Simulated and Insect Herbivory Effects on Protein Precipitable Phenolic and Nitrogen Concentrations of Two Legumes.

Protein precipitating polyphenolics (PPP) are phenolic compounds in plants that are believed to serve as a defense against herbivory. Their levels appear to increase when stress is applied to plants. Agronomic studies comparing simulated herbivory with insect herbivory of forages have not focused on plant phenolic response. Our study looked at how varying levels of simulated and differential grasshopper (Melanoplus differentialis) herbivory and plant ontogeny affected 1) PPP concentration and 2) N concentration of panicled tickclover (Desmodium paniculatum; PTC) and sericea lespedeza (Lespedeza cuneata; SL) leaf regrowth. Results show no difference (P=<0.05) in percent N across treatments for PTC, with the exception of 100% clip which was, on average, 1.8 times greater (P=<0.05) than the other treatments. Similarly, percent N in SL was 1.3 times greater (P=<0.05) in the control and the 100% clip than the remaining treatments. There were no differences (P>0.05) in the percent N in the second harvest for either plant, although it was 1.1 times greater (P=<0.05) in SL than in PTC. For the first harvest, percent PPP of the PTC control was greater (P=<0.05) than the other treatments; however, no such difference (P>0.05) was observed in SL. Additionally, there were no differences (P>0.05) in percent PPP across treatments for both plants, with the exception (P=<0.05) of the 100% clip for PTC. These results indicate that varying types of leaf removal do not affect N or PPP in SL and PTC.