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1.
Recent (13) CO(2) canopy pulse chase labeling studies revealed that photosynthesis influences the carbon isotopic composition of soil respired CO(2) (δ(13) C(SR)) even on a diel timescale. However, the driving mechanisms underlying these short-term responses remain unclear, in particular under drought conditions. The gas exchange of CO(2) isotopes of canopy and soil was monitored in drought/nondrought-stressed beech (Fagus sylvatica) saplings after (13) CO(2) canopy pulse labeling. A combined canopy/soil chamber system with gas-tight separated soil and canopy compartments was coupled to a laser spectrometer measuring mixing ratios and isotopic composition of CO(2) in air at high temporal resolution. The measured δ(13) C(SR) signal was then explained and substantiated by a mechanistic carbon allocation model. Leaf metabolism had a strong imprint on diel cycles in control plants, as a result of an alternating substrate supply switching between sugar and transient starch. By contrast, diel cycles in drought-stressed plants were determined by the relative contributions of autotrophic and heterotrophic respiration throughout the day. Drought reduced the speed of the link between photosynthesis and soil respiration by a factor of c. 2.5, depending on the photosynthetic rate. Drought slows the coupling between photosynthesis and soil respiration and alters the underlying mechanism causing diel variations of δ(13) C(SR). 相似文献
2.
The main aim of this study was to test various hypotheses regarding the changes in 13C of emitted CO 2 that follow the addition of C 4-sucrose to the soil of a C 3-ecosystem. It forms part of an experimental series designed to assess whether or not the contributions from C 3-respiration (root and microbial) and C 4-respiration (microbial) to total soil respiration can be calculated from such changes. A series of five experiments, three on sieved (root-free) mor-layer material, and two in the field with intact mor-layer (and consequently with active roots), were performed. Both in the experiments on sieved mor-layer and the field experiments, we found a C 4-sucrose-induced increase in C 3-respiration that accounted for between 30% and 40% of the respiration increase 1 h after sucrose addition. When the course of C 3-, C 4- and total respiration was followed in sieved material over four days following addition of C 4-sucrose, the initially increased respiration of C 3-C was transient, passing within less than 24 h. In a separate pot experiment, neither ectomycorrhizal Pinus sylvestrisL. roots nor non-mycorrhizal roots of this species showed respiratory changes in response to exogenous sucrose. No shift in the 13C of the evolved CO 2 after adding C 3-sucrose to sieved mor-layer material was found, confirming that the sucrose-induced increase in respiration of endogenous C was not an artefact of discrimination against 13C during respiration. Furthermore, we conclude that the C 4-sucrose induced transient increase in C 3-respiration is most likely the result of accelerated turnover of C in the microbial biomass. Thus, neither respiration of mycorrhizal roots, nor processes discriminating against 13C were likely sources of error in the field. The estimated 13C of evolved soil CO 2 in three field experiments lay between –25.2 and –23.6. The study shows that we can distinguish between CO 2 evolved from microbial mineralisation of added C 4-sucrose, and CO 2 evolved from endogenous carbon sources (roots and microbial respiration). 相似文献
3.
Respiration rates and chemical characteristics of soil organic layers were measured at 40 experimental plots, 5 sampling sites per plot, in a moderately polluted Niepoomice Forest, S. Poland. The respiration rate was positively related to pH, water content and concentrations of Ca and K, and negatively to N tot, Zn and Pb (p < 0.001 for all variables). No significant correlation was found between the respiration rate and Na, Cu or Cd (p > 0.25 in all cases). The regression model explained 73% of the total variance. Analysis of variance components revealed that ca. 35% of the total variance in the respiration rate can be explained by the vegetation types covering the area: oak-hornbeam vs. pine-oak forests. The next 40% was explained by the variability between sampling plots and the remaining 25% by within-plot variability among sampling sites. Similar results were obtained for water content. The variance in pH was split 30%:39%:31% between vegetation types:plots:sampling sites. No variance in Ca and Na was explained by the forest type, and approximately half of the variance was due to between-plot and half to within-plot variability. In contrast, potassium concentration differed between forest types (58% variance explained), more than 25% of total variance was due to between-plot variability and only 15% due to within-plot variability. For Zn the results were 1%, 66% and 33%, for Cu 0%, 38% and 62%, for Pb 48%, 18% and 34%, and for Cd 0%, 33% and 67%, respectively. The study clearly shows (1) substantial variance in some soil characteristics between sampling sites and (2) a different split of variance among spatial scales for different soil characteristics. 相似文献
4.
Background and AimsPhosphorus (P) mineralisation from crop residues is usually predicted from total P or carbon: phosphorus (C: P) ratios. However, these measures have limited accuracy as they do not take into account the presence of different P species that may be mineralised at different rates. In this study P speciation was determined using solution 31P nuclear magnetic resonance (NMR) spectroscopy to understand the potential fate of residue P in soils. MethodsMature above-ground biomass of eight different crops sampled from the field was portioned into stem, chaff and seed. ResultsThe main forms of P detected in stem and chaff were orthophosphate (25–75 %), phospholipids (10–40 %) and RNA (5–30 %). Phytate was the dominant P species in seeds, and constituted up to 45 % of total P in chaff but was only detected in minor amounts (<1 %) in stem residue. The majority (65–95 %) of P in stems was water-extractable, and most of this was detected as orthophosphate. However, this includes organic P that may have been hydrolysed during the water extraction. ConclusionsThis study indicates that the majority of residue P in aboveground plant residues has the potential to be delivered to soil in a form readily available to plants and soil microorganisms. 相似文献
5.
The stable carbon isotope ratios (δ13C) of dominant tree and shrub species in typical temperate broad-leaved forests in Dongling Mountain, northwestern part of Beijing, China, were studied. The results indicated that the values of foliar 8 13C differed among the species tested, in the following order of Prunus armeniaca var. ansu Maxim. > Fraxinus rhychophylla Hce. ≈ Virex negundo var. heterophylla (Franch.) ReM. ≈ Quercus liaotungensis Koiz. ≈ Syringa pekinensis Rupr. > Juglans mandshurica Maxim. The δ13C values were also affected by the maturity of leaves. The newly-developed leaves had higher δ13C values than the mature ones, especially in Juglans mandshurica and Quercus liaotungensis. The conditions of habitats, particularly soil depth and moisture content, also had pronounced effect on foliar δ13C. The foliar δ13C values of plants grown in dry habitats were higher than those in moist ones. They were also affected by the position of leaves in the canopy: leaves at upper canopy showed higher δ13C values than the lower ones. It is suggested that stable isotope technique may be effective for the study of ecophysiology of plants in the warm temperate regions of China. 相似文献
7.
Stable isotope analyses are often used to calculate relative contributions of multiple food sources in an animals diet. One prerequisite for a precise calculation is the determination of the diet-tissue fractionation factor. Isotopic ratios in animals are not only affected by the composition of the diet, but also by the amount of food consumed. Previous findings regarding the latter point are controversial. As stable isotope analyses have often been used to investigate aquatic food webs, an experiment with carp ( Cyprinus carpio L.) was carried out to test the influence of the feeding level and individual metabolic rate on 13C and 15N values of the whole body. After an initial phase, 49 carp were assigned randomly to four groups and fed the same diet at different levels for 8 weeks. For 15 fish, the energy budget was determined by indirect calorimetry. Feed and individual fish were analysed for their proximate composition, gross energy content and 13C and 15N values. 13C and 15N values differed significantly at different feeding levels. While 13C values of the lipids and 15N values decreased with increasing feeding rate, 13C values of the lipid-free matter showed a non-linear pattern. Data obtained from fish held in the respirometric system revealed a relationship between 13C values and the percentage retention of metabolizable energy. Our results show that reconstructing the diets of fish from the isotopic ratios when the feeding level and individual metabolic rates are unknown would introduce an error into the data used for back-calculation of up to 1 for both 13C and 15N values and may have substantial effects on the results of calculated diets. As other workers have pointed out, the development and application of stable isotopes to nutritional ecology studies is a field in its infancy and gives rise to erroneous, misleading results without nutritional, physiological and ecological knowledge. 相似文献
8.
The world's soils contain a large amount of carbon so that even a fractionally small loss or gain could have a quantitatively important feedback effect on net CO 2 emissions to the atmosphere. It is therefore important to fully understand the temperature dependence of soil‐carbon decomposition. Evidence from various observations can be used to quantify the temperature dependence of carbon efflux, but it is important to ensure that confounding factors, such as changing water relations or availability of readily decomposable substrate, are fully considered in inferring an underlying temperature response from observed response patterns. A number of recent findings from soil‐warming experiments have led to the suggestion that stimulation of soil‐carbon efflux by increasing temperature is only transitory before acclimation takes place and carbon efflux rates return to similar rates as before the increase in temperature. It is shown here that this response pattern can be explained through a simple two‐pool soil‐carbon model with no acclimation response needing to be invoked. The temporal pattern is, instead, due to depletion of readily decomposable substrate. It shows that findings of reduced respiration rate in soil‐warming experiments are consistent with unchanged high temperature sensitivity of organic carbon decomposition and affirms that there is, indeed, a danger of positive feedback between global warming and the release of soil organic carbon that can lead to further warming. 相似文献
9.
In 2005 and 2006, air samples were collected at the base of a Douglas-fir watershed to monitor seasonal changes in the delta13CO2 of ecosystem respiration (delta13C(ER)). The goals of this study were to determine whether variations in delta13C(ER) correlated with environmental variables and could be used to predict expected variations in canopy-average stomatal conductance (Gs). Changes in delta13C(ER) correlated weakly with changes in vapor pressure deficit (VPD) measured 0 and 3-7 days earlier and significantly with soil matric potential (psi(m)) (P value <0.02) measured on the same day. Midday G (s) was estimated using sapflow measurements (heat-dissipation method) at four plots located at different elevations within the watershed. Values of midday Gs from 0 and 3-7 days earlier were correlated with delta13C(ER), with the 5-day lag being significant (P value <0.05). To examine direct relationships between delta13C(ER) and recent Gs, we used models relating isotope discrimination to stomatal conductance and photosynthetic capacity at the leaf level to estimate values of stomatal conductance ("Gs-I") that would be expected if respired CO2 were derived entirely from recent photosynthate. We compared these values with estimates of Gs using direct measurement of transpiration at multiple locations in the watershed. Considering that the approach based on isotopes considers only the effect of photosynthetic discrimination on delta13C(ER), the magnitude and range in the two values were surprisingly similar. We conclude that: (1) delta13C(ER) is sensitive to variations in weather, and (2) delta13C(ER) potentially could be used to directly monitor average, basin-wide variations in Gs in complex terrain if further research improves understanding of how delta13C(ER) is influenced by post-assimilation fractionation processes. 相似文献
10.
We evaluated the effects of ecosystem composition and structure (species richness and diversity, cover and spatial attributes of vegetation), abiotic factors (climate and topographical features) and the condition of the bare-ground areas (evaluated using soil-surface indicators) on the performance of Stipa tenacissima [evaluated using foliar 13C, 15N, nitrogen concentration and the carbon-to-nitrogen (C:N) ratio] in 15 steppes of SE Spain. Foliar 13C values of S. tenacissima showed a low degree of variation in the studied steppes, with average values ranging from –24.1 to –22.9. Higher variation was found in the 15N values, which ranged from –5.5 to –2.4. The nitrogen concentration and the C:N ratio varied between 5.0 and 8.0 mg g –1, and between 55.4 and 85.3, respectively. The 13C values became less negative with increasing spatial aggregation of perennial vegetation, while the C:N values increased with increasing perennial vegetation cover. The 15N values became more negative with increasing infiltration in the bare-ground areas, but the nitrogen concentration was not related to any of the environmental variables measured. Our results suggest that the relative importance of ecosystem structure and soil-surface conditions in the bare ground areas was higher than that of abiotic factors as determinants of the performance of S. tenacissima. The results also show that even subtle changes in these ecosystem features may lead to modifications in plant performance in semiarid S. tenacissima steppes, and thus to modifications in the associated ecosystem functions in the mid- to long-term. 相似文献
11.
Stable isotopes ( δ15N and δ13C) are being widely applied in ecological research but there has been a call for ecologists to determine species- and tissue-specific diet discrimination factors (? 13C and ? 15N) for their study animals. For large sharks stable isotopes may provide an important tool to elucidate aspects of their ecological roles in marine systems, but laboratory based controlled feeding experiments are impractical. By utilizing commercial aquaria, we estimated ? 15N and ? 13C of muscle, liver, vertebral cartilage and a number of organs of three large sand tiger ( Carcharias taurus) and one large lemon shark ( Negaprion brevirostris) under a controlled feeding regime. For all sharks mean ± SD for ? 15N and ? 13C in lipid extracted muscle using lipid extracted prey data were 2.29‰ ± 0.22 and 0.90‰ ± 0.33, respectively. The use of non-lipid extracted muscle and prey resulted in very similar ? 15N and ? 13C values but mixing of lipid and non-lipid extracted data produced variable estimates. Values of ? 15N and ? 13C in lipid extracted liver and prey were 1.50‰ ± 0.54 and 0.22‰ ± 1.18, respectively. Non-lipid extracted diet discrimination factors in liver were highly influenced by lipid content and studies that examine stable isotopes in shark liver, and likely any high lipid tissue, should strive to remove lipid effects through standardising C:N ratios, prior to isotope analysis. Mean vertebral cartilage ? 15N and ? 13C values were 1.45‰ ± 0.61 and 3.75‰ ± 0.44, respectively. Organ ? 15N and ? 13C values were more variable among individual sharks but heart tissue was consistently enriched by ~ 1–2.5‰. Minimal variability in muscle and liver δ15N and δ13C sampled at different intervals along the length of individual sharks and between liver lobes suggests that stable isotope values are consistent within tissues of individual animals. To our knowledge, these are the first reported diet–tissue discrimination factors for large sharks under semi-controlled conditions, and are lower than those reported for teleost fish. 相似文献
12.
The size of the nucleus varies among different cell types, species, and disease states, but mechanisms of nuclear size regulation are poorly understood. We investigated nuclear scaling in the pseudotetraploid frog Xenopus laevis and its smaller diploid relative Xenopus tropicalis, which contains smaller cells and nuclei. Nuclear scaling was recapitulated in vitro using egg extracts, demonstrating that titratable cytoplasmic factors determine nuclear size to a greater extent than DNA content. Nuclear import rates correlated with nuclear size, and varying the concentrations of two transport factors, importin α and Ntf2, was sufficient to account for nuclear scaling between the two species. Both factors modulated lamin B3 import, with importin α increasing overall import rates and Ntf2 reducing import based on cargo size. Importin α also contributes to nuclear size changes during early X. laevis development. Thus, nuclear transport mechanisms are physiological regulators of both interspecies and developmental nuclear scaling. 相似文献
13.
We present a comprehensive dataset of hourly, daily, and monthly measurements of carbon isotope measurements of CO 2 in canopy air from a temperate deciduous forest with the aim to identify the relevance of short-term variations in the isotopic signature of ecosystem respiration ( 13C R) and to understand its underlying physiological processes. We show that during daytime low vertical mixing inside the canopy can lead to decoupling of the air in the lower and upper canopy layer resulting in large spatial variation of 13C in CO 2 of canopy air. Intercept of Keeling Plots also showed large temporal variation (3.8) over the course of the day demonstrating that intercepts can differ between day and night and suggesting that choosing the right time for sampling is essential to capture the isotopic signature of ecosystem respiration ( 13C R). 13C R as obtained from night-time measurements showed large variation of up to 2.65 on a day-to-day basis, which was similar to the observed variation of 13C R over the seasonal cycle (3.08). This highlights the importance of short-term physiological processes within ecosystems for the isotopic composition of CO 2 in the atmosphere, not reflected by bulk plant and soil organic samples. At daily and monthly time scales, 13C R increased with increasing ratio of vapour pressure deficit to photosynthetically active radiation, measured 4–5 days before. This suggests that ecosystem respiration was isotopically linked to assimilation. Furthermore, assimilates recently fixed in the canopy seem to form a labile carbon pool with a short mean residence time that is respired back to the atmosphere after 4–5 days. 相似文献
14.
The molecular networks that control endoplasmic reticulum (ER) redox conditions in mammalian cells are incompletely understood. Here, we show that after reductive challenge the ER steady‐state disulphide content is restored on a time scale of seconds. Both the oxidase Ero1α and the oxidoreductase protein disulphide isomerase (PDI) strongly contribute to the rapid recovery kinetics, but experiments in ERO1‐deficient cells indicate the existence of parallel pathways for disulphide generation. We find PDI to be the main substrate of Ero1α, and mixed‐disulphide complexes of Ero1 primarily form with PDI, to a lesser extent with the PDI‐family members ERp57 and ERp72, but are not detectable with another homologue TMX3. We also show for the first time that the oxidation level of PDIs and glutathione is precisely regulated. Apparently, this is achieved neither through ER import of thiols nor by transport of disulphides to the Golgi apparatus. Instead, our data suggest that a dynamic equilibrium between Ero1‐ and glutathione disulphide‐mediated oxidation of PDIs constitutes an important element of ER redox homeostasis. 相似文献
15.
Carbon isotopic composition of soils subjected to C 3–C 4 vegetation change can be used to estimate C turnover in bulk soil and in soil organic matter (SOM) pools with fast and intermediate
turnover rates. We hypothesized that the biological availability of SOM pools is inversely proportional to their thermal stability,
so that thermogravimetry can be used to separate SOM pools with contrasting turnover rates. Soil samples from a field plot
cultivated for 10.5 years with the perennial C 4 plant Miscanthus× gigantheus were analyzed by thermogravimetry coupled with differential scanning calorimetry (DSC). Three SOM fractions were distinguished
according to the differential weight losses and exothermic or endothermic reactions measured by DSC. The δ 13C and δ 15N values of these three fractions obtained by gradual soil heating were measured by IRMS. The weight losses up to 190 °C mainly
reflected water evaporation because no significant C and N losses were detected and δ 13C and δ 15N values of the residual SOM remained unchanged. The δ 13C values (−16.4‰) of SOM fraction decomposed between 190 and 390 °C (containing 79% of total soil C) were slightly closer
to that of the Miscanthus plant tissues (δ 13C = −11.8‰) compared to the δ 13C values (−16.8‰) of SOM fraction decomposed above 390 °C containing the residual 21% of SOM. Thus, the C turnover in the
thermally labile fraction was faster than that in thermally stable fractions, but the differences were not very strong. Therefore,
in this first study combining TG-DSC with isotopic analysis, we conclude that the thermal stability of SOM was not very strongly
related to biological availability of SOM fractions. In contrast to δ 13C, the δ 15N values strongly differed between SOM fractions, suggesting that N turnover in the soil was different from C turnover. More
detailed fractionation of SOM by thermal analysis with subsequent isotopic analysis may improve the resolution for δ 13C. 相似文献
17.
We warmed the top soil of a mature coniferous forest stand by means of heating cables on control and trenched plots within
24 h by 10°C at 1 cm soil depth (9°C at 5 cm depth) and measured the effect on the autotrophic (R A) and heterotrophic (R H) component of total soil CO 2 efflux (R S). The short time frame of warming enabled us to exclude confounding fluctuations in soil moisture and carbon (C) flow from
the canopy. The results of the field study were backed up by a lab soil incubation experiment. During the first 12 h of warming,
R A strongly responded to soil warming; The Q
10 values were 5.61 and 6.29 for 1 and 5 cm soil depth temperature. The Q
10 values for R A were almost twice as high as the Q
10 values of R H (3.04 and 3.53). Q
10 values above 5 are above reasonable plant physiological values for root respiration. We see interactions of roots, mycorrhizae
and heterotrophic microbes, combined with fast substrate supply to the rhizosphere as an explanation for the high short-term
temperature response of R A. When calculated over the whole duration (24 h) of the field soil-warming experiment, temperature sensitivities of R A and R H were similar (no significant difference at P < 0.05); Q
10 values were 3.16 and 3.96 for R A and 2.94 and 3.35 for R H calculated with soil temperatures at 1 and 5 cm soil depth, respectively. Laboratory incubation showed that different soil
moisture contents of trenched and control plots affected rates of R H, but did not affect the temperature sensitivity of R H. We conclude that a single parameter is sufficient to describe the temperature sensitivity of R S in soil C models which operate on larger temporal and spatial scales. The strong short-term response of R A may be of relevance in soils suspected to experience increasingly strong diurnal temperature variations. 相似文献
18.
Organic carbon and aggregate stability are key features of soil quality and are important to consider when evaluating the potential of agricultural soils as carbon sinks. However, we lack a comprehensive understanding of how soil organic carbon (SOC) and aggregate stability respond to agricultural management across wide environmental gradients. Here, we assessed the impact of climatic factors, soil properties and agricultural management (including land use, crop cover, crop diversity, organic fertilization, and management intensity) on SOC and the mean weight diameter of soil aggregates, commonly used as an indicator for soil aggregate stability, across a 3000 km European gradient. Soil aggregate stability (−56%) and SOC stocks (−35%) in the topsoil (20 cm) were lower in croplands compared with neighboring grassland sites (uncropped sites with perennial vegetation and little or no external inputs). Land use and aridity were strong drivers of soil aggregation explaining 33% and 20% of the variation, respectively. SOC stocks were best explained by calcium content (20% of explained variation) followed by aridity (15%) and mean annual temperature (10%). We also found a threshold-like pattern for SOC stocks and aggregate stability in response to aridity, with lower values at sites with higher aridity. The impact of crop management on aggregate stability and SOC stocks appeared to be regulated by these thresholds, with more pronounced positive effects of crop diversity and more severe negative effects of crop management intensity in nondryland compared with dryland regions. We link the higher sensitivity of SOC stocks and aggregate stability in nondryland regions to a higher climatic potential for aggregate-mediated SOC stabilization. The presented findings are relevant for improving predictions of management effects on soil structure and C storage and highlight the need for site-specific agri-environmental policies to improve soil quality and C sequestration. 相似文献
19.
Foliar nitrogen isotope (δ 15N) composition patterns have been linked to soil N, mycorrhizal fractionation, and within-plant fractionations. However, few studies have examined the potential importance of the direct foliar uptake of gaseous reactive N on foliar δ 15N. Using an experimental set-up in which the rate of mycorrhizal infection was reduced using a fungicide, we examined the influence of mycorrhizae on foliar δ 15N in potted red maple ( Acer rubrum) seedlings along a regional N deposition gradient in New York State. Mycorrhizal associations altered foliar δ 15N values in red maple seedlings from 0.06 to 0.74 ‰ across sites. At the same sites, we explored the predictive roles of direct foliar N uptake, soil δ 15N, and mycorrhizae on foliar δ 15N in adult stands of A. rubrum, American beech ( Fagus grandifolia), black birch ( Betula lenta), and red oak ( Quercus rubra). Multiple regression analysis indicated that ambient atmospheric nitrogen dioxide (NO 2) concentration explained 0, 69, 23, and 45 % of the variation in foliar δ 15N in American beech, red maple, red oak, and black birch, respectively, after accounting for the influence of soil δ 15N. There was no correlation between foliar δ 13C and foliar %N with increasing atmospheric NO 2 concentration in most species. Our findings suggest that total canopy uptake, and likely direct foliar N uptake, of pollution-derived atmospheric N deposition may significantly impact foliar δ 15N in several dominant species occurring in temperate forest ecosystems. 相似文献
20.
We tested the reliability of herbivore faecal δ 13C and δ 15N values for reconstructing diet through review of an extensive database derived from a 3-year study of ungulates in South Africa's Kruger National Park. Faeces are a useful material for stable isotope studies of diet because they record dietary turnover at very short time scales, and because sampling is non-invasive. However, the validity of faecal isotope proxies may be questioned because they represent only undigested food remains. Results from Kruger Park confirm that free-ranging browsers have faecal δ 13C consistent with C 3 feeding, grazer faeces are C 4, and mixed-feeder faeces intermediate. Although the respective ranges do not overlap, there is significant variation in faecal δ 13C of browsers and grazers (~2.0–4.0‰) across space and through time. We demonstrate that most (~70%) of this variation can be ascribed to corresponding patterns of variation in the δ 13C of C 3 and C 4 plants, respectively, re-enforcing the fidelity of faecal isotope proxies for diet but highlighting a need for mixing models that control for variations in plant δ 13C in order to achieve accurate diet reconstructions. Predictions for the effects of climate (rainfall) and ecophysiology on 15N-abundance variations in mammals do not persist in faeces. Rather, faecal δ 15N tracks changes in plant δ 15N, with further fractionation occurring primarily due to variations in dietary protein (reflected by %N). Controlling for these effects, we show that a dual-isotope multiple source mixing model (Isosource) can extend diet reconstructions for African savanna herbivores beyond simplified C 3/C 4 distinctions, although further understanding of variations in mammal δ 15N are needed for greater confidence in this approach. 相似文献
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