Soil Phosphorus Heterogeneity Improves Growth and P Nutrition of Norway Spruce Seedlings

Jörg Prietzel

doi:10.3389/ffgc.2020.00059

Abstract

Phosphorus (P) nutrition of forest trees depends on soil P supply, which is poor on sites with sandy, quartz-rich soils and shallow calcareous soils. Soil P is distributed heterogeneously at different spatial scales. I tested the hypothesis that in P-limited forest ecosystems soil P enrichment in hotspots results in improved tree P nutrition and growth compared to soils where the same P amount is distributed evenly. In two field P fertilization experiments, Norway spruce (Picea abies) and European beech (Fagus sylvatica) seedlings were grown in soils with experimental homogeneous or heterogeneous P enrichment. The soils were amended with P to equal amounts of total P, but different patterns of P enrichment and/or as different P forms (orthophosphate [oPO4]; inositol hexaphosphate [IHP]). One experiment (Achenpass) was conducted with P-poor calcareous soil material of a Rendzic Leptosol (low-P soil), the other (Mitterfels) with Bw horizon material of a Cambisol that had formed on silicate bedrock and was characterized by moderate P concentrations (moderate-P soil). Half of the spruce seedlings additionally received experimentally elevated N deposition. At the low-P calcareous site, shoot and foliage biomass as well as foliar P, N, and S amounts of Norway spruce seedlings were considerably (+70–80%) and significantly larger on soils with spatially heterogeneous compared to homogeneous P distribution. Elevated N deposition reduced soil P heterogeneity effects on spruce by improving seedling growth on soils with homogeneous P distribution. No soil P form diversity effects were observed for spruce seedlings on calcareous soil. At the silicate site with moderate P supply, all seedlings showed excellent P nutrition. Here, only marginal, insignificant positive effects of heterogeneous soil P distribution were observed for the growth of spruce and beech seedlings without elevated N deposition, but foliar P concentrations of spruce seedlings increased significantly. Elevated N deposition resulted in a positive effect of heterogeneous vs. homogeneous soil P distribution on spruce growth (+39%; eta squared: 0.163; p=0.135) and P nutrition. Our results showed that soil P concentration heterogeneity is beneficial for spruce growth and P nutrition at sites with P-poor calcareous soils, and at silicate sites with ongoing N eutrophication.

Highlights

For most forest ecosystems, the majority of its total phosphorus (P) stock is bound in the soil
Norway Spruce Both shoot and foliage biomass of Norway spruce seedlings grown on soil with heterogeneous P amendment was considerably and significantly (Table 2; Supplementary Table 1) larger than for spruces grown on soil with homogeneous P application
Root biomass was markedly smaller, and shoot/root ratios of spruce seedlings were increased by 50% on plots with heterogeneous compared to homogeneous soil P distribution

Summary

Introduction

For most forest ecosystems, the majority of its total phosphorus (P) stock is bound in the soil. Phosphorus nutrition of all major tree species in forests of Central Europe such as Norway spruce (Picea abies) and European beech (Fagus sylvatica) strongly depends on soil P supply which is poor on sites with sandy, quartz-rich soils (Ilg et al, 2009; Achat et al, 2016; Lang et al, 2016, 2017; Augusto et al, 2017) or shallow initial calcareous soils (Prietzel et al, 2015, 2016). Tree P nutrition in many European forest ecosystems has deteriorated markedly, which often has been attributed to effects of elevated atmospheric N deposition (Mohren et al, 1986; Prietzel and Stetter, 2010; Jonard et al, 2015)

Methods

Results

Conclusion