The Sign and Strength of Plant-Soil Feedback for the Invasive Shrub, Lonicera maackii, Varies in Different Soils

Kelly Schradin,Don Cipollini

doi:10.3390/f3040903

Abstract

Plants alter soil characteristics causing changes in their subsequent growth resulting in positive or negative feedback on both their own fitness and that of other plants. In a greenhouse study, we investigated whether the sign and strength of feedback changed across two distinct soil types, and whether effects were due to shifts in biotic or abiotic soil traits. Using soils from two different locations, we examined growth of the exotic invasive shrub, Lonicera maackii and the related native shrub, Diervilla lonicera, in unconditioned soils and in soils conditioned by previous growth of L. maackii, D. lonicera, and Fraxinus pennsylvanica. In a sandy acidic soil, L. maackii showed positive feedback in unsterilized soils, but its growth decreased and positive feedback became negative with sterilization in this soil. In a loamy circumneutral soil, L. maackii displayed neutral to negative feedback in unsterilized soils, but sterilization significantly increased growth in all conditioning treatments and caused feedback to become strongly negative. Native D. lonicera displayed negative feedback in unsterilized soil of both the sandy and loamy types, but sterilization either eliminated or reversed feedback relationships. Soil conditioning by L. maackii and F. pennsylvanica had very similar feedbacks on L. maackii and D. lonicera. While some abiotic soil traits varied across soil types and were affected by conditioning, soil biota sensitive to sterilization were apparently important mediators of both positive and negative feedback effects.

Highlights

Changes in soil properties are an increasingly recognized impact of invasive species that may leave lasting effects in the soil [1,2,3,4,5,6,7]
Plants can affect the presence of nutrient cycling microbes which in turn can create positive feedback mediated by effects on nutrient cycling [3,15,16,17,18]
Effects of Soil Type and Conditioning on Soil Properties. Conditioned soils of both types were analyzed for pH, nutrient and phenolic levels, and other properties, but were not compared statistically because only one pooled sample per conditioning treatment per soil type was analyzed, but several general patterns were observed in the data

Summary

Introduction

Changes in soil properties are an increasingly recognized impact of invasive species that may leave lasting effects in the soil [1,2,3,4,5,6,7]. The soil rhizosphere develops characteristics, such as changes in pH, mineral composition, or microbial community composition, that can have effects that feed back on the plant’s own fitness, and on that of other species [1,3,8,9,10]. Plant growth is highly regulated by soil organisms, both beneficial and pathogenic, and many plant-soil feedback effects are due to alterations in microbial interactions. In their native ranges, invasive plants are often suppressed by soil organisms such as parasitic fungi and nematodes, but in introduced habitats, they may not be exposed to these same natural enemies [3,13]. The tendency for plant soil feedbacks to be positive in introduced habitats (versus negative in native habitats) may be partly responsible for nonnative plants becoming invasive in introduced areas [4,19,20]

Methods

Results

Conclusion