Drought response in herbaceous plants: A test of the integrated framework of plant form and function

Authors: FUNK, JENNIFER - University Of California, Davis; Larson, Julie Elizab; BLAIR, MEGAN - Chapman University; NGUYEN, MONICA - Chapman University; RIVERA, BEN - University Of California, Davis

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2023
Publication Date: 1/2/2024
Citation: Funk, J.L., Larson, J.J., Blair, M.D., Nguyen, M.A., Rivera, B.J. 2024. Drought response in herbaceous plants: A test of the integrated framework of plant form and function. Functional Ecology. 38(3):679-691. https://doi.org/10.1111/1365-2435.14495.
DOI: https://doi.org/10.1111/1365-2435.14495

Interpretive Summary: Global efforts suggest that a few measurable plant traits can capture critical differences in plant function and performance, but it is unclear whether these can predict drought response in local dryland communities. We found that common leaf and root traits related to resource acquisition and conservation were less important than small plant size and perennial life history in predicting seedling drought survival among herbaceous California grassland species. This advantage may result from smaller seedlings having less photosynthetically-active tissue to maintain, and sheds light on key functional pathways for establishment success during restoration in dryland systems.

Technical Abstract: 1. Multidimensional trait frameworks are increasingly used to understand plant strategies for growth and survival. However, it is unclear if frameworks developed at a global level can be applied in local communities and how well these frameworks—based largely on plant morphological traits—align with plant physiology and response to stress. 2. We tested the ability of an integrated framework of plant form and function to characterise seedling trait variation and drought response among 22 grasses and forbs common in a semi-arid grassland. We measured above-ground and below-ground traits, and survival to explore how drought response is linked to three trait dimensions (resource conservation, microbial collaboration, and plant size) associated with the framework as well as non-morphological dimensions (e.g. physiological traits) that are under-represented in global trait frameworks. 3. We found support for three globally-recognised axes representing trade-offs in strategies associated with tissue investment (leaf nitrogen, leaf mass per area, root tissue density), below-ground resource uptake (root diameter, specific root length), and size (shoot mass). However, in contrast to global patterns, above-ground and below-ground resource conservation gradients were oppositely aligned: root tissue density was positively correlated with leaf N rather than leaf mass per area. This likely reflects different investment strategies of annual and perennial herbaceous species, as fast-growing annual species invested in lower density roots and less nitrogen-rich leaves to maximise plant-level carbon assimilation. Species with longer drought survival minimised water loss through small above-ground size and low leaf-level transpiration rates, and drought survival was best predicted by a principal component axis representing plant size. 4. Contrary to our expectations, drought survival in seedlings did not align with the conservation or collaboration axes suggesting that seedlings with different functional strategies can achieve similar drought survival, as long as they minimise water loss. Our results also show that within local communities, expected trait relationships could be decoupled as some plant groups achieve similar performance through different trait combinations. The effectiveness of species mean trait values in predicting drought response highlights the value of trait-based methods as a versatile tool for understanding ecological processes locally across various ecosystems.