**4. Nutrient cycling in the Atlantic Forest**

The biogeochemical cycling is one of the most studied nutrient cycles in the Atlantic Forest, mainly in terms of deposition, accumulation and decomposition of litterfall. This litter is composed predominantly of leaves, branches, bark, trunks of fallen trees, flowers, fruit, dead animals, etc. In general, the percentage of leaves in relation to the other litter components ranges from 60% to 80% of the total material. The biomass of senescent leaves that fall onto the forest floor represents part of net primary production (NPP) of vegetation [26, 27].

Most nutrients uptaken by the trees return to the soil through senescence of their organic components. The intensity of nutrient cycling depends mainly of the deposition of organic material. It is considered the most important form of nutrient transfer from the plant to the forest soil in the ecosystem [28]. According to Viera and Schumacher [28], there is variation between species regarding the amount of nutrients retained and returned. For them, there are species that retain most nutrients absorbed, while others return most nutrients absorbed, and there are also those in which retention is equal to return. This retention and return ratio is linked to different translocation rates of species [29], age, soil and climate conditions [3], as well as environmental aspects, varying from species to species [5].

The continuous supply of litterfall enables storage of soil organic carbon (SOC) and nutrient availability. These nutrients, after litter decomposition, help to keep soil fertility in native forests [30, 31]. Litter provides nutrients, energy and matter to microorganisms in the soil and roots, which is important in tropical forests where litterfall is intense and decomposition is faster [30, 32] than in temperate forests. Litterfall is responsible for important environmental services. It helps intercept rainfall and its storage in the soil increases infiltration rate and surface flow conditioning of water and soil [33], thus avoiding the beginning of erosion processes.

In the Atlantic Forest, due to the different types of forest formations, we can observe a diversity of environments, where each one offers a distinct pattern of litter deposition and accumulation (**Table 1**). For example, seasonal forests have a seasonal deposition pattern due to a period of lower precipitation and low temperatures, triggering leaf abscission. The amount of litter is also influenced by the replacement of mature, older and less efficient foliar tissue by new leaves [27, 34, 35].

Nutrient cycling in forests can be generalized into three models: geochemical, biogeochemical and biochemical cycling [22]. Geochemical cycling is characterized by the input and output of nutrients in the ecosystem. Atmospheric deposition (wet and dry), fertilization, biological fixation and rocks weathering are responsible for most nutrients input [23]. While, leaching, volatilization and harvest biomass are responsible for most nutrients output [24]. The biogeo‐ chemical cycle is characterized by the transfer of nutrients between the plant and the soil. In this cycle, plants absorb nutrients form soil reserves and then return them to the soil via litterfall (litter decay), roots decay or plant death [24]. Biochemical cycling is the translocation of nutrients inside the plant (internal cycle). Once soil nutrients are absorbed, some of these elements are in constant mobilization within the plant, mostly from older to younger tissues.

118 Tropical Forests - The Challenges of Maintaining Ecosystem Services while Managing the Landscape

The dynamic process of nutrient cycling in native or exotic forest ecosystems is shown in

The biogeochemical cycling is one of the most studied nutrient cycles in the Atlantic Forest, mainly in terms of deposition, accumulation and decomposition of litterfall. This litter is composed predominantly of leaves, branches, bark, trunks of fallen trees, flowers, fruit, dead animals, etc. In general, the percentage of leaves in relation to the other litter components ranges from 60% to 80% of the total material. The biomass of senescent leaves that fall onto the

Most nutrients uptaken by the trees return to the soil through senescence of their organic components. The intensity of nutrient cycling depends mainly of the deposition of organic material. It is considered the most important form of nutrient transfer from the plant to the forest soil in the ecosystem [28]. According to Viera and Schumacher [28], there is variation between species regarding the amount of nutrients retained and returned. For them, there are species that retain most nutrients absorbed, while others return most nutrients absorbed, and there are also those in which retention is equal to return. This retention and return ratio is linked to different translocation rates of species [29], age, soil and climate conditions [3], as

The continuous supply of litterfall enables storage of soil organic carbon (SOC) and nutrient availability. These nutrients, after litter decomposition, help to keep soil fertility in native forests [30, 31]. Litter provides nutrients, energy and matter to microorganisms in the soil and roots, which is important in tropical forests where litterfall is intense and decomposition is faster [30, 32] than in temperate forests. Litterfall is responsible for important environmental services. It helps intercept rainfall and its storage in the soil increases infiltration rate and surface flow conditioning of water and soil [33], thus avoiding the beginning of erosion

In the Atlantic Forest, due to the different types of forest formations, we can observe a diversity of environments, where each one offers a distinct pattern of litter deposition and accumulation

forest floor represents part of net primary production (NPP) of vegetation [26, 27].

well as environmental aspects, varying from species to species [5].

**Figure 2**.

processes.

**4. Nutrient cycling in the Atlantic Forest**


*Note:* Secondary forest in early (1), intermediate (2) and advanced (3) stages of succession.

**Table 1.** Annual deposition and accumulation of litterfall in the soil in different forest types in the Brazilian Atlantic Forest.

In tropical forests, such as the Atlantic Forest, litterfall deposition is influenced by latitude and altitude. According to Alves et al. [52], the vegetation structure can vary greatly according to the altitude, since lower altitudinal gradients can present significant changes in edaphic conditions, due to topographic and climate variations. Thus, species that grow in environments with adequate light, water and nutrient availability have high productivity compared to those that develop in environments with low availability of these resources. For example, Montane Forests are less productive than Lowland Forests, since temperature reduction, increased cloudiness, lower reserves of nutrients in the soil and water saturation of the soil are factors that limit the NPP in Montane Forests [26, 53]. In addition, the Atlantic Forest located at higher altitudes is more susceptible to the action of winds, more intense thermal inversions and greater terrain slope. All these aspects, along with its solar orientation, can increase or reduce incident radiation that will affect the phytosociological structure and composition of the forest.

The different types of the Atlantic Forest biome feature a distinct nutrient transfer via litter deposition. This may be linked to the different developmental stages of the forest. In each stage, the vegetation displays distinct control forms of nutrient demands through storage and redistribution in biomass [54] (**Table 2**).


**Table 2.** Nutrients transferred to the soil annually via litter deposition in different forest types in the Brazilian Atlantic Forest.

Under similar climate and soil conditions, variation in litter accumulation occurs by both the amount and the composition (contents of lignin, polyphenols and nutrients) of the material deposited, influencing decomposition speed and nutrient release [58]. In general, N and Ca are the nutrients that are most accumulated on the soil in the Atlantic Forest (**Table 3**). In forests established in weathered soils, accumulated litterfall ensures nutrient cycling. This litter, along with the soil, regulates many fundamental processes in the dynamics of ecosystems, such as primary production and nutrient release [59].

The amount of nutrients in litter deposed or accumulated varies according to the forest type and edafoclimatic conditions. Abiotic and biotic factors affect litter production, namely the vegetation type, altitude, latitude, rainfall, temperature, light incidence, relief, water availa‐ bility and soil characteristics [60]. Likewise, nutrient concentration and content in this litter vary according to the soil type, vegetation, population density, the ability of species to absorb, use and translocate nutrients before leaf senescence, as well as the percentage of leaves in


relation to other components of the natural habitat (soil and climate conditions) and the tree age [29, 61].

**Table 3.** Nutrients stored in accumulated litter on the soil in different forest types in the Brazilian Atlantic Forest.

The availability of nutrients in the accumulated litterfall occurs during decomposition. Decomposition is controlled by the nature of the scavenging community (animals and microorganisms), by the organic matter characteristics, which determines its degradability (quality) and by the physical‐chemical aspects of the environment, which operates in the edaphic or microscale conditions [62].

Similar to litter decomposition, the rate at which nutrients are released depends on the chemical composition of the litter, the structural nature of the nutrient in the litter and the availability of external nutrient sources [63]. The release of nutrients in the litter depends on its quality, on macro‐ and micro‐climatic variables and on biotic activities. The climate fac‐ tors that influence litter decomposition the most are temperature and soil moisture [63]. Ac‐ cording to the authors, another primordial factor responsible for higher or lower decomposition rate is the structural composition of tissues because tissues that contain high‐ er contents of cellulose, hemicellulose and lignin are more resistant to decomposition than tissues with lower contents of these compounds.
