Do soil fertilization and forest canopy foliage affect the growth and photosynthesis of Amazonian saplings?

Most Amazonian soils are highly weathered and poor in nutrients. Therefore, photosynthesis and plant growth should positively respond to the addition of mineral nutrients. Surprisingly, no study has been carried out in situ in the central Amazon to address this issue for juvenile trees. The objective of this study was to determine how photosynthetic rates and growth of tree saplings respond to the addition of mineral nutrients, to the variation in leaf area index of the forest canopy, and to changes in soil water content associated with rainfall seasonality. We assessed the effect of adding a slow-release fertilizer. We determined plant growth from 2010 to 2012 and gas exchange in the wet and dry season of 2012. Rainfall seasonality led to variations in soil water content, but it did not affect sapling growth or leaf gas exchange parameters. Although soil amendment increased phosphorus content by 60 %, neither plant growth nor the photosynthetic parameters were influenced by the addition of mineral nutrients. However, photosynthetic rates and growth of saplings decreased as the forest canopy became denser. Even when Amazonian soils are poor in nutrients, photosynthesis and sapling growth are more responsive to slight variations in light availability in the forest understory than to the availability of nutrients. Therefore, the response of saplings to future increases in atmospheric [CO2] will not be limited by the availability of mineral nutrients in the soil

Soil water storage in an upland forest after selective logging in Central Amazonia Armazenamento de água no solo após extração seletiva de madeira em floresta de terra firme na Amazônia Central

Soil water storage of Central Amazonian soil profiles in upland forest plots subjected to selective logging (in average, 8 trees or 34, 3 m³ of timber per hectare were removed) was measured in four layers, down to a depth of 70 cm. The study lasted 27-months and was divided in two phases: measurements were carried out nearly every week during the first 15 months; in the following year, five intensive periods of measurements were performed. Five damage levels were compared: (a) control (undisturbed forest plot); (b) centre of the clearing/gap; (c) edge of the gap; (d) edge of the remaining forest; and (e) remaining forest. The lowest values for water storage were found in the control (296 ± 19.1 mm), while the highest were observed (333 ± 25.8 mm) in the centre of the gap, during the dry period. In the older gaps (7.5-8.5 year old), soil water storage was similar to the remaining and the control forest, indicating a recovery of hydric soil properties to nearly the levels prior to selective logging.<br>Foi medido o armazenamento de água em perfis de solo de 0-70 cm, divididos em quatro camadas em parcelas de floresta de terra firme na Amazônia Central, submetidas à extração seletiva de madeira, tendo sido retiradas, em média, 8 árvores por hectare ou 34 m³ de madeira. O estudo foi realizado num período de 27 meses em duas fases: na primeira, as medidas foram, na sua maioria, semanais, num período de 15 meses. Na segunda, as medidas foram feitas em cinco períodos intensivos. Foram comparados cinco tratamentos: (a) controle (floresta intacta), (b) centro da clareira, (c) borda da clareira, (d) borda da floresta remanescente e (e) floresta remanescente. Os valores mais baixos de armazenamento de água no solo (296 ± 19,1 mm) foram encontrados no controle, enquanto os mais altos foram medidos no centro da clareira (333 ± 25,8 mm), no período seco. Nas clareiras mais antigas (7,5-8,5 anos de idade), os armazenamentos de água no solo foram similares aos da floresta remanescente e controle, indicando a recuperação das propriedades hídricas do solo após a extração seletiva de madeira

Efeito da colheita seletiva de madeira sobre algumas características físicas de um latossolo amarelo sob floresta na Amazônia Central Effect of selective logging on some physical characteristics of a yellow latosol under rainforest in Central Amazonia State

A colheita seletiva de madeira pode vir a ser uma forma sustentável de uso da terra para ecossistemas florestais da Amazônia, uma vez que permite a manutenção de parte considerável da biomassa florestal, diminuindo, assim, a perturbação nas áreas exploradas. Neste sentido, o presente estudo teve como objetivo avaliar o efeito da exploração seletiva de madeira sobre as características físicas de um Latossolo Amarelo. A área de estudo localiza-se a cerca de 80 km ao norte de Manaus e a vegetação é do tipo Floresta Ombrófila Densa. O número de árvores retiradas com um trator de esteiras D6, por arraste, em 1993, variou de sete a dez árvores/ha (DAP > 55 cm). O delineamento experimental foi do tipo blocos ao acaso, com três repetições. Seis tratamentos foram avaliados, equivalendo às seguintes classes de perturbação identificadas na área: trilha de trator, centro de clareira, borda da clareira/floresta, borda da floresta/clareira, floresta remanescente e floresta-controle. A colheita seletiva de madeira provocou modificações nas características físicas do solo, principalmente nas trilhas de trator, e representou, em média, 13,8 % da área total explorada. Os valores de densidade do solo e resistência à penetração foram maiores para o solo sob estas áreas, enquanto a macroporosidade e o volume de água disponível para as plantas apresentaram-se menores do que nas demais classes de perturbação. Estas classes foram menos afetadas, não se estabelecendo diferenças significativas para as características físicas do solo entre estas e a floresta-controle, indicando, assim, a colheita seletiva como uma prática de menor impacto para o solo dos ecossistemas florestais da Amazônia.<br>Selective logging may become a form of sustainable use of Amazon forest ecosystems since most part of the forest biomass is maintained and the impacts on the exploited area are lower than in comparison to those under other land uses. The objective of this study was to evaluate the effects of selective logging on some soil physical characteristics. The study area lies about 80 km north of Manaus and the vegetation is a humid tropical rainforest. Seven to ten trees/ha (DAP > 55 cm) were felled and removed by a D6 bulldozer, in 1993. Six disturbance classes were defined in the logged plots, with three replicates each: tractor track, center of clearing, edge of clearing, edge of forest, remaining forest and control forest. Soil under tractor tracks represented 13.8 % of the exploited area, and showed higher values of bulk density, and penetration resistance, and lower macroporosity and available water for plants than the other disturbance classes. The other classes were less affected and no significant differences were observed between their soil properties and the control forest, indicating selective logging as a practice that causes less impact on soils of Amazon forest ecosystems

Efeito da pressão antrópica sobre igarapés na Reserva Florestal Adolpho Ducke, área de floresta na Amazônia Central

Foram investigadas variáveis físico-químicas e químicas de ambientes aquáticos, em área de floresta primária de terra firme, próxima à área urbana, no município de Manaus. Os cursos de águas superficiais investigados drenam tanto área de floresta primária como urbanizada e, na região, são chamados igarapés. Dois desses igarapés têm suas nascentes na área urbana, adentram a área de floresta e lá se juntam. Ainda dentro da mesma área o igarapé resultante encontra-se com um outro que drena apenas área de floresta primária. Neste estudo foram pesquisadas as variáveis ambientais: pH, condutividade elétrica da água, os cátions (Na+, K+, Ca2+, Mg2+ e Fe2+) e material em suspensão. Foi possível observar diferenças significativas nas médias da concentração de íons hidrogênio, na condutividade elétrica e na quantidade de material em suspensão, entre os igarapés estudados. No igarapé cuja nascente encontra-se dentro da reserva, os valores médios correspondentes ao pH, condutividade elétrica e material em suspensão foram, respectivamente, 4,47; 6,44 mS cm-1 e 1,25 mg L-1; e os valores mais elevados registrados nos impactados foram 6,84, 141,50 mS cm-1 e 9,50 mg L-1. Os resultados mostram que o igarapé que drena área de floresta mantém suas características naturais por estar protegido das atividades antrópicas, e os que provêm da área urbana encontram-se impactados.Physicochemical and chemical variables from water environments were investigated in an area of upland primary forest, near an urban area, in the municipality of Manaus. The investigated surface water streams drain both primary forest and urbanized areas, and are called igarapés in the region. The headwaters of two of these streams are in the urban area, and they run to the forest area and join to make up another stream, and later are joined with another stream which headwaters are located inside the primary forest. This study encompassed the following environmental variables: pH, water electrical conductivity, Na+, K+, Ca2+, Mg2+ and Fe2+ cations and suspended material. It was possible to see significant differences in the concentration of hydrogen ions, electrical conductivity and in the suspended material content, among the studied streams. In the stream in which the headwaters are within the reserve, the mean values corresponding to pH, electrical conductivity and suspended material were 4.47; 6.44 mS cm-1 and 1.25 mg L-1, respectively; and the highest values found in the impacted ones were 6.84, 141.50 mS cm-1 and 9.50 mg L-1. The results show that the stream which drains the forest area maintains its natural characteristics as it is protected from human activities, and the ones which come from the urban area are impacted

Molecular links between whitesand ecosystems and blackwater formation in the Rio Negro watershed

Tropical rivers such as the Rio Negro constitute a major portion of the global aquatic flux of dissolved organic carbon (DOC) entering the ocean, but the exact amount, source contributions and fate of terrestrial DOC remain unknown. We investigated the role of valley and upland whitesand ecosystems (WSEs) and terra firme plateaus in forming blackwater tributaries in the Rio Negro basin to develop novel constraints for the terrestrial export of carbon. 5709 molecular markers from ground- and surface waters of two contrasting valley and upland sites feeding Rio Negro tributaries were identified by ultrahigh resolution mass spectrometry (FT-MS), analyzed by multivariate statistics and compared to known Rio Negro markers. In a Principal Coordinates Analysis, valley and upland DOC molecular composition differed by 78% from plateau DOC, which was characterized by reworked, aliphatic and unsaturated N- and S-containing molecules, while valley and upland DOC contained mainly condensed aromatics, aromatics and oxidized unsaturated structures. Valley and upland samples differed by 10% in molecular DOC composition and by their isotopic content (14C of SPE-DOC, 18O and 2H of water) which indicated differences in hydrology and C turnover. Against expectation, markers of widespread whitesand valleys did not emerge as a major source of Rio Negro markers, but specific upland markers did. Pubchem suggested chromene and benzofuran structures as promising candidates for further study. Our findings indicate that the export of molecular markers diverges from expected transport-limited DOC behavior, and thereby opens new avenues for source annotation beyond DOC quantity. Terrestrial DOC from upland whitesand areas is a major source of specific blackwater molecules missing in the regional ecosystem C balance, whereas C export from the whitesand valleys and especially from terra firme plateaus represents mainly recycled and transformed carbon not directly affecting the ecosystem C balance and possibly, the watersheds downstream molecular signature. Our study highlights the potential of high-resolution techniques to constrain carbon balances of ecosystems and landscapes by novel molecular markers. A comparison with other terrestrial DOM datasets indicated molecular similarities with temperate acidic soils and tropical rivers that warrant further analysis of common DOM markers. Implications, limitations, and future challenges are discussed in the light of potential applications of diagnostic molecular links for DOC source annotation and estimation of terrestrial DOM export in the land-to-ocean continuum.ISSN:0016-7037ISSN:1872-953