. The ecology of delta marshes of coastal Louisiana : a community profile . 500 Plan Biomass Plant Heighl 5 ID 15 20 DISTANCE FROM STREAM (m) 70 50 I O z < -30 10 Figure 44. Variation in total aboveground biomass and height of Spartina a1terni flora with distance inland from the marsh edge in a Barataria basin salt marsh (Buresh 1978). Live y//A â Total ^H 2000 1 1 1800 1 1 '^ 1600 1 1400 w 1200 3 1000 S 800 < a 600 o 5 400 200 /; ?1 INLAND POSITION ON TRANSECT GULF Figure 45. Gulf-inland variations in live and total biomass in Spartina alterniflora marshes (Gosselink et al. 1977y] The t
. The ecology of delta marshes of coastal Louisiana : a community profile . 500 Plan Biomass Plant Heighl 5 ID 15 20 DISTANCE FROM STREAM (m) 70 50 I O z < -30 10 Figure 44. Variation in total aboveground biomass and height of Spartina a1terni flora with distance inland from the marsh edge in a Barataria basin salt marsh (Buresh 1978). Live y//A â Total ^H 2000 1 1 1800 1 1 '^ 1600 1 1400 w 1200 3 1000 S 800 < a 600 o 5 400 200 /; ?1 INLAND POSITION ON TRANSECT GULF Figure 45. Gulf-inland variations in live and total biomass in Spartina alterniflora marshes (Gosselink et al. 1977y] The third example shows the increase in biomass from the coast inland. The first two examples illustrate complex gradients in the physiological sense; the last may be due simply to a gradient of decreasing salinity. Physiologically a plant growing in a marsh has to solve one or both of two problems. All marsh plants are periodically exposed to high salt concentrations and to anoxic soil conditions and accompanying sediment chemical changes. As indicated earlier, the dominant salt and brackish marsh plants are salt tolerant rather than salt requiring. Generally, growth is depressed as salt concentration increases (Parrondo et al. 1978). One reason for this is that the high concentration of salt surrounding the roots makes it osmotically difficult for plant cells to absorb water. The plant could get around this problem by simply absorbing salt to decrease the internal osmotic potential. But this leads to biochemical problems because the Na and CI ions interfere with the activity of many enzymes, probably through steric effects. For example,the enzyme-mediated absorption of the radio- tracer, rubidium (Rb) by excised roots of S^. al terniflora and D. spicata is strongly inhibited by salt in the root medium (Figure 46). This may occur be- cause Na replaces Ca, which has been shown to stimulate ion uptake, on the cell membranes. Plants have adapted to the problems posed by salt in a num
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