Multiple soil resources could limit aboveground net primary production (ANPP) and individual tree growth, but most studies have focused on growth as a function of nitrogen (N) availability in temperate forests and phosphorus (P) availability in tropical forests. In addition to soil resource availability, individual tree growth is affected by competition among neighboring trees, but relationships of local-scale soil resources to tree growth have not been assessed in conjunction with competition. I hypothesized that temperate tree diameter growth and ANPP are correlated with soil base cation availability as well as N. Similarly, tropical tree diameter growth and site-level basal area increment (BAI) should be correlated not only with soil P, but also with the base cations. Furthermore, I hypothesized that the relative effect on diameter growth of competition between neighboring trees strengthens if plant interactions are determined by a tolerance-competitiveness tradeoff. Alternately, competition should be important at all sites if plant interactions are governed by species' relative abilities to most efficiently exploit available soil resources. Finally, I hypothesized that diameter growth, leaf nutrient content, and photosynthesis should increase in response to fertilization of individual temperate forest trees with calcium (Ca) and / or N. To address these hypotheses, I tested correlations between growth and production and a suite of resources including water, multiple measures of inorganic N availability, phosphate (PO4), total P, and extractable base cations (Ca, potassium (K), magnesium (Mg)), in northern hardwood forests distributed across a multi-resource gradient and in lowland wet tropical forests growing across a strong soil P gradient. I also developed individual-based growth models as functions of local neighborhood index and fine-scale estimates of soil resources for single species in both biomes and a variety of functional groups from the tropical sites. In temperate forests, wood productivity was strongly correlated with soil Ca at low-fertility sites but with N at high fertility, whereas leaf production was correlated with N across all sites. Diameter growth of individual temperate trees was unrelated to soil resource availability or competition among species dominant at low-fertility sites; for species dominant at high-fertility sites, diameter growth was related to several soil resources (Ca, K, N), and demonstrated strong correlations with local neighborhood indices. Across tropical sites, individual diameter growth and site mean BAI were correlated with both base cations and total P. The Fabaceae (legumes) showed extremely weak correlation of individual growth to soil resources, and no relationship of site mean BAI to resources. In contrast, the Arecaceae (palms) and species with low wood density exhibited robust correlations of BAI to total soil P, while BAI was correlated with soil base cation availability for non-legume dicots and species with higher wood density. My results were consistent with limitation of temperate forest productivity by N or Ca; anthropogenic N deposition may therefore have mixed effects, with increasing production in N-limited systems but decreasing production in base cation-limited systems. Also for temperate forests, an increase in the strength of competition in species common at high fertility suggests that communities may be structured according to a tolerance-competition tradeoff. In lowland tropical forests, legumes may partially escape soil resource limitation, while growth of other functional groups may be limited by either soil P or base cations; consequently, base cations could be potentially limiting resources globally.
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