Variação temporal e espacial na produtividade de raízes finas em uma floresta da Amazônia central

Understanding the primary productivity in many ecosystems, including tropical forests is necessary due to the scarcity of information on many of its components, as well as its importance in the carbon cycle in terrestrial ecosystems. Most studies have focused on investigating the productivity of forests in their above-ground components, so that little is known yet about the dynamics of productivity and nutrient cycling made by the roots below ground, which is mainly linked to difficult to have to study this compartment in forest ecosystems. Moreover, the few studies on the productivity of existing roots in the Amazon, were made in a small number of plots and on short time, so that was given little attention to the spatial variability and temporal productivity of fine roots. In this context stocks and productivity of fine roots (Rp) were evaluated in 9 plots of 0,5 ha in upland forests located in the Forest Reserve Adolfo Ducke. The soils had their physical and chemical properties evaluated over time. Having been to Rp analyzed in relation to the role of controlling environmental factors and regional topographic position (plateaux, slope and valley bottoms). The areas of plateaux had a lower value of Rp (1,58±0,12 Mg C ha-1 yr-1) when compared with the valley bottoms (2,48±0,28 Mg C ha-1 yr-1). The slope areas behaved similarly to plateaux areas with 1,57±0.08 Mg C ha-1 yr-1. As to the residence time in the soil fine roots in the areas of valley bottoms have an average time of 5 months and the areas of plateaux 3 on average three months. The Rp was not sensitive to the availability of nutrients in the soil, but it seems to respond to the levels of water availability, but in a complex way. The forest structure has also strong influence on levels of Rp. Net primary productivity (NPP) was calculated with literature data of assistance to the same study plots in 8,34 Mg C ha-1 yr-1 to plateaux, 7,82 Mg C ha-1 yr-1 for slope area and 7,81 Mg C ha-1 yr-1 for the velley bottoms respectively. However allocation between above and below ground was different with valley bottoms average allocating the NPP 32% below ground, while plateaux + slope area allocated only 19,8%. The morphology of the fine roots of the slopes and valley bottoms showed no changes regarding the availability of water in as the plateaus in the dry season had higher mortality. The information presented here has the potential to contribute to the improvement of regional estimates of primary productivity in the Amazon, allowing modeling its dynamics from other variables more easily measurable, especially precipitation and forest biomass.A compreensão da produtividade primária em muitos ecossistemas, incluindo florestas tropicais faz-se necessária, devido à escassez de informações em vários de seus componentes, assim como sua importância no ciclo do carbono em ecossistemas terrestres. A maior parte dos estudos tem enfocado em investigar a produtividade das florestas nos seus componentes acima do solo, de forma que pouco se conhece ainda sobre a dinâmica da produtividade e da ciclagem de nutrientes feitas pelas raízes abaixo do solo, o que está ligado principalmente à dificuldade de se tem em estudar esse compartimento em ecossistemas florestais. Além disso, os poucos estudos sobre produtividade de raízes existentes na Amazônia, foram feitos em um número pequeno de parcelas e sobre curto intervalo de tempo, de forma que foi dada pouca atenção à variabilidade espacial ou temporal da produtividade de raízes finas. Neste contexto os estoques e a produtividade de raízes finas (RP) foram avaliadas em 9 parcelas de 0,5 ha em florestas de terra firme localizadas na Reserva Florestal Adolfo Ducke. Os solos tiveram suas propriedades físicas e químicas avaliadas ao longo do tempo. Tendo sido a Rp analisadas em relação ao papel controlador dos fatores ambientais e da posição topográfica regional (platô, vertente e baixio). As áreas de platô tiveram um menor valor de RP (1,58±0,12 Mg C ha-1 ano- 1) quando comparada com os valores de baixio (2,48±0,28 Mg C ha-1 ano-1). As áreas de vertente se comportaram de forma semelhante às áreas do platô com 1,57±0,08 Mg C ha-1 ano -1. Em quanto ao tempo de residência no solo as raízes finas nas áreas de baixio têm em media um tempo de 5 meses e as áreas de platô 3 em media três meses. A RP não se mostrou sensível à disponibilidade de nutrientes no solo, mas parece responder aos níveis de disponibilidade de água, porém de forma complexa. A estrutura da floresta tem também forte influência nos níveis de Rp. A produtividade primária líquida (PPL) foi calculada, com auxilio de dados da literatura para as mesmas parcelas de estudo, em 8,34 Mg C ha-1 ano-1 para platô, 7,82 Mg C ha-1 ano-1 para a vertente e 7,81 Mg C ha-1 ano-1 para o baixio, respectivamente. Entretanto a alocação entre acima e abaixo do solo foi diferente, com baixios alocando em média 32% da PPL abaixo do solo enquanto platô+vertente alocaram apenas 19,8%. A morfologia das raízes finas das vertentes e baixios não apresentaram mudanças em relação a disponibilidade de agua, em quanto os platôs na estação seca tiveram maior mortalidade. As informações aqui apresentadas tem potencial para contribuir para o aperfeiçoamento das estimativas regionais de produtividade primária na Amazônia, permitindo modelar sua dinâmica a partir de outras variáveis mais facilmente mensuráveis, notadamente a precipitação e a biomassa florestal

Direct evidence for phosphorus limitation on Amazon forest productivity

The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% of the Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2 fertilization4, with major implications for future carbon sequestration and forest resilience to climate change.The authors acknowledge funding from the UK Natural Environment Research Council (NERC), grant number NE/L007223/1. This is publication 850 in the technical series of the BDFFP. C.A.Q. acknowledges the grants from Brazilian National Council for Scientific and Technological Development (CNPq) CNPq/LBA 68/2013, CNPq/MCTI/FNDCT no. 18/2021 and his productivity grant. C.A.Q., H.F.V.C., F.D.S., I.A., L.F.L., E.O.M. and S.G. acknowledge the AmazonFACE programme for financial support in cooperation with Coordination for the Improvement of Higher Education Personnel (CAPES) and the National Institute of Amazonian Research as part of the grants CAPES-INPA/88887.154643/2017-00 and 88881.154644/2017-01. T.F.D. acknowledges funds from FundacAo de Amparo a Pesquisa do Estado de SAo Paulo (FAPESP), grant 2015/50488-5, and the Partnership for Enhanced Engagement in Research (PEER) programme grant AID-OAA-A-11-00012. L.E.O.C.A. thanks CNPq (314416/2020-0)

Direct evidence for phosphorus limitation on Amazon forest productivity

The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% of the Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2 fertilization4, with major implications for future carbon sequestration and forest resilience to climate change

Carbono orgânico e nutrientes em solos antrópicos e adjacentes sob floresta secundária na Amazônia Central

Most soils in the Amazon, land is usually weathered and have low chemical fertility. However, there are also anthropogenic A horizon soils, dark colored, popularly called "Terra Preta" (ICC), which generally have high fertility with high levels of P, Ca, Mg, Mn, Zn and organic matter , high pH (5.5 to 6.5), high cation exchange capacity, low potential acidity (H + Al) and high base saturation, when compared to adjacent soils. The Terra Preta in Amazonia have elevated levels of carbon, with concentrations up to 150 g C kg-1 soil, compared to the surrounding soils with 20-30 g C kg-1 soil. The ability of TPIs to store and retaining stable carbon are high, it is potentially an important mechanism for mitigating the greenhouse effect and needs to be better assessed and understood. This study aimed to estimate the levels and dynamics of dissolved organic carbon (DOC) and nutrient content in soil profiles and anthropogenic soils adjacent secondary forest in central Amazonia. The experimental design was a randomized block design with three replicates each block being a trial site: Autazes Mirim (ATM) Meeting of the Waters (EA), Rio Preto da Eva (RPE). Collections were made in two soils at each site: soil horizon with man-made and man-made adjacent without horizons. We are the anthropogenic Terra Preta (TP) and Land Mulatas (TM) in the adjacent Oxisols Yellow (LA) in three locations. In each area three systems were installed to extract soil solution, each system consisted of three extractants at different depths up to 1m. Were also made to retrieve samples of soil up to 1m for determination of chemical and physical characteristics. There was significant difference in carbon stocks between the soils and sites studied: Carbon stocks were Autazes Mirim (ATM) in TP 172 Mg C/ha-1 in TM 192 Mg C/ha-1 and LA C/ha-1 of 233 Mg. In as found in Waters (EA) for TP was 213 Mg C/ha-1 in TM C/ha-1 112 Mg and 77 Mg C/ha-1 LA, and finally in Rio Preto da Eva (RPE) values were in the TP C/ha-1 165 Mg, 151 Mg C/ha-1 in TM and LA 179 Mg C/ha-1. The highest values of DOC mobilized were found in adjacent soil (624, 297 and 662 mg L-1 for ATM, EA and RP, respectively), are intermediates for the Lands Mulatas (511, 371 and 634 mg L-1 for ATM EA and EPR, respectively) and lowest for Black Earth (464, 189 and 465 mg L-1 for ATM, EA and EPR, respectively). Once knowing the relationship between chemical and physical properties of soils and its relationship with the DOC could improve the understanding of leaching processes in soils with anthropogenic A horizon and soil without these horizons.Na Amazônia ocorrem solos com horizonte A antrópico, de coloração escura, popularmente denominados de "Terras Pretas de Índio" (TPI), que geralmente apresentam alta fertilidade, com elevados teores de P, Ca, Mg, Mn, Zn e de matéria orgânica, elevado pH (5,5–6,5), alta capacidade de troca catiônica, baixa acidez potencial (H + Al) e alta saturação por bases, quando comparados aos solos adjacentes. As Terras Pretas de Índio da Amazônia têm níveis elevados de carbono, com concentrações de até 150 g C kg-1 de solo, em comparação aos solos circunvizinhos com 20–30 g C kg-1 de solo. A capacidade das TPIs de estocar e reter carbono estável são elevados, sendo potencialmente um importante mecanismo para a mitigação do efeito estufa e precisa ser melhor avaliada e entendida. Este estudo teve como objetivo estimar os teores e a dinâmica do carbono orgânico dissolvido (COD) e os teores de nutrientes em perfis de solos antrópicos e solos adjacentes sob floresta secundária na Amazônia central. O delineamento experimental foi o de blocos inteiramente ao acaso com três repetições sendo cada bloco um local de avaliação: Autaz Mirim (ATM), Encontro das Águas (EA), Rio Preto da Eva (RPE). Foram feita coletas em dois solos em cada local: Solos com horizonte antrópicos e adjacentes sem horizontes antrópicos. Nos antrópicos estão as Terras Pretas (TP) e Terras Mulatas (TM), no adjacente os Latossolos Amarelo (LA) nos três locais. Em cada área foram instalados três sistemas de extração de solução do solo; cada um dos sistemas constou de três extratores a diferentes profundidades até 1m. Foram feitas também coletas de amostras de solo até 1m para determinação de características químicas e físicas. Verificou-se diferencia significativas nos estoques de carbono entre os solos e locais estudados: Os estoques de carbono foram para Autaz Mirim (ATM) em TP de 172 Mg C/ha-1, em TM de 193 Mg C/ha-1 e LA de 232 Mg C/ha-1. Em quanto em Encontra das Águas (EA) foi para TP de 213 Mg C/ha-1, em TM de 112 Mg de C/ha-1 e LA de 176 Mg C/ha-1, e finalmente em Rio Preto da Eva (RPE) os valores foram em TP de 165 Mg C/ha-1, em TM 151 Mg C/ha-1 e LA de 179 Mg C/ha-1. Os mais altos valores mobilizados de COD foram encontrados nos solos adjacentes (624; 297 e 662 mg L-1 para ATM, EA e RP, respectivamente), sendo intermediários para as Terras Mulatas (511; 371 e 634 mg L-1 para ATM, EA e RPE, respectivamente) e mais baixos para Terra Preta (464; 189 e 465 mg L-1 para ATM, EA e RPE, respectivamente). Uma vez conhecendo as relações entre propriedades químicas e físicas dos solos e sua relação com o COD poderemos melhorar o entendimento dos processos de lixiviação nos solos com horizonte A antrópico e dos solos sem estes horizonte

Weak phylogenetic and habitat effects on root trait variation of 218 Neotropical tree species

Introduction Tropical forests harbor a large diversity of closely related tree species that can thrive across habitats. This biodiversity has been found to correspond to large functional diversity in aboveground traits, and likely also relates to belowground trait variation. Globally, root trait (co-)variation is driven by different belowground resource strategies of species, environmental variation, and phylogeny; however, these patterns mostly reflect observations from temperate biomes and remain unconfirmed in tropical trees. We examine phylogenetic and environmental effects on root trait (co-)variation of trees across habitats in an Amazonian rainforest. Methods Roots of 218 tree species from ten dominant families were sampled across three major habitats near Manaus, Brazil. We quantified five morphological and architectural root traits to (i) investigate how they reflected different resource strategies across species, (ii) compare them between families and superorders to test phylogenetic effects, and (iii) compare them between habitats to determine environmental effects on root trait expressions and variability. Results Root traits discriminated species along a tradeoff between root diameter and root branching and, secondly, due to variation in root tissue density. Our results further show weak phylogenetic effects on tropical tree root variation, for example, families from the same superorder showed large divergence in their root traits, while those from different superorders often overlapped in their root morphology and architecture. Root traits differed significantly between habitats but habitat type had only little effect on overall root trait variation. Discussion Our work suggests that the dimensions and drivers that underlie (co-)variation in tropical root traits may differ from global patterns defined by mostly temperate datasets. Due to (a)biotic environmental differences, different root trait dimensions may underlie the belowground functional diversity in (Neo)tropical forests, and we found little evidence for the strong phylogenetic conservatism observed in root traits in temperate biomes. We highlight important avenues for future research on tropical roots in order to determine the degree of, and shifts in functional diversity belowground as communities and environments change in tropical forests.info:eu-repo/semantics/publishe

Weak phylogenetic and habitat effects on root trait variation of 218 Neotropical tree species

International audienceIntroduction: Tropical forests harbor a large diversity of closely related tree species that can thrive across habitats. This biodiversity has been found to correspond to large functional diversity in aboveground traits, and likely also relates to belowground trait variation. Globally, root trait (co-)variation is driven by different belowground resource strategies of species, environmental variation, and phylogeny; however, these patterns mostly reflect observations from temperate biomes and remain unconfirmed in tropical trees. We examine phylogenetic and environmental effects on root trait (co-)variation of trees across habitats in an Amazonian rainforest.Methods: Roots of 218 tree species from ten dominant families were sampled across three major habitats near Manaus, Brazil. We quantified five morphological and architectural root traits to (i) investigate how they reflected different resource strategies across species, (ii) compare them between families and superorders to test phylogenetic effects, and (iii) compare them between habitats to determine environmental effects on root trait expressions and variability.Results: Root traits discriminated species along a tradeoff between root diameter and root branching and, secondly, due to variation in root tissue density. Our results further show weak phylogenetic effects on tropical tree root variation, for example, families from the same superorder showed large divergence in their root traits, while those from different superorders often overlapped in their root morphology and architecture. Root traits differed significantly between habitats but habitat type had only little effect on overall root trait variation.Discussion: Our work suggests that the dimensions and drivers that underlie (co-)variation in tropical root traits may differ from global patterns defined by mostly temperate datasets. Due to (a)biotic environmental differences, different root trait dimensions may underlie the belowground functional diversity in (Neo)tropical forests, and we found little evidence for the strong phylogenetic conservatism observed in root traits in temperate biomes. We highlight important avenues for future research on tropical roots in order to determine the degree of, and shifts in functional diversity belowground as communities and environments change in tropical forests

Soil-induced impacts on forest structure drive coarse woody debris stocks across central Amazonia

Background: Coarse woody debris (CWD) is an essential component in tropical forest ecosystems and its quantity varies widely with forest types.\ud \ud Aims: Relationships among CWD, soil, forest structure and other environmental factors were analysed to understand the drivers of variation in CWD in forests on different soil types across central Amazonia.\ud \ud Methods: To estimate CWD stocks and density of dead wood debris, 75 permanent forest plots of 0.5 ha in size were assessed along a transect that spanned ca. 700 km in undisturbed forests from north of the Rio Negro to south of the Rio Amazonas. Soil physical properties were evaluated by digging 2-m-deep pits and by taking auger samples.\ud \ud Results: Soil physical properties were the best predictors of CWD stocks; 37% of its variation was explained by effective soil depth. CWD stocks had a two-fold variation across a gradient of physical soil constraints (i.e. effective soil depth, anoxia and soil structure). Average biomass per tree was related to physical soil constraints, which, in turn, had a strong relationship with local CWD stocks.\ud \ud Conclusions: Soil physical properties appear to control average biomass per tree (and through this affect forest structure and dynamics), which, in turn, is correlated with CWD production and stocks

Soil physical conditions limit palm and tree basal area in Amazonian forests

Background: Trees and arborescent palms adopt different rooting strategies and responses to physical limitations imposed by soil structure, depth and anoxia. However, the implications of these differences for understanding variation in the relative abundance of these groups have not been explored. Aims: We analysed the relationship between soil physical constraints and tree and palm basal area to understand how the physical properties of soil are directly or indirectly related to the structure and physiognomy of lowland Amazonian forests. Methods: We analysed inventory data from 74 forest plots across Amazonia, from the RAINFOR and PPBio networks for which basal area, stand turnover rates and soil data were available. We related patterns of basal area to environmental variables in ordinary least squares and quantile regression models. Results: Soil physical properties predicted the upper limit for basal area of both trees and palms. This relationship was direct for palms but mediated by forest turnover rates for trees. Soil physical constraints alone explained up to 24% of palm basal area and, together with rainfall, up to 18% of tree basal area. Tree basal area was greatest in forests with lower turnover rates on well-structured soils, while palm basal area was high in weakly structured soils. Conclusions: Our results show that palms and trees are associated with different soil physical conditions. We suggest that adaptations of these life-forms drive their responses to soil structure, and thus shape the overall forest physiognomy of Amazonian forest vegetation. © 2014 Copyright 2013 Botanical Society of Scotland and Taylor & Francis