Impacts of insect biological control on soil N transformations in Tamarix-invaded ecosystems in the Great Basin, USA

We investigated impacts of biocontrol of Tamarix spp. by Diorhabda carinulata on soil nitrogen (N) transformations by surveying organic and mineral soils from three sites. Potential net N mineralization was assayed using laboratory incubations. Results partially supported our hypothesis that herbivory would result in stimulated net N mineralization rates after one year of herbivory exposure, and did not support our hypothesis that herbivory would result in a sustained increase in rates after several years of exposure. Short-term effects differed by site, likely influenced by differences in prevailing soil N status, with net mineralization stimulated at a low fertility site but not at a high fertility site. In the longer-term, there was no impact on overall net N mineralization rates, even though there was a trend towards greater N immobilization in mineral soil. This may result from declining organic matter inputs to soil due to progressive growth limitations from herbivore-induced stress. Results suggest soil N availability will increase in the short-term and eventually decrease in the longer-term at low fertility sites, while soil N availability will not be impacted by herbivory at high fertility sites. Widespread management implications will require further research at sites spanning a range of edaphic characteristics.

► We studied short and longer-term Tamarix biocontrol impacts on soil N availability.
► Short-term, N mineralization was stimulated at a low but not high fertility site.
► Longer-term, there was a trend towards greater N immobilization in mineral soils.
► However, there was no overall long-term effect when including organic soils.
► Results suggest that impacts of Tamarix biocontrol depend on site fertility.