COS 38-1 - Local perennial plants affect the occurrence and fitness related traits of annual grasses along an aridity gradient

Background/Question/Methods

Positive plant interactions are well-known drivers of plant community dynamics, especially in stressful landscapes. As environmental stressors increase, it is crucial to examine mechanisms such as positive plant interactions that may influence adaptation at both the macroclimate and microclimate levels. Less well-known is whether interspecific positive interactions can drive differences in the spatial association and intraspecific variation of annual grasses. Here we investigate the responses of two closely related annual grass species Brachypodium hybridum and Brachypodium distachyon to neighboring perennial plants at two different spatial scales.

We first examine how the spatial association and phenotypic trait differences of Brachypodium to neighboring perennial plants vary between ten sites along an aridity gradient in southeastern Spain. Further, under controlled conditions, and from seed collected only from our most arid site, we tested if any fitness-related trait differences were heritable.

Results/Conclusions

We found that as the degree of aridity increases, both Brachypodium species are less associated with neighboring perennial plants t(8) = 2.4, p< 0.05. We also found that plants collected underneath perennial plants in natural populations were taller t(203) = -7.9, p < 0.001, had more spikelets t(204) = -2.4, p < 0.05, and had higher seed numbers t(151) = -2.2, p < 0.05 than plants found outside perennial plants. Further, from the F2 generation of 600 plants from seed that we had collected at our most arid site, we found that plants found underneath canopy cover had higher seed output (β= -0.45, p< 0.05) and higher seed weights t(53) = -3.1, p < 0.01) than plants that had originated from outside the canopy cover.



Based on these findings, we conclude that in patchy landscapes dominated by perennial plants, both B.hybridum and B. distachyon respond, in partly unexpected ways, to both the macroclimate (aridity gradient) and the microclimate as provided by neighboring perennial plants.