Differences In Physiological Performance Research Articles

Differences in Physiological Performance and Gut Microbiota between Deep-Sea and Coastal Aquaculture of Thachinotus Ovatus: A Metagenomic Approach.

Aquaculture has become the fastest growing sector in global agriculture. The environmental degradation, diseases, and high density of mariculture has made for an inevitable shift in mariculture production from coastal to deep-sea areas. The influence that traditional coastal and emerging deep-sea farming environments exert on aquatic growth, immunity and gut microbial flora is unclear. To address this question, we compared the growth performance, physiological indicators and intestinal microbiological differences of deep-sea and coastal aquaculture in the Guangxi Beibu Gulf of China. The results showed that the growth performance and the complement of C3 and C4 (C3, C4), superoxide dismutase (SOD), and lysozyme (LYS), these physiological and biochemical indicators in the liver, kidney, and muscle of Trachinotus ovatus (T. ovatus), showed significant differences under different rearing conditions. Metagenome sequencing analysis showed Ascomycota, Pseudomonadota, and Bacillota were the three dominant phyla, accounting for 52.98/53.32 (coastal/deep sea), 24.30/22.13, and 10.39/11.82%, respectively. Aligned against the CARD database, a total of 23/2 (coastal/deep-sea) antibiotic resistance genes were screened and grouped into 4/2 genotypes. It indicated that compared with deep-sea fish, higher biological oxygen levels (3.10 times), inorganic nitrogen (110.00 times) and labile phosphate levels (29.00 times) in coastal waters might contributed to the existence of eutrophication with antibiotic resistance. The results of the study can provide complementary data on the study of the difference between deep-sea farming and traditional coastal farming, serving as a reference to future in-depth work on the transformation of fisheries development and scientific standardization of deep-sea farming.

Almond Tree Adaptation to Water Stress: Differences in Physiological Performance and Yield Responses among Four Cultivar Grown in Mediterranean Environment.

Maximizing water use efficiency, yield, and plant survival under drought is a relevant research issue for almond-tree-growing areas worldwide. The intraspecific diversity of this species may constitute a valuable resource to address the resilience and productivity challenges that climate change poses to crop sustainability. A comparative evaluation of physiological and productive performance of four almond varieties: 'Arrubia', 'Cossu', 'Texas', and 'Tuono', field-grown in Sardinia, Italy, was performed. A great variability in the plasticity to cope with soil water scarcity and a diverse capacity to adapt to drought and heat stresses during fruit development were highlighted. The two Sardinian varieties, Arrubia and Cossu, showed differences in water stress tolerance, photosynthetic and photochemical activity, and crop yield. 'Arrubia' and 'Texas' showed greater physiological acclimation to water stress while maintaining higher yields, as compared to the self-fertile 'Tuono'. The important role of crop load and specific anatomical traits affecting leaf hydraulic conductance and leaf gas exchanges efficiency (i.e., dominant shoot type, leaf size and roughness) was evidenced. The study highlights the importance of characterizing the relationships among almond cultivar traits that affect plant performance under drought in order to better assist planting choices and orchard irrigation management for given environmental contexts.

Flying on empty: reduced mitochondrial function and flight capacity in food-deprived monarch butterflies.

Mitochondrial function is fundamental to organismal performance, health and fitness - especially during energetically challenging events, such as migration. With this investigation, we evaluated mitochondrial sensitivity to ecologically relevant stressors. We focused on an iconic migrant, the North American monarch butterfly (Danaus plexippus), and examined the effects of two stressors: 7days of food deprivation and infection by the protozoan parasite Ophryocystis elektroscirrha (known to reduce survival and flight performance). We measured whole-animal resting metabolic rate (RMR) and peak flight metabolic rate, and mitochondrial respiration of isolated mitochondria from the flight muscles. Food deprivation reduced mass-independent RMR and peak flight metabolic rate, whereas infection did not. Fed monarchs used mainly lipids in flight (respiratory quotient 0.73), but the respiratory quotient dropped in food-deprived individuals, possibly indicating switching to alternative energy sources, such as ketone bodies. Food deprivation decreased mitochondrial maximum oxygen consumption but not basal respiration, resulting in lower respiratory control ratio (RCR). Furthermore, food deprivation decreased mitochondrial complex III activity, but increased complex IV activity. Infection did not result in any changes in these mitochondrial variables. Mitochondrial maximum respiration rate correlated positively with mass-independent RMR and flight metabolic rate, suggesting a link between mitochondria and whole-animal performance. In conclusion, low food availability negatively affects mitochondrial function and flight performance, with potential implications for migration, fitness and population dynamics. Although previous studies have reported poor flight performance in infected monarchs, we found no differences in physiological performance, suggesting that reduced flight capacity may be due to structural differences or low energy stores.

Assessing Microbial Metabolic and Biological Diversity to Inform Natural Product Library Assembly.

The pressing need for novel chemical matter to support bioactive compound discovery has led natural product researchers to explore a wide range of source organisms and environments. One of the implicit guiding principles behind those efforts is the notion that sampling different environments is critical to accessing unique natural products. This idea was tested by comparing fungi from disparate biomes: aquatic sediments from Lake Michigan (USA) and terrestrial samples taken from the surrounding soils. Matched sets of Penicillium brevicompactum, Penicillium expansum, and Penicillium oxalicum from the two source environments were compared, revealing modest differences in physiological performance and chemical output. Analysis of LC-MS/MS-derived molecular feature data showed no source-dependent differences in chemical richness. High levels of scaffold homogeneity were also observed with 78-83% of scaffolds shared among the terrestrial and aquatic Penicillium spp. isolates. A comparison of the culturable fungi from the two biomes indicated that certain genera were more strongly associated with aquatic sediments (e.g., Trichoderma, Pseudeurotium, Cladosporium, and Preussia) versus the surrounding terrestrial environment (e.g., Fusarium, Pseudogymnoascus, Humicola, and Acremonium). Taken together, these results suggest that focusing efforts on sampling the microbial resources that are unique to an environment may have a more pronounced effect on enhancing the sought-after natural product diversity needed for chemical discovery and screening collections.

Photosynthetic activity of oil palm (Elaeis guineensis) and interspecific hybrid genotypes (Elaeis oleifera × Elaeis guineensis), and response of hybrids to water deficit

Climate change raises significant challenges for oil palm performance, as its physiology can be differentially affected by water deficit depending on genotype. Therefore, the aim of the present study was to assess the leaf gas exchange and photochemical activity in oil palm seedlings of two genotypes of Elaeis guineensis (G) and four interspecific hybrids of E. oleifera × E. guineensis (OG) and evaluate the effect of water deficit for 15 days on water status and photosynthetic traits in a subset of two OG genotypes. Significant differences in gas exchange and photochemical activity variables occurred among well watered seedlings of G and OG genotypes, showing a wide range of variation in photosynthetic rate, stomatal conductance, water use efficiency and electron transport rate. In the two selected OG genotypes, water deficit caused a reduction in leaf relative water content, photosynthetic rate, stomatal conductance, transpiration rate and water use efficiency of 20, 99, 60, 52 and 98 %, respectively; maximum rate of RuBisCO carboxylation, maximum electron transport rate, and triose phosphate utilization rate were markedly reduced (70 – 80 %) by water deficit. The response of gas exchange and biochemical related variables to water deficit seemed to be bimodal, with stomatal closure being the first response and reduction of biochemical photosynthetic capacity the second one. There were differences in physiological performance among genotypes in well watered plants, and both OG genotypes were sensitive to WD but showed different responses, suggesting possible genotypic differences in tolerance.

Waterlogging Causes Early Modification in the Physiological Performance, Carotenoids, Chlorophylls, Proline, and Soluble Sugars of Cucumber Plants.

Waterlogging occurs because of poor soil drainage and/or excessive rainfall and is a serious abiotic stress affecting plant growth because of declining oxygen supplied to submerged tissues. Although cucumber (Cucumis sativus L.) is sensitive to waterlogging, its ability to generate adventitious roots facilitates gas diffusion and increases plant survival when oxygen concentrations are low. To understand the physiological responses to waterlogging, a 10-day waterlogging experiment was conducted. The objective of this study was to measure the photosynthetic and key metabolites of cucumber plants under waterlogging conditions for 10 days. Plants were also harvested at the end of 10 days and analyzed for plant height (ht), leaf number and area, fresh mass (FM), dry mass (DM), chlorophyll (Chl), carotenoid (CAR), proline, and soluble sugars. Results indicated that cucumber plants subjected to the 10-day waterlogging stress conditions were stunted, had fewer leaves, and decreased leaf area, FM, and DM. There were differences in physiological performance, Chl, CAR, proline, and soluble sugars. Overall, waterlogging stress decreased net photosynthesis (A), having a negative effect on biomass accumulation. However, these decreases were also dependent on other factors, such as plant size, morphology, and water use efficiency (WUE) that played a role in the overall metabolism of the plant.

Comparison of thermal tolerance and standard metabolic rate of two Great Lakes invasive fish species

Abstract Round goby (Neogobius melanostomus) and western tubenose goby (Proterorhinus semilunaris) invaded the Laurentian Great Lakes at approximately the same time and area yet have shown substantial differences in their post-invasion success with more rapid establishment and development of much larger abundances of round goby populations throughout the invaded habitat. In this study, we compared differences in physiological performance (thermal tolerance and standard metabolic rate) between round and tubenose goby collected from the Huron-Erie corridor. Tubenose goby were observed to have lower thermal tolerance but exhibited similar standard metabolic rate across environmental temperatures compared to round goby. At temperatures exceeding 31 °C, tubenose goby demonstrated significantly higher mortalities and shorter times to death relative to round goby. The observed differences in thermal tolerance were consistent with differences in the native geographic ranges observed for each species at their southern ranges. The observed differences in physiological performance combined with species differences in other life history traits such body size, reproduction, feeding ecology and habitat affiliation may also explain differences in the invasiveness experienced by these two Great Lakes invasive fish including a greater ability of round gobies to occupy extreme habitats with large water temperature fluctuations.

Heritability of energy intake and allocation and their correlated responses to selection on growth traits in cultured juvenile and adult red abalone Haliotis rufescens

Increasing abalone growth rates and their physiological efficiency in the use of energy through selective breeding could improve abalone production. High potential responses to selection for growth traits have been estimated in several abalone species; however, the genetic bases underlying individual differences in physiological performance are unknown. The aims of this study were to estimate the heritable variation of physiological traits associated with energy intake and allocation for the red abalone Haliotis rufescens; and the potential correlated responses to selection between growth and physiological traits at three developmental stages. Growth traits (shell length and width, and total mass) and physiological traits [energy intake, standard metabolic rate (SMR), and energy losses by ammonia excretion and feces] were measured in individuals belonging to 60 full-sib families in 2-years old juveniles, 3-y old young adults, and 4-y old near-harvest adult (n = 500–380 individuals/age; total n = 1300). Food intake showed significant h2 in juveniles and young adults (0.37 and 0.14, respectively); but near zero h2 in near-harvest adults. Variation in energy required for SMR showed low but significant h2 (0.13) in young and near-harvest adults. Variation in energy lost through ammonia excretion showed significant h2 in juveniles (0.33) and in near-harvest adults (0.14). Heritability for variation in the energy losses through feces was not significant. Heritabilities for growth traits were all moderate to high and significant for young and pre-harvest adults, but were not significant for juveniles. At the young adult stage, food intake was negatively and highly genetically correlated with each of the growth traits (−0.70 to −0.85); and at the near-harvest adult stage both SMR and ammonia excretion showed high-negative genetic correlations with each growth trait (−0.88 to −1.00). Thus, estimated correlated response to selection indicated that if selection was exerted for higher growth (choosing 5% best individuals), we would be indirectly selecting for abalones with lower food intake (correlated responses of −11 to −15%); or lower metabolic demands of (−14 to −24%), if the selection was applied to young or near-harvest adults, respectively. In turn, shell length could be enhanced up to 18% per generation. These results suggest that higher growth in red abalone is genetically associated with a more efficient use of food and a lower metabolic demand. The possibility to reduce food intake or metabolic demands by selecting for faster growing abalones would be a very positive development for the sustainability of this culture.

Does habitat fragmentation promote climate‐resilient phenotypes?

Understanding how individual differences in physiological performance modify behavioral responses to environmental variability and its fitness consequences is key to predicting the vulnerability of species and populations to environmental change. For many species, summit metabolic rate (MSUM; the upper limit to heat production) and basal metabolic rate (BMR; the lower limit related to energy acquisition and processing) often constrain aspects of physiological performance and behavioral activity. We examined the relationship between metabolic phenotypes, foraging behavior, and survival in overwintering black‐capped chickadees Poecile atricapillus inhabiting contiguous and fragmented forested landscapes. We found that birds with lower summit metabolic rates were generally more sensitive to winter weather and increased their use of supplemental feeding stations as ambient temperatures decreased. In highly fragmented forests, this relationship may have incurred strong survival consequences, as birds with lower summit metabolic rates were less likely to survive the winter season. Additionally, we found that chickadee populations persisting in fragmented landscapes were characterized by slightly higher thermogenic capacity (MSUM) and lower maintenance metabolic costs (BMR). We suggest that habitat loss and fragmentation present unique selection pressures that alter the relationships between environmental variability, behavior and physiology, and result in context‐specific fitness consequences.

Ecotypes of Gracilaria caudata (Gracilariales, Rhodophyta): physiological and morphological approaches considering life history phases

On the Brazilian coast, the red alga Gracilaria caudata J. Agardh is exploited for agar production. In view of its economic importance for potential mariculture, this work aimed to elucidate and characterize ecotypes along an extended Brazilian coastline by evaluating the effects of irradiance (70 and 150 μmol photons m−2 s−1) on the number of differentiated branches, growth rates (GRs), photosynthesis parameters, and pigment content of female gametophytes and tetrasporophytes from three distinct geographical areas: Ceara State (CE), Bahia State (BA), and Sao Paulo State (SP). Compared to low irradiance, high irradiance promoted higher GRs and a greater number of differentiated branches, as well as maximum electron transport rate (ETRmax) and maximum photosynthesis (P max) in both phases. However, irrespective of population or irradiance, tetrasporophytes had higher ETRmax (3.30 μmol e− m−2 s−1) than gametophytes (2.54 μmol e− m−2 s−1), corroborating the hypothesis that tetrasporophytes have better physiological performance than gametophytes, implicating correspondingly better adaptive abilities. Under high irradiance, regardless of the period of cultivation (14 or 28 days), strains from CE presented the highest GR (15% day−1) when compared to strains from SP (14% day−1) and BA (13% day−1). CE strains also had the highest number of differentiated branches and P max. Based on these results, we suggest that CE strains are the best candidates for future experimental mariculture tests. Importantly, overall differences in physiological performance among the strains from different populations give evidence of intraspecific diversity, thus supporting the hypothesis of ecotypic differentiation and allowing this study to define different G. caudata ecotypes.

Seasonal changes in tissue-water relations for eight species of ferns during historic drought in California.

California experienced severe drought between 2012 and 2016. During this period, we compared seasonal changes in tissue-water relations among eight fern species in the Santa Monica Mountains of southern California to elucidate differential mechanisms of drought survival and physiological performance during extreme water deficits. We monitored seasonal changes in water potential (Ψmd) and dark-adapted chlorophyll fluorescence (Fv/Fm), assessed tissue-water relations including osmotic potential at saturation and the turgor loss point (Ψπ, sat and Ψπ, tlp), and measured, for two evergreen species, xylem-specific and leaf-specific hydraulic conductivity (Ks and Kl) and vulnerability of stem xylem to water stress-induced embolism (water potential at 50% loss hydraulic conductivity, Ψ50). Species grew in either riparian or chaparral understory. The five chaparral species had a wider range of seasonal water potentials, root depths, and frond phenological traits, including one evergreen, two summer-deciduous, and two desiccation-tolerant (resurrection) species. Evergreen species were especially diverse, with an evergreen riparian species maintaining seasonal water potentials above -1.3 MPa, while an evergreen chaparral species had seasonal water potentials below -8 MPa. In those two species the Ψ50 values were -2.5 MPa and -4.3 MPa, respectively. Observed differences in physiological performance among eight fern species reflected niche partitioning in water utilization and habitat preference associated with distinct phenological traits. We predict differential survival among fern species as future drought events in California intensify, with desiccation-tolerant resurrection ferns being the most resistant.

Loss of thermal refugia near equatorial range limits.

This study examines the importance of thermal refugia along the majority of the geographical range of a key intertidal species (Patella vulgata Linnaeus, 1758) on the Atlantic coast of Europe. We asked whether differences between sun-exposed and shaded microhabitats were responsible for differences in physiological stress and ecological performance and examined the availability of refugia near equatorial range limits. Thermal differences between sun-exposed and shaded microhabitats are consistently associated with differences in physiological performance, and the frequency of occurrence of high temperatures is most probably limiting the maximum population densities supported at any given place. Topographical complexity provides thermal refugia throughout most of the distribution range, although towards the equatorial edges the magnitude of the amelioration provided by shaded microhabitats is largely reduced. Importantly, the limiting effects of temperature, rather than being related to latitude, seem to be tightly associated with microsite variability, which therefore is likely to have profound effects on the way local populations (and consequently species) respond to climatic changes.

Electromagnetically braked versus mechanically braked cycle ergometers: Effects of aerobic power and total physical workloads

OBJECTIVE: To determine the differences in physiological performance at constant submaximal load and aerobic power levels of electromagnetically and mechanically braked cycle ergometers. METHOD: Nineteen trained male athletes who specialize in cycling and triathlons participate in this study (age, 20.21 ± 3.50 years; body mass, 73.36 ± 13.19 kg; height, 178.73 ± 8.54 cm). A randomized cross-over study design was used to compare a mechanically braked Monark cycle ergometer (MCE) and an electromagnetically braked Lode Excalibur cycle ergometer (ECE). After the V O2max test, total physical work capacity and work efficiency (GE) were analysed during 60% of V O2max constant loading submaximal tests with MCE and ECE. A paired sample t-test was used to compare V O2max and constant loading submaximal test data of the ergometers. RESULTS: Applying the ECE system resulted in a significantly higher V O2max value (9.3%; p = 0.004), similar respiratory exchange ratio value (1.8% lower; p = 0.290), similar power output at exhaustion point (1% higher; p = 0.620), significantly higher total energy expenditure at exhaustion point and mean cadence (Cadmean) value (12%; p = 0.025, 9.6%; p = 0.000) respectively. In the constant loading submaximal tests, however, significant differences were found in mean power output (p = 0.013), Cadmean (p = 0.000), and GE (p = 0.000) values. CONCLUSION: Since the ECE system was associated with a higher V O2max and allowed test performance at the expected V O2 consumption at constant submaximal loads, we recommend using the ECE for determination of aerobic power and total physical workloads.

Developing controlled environment screening for high-temperature tolerance in cotton that accurately reflects performance in the field.

In this study we investigated the heat tolerance of high yielding Australian cotton (Gossypium hirsutum L.) cultivars using a multi-level approach encompassing physiological assays and measurements of performance. Two cultivars with known field performance were evaluated for heat tolerance under optimal (32°C) and high (42°C) temperatures in a growth cabinet with a cell membrane integrity assay. Impacts of temperature on growth were evaluated with leaf level measurements of gas exchange and chlorophyll fluorescence. To extend the multi-level approach, the expression of a Rubisco activase regulating gene (GhRCAα2) was also determined. Consistent with previously determined differences in the field, cultivar Sicot 53 outperformed Sicala 45 for the cell membrane integrity assay; this finding was reflective of cultivar differences in gas exchange and chlorophyll fluorescence. Cultivar differences were also consistent for expression of GhRCAα2, which may also help explain differences in physiological performance, particularly photosynthesis. This study reaffirmed that physiological and molecular assays were sufficiently sensitive to resolve genotypic differences in heat tolerance and that these differences translate to physiological performance. By comparing performance under high temperatures in the growth cabinet and field, this approach validates the use of rapid screening tools in conjunction with a multi-level approach for heat tolerance detection.

Structural and hydraulic correlates of heterophylly in Ginkgo biloba

This study investigates the functional significance of heterophylly in Ginkgo biloba, where leaves borne on short shoots are ontogenetically distinct from those on long shoots. Short shoots are compact, with minimal internodal elongation; their leaves are supplied with water through mature branches. Long shoots extend the canopy and have significant internodal elongation; their expanding leaves receive water from a shoot that is itself maturing. Morphology, stomatal traits, hydraulic architecture, Huber values, water transport efficiency, in situ gas exchange and laboratory-based steady-state hydraulic conductance were examined for each leaf type. Both structure and physiology differed markedly between the two leaf types. Short-shoot leaves were thinner and had higher vein density, lower stomatal pore index, smaller bundle sheath extensions and lower hydraulic conductance than long-shoot leaves. Long shoots had lower xylem area:leaf area ratios than short shoots during leaf expansion, but this ratio was reversed at shoot maturity. Long-shoot leaves had higher rates of photosynthesis, stomatal conductance and transpiration than short-shoot leaves. We propose that structural differences between the two G. biloba leaf types reflect greater hydraulic limitation of long-shoot leaves during expansion. In turn, differences in physiological performance of short- and long-shoot leaves correspond to their distinct ontogeny and architecture.

Wood 13C, 18O and radial growth responses of residual red pine to variable retention harvesting

Variable retention harvests are used to enhance the development of structural complexity in managed forests by retaining living trees and other structural legacies from the pre-harvest ecosystem. While harvesting should increase resource availability to residual trees, greater crown exposure may also increase environmental stress, which makes it difficult to predict growth in different structural environments. We used stable carbon isotope ratios (delta(13)C) of annual rings from red pine trees (Pinus resinosa Ait.) as an index of intrinsic water use efficiency (iWUE), the ratio of photosynthetic carbon assimilation (A) to stomatal conductance (g(s)), to better understand how differences in physiological performance relate to growth responses following harvests that left residuals dispersed, aggregated between small (0.1 ha) gaps or aggregated between large (0.3 ha) gaps. Stable oxygen isotope ratios (delta(18)O) were used as an index of g(s) to investigate the drivers behind changes in iWUE. Retention harvesting did not appear to affect delta(13)C or delta(18)O at the stand scale when compared to unharvested control stands, but there was a significant, negative correlation between residual tree delta(13)C and plot basal area in the second and third years after harvesting that suggests declining iWUE as overstory competition increases. Residual tree delta(18)O was similar across treatments and basal areas. Trees in variable retention harvests showed small but positive increases in radial growth from the pre-treatment to post-treatment measurement periods, while radial growth declined in unharvested control stands. There were no significant differences in radial growth among retention treatments. Our results suggest residual red pine in relatively open environments benefit from greater A but do not show evidence of changes in g(s) that would indicate altered water relations.

Ecophysiological Competence of Populus alba L., Fraxinus angustifolia Vahl., and Crataegus monogyna Jacq. Used in Plantations for the Recovery of Riparian Vegetation

In many semi-arid environments of Mediterranean ecosystems, white poplar (Populus alba L.) is the dominant riparian tree and has been used to recover degraded areas, together with other native species, such as ash (Fraxinus angustifolia Vahl.) and hawthorn (Crataegus monogyna Jacq.). We addressed three main objectives: (1) to gain an improved understanding of some specific relationships between environmental parameters and leaf-level physiological factors in these riparian forest species, (2) to compare the leaf-level physiology of these riparian species to each other, and (3) to compare leaf-level responses within native riparian plots to adjacent restoration plots, in order to evaluate the competence of the plants used for the recovery of those degraded areas. We found significant differences in physiological performance between mature and young white poplars in the natural stand and among planted species. The net assimilation and transpiration rates, diameter, and height of white poplar plants were superior to those of ash and hawthorn. Ash and hawthorn showed higher water use efficiency than white poplar. White poplar also showed higher levels of stomatal conductance, behaving as a fast-growing, water-consuming species with a more active gas exchange and ecophysiological competence than the other species used for restoration purposes. In the restoration zones, the planted white poplars had higher rates of net assimilation and water use efficiency than the mature trees in the natural stand. We propose the use of white poplar for the rapid restoration of riparian vegetation in semi-arid Mediterranean environments. Ash and hawthorn can also play a role as accompanying species for the purpose of biodiversity.

Diurnal fluctuations of gas exchange and water potential in different stand structures of Pinus ponderosa

Leaf-level gas exchange and leaf water potential (Ψleaf) measurements were made over a diurnal time-course in multi-aged and even-aged stand structures of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) in central Oregon (June) and western Montana (July) to test for differences in physiological performance due to stand structure. Total site occupancy was similar between the geographic regions as measured by basal area, leaf area index, and stand density index. No differences in net photosynthesis (A net), stomatal conductance (g s), transpiration (E), instantaneous water use efficiency (WUE) or Ψleaf were observed in June in Oregon. As a whole, even-aged plots appeared to be more water-stressed than multi-aged plots that were able to maintain higher rates of E in July in Montana. There were no differences in WUE between multi-aged and even-aged stand structures in Montana, but because both A net and E tended to be less in even-aged trees, overall productivity and efficiency of foliage may be less than in multi-aged stand structures. It is concluded that under environmental conditions that are not limited by water, patterns in gas exchange and water use are unaffected by stand structure. The data from this study further suggest that water-limiting conditions found later in the growing season may influence diurnal gas exchange patterns in a way that could result in lower productivity in even-aged stand structures.

Sexual dimorphism in physiological performance of whiptail lizards (genus Cnemidophorus).

Numerous studies have examined sexual dimorphism in the morphology and behavior of vertebrates; very few, however, have explicitly investigated the possibility of gender differences in physiological performance, despite the observations of such differences in humans. In this study, I investigated physiological sexual dimorphism in the lizard genus Cnemidophorus by measuring five whole-animal traits, all of which are likely to influence fitness in these species: burst speed, endurance, maximal exertion capacity, standard metabolic rate, and evaporative water loss rate. Because at least some of these traits are known to be strongly influenced by body size, I tested for dimorphism using both absolute and size-corrected trait values. An examination of six Cnemidophorus species and subspecies revealed a strong trend toward higher absolute trait values in males for all variables except endurance. Most of the dimorphism in standard metabolic rate and evaporative water loss rate could be explained by differences in body mass between males and females; for the locomotor traits, however, body size explained only a small fraction of the overall sexual dimorphism. The portion of trait differences not explained by body size was likely due to gender differences in physiology, such as differences in relative muscularity and fat content.

Forest growth along a rainfall gradient in Hawaii: Acacia koa stand structure, productivity, foliar nutrients, and water- and nutrient-use efficiencies.

We tested whether variation in growth of native koa (Acacia koa) forest along a rainfall gradient was attributable to differences in leaf area index (LAI) or to differences in physiological performance per unit of leaf area. Koa stands were studied on western Kauai prior to Hurricane Iniki, and ranged from 500 to 1130 m elevation and from 850 to 1800 mm annual precipitation. Koa stands along the gradient had basal area ranging from 8 to 42 m2/ha, LAI ranging from 1.4 to 5.4, and wood increment ranging from 0.7 to 7.1 tonnes/ha/year. N, P, and K contents by weight of sun leaves (phyllodes) were negatively correlated with specific leaf mass (SLM, g m-2) across sites; on a leaf area basis, N increased whereas P and K decreased with SLM. LAI, aboveground woody biomass increment, and production per unit leaf area (E) increased as phyllode δ13C became more negative. The δ13C data suggested that intrinsic water-use efficiency (ratio of assimilation to conductance) increased as water availability decreased. In five of the six sites, phyllode P contents increased as LAI increased, but biomass increment and E were not correlated with phyllode nutrient contents, suggesting that productivity was limited more by water than by nutrient availability. Because vapor pressure deficits increased with decreasing elevation, actual water-use efficiency (ratio of assimilation to transpiration) was lower at drier, low-elevation sites. There was a trade-off between intrinsic water-use efficiency and production per unit of canopy N or P across the gradient. In summary, koa responds to water limitation both by reducing stand LAI and by adjusting gas exchange, which results in increased intrinsic water-use efficiency but decreased E.