Tracing mangrove carbon in suspended matter and aquatic fauna of the Gautami–Godavari Delta,Bay of Bengal (India)

Stable carbon isotopic composition and C/N ratio were used to trace the input of carbon associated with mangrove litter into the estuary of the Godavari–Gautami delta system and Kakinada bay (Andhra Pradesh, India). Suspended organic matter in the mangrove channels was more depleted in ¹³C (average ¹³C = –24.5) than in Kakinada bay which showed ¹³C values for suspended matter (average ¹³C = –22.7) closer to those expected for marine phytoplankton. Suspended organic matter from mangrove channels was enriched in nitrogen (average C/N atom ratio 12.7) and ¹³C (average ¹³C = –24.5) relative to mangrove leaf litter, which had a C/N ratio of 75 and a ¹³C value of –28. Lowest C/N ratios for suspended matter were observed during southwest monsoon when rainfall was highest. Although in general, mangrove litter fall was also lower during this period, no clear correlation was observed between litter fall and C/N ratio of suspended matter. In general, the composition of suspended matter pointed towards phytoplankton as a major component. Isotopic composition of zooplankton suggested selective feeding on ¹³C-enriched, marine phytoplankton in open Kakinada bay and on ¹³C-depleted organic matter, such as estuarine phytoplankton and mangrove litter, in the mangrove channels. From the ¹³C signature, it appeared that mangrove carbon was present to some extent in zooplankton and macrofauna from the mangrove mudflats and channels, but the signal rapidly decreased in Kakinada bay. Nitrogen isotopic composition of zooplankton and macrofauna indicated a progressive enrichment of ¹⁵N away from the mangrove forest towards the northern part of Kakinada bay, in approach of Kakinada city. This is thought to reflect input of anthropogenic nitrogen enriched in ¹⁵N and subsequent uptake of this enriched nitrogen into the aquatic food chain.     

Uptake of organic matter by the roots of sweet potato: Analysis of the δ14C value of plants

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.     

Forest- and pasture-derived carbon contributions to carbon stocks and microbial respiration of tropical pasture soils

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.     

Stable isotope ratio as a tracer of mangrove carbon in Malaysian ecosystems

Summary The ratio of stable carbon isotopes (¹³C) in plants and animals from Malaysian mangrove swamps, coastal inlets, and offshore waters was determined. Vascular plants of the swamps were isotopically distinct ( x±s.d.=-27.1±1.2) from plankton (-21.0±0.3) and other algae (-18.7±2.2). Animals from the swamps (-20.9±4.1) and inlets (-19.8±2.5) had a wide range of isotope ratios (-28.6 to-15.4), indicating consumption of both mangrove and algal carbon. Several commercially important species of bivalves, shrimp, crabs, and fish obtained carbon from mangrove trees. Mangrove carbon was carried offshore as detritus and was isotopically distinguishable in suspended particulate matter and sediments. Animals collected from 2 to 18 km offshore, however, showed no isotopic evidence of mangrove carbon assimilation, with ratios (-16.5±1.1, range-19.1 to-13.1) virtually identical to those reported for similar animals from other plankton-based ecosystems. Within groups of animals, isotope ratios reflected intergencric and interspecific differences in feeding and trophic position. In particular, there was a trend to less negative ratios with increasing trophic level.     

Stable isotope ratios of soil carbonate and soil organic matter as indicators of forest invasion of prairie near Ames,Iowa

Stable isotope ratios of pedogenic carbonate and organic matter were measured in a prairie-transition-forest soil biosequence near Ames, Iowa to determine the vegetation succession. The modern vegetation is dominated by non-native C₃ plants which have been introduced by agricultural practices. The ¹³C values of soil organic matter from the prairie and forest endmembers indicate C₄ and C₃ dominated ecosystems, respectively, during the accumulation of soil organic matter. Pedogenic carbonate from all soils, including rare pedogenic carbonate from the forested soil, has an average ¹³C of-2.0, indicating that the carbonate formed under a C₄ vegetation. These results indicate that the ecosystem was a C₄-dominated prairie and therefore suggest a recent arrival of forests and other C₃ plants in the area. This study also implies that the primary features of the transitional Lester soil series, which has soil properties intermediate between Alfisols and Molisolls, formed under prairie conditions and were overprinted by an invading forest.     

δ13C signature of organic carbon in estuarine bottom sediment as an indicator of carbon export from adjacent marshes

The ¹³C signature of organic carbon in estuarine bottom sediment in Louisiana Barataria Basin was used for estimating carbon flux from adjacent marsh. The stable carbon isotope composition of plants, soils and sediments from the basin were determined. The ¹³C content of marsh vegetation ranged from -26.3 to -27.8% for C₃ freshwater vegetation in the upper basin to -13.0 to -13.3% for C₄ vegetation in the lower basin. The ¹³C content of the highly organic marsh soils were similar to ¹³C content of vegetation present. The ¹³C content of organic carbon from bottom sediment of open water bodies ranged from 27.3 in the upper basin (freshwater) to 16.4 in bottom sediment of salt marsh ponds. The¹³C signature of organic carbon in bottom sediment from saline regions corresponded to the size of the body of water. The smaller salt marsh ponds contain sediment with ¹³C values close to that of the C₄ plantSpartina alterniflora. Results suggest that phytoplankton rather thanSpartina alterniffora is the likely organic source in bottom sediment of the larger bay near the coast (e.g. Caminada Bay).     

Carbon-isotope discrimination by leaves of Flaveria species exhibiting different amounts of C3-and C4-cycle co-function

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     

Effect of size on the energy acquired in species of the fish from a neotropical reservoir,Brazil

In this paper we analysed autotrophic sources of the carbon ( ¹³C) and the trophic position ( ¹⁵N) of Leporinus friderici in the influence area of Corumbá Reservoir, Brazil. We collected samples of muscles of fish from different sizes riparian vegetation, C₄ grasses, zooplankton, periphyton and particulate organic carbon (POC). There were significant differences for the carbon isotope proportion found in muscles of L.friderici in the different size groups analysed. The highest values of ¹³C recorded for middle sized individuals is attributed to the large contribution of C₄ plants in their diet. Small individuals sampled upstream also receive similar contribution from C₄ plants. In contrast the same size group sampled downstream from the reservoir, has a much smaller of C₄ plants. The ¹³C negative character of small individuals from downstream is due to the larger contribution of C₃ plants (except periphyton). At larger sizes we found intermediate ¹³C values. The ¹⁵N proportions we found for each size group were not significantly different, however we found decreasing mean values with increasing size. The trophic level calculated from the dietary data was higher than that found with the ¹³C concentration in the muscle, except for small individuals, when the values were equal.     

Beaver alter stable carbon isotope ratios of benthic particulate organic matter

Beaver are well known to influence the geomorphology and geochemistry of boreal waters, in addition to being prominent vectors in the selective import of deciduous coarse woody debris (CWD). Because the stable carbon isotope ratios of deciduous trees are lower than those of coniferous trees, the possibility exists that the ¹³C values of particulate organic matter near beaver lodges may differ from those characteristic for littoral regions without beaver activity. In agreement with this supposition, ¹³C was found to significantly increase in progressively smaller size fractions of CWD collected from near lodges, probably due to the more rapid breakdown, decomposition and disappearance of deciduous material.     

Hydrogen isotope discrimination in higher plants: Correlations with photosynthetic pathway and environment

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.     

Ecosystem Modulation of Dissolved Carbon Age in a Temperate Marsh-Dominated Estuary

We measured the concentrations and isotopic values (¹⁴C and ¹³C) of dissolved inorganic, dissolved organic, and particulate organic carbon (DIC, DOC, and POC, respectively) in the Parker River watershed and estuary in Massachusetts, USA, to determine the age of carbon (C) entering the estuary and how estuarine processing affects the quantity and apparent age of C transported to the Gulf of Maine. The watershed measurements indicated the transport of ¹⁴C-enriched modern DIC and DOC and variably aged POC from the watershed to the estuary. The transport of organic matter from the watershed was dominated by DOC transport, with POC making up less than 10% of the total. Surveys within the watershed aimed at determining which land-use type dominated the DOC export indicated that wetlands, although they made up only around 20% of the land use, could be responsible for approximately 75% of the DOC export. We therefore conclude that the wetland land uses of the Parker River watershed are exporting mainly ¹⁴C-enriched modern DOC. DIC isotopes indicate that the source of DIC in the Parker River watershed is dominated by the weathering of noncarbonate parent material by ¹⁴C-enriched carbon dioxide (CO₂) originating from the respiration of young organic matter in soils. Transects in the estuary displayed net additions of all C species. For DOC and DIC, the export of this internally added DOC and DIC was approximately equal to the amount being exported from the watershed, showing the importance of focusing on estuaries when estimating the export of C to the coastal ocean. With respect to DIC, the total input is even larger when the atmospheric exchange of excess pCO₂ is calculated. The ¹⁴C-DOC and ¹⁴C-DIC transects indicate that the internally added DOC and DIC is ¹⁴C-enriched modern material. The source of this material is the fringing marshes and estuarine phytoplankton, with the relative importance of these two sources changing over time. Taken together, the bulk C and ¹⁴C measurements show that the estuary is adding significant quantities of young DOC despite the presence of vast quantities of old marsh peat flanking the entire estuary. Furthermore, the DIC data indicate that ¹⁴C-enriched modern material is what is fueling the majority of heterotrophic respiration within the system.     

Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge,NE Bavaria

Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The ¹³C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (¹³C between-25.3 and-27.8) were significantly less depleted in ¹³C than needles (¹³C between-27.3 and-29.1), and ¹³C in twigs increased consistently with age. The ¹⁵N values of needles ranged between-2.5 and-4.1 and varied according to stand and age. In young needles ¹⁵N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in ¹⁵N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. ¹⁵N values in twigs were more negative than in needles (-3.5 to-5.2) and showed age- and stand-dependent trends that were similar to the needles. ¹⁵N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4 in the mineral soil. The ¹⁵N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed.     

Stable carbon and oxygen isotopic compositions of recent charophyte oosporangia and water from Malham Tarn,U.K.: palaeontological implications

Charophyte oosporangia and water samples from a highly calcareous lake were measured for stable carbon and oxygen isotopic composition. The time period over which the oosporangia calcify is short, thus any biochemical relationship between the water and oosporangia"s calcite represents only one time window (late Summer in Malham Tam). This important temporal restraint must also apply to interpretations of all fossil material measured. The ¹⁸O_c of the charophyte oosporangia is deduced to be in equilibrium with the ¹⁸O of the water for a given temperature. The ¹³ C_c of the charophyte oosporangia was approximately 2.5 per mil lower than the ¹³C_DIC in the water we measured. With the release Of CO₂ with phosphoric acid from the charophyte oosporangia, there was no significant difference in the ¹⁸O_c values obtained, regardless of whether or not the carbonate was separated from the organic center, however ¹³C_c values were marginally lower for carbonate plus organic center measurements. Our results indicate that fossil charophyte gyrogonites can be used to elucidate the geochemistry of the ancient water body in which they lived.     

Oxygen and carbon isotope composition of parasitic plants and their hosts in southwestern Australia

We measured leaf dry matter ¹⁸O and ¹³C in parasitic plants and their hosts growing in southwestern Australia. Parasite/host pairs included two mistletoe species, three species of holoparasites, and five species of root hemiparasites. Among these parasite functional types, significant variation was observed in parasite/host isotopic differences for both ¹⁸O (P<0.0001, n=65) and ¹³C (P<0.0001, n=64). Mistletoes were depleted in both ¹⁸O and ¹³C compared to their hosts; parasite/host differences were –4.0 for ¹⁸O (P<0.0001) and –1.9 for ¹³C (P<0.0001). The lower ¹⁸O in mistletoe leaf dry matter compared to their hosts is consistent with the frequently observed high transpiration rates of these parasites. Root hemiparasites were also depleted in ¹⁸O and ¹³C compared to their hosts, but not to the same extent as mistletoes; parasite/host differences were –1.0 for ¹⁸O (P=0.04) and –1.2 for ¹³C (P=0.0006). In contrast to mistletoes and root hemiparasites, holoparasites were enriched in both ¹⁸O and ¹³C compared to their hosts; parasite/host differences were +3.0 for ¹⁸O (P<0.0001) and +1.5 for ¹³C (P=0.02). The enrichment in ¹⁸O for holoparasite dry matter did not result from more enriched tissue water; holoparasite tissue water ¹⁸O was less than host leaf water ¹⁸O by a difference of –3.8 when sampled at midday (P=0.0003). Enrichment of holoparasites in ¹³C compared to their hosts is consistent with a generally observed pattern of enrichment in heterotrophic plant tissues. Results provide insights into the ecology of parasitic plants in southwestern Australia; additionally, they provide a context for the formulation of specific hypotheses aimed at elucidating mechanisms underlying isotopic variations among plants.     

Carbon isotope composition in relation to leaf gas exchange and environmental conditions in Hawaiian Metrosideros polymorpha populations

Summary Carbon isotope composition, photosynthetic gas exchange, and nitrogen content were measured in leaves of three varieties of Metrosideros polymorpha growing in sites presenting a variety of precipitation, temperature and edaphic regimes. The eight populations studied could be divided into two groups on the basis of their mean foliar ¹³C values, one group consisting of three populations with mean ¹³C values ca.-26 and another group with ¹³C values ca.-28. Less negative ¹³C values appeared to be associated with reduced physiological availability of soil moisture resulting from hypoxic conditions at a poorly drained high elevation bog site and from low precipitation at a welldrained, low elevation leeward site. Gas exchange measurements indicated that foliar ¹³C and intrinsic wateruse efficiency were positively correlated. Maximum photosynthetic rates were nearly constant while maximum stomatal conductance varied substantially in individuals with foliar ¹³C ranging from-29 to-24. In contrast with the patterns of ¹³C observed, leaf nitrogen content appeared to be genetically determined and independent of site characteristics. Photosynthetic nitrogenuse efficiency was nearly constant over the range of ¹³C observed, suggesting that a compromise between intrinsic water- and N-use efficiency did not occur. In one population variations in foliar ¹³C and gas exchange with leaf cohort age, caused the ratio of intercellular to atmospheric partial pressure of CO₂ predicted from gas exchange and that calculated from ¹³C to be in close agreement only in the two youngest cohorts of fully expanded leaves. The results indicated that with suitable precautions concerning measurement protocol, foliar ¹³C and gas exchange measurements were reliable indicators of potential resource use efficiency by M. polymorpha along environmental gradients.     

Effect of organic and inorganic fertigation on yields, δ15N values, and δ13C values of tomato (Lycopersicon esculentum Mill. cv. Saturn)

We examined the effects of fertilizer application, especially the effects of fertigation and types of fertilizer (inorganic and organic) on yields and ¹⁵N and ¹³C values of tomato (Lycopersicon esculentum Mill. cv. Saturn). Fertigation is a method in which an appropriate diluted liquid fertilizer is applied to the plants each time they are drip-irrigated. We developed a method of organic fertigation using corn steep liquor (CSL) as the liquid fertilizer, because it is an industrial byproduct of cornstarch manufacture and can be used very effectively. We compared fruit yield, mineral content, ¹⁵N value, and ¹³C value of tomatoes grown under three different fertilizer treatments, basal dressing: basal dressing with granular chemical fertilizer; inorganic fertigation: fertigation with liquid chemical fertilizer; and organic fertigation: fertigaion with CSL. Mineral contents of tomatoes grown with basal dressing were generally lower than those grown under either fertigation treatment. These results indicated that yields and mineral contents were influenced more by the method of fertilizer application than by whether the fertilizers were inorganic or organic. There were, however, significant differences in the ¹⁵N values of tomato fruits grown under different types of fertilizer applications, especially between inorganic and organic fertilizers. The ¹⁵N value of the chemical fertilizer used for basal dressing was 0.81 ± 0.45{}, that of the chemical fertilizer for fertigation was 0.00 ± 0.04{}, and that of CSL was 8.50 ± 0.71{}. The ¹⁵N values of the soils reflected the ¹⁵N values of the fertilizers. Moreover, the ¹⁵N values of the fruits corresponded to the ¹⁵N values of the applied fertilizers. The ¹⁵N values were 3.18 ± 1.34{} in the fruits grown with a basal dressing of chemical fertilizer, 0.30 ± 0.61 in those grown under inorganic fertigation, and 7.09 ± 0.68 in those grown under organic fertigation. On the other hand, although the ¹³C values in the soil also reflected the ¹³C values of the applied fertilizers, there was no significant difference in the ¹³C values of fruits among the different treatments. In conclusion, because the ¹⁵N values of fertilizers correlated well with those of the fruits, it may be possible to use ¹⁵N values as an indicator of organic products.     

Seasonal and diel relationships between the isotopic compositions of dissolved and particulate organic matter in freshwater ecosystems

A study of the isotopic composition of organic matter was conducted in a freshwater marsh over seasonal and diel time scales to determine the sources of dissolved organic matter (DOM) and the processes leading to its formation. Bulk C and N isotopic compositions of the bacterial fraction (0.2–0.7 m) and particulate organic matter (POM; 0.7–10 m) were compared on a seasonal basis with the change in ¹³C of DOM. The bulk isotopic data support the idea that DOM was, in part, derived from the breakdown of larger organic matter fractions. The bacterial fraction and POM were compositionally similar throughout the year, based on a comparison of the ¹³C of individual amino acids in each fraction. Annual variation in the ¹³C of amino acids in DOM was greater relative to the variation in larger fractions indicating that microbial reworking was an important factor determining the proteinaceous component of DOM. The ¹³C enrichment of serine and leucine in each organic matter fraction suggested microbial reworking was an important factor determining organic matter composition during the most productive times of year. Changes in the bulk ¹³C of DOM were more significant over daily, relative to seasonal, time scales where values ranged by 6 and followed changes in chlorophyll a concentrations. Although bulk ¹³C values for POM ranged only from –29 to –28 during the same diel period, the ¹³C of alanine in POM ranged from –30 to –22. Alanine is directly synthesized from pyruvate and is therefore a good metabolic indicator. The ¹³C of individual amino acids in DOM revealed the diel change in the importance of autotrophic versus heterotrophic activity in influencing DOM composition. Diel changes in the ¹³C of phenylalanine, synthesized by common pathways in phytoplankton and bacteria, were similar in both DOM and POM. The diel change in ¹³C of isoleucine and valine, synthesized through different pathways in phytoplankton and bacteria, were distinctly different in DOM versus POM. This disparity indicated a decoupling of the POM and DOM pools, which suggests a greater source of bacterial-derived organic matter at night. The results of this study demonstrate the use of the isotopic composition of individual amino acids in determining the importance of microbial reworking and autotrophic versus heterotrophic contributions to DOM over both diel and seasonal time scales.     

Isotope variability of particulate organic matter at the PN section in the East China Sea

The source of particulate organic matter at the PN section in the East China Sea has been evaluated using stable carbon and nitrogen isotopes. The results showed that the ¹³C and ¹⁵N compositions varied from –19 to –31 and 0.7–9.5 respectively, and the isotope compositions were statistically distinct, enabling, by use of a simple components mixing equations, assessment of the ability of each tracer to estimate the terrestrial, Kuroshio Water, marine and remineralized sources' contributions. The dominance of terrestrial inputs of the Changjiang could be observed 250 km far from the river mouth in the East China Sea. In the shelf water column, the remineralization of biogenic organic matter becomes an important source except for the terrigenous and marine sources. The estimation of sources recorded by ¹³C data was partly confirmed by equivalent ¹⁵N and C/N compositions that reflected greater control by organic matter diagenesis and biological processing. However, the lighter contribution of ¹³C data of the Kuroshio samples also indicates the alteration of the isotope values by microbial or other processes. The net export flux of POC in the PN section is estimated to be 4.1 kmol C/s and the annual export is 129 Gmol C/yr, which is account for 20% of the East China Sea.     

Termite ecology in a dry evergreen forest in Thailand in terms of stable (δ 13C and δ 15N) and radio (14C, 137Cs and 210Pb) isotopes

Stable (¹³C and ¹⁵N) and radio- (¹⁴C, ¹³⁷Cs and ²¹⁰Pb) isotopes were determined for termites that have been sampled from a dry evergreen forest in Thailand. A wood-feeding termite, Microcerotermes crassus, was separated from soil-feeders: Termes propinquus, Termes comis and Dicuspiditermes makhamensis by ¹³C and ¹⁵N values. The Termes group in Thailand had less diverse values in ¹³C and ¹⁵N than those in Australia, where the feeding habits of the Termes group are more diverse. Other soil-feeding termites produced similar ¹³C values, but a larger range in ¹⁵N values. ¹⁴C-percent modern carbon (pMC) values suggest that the soil-feeding termites used younger carbon than the wood-feeding termites, and this was consistent with the termites from Cameroon, central Africa. Values of ¹³C and ¹⁴C-pMC indicate that surface soil was used by a soil-feeding termite, D. makhamensis, in making the nest mounds, and deeper soil (10–30 cm) by a fungus-growing termite, Macrotermes carbonarius. ²¹⁰Pb and ¹³⁷Cs were scarcely incorporated into the termites, although ²¹⁴Pb was recovered from the workers. The results suggest that stable- and radioisotopes are useful in the study of detritivorous animals, organic matter decomposition and ecosystem engineering.Takuya Abe - deceased.     

Carbon isotopes and carbon turnover in cotton and wheat FACE experiments

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.