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We examined a 6‐year record of automated chamber‐based soil CO2 efflux (Fs) and the underlying processes in relation to climate and canopy gas exchange at an AmeriFlux site in a seasonally drought‐stressed pine forest. Interannual variability of Fs was large (CV=17%) with a range of 427 g C m?2 yr?1 around a mean annual Fs of 811 g C m?2 yr?1. On average, 76% of the variation of daily mean Fs could be quantified using an empirical model with year‐specific basal respiration rate that was a linear function of tree basal area increment (BAI) and modulated by a common response to soil temperature and moisture. Interannual variability in Fs could be attributed almost equally to interannual variability in BAI (a proxy for above‐ground productivity) and interannual variability in soil climate. Seasonal total Fs was twice as sensitive to soil moisture variability during the summer months compared with temperature variability during the same period and almost insensitive to the natural range of interannual variability in spring temperatures. A strong seasonality in both root respiration (Rr) and heterotrophic respiration (Rh) was observed with the fraction attributed to Rr steadily increasing from 18% in mid‐March to 50% in early June through early July before dropping rapidly to 10% of Fs by mid‐August. The seasonal pattern in Rr (10‐day averages) was strongly linearly correlated with tree transpiration (r2=0.90, P<0.01) as measured using sap flux techniques and gross ecosystem productivity (GEP, r2=0.83, P<0.01) measured by the eddy‐covariance approach. Rr increased by 0.43 g C m?2 day?1 for every 1 g C m?2 day?1 increase in GEP. The strong linear correlation of Rr to seasonal changes in GEP and transpiration combined with longer‐term interannual variability in the base rate of Fs, as a linear function of BAI (r2=0.64, P=0.06), provides compelling justification for including canopy processes in future models of Fs.  相似文献   

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The purpose of this paper is to describe the effects of CO2 and N treatments on soil pCO2, calculated CO2 efflux, root biomass and soil carbon in open-top chambers planted with Pinus ponderosa seedlings. Based upon the literature, it was hypothesized that both elevated CO2 and N would cause increased root biomass which would in turn cause increases in both total soil CO2 efflux and microbial respiration. This hypothesis was only supported in part: both CO2 and N treatments caused significant increases in root biomass, soil pCO2, and calculated CO2 efflux, but there were no differences in soil microbial respiration measured in the laboratory. Both correlative and quantitative comparisons of CO2 efflux rates indicated that microbial respiration contributes little to total soil CO2 efflux in the field. Measurements of soil pCO2 and calculated CO2 efflux provided inexpensive, non-invasive, and relatively sensitive indices of belowground response to CO2 and N treatments.  相似文献   

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Contrasting soil respiration in young and old-growth ponderosa pine forests   总被引:14,自引:0,他引:14  
Three years of fully automated and manual measurements of soil CO2 efflux, soil moisture and temperature were used to explore the diel, seasonal and inter‐annual patterns of soil efflux in an old‐growth (250‐year‐old, O site) and recently regenerating (14‐year‐old, Y site) ponderosa pine forest in central Oregon. The data were used in conjunction with empirical models to determine which variables could be used to predict soil efflux in forests of contrasting ages and disturbance histories. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. Soil CO2 efflux at both sites showed large inter‐annual variability that could be attributed to soil moisture availability in the deeper soil horizons (O site) and the quantity of summer rainfall (Y site). Seasonal patterns of soil CO2 efflux at the O site showed a strong positive correlation between diel mean soil CO2 efflux and soil temperature at 64 cm depth whereas diel mean soil efflux at the Y site declined before maximum soil temperature occurred during summer drought. The use of diel mean soil temperature and soil water potential inferred from predawn foliage water potential measurements could account for 80% of the variance of diel mean soil efflux across 3 years at both sites, however, the functional shape of the soil water potential constraint was site‐specific. Based on the similarity of the decomposition rates of litter and fine roots between sites, but greater productivity and amount of fine litter detritus available for decomposition at the O site, we would expect higher rates of soil CO2 efflux at the O site. However, annual rates were only higher at the O site in one of the 3 years (597 ± 45 vs. 427 ± 80 g C m?2). Seasonal patterns of soil efflux at both sites showed influences of soil water limitations that were also reflected in patterns of canopy stomatal conductance, suggesting strong linkages between above and below ground processes.  相似文献   

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美国黄松组织培养不定根诱导的研究   总被引:7,自引:0,他引:7  
以GD、SH和1/2SH基本培养基对美国黄松不定芽进行不定根的诱导。试验结果表明基本培养基的种类对不定芽形成不定根起主要作用。在1/2SH培养基上附加0.5mg/L的NAA不定根的诱导率为3.3%。试验首次在离体培养条件下,以美国黄松种胚为外植体获得了再生小植株。  相似文献   

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Seasonal and annual respiration of a ponderosa pine ecosystem   总被引:2,自引:0,他引:2  
The net ecosystem exchange of CO2 between forests and the atmosphere, measured by eddy covariance, is the small difference between two large fluxes of photosynthesis and respiration. Chamber measurements of soil surface CO2 efflux (Fs), wood respiration (Fw) and foliage respiration (Ff) help identify the contributions of these individual components to net ecosystem exchange. Models developed from the chamber data also provide independent estimates of respiration costs. We measured CO2 efflux with chambers periodically in 1996–97 in a ponderosa pine forest in Oregon, scaled these measurements to the ecosystem, and computed annual totals for respiration by component. We also compared estimated half-hourly ecosystem respiration at night (Fnc) with eddy covariance measurements. Mean foliage respiration normalized to 10 °C was 0.20 μmol m–2 (hemi-leaf surface area) s–1, and reached a maximum of 0.24 μmol m–2 HSA s–1 between days 162 and 208. Mean wood respiration normalized to 10 °C was 5.9 μmol m–3 sapwood s–1, with slightly higher rates in mid-summer, when growth occurs. There was no significant difference (P > 0.10) between wood respiration of young (45 years) and old trees (250 years). Soil surface respiration normalized to 10 °C ranged from 0.7 to 3.0 μmol m–2 (ground) s–1 from days 23 to 329, with the lowest rates in winter and highest rates in late spring. Annual CO2 flux from soil surface, foliage and wood was 683, 157, and 54 g C m–2 y–1, with soil fluxes responsible for 76% of ecosystem respiration. The ratio of net primary production to gross primary production was 0.45, consistent with values for conifer sites in Oregon and Australia, but higher than values reported for boreal coniferous forests. Below-ground carbon allocation (root turnover and respiration, estimated as Fs– litterfall carbon) consumed 61% of GPP; high ratios such as this are typical of sites with more water and nutrient constraints. The chamber estimates were moderately correlated with change in CO2 storage in the canopy (Fstor) on calm nights (friction velocity u* < 0.25 m s–1; R2 = 0.60); Fstor was not significantly different from summed chamber estimates. On windy nights (u* > 0.25 m s–1), the sum of turbulent flux measured above the canopy by eddy covariance and Fstor was only weakly correlated with summed chamber estimates (R2 = 0.14); the eddy covariance estimates were lower than chamber estimates by 50%.  相似文献   

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We measured CO2 efflux from intact root/rhizosphere systems of 155 day old loblolly (Pinus taeda L.) and ponderosa (Pinus ponderosa Dougl. ex Laws.) pine seedlings in order to study the effects of elevated atmospheric CO2 on the below-ground carbon balance of coniferous tree seedlings. Seedlings were grown in sterilized sand culture, watered daily with either 1, 3.5 or 7 mt M NH 4 + , and maintained in an atmosphere of either 35 or 70 Pa CO2. Carbon dioxide efflux (mol CO2 plant–1 s–1) from the root/rhizosphere system of both species significantly increased when seedlings were grown in elevated CO2, primarily due to large increases in root mass. Specific CO2 efflux (mol CO2 g root–1 s–1) responded to CO2 only under conditions of adequate soil nitrogen availability (3.5 mt M). Under these conditions, CO2 efflux rates from loblolly pine increased 70% from 0.0089 to 0.0151 mol g–1 s–1 with elevated CO2 while ponderosa pine responded with a 59% decrease, from 0.0187 to 0.0077 mol g–1 s–1. Although below ground CO2 efflux from seedlings grown in either sub-optimal (1 mt M) or supra-optimal (7 mt M) nitrogen availability did not respond to CO2, there was a significant nitrogen treatment effect. Seedlings grown in supra-optimal soil nitrogen had significantly increased specific CO2 efflux rates, and significantly lower total biomass compared to either of the other two nitrogen treatments. These results indicate that carbon losses from the root/rhizosphere systems are responsive to environmental resource availability, that the magnitude and direction of these responses are species dependent, and may lead to significantly different effects on whole plant carbon balance of these two forest tree species.  相似文献   

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Tree root respiration utilizes a major portion of the primary production in forests and is an important process in the global carbon cycle. Because of the lack of ecologically relevant methods, tree root respiration in situ is much less studied compared with above-ground processes such as photosynthesis and leaf respiration. This study introduces a new (13)C natural tracer method for measuring tree root respiration in situ. The method partitions tree root respiration from soil respiration in buried root chambers. Rooting media substantially influenced root respiration rates. Measured in three media, the fine root respiration rates of longleaf pine were 0.78, 0.27 and 0.18 mg CO(2) carbon mg(-1) root nitrogen d(-1) at 25 degrees C in the native soil, tallgrass prairie soil, and sand-vermiculite mixture, respectively. Compared with the root excision method, the root respiration rate of longleaf pine measured by the field chamber method was 18% higher when using the native soil as rooting medium, was similar in the prairie soil, but was 42% lower if in the sand-vermiculite medium. This natural tracer method allows the use of an appropriate rooting medium and is capable of measuring root respiration nondestructively in natural forest conditions.  相似文献   

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ABSTRACT.   There is growing recognition of the need to conserve areas used by birds during migration, including forest and upland habitats. Because extensive thinning and burning treatments are planned for ponderosa pine ( Pinus ponderosa ) forests in the southwestern United States, information on the use of these forests by landbirds during migration is needed for conservation planning. We compared species richness among spring, breeding, and fall seasons at 69 points in a ponderosa pine forest to assess changes in landbird communities and the role of different ponderosa pine cover types in habitat selection among seasons. We detected a total of 64 bird species. Bird community similarity was lowest between the breeding and fall seasons and highest between the spring and breeding seasons. Twenty percent of the species detected were present exclusively in the fall and, of these, over half were Neotropical migrants. Only two species (3%) were detected exclusively during the spring. Although we found little difference in bird species similarity among vegetative cover types during the breeding season, forests that contained a deciduous component exhibited higher bird species similarity with each other than with habitats that did not include a deciduous component in spring and fall. In addition, foliage foragers dominated the community in spring and fall, and all Neotropical migrants detected exclusively in fall were found in ponderosa pine forests with a deciduous component. Our results indicate that ponderosa pine forests may be important to migrating or dispersing landbirds in autumn, especially if there is a deciduous component.  相似文献   

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Forest fire dramatically affects the carbon storage and underlying mechanisms that control the carbon balance of recovering ecosystems. In western North America where fire extent has increased in recent years, we measured carbon pools and fluxes in moderately and severely burned forest stands 2 years after a fire to determine the controls on net ecosystem productivity (NEP) and make comparisons with unburned stands in the same region. Total ecosystem carbon in soil and live and dead pools in the burned stands was on average 66% that of unburned stands (11.0 and 16.5 kg C m−2, respectively, P<0.01). Soil carbon accounted for 56% and 43% of the carbon pools in burned and unburned stands. NEP was significantly lower in severely burned compared with unburned stands (P<0.01) with an increasing trend from −125±44 g C m−2 yr−1 (±1 SD) in severely burned stands (stand replacing fire), to −38±96 and +50±47 g C m−2 yr−1 in moderately burned and unburned stands, respectively. Fire of moderate severity killed 82% of trees <20 cm in diameter (diameter at 1.3 m height, DBH); however, this size class only contributed 22% of prefire estimates of bole wood production. Larger trees (> 20 cm DBH) suffered only 34% mortality under moderate severity fire and contributed to 91% of postfire bole wood production. Growth rates of trees that survived the fire were comparable with their prefire rates. Net primary production NPP (g C m−2 yr−1, ±1 SD) of severely burned stands was 47% of unburned stands (167±76, 346±148, respectively, P<0.05), with forb and grass aboveground NPP accounting for 74% and 4% of total aboveground NPP, respectively. Based on continuous seasonal measurements of soil respiration in a severely burned stand, in areas kept free of ground vegetation, soil heterotrophic respiration accounted for 56% of total soil CO2 efflux, comparable with the values of 54% and 49% previously reported for two of the unburned forest stands. Estimates of total ecosystem heterotrophic respiration (Rh) were not significantly different between stand types 2 years after fire. The ratio NPP/Rh averaged 0.55, 0.85 and 1.21 in the severely burned, moderately burned and unburned stands, respectively. Annual soil CO2 efflux was linearly related to aboveground net primary productivity (ANPP) with an increase in soil CO2 efflux of 1.48 g C yr−1 for every 1 g increase in ANPP (P<0.01, r2= 0.76). There was no significant difference in this relationship between the recently burned and unburned stands. Contrary to expectations that the magnitude of NEP 2 years postfire would be principally driven by the sudden increase in detrital pools and increased rates of Rh, the data suggest NPP was more important in determining postfire NEP.  相似文献   

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While there is strong evidence for hydraulic redistribution (HR) of soil water by trees, it is not known if common mycorrhizal networks (CMN) can facilitate HR from mature trees to seedlings under field conditions. Ponderosa pine (Pinus ponderosa) seedlings were planted into root-excluding 61-microm mesh barrier chambers buried in an old-growth pine forest. After 2 yr, several mature trees were cut and water enriched in D(2)O and acid fuchsin dye was applied to the stumps. Fine roots and mycorrhizal root tips of source trees became heavily dyed, indicating reverse sap flow in root xylem transported water from stems throughout root systems to the root hyphal mantle that interfaces with CMN. Within 3 d, D(2)O was found in mesh-chamber seedling foliage > 1 m from source trees; after 3 wk, eight of 10 mesh-chamber seedling stem samples were significantly enriched above background levels. Average mesh-chamber enrichment was 1.8 x greater than that for two seedlings for which the connections to CMN were broken by trenching before D(2)O application. Even small amounts of water provided to mycorrhizas by HR may maintain hyphal viability and facilitate nutrient uptake under drying conditions, which may provide an advantage to seedlings hydraulically linked by CMN to large trees.  相似文献   

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Aim Woody plant expansion and infilling in grasslands and savannas are occurring across a broad range of ecosystems around the globe and are commonly attributed to fire suppression, livestock grazing, nutrient enrichment and/or climate variability. In the western Great Plains, ponderosa pine (Pinus ponderosa) woodlands are expanding across broad geographical and environmental gradients. The objective of this study was to reconstruct the establishment of ponderosa pine in woodlands in the west‐central Great Plains and to identify whether it was mediated by climate variability. Location Our study took place in a 400‐km wide region from the base of the Front Range Mountains (c. 105° W) to the central Great Plains (c. 100° W) and from Nebraska (43° N) to northern New Mexico (36° N), USA. Methods Dates for establishment of ponderosa pine were reconstructed with tree rings in 11 woodland sites distributed across the longitudinal and latitudinal gradients of the study area. Temporal trends in decadal pine establishment were compared with summer Palmer Drought Severity Index (PDSI). Annual trends in pine establishment from 1985 to 2005 were compared with seasonal PDSI, temperature and moisture availability. Results Establishment of ponderosa pine occurred in the study area in all but one decade (1770s) between the 1750s and the early 2000s, with over 35% of establishment in the region occurring after 1980. Pine establishment was highly variable among sites. Across the region, decadal pine establishment was persistently low from 1940 to 1960, when PDSI was below average. Annual pine establishment from 1985 to 2005 was positively correlated with summer PDSI and inversely correlated with minimum spring temperatures. Main conclusions Most ponderosa pine woodlands pre‐date widespread Euro‐American settlement of the region around c. ad 1860 and currently have stable tree populations. High variability in the timing of establishment of pine among sites highlights the multiplicity of factors that can drive woodland dynamics, including land use, fire history, CO2 enrichment, tree population dynamics and climate. Since the 1840s, the influence of climate was most notable across the study area during the mid‐20th century, when the establishment of pine was suppressed by two significant droughts. The past sensitivity of establishment of ponderosa pine to drought suggests that woodland expansion will be negatively affected by predicted increases in temperature and drought in the Great Plains.  相似文献   

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The b/c intron of the mitochondrial nad1 gene, was sequenced to characterize the indel region of ponderosa pine, Pinus ponderosa. The sequence in ponderosa pine was aligned with the sequence in Scots pine, Pinus sylvestris, to design seven primers that are useful for sequencing and for revealing size variation in amplified fragments in ponderosa pine, Scots pine, and limber pine, Pinus flexilis. These primers reveal variability in all three species, and the pattern of variability within ponderosa pine is described by a preliminary survey. The indel region of ponderosa pine contains three distinct elements with lengths of 31, 32, and 34 bp. Received: 1 March 2000 / Accepted: 14 April 2000<@head-com-p1a.lf>Communicated by P.M.A. Tigerstedt  相似文献   

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Seasonal activity of superoxide dismutase (SOD, EC 1.15.1.1). ascorbate peroxidase (APOD, EC 1.11.1.11) and guaiacol-oxidizing enzymes (GPODs, EC 1.11.1.7) was examined in needles of 12- to 15-year-old ponderosa pine (Pinus ponderosa Laws.) trees which received ozone (O3) and acid precipitation treatment. Individual branches were enclosed in branch exposure chambers delivering either charcoal-filtered (O3-reduced) air, ambient air, or air with twice ambient (2 x ambient) concentrations of O3. Acid precipitation treatments were rain of pH 3.0 or 5.1 or no rain. Changes in antioxidant enzyme activity were not a consistent response to O3 fumigation or acid precipitation, but when observed, they occurred most often in the O3-sensitive clone and in symptomatic, fumigated branches. In the second year of fumigation. O3 fleck symptoms appeared on needles of the sensitive clone as early as July and APOD activities were significantly increased by O3 at all sampling dates. In the tolerant clone, antioxidant enzyme activities were not significantly changed by O3 in the first season of fumigation (March to December 1990), not even during an episode when ambient O3 concentrations reached 125 nl 1?1 (240 nl 1?1 in 2x ambient chambers). No foliar symptoms were observed on needles of the tolerant clone during this year. However, in the second year of fumigation (1992), O3 fleck symptoms were observed on the tolerant clone and APOD activities were significantly increased in previous-year needles. The tolerant clone had SOD, APOD, and GPOD activities at least 40% higher than those of the sensitive clone before fumigation and 65, 178, and 119% higher, respectively, during both years of fumigation. The higher constitutive levels of these enzymes may have protected against foliar injury in 1990, however in 1992 we concluded that the stimulations in antioxidant enzyme activities observed in symptomatic branches of both clones were a consequence of O3 injury. Total (intra- and extracellular) activities of the antioxidant enzymes did not appear to be good indicators of O3 tolerance. Phenotypically, the O3-tolerant clone was much more vigorous and in both years of fumigation, gas exchange rates were 30 to 71% higher than in the sensitive clone (P. D. Anderson, unpublished data). The greater vigor of the tolerant clone may allow more carbon allocation to protective and repair processes which include, but are not restricted to, the turnover of antioxidant enzymes and metabolites.  相似文献   

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