The aim of this work was to study the effect of long-term contrasting cropping systems on the indigenous arbuscular mycorrhizal fungal (AMF) spore populations in the soil of a field experiment located in western Finland. Conventional and low-input cropping systems were compared, each with two nutrient management regimes. The conventional cropping system with a non-leguminous 6-year crop rotation (barley-barley-rye-oat-potato-oat) was fertilized at either full (rotation A) or half (rotation B) the recommended rate. In the low-input cropping system, plant residues were returned to the plots either as such (rotation C) or composted (rotation D). In the rotation of this system, 1 year with barley was replaced by clover, and oat was cultivated mixed with pea. Thus, the 6-year rotation was barley-red clover-rye-oat + pea-potato-oat + pea. Each rotation was replicated three times, starting the 6-year rotation in three different years, these being designated point 1, point 2, and point 3, respectively. In the low-input system, biotite and rock phosphate were used to compensate for K and P in the harvested yield, while animal manure was applied at the start only. After 13 years, rotation points 1 and 3 were studied. Barley was the standing crop in all plots of rotation point 1, while oat and oat + pea were grown in rotations C and D, respectively. AMF spores were studied by direct extraction and by trapping, sampled on 15 June and 15 August. In addition, a special assay was designed for isolation of fast colonizing, dominating AMF. The cropping system did not significantly affect AMF spore densities, although the low-input cropping system with composted plant residues had the highest density with 44 spores on average and the conventional system with full fertilization 24 spores per 100 cm(3) soil in the autumn samples. Species richness was low in the experimental area. Five Glomus spp., one Acaulospora, and one Scutellospora were identified at the species level. In addition to these, three unidentified Glomus spp. were found. Species richness was not affected by cropping system, rotation point, or their interactions. The Shannon-Wiener index of AMF spore distributions was significantly higher in the fully fertilized than in the half-fertilized conventional plots. Glomus claroideum was the most commonly identified single species in the experimental area. It occurred in all the cropping systems and their various rotation points, representing about 30% of the total number of identified spores. In August, G. claroideum accounted for as much as 45-55% of the total numbers of spores identified in the conventional system with halved fertilization. In contrast, Glomus mosseae occurred more commonly in June (26%) than in August (9%). A bioassay using roots as inoculum for isolation and culture of dominating AMF was successfully developed and yielded only G. claroideum. This indicates a high probability of being able to more generally identify, isolate, and culture fast colonizing generalist AMF for use as inoculants in agriculture...

Systemic-and seed-transmitted fungal endophytes are suggested to enhance competitive dominance of agronomic grasses by increasing plant growth and defence against herbivores. We studied whether Neotyphodium uncinatum endophyte infection frequencies of meadow fescue (Schedonorus pratensis) and botanical composition of pastures are affected by 4, 5, 7 and 21 years of grazing by dairy cattle. We then examined with one greenhouse and two field experiments, whether endophyte infection and clipping affect regrowth of young or mature plants relative to nutrient availability in soil. The frequencies of infected plants and the number of plant species were less in grazed parts of the pastures. Endophytes significantly reduced relative regrowth and dry biomass of regrowth of the grass irrespective of nutrient levels in a 1-year-old field (on an average 18% in 2 months) and under high nutrient conditions in the greenhouse experiment (on an average 3% in 3 months) respectively. However, effects of endophytes were not detected in 5-year-old fields and under low nutrient conditions in the greenhouse. In contrast to past studies, our results demonstrate that grazing may negatively affect endophyte-grass symbiosis and number of plant species of successional pastures, and suggest that the effects of endophytes may be linked to the ontogeny of the host.

The effects various rates of nitrogen application on accumulation of dry matter and nitrogen in potato (Solanum tuberosum L.) were studied during a short growing period of 140-180 days, at MTT Agrifood Research Finland in 2000-2001. The treatments were 0, 60 and 120 kg N ha -1 and the potato cultivars tested were Van Gogh and Nicola. Four successive harvests were made during the course of the experiment to monitor changes in the accumulation of dry matter and nitrogen over the season. Applications of nitrogen substantially increased haulm dry matter accumulation and to an even greater extent their nitrogen contents. The highest dry matter values were generally registered at 120 kg N ha -1 . Dry matter and nitrogen content of haulms started to decline during the later part of season and most nitrogen was relocated to tubers. The results suggest that an application of only 60 kg N ha -1 was sufficient to promote rapid canopy development and there were only small reductions in dry matter and nitrogen accumulation until late in the season when the canopy started to senesce as nitrogen supply diminished. Tuber yield, plant dry matter and nitrogen accumulation at maturity were related to crop nitrogen supply. Although application of the high rate, 120 N kg ha -1 , resulted in a significant increase in dry matter accumulation, this was not reflected in the profit because the higher nitrogen application reduced dry matter content of tubers by 2.6% in 2000 and by 1.1% in 2001 relative to the use of 60 kg N ha -1 . Apparent fertilizer nitrogen recovery values on a whole plant basis ranged from 53 to 75%. The proportion of fertilizer recovered in tubers clearly declined with increase in nitrogen supply.