Inter-site variation in allometry and wood density of Goupia glabra Aubl. in Amazonia.

The present study aims to compare the allometry and wood density of Goupia glabra Aubl. (Goupiaceae) in two different terra-firme sites in Amazonian forest. A total of 65 trees ≥ 10 cm DBH was sampled in both sites, with 39 trees in Nova Olinda do Norte (NOlinda, near the Amazon River) and 29 trees in Apuí (near the southern edge of the Amazon forest). Except for the relationship between DBH (diameter at breast height) and Ht (total height), allometric relationships for G.glabra differed significantly between sites. Apuí had lower intercept and greater slope for log10 (DBH) versus log10 (Hs - stem height), and, conversely, greater intercept and lower slope for log10 (DBH) versus log10 (Ch - crown height). The slope differed significantly between the sites for DBH versus Cd (crown diameter), with greater slope found for NOlinda. Mean basic wood density in Apuí was 8.8% lower than in NOlinda. Our findings highlight the variation in adaptive strategy of G. glabra due to environmental differences between sites. This is probably because of different canopy-understory light gradients, which result in differentiation of resource allocation between vertical and horizontal growth, which, in turn, affects mechanical support related to wood density. We also hypothesize that differences in soil fertility and disturbance regimes between sites may act concomitantly with light.

Inter-site variation in allometry and wood density of Goupia glabra Aubl. in Amazonia / Variação entre-sítios na alometria e densidade da madeira de Goupia glabra Aubl. na Amazônia

Abstract The present study aims to compare the allometry and wood density of Goupia glabra Aubl. (Goupiaceae) in two different terra-firme sites in Amazonian forest. A total of 65 trees ≥ 10 cm DBH was sampled in both sites, with 39 trees in Nova Olinda do Norte (NOlinda, near the Amazon River) and 29 trees in Apuí (near the southern edge of the Amazon forest). Except for the relationship between DBH (diameter at breast height) and Ht (total height), allometric relationships for G.glabra differed significantly between sites. Apuí had lower intercept and greater slope for log10 (DBH) versus log10 (Hs – stem height), and, conversely, greater intercept and lower slope for log10 (DBH) versus log10 (Ch – crown height). The slope differed significantly between the sites for DBH versus Cd (crown diameter), with greater slope found for NOlinda. Mean basic wood density in Apuí was 8.8% lower than in NOlinda. Our findings highlight the variation in adaptive strategy of G. glabra due to environmental differences between sites. This is probably because of different canopy-understory light gradients, which result in differentiation of resource allocation between vertical and horizontal growth, which, in turn, affects mechanical support related to wood density. We also hypothesize that differences in soil fertility and disturbance regimes between sites may act concomitantly with light.

Resumo O presente estudo tem como objetivo comparar a alometria e a densidade da madeira de Goupia glabra em dois diferentes sítios de floresta de terra firme na Amazonia. Um total de 65 árvores com DAP ≥ 10 cm foi amostrado em ambos os sítios, sendo 39 árvores em Nova Olinda do Norte (NOlinda, próximo ao rio Amazonas) e 29 em Apuí (próximo à borda sul da Amazônia). Exceto para a relação entre o DBH (diâmetro a altura do peito) e a Ht (altura total), as relações alométricas para G. glabra diferiu significativamente entre os sítios. Apuí apresentou menor intercepto e maior inclinação para a relação log10 (DBH) versus log10 (Hs – altura do fuste) e, ao contrário, maior intercepto e menor inclinação para log10 (DBH) versus log10 (Ch – altura da copa). A inclinação diferiu significativamente entre os sítios para DBH versus Cd (diâmetro da copa), com maior inclinação encontrada para NOlinda. A densidade básica média da madeira in Apuí foi 8.8% menor do que em NOlinda. Os resultados deste estudo destacam a variação na estratégia adaptativa de G. glabra devido às diferenças ambientais entre os sítios. Isto é provavelmente consequência dos diferentes gradientes de luz o que resulta na diferenciação na alocação de recursos entre o crescimento vertical e horizontal o que, por sua vez, afeta o suporte mecânico relacionado à densidade da madeira. Nós também levantamos a hipótese de que as diferenças em termos de fertilidade e regimes de distúrbios entre os sítios podem agir concomitantemente com o regime de luz.

Members of the ethylene signalling pathway are regulated in sugarcane during the association with nitrogen-fixing endophytic bacteria.

Nitrogen-fixing bacteria have been isolated from sugarcane in an endophytic and beneficial interaction that promotes plant growth. In this work, for the first time, the involvement of ethylene signalling in this interaction was investigated by molecular characterizing members of this pathway in sugarcane. The expression pattern of a putative ethylene receptor (SCER1) and two putative ERF transcription factors (SCERF1 and SCERF2) show exclusive modulation in plants inoculated with the diazotrophic endophytes. The gene expression profile of SCER1, SCERF1, and SCERF2 is differentially regulated in sugarcane genotypes that can establish efficient or inefficient associations with diazotrophic micro-organisms, exhibiting high or low biological nitrogen fixation (BNF) rates, respectively. In addition, SCER1, SCERF1, and SCERF2 expression is different in response to interactions with pathogenic and beneficial micro-organisms. Taken together, that data suggest that SCER1, SCERF1, and SCERF2 might participate in specific ethylene signalling cascade(s) that can identify a beneficial endophytic association, modulating sugarcane responses toward the diazotrophic endophytes.

SHR5: a novel plant receptor kinase involved in plant-N2-fixing endophytic bacteria association.

Endophytic nitrogen-fixing bacteria have been isolated from graminaceous plants such as maize, rice, and sugarcane. They are thought to promote plant growth, not only by fixing nitrogen, but also by the production of plant hormones. The molecular mechanisms involved in this interaction are not yet clear. In this work, the identification of a receptor-like kinase (RLK), named SHR5, which may participate in signal transduction involved in the establishment of plant-endophytic bacteria interaction is described for the first time. SHR5 seems to be part of a novel subclass of RLKs present in a wide range of plant species. The expression of this gene is down-regulated in sugarcane plants associated exclusively with beneficial endophytic bacteria and is not a general response caused by micro-organisms or abiotic stress. In addition, more successful sugarcane-endophytic bacteria associations have a more pronounced decrease in SHR5 expression, suggesting that SHR5 mRNA levels in plant cells are inversely related to the efficiency of the association.