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Dryad

Drought tolerant grassland species are generally more resistant to competition

Mount, Hailey1; Smith, Melinda (Mendy)2; Knapp, Alan2; Griffin-Nolan, Robert3; Collins, Scott4; Atkins, David1; Stears, Alice1; Laughlin, Daniel1

Published Nov 27, 2023 on Dryad. https://doi.org/10.5061/dryad.1jwstqk1x

Data files

Nov 27, 2023 version files 2.01 MB

Abstract

  1. Plant populations are limited by resource availability and exhibit physiological trade-offs in resource acquisition strategies. These trade-offs may constrain the ability of populations to exhibit fast growth rates under water limitation and high cover of neighbors. However, traits that confer drought tolerance may also confer resistance to competition. It remains unclear how fitness responses to these abiotic conditions and biotic interactions combine to structure grassland communities and how this relationship may change along a gradient of water availability.
  2. To address these knowledge gaps, we estimated the low-density growth rates of populations in drought conditions with low neighbor cover and in ambient conditions with average neighbor cover for 82 species in six grassland communities across the Central Plains and Southwestern United States. We assessed the relationship between population tolerance to drought and resistance to competition and determined if this relationship was consistent across a precipitation gradient. We also tested whether population growth rates could be predicted using plant functional traits.
  3. Across six sites, we observed a positive correlation between low-density population growth rates in drought and in the presence of interspecific neighbors. This positive relationship was particularly strong in grasslands of the northern Great Plains but weak in the most xeric grasslands. High leaf dry matter content and low (more negative) leaf turgor loss point were associated with high population growth rates in drought and with neighbors in most grassland communities.
  4. Synthesis: A better understanding of how both biotic and abiotic factors impact population fitness provides valuable insights into how grasslands will respond to extreme drought. Our results advance plant strategy theory by suggesting that drought tolerance increases population resistance to interspecific competition in grassland communities. However, this relationship is not evident in the driest grasslands where aboveground competition is likely less important. Leaf dry matter content and turgor loss point may help predict which populations will establish and persist based on local water availability and neighbor cover, and these predictions can be used to guide the conservation and restoration of biodiversity in grasslands.