Linking the Phosphorus and Carbon Cycles

Availability Really Limit Moist Tropical Forest Productivity  

FIGURE 2 The relationship between leaf photosynthetic rate and leaf phosphorus concentration of tropical trees (from Cromer et at., 1993 Raaimakers et al., 1995 Raich etal, 1995, Lovelock t fd/., 1997). 

2 Tropical Plant Responses to Increases Atmospheric CO2 Concentrations 

From Sec. 4.1 it can be concluded that plants typically found on nutrient-poor tropical soils may be relatively slow-growing, at least by the standards of the moist tropics. And also given that many species associated with these forests do not appear to be able to respond significantly to phosphorus fertilization (Sec. 4.1) it might also be argued that these species may not be able to significantly increase their growth in response to increases in ambient [CO,] (Poorter, 1993, 1998). On the other hand, Lloyd and Farquhar 

Such methodological concerns with model communities aside, the tendency seems to be for potted tropical plants to show significant growth responses to elevated [CO ], but for model communities these responses are much reduced or absent. Clearly, much more work is required to elucidate the basis of these contradictory results. Nevertheless in what follows, we assume that moist tropical forest trees increase their productivity in a manner typical of C3 plants, investigating the extent to which changes in phosphorus availability might modify that response. 

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