Contrasting strategies of nutrient demand and use between savanna and forest ecosystems in a neotropical transition zone

[摘要] The total demand for and uptake of nutrients by vegetation is rarely quantified or compared across vegetation types. Here, we describe differentnutrient use and allocation strategies in neotropical savanna (cerrado) and transitional forest (cerradão) tree communities composed ofdifferent species, report leaf nutrient resorption and calculate ecosystem-level nutrient use efficiency. 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 vegetationbiomass. Species from the two vegetation communities showed similar mean nutrient concentrations and nutrient resorption efficiency, except for wood P concentration that was fourfold higher in cerrado than cerradão species. The cerradão showed higher canopy NPP, while fine roots andwood 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 generally contributing 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, cerrado showed higher nutrient demand fromfine roots (over 35 % of the total nutrient demand) and for the wood component (over 13 % of the total nutrient demand), while ∼  60 %–70 % of the cerradão nutrient demand was allocated to the canopy. The proportional difference in nutrient allocation to thedifferent biomass components suggests cerrado species allocate less nutrients to a given fine root biomass, but more nutrients to a given woodbiomass. Our findings suggest that cerradão species are more limited in P and K than cerrado species, inducing higher resorptionto compensate for low uptake. Moreover, we found that N uptake for cerradão was higher with lower N  use efficiency, i.e. theamount of production per nutrient unit, leading higher N demand compared to the cerrado. This difference in nutrient dynamics explains howsimilar soils and the same climate dominated by savanna vegetation can also support forest-like formations. Tree species composition is likely themajor factor regulating nutrient use, limiting vegetation transitions and influencing nutrient demand at landscape scales.

[学科分类] 大气科学