REVIEW AND SYNTHESIS Relationships am ong net primary productivity, nutrients and climate in tropical rain forest: a pan-tropical analysis

Tropical rain forests play a dominant role in global biosphere-atmosphere C O 2 exchange. A lthough climate and nutrient availability regulate net primary production (NPP) and decomposition in aU terrestrial ecosystems, the nature and extent o f such controls in tropical forests remain poorly resolved. We conducted a meta-analysis o f carbon-nutrient-chmate relationships in 113 sites across the tropical forest biome. O ur analyses showed that mean annual temperature was the strongest predictor o f aboveground N PP (ANPP) across aU tropical forests, but this relationship was driven by distinct temperature differences between upland and lowland forests. Within lowland forests (< 1 0 0 0 m), a regression tree analysis revealed that foliar and sod-based measurements o f phosphorus (P) were the only variables that explained a significant proportion o f the variation in ANPP, although the relationships were weak. However, foliar P, foliar nitrogen (N), litter decomposition rate (k), sod N and sod respiration were ad directly related with total surface (0-10 cm) soil P concentrations. O ur analysis provides some evidence that P availabdity regulates N PP and other ecosystem processes in lowland tropical forests, but more importantly, underscores the need for a series o f large-scale nutrient manipulations — especially in lowland forests to elucidate the m ost im portant nutrient interactions and controls. Cory C. Cleveland,^* Alan R. Townsend,^ Philip Taylor,^ Silvia Alvarez-Clare,'^ M ercedes M. C. Bustamante,^ G eorge Chuyong,® Solom on Z. Dobrowski,^ Pauline Grierson,® Kyle E. Harms,® Benjamin Z. Moulton,^® Alison Marklein,^® William P arton," Stephen Porder,^^ Sasha C. Reed,^® Carlos A. Sierra,^'^ W hendee L. Silver,^® Edmund V. J. Tanner^® and William