No description available.

The application of crop residues is one of the most common agricultural practices used to maintain soil ecosystems and crop productivity. This thesis focuses on the oil palm (Elaeis guineensis) agroecosystem, an important tropical crop that has expanded rapidly over the past four decades. Both land conversion and business-as-usual practices within the plantations have contributed to soil degradation. The application of oil palm residues, such as empty fruit bunches (EFB) and oil palm fronds, are thought to have positive effects on the soil ecosystem; yet there is currently a deficit of knowledge on their effectiveness. This thesis aims to examine the effects of oil palm residue application on soil physicochemical properties, soil biota, and ecosystem functions. It reports the results of extensive field trials, sample collection, and statistical analysis of crop residue applications in oil palm plantations in Central Sumatra, Indonesia. Four key results emerged from the thesis. First, in this study site land conversion from secondary forest to oil palm does not affect litter decomposition rate, but positively influences soil fauna activity. Second, there is greater soil fauna activity following EFB application than oil palm fronds or chemical fertilizers, and the fauna activity is highly associated with changes in soil chemical properties and soil moisture conditions. Third, EFB application enhances soil ecosystem functions, through the direct provision of organic matter, and by influencing soil biota. Finally, over 15 years of application, EFB appears to be effective in maintaining or increasing annual crop yield in comparison to chemical fertiliser treatment. Temporal changes in crop yield under EFB application appear to be associated with climatic conditions and soil organic carbon. Overall, these findings improve our understanding of the potential of oil palm residue applications to increase soil quality, soil biota, and ecosystem functions. They also provide useful information for a wider audience of soil ecologists, agricultural managers, and policy makers to improve sustainable management of the oil palm ecosystem.

Soil microorganisms have a variety of beneficial and deleterious effects on plants, impacting such processes as plant growth, soil nutrient cycling, crop yield, disease resistance and tolerance to an array of biotic and abiotic stressors. The disruption of soil microbial community structures, particularly when beneficial soil biota are altered, has been shown to reduce crop yield and leave plants susceptible to disease. Long-term disruption of microbial communities may occur with repeated fumigation, being the application of gaseous pesticides, in agricultural soils. For this reason, we characterized bacterial, fungal, oomycete and nematode populations in paired fumigated and nonfumigated potato fields located in Idaho, Oregon, Washington and Minnesota. Samples were taken at three distinct timepoints: one before a fall fumigation event and two others at important stages in potato production, row closure and vine death. Soil biota populations were assessed by targeting the 16S, 18S and ITS1 gene regions. FunGuild, a database capable of guild and trophic assignment of fungal lineages, was used to sort fungal OTUs in different trophic modes. Fungal analyses indicated an increase in relative abundances of saprotrophic fungal populations and a decrease in pathotrophic fungal populations, both during row closure. Principally, the fungal genera of Humicola and Mortierella were responsible for the increase of saprotrophs while Alternaria decreased the most for pathotrophs. Other fungi occupying multiple trophic modes, such as Fusarium, also decreased during row closure. We found that fumigation treatments, in combination with various pesticide and fertilizer applications, alter both alpha- and beta- bacterial soil diversity although certain treatments, i.e. chloropicrin, may alter bacterial populations more than other treatment types such as metam-sodium. Nematode populations were likewise distinct at each location with soils from Boardman, OR, Minidoka, ID and Pine Point, MN with these having higher levels of nematodes associated with better soil health, i.e. Dorylaimidae. Conversely, nematodes associated with plant pathogenesis were found in higher relative abundances at Minidoka, ID and Quincy, WA. In this study, we characterize the populations of bacteria, fungi, oomycetes and nematodes with an emphasis on fungal taxa. We found that relative abundances of fungal trophic modes vary temporally. Additionally, we catalogue several other high abundance taxa with seasonal differential abundances whose functional capacity in potatoes remain uncharacterized.

My PhD thesis is focused on study of plant-soil interactions. Chapter 1 is focused on general introduction to the interactions between plants and soil biota in terms of relationships between soil organisms and aboveground biomass as well as root biomass. Chapter 2 is focused on food interaction of Folsomia candida and soil microscopic fungi (Penicillium chrysogenum, Penicillium expansum, Absidia glauca, and Cladosporium herbarum). Fungi were grown separately on Petri dishes or on different litter type (oak, alder and willow) separately as well. Laboratory experiments showed that food preference was more influenced by different litter types than fungal species. In chapter 3 was studied long-term production of hybrid sorrel and its effect on the composition of the soil meso and macrofauna, basal soil respiration, microbial biomass and composition of cultivable fraction of soil microscopic fungi in comparison with oilseed rape and cultural meadow. There was found that long-term production of hybrid sorrel affects the composition of soil fauna, while the microbial activity of the soil was more affected by agriculture practices, especially tillage. In chapter 4 was studied the effect of native (Salix viminialis and Phalaris arudinacea) and introduced (Reynoutria sachalinensis, Silphium perfoliatum and...

Durch die Zunahme der Biogasproduktion in den letzten Jahren hat sich auch die Menge von Gärprodukten, die verbleibenden Rückstände, entsprechend erhöht. In Deutschland fallen jährlich mehr als 50 Millionen Tonnen Gärprodukte an, die als Dünger verwendet werden. Damit werden Nährstoffe in den Kreislauf landwirtschaftlicher Ökosysteme zurück-geführt. Allerdings sind die agroökologischen Wirkungen noch nicht hinreichend erforscht. Aus diesem Grund wurden die folgenden Parameter untersucht: Einfluss von trockenen und flüssigen Gärprodukten auf dem Ertrag von drei ausgewählten Fruchtarten im Vergleich zu oder in Kombination mit Mineraldünger in On-Farm Versuchen; Wachstum, Entwicklung und Ertrag von zwei ausgewählten Fruchtarten im Vergleich zu Mineraldünger, Gülle und Stallmist in einer vollständig randomisierten Blockanlage; Einfluss auf ausgewählte Bodenlebewesen im Vergleich zu Mineraldünger, Gülle und Stallmist in einer vollständig randomisierten Blockanlage. Zusätzlich wurde die Mineralisierung von flüssigen und festen Gärprodukten im Vergleich zu Gülle und Stallmist untersucht, um Effekte der verschiedenen Düngestoffe auf die Humusbildung unter kontrollierten Bedingungen zu bestimmen. / With the increase of biogas production in recent years, the amount of digestates or the remaining residues increased accordingly. Every year in Germany more than 50 million tons of digestates are produced, which are used as fertilizer. Thus nutrients return into the circulation of agricultural ecosystems. However, the agro-ecological effects have not been deeply researched until now. For this reason, the following parameters were quantified: the influence of dry and liquid fermentation products on the yield of three selected crops in comparison to or in combination with mineral-N-fertilizers in on-farm experiments; the growth, development and yield of two selected crops in comparison to mineral-N-fertilizer, liquid manure and farmyard manure in a randomized complete block design; selected soil organisms as compared to mineral-N-fertilizer, liquid manure and farmyard manure in a randomized complete block design. In addition, the mineralization of dry and wet digestates in comparison with liquid manure and farmyard manure was investigated in order to evaluate the effects of different fertilizers on the humus formation under controlled conditions.

Comprendre comment les variations du climat pourraient influencer le recrutement des arbres en forêt est un défi car la germination, la croissance et la survie des semis sont particulièrement sensibles aux facteurs biotiques et abiotiques. Plusieurs modèles conceptuels généraux, (la « stress gradient hypothesis » SGH et « latitudinal herbivory theory » LHT,) suggèrent que la nature et l'intensité des interactions biotiques varient le long de gradients environnementaux. Ces modèles constituent une base théorique utile pour déterminer le rôle des interactions biotiques dans la réponse des communautés végétales aux variations du climat. Cependant, les études portant sur la SGH se sont limitées aux interactions directes entre plantes et ont négligé les interactions complexes. Les théories développées pour des niveaux trophiques supérieurs (comme la LHT) sont quant-à elles sujettes à débat et ne considèrent qu'un nombre limité d'interactions. Les interactions avec les micro-organismes du sol ont par exemple été négligées. Dans cette thèse, j'ai analysé comment les interactions directes et indirectes entre les semis, les arbres adultes, la végétation herbacée, les insectes herbivores et les pathogènes du sol varient en nature et en intensité le long de gradients climatiques. Pour explorer les interactions entre plantes, j'ai effectué une expérimentation s'appuyant sur la variabilité spatio-temporelle des conditions climatiques dans les Alpes. Les résultats montrent que les effets directs de compétition de la canopée et de la végétation herbacée augmentent avec la température. Cependant, pour les sites les plus chauds, la facilitation indirecte pourrait limiter la compétition directe des herbacées. Pour les interactions avec insectes herbivores,nous avons montré que le long de gradients d'altitude et de latitude, l'herbivorie est minimale là où les stress thermiques et hydriques est fort. Enfin, pour les interactions avec les micro-organismes du sol, nous avons mesuré en chambre de culture la survie de plantules de hêtre dans des sols, stérilisés ou non, collectés le long d'un gradient d'altitude. Les résultats montrent que les effets négatifs des micro-organismes sont plus faibles quand les communautés microbiennes proviennent de sols d'altitudes. Cette thèse suggère que les effets directs négatifs des plantes, des insectes herbivores et des pathogènes du sol sur les semis dominent dans les environnements chauds et productifs et s'atténuent dans des conditions plus froides. Les interactions indirectes semblent varier inversement et pourraient ainsi tamponner l'effet des interactions directes. / Understand how climate change could influence forest tree recruitment is a challenge because germination, seedling growth and seedling survival are especially sensitive to biotic and abiotic factors. Several conceptual models (as the “Stress Gradient Hypothesis”, SGH, and the “Latitudinal Herbivory Theory”, LHT) propose that the nature and intensity of biotic interactions vary along environmental gradients. These models constitute a useful theoretical basis to determine the role played by biotic interactions in the response of vegetation communities to climate variations. However, SGH studies have nevertheless been limited until now to direct interactions between plants and have neglected complex interactions. Theories including higher trophic levels, as the LGH, are still debated and have focused on a limited number of interactions. For example, interactions with soil biota have been neglected. In this thesis, we have analysed how direct and indirect interactions between seedlings, adult trees, ground vegetation, herbivorous insects, and soil pathogens vary in nature and intensity along climate gradients. To study interactions between plants, we established an experimentation using the spatio-temporal climatic variability in the French Alps. The results show that the direct effects of competition from adult tree canopy and ground vegetation diminish at higher altitudes. However, for warmer sites, indirect facilitation by canopy could limit direct competition by ground vegetation. To study the interactions between seedlings and herbivorous insects, we have analysed the altitudinal and latitudinal variation of herbivory on young trees across Europe. Results show that herbivory is the lowest where temperature and water stresses are strong. Finally, to study interactions with soil microorganisms, we have measured in a greenhouse the survival of European beech seedlings on soils either sterilized or not, collected along an altitudinal gradient. The results show that the negative effect of microorganisms is lower when microbe communities come from higher altitudes. The results suggest that the negative direct effects of plants, herbivorous insects and soil pathogens on seedlings are dominant in warm and productive environments and diminish in cold environments. Indirect interactions seem to vary inversely and could buffer the effects of direct interactions.

No description available.