shaping the regional species pool.     

Relationship between the percentage of body fat and surrogate indices of fatness in male and female Polish active and sedentary students

Background

Limited data have indicated that body mass index (BMI), waist circumference (WC), waist to hip ratio (WHR) and waist to height ratio (WHtR) of athletes and young adults provide misleading results concerning body fat content. This study was aimed at the evaluation of the relationship between different surrogate indices of fatness (BMI, WC, WHR, WHtR and body adiposity index (BAI)) with the percentage of body fat in Polish students with respect to their sex and physical activity.

Methods

A total of 272 students volunteered to participate in the study. Of these students, 177 physical education students (90 males and 87 females) were accepted as active (physical activity of 7 to 9 hours/week); and 95 students of other specializations (49 males and 46 females) were accepted as sedentary (physical activity of 1.5 hours/week). Weight, height, waist and hip circumferences were measured, and BMI, WHR, WHtR and BAI were calculated. Body fat percentage was assessed using four skinfold measurements.

Results

Classification of fatness according to the BMI and the percentage of body fat have indicated that BMI overestimates fatness in lean subjects (active men and women, sedentary men), but underestimates body fat in obese subjects (sedentary women). In all groups, BMI, WHR, WHtR and BAI were significantly correlated with the percentage of body fat (with the exception of WHR and hip circumference in active and sedentary women, respectively). However, coefficients of determination not exceeding 50% and Lin’s concordance correlation coefficients lower than 0.9 indicated no relationship between measured and calculated body fat.

Conclusion

The findings in the present study support the concept that irrespective of physical activity and sex none of the calculated indices of fatness are useful in the determination of body fat in young adults. Thus, it seems that easily calculated indices may contribute to distorted body image and unhealthy dietary habits observed in many young adults in Western countries, but also in female athletes.     

Influence of volcanic activity on the population genetic structure of Hawaiian Tetragnatha spiders: fragmentation, rapid population growth and the potential for accelerated evolution

Volcanic activity on the island of Hawaii results in a cyclical pattern of habitat destruction and fragmentation by lava, followed by habitat regeneration on newly formed substrates. While this pattern has been hypothesized to promote the diversification of Hawaiian lineages, there have been few attempts to link geological processes to measurable changes in population structure. We investigated the genetic structure of three species of Hawaiian spiders in forests fragmented by a 150-year-old lava flow on Mauna Loa Volcano, island of Hawaii: Tetragnatha quasimodo (forest and lava flow generalist), T. anuenue and T. brevignatha (forest specialists). To estimate fragmentation effects on population subdivision in each species, we examined variation in mitochondrial and nuclear genomes (DNA sequences and allozymes, respectively). Population subdivision was higher for forest specialists than for the generalist in fragments separated by lava. Patterns of mtDNA sequence evolution also revealed that forest specialists have undergone rapid expansion, while the generalist has experienced more gradual population growth. Results confirm that patterns of neutral genetic variation reflect patterns of volcanic activity in some Tetragnatha species. Our study further suggests that population subdivision and expansion can occur across small spatial and temporal scales, which may facilitate the rapid spread of new character states, leading to speciation as hypothesized by H. L. Carson 30 years ago.     

Age and growth of the sandbar shark, Carcharhinus plumbeus, in Hawaiian waters through vertebral analysis

Age and growth estimates were determined for the sandbar shark, Carcharhinus plumbeus, from Oahu, Hawaii in the central Pacific Ocean. Age estimates were obtained through vertebral centra analysis of 187 sharks. We verified our age estimates through marginal increment analysis of centra and oxytetracycline marking methods of at liberty sandbar sharks. Sizes of sampled sharks ranged from 46 to 147 cm pre-caudal length. Four growth models were fitted to length-at-age data; two forms of the von Bertalanffy growth model, the Gompertz growth model, and a logistic growth model. Males and females exhibited statistically significant differences in growth, indicating that females grow slower and attain larger sizes than males. Growth parameter estimates revealed slower growth rates than previously estimated (based on captive specimens) for Hawaiian sandbar sharks. The von Bertalanffy growth model using empirical length-at-birth provided the best biological and statistical fit to the data. This model gave parameter estimates of L _∞ = 138.5 cm PCL and k = 0.12 year⁻¹ for males and L _∞ = 152.8 cm PCL, k = 0.10 year⁻¹ for females. Male and female sandbar sharks mature at approximately 8 and 10 years of age, respectively.     

FTO gene associated fatness in relation to body fat distribution and metabolic traits throughout a broad range of fatness

Background

A common single nucleotide polymorphism (SNP) of FTO (rs9939609, T/A) is associated with total body fatness. We investigated the association of this SNP with abdominal and peripheral fatness and obesity-related metabolic traits in middle-aged men through a broad range of fatness present already in adolescence.

Methodology/Principal Findings

Obese young Danish men (n = 753, BMI≥31.0 kg/m²) and a randomly selected group (n = 879) from the same population were examined in three surveys (mean age 35, 46 and 49 years, respectively). The traits included anthropometrics, body composition, oral glucose tolerance test, blood lipids, blood pressure, fibrinogen and aspartate aminotransferase. Logistic regression analysis was used to assess the age-adjusted association between the phenotypes and the odds ratios for the FTO rs9939609 (TT and TA genotype versus the AA genotype), for anthropometrics and body composition estimated per unit z-score. BMI was strongly associated with the AA genotype in all three surveys: OR = 1.17, p = 1.1*10⁻⁶, OR = 1.20, p = 1.7*10⁻⁷, OR = 1.17, p = 3.4*10⁻³, respectively. Fat body mass index was also associated with the AA genotype (OR = 1.21, p = 4.6*10⁻⁷ and OR = 1.21, p = 1.0*10⁻³). Increased abdominal fatness was associated with the AA genotype when measured as waist circumference (OR = 1.21, p = 2.2*10⁻⁶ and OR = 1.19, p = 5.9*10⁻³), sagittal abdominal diameter (OR = 1.17, p = 1.3*10⁻⁴ and OR = 1.18, p = 0.011) and intra-abdominal adipose tissue (OR = 1.21, p = 0.005). Increased peripheral fatness measured as hip circumference (OR = 1.19, p = 1.3*10⁻⁵ and OR = 1.18, p = 0.004) and lower body fat mass (OR = 1.26, p = 0.002) was associated with the AA genotype. The AA genotype was significantly associated with decreased Stumvoll insulin sensitivity index (OR = 0.93, p = 0.02) and with decreased non-fasting plasma HDL-cholesterol (OR = 0.57, p = 0.037), but not with any other of the metabolic traits. However, all significant results for both body fat distribution and metabolic traits were explained by a mediating effect of total fat mass.

Conclusion

The association of the examined FTO SNP to general fatness throughout the range of fatness was confirmed, and this association explains the relation between the SNP and body fat distribution and decreased insulin sensitivity and HDL-cholesterol. The SNP was not significantly associated with other metabolic traits suggesting that they are not derived from the general accumulation of body fat.     

Body fat distribution of children and adolescents in Abeokuta,Southwest Nigeria

Excessive central fat in children and adolescents is a risk factor for cardiovascular and metabolic disorders. This study aimed to compare the body fat distribution patterns of children and adolescents in Abeokuta, Nigeria with international reference standards. Five hundred seventy children aged 5 to 19 years were selected from seven schools using multistage random sampling. Weight, height, triceps and subscapular skinfold thickness (TSF, SSF), and circumference at the waist and hips (WC, HC) were measured. Body mass index (BMI), subscapular:triceps skinfold ratio (STR), waist:hip circumference ratio (WHR), and waist: height ratio (WHtR) were derived. Females had higher mean BMI, TSF, SSF, WC, HC, WHR, and WHtR, while males had significantly higher STR. The mean BMI, WC, TSF, and SSF values were lower for our subjects than for African‐American subjects at all ages. On the other hand, in both sexes, STR was higher among Nigerian than African‐American subjects up to 12 years old. Thereafter the values were similar. The mean WC was similar to those reported for African‐American males up to 8 years, and females up to 7 years of age; thereafter, African‐American had higher values. The prevalence of central obesity using WC and WHtR measures was 4.4% and 5.8%, respectively. There is a need to validate each index against serum lipid profiles and other cardiovascular and metabolic risk factors. Am J Phys Anthropol 150:647–654, 2013. © 2013 Wiley Periodicals, Inc.     

Beyond thriftiness: independent and interactive effects of genetic and dietary factors on variations in fat deposition and distribution across populations

The thrifty genotype hypothesis initiated speculation that feast and famine cycling throughout history may have led to group-specific alterations of the human genome, thereby augmenting the capacity for excessive fat mass accrual when immersed in the modern-day obesogenic environment. Contemporary work, however, suggests alternative mechanisms influencing fuel utilization and subsequent tissue partitioning to be more relevant in the etiology of population-based variation in adipose storage. The objective of this study was to evaluate the independent and interactive contribution of ancestral admixture as a proxy for population-based genetic variation and diet on adipose tissue deposition and distribution in peripubertal children and to identify differences in racial/ethnic and sex groups. Two-hundred seventy-eight children (53% male) aged 7-12 years, categorized by parental self-report as African- (n = 91), European- (n = 110), or Hispanic American (n = 77), participated. Ancestral genetic admixture was estimated using 140 ancestry informative markers. Body composition was evaluated by dual-energy X-ray absorptiometry; energy expenditure by indirect calorimetry and accelerometry; and diet by 24-h-recall. Admixture independently contributed to all adiposity parameters; i.e., estimates of European and Amerindian ancestries were positively associated with all adiposity parameters, whereas African genetic admixture was inversely associated with adiposity. In boys, energy intake was associated with adiposity, irrespective of macronutrient profile, whereas in girls, the relationship was mediated by carbohydrate. We also observed moderating effects of energy balance/fuel utilization of the interaction between ancestral genetic admixture and diet. Interactive effects of genetic and non-genetic factors alter metabolic pathways and underlie some of the present population-based differences in fat storage.     

Isolation and characterization of polymorphic microsatellite loci in the Hawaiian flycatcher,the elepaio (Chasiempis sandwichensis)

Thirteen polymorphic microsatellite loci were isolated and characterized from two clades of an endemic Hawaiian flycatcher, the elepaio (Chasiempis sandwichensis). Seven dinucleotide repeats and one trinucleotide repeat were cloned from Kauai elepaio; five dinucleotide repeats were cloned from Oahu elepaio. Polymorphism was assessed in a sample of Oahu elepaio (n = 22) revealing two to 16 alleles per locus. Observed heterozygosity ranged from 0.14 to 0.91. However, linkage analysis exposed highly significant linkage disequilibrium between two of the most polymorphic loci. Twelve loci are therefore expected to be useful for investigations of population structure.     

Growth, biomass allocation and photosynthesis of invasive and native Hawaiian rainforest species

Growth, biomass allocation, and photosynthetic characteristics of seedlings of five invasive non-indigenous and four native species grown under different light regimes were studied to help explain the success of invasive species in Hawaiian rainforests. Plants were grown under three greenhouse light levels representative of those found in the center and edge of gaps and in the understory of Hawaiian rainforests, and under an additional treatment with unaltered shade. Relative growth rates (RGRs) of invasive species grown in sun and partial shade were significantly higher than those for native species, averaging 0.25 and 0.17 g g⁻¹ week⁻¹, respectively, while native species averaged only 0.09 and 0.06 g g⁻¹ week⁻¹, respectively. The RGR of invasive species under the shade treatment was 40% higher than that of native species. Leaf area ratios (LARs) of sun and partial-shade-grown invasive and native species were similar but the LAR of invasive species in the shade was, on average, 20% higher than that of native species. There were no differences between invasive and native species in biomass allocation to shoots and roots, or in leaf mass per area across light environments. Light-saturated photosynthetic rates (Pmax) were higher for invasive species than for native species in all light treatments. Pmax of invasive species grown in the sun treatment, for example, ranged from 5.5 to 11.9 μmol m⁻² s⁻¹ as compared with 3.0−4.5 μmol m⁻² s⁻¹ for native species grown under similar light conditions. The slope of the linear relationship between Pmax and dark respiration was steeper for invasive than for native species, indicating that invasive species assimilate more CO₂ at a lower respiratory cost than native species. These results suggest that the invasive species may have higher growth rates than the native species as a consequence of higher photosynthetic capacities under sun and partial shade, lower dark respiration under all light treatments, and higher LARs when growing under shade conditions. Overall, invasive species appear to be better suited than native species to capturing and utilizing light resources, particularly in high-light environments such as those characterized by relatively high levels of disturbance. Received: 30 December 1997 / Accepted: 1 September 1998     

Association of eating frequency with body fatness in pre- and postmenopausal women

Objective: To examine associations between eating frequency (EF) and body fatness in pre‐ and postmenopausal women, after excluding potential low‐energy reporters. Research Methods and Procedures: In this cross‐sectional study of 220 free‐living women, 64 pre‐ and 50 postmenopausal non‐low‐energy‐reporting women were further analyzed (age, 24 to 74 years; BMI, 18.5 to 38.6 kg/m²). Anthropometric and body composition measurements (DXA) were performed in all study participants. EF, energy, and macronutrient intake were assessed by 3‐day food record. Physical activity level and energy expenditure were assessed by self‐reported questionnaire. Results: No association between EF and adiposity indices was detected in premenopausal women. In contrast, EF was positively correlated with percentage body fat in postmenopausal women (r = 0.30, p = 0.03). EF was positively correlated with total energy intake in both groups and with total energy expenditure in premenopausal women only (r = 0.34, p = 0.02). Multivariate analysis revealed that, in postmenopausal women, EF was a significant predictor of body fatness (standardized β = 0.41, p = 0.01). Discussion: Frequent eating was not found to be related to adiposity in premenopausal women, but it was associated with increased body fat in postmenopausal women. Possible explanations could be that the frequent eating is not associated with a physically active lifestyle in postmenopausal women or that frequent eating predisposes women after menopause to a higher energy intake by increasing food stimuli and rendering it more difficult for them to control energy balance.     

Scoring system for estimating age in the foot skeleton

This study assesses chronological age of immature individuals from the degree of ossification evident in the foot skeleton. We considered all tarsal and ray bones in various combinations to determine the most sensitive indicators of chronological age. Skeletal maturity was rated according to a subjective but simple scoring system applied to radiographs of normal feet of children of known chronological age. Scales for assessing the primary center of ossification, secondary center of ossification, and state of fusion are defined. In general, as expected, females show earlier onset of skeletal maturity than males; in particular, females in our sample are skeletally mature in most elements beginning 48 months prior to the earliest incidence of skeletal maturity in males for the same bones. Females in our sample show a marked tendency toward skeletal maturity of all elements by 150 months of age, while males do not show the same tendency until approximately 200 months of age. In general within each sex, consecutive states of fusion show broad overlap in range of chronological age within each bone. Combining scores from several different bones enables a reasonable estimate of potential age in a test application of the model.     

Relationships of resting energy expenditure with body fat distribution and abdominal fatness in Japanese population

Body fat distribution and abdominal fatness are indicators of risks for coronary heart disease. However, the relationships between resting energy expenditure (REE) and the body fat distribution or the abdominal fatness are unclear. We examined the relationships of REE with whole-body fat distribution (waist, hip and waist-to-hip ratio: WHR) and abdominal fatness (intra-abdominal fat: IF and subcutaneous fat: SF) after adjustment for body composition. 451 men and 471 women were subdivided into two groups, 40-59 years: middle-aged group and 60-79 years: elderly group. REE was measured by an indirect calorimetry system. Percentage of fat mass (%FM), fat mass (FM) and fat-free mass (FFM) were assessed by a dual-energy x-ray absorptiometry method. The IF area (IFA) and SF area (SFA) at the level of the umbilicus were measured using computed tomography. Circumference of waist and hip were measured in a standing position. The WHR, waist circumference and SFA did not significantly (p>0.05) associate with the REE after adjusting for FM, FFM and age in any of the groups. The adjusted REE was significantly and inversely correlated with hip (r=-0.159, p<0.05) and IFA (r=-0.131, p<0.05) in the elderly men. These results suggest that lower REE may contribute to greater hip and IFA rather than WHR and waist in elderly men.     

Physical maturation and age estimates of yellow baboons,Papio cynocephalus,in Amboseli National Park,Kenya

In a longitudinal study of individually identified wild baboons in Amboseli National Park, Kenya, we collected data on physical development and reproductive maturation. Confirming and extending our earlier results, we demonstrated that the ratio of ages at which developmental milestones occur in the field as compared to those under extensive provisioning or in captivity were approximately 5:3. The age range for some developmental milestones was quite narrow and discrete, while for others there was considerable between-individual variability and more gradual changes. For infants, only the change from pink to gray of the paracallosal skin occurred within a brief age span. For older animals two important developmental events are readily identified and occur within a fairly narrow age range: Rapid enlargement of testes at 5 to 6 years for males and onset of menarche at 4 to 5 ½ years for females. In the present report, we considered some consequences of accelerated or delayed maturation. We further explored the need to employ different age-class criteria for different research problems.     

Erosion and landscape development affect plant nutrient status in the Hawaiian Islands

We quantified variation in plant nutrient concentrations and provenance along catenas in landscapes of three different ages (0.15, 1.4, and 4.1 ma) in the Hawaiian Islands. Strontium (Sr) isotopes demonstrate that erosion provides a renewed source of rock-derived nutrients to slopes in landscapes of all ages, in some cases reversing a million years of ecosystem development in a distance of 100 m. However the effects of this input vary with landscape age. Plants on uneroded surfaces in a 0.15-ma landscape derive ~20% of their Sr from local bedrock (foliar ⁸⁷Sr/⁸⁶Sr~0.7085), while on adjacent slopes this increases to ~80% (foliar ⁸⁷Sr/⁸⁶Sr~0.7045). Despite this shift in provenance, foliar N and P do not vary systematically with slope position. Conversely, eroded slopes in a 4.1-ma landscape show smaller increases in rock-derived cations relative to stable uplands (foliar ⁸⁷Sr/⁸⁶Sr~0.7075 vs 0.7090), but have >50% higher foliar N and P. These results demonstrate both that erosion can greatly increase nutrient availability in older landscapes, and that the ecological effects of erosion vary with landscape age. In addition, there can be as much biogeochemical variation on fine spatial scales in eroding landscapes as there is across millions of years of ecosystem development on stable surfaces.     

Intraspecific variation in seedling drought tolerance and associated traits in a critically endangered,endemic Hawaiian shrub

ABSTRACT

Background

Climates are changing at a rate that exceeds the adaptive capacity of species, especially endangered species. Genetic variation and phenotypic plasticity are important for population persistence, yet few studies have linked traits to seedling performance under drought in endangered species.     

Nutrient and mineralogical control on dissolved organic C, N and P fluxes and stoichiometry in Hawaiian soils

We measured DOM fluxes from the O horizon of Hawaiiansoils that varied in nutrient availability and mineralcontent to examine what regulates the flux ofdissolved organic carbon (DOC), nitrogen (DON) andphosphorus (DOP) from the surface layer of tropicalsoils. We examined DOM fluxes in a laboratory study from N, P and N+Pfertilized and unfertilized sites on soils that rangedin age from 300 to 4 million years old. The fluxesof DOC and DON were generally related to the % Cand % N content of the soils across the sites. Ingeneral, CO₂ and DOC fluxes were not correlatedsuggesting that physical desorption, dissolution andsorption reactions primarily control DOM release fromthese surface horizons. The one exception to thispattern was at the oldest site where there was asignificant relationship between DOC and CO₂flux. The oldest site also contained the lowestmineral and allophane content of the three sites andthe DOC-respiration correlation indicates arelationship between microbial activity and DOC fluxat this site. N Fertilization increased DON fluxes by50% and decreased DOC:DON ratios in the youngest,most N poor site. In the older, more N rich sites, Nfertilization neither increased DON fluxes nordecreased DOM C:N ratios. Similarly, short termchanges in N availability in laboratory-based soil Nand P fertilization experiments did not affect the DOMC:N ratios of leachate. DOM C:N ratios were similar tosoil organic matter C:N ratios, and changes in DOM C:Nratios with fertilization appeared to have beenmediated through long term effects on SOM C:N ratiosrather than through changes in microbial demand for Cand N. There was no relationship between DON andinorganic N flux during these incubations suggestingthat the organic and inorganic components of N fluxfrom soils are regulated by different factors and thatDON fluxes are not coupled to immediate microbialdemand for N. In contrast to the behavior of DON, thenet flux of dissolved organic phosphorus (DOP) and DOMC:P ratios responded to both long-term P fertilizationand natural variation in reactive P availability. There was lower DOP flux and higher DOM C:P ratiosfrom soils characterized by low P availability andhigh DOP flux and narrow DOM C:P ratios in sites withhigh P availability. DOP fluxes were also closelycorrelated with dissolved inorganic P fluxes. PFertilization increased DOP fluxes by 73% in theyoungest site, 31% in the P rich intermediate agesite and 444% in the old, P poor site indicating thatDOP fluxes closely track P availability in soils.     

Nitrogen Fixation in Bryophytes, Lichens, and Decaying Wood along a Soil-age Gradient in Hawaiian Montane Rain Forest

We determined rates of acetylene reduction and estimated total nitrogen fixation associated with bryophytes, lichens, and decaying wood in Hawaiian montane rain forest sites with underlying substrate ranging in age from 300 to 4.1 million years. Potential N fixation ranged from ca 0.2 kg/ha annually in the 300‐year‐old site to ca 1 kg/ha annually in the 150,000‐year‐old site. Rates of acetylene reduction were surprisingly uniform along the soil‐age gradient, except for high rates in symbiotic/associative fixers at the 150,000‐year‐old site and in heterotrophic fixers at the 2100‐year‐old site. Low fixation at the youngest site, where plant production is known to be N‐limited, suggests that demand for N alone does not govern N fixation. Total N fixation was highest in sites with low N:P ratios in leaves and stem wood, perhaps because epiphytic bryophytes and lichens depend on canopy leachate for mineral nutrients and because heterotrophic fixation is partly controlled by nutrient supply in the decomposing substrate; however, differences in substrate cover, rather than in fixation rates, had the largest effect on the total N input from fixation at these sites.