Is a leaf life span enough to display changes on developmental instability and nitrogen after simulated herbivory?

Abstract

Herbivory is a main source of plant damage and injured plants might present decrements in nutrients, delayed growth and low reproductive outputs. Therefore, herbivory can be considered a stressful agent to plants. In this study, we investigated short-term changes in stress and nutrient levels of the invasive plant species Tithonia diversifolia (Asteraceae) after simulated herbivory. Parameters such as leaf fluctuating asymmetry (FA, a measure of plant stress, also known as developmental instability) and nitrogen levels were compared between control and treated plants reared in a greenhouse. We expected high levels of FA and significant changes in nitrogen in injured leaves. FA was assessed by measuring the right and left sides of leaves, from the leaf edge to the midrib, at the middle point of the leaves; nitrogen was evaluated through the Kjeldahl method. Though non-significant, at the end of the study, injured leaves were 22% more asymmetric than control leaves, and before-after comparisons revealed that FA increased by 33% in leaves after leaf damage. In addition, FA was positively and significantly related to leaf area loss. Nitrogen did not present changes after simulated herbivory. The control group showed non-significant changes in FA and nitrogen. FA was concluded to be a rapid estimator of plant stress following leaf damage, as during its short lifespan (45days), leaves displayed tentatively increased developmental instability. We consider that leaf damage is a predictor of plant developmental instability and that FA can be used to detect and compare stress levels in plants after herbivory damage.