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1.
Response of soil respiration to simulated N deposition in a disturbed and a rehabilitated tropical forest in southern China 总被引:3,自引:1,他引:2
Jiangming Mo Wei Zhang Weixing Zhu Yunting Fang Dejun Li Ping Zhao 《Plant and Soil》2007,296(1-2):125-135
Responses of soil respiration (CO2 emission) to simulated N deposition were studied in a disturbed (reforested forest with previous understory and litter harvesting)
and a rehabilitated (reforested forest with no understory and litter harvesting) tropical forest in southern China from October
2005 to September 2006. The objectives of the study were to test the following hypotheses: (1) soil respiration is higher
in rehabilitated forest than in disturbed forest; (2) soil respiration in both rehabilitated and disturbed tropical forests
is stimulated by N additions; and (3) soil respiration is more sensitive to N addition in disturbed forest than in rehabilitated
forest due to relatively low soil nutrient status in the former, resulting from different previous human disturbance. Static
chamber and gas chromatography techniques were employed to quantify the soil respiration, following different N treatments
(Control, no N addition; Low-N, 5 g N m−2 year−1; Medium-N, 10 g N m−2 year−1), which had been applied continuously for 26 months before the respiration measurement. Results showed that soil respiration
exhibited a strong seasonal pattern, with the highest rates observed in the hot and wet growing season (April–September) and
the lowest rates in winter (December–February) in both rehabilitated and disturbed forests. Soil respiration rates exhibited
significant positive exponential relationship with soil temperature and significant positive linear relationship with soil
moisture. Soil respiration was also significantly higher in the rehabilitated forest than in the disturbed forest. Annual
mean soil respiration rate in the rehabilitated forest was 20% lower in low-N plots (71 ± 4 mg CO2-C m−2 h−1) and 10% lower in medium-N plots (80 ± 4 mg CO2-C m−2 h−1) than in the control plots (89 ± 5 mg CO2-C m−2 h−1), and the differences between the control and low-N or medium-N treatments were statistically significant. In disturbed forest,
annual mean soil respiration rate was 5% lower in low-N plots (63 ± 3 mg CO2-C m−2 h−1) and 8% lower in medium-N plots (61 ± 3 mg CO2-C m−2 h−1) than in the control plots (66 ± 4 mg CO2-C m−2 h−1), but the differences among treatments were not significant. The depressed effects of experimental N deposition occurred
mostly in the hot and wet growing season. Our results suggest that response of soil respiration to elevated N deposition in
the reforested tropical forests may vary depending on the status of human disturbance.
Responsible Editor: Hans Lambers. 相似文献
2.
To develop an integrated process of CO2-fixation and H2 photoproduction by marine green microalga Platymonas subcordiformis, the impact of algal cells grown in CO2-supplemented air bubble column bioreactor was investigated on H2 photoproduction regulated by carbonylcyanide m-chlorophenylhrazone. Highest cell growth (3.85 × 106 cells ml−1), starch content (0.25 ± 0.08 mg per 106 cells) and hydrogen production (50 ± 3 ml l−1) were achieved at 3% CO2-supplemented culture, which are respectively 1.4, 2.1, 1.5-fold of the air-supplemented culture. Improved H2 production correlated well with the increase in starch accumulation. In this process, the algal cells have been recycled
for stable H2 production of 40–50 ml l−1 over five cycles. 相似文献
3.
N2O, CH4 and CO2 emissions from seasonal tropical rainforests and a rubber plantation in Southwest China 总被引:2,自引:1,他引:1
Christian Werner Xunhua Zheng Janwei Tang Baohua Xie Chunyan Liu Ralf Kiese Klaus Butterbach-Bahl 《Plant and Soil》2006,289(1-2):335-353
The main focus of this study was to evaluate the effects of soil moisture and temperature on temporal variation of N2O, CO2 and CH4 soil-atmosphere exchange at a primary seasonal tropical rainforest (PF) site in Southwest China and to compare these fluxes with fluxes from a secondary forest (SF) and a rubber plantation (RP) site. Agroforestry systems, such as rubber plantations, are increasingly replacing primary and secondary forest systems in tropical Southwest China and thus effect the N2O emission in these regions on a landscape level. The mean N2O emission at site PF was 6.0 ± 0.1 SE μg N m−2 h−1. Fluxes of N2O increased from <5 μg N m−2 h−1 during dry season conditions to up to 24.5 μg N m−2 h−1 with re-wetting of the soil by the onset of first rainfall events. Comparable fluxes of N2O were measured in the SF and RP sites, where mean N2O emissions were 7.3 ± 0.7 SE μg N m−2 h−1 and 4.1 ± 0.5 SE μg N m−2 h−1, respectively. The dependency of N2O fluxes on soil moisture levels was demonstrated in a watering experiment, however, artificial rainfall only influenced the timing of N2O emission peaks, not the total amount of N2O emitted. For all sites, significant positive correlations existed between N2O emissions and both soil moisture and soil temperature. Mean CH4 uptake rates were highest at the PF site (−29.5 ± 0.3 SE μg C m−2 h−1), slightly lower at the SF site (−25.6 ± 1.3 SE μg C m−2 h−1) and lowest for the RP site (−5.7 ± 0.5 SE μg C m−2 h−1). At all sites, CH4 uptake rates were negatively correlated with soil moisture, which was also reflected in the lower uptake rates measured in the watering experiment. In contrast to N2O emissions, CH4 uptake did not significantly correlate with soil temperature at the SF and RP sites, and only weakly correlated at the PF site. Over the 2 month measurement period, CO2 emissions at the PF site increased significantly from 50 mg C m−2 h−1 up to 100 mg C m−2 h−1 (mean value 68.8 ± 0.8 SE mg C m−2 h−1), whereas CO2 emissions at the SF and RP site where quite stable and varied only slightly around mean values of 38.0 ± 1.8 SE mg C m−2 h−1 (SF) and 34.9 ± 1.1 SE mg C m−2 h−1 (RP). A dependency of soil CO2 emissions on changes in soil water content could be demonstrated for all sites, thus, the watering experiment revealed significantly higher CO2 emissions as compared to control chambers. Correlation of CO2 emissions with soil temperature was significant at the PF site, but weak at the SF and not evident at the RP site. Even though we demonstrated that N and C trace gas fluxes significantly varied on subdaily and daily scales, weekly measurements would be sufficient if only the sink/ source strength of non-managed tropical forest sites needs to be identified. 相似文献
4.
Jan Pilarski 《Acta Physiologiae Plantarum》2002,24(1):29-36
It has been demonstrated that during the whole year the stems are photosyntheticaly active and capable of assimilating atmospheric
CO2. The intensity of photosynthesis varies. During the vegetation period the registered net photosynthesis lasted up to 13 hours
per day, and in the leafless period for 2–3 hours a day. Photosynthesis was registered also at temperatures below zero (−3
°C) as a reduced CO2 evolution in light in comparison with darkness. The maximal net photosynthesis values during the vegetation period amounted
to 6 up 8 μmol (CO2)·m−2·s−1, and in the leafless period 0.5 – 1 μmol (CO2)·m−2·s−1, and they were close to being up to twice as big as the values obtained of darkness respiration. An increase of the photosynthetic
activity of stems preceded the spring development of the leaves. 相似文献
5.
Algesten G Sobek S Bergström AK Jonsson A Tranvik LJ Jansson M 《Microbial ecology》2005,50(4):529-535
We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were
made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated
to dissolved organic carbon (DOC) concentration in the water (r2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed
layer (r2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration.
Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic
(<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In
addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water
column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources. 相似文献
6.
Amanda M. Grannas Christopher B. Martin Yu-Ping Chin Matthew Platz 《Biogeochemistry》2006,78(1):51-66
The hydroxyl radical (OH·) plays an important role in the environmental chemistry and biogeochemistry of surface waters. OH·
acts as a strong oxidant within the irradiated water column, and affects the bioavailability, cycling, and mineralization
of dissolved organic matter (DOM), the speciation and redox state of important trace metals e.g., iron and copper, and the
fate of persistent organic pollutants (POPs). The generation of this species from irradiated DOM may be especially important
in Arctic surface waters during the boreal summer, which contains high levels of DOM and experiences continual solar irradiance.
Here, we investigate the OH· produced from laser irradiated Arctic DOM isolated from Toolik Lake, AK (68°38′ N, 149°43′ W).
We measured the wavelength dependence of OH· production for aqueous solutions of DOM and report that the greatest OH· production
occurs at wavelengths less than 360 nm. OH· production rates ranged from 1.7 (±0.1)×10−7 M h−1 to 6.4 (±0.2)×10−7 M h−1, with the rate depending on both irradiation wavelength and to a lesser degree the method used to isolate the DOM matrix.
These findings lead to a better understanding of the potentially important photo-oxidation processes that may impact DOM cycling
in the Arctic. 相似文献
7.
Using experimental mesocosms, we tested the strength of bottom–up controls by nutrients and top–down controls by an omnivorous
fish (Hyphessobrycon bifasciatus; family Characidae), and the interaction between them on the CO2 partial pressure (pCO2) in the surface waters of a tropical humic lake (Lake Cabiúnas, Brazil). The experiment included the addition of nutrients
and fish to the mesocosms in a factorial design. Overall, persistent CO2 emissions to the atmosphere, supported by an intense net heterotrophy, were observed in all treatments and replicates over
the 6-week study period. The CO2 efflux (average ± standard error) integrated over the experiment was similar among the control mesocosms and those receiving
only fish or only nutrients (309 ± 2, 303 ± 16, and 297 ± 17 mmol CO2 m−2 day−1, respectively). However, the addition of nutrients in the presence of fish resulted in a high algal biomass and daytime net
autotrophy, reducing the CO2 emissions by 35% (by 193 ± 7 mmol CO2 m−2 day−1). These results indicate that high CO2 emissions persist following the eutrophication of humic waters, but that the magnitude of these emissions might depend on
the structure of the food web. In conclusion, fish and nutrients may act in a synergistic manner to modulate persistent CO2 emissions from tropical humic lakes. 相似文献
8.
Soil surface CO2 flux was measured in hollow and hummock microhabitats in a peatland in north central Minnesota from June to October in 1991.
We used a closed infrared gas exchange system to measure soil CO2 flux. The rates of CO2 evolution from hummocks (9.8 ± 3.5 g m−2 d−1, [mean ± SE]) were consistently higher than those from hollows (5.4 ± 2.9 g m−2 d−1) (the hummock values included the contribution of moss dark respiration, which may account for 10–20% of the total measured
flux). The soil CO2 flux was strongly temperature-dependent (Q10 ≈ 3.7) and appeared to be linearly related to changes in water table depth. An empirical multiplicative model, using peat
temperature and water table depth as independent variables, explained about 81% of the variance in the CO2 flux data. Using the empirical model with measurements of peat temperature and estimates of hollow/hummock microtopographic
distribution (relative to water table elevation), daily rates of “site-averaged” CO2 evolution were calculated. For the six-month period (May–October), the total soil CO2 released from this ecosystem was estimated to be about 1340 g CO2 m−2.
Published as Paper No. 9950, Journal Series, Nebraska Agricultural Research Division, University of Nebraska, Lincoln, NE,
USA. 相似文献
9.
In an experimental site for reforestation of degraded area, three-year-old plants of Bertholletia excelsa Humb. & Bonpl. were subjected to different fertilization treatments: T0 = unfertilized control, T1 = green fertilization
(branches and leaves) and T2 = chemical fertilization. Higher net photosynthetic rates (P
N) were observed in T1 [13.2±1.0 μmol(CO2) m−2 s−1] compared to T2 [8.0±1.8 μmol(CO2) m−2 s−1] and T0 [4.8±1.3 μmol(CO2) m−2 s−1]. Stomatal conductance (g
s), transpiration rate (E) and water use efficiency (WUE) of individuals of T1 and T2 did not differ significantly, however, they were by 88, 55 and
63%, respectively, higher in T1 than in the control. The mean values of variable fluorescence (Fv), performance index (P.I.) and total chlorophyll [Chl (a+b)] were higher in T1. Our results indicate that green fertilization improves photosynthetic structure and function in plants
of B. excelsa in young phase. 相似文献
10.
Characteristics of net ecosystem carbon dioxide exchange (NEE) from August to October of Alpine meadow on the Tibetan Plateau, China 总被引:3,自引:0,他引:3
Xu Lingling Zhang Xianzhou Shi Peili Yu Guirui Sun Xiaomin 《Frontiers of Biology in China》2006,1(4):418-422
The Alpine meadow is one of the vegetation types widely distributed on the Tibetan Plateau in China with an area of about
1.2 million square kilometers. The Damxung rangeland station, located in the hinterland of the Tibetan Plateau, is covered
with an typical vegetation. The continuous carbon flux data (from August to middle October, 2003) measured with the open-path
eddy covariance system was used to analyze the diurnal variation pattern of net ecosystem carbon dioxide exchange (NEE) and
its relationship with the environmental factors, such as photosynthetically active radiation (PAR), precipitation, and temperature.
Results showed that NEE presented obvious diurnal variation pattern with single-peak of diurnal maximum carbon assimilation
at 11: 00–12: 00 (local time) with an average of −0.268 mg CO2·m−2·s−1, i.e., −6.08 μmol CO2·m−2·s−1. During the daytime, NEE fitted fairly well with PAR in a rectangular hyperbola function with the apparent quantum yield
(0.020 3 μmol CO2 μmol−1 PAR) and maximum ecosystem assimilation (9.741 1 μmol CO2·m−2·s−1). During the night-time, NEE showed a good exponential relation with the soil temperature at 5 cm depth.
__________
Translated from Acta Ecologica Sinica 2005, 25(8): 1948–1952 [译自: 生态学报, 2005, 25(8): 1948–1952] 相似文献
11.
The morphological, anatomical and physiological variations of leaf traits were analysed during Quercus ilex L. leaf expansion. The leaf water content (LWC), leaf area relative growth rate (RGRl) and leaf dry mass relative growth rate (RGRm) were the highest (76±2 %, 0.413 cm2 cm−2 d−1, 0.709 mg mg−1 d−1, respectively) at the beginning of the leaf expansion process (7 days after bud break). Leaf expansion lasted 84±2 days when
air temperature ranged from 13.3±0.8 to 27.6±0.9 °C. The net photosynthetic rate (P
N), stomatal conductance (g
s), and chlorophyll content per fresh mass (Chl) increased during leaf expansion, having the highest values [12.62±1.64 μmol
(CO2) m−2 s−1, 0.090 mol (H2O) m−2 s−1, and 1.03±0.08 mg g−1, respectively] 56 days after bud break. Chl was directly correlated with leaf dry mass (DM) and P
N. The thickness of palisade parenchyma contributed to the total leaf thickness (263.1±1.5 μm) by 47 %, spongy layer thickness
38 %, adaxial epidermis and cuticle thickness 9 %, and abaxial epidermis and cuticle thickness 6 %. Variation in leaf size
during leaf expansion might be attributed to a combination of cells density and length, and it is confirmed by the significant
(p<0.001) correlations among these traits. Q. ilex leaves reached 90 % of their definitive structure before the most severe drought period (beginning of June — end of August).
The high leaf mass area (LMA, 15.1±0.6 mg cm−2) at full leaf expansion was indicative of compact leaves (2028±100 cells mm−2). Air temperature increasing might shorten the favourable period for leaf expansion, thus changing the final amount of biomass
per unit leaf area of Q. ilex. 相似文献
12.
Witjaksono Bruce A. Schaffer Angel M. Colls Richard E. Litz Pamela A. Moon 《In vitro cellular & developmental biology. Plant》1999,35(3):238-244
Summary The proliferation and survival of avocado nodal cultures of juvenile origin were affected by the form and concentration of
nitrogen. Optimum growth was achieved on modified Murashige and Skoog medium containing 67% KNO3 and 33% NH4NO3 with total N of 40 mM supplemented with 100 mg l−1
myo-inositol, 1 mg l−1 thiamine HCl, 30 g l−1 sucrose, and 4.44 μM BA with a 16-h photoperiod (120–150 μmol m−2 s−1). Proliferating shoots and plantlets were photosynthetically active. Better shoot growth and accumulation of higher biomass
occurred in a CO2-enriched environment than under ambient CO2 conditions. CO2 assimilation efficiency, however, was higher under the latter conditions than in a CO2-enhanced environment, e.g., 31±7 and 17±2 μmol CO2 m−2 s−1, respectively. The net CO2 assimilation rates of in vitro grown plantlets were comparable to those of seedlings ex vitro. 相似文献
13.
The aim of this study is to infer past changes in total organic carbon (TOC) content of lake water during the Holocene in
eight boreal forest, tree-limit and alpine lakes using a new technique – near-infrared spectroscopy (NIRS). A training set
of 100 lakes from northern Sweden covering a TOC gradient from 0.7 to 14.9 mg l−1 was used to establish a relationship between the NIRS signal from surface sediments (0–1 cm) and the TOC content of the water
mass. The NIRS model for TOC has a root mean squared error (RMSECV) of calibration of 1.6 mg l−1 (11% of the gradient) assessed by internal cross-validation (CV), which yields an R2cv of 0.61. The results show that the most dramatic change among the studied lakes occurs in both tree-line lakes around 1000 yrs
BP when the TOC content decreases from ca. 7 to 3 mg l−1 at the present, which is probably due to a descending tree-limit. The TOC content in the alpine lakes shows a declining trend
throughout most of the Holocene indicating that TOC may be more directly correlated to climate in alpine lakes than forest
lakes. All boreal forest lakes show a declining trend in TOC during the past 3000 yrs with the largest amplitude of change
occurring in the lake with a connected mire. The results indicate that a change to a warmer and more humid climate can increase
the TOC levels in lakes, which in turn may increase the saturation of CO2 in lake waters and the emission of CO2 to the atmosphere. 相似文献
14.
Variation of chromophoric dissolved organic matter and possible attenuation depth of ultraviolet radiation in Yunnan Plateau lakes 总被引:2,自引:0,他引:2
The increase of ultraviolet radiation (UVR, 280–400 nm) caused by stratospheric ozone depletion has profound effects on aquatic
ecosystems. High-altitude lakes in the Yunnan Plateau are exposed to high intensities of UVR and contain low concentrations
of chromophoric dissolved organic matter (CDOM). Thirty-eight lakes in the Yunnan Plateau with elevations from 1291 to 3809
m above sea level were investigated to study CDOM concentrations and possible effects of UVR on the lake ecosystem. The attenuation
of UVR in the Yunnan Plateau lakes was calculated from the absorption coefficient of CDOM based on an empirical relationship
from lakes in the Alps and Pyrenees mountains. Absorption coefficients [α(λ)] at 320 nm [α(320)] ranged from 0.52 to 14.05 m−1 (mean ± standard deviation, 4.40 ± 3.85 m−1) and at 380 nm [α(380)] from 0.05 to 4.51 m−1 (1.40 ± 1.30 m−1). The exponential slope coefficient for the relationship of wavelength to α(λ) ranged from 16.2 to 41.4 μm−1 (21.74 ± 4.93 μm−1) over the 280–400 nm interval. Normalized fluorescence emission (NFLU) at 450 nm from an excitation wavelength of 355 nm,
F
n(355), averaged 7.93 ± 3.22 NFLU. A significant positive relationship was found between α(355) and F
n(355). The estimated diffuse attenuation coefficients of UV-B (320 nm) and UV-A (380 nm) ranged from 0.55 to 15.77 m−1 and from 0.24 to 6.73 m−1; the corresponding 1% attenuation depths ranged from 0.29 to 8.44 m and from 0.68 to 19.12 m. Twenty-five of 38 lakes had
1% UV-B attenuation depths of 1.5 m or more. The median 1% attenuation depth was 28.8% of the sampling depth for UV-B radiation
and 60% for UV-A. In addition to CDOM, chlorophyll α (Chla) and total suspended matter (TSM) also may contribute to attenuation of UVR. 相似文献
15.
Moro D Bradshaw SD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):538-548
A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of
two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day−1 and 1.2 ± 0.4 ml · day−1, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day−1 and 2.0 ± 0.3 ml · day−1, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher
in M. domesticus (1.1 ± 0.1 mg H2O · g−0.122 · h−1) than in L. lakedownensis (0.6 ± 0.1 mg H2O · g−0.122 · h−1). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following
an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations
up to 1 mol · l−1, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate
was significantly higher in M. domesticus (3.3 ± 0.2 mg O2 · g−0.75 · h−1) than in L. lakedownensis (2.5 ± 0.1 mg O2 · g−0.75 · h−1). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose
relatively high sodium fluxes may reflect sodium associated with available food.
Accepted: 16 August 1999 相似文献
16.
Daniel Comstedt Björn Boström John D. Marshall Anders Holm Michelle Slaney Sune Linder Alf Ekblad 《Ecosystems》2006,9(8):1266-1277
This study examines the effect of elevated atmospheric carbon dioxide [CO2] (+340 ppm, 13C-depleted) and/or elevated air temperature (2.8–3.5°C) on the rate and δ13C of soil respiration. The study was conducted in a boreal Norway spruce forest using temperature-controlled whole-tree chambers
and 13C as a marker for root respiration. The δ13C of needle carbohydrates was followed after the onset of the CO2 treatment in August 2001 and during a 2.5-week period in the summer of 2002. Averaged over the growing seasons of 2002 and
2003, we observed a 48% and 62% increase, respectively, in soil respiration in response to elevated [CO2], but no response to elevated air temperature. The percentage increase in response to elevated [CO2] varied seasonally (between 10% and 190% relative to the control), but the absolute increase varied less (39 ± 11 mg C m−2 h−1; mean ± SD). Data on δ13C of soil respiration indicate that this increase in soil respiration rate resulted from increased root/rhizosphere respiration
of recently fixed carbon. Our results support the hypothesis that root/rhizosphere respiration is sensitive to variation in
substrate availability. 相似文献
17.
An investigation into the changing phytoplankton biomass and total water column production during autumn sea ice formation
in the eastern Weddell Sea, Antarctica showed reduced biomass concentrations and extremely low daily primary production. Mean
chlorophyll-a concentration for the entire study period was extremely low, 0.15±0.01 mg.m−3 with a maximum of 0.35 mg.m−3 found along the first transect to the east of the grid. Areas of low biomass were identified as those either associated with
heavy grazing or with deep mixing and corresponding low light levels. In most cases phytoplankton in the <20-μm size classes
dominated. Integrated biomass to 100 m ranged from 7.1 to 28.0 mg.m−2 and correlated positively with surface chlorophyll-a concentrations. Mean PBmax (photosynthetic capacity) and αB (initial slope of the photosynthesis-irradiance curve) were 1.25±0.19 mgC. mgChla
−1.h−1 and 0.042±0.009 mgC.mgChla
−1.h−1.(μmol.m−2.s−1)−1 respectively. The mean index of photoadaptation,I
k, was 32.2±4.0 μmol.m−2.s−1 and photoinhibition was found in all cases. Primary production was integrated to the critical depth (Z
cr) at each production station and ranged from 15.6 to 41.5 mgC.m−2.d−1. It appears that, other than grazing intensity, the relationship between the critical depth and the mixing depth (Z
mix) is an important factor as, ultimately, light availability due both to the late season and growing sea ice cover severely
limits production during the austral autumn. 相似文献
18.
CO2 and N-fertilization effects on fine-root length, production, and mortality: a 4-year ponderosa pine study 总被引:1,自引:0,他引:1
We conducted a 4-year study of juvenile Pinus ponderosa fine root (≤2 mm) responses to atmospheric CO2 and N-fertilization. Seedlings were grown in open-top chambers at three CO2 levels (ambient, ambient+175 μmol/mol, ambient+350 μmol/mol) and three N-fertilization levels (0, 10, 20 g m−2 year−1). Length and width of individual roots were measured from minirhizotron video images bimonthly over 4 years starting when the seedlings were 1.5 years old. Neither CO2 nor N-fertilization treatments affected the seasonal patterns of root production or mortality. Yearly values of fine-root length standing crop (m m−2), production (m m−2 year−1), and mortality (m m−2 year−1) were consistently higher in elevated CO2 treatments throughout the study, except for mortality in the first year; however, the only statistically significant CO2 effects were in the fine-root length standing crop (m m−2) in the second and third years, and production and mortality (m m−2 year−1) in the third year. Higher mortality (m m−2 year−1) in elevated CO2 was due to greater standing crop rather than shorter life span, as fine roots lived longer in elevated CO2. No significant N effects were noted for annual cumulative production, cumulative mortality, or mean standing crop. N availability did not significantly affect responses of fine-root standing crop, production, or mortality to elevated CO2. Multi-year studies at all life stages of trees are important to characterize belowground responses to factors such as atmospheric CO2 and N-fertilization. This study showed the potential for juvenile ponderosa pine to increase fine-root C pools and C fluxes through root mortality in response to elevated CO2. 相似文献
19.
Light response characteristics of a morphologically diverse group of southern hemisphere conifers as measured by chlorophyll fluorescence 总被引:5,自引:0,他引:5
Unlike northern hemisphere conifer families, the southern family, Podocarpaceae, produces a great variety of foliage forms
ranging from functionally broad-, to needle-leaved. The production of broad photosynthetic surfaces in podocarps has been
linked qualitatively to low-light-environments, and we undertook to assess the validity of this assumption by measuring the
light response of a morphologically diverse group of podocarps. The light response, as apparent photochemical electron transport
rate (ETR), was measured by modulated fluorescence in ten species of this family and six associated species (including five
Cupressaceae and one functionally needle-leaved angiosperm) all grown under identical glasshouse conditions. In all species,
ETR was found to increase as light intensity increased, reaching a peak value (ETRmax) at saturating quantum flux (PPFDsat), and decreasing thereafter. ETRmax ranged from 217 μmol electrons · m−2 · s−1 at a PPFDsat of 1725 μmol photons · m−2 · s−1 in Actinostrobus acuminatus to an ETR of 60 μmol electrons · m−2 · s−1 at a PPFDsat of 745 μmol electrons · m−2 · s−1 in Podocarpus dispermis. Good correlations were observed between ETRmax and both PPFDsat and maximum assimilation rate measured by gas-exchange analysis. The effective quantum yield at light saturation remained
constant in all species with an average value of 0.278 ± 0.0035 determined for all 16 species. Differences in the shapes of
light response curves were related to differences in the response of non-photochemical quenching (q
n), with q
n saturating faster in species with low PPFDsat. Amongst the species of Podocarpaceae, the log of average shoot width was well correlated with PPFDsat, wider leaves saturating at lower light intensities. This suggests that broadly flattened shoots in the Podocarpaceae are
an adaptation to low light intensity.
Received: 15 April 1996 / Accepted: 30 September 1996 相似文献
20.
Metabolic hotspots at land–water interfaces are important in supporting biogeochemical processes. Here we confirm the generality
of land–aquatic interfaces as biogeochemical hot spots by extending this concept to marine beach cast materials. In situ atmospheric
pCO2, from a respiration chamber (10 cm in diameter and 20 cm high) inserted into wrack deposits, was determined using a high-precision
(±1 ppm) non-dispersive infrared gas analyzer (EGM-4, PP-systems) at 1 minute recording intervals. The wrack deposits supported
high metabolic activities, with CO2 fluxes averaging (±SE) 6.62 ± 0.88 μmol C m−2 s−1, compared to median value of 0.98 μmol C m−2 s−1 (mean 2.21 ± 1.25 μmol C m−2 s−1) for bare sand adjacent to deposits. Wrack metabolic rates ranged 40-fold across beaches, from a minimum of 0.57 ± 0.22 μmol
C m−2 s−1 to a maximum of 20.8 ± 5.04 μmol C m−2 s−1, both derived from beaches with deposits dominated by Sargassum. Rates tended to increase significantly (F test, P < 0.05) from the shoreline to reach maximum rates at about 10 m from the shoreline, declining sharply further from the shoreline,
and increased with increasing thickness of the deposits (maximum about 10 cm deep), declining for thicker deposits. Wrack
differing in composition had similar metabolic rates, although deposits consisting of a mixture of seagrass and algae tended
to show somewhat higher rates. Our results show a meter square of wrack deposit supports a metabolic rate equivalent to that
supported by 3 m2 of living seagrass or macroalgal habitat. In wrack, the marine environment provides organic material and moisture and the
land environment provides oxygen to render wrack ecosystems an efficient metabolic reactor. Intense wrack metabolism should
also be conducive to organismal growth by supporting the development of a cryptic, but diverse wrack-based food web. 相似文献