Insect biological control accelerates leaf litter decomposition and alters short‐term nutrient dynamics in aTamarix‐invaded riparian ecosystem

Abstract

Insect herbivory can strongly influence ecosystem nutrient dynamics, yet the indirect effects of herbivore‐altered litter quality on subsequent decomposition remain poorly understood. The northern tamarisk beetle Diorhabda carinulata was released across several western states as a biological control agent to reduce the extent of the invasive tree Tamarix spp. in highly‐valued riparian ecosystems; however, very little is currently known about the effects of this biocontrol effort on ecosystem nutrient cycling. In this study, we examined alterations to nutrient dynamics resulting from beetle herbivory in a Tamarix‐invaded riparian ecosystem in the Great Basin Desert in northern Nevada, USA, by measuring changes in litter quality and decomposition, as well as changes in litter quantity. Generally, herbivory resulted in improved leaf litter chemical quality, including significantly increased nitrogen (N) and phosphorus (P) concentrations and decreased carbon (C) to nitrogen (C:N), C:P, N:P, and lignin:N ratios. Beetle‐affected litter decomposed 23% faster than control litter, and released 16% more N and 60% more P during six months of decomposition, as compared to control litter. Both litter types showed a net release of N and P during decomposition. In addition, herbivory resulted in significant increases in annual rates of total aboveground litter and leaf litter production of 82% and 71%, respectively, under the Tamarix canopy. Our finding that increased rates of N and P release linked with an increased rate of mass loss during decomposition resulting from herbivore‐induced increases in litter quality provides new support to the nutrient acceleration hypothesis. Moreover, results of this study demonstrate that the introduction of the northern tamarisk beetle as biological control to a Tamarix‐invaded riparian ecosystem has lead to short‐term stimulation of nutrient cycling. Alterations to nutrient dynamics could have implications for future plant community composition, and thus the potential for restoration of Tamarix‐invaded ecosystems.

Insect outbreaks alter nutrient dynamics in a southern African savanna: patchy defoliation ofColophospermum mopanesavanna byImbrasia belinalarvae

“…, Frost , Uselmann et al . ), but not in a dry environment, where frass stayed undecomposed on the soil surface (Hunter ).…”

“…Regardless of the amounts of N returned to soil in litter and frass, soils had similar N values (for N, hypothesis 2 did not hold). Elsewhere, lepidopteran outbreaks have resulted in an increase in soil N content in wet environments (Fogal & Slansky 1985, Hollinger 1986, Chapman et al 2003, Frost 2005, Uselmann et al 2011, but not in a dry environment, where frass stayed undecomposed on the soil surface (Hunter 2001).…”

Longer term effects of biological control on tamarisk evapotranspiration and carbon dioxide exchange

“…A greenhouse experiment determined that beetle herbivory damages leaf and stem tissues and produces transient upward spikes in water loss both during the day and nighttime due to wounding and uncontrolled water loss (Snyder, Uselman, Jones, & Duke, 2010). After herbivory, significant beetle damage causes the leaves to desiccate and prematurely senesce (Uselman, Snyder, & Blank, 2011). The net effect on ET will depend on the intensity of beetle defoliation and the ability of tamarisk to regrow leaves.…”

Ecosystem consequences of selective feeding of an insect herbivore: palatability-decomposability relationship revisited

“…However, the present study found no evidence of such a positive relationship, and even showed a negative relationship between palatability and decomposability. However, the plant responses to insect herbivory would be an important factor in determining the relationship between palatability and decomposability through changes in the litter decomposition process (Findlay et al, 1996;Uselman et al, 2011). These findings indicate that L. dispar larvae may accelerate the decomposition process in temperate deciduous forests through selective feeding on plants with relatively low litter decomposability and producing frass with higher decomposability than the litter.…”