Nitrogen and Phosphorus Limitation of Biomass Growth in a Tropical Secondary Forest

Abstract

Abstract. Understanding secondary successional processes in Amazonian terrestrial ecosystems is becoming increasingly important as continued deforestation expands the area that has become secondary forest, or at least has been through a recent phase of secondary forest growth. Most Amazonian soils are highly weathered and relatively nutrient poor, but the role of nutrients as a factor determining successional processes is unclear. Soils testing and chronosequence studies have yielded equivocal results regarding the possible role of nutrient limitation. The objective of this paper is to report the first two years' results of a nitrogen (N) and phosphorus (P) fertilization experiment in a 6-yr-old secondary forest growing on an abandoned cattle pasture on a clayey Oxisol. Growth of remnant grasses responded significantly to the N ϩ P treatment, whereas tree biomass increased significantly following N-only and N ϩ P treatments. The plants took up about 10% of the 50 kg P/ha of the first year's application, and recovery in soil fractions could account for the rest. The trees took up about 20% of the 100 kg N/ha of the first year's application. No changes in soil inorganic N, soil microbial biomass N, or litter decomposition rates have been observed so far, but soil faunal abundances increased in fertilized plots relative to the control in the second year of the study. A pulse of nitric oxide and nitrous oxide emissions was measured in the N-treated plots only shortly after the second year's application. Net N mineralization and net nitrification assays demonstrated strong immobilization potential, indicating that much of the N was probably retained in the large soil organic-N pool. Although P availability is low in these soils and may partially limit biomass growth, the most striking result of this study so far is the significant response of tree growth to N fertilization. Repeated fire and other losses of N from degraded pastures may render tree growth N limited in some young Amazonian forests. Changes in species composition and monitoring of long-term effects on biomass accumulation will be addressed as this experiment is continued.

Effects of nitrogen additions on above- and belowground carbon dynamics in two tropical forests

“…In contrast, a review by LeBauer and Treseder (2008) suggested that tropical forests may exhibit N limitation to NPP. Outside of forests on young Hawaiian soils, the results in LeBauer and Treseder (2008) are strongly influenced by responses in dry tropical forests (Campo and Vazquez-Yanes 2004), early successional humid forests (Davidson et al 2004), and high elevation ([2000 masl) tropical forests (Tanner et al 1992). For a mature Indonesian lowland tropical forest on highly weathered soils included in the review, NPP did not respond to N fertilization (Mirmanto et al 1999), and a Hawaiian study on old, highly weathered soils also did not observe a response of NPP to N fertilization (Harrington et al 2001).…”

Mortality as a key driver of the spatial distribution of aboveground biomass in Amazonian forest: results from a dynamic vegetation model

“…Second, carbon allocation should fall in the intervals given by the ground measurements. Then, because photosynthesis increases with nutrient availability (Davidson et al, 2004;Quesada et al, 2009), and because allocation does not seem to vary with it , model photosynthesis parameters could be adjusted to reach the NPP AGW value derived from AGWB and Eq. (7).…”

Climatic patterns modulate ecosystem and soil respiration responses to fertilization in an alpine meadow on the Tibetan Plateau, China

“…N and P often co-limit plant growth in some ecosystems, and P limitation has been observed in equatorial regions, tropical forests, and freshwater ecosystems (Davidson et al 2004). Supplying both N and P can enhance the growth and reproduction of photosynthetic biota as well as large-scale ecosystem primary production (Elser et al 2007;LeBauer and Treseder 2008).…”