Decomposition and biological colonization of native and exotic leaf litter in a Central Spain stream

Abstract

Decomposition and biological colonization of native and exotic leaf litter in a Central Spain streamRiparian invasion by exotic trees may lead to changes in the quality of leaf-litter inputs to freshwater ecosystems. Leaflitter inputs are especially important in headwater streams, where aquatic food webs largely depend on the organic matter provided by the terrestrial vegetation. In a headwater stream of Central Spain, North of Guadalajara Province (Tagus basin) we compared the decomposition and biological colonization of leaf litter among two exotic (Ailanthus altissima Mill. Swingle and Robinia pseudoacacia L.) and two native trees (Fraxinus angustifolia Vahl. and Populus alba L.) co-existing in riparian zones. We hypothesized a lower biological colonization of exotic leaves due to organisms have not co-evolved with the exotic trees according to the Novel Weapons Hypothesis (NWH) and, consequently, lower decomposition rates of exotic leaves. To test our hypothesis, litter bags with different mesh sizes (coarse (C) and fine (F)), were used to distinguish between the total and microbial decomposition. The litter bags were placed in the stream and recovered after 2, 20, 39, 62 and 82 days of incubation. After each collection, we assessed the amount of remaining litter, analysed the nitrogen (N) and phosphorous (P) in the litter, identified the macroinvertebrates and quantified the fungal biomass. Consistent with our hypothesis, we found greater fungal biomass buildup on native leaves than on exotic leaves. However, decomposition rates (k) were species-specific, being the ranking in C-bags (A. altissima = F. angustifolia > P. alba > R. pseudoacacia) slightly different than in F-bags (A. altissima > F. angustifolia > P. alba > R. pseudoacacia). The k in both the C-bags and F-bags were correlated with leaf traits, such as lignin, acid detergent fibre (ADF) and lignin:P. There was not a clear effect of the exotic species on macroinvertebrate variables, but the contribution of macroinvertebrates to litter decomposition was lower in exotic litter than in native litter, as shown by a lower ratio between k in C-bags and k in F-bags (k C : k F ). Our results supported that invasive species might impact both biological colonization and decomposition rates in stream ecosystems by the addition of different quality leaf litter when compared to native vegetation. The differences in the biological colonization may be explained by the NWH, but differences in the decomposition rates were better explained by litter quality.

Diversity of cellulolytic and xylanolytic fungi associated with the digestive tract of aquatic insect larvae in streams of the Amazon Forest and Cerrado in Brazil

“…Thus, knowing the variations in physiognomy of the riparian vegetation in the Amazon Forest and the Cerrado, and that different plant species make up such riparian areas, the mycobiome is expected to reflect those differences. Other work has shown that there are different fungal communities on the leaves of different plant species in streams (Medina-Villar et al, 2015). Therefore, it should be expected that biogeographical factors may determine the intestinal microbiota of the larvae since larvae depend on plant substrates, that provide not only the nutrients but also part of the mycobiome for them.…”

Effects of leaf litter extracts from four tree species on aquatic invertebrates: an ecotoxicological risk assessment approach

“…pseudoacacia) are among the 100 most aggressive invasive exotic species in Europe and Spain (GEIB 2006;DAISIE, 2015) and they frequently invade riparian forests in Central Spain (Castro-Díez et al 2014;Castro-Díez and Alonso 2017). As natives, Populus alba L., (Salicaceae) and Fraxinus angustifolia Vahl, (Oleaceae) were selected, because they naturally occur in the riparian habitats invaded by A. altissima and R. pseudoacacia in Central Spain (Castro-Díez et al 2014;Medina-Villar et al 2015a, 2015b, where the leaf litter sampling sites were located.…”

“…By contrast, leaves with a high amount of calcium may be beneficial for crustacean communities (Ohta et al 2014). Previous studies on the effects of leaf litter in aquatic ecosystems have mainly focused on the structure and function of the invertebrate and the microbial community (Cummins et al 1989;Abelho and Graça 1996;Alonso et al 2010;Bottollier-Curtet et al 2011;Medina-Villar et al 2015a;Santschi et al 2018). Less attention has been paid to the potential toxicological effects of leaf litter to particular species of aquatic organisms (Kamara and Pflugmacher 2007;Krevŝ et al 2013).…”

Leaf litter age regulates the effect of native and exotic tree species on understory herbaceous vegetation of riparian forests

“…In fact, positive effects of litter could surpass the negative ones, favoring plant growth (Meisner, de Boer, Cornelissen, & van der Putten, 2012). Often, invasions by exotic trees introduce litter with different physical-chemical composition, decomposition rates and nitrogen release rates than had the native tree species replaced by them (Incerti et al, 2018;Jo, Fridley, & Frank, 2016;Medina-Villar, Alonso, Vázquez-de-Aldana, Pérez-Corona, & Castro-Díez, 2015a;Medina-Villar, Castro-Díez et al, 2015b), which could affect understory plant communities. However, it is poorly understood if differently aged litter from exotic and native tree species can have different net effects on the germination and growth of understory plants.…”

“…A. altissima and R. pseudoacacia are considered two aggressive invasive trees in Central Spain and worldwide (GEIB, 2006;Pyšek et al, 2009;Sanz-Elorza et al, 2004) and their ability to inhibit plant growth and germination by means of allelopathy has been reported (De Feo, De Martino, Quaranta, & Pizza, 2003;Nasir, Iqbal, Hiradate, & Fujii, 2005;Pisula & Meiners, 2010). Previous studies showed that litter from U. pumila, A. altissima and R. pseudoacacia had different chemical composition and/or decomposition rates than litter from co-existing native species (Alonso, González-Muñoz, & Castro-Díez, 2010;Castro-Díez, González-Muñoz, Alonso, Gallardo, & Poorter, 2009;Castro-Díez, Fierro-Brunnenmeister, González-Muñoz, & Gallardo, 2012;González-Muñoz, Castro-Díez, & Parker, 2013;Medina-Villar et al, 2015a, 2015b. Bioassays using litter leachates from A. altissima and R. pseudoacacia did not consistently show greater phytotoxicity regarding native species (Catalán et al, 2013;Medina-Villar et al, 2017).…”