Interactions among Tamarix (Tamaricaceae), Opsius stactogalus (Cicadellidae), and Litter Fungi Limit Riparian Plant Establishment

Gibney M Siemion,Lawrence E Stevens

doi:10.4236/ae.2015.32008

Abstract

One of the most significant plant invasions in the U.S. has been that of the Old World genus Tamarix. While Tamarix spp. is widely studied, surprisingly little is known about more complex trophically-linked community mechanisms influencing under-canopy succession. We investigated multi- trophic interactions among Tamarix spp., nonnative host-specific Opsius stactogalus leafhopper distribution and honeydew production, and the Tamarix spp. canopy floor fungal assemblage. We quantified leafhopper abundance and honeydew throughfall, and tested under-canopy seed viability and seedling mortality across a 1600 m elevation gradient in the lower Colorado River basin in 2007. We conducted field and laboratory experiments in 2007-08 to test the effects of Tamarix spp. litter fungi, synthetic honeydew, and the combination of those variables on germination and seedling survivorship of three common, co-occurring phreatophyte (riparian groundwater-dependent plant) species. Tamarix spp. litter and honeydew treatments reduced understory seed viability and recruitment of two native, woody riparian species (Populus fremontii and Baccharis salicina), as well as Tamarix spp. Four major patterns were detected. 1) Litter fungi alone and synthetic honeydew alone reduced seed viability and seedling survivorship of all three species by two- to four-fold. 2) Synthetic honeydew + litter reduced Tamarix spp. and P. fremontii seed and seedling viability by up to 10-fold. 3) Synthetic honeydew concentration and seedling mortality were positively related among all three plant species. 4) B. salicina was less susceptible to all treatments than Tamarix spp. and P. fremontii. These results indicate that complex interactions among nonnative Tamarix spp., nonnative Opsius leafhopper honeydew production, and soil fungi may influence riparian phreatophyte recruitment and succession.

Highlights

Nonnative plant species invasions are a global threat to biodiversity [1], and one of the most significant plant invasions in the U.S has been that of the Old World genus Tamarix (Tamarix spp. hybrids of hybrids of T. ramosissima X T. chinensis, hereafter referred to as Tamarix spp.) [2]
We found no seedlings of Tamarix spp., P. fremontii, or B. salicina under Tamarix spp. canopies at any of the four field sites on any sample date
Seedlings of all species were observed in open riparian areas outside of Tamarix spp. canopies at most sites

Summary

Introduction

Nonnative plant species invasions are a global threat to biodiversity [1], and one of the most significant plant invasions in the U.S has been that of the Old World genus Tamarix (Tamarix spp. hybrids of hybrids of T. ramosissima X T. chinensis, hereafter referred to as Tamarix spp.) [2]. Since its introduction in the 1800s, Tamarix spp. has escaped cultivation and hybrids have invaded more than one million ha of riparian habitat in the western U.S [3]. There was a general increase in riparian vegetation throughout this region after the early 1900s [4], as Tamarix spp. invaded many riparian systems [2] [5]. Native riparian forests provide habitat, migration corridors, and terrestrial food resources for aquatic and riparian biota [6] [7]. In the arid Southwest, riparian habitats make up 50% of the region’s biota [8]. Anthropogenic influences, including flow regulation and livestock grazing, have limited recruitment of native phreatophytic riparian trees, such as Fremont cottonwood (Populus fremontii [7]), but have enhanced invasion of Tamarix spp. Anthropogenic influences, including flow regulation and livestock grazing, have limited recruitment of native phreatophytic riparian trees, such as Fremont cottonwood (Populus fremontii [7]), but have enhanced invasion of Tamarix spp. [2] [9] [10]

Methods

Results

Conclusion