Leaf Nitrogen and Protein Precipitable Phenolic Concentration Responses to Insect Herbivory Differ Between Plant Functional Types.

Protein precipitating phenolics (PPP) are condensed tannins with the ability to bind to plant proteins, and are hypothesized to be a plant defense against herbivory.  As such, herbivory intensity may play a role in inducing PPP concentration changes.  This study examined how insect herbivory affects leaf nitrogen and PPP concentrations in two plant functional groups.  Leaves of Neptunia lutea (yellow-puff; YP), Dalea multiflora (round-head dalea; RHD), and Desmanthus illinoinses (Illinois bundleflower; IB), three warm-season perennial herbaceous legumes, and the climbing vine Smilax bona-nox (greenbrier; GB) were collected along three roadside locations in Erath County, TX.  Tissue removal coupled with bite marks was evidence for leaf damage by insects.  Protein precipitable phenolic concentrations were determined by reacting leaf tissue extracts with bovine serum albumin.  Of the legume species, YP and IB consistently had greater (P≤0.05) N concentrations than RHD.  The legume species in order of greatest to least (P≤0.05) insect herbivory damage and PPP concentration were YP, IB, and RHD.  Greenbrier consistently had the lowest (P≤0.05) N concentration and greatest (P≤0.05) insect herbivory damage of the four species.  The PPP concentration of GB was similar (P≤0.05) to that of IB at Site 1, less (P≤0.05) than IB at Site 2, and greater (P≤0.05) than that of RHD at Sites 1 and 2.  Nitrogen concentration appears to have influenced insect herbivory preference within legume species, but additional factors likely played a role in insect preference for GB.  Protein precipitable phenolic concentrations of legumes appear to be positively correlated (R²=0.57) with the degree of insect herbivory received.  Factors other than insect herbivory appear to influence GB PPP concentration.  Differences in nutrient and protein precipitable phenolic allocations seem to exist between the two plant functional groups.  Expanded research is needed to determine additional characteristics of GB influencing insect herbivory.