Reply on RC2

Abstract

The total demand and uptake of nutrients by vegetation is rarely quantified or compared across vegetation types. Here, we describe different nutrient use and allocation strategies in Neotropical savanna (cerrado) and transitional forest (cerradão) sites, report leaf nutrient resorption and calculate ecosystem-level nutrient use efficiency. For the first time, we couple net primary productivity (NPP) estimates with nutrient stoichiometry to quantify nutrient demand and nutrient flows at the whole stand scale for different components of vegetation biomass. The two vegetation types showed similar mean nutrient concentration and nutrient resorption efficiency except for wood P concentration that was 4-fold higher in cerrado than cerradão species. The cerradão showed higher canopy NPP, while fine roots and wood NPP were similar for the two vegetation types. Nutrient requirement in the two vegetation types was dominated by the demands of the canopy, with canopy resorption contributing generally more than 50 % of the total canopy demand for nutrients, while less than 35 % of N, P, K, Ca and Mg were allocated to wood or fine roots. Proportionally, the savanna site showed higher nutrient demand from fine-roots (over 35 % of total nutrient demand) and for the wood component (over 13 % of total nutrient demand), while ~60–70 % of cerradão nutrient demand was allocated to the canopy. The proportional difference in nutrient allocation to the different biomass components suggesting cerrado species are more efficient in fine root production, but less efficient in producing wood. Our findings suggest that cerradão species are limited in P and K, inducing a higher resorption to compensate for low uptake. Moreover, we found that N uptake for cerradão was higher with lower N use efficiency, leading higher N demand compared to the cerrado. This trade-off explains how similar soils and the same climate dominated by savanna vegetation can also support forest-like formations. The lack of difference in Ca and Mg use and uptake efficiency also suggests these ecosystems are able to acquire all Ca and Mg they need. Tree species composition is likely the major factor regulating nutrient use, limiting vegetation transitions and influencing nutrient demand at landscape scales.