Diversity of decay resistance strategies of durable tropical woods species: Bocoa prouacencsis Aublet, Vouacapoua americana Aublet, Inga alba (Sw.) Wild

https://doi.org/10.1016/j.ibiod.2014.06.012Get rights and content

Highlights

  • Study of decay resistance, density, wood extractives of three durable wood species.

  • We studied the correlation between these wood properties.

  • We highlighted strategies of decay resistance according to extractives content and density.

Abstract

The study of decay resistance in wood is of interest for wood end-users but also for the global carbon balance since wood biodegradation is a key driver of forest ecosystem functioning through its impacts on carbon and nutrient cycling. We studied the density and wood extractive contents in order to understand decay resistance against soil microflora after 90 days exposure of sapwood and heartwood from three Neotropical wood species known for their decay resistance: Bocoa prouacensis, Vouacapoua americana, Inga alba. Decay resistance was correlated with density more than wood extractive content. The results highlighted different decay resistance strategies. In B. prouacensis, both sapwood and heartwood were highly resistant due to the high density and high content of antifungal wood extractives. In V. americana heartwood, decay resistance was due to the high synergistic-acting wood extractive content. Conversely, with the least dense wood species I. alba, we found that decay resistance was due to the antifungal wood extractives synthesized early in the sapwood. In conclusion, we showed that the three wood species with the same level of heartwood decay resistance performance had different decay resistance strategies according to the anatomic and defensive wood traits.

Introduction

The study of wood's decay resistance is of crucial interest for wood end-users but also for the global carbon balance as wood biodegradation is a key driver of forest ecosystem functioning through its impacts on carbon and nutrient cycling. The factor controlling wood biodegradation and their interaction with the environment are still poorly understood and consequently wood biodegradation is incorporate in global carbon model in highly generalized forms (Cramer et al., 2001, Cornwell et al., 2009). There have been substantial numbers of studies on wood biodegradation particularly from temperate and boreal ecosystem but there is a striking knowledge gap for wood biodegradation rate and processes in tropical forest. The missing of knowledge could be at the origin of approximations and more studies on biotics determinants of wood biodegradation rates linked to trait contribution to wood biodegradation are needed to reduce uncertainties in global carbon cycling models. Chemical and anatomical wood traits play a key role on decay resistance and are useful in predicting biodegradation of woody species (Cornwell et al., 2009).

Van Geffen et al. (2010) studied the wood decomposition trait relationship using a large set of traits of potential importance on wood biodegradation. He concluded that tree diameter at breast height (DBH) played a key role because the surface aera: volume ratio affect the accessibility to the substrate to by micro-organisms. But he signaled also that wood density was an unimportant trait for predicting interspecific differences in wood decomposition. This is, however, in line with the results of a global meta-analysis of 36 wood decomposition studies, which showed that wood density could not explain the difference in decomposition rates between gymnosperms (lower wood density, slower decomposition) and angiosperms decomposing in a common environment (Weedon et al., 2009). While other authors showed that: the denser woods are less degraded (Yamamoto and Hong, 1994, Chave et al., 2009). The chemical trait played also a key role as lignin (Syafii et al., 1988). About, secondary metabolites, there is large variation in the amount of secondary chemicals in wood, especially among tropical angiosperms (Cornwell et al., 2009). Heartwood formation is chemical defense mechanism that takes place between the sapwood and heartwood. During heartwood formation, secondary metabolites such as tannins, gums, and other colored materials accumulate in the heartwood. Consequently, wood decay resistance is acquired as a result of heartwood formation (Taylor and Gartner, 2002). All types of insects and pathogenic fungi are confronted with a less permeable tissue (Neya et al., 2004) impregnated with insecticidal (Rodrigues et al., 2011) and/or antifungal compounds (Debell et al., 1999, Niamké et al., 2012). Rodrigues et al. (2009) documented a diverse range of defense mechanisms in tropical wood species: Eperua falcata impregnates its wood with large amounts of weakly antifungal compounds acting in synergy, while Tabebuia serratifolia and Sextonia rubra woods are naturally impregnated with antifungal agents. Van Geffen et al. (2010) concluded that the inhibiting effect of phenolic extractives on wood decomposition rates is not correlated; the amount of phenolic extractives cannot explain inter-specific variation in wood decomposition. But, the chemical nature of the wood extractives is preponderant and is one of the reasons why some low-density timbers such as Cedrela spp. are more resistant (e.g. fungal decay) than high density wood species (Antwi-Boasiako and Pitman, 2009). The causes of decay resistance are complex and take into account the wood extractives or density alone is not so simple.

The comprehension of the causes of decay resistance of wood allows to understand the influence of some traits like anatomical, chemical ones in biodegradation processes. This study was carried out to gain insight into the cause of decay resistance of three durable wood species: Bocoa prouacensis Aublet, Vouacapoua americana Aublet, Inga alba (Sw) Wild, by studying density, wood extractive content in sapwood and in the heartwood and secondly by establishing correlations with decay resistance against soil microflora. We focused on new data which could highlight the diverse range of decay resistance strategies in these three durable wood species.

Section snippets

Plant material and sampling

We collected stems (Paracou Forest 5°15′ N, 52°55′ W, in French Guiana), of three wood species belonging to Fabaceae and known for their resistance against wood-rotting fungi: Bocoa prouacensis Aublet (classified as very durable wood, class 1), Vouacapoua americana Aublet (classified as a very durable wood, class 1), Inga Alba (Sw.) Wild (classified as a durable wood, class 2). We also collected a non-durable species Virola michelii Heckel (Myristicaceae) with undifferentiated heartwood in

Results

Table 2 shows Pearson correlations between decay resistance and wood properties (density and wood extractive content) and also the final moisture content observed after soil microflora exposure, a factor which influences the biodegradation level. Decay resistance was highly correlated with final humidity (R² = 0.84) and negatively correlated with density (R² = −0.65). The decay resistance rate was the same as the rate for heartwood from the four wood species: B. prouacensis (1.05) > V. americana

Discussion

Overall, decay resistance, wood extractive content and density values were in accordance with those found in the literature (Scheffer and Morrell, 1998, Paradis et al., 2012). Virulence of V. michelii (control), which has undifferentiated heartwood, were confirmed, i.e. there was no significant difference between sapwood and heartwood with respect to mass losses and total wood extractive content. Conversely, the results obtained with the three durable species showed that the high decay

Conclusion

The aim of our study was to highlight different decay resistance strategies in three durable wood species: B. prouacensis, V. americana and I. alba according the both wood properties: density and wood extractive content. Our results showed that decay resistance is more correlated with density than wood extractive content. But it is important to take the qualitative extractive aspects rather than the wood extractive content into account. We also highlighted three decay resistance strategies in

Acknowledgment

This work has benefited from an “Investissement d'Avenir” grant managed by Agence Nationale de la Recherche (CEBA, ref. ANR-10-LABX-0025).

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