Short-term plant-decomposer feedbacks in grassland plants

Plant species differ in their effects on ecosystem productivity and it is recognised that these effects are partly due to plant species-specific influences on soil processes. Until recently, however, not much attention was given to the potential role played by soil biota in these species-specific effects. While soil decomposers are responsible for governing the availability of nutrients for plant production, they simultaneously depend on the amount of carbon provided by plants. Litter and rhizodeposition constitute the two basal resources that plants provide to soil decomposer food webs. While it has been shown that both of these can have effects on soil decomposer communities that differ among plant species, the putative significance of these effects for plant nitrogen (N) acquisition is currently understudied. My PhD work aimed at clarifying whether the species-specific influences of three temperate grassland plants on the soil microfood-web, through rhizodeposition and litter, can feed back to plant N uptake. The methods and approach used (15N labelling of plant litter in microcosm experiments) revealed to be an effective combination of tools in studying these feedbacks. Plant effects on soil organisms were shown to differ significantly between plant species and the effects could be followed across several trophic levels. The labelling of litter further permitted the evaluation of plant acquisition of N derived from soil organic matter. The results show that the structure of the soil microfood-web can have a significant role in plant N acquisition when the structure is experimentally manipulated, such as when comparing systems consisting of microbes to those consisting of microbes and their grazers. However, despite this, the results indicate that differences in N uptake from soil organic matter between different plant species are not related to the effects these species exert on the structure of the soil microfood-web. Rather, these differences in N uptake seem to be determined by other species-specific traits of live plants and their litter. My results thus indicate that different resources provided by different plant species may not induce species-specific decomposer feedbacks on plant N uptake from soil organic matter. This further suggests that the species-specific plant effects on soil decomposer communities may not, at least in the short term, have significant consequences on plant production.

Mycorrhizal fungi and nitrogen dynamics in drained peatland

Fungi have a fundamental role in carbon and nutrient transformations in the acids soils of boreal regions, such as peatlands, where high amounts of carbon (C) and nutrients are stored in peat, the pH is relatively low and the nutrient uptake of trees is highly dependent on mycorrhizae. In this thesis, the aim was to examine nitrogen (N) transformations and the availability of dissolved N compounds in forestry-drained peatlands, to compare the fungal community biomass and structure at various peat N levels, to investigate the growth of ectomycorrhizal fungi with variable P and K availability and to assess how the ectomycorrhizal fungi (ECM) affect N transformations. Both field and laboratory experiments were carried out. The peat N concentration did not affect the soil fungal community structure within a site. Phosphorus (P) and potassium (K) deficiency of the trees as well as the degree of decomposition and dissolved organic nitrogen (DON) concentration of the peat were shown to affect the fungal community structure and biomass of ECMs, highlighting the complexity of the below ground system on drained peatlands. The biomass of extrametrical mycorrhizal mycelia (EMM) was enhanced by P and/or K deficiency of the trees, and ECM biomass in the roots was increased by P deficiency. Thus, PK deficiency in drained peatlands may increase the allocation of C by the tree to ECMs. It was also observed that fungi can alter N mineralization processes in the rhizosphere but variously depending on fungal species and fertility level of peat. Gross N mineralization did not vary but the net N mineralization rate significantly increased along the N gradient in both field and laboratory experiments. Gross N immobilization also significantly increased when the peat N concentration increased. Nitrification was hardly detectable in either field or laboratory experiments. During the growing season, dissolved inorganic N (DIN) fluctuated much more than the relatively stable DON. Special methodological challenges associated with sampling and analysis in microbial studies on peatlands are discussed.

Lymphatic vascular maturation : Roles of FOXC2, NFATc1 and liprin ß1

The blood vascular system is a closed circulatory system, responsible for delivering oxygen and nutrients to the tissues. In contrast, the lymphatic vascular system is a blind-ended transport system that collects the extravasated tissue fluid from the capillary beds, and transports it back to the blood circulation. Failure in collecting or transporting the lymph, due to defects in the lymphatic vasculature, leads to accumulation of extra fluid in the tissues, and consequently to tissue swelling lymphedema. The two vascular systems function in concert. They are structurally related, but their development is regulated by separate, however overlapping, molecular mechanisms. During embryonic development, blood vessels are formed by vasculogenesis and angiogenesis, processes largely mediated by members of the vascular endothelial growth factor (VEGF) family and their tyrosine kinase receptors. The lymphatic vessels are formed after the cardiovascular system is already functional. This process, called lymphangiogenesis, is controlled by distinct members of the VEGF family, together with the transcription factors Prox1 and Sox18. After the primary formation of the vessels, the vasculature needs to mature and remodel into a functional network of hierarchically organized vessels: the blood vasculature into arteries, capillaries and veins; and the lymphatic vasculature into lymphatic capillaries, responsible for the uptake of the extravasated fluid from the tissues, and collecting vessels, responsible for the transport of the lymph back to the blood circulation. A major event in the maturation of the lymphatic vasculature is the formation of collecting lymphatic vessels. These vessels are characterized by the presence of intraluminal valves, preventing backflow of the lymph, and a sparse coverage of smooth muscle cells, which help in pumping the lymph forward. In our study, we have characterized the molecular and morphological events leading to formation of collecting lymphatic vessels. We found that this process is regulated cooperatively by the transcription factors Foxc2 and NFATc1. Mice lacking either Foxc2 or active NFATc1 fail to remodel the primary lymphatic plexus into functional lymphatic capillaries and collecting vessels. The resulting vessels lack valves, display abnormal expression of lymphatic molecules, and are hyperplastic. Moreover, the lymphatic capillaries show aberrant sprouting, and are abnormally covered with smooth muscle cells. In humans, mutations in FOXC2 lead to Lymphedema-Distichiasis (LD), a disabling disease characterized by swelling of the limbs due to insufficient lymphatic function. Our results from Foxc2 mutant mice and LD patients indicate that the underlying cause for lymphatic failure in LD is agenesis of collecting lymphatic valves and aberrant recruitment of periendothelial cells and basal lamina components to lymphatic capillaries. Furthermore, we show that liprin β1, a poorly characterized member of the liprin family of cytoplasmic proteins, is highly expressed in lymphatic endothelial cells in vivo, and is required for lymphatic vessel integrity. These data highlight the important role of FOXC2, NFATc1 and liprin β1 in the regulation of lymphatic development, specifically in the maturation and formation of the collecting lymphatic vessels. As damage to collecting vessels is a major cause of lymphatic dysfunction in humans, our results also suggest that FOXC2 and NFATc1 are potential targets for therapeutic intervention.

Content of zinc, iron and their absorption inhibitors in Nicaraguan common beans (Phaseolus vulgaris L.).

Protein-energy malnutrition and mineral deficiencies are two of the three forms of nutritional deficiencies that affect most developing countries due to inadequate access to food and diets based on a sole crop. Common bean (Phaseolus vulgaris L.) is the staple crop of Nicaragua and it has the potential to improve the nutritional status of the poorest group of the nation. Its high content of both protein and nonhaem iron provides many nutrients, but inhibitors also may prevent absorption of iron and zinc by the human consumer. A proper production chain must be followed to ensure the best grain quality for the consumer. To achieve food security, both production and high nutritional content must be maintained. Four nationally important accessions of common bean, with different harvesting dates, were selected to be submitted to two treatments: to evaluate the impact of storage conditions on the end quality of the grain. The duration of the study was six months with sampling every six weeks, and the two treatments were controlled one stored at 40°C and 75 RH %, and the other was stored in in-situ conditions. Proximate and mineral composition was evaluated as well as tannin, phytate and bioavailability. Significant differences among different accessions were found, being the most significant in protein, Fe and Zn content, tannins and phytate. Protein values ranged from 21-23%. Iron content was 61-81 mg/kg but only 3-4% was bioavailable. Zinc content was 21-25 mg/kg and 10-12% was bioavailable. The concentration of phytate ranged from 8.6-9.6 mg/g while tannin values ranged within 37.7-43.8 mg/g. Storage at high temperatures was demonstrated to have an impact on certain nutritional compounds and proved detrimental to final grain quality. Soluble sugar content and tannin content decreased after six months in both storage conditions, IDF decreased in the in-situ and SDF in the stress. The iron content and bioavailability in INTA Biofortificado were not as outstanding as expected, so experiments should be conducted to compare its iron uptake and delivery with other cultivars.

Jakojuuriviljelyn vaikutus kasvihuonekurkun (Cucumis sativus L.) kasvuun ja kehitykseen

Kasvit ottavat vettä parhaiten kasteluravinneliuoksesta, jonka ravinnepitoisuus on pieni. Intensiivisessä kasvihuonetuotannossa käytetään silti kastelulannoituksessa usein korkeita ravinnepitoisuuksia ravinnepuutosten ja satotappioiden välttämiseksi. Jakojuuriviljelyssä kasvin juuriston annetaan kasvaa kahteen erilliseen kasvualustaosioon. Tällöin toiselle puolelle annetaan johtokyvyltään väkevää ja toiselle puolelle laimeaa ravinneliuosta. Erityisesti kasvihuonekurkun, joka on herkkä kasvualustan suolaisuuden aiheuttamille vedensaantiongelmille, on todettu hyötyvän tästä tekniikasta, mikä näkyy kasvaneina satoina. Tämän MTT Piikkiössä toteutetun kasvihuonekurkun jakojuuriviljelytutkimuksen tavoitteena oli tarkentaa tekniikkaa erityisesti kasteluliuosten johtokyvyn osalta. Yhtenäisjuuriviljelyn ja perinteisen jakojuuriviljelyn lisäksi kokeessa oli kaksi jakojuuriviljelykäsittelyä, joissa ravinneliuosväkevyyksiä vaihdettiin väliajoin juuriston toimintakyvyn parantamiseksi. Erillisessä osakokeessa tutkittiin erilaisten johtokyky-yhdistelmien vaikutusta kasvihuonekurkun vegetatiiviseen kasvuun maanpäällisten ja -alaisten kasvinosien välillä sekä juurten morfologiaan ja anatomiaan. Tulokset osoittivat, että jakojuuriviljely lisäsi kasvihuonekurkun sadontuottoa jopa 16 %, mutta ei vaikuttanut koko viljelykauden veden tai ravinteiden ottoon. Yhtenäisjuuriviljelyssä muodostui eniten piikkikärkisiä hedelmiä, mikä viittaa vedensaantiongelmiin haihdutustarpeen ollessa suurin. Viljelytekniikalla ei ollut vaikutusta kasvien vegetatiiviseen kasvuun tai kasvuston rakenteeseen. Lehtiruodeista tehdyt nitraatti- ja kaliummittaukset osoittivat, ettei kasteluliuosten ravinnepitoisuuksilla ollut vaikutusta juurten ravinteiden ottoon. Erilaisilla johtokyky-yhdistelmillä oli huomattavampi vaikutus kasvihuonekurkun juurten painoon kuin verson painoon tai varren pituuskasvuun. Lehtiruotianalyysit viittasivat ravinteiden erilaiseen allokointiin eri johtokyky-yhdistelmissä. Korkeiden johtokykyjen aiheuttama osmoottinen stressi johti muutoksiin juurten morfologiassa ja anatomiassa. Tulosten perusteella jakojuuriviljely paransi kehittyvien hedelmien kohdevahvuutta suhteessa muihin kohteisiin vaikuttamatta vegetatiiviseen kasvuun. Kun laimean ja väkevän ravinneliuoksen puolia vaihdettiin, juuristo otti joustavasti vettä ja ravinteita olosuhteiden määräämästä edullisemmasta johtokyvystä, jolloin kasvihuonekurkun viljelyssä saavutettiin merkittävä satoetu. Juuriston jakaminen vaikuttanee kasvien hormoniaineenvaihduntaan ja voi heikentää juuriston kasvua heikentämättä sen toimintakykyä, jolloin yhteyttämistuotteita kohdennetaan tehokkaammin maanpäällisten osien kasvuun.