Linkages between Phosphorus and Plant Diversity in Central European Forest Ecosystems—Complementarity or Competition?

Arne Cierjacks,Ingo Kowarik,Daniel Ziche,Nicole Wellbrock,Isaak Rieger

doi:10.3390/f10121156

Abstract

The phosphorus nutrition status of European forests has decreased significantly in recent decades. For a deeper understanding of complementarity and competition in terms of P acquisition in temperate forests, we have analyzed α-diversity, organic layer and mineral soil P, P nutrition status, and different concepts of P use efficiency (PUE) in Fagus sylvatica L. (European beech) and Picea abies (L.) H. Karst. (Norway spruce). Using a subset of the Second National Soil Survey in Germany, we correlated available data on P in the organic layer and soil with α-diversity indices for beech and spruce forests overall and for individual vegetation layers (tree, shrub, herb, and moss layers). Moreover, we investigated α-diversity feedbacks on P nutrition status and PUE of both tree species. The overall diversity of both forest ecosystems was largely positively related to P content in the organic layer and soil, but there were differences among the vegetation layers. Diversity in the tree layer of both forest ecosystems was negatively related to the organic layer and soil P. By contrast, shrub diversity showed no correlation to P, while herb layer diversity was negatively related to P in the organic layer but positively to P in soil. A higher tree layer diversity was slightly related to increased P recycling efficiency (PPlant/Porganic layer) in European beech and P uptake efficiency (PPlant/Psoil) in Norway spruce. The diversity in the herb layer was negatively related to P recycling and uptake efficiency in European beech and slightly related to P uptake efficiency in Norway spruce. In spruce forests, overall and herb species richness led to significantly improved tree nutrition status. Our results confirm significant, non-universal relationships between P and diversity in temperate forests with variations among forest ecosystems, vegetation layers, and P in the organic layer or soil. In particular, tree species diversity may enhance complementarity and hence also P nutrition of dominant forest trees through higher PUE, whereas moss and herb layers seemed to show competitive relationships among each other in nutrient cycling.

Highlights

As phosphorus is an essential nutrient (e.g., [1,2]), plants and plant communities must adapt when facing P limitations
We found significantly higher values for P uptake efficiency than for P recycling efficiency across forest ecosystems (KW test, p < 0.001)
This study has revealed significant relationships between α-diversity and P in the organic layer and soil in two types of central European forest ecosystems

Summary

Introduction

As phosphorus is an essential nutrient (e.g., [1,2]), plants and plant communities must adapt when facing P limitations. Responses of plants to limited P in soils include increases in the root system (biomass, lateral roots, root turnover, and root hairs) and P transporter proteins [3] or in P use efficiency. Nutrient limitation often promotes a heterogeneous distribution of nutrients along with greater niche dimensionality [11]. Greater niche dimensionality in turn suggests a higher number of species with complementary traits and a more efficient use of nutrients which at the same time reduces competition for resource supplies between plant species [12,13,14,15]. Competitive exclusion is expected to be the main force responsible for reducing plant diversity as resource availability increases aboveground and belowground [16,17,18,19,20]

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