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Rice carbon balance under elevated CO2 总被引:2,自引:1,他引:1
Hidemitsu Sakai Kazuyuki Yagi Kazuhiko Kobayashi Shigeto Kawashima 《The New phytologist》2001,150(2):241-249
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Pascal A. Niklaus 《Global Change Biology》1998,4(4):451-458
Microbial responses to three years of CO2 enrichment (600 μL L–1) in the field were investigated in calcareous grassland. Microbial biomass carbon (C) and soil organic C and nitrogen (N) were not significantly influenced by elevated CO2. Microbial C:N ratios significantly decreased under elevated CO2 (– 15%, P = 0.01) and microbial N increased by + 18% (P = 0.04). Soil basal respiration was significantly increased on one out of 7 sampling dates (+ 14%, P = 0.03; December of the third year of treatment), whereas the metabolic quotient for CO2 (qCO2 = basal respiration/microbial C) did not exhibit any significant differences between CO2 treatments. Also no responses of microbial activity and biomass were found in a complementary greenhouse study where intact grassland turfs taken from the field site were factorially treated with elevated CO2 and phosphorus (P) fertilizer (1 g P m–2 y–1). Previously reported C balance calculations showed that in the ecosystem investigated growing season soil C inputs were strongly enhanced under elevated CO2. It is hypothesized that the absence of microbial responses to these enhanced soil C fluxes originated from mineral nutrient limitations of microbial processes. Laboratory incubations showed that short-term microbial growth (one week) was strongly limited by N availability, whereas P was not limiting in this soil. The absence of large effects of elevated CO2 on microbial activity or biomass in such nutrient-poor natural ecosystems is in marked contrast to previously published large and short-term microbial responses to CO2 enrichment which were found in fertilized or disturbed systems. It is speculated that the absence of such responses in undisturbed natural ecosystems in which mineral nutrient cycles have equilibrated over longer periods of time is caused by mineral nutrient limitations which are ineffective in disturbed or fertilized systems and that therefore microbial responses to elevated CO2 must be studied in natural, undisturbed systems. 相似文献
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- 1 In order to study the dynamics of primary production and decomposition in the lake littoral, an interface zone between the pelagial, the catchment and the atmosphere, we measured ecosystem/atmosphere carbon dioxide (CO2) exchange in the littoral zone of an eutrophic boreal lake in Finland during two open water periods (1998–1999). We reconstructed the seasonal net CO2 exchange and identified the key factors controlling CO2 dynamics. The seasonal net ecosystem exchange (NEE) was related to the amount of carbon accumulated in plant biomass.
- 2 In the continuously inundated zones, spatial and temporal variation in the density of aerial shoots controlled CO2 fluxes, but seasonal net exchange was in most cases close to zero. The lower flooded zone had a net CO2 uptake of 1.8–6.2 mol m?2 per open water period, but the upper flooded zone with the highest photosynthetic capacity and above‐ground plant biomass, had a net CO2 loss of 1.1–7.1 mol m?2 per open water period as a result of the high respiration rate. The excess of respiration can be explained by decomposition of organic matter produced on site in previous years or leached from the catchment.
- 3 Our results from the two study years suggest that changes in phenology and water level were the prime cause of the large interannual difference in NEE in the littoral zone. Thus, the littoral is a dynamic buffer and source for the load of allochthonous and autochthonous carbon to small lakes.
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Increased fire frequency in the Great Basin of North America's intermountain West has led to large‐scale conversion of native sagebrush (Artemisia tridentata Nutt.) communities to postfire successional communities dominated by native and non‐native annual species during the last century. The consequences of this conversion for basic ecosystem functions, however, are poorly understood. We measured net ecosystem CO2 exchange (NEE) and evapotranspiration (ET) during the first two dry years after wildfire using a 4‐m diameter (16.4 m3) translucent static chamber (dome), and found that both NEE and ET were higher in a postfire successional ecosystem (?0.9–2.6 µ mol CO2 m?2 s?1 and 0.0–1.0 mmol H2O m?2 s?2, respectively) than in an adjacent intact sagebrush ecosystem (?1.2–2.3 µ mol CO2 m?2 s?1 and ?0.1–0.8 mmol H2O m?2 s?2, respectively) during relatively moist periods. Higher NEE in the postfire ecosystem appears to be due to lower rates of above‐ground plant respiration while higher ET appears to be caused by higher surface soil temperatures and increased soil water recharge after rains. These patterns disappeared or were reversed, however, when the conditions were drier. Daily net ecosystem productivity (NEP; g C m?2 d?1), derived from multiple linear regressions of measured fluxes with continuously measured climate variables, was very small (close to zero) throughout most of the year. The wintertime was an exception in the intact sagebrush ecosystem with C losses exceeding C gains leading to negative NEP while C balance of the postfire ecosystem remained near zero. Taken together, our results indicate that wildfire‐induced conversion of native sagebrush steppe to ecosystems dominated by herbaceous annual species may have little effect on C balance during relatively dry years (except in winter months) but may stimulate water loss immediately following fires. 相似文献
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JIAHONG LI THOMAS L. POWELL TROY J. SEILER DAVID P. JOHNSON HANS P. ANDERSON ROSVEL BRACHO† BRUCE A. HUNGATE‡ CHARLES R. HINKLE§ BERT G. DRAKE 《Global Change Biology》2007,13(6):1101-1113
Hurricane disturbances have profound impacts on ecosystem structure and function, yet their effects on ecosystem CO2 exchange have not been reported. In September 2004, our research site on a fire‐regenerated scrub‐oak ecosystem in central Florida was struck by Hurricane Frances with sustained winds of 113 km h−1 and wind gusts as high as 152 km h−1. We quantified the hurricane damage on this ecosystem resulting from defoliation: we measured net ecosystem CO2 exchange, the damage and recovery of leaf area, and determined whether growth in elevated carbon dioxide concentration in the atmosphere (Ca) altered this disturbance. The hurricane decreased leaf area index (LAI) by 21%, which was equal to 60% of seasonal variation in canopy growth during the previous 3 years, but stem damage was negligible. The reduction in LAI led to a 22% decline in gross primary production (GPP) and a 25% decline in ecosystem respiration (Re). The compensatory declines in GPP and Re resulted in no significant change in net ecosystem production (NEP). Refoliation began within a month after the hurricane, although this period was out of phase with the regular foliation period, and recovered 20% of the defoliation loss within 2.5 months. Full recovery of LAI, ecosystem CO2 assimilation, and ecosystem respiration did not occur until the next growing season. Plants exposed to elevated Ca did not sustain greater damage, nor did they recover faster than plants grown under ambient Ca. Thus, our results indicate that hurricanes capable of causing significant defoliation with negligible damage to stems have negligible effects on NEP under current or future CO2‐enriched environment. 相似文献
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Stomatal function mediates physiological trade‐offs associated with maintaining a favourable H2O balance in leaf tissues while acquiring CO2 as a photosynthetic substrate. The C3 and C4 species appear to have different patterns of stomatal response to changing light conditions, and variation in this behaviour may have played a role in the functional diversification of the different photosynthetic pathways. In the current study, we used gain analysis theory to characterize the stomatal conductance response to light intensity in nine different C3, C4 and C3‐C4 intermediate species Flaveria species. The response of stomatal conductance (gs) to a change in light intensity represents both a direct (related to a change in incident light intensity, I) and indirect (related to a change in intercellular CO2 concentration, Ci) response. The slope of the line relating the change in gs to Ci was steeper in C4 species, compared with C3 species, with C3‐C4 species having an intermediate response. This response reflects the greater relative contribution of the indirect versus direct component of the gs versus I response in the C4 species. The C3‐C4 species, Flaveria floridana, exhibited a C4‐like response whereas the C3‐C4 species, Flaveria sonorensis and Flaveria chloraefolia, exhibited C3‐like responses, similar to their hypothesized position along the evolutionary trajectory of the development of C4 photosynthesis. There was a positive correlation between the relative contribution of the indirect component of the gs versus I response and water use efficiency when evaluated across all species. Assuming that the C3‐C4 intermediate species reflect an evolutionary progression from fully expressed C3 ancestors, the results of the current study demonstrate an increase in the contribution of the indirect component of the gs versus I response as taxa evolve toward the C4 extreme. The greater relative contribution of the indirect component of the stomatal response occurs through both increases in the indirect stomatal components and through decreases in the direct. Increases in the magnitude of the indirect component may be related to the maintenance of higher water use efficiencies in the intermediate evolutionary stages, before the appearance of fully integrated C4 photosynthesis. 相似文献
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Soil CO2 efflux in a boreal pine forest under atmospheric CO2 enrichment and air warming 总被引:3,自引:0,他引:3
The response of forest soil CO2 efflux to the elevation of two climatic factors, the atmospheric concentration of CO2 (↑CO2 of 700 μmol mol−1 ) and air temperature (↑ T with average annual increase of 5°C), and their combination (↑CO2 +↑ T ) was investigated in a 4-year, full-factorial field experiment consisting of closed chambers built around 20-year-old Scots pines ( Pinus sylvestris L.) in the boreal zone of Finland. Mean soil CO2 efflux in May–October increased with elevated CO2 by 23–37%, with elevated temperature by 27–43%, and with the combined treatment by 35–59%. Temperature elevation was a significant factor in the combined 4-year efflux data, whereas the effect of elevated CO2 was not as evident. Elevated temperature had the most pronounced impact early and late in the season, while the influence of elevated CO2 alone was especially notable late in the season. Needle area was found to be a significant predictor of soil CO2 efflux, particularly in August, a month of high root growth, thus supporting the assumption of a close link between whole-tree physiology and soil CO2 emissions. The decrease in the temperature sensitivity of soil CO2 efflux observed in the elevated temperature treatments in the second year nevertheless suggests the existence of soil response mechanisms that may be independent of the assimilating component of the forest ecosystem. In conclusion, elevated atmospheric CO2 and air temperature consistently increased forest soil CO2 efflux over the 4-year period, their combined effect being additive, with no apparent interaction. 相似文献
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Graham J. Hymus David P. Johnson Sabina Dore† Hans P. Anderson C. Ross Hinkle‡ Bert G. Drake 《Global Change Biology》2003,9(12):1802-1812
We report the results of a 2‐year study of effects of the elevated (current ambient plus 350 μmol CO2 mol?1) atmospheric CO2 concentration (Ca) on net ecosystem CO2 exchange (NEE) of a scrub–oak ecosystem. The measurements were made in open‐top chambers (OTCs) modified to function as open gas‐exchange systems. The OTCs enclosed samples of the ecosystem (ca. 10 m2 surface area) that had regenerated after a fire, 5 years before, in either current ambient or elevated Ca. Throughout the study, elevated Ca increased maximum NEE (NEEmax) and the apparent quantum yield of the NEE (φNEE) during the photoperiod. The magnitude of the stimulation of NEEmax, expressed per unit ground area, was seasonal, rising from 50% in the winter to 180% in the summer. The key to this stimulation was effects of elevated Ca, and their interaction with the seasonal changes in the environment, on ecosystem leaf area index, photosynthesis and respiration. The separation of these factors was difficult. When expressed per unit leaf area the stimulation of the NEEmax ranged from 7% to 60%, with the increase being dependent on increasing soil water content (Wsoil). At night, the CO2 effluxes from the ecosystem (NEEnight) were on an average 39% higher in elevated Ca. However, the increase varied between 6% and 64%, and had no clear seasonality. The partitioning of NEEnight into its belowground (Rbelow) and aboveground (Rabove) components was carried out in the winter only. A 35% and 27% stimulation of NEEnight in December 1999 and 2000, respectively, was largely due to a 26% and 28% stimulation of Rbelow in the respective periods, because Rbelow constituted ca. 87% of NEEnight. The 37% and 42% stimulation of Rabove in December 1999 and 2000, respectively, was less than the 65% and 80% stimulation of the aboveground biomass by elevated Ca at these times. An increase in the relative amount of the aboveground biomass in woody tissue, combined with a decrease in the specific rate of stem respiration of the dominant species Quercus myrtifolia in elevated Ca, was responsible for this effect. Throughout this study, elevated Ca had a greater effect on carbon uptake than on carbon loss, in terms of both the absolute flux and relative stimulation. Consequently, for this scrub–oak ecosystem carbon sequestration was greater in the elevated Ca during this 2‐year study period. 相似文献
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Canopy photosynthesis of crops and native plant communities exposed to long-term elevated CO2 总被引:8,自引:3,他引:5
Abstract. There have been seven studies of canopy photosynthesis of plants grown in elevated atmospheric CO2 : three of seed crops, two of forage crops and two of native plant ecosystems. Growth in elevated CO2 increased canopy photosynthesis in all cases. The relative effect of CO2 was correlated with increasing temperature: the least stimulation occurred in tundra vegetation grown at an average temperature near 10°C and the greatest in rice grown at 43°C. In soybean, effects of CO2 were greater during leaf expansion and pod fill than at other stages of crop maturation. In the longest running experiment with elevated CO2 treatment to date, monospecific stands of a C3 sedge, Scirpus olneyi (Grey), and a C4 grass, Spartina patens (Ait.) Muhl., have been exposed to twice normal ambient CO2 concentrations for four growing seasons, in open top chambers on a Chesapeake Bay salt marsh. Net ecosystem CO2 exchange per unit green biomass (NCEb ) increased by an average of 48% throughout the growing season of 1988, the second year of treatment. Elevated CO2 increased net ecosystem carbon assimilation by 88% in the Scirpus olneyi community and 40% in the Spartina patens community. 相似文献
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In diverse plant communities the relative contribution of species to community biomass may change considerably in response to elevated CO2. Along with species‐specific biomass responses, reproduction is likely to change as well with increasing CO2 and might further accelerate shifts in species composition. Here, we ask if, after 5 years of CO2 exposure, seed production and seed quality in natural nutrient‐poor calcareous grassland are affected by elevated CO2 (650 μ L L?1 vs 360 μ L L?1) and how this might affect long‐term community dynamics. The effect of elevated CO2 on the number of flowering shoots (+ 24%, P < 0.01) and seeds (+ 29%, P = 0.06) at the community level was similar to above ground biomass responses in this year, suggesting that the overall allocation to sexual reproduction remained unchanged. Compared among functional groups of species we found a 42% increase in seed number (P < 0.01) of graminoids, a 33% increase (P = 0.07) in forbs, and no significant change in legumes (? 38%, n.s.) under elevated CO2. Large responses particularly of two graminoid species and smaller responses of many forb species summed up to the significant or marginally significant increase in seed number of graminoids and forbs, respectively. In several species the increase in seed number resulted both from an increase in flowering shoots and an increase in inflorescence size. In most species, seeds tended to be heavier (+ 12%, P < 0.01), and N‐concentration of seeds was significantly reduced in eight out of 13 species. The fraction of germinating seeds did not differ between seeds produced in ambient and elevated CO2, but time to germination was significantly shortened in two species and prolonged in one species when seeds had been produced in elevated CO2. Results suggest that species specific increases in seed number and changes in seed quality will exert substantial cumulative effects on community composition in the long run. 相似文献
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Respiration measured as CO2 efflux was determined at various soil O2 and CO2 concentrations for individual, attached roots of a succulent perennial from the Sonoran Desert, Agave deserti Engelm. The respiration rate increased with increasing O2 concentration up to about 16% O2 for established roots and 5% O2 for rain roots (fine branch roots on established roots induced by wetting of the soil) and then remained fairly constant up to 21% O2 . When O2 was decreased from 21 to 0%, the respiration rates were similar to those obtained with increasing O2 concentration. The CO2 concentration in the root zone, which for the shallow-rooted A. deserti in the field was about 1 000 μl l-1 , did not affect root respiration at concentrations up to 2 000 μl l-1 , but higher concentrations reduced it, respiration being abolished at 20 000 μl l-1 (2%) CO2 for both established and rain roots. Upon lowering CO2 to 1 000 μl l-1 after exposure to concentrations up to 10000 μl l-1 CO2 , inhibition of respiration was reversible. Uptake of the vital stain neutral red by root cortical cells was reduced to zero, indicating cell death, in about 4 h at 2% CO2 , substantiating the detrimental effects of high soil CO2 concentrations on roots of A. deserti . This CO2 response may explain why roots of desert succulents tend to occur in porous, well-aerated soils. 相似文献
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Water repellency is a widespread characteristic of soils that can modify soil moisture content and distribution and is implicated in important processes such as aggregation and carbon sequestration. Repellency arises as a consequence of organic matter inputs; as elevated atmospheric CO2 is known to modify such inputs, we tested the repellency of a grassland soil after 5 years of exposure to elevated CO2 in a free air carbon dioxide enrichment experiment. Using a water droplet penetration time test, we found a significant reduction in repellency at elevated CO2 in samples at field moisture content. As many of the processes potentially influenced by repellency have been shown to be modified at elevated CO2 (e.g. soil aggregation, C sequestration, recruitment from seed), we suggest that further exploration of this phenomenon could enhance our understanding of CO2 effects on ecosystem function. The mechanism responsible for the change in repellency has not been identified. 相似文献
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YaiR. Rosenthal 《Global Change Biology》1998,4(5):539-547
The effects of elevated CO2 on tropical ecosystems were studied in the artificial rain forest mesocosm at Biosphere 2, a large-scale and ecologically diverse experimental facility located in Oracle, Arizona. The ecosystem responses were assessed by comparing the whole-system net gas exchange (NEE) upon changing CO2 levels from 900 to 450 ppmV. The day-NEE was significantly higher in the elevated CO2 treatment. In both experiments, the NEE rates were similar to values observed in natural analogue systems. Variations in night-NEE, reflecting both soil CO2 efflux and plants respiration, covaried with temperature but showed no clear correlation with atmospheric CO2 levels. After correcting for changes in CO2 efflux we show that the rain forest net photosynthesis increased in response to increasing atmospheric CO2. The photosynthetic enhancement was expressed in higher quantum yields, maximum assimilation rates and radiation use efficiency. The results suggest that photosynthesis in large tropical trees is CO2 sensitive, at least following short exposures of days to weeks. Taken at face value, the data suggest that as a result of anthropogenic emissions of CO2, tropical rain forests may shift out of steady state, and become a carbon sink at least for short periods. However, a better understanding of the unique conditions and phenomena in Biosphere 2 is necessary before these results are broadly useful. 相似文献
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The nature of the interaction between drought and elevated CO2 partial pressure (pCa) is critically important for the effects of global change on crops. Some crop models assume that the relative responses of transpiration and photosynthesis to soil water deficit are unaltered by elevated pCa, while others predict decreased sensitivity to drought at elevated pCa. These assumptions were tested by measuring canopy photosynthesis and transpiration in spring wheat (cv. Minaret) stands grown in boxes with 100 L rooting volume. Plants were grown under controlled environments with constant light (300 µmol m?2 s?1) at ambient (36 Pa) or elevated (68 Pa) pCa and were well watered throughout growth or had a controlled decline in soil water starting at ear emergence. Drought decreased final aboveground biomass (?15%) and grain yield (?19%) while elevated pCa increased biomass (+24%) and grain yield (+29%) and there was no significant interaction. Elevated pCa increased canopy photosynthesis by 15% on average for both water regimes and increased dark respiration per unit ground area in well‐watered plants, but not drought‐grown ones. Canopy transpiration and photosynthesis were decreased in drought‐grown plants relative to well‐watered plants after about 20–25 days from the start of the drought. Elevated pCa decreased transpiration only slightly during drought, but canopy photosynthesis continued to be stimulated so that net growth per unit water transpired increased by 21%. The effect of drought on canopy photosynthesis was not the consequence of a loss of photosynthetic capacity initially, as photosynthesis continued to be stimulated proportionately by a fixed increase in irradiance. Drought began to decrease canopy transpiration below a relative plant‐available soil water content of 0.6 and canopy photosynthesis and growth below 0.4. The shape of these responses were unaffected by pCa, supporting the simple assumption used in some models that they are independent of pCa. 相似文献
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Responses of tomato leaves in a greenhouse to light and CO2 were examined at the transient stage at the end of winter, when both photoperiod and irradiance gradually increase. Additionally, CO2 fluxes were calculated for a greenhouse without supplementary lighting and without CO2 enrichment based on CO2 sinks (plant photosynthesis) and CO2 sources (plant and substrate respiration). In January, tomato leaves in the greenhouse showed low photosynthesis with a maximum assimilation of 6–8 μmol CO2 m−2 s−1, a quantum yield of 0.06 μmol CO2 μmol−1 photosynthetic active radiation (PAR) and a low light compensation point of 26 μmol PAR m−2 s−1, a combination which classifies them as shade leaves. In February, tomato leaves increased their light compensation point to 39 μmol PAR m−2 s−1 and quantum yield to 0.08, the former indicating the adaptation to increased irradiance and photoperiod. These tomato leaves increased their transpiration from 0.4 to 0.9 in January to ∼2 mmol H2O m−2 s−1 in February. Both photosynthesis and transpiration were primarily limited by light but neither by stomatal conductivity nor by CO2. In January, light response of photosynthesis, dark respiration and transpiration were negligibly affected by increasing CO2 concentrations from 600 to 900 ppm CO2 under low light conditions, indicating no benefit of CO2 enrichment unless light intensity increased. In February, tomato leaves were photoinhibited at inherent greenhouse CO2 concentrations on the first sunny day; this photoinhibition was further enhanced by an increased CO2 concentration of 1000 ppm. CO2 fluxes in the greenhouse appeared strongly dependent on solar radiation. After exceeding the light compensation point in the morning, greenhouse CO2 concentrations decreased by 58 or by 110 ppm CO2 h−1 on a sunny day in January or February and by 23 ppm on overcast days in both months. Calculated per overall tomato canopy, plant photosynthesis contributed 42–50% to the morning CO2 depletion in the greenhouse. Dark respiration of tomato leaves was ∼2 μmol CO2 m−2 s−1 in January and ∼3 μmol CO2 m−2 s−1 in February. This dark respiration resulted in rises of 15 and 17 ppm CO2 h−1 at night in the greenhouse compartment and was identified as primary source of CO2. Respiration of the substrate used to grow the plants, which produced 7.3 ppm CO2 h−1, was identified as secondary source of CO2. The combined plant and substrate respiration resulted in peaks of up to 900 ppm CO2 in the greenhouse before dawn. 相似文献