Forest litter amendment during nursery stage influence field performance and ectomycorrhizal community of Scots pine (Pinus sylvestris L.) seedlings outplanted on four different sites

Our recent studies have demonstrated that forest litter used in a bare-root forest nursery promoted survival and growth of two-year-old Scots pine seedlings and positively shaped the development of their ectomycorrhizal (ECM) fungal communities. To determine whether the beneficial effects of litter treatment can be extended to the next growing seasons, litter-treated seedlings were outplanted to four sites with different environmental conditions: forest clear-cut (S1), area formerly polluted by emissions from nitrogen fertilizer plant (S2), abandoned agricultural land (S3,) and coastal sand dunes (S4). Seedlings grown in mineral nursery soil without litter amendment served as controls. Height and survival of seedlings were measured over three consecutive years after outplanting. At the end of the third growing season, the mycorrhizal status of seedlings was assessed using DNA-based identification techniques. Litter treatment during the nursery phase significantly improved the height of seedlings at the end of the first growing season at all tested sites. In the second and third growing seasons after outplanting, the heights of litter treated seedlings remained greater compared to control seedlings at three of the four sites; however, at the abandoned agricultural site (S3), significantly lower growth of litter-treated seedlings was observed. After the third growing season, the differences in seedling heights at the forest clear-cut (S1) and the site formerly polluted by nitrogen (S2) were not statistically significant. Survival of all outplanted seedlings varied by season and study site, but litter treated seedlings showed a clear tendency towards enhanced survival. Three years after outplanting, the survival rates of litter-treated seedlings ranged from approximately 81% at S4 to 96% at S2; for control seedlings, survival rates ranged from 63% at S4 to 81% at S3. At sites S1, S2 and S4, the survival of litter-treated seedling was significantly higher. There was a substantial transformation in ECM community composition with low persistence of suilloid mycorrhizas for both litter-treated and control seedlings three years after outplanting. Two-way analysis of similarities (ANOSIM) indicated that differences in ECM fungal community composition across seedlings from different sites likely were due to site specificity rather than previous litter treatment. Our results indicated that nursery soil amended with pine forest litter creates favourable conditions for the production of pine seedlings with better root quality and high abundance of suilloid mycorrhizas, thus allowing for potential reductions in mortality after outplanting on unfavourable sites. (C) 2017 Elsevier B.V. All rights reserved.