Faster N Release, but Not C Loss, From Leaf Litter of Invasives Compared to Native Species in Mediterranean Ecosystems

Abstract

Plant invasions can have relevant impacts on biogeochemical cycles, whose extent, in Mediterranean ecosystems, have not yet been systematically assessed comparing litter carbon (C) and nitrogen (N) dynamics between invasive plants and native communities. We carried out a 1-year litterbag experiment in 4 different plant communities (grassland, sand dune, riparian and mixed forests) on 8 invasives and 24 autochthonous plant species, used as control. Plant litter was characterized for mass loss, N release, proximate lignin and litter chemistry by 13C CPMAS NMR. Native and invasive species showed significant differences in litter chemical traits, with invaders generally showing higher N concentration and lower lignin/N ratio. Mass loss data revealed no consistent differences between native and invasive species, although some woody and vine invaders showed exceptionally high decomposition rate. In contrast, N release rate from litter was faster for invasive plants compared to native species. N concentration, lignin content and relative abundance of methoxyl and N-alkyl C region from 13C CPMAS NMR spectra were the parameters that better explained mass loss and N mineralization rates. Our findings demonstrate that during litter decomposition invasive species litter has no different decomposition rates but greater N release rate compared to natives. Accordingly, invasives are expected to affect N cycle in Mediterranean plant communities, possibly promoting a shift of plant assemblages.

Invasion of temperate deciduous broadleaf forests by N‐fixing tree species – consequences for stream ecosystems

“…hereafter; e.g. A. melanoxylon, A. longifolia and A. saligna) decompose slowly, accumulating in a thick layer on the soil surface, and promoting continuous N enrichment of the soil (Marchante et al, 2008(Marchante et al, , 2019Incerti et al, 2018). The N-rich soil of Acacia stands changes the N nutrition of nearby non-N-fixing plants that are able to use fixed atmospheric N (Hoogmoed et al, 2014), which can translate into an increase in their foliar N concentration (Hellmann et al, 2011).…”

“…5A). Moreover, the accumulation of large amounts of Acacia litter on soils as a result of slow decomposition, at least for species with phyllodes (Incerti et al, 2018;Marchante et al, 2019), may lead to high amounts of lateral litter inputs to streams during high rainfall events on steep slopes.…”

The N-fixing legume Periandra mediterranea constrains the invasion of an exotic grass (Melinis minutiflora P. Beauv) by altering soil N cycling

“…However, such competition seems to has been overcome by the invasive species by restoring proteolytic activity when it reached the maximum invasion in T4, possibly also via root exudation, stimulating the proteolitic activity. Since soil protease may be derived either from microbial or plant exudation 30 , the increase in this enzyme in both P. mediterranea and in fully invaded M. minutiflora plots (T2 and T4) may also be explained by the capacity of these species to act directly via protease exudation or indirectly through the stimulation of decomposing microbial populations, thereby increasing N release 13 . In previous studies, soil protease activity was increased under both leguminous species 31 and invasive grass species 32 .…”

“…Indeed, Incerti et al . 13 observed a greater N release from litter of invasive species as compared to natives, confirming the high dependence of invasive species on N. Thus, the competitive equilibrium for NH 4 + observed in T3 was disrupted when the invader stimulated the oxidation of NH 4 + to NO 3 − (T4), which was found elevated only in the fully invaded plots, suggesting that it was the main N form used by the invasive plants; this has also been observed by Ribeiro et al . 3 .…”

“…In consequence occurs alterations in nutrient cycling and availability, especially nitrogen 12 . Feedback between plant invasion and nitrogen cycling is often mediated by an increase in N release from the litter 13 and alterations in specific soil microbial communities involved in N cycling 3,14–17 . Inorganic N forms, such as ammonium (NH 4 + ) and nitrate (NO 3 − ), become available to plants after the mineralization of organic compounds containing N, especially those from leguminous plants, through the action of microbial extracellular enzymes.…”