TY - JOUR

T1 - Production in aquatic macrophyte communities

T2 - A theoretical and empirical study ofthe influence of spatial light distribution

AU - Binzer, Thomas

AU - Sand-Jensen, Kaj

PY - 2002

Y1 - 2002

N2 - Many terrestrial plant canopies regulate spatial patterns in leaf density and leaf inclination to distribute lightevenly between the photosynthetic tissue and to optimize light utilization efficiency. Sessile aquatic macrophytes,however, cannot maintain the same well-defined three-dimensional structure because of the strong drag and shearforces of moving water. This difference in canopy structure has been suggested to account for the three- to fivefoldhigher gross production rates in terrestrial than aquatic communities. To evaluate the effect of community structurein aquatic habitats, we combined a simple mechanistic model and empirical measurements on artificially structuredmacroalgal communities (Ulva lactuca) with varying thallus absorptance and community density. Predicted andmeasured values corresponded closely and revealed that gross production in high-light environments was markedlyenhanced by a vertical orientation of thalli when absorptance and community density were both high. This resultimplies that aquatic macrophytes of high thallus absorptance and community density exposed to high light arelimited in attaining high gross production rates because of their inability to distribute photons evenly between thephotosynthetic tissues. As scattering and attenuation in the water column increase, the effect of thallus structure onproduction declines and thin transparent macrophytes are more efficient at utilizing light than thick opaque macrophytes.The results confirm that inefficient distribution of light can account for the low community productionrates in aquatic habitats and the depth distribution of form-functional groups of macroalgae with different canopystructure.

AB - Many terrestrial plant canopies regulate spatial patterns in leaf density and leaf inclination to distribute lightevenly between the photosynthetic tissue and to optimize light utilization efficiency. Sessile aquatic macrophytes,however, cannot maintain the same well-defined three-dimensional structure because of the strong drag and shearforces of moving water. This difference in canopy structure has been suggested to account for the three- to fivefoldhigher gross production rates in terrestrial than aquatic communities. To evaluate the effect of community structurein aquatic habitats, we combined a simple mechanistic model and empirical measurements on artificially structuredmacroalgal communities (Ulva lactuca) with varying thallus absorptance and community density. Predicted andmeasured values corresponded closely and revealed that gross production in high-light environments was markedlyenhanced by a vertical orientation of thalli when absorptance and community density were both high. This resultimplies that aquatic macrophytes of high thallus absorptance and community density exposed to high light arelimited in attaining high gross production rates because of their inability to distribute photons evenly between thephotosynthetic tissues. As scattering and attenuation in the water column increase, the effect of thallus structure onproduction declines and thin transparent macrophytes are more efficient at utilizing light than thick opaque macrophytes.The results confirm that inefficient distribution of light can account for the low community productionrates in aquatic habitats and the depth distribution of form-functional groups of macroalgae with different canopystructure.

M3 - Journal article

VL - 47

SP - 1742

EP - 1750

JO - Limnology and Oceanography

JF - Limnology and Oceanography

SN - 0024-3590

IS - 6

ER -