Insect Herbivory Increases Litter Quality and Decomposition: An Extension of the Acceleration Hypothesis

Abstract

Herbivore alteration of litter inputs may change litter decomposition rates and influence ecosystem nutrient cycling. In a semiarid woodland at Sunset Crater National Monument, Arizona, long-term insect herbivore removal experiments and the presence of herbivore resistant and susceptible pinyon pines (Pinus edulis) have allowed characterization of the population-and community-level effects of herbivory. Here we report how these same two herbivores, the mesophyll-feeding scale insect Matsucoccus acalyptus and the stem-boring moth Dioryctria albovittella alter litter quality, dynamics, and decomposition in this ecosystem. We measured aboveground litterfall, litter chemical composition, and first-year litter decomposition rates for trees resistant and susceptible to both herbivores and for susceptible trees from which herbivores had been experimentally removed for 16-18 years. Both herbivores significantly increased nitrogen concentration and decreased lignin:nitrogen and carbon:nitrogen ratios of aboveground litter. Herbivory by scale insects also increased litter phosphorus concentration and annual needle litterfall mass. Consistent with its increased chemical quality, litter from herbivore-susceptible trees decomposed more rapidly in the first year. These results suggest that herbivory may increase nutrient cycling rates in this system by altering the chemical quality of litter, a mechanism that augments the nutrient acceleration hypothesis. The distribution of trees resistant and susceptible to the two herbivores at our site, and their associated variation in litter quality and decomposition, likely creates a mosaic of litter quality and nutrient cycling rates at the landscape scale. Further, because the differences in litter quality are associated with tree resistance and susceptibility traits, our findings are among the first to establish that intraspecific genetic variation may affect ecosystem function.

Insect herbivory, organic matter deposition and effects on belowground organic matter fluxes in a central European oak forest

“…insect pellets, honeydew) (Chapman et al 2003;Hunter 2001;Schowalter et al 1991;Stadler et al 2001). Through this transformation, herbivorous insects may promote mineralisation activity, leading to accelerated decomposition rates and hence to an intensified release of nutrients and carbon (Ritchie et al 1998;Chapman et al 2003;Lovett and Ruesink 1995;Stadler et al 2001;le Mellec et al 2009). How strongly insect mass attacks can impact forest stands on the ecosystem level was demonstrated by the study of Kurz et al (2008), where the devastation of millions of hectares by a bark beetle infestation led to an enormous increase of CO 2 emissions during the growing season.…”

Coconut Leaf Age and Coconut Rhinoceros Beetle Herbivory Influence Leaflet Nutrients, Metals, and Lignin

“…For example, carbon/nitrogen and lignin/nitrogen were reduced by CRB herbivory of the coconut leaves (Table 4). These litter traits are among those that often predict a more rapid litter decomposition speed and they have been highlighted as traits that insect herbivory can directly influence [5]. Based on the combined results, CRB herbivory of coconut leaves will speed up decomposition and nutrient turnover during leaf afterlife effects in agroforestry settings.…”

“…The pH was 7. 5 These field methods ensured that the known factors that may influence the leaf chemistry were controlled to the selection bias during the test of the CRB damage. The soils were homogeneous, all leaves were full sun emergent leaves, their position along the massive rachis was homogeneous, the tree height was constrained, and seasonal effects were not a factor due to the mid-September collection dates.…”

“…The direction and extent of changes to the litter quality caused by insect herbivory are not universal. Following herbivory, herbivory, the litter quality and the speed of litter decomposition can be increased or decreased, depending on the host-herbivore combination [5][6][7]. Therefore, information on the leaf and litter chemistry changes following CRB herbivory is needed to better inform horticultural decisions and to improve the management of plant nutrition in low input agroforest systems containing coconut trees with CRB infestations.…”

Agroenergy Crops Influence the Diversity, Biomass, and Guild Structure of Terrestrial Arthropod Communities

“…Paralleling community-level responses, we found that herbivore biomass was enhanced in more diverse and forest-dominated landscapes. Herbivores are not known to directly control grass biomass in prairie systems but may control forb biomass and have important indirect effects [49], such as increasing litter quality and decomposition [50], contributing nutrients [51], and changing the throughfall chemistry [52] and energy demands [53] of damaged plants.…”