Tree leaf litter composition and nonnative earthworms influence plant invasion in experimental forest floor mesocosms

Abstract

Dominant tree species influence community and ecosystem components through the quantity and quality of their litter. Effects of litter may be modified by activity of ecosystem engineers such as earthworms. We examined the interacting effects of forest litter type and earthworm presence on invasibility of plants into forest floor environments using a greenhouse mesocosm experiment. We crossed five litter treatments mimicking historic and predicted changes in dominant tree composition with a treatment of either the absence or presence of nonnative earthworms. We measured mass loss of each litter type and growth of a model nonnative plant species (Festuca arundinacea, fescue) sown into each mesocosm. Mass loss was greater for litter of tree species characterized by lower C:N ratios. Earthworms enhanced litter mass loss, but only for species with lower C:N, leading to a significant litter 9 earthworm interaction. Fescue biomass was significantly greater in treatments with litter of low C:N and greater mass loss, suggesting that rapid decomposition of forest litter may be more favorable to understory plant invasions. Earthworms were expected to enhance invasion by increasing mass loss and removing the physical barrier of litter. However, earthworms typically reduced invasion success but not under invasive tree litter where the presence of earthworms facilitated invasion success compared to other litter treatments where earthworms were present. We conclude that past and predicted future shifts in dominant tree species may influence forest understory invasibility. The presence of nonnative earthworms may either suppress of facilitate invasibility depending on the species of dominant overstory tree species and the litter layers they produce.

Comparative study of earthworm communities, microbial biomass, and plant nutrient availability under 1-year Cajanus cajan (L.) Millsp and Lablab purpureus (L.) Sweet cultivations versus natural regrowths in a guinea savanna zone

“…These results are in line with observations made in previous studies which showed that plant species influence soil organisms through the quantity and the quality of their litter (Gonzàlez and Zou 1999;Belote and Jones 2009;Norgrove et al 2009). In both trials, the density of earthworms was responsive to the introduction of legumes, particularly the detritivores (name- ly D. saliens and D. baeri) and polyhumics (such as S. zielae).…”

“…Based upon the classification made by Jamaludheen and Kumar (1999) and considering N contents in litters of this study, leaf litter from L. purpureus and C. odorata can be considered as N rich (N>15 mg g −1 ) while that of C. cajan was fairly N rich (10 mg g −1 <N<15 mg g −1 ) and that from the savanna, N poor (N<0.10 mg g −1 ). These N content levels have great influence on soil biological activity and nutrient cycling (Tian et al 1993;Belote and Jones 2009).…”

“…Since there was a chance that multivariate correlations between leaf litter quality parameters and earthworm densities exist (Tian et al 1993;Belote and Jones 2009), multiple regressions using General Linear Model procedures were performed on the data to determine how much variation in available P or N can be explained by litters or earthworms. All these statistical analyses were carried out using STATISTICA 6.0 Software program (Statistica, Tulsa, OK, USA).…”

“…However, their efficiency in nutrient cycling depends upon abiotic factors such as the characteristics of organic residues (Knapp et al 2011). In this respect, earthworms which are recognized as significantly impacting nutrient cycling and soil fertility (Blanchart et al 1997;Fonte et al 2009;Le Bayon and Milleret 2009) were reported to be influenced by the diversity (Tondoh et al 2007), the quantity (Norgrove et al 2003;Curry et al 2008), and the quality (Tian et al 1993;Belote and Jones 2009;Norgrove et al 2009) of plant litters. Therefore, it would be highly relevant to examine the influence of the introduced legumes on the communities and the activities of these organisms.…”

Mutualisms: Key Drivers of Invasions … Key Casualties of Invasions

“…The most dramatic changes have been documented in island ecosystems such as those on Hawaii (Waring et al 1993 ) and New Zealand dependence are the most robust against disturbances promoting extinctions (Ollerton et al 2003 ), such results suggest that the invasive species and its mutualists might be more resistant to disturbances, which would increase the probability of permanence and survival of such invasive in the network. This, added to a preferential interaction among invasive species, might lead to invasional meltdown, precipitating an even higher impact of the invasion on the native community, similar to those reported for other systems and interactions (see, for example, Grosholz 2005 ;Griffen et al 2008 ;Belote & Jones 2009 ).…”