Figure 2.

Results of meta-analysis that suggest response to Nr additions in the form of NO3− leads to a smaller positive effect on aboveground biomass of Spartina plants than when other forms of nitrogen enrichment are added. (a) Log response ratios of studies that report response to Nr in enriched compared with reference salt marsh samples separated by the form of N added. (b) Box and whisker plot of the log response ratios reported in panel (a). The center line represents the median response, upper and lower edges of the box represent the upper and lower quartiles, respectively, and the whiskers indicate the highest and lowest values. (c) Log response ratio plotted as a function of the amount of N added. (d) Aboveground biomass by different Spartina ecotypes to the direct addition of NO3− (brown) and NH4⁺ (yellow) under identical experimental conditions. Source: The data were plotted from table 1 in Mendelssohn (1979a).