Tradeoffs and synergies among plant traits can provide insights into constraints on plant form and function, and facilitate predictions of plant responses land management and global change. In semiarid grasslands, traits that regulate plant responses to drought are likely to be of particular importance. It remains unclear, however, how drought resistance traits are related to traits that influence other key functions such as herbivore defense and growth. Drought and herbivory are hypothesized to exert convergent selection pressures, favoring traits such as short stature and basal meristems. This hypothesis has been supported for morphological traits, but is largely untested for structural and physiological traits. Both drought tolerance and escape may be related to plant economic traits, but tests to date have produced mixed results. Here we address these knowledge gaps in two semiarid grasslands of the western Great Plains: the shortgrass steppe and mixedgrass prairie. We describe trait covariation among 37 species from each grassland for a broad set of traits that regulate drought tolerance, drought escape, herbivore defense, and plant economics. We then relate those traits to species’ sensitivity to annual variation in precipitation.
Results/Conclusions
Drought tolerance was closely related to other functions: drought tolerant species (those with low leaf osmotic potential and high leaf dry matter content), were also well defended against herbivores (with tough, lignified leaves), and had ‘slow’ economic traits associated with efficient resource use (low leaf nitrogen, leaf phosphorus, specific leaf area; high stem density). Conversely, species that escaped drought through early senescence had lower drought tolerance, lower herbivore resistance, and ‘fast’ economic traits associated with rapid resource acquisition and use. Leaf dry matter content stands out as a key trait in these semiarid grasslands, likely because it is directly related to drought tolerance, herbivory, and leaf economics. Both drought tolerance and economic traits were also closely related to precipitation sensitivity, with drought tolerant species having similar abundance across years, and ‘fast’ species being much more abundant in wet than dry years. These results demonstrate that plant strategies for coping with limited and variable water are coordinated with both their potential growth rates and their interactions with herbivores. Consequently, it should be possible to use plant traits to predict how changes in land management and climate will influence drought resistance, productivity and forage quality.