Genotypic variations in carbon isotope discrimination, transpiration efficiency, and biomass production in rice as affected by soil water conditions and N

Genotypic and environmental (soil water regime and N level) variation in carbon isotope discrimination (CID) in relation to the gas exchange, transpiration efficiency (A/T), and biomass production were investigated in field experiments using eleven rice (Oryza sativa L.) genotypes. The results showed that genotype was more dominant for variation in CID than in total biomass. Genotypic ranking in CID was consistent across environments because of small genotype × environment interactions. Japonica genotypes tended to have lower CID than indica genotypes. Higher soil water and lower N rate significantly increased CID. Variation in CID was slightly smaller for water regime than for genotype. There was a negative correlation between CID andA/T among genotypes within water regimes. Genotypic variation in CID was associated mainly with variation in stomatal conductance under all soil water regimes and with photosynthetic capacity in late growth stages under aerobic soil conditions. The decrease in CID at higher N was probably due to lower stomatal conductance under aerobic soil conditions and to higher photosynthetic rates under submerged soil conditions. The correlation between biomass and CID was not clear in aerobic soil, whereas it was positive in submerged soil, which indicated that the significance of lower or higher CID for improving biomass productivity may differ under different soil water regimes. Overall, the results implied a possible use of CID as a selection criterion for genotypic improvement inA/T and productivity in rice.     

Testing the branch autonomy theory: a 13C/14C double-labelling experiment on differentially shaded branches

The impact of a heterogeneous within‐crown light environment on carbon allocation was investigated on young walnut trees trained on two branches: one left in full sunlight, the other shaded until leaf fall resulting in 67% reduction in photosynthetically active radiation. In September, the two branches were separately labelled with ¹⁴CO₂ and ¹³CO₂, respectively, so that the photosynthates from each branch could be traced independently at the same time. Although some carbon movements could be detected within 5 d in both directions (including from the shaded branch to the sun branch), between‐branch carbon movements were very limited: approximately 1% of the diurnal net assimilation of a branch. At this time of the year branch autonomy was nearly total, leading to increased relative respiratory losses and a moderate growth deficit in the shaded branch. The ratio of growth to reserve storage rate was only slightly affected, indicating that reserves acted not as a mere buffer for excess C but as an active sink for assimilates. In winter, branch autonomy was more questionable, as significant amounts of carbon were imported into both branches, possibly representing up to 10% of total branch reserves. Further within‐plant carbon transfers occurred in spring, which totally abolished plant autonomy, as new shoots sprouted on each branch received significantly more C mobilized from tree‐wide reserves than from local, mother‐branch located reserves. This allowed great flexibility of tree response to environment changes at the yearly time scale. As phloem is considered not functional in winter, it is suggested that xylem is involved as the pathway for carbohydrate movements at this time of the year. This is in agreement with other results regarding sugar exchanges between the xylem vessels and the neighbouring reserve parenchyma tissues.     

Integrated responses of hydraulic architecture, water and carbon relations of western hemlock to dwarf mistletoe infection

Dwarf mistletoe (Arceuthobium spp.) is a hemiparasite that is said to be the single‐most destructive pathogen of commercially valuable coniferous trees in many regions of the world. Although its destructive nature is well documented in many respects, its effects on the physiology of its host are poorly understood. In the present study, water and carbon relations were characterized over a range of scale from leaf to whole tree in large (40‐ to 50‐m‐tall) individuals of western hemlock (Tsuga heterophylla (Raf.) Sarg.) that were either heavily infected, or uninfected with hemlock dwarf mistletoe (Arceuthobium tsugense). Specific hydraulic conductivity (k_s) of infected branches was approximately half that of uninfected branches, yet leaf‐specific conductivity (k_L) was similar because leaf area : sapwood area ratios (A_L : A_S) of infected branches were lower. Pre‐dawn and minimum leaf water potential and stomatal conductance (g_s) were similar among infected and uninfected trees because adjustments in hydraulic architecture of infected trees maintained k_L despite reduced k_s. Maximum whole‐tree water use was substantially lower in infected trees (approximately 55 kg d^?1) than in uninfected trees (approximately 90 kg d^?1) because reduced numbers of live branches in infected trees reduced whole‐tree A_L : A_S in a manner consistent with that observed in infected branches. Maximum photosynthetic rates of heavily infected trees were approximately half those of uninfected trees. Correspondingly, leaf nitrogen content was 35% lower in infected trees. Foliar δ¹³C values were 2.8‰ more negative in infected than in uninfected individuals, consistent with the absence of stomatal adjustment to diminished photosynthetic capacity. Adjustments in hydraulic architecture of infected trees thus contributed to homeostasis of water transport efficiency and transpiration on a leaf area basis, whereas both carbon accumulation and photosynthetic water use efficiency were sharply reduced at both the leaf and whole‐tree scale.     

Dual polarity accurate mass calibration for electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry using maltooligosaccharides

In view of the fact that memory effects associated with instrument calibration hinder the use of many mass-to-charge (m/z) ratios and tuning standards, identification of robust, comprehensive, inexpensive, and memory-free calibration standards is of particular interest to the mass spectrometry community. Glucose and its isomers are known to have a residue mass of 162.05282 Da; therefore, both linear and branched forms of polyhexose oligosaccharides possess well-defined masses, making them ideal candidates for mass calibration. Using a wide range of maltooligosaccharides (MOSs) derived from commercially available beers, ions with m/z ratios from approximately 500 to 2500 Da or more have been observed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and time-of-flight mass spectrometry (TOF-MS). The MOS mixtures were further characterized using infrared multiphoton dissociation (IRMPD) and nano-liquid chromatography/mass spectrometry (nano-LC/MS). In addition to providing well-defined series of positive and negative calibrant ions using either electrospray ionization (ESI) or matrix-assisted laser desorption/ionization (MALDI), the MOSs are not encumbered by memory effects and, thus, are well-suited mass calibration and instrument tuning standards for carbohydrate analysis.     

The effects of shredding invertebrates on the transfer of organic carbon from littoral leaf litter to water-column bacteria

Leaf litter can be of great importance for the productivity of small oligotrophic lakes surrounded by deciduous forests. Feeding invertebrate shredders produce particulate organic leftovers, but their feeding also enhances the release of dissolved organic carbon (DOC). We tested whether invertebrate-mediated DOC release affects the production of heterotrophic water-column bacteria. Submersed leaves were incubated in microcosms with and without shredders; and DOC, absorbance, bacterial abundance and bacterial production in the water column were monitored. We also measured dry weight of the organic particles (FPOC, fine particulate organic carbon, leaf residues and shredders). Total leaf-litter carbon decreased by nearly 80% in the presence of shredders, and on average 56% of the initial leaf carbon ended up as FPOC after 126 days of incubation. Without shredders FPOC production was almost zero, and 72% of the added leaf carbon could be retrieved as leaves when the experiment ended. Both these figures include the rapid release of DOC during the first week of leaf incubation in the lake water (equivalent to 16–19% of total added leaf carbon). Although bacterial production in the water was several times higher in treatments with shredders, bacterial consumption of leaf-derived DOC from shredding was obviously of minor importance in the total carbon budget. This result suggests, although shredders have a strong impact on transformation of leaves to FPOC, they do not greatly enhance the initial rate of mineralization of the leaf-derived detritus.     

Dissolved Organic Carbon in Terrestrial Ecosystems: Synthesis and a Model

The movement of dissolved organic carbon (DOC) through soils is an important process for the transport of carbon within ecosystems and the formation of soil organic matter. In some cases, DOC fluxes may also contribute to the carbon balance of terrestrial ecosystems; in most ecosystems, they are an important source of energy, carbon, and nutrient transfers from terrestrial to aquatic ecosystems. Despite their importance for terrestrial and aquatic biogeochemistry, these fluxes are rarely represented in conceptual or numerical models of terrestrial biogeochemistry. In part, this is due to the lack of a comprehensive understanding of the suite of processes that control DOC dynamics in soils. In this article, we synthesize information on the geochemical and biological factors that control DOC fluxes through soils. We focus on conceptual issues and quantitative evaluations of key process rates to present a general numerical model of DOC dynamics. We then test the sensitivity of the model to variation in the controlling parameters to highlight both the significance of DOC fluxes to terrestrial carbon processes and the key uncertainties that require additional experiments and data. Simulation model results indicate the importance of representing both root carbon inputs and soluble carbon fluxes to predict the quantity and distribution of soil carbon in soil layers. For a test case in a temperate forest, DOC contributed 25% of the total soil profile carbon, whereas roots provided the remainder. The analysis also shows that physical factors—most notably, sorption dynamics and hydrology—play the dominant role in regulating DOC losses from terrestrial ecosystems but that interactions between hydrology and microbial–DOC relationships are important in regulating the fluxes of DOC in the litter and surface soil horizons. The model also indicates that DOC fluxes to deeper soil layers can support a large fraction (up to 30%) of microbial activity below 40 cm. Received 14 January 2000; accepted 6 September 2000     

不同离子辐照对离体质粒DNA损伤与转化活性的影响

利用 30Kev的N+ 、Ar+ 离子辐照离体质粒DNA ,分析了不同离子对DNA单双链断裂及转化活性的影响。结果表明 :N+ 、Ar+ 离子辐照均可引起质粒DNA单双链断裂和转化活性的变化 ,且随着辐照剂量的增加 ,单双链断裂频率增加 ,转化活性下降。Ar+对离体质粒DNA比N+ 具有更强的单双链断裂效应 ,且从 9× 10 15Ar+ cm2 剂量开始 ,质粒可完全丧失转化活性。质粒转化活性的大小与DNA单双链断裂频率呈正相关     

麦白霉素发酵培养基的改进

研究了淀粉水解液全部替代葡萄糖作为碳源发酵麦白霉素的工艺条件。用正交实验得出摇瓶培养基消毒后的最佳基质浓度为总糖5.0g/100mL,还原糖3.8g/100mL,氨基氮60mg/mL,溶解磷300μg/mL。以50L发酵罐进行实验,得出了麦白霉素的发酵代谢曲线和淀粉的适宜水解条件。经30t发酵罐放大实验结果表明,与葡萄糖作碳源相比,用淀粉水解液作碳源发酵麦白霉素,发酵单位提高23.0％,生产成本降低38.0％。     

Importance of discards of a beam trawl fishery as input of organic matter into nursery areas within the Tagus estuary

The brown-shrimp beam trawl fishery carried out within the Tagus estuary produces discards due to the little commercial interest of most of the species caught. Between 1994 and 1996, monthly samples were collected in the two major fishing areas within the Tagus estuary, using a beam trawl, in order to estimate the amount of fish and crustaceans caught per unit of effort. The fishing effort of the commercial fleet was determined based on surveys of professional fishermen. Mortality estimates of discards were also evaluated experimentally. The main fish and crustacean species discarded after capture were Crangon crangon (Linnaeus, 1758), Liza ramada (Risso, 1826), Carcinus maenas (Linnaues, 1758) and Pomatoschistus minutus (Pallas, 1770). The estimated total amount of fishery discards in the upper part of the Tagus estuary is approximately 1500 tonnes per year, which represents ca. 90% of the captures. The mortality rate of the fishes and crustaceans discarded varied according to species and season, with the highest rates during Summer months. Considering nitrogen and carbon content of the main discarded species, an input of particulate organic matter of more than 140 tonnes of carbon and 35 tonnes of nitrogen per year were estimated for these estuarine areas.     

Evaluation of a eutrophic coastal lagoon ecosystem from the study of bottom sediments

Morphological reconstruction and biogeochemical characterisation of the lagoon of Comacchio (Italy) were carried out in order to provide recommendations for the recovery, conservation and sustainable management of the Fattibello-Spavola coastal lagoon ecosystem. Samples were taken in two seasons: July 1997 and November 1998. The irregular morphology of the Fattibello lagoon affects depositional processes and seawater exchange (tidal currents). Several depressions retain part of the dense water of the saline wedge; these stagnant waters became sinks for fine terrigenous and organic matter. The basin is already extensively supplied with N and P compounds from land. The inflow is demonstrated by the large quantity of organic C, N and organic and inorganic P compounds in the superficial sediment. The ratios between the various forms of macronutrients indicate that the organic matter is primarily of autochthonous origin, with relatively low C/N ratios (8.4±0.6 and 8.1±0.6 in July and November, respectively). Shallow areas were almost always oxygenated by tidal currents and thus rich in organisms, with a predominance of molluscs and Ficopomatus enigmaticus. However, the trophic equilibrium of the ecosystem was affected by the accumulation of organic matter in the depressions, favoured by the increased hydrodynamics during the autumn. These accumulations generate high oxygen consumption and release considerable quantities of nutrients into the water column, with the risk of serious dystrophy throughout the basin during the summer. Local dredging and an improvement of the circulation have been suggested and carried out to contain these processes. Reclamation measures in the longer term were proposed.