Patchiness in patterns of growth and survival of two grasses

Summary Individuals of two perennial bunch grasses, Bouteloua rigidiseta and Aristida longiseta, were transplanted into otherwise undisturbed natural short-grass vegetation in which these species are dominants. Significant differences in survivorship and growth rate were found among quadrats for both species. The relative favorability of quadrats for Bouteloua, but not for Aristida, changed during the course of the two year study. For neither species was a consistent relationship between pre-existing density and transplant performance found. However, one patch type was identified in which Bouteloua transplants grow well, although this species is not naturally present there, apparently because it cannot establish. Microsite differences, created by different soil in transplanted peat pots, were also found to be important. Bouteloua had a higher survivorship the first year, Aristida the second, which suggests that Aristida is the more tolerant of drier years.     

Environmental distribution of colony growth form in the favositid Pleurodictyum americanum

Pandolfi, John M. & Burke, Collette D. 1989 01 15: Environmental distribution of colony growth form in the favositid Pleurodictyum americanum. Lethaia , Vol. 22, pp. 69–84. Oslo. ISSN 0024–1164.
Colony growth form is of fundamental importance to understanding the ecology of both modern and ancient marine sessile colonial animals. Fourier shape analysis of the coral Pleurodictyun americantum (Tabulata: Favositida) from the Middle Devonian Hamilton Group of New York State, indicates that colony growth form is variable between environments. Discriminate function analysis of harmonics 2–6 of 51 assemblages of Pleurodictyum americanum (N = 1900) shows that this species displays an onshore to offshore gradient in colony shape. Offshore environments characterized by low levels of turbidity, oxygen, and light contain more flattened, less hemispherical growth forms, whereas onshore environments characterized by high levels of turbidity, oxygen, and light contain more hemispherical, less flattened growth forms. Harmonic shape analysis detected subtle differences among samples of P. americanum from different environments, but also showed that distinctive morphotypes are distributed within horizons. as well as between them. In fact, no one-to-one correspondence in growth form to environment is apparent; growth forms are distributed within environments, suggesting that genetic factors may have had a greater influence over coral growth form than environment. In tabulate corals, patterns of within species variability must be determined before growth form may be useful in interpreting ancient environments. □ Tabulate coral, Fourier shape analysis, morphological variability, growth form, Devonian, Hamilton Group, New York .     

Clonal integration improves compensatory growth in heavily grazed ramet populations of two inland-dune grasses

Herbaceous species possess several mechanisms to compensate for tissue loss. For clonal herbaceous species, clonal integration may be an additional mechanism. This may especially hold true when tissue loss is very high, because other compensatory mechanisms may be insufficient. On inland dunes in northern China, we subjected Bromus ircutensis and Psammochloa villosa ramets within 0.5 m×0.5 m plots to three clipping treatments, i.e., no clipping, moderate (50% shoot removal) and heavy clipping (90% shoot removal), and kept rhizomes at the plot edges connected or disconnected. Moderate clipping did not reduce ramet, leaf or biomass density of either species. Under moderate clipping, rhizome connection significantly improved the performance of Psammochloa, but not that of Bromus. Heavy clipping reduced ramet, leaf and biomass density in the disconnected plots of both species, but such negative effects were negated or greatly ameliorated when the rhizomes were connected. Therefore, clonal integration contributed greatly to the compensatory growth of both species. The results suggest that clonal integration is an additional compensatory mechanism for clonal plants and may be important for their long-term persistence in the heavily grazed regions in northern China.     

Seasonal root growth in the arctic tussock tundra

Summary The quantity of growing root tips per unit of soil volume was analyzed in a central Alaskan tussock tundra site. By June 10, the aboveground fraction of the vegetation had initiated the flush of spring growth and flowering while less than 5 active root tips cm^-3 were found. By June 25 this value had increased to 30 root tips cm^-3. Similar values in July were followed by a complete cessation of root growth after the first week of August. By then, leaf senescence had also become visible. In the spring, low root temperatures were responsible for the time lag between shoot growth initiation and the beginning of root growth. In early August, root growth stopped in spite of adequate soil temperatures and accumulated carbohydrate for root growth. It is proposed that use of reserve carbohydrate for root growth in August would compromise the flush of spring growth in the following year.     

State-dependent incubation behaviour in the high arctic barnacle geese

Energetic trade-offs between time spent on incubation and times spent on foraging for nesting birds give individuals in good body condition the possibility to incubate more continuously. In the present paper, the incubation behaviour of female barnacle geese Branta leucopsis was quantified in a colony in Svalbard. Females were weighted in early incubation and feeding recess lengths and frequencies were recorded. The feeding behaviour during the course of incubation was significantly correlated to by body mass, and heavy females had both fewer and shorter feeding recesses than lighter females. Moreover, there was an increase in the number of feeding recesses and the total feeding time as the incubation period progressed. Neither clutch size nor egg laying date had an effect on incubation behaviour. However, clutch size was positively related to female body mass suggesting that high-quality females produce large clutches but also allocate more body reserves to incubation. Females left the nest to feed at all times of the day, but more frequently during day time. This was not related to their body mass. Females presumably leave their nest at the time of day when the costs to reheat eggs are at a minimum. The diurnal rhythm may also be adjusted to the activity by egg predators. Overall the results support the state-dependent hypothesis for incubation behaviour, suggesting that body condition at the start of incubation is an important factor for incubation behaviour in barnacle geese.     

MukE and MukF form two distinct high affinity complexes

The MukBFE complex is essential for chromosome segregation and condensation in Escherichia coli. MukB is functionally related to the structural maintenance of chromosomes (SMC) proteins. Similar to SMCs, MukB requires accessory proteins (MukE and MukF) to form a functional complex for DNA segregation. MukF is a member of the kleisin family, which includes proteins that commonly mediate the interaction between SMCs and other accessory proteins, suggesting that the similarities between the MukBFE and the SMC complexes extend beyond MukB. Although SMCs have been carefully studied, little is known about the roles of their accessory components. In the present work, we characterize the oligomeric states of MukE and MukF using size exclusion chromatography and analytical ultracentrifugation. MukE self-associates to form dimers (K(D) 18 +/- 3 mum), which in turn interact with the MukF dimer to form two distinct high affinity complexes having 2:2 and 2:4 stoichiometries (F:E). Intermediate complexes are not found, and thus we propose that the equilibrium between these two complexes determines the formation of a functional MukBFE with stoichiometry 2:2:2.     

Environmental and internal control of seasonal growth in seaweeds

All 6 naupliar stages of Scutellidium hippolytes (Kröyer, 1863), belonging to Tisbidae are described. A key for the identification of the naupliar stages is given. Naupliar peculiarities are discussed in the light of phylogenetic affinities. The nauplii are compared with those of the tisbids Tisbe gracilis and Drescheriella glacialis.     

Reproductive effort and phenology of seed production of savanna grasses with different growth form and life history

The phenology of seed production in natural savanna grasslands was studied in the grass speciesAristida congesta, Cymbopogon plurinodis, Cynodon dactylon, Digitaria eriantha ssp.pentzii, Eragrostis rigidior, Eragrostis superba, Panicum coloratum, Schmidtia pappophoroides, Tragus berteronianus andUrochloa panicoides. Maximum seed production varied according to life history strategy and growth form from 0.03 mg seed g^-1 shoot dry weight in the perennialD. eriantha ssp.pentzii which produces long stolons and 14.8 mg seed g^-1 shoot inE rigidior, which produces short geniculate stolons, to 169.1 mg g^-1 in the annualT. berteronianus. Seed production was in most species divided over several peaks during the season. Peaks of seed production were observed 3 to 7 months after the onset of the growth season depending on the start of the rains and the life history strategy and growth form of the species. Seed production varied from maxima of 180 seeds m^-2 inD. eriantha ssp.pentzii to 47000 seeds m^-2 in annual stands ofT. berteronianus. Except for annual grasslands withU. panicoides, seedling emergence data reported are smaller by at least a factor of 10 than the observed seed production. Among other factors, a low quality of produced seeds, predation by birds and insects and previous grazing by livestock may have contributed to this difference.     

Population growth and intrinsic rate of natural increase of the high arctic nematode Chiloplacus sp. at low and high temperatures

Summary Population growth of the High Arctic free-living soil nematode Chiloplacus sp. was measured at 0°, 2°, 5°, 10°, 15°, 20° and 25° C. The corresponding values of the intrinsic rate of natural increase, r, were 0, 0.0178, 0.0605, 0.0823, 0.1216, 0.1384 and 0.2131 respectively. The relation of r to temperature is described by the function r=0.0088+0.0075T. Chiloplacus sp. grows and reproduces at lower temperatures than do many other nematodes, and has shorter generation times at comparable low temperatures, suggesting rate compensation to low temperature.     

Moisture relationships of the high arctic collembolan Onychiurus arcticus

Abstract. Rates of desiccation, rehydration and survival, under conditions of 0 and 100% relative humidity, were investigated in the high arctic collembolan Onychiurus arcticus (Tullberg) over a range of temperatures from -3 to 10C. Desiccation, measured over 4h in a dry environment, was rapid and highly significantly correlated with saturated vapour pressure deficit (SVPD). At 10C animals lost over 60% of body moisture in under 1h. Under moist conditions body weight remained constant. Survival, measured over 4h under dry conditions, showed a highly significant negative correlation with SVPD across the range of temperatures. Survival in moist controls was 100%. Partially desiccated animals were able to rehydrate using free water or moisture from a saturated atmosphere, but uptake of the former was faster. Rates of water uptake were around 30 times slower than rates of loss through desiccation. Animals given free water regained initial weights in 24-144h, dependent on temperature. Uptake rates of free water, measured over the time necessary fully to rehydrate, were highly significantly correlated with temperature, whereas those for atmospheric moisture were not. Over the time scales used in the experiments, three linear regression equations accurately predict rates of desiccation, rehydration and survival from SVPD or temperature. Ecological adaptation by O.arcticus to the highly contrasting climatic environments of the arctic summer and winter seasons is discussed in the context of climate change.     

Potential for mercury reduction by microbes in the high arctic

The contamination of polar regions due to the global distribution of anthropogenic pollutants is of great concern because it leads to the bioaccumulation of toxic substances, methylmercury among them, in Arctic food chains. Here we present the first evidence that microbes in the high Arctic possess and express diverse merA genes, which specify the reduction of ionic mercury [Hg(II)] to the volatile elemental form [Hg(0)]. The sampled microbial biomass, collected from microbial mats in a coastal lagoon and from the surface of marine macroalgae, was comprised of bacteria that were most closely related to psychrophiles that had previously been described in polar environments. We used a kinetic redox model, taking into consideration photoredox reactions as well as mer-mediated reduction, to assess if the potential for Hg(II) reduction by Arctic microbes can affect the toxicity and environmental mobility of mercury in the high Arctic. Results suggested that mer-mediated Hg(II) reduction could account for most of the Hg(0) that is produced in high Arctic waters. At the surface, with only 5% metabolically active cells, up to 68% of the mercury pool was resolved by the model as biogenic Hg(0). At a greater depth, because of incident light attenuation, the significance of photoredox transformations declined and merA-mediated activity could account for up to 90% of Hg(0) production. These findings highlight the importance of microbial redox transformations in the biogeochemical cycling, and thus the toxicity and mobility, of mercury in polar regions.     

Chrysophyte cysts in 36 Canadian high arctic ponds

Chrysophyte stomatocysts were described from the surface sediments and other habitats (moss, rocks, and open water) of 36 ponds located on Cape Herschel, Ellesmere Island in the Canadian high Arctic (78°37'N). Thirty-five distinct stomatocyst types were described using scanning electron microscopy (SEM); 1 other cyst was common, but was not observed with SEM. Our study ponds were diverse limnologically and contained distinct cyst floras, but the cause(s) of the floristic differences are as yet unclear. Two ponds with extreme values of water chemistry (i.e. high salinity and low pH) supported unique cyst floras. Distinctive cyst floras were also observed in ponds with high nutrient input from nesting birds and/or with diverse microhabitats (e.g. moss banks), which may provide substrate for periphytic chrysophytes. Arctic pond cyst floras are typically less diverse than those from temperate regions. Highly ornamented cysts are also less common in arctic waters, but the reason for this is unknown. Stomatocysts could be used to augment paleolimnological research in arctic ponds, if the environmental factors controlling cyst distributions and possibly degree of ornamentation can be elucidated.     

Arboreal and prostrate conifers coexisting in Mediterranean high mountains differ in their climatic responses

In contrast to most high elevation areas, plant growth at Mediterranean mountains is exposed to a summer drought period, which represents an additional climatic constraint to low temperatures. Although arboreal and shrubby conifers coexist at high altitudes, most dendroecological studies have focused on climatic responses of tree species, whereas those of shrubby species remain mostly unexplored. We built tree-ring width chronologies for two conifer species, a shrub (Juniperus sabina) and a tree (Pinus sylvestris), coexisting at three high-altitude localities of the Iberian System mountains, eastern Spain. We analyzed their climate–growth relationships for the period 1950–2009 using correlation analyses and multiple regressions. Coexisting species responded to year-to-year climatic variability in different ways. Radial growth in junipers and pines responded positively to April and May temperatures, respectively. Summer drought constrained growth in both cases, although its impact was stronger on junipers than on pines. Our findings suggest that junipers respond earlier than pines to spring temperatures due to their prostrate morphology which may enhance a fast warming of their cambial meristems after snowmelt. The higher dependence of J. sabina on summer rainfall as compared with co-occurring pines confirms that drought stress negatively impacts secondary growth in Mediterranean mountains. This sensitivity to water availability may be caused by the juniper shallow root systems, which mainly use superficial soil water. The climatic signal registered in J. sabina allows studying the response of other similar shrubby woody species growing in Mediterranean alpine areas to the ongoing climate warming, which could also reduce water availability.     

A comparative study on plant growth and root plasticity responses of two Brachiaria forage grasses grown in nutrient solution at low and high phosphorus supply

Brachiaria forage grasses are widely used for livestock production in the tropics. Signalgrass (Brachiaria decumbens cv. Basilisk, CIAT 606) is better adapted to low phosphorus (P) soils than ruzigrass (B. ruziziensis cv. Kennedy, CIAT 654), but the physiological basis of differences in low-P adaptation is unknown. We characterized morphological and physiological responses of signalgrass and ruzigrass to low P supply by growing both grasses for 30 days in nutrient solution with two levels of P supply using the hydroxyapatite pouch system. Ruzigrass produced more biomass at both levels of P supply whilst signalgrass appears to be a slower-growing grass. Both grasses increased biomass allocation to roots and had higher root acid phosphatase and phytase activities at low P supply. At low P supply, ruzigrass showed greater morphological plasticity as its leaf mass density and lateral root fraction increased. For signalgrass, morphological traits that are not responsive to variation in P supply might confer long-term ecological advantages contributing to its superior field persistence: greater shoot tissue mass density (dry matter content) might lower nutrient requirements while maintenance of lateral root growth might be important for nutrient acquisition in patchy soils. Physiological plasticity in nutrient partitioning between root classes was also evident for signalgrass as main roots had higher nutrient concentrations at high P supply. Our results highlight the importance of analyzing morphological and physiological trait profiles and determining the role of phenotypic plasticity to characterize differences in low-P adaptation between Brachiaria genotypes.     

Acquisition and allocation of resources in two waterlogging-tolerant grasses

This study focuses on the following questions: (i) whether reductions in root:shoot ratio have a cost in terms of nutrient balance of the plant, and (ii) whether changes in resource-allocation patterns are proportional among different resources. Our approach was to analyse the variations in the allocation pattern induced by soil waterlogging. A pot experiment was conducted to analyse the effects of waterlogging on biomass, phosphorus (P) and nitrogen (N) accumulation of Paspalum dilatatum and Danthonia montevidensis , two waterlogging-tolerant grasses. When changing from oxic to anoxic conditions, a common response of these and other waterlogging-tolerant grasses is a reduction in allocation to below-ground resources. It was observed that (i) the reduction in root:shoot ratio caused by waterlogging did not have a cost in terms of capacity for nutrient uptake; (ii) resource partitioning within aerial parts was less sensitive to treatments than partitioning between roots and shoots; and (iii) biomass does not appear to be a useful currency for evaluating nutrient-allocation patterns, as the allocation of P and N was inadequately represented by biomass. The results presented here indicate that the existence of compensation mechanisms reduces the predictive value of the partition of resources for the capacity of plants to acquire resources. Data on the allocation of nutrients in relation to biomass suggest that the assumptions of independence in the allocation pattern between biomass and limiting nutrients under the effects of environmental factors can be extended.     

Zeitgebers for animals in the continuous daylight of high arctic summer

Summary To find out which of daily oscillating environmental factors in the continuous daylight of arctic summer are responsable for synchronization of animal activity period with the rotation of the earth, in Spitsbergen (78° N) a whole summer continuous measurements of temperature (°C), light intensity (lux) and spectral composition of the light (colour temperature in °K) were done. With a daily amplitude of 4–5° C in the air, resp. 10° C at the ground surface, temperature can only act as a Zeitgeber for heterothermic animals. Measurements of light intensity (with a photocell directed vertical upward to the zenith) showed relatively large daily oscillations. But since light intensity depends on the cosine of the angle of incidence of the light (Lambert's cosine law) and in high latitudes the angle of incidence of the sun is always very great, in fact measurements have to be done with the photocell directed to the sun or, as the latter meets with mechanical problems, all dates got with the photocell vertical upward must be converted after Lambert's cosine law. Converted dates of light intensity oscillate not nearly as intense as measured dates. This small daily amplitude of light intensity, which in addition is strongly influenced by sudden changes of the wheather, can hardly come into consideration as a Zeitgeber of animal activity period. Colour temperature however showed large and regular daily oscillations and therefore could be a Zeitgeber of animal activity period in high arctic summer, particularly because in the laboratory the synchroniing effect of an artificial daily alternation of colour temperature is already proved. Nest (feeding) activity of local snowbuntings and perch hopping activity of greenfinches, brought from Germany, were registrated with light traps. Activity period of both bird species was clearly synchronized with the rotation of the earth. In a narrow valley the activity pattern of greenfinches was identical as in open country, in spite of temporarily total other conditions of light intensity (shading by mountains). Apparently even the activity period of non arctic animals can be synchronized by weak Zeitgebers like colour temperature.     

Characteristics of successful competitors: an evaluation of potential growth rate in two cold desert tussock grasses

Summary Within the first few weeks after seedling emergence, Agropyron desertorum, a more competitive tussock grass, had a much higher mean relative growth rate (RGR) than Agropyron spicatum, a very similar, but less competitive species. However, beyond the early seedling stage, the two grasses had a remarkably similar whole-plant RGR in hydroponic culture and aboveground RGR in glasshouse soil, if root temperatures were above approximately 12°C. At soil temperatures between 5 and 12°C, A. desertorum exhibited a 66% greater aboveground RGR than A. spicatum (P<0.05). Both species responded similarly to warming soil temperatures. In the field, however, tiller growth rates were generally similar. Neither species showed marked tiller elongation until a couple of weeks after snowmelt, by which time soil temperatures, at least to a depth of 10 cm, were above 12°C for a significant portion of the day. Aboveground biomass accumulation over a three-year period indicated that both grasses had similar potential growth rates whereas Artemisia tridentata ssp. vaseyana, a common neighbor planted in the same plots, had a much greater potential growth rate. The greater competitive ability of adult A. desertorum, as compared to A. spicatum, cannot be attributed to appreciable differences in potential growth rates.     

Distribution and growth of benthic macroinvertebrates among different patch types of the littoral zones of two arctic lakes

1. To evaluate the effect of habitat patch heterogeneity on abundance and growth of macroinvertebrates in arctic lakes, macroinvertebrate abundance, individual biomass, and potential food resources were studied in three patch types in two arctic lakes on the Alaskan North Slope near the Toolik Lake Field Station. An experiment was conducted to determine which sediment patch type supported higher growth rates for Chironomus sp., a commonly occurring macroinvertebrate. 2. Potential organic matter (OM) resources were significantly higher in both rock and macrophyte patches than in open‐mud patches. Total macroinvertebrate densities in both lakes were highest in rock patches, intermediate in macrophytes and lowest in open‐mud. The open‐mud patches also had lower species richness compared with other patch types. Additionally, individual biomass for one clam species and two chironomid species was significantly greater in rock patches than in open‐mud. 3. In a laboratory experiment, Chironomus showed two to three times greater mass increase in sediments from macrophyte and rock patches than from open‐mud patches. Rock and macrophyte experimental sediments had at least 1.5 × the percentage OM as open‐mud sediments. 4. Chlorophyll a appeared to be the best predictor for invertebrate abundances across all patch types measured, whereas OM content appeared to be the variable most closely associated with Chironomus growth. 5. Our results combined with previous studies show that the relationships between macroinvertebrate community structure, individual growth, and habitat heterogeneity are complex, reflecting the interaction of multiple resources, and biotic interactions, such as the presence or absence of a selective vertebrate predator (lake trout, Salvelinus namaycush).     

Exercise metabolism in two species of cod in arctic waters

The northern range of Atlantic cod (Gadus morhua), overlaps the southern range of the Greenland cod (Gadus ogac), in the coastal waters of Western Greenland. The availability of a temperate water species (G. morhua) in the same area and oceanographic conditions as a polar species (G. ogac) presented us with the ideal circumstances to test the hypothesis of metabolic cold adaptation (MCA) since many of the problems associated with MCA studies (adaptation of the animals beyond their normal temperature range or mathematical extrapolation of data to common temperatures) could thus be avoided. We therefore used a swim tunnel to measure oxygen consumption in fish at 4°C over a range of swimming speeds and following exhaustion, monitored the size of the oxygen debt and time of oxygen debt repayment. There were no significant differences in standard (60–72 mg O₂ kg^–1· hr^–1), routine (76 mg O₂ kg^–1·hr^–1), active (137mg O₂ kg^–1·hr^–1), or maximal (157 mg O₂ kg^–1·hr^–1) metabolic rate, metabolic scope (2.5) or critical swimming speed (2.2 BL·s^–1) between the two species. Following exhaustive swimming, however, the half-time for oxygen debt repayment in G. ogac (43 min) was almost twice that of G. morhua (25 min). Despite its circumpolar distribution, therefore, there was no evidence of MCA in G. ogac.