国立情報学研究所で電子化したコンテンツを使用している。

Le priming effect (PE) est la sur-minéralisation de la matière organique du sol (MOS) après un apport de matière organique fraiche. Ce phénomène serait généré par deux mécanismes distincts, la décomposition stœchiométrique et le « nutrient mining », ayant leur propre dynamique, leurs propres acteurs, leurs propres déterminants et leur propre stock de MO ciblés. Le premier serait plutôt lié à la séquestration de MO dans les sols et l’autre à sa déstabilisation. Comprendre comment piloter l’équilibre entre ces processus à travers les pratiques agricoles, permettrait d’améliorer durablement la fertilité des sols cultivés en milieu tropical dans un contexte de changement climatique. Pour identifier les déterminants, les acteurs et les effets du climat et des pratiques agricoles sur les différents processus générateurs de PE, nous avons combiné la caractérisation physicochimique des sols, la caractérisation des communautés microbiennes et le suivi de la minéralisation des MO par les techniques isotopiques. Ainsi, nous avons pu identifier différentes populations bactériennes et fongiques, associées à chacun des processus, que nous avons classées dans des guildes fonctionnelles. La taille de ces guildes déterminait l’équilibre entre les processus, et était corrélée à la qualité de la MO présente dans le sol. Plus précisément, nous avons montré que le PE stœchiométrique était favorisé dans les sols enrichis en matière organique peu évoluée et en nutriments N et P, entretenant donc une forte communauté de décomposeurs. Ces décomposeurs devaient ainsi limiter l’accès des mineurs à la nouvelle matière organique fraichement apportée et limiter le PE par « nutrient mining ». Sur parcelles agricoles, nos résultats suggéraient que le non labour, l’association légumineuses-céréales, et l’apport de compost favorisaient ces décomposeurs responsables du priming effect stœchiométrique et donc potentiellement la stabilisation durable de la matière organique dans les sols. / The priming effect (PE) is the supplementary mineralization of soil organic matter (MOS) after the addition of fresh organic matter. This phenomenon would be generated by two distinct mechanisms, stoichiometric decomposition and "nutrient mining", having their own dynamics, their own actors, their own determinants and their own MO stock targeted. The first would be related to the sequestration of MO in the soil and the other to its destabilization. Understanding how to manage the balance between these processes through agricultural practices, would allow to improve the fertility of soil cultivated in a tropical environment in a context of climate change.To identify the determinants, actors and effects of climate and agricultural practices on the various processes generating PE, we have combined soil physicochemical characterization, characterization of microbial communities and monitoring of mineralization of MO by isotopic techniques. Thus, we were able to identify different bacterial and fungal populations, associated with processes, which we classified in the functional guilds. The size of these guilds determined the balance between the processes, and was correlated with the quality of the MO present in the soil. Specifically, we showed that stoichiometric PE was favored in soils enriched with high quality organic matter and nutrients, N and P, thus maintaining a strong community of decomposers. These decomposers also limit the access of miners to the provided new organic matter hence limiting PE by "nutrient extraction". On agricultural plots, our results suggest that non-tillage, legume-cereal rotations and compost amendments favor these decomposers responsible for the stoichiometric priming effect and thus potentially the long-term stabilization of organic matter in soils.

It is increasingly being recognized that the soil microbes can mineralize recalcitrant soil organic matter (SOM) by using the fresh carbon (C) as a source of energy, a process called priming effect (PE). It has been shown mostly in lab incubations that PE can have important consequences for sequestration of organic C in soils. However, the importance of PE in C and N dynamics of ecosystems remains little known. The soil-plant interactions and rhizospheric processes can modulate the rates of PE and its consequences on C and N dynamics in an ecosystem. The objective of this thesis was to determine the role of PE in the C and N dynamics of permanent grasslands and the modulation of this role in response to management (plant clipping, fertilization) and global warming. Moreover, it was aimed to identify the microbial groups involved in PE and to unravel the way, e.g. absorption of N, root exudations and litter deposition, by which plant can induce PE. The thesis was based on a new approach allowing continuous dual labelling of multiple grassland plants with 13C- and 14C-CO2. The dual labelling permitted the separation of soil-derived CO2 from plant-derived CO2, the calculation of PE and the determination of mean age of soil-derived CO2-C. Moreover, phospholipids fatty-acids analysis (PLFA) permitted to correlate the variation of PE with changes in microbial community composition. Our work showed that the increased SOM mineralization under grasses was consistently two to three times more than that in bare soils (i.e. PE) over long term (511 days). This reveals that the PE plays key role in ecosystem CO2-C flux and indicates that a very large pool of SOM is under the control of PE. Moreover, we report that 15,000 years old organic C from an undisturbed deep soil can be mineralized after the supply of fresh C by living plants to soil microbes. This result supports the idea that the SOM in deep soils is stable due to the energy-limitation of microbes and the ‘inert' pool of organic C defined in current models is not so ‘inert' finally. The supply of N in soil-plant system through the use of fertilizer or legume decreased the PE suggesting that the C storage in soils is limited by nutrient supply. Similarly, plant clipping reduced the plant N uptake thereby PE. Collectively these results suggest synchronization between plant N uptake and SOM mineralization supporting the idea that soils under permanent plant cover function as a bank of nutrients for the plant, maximizing plant productivity and nutrient retention. An innovative method clearly showed that the root exudation is the major way by which grassland plants induce PE. Moreover, saprophytic fungi are suggested as the key actors in the mineralization of recalcitrant SOM & PE. Lastly, we developed a new theory on temperature response of SOM mineralization by taking into account the energy-limitation of microbes and the temperature-dependent inactivation of enzymes. This theory predicts a negative relationship between temperature and mineralization of recalcitrant SOM, which was supported by experimental results. This finding challenges the classical paradigm of positive relationship between temperature and recalcitrant SOM mineralization. Overall, these investigations on plant-soil systems reinforce the idea that PE and underlying mechanisms play a key role in ecosystem C and N dynamics and even suggest that this role was underestimated in lab experiments. / It is increasingly being recognized that the soil microbes can mineralize recalcitrant soil organic matter (SOM) by using the fresh carbon (C) as a source of energy, a process called priming effect (PE). It has been shown mostly in lab incubations that PE can have important consequences for sequestration of organic C in soils. However, the importance of PE in C and N dynamics of ecosystems remains little known. The soil-plant interactions and rhizospheric processes can modulate the rates of PE and its consequences on C and N dynamics in an ecosystem. The objective of this thesis was to determine the role of PE in the C and N dynamics of permanent grasslands and the modulation of this role in response to management (plant clipping, fertilization) and global warming. Moreover, it was aimed to identify the microbial groups involved in PE and to unravel the way, e.g. absorption of N, root exudations and litter deposition, by which plant can induce PE. The thesis was based on a new approach allowing continuous dual labelling of multiple grassland plants with 13C- and 14C-CO2. The dual labelling permitted the separation of soil-derived CO2 from plant-derived CO2, the calculation of PE and the determination of mean age of soil-derived CO2-C. Moreover, phospholipids fatty-acids analysis (PLFA) permitted to correlate the variation of PE with changes in microbial community composition. Our work showed that the increased SOM mineralization under grasses was consistently two to three times more than that in bare soils (i.e. PE) over long term (511 days). This reveals that the PE plays key role in ecosystem CO2-C flux and indicates that a very large pool of SOM is under the control of PE. Moreover, we report that 15,000 years old organic C from an undisturbed deep soil can be mineralized after the supply of fresh C by living plants to soil microbes. This result supports the idea that the SOM in deep soils is stable due to the energy-limitation of microbes and the ‘inert' pool of organic C defined in current models is not so ‘inert' finally. The supply of N in soil-plant system through the use of fertilizer or legume decreased the PE suggesting that the C storage in soils is limited by nutrient supply. Similarly, plant clipping reduced the plant N uptake thereby PE. Collectively these results suggest synchronization between plant N uptake and SOM mineralization supporting the idea that soils under permanent plant cover function as a bank of nutrients for the plant, maximizing plant productivity and nutrient retention. An innovative method clearly showed that the root exudation is the major way by which grassland plants induce PE. Moreover, saprophytic fungi are suggested as the key actors in the mineralization of recalcitrant SOM & PE. Lastly, we developed a new theory on temperature response of SOM mineralization by taking into account the energy-limitation of microbes and the temperature-dependent inactivation of enzymes. This theory predicts a negative relationship between temperature and mineralization of recalcitrant SOM, which was supported by experimental results. This finding challenges the classical paradigm of positive relationship between temperature and recalcitrant SOM mineralization. Overall, these investigations on plant-soil systems reinforce the idea that PE and underlying mechanisms play a key role in ecosystem C and N dynamics and even suggest that this role was underestimated in lab experiments.

Le sol est un compartiment majeur de stockage du carbone (C) organique de l’écosystème terrestre. Il joue un rôle important dans la régulation du climat. Toute variation des flux de carbone entre l’atmosphère et l’écosystème terrestre pourrait avoir un impact important sur l’augmentation de CO2 dans l’atmosphère, mais aussi sur la diminution des teneurs en matière organique du sol et donc sur la fertilité des sols. Au Nord Cameroun, les sols sont exposés à de longues périodes sèches (5 à 6 mois par an) qui alternent avec une saison humide. La période de transition entre ces deux saisons, peut durer de mi-avril à fin juin et est caractérisée par des pluies très irrégulières. Ces cycles d’humectation-dessiccation pourraient selon la littérature accentuer la minéralisation du carbone organique du sol et le cycle des éléments nutritifs. L’objectif de cette étude est de quantifier l’impact des cycles humectation-dessiccation sur la minéralisation du carbone dans un contexte soudano-sahélien. Pour faire des mesures représentatives sur le terrain, il est nécessaire d’étudier la variation sur 24 heures de la respiration du sol après humectation suite à une période sèche. Cette mise au point méthodologique a montré que la respiration du sol présente une courbe quadratique au cours de la journée, devenant presque linéaire au cours de la nuit. La température et l’humidité du sol ont permis d’expliquer au moins 73% des variations sur 24 heures. Ces observations ont été utilisées pour proposer une méthode pour estimer la respiration moyenne diurne et nocturne après humectation des sols. La méthode proposée dans cette étude a l’avantage d’être basée sur un nombre réduit de mesures et est par conséquent plus facile à mettre en œuvre pour suivre la respiration du sol sur 24 heures après les premières pluies. Une première étude expérimentale de terrain a permis de montrer que la ré-humectation des sols et le mode de gestion des pailles ont augmenté la minéralisation du carbone de ces sols. En revanche, la fréquence des cycles humectation-dessiccation des sols sur une période de 50 jours n’a pas augmenté la minéralisation cumulée du carbone des sols. Au Nord Cameroun, la minéralisation rapide des pailles rend difficile l’augmentation des stocks de carbone du sol par conservation des pailles des cultures précédentes à la surface du sol. Dans une seconde expérimentation de laboratoire, en conditions contrôlées, les cycles humectation-dessiccation n’ont pas augmenté la minéralisation du carbone organique du sol et de l’azote (N) par rapport aux sols maintenus humides. Cependant, les émissions de CO2 ont augmenté avec l’addition de paille enrichie en carbone-13. Cette addition de la paille marquée a augmenté la minéralisation de la matière organique du sol (priming effect). La minéralisation de la paille a diminué avec les cycles humectation-dessiccation et la quantité de paille restante était de 102 µg Cg-1 sol sur les sols ré-humectés contre 48 µg Cg-1 sol sur les sols maintenus humides. L’absence de cette réponse de la minéralisation du carbone et d’azote du sol aux cycles humectation-dessiccation pourrait être liée à une baisse de l’activité microbienne durant les périodes de dessèchement et l’absence d’une augmentation soutenue des taux de minéralisation du carbone avec les cycles ultérieurs d’humectation-dessiccation. / Soil as a major storage component for terrestrial ecosystem’s organic carbon plays an important role in regulating climate and agricultural production. Any variation of carbon fluxes between the atmosphere and the terrestrial ecosystem can have a significant impact on the increase of carbon dioxide in the atmosphere but also the decrease in soil organic matter and thus accelarate soil fertility degradation. In northern Cameroon, the transition period between long dry periods with a wet season is characterized by very irregular rainfall that can last several weeks. These wetting-drying cycles can accentuate the mineralization of soil organic carbon and nutrient cycling. The objective of this study is to assess the impact of wet-dry cycles on carbon mineralization in a sudano-sahelian context. From methodological stand field measurements require to study the soil respiration variation over 24 hours after a wet period. This methodological test has shown that soil respiration has a quadratic curve during the day, becoming almost linear during the night. The temperature and soil moisture have explained together the variation over 24 hours (at least 73% ; p< 0.001). These observations have been used to propose a method for estimating the mean daytime and nighttime soil respiration after wetting the soil. Indeed the method proposed in this study has the advantage of being based on a small number of measurements and is, therefore, easier to implement to monitor 24-h soil respiration after the first rains following a long dry period. A first experiment has shown that the wetting of the soil and mulching increased soil carbon mineralization. However, wetting-drying cycles on soil did not increase the cumulative mineralization of soil carbon more than keeping the soil continuously moist. Indeed, in northern Cameroon, the rapid mineralization of crop residues makes it difficult to increase soil carbon stocks by mulching. In a second laboratory experiment, the wetting-drying cycles did not increase organic carbon and nitrogen mineralization from soils added with straw. However, carbon dioxide emissions increased on straw amended soils compared to soils without straw. This addition of the labeled straw increased mineralization of soil organic matter (priming effect). The mineralization of the straw also decreased with the wetting-drying cycles, thus the amount of straw remaining on soils was 102 µg C g-1 soil on re-wetted soils compared to 48 µg C g-1 soil for those with constant moisture. The lack of response for C and N mineralization during wetting-drying cycles may be linked to a decrease of microbial activity during dry periods and the lack of a steady increase in the carbon mineralization rate with subsequent wetting-drying cycles.

文字的意義是怎樣的儲存於我們的記憶？又是透過怎樣的方式來了解文字中的意義呢？本研究藉由語義促發效果的探討，一方面檢視語義與連結促發作用對字彙辨識的影響，另一方面提供中文的辨識歷程及記憶表徵方面的訊息。 本研究在三個相關的實驗中，藉著操弄了各種獨變項來回答上述的問題，第一個獨變項是促發項與目標項的關係；例如，促發項與目標項配對不但會形成（1）雙字詞，且彼此具有相似的意義（如，酣—睡），（2）雙字詞，但彼此具有不同的意義（如，餅—乾），（3）促發項與目標項之間具有相似的意義成分，但不會形成雙字詞（如，扔—丟），以及（4）促發項與目標項之間沒有意義上的關聯。本研究操弄的第二個獨變項是相關配對佔所有刺激的百分比（50％與25％），第三個獨變項則是促發項與目標項之間的聯想強度（高聯想與低聯想）。 綜觀本三個實驗的結果發現（1）當促發項與目標項具有意義上的關聯時，有加速文字辨識的歷程，（2）在高相關配對百分比的情境中，不論高、低聯想強度，意義關聯的刺激配對有顯著的促發效果，（3）在低相關配對百分比的情境中，刺激配對形成雙字詞，但彼此具有不同的意義，則高、低聯想強度都有顯著的促發效果；至於刺激配對形成雙字詞，且彼此具有相似的意義以及刺激配對具有相似的意義成分，但不會形成雙字詞時，則只有高聯想強度有顯著的促發效果，但低聯想強度沒有顯著的促發效果。 這樣的結果顯示在字彙判斷作業中，當促發項與目標項只有意義相似性的成分時，並無法加速受試者對文字的辨識。至於當促發項與目標項形成雙字詞，但彼此具有不同的意義時，並不同於其他的刺激配對，其促發效果可能是藉由組合線索，觸及字彙層次的連結訊息，因而加快文字的辨識速度。

The priming effect (PE), characterized as the enhanced microbial processing of bio-recalcitrant organic matter with the addition of labile substrates, has been hypothesized to moderate carbon (C) cycling in aquatic systems. In this study, aquatic PEs were evaluated through bacterial respiration and dissolved organic C consumption in incubations of water collected from three locations along the York River estuary. Incubations from White’s Landing on the Pamunkey River, a tidal freshwater tributary of the York, and from Croaker Landing in the middle of the estuary, displayed positive PEs when amended with labile C. In contrast, amended incubations from Gloucester Point, near the mouth of the estuary, displayed negative PEs, or reduced relative C metabolism, based on our calculations, This study provides empirical evidence for the occurrence of aquatic PEs and serves to elucidate how they may enhance or retard the processing and mineralization of organic C during transport to the ocean.

Compounding, constructing new words out of previously known words by means of simple concatenation mostly, can be counted as one of the major word production mechanisms in the majority of languages. Their importance in the history of human languages warrants a detailed study with respect to the language faculty and related cognitive aspects. In the last decade, compound production as well as comprehension have become highly debated and investigated areas of research. Morphological priming is one frequently employed paradigm for the investigation of compounding. Whether morphologically complex words undergo a decomposition-composition process, respectively, during comprehension and production or whether they are all listed in full form in the lexicon is one key question hitherto addressed in several studies related to English, German, Dutch and Chinese nominal compound words. The present study is concerned with compound production in Turkish. Various types of Turkish compounds were investigated ((i) bare JCs (

During the production of language, speakers tend to use the same structural patterns from one utterance to the next if it is possible to do so. For example, if a speaker uses a passive or dative construction, he/she is relatively more likely to use the same construction again in the next utterance (e.g., Bock, 1986; Bock & Loebell, 1990; Hartsuiker & Kolk, 1998): the sentence structure "persists".The current study investigates syntactic persistence in first and second language speakers of English and Korean using within-language primes (Experiments 1A, 1B, and 2) and across-language primes (Experiment 3). The target structures were transitive alternate structures (active and passive) and dative alternate structures (double object dative/DAT-ACC dative and prepositional dative/ACC-DAT dative). The experimental paradigm involved repetition of an auditory stimulus, followed by picture description. Overall, syntactic priming effects were found, although various magnitudes were observed as a function of structure; strong effects were found for "shared" syntactic constructions across languages (e.g., active vs. passive) and weak priming effects were found for syntactic constructions not shared (e.g., double object dative vs. prepositional dative) between English and Korean. Other asymmetrical priming effects were observed, reflecting differences between Korean and English such that reliable priming effects were found from L1 to L2, but not from L2 to L1 for Korean-as-L2 speakers (English-as-L1) These patterns of asymmetrical priming imply that cross-linguistic differences might interfere with syntactic persistence in production process unless speakers are highly advanced proficient bilinguals. Also, the present study showed that syntactic priming appears to be sensitive to the order of case-marked phrases in the cross-language priming condition. This finding indicates that the order of case-marked arguments is involved in syntactic repetition. It shed lights on further universal accounts of syntactic priming.

No description available.

The aim of this thesis was to assess the effect of root exudates on the biodegradability of dissolved organic matter. The experiment was done in laboratory conditions, using the dissolved organic matter sampled in a spruce swamp forest located in Šumava National Park and an artificial mixture of root exudates prepared according to known composition of root exudates released by peatland plants. Main hypothesis was that the input of root exudates into the peatland pore water will affect decomposition of less-degradable dissolved organic matter, with the resulting effect dependent on the quantity and quality (C:N ratio) of the input.