Effects of insect mass outbreaks on the C and N balance in forest ecosystems

by Maren Marine Grüning
Doctoral thesis
Date of Examination:2019-05-31
Date of issue:2019-06-27
Advisor:Prof. Dr. Michaela Dippold
Referee:Prof. Dr. Michaela Dippold
Referee:Prof. Dr. Hermann Jungkunst
Persistent Address: http://dx.doi.org/10.53846/goediss-7529

 

 

Files in this item

Name:eDiss Grüning.pdf
Size:3.03Mb
Format:PDF

The following license files are associated with this item:

Abstract

English

Intensive defoliation by phytophagous insects in forests is accompanied by high amounts of organic litter deposition which affects biogeochemical processes in soil, thereby changing nutrient recycling and release as well as the soil microbial community. Besides its effects on soil, defoliation has negative impacts on tree health, thus changing the trees’ metabolic processes and altering tree-soil interactions. In this thesis mass outbreaks of the nun moth (Lymantria monacha L.) and the pine-tree lappet (Dendrolimus pini L.) in two Scots pine forests (Pinus sylvestris L.) and two non-infested control forests in the federal state of Brandenburg, Germany, were investigated. The C and N inputs (solid and liquid) and the outputs (soil solution and gaseous soil emissions) during the outbreak years were quantified. Effects of soil C and N pools on microbial populations were quantitatively and qualitatively characterized by DNA-based methods (qPCR and DGGE followed by DNA sequencing) in the organic layers, the mineral soil, and other forest compartments. An additional microcosm incubation experiment with different organic matter treatments examined the effects of insect feces compared to needle litter on soil CO2 and N2O fluxes. Consequences of insect induced defoliation for tree nutrition and tree health were detected by a 15N uptake experiment of fine roots and the quantification of different N metabolites in needles and fine roots of infested and non-infested Scots pines. Further, effects on the trees phyllosphere and the understorey vegetation were detected by the above-mentioned DNA-based methods. The findings demonstrate that C and N pools, fluxes and turnover processes in the tree-soil-atmosphere continuum are heavily affected by insect mass outbreaks. Increased organic input triggered a change in microbial abundance and resulted in increased losses of C and N. At the same time, tree nutrition, phyllospheric colonization by microorganisms and mycorrhizal symbiosis is altered by the insect outbreaks. These results illustrate the complexity of process and flux modifications by insects and reveal the importance to evaluate changes differentiated temporally and spatially in multiple forest compartments to assess feedback links at ecosystem scale.
Keywords: Carbon; Nitrogen; Pinus sylvestris; Lymantria monacha; Brandenburg; Disturbances; Soil microbiology; Forest; Insects; Phyllosphere; N uptake; Dendrolimus pini; CO2; N2O; qPCR; DGGE; Scots pine; Pests; Global warming
 
Statistik