Dinâmica de nitrogênio em microbacias na Mata Atlântica e Cerrado no Nordeste brasileiro

The aim of this study was to determine concentrations of nitrogen (N) in two biomes, Atlantic Forest (AF) and Cerrado (CR), at the interface between terrestrial and aquatic ecosystems. This involved evaluating N in vegetation (litterfall), soil and water in small watersheds in environmental protection areas in northeastern Brazil. Soil chemical and physical analyzes were performed and mineralization and nitrification rates were determined. The forms of organic, inorganic and particulate nitrogen in water were determined by spectrophotometry. Two collections were carried out, one in the dry season (October and November 2019) and another in the rainy season (February and March 2020), in two environmental preservation areas, Estação Veracel Private Natural Heritage Reserve - (Atlantic Forest) and Chapada Diamantina National Park (Cerrado), with five small watersheds sampled in each biome. The N concentration in litterfall was similar in both biomes, with averages of 0.69%. In relation to soil and water, N concentrations were higher in AF compared to CR, with concentrations of 0.95 ± 0.40 and 0.59 ± 0.14 µg.Ng-1 of nitrate in the soils of AF and CR, respectively, and 3.53 ± 2.51 µM of nitrate in water in AF and 0.76 ± 0.78 µM in CR.The Brazilian biomes influence the biogeochemical cycles since they present a diversity of phytophysiognomies associated with the specific chemical, physical and biological characteristics of each region. The aim of this study was to verify the influence of two biomes, Atlantic Forest (AF) and Cerrado/”Campo Rupestre” (CR), on nitrogen concentrations (N) at the interface between terrestrial-aquatic ecosystems through the evaluation of N in vegetation (litterfall), soil and streamwater areas of environmental protection in northeastern Brazil. Samples were collected during the dry and rainy periods in five streams in each biome located in preservation areas. The results showed that no significant differences were observed in the production and N concentration in litterfall between the biomes. In spite of the soil and water, the N concentrations were higher in the sites located in the Atlantic Forest compared to the “Campo Rupestre”. The low moisture and low net mineralization and nitrification in “Campo Rupestre” result in lower concentrations of N in the soil. This lower concentration associated with edaphoclimatic conditions in CR was responsible for the reduction of N leaching in soil resulting in lower concentrations of N in water.O objetivo deste estudo foi determinar as concentrações de nitrogênio (N) em dois biomas, Mata Atlântica (AF) e Cerrado (CR), na interface entre os ecossistemas terrestre-aquático, avaliando o N na vegetação (serapilheira), no solo e na água em microbacias em áreas de proteção ambiental no nordeste brasileiro. Foram realizadas análises químicas e físicas do solo e determinadas as taxas de mineralização e nitrificação. Na água, foram determinadas as formas de nitrogênio orgânico, inorgânico e particulado por espectrofotometria. Foram realizadas duas coletas, uma no período seco (outubro e novembro de 2019) e outra no chuvoso (fevereiro e março de 2020) em duas áreas de preservação ambiental, na Reserva Particular de Patrimônio Natural - Estação Veracel (Mata Atlântica) e Parque Nacional Chapada Diamantina (Cerrado), sendo amostrados cinco microbacias em cada bioma. A concentração de N na serapilheira foi semelhante entre os biomas, apresentando médias de 0,69%. Em relação ao solo e a água, as concentrações de N foram maiores na AF comparados a CR, com concentrações de 0,95 ± 0,40 e 0,59 ± 0,14 µg.Ng-1 de nitrato no solo de AF e CR, respectivamente e 3,53 ± 2,51 µM de nitrato na água em AF e 0,76 ± 0,78 µM em CR

Litter inputs and standing stocks in riparian zones and streams under secondary forest and managed and abandoned cocoa agroforestry systems

Background Cocoa is an important tropical tree crop that is mainly cultivated in agroforestry systems (AFS). This system, known as cabruca in northeastern Brazil, holds promise to reconcile biodiversity conservation and economic development. However, since cocoa AFS alters forest structure composition, it can affect litter dynamics in riparian zones and streams. Thus, our objective was to determine litter inputs and standing stocks in riparian zones and streams under three types of forest: managed cocoa AFS, abandoned cocoa AFS, and secondary forest. Methods We determined terrestrial litter fall (TI), vertical (VI) and lateral (LI) litter inputs to streams, and litter standing stocks on streambeds (BS) in the Atlantic Forest of northeastern Brazil. Litter was collected every 30 days from August 2018 to July 2019 using custom-made traps. The litter was dried, separated into four fractions (leaves, branches, reproductive organs, and miscellaneous material) and weighed. Results Terrestrial litter fall was similar in all forests, ranging from 89 g m−2 month−1 in secondary forest (SF) to 96 g m−2 month−1 in abandoned cocoa AFS (AC). Vertical input were higher in AC (82 g m−2 month−1) and MC (69 g m−2 month−1) than in SF (40 g m−2 month−1), whereas lateral input were higher in MC (43 g m−2 month−1) than in AC (15 g m−2 month−1) and SF (24 g m−2 month−1). Standing stocks followed the order SF > AC > MC, corresponding to 425, 299 and 152 g m−2. Leaves contributed most to all litter fractions in all forests. Reproductive plant parts accounted for a larger proportion in managed AFS. Branches and miscellaneous litter were also similar in all forests, except for higher benthic standing stocks of miscellaneous litter in the SF. Despite differences in the amounts of litter inputs and standing stocks among the forests, seasonal patterns in the abandoned AFS (AC) were more similar to those of the secondary forest (SF) than the managed AFS, suggesting potential of abandoned AFS to restore litter dynamics resembling those of secondary forests