Above- and below-ground net primary productivity across ten Amazonian forests on contrasting soils

TLDR: In this paper, the authors quantify the above and below ground NPP of ten Amazo-nian forests to address two questions: (1) How do Ama- zonian forests allocate productivity among its above- and below-ground components?

Abstract: The net primary productivity (NPP) of tropi- cal forests is one of the most important and least quan- tified components of the global carbon cycle. Most rel- evant studies have focused particularly on the quantifica- tion of the above-ground coarse wood productivity, and lit- tle is known about the carbon fluxes involved in other el- ements of the NPP, the partitioning of total NPP between its above- and below-ground components and the main en- vironmental drivers of these patterns. In this study we quantify the above- and below-ground NPP of ten Amazo- nian forests to address two questions: (1) How do Ama- zonian forests allocate productivity among its above- and below-ground components? (2) How do soil and leaf nu- trient status and soil texture affect the productivity of Ama- zonian forests? Using a standardized methodology to mea- sure the major elements of productivity, we show that NPP varies between 9.3±1.3 Mg C ha 1 yr 1 (mean±standard er- ror), at a white sand plot, and 17.0±1.4 Mg C ha 1 yr 1 at a very fertile Terra Preta site, with an overall average of 12.8±0.9 Mg C ha 1 yr 1 . The studied forests allocate on average 64±3% and 36±3% of the total NPP to the above- and below-ground components, respectively. The ratio of above-ground and below-ground NPP is almost invariant with total NPP. Litterfall and fine root production both in- crease with total NPP, while stem production shows no over- all trend. Total NPP tends to increase with soil phospho- rus and leaf nitrogen status. However, allocation of NPP to below-ground shows no relationship to soil fertility, but ap- pears to decrease with the increase of soil clay content.