共查询到20条相似文献,搜索用时 31 毫秒
1.
Mitsuru Hirota Pengcheng Zhang Song Gu Haihua Shen Takeo Kuriyama Yingnian Li Yanhong Tang 《Journal of plant research》2010,123(4):531-541
Characterizing the spatial variation in the CO2 flux at both large and small scales is essential for precise estimation of an ecosystem’s CO2 sink strength. However, little is known about small-scale CO2 flux variations in an ecosystem. We explored these variations in a Kobresia meadow ecosystem on the Qinghai-Tibetan plateau in relation to spatial variability in species composition and biomass. We
established 14 points and measured net ecosystem production (NEP), gross primary production (GPP), and ecosystem respiration
(Re) in relation to vegetation biomass, species richness, and environmental variables at each point, using an automated chamber
system during the 2005 growing season. Mean light-saturated NEP and GPP were 30.3 and 40.5 μmol CO2 m−2 s−1 [coefficient of variation (CV), 42.7 and 29.4], respectively. Mean Re at 20°C soil temperature, Re20, was −10.9 μmol CO2 m−2 s−1 (CV, 27.3). Re20 was positively correlated with vegetation biomass. GPPmax was positively correlated with species richness, but 2 of the 14 points were outliers. Vegetation biomass was the main determinant
of spatial variation of Re, whereas species richness mainly affected that of GPP, probably reflecting the complexity of canopy
structure and light partitioning in this small grassland patch. 相似文献
2.
Taku M. Saitoh Ichiro Tamagawa Hiroyuki Muraoka Na-Yeon M. Lee Yuichiro Yashiro Hiroshi Koizumi 《Journal of plant research》2010,123(4):473-483
We investigated carbon dioxide (CO2) exchange and its environmental response during two years with contrasting climate (2006 and 2007) in a cool-temperate mixed
evergreen coniferous forest dominated by Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa). The study, which was conducted in a mountainous region of central Japan, used the eddy-covariance technique. Our results
(crosschecked using the common u
* approach and van Gorsel’s alternative approach) showed that annual gross primary production (GPP) and ecosystem respiration
(RE) were at least 6% higher in the dry year than in the wet year, whereas net ecosystem exchange (NEE) was similar in both
years. Without soil water stress, strong light stress or seasonality of plant area index during most of the study period,
the forest had high metabolic activity. GPP and RE differed greatly between the two years, especially in spring (April–May)
and summer (July–September), respectively. The spring GPP difference (>20%) was influenced by different winter air temperatures
and snow melt timing, which controlled photosynthetic capacity in spring, and by different spring light intensities. The annual
NEE differed depending on the evaluation method used, but the mean 2-year NEE estimated by the u
* threshold approach [−3.39 ± 0.11 (SD) MgC ha−1 year−1] appears more reasonable in comparison with results from other forests. 相似文献
3.
Deepa Dhital Yuichiro Yashiro Toshiyuki Ohtsuka Hibiki Noda Yoko Shizu Hiroshi Koizumi 《Journal of plant research》2010,123(4):519-530
The ecosystem carbon budget was estimated in a Japanese Zoysia japonica grassland. The green biomass started to grow in May and peaked from mid-July to September. Seasonal variations in soil CO2 flux and root respiration were mediated by changes in soil temperature. Annual soil CO2 flux was 1,121.4 and 1,213.6 g C m−2 and root respiration was 471.0 and 544.3 g C m−2 in 2007 and 2008, respectively. The root respiration contribution to soil CO2 flux ranged from 33% to 71%. During the growing season, net primary production (NPP) was 747.5 and 770.1 g C m−2 in 2007 and 2008, respectively. The biomass removed by livestock grazing (GL) was 122.1 and 102.7 g C m−2, and the livestock returned 28.2 and 25.6 g C m−2 as fecal input (FI) in 2007 and 2008, respectively. The decomposition of FI (DL, the dry weight loss due to decomposition)
was very low, 1.5 and 1.4 g C m−2, in 2007 and 2008. Based on the values of annual NPP, soil CO2 flux, root respiration, GL, FI, and DL, the estimated carbon budget of the grassland was 1.7 and 22.3 g C m−2 in 2007 and 2008, respectively. Thus, the carbon budget of this Z. japonica grassland ecosystem remained in equilibrium with the atmosphere under current grazing conditions over the 2 years of the
study. 相似文献
4.
Erica A. H. Smithwick Daniel M. Kashian Michael G. Ryan Monica G. Turner 《Ecosystems》2009,12(5):792-806
Long-term, landscape patterns in inorganic nitrogen (N) availability and N stocks following infrequent, stand-replacing fire
are unknown but are important for interpreting the effect of disturbances on ecosystem function. Here, we present results
from a replicated chronosequence study in the Greater Yellowstone Ecosystem (Wyoming, USA) directed at measuring inorganic
N availability (ion-exchange resin bags) and ecosystem N pools among 77 lodgepole pine stands that varied in age and density.
Inorganic N availability ranged from 0.07 to 3.20 μN bag−1 d−1 and nitrate (NO3−) was, on average, 65% of total resin-sorbed N. Total ecosystem N stocks (live + detrital + soil) averaged 109.9 ± 3.0 g N m−2 (range = 63.7–185.8 g N m−2). Live N was 14%, detrital N was 29%, and soil N was 57% of total stocks. Soil NO3−, total ecosystem N, live N, and detrital N generally increased with stand age, but soil N stocks decreased. Models (AICc) to predict soil N availability and N stocks included soil P, soil Ca, bulk density, and pH in addition to age (adj R
2 ranged from 0.18 to 0.53) and density was included only for live N stocks. Patterns of N stocks and N availability with density
were strongest for young stands (<20 years) regenerating from extensive fire in 1988; for example, litterfall N stocks increased
with density (adj R
2 = 0.86, P < 0.001) but inorganic N availability declined (adj R
2 = 0.47, P < 0.003). Across the complex Yellowstone landscape, we conclude that N stocks and N availability are best predicted by a
combination of local soil characteristics in addition to factors that vary at landscape scales (stand density and age). Overall,
total ecosystem N stocks were recovered quickly following stand-replacing fire, suggesting that moderate increases in fire
frequency will not affect long-term landscape N storage in Greater Yellowstone.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Author contributions EAHS, MGT, and MGR conceived the study; DMK performed field research; EAHS and DMK oversaw laboratory analyses and analyzed
data; EAHS wrote the paper. 相似文献
5.
Sotiris Haliapas Traianos A. Yupsanis Thomas D. Syros George Kofidis Athanasios S. Economou 《Acta Physiologiae Plantarum》2008,30(6):807-815
Petunia × hybrida was grown under high (H), medium (M) and low (L) light intensity [photoperiod; 16 h d−1, photosynthetic photon flux density (PPFD); 360, 120 and 40 μmol m−2 s−1, respectively] as well as under end-of-day (EOD) red (R) and far-red (FR) light quality treatments [photoperiod; 14.5 h d−1, PPFD; 30 μmol m−2 s−1 EOD; 15 min, Control (C) light; without EOD light treatment]. Shoot growth, leaf anatomical and photosynthetic responses
as well as the responses of peroxidase (POD) isoforms and their specific activities following transition to flowering (1–6 weeks)
were evaluated. Flower bud formation of Petunia × hybrida was achieved at the end of the 4th week for H light treatment and on the end of the 6th week for FR light treatment. No flower
bud formation was noticed in the C and R light treatments. H and M light treatments induced lower chlorophyll (Chla, Chlb,
Chla+b) concentrations in comparison to L light. On the other hand R and FR light chlorophyll content were similar to C light.
Photosynthetic parameters [CO2 assimilation rate (A), transpiration rate (E) and stomatal conductance (g
s) values] were higher in the H light treated plants in comparison to M and L light treated plants. A, E and g
s values of R and FR light were similar to C light plants. Leaf anatomy revealed that total leaf thickness, thickness of the
contained tissues (epidermis, palisade and spongy parenchyma) and relative volume percentages of the leaf histological components
were differently affected within the light intensity and the light quality treatments. POD specific activities increased from
the 1st to the 6th week during transition to flowering. Native-PAGE analysis revealed the appearance of four anionic POD (A1–A4) isoforms in all light treatments. On the basis of the leaf anatomical, photosynthetic and plant morphological responses,
the production of high quality Petunia × hybrida plants with optimal flowering times could be achieved through the control of both light intensity and light quality. The
appearance of A1 and A2 anionic POD isoforms could be also used for successful scheduling under light treatments. 相似文献
6.
Headwater streams are key sites of nutrient and organic matter processing and retention, but little is known about temporal
variability in gross primary production (GPP) and ecosystem respiration (ER) rates as a result of the short duration of most
metabolism measurements in lotic ecosystems. We examined temporal variability and controls on ecosystem metabolism by measuring
daily rates continuously for 2 years in Walker Branch, a first-order deciduous forest stream. Four important scales of temporal
variability in ecosystem metabolism rates were identified: (1) seasonal, (2) day-to-day, (3) episodic (storm-related), and
(4) inter-annual. Seasonal patterns were largely controlled by the leaf phenology and productivity of the deciduous riparian
forest. Walker Branch was strongly net heterotrophic throughout the year with the exception of the open-canopy spring when
GPP and ER rates were co-equal. Day-to-day variability in weather conditions influenced light reaching the streambed, resulting
in high day-to-day variability in GPP particularly during spring (daily light levels explained 84% of the variance in daily
GPP in April). Episodic storms depressed GPP for several days in spring, but increased GPP in autumn by removing leaves shading
the streambed. Storms depressed ER initially, but then stimulated ER to 2–3 times pre-storm levels for several days. Walker
Branch was strongly net heterotrophic in both years of the study, with annual GPP being similar (488 and 519 g O2 m−2 y−1 or 183 and 195 g C m−2 y−1) but annual ER being higher in 2004 than 2005 (−1,645 vs. −1,292 g O2 m−2 y−1 or −617 and −485 g C m−2 y−1). Inter-annual variability in ecosystem metabolism (assessed by comparing 2004 and 2005 rates with previous measurements)
was the result of the storm frequency and timing and the size of the spring macroalgal bloom. Changes in local climate can
have substantial impacts on stream ecosystem metabolism rates and ultimately influence the carbon source and sink properties
of these important ecosystems. 相似文献
7.
Ecosystem Metabolism in Piedmont Streams: Reach Geomorphology Modulates the Influence of Riparian Vegetation 总被引:1,自引:0,他引:1
We measured the impact of riparian zone vegetation on ecosystem metabolism in paired forested and meadow reaches on 13 streams
in southeastern Pennsylvania and Maryland, USA. Metabolism estimates were based on open-system measurements of dissolved oxygen
changes, with reaeration determined from propane evasion. Daily gross primary productivity (GPP) in meadow and forested reaches
averaged 2.85 and 0.86 g O2 m−2 d−1, respectively, at water temperatures of 12°C or greater when the forest canopy was developed and 1.74 and 1.09 g O2 m−2 d−1, respectively, at temperatures below 12°C when the canopy was bare. Community respiration (CR24) also was greater in meadow reaches than in forested reaches, averaging 5.58 and 3.57 g O2 m−2 d−1, respectively, in the warm season and 4.87 and 2.88 g O2 m−2 d−1, respectively, during the cold season. Thus, both meadow and forested reaches were heterotrophic. Forested reaches were always
wider and nearly always shallower than companion meadow reaches. When ecosystem function was assessed per unit of stream length,
the difference in average GPP between meadow and forested reaches was reduced from three-fold to 1.9-fold in the warm season,
and mean GPP was greater in the forested reaches during the cold season. Mean CR24 per meter stream length was greater in forested reaches during both seasons. Even though riparian shading reduced primary
productivity per unit area of streambed, the greater stream width of the forested reaches counteracted that reduction in part.
Thus, when rates of ecosystem function were expressed per length of stream, differences between reaches were always smaller
than when expressed per area, and activity per unit stream length was sometimes greater in forested reaches than in meadow
reaches. 相似文献
8.
Measurement of net ecosystem production and ecosystem respiration in a Zoysia japonica grassland,central Japan,by the chamber method 总被引:1,自引:0,他引:1
Dhital Deepa Muraoka Hiroyuki Yashiro Yuichiro Shizu Yoko Koizumi Hiroshi 《Ecological Research》2010,25(2):483-493
Measuring light, temperature, soil moisture, and growth provides a better understanding of net ecosystem production (NEP),
ecosystem respiration (R
eco), and their response functions. Here, we studied the variations in NEP and R
eco in a grassland dominated by a perennial warm-season C4 grass, Zoysia japonica. We used the chamber method to measure NEP and R
eco from August to September 2007. Biomass and leaf area index (LAI) were also measured to observe their effects on NEP and R
eco. Diurnal variations in NEP and R
eco were predicted well by light intensity (PPFD) and by soil temperature, respectively. Maximum NEP (NEPmax) values on days of year 221, 233, 247, and 262, were 2.44, 2.55, 3.90, and 4.17 μmol m−2 s−1, respectively. Throughout the growing period, the apparent quantum yield (α) increased with increasing NEPmax that ranged from 0.0154 to 0.0515, and NEP responded to the soil temperature changes by 44% and R
eco changes by 48%, and R
eco responded from 88 to 94% with the soil temperature diurnally. NEP’s light response and R
eco’s temperature response were affected by soil water content; more than 27% of the variation in NEP and 67% of the variation
in R
eco could be explained by this parameter. NEP was strongly correlated with biomass and LAI, but R
eco was not, because environmental variables affected R
eco more strongly than growth parameters. Using the light response of NEP, the temperature response of R
eco, and meteorological data, daily NEP and R
eco were estimated at 0.67, 0.81, 1.17, and 1.56 g C m−2, and at 2.88, 2.50, 3.51, and 3.04 g C m−2, respectively, on days of year 221, 233, 247, and 262. The corresponding daily gross primary production (NEP + R
eco) was 3.5, 3.3, 4.6, and 4.6 g C m−2. 相似文献
9.
Klaus S. Larsen Andreas Ibrom Claus Beier Sven Jonasson Anders Michelsen 《Biogeochemistry》2007,85(2):201-213
We measured net ecosystem CO2 flux (F
n) and ecosystem respiration (R
E), and estimated gross ecosystem photosynthesis (P
g) by difference, for two years in a temperate heath ecosystem using a chamber method. The exchange rates of carbon were high
and of similar magnitude as for productive forest ecosystems with a net ecosystem carbon gain during the second year of 293 ± 11 g C m−2 year−1 showing that the carbon sink strength of heather-dominated ecosystems may be considerable when C. vulgaris is in the building phase of its life cycle. The estimated gross ecosystem photosynthesis and ecosystem respiration from October
to March was 22% and 30% of annual flux, respectively, suggesting that both cold-season carbon gain and loss were important
in the annual carbon cycle of the ecosystem. Model fit of R
E of a classic, first-order exponential equation related to temperature (second year; R
2 = 0.65) was improved when the P
g rate was incorporated into the model (second year; R
2 = 0.79), suggesting that daytime R
E increased with increasing photosynthesis. Furthermore, the temperature sensitivity of R
E decreased from apparent Q
10 values of 3.3 to 3.9 by the classic equation to a more realistic Q
10 of 2.5 by the modified model. The model introduces R
photo, which describes the part of respiration being tightly coupled to the photosynthetic rate. It makes up 5% of the assimilated
carbon dioxide flux at 0°C and 35% at 20°C implying a high sensitivity of respiration to photosynthesis during summer. The
simple model provides an easily applied, non-intrusive tool for investigating seasonal trends in the relationship between
ecosystem carbon sequestration and respiration. 相似文献
10.
V. I. Kolmakov O. V. Anishchenko E. A. Ivanova M. I. Gladyshev N. N. Sushchik 《Journal of applied phycology》2008,20(3):289-297
Periphyton (epilithon) gross primary production (GPP) was estimated using the DCMU-fluorescence method in the Yenisei River.
In the unshaded littoral zone, chlorophyll a concentration (Chl a) and GPP value varied from 0.83 to 973.74 mg m−2and 2–304,425 O2 m−2 day−1 (0.64–95 133 mg C m−2 day−1), respectively. Positive significant correlation (r = 0.8) between daily GPP and periphyton Chl a was found. Average ratio GPP:Chl a for periphyton was 36.36 mg C mg Chl a m−2 day−1. The obtained GPP values for the Yenisei River have a high significant correlation with values predicted by a conventional
empirical model for stream periphyton. We concluded that the DCMU-fluorescence method can be successfully used for measuring
of gross primary production of stream phytoperiphyton at least as another useful tool for such studies. 相似文献
11.
Bacterial carbon demand, an important component of ecosystem dynamics in polar waters and sea ice, is a function of both bacterial
production (BP) and respiration (BR). BP has been found to be generally higher in sea ice than underlying waters, but rates
of BR and bacterial growth efficiency (BGE) are poorly characterized in sea ice. Using melted ice core incubations, community
respiration (CR), BP, and bacterial abundance (BA) were studied in sea ice and at the ice–water interface (IWI) in the Western
Canadian Arctic during the spring and summer 2008. CR was converted to BR empirically. BP increased over the season and was
on average 22 times higher in sea ice as compared with the IWI. Rates in ice samples were highly variable ranging from 0.2
to 18.3 μg C l−1 d−1. BR was also higher in ice and on average ~10 times higher than BP but was less variable ranging from 2.39 to 22.5 μg C l−1 d−1. Given the high variability in BP and the relatively more stable rates of BR, BP was the main driver of estimated BGE (r
2 = 0.97, P < 0.0001). We conclude that microbial respiration can consume a significant proportion of primary production in sea ice and
may play an important role in biogenic CO2 fluxes between the sea ice and atmosphere. 相似文献
12.
Light acclimatisation capabilities of Elodea nuttallii at nearly ambient DIC conditions were investigated by determining growth characteristics, main photosynthetic parameters
and pigmentation of plants incubated at 5 different irradiances (10–146 μmol photons m−2 s−1). Positive net growth was observed under all light treatments tested. Maximum ratio root versus shoot (r:s) of 1.86 was achieved
at medium irradiances (72–94 μmol photons m−2 s−1), whereas at low (10 μmol photons m−2 s−1) and high irradiances (146 μmol photons m−2 s−1) r:s was significantly lower (0.39 and 1.05, respectively). With respect to main photosynthetic parameters, an increase of
light compensation points (E
c), attended by decreasing ratios of light saturation points of photosynthesis (E
k)/irradiance were observed. E
c values were comparable to other low-light adapted macrophytes, which indicate that E. nuttallii can be regarded as a low-light adapted plant, under photorespiratory conditions. This was also confirmed by maximum E
k values of just 73 μmol photons m−2 s−1. Further support was achieved from pigmentation and non-photochemical quenching (NPQ) data, both indicating rather limited
acclimatisation ability at light treatments above 90 μmol photons m−2 s−1. These results are discussed with respect to the competitive abilities of E. nuttallii under nearly ambient (photorespiratory) DIC conditions, especially in dense stands and turbid phytoplankton-dominated waters. 相似文献
13.
Altitudinal changes in carbon storage of temperate forests on Mt Changbai, Northeast China 总被引:8,自引:0,他引:8
Biao Zhu Xiangping Wang Jingyun Fang Shilong Piao Haihua Shen Shuqing Zhao Changhui Peng 《Journal of plant research》2010,123(4):439-452
A number of studies have investigated regional and continental scale patterns of carbon (C) stocks in forest ecosystems; however,
the altitudinal changes in C storage in different components (vegetation, detritus, and soil) of forest ecosystems remain
poorly understood. In this study, we measured C stocks of vegetation, detritus, and soil of 22 forest plots along an altitudinal
gradient of 700–2,000 m to quantify altitudinal changes in carbon storage of major forest ecosystems (Pinus koraiensis and broadleaf mixed forest, 700–1,100 m; Picea and Abies forest, 1,100–1,800 m; and Betula ermanii forest, 1,800–2,000 m) on Mt Changbai, Northeast China. Total ecosystem C density (carbon stock per hectare) averaged 237 t C ha−1 (ranging from 112 to 338 t C ha−1) across all the forest stands, of which 153 t C ha−1 (52–245 t C ha−1) was stored in vegetation biomass, 14 t C ha−1 (2.2–48 t C ha−1) in forest detritus (including standing dead trees, fallen trees, and floor material), and 70 t C ha−1 (35–113 t C ha−1) in soil organic matter (1-m depth). Among all the forest types, the lowest vegetation and total C density but the highest
soil organic carbon (SOC) density occurred in Betula ermanii forest, whereas the highest detritus C density was observed in Picea and Abies forest. The C density of the three ecosystem components showed distinct altitudinal patterns: with increasing altitude, vegetation
C density decreased significantly, detritus C density first increased and then decreased, and SOC density exhibited increasing
but insignificant trends. The allocation of total ecosystem C to each component exhibited similar but more significant trends
along the altitudinal gradient. Our results suggest that carbon storage and partitioning among different components in temperate
forests on Mt Changbai vary greatly with forest type and altitude. 相似文献
14.
The effects of seasonality and dilution stress on the functioning of Rambla Salada, a hypersaline Mediterranean stream in
SE Spain, were evaluated. The stream is subject to diffuse freshwater inputs from the drainage of intensively irrigated agriculture
in the catchment and periodic losses of water through an irrigation channel. Metabolic rates and the biomass of primary producers
and consumers were estimated over a 2-year period. During the first year several dilution events occurred, while during the
second year the salinity recovery reached predisturbance levels. Functional indicators were compared in the disturbance and
recovery salinity periods. Primary production and respiration rates in the Rambla Salada ranged between 0.07–21.05 and 0.19–17.39 g
O2 m−2 day−1, respectively. The mean values for these variables were 7.35 and 5.48 g O2 m−2 day−1, respectively. Mean net daily metabolism rate was 1.87 ± 0.52 g O2 m−2 day−1 and mean production/respiration ratio was 2.48 ± 1.1, reflecting autotrophic metabolism. The metabolic rates showed the typical
seasonal pattern of Mediterranean open canopy streams. Therefore, gross primary production (GPP) and ecosystem respiration
(ER) registered maximum values in summer, intermediate values in spring and autumn and minimum values in winter. The metabolic
rates and biomass of consumers were greater in the disturbance period than in the recovery period. However, they did not show
significant differences between periods due to their important dependence on seasonal cycle. Seasonality accounted for much
of the temporal variability in GPP and ER (76% and 83% in the multiregression models, respectively). Light availability seems
to be the most important factor for GPP and ER in the Rambla Salada. Autotrophic biomass responded more to variations in discharge
and conductivity than to seasonal variations. In fact, it was severely affected by freshwater inputs after which the epipelic
biomass decreased significantly and Cladophora glomerata proliferated rapidly. Epipelic algal biomass was the most sensitive parameter to dilution disturbance.
Handling editor: Luigi Naselli-Flores 相似文献
15.
The increased frequency of heavy rains as a result of global climate change can lead to flooding and changes in light availability
caused by the presence of thick clouds. To test the hypothesis that reduction in light availability can alleviate the harmful
effects of soil flooding on photosynthesis, the authors studied the effects of soil flooding and acclimation from high to
low light on the photosynthetic performance of Eugenia uniflora. Seedlings acclimated to full sunlight (about 35 mol m−2 d−1) for 5 months were transferred to partial sunlight (about 10 mol m−2 d−1) and were either subjected to soil flooding or not flooded. Chlorophyll fluorescence was measured throughout the flooding
period and leaf gas exchange was measured 16 days after flooding was initiated. Minimal fluorescence yield (Fo) was significantly
higher and the quantum efficiency of open PSII centres (Fv/Fm) was significantly lower in flooded than in non-flooded plants
in full sunlight. Sixteen days after flooding was initiated, stomatal conductance (gssat) and net photosyntheses expressed on a leaf area (Asat-area), weight (Asat-wt) and chlorophyll (Asat-Chl) basis decreased in response to soil flooding. Flooding decreased stomatal conductance by similar amounts in full and partial
sunlight, but Asat-area in partial and full sunlight was 3.4 and 16.8 times lower, respectively, in flooded than in non-flooded plants. These results
indicate that changes from full to partial sunlight during soil flooding can alleviate the effects of flooding stress on photosynthesis
in E. uniflora seedlings acclimated to full sunlight. The responses of photosynthesis in trees to flooding stress may be dependent on changes
in light environment during heavy rains. 相似文献
16.
Variability and future alterations in regional and global climate patterns may exert a strong control on the carbon dioxide
(CO2) exchange of grassland ecosystems. We used 6 years of eddy-covariance measurements to evaluate the impacts of seasonal and
inter-annual variations in environmental conditions on the net ecosystem CO2 exchange (NEE), gross ecosystem production (GEP), and ecosystem respiration (ER) of an intensively managed grassland in the
humid temperate climate of southern Ireland. In all the years of the study period, considerable uptake of atmospheric CO2 occurred in this grassland with a narrow range in the annual NEE from −245 to −284 g C m−2 y−1, with the exception of 2008 in which the NEE reached −352 g C m−2 y−1. None of the measured environmental variables (air temperature (Ta), soil moisture, photosynthetically active radiation,
vapor pressure deficit (VPD), precipitation (PPT), and so on) correlated with NEE on a seasonal or annual scale because of
the equal responses from the component fluxes GEP and ER to variances in these variables. Pronounced reduction of summer PPT
in two out of the six studied years correlated with decreases in both GEP and ER, but not with NEE. Thus, the stable annual
NEE was primarily achieved through a strong coupling of ER and GEP on seasonal and annual scales. Limited inter-annual variations
in Ta (±0.5°C) and generally sufficient soil moisture availability may have further favored a stable annual NEE. Monthly ecosystem
carbon use efficiency (CUE; as the ratio of NEE:GEP) during the main growing season (April 1–September 30) was negatively
correlated with temperature and VPD, but positively correlated with soil moisture, whereas the annual CUE correlated negatively
with annual NEE. Thus, although drier and warmer summers may mildly reduce the uptake potential, the annual uptake of atmospheric
CO2, in this intensively managed grassland, may be expected to continue even under predicted future climatic changes in the humid
temperate climate region. 相似文献
17.
In the interest of determining productivity across a range of spatial scales (meters to many kilometers) and in different
reef environments, this paper proposes a technique for measuring productivity based on remote sensing of optical absorptance
and light-use efficiency. The concept is straightforward: gross primary production equals plant-incident irradiance multiplied
by plant absorptance multiplied by the plant’s light-use efficiency (GPP = E
d
Aε). Both E
d and A are derivable from various remote sensing data sources, thus the approach is feasible. This paper presents a demonstration
of the application for Kaneohe Bay, Oahu, HI based on Quickbird satellite imagery and SHOALS LIDAR data. E
d is modeled at every point in the image, and the image itself is inverted to provide A. Organismal-scale ε reported in the literature is taken as a surrogate for community-scale ε. The resulting GPP image compares well with the range of GPP values for reef-flats in general, as well as the distribution
and range of GPP for Kaneohe Bay in particular. Though results likely can be improved by using spectral imagery and more accurate
values for ε, this concept study demonstrates the tractability of this approach for measuring coral reef GPP. 相似文献
18.
Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25,
35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate
(P
N) of sweet corn was found for the lowest temperature of 28–34 μmol m−2 s−1 while the P
N for the highest temperature treatment was 50–60 % lower. We detected a gradual decline of about 1 P
N unit per 1 °C increase in temperature. Maximum transpiration rate (E) fluctuated between 0.36 and 0.54 mm h−1 (≈5.0–6.5 mm d−1) for the high temperature treatment and the minimum E fluctuated between 0.25 and 0.36 mm h−1 (≈3.5–5.0 mm d−1) for the low temperature treatment. Cumulative CO2 fixation of the 40/35 °C treatment was 33.7 g m−2 d−1 and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to
5 g(CO2) kg−1(H2O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, P
N, and E of Zea: the high temperature which reduced P
N, vapor pressure deficit (VPD) that was directly related to E but did not affect P
N, and quasi stem conductance (QC) that was directly related to P
N but did not affect E. As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment. 相似文献
19.
Future Spruce Budworm Outbreak May Create a Carbon Source in Eastern Canadian Forests 总被引:2,自引:0,他引:2
Caren C. Dymond Eric T. Neilson Graham Stinson Kevin Porter David A. MacLean David R. Gray Michel Campagna Werner A. Kurz 《Ecosystems》2010,13(6):917-931
Spruce budworm (Choristoneura fumiferana Clem.) is an important and recurrent disturbance throughout spruce (Picea sp.) and balsam fir (Abies balsamea L.) dominated forests of North America. Forest carbon (C) dynamics in these ecosystems are affected during insect outbreaks
because millions of square kilometers of forest suffer growth loss and mortality. We tested the hypothesis that a spruce budworm
outbreak similar to those in the past could switch a forest from a C sink to a source in the near future. We used a model
of ecosystem C to integrate past spruce budworm impact sequences with current forest management data on 106,000 km2 of forest in eastern Québec. Spruce budworm-caused mortality decreased stand-level merchantable C stocks by 11–90% and decreased
ecosystem C stocks by 2–10% by the end of the simulation. For the first 13 years (2011–2024), adding spruce budworm significantly
reduced ecosystem C stock change for the landscape from a sink (4.6 ± 2.7 g C m−2 y−1 in 2018) to a source (−16.8 ± 3.0 g C m−2 y−1 in 2018). This result was mostly due to reduced net primary production. The ecosystem stock change was reduced on average
by 2 Tg C y−1 for the entire simulated area. This study provides the first estimate that spruce budworm can significantly affect the C
sink or source status of a large landscape. These results indicate that reducing spruce budworm impacts on timber may also
provide an opportunity to mitigate a C source. 相似文献
20.
Highly productive papyrus (Cyperus papyrus L.) wetlands dominate many permanently flooded areas of tropical East Africa; however, the cycling of carbon and water within
these ecosystems is poorly understood. The objective of this study was to utilise Eddy Covariance (EC) techniques to measure
the fluxes of carbon dioxide and water vapour between papyrus vegetation and the atmosphere in a wetland located near Jinja,
Uganda on the Northern shore of Lake Victoria. Peak, midday rates of photosynthetic CO2 net assimilation were approximately 40 μmol CO2 m−2 s−1, while night time losses through respiration ranged between 10 and 20 μmol CO2 m−2 s−1. Numerical integration of the flux data suggests that papyrus wetlands have the potential to sequester approximately 0.48 kg C m−2 y−1. The average daily water vapour flux from the papyrus vegetation through canopy evapotranspiration was approximately 4.75 kg
H2O m−2 d−1, which is approximately 25% higher than water loss through evaporation from open water. 相似文献