Recycling of nitrogen in herbivore feces: plant recovery, herbivore assimilation, soil retention, and leaching losses.
Herbivores directly and indirectly affect ecosystem functioning in forests. Feces deposition is a direct effect that supplies ephemeral N pulses to soils. Herbivore-mediated changes in plant N allocation and uptake are indirect effects that can also influence soil N availability. These effects may interact if defoliation influences the ability of plants to recover fecal N, and this may affect subsequent generations of herbivores. We added (15)N-enriched insect feces (frass) to a series of replicated red oak, Quercus rubra, mesocosms that had been damaged experimentally and then followed the frass N over the course of 2 years. In the first season, some frass N was mineralized in the soil and leached in organic form from the mesocosms within 1 week of deposition. Within 1 month, frass N had been acquired by the oaks and enriched the foliage; late-season herbivores assimilated the frass N within the same growing season. In the second season, herbivore damage from the previous year lowered total leaf N contents and (15)N recovered in the foliage. A subsequent cohort of early-season herbivores fed on this foliage consequently derived less of their N from the previous year's frass, and feral leaf rollers colonized fewer of these saplings. The 0- to 5-cm soil fraction was the largest N sink measured, and 42% of the frass N was recovered in the soil. The results demonstrate that: (1) some frass N can be recycled rapidly into foliage and assimilated by successive cohorts of herbivore within the same season; (2) damage can affect N allocation in the following year's foliage, influencing N availability to and host selection by herbivores; and (3) leaching losses occur soon after deposition but are buffered by soil pools, which are the largest sinks for frass N.
Frost
Christopher J
CJ
Institute of Ecology, University of Georgia, Athens, GA 30602-2202, USA. cfrost@psu.edu
Hunter
Mark D
MD
D000704:Analysis of Variance; D000818:Animals; D017753:Ecosystem; D005243:Feces / Q000737:chemistry*; D005845:Georgia; D007313:Insecta; D013058:Mass Spectrometry; D009587:Nitrogen Isotopes / Q000032:analysis* / Q000493:pharmacokinetics; D018515:Plant Leaves / Q000378:metabolism*; D029963:Quercus / Q000378:metabolism*; D012987:Soil / Q000032:analysis*
D009587:Nitrogen Isotopes; D012987:Soil