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1.
Influence of climate-driven shifts in biomass allocation on water transport and storage in ponderosa pine 总被引:12,自引:0,他引:12
Conifers decrease the amount of biomass apportioned to leaves relative to sapwood in response to increasing atmospheric evaporative demand. We determined how these climate-driven shifts in allocation affect the aboveground water relations of ponderosa pine growing in contrasting arid (desert) and humid (montane) climates. To support higher transpiration rates, a low leaf:sapwood area ratio (AL/AS) in desert versus montane trees could increase leaf-specific hydraulic conductance (KL). Alternatively, a high sapwood volume:leaf area ratio in the desert environment may increase the contribution of stored water to transpiration. Transpiration and hydraulic conductance were determined by measuring sap flow (JS) and shoot water potential during the summer (June-July) and fall (August-September). The daily contribution of stored water to transpiration was determined using the lag between the beginning of transpiration from the crown at sunrise and JS. In the summer, mean maximum JS was 31.80LJ.74 and 24.34Dž.05 g m-2 s-1 for desert and montane trees (a 30.6% difference), respectively. In the fall, JS was 25.33NJ.52 and 16.36dž.64 g m-2 s-1 in desert and montane trees (a 54.8% difference), respectively. JS was significantly higher in desert relative to montane trees during summer and fall (P<0.05). Predawn and midday shoot water potential and sapwood relative water content did not differ between environments. Desert trees had a 129% higher KL than montane trees in the summer (2.41᎒-5 versus 1.05᎒-5 kg m-2 s-1 MPa-1, P<0.001) and a 162% higher KL in the fall (1.97᎒-5 versus 0.75᎒-5 kg m-2 s-1 MPa-1, P<0.001). Canopy conductance decreased with D in all trees at all measurement periods (P<0.05). Maximum gC was 3.91 times higher in desert relative to montane trees averaged over the summer and fall. Water storage capacity accounted for 11 kg (11%) and 10.6 kg (17%) of daily transpiration in the summer and fall, respectively, and did not differ between desert and montane trees. By preventing xylem tensions from reaching levels that cause xylem cavitation, high KL in desert ponderosa pine may facilitate its avoidance. Thus, the primary benefit of low leaf:sapwood allocation in progressively arid environments is to increase KL and not to increase the contribution of stored water to transpiration. 相似文献
2.
Carbon isotope discrimination in photosynthetic bark 总被引:1,自引:0,他引:1
Lucas A. Cernusak John D. Marshall Jonathon P. Comstock Nick J. Balster 《Oecologia》2001,128(1):24-35
We developed and tested a theoretical model describing carbon isotope discrimination during photosynthesis in tree bark. Bark photosynthesis reduces losses of respired CO2 from the underlying stem. As a consequence, the isotopic composition of source CO2 and the CO2 concentration around the chloroplasts are quite different from those of photosynthesizing leaves. We found three lines of evidence that bark photosynthesis discriminates against 13C. First, in bark of Populus tremuloides, the '13C of CO2 efflux increased from -24.2 in darkness to -15.8 in the light. In Pinus monticola, the '13C of CO2 efflux increased from -27.7 in darkness to -10.2 in the light. Observed increases in '13C were generally in good agreement with predictions from the theoretical model. Second, we found that '13C of dark-respired CO2 decreased following 2-3 h of illumination (P<0.01 for Populus tremuloides, P<0.001 for Pinus monticola). These decreases suggest that refixed photosynthate rapidly mixes into the respiratory substrate pool. Third, a field experiment demonstrated that bark photosynthesis influenced whole-tissue '13C. Long-term light exclusion caused a localized increase in the '13C of whole bark and current-year wood in branches of P. monticola (P<0.001 and P<0.0001, respectively). Thus bark photosynthesis was shown to discriminate against 13C and create a pool of photosynthate isotopically lighter than the dark respiratory pool in all three experiments. Failure to account for discrimination during bark photosynthesis could interfere with interpretation of the '13C in woody tissues or in woody-tissue respiration. 相似文献
3.
13C content of ecosystem respiration is linked to precipitation and vapor pressure deficit 总被引:6,自引:0,他引:6
David R. Bowling Nate G. McDowell Barbara J. Bond Beverly E. Law James R. Ehleringer 《Oecologia》2002,131(1):113-124
Variation in the carbon isotopic composition of ecosystem respiration ('13CR) was studied for 3 years along a precipitation gradient in western Oregon, USA, using the Keeling plot approach. Study sites included six coniferous forests, dominated by Picea sitchensis, Tsuga heterophylla, Pseudotsuga menziesii, Pinus ponderosa, and Juniperus occidentalis, and ranged in location from the Pacific coast to the eastern side of the Cascade Mountains (a 250-km transect). Mean annual precipitation across these sites ranged from 227 to 2,760 mm. Overall '13CR varied from -23.1 to -33.1, and within a single forest, it varied in magnitude by 3.5-8.5. Mean annual '13CR differed significantly in the forests and was strongly correlated with mean annual precipitation. The carbon isotope ratio of carbon stocks (leaves, fine roots, litter, and soil organic matter) varied similarly with mean precipitation (more positive at the drier sites). There was a strong link between '13CR and the vapor saturation deficit of air (vpd) 5-10 days earlier, both across and within sites. This relationship is consistent with stomatal regulation of gas exchange and associated changes in photosynthetic carbon isotope discrimination. Recent freeze events caused significant deviation from the '13CR versus vpd relationship, resulting in higher than expected '13CR values. 相似文献
4.
Photosynthetic activity of the moss Sanionia uncinata (Hedw.) Loeske was investigated on Léonie Island (67°35'S, 68°20'W, Antarctic Peninsula) in response to short-term changes of UV-B radiation. The UV-environment of natural mat formations dominated by S. uncinata was altered using filter screens. Two filter experiments were conducted in the Antarctic summers 1998 and 1999. A third filter experiment was conducted during springtime ozone depletion in October 1998. Photosynthetic activity of S. uncinata was mainly determined by photosynthetically active photon flux density (PPFD). Light response of relative electron transport rate through photosystem II (rel ETR=jF/Fm'2PPFD) remained unaffected by ambient summer levels of UV-B radiation. The same was found for net photosynthesis and dark respiration. In October 1998, S. uncinata was mainly metabolically inactive due to low temperatures. No significant levels of DNA-damage measured as cyclobutane pyrimidine dimers (CPDs) were induced by ambient summer levels of UV-B. Artificially enhanced UV-B radiation supplying a Setlow-DNA-dose of 8.7 kJ mф dayу UV-B led to formation of 7Dž CPD (106 nucleotides)-1. It is concluded that current ambient summer levels of UV-B radiation do not affect photosynthetic activity in S. uncinata. 相似文献
5.
Water availability and carbon isotope discrimination in conifers 总被引:22,自引:0,他引:22
The stable C isotope composition ('13C) of leaf and wood tissue has been used as an index of water availability at both the species and landscape level. However, the generality of this relationship across species has received little attention. We compiled literature data for a range of conifers and examined relationships among landscape and environmental variables (altitude, precipitation, evaporation) and '13C. A significant component of the variation in '13C was related to altitude (discrimination decreased with altitude in stemwood, 2.53 km-1 altitude, r2=0.49, and in foliage, 1.91 km-1, r2=0.42), as has been noted previously. The decrease in discrimination with altitude was such that the gradient in CO2 partial pressure into the leaf (Pa-Pi) and altitude were generally unrelated. The ratio of precipitation to evaporation (P/E) explained significant variation in Pa-Pi of stemwood (r2=0.45) and foliage (r2=0.27), but only at low (<0.8) P/E. At greater P/E there was little or no relationship, and other influences on '13C probably dominated the effect of water availability. We also examined the relationship between plant drought stress (O) and '13C within annual rings of stemwood from Pinus radiata and Pinus pinaster in south-western Australia. Differential thinning and fertiliser application produced large differences in the availability of water, nutrients and light to individual trees. At a density of 750 stems ha-1, O and '13C were less (more negative) than at 250 stems ha-1 indicating greater drought stress and less efficient water use, contrary to what was expected in light of the general relationship between discrimination and P/E. The greater '13C of trees from heavily thinned plots may well be related to an increased interception of radiation by individual trees and greater concentrations of nutrients in foliage - attributes that increase rates of photosynthesis, reduce Pi and increase '13C. '13C was thus modified to a greater extent by interception of radiation and by nutrient concentrations than by water availability and the '13C-O relationship varied between thinning treatments. Within treatments, the relationship between '13C and O was strong (0.38<r2<0.58). We conclude that '13C may well be a useful indicator of water availability or drought stress, but only in seasonally dry climates (P/E<1) and where variation in other environmental factors can be accounted for. 相似文献
6.
Dana M. Bergstrom George R. Stewart Patricia M. Selkirk Susanne Schmidt 《Oecologia》2002,130(2):309-314
'15N signatures of fossil peat were used to interpret past ecosystem processes on tectonically active subantarctic Macquarie Island. By comparing past vegetation reconstructed from the fossil record with present-day vegetation analogues, our evidence strongly suggests that changes in the '15N signatures of fossil peat at this location reflect mainly past changes in the proportion of plant nitrogen derived from animal sources. Associated with uplift above sea level over the past 8,500 years, fossil records in two peat deposits on the island chronicle a change from coastal vegetation with fur and elephant seal disturbance to the existing inland herbfield. Coupled with this change are synchronous changes in the '15N signatures of peat layers. At two sites 15N-enriched peat '15N signatures of up to +17 were associated with a high abundance of pollen of the nitrophile Callitriche antarctica (Callitrichaceae). At one site fossil seal hair was also associated with enriched peat '15N. Less 15N enriched '15N signatures (e.g. -1.9 to +3.9) were measured in peat layers which lacked animal associated C. antarctica and Acaena spp. Interpretation of a third peat profile indicates continual occupation of a ridge site by burrowing petrels for most of the Holocene. We suggest that 15N signatures of fossil peat remained relatively stable with time once deposited, providing a significant new tool for interpreting the palaeoecology. 相似文献
7.
Glasshouse experiments were conducted to study the response of non-host Brassica rapa and host Sorghum bicolor to inoculation with the arbuscular mycorrhizal fungus (AMF) Glomus etunicatum when given different levels of N (0.9 mmol kg-1 sand, 2.7 mmol kg-1 sand, 8.1 mmol kg-1 sand) and P (3.6 µmol kg-1 sand, 10.7 µmol kg-1 sand, 32.0 µmol kg-1 sand) fertiliser. On both plant species, the presence of G. etunicatum inoculum (+AMF) was associated with significant changes of shoot '15N values, with +AMF plants having larger average '15N values than uninoculated plants (-AMF). These values are the largest average differences in shoot '15N yet recorded for AMF and nutrient effects. B. rapa shoot '15N average differences ranged from 1.67 to 2.70, while for S. bicolor they range between 2.07 and 4.40. For shoot '13C only the non-host B. rapa responded to -AMF and added N. Although the harvested dry weight biomass (-35.2% B. rapa; +39.8% S. bicolor) of both plant species responded to AMF inoculation, no direct relationship was observed between isotopic discrimination and growth inhibition for the non-host B. rapa. In this paper we discuss some implications regarding AMF inocula on the basis of our findings and current literature. 相似文献
8.
Chantal Salen-Picard Audrey M. Darnaude Denise Arlhac Mireille L. Harmelin-Vivien 《Oecologia》2002,133(3):380-388
The Rhone river is the most important input to the Mediterranean Sea, responsible for 50% of the primary productivity of the Gulf of Lions. A highly variable amount of 1-23᎒6 t year-1 of terrestrial material is exported to the sea by the Rhone and stocked on the continental shelf for the most part. Soft-bottom communities off the Rhone delta were dominated by polychaetes both in species richness and abundance, and exhibited strong temporal fluctuations mainly related to flooding events. Floods caused pulses of organic matter followed, with different time lags, by peaks of polychaetes. Opportunistic, short-lived species, such as Mediomastus sp. and Aricidea claudiae, exhibited high short-term peaks in density and biomass a few months after flooding events. Conversely, long-lived species, such as Laonice cirrata and Sternaspis scutata, peaked in density and biomass with a time lag of 1-3 years, and their population increase lasted for a few years. The common sole, Solea solea, is a voracious predator of polychaetes which represent >80% of its prey. A positive correlation was found between the mean annual discharge of the Rhone river and the annual commercial landings of S. solea with a time lag of 5 years in the two fishing harbours (Sete and Martigues) located close to the Rhone delta. The long-term increase in food (i.e. polychaete density and biomass) after flooding events might favour the different stages of the sole life cycle, enhancing its population size for several years. Fluctuations of sole fishery yields in the Gulf of Lions could be influenced by climate, as the Rhone river flow is related to the North Atlantic Oscillation that drives precipitation over Western Europe. 相似文献
9.
Soil microbial community and bacterial functional diversity at Machu Picchu, King George Island, Antarctica 总被引:2,自引:0,他引:2
The objective of this study was to evaluate the potential contribution of the soil microbial community in the vicinity of two plant covers, Sanionia uncinata and Deschampsia antarctica, at Machu Picchu Station, King George Island, Antarctica. Soil samples were collected at the study site during the southern (pole) summer period from 0-5 cm and 5-10 cm depths, for chemical and biological analyses. Soil microbial biomass reached a maximal value of 144 µg g-1 in soil samples taken from under the S. uncinata upper layer plant. qCO2 ranged from 167 to 239 µg CO2.mgCmic.h-1 at the 0-5 and 5-10 cm depths, respectively. CO2 evolution showed values of 54.3 mg.m-2 h-1 beneath plant cover and 55.9 mg.m-2 h-1 in the open space. CO2 evolved by substrate induced respiration in the soil samples taken under the plant cover in the summer period, oscillated between 0.25 and 4.78 µg CO2 g-1 h-1. The data obtained from this short study may provide evidence that both activity and the composition and substrate utilization of the microbial community appear to change substantially across the moisture level and sample location. 相似文献
10.
The biology and evolution of Antarctic saline lakes in relation to salinity and trophy 总被引:3,自引:0,他引:3
. Five brackish to hypersaline lakes (Highway, Ace, Pendent, Williams and Rookery) in the Vestfold Hills, eastern Antarctica were investigated during the austral summer of 1999/2000. The aims were to characterise the functional dynamics of the plankton and gain an understanding of how the different environments in the lakes have led to the evolution of different communities. The plankton was dominated by microorganisms and differed across the salinity spectrum in relation to trophy, age and the presence of meromixis. However, some elements of the plankton were common to all of the lakes, e.g. the mixtrophic ciliate, Mesodinium rubrum, which reached abundances of 2.7᎒5 l-1 and spanned a salinity gradient of 4-63. Marine dinoflagellate species also occurred in all of the lakes, often at high abundances in Highway Lake, Pendent Lake and Lake Williams. During December (mid-summer), primary production showed an increase along the salinity gradient from Highway Lake to Lake Williams; however, it was low in hyper-nutrified Rookery Lake because of the turbidity of the waters. Bacterial production followed the same trend and was extremely high in Rookery Lake (327 µg l-1 h-1 in January). The lakes possessed a marine microbial plankton that has become very simplified through time, and now contains a small number of highly successful species, which were pre-adapted to surviving in extreme Antarctic lakes. 相似文献
11.
Primary production, light and vertical mixing in Potter Cove, a shallow bay in the maritime Antarctic 总被引:3,自引:1,他引:2
Phytoplankton photosynthesis was measured during spring-summer 1991-1992 in the inner and outer part of the shallow Potter Cove, King George Island. Strong winds characterise this area. Wind-induced turbulent mixing was quantified by means of the root-mean square expected vertical displacement depth of cells in the water column, Zt. The light attenuation coefficient was used as a measure of the influence of the large amount of terrigenous particles usually present in the water column; 1% light penetration ranged between 30 and 9 m, and between 30 and 15 m for the inner and outer cove, respectively. Obvious differences between photosynthetic capacity [P*max; averages 2.6 and 0.6 µg C (µg chlorophyll-a)-1 h-1] and photosynthetic efficiency {!*; 0.073 and 0.0018 µg C (µg chlorophyll-a)-1 h-1 [(µmol m-2 s-1)-1]} values were obtained for both sites during low mixing conditions (Zt from 10 to 20 m), while no differences were found for high mixing situations (Zt>20 m). This suggests different photoacclimation of phytoplankton responses, induced by modifications of the light field, which in turn are controlled by physical forcing. Our results suggest that although in experimental work P*max can be high, wind-induced mixing and low irradiance will prevent profuse phytoplankton development in the area. 相似文献
12.
Analysis of the natural variations in stable isotope ratios in animal tissue may be a powerful tool to reveal the trophic position and feeding preferences of generalist predators such as lycosid spiders. In the present study, changes in 15N/14N and 13C/12C ratios in the lycosid spider Pardosa lugubris (Araneae: Lycosidae), fed with prey of different quality, were investigated. Experimental food chains included three trophic levels: prey media, prey organism and predator. In order to analyse the time course of stable isotope enrichment, different life stages of P. lugubris feeding on Drosophila melanogaster were studied. The 15N content of hatchlings of P. lugubris was significantly lower than that of their mothers, indicating the existence of nitrogen pools with different 15N signatures in female P. lugubris. With duration of feeding and progressing development, age and body weight, the 15N content in spiderlings increased. Starvation resulted in 15N and 13C enrichment in P. lugubris. Being fed with prey of different quality resulted in varying patterns of stable isotope enrichment. 15N but not 13C content consistently increased when fed on high quality prey (Heteromurus nitidus, D. melanogaster and a mixed diet consisting of H. nitidus and D. melanogaster). In contrast, low quality prey (Rhopalosiphum padi, Folsomia candida and a mixed diet consisting of H. nitidus, D. melanogaster and F. candida) resulted in deviations from postulated patterns of stable isotope enrichment with 15N content being similar to that of starving spiderlings. When fed on high quality prey, 15N enrichment of P. lugubris was close to ca. 3. It is concluded that the analysis of variations in the natural abundance of stable isotopes is particularly helpful in revealing the trophic structure of terrestrial food webs in which polyphagous feeders predominate, as is the case in litter and soil. 相似文献
13.
A sediment trap deployment was made at a station (64°42'S, 139°59'E) at five depths (537, 796, 1,259, 1,722, 2,727 m) in the marginal ice zone (MIZ) of the Antarctic Ocean during a summer productive period from 26 December 1994 to 20 January 1995. This aim of the study was to reveal a possible occurrence of a sporadic bloom in surface layers and to evaluate the role of fast-sinking particles in transportation processes of bloom-derived material down to mesopelagic and bathypelagic layers. During the observation, a marked flux increase (70.5 mg C m-2 day-1, 7.7 mg N m-2 day-1) was observed at the depth of 537 m on 7-9 January. The increased flux at 537 m decreased with depth and time. The same mass of sinking particles forming the flux maximum at each depth sank down from the shallowest trap (537 m) to the deepest trap (2,727 m) within 4-11 days, indicating that these particles were transported downward to the bottom with the sinking rate of >200 m day-1. Collected particles were composed of two major particle fractions; one was dominated by fecal pellets of macrozooplankton (mainly Euphausia superba) with relatively fast sinking rates (FSP; fast-sinking particles) and the other by minute diatoms of Fragilariopsis curta with slow sinking rates (SSP; slowly sinking particles). According to the comparison of time depth changes of these two fractions, the SSP had unexpectedly faster sinking rates comparable with the FSP during the periods of maximum fluxes, probably indicating the SSP were transformed from the FSP during sinking. The present result strongly suggests that a local bloom of F. curta and intensified zooplankton grazing activities occurred in surface layers in a few days in the MIZ, and then the egested fecal pellets were rapidly transported downward with fragmentation processes into small-sized minute particles in mesopelagic and bathypelagic layers. 相似文献
14.
A meso-scale oceanographic grid survey was conducted during the first cruise of the Marion Offshore Ecosystem Variability Study in the upstream region of the Prince Edward Islands in austral autumn (April/May) 2001. Mesozooplankton samples, collected using a Bongo net (fitted with 200-µm and 300-µm mesh nets), were separated into three size fractions, 200-500 µm, 500-1,000 µm, 1,000-2,000 µm, by reverse filtration. Total surface (depth<5 m) chlorophyll-a concentration during the study ranged between 0.11 and 0.34 µg l-1 and was always dominated by picophytoplankton (0.45-2.0 µm). Total mesozooplankton abundance and biomass during the survey ranged between 49 and 1,512 ind. m-3 and between 0.7 and 25 mg Dwt. m-3, respectively. Throughout the survey, the 200 to 500 µm class numerically dominated the mesozooplankton community, with an average of ~69% (SD=ᆠ.3%). The dominant species in the 200- to 500-µm size fraction were the copepods, Oithona similis, Calanus simillimus and Metridia lucens, and the pteropod, Limacina retroversa. However, in terms of biomass, the 1,000- to 2,000-µm group was predominant, with dry weight values constituting an average of ~66% (SD=ᆞ.2%). The most well-represented species in this group were the carnivorous Euphausia vallentini, Thysanoessa vicina, Sagitta gazellae and Eukrohnia hamata. Three distinct groupings of stations were identified by numerical analysis. The different station groupings identified reflect changes in the relative contributions of the dominant species, as opposed to the presence/absence of species. 相似文献
15.
Leaves from several desert and woodland species, including gymnosperms and angiosperms with both C3 and C4 physiology, were analyzed to detect trends in '13Cleaf with elevation and slope aspect along two transects in southeastern Utah and south-central New Mexico, USA. The main difference between the two transects is the steeper elevational gradient for mean annual and summer precipitation in the southern transect. For any given species, we found that isotopic differences between individual plants growing at the same site commonly equal differences measured for plants along the entire altitudinal gradient. In C3 plants, '13Cleaf values become slightly enriched at the lowest elevations, the opposite of trends identified in more humid regions. Apparently, increasing water-use efficiency with drought stress offsets the influence of other biotic and abiotic factors that operate to decrease isotopic discrimination with elevation. For some species shared by the two transects (e.g., Pinus edulis and Cercocarpus montanus), '13Cleaf values are dramatically depleted at sites that receive more than 550 mm mean annual precipitation, roughly the boundary (pedalfer-pedocal) at which soils commonly fill to field capacity in summer and carbonates are leached. We hypothesize that, in summer-wet areas, this may represent the boundary at which drought stress overtakes other factors in determining the sign of '13Cleaf with elevation. The opposition of isotopic trends with elevation in arid versus humid regions cautions against standard correction for elevation in comparative studies of '13Cleaf. 相似文献
16.
Sea lion and seal populations in Alaskan waters underwent various degrees of decline during the latter half of the twentieth century and the cause(s) for the declines remain uncertain. The stable carbon (13C/12C) and nitrogen (15N/14N) isotope ratios in bone collagen from wild Steller sea lions (Eumetopias jubatus), northern fur seals (Callorhinus ursinus) and harbor seals (Phoca vitulina) from the Bering Sea and Gulf of Alaska were measured for the period 1951-1997 to test the hypothesis that a change in trophic level may have occurred during this interval and contributed to the population declines. A significant change in '15N in pinniped tissues over time would imply a marked change in trophic level. No significant change in bone collagen '15N was found for any of the three species during the past 47 years in either the Bering Sea or the Gulf of Alaska. However, the 15N in the Steller sea lion collagen was significantly higher than both northern fur seals and harbor seals. A significant decline in '13C (almost 2 over the 47 years) was evident in Steller sea lions, while a declining trend, though not significant, was evident in harbor seals and northern fur seals. Changes in foraging location, in combination with a trophic shift, may offer one possible explanation. Nevertheless, a decrease in '13C over time with no accompanying change in '15N suggests an environmental change affecting the base of the foodweb rather than a trophic level change due to prey switching. A decline in the seasonal primary production in the region, possibly resulting from decreased phytoplankton growth rates, would exhibit itself as a decline in '13C. Declining production could be an indication of a reduced carrying capacity in the North Pacific Ocean. Sufficient quantities of optimal prey species may have fallen below threshold sustaining densities for these pinnipeds, particularly for yearlings and subadults who have not yet developed adequate foraging skills. 相似文献
17.
M. Sobrado 《Trees - Structure and Function》2002,16(1):1-4
This study assessed the effects of salinity changes over space and time upon leaf gland secretion in Avicennia germinans trees growing naturally in an area featuring markedly seasonal rainfall. Soil ? (, soil N MPa) during the wet season was -0.95ǂ.05 and -2.12ǂ.08 at low and high salinity sites, respectively. During the dry season, these values decreased to -3.24ǂ.09 at low salinity and to -5.75ǂ.06 at high salinity. Consequently, predawn and midday plant water potential were lowered during drought at both sites. The rates of secretion (mmol m-2 h-1 ) increased during drought from 0.91ǂ.12 during the wet season to 1.93ǂ.12 at low salinity, and from 1.69ǂ.12 during the wet season to 2.81ǂ.15 at high salinity. Conversely, stomatal conductance (gs) was lowered by both salinity and drought. As xylem osmolality increased during drought, secretion tended to rise exponentially, and gs decayed hyperbolically. Thus, a trade-off is obtained between enhancement in salt secretion and control of water loss suggested by gs. 相似文献
18.
Krzysztof Jazdzewski Claude Broyer Magdalena Pudlarz Dariusz Zielinski 《Polar Biology》2001,24(12):910-917
Quantitative samples of benthos were taken on a stony beach in the maritime Antarctic (Admiralty Bay, King George Island, South Shetland Islands) during a complete annual cycle. The sampled habitat consisted of cobbles lying on sand and gravel in the fringe between the littoral and sublittoral zones; samples were always taken at low tide just below the water line. In this habitat, abundant macroalgal detritus was observed between stones. This stony beach appeared to be very rich in vagile fauna settled between and under stones. Macrobenthos consisted mainly of amphipods (ca. 85% of total number), gastropods (11%) and nemerteans (3%). The abundance of whole macrofauna ranged to over 50,000 ind. m-2 and its biomass over 600 g m-2 (FW). Seven species of Amphipoda and four species of Gastropoda were found. Amphipoda were dominated by Gondogeneia antarctica (over 70% of all amphipods) and Paramoera edouardi (over 20%), whereas among gastropods Laevilitorina antarctica prevailed (over 70%). Unexpectedly high abundance and biomass of Amphipoda were observed in the first half of winter (May/July), surpassing otherwise important summer amphipod abundance. The probable reason for this phenomenon could be high autumn abundance of decaying algae on the beach in the tidal zone, providing detritus that is probably the main food source for Amphipoda. 相似文献
19.
In-situ estimates of fast-ice algal productivity at Cape Evans, McMurdo Sound, in 1999 were lower than at the same site in previous years. Under-ice irradiance was between 0 and 8 µmol photons m-2 s-1; the ice was between 1.9 and 2.0 m thick and the algal biomass averaged 150 mg chl a m-2, although values as high as 378 mg chl a m-2 were recorded. Production on 11 and 12 November was between 0.053 and 1.474 mg C m-2 h-1. When the data from 11 November were fitted to a hyperbolic tangent function, a multilinear regression gave estimates for Pmax of 0.571 nmol O2 cm-2 s-1, an ! of 0.167 nmol O2 cm-2 s-1 µmol-1 photons m-2 s-1 and an Ek of 3.419 µmol photons m-2 s-1. A Pmax of 2.674 nmol O2 cm-2 s-1, an ! of 0.275 nmol O2 cm-2 s-1 µmol-1 photons m-2 s-1, r of 0.305 nmol O2 cm-2 s-1 and an Ek of 9.724 µmol-1 photons m-2 s-1 were estimated from the 12 November data. The sea-ice algal community was principally comprised of Nitzschia stellata, Entomoneis kjellmanii and Berkeleya adeliensis. Other taxa present included N. lecointei, Fragilariopsis spp., Navicula glaciei, Pleurosigma spp. and Amphora spp. Variations in the method for estimating the thickness of the diffusive boundary layer were not found to significantly affect the measurements of oxygen flux. However, the inability to accurately measure fine-scale variations in biomass is thought to contribute to the scatter of the P versus E data. 相似文献
20.
Frieda L. Henskens Michael Battaglia Maria L. Cherry Christopher L. Beadle 《Trees - Structure and Function》2001,15(6):365-377
We examine the effects of spacing and layout on the growth and form of 3- to 4-year-old Eucalyptus globulus in a farm forestry context. Four planting layouts were chosen. These represented the range commonly in use in farm forestry: block plantings (2Ǹ m), triple rows (2Ǹ m) at 10-m intervals, single rows (2᎒ m) and isolated trees (10᎒ m). The physiological significance of key results is interpreted in terms of changes in the parameters of a simple plantation growth model. Under conditions where levels of direct light are high, for example during summer, block-planted trees intercepted only 38% of the light intercepted by isolated trees. On a stand basis, however, the combination of incident radiation and ground coverage declined with lower stand densities. While stand leaf area index declined from around 6 to 1 with increased spacing, individual tree leaf areas rose from around 50 m2 in block plantings to 150 m2 in isolated trees. The proportion of above-ground biomass found in stems declined with increasing spacing as the mass in foliage and branches increased. Stems accounted for 65% of above-ground biomass in block-planted trees but only 35% in isolated trees. The contributions of leaves and branches correspondingly rose from 19% to 35% and from 16% to 29%, respectively. Changes in biomass distribution were accompanied by increasing branch number, branch thickness, flatter branch angles and the longer retention of lower branches with greater spacing. These changes have implications for the merchantability of the timber. The efficiency of above-ground radiation conversion was constant at 0.67 g MJ-1 irrespective of spacing. We estimated that foliar maintenance respiration (Rm) accounted for about 90% of above-ground Rm. On a stand basis Rm costs block plantings 23.90 t DM ha-1 year-1 (50% annual above-ground photosynthetic production) compared with 6.22 t DM ha-1 year-1 (40% annual above-ground photosynthetic production) in stands of isolated trees. 相似文献