TITLE:
Relationship between Leaf Micro- and Macro-Nutrients in Top Canopy Trees in a Mixed Forest in the Upper Rio Negro in the Amazon Region
AUTHORS:
M. A. Sobrado
KEYWORDS:
Amazon Forests, Amazon Caatinga, Leaf Ionome Homeostasis, Leaf N-P and Micronutrients, Micro-Nutrient Deficiency, Micronutrients Toxicity, Mixed Forest, N-P Co-Limitation, Plant Nutrient Balance, Oxisol, Podzol
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.5 No.10,
May
6,
2014
ABSTRACT: The mixed forests
of the upper Rio Negro at the northern of the Amazon basin grow in oxisol soils
that are extremely infertile. These areas exhibit deficiencies in several
macro-nutrients, and may also be characterized by the shortage or toxic excess
of some micronutrients. The overall goal of this research is to collect more
comprehensive information regarding the micronutrient composition of the
upper Rio Negro forests as well as discern the relationship between leaf micro-
and macro-nutrients that may contribute to the homeostasis and balance of the
ionome. Firstly, the nutrient composition within the oxisol soil and leaf
tissues of two top canopy tree species from the mixed forests was determined.
We then analyzed the relationship between leaf micronutrient composition with N
and P levels of the two species and that of species inhabiting the Amazon caatinga.
Extractable soil Zn, B, Mn and Cu were very low in the mixed forest. In
contrast, Fe and Al levels were potentially toxic. The analysis of leaf N/P
ratios revealed for the first time the co-limitation of N and P in the mixed
forest. This contrasts with species from the adjacent Amazon caatinga toposequence
that are characterized by strong N limitation. All micronutrients within leaves
of species inhabiting the mixed forest were also found to have low
concentrations. Moreover, Fe and Al were detected at concentrations well below
those reported for accumulator species. This suggested that leaf ion
homeostasis was maintained under potentially toxic soil Fe and Al conditions.
Leaf micronutrient (Fe, Zn and B) contents mirrored that of leaf N and P
contents, and comparable Fe/N, Fe/P, Zn/N, Zn/P, B/N as well as B/P ratios were
found across species and forest types. Therefore, forest species exhibited the
capability to maintain leaf nutrient balances under soil conditions with
deficient or toxic levels of micronutrients.