Soil light organic matter fractions in slash‑and‑mulch agroforestry system under fallow vegetation management

O objetivo deste trabalho foi avaliar os impactos do ciclo pousio‑cultivo sobre as frações leves da matéria orgânica do solo (MOS), em sistema agroflorestal sequencial de corte e trituração, com diferentes manejos de capoeira, na Amazônia Oriental. A amostragem foi realizada nas fases de pré‑pousio, pós‑pousio e pós‑cultivo de milho. Foram determinados os estoques de matéria orgânica leve livre (MOL‑L) e matériaorgânica leve oclusa (MOL‑O), carbono orgânico total (COT), nitrogênio total (NT) e estoques de C e N na MOL‑L e na MOL‑O. Não houve efeito do manejo da capoeira nas variáveis estudadas, exceto quanto ao NT a 30–50 cm e à MOL‑O a 10–20 cm de profundidade do solo. As frações da matéria orgânica leve foram afetadas pelas fases do sistema agroflorestal sequencial de corte e trituração. Os maiores estoques de C e N foram observados na MOL‑L, nos períodos pós‑pousio e pós‑cultivo. Embora os estoques de C e N totais do solo não tenham aumentado, o aumento da MOL‑L e de seus estoques de C e N indica melhoria e manutenção da qualidade do solo no sistema de corte e trituração da biomassa acumulada em 23 meses de pousio, mesmo após período de cultivo.The objective of this work was to evaluate the impacts of fallow to crop cycle on the light fractions of soil organic matter (SOM) in a slash‑and‑mulch agroforestry system with different fallow vegetation management, in the Eastern Amazon. Sampling was carried out in the pre‑fallow, post‑fallow, and post‑cultivation stages. Stocks of free light organic matter (F‑LOM) and occluded light organic matter (O‑LOM), total organic carbon (TOC), total nitrogen (TN), and C and N stocks on F‑LOM and O‑LOM were determined. There was no effect of fallow management in the studied variables, except for TN at 30–50 cm and O‑LOM at 10–20 cm soil depth. Light organic matter fractions were affected by the phases of the agroforestry slash‑and‑mulch system. The highest C and N stocks were observed in F‑LOM in the post‑fallow and post‑cultivation periods. Although there was no increase in total C and N stocks, the increase in F‑LOM and its stocks of C and N indicates the improvement and maintenance of soil quality in the slash-and-mulch system of biomass accumulated in 23 months of fallow, even after crop phase

Morphological parameters to determine differential tolerance of rice cultivars to aluminium toxicity

Dois experimentos em casa de vegetação foram conduzidos visando identificar parâmetros morfológicos ligados à tolerância ao alumínio (Al) e estabelecer a concentração de Al e o tempo de cultivo suficientes para a expressão da tolerância ao Al, em duas cultivares de arroz, em solução nutritiva. Plantas de determinado comprimento radicular máximo foram transferidas para solução nutritiva com quatro concentrações de Al (0, 80, 160 e 320 mmol L-1), a pH 4,0. Em cada coleta, foram medidos o comprimento máximo radicular, área radicular, área foliar e massa seca de raízes e parte aérea. Apenas os parâmetros morfológicos ligados ao sistema radicular possibilitaram o reconhecimento da tolerância diferencial das cultivares; a elongação radicular relativa foi a medida mais sensível. Quatro dias de exposição ao Al foram suficientes para a detecção da tolerância diferencial por meio da elongação radicular relativa. Os procedimentos estabelecidos nos experimentos podem ser utilizados para a avaliação de um número maior de cultivares.Two nutrient solution greenhouse experiments were conducted to identify morphological parameters that express Al tolerance and to determine the influence of period of plant growth and Al concentration necessary for tolerance discrimination, in two rice cultivars. Plants of known maximum root length were transferred to nutrient solution at four levels of Al (0, 80, 160 and 320 mmol L-1) with a pH 4.0. In each collection, the new maximum root length was measured in addition to root and leaf areas, and root and shoot dry weights. Only the morphological parameters related to the root system differentiated Al tolerance of the cultivars, and relative root elongation was the most sensitive. Four days of exposure to Al were sufficient to detect differences in Al tolerance by means of relative root elongation. The methods established in this study can be useful in evaluating larger number of cultivars

BIOMASS AND NUTRIENT ACCUMULATION OF TWO LEGUMINOUS TREES IN AN IMPROVED FALLOW IN AMAZON RAIN FOREST

A vegeta\ue7\ue3o de pousio \ue9 um dos principais componentes dos sistemas agroflorestais sequenciais de derrubada e queima, praticados tradicionalmente pela agricultura familiar na Amaz\uf4nia. A remo\ue7\ue3o progressiva de nutrientes do solo por essa pr\ue1tica implica redu\ue7\uf5es cont\uednuas nos estoques de carbono e nutrientes causando decl\uednio da produtividade do solo, perda da capacidade de regenera\ue7\ue3o e diminui\ue7\ue3o da diversidade de esp\ue9cies da vegeta\ue7\ue3o. O melhoramento de pousio com esp\ue9cies leguminosas fixadoras do nitrog\ueanio atmosf\ue9rico pode contribuir para uma maior produ\ue7\ue3o de biomassa e ac\ufamulo de nutrientes em compara\ue7\ue3o com a vegeta\ue7\ue3o espont\ue2nea, atendendo \ue0 demanda nutricional das culturas subsequentes, podendo ser considerada como uma tecnologia de produ\ue7\ue3o sustent\ue1vel. Esse trabalho avaliou o efeito da aduba\ue7\ue3o fosfatada de baixa solubilidade no ac\ufamulo de biomassa e nutrientes da parte a\ue9rea de leguminosas arb\uf3reas utilizadas em melhoramento de vegeta\ue7\ue3o de pousio. O experimento foi conduzido por 23 meses, em um sistema agroflorestal de \u201ccorte e tritura\ue7\ue3o\u201d em Marapanim, Par\ue1. Foram utilizadas as esp\ue9cies tachi-branco - Sclerolobium paniculatum Vogel e ing\ue1 - Inga edulis Mart e foram estimados biomassa, teor e estoque de nutrientes dos compartimentos folha, galho e tronco. Houve ac\ufamulo de biomassa, estoques de P, Ca e Mg nas folhas, estoque de P nos galhos e o teor de c\ue1lcio nas folhas das leguminosas \ue9 limitado por f\uf3sforo, segundo os resultados encontrados. A esp\ue9cie Inga edulis apresentou maiores teores de pot\ue1ssio, c\ue1lcio e magn\ue9sio nos compartimentos folha, galho e tronco, enquanto que a esp\ue9cie Sclerolobium paniculatum apresentou maiores ac\ufamulos de biomassa e estoques de nitrog\ueanio, f\uf3sforo, pot\ue1ssio, c\ue1lcio e magn\ue9sio nos compartimentos folha, galho e tronco.The fallow vegetation is the main component of sequential agroforestry systems in Amazon rain forest.The progressive removal of soil nutrient by slash/mulch agriculture involves continuing losses in carbon and nutrient stocks, leading to decline in soil productivity, low regeneration ability and decrease of species diversity of fallow vegetation. The fallow vegetation management by introducing fast growing leguminous trees has the potential to accumulate more biomass and nutrients to serve the nutrient demands of crops and its management has been considered as a sustainable technology production. This study aimed to evaluate the effect of low solubility of phosphorus fertilizer in the biomass and nutrient stocks of leguminous trees used in fallow improvement. The experiment was conducted for 23 months in a sequential agroforestry slash-and-mulch system in eastern Amazon forest. The species selected were tachi-branco - Sclerolobium paniculatum Vogel and inga - Inga edulis Mart. Biomass and nutrient stocks and nutrient concentrations of leaf, branch and trunk were estimated. Phosphorus fertilization had a positive effect on calcium concentration in the leaves and stocks of biomass and nutrient contents (phosphorus, calcium and magnesium) in the leaves of legume trees. Inga edulis showed higher levels of potassium, calcium and magnesium concentrations in leaves, while Sclerolobium paniculatuttm showed higher biomass and stocks of nitrogen, phosphorus, potassium, calcium and magnesium in leaf, branch and trunk

Litter flux in a successional forest ecosystem under nutrient manipulation in Eastern Amazon / Fluxo de serapilheira em um ecossistema florestal sucessional sob manipulação de nutrientes na Amazônia Oriental

The aim of this work was to evaluate the dynamics of Ca and Mg cations, via litter, in a successional forest ecosystem, on the middle plateau of the Apeú river, in Castanhal, northeast of Pará (1º19’ S, 47º57’ W). The magnitude of this phenomenon can be explained by the functional role of the floristic structure, with dominant species, Myrcia sylvatica (G. mey) DC., Myrcia bracteata (Rich) DC., Miconia ciliata (Rich) DC., Lacistema pubescens Mart., Lacistema aggregatum (Berg.) Rusby, Vismia guianensis (Aubl.) Choisy, Cupania scrobiculata Rich. and Ocotea guianensis Aubl, which consisted in the determinant factors, associated to the natural hydroperiodic effect. The evaluation  of analytical results, in litter removal treatment, of the mean mass of Ca ranged from 0.018 to 0.076 g m-2month-1, while Mg varied from 0.006 to 0.028 g m-2month-1, being significantly (P<0.05) different from control in treatment and time. However, the flux distribution was influenced by the season, being higher in the dry period. The flux values of Ca (0.047 ± 0.015 g m-2month-1) were significantly higher (P<0.05) than those of Mg (0.015 ± 0.004 g m-2month-1), independently of the manipulation via treatment, phenomenon explained by the dynamics of Calcium in the biogeochemical cycle

Plasticity in leaf-level water relations of tropical rainforest trees in response to experimental drought

Summary The tropics are predicted to become warmer and drier, and understanding the sensitivity of tree species to drought is important for characterizing the risk to forests of climate change. This study makes use of a long-term drought experiment in the Amazon rainforest to evaluate the role of leaf-level water relations, leaf anatomy and their plasticity in response to drought in six tree genera. The variables (osmotic potential at full turgor, turgor loss point, capacitance, elastic modulus, relative water content and saturated water content) were compared between seasons and between plots (control and through-fall exclusion) enabling a comparison between short- and long-term plasticity in traits. Leaf anatomical traits were correlated with water relation parameters to determine whether water relations differed among tissues. The key findings were: osmotic adjustment occurred in response to the long-term drought treatment; species resistant to drought stress showed less osmotic adjustment than drought-sensitive species; and water relation traits were correlated with tissue properties, especially the thickness of the abaxial epidermis and the spongy mesophyll. These findings demonstrate that cell-level water relation traits can acclimate to long-term water stress, and highlight the limitations of extrapolating the results of short-term studies to temporal scales associated with climate change

Limited acclimation in leaf anatomy to experimental drought in tropical forest trees

Dry periods are predicted to become more frequent and severe in the future in some parts of the tropics, including Amazonia, potentially causing reduced productivity, higher tree mortality and increased emissions of stored carbon. Using a long-term (12 year) through-fall exclusion (TFE) experiment in the tropics, we test the hypothesis that trees produce leaves adapted to cope with higher levels of water stress, by examining the following leaf characteristics: area, thickness, leaf mass per area, vein density, stomatal density, the thickness of palisade mesophyll, spongy mesophyll and both of the epidermal layers, internal cavity volume and the average cell sizes of the palisade and spongy mesophyll. We also test whether differences in leaf anatomy are consistent with observed differential drought-induced mortality responses among taxa, and look for relationships between leaf anatomy, and leaf water relations and gas exchange parameters. Our data show that trees do not produce leaves that are more xeromorphic in response to 12 years of soil moisture deficit. However, the drought treatment did result in increases in the thickness of the adaxial epidermis (TFE: 20.5 ± 1.5 µm, control: 16.7 ± 1.0 µm) and the internal cavity volume (TFE: 2.43 ± 0.50 mm(3) cm(−2), control: 1.77 ± 0.30 mm(3 )cm(−2)). No consistent differences were detected between drought-resistant and drought-sensitive taxa, although interactions occurred between drought-sensitivity status and drought treatment for the palisade mesophyll thickness (P = 0.034) and the cavity volume of the leaves (P = 0.025). The limited response to water deficit probably reflects a tight co-ordination between leaf morphology, water relations and photosynthetic properties. This suggests that there is little plasticity in these aspects of plant anatomy in these taxa, and that phenotypic plasticity in leaf traits may not facilitate the acclimation of Amazonian trees to the predicted future reductions in dry season water availability

Foliar water uptake in Amazonian trees: evidence and consequences

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordThe absorption of atmospheric water directly into leaves enables plants to alleviate the water stress caused by low soil moisture, hydraulic resistance in the xylem and the effect of gravity on the water column, while enabling plants to scavenge small inputs of water from leaf-wetting events. By increasing the availability of water, and supplying it from the top of the canopy (in a direction facilitated by gravity), foliar uptake (FU) may be a significant process in determining how forests interact with climate, and could alter our interpretation of current metrics for hydraulic stress and sensitivity. FU has not been reported for lowland tropical rainforests; we test whether FU occurs in six common Amazonian tree genera in lowland Amazônia, and make a first estimation of its contribution to canopy–atmosphere water exchange. We demonstrate that FU occurs in all six genera and that dew-derived water may therefore be used to “pay” for some morning transpiration in the dry season. Using meteorological and canopy wetness data, coupled with empirically derived estimates of leaf conductance to FU (kfu), we estimate that the contribution by FU to annual transpiration at this site has a median value of 8.2% (103 mm/year) and an interquartile range of 3.4%–15.3%, with the biggest sources of uncertainty being kfu and the proportion of time the canopy is wet. Our results indicate that FU is likely to be a common strategy and may have significant implications for the Amazon carbon budget. The process of foliar water uptake may also have a profound impact on the drought tolerance of individual Amazonian trees and tree species, and on the cycling of water and carbon, regionally and globally.Natural Environment Research Council (NERC)Australian Research Council (ARC)CNPQEuropean Union FP7Royal SocietyCoordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES

Alternativas à agricultura de corte e queima em processos de transição agroecológica: um desafio para a agricultura amazónica

A paisagem agrícola amazônica abriga uma diversidade de situações onde, com frequência, ocorre a prática do corte-e-queima para preparo de área para plantio. A constatação dos impactos adversos dessa prática evidencia a necessidade de promover a sua substituição via sistemas alternativos que viabilizem a produção agrícola, reduzindo ou evitando o uso do fogo. Embora muitas alternativas disponíveis tenham características de passos de processos de transição agroecológica e a ampliação da sua adoção possa ser beneficiada pela implantação de estratégias de transição social agroecológica, este tipo de prática não vem sendo abordado em estudos sobre processos de transição agroecológica. Este artigo se propõe a analisar exemplos de práticas alternativas à derruba-e-queima na Amazônia brasileira, à luz de processos de transição agroecológica e social agroecológica, como subsídio ao avanço no seu desenvolvimento e adoção, e à formulação e implantação de políticas públicas.The Amazonian agricultural landscape is home to a diversity of situations where often occurs the practice of slash-and-burn for land preparation for planting. The observation of the adverse impacts of this practice highlights the need to promote its replacement via alternative systems that enable agricultural production, reducing or avoiding the use of fire. Although many of the available alternatives have characteristics of ecological transition process steps and the expansion of its adoption can be benefited by the implementation of social-ecological transition strategies, this type of practice has not been addressed in studies on agroecological transition processes. This article sets out to analyse examples of alternatives to practices of slash-and-burn in the Brazilian Amazon, in the light of processes of agroeclogical and social-agroecological transitions, as subsidy to the advancement in their development and adoption and to the formulation and implementation of public policies.Eje A1 Sistemas de producción de base agroecológica (Trabajos científicos)Facultad de Ciencias Agrarias y Forestale

Alternativas à agricultura de corte e queima em processos de transição agroecológica: um desafio para a agricultura amazónica

A paisagem agrícola amazônica abriga uma diversidade de situações onde, com frequência, ocorre a prática do corte-e-queima para preparo de área para plantio. A constatação dos impactos adversos dessa prática evidencia a necessidade de promover a sua substituição via sistemas alternativos que viabilizem a produção agrícola, reduzindo ou evitando o uso do fogo. Embora muitas alternativas disponíveis tenham características de passos de processos de transição agroecológica e a ampliação da sua adoção possa ser beneficiada pela implantação de estratégias de transição social agroecológica, este tipo de prática não vem sendo abordado em estudos sobre processos de transição agroecológica. Este artigo se propõe a analisar exemplos de práticas alternativas à derruba-e-queima na Amazônia brasileira, à luz de processos de transição agroecológica e social agroecológica, como subsídio ao avanço no seu desenvolvimento e adoção, e à formulação e implantação de políticas públicas.The Amazonian agricultural landscape is home to a diversity of situations where often occurs the practice of slash-and-burn for land preparation for planting. The observation of the adverse impacts of this practice highlights the need to promote its replacement via alternative systems that enable agricultural production, reducing or avoiding the use of fire. Although many of the available alternatives have characteristics of ecological transition process steps and the expansion of its adoption can be benefited by the implementation of social-ecological transition strategies, this type of practice has not been addressed in studies on agroecological transition processes. This article sets out to analyse examples of alternatives to practices of slash-and-burn in the Brazilian Amazon, in the light of processes of agroeclogical and social-agroecological transitions, as subsidy to the advancement in their development and adoption and to the formulation and implementation of public policies.Eje A1 Sistemas de producción de base agroecológica (Trabajos científicos)Facultad de Ciencias Agrarias y Forestale

Plasticity in leaf-level water relations of tropical rainforest trees in response to experimental drought

The tropics are predicted to become warmer and drier, and understanding the sensitivity of tree species to drought is important for characterizing the risk to forests of climate change. This study makes use of a long-term drought experiment in the Amazon rainforest to evaluate the role of leaf-level water relations, leaf anatomy and their plasticity in response to drought in six tree genera. The variables (osmotic potential at full turgor, turgor loss point, capacitance, elastic modulus, relative water content and saturated water content) were compared between seasons and between plots (control and through-fall exclusion) enabling a comparison between short- and long-term plasticity in traits. Leaf anatomical traits were correlated with water relation parameters to determine whether water relations differed among tissues. The key findings were: osmotic adjustment occurred in response to the long-term drought treatment; species resistant to drought stress showed less osmotic adjustment than drought-sensitive species; and water relation traits were correlated with tissue properties, especially the thickness of the abaxial epidermis and the spongy mesophyll. These findings demonstrate that cell-level water relation traits can acclimate to long-term water stress, and highlight the limitations of extrapolating the results of short-term studies to temporal scales associated with climate change