I've been studying chenopods and their salt bladder system - which is important both physiologically and defensively for the plant - for awhile and with some gentle nudging from my committee, I've been trying to place the chenopod system into a broader context. Namely, what ecologically and evolutionarily differs between a plant which sequesters its chemical defenses (alkaloids, tannins, etc.) in its tissues and one which secretes them onto plant surfaces?
|Glandular trichomes (secretory and non-secretory) cover the surfaces of Trichostema laxum.|
I therefore set up a series of experiments examining these questions. In one, I simulated rain on individuals in a population of Atriplex rosea - a chenopod with defensive exudates - while holding other individuals as controls and rainfall controls (which received water at the base, not on the leaves) and assessed herbivory at the end of the season. Perhaps unsurprisingly, I found a significant increase in herbivory in the group which received rainfall, suggesting that instead of helping these arid, water-starved plants, the rainfall and subsequent removal of exudates (which are entirely water-soluble in A. rosea) actually increased its susceptibility to herbivores.
|Chenopods with external defenses (Atriplex prostrata and rosea) and without (Chenopodiastrum murale) at my field site.|