共查询到20条相似文献,搜索用时 31 毫秒
1.
Long-term management plans for restoration of natural flow conditions through the Everglades increase the importance of understanding
potential nutrient impacts of increased freshwater delivery on Florida Bay biogeochemistry. Planktonic communities respond
quickly to changes in water quality, thus spatial variability in community composition and relationships to nutrient parameters
must be understood in order to evaluate future downstream impacts of modifications to Everglades hydrology. Here we present
initial results combining flow cytometry analyses of phytoplankton and bacterial populations (0.1–50 μm size fraction) with measurements of δ13C and δ15N composition and dissolved inorganic nutrient concentrations to explore proxies for planktonic species assemblage compositions
and nutrient cycling. Particulate organic material in the 0.1–50 μm size fraction was collected from five stations in Northeastern and Western Florida Bay to characterize spatial variability
in species assemblage and stable isotopic composition. A dense bloom of the picocyanobacterium, Synechococcus elongatus, was observed at Western Florida Bay sites. Smaller Synechococcus sp. were present at Northeast sites in much lower abundance. Bacteria and detrital particles were also more abundant at Western
Florida Bay stations than in the northeast region. The highest abundance of detritus occurred at Trout Creek, which receives
freshwater discharge from the Everglades through Taylor Slough. In terms of nutrient availability and stable isotopic values,
the S. elongatus population in the Western bay corresponded to low DIN (0.5 μM NH
4
+
; 0.2 μM NO
3
−
) concentrations and depleted δ15N signatures ranging from +0.3 to +0.8‰, suggesting that the bloom supported high productivity levels through N2-fixation. δ15N values from the Northeast bay were more enriched (+2.0 to +3.0‰), characteristic of N-recycling. δ13C values were similar for all marine Florida Bay stations, ranging from −17.6 to −14.4‰, however were more depleted at the
mangrove ecotone station (−25.5 to −22.3‰). The difference in the isotopic values reflects differences in carbon sources.
These findings imply that variations in resource availability and nutrient sources exert significant control over planktonic
community composition, which is reflected by stable isotopic signatures. 相似文献
2.
Several lichens and the terrestrial alga Trentepohlia were found to have extremely depleted 15N signatures at two sites near the Rotorua geothermal area, New Zealand. Values, typically −20‰, with several extreme cases
of −24‰, are more isotopically depleted than any previously quoted δ15N signature for vegetation growing in natural environments. For Trentepohlia, distance from a geothermal source did not affect isotopic signature. A 100-km transect showed that the phenomenon is widespread
and the discrimination is not related to substrate N, or to elevation. Rainfall NHx and atmospheric gaseous NH3 (NH3(g)) were shown to be isotopically depleted in the range −1‰ to −8‰ and could not, of themselves, be responsible for the plant
values obtained. A simulation of Trentepohlia thallus was created using an acidified fiberglass mat and was allowed to absorb NH3(g) from the atmosphere. Mats exposed at the geothermal sites and on farmland showed a significant further depletion of 15N to −17‰. We hypothesize that the extreme isotopic depletion is due to dual fractionation: firstly by the volatilization
of NH3(g) from aqueous sources into the atmosphere; secondly by the diffusive assimilation of that NH3(g) into vegetation. We further hypothesize that lithophytes, epiphytes, and higher plants, growing on strongly N-limited substrates,
will show this phenomenon more or less, depending on the proportion of diffusively assimilated NH3(g) utilized as a N source. Many of the isotopically depleted δ15N signatures in vegetation, previously reported in the literature, especially epiphytes, may be due to this form of uptake
depending on the concentration of atmospheric NH3(g), and the degree of reliance on that form of N. 相似文献
3.
The C isotope composition of leaf dark-respired CO2 (δ13Cl) integrates short-term metabolic responses to environmental change and is potentially recorded in the isotopic signature
of ecosystem-level respiration. Species differences in photosynthetic pathway, resource acquisition and allocation patterns,
and associated isotopic fractionations at metabolic branch points can influence δ13Cl, and differences are likely to be modified by seasonal variation in drought intensity. We measured δ13Cl in two deep-rooted C3 trees (Prosopis velutina and Celtis reticulata), and two relatively shallow-rooted perennial herbs (a C3 dicot Viguiera dentata and a C4 grass Sporobolus wrightii) in a floodplain savanna ecosystem in southeastern Arizona, USA during the dry pre-monsoon and wet monsoon seasons. δ13Cl decreased during the nighttime and reached minimum values at pre-dawn in all species. The magnitude of nocturnal shift in
δ13Cl differed among species and between pre-monsoon and monsoon seasons. During the pre-monsoon season, the magnitude of the nocturnal
shift in δ13Cl in the deep-rooted C3 trees P. velutina (2.8 ± 0.4‰) and C. reticulata (2.9 ± 0.2‰) was greater than in the C3 herb V. dentata (1.8 ± 0.4‰) and C4 grass S. wrightii (2.2 ± 0.4‰). The nocturnal shift in δ13Cl in V. dentata and S. wrightii increased to 3.2 ± 0.1‰ and 4.6 ± 0.6‰, respectively, during the monsoon season, but in C3 trees did not change significantly from pre-monsoon values. Cumulative daytime net CO2 uptake was positively correlated with the magnitude of the nocturnal decline in δ13Cl across all species, suggesting that nocturnal δ13Cl may be controlled by 13C/12C fractionations associated with C substrate availability and C metabolite partitioning. Nocturnal patterns of δ13Cl in dominant plant species in the semiarid savanna apparently have predictable responses to seasonal changes in water availability,
which is important for interpreting and modeling the C isotope signature of ecosystem-respired CO2. 相似文献
4.
Corals rely on stored energy reserves (i.e., lipids, carbohydrates, and protein) to survive bleaching events. To better understand
the physiological implications of coral bleaching on lipid catabolism and/or synthesis, we measured the δ13C of coral total lipids (δ13CTL) in experimentally bleached (treatment) and non-bleached (control) Porites compressa and Montipora capitata corals immediately after bleaching and after 1.5 and 4 months of recovery on the reef. Overall δ13CTL values in treatment corals were significantly lower than in control corals because of a 1.9 and 3.4‰ decrease in δ13CTL immediately after bleaching in P. compressa and M. capitata, respectively. The decrease in δ13CTL coincided with decreases in total lipid concentration, indicating that corals catabolized δ13C-enriched lipids. Since storage lipids are primarily depleted during bleaching, we hypothesize that they are isotopically
enriched relative to other lipid classes. This work further helps clarify our understanding of changes to coral metabolism
and biogeochemistry when bleached and helps elucidate how lipid classes may influence recovery from bleaching and ultimately
coral survival. 相似文献
5.
Influence of stand structure on carbon-13 of vegetation, soils, and canopy air within deciduous and evergreen forests in Utah, United States 总被引:15,自引:0,他引:15
Carbon isotope ratios (δ13C) were studied in evergreen and deciduous forest ecosystems in semi-arid Utah (Pinus contorta, Populus tremuloides, Acer negundo and Acer grandidentatum). Measurements were taken in four to five stands of each forest ecosystem differing in overstory leaf area index (LAI) during
two consecutive growing seasons. The δ13Cleaf (and carbon isotope discrimination) of understory vegetation in the evergreen stands (LAI 1.5–2.2) did not differ among canopies
with increasing LAI, whereas understory in the deciduous stands (LAI 1.5–4.5) exhibited strongly decreasing δ13Cleaf values (increasing carbon isotope discrimination) with increasing LAI. The δ13C values of needles and leaves at the top of the canopy were relatively constant over the entire LAI range, indicating no
change in intrinsic water-use efficiency with overstory LAI. In all canopies, δ13Cleaf decreased with decreasing height above the forest floor, primarily due to physiological changes affecting c
i/c
a (> 60%) and to a minor extent due to δ13C of canopy air (< 40%). This intra-canopy depletion of δ13Cleaf was lowest in the open stand (1‰) and greatest in the denser stands (4.5‰). Although overstory δ13Cleaf did not change with canopy LAI, δ13C of soil organic carbon increased with increasing LAI in Pinus contorta and Populus tremuloides ecosystems. In addition, δ13C of decomposing organic carbon became increasingly enriched over time (by 1.7–2.9‰) for all deciduous and evergreen dry temperate
forests. The δ13Ccanopy of CO2 in canopy air varied temporally and spatially in all forest stands. Vertical canopy gradients of δ13Ccanopy, and [CO2]canopy were larger in the deciduous Populus tremuloides than in the evergreen Pinu contorta stands of similar LAI. In a very wet and cool year, ecosystem discrimination (Δe) was similar for both deciduous Populus tremulodies (18.0 ± 0.7‰) and evergreen Pinus contorta (18.3 ± 0.9‰) stands. Gradients of δ13Ccanopy and [CO2]canopy were larger in denser Acer spp. stands than those in the open stand. However, 13C enrichment above and photosynthetic draw-down of [CO2]canopy below tropospheric baseline values were larger in the open than in the dense stands, due to the presence of a vigorous understory
vegetation. Seasonal patterns of the relationship δ13Ccanopy versus 1/[CO2]canopy were strongly influenced by precipitation and air temperature during the growing season. Estimates of Δe for Acer spp. did not show a significant effect of stand structure, and averaged 16.8 ± 0.5‰ in 1933 and 17.4 ± 0.7‰ in 1994. However,
Δe varied seasonally with small fluctuations for the open stand (2‰), but more pronounced changes for the dense stand (5‰).
Received: 15 April 1996 / Accepted: 19 October 1996 相似文献
6.
Desert plants have unique strategies for survival and growth to cope with the limited water availability in arid regions.
The stable carbon isotope (δ
13C) provides an integrated measurement of internal plant physiological and external environmental properties affecting photosynthetic
gas exchange and water use efficiency. The δ
13C values of 84 species in the Junggar Basin were categorized into two groups (ranged from −30.1 to −23.3‰ for C3 and −14.9 to −9.9‰ for C4 species, respectively). No life form differences in δ
13C values were detected in C3 (p = 0.78) and C4 plants (p = 0.63). Small differences among life forms were observed in δ
13C values in C4 species with shrubs slightly depleted (−13.3‰) relative to perennials (−13.1‰) and annuals (−12.5‰). These differences suggested
that δ
13C value could not represent a plant functional group classification based on life forms in C4 plants in extremely arid regions. Ephemerals are all using C3 photosynthetic pathway and no significant differences (p = 0.92) in δ
13C values were observed between annuals (−26.5‰) and perennials (−26.4‰). The δ
13C values of Tulipa iliensis (an important ephemeral species distributed widely in the Junggar Basin) among nine natural populations were positively correlated
with leaf (r
2 = 0.46, p = 0.046) and soil (r
2 = 0.67, p = 0.007) total nitrogen content, and negatively correlated with leaf (r
2 = 0.48, p = 0.039) and soil (r
2 = 0.79, p = 0.001) water content. This indicated that the variation in δ
13C values of T. iliensis was probably caused by both water availability associated stomatal openness and nitrogen availability associated photosynthetic
capacity. T. iliensis is very sensitive to water and nitrogen availability in soil. 相似文献
7.
We analysed plant growth, ion accumulation, leaf water relations, and gas exchange of Avicennia germinans (L.) L. subjected to a long-term, controlled salinity gradient from 0 to 55 ‰. Growth and leaf area were affected by salinity
higher than 10 ‰. As salinity increased, the predawn leaf water potential (Ψw) and leaf osmotic potential (Ψs) decreased. Leaf Ψw was at least −0.32 MPa lower than the Ψw of solution. Na+ and K+ ions explained about 78 % of decrease in Ψs. K+ tissue water concentration decreased by more than 60 % in all salinity treatments as compared with those grown at 0 ‰. Inversely,
Na+ concentration in tissue water increased with nutrient solution salinity. The maximum net photosynthetic rate (P
N) and stomatal conductance (g
s) decreased by 68 and 82 %, respectively, as salinity increased from 0 to 55 ‰; the intercellular CO2 concentration (C
i) followed the same trend. The P
N as a function of C
i showed that both the initial linear slope and upper plateau of the P
N
vs. C
i curve were markedly affected by high salinity (40 and 55 ‰). 相似文献
8.
Foliar δ13C values of Calligogum kozlovi and Haloxylon ammodendron ranged from −13.13 to −15.11 ‰, while those of the rest 11 species were in the range of −22.22 to −27.73 ‰. This indicates
that two of 13 dominant plant species in the Qaidam Basin possess a C4 photosynthetic pathway. Significant differences were observed for the average foliar δ13C values between C3 or C4 plant communities, between grass and shrub communities, even between the same species derived from different sites. Precipitation
accounted for the major part of the differences. 相似文献
9.
This study explores the giant oyster Hyotissa hyotis as a novel environmental archive in tropical reef environments of the Indo-Pacific. The species is a typical accessory component
in coral reefs, can reach sizes of tens of centimetres, and dates back to the Late Pleistocene. Here, a 70.2-mm-long oxygen
and carbon isotope transect through the shell of a specimen collected at Safaga Bay, northern Red Sea, in May 1996, is presented.
The transect runs perpendicularly to the foliate and vesicular layers of the inner ostracum near the ligament area of the
oyster. The measured δ18O and δ13C records show sinusoidal fluctuations, which are independent of shell microstructure. The δ13C fluctuations exhibit the same wavelength as the δ18O fluctuations but are phase shifted. The δ18O record reflects the sea surface temperature variations from 1957 until 1996, possibly additionally influenced by the local
evaporation. Due to locally enhanced evaporation in the semi-enclosed Safaga Bay, the δ18Oseawater value is estimated at 2.17‰, i.e., 0.3–0.8‰ higher than published open surface water δ18O values (1.36–1.85‰) from the region. The mean water temperature deviates by only 0.4°C from the expected value, and the
minimum and maximum values are 0.5°C lower and 2.9°C higher, respectively. When comparing the mean monthly values, however,
the sea surface temperature discrepancy between reconstructed and global grid datasets is always <1.0°C. The δ13C signal is weakly negatively correlated with regional chlorophyll a concentration and with the sunshine duration, which may
reflect changes in the bivalve’s respiration. The study emphasises the palaeogeographic context in isotope studies based on
fossils, because coastal embayments might not reflect open-water oceanographic conditions. 相似文献
10.
Voigt CC Grasse P Rex K Hetz SK Speakman JR 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(1):9-16
We analysed the stable carbon isotope ratio in exhaled CO2 (δ13Cbreath) of free-ranging vampires to assess the type of metabolized substrate (endogenous or exogenous substrate) and its origin,
i.e. whether the carbon atoms came from a C4 food web (grass and cattle) or the C3 food web in which they were captured (a rainforest remnant and its mammals). For an improved understanding of factors influencing
the δ13Cbreath of vampires, we conducted feeding experiments with captive animals. The mean δ13Cbreath of starved bats was depleted in 13C in relation to the diet by 4.6‰ (n = 10). Once fed with blood, δ13Cbreath levelled off within a short time approximately 2.2‰ above the stable carbon isotope signature of the diet. The median time
required to exchange 50% of the carbon atoms in exhaled CO2 with carbon atoms from the ingested blood was 18.6 min (mean 29.5 ± 19.0 min, n = 5). The average δ13C of wing membrane and fur in free-ranging vampire bats suggested that bats almost exclusively foraged for cattle blood during
the past weeks. The δ13Cbreath of the same bats averaged −19.1‰. Given that all free-ranging vampires were starving and that the δ13C of cattle was more in enriched in 13C by 5–6‰ than the δ13Cbreath of vampires, we conclude that the vampire bats of our study metabolised fat that was predominantly built from carbon atoms
originating from cattle blood. Since δ13C of wing membrane and fur integrates over weeks and months respectively and δ13Cbreath over hours and days, we also conclude that vampire bats of the studied population consistently ignored rainforest mammals
and chose cattle as their prey during and prior to our study. 相似文献
11.
Family Chenopodiaceae is an intriguing lineage, having the largest number of C4 species among dicots, including a number of anatomical variants of Kranz anatomy and three single-cell C4 functioning species. In some previous studies, during the culture of Bienertia cycloptera Bunge ex Boiss., carbon isotope values (δ13C values) of leaves deviated from C4 to C3−C4 intermediate type, raising questions as to its mode of photosynthesis during growth in natural environments. This species
usually co-occurs with several Kranz type C4 annuals. The development of B. cycloptera morphologically and δ13C values derived from plant samples (cotyledons, leaves, bracts, shoots) were analyzed over a complete growing season in a
salt flat in north central Iran, along with eight Kranz type C4 species and one C3 species. For a number of species, plants were greenhouse-grown from seeds collected from the site, in order to examine leaf
anatomy and C4 biochemical subtype. Among the nine C4 species, the cotyledons of B. cycloptera, and of the Suaeda spp. have the same respective forms of C4 anatomy occurring in leaves, while cotyledons of members of tribe Caroxyloneae lack Kranz anatomy, which is reflected in
the δ13C values found in plants grown in the natural habitat. The nine C4 species had average seasonal δ13C values of −13.9‰ (with a range between species from −11.3 to −15.9‰). The measurements of δ13C values over a complete growing season show that B. cycloptera performs C4 photosynthesis during its life cycle in nature, similar to Kranz type species, with a seasonal average δ13C value of −15.2‰.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
12.
Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana) 总被引:2,自引:0,他引:2
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.
Received: 3 March 1996 / Accepted: 19 October 1996 相似文献
13.
We studied the nutritional modes of the orchid Serapias strictiflora and its mycorrhizal fungus Epulorhiza sp. using the differences in carbon isotopic composition (δ13C) of C3 orchid and C4 maize tissues. We found that if cultivated in substrate lacking any organic compounds, the mycorrhizal extraradical mycelia
(δ13C = −26.3 ± 0.2 ‰) developed well, despite being fully dependent on nutrition from orchid roots (δ13C = −28.6 ± 0.1 ‰). If the mycorrhizal fungus had additional access to and colonized decaying maize roots (δ13C = −14.6 ± 0.1 ‰), its isotopic composition (δ13C = −21.6 ± 0.4 ‰) reflected a mixture of biotrophy and saprotrophy. No statistically significant differences in δ13C of new storage tubers were found between Epulorhiza-associated orchids with (δ13C = -28.2 ± 0.1 ‰) and without access to maize roots (δ13C = −28.6 ± 0.2 ‰). We conclude that autotrophy is the predominant nutritional mode of mature S. strictiflora plants and that they supply their mycorrhizal fungus with substantial amount of carbon (69 ± 3 % of the fungus demand), even
if the fungus feeds saprotrophically. 相似文献
14.
The δ15N and δ13C values of particulate organic material (POM) were analyzed from 35 sites in the Florida Keys over the time interval 2000
to 2002. The sites within the study area were delineated into nine transects stretching from Key West to Key Largo. Each transect
consisted of three to five sites extending from close to the Keys to the edge of the reef tract. The POM had mean δ15N and δ13C values of +3.6‰ (σ = ±3.2‰) and −19.9‰ (σ = ±0.6‰) respectively. Over the study period there were no statistically significant
changes in δ15N, δ13C, or C:N. For the majority of the sampling dates, the δ13C values showed a distinct inshore (δ13C = −18.3‰, σ = ±1.0‰) to offshore gradient (δ13C = −21.4, σ = ±0.9‰). In contrast, the δ15N values showed no consistent patterns related to the distance from land. The more positive δ13C values of the nearshore samples suggest that the source of the carbon and the nitrogen in the POM in the nearshore was mainly
derived from the degradation of seagrass detritus and not from the input of anthropogenically derived material from the Florida
Keys. In contrast, the POM on the outer reef was dominated by marine plankton. As mineralization and nitrification of the
organic nitrogen pool are major contributors to the dissolved inorganic nitrogen in the water column, it is unlikely that
variations in the δ15N of the algae and other benthic organisms reported in the Florida Keys are related to the input of sewage. 相似文献
15.
During microbial breakdown of leaf litter a fraction of the C lost by the litter is not released to the atmosphere as CO2 but remains in the soil as microbial byproducts. The amount of this fraction and the factors influencing its size are not
yet clearly known. We performed a laboratory experiment to quantify the flow of C from decaying litter into the soil, by means
of stable C isotopes, and tested its dependence on litter chemical properties. Three sets of 13C-depleted leaf litter (Liquidambar styraciflua L., Cercis canadensis L. and Pinus taeda L.) were incubated in the laboratory in jars containing 13C-enriched soil (i.e. formed C4 vegetation). Four jars containing soil only were used as a control. Litter chemical properties
were measured using thermogravimetry (Tg) and pyrolysis–gas chromatography/mass spectrometry–combustion interface–isotope
ratio mass spectrometry (Py–GC/MS–C–IRMS). The respiration rates and the δ13C of the respired CO2 were measured at regular intervals. After 8 months of incubation, soils incubated with both L. styraciflua and C. canadensis showed a significant change in δ13C (δ13Cfinal = −20.2 ± 0.4‰ and −19.5 ± 0.5‰, respectively) with respect to the initial value (δ13Cinitial = −17.7 ± 0.3‰); the same did not hold for soil incubated with P. taeda (δ13Cfinal:−18.1 ± 0.5‰). The percentages of litter-derived C in soil over the total C loss were not statistically different from one
litter species to another. This suggests that there is no dependence of the percentage of C input into the soil (over the
total C loss) on litter quality and that the fractional loss of leaf litter C is dependent only on the microbial assimilation
efficiency. The percentage of litter-derived C in soil was estimated to be 13 ± 3% of total C loss. 相似文献
16.
Application of tree leaves (C3 plants) on maize (Zea mays L.) (C4 plant) fields is an agroforestry management technology to restore or maintain soil fertility. The rate at which the tree
leaves decompose is crucial for the nutrient supply to the crop. We studied the in situ decomposition of Sesbania sesban (L.) Merr. leaves or C3 sugar for 4 – 8 days after application to a maize field in Kenya. By using the difference of around 10‰ in natural abundance
of 13C between the endogenous soil C (mainly C4) and the applied C (C3), we could calculate the contributions of the two C sources to soil respiration. The δ13C value of the basal respiration was from –15.9 to –16.7‰. The microbial response to the additions of leaves and sugar to
this tropical soil was immediate. Application of sesbania leaves gave an initial peak in respiration rates that lasted from
one to less than 6 days, after which it levelled off and remained about 2 – 3 times higher (230–270 mg C m-2 h-1) than the control respiration rates throughout the rest of the experiment (5 – 8 days). In the sugar treatment, there was
no initial peak in respiration rate. The respiration rate was 170 mg C m-2 h-1 after 4 days. At the end of the experiments, after 4–8 days, as much as 14–17% of the added C had been respired and about
60% of the total respiration was from the added sesbania leaves or C3 sugar. This non-destructive method allows repeated measurements of the actual rate of C mineralisation and facilitates decomposition
studies with high temporal resolution in the field.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
Spatial patterns of foliar stable carbon isotope compositions of C<Subscript>3</Subscript> plant species in the Loess Plateau of China 总被引:1,自引:0,他引:1
The spatial pattern of foliar stable carbon isotope compositions (δ13C) of dominant species and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian,
Ansai, Mizhi and Shenmu, standing from south to north in the Loess Plateau of China, was studied. The results showed that
in the 121 C3 plant samples collected from the Loess Plateau, the foliar δ13C value ranged from −22.66‰ to −30.70‰, averaging −27.04‰. The foliar δ13C value varied significantly (P<0.01) among the seven sites, and the average δ13C value increased by about 1.69‰ from Yangling in the south to Shenmu in the north as climatic drought increased. There was
a significant difference in foliar δ13C value among three life-forms categorized from all the plant samples in the Loess Plateau (P<0.001). The trees (−26.74‰) and shrubs (−26.68‰) had similar mean δ13C values, both significantly (P<0.05) higher than the mean δ13C value of herbages (−27.69‰). It was shown that the trees and shrubs had higher WUEs and employed more conservative water-use
patterns to survive drier habitats in the Loess Plateau. Of all the C3 species in the Loess Plateau, the foliar δ13C values were significantly and negatively correlated with the mean annual rainfall (P<0.001) and mean annual temperature (P<0.05), while being significantly and positively correlated with the latitude (P<0.001) and the annual solar radiation (P<0.01). In general, the foliar δ13C values increased as the latitude and solar radiation increased and the rainfall and temperature decreased. The annual rainfall
as the main influencing factor could explain 13.3% of the spatial variations in foliar δ13C value. A 100 mm increment in annual rainfall would result in a decrease by 0.88‰ in foliar δ13C values. 相似文献
18.
Understanding what governs patterns of soil δ15N and δ13C is limited by the absence of these data assembled throughout the development of individual ecosystems. These patterns are important because stable isotopes of soil organic N and C are integrative indicators of biogeochemical processing of soil organic matter. We examined δ15N of soil organic matter (δ15NSOM) and δ13CSOM of archived soil samples across four decades from four depths of an aggrading forest in southeastern USA. The site supports an old-field pine forest in which the N cycle is affected by former agricultural fertilization, massive accumulation of soil N by aggrading trees over four decades, and small to insignificant fluxes of N via NH3 volatilization, nitrification, and denitrification. We examine isotopic data and the N and C dynamics of this ecosystem to evaluate mechanisms driving isotopic shifts over time. With forest development, δ13CSOM became depth-dependent. This trend resulted from a decline of ~2‰ in the surficial 15 cm of mineral soil to −26.0‰, due to organic matter inputs from forest vegetation. Deeper layers exhibited relatively little trend in δ13CSOM with time. In contrast, δ15NSOM was most dynamic in deeper layers. During the four decades of forest development, the deepest layer (35–60 cm) reached a maximum δ15N value of 9.1‰, increasing by 7.6‰. The transfer of >800 kg ha−1 of soil organic N into aggrading vegetation and the forest floor and the apparent large proportion of ectomycorrhizal (ECM) fungi in these soils suggest that fractionation via microbial transformations must be the major process changing δ15N in these soils. Accretion of isotopically enriched compounds derived from microbial cells (i.e., ECM fungi) likely promote isotopic enrichment of soils over time. The work indicates the rapid rate at which ecosystem development can impart δ15NSOM and δ13CSOM signatures associated with undisturbed soil profiles. 相似文献
19.
The vertical profile of stable carbon isotope ratios (δ13C) of leaves was analyzed for 13 tree species in a cool-temperate deciduous forest in Japan. The vertical distribution of
long-term averaged δ13C in atmospheric CO2 (δa) was estimated from δ13C of dry matter from NADP-malic enzyme type C4 plant (Zea mays L. var. saccharata Sturt.) grown at a tower in the forest for 32␣days, assuming constant Δ value (3.3‰) in Z. mays against height. The δa value obtained from δ13C in Z.␣mays was lowest at the forest floor (−9.30 ± 0.03‰), increased with height, and was almost constant above 10␣m (−7.14 ± 0.14‰).
Then leaf Δ values for the tree species were calculated from tree leaf δ13 C andδa. Mean leaf Δ values for the three tall deciduous species (Fraxinus mandshurica, Ulmus davidiana, and Alnus hirsuta) were significantly different among three height levels in the forest: 23.1 ± 0.7‰ at the forest floor (understory), 21.4 ± 0.5‰
in lower canopy, and 20.5 ± 0.3‰ in upper canopy. The true difference in tree leaf Δ among the forest height levels might
be even greater, because Δ in Z. mays probably increased with shading by up to ∼‰. The difference in tree leaf Δ among the forest height levels would be mainly
due to decreasing intercellular CO2 (C
i) with the increase in irradiance. Potential assimilation rate for the three tree species probably increased with height,
since leaf nitrogen content on an area basis for these species also increased with height. However, the increase in stomatal
conductance for these tree species would fail to meet the increase in potential assimilation rate, which might lead to increasing
the degree of stomatal limitation in photosynthesis with height.
Received: 30 September 1995 / Accepted: 25 October 1996 相似文献
20.
The relative abundance of carbon isotope (δ13C) was measured in four C3 species (Sophora viccifolia, Quercus liaotungensis, Ostryopsis davidiana and Zizyphus jujuba var. spinosa) of the Loess Plateau in China from the 1930’s to 2002. The results showed that the δ13C values in the four species varied from −25.05‰ to −29.75‰ with their a average at −27.04‰. A decrease in the δ13C value with time was found in all the four species, which indicating that the water use efficiencies (WUEs) of all the measured
species declined during 70 years. However, the decrease in δ13C value differed among the four species with its significant decreases measured in two of the species, Sophora viciifolia and Quercus liaotungensis, its relatively significant decrease found in Ostryopsis davidiana, and its slight decrease appearing in Zizyphus jujuba var. spinosa. in the δ13C values in the four species decreased by 14.65 ‰, 14.46‰, 11.99‰ and 2.44‰, respectively. The different species were shown
to have different sensitivities to climatic change, and Zizyphus jujuba var. spinosa was found to be the most drought-tolerant species of the four, which had a high WUE. 相似文献