VARIABLE IMPACT OF SOIL NEMATODES ON ABOVE-GROUND HERBIVORES OF APOCYNUM CANNABINUM AND ASCLEPIAS SYRIACAPublic
Plants must constantly deal with herbivory from both above and below-ground feeders. One class of below-ground feeders are plant-parasitic nematodes (PPNs). Interaction of plant-parasitic nematodes on crop plants is well studied but poorly understood in non-agriculture settings. Studies that have looked at a type of PPN called the root-knot nematode in milkweed showed a marked decrease in plant defense chemicals as well as a decrease in aphid (a sap-sucking insect) population when conducted in a greenhouse study. The successional fields at Blandy Experimental Farm (BEF) are intentionally left to natural growth and development of plants and provided a unique opportunity to see if PPNs increase plant toxins in the field and subsequently change herbivory by leaf chewing insects. I tested this assumption for both milkweed and dogbane, which have similar chemical defenses. I extracted and counted nematodes from soil around 61 milkweed or dogbane plants in the field, as well as collected data on herbivore presence and measures of plant height, latex production, total leaf area consumed on study plants, and leaf specific mass. I found that the presence of nematodes was significantly lower in the rhizosphere of dogbane compared to milkweed and that nematodes were positively correlated to total leaf area consumed by above-ground herbivores, which is the opposite of what has been found in greenhouse settings. This research is the first to examine nematodes in natural old field settings and informs the understanding of above and below-ground interactions.
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