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1.
Weixin Cheng 《Plant and Soil》1996,183(2):263-268
Due to the limitations in methodology it has been a difficult task to measure rhizosphere respiration and original soil carbon decomposition under the influence of living roots. 14C-labeling has been widely used for this purpose in spite of numerous problems associated with the labeling method. In this paper, a natural 13C method was used to measure rhizosphere respiration and original soil carbon decomposition in a short-term growth chamber experiment. The main objective of the experiment was to validate a key assumption of this method: the 13C value of the roots represents the 13C value of the rhizosphere respired CO2. Results from plants grown in inoculated carbon-free medium indicated that this assumption was valid. This natural 13C method was demonstrated to be advantageous for studying rhizosphere respiration and the effects of living roots on original soil carbon decomposition. 相似文献
2.
Influence of rhizodeposition under elevated CO2 on plant nutrition and soil organic matter 总被引:2,自引:0,他引:2
Zoe G. Cardon 《Plant and Soil》1995,187(2):277-288
Atmospheric CO2 concentrations can influence ecosystem carbon storage through net primary production (NPP), soil carbon storage, or both. In assessing the potential for carbon storage in terrestrial ecosystems under elevated CO2, both NPP and processing of soil organic matter (SOM), as well as the multiple links between them, must be examined. Within this context, both the quantity and quality of carbon flux from roots to soil are important, since roots produce specialized compounds that enhance nutrient acquisition (affecting NPP), and since the flux of organic compounds from roots to soil fuels soil microbial activity (affecting processing of SOM).From the perspective of root physiology, a technique is described which uses genetically engineered bacteria to detect the distribution and amount of flux of particular compounds from single roots to non-sterile soils. Other experiments from several labs are noted which explore effects of elevated CO2 on root acid phosphatase, phosphomonoesterase, and citrate production, all associated with phosphorus nutrition. From a soil perspective, effects of elevated CO2 on the processing of SOM developed under a C4 grassland but planted with C3 California grassland species were examined under low (unamended) and high (amended with 20 g m–2 NPK) nutrients; measurements of soil atmosphere 13C combined with soil respiration rates show that during vegetative growth in February, elevated CO2 decreased respiration of carbon from C4 SOM in high nutrient soils but not in unamended soils.This emphasis on the impacts of carbon loss from roots on both NPP and SOM processing will be essential to understanding terrestrial ecosystem carbon storage under changing atmospheric CO2 concentrations.Abbreviations SOM
soil organic matter
- NPP
net primary productivity
- NEP
net ecosystem productivity
- PNPP
p-nitrophenyl phosphate 相似文献
3.
Our investigations of diurnal variations of the 13C/12C ratio and CO2 content in soil air were carried out in three environments during periods of high biosphere activity. It has been observed that diurnal variation of CO2 concentration is negatively correlated 13. Particularly great variations occurred at shallow soil depths (10–30 cm) when the plant cover activity was high while the soil temperature was rather low. Under such conditions the 13 variations had the magnitude of 4, while the CO2 concentration varied more than doubly. The maximum of the 13C/12C ratlo and the minimum of the CO2 concentration in a cultivated field with winter wheat took place in the afternoon, whereas in deciduous forest similar patterns were observed at dawn. In these cases soil temperatures at 10 cm depths varied less than 2°C. Hence, under wheat the variation in root respiration rate seem to be the main reason of the recorded varations. In an uncultivated grass-field during the hottest period in summer we did not measure any distinct variations of CO2 properties in spite of the fact that soil temperature varied up to 5°C. This might be due to dominant microbial respiration at the high soil temperature, which exceeded 20°C. 相似文献
4.
The carbon isotope composition of an animals breath reveals the composition of the nutrients that it catabolizes for energy. Here we describe the use of Keeling plots, a method widely applied in ecosystem ecology, to measure the 13C of respired CO2 of small vertebrates. We measured the 13C of Rufous Hummingbirds (Selasphorus rufus) in the laboratory and of Mourning (Zenaida macroura) and White-winged (Z. asiatica) Doves in the field. In the laboratory, when hummingbirds were fed a sucrose based C3 diet, the 13C of respired CO2 was not significantly different from that of their diet (13CC3 diet). The 13C of respired CO2 for C3 fasted birds was slightly, albeit significantly, depleted in 13C relative to 13CC3 diet. Six hours after birds were shifted to a sucrose based C4 diet, the isotopic composition of their breath revealed that birds were catabolizing a mixture of nutrients derived from both the C3 and the C4 diet. In the field, the 13C of respired CO2 from Mourning and White-winged Doves reflected that of their diets: the CAM saguaro cactus (Carnegeia gigantea) and C3 seeds, respectively. Keeling plots are an easy, effective and inexpensive method to measure 13C of respired CO2 in the lab and the field. 相似文献
5.
Carbon-isotope ratios were examined as 13C values in several C3, C4, and C3–C4
Flaveria species, and compared to predicted 13C, values generated from theoretical models. The measured 13C values were within 4 of those predicted from the models. The models were used to identify factors that contribute to C3-like 13C values in C3–C4 species that exhibit considerable C4-cycle activity. Two of the factors contributing to C3-like 13C values are high CO2 leakiness from the C4 pathway and pi/pa values that were higher than C4 congeners. A marked break occurred in the relationship between the percentage of atmospheric CO2 assimilated through the C4 cycle and the 13C value. Below 50% C4-cycle assimialtion there was no significant relationship between the variables, but above 50% the 13C values became less negative. These results demonstrate that the level of C4-cycle expression can increase from, 0 to 50% with little integration of carbon transfer from the C4 to the C3 cycle. As expression increaces above 50%, however, increased integration of C3- and C4-cycle co-function occurs.Abbreviations and symbols RuBP carboxylase
ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39)
- PEP carboxylase
phosphoenolpyruvate carboxylase (EC 4.1.1.31)
- pa
atmospheric CO2 partial pressure
- pi
intercellular CO2 partial pressure
-
isotope ratio
-
quantum yield for CO2 uptake 相似文献
6.
Spatial and temporal distribution of carbon isotopes in soil organic matter at the Dinghushan Biosphere Reserve, South China 总被引:6,自引:0,他引:6
Qingqiang Chen Chengde Shen Yanmin Sun Shaolin Peng Weixi Yi Zhi’an Li Mantao Jiang 《Plant and Soil》2005,273(1-2):115-128
The spatial and temporal distribution of carbon isotopes (13C, 14C) in soil organic matter (SOM) were studied based on SOM content, SOM 14C and SOM 13C of thinly layered soil samples for six soil profiles with different elevations at the Dinghushan Biosphere Reserve (DHSBR), South China. The results indicate that variations of SOM 13C with depth of the soil profiles at different elevations are controlled by soil development, and correlate well with SOM composition in terms of SOM compartments with different turnover rates, and SOM turnover processes at the DHSBR. The effect of carbon isotope fractionation was obvious during transformation of organic matter (OM) from plant debris to SOM in topsoil and SOM turnover processes after the topsoil was buried, which resulted in great increments of OM 13C, respectively. Increments of SOM 13C of topsoil from 13C of plant debris were controlled by SOM turnover rates. Both topsoil SOM 13C and plant debris 13C increase with elevation, indicating regular changes in vegetation species and composition with elevation, which is consistent with the vertical distribution of vegetation at the DHSBR. The six soil profiles at different elevations had similar characteristics in variations of SOM 13C with depth, alterations of SOM contents with depth and that SOM 14C apparent ages increasing with depth, respectively. These are presumably attributed to the regular distribution of different SOM compartments with depth because of their regular turnover during soil development. Depth with the maximal SOM 13C value is different in mechanism and magnitude with penetrating depth of 14C produced by nuclear explosion into atmosphere from 1952 to 1962, and both indicate controls of topography and vegetation on the distribution of SOM carbon isotopes with depth. Elevation exerts indirect controls on the spatial and temporal distribution of SOM carbon isotopes of the studied mountainous soil profiles at the DHSBR. This study shows that mountainous soil profiles at different elevations and with distinctive aboveground vegetation are presumably ideal sites for studies on soil carbon dynamics in different climatic-vegetation zones. 相似文献
7.
Sucrose application,soil microbial respiration and evolved carbon dioxide isotope enrichment under contrasting land uses 总被引:2,自引:1,他引:1
Heterotrophic decomposition of organic matter dictates that substrate supply rate, including energy and nutrients, can limit soil microbial activity. In New Zealand, soils are naturally deficient in nitrogen and phosphorus. Fertiliser application is a part of pastoral agriculture, the countrys most widespread land use. We postulated that organic soils under grazed pasture and pristine forest would be at the extremes of substrate quality and supply rate, and thus potential microbial response to food opportunities. Soil microbial responses to the addition of fresh energy (sucrose) were determined by laboratory experiments with root-free samples and intact cores including roots. Responses were quantified by respiration and respired carbon (C) isotope (13C) enrichment measurements. A supra-trace sucrose dose (0.002 mol kg–1 (soil)) caused the forest soils microbial respiration rate to nearly double within 2 h. The peak response took 20 h, and saturation occurred beyond a sucrose dose of 0.05 mol kg–1 (soil). Intact soil cores from the forest had similar respiration rates and responses. For root-free soil samples from the grazed pasture, respiration response to sucrose was nearly immediate, dose dependent, and there was up to a 9-fold increase in the rate. Intact cores from the pasture had much higher respiration rates, but a similar response to sucrose. For both soils, the similarity of sucrose application effects on respiration and relative 13C enrichment of the respired carbon was striking. 相似文献
8.
Forest- and pasture-derived carbon contributions to carbon stocks and microbial respiration of tropical pasture soils 总被引:3,自引:0,他引:3
Christopher Neill Brian Fry Jerry M. Melillo Paul A. Steudler Jener F. L. Moraes Carlos C. Cerri 《Oecologia》1996,107(1):113-119
The clearing of tropical forest for pasture leads to important changes in soil organic carbon (C) stocks and cycling patterns. We used the naturally occurring distribution of13C in soil organic matter (SOM) to examine the roles of forest- and pasture-derived organic matter in the carbon balance in the soils of 3- to 81-year-old pastures created following deforestation in the western Brazilian Amazon Basin state of Rondônia. Different 13C values of C3 forest-derived C (-28) and C4 pasture-derived C (-13) allowed determination of the origin of total soil C and soil respiration. The 13C of total soil increased steadily across ecosystems from -27.8 in the forest to -15.8 in the 81-year-old pasture and indicated a replacement of forest-derived C with pasture-derived C. The 13C of respired CO2 increased more rapidly from -26.5 in the forest to -17 in the 3- to 13-year-old pastures and indicated a faster shift in the origin of more labile SOM. In 3-year-old pasture, soil C derived from pasture grasses made up 69% of respired C but only 17% of total soil C in the top 10 cm. Soils of pastures 5 years old and older had higher total C stocks to 30 cm than the original forest. This occurred because pasture-derived C in soil organic matter increased more rapidly than forest-derived C was lost. The increase of pasture-derived C in soils of young pastures suggests that C inputs derived from pasture grasses play a critical role in development of soil C stocks in addition to fueling microbial respiration. Management practices that promote high grass production will likely result in greater inputs of grass-derived C to pasture soils and will be important for maintaining tropical pasture soil C stocks. 相似文献
9.
Summary An attempt has been made to evaluate the contribution of soil respired CO2 to the total assimilation of a forest tree, by heeding the 13C-concentrations of CO2 from the free atmosphere and from mineralization processes within the soil respectively. An expression has been derived, according to which the assimilated fraction of CO2 from the soil at a particular height of a tree is given by the 13C-value of the corresponding leaves, 13C of atmospheric CO2, 13C of soil respired CO2 and the physiological state of the leaves expressed as the ratio of total respiration over gross photosynthesis and internal over external CO2-concentration. In the particular case investigated, a 13C-difference of 5 has been determined from bottom to top of a beech tree which results in a CO2 contribution from the soil of about 22% for the lower forest strata, while the total contribution of soil respired CO2 accounts for about 5% of the overall assimilation. 相似文献
10.
Summary A method of monitoring and collecting CO2 samples in the field has been developed which has been used to study both temporal and spatial variations in canopy CO2 isotopic signatures in two contrasting tropical forest formations in Trinidad. These have been related to vertical gradients in the carbon isotope ratio (13C) of organic material in conjunction with measurements of other environmental parameters. The 13C of leaf material from two canopies showed a gradient with respect to height, more negative values being found low in the understorey. The deciduous secondary forest, (Simla) showed a difference of 4.6 and the semi-evergreen seasonal canopy (Aripo), 2.8. The range of 13C values at Simla was 4 less negative than those at Aripo. In order to relate these measurements to the interaction between diffusion or carboxylation limitation, and source CO2 effects, variations in environmental parameters through the canopy have been compared with changes in CO2 partial pressure (P
a) and isotopic composition 13C throughout the day during the dry season. Values of P
a20 m above the ground at Aripo varied from 380 vpm at dawn to 340 vpm at midday, at which time the partial pressure 15 cm above the ground was 375 vpm. The CO2 partial pressure did not stabilise during the course of the day, and there was good correlation (r
2=0.82) between a and P
a, with more negative values of a occuring in the understorey. Diuraal changes of 2 were evident at all canopy positions. In the more open canopy at Simla, these gradients were similar, but less marked. Leaf-air vapour pressure deficit (VPD) showed no relationship with height, possibly as a result of minimal water flux from both the soil and the canopy due to low soil water content; VPD was 1.5 kPa higher at midday than dawn. A 3° C temperature gradient between the understorey and upper canopy was observed at Aripo but not in the more open Simla canopy. CO2 partial pressure stabilised for only 4 h in the middle of the day, while other parameters showed no stable period. The proportion of floor respired CO2 reassimilated at Aripo has been calculated as 26%, 19%, and 8% for the periods 0600–1000, 1000–1400, and 1400–1800 hours. In order to quantify source CO2 effects, measurements of the environmental parameters and assimilation rate must be made at all canopy positions and throughout the day. 相似文献
11.
This study investigated the relationship between 13C of ecosystem components, soluble plant carbohydrates and the isotopic signature of ecosystem respired CO2 (13CR) during seasonal changes in soil and atmospheric moisture in a beech (Fagus sylvatica L.) forest in the central Apennine mountains, Italy. Decrease in soil moisture and increase in air vapour pressure deficit during summer correlated with substantial increase in 13C of leaf and phloem sap soluble sugars. Increases in 13C of ecosystem respired CO2 were linearly related to increases in phloem sugar 13C (r2=0.99, P0.001) and leaf sugar 13C (r2=0.981, P0.01), indicating that a major proportion of ecosystem respired CO2 was derived from recent assimilates. The slopes of the best-fit lines differed significantly (P0.05), however, and were about 0.86 (SE=0.04) for phloem sugars and about 1.63 (SE=0.16) for leaf sugars. Hence, changes in isotopic signature in phloem sugars were transferred to ecosystem respiration in the beech forest, while leaf sugars, with relatively small seasonal changes in 13C, must have a slower turnover rate or a significant storage component. No significant variation in 13C was observed in bulk dry matter of various plant and ecosystem components (including leaves, bark, wood, litter and soil organics). The apparent coupling between the 13C of soluble sugars and ecosystem respiration was associated with large apparent isotopic disequilibria. Values of 13CR were consistently more depleted by about 4 relative to phloem sugars, and by about 2 compared to leaf sugars. Since no combination of the measured pools could produce the observed 13CR signal over the entire season, a significant isotopic discrimination against 13C might be associated with short-term ecosystem respiration. However, these differences might also be explained by substantial contributions of other not measured carbon pools (e.g., lipids) to ecosystem respiration or contributions linked to differences in footprint area between Keeling plots and carbohydrate sampling. Linking the seasonal and inter-annual variations in carbon isotope composition of carbohydrates and respiratory CO2 should be applicable in carbon cycle models and help the understanding of inter-annual variation in biospheric sink strength. 相似文献
12.
Summary To determine whether sweet potato (Ipomoea batatas (L.) Poir.) takes up organic matter through the roots from the medium, the concentrations of natural14C (14C) in plant organic matter, atmospheric CO2 and compost applied to media were examined under soil and sand culture conditions. In these experiments, three kinds of composts of different 14C were used. CO2 derived from the mineralization of compost was continuously pumped out from the pots and its direct uptake by the leaves was prevented.14C of plant parts harvested after the 43 days experimental period were affected by the 14C of the compost in the treatments where the compost of rice straw was applied, and which suggested that a significant amount of plant carbon was derived from the compost. 相似文献
13.
Measurements were made of the concentration and stable oxygen isotopic ratio of carbon dioxide in air samples collected on a diurnal basis at two heights within a Pinus resinosa canopy. Large changes in CO2 concentration and isotopic composition were observed during diurnal time courses on all three symple dates. In addition, there was strong vertical stratification in the forest canopy, with higher CO2 concentrations and more negative 18O values observed closer to the soil surface. The observed daily increases in 18O values of forest CO2 were dependent on relative humidity consistent with the modelled predictions of isotopic fractionation during photosynthetic gas exchange. During photosynthetic gas exchange, a portion of the CO2 that enters the leaf and equilibrates with leaf water is not fixed and diffuses back out of the leaf with an altered oxygen isotopic ratio. The oxygen isotope ratio of CO2 diffusing out of a leaf depends primarily on the 18O content of leaf water which changes in response to relative humidity. In contrast, soil respiration caused a decline in the 18O values of forest CO2 at night, because CO2 released from the soil has equilibrated with soil water which has a lower 18O content than leaf water. The observed relationship between diurnal changes in CO2 concentration and oxygen isotopic composition in the forest environment were consistent with a gas mixing model that considered the relative magnitudes of CO2 fluxes associated with photosynthesis, respiration and turbulent exchange between the forest and the bulk atmosphere. 相似文献
14.
Summary The ratio of deuterium to hydrogen (expressed as D) in hydrogen released as water during the combustion of dried plant material was examined. The D value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C3 plants show mean D values of-132 for shoots and -117 for roots; C4 plants show mean D values of -91 for shoots and-77 for roots and CAM plants a D value of-75 for roots and shoots. The difference between the D value of shoot material from C3 and C4 plants was confirmed in species growing under a range of glasshouse conditions. This difference in D value between C3 and C4 species does not appear to be due to differences in the D value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C3 and C4 plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in D values are discussed. In CAM plants grown in the laboratory or collected from the field D values range from-75 to +50 and are correlated with 13C values. When deprived of water, the D value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different D value of available water in areas of increasing aridity. Whatever the origin of the variable D value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions. 相似文献
15.
Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition 总被引:12,自引:1,他引:11
We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (13CPOC) and suspended matter (13CPOC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest 13CDIC values are observed due to enhanced input of CO2 from decomposition of 13C-depleted terrestrial plant detritus (average 13CDIC = –/14.3). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative 13CDIC values (average 13CDIC = –9.9). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 gl–1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 gl–1. Furthermore, in winter the very narrow range of 13CPOC (from –26.5 to –27.6) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer 13CPOC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in 13C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of 13C/12C fractionation by phytoplankton is attempted. 相似文献
16.
The effect of interspecific competition and element additions (N and P) on four grassland species (Poa pratensis, Lolium perenne, Festuca valida, Taraxacum officinale) grown under field conditions was studied. Two grasses (L. perenne, F. valida) grown in monoculture (absence of competition) showed lower carbon isotope discrimination (13C) and enriched 15N values. Nitrogen addition (as urea) had inconsistent effects on species 13C while caused enrichment of 15N of P. pratensis and F. valida but strong depletion of 15N of T. officinale. Phosphorous had no significant effect on 13C but depleted 15N of all species. 相似文献
17.
Steven W. Leavitt Eldor A. Paul Abraham Galadima Francis S. Nakayama Shelley R. Danzer Hyrum Johnson Bruce A. Kimball 《Plant and Soil》1995,187(2):147-155
The Maricopa cotton and wheat FACE (free-air CO2 enrichment) experiments offer propitious opportunity to quantify carbon turnover. The commercial CO2 (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqiTdq2aaW% baaSqabeaacaaIXaGaaG4maaaakiaaboeacqGHijYUcqGHsislcaaI% ZaGaaG4naiaacwcaliaad+gaaaa!3FCB!\[\delta ^{13} {\text{C}} \approx - 37\% o\]) used to elevate CO2 concentration in field plots provided a strongly 13C-depleted tracer. Soil CO2 and 13C of soil organic carbon (SOC) in CO2-enriched and Control plots were measured between the final cotton FACE project (October 1991) and the end of the second wheat experiment (June 1994). The initial 13C-depletion in SOC of cotton FACE plots (measured by the difference in 13C between FACE and Control plots) persisted at the same level (1.9) 1.5 years after the experiment ended. A similar depletion was observed in soil CO2 evolved in the same plots, indicating ongoing decomposition of the new SOC. The SOC 13C of wheat plots before and after two growing seasons showed increasing 13C-depletion in FACE relative to Control. Isotopic mass balance was consistent with 5–6% new carbon input from the two wheat crops. This is lower than the 12–13% calculated for FACE cotton and perhaps a consequence of the larger root system of cotton or the 3-year duration of the cotton experiments versus 2 years for the wheat. 相似文献
18.
Is growth of soil microorganisms in boreal forests limited by carbon or nitrogen availability? 总被引:11,自引:2,他引:9
To study whether the biomass of soil microorganisms in a boreal Pinus sylvestris-Vaccinium vitis-idaea forest was limited by the availability of carbon or nitrogen, we applied sucrose from sugar cane, a C4 plant, to the organic mor-layer of the C3–C dominated soil. We can distinguish between microbial mineralization of the added sucrose and respiration of endogenous carbon (root and microbial) by using the C4-sucrose as a tracer, exploiting the difference in natural abundance of 13C between the added C4-sucrose (13C –10.8) and the endogenous C3–carbon (13C –26.6 ). In addition to sucrose, NH4Cl (340 kg N ha–1) was added factorially to the mor-layer. We followed the microbial activity for nine days after the treatments, by in situ sampling of CO2 evolved from the soil and mass spectrometric analyses of 13C in the CO2. We found that microbial biomass was limited by the availability of carbon, rather than nitrogen availability, since there was a 50% increase in soil respiration in situ between 1 h and 5 days after adding the sucrose. However, no further increase was observed unless nitrogen was also added. Analyses of the 13C ratios of the evolved CO2 showed that increases in respiration observed between 1 h and 9 days after the additions could be accounted for by an increase in mineralization of the added C4–C. 相似文献
19.
Photosynthetic carbon uptake and respiratory C release from soil are major components of the global carbon balance. The use of 13C depleted CO2 (13C = –30) in a free air CO2 enrichment experiment in a mature deciduous forest permitted us to trace the carbon transfer from tree crowns to the rhizosphere of 100–120 years old trees. During the first season of CO2 enrichment the CO2 released from soil originated substantially from concurrent assimilation. The small contribution of recent carbon in fine roots suggests a much slower fine root turnover than is often assumed.13C abundance in soil air correlated best with temperature data taken from 4 to 10 days before air sampling time and is thus rapidly available for root and rhizosphere respiration. The spatial variability of 13C in soil air showed relationships to above ground tree types such as conifers versus broad-leaved trees. Considering the complexity and strong overlap of roots from different individuals in a forest, this finding opens an exciting new possibility of associating respiration with different species. What might be seen as signal noise does in fact contain valuable information on the spatial heterogeneity of tree-soil interaction. 相似文献
20.
We present a comprehensive dataset of hourly, daily, and monthly measurements of carbon isotope measurements of CO2 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 (13CR) 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 CO2 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 (13CR). 13CR 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 13CR over the seasonal cycle (3.08). This highlights the importance of short-term physiological processes within ecosystems for the isotopic composition of CO2 in the atmosphere, not reflected by bulk plant and soil organic samples. At daily and monthly time scales, 13CR 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