Additive and non‐additive responses of seedlings to simulated herbivory and drought

Abstract

Drought is a global threat, increasing in severity and frequency throughout tropical ecosystems. Although plants often face drought in conjunction with biotic stressors, such as herbivory or disease, experimental studies infrequently test the simultaneous effects of drought and biotic stress. Because multiple simultaneous stressors may have non-additive and complex effects on plant performance, it is difficult to predict plant responses to multiple threats from research examining one stress at a time. Using an experimental approach in the greenhouse, we investigated potential nonadditivity in seedling growth and survival to simulated drought and herbivory across a phylogenetically diverse pool of ten Hawaiian plant species. Overall, seedlings showed limited tolerance, defined as similar growth and survival in stressed compared with control (non-stressed) plants, to simulated herbivory and drought, with the combined effects of both stressors to be generally additive and negative across species. Significant variation in stress tolerance was detected among species, and species variation was explained, at least in part, by functional traits such that species with larger root/shoot ratios and smaller seeds, tended to demonstrate greater herbivory and drought tolerance. Future research incorporating additional trait analysis and different stressors could shed light on mechanisms underlying seedling stress tolerance and clarify whether additivity, as detected in this study, extends across other combinations of stressors. Such work will provide needed insights into the regeneration of seedlings in tropical forests under threats of herbivory and climate change.

Island plant functional syndromes and competition with invasive species

“…The synchrony and common non‐additivities among multiple global threats to island plants (Barton et al, 2021; Barton & Shiels, 2020; Macinnis‐Ng et al, 2021) challenge identification of the primary drivers of biodiversity losses. Predicting that invasive plants displace native plants by out‐competing them could be an important mechanism, but it is also likely that simultaneous losses in pollination, seed dispersal, reduced population sizes, and climate change contribute directly to the competition dynamics.…”

“…The synchrony and common non-additivities among multiple global threats to island plants (Barton et al, 2021;Barton & Shiels, 2020;Macinnis-Ng et al, 2021) tional traits sampled for representative numbers of species (Table 1).…”

Defoliation in Perennial Plants: Predictable and Surprising Results in Senna spp.

“…Depending on the life history and habitat of the plant, the effects may be expressed the same, or the following, year [ 5 , 6 , 7 ]. Some damaged plants may regrow to the size of uneaten plants; compensation for herbivory [ 8 , 9 ] is facilitated by greater root/shoot ratios [ 10 ], storage organs [ 11 , 12 ], or by upregulation of the plant’s physiological responses and growth [ 13 , 14 ]. Additionally, other plants may regrow even larger or reproduce more than uneaten plants, a phenomenon called over-compensation [ 15 ].…”

Herbivory Amplifies Adverse Effects of Drought on Seedling Recruitment in a Keystone Species of Western North American Rangelands

“…For instance, defoliation caused by herbivory reduces the area for transpiration and, in some plants, increases the reallocation of NSCs to the roots [ 15 ]. These effects may partly offset herbivory’s adverse effects on drought tolerance, leading to non-additive responses where the impact of the two stressors is less than the sum of their individual effects [ 9 , 16 ].…”

“…This damage was often not immediately fatal since seedlings resprouted after herbivory. However, as discussed earlier, results in other species have suggested that herbivory might make A. tridentata seedlings more susceptible to abiotic stresses, particularly drought [ 16 ]. To analyze the plausible effect of herbivory on the seedlings, we placed 10-month-old seedlings of A.tridentata ssp.…”