Jacqueline Baar

Molecular diversity of arbuscular mycorrhizal fungi in onion roots from organic and conventional farming systems in the Netherlands

Diversity and colonization levels of naturally occurring arbuscular mycorrhizal fungi (AMF) in onion roots were studied to compare organic and conventional farming systems in the Netherlands. In 2004, 20 onion fields were sampled in a balanced survey between farming systems and between two regions, namely, Zeeland and Flevoland. In 2005, nine conventional and ten organic fields were additionally surveyed in Flevoland. AMF phylotypes were identified by rDNA sequencing. All plants were colonized, with 60% for arbuscular colonization and 84% for hyphal colonization as grand means. In Zeeland, onion roots from organic fields had higher fractional colonization levels than those from conventional fields. Onion yields in conventional farming were positively correlated with colonization level. Overall, 14 AMF phylotypes were identified. The number of phylotypes per field ranged from one to six. Two phylotypes associated with the Glomus mosseae–coronatum and the G. caledonium–geosporum species complexes were the most abundant, whereas other phylotypes were infrequently found. Organic and conventional farming systems had similar number of phylotypes per field and Shannon diversity indices. A few organic and conventional fields had larger number of phylotypes, including phylotypes associated with the genera Glomus-B, Archaeospora, and Paraglomus. This suggests that farming systems as such did not influence AMF diversity, but rather specific environmental conditions or agricultural practices.

Molecular analysis of ectomycorrhizal basidiomycete communities in a Pinus sylvestris L. stand reveals long-term increased diversity after removal of litter and humus layers

Abstract The number of fruiting bodies of ectomycorrhizal species in pine forests in The Netherlands has decreased dramatically in recent decades. This decrease has been attributed to an increase in nitrogen deposition and the accumulation of litter and humus. The effects of sod cutting and the removal of litter and humus, to restore ectomycorrhizal diversity in a Scots pine forest in Dwingeloo, The Netherlands, were investigated previously from 1990 to 1993. Removal of the litter and humus resulted in a significant increase in the numbers of species and fruiting bodies of ectomycorrhizal fungi. However, until now all data were obtained by counting fruiting bodies and the effects on mycelial development below ground were not assessed. To investigate hyphal development, DNA was extracted from bulk soil and polymerase chain reaction products were obtained by amplification using basidiomycete-specific internal transcribed spacer (ITS) primers. The differences in diversity between the control plots and the treated plots were analyzed using denaturing gradient gel electrophoresis. To assess the species composition and differences, ITS regions of the amplified fragments were cloned and sequenced. Sequences were compared with sequences from GenBank and from fruiting bodies collected from the same plots. Data indicated increased below-ground ectomycorrhizal diversity in the plots that had been subjected to removal of the litter and humus layers.

Ectomycorrhizal root development in wet Alder carr forests in response to desiccation and eutrophication.

Abstract. Effects of desiccation and eutrophication on ectomycorrhizal (ECM) root development in wet Alder carr forests in The Netherlands were studied. In northwestern Europe, wet Alder carr forests are found mostly in peatlands and along streams, forming an important component of wetland ecosystems. The dominant tree species in wet Alder carr forests is Alnus glutinosa (L.) Gaertn. (Black alder), which associates with ectomycorrhizal fungi. During recent decades, wet Alder carr forests in Europe have declined because of desiccation and eutrophication, particularly in The Netherlands. In the present study, the number of root tips of A. glutinosa trees was highest in an undisturbed wet Alder carr forest in a peatland area. Eutrophication in the peatland area significantly inhibited ectomycorrhizal (ECM) root development of A. glutinosa. In the eutrophied forest, ECM root tips were observed only close to A. glutinosa trees growing on hummocks. The concentrations of nitrate and potassium in soil water of the eutrophied forest were significantly higher than in the undisturbed forest, while magnesium and iron concentrations and the pH were significantly lower. The number of ECM root tips of A. glutinosa in a desiccated forest along a stream was generally lower than in an undisturbed wet Alder carr forest on waterlogged soil in the same area. The sulphate concentration in soil water in the desiccated forest was significantly higher than in the forest on waterlogged soil. ECM root development of A. glutinosa may have been negatively affected by the chemical composition of the soil water.