Differing selection in alternative competitive environments: shade-avoidance responses and germination timing.

Area of Science:

• Plant Ecology
• Evolutionary Biology
• Agricultural Science

Background:

• Stem elongation in plants is a key adaptation for light competition.
• Interspecific competition varies with competitor species, influencing the timing and benefits of elongation.
• The plastic response of stem elongation to competition is crucial for plant fitness.

Purpose of the Study:

• To investigate the role of stem elongation timing in plant adaptation to interspecific competition.
• To evaluate selection pressures on stem elongation at different life stages and in combination with germination timing.
• To understand how different competitive environments (cornfields, soybean fields, weedy sites) affect selection on velvetleaf (Abutilon theophrasti) elongation.

Main Methods:

• Phenotypic selection analyses were used to assess selection on stem elongation.
• Path analysis evaluated the combined effects of germination timing and elongation on fitness.
• Velvetleaf were grown in three distinct environments mimicking natural populations.

Main Results:

• Selection favored increased seedling-stage elongation in high-density weedy sites.
• Selection favored increased elongation at later nodes in soybean fields, allowing plants to overtop competitors.
• Selection disfavored late elongation in cornfields, where velvetleaf cannot overtop corn.
• Early emergence combined with stem elongation conferred the highest fitness in weedy environments.
• Late emergence favored reduced elongation, likely due to inability to overtop neighbors.

Conclusions:

• The timing of stem elongation is a critical factor in competitive success.
• Different competitive environments exert selection for stem elongation at distinct life-history stages.
• Plant emergence timing significantly interacts with stem elongation to influence fitness and competitive ability.