Plant invasions may alter the soil system by changing litter quality and quantity, thereby affecting soil community and ecosystem processes. We investigated the effect of Tamarix ramosissima invasion on the decomposer fauna and litter decomposition process, as well as the importance of litter quality in decomposition. Litter decomposition and decomposer communities were evaluated in two monospecific saltcedar forests and two native forests in Argentina, in litterbags containing either local litter (saltcedar or dominant native species) or a control litter. Saltcedar invasion produced an increase in Collembola, Acari, and total mesofauna abundance, regardless of the litter type. Control litter decomposition was higher in the native forest than in the saltcedar forest, showing that increased abundance of decomposer fauna does not necessarily accelerate decomposition processes. Local litter decomposition was not different between forests, suggesting that decomposer fauna of both ecosystems is adapted to efficiently decompose the autochthonous litter. Our results suggest that the introduction of a resource with higher quality than the local one has a negative effect on decomposition in both ecosystems, which is more pronounced in the invaded forest than in the native forest. This finding stresses the low plasticity of saltcedar decomposer community to adapt to short-term environmental changes. 1. Introduction Saltcedar (Tamarix spp.), a tree native to Eurasia, was introduced to North America, Australia, and Mexico in the mid-1800s for use as an ornamental plant, in windbreaks, and to prevent erosion in arid regions [1, 2]. In the last 50 years, saltcedar has spread rapidly along many rivers in North America [1]. In Argentina, the presence of four species of Tamarix has been confirmed: T. gallica L., T. ramosissima Ledebour, T. chinensis Loureiro, and T. parviflora DC. The first three species grow spontaneously and frequently invade natural and seminatural environments, colonizing riparian habitats in arid and semiarid continental zones, and coastal areas. Recent surveys have shown that the genus distribution covers a strip between 49°07′ and 22°91′S and 70°03′ and 57°10′W [3]. Saltcedar invasions are associated with several negative effects that can alter species composition and ecosystems processes. Several impacts have been attributed to saltcedar, such as displacement of native species [1], decline in ecological functions [4], increased frequency of fire [5], lowering of water tables, lower river flow rates and lake levels [1], and soil salinization
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