共查询到20条相似文献,搜索用时 31 毫秒
1.
Summary Carbon dioxide exchange rates in excised 2-year-old shoot sections of five common moss species were measured by infrared gas analysis in mosses collected from different stands of mature vegetation near Fairbanks, Alaska. The maximum rates of net photosynthesis ranged from 2.65 mg CO2 g-1h-1 in Polytrichum commune Hedw. to 0.25 in Spagnum nemoreum Scop. Intermediate values were found in Sphagnum subsecundum Nees., Hylocomium splendens (Hedw.) B.S.G., and Pleurozium schreberi (Brid.) Mitt. Dark respiration rates at 15°C ranged from 0.24 mg CO2 g-1h-1 in S. subsecundum to 0.57 mg CO2 g-1h-1 in H. splendens. The dark respiration rates were found to increase in periods of growth or restoration of tissue (i.e., after desiccation). There was a strong decrease in the rates of net photosynthesis during the winter and after long periods of desiccation.Due to increasing amounts of young, photosynthetically active tissue there was a gradual increase in the rates of net photosynthesis during the season to maximum values in late August. As an apparent result of constant respiration rates and increasing gross photosynthetic rates, the optimum temperature for photosynthesis at light saturation and field capacity increased during the season in all species except Polytrichum, with a corresponding drop in the compensation light intensities. Sphagnum subsecundum seemed to be the most light-dependent species.Leaf water content was found to be an important limiting factor for photosynthesis in the field. A comparison between sites showed that the maximum rates of net photosynthesis increased with increasing nutrient content in the soil but at the permafrostfree sites photosynthesis was inhibited by frequent moisture stress. 相似文献
2.
The effects of salinity, light intensity and sediment on Gracilaria tenuistipitata C.F. Chang & B.M. Xia on growth, pigments, agar production, and net photosynthesis rate were examined in the laboratory under varying conditions of salinity (0, 25 and 33 psu), light intensity (150, 400, 700 and 1000 µmol photons m?2 s?1) and sediment (0, 0.67 and 2.28 mg L?1). These conditions simulated field conditions, to gain some understanding of the best conditions for cultivation of G. tenuistipitata. The highest growth rate was at 25 psu, 700 µmol photons m?2 s?1 with no sediments, that provided a 6.7% increase in weight gain. The highest agar production (24.8 ± 3.0 %DW) was at 25 psu, 150–400 µmol photons m?2 s?1 and no sediment. The highest pigment contents were phycoerythrin (0.8 ± 0.5 mg g?1FW) and phycocyanin (0.34 ± 0.05 mg g?1 FW) produced in low light conditions, at 150 µmol photons m?2 s?1. The highest photosynthesis rate was 161.3 ± 32.7 mg O2 g?1 DW h?1 in 25 psu, 400 µmol photons m?2 s?1 without sediment in the short period of cultivation, (3 days) and 60.3 ± 6.7 mg O2 g?1 DW h?1 in 25 psu, 700 µmol photons m?2 s?1 without sediment in the long period of cultivation (20 days). The results indicated that salinity was the most crucial factor affecting G. tenuistipitata growth and production. This would help to promote the cultivation of Gracilaria cultivation back into the lagoon using these now determined baseline conditions. Extrapolation of the results from the laboratory study to field conditions indicated that it was possible to obtain two crops of Gracilaria a year in the lagoon, with good yields of agar, from mid‐January to the end of April (dry season), and from mid‐July to the end of September (first rainy season) when provided sediment was restricted. 相似文献
3.
Summary Laboratory measurements on the CO2 exchange and data on actual field temperatures and irradiation were used to compute (by simulation) an annual carbon budget for the Empetrum nigrum/Sphagnum fuscum community. A net fixation of 160 g CO2 m-2 was predicted for the growing season. This was already the figure at the beginning of July, after which no significant change occured. For one day in June (when CO2 exchange was most intense), estimates of c. 10 and 7 g CO2 m-2 for total photosynthesis and total respiration were derived, respectively. The annual net result is in accordance with earlier estimates of production and carbon accumulation in similar ecosystems, thereby partly validating the model. Radical changes in the annual peat production are to be expected, if the mean temperature changes even one or two Celsius degrees; an increase of 2° C resulted in an equilibrium in the carbon flow between bog and atmosphere (i.e. no net change in the carbon content of the bog). 相似文献
4.
Edwin Van Der Heijden Steven K. Verbeek Pieter J. C. Kuiper 《Global Change Biology》2000,6(2):201-212
Sphagnum bogs play an important role when considering the impacts of global change on global carbon and nitrogen cycles. Sphagnum recurvum P. Beauv. var. mucronatum (Russ.) was grown at 360 (ambient) and 700 μL L?1 (elevated) atmospheric [CO2] in combination with different nitrogen deposition rates (6, 15, 23 g N m?2 y?1), in a short‐ and long‐term growth chamber experiment. After 6 months, elevated atmospheric [CO2] in combination with the lowest nitrogen deposition rate, increased plant dry mass by 17%. In combination with a high nitrogen deposition rate, biomass production was not significantly stimulated. At the start of the experiment, photosynthesis was stimulated by elevated atmospheric [CO2], but it was downregulated to control levels after three days of exposure. Elevated [CO2] substantially reduced dark respiration, which resulted in a continuous increase in soluble sugar content in capitula. Differences in growth response among different nitrogen and CO2 treatments could not be related to measured carbon exchange rates, which was mainly due to interference of microbial respiration. Doubling atmospheric [CO2] reduced total nitrogen content in capitula but not in stems at all nitrogen deposition rates. Reduction in total nitrogen content coincided with a decrease in amino acids, but soluble protein levels remained unaffected. Thus, elevated [CO2] induced a substantial shift in the partitioning of nitrogen compounds in capitula. Soluble sugar concentration was negatively correlated with total nitrogen content, which implies that the reduction in amino acid content in capitula, exposed to elevated [CO2], might be caused by the accumulation of soluble sugars. Growth was not stimulated by increased nitrogen deposition. High nitrogen deposition, resulting in a capitulum nitrogen content in excess of 15 mg g?1 dw, was detrimental to photosynthesis, reduced water content and induced necrosis. We propose a capitulum nitrogen content of 15 mg g?1 dw as a possible bioindicator for the detection of nitrogen pollution stress in oligo‐mesotrophic peat bog ecosystems. At the lowest nitrogen deposition level, nitrogen recovery was higher than 100%, which indicates substantial dry deposition and/or gaseous nitrogen fixation by bacteria, associated with Sphagnum. Increasing nitrogen deposition rates decreased nitrogen recovery percentages, which indicates reduced efficiency of nitrogen fixation. 相似文献
5.
Seasonal variation in energy fluxes and carbon dioxide exchange for a broad-leaved semi-arid savanna (Mopane woodland) in Southern Africa 总被引:2,自引:0,他引:2
We studied the seasonal variation in carbon dioxide, water vapour and energy fluxes in a broad‐leafed semi‐arid savanna in Southern Africa using the eddy covariance technique. The open woodland studied consisted of an overstorey dominated by Colophospermum mopane with a sparse understorey of grasses and herbs. Measurements presented here cover a 19‐month period from the end of the rainy season in March 1999 to the end of the dry season September 2000. During the wet season, sensible and latent heat fluxes showed a linear dependence on incoming solar radiation (I) with a Bowen ratio (β) typically just below unity. Although β was typically around 1 at low incoming solar radiation (150 W m?2) during the dry season, it increased dramatically with I, typically being as high as 4 or 5 around solar noon. Thus, under these water‐limited conditions, almost all available energy was dissipated as sensible, rather than latent heat. Marked spikes of CO2 release occurred at the onset of the rainfall season after isolated rainfall events and respiration dominated the balance well into the rainfall season. During this time, the ecosystem was a constant source of CO2 with an average flux of 3–5 μmol m?2 s?1 to the atmosphere during both day and night. But later in the wet season, for example, in March 2000 under optimal soil moisture conditions, with maximum leaf canopy development (leaf area index 0.9–1.3), the peak ecosystem CO2 influx was as much as 10 μmol m?2 s?1. The net ecosystem maximum photosynthesis at this time was estimated at 14 μmol m?2 s?1, with the woodland ecosystem a significant sink for CO2. During the dry season, just before leaf fall in August, maximum day‐ and night‐time net ecosystem fluxes were typically ?3 μmol m?2 s?1 and 1–2 μmol m?2 s?1, respectively, with the ecosystem still being a marginal sink. Over the course of 12 months (March 1999–March 2000), the woodland was more or less carbon neutral, with a net uptake estimated at only about 1 mol C m?2 yr?1. The annual net photosynthesis (gross primary production) was estimated at 32.2 mol m?2 yr?1. 相似文献
6.
Marja Maljanen Pertti J. Martikainen Jari Walden Jouko Silvola 《Global Change Biology》2001,7(6):679-692
The CO2 dynamics were measured in an organic soil in eastern Finland during the growing season and wintertime, and the annual CO2 balance was calculated for plots where barley or grass was grown. During the summer, the CO2 dynamics were measured by transparent and opaque chambers using a portable infrared gas analyser for the CO2 analyses. During the winter, the CO2 release was measured by opaque chambers analysing the samples in the laboratory with a gas chromatograph. Statistical response functions for CO2 dynamics were constructed to evaluate the annual CO2 exchange from the climatic data. The net CO2 exchange was calculated for every hour in the snow‐free season. The carbon balance varied extensively depending on the weather conditions, and type and phenology of vegetation. During the growing season, the grassland was a net source while the barley field was a net sink for CO2. However, both soils were net sources for CO2 when autumn, winter and spring were included also. The annual CO2 emissions from the grassland and barley soil were 750 g CO2‐C m?2 and 400 g CO2‐C m?2, respectively. The carbon accumulated in root and shoot biomass during the growing season was 330 g m?2 for grass and 520 g m?2 for barley. The C in the aboveground plant biomass ranged from 43 to 47% of the carbon fixed in photosynthesis (PG) and the proportion of C in the root biomass was 10% of the carbon fixed in photosynthesis. The bare soils had 10–60% higher net CO2 emission than the vegetated soils. These results indicate that the carbon balance of organic soils is affected by the characteristics of the prevailing plant cover. The dry summer of 1997 may have limited the growth of grass in the late summer thus reducing photosynthesis, which could be one reason for the high CO2 release from this grass field. 相似文献
7.
Summary The CO2 exchange of the Empetrum nigrum-Sphagnum fuscum community of a raised bog was studied in the laboratory at different temperature (from 5 to 30° C) and irradiance (up to 128 W m-2) combinations during one growing season. The total CO2 exchange was divided into three components, namely those due to Empetrum nigrum, Sphagnum fuscum, and peat, respectively. At the optimum temperature (10 to 15° C) the maximum net CO2 exchange of Empetrum nigrum was c. 200 and that of Sphagnum fuscum c. 250 mg CO2 m-2h-1. The total respiration in peat increased exponentially from 50 to 350 mg CO2 m-2h-1 with increasing temperature from 5 to 30° C. About 40% of the CO2 fixed by the community in optimal temperature and irradiation conditions was released immediately. 相似文献
8.
P. M. Anthoni A. Knohl C. Rebmann A. Freibauer M. Mund W. Ziegler O. Kolle E.-D. Schulze 《Global Change Biology》2004,10(12):2005-2019
Eddy covariance was used to measure the net CO2 exchange (NEE) over ecosystems differing in land use (forest and agriculture) in Thuringia, Germany. Measurements were carried out at a managed, even‐aged European beech stand (Fagus sylvatica, 70–150 years old), an unmanaged, uneven‐aged mixed beech stand in a late stage of development (F. sylvatica, Fraxinus excelsior, Acer pseudoplantanus, and other hardwood trees, 0–250 years old), a managed young Norway spruce stand (Picea abies, 50 years old), and an agricultural field growing winter wheat in 2001, and potato in 2002. Large contrasts were found in NEE rates between the land uses of the ecosystems. The managed and unmanaged beech sites had very similar net CO2 uptake rates (~?480 to ?500 g C m?2 yr?1). Main differences in seasonal NEE patterns between the beech sites were because of a later leaf emergence and higher maximum leaf area index at the unmanaged beech site, probably as a result of the species mix at the site. In contrast, the spruce stand had a higher CO2 uptake in spring but substantially lower net CO2 uptake in summer than the beech stands. This resulted in a near neutral annual NEE (?4 g C m?2 yr?1), mainly attributable to an ecosystem respiration rate almost twice as high as that of the beech stands, despite slightly lower temperatures, because of the higher elevation. Crops in the agricultural field had high CO2 uptake rates, but growing season length was short compared with the forest ecosystems. Therefore, the agricultural land had low‐to‐moderate annual net CO2 uptake (?34 to ?193 g C m?2), but with annual harvest taken into account it will be a source of CO2 (+97 to +386 g C m?2). The annually changing patchwork of crops will have strong consequences on the regions' seasonal and annual carbon exchange. Thus, not only land use, but also land‐use history and site‐specific management decisions affect the large‐scale carbon balance. 相似文献
9.
The relationships of monoterpene emission with temperature, light, photosynthesis and stomatal conductance (gs) were studied in Quercus ilex L. trees throughout the four annual seasons under field conditions. The highest monoterpene emission was measured in spring and summer (midday average of 11 μg [g DW]?1 h?1), whereas the lowest rates were found in autumn and winter (midday averages of 0.51 and 0.23 μg [g DW]?1 h?1, respectively). In spring and summer, limonene was the monoterpene emitted at highest rate (midday averages of 5.27–6.69 μg [g DW]?1 h?1), whereas α-pinene was emitted the most in autumn and winter (midday averages of 0.31 μg [g DW]?1 h?1). The monoterpenes limonene, α-pinene and β-pinene represented about 75–95% of total detected monoterpenes. The total monoterpene emission rates represented about 0.04% of carbon fixed in autumn, 0.17% in winter, 0.84–2.51% in spring and 1.22–5.13% in summer. Significant correlations of total monoterpene emission with temperature were found when considering either summer emission or the emission over the entire year, whereas significant correlations with net photosynthetic rates were only found when considering summer season. Among individual terpenes, the most volatile, α-pinene and β-pinene, were more correlated with temperature than with net photosynthetic rates whereas the less volatile limonene was more correlated with net photosynthetic rate. Thus, under field conditions it seems that dependency of monoterpene emission on photosynthetic rate or temperature is partly related with volatility of the compounds. Influences of seasonality, temperature, photosynthetic rates and volatility should be considered in inventories and models of emission rates in Mediterranean ecosystems. 相似文献
10.
Summary The gas exchange and water relations of two Sonoran Desert plants was measured throughout a 12-month period. Seasonal photosynthesis patterns of both plants followed the seasonal variation in plant water potential. Ambrosia deltoidea, a drought-deciduous shrub, is mainly winter-spring active since maximum photosynthesis rates of 38 mg CO2 dm-2 h-1 were measured at this time. This plant is characterized by marked seasonal variations in plant water potential, and was deciduous for approximately 120 days when plant water potential was below-50 bars. Olneya tesota, a non-riparian microphyllous tree, is evergreen and photosynthetically active throughout the entire year, although demonstrating maximum photosynthesis rates of 12 mg CO2 dm-2 h-1 in spring and summer. The deep-rooted tree species maintains a favorable year-round water balance since minimum plant water potentials were seldom below-33 bars. The two species maintain a relatively high water use efficiency throughout the year, despite the high evaporative gradient characteristic of the Sonoran Desert.The leaves are the major site for carbon assimilation, contributing 87 and 81% of the annual carbon gain for the shrub and tree species, respectively. Above-ground gross primary production throughout the 12-month period was estimated solely from the leaf 14CO2 assimilation studies. This production estimate was compared to above-ground net primary production determined by the harvest method. For both plant species gross production was interpreted to exceed net production by nearly a three-fold difference. On a per plant basis gross production was estimated to be 1.14 and 7.42 kg dry wt plant-1 yr-1 for A. deltoidea and O. tesota. The large difference between net and gross production is probably related to year-round utilization of carbon.This research was supported by National Science Foundation Grant BMS 74-02671-A04 through the U.S./I.B.P. Desert Biome at Utah State University 相似文献
11.
Methane emissions from wetlands and their relationship with vascular plants: an Arctic example 总被引:5,自引:0,他引:5
This paper investigates the relationship between vascular plant production and CH4 emissions from an arctic wet tundra ecosystem in north‐east Greenland. Light intensity was manipulated by shading during three consecutive growing seasons (1998–2000). The shading treatment resulted in lower carbon cycling in the ecosystem as mean seasonal net ecosystem exchange (NEE) decreased from ?336 to ?196 mg CO2 m?2 h?1 and from ?476 to ?212 mg CO2 m?2 h?1 in 1999 and 2000, respectively, and total ecosystem respiration decreased from 125 to 94 mg CO2 m?2 h?1 in 1999 and from 409 to 306 mg CO2 m?2 h?1 in 2000. Seasonal mean CH4 emissions in controls and shaded plots were, respectively, 6.5 and 4.5 mg CH4 m?2 h?1 in 1999 and 8.3 and 6.2 mg CH4 m?2 h?1 in 2000. We found that CH4 emission was sensitive to NEE and carbon turnover, and it is reasonable to assume that the correlation was due to a combined effect of vegetative CH4 transport and substrate quality coupled to vascular plant production. Total above‐ground biomass was correlated to mean seasonal CH4 emission, but separation into species showed that plant‐mediated CH4 transport was highly species dependent. Potential CH4 production peaked at the same depth as maximum root density (5–15 cm) and treatment differences further suggest that substrate quality was negatively affected by decreased NEE in the shaded plots. The concentration of dissolved CH4 decreased in the control plots as the growing season progressed while it was relatively stable in the shaded plots. This suggests that a progressively better developed root system in the controls increased the capacity to transport CH4 from the soil to the atmosphere. In conclusion, vascular plant photosynthetic rate and subsequent allocation of recently fixed carbon to below‐ground structures seemed to influence both vegetative CH4 transport and substrate quality. 相似文献
12.
The effects on photosynthesis of CO2 and desiccation in Porphyra haitanensis were investigated to establish the effects of increased atmospheric CO2 on this alga during emersion at low tides. With enhanced desiccation, net photosynthesis, dark respiration, photosynthetic efficiency, apparent carboxylating efficiency and light saturation point decreased, while the light compensation point and CO2 compensation point increased. Emersed net photosynthesis was not saturated by the present atmospheric CO2 level (about 350?ml?m?3), and doubling the CO2 concentration (700?ml?m?3) increased photosynthesis by between 31% and 89% at moderate levels of desiccation. The relative enhancement of emersed net photosynthesis at 700?ml?m?3 CO2 was greater at higher temperatures and higher levels of desiccation. The photosynthetic production of Porphyra haitanensis may benefit from increasing atmospheric CO2 concentration during emersion. 相似文献
13.
The effects of varying nitrogen supply on canopy leaf area, response of leaf net photosynthesis (An) to quantum flux density (Q), and fruit yields of kiwifruit vines (Actinidia deliciosa var. deliciosa) were examined in a two-year field experiment. Vines were grown with 0, 250 or 750 kg N ha?1 year?1. The responses to nitrogen supply were compared with responses to shade, to examine the impact of reduced carbon assimilation on canopy leaf area and fruit yields. Nitrogen supply did not affect significantly any of the measured variables during the first season of the experiment. In the second season, canopy leaf area was reduced significantly where nitrogen supply was limited. The quantum efficiency of photosynthesis (φq) increased from 0. 03 mol CO2 mol?1 Q soon after leaf emergence to more than 0. 05 mol CO2 mol?1 Q during the middle of the growing season. The quantum saturated rate of An (Asat) also increased during the season, from 7–10 μmol CO2 m?2 s?1 soon after leaf emergence, to 15–20 (μmol CO2 m?2 s?1 during the middle of the growing season. φq and Asat increased significantly with nitrogen supply at all measurement times during the second season. For vines with high nitrogen, fruit yields in both seasons were similar, averaging 3. 05 kg m?2. Fruit yields in the second season were reduced significantly where nitrogen supply was limited, due to reduced fruit numbers. The relative effects of reduced leaf area and reduced leaf photosynthesis for carbon assimilation by nitrogen deficient vines were examined using a mathematical model of canopy photosynthesis for kiwifruit vines. Simulations of canopy photosynthesis indicated that effects on leaf area and on leaf photosynthesis were of similar importance in the overall effects of nitrogen deficiency on carbon assimilation. The effects of nitrogen supply on fruit numbers (i. e. flower development) preceded the measured effects on carbon assimilation, indicating that the nitrogen supply affected carbon partitioning to reserves in the first season. 相似文献
14.
Studies of Elodea nuttallii grown under photorespiratory conditions. I. Photosynthetic characteristics 总被引:1,自引:1,他引:0
Abstract. The photosynthetic characteristics of Elodea nuttallii grown in wastewater in continuous flow reactors in a greenhouse were investigated. The diurnal changes in dissolved inorganic carbon (DIC), dissolved oxygen (DO) and pH were monitored. Photosynthesis removed both CO2(aq) and HCO3? from the reactors. A stoichiometry of 1.19:1 was observed between HCO3? removal during photosynthesis and OH? production during photosynthesis, consistent with theories regarding direct bicarbonate utilization. In laboratory experiments, the light compensation points (гPPFD) were similar (31–35μmol m?2 s?1) to reported values for other macrophytes; however, the light saturation level was high (1100μmol m?2 s?1) and similar to values reported for aerial portions Of heterophyllous macrophytes. The kinetics of photosynthetic oxygen evolution (Km (CO2) = 96mmol m?3; Vmax= 133mmol g?1 Chl h?1) and the CO2 compensation point (г= 44cm3 m?3) suggested an adaptive, low photorespiratory state in response to low carbon concentrations. Photosynthetic Vmax values were slightly, but significantly higher (P 0.001) at pH 8.0 compared to pH 4.5. While CO2 utilization at pH 8 could account for most of the observed phototsynthetic rates, an HCO3? component was present, suggesting two separate transport systems for HCO3? and CO2(aq) in E. nuttallii. The activity of RUBISCO (160.3 mmol g?1 Chl h?1 was one of the highest reported values for aquatic macrophytes. Compared to RUBISCO, we observed lower activities of the β-carboxylating enzymes phopho enolpyruvate carboyxlase (PEPcase), 24.1 mmol g?1 Chl h?1; phosphor enol pyruvate carboxykinase (PEPCKase), 14 mmol g?1 Chl h?1. This suggests that the potential light-independent fixation of carbon in E. nuttallii was much less than RUBISCO-dependent fixation. The RUBISCO/PEPcase ratio was 6.6, indicating that E. nuttallii was similar to Myriophyllum sp. in possessing a physiological adaptation to low CO2 levels which is hypothesized to include carbonic anhydrase (CA) and an active transport system for HCO3?. CA levels were surprisingly low in E. nuttallii (14.2 EUmg Chl?). 相似文献
15.
Direct and acclimatory responses of stomatal conductance to elevated carbon dioxide in four herbaceous crop species in the field 总被引:3,自引:0,他引:3
James A. Bunce 《Global Change Biology》2001,7(3):323-331
In order to separate the net effect of growth at elevated [CO2] on stomatal conductance (gs) into direct and acclimatory responses, mid‐day values of gs were measured for plants grown in field plots in open‐topped chambers at the current ambient [CO2], which averaged 350 μmol mol?1 in the daytime, and at ambient + 350 μmol mol?1[CO2] for winter wheat, winter barley, potato and sorghum. The acclimatory response was determined by comparing gs measured at 700 μmol mol?1[CO2] for plants grown at the two [CO2]. The direct effect of increasing [CO2] from 350 to 700 μmol mol?1 was determined for plants grown at the lower concentration. Photosynthetic rates were measured concurrently with gs. For all species, growth at the higher [CO2] significantly reduced gs measured at 700 μmol mol?1[CO2]. The reduction in gs caused by growth at the higher [CO2] was larger for all species on days with low leaf to air water vapour pressure difference for a given temperature, which coincided with highest conductances and also the smallest direct effects of increased [CO2] on conductance. For barley, there was no other evidence for stomatal acclimation, despite consistent down‐regulation of photosynthetic rate in plants grown at the higher [CO2]. In wheat and potato, in addition to the vapour pressure difference interaction, the magnitude of stomatal acclimation varied directly in proportion to the magnitude of down‐regulation of photosynthetic rate through the season. In sorghum, gs consistently exhibited acclimation, but there was no down‐regulation of photosynthetic rate. In none of the species except barley was the direct effect the larger component of the net reduction in gs when averaged over measurement dates. The net effect of growth at elevated [CO2] on mid‐day gs resulted from unique combinations of direct and acclimatory responses in the various species. 相似文献
16.
Biomass, akinete numbers, net photosynthesis, and respiration of Pithophora oedogonia were monitored over two growing seasons in shallow Surrey Lake, Indiana. Low rates of photosynthesis occurred from late fall to early spring and increased to maximum levels in late spring to summer (29–39 mgO2·g?1 dry wt·h?1). Areal biomass increased following the rise in photosynthesis and peaked in autumn (163–206g dry wt·m?2). Photosynthetic rates were directly correlated with temperature, nitrogen, and phosphorus over the entire annual cycle and during the growing season. Differences in photosynthetic activity and biomass between the two growing seasons (1980 and 1981) were apparently related to higher, early spring temperatures and higher levels of NO3-N and PO4-P in 1981. Laboratory investigations of temperature and light effects on Pithophora photosynthesis and respiration indicated that these processes were severely inhibited below 15°C. The highest Pmax value occurred at 35°C (0.602 μmol O2·mg?1 chl a·min?1). Rates of dark respiration did not increase above 25°C thus contributing to a favorable balance of photosynthetic production to respiratory utilization at high temperatures. Light was most efficiently utilized at 15°C as indicated by minimum values of Ik(47 μE·m?2·s?1) and Ic (6 μE·m?2·s?1). Comparison of P. oedogonia and Cladophora glomerata indicated that the former was more tolerant of temperatures above 30°C. Pithophora's tolerance of high temperature and efficient use of low light intensity appear to be adaptive to conditions found within the dense, floating algal mats and the shallow littoral areas inhabited by this filamentous alga. 相似文献
17.
Growth, photosynthesis, dark respiration and pigment contents were monitored in adult sporophytes of the Antarctic brown alga Desmarestia menziesii J. Agardh grown under fluctuating Antarctic daylength conditions. Growth rates were closely coupled to daylength variations with values varying from 0.05% d?1 in winter condition (July-August) to 0.5% d?1 in early summer (December). Photosynthetic pigments had maximum values of 1.8 mg g?1 FW (chlorophyll a), 0.4 mg g?1 FW (chlorophyll c) and 0.9 mg g?1 FW (fucoxanthin) in summer. These changes were also closely related to individual size and biomass of the plants. Net photosynthesis (Pmax), on a fresh weight basis, showed a clear seasonal pattern with highest rates of 25μmol O2 g?1 FW h?1 in October and minima close to 9μmol O2 g?1 FW h?1 in April. Dark respiration was high in spring (13μmol O2 g?1 FW h?1) approximately coinciding with growth peaks. Likewise, photosynthetic efficiency (α) and the initial saturating light point of photosynthesis (lk) increased significantly in spring [1.3 μimol O2 g?1 FW h?1 (μmol m?2 s?1)?1 and 26μmol photons m?2 s?1, respectively]. In the case of α, no significant differences between fresh weight and Chl a based rates were found. The results of the present study are the first that demonstrate seasonality of physiological parameters in D. menziesii sporophytes and confirm also that phenology and physiology of macroalgae can be simulated in the laboratory. On the other hand this study adds new elements to the explanation of the life strategy of D. menziesii, in particular that algal growth and photosynthesis occur under a programmed seasonal pattern. 相似文献
18.
Philipp Egli Stefan Maurer Dieter Spinnler Werner Landolt Madeleine S. Günthardt‐Goerg Christian Krner 《Oikos》2001,92(2):279-290
Young beech (Fagus sylvatica) and spruce (Picea abies) trees from different provenances or genotypes were grown in competition in large model ecosystems and were exposed to two concentrations of atmospheric CO2 (370 vs 570 μmol mol?1), two levels of wet nitrogen deposition (7 vs 70 kg N ha?1 yr?1), and two native forest soils (acidic vs calcareous) for four years in open‐top chambers. The 2×2×2 factorial experimental design was fully replicated (n=4) with each CO2×N combination applied to each soil type. Exposure to atmospheric CO2 enrichment stimulated daytime net ecosystem CO2 flux (NEC) as measured during sunny days in the middle of the third growing season. Nevertheless, we observed substantial down‐regulation of NEC, with larger adjustments on acidic than on calcareous soil. NEC adjustment was associated with slightly reduced leaf area index (LAI) on the acidic soil (no response on calcareous soil), enhanced soil CO2 efflux from both substrate types, and, most importantly, with down‐regulation of CO2 uptake at the leaf scale. Downward adjustment of light‐saturated single‐leaf photosynthesis (A) and of Rubisco was more pronounced in beech than in spruce and these species‐specific differences increased over time. By year four, A adjustment (except in one specific treatment combination in each species) had become complete in beech but had disappeared in spruce. At no time did we observe a genotype or provenance effect on the downward adjustment of carbon fluxes, and nitrogen deposition rate generally had little effect as well. Overall, our results suggest that tree species and soil quality will have profound effects on ecosystem CO2 fluxes under continued atmospheric CO2 enrichment. 相似文献
19.
SAIRAH Y. MALKIN SERGHEI A. BOCANIOV RALPH E. SMITH STEPHANIE J. GUILDFORD ROBERT E. HECKY 《Freshwater Biology》2010,55(12):2468-2483
1. Despite the recognition of its importance, benthic primary production is seldom reported, especially for large lakes. We measured in situ benthic net primary production by monitoring flux in dissolved inorganic carbon (DIC) concentration in benthic incubation chambers, based on continuous measurements of CO2(aq) flux, alkalinity, and the temperature‐dependent dissociation constants of carbonic acid (K1 and K2). This methodology has the advantages of monitoring net primary production directly as change in carbon, maintaining continuous water recirculation, and having sufficient precision to detect change in DIC over short (i.e. 15 min) incubations, even in alkaline waters. 2. Benthic primary production on Cladophora‐dominated rocky substrata in western Lake Ontario was measured biweekly. Maximum biomass‐specific net photosynthetic rates were highest in the spring (2.39 mgC g Dry Mass?1 h?1), decreased to negative rates by early summer (?0.76 mgC g DM?1 h?1), and exhibited a regrowth in late summer (1.98 mgC g DM?1 h?1). 3. A Cladophora growth model (CGM), previously validated to predict Cladophora biomass accrual in Lake Ontario, successfully simulated the seasonality and magnitude of biomass‐specific primary production during the first cohort of Cladophora growth. Averaged over this growing season (May–Aug), mean areal net benthic production at the estimated depth of peak biomass (2 m) was 405 mg C m?2 d?1. 4. We measured planktonic primary production in proximity to the benthic study and constructed a depth‐resolved model of planktonic production. Using the CGM, benthic primary production was compared with planktonic primary production for the period May–Aug. Net benthic production from the shoreline to the 12 m contour (1–2 km offshore) equalled planktonic production. Closer to shore, benthic primary production exceeded planktonic primary production. Failure to account for benthic primary production, at least during abundant Cladophora growth, will lead to large underestimates in carbon and nutrient flows in the nearshore zone of this Great Lake. 相似文献
20.
Fluxes of carbon, water and energy over Brazilian cerrado: an analysis using eddy covariance and stable isotopes 总被引:4,自引:0,他引:4
A. C. MIRANDA H. S. MIRANDA J. LLOYD J. GRACE R. J. FRANCEY J. A. MCINTYRE P. MEIR P. RIGGAN R. LOCKWOOD J. BRASS 《Plant, cell & environment》1997,20(3):315-328
We present the energy and mass balance of cerrado sensu stricto (a Brazilian form of savanna), in which a mixture of shrubs, trees and grasses forms a vegetation with a leaf area index of 1·0 in the wet season and 0·4 in the dry season. In the wet season the available energy was equally dissipated between sensible heat and evaporation, but in the dry season at high irradiance the sensible heat greatly exceeded evaporation. Ecosystem surface conductance gs in the wet season rose abruptly to 0·3 mol m?2 s?1 and fell gradually as the day progressed. Much of the total variation in gs was associated with variation in the leaf-to-air vapour pressure deficit of water and the solar irradiance. In the dry season the maximal gs values were only 0·1 mol m?2 s?1. Maximal net ecosystem fluxes of CO2 in the wet and dry season were –10 and –15 μmol CO2 m?2 s?1, respectively (sign convention: negative denotes fluxes from atmosphere to vegetation). The canopy was well coupled to the atmosphere, and there was rarely a significant build-up of respiratory CO2 during the night. For observations in the wet season, the vegetation was a carbon dioxide sink, of maximal strength 0·15 mol m?2 d?1. However, it was a source of carbon dioxide for a brief period at the height of the dry season. Leaf carbon isotopic composition showed all the grasses except for one species to be C4, and all the palms and woody plants to be C3. The CO2 coming from the soil had an isotopic composition that suggested 40% of it was of C4 origin. 相似文献