Early interactions between arbuscular mycorrhizal fungi and Frankia during colonisation and root nodulation of Alnus glutinosa

Glasshouse experiments showed significant differences in early interactions of Alnus glutinosa with five different arbuscular mycorrhizal species and Frankia. Thirty and 60 days after inoculation of roots with AMF alone, colonisation was highest with Glomus hoi and G. mosseae followed by Gigaspora rosea. Lowest colonisation was with Acaulospora scrobiculata and Scutellospora castanea. In associations with AMF resulting in relatively low colonisation, e.g. S. castanea, plant biomass after 60 days was higher than in un-inoculated controls but when inoculated with Frankia also was equal to controls. In contrast, the biomass of plants with high levels of AMF colonisation e.g. with G. hoi, was equal to the controls when alone but was lower in dual symbiosis with Frankia. This effect was particularly marked 30 days after inoculation. There was also a depressive effect of nodulation on plant biomass 30 days after dual inoculation that was less apparent after 60 days. This effect was most marked for AMF giving rise to the highest levels of colonisation (G. hoi and Gi. rosea). The data suggest that in dual inoculated alder seedlings, inhibitory effects on early growth can result, possibly from competition with micro-symbionts for resources such as photosynthates. However, effects may only be temporary, to be relieved as seedlings develop a larger shoot system with greater photosynthetic capacity

Long term evolution of tree growth, understorey vegetation and soil properties in a silvopastoral system of northern Greece

Tree growth, understorey characteristics and soil parameters were evaluated in a silvopastoral system in northern Greece at seven and twelve years after its establishment. The experiment was laid out in 1992 and included three understorey treatments (grass, legume and control- unsown), two tree species - sycamore (Acer pseudoplatanus L.) and Scots pine (Pinus sylvestris L.) and two tree spacings (2.5 x 2.5 m and 3.5 x 3.5 m). Tree height was taller in the control and in the dense stands while Scots pine had better growth but, higher mortality than sycamore in the both periods. In 2004, understorey vegetation was uniform under the three understorey treatments and a significant decrease in sward above ground biomass was recorded under the dense treatment, compared with the open stand. In the same year, organic C and N, Mg and K concentrations as well as arbuscular mycorrhizal fungi spore numbers were found significantly higher under sycamore than Scots pine plots in the 0-20 cm soil depth. The results show that, although understorey vegetation became uniform over time, the initial plant composition of the understorey treatments continued to affect tree growth, indicating the importance of the understorey vegetation at the establishment stage of silvopastoral systems. However, as time passed initial tree spacing started to affect tree growth and tree species, particularly sycamore to improve soil properties. These results indicate an evolution of the initial silvopastoral system to a forest.</p