A mechanistic basis for underyielding in phytoplankton communities

Area of Science:

• Aquatic ecology
• Ecosystem functioning
• Biodiversity research

Background:

• Species richness often enhances plant community biomass production through overyielding.
• Overyielding is typically observed in terrestrial and submerged plant communities where resource use complementarity is significant.
• The applicability of these findings to free-floating phytoplankton, with limited spatial resource partitioning, remains unclear.

Purpose of the Study:

• To investigate if biodiversity enhances biomass production in free-floating phytoplankton communities.
• To determine how species and community biovolume relate to the number of functional groups in phytoplankton.
• To test the hypothesis that increased functional groups promote overyielding in phytoplankton.

Main Methods:

• Aquatic microcosm experiments were conducted using eight phytoplankton species from four functional groups.
• Community biovolume was measured in relation to the number of functional groups present.
• Monocultures and mixtures were analyzed to assess overyielding and underyielding effects.

Main Results:

• Overyielding was not detected in any of the tested algal communities.
• Total community biovolume decreased as the number of functional groups increased, indicating underyielding.
• Underyielding was primarily driven by a negative dominance effect, where fast-growing species inhibited slower-growing, high-biovolume species.

Conclusions:

• Biodiversity-ecosystem functioning relationships observed in substrate-bound plants may not directly translate to free-floating phytoplankton.
• Resource use complementarity and functional diversity played minor roles in phytoplankton communities, likely due to uniform resource distribution.
• Community biovolume in phytoplankton is largely dictated by the identity of dominant species rather than functional diversity.