Growth, physiology, and early root development in seedlings of different woody species treated with biostumulants

The demand for saplings has risen in the last years as a consequence of massive planting campaigns targeted at increasing canopy cover. To test the hypothesis that algae extract can improve root growth and morphology, an experiment was carried out at the Ersaf forest nursery (Curno, BG, Italy). Seeds of Amelanchier ovalis, Carpinus betulus, Crataegus monogyna, Fagus sylvatica and Ligustrum vulgare were seeded in trays using a substrate amended with 0x, 1x, 2x or 3x the label dose (1 kg/m3) of a pure Ascophyllum nodosum extract. After germination, 6400 seedlings were arranged according to a randomized complete block design with 10 blocks and grown under nursery conditions for 1 year. Thereafter, plants were transplanted into 1.7 L forest containers for one additional growing season. To measure biomass production, plants were cut at the flare and roots cleaned with a flush of air. Roots, stems, and leaves were oven-dried and weighed separately. Total plant leaf area was measured after scanning all leaves with an A3 scanner. Total root length was measured using the root line intersect method. Specific root length was calculated as root length/root dry biomass. Biomass and leaf area were measured 2, 6, 12, 24 and 72 weeks after germination. Leaf gas exhange was measured 2, 6, 12, 24, 48, and 72 weeks after germination using an infra-red gas analyser (Ciras-2, PP-System, USA). Chlorophyll content was measured using a spad-meter, on the same days as leaf gas exchange. Species differed for growth rate, biomass allocation to roots and specific root length. Biostimulants increased stem and whole plant dry weights for 1 year only when applied at 3x label dose. Similarly, significant effects on leaf gas exchange were found only at the highest dose, and were mostly due to higher chlorophyll content than to lower stomatal limitations to photosynthesis. Results suggest that substrate amendment with Ascophyllum extracts may have short-term positive effects on plant and root growth, likely due to a nutritional boost. However, they did not trigger structural changes in plant traits that can enhance transplant tolerance in the long run.