Effects of Epiphytes on Leaf Photosynthesis

Seagrass leaves are colonized by a diverse array of epiphytes (Borowitzka et al., Chapter 19) that make significant contributions to the overall productivity of seagrass ecosystems (Penhale, 1977; Mazzella

3.21 - 4.81 | | 2000.1 - 3000.1 4.81 - 6.41 | j 3000.1 - 4000,1 6.41 - 8.01 ^m 4000.1 - 5000.1

3.61 - 11.21 [ 1 6000.1 - 7000.1 11.21- 12.81 7000.1 - 8000.1 12.81 - 14.41 [ S000 1 - 9321.872

Fig. 9. Predicted eelgrass densities and depth distribution of eelgrass shoots in Dumas Bay, Washington, USA for different scenarios of water clarity. (A) 50 mg m-3 chlorophyll a, 25 mg L-1 total suspended solids. (B) 30 mg m-3 chlorophyll a, 25 mg L-1 total suspended solids. (C) 30 mg m-3 chlorophyll a, 10 mg L-1 total suspended solids. From Berry et al. (2003). Bathymetry is indicated by blue shading. Unvegetated tidal flats are illustrated in brown.

Fig. 10. Relationship between seagrass photosynthesis and seawater pH derived from manipulation of dissolved aqueous CO2 concentrations. Redrawn from Invers et al. (2001).

I I Existing Beds (110 shoots m-2) I I >150 shoots m-2 □ 110 to 150 shoots m-2 I I <110 shoots m-2

Fig. 11. Predicted effect of increased ambient CO2 concentrations on eelgrass distributions in Elkhorn Slough, California, USA. Seal Bend is the O-shaped region in the middle of the channel. Elkhorn Slough drains westward into Monterey Bay (left side) from an upland watershed to the east (right side). From Zimmerman and Palacios (2002).

Fig. 11. Predicted effect of increased ambient CO2 concentrations on eelgrass distributions in Elkhorn Slough, California, USA. Seal Bend is the O-shaped region in the middle of the channel. Elkhorn Slough drains westward into Monterey Bay (left side) from an upland watershed to the east (right side). From Zimmerman and Palacios (2002).

and Alberte, 1986; Klumpp et al., 1992). The complex biofilms produced by the growth of these organisms creates physical barriers to light absorption, gas exchange (particularly CO2) and nutrient uptake (e.g. Sand-Jensen, 1977; Bulthuis and Woelkerling, 1983; Van Montrfrans et al., 1984), and epiphyte accumulation has been implicated as an important agent contributing to the decline of seagrass meadows in eutrophic waters (Hemminga and Duarte, 2000). It is now possible to measure the optical properties of intact leaf-epiphyte communities accurately and quantify their specific effects on leaf photosynthesis (Drake et al., 2003). Epiphytes exhibit varying degrees of chlorophyll-like absorption spectra, preferentially absorbing blue and red light. The resulting spectral bias imposed on the light actually reaching the seagrass leaf produced a two-fold greater reduction in leaf photosynthesis calculated from PUR relative to similar calculations based on PAR. Important challenges, however, remain with regard to the incorporation of leaf epiphytes into the vertically resolved model described here. In particular, epiphytes distributions are characterized by strong spatial gradients within and among leaves that also show significant temporal variability (Bulthuis and Woelkerling, 1983; Kirchmanetal., 1984; Tornblom and Sondergaard, 1999). These relationships, their seasonal variations and responses to environmental change (eutrophication, CO2 increase, etc.) deserve more extensive quantification.

Was this article helpful?

0 0

Post a comment