Carbon partitioning in ectomycorrhizal Scots pine seedlings

The complete carbon budget and the turnover rate of assimilated carbon of ectomycorrhizal Scots pine seedlings growing on natural humus were determined in microcosm conditions. The main aim was to improve understanding of the partitioning of the assimilated carbohydrates within seedlings associated with multiple ectomycorrhizal fungi, and to discover carbon dynamics of the mycorrhizosphere.Plant photosynthesis and below-ground respiration were measured in order to obtain the actual carbon assimilation and respiration rates at the time of measurements. Soon after the photosynthesis and respiration rate measurements the seedlings were pulse-labeled with ¹⁴CO₂ to follow carbon allocation to different plant, fungal and soil compartments and rhizosphere respiration. Long-term carbon allocation during the entire life span of the seedlings was estimated by measuring plant and mycorrhizal root-tip biomass. The ectomycorrhizal community was analyzed using morphotyping and ITS-sequencing.The ¹⁴C label was detected in rhizosphere respiration after 12 h and it peaked between 36 and 60 h after labeling. More than half of the assimilated carbon was allocated below-ground as biomass or respiration and higher mycorrhizal biomass increased the below-ground carbon turnover. The presence of Suillus variegatus affected the plant carbon balance in several ways. When S. variegatus was present, the below-ground respiration increased and this carbon loss was compensated by higher photosynthetic activity. Other fungal species did not differ between each other in their effects on carbon balance. Our findings indicate that some root-associated mycorrhizal fungal symbionts can significantly alter plant CO₂ exchange, biomass distribution, and the allocation of recently photosynthesized plant-derived carbon.     

Priming effects: Interactions between living and dead organic matter

In this re-evaluation of our 10-year old paper on priming effects, I have considered the latest studies and tried to identify the most important needs for future research. Recent publications have shown that the increase or decrease in soil organic matter mineralization (measured as changes of CO₂ efflux and N mineralization) actually results from interactions between living (microbial biomass) and dead organic matter. The priming effect (PE) is not an artifact of incubation studies, as sometimes supposed, but is a natural process sequence in the rhizosphere and detritusphere that is induced by pulses or continuous inputs of fresh organics. The intensity of turnover processes in such hotspots is at least one order of magnitude higher than in the bulk soil. Various prerequisites for high-quality, informative PE studies are outlined: calculating the budget of labeled and total C; investigating the dynamics of released CO₂ and its sources; linking C and N dynamics with microbial biomass changes and enzyme activities; evaluating apparent and real PEs; and assessing PE sources as related to soil organic matter stabilization mechanisms. Different approaches for identifying priming, based on the assessment of more than two C sources in CO₂ and microbial biomass, are proposed and methodological and statistical uncertainties in PE estimation and approaches to eliminating them are discussed. Future studies should evaluate directions and magnitude of PEs according to expected climate and land-use changes and the increased rhizodeposition under elevated CO₂ as well as clarifying the ecological significance of PEs in natural and agricultural ecosystems. The conclusion is that PEs - the interactions between living and dead organic matter - should be incorporated in models of C and N dynamics, and that microbial biomass should regarded not only as a C pool but also as an active driver of C and N turnover.     

雹灾后施氮配合中耕对棉花14C同化物生产及运转分配的影响

运用＾１５Ｎ和＾１４Ｃ示踪技术，研究了雹灾后施氮配合中耕对棉株吸氮动态，吸氮量，＾１４Ｃ同化物生产及运转分配的影响。研究结果表明，蕾期遭受雹灾后及对施氮并配合中耕，可使棉株开始吸收肥料氮的时间提前，棉株吸氮量、含氮量和肥料利用率也显著提高。棉株花铃期的相对光合作用强度（以放射性比强表示）和＾１４ＣＯ２同化量均显著高于单纯施氮处理和对照。而且，棉株的同化产物以较大的比例转运至生殖器官特别是成铃中，并     

冬小麦各生育期~(14)C-光合产物的分配与再分配

利用示踪同位素碳~(14)研究了冬生长阶段光合产物的分配以及冬后各阶段的连续分配情况.结果表明,光合产物生成后,分配并不停止.在冬后各阶段观察到存在着连续再分配.连续分配中心从地下根系、分蘖节、主茎叶,逐渐向上,直至穗部.然而,除了该中心外,其它器官或组织也能获得一定数量的光合产物.     

Earthworm ecological groupings based on C analysis

We report the first use of ¹⁴C isotope analysis to investigate the ecological grouping of earthworms. Mature endogeic (Allolobophora caliginosa), mature epigeic (Lumbricus rubellus), and semimature anecic worms (A. longa) were collected in September 2002 from a woodland site at Lancaster, UK. Because anecic worms are known to have a variable feeding behaviour and can show dietary changes during ontogeny, additional immature and mature specimens of A. longa were also collected from the same site in January 2004. Epigeic earthworms showed the lowest radiocarbon concentration (0-3-years old), implying that they assimilated more recently fixed carbon than the anecic or endogeic earthworms. The age of carbon assimilated in mature anecic species (5-7-years old) was closer to that of endogeic species (5-8-years old) than to epigeics, suggesting that a greater proportion of older, more mineralised organic matter may form part of the diet of the anecic earthworms than previously thought. These results suggest that ¹⁴C approaches are useful in the study of the feeding behaviour of detritivorous animals by providing in situ information on the age of the carbon assimilated by the worms. This can then be related to their role in ecosystem functioning, particularly in carbon cycling.     

Carbon cycling in subarctic tundra; seasonal variation in ecosystem partitioning based on in situ C pulse-labelling

Carbon assimilation and allocation were studied in a tundra ecosystem in northern Scandinavia. Seasonal variation in the below-ground carbon allocation to dissolved organic carbon (DOC), coarse-, fine-, and hair roots was investigated using in situ ¹⁴C pulse-labelling, adding 2-3 MBq ¹⁴CO₂ dm⁻² to the above-ground vegetation. Combining the allocation data with regression models of the seasonal carbon flux made it possible to estimate a temporally explicit ecosystem carbon allocation budget.The ecosystem was a net source of CO₂, losing on average 0.97 g C m⁻² d⁻¹ to the atmosphere, with little variation through the season. There was, however, significant temporal variation in partitioning of recently assimilated carbon. Allocation to below-ground compartments over 32 days following labelling increased from 18% in June to 55% in September. Above-ground allocation showed the opposite trend. Hair roots and DOC were strong sinks in the autumn. Transport of newly assimilated carbon occurred rapidly throughout the season, ¹⁴C appearing in all sampled pools within 4 h of labelling.The seasonal variation in carbon partitioning observed in this study has implications for the residence time of assimilated carbon in the ecosystem. A relatively greater allocation to rapidly decomposing pools, such as hair roots and DOC, would tend to reduce incorporation into woody tissue, increasing the overall rate of carbon cycling and decreasing ecosystem storage. The results of this study will be of value for building and validating mechanistic models of ecosystem carbon flow in tundra and subarctic ecosystems.     

Carbon fluxes in soil food webs of increasing complexity revealed by C labelling and C natural abundance

Soil food webs are mainly based on three primary carbon (C) sources: root exudates, litter, and recalcitrant soil organic matter (SOM). These C sources vary in their availability and accessibility to soil organisms, which could lead to different pathways in soil food webs. The presence of three C isotopes (¹²C, ¹³C and ¹⁴C) offers an unique opportunity to investigate all three C sources simultaneously. In a microcosm experiment we studied the effect of food web complexity on the utilization of the three carbon sources. We choose an incomplete three factorial design with (i) living plants, (ii) litter and (iii) food web complexity. The most complex food web consisted of autochthonous microorganisms, nematodes, collembola, predatory mites, endogeic and anecic earthworms. We traced C from all three sources in soil, in CO₂ efflux and in individual organism groups by using maize grown on soil developed under C₃ vegetation and application of ¹⁴C labelled ryegrass shoots as a litter layer. The presence of living plants had a much greater effect on C pathways than food web complexity. Litter decomposition, measured as ¹⁴CO₂ efflux, was decreased in the presence of living plants from 71% to 33%. However, living plants increased the incorporation of litter C into microbial biomass and arrested carbon in the litter layer and in the upper soil layer. The only significant effect of food web complexity was on the litter C distribution in the soil layers. In treatments with fungivorous microarthropods (Collembola) the incorporation of litter carbon into mineral soil was reduced. Root exudates as C source were passed through rhizosphere microorganisms to the predator level (at least to the third trophic level). We conclude that living plants strongly affected C flows, directly by being a source of additional C, and indirectly by modifying the existing C flows within the food web including CO₂ efflux from the soil and litter decomposition.     

~(14)C-丁草胺、~(14)C-毒死蜱和~(14)C-DDT在日本林蛙中的生物学行为(英文)

用同位素示踪技术研究了14 C 丁草胺、14 C 毒死蜱和14 C DDT在日本林蛙 (RanajaponicajaponicaGuenther)中的生物学行为。结果发现 ,14 C 丁草胺、14 C 毒死蜱和14 C DDT在 2 4h后分布到青蛙的各个器官组织 ,并分别以胆囊、小肠、小肠为它们的特异性浓集器官。与胆囊或小肠的14 C放射性活度比较 ,其它器官组织中的要小得多。14C DDT在日本林蛙中较难降解 ,2 4h后DDT母体在肝和脂肪组织中占DDT代谢物的54 6%和 88 4%。青蛙中的14 C 丁草胺、14 C 毒死蜱和14 C DDT可被丙酮提取 ,但三者之间以及在青蛙的器官之间有差异     

Organic C and N stabilization in a forest soil: Evidence from sequential density fractionation

In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size particles. When fractionated according to particle density, C and N concentration (per g fraction) and C/N of these soil organo-mineral particles decrease with increasing particle density across soils of widely divergent texture, mineralogy, location, and management. The variation in particle density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these particles, and (2) variations in density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases with increasing particle density. The decrease in C/N can be explained at least partially by especially stable sorption of nitrogenous N-containing compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which other organics could sorb more readily than onto the unconditioned mineral surfaces (“onion” layering model).To explore mechanisms underlying this trend in C concentration and C/N with particle density, we sequentially density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm⁻³ and analyzed the six fractions for measures of organic matter and mineral phase properties.All measures of OM composition showed either: (1) a monotonic change with density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing density, and ¹⁴C mean residence time (MRT) increased with particle density from ca. 150 years to >980 years in the four organo-mineral fractions. In contrast, C/N, ¹³C and ¹⁵N concentration all showed the second pattern. All these data are consistent with a general pattern of an increase in extent of microbial processing with increasing organo-mineral particle density, and also with an “onion” layering model.X-ray diffraction before and after separation of magnetic materials showed that the sequential density fractionation (SDF) isolated pools of differing mineralogy, with layer-silicate clays dominating in two of the intermediate fractions and primary minerals in the heaviest two fractions. There was no indication that these differences in mineralogy controlled the differences in density of the organo-mineral particles in this soil. Thus, our data are consistent with the hypothesis that variation in particle density reflects variation in thickness of the organic accumulations and with an “onion” layering model for organic matter accumulation on mineral surfaces. However, the mineralogy differences among fractions made it difficult to test either the layer-thickness or “onion” layering models with this soil. Although SDF isolated pools of distinct mineralogy and organic-matter composition, more work will be needed to understand mechanisms relating the two factors.     

水稻新品种“南京14”对病虫的多抗性研究

 经3年鉴定，中籼稻新品种南京14抗白叶枯病，抗稻瘟病中D#-3、中E#-3、中F#-1和中G#-1小种，抗褐稻虱，中抗白背稻虱，而且抗性稳定。在江淮稻区种植获得高产，且农药使用减少，有利无公害稻谷生产。