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Nitrogen isotope composition of tomato (Lycopersicon esculentum Mill. cv. T-5) grown under ammonium or nitrate nutrition (1996)

EVANS, R. D. ; BLOOM, A. J. ; SUKRAPANNA, S. S. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Plant, cell & environment 19 (1996), S. 0

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ISSN: 1365-3040

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Studies that quantify plant δ15N often assume that fractionation during nitrogen uptake and intra-plant variation in δ15N are minimal. We tested both assumptions by growing tomato (Lycopersicon esculetum Mill. cv. T-5) at NH4+ or NO−3 concentrations typical of those found in the soil. Fractionation did not occur with uptake; whole-plant δ15N was not significantly different from source δ15 N for plants grown on either nitrogen form. No intra-plant variation in δ15N was observed for plants grown with NH+4. In contrast. δ15N of leaves was as much as 5.8% greater than that of roots for plants grown with NO−3. The contrasting patterns of intra-plant variation are probably caused by different assimilation patterns. NH+4 is assimilated immediately in the root, so organic nitrogen in the shoot and root is the product of a single assimilation event. NO−3 assimilation can occur in shoots and roots. Fractionation during assimilation caused the δ15N of NO−3 to become enriched relative to organic nitrogen; the δ15N of NO−3 was 11.1 and 12.9% greater than the δ15N of organic nitrogen in leaves and roots, respectively. Leaf δ15N may therefore be greater than that of roots because the NO−3 available for assimilation in leaves originates from a NO−3 pool that was previously exposed to nitrate assimilation in the root.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00010.x

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Carbon isotope composition of C4 grasses is influenced by light and water supply (1996)

BUCHMANN, N. ; BROOKS, J. R. ; RAPP, K. D. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Plant, cell & environment 19 (1996), S. 0

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ISSN: 1365-3040

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The carbon isotope composition of C4 grasses has the potential to be used as an indicator of changes in the isotopic composition and concentration of atmospheric CO2, especially for climate reconstruction. The usefulness of C4 grasses for this purpose hinges on the assumption that their photosynthetic discrimination against 13C remains constant in a wide range of environmental conditions. We tested this assumption by examining the effects of light and water stress on the carbon isotope composition of C4 grasses using different biochemical subtypes (NADP-ME, NAD-ME, PCK) in glasshouse experiments. We grew 14 different C4 grass species in four treatments: sun-watered, sun-drought, shade-watered and shade-drought. Carbon isotope discrimination (Δ) rarely remained constant. In general, Δ values were lowest in sun-watered grasses, greater for sun-drought plants and even higher for plants of the shade-watered treatment. The highest Δ values were generally found in the most stressed grasses, the shade-drought plants. Grasses of the NADP-ME subtype were the least influenced by a change in environmental variables, followed by PCK and NAD-ME subtypes. Water availability affected the carbon isotope discrimination less than light limitation in PCK and NAD-ME subtypes, but similarly in NADP-ME subtypes.In another experiment, we studied the effect of increasing light levels (150 to 1500 μmol photons m−2 s−1) on the Δ values of 18 well-watered C4 grass species. Carbon isotope discrimination remained constant until photon flux density (PFD) was less than 700 μmol photons m−2 s−1. Below this light level, Δ values increased with decreasing irradiance for all biochemical subtypes. The change in A was less pronounced in NADP-ME and PCK than in NAD-ME grasses. Grasses grown in the field and in the glasshouse showed a similar pattern. Thus, caution should be exercised when using C4 plants under varying environmental conditions to monitor the concentration or carbon isotopic composition of atmospheric CO2 in field/glasshouse studies or climate reconstruction.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00331.x

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Rooting depth, water availability, and vegetation cover along an aridity gradient in Patagonia (1996)

Schulze, E. -D. ; Mooney, H. A. ; Sala, O. E. ; [et al.]

Springer

Oecologia 108 (1996), S. 503-511

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ISSN: 1432-1939

Keywords: Patagonia-vegetation ; Root distribution ; 13C-, 18O-, D-Isotope composition ; Water ; Plant succession

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Above-and belowground biomass distribution, isotopic composition of soil and xylem water, and carbon isotope ratios were studied along an aridity gradient in Patagonia (44–45°S). Sites, ranging from those with Nothofagus forest with high annual rainfall (770 mm) to Nothofagus scrub (520 mm), Festuca (290 mm) and Stipa (160 mm) grasslands and into desert vegetation (125 mm), were chosen to test whether rooting depth compensates for low rainfall. Along this gradient, both mean above-and belowground biomass and leaf area index decreased, but average carbon isotope ratios of sun leaves remained constant (at-27‰), indicating no major differences in the ratio of assimilation to stomatal conductance at the time of leaf growth. The depth of the soil horizon that contained 90% of the root biomass was similar for forests and grasslands (about 0.80–0.50 m), but was shallower in the desert (0.30 m). In all habitats, roots reached water-saturated soils or ground water at 2–3 m depth. The depth profile of oxygen and hydrogen isotope ratios of soil water corresponded inversely to volumetric soil water contents and showed distinct patterns throughout the soil profile due to evaporation, water uptake and rainfall events of the past year. The isotope ratios of soil water indicated that high soil moisture at 2–3 m soil depth had originated from rainy periods earlier in the season or even from past rainy seasons. Hydrogen and oxygen isotope ratios of xylem water revealed that all plants used water from recent rain events in the topsoil and not from water-saturated soils at greater depth. However, this study cannot explain the vegetation zonation along the transect on the basis of water supply to the existing plant cover. Although water was accessible to roots in deeper soil layers in all habitats, as demonstrated by high soil moisture, earlier rain events were not fully utilized by the current plant cover during summer drought. The role of seedling establishment in determining species composition and vegetation type, and the indirect effect of seedling establishment on the use of water by fully developed plant cover, are discussed in relation to climate change and vegetation modelling.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00333727

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Leaf carbon isotope discrimination and nitrogen content for riparian trees along elevational transects (1997)

Sparks, J. P. ; Ehleringer, J. R.

Springer

Oecologia 109 (1997), S. 362-367

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ISSN: 1432-1939

Keywords: Key words Stable isotope ; Carbon isotope ratio ; Carbon isotope discrimination ; Riparian ecosystem ; Water-use efficiency

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Leaf carbon isotope discrimination (Δ), seasonal estimates of the leaf-to-air water vapor gradient on a molar basis (ω), and leaf nitrogen contents were examined in three riparian tree species (Populus fremontii, P. angustifolia, and Salix exigua) along elevational transects in northern and southern Utah USA (1500–2670 m and 600–1820 m elevational gradients, respectively). The ω values decreased with elevation for all species along transects. Plants growing at higher elevations exhibited lower Δ values than plants at lower elevations (P. fremontii, 22.9‰ and 19.5‰, respectively; P. angustifolia, 23.2‰ and 19.2‰, respectively; and S.␣exigua, 21.1‰ and 19.1‰, respectively). Leaf nitrogen content increased with elevation for all species, suggesting that photosynthetic capacity at a given intercellular carbon dioxide concentration was greater at higher elevations. Leaf Δ and nitrogen content values were highly correlated, implying that leaves with higher photosynthetic capacities also had lower intercellular carbon dioxide concentrations. No significant interannual differences were detected in carbon isotope discrimination.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050094

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5

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Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana) (1997)

Buchmann, N. ; Guehl, J.-M. ; Barigah, T. S. ; [et al.]

Springer

Oecologia 110 (1997), S. 120-131

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ISSN: 1432-1939

Keywords: Key words Carbon discrimination ; δ13C ; δ18O ; Canopy CO2 profiles ; Soil respiration.

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Canopy CO2 concentrations in a tropical rainforest in French Guiana were measured continuously for 5 days during the 1994 dry season and the 1995 wet season. Carbon dioxide concentrations ([CO2]) throughout the canopy (0.02–38 m) showed a distinct daily pattern, were well-stratified and decreased with increasing height into the canopy. During both seasons, daytime [CO2] in the upper and middle canopy decreased on average 7–10 μmol mol−1 below tropospheric baseline values measured at Barbados. Within the main part of the canopy (≥ 0.7 m), [CO2] did not differ between the wet and dry seasons. In contrast, [CO2] below 0.7 m were generally higher during the dry season, resulting in larger [CO2] gradients. Supporting this observation, soil CO2 efflux was on average higher during the dry season than during the wet season, either due to diffusive limitations and/or to oxygen deficiency of root and microbial respiration. Soil respiration rates decreased by 40% after strong rain events, resulting in a rapid decrease in canopy [CO2] immediately above the forest floor of about 50␣μmol mol−1. Temporal and spatial variations in [CO2]canopy were reflected in changes of δ13Ccanopy and δ18Ocanopy values. Tight relationships were observed between δ13C and δ18O of canopy CO2 during both seasons (r 2 〉 0.86). The most depleted δ13Ccanopy and δ18Ocanopy values were measured immediately above the forest floor (δ13C = −16.4‰; δ18O = 39.1‰ SMOW). Gradients in the isotope ratios of CO2 between the top of the canopy and the forest floor ranged between 2.0‰ and 6.3‰ for δ13C, and between 1.0‰ and 3.5‰ for δ18O. The δ13Cleaf and calculated c i/c a of foliage at three different positions were similar for the dry and wet seasons indicating that the canopy maintained a constant ratio of photosynthesis to stomatal conductance. About 20% of the differences in δ13Cleaf within the canopy was accounted for by source air effects, the remaining 80% must be due to changes in c i/c a. Plotting 1/[CO2] vs. the corresponding δ13C ratios resulted in very tight, linear relationships (r 2 = 0.99), with no significant differences between the two seasons, suggesting negligible seasonal variability in turbulent mixing relative to ecosystem gas exchange. The intercepts of these relationships that should be indicative of the δ13C of respired sources were close to the measured δ13C of soil respired CO2 and to the δ13C of litter and soil organic matter. Estimates of carbon isotope discrimination of the entire ecosystem, Δe, were calculated as 20.3‰ during the dry season and as 20.5‰ during the wet season.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050140

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6

Electronic Resource

A global analysis of root distributions for terrestrial biomes (1996)

Jackson, R. B. ; Canadell, J. ; Ehleringer, J. R. ; [et al.]

Springer

Oecologia 108 (1996), S. 389-411

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ISSN: 1432-1939

Keywords: Terrestrial biomes ; Cumulative root fraction ; Root biomass ; Rooting density ; Soil depth

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Understanding and predicting ecosystem functioning (e.g., carbon and water fluxes) and the role of soils in carbon storage requires an accurate assessment of plant rooting distributions. Here, in a comprehensive literature synthesis, we analyze rooting patterns for terrestrial biomes and compare distributions for various plant functional groups. We compiled a database of 250 root studies, subdividing suitable results into 11 biomes, and fitted the depth coefficient β to the data for each biome (Gale and Grigal 1987). β is a simple numerical index of rooting distribution based on the asymptotic equation Y=1-βd, where d = depth and Y = the proportion of roots from the surface to depth d. High values of β correspond to a greater proportion of roots with depth. Tundra, boreal forest, and temperate grasslands showed the shallowest rooting profiles (β=0.913, 0.943, and 0.943, respectively), with 80–90% of roots in the top 30 cm of soil; deserts and temperate coniferous forests showed the deepest profiles (β=0.975 and 0.976, respectively) and had only 50% of their roots in the upper 30 cm. Standing root biomass varied by over an order of magnitude across biomes, from approximately 0.2 to 5 kg m-2. Tropical evergreen forests had the highest root biomass (5 kg m-2), but other forest biomes and sclerophyllous shrublands were of similar magnitude. Root biomass for croplands, deserts, tundra and grasslands was below 1.5 kg m-2. Root/shoot (R/S) ratios were highest for tundra, grasslands, and cold deserts (ranging from 4 to 7); forest ecosystems and croplands had the lowest R/S ratios (approximately 0.1 to 0.5). Comparing data across biomes for plant functional groups, grasses had 44% of their roots in the top 10 cm of soil. (β=0.952), while shrubs had only 21% in the same depth increment (β=0.978). The rooting distribution of all temperate and tropical trees was β=0.970 with 26% of roots in the top 10 cm and 60% in the top 30 cm. Overall, the globally averaged root distribution for all ecosystems was β=0.966 (r 2=0.89) with approximately 30%, 50%, and 75% of roots in the top 10 cm, 20 cm, and 40 cm, respectively. We discuss the merits and possible shortcomings of our analysis in the context of root biomass and root functioning.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00333714

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Carbon isotope dynamics in Abies amabilis stands in the Cascades (1998)

Buchmann, N ; Hinckley, T M ; Ehleringer, J R

Canadian Science Publishing

In: Canadian Journal of Forest Research. 1998; 28(6): 808-819. Published 1998 Jun 01. doi: 10.1139/x98-040.

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Publication Date: 1998-06-01

Description: Carbon isotope ratios ( delta 13C) of canopy air and carbon isotope discrimination at the ecosystem level were studied in three montane Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes) stands, an old-growth and two younger stands. Spatial and temporal variations of canopy CO2 concentrations ([CO2]) and their delta 13C were strongly related to stand structure. Within the old-growth stand, both daytime canopy [CO2] and canopy delta 13C stayed close to those of the troposphere, either indicating low overall photosynthetic rates or high turbulent mixing. Pronounced periods of photosynthetic drawdown below baseline [CO2] accompanied by more enriched canopy delta 13C were observed for the two younger and denser stands. Canopy [CO2] profiles seemed closely related to changes in soil conditions. Soil respiration rates were positively related to soil temperature, but negatively to soil moisture. delta 13C of soil-respired CO2 stayed relatively constant at -24.55 ± 0.20%oduring the growing season. Significant relationships existed between canopy delta 13C and 1/[CO2] in all three stands. Using the intercepts of these regressions, we calculated an average delta 13C for ecosystem respiration of -26.4 ± 0.1%o. Ecosystem carbon isotope discrimination ( DELTA e), an integrating measure for carbon exchange between the troposphere and the entire ecosystem, stayed relatively constant through time. DELTA e showed no significant stand structure effect (leaf area index, density) and averaged 18.9%o for the old-growth and 19.2 ± 0.2%ofor the two younger stands.

Print ISSN: 0045-5067

Electronic ISSN: 1208-6037

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition