Agriculture Science Developments, 2(8) August 2013, Pages: 59-66
TI Journals
ISSN
2306-7527
Agriculture Science Developments
www.tijournals.com
Concentration of Nutrients in Litter as a Function of Soil Type,
Climate and Forest Composition in Amazon
Aprile F. *1, Siqueira G.W. 2, Darwich, A.J. 3, Santos V.C. dos 4, Ribeiro A.A. 5
1
West of Pará Federal University, 68040-070 Pará, Brazil.
Pará Federal University, 66075-100 Pará, Brazil.
3
National Institute of Research in Amazonian, 69060-001 Amazonas, Brazil.
2,4,5
AR TIC LE INF O
AB STR AC T
Keywords:
The present work aimed to study the concentration of nutrients variation in litter of ecosystems
upland and floodplain of the Brazilian Amazon, and to relate these nutrient concentrations to the
different types of soils, climate and forest composition. Samples were collected during the drought
and rainfall seasons from 2005 to 2012 in five ecosystems of the Amazon: upland forest (UF1) and
wetland forest (WF) of the Negro River; upland forest (UF2) and lowland forest (LF) of the
Solimões River; and upland forest (UF3) of south-central Pará State. We estimated the amount
quantity of litter on the soil surface, and analyzed the contents of C, N, P, Na, K, Ca and Mg
according to the procedures of analysis of soils and plants. The nutritional content depending on
the type and age of leaf litter was also studied. We found that litter quantity and nutrient
concentrations both showed seasonal pattern, with highest levels during the dry season. The
estimated annual quantity of litter ranged from 2.8 to 9.8 t ha-1 during the dry season, and 1.8 to
6.4 t ha-1 in the rainy season. Of the five ecosystems studied, LF and UF2 were the environments
with higher concentrations of nutrients. In general, the relative concentration of macro and
micronutrients in litter of the ecosystems studied are given as follows: C>N>Ca>Na>K>Mg>P.
The litter consisting predominantly of young leaves had higher content of organic nitrogen,
phosphorus and potassium, while the litter stabilized with adult-old leaves, showed higher levels of
calcium and magnesium.
Litter
Quantitative analyze
Nutrients
Total carbon
Seasonality
Climate change
Amazon
© 2013 Agric. sci. dev. All rights reserved for TI Journals.
1.
Introduction
The residual layer known as vegetative litter is composed of plant debris (leaves, twigs, stems, bark, fruits, flowers, branches and trunks)
and animals, covering the soil surface. It can be neatly classified into thin litter layer, predominantly composed of leaves and depth of 2 cm,
and thick leaf litter, formed especially of fruits, branches and trunks above this depth. The litter volume is directly related to system
productivity, reflecting the balance between the processes of decomposition and assimilation. Many factors are directly related to
productivity, quality and quantity of litter including climatic conditions and vegetation type.
The production of vegetative is affected by the climate, particularly seasonality of temperature and rainfall, so that in the equatorial forests
like the Amazon rainforest, the rainfall is the controlling factor of litter production. In periods of dry in the upland region of the Amazon,
there is an increase of litter production, especially from shrubs and trees. This process is clear in the peripheral region of the southern
Amazon, where this biome suffers from interference of drier climate of the Cerrado biome. In the Amazon floodplain the most important
controlling factor in the litter production seems to be hydrological cycle seasonality.
Litter, especially the fine fraction, acts as a direct indicator of primary productivity of forest ecosystems, having an role in the protection
and renewal [1], and maintenance of temperature and soil moisture. Litter contributes to productivity of the soil by providing organic
compounds rich in carbon, nitrogen and phosphorus, which are then degraded to free inorganic forms, easily assimilated by the local biota.
The nutrients movement in an ecosystem depends on composition and structure of the associated compartments, as well as the speed of
transfer between compartments. Nutrient cycling involves exchanges of mineral elements between the biotic and abiotic system that
surrounds them, and it usually has as an arbitrary point the soil. However, in the Amazon rainforest it has been understood that the first
arbitrary point is the biomass, which accounts for the major reservoir of carbon and other elements in the ecosystem. Studies have shown
that the Amazon rainforest is one of the most oligotrophic of the world, and therefore provides mechanisms for retention and greatly
improved nutrient cycling [2]. This oligotrophic condition of the forest is caused especially by the high degree of weathering process
followed by leaching of the soil, corroborating the residual vegetative layer concentration in the forest is the result of the interaction
between forest and climate.
Considering the high degree of weathering that occurs in the equatorial forests, whose average rainfall of 2500 mm year -1, and it can reach
more than 6000 mm year -1 in the pre-Andean region, the litter has role interception of rain, dampening them, and thereby minimizing
erosive effects. Areas deforested for planting in the Amazon region suffer greater erosion pressure, by the absence of a residual vegetative
* Corresponding author.
Email address: [email protected]
Aprile F. et al.
60
Agricult ure Sci ence Developments, 2( 8) August 2013
layer that protects the soil. Through a vertical gradient of decomposition, the litter layer is responsible for the storage of water in the soil as
well as by increased infiltration rates and surface conditioning of flows.
The aim of this research was to study the change in nutrients concentration (C, N, P, Na, K, Ca and Mg) present in the fine litter (ɸ  2 cm)
produced in the upland (Terra-firme), lowland (Várzea) and wetland (Igapó) ecosystems of the Brazilian Amazon, and to relate the
concentrations found with different types of soils, climate interference (seasonality and hydrological cycle), litter production and forest
composition.
2.
Methodology
2.1 Study Area
The study area is located in the South Western and Central Amazon. According to the climatic classification of Köppen-Geiger, the climate
in most of the region studied is classified as "Am" constantly hot and humid or monsoon climate. There is also a pronounced dry season in
the Amazon Peripheral South, where the climate is classified as "Aw" slightly warm and with a dry tropical climate with dry winter season.
The efforts of this study were concentrated in ecosystems of upland, lowland (floodplain) and wetland, specifically in the Terra-firme
Forest (UF1, 03º01'-03º02'S, 60º14'-60º16'W) and Igapó Forest (WF, 03º00'-03º01'S, 60º09'-60º10'W) both of the Negro River basin; Terrafirme Forest (UF2, 03º48'-03º49'S, 60º19'-60º20'W) and Várzea Forest (LF, 03º09'-03º11'S, 59º54'-59º55'W) both of the Solimões River
basin, and all in Western Amazonia, and Terra-firme Forest (UF3, 06º04'-06º05'S, 49º55'-49º56'W) of south-central Pará State, in the
Amazon Peripheral South (Figure 1).
The ecological region of Dense Tropical Forest or Terra-firme Forest (UF), also defined as upland non-flooded forest, occupies about 80%
of the Amazon, and is characterized by high richness and species diversity, predominantly tall forest with high biomass (dense), extending
over large areas of upland Amazonian, crystalline shells, and Pleistocene terraces. The region was formed by a complex mosaic, where the
UF includes several types of vegetation according to the topography, geography, geology and climate including: vine forest, bamboo forest,
mountain forest, cloud forest and campinarana. The dominant species among the tall trees belong to the families Leguminosae,
Lecythidaceae and Sapotaceae. The soil composition is varied. In UF1 and UF3 regions, the soils consist of sand, with low fertility, while
in UF2 region the soil is sandy-clay (Figure 1). Lowland forests (floodplain) are composed of plant structure dynamics (grasses, shrubs and
trees) in an obvious phase of succession, these occur in areas with alluvial sediments of Quaternary and periodical flooding. The wetland
forests (WF) have floristic and structural characteristics quite different from upland forest (UF), due to geomorphological and hydrological
differences such as variation in river levels and duration of flooding. The Igapó Forest is a typical wetland forest, made up of flooded
vegetation, in the floodplain of the Negro River and other rivers of black or clear water. In Igapó the forest is almost permanently flooded,
although it is also governed by the hydrological cycle. The water supply comes from the marshy part of the forest streams with low nutrient
content. A striking feature of the Igapó is the acidic water (pH < 4.5) which is dark-wine colored by the humic acids leached by rain. Soils
are hydromorphic, with high concentrations of humic material. The Várzea Forest (LF) represents a complex system of countless islands,
dams, channels, lakes and oxbows, which are constantly changing to their size and shape due to the hydrologic cycle, precipitation and
sediment load. The floodplain is one of the richest ecosystems in the Amazon in terms of biological productivity, biodiversity and natural
resources. The vegetation consists of wetland forests and macrophytes in lakes and oxbows, providing food and shelter for aquatic and
terrestrial life, in soils predominantly formed by sandy-clay.
2.2 Analytical Procedures
Samples were collected between May and August (dry season) and November and February (rainy season) 2005 to 2012 in five ecosystems
of the Amazon (see study area and Figure 1): UF1, WF, UF2, LF and UF3. These ecosystems are distinguished especially by the frequency
and abundance of rainfall and differences in local hydrological cycle.
Litter samples were collected using a PVC frame 0.5 m x 0.5 m. Each sample was obtained from combining three plots collected at
random, without distinction between leaves, branches, residual or reproductive elements. However, for chemical analysis was consider only
the fine litter, which includes timber with a diameter  2 cm. This distinction was made to be possible to compare the nutrient
concentrations and contents of leaf litter of forests later. The samples were placed in paper bags and carried to the laboratories of Water
Chemistry of INPA and UFPA. The samples were weighed and placed to dry in a ventilated oven at 60 °C to constant weight. After drying,
the biomass was determined by weighing the sample and estimated the amount annual quantity of litter (t ha-1) on the soil surface.
The samples were ground in a Wiley mill's electric brand with 30 mesh sieve and homogenized in the Soil Laboratory of INPA, for further
implementation of qualitative and quantitative determinations of nutrients. All nutrient elements analyzed were expressed in kg ha-1. The
total organic carbon was determined by wet combustion, by oxidation with potassium dichromate and sulfuric acid at 100 °C and titrated
with ammonium ferrous sulfate, using diphenylamine as an indicator [3]. Total nitrogen was determined by digesting in autoclave for 30
minutes with a solution of potassium perssulfato oxidative and boric acid [3, 4]. Organic nitrogen was determined by the Kjeldahl method
modified by [5], which consists in an oxidation with sulfuric acid and mixed catalyst (80 g of K2SO4, 2 g of Se, 5 g of CuSO4) at 350 °C,
followed by a distillation in a Markan system with boric acid, and titrating with sulfuric acid 0.01 N. Total phosphorus was determined by
the ascorbic acid method with acid extraction (H 2SO4 0.025 N + HCl 0.05 N) and reading in spectrophotometer [6]. Upon digestion with
nitric and perchloric acid we determined the calcium and magnesium by reading atomic absorption spectrophotometry, and sodium and
potassium flame photometry [3, 7].
The results were analyzed statistically using the Statistica  7.0 [8]. For comparative analysis of the five ecosystems studied was used
Multivariate Analysis of Variance (MANOVA), and for comparisons of means was used Multiple Comparison Test LSD (least significant
difference), calculated for all variables [9]. Was also studied the nutritional pattern of the litter depending on young leaves or adult-old
leaves predominance in the samples selected for analysis. We understand that the litter is composed of young leaves of greenish or
yellowish, still with some humidity and soft texture, and adult-old leaves, with various shades of brown, dehydrated and brittle texture.
Concentration of Nutrients in Litter as a Function of Soil Type, Climate and Forest Composition in Amazon
61
Agri culture Scienc e Developments , 2(8) Augus t 2013
Figure 1. Scope of the study area indicating the sampling sites (Source: Google Maps, 2012).
3.
Results
The amount quantity or supply of litter along the hydrological year, on average, significantly differ from one climate period to another
period (p < 0.01; F= 15.33), with an estimated 6.32.8 t ha-1 in the dry and 4.11.8 t ha-1 in rainy season (Figure 2). Individually, the
floodplain forest (LF) and upland forest of the Solimões River (UF2) had the highest annual estimates of litter biomass with 9.8 t ha-1 and
8.6 t ha-1 in the dry and 6.4 t ha-1 and 5.6 t ha-1 during the rainy season. The results show that higher productivity residual of plant material
during periods of dry. Other studies in tropical forests, relating the rates of litter production with rainfall, confirm this trend [10-12].
The period of dry in the Amazon region follows a pattern of alternating single mode between rainy and dry seasons, and the frequency and
concentration of each period depends on the geographic distribution. In this sense, water stress, which appears as a determinant for litter
production, is more intense in the Amazon region in the areas of transition (ecotones), especially between the Amazon Forest and the
Caatinga biomes, and between the Amazon Forest and Cerrado. However, it seems that the effect of water stress on the production of the
forest litter is not enough, since the results found in the uplands of south-central Pará State (UF3) were lower than those found in Central
Amazon Floodplain. Other factors seem to be interfering with different litter amounts productivity in Amazonian environments. According
62
Aprile F. et al.
Agricult ure Sci ence Developments, 2( 8) August 2013
to [13], variations in the volume of litter on the soil of tropical forests are related to the seasonality of litter production, climate and
presence of decomposing organisms.
The supply of litter produced directly influences the levels of nutrients that are circulating through the soil, especially carbon. The
concentrations of total organic carbon ranged from 1216 to 4298 kg ha -1 , mean 28701324 kg ha-1 for dry periods, and from 961 to 2536 kg
ha-1 mean 1812696 kg ha-1 for the rainy periods (Figure 2), respectively, for the forest ecosystems of upland southern Pará State (UF3)
and floodplain forest (LF). Since both LF and UF2 are located in the Solimões River basin, where the soils are predominantly clay and
there is an annual deposit of sediments from Andes on the flood plain, they had the highest concentrations of carbon (Figure 2). The
organic carbon represented during the study period was between 40% and 50% of the litter biomass, this percentage remained the same,
even during periods of rain, for all ecosystems studied.
The macronutrients N and P (Figure 3) were more variable, the mean levels of total organic nitrogen ranged between 30 and 110 kg ha -1
with mean 7334 kg ha-1 for periods of dry, and between 20 and 72 kg ha-1 with mean 4722 kg ha-1 for rainy seasons, with a significant
difference between sampling periods (p < 0.01; F= 14.10). The higher concentrations of N organic were found in the Terra-firme forest
(UF2) and floodplain forest (LF), both in the Solimões River basin. Total phosphorus ranged between 1.1 and 5.4 kg ha-1 mean 3.11.9 kg
ha-1 for the dry periods and between 0.8 and 3.5 kg ha-1 mean 2.11.2 kg ha-1 for the rainy periods, had no significant difference between
the sampling periods (p > 0.01; F= 6.84). The average concentrations of nitrogen and phosphorus were within the values reported by other
studies conducted in tropical and equatorial forests (Table 1). The average of P obtained exclusively for the floodplain forest (LF) was
slightly higher, so that although the P level is almost always found in low concentrations in tropical forests, as reported by [14, 15], due to
the high degree of weathering of soils, it seems that the annual supply of nutrients from the Andean and pre-Andean regions through
precipitation and flood-pulse to the floodplain, maintains the high supply of phosphorous in the system. The intense and continuing
precipitation that occurs in these Neotropical sites is the largest input flow of phosphorus in the forest system. However, it has not a
significant contribution on the nitrogen flow [16], which in this case depends largely on the litter decomposition for entering the forest
system. The difference in the nutritional composition of ecosystems has been attributed to several joint factors, as the volume and
composition of the litter, soil type and its capacity for aggregation and porosity. The particle size was shown to be inversely proportional to
phosphorus concentration in the litter. The calculation of the normal probability of phosphorus revealed linearity tending to curve, which
indicates a ratio between particle size and their concentrations. The highest concentrations of phosphorus were found in particles of size 
0.3 mm, range 4.6 and 5.4 kg ha-1.
Figure 2. Storage and organic carbon concentration (kg ha-1) in the litter of five Amazonian ecosystems (UF1, WF, UF2, LF and UF3)
for periods of dry and rainy between 2005 and 2011.
Figure 3. Concentration of organic N and total P (kg ha-1 ) in the litter of five Amazonian ecosystems (UF1, WF, UF2, LF and UF3)
for periods of dry and rainy between 2005 and 2011.
Concentration of Nutrients in Litter as a Function of Soil Type, Climate and Forest Composition in Amazon
63
Agri culture Scienc e Developments , 2(8) Augus t 2013
The largest variations among the alkali and alkaline earth elements (Figure 4) were due to the element calcium, which in the ecosystems of
the Solimões (UF2 and LF) appears at high concentrations, as opposed to what occurs in terrestrial ecosystems irrigated by the black waters
of the Negro River and forest streams (UF1 and WF). In fact, the low concentration of calcium in the wetlands (Igapó) is known, and is a
barrier to the diversity and abundance of molluscs (snails and mussels), which need calcium for their shells. Calcium in the biomass of litter
ranged between 8-128 kg ha-1 (mean 5761 kg ha-1) during the dry season, and between 5–83 kg ha-1 (mean 3740 kg ha-1) in the rainy
periods. The high concentration of calcium in leaf systems seems to be associated with low mobility of the elements in plant tissues, as well
as the age of the leaf [17, 18], because calcium is deposited in the thickest regions of the secondary cell walls in the form of calcium
pectates, who are immobilized until the falls [18]. Apparently, magnesium can also accumulate in the cell walls of plants in the form of
magnesium pectate, similarly to what occurs with the calcium. The other elements varied during dry and rainy as follows: sodium between
6 and 29 kg ha-1 mean 1410 kg ha-1 and between 4 and 19 kg ha-1 mean 97 kg ha-1; potassium ranged between 3 and 22 kg ha-1 mean
128 kg ha-1 and between 2 and 14 kg ha-1 mean 85 kg ha-1; and magnesium ranged between 3 and 19 kg ha-1 mean 107 kg ha-1 and
between 2 and 12 kg ha-1 mean 65 kg ha-1 , respectively. The contents of alkaline elements changed spatial and seasonality, showing
statistically significant differences (p < 0.01; F= 16.95) between the two sampling periods. Despite this seasonal variation, the results were
within the values reported by other studies in the Amazon (Table 1). The relative concentration of macro and micronutrients in the litter of
Amazonian ecosystems studied ranged as follows: C>N>Ca>Na>K>Mg>P for upland forest and wetland from Negro River basin (UF1 and
WF) and C>Ca>N>Na>K>Mg>P for upland forests (UF2 and UF3) and floodplain forest (LF) of the Solimões River basin.
Figure 4. Concentration of total Na, K, Ca and Mg (kg ha-1 ) in the litter of five Amazonian ecosystems (UF1, WF, UF2, LF and UF3)
for periods of dry and rainy between 2005 and 2011.
Table 1. Comparison between the mean annual content (kg ha-1) of foliar nutrients (Lea) and litter (Lit) of several tropical
and equatorial humid forests with the results obtained in this study (rounded data).
Ecosystem
Local
Upland (Lit)
Occidental Amazonia
Supply
4620 2307 63 2.4 6.9 6.4 7.8 5.5 this study
C
N
P Na
K Ca Mg Reference
Wetland (Lit)
Occidental Amazonia
3960 1631 38 1.3 5.5 4.8 6.3 3.7 this study
Upland (Lit)
Occidental Amazonia
7095 3262 84 3.8 18.4 15 98 13.8 this study
Lowland (Lit)
Occidental Amazonia
8085 3417 91 4.4 23.5 18 105 15.4 this study
Upland (Lit)
Amazonia of South
2310 1088 25 1.0 4.6 2.8 17 2.3 this study
Lowland (Lit)
Central Amazonia
5600
294 3.0
-
8.0 21 18
[2, 19]
Upland (Lit)
Central Amazonia
8250 3880 151 3.0
-
15 37 14
[20]
Andina (Lit)
Occidental Andes
-
-
583 29 7.0 59 216 55
[21]
Wetland (Lit)
Venezuelan Amazonia
-
-
137 10
-
20 178 30
[22]
Wetland (Lit)
Amazonia of North
-
-
49 2.0
-
8.0 32 8.0
[23]
Upland (Lit)
Central Amazonia
2720
-
- 0.1
-
2.4 2.7 1.4
[24]
Lowland (Lea)*
Amazonia of North
-
-
19 1.2
-
10.3 4.7 2.4
[15]
Upland (Lea)*
Venezuelan Amazonia
-
-
17 0.7
-
3.9 3.6 1.2
[18]
Upland (Lea)*
Venezuelan Amazonia
-
-
16 0.6
-
5.1 4.1 1.7
[18]
-1
* Values showed in g kg .
-
Aprile F. et al.
64
Agricult ure Sci ence Developments, 2( 8) August 2013
4.
Discussion
The low availability of nitrogen and phosphorus in soils, and adaptations of native plants to these low concentrations, has been the subject
of several studies in the tropics, especially in the Amazon [14, 15, 17, 25-31]. Studies revealed that nutrients concentration in leaf systems
show that there are several abiotic factors involved in the process, and seasonality, citing soil type and forest vegetation (litter), the
concentration of light and leaf age [17, 25-27]. Although these studies have been made in leaf systems, the leaves represent concentrations,
the main constituent of shallow litter, representing, in some cases, more than 80% of the waste material. The smaller fractions of N and P
found in ecosystems UF1, WF and UF3 are probably related to sandy soil composition. Sandy soils have vegetation with low concentration
of nitrogen and phosphorus in the leaves, and intermediate concentrations of cationic elements [15], which in turn would explain the lower
levels found in the litter of these ecosystems. According to [1, 32], the dense tropical forest, which covers most of the Amazon region, is
supported predominantly by soils of low fertility and natural chemistry, depending on the efficient recycling of organic matter produced by
the forest itself. It is reported by [20] that upland forests owe their survival and productivity to the high plant diversity, consisting of native
species adapted to climatic conditions and soil nutrition.
The equatorial vegetation is heterogeneous, contrary to what was thought for many decades, with high diversity and successional stages,
and with different growth rates. This high genetic variability is the result of pressure imposed by abiotic processes, especially the wide
variety of local and regional climates, different relief and soil composition. Sandy soils of low fertility interfere with the growth of
vegetation, which in this region is adapted to nutritional stress conditions, showing slow growth, with also slow production of biomass, and
nutrient loss by senescence of the leaves or by the leaching process. In the latter case, the high rainfall in the Amazon region associated
with the illegal use and occupation of land for agriculture have contributed greatly to the loss of macro and micronutrients by leaching. The
deficiencies of micronutrients have become major constraints to productivity, stability and sustainability of soils [33]. Soils with finer
particles and with higher organic matter can generally offer a greater reserve of nutrients, while coarse textured soils such as sand have
fewer reserves and tend to get depleted rather quickly [33, note of the authors].
In regard to Amazonian soils composition and their fertility, we sought to analyze the nutritional behavior of nitrogen in their total and
organic forms, depending on young or adult-old leaves predominance in litter content. The results showed a significant difference between
the samples analyzed, and the litter mostly from young leaves (curve a in Figure 5) showed a higher content of organic nitrogen in relation
to the leaf litter consisting preferably by adult-old leaves (curve b of Figure 5). The rates [N-org/N-tot x100] were 59 for young leaves and
24 for adult-old leaves. The same trend was observed for the elements phosphorus and potassium, which showed higher concentrations in
fresh litter preferably formed by younger leaves (Figure 6). Since the elements calcium and magnesium, both had a negative effect, having
highest concentration in the older leaves, litter stabilized in the leaves deeper in the mass of residual cover (Figure 6). These results seem to
be fairly consistent, according to [17], in the forest ecosystems the young leaves tend to have higher concentrations of N, P and K, while in
the older leaves there is a decrease in these nutrients while simultaneously Ca and Mg increase, depending on the processes of transport of
nutrients and accumulation of photosynthetic products in the leaf.
Litter plays an important role in nutrient cycling through decomposition processes, restoring soil nutrient elements to be later absorbed by
forest ecosystems. Micronutrients play a vital role in maintaining soil health [33]. Elements such as phosphorus and potassium, from
geological sources, are released by weathering, and depend heavily on the litter for them to be fixed in the soil in mineral form, thus
enabling this return to the cycle. Decomposition plays an important role in nutrient cycling, especially in the Amazon region, where this
process is enhanced by high humidity and temperature, which on average stay above 70% and 28 °C throughout the year in the forest
interior. The speed of decomposition of organic compounds varies depending on the amount of rain and soil temperature. Decomposition of
litter is influenced by physical and biological factors that may alter the physiological ecology of soil microorganisms [34]. In this sense, the
Amazon carries another advantage over arid and temperate ecosystems, in having high microorganisms diversity involved in organic
decomposition (bacteria, fungi, lichens, micro and macroinvertebrates). According to [20], the release of mineral nutrients contained in the
litter and soil organic matter is mainly controlled by soil biota. Mycorrhizal fungi have a major role in the cycling of nutrients, especially N
and P in poor acid soils in the tropics. Nutrient dynamics in leaf litter decomposition seems to be determined by the chemical composition
of the first material, especially the ratio between carbon and nitrogen [31].
Figure 5. Content of total nitrogen (Ntot) and organic nitrogen (Norg) in litter with different leaves contents: a) young leaves, b) adult-old leaves.
Curve a: Norg=61.03Ln(Ntot)-216.25 and R2=0.9454; Curve b: Norg=25.84Ln(Ntot)-91.46 and R2=0.8982.
Concentration of Nutrients in Litter as a Function of Soil Type, Climate and Forest Composition in Amazon
65
Agri culture Scienc e Developments , 2(8) Augus t 2013
Figure 6. Accumulative-releasing behavior of nutrients (N, P, K, Ca and Mg) in litter with different leaves contents.
5.
Conclusion
Litter supplies and nutrient concentrations showed a seasonal pattern, after the weather patterns in the Amazon region. There is a supply of
litter and nutrients much greater during periods of dry. The organic carbon represented throughout the period ranges between 40-50% of
litter production. Of the five ecosystems studied, the floodplain forest seasonally flooded by white waters rich in sediments of the Solimões
River, and the adjacent uplands were the systems with the highest levels of nutrients. We believe that part of this is due to precipitation and
the flood-pulse in the Várzea, which maintains the high supply of nutrients in the system. In general, the relative concentration of macro
and micronutrients in litter of the ecosystems studied are given as follows: C>N>Ca>Na>K>Mg>P. Another important confirmation is that
the litter is mostly from young leaves which have a higher content of organic nitrogen, phosphorus and potassium, while the stabilized
litter, is composed of old leaves, which showed higher levels of calcium and magnesium. Litter plays an important role in nutrient cycling
of all ecosystems in the Amazon region, studies should be undertaken to explain the role of fine and coarse litter in nutrient cycling and
decomposition, as well as carbon sequestration from the atmosphere.
Acknowledgements
The authors thank to Dr. Richard Carl Vogt at the National Institute of Research of Amazonian – INPA for valuable helpful with the
revision.
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