Substrate Enrichment with Clinoptilolite: Limits and Possibilities for Container-Grown Seedling Propagation

Abstract

This study examines the benefits of adding clinoptilolite (zeolite) to forest nursery substrates (growth medium) to optimise cultivation of European beech (Fagus sylvatica L.) seedlings. Ten growth medium variants were tested, each consisting of a basic peat substrate (nutrient-enriched / non-enriched) with the addition of different quantities of zeolite in different forms (ammonium nitrate and potassium sulphate-enriched / non-enriched). Zeolite had a limiting effect on plant growth, with greater seedling growth in substrates with a low proportion of zeolite (5%), and lower root biomass and root: shoot ratios in substrates with higher proportions. In the latter case, exchangeably-bound divalent base cations (Ca2 + and Mg2+) were enriched in both the sorption complex and aqueous solution due to cation exchange. At the same time, antagonistic K+ cations were depleted in leaves, despite high concentrations in the substrate. Higher doses also reduced above-ground height/root collar diameter, with substrate type as main cause, irrespective of zeolite content. These findings confirm a dose-dependent effect of zeolite, with low concentrations (5%) stimulating seedling growth and higher doses (especially 20%) leading to impaired rood development, primarily due to K+ deficiency caused by Ca2+ and Mg2+ antagonism. By identifying physiological thresholds for zeolite use in silvicultural substrates, we provide important new information for ensuring the success of European beech seedling cultivation for climate-resilient regeneration projects.