Summary A new disease of unknown bacterial aetiology has been observed in eucalyptus stands since 2009. It is characterized by die‐back, wilting and lesions on the branches, petiole and midrib in association with macroscopic and microscopic bacterial ooze. To date, this disease has been observed in stands of clonal Eucalyptus saligna, E. grandis and E. urophylla x E. grandis hybrids and in E. dunnii seedling plantations in the states of São Paulo, Rio Grande do Sul and Mato Grosso do Sul. Considering the economic importance of eucalyptus plantations and the potential losses caused by this disease, this study aimed to identify and characterize the causal agent. Thirty‐four strains were obtained from infected plants, which were collected in the field from four locations. The inoculation of detached leaves and intact rooted cuttings supported pathogenicity in eucalyptus. The phylogenetic analysis of four housekeeping genes (16S rDNA, gapA, recA and rpoB) as well as biochemical tests confirmed the identity of strains belonging to the species Erwinia psidii. This is the first report of E. psidii as the cause of wilt and die‐back in Eucalyptus spp. in Brazil.
RESUMO -Este trabalho objetivou quantificar a biomassa e os nutrientes, bem como os efeitos na produtividade e no sítio, de acordo com a intensidade de colheita, em povoamento de Eucalyptus dunnii com 4 anos, em Alegrete, RS. Realizou-se um inventário da unidade amostral para a caracterização dendrométrica do povoamento. As árvores foram compartimentalizadas em raiz, madeira do tronco, casca do tronco, galhos e folhas. Amostras foram retiradas e analisadas quanto aos teores de nutrientes. A biomassa arbórea total foi de 121,9 Mg ha -1 , apresentando a seguinte ordem de distribuição dos componentes: madeira do tronco > raiz > galhos > casca do tronco > folhas. Em termos totais, na biomassa acima do solo, observaram-se 985 kg ha -1de macronutrientes e 32,5 kg ha -1 de micronutrientes, distribuídos em: N (24%), P (2%), K (23%), Ca (34%), Mg (13%) e S (4%) e em B (3%), Cu (1%), Fe (7%), Mn (87%) e Zn (2%). Entre os três cenários de colheita avaliados, Ca e K foram os elementos que apresentaram o maior risco para a manutenção da produtividade.Palavras-chave: Manejo nutricional; Solos florestais; Sustentabilidade. BIOMASS AND NUTRIENTS OF Eucalyptus dunnii Maiden STAND IN PAMPA GAÚCHOABSTRACT -The study aimed to quantify biomass and nutrients as well as the effects on productivity and on site, according to the intensity of harvest in stand of Eucalyptus dunnii, with four years in Alegrete-RS. The inventory was conducted for the dendrometric characterization of the stand. The trees were compartmentalized in root, stem wood, stem bark, branches and leaves. Samples were collected and analyzed for the concentration of nutrients. The total tree biomass was 121.9 Mg ha -1, with the following distribution order of components: stem wood > root >branches> stem bark > leaves. In overall terms, for aboveground biomass, there was 985 kg ha -1 macronutrients and 32,5 kg ha -1 micronutrient, distributed: N ( 24%), P ( 2%) , K (23 %) , Ca ( 34%) , Mg (13% ) and S ( 4%) and B (3%) , Cu (1%), Fe ( 7%), Mn ( 87%) and Zn (2%). Among the three harvesting scenarios evaluated Ca and K were the elements that showed the greatest risk to the maintenance of productivity.
ResumoA liberação de nutrientes via decomposição da serapilheira foliar representa parte significativa da ciclagem biogeoquímica. Avaliou-se a decomposição e a liberação de nutrientes da serapilheira foliar de Eucalyptus dunnii estabelecido no Bioma Pampa. Após o fechamento das copas das árvores (18 meses de idade) instalaram-se sobre o solo 648 litterbags distribuídos em três parcelas, realizando-se coletas mensais (18 amostras) durante um período de 36 meses. Para cada amostra foi pesada a massa remanescente e determinada a concentração de nutrientes. A massa foliar remanescente após três anos foi de 27,4%. O coeficiente de decomposição (k) foi de 0,37, com um tempo de meia vida (t 1/2 ) de 1,55 anos. A serapilheira foliar, após dois anos em decomposição, liberou mais de 50% da quantidade inicial de cada nutriente avaliado, com exceção ao Fe, Cu e Zn. O potássio foi o nutriente com maior percentual de liberação nos meses iniciais de decomposição da serapilheira foliar, com 60% no primeiro mês e mais de 80% aos três meses. Para os demais nutrientes a liberação foi lenta e gradual, como observado, principalmente, para N e P, com 19 e 39% ao final de 12 meses e com 60 e 67% ao final dos 36 meses de decomposição da serapilheira foliar, respectivamente. Palavras-chave: nutrição florestal; litterbag; ciclagem de nutrientes. AbstractThe release of nutrients by leaf litter decomposition is a significant part of biogeochemical cycling. The decomposition and nutrient release from leaf litter of Eucalyptus dunnii located in the Pampa Biome was evaluated. After closing of the canopy (18 months old), 648 litterbags were distributed in three plots on the soil; and, 18 samples per month during 36 months were collected. For each sample, the remaining mass was weighed and the concentration of nutrients determined. The remaining leaf mass after three years was 27.4%. The decomposition coefficient (k) was 0.37 with a half-life time (t 1/2 ) of 1.55 years. The leaf litter after two years decomposition released more than 50% of the initial amount of each nutrient evaluated, except for the Fe, Cu and Zn. Potassium was the nutrient with the highest percentage of release during the initial months of decomposition of leaf litter, with 60% in the first month and more than 80% at three months. For other nutrients release was slow and gradual, as seen mainly for N and P, with 19 and 39% after 12 months and 60 and 67% at the end of 36 months of decomposition of leaf litter, respectively.
Atmospheric deposition is responsible for the ions input, which may be due to dust and aerosols and rainfall. During rainfall a portion is intercepted by the tree canopy and returned to the atmosphere by evapotranspiration, another part crosses the forest canopy called throughfall and stemflow. The objective of the study was to quantify incident rainfall partitioning into throughfall, stemflow and canopy interception in a Eucalyptus dunnii stand in southern Brazil. Four plots of 20 m × 21 m were demarcated. The rainfall consists 3 rain collectors in an open area. The throughfall consisted 3 collectors per plot in the line, interlining and diagonal positions of the trees. The stemflow consisted in the installation of three systems per plot formed by a hose in the trunk of the tree that leads the solution to a reservoir. The adjustment of the throughfall, stemflow and canopy interception in function of the incident precipitation was of 99%, 90% and 52%. As the volume of rainfall increases, the coefficient of variation decreases. The annual rainfall was 1903 mm, with a canopy interception average of 8.9%.
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