Effect of Herbivory and Plant Species Replacement on Primary Production

We tested the hypothesis that herbivory accelerates nutrient cycling through nutrient-rich soils and decelerates nutrient cycling through nutrient-poor soils in a welldrained arctic tundra heath by measuring effects of herbivory on soil and plant properties in control areas and areas treated with NPK fertilizer. The impact of herbivores was studied with two types of exclosures, one excluding reindeer and the other excluding both rodents and reindeer. We predicted that herbivores would enhance soil microbial processes in the fertilized areas, but retard them in the unfertilized ones.Microbial respiration and microbial C were significantly lower in grazed areas than in herbivore exclosures in both unfertilized and fertilized treatments, indicating that herbivores limit the C available for the soil microbes. Microbial N was significantly increased in the exclosures in the fertilized treatment, but there were no effects in the unfertilized one. This reflects both an increase in resources by fertilization and the effect of herbivores on microbial N acquisition: there was surplus N in the fertilized areas to be immobilized by microbial biomass only when access by herbivores was prevented. Thus, mammalian grazers affect the resource coupling between the plant and microbial trophic levels. Fertilization did not affect the soil inorganic, organic, or microbial N contents, or litter decomposition rates, but it significantly increased soil and microbial P. Microbial C was significantly decreased by fertilization, contradicting some earlier fertilization studies in the arctic.One reason for deceleration of soil nutrient cycling in our study area may be that herbivory by both reindeer and rodents occurs mainly outside the growing season; hence, mammalian waste products do not contribute to soil nutrient availability at the times of highest nutrient demands by plants. In addition, grazing during reindeer migrations is likely to cause net resource output from the system.

Section: Interactions Among Grazing Plant Species Composition and Smentioning

confidence: 99%

Soil Microbial Responses to Herbivory in an Arctic Tundra Heath at Two Levels of Nutrient Availability

Stark¹,

Grellmann²

2002

“…Their selective feeding can stimulate or reduce decomposition, partially depending on the herbivores' preferred foliage. For example, if herbivores prefer to consume faster decomposing plants, slower decomposing, poorer quality plants increase in abundance, resulting in poorer resources for decomposers, and thereby decreasing decomposition rates (Pastor et al 1988, Brown and Gange 1992, de Mazancourt and Loreau 2000, Schmitz et al 2000, Feeley and Terborgh 2005. The opposite pathway can also occur where herbivore preference for slower decomposing plants can increase rates of decomposition (McNaughton 1985, Holland 1995, Belovsky and Slade 2000, 2002.…”

Section: Introductionmentioning

confidence: 99%

Tropical herbivorous phasmids, but not litter snails, alter decomposition rates by modifying litter bacteria

Prather

Belovsky

Cantrell

et al. 2018

Consumers can alter decomposition rates through both feces and selective feeding in many ecosystems, but these combined effects have seldom been examined in tropical ecosystems. Members of the detrital food web (litter-feeders or microbivores) should presumably have greater effects on decomposition than herbivores, members of the green food web. Using litterbag experiments within a field enclosure experiment, we determined the relative effects of common litter snails (Megalomastoma croceum) and herbivorous walking sticks (Lamponius portoricensis) on litter composition, decomposition rates, and microbes in a Puerto Rican rainforest, and whether consumer effects were altered by canopy cover presence. Although canopy presence did not alter consumers' effects, focal organisms had unexpected influences on decomposition. Decomposition was not altered by litter snails, but herbivorous walking sticks reduced leaf decomposition by about 50% through reductions in high quality litter abundance and, consequently, lower bacterial richness and abundance. This relatively unexplored but potentially important link between tropical herbivores, detritus, and litter microbes in this forest demonstrates the need to consider autotrophic influences when examining rainforest ecosystem processes.

“…Insect herbivory can alter nutrient flux from aboveground to belowground systems via several pathways (Bardgett andWardle 2003, Schowalter 2006) including additions of frass and carcasses (Frost and Hunter 2004) and changes in the quantity and chemistry of litter inputs (Hunter 2001). Changes in litter chemistry can occur when herbivores disproportionally remove high-quality forage (Ritchie et al 1998, de Mazancourt andLoreau 2000) or, more directly, through herbivore-induced changes in the nutrient or secondary chemical composition of infested plants that carry over to the litter. This ''afterlife'' effect has received relatively little attention, but recent work suggests it may be common and strong enough to significantly influence nutrient dynamics (Chapman et al 2003, 2006, Schweitzer et al 2005.…”

Section: Introductionmentioning

confidence: 99%

Long‐term Burning Interacts With Herbivory to Slow Decomposition

Kay

Mankowski

Hobbie

2008

Fires can generate spatial variation in trophic interactions such as insect herbivory. If trophic interactions mediated by fire influence nutrient cycling, they could feed back on the more immediate consequences of fire on nutrient dynamics. Here we consider herbivore-induced effects on oak litter quality and decomposition within a long-term manipulation of fire frequency in central Minnesota, USA. We focused on bur oak (Quercus macrocarpa) trees, which are common across the fire frequency gradient and are often heavily infested with either lace bugs (Corythuca arcuata) or aphids (Hoplochaithropsus quercicola). We used targeted exclusion to test for herbivore-specific effects on litter chemistry and subsequent decomposition rates. Lace bug exclusion led to lower lignin concentrations in litterfall and subsequently accelerated decomposition. In contrast, aphid exclusion had no effect on litterfall chemistry or on decomposition rate, despite heavy infestation levels. Effects of lace bug herbivory on litterfall chemistry and decomposition were similar in burned and unburned areas. However, lace bug herbivory was much more common in burned than in unburned areas, whereas aphid herbivory was more common in unburned areas. These results suggest that frequent fires promote oak-herbivore interactions that decelerate decomposition. This effect should amplify other influences of fire that slow nitrogen cycling.