Short-term microbial effects on n-alkane during the early phase degradation and consequential modification of biomarkers in a lowland subtropical rainforest in southern Taiwan: A litterbag experiment

Abstract

Accurate reconstructions of past environments are critical and urgent because they can help understand how modern environments might respond to current climatic and land-use changes. However, the effect of microbial degradation and consequential modification in plant-derived-biomarkers during the early degradation phase is not yet apparent, that might bias the paleoenvironmental investigation. In this regard, a litterbag experiment was conducted to reveal the microbial effects on n-alkane-associated biomarker changes associated with three habitats (ravine, windward, and leeward) in a lowland subtropical rainforest in southern Taiwan. Freshly collected leaves of plant species Iles rotunda, Ficus benjamina, and Castanopsis carlesii were distributed in the habitat leaf litterbag experiment for 15 and 75 days incubation, respectively. The results revealed that the average leaf decomposition rate was 19.4% ± 6.4% during the first 15 days and 39% ± 11% within 75 days incubation for all leaves. The overall leaf mass degradation of I. rotunda, F. benjamina and C. carlesii in the ravine after 75 days was 58%, 51% and 41%, respectively, which were higher than those in the windward (28%, 36% and 38%) and leeward habitats (35%, 26% and 42%, respectively) indicating higher decomposition rate in the ravine habitat than the others. The predominant n-alkanes in I. rotunda were C₃₁ and C₂₉, whereas in F. benjamina these were C₃₁, C₂₉, and C₃₃, and in C. carlesii it was C₃₁. After 75 days, the ravine habitat showed a 60% decrease in the total n-alkane concentration compared to windward and leeward habitats, suggesting the microbial community associated with the ravine habitat has a higher efficiency of degrading n-alkanes. However, the biomarkers such as carbon preference index (CPI), average carbon length (ACL) and the C₃₁/C₂₉ ratio did not show statistical difference in all habitats from 15 to 75 days incubation. The next-generation sequencing revealed that microbial communities changed significantly from 15 to 75 days in all habitats. The alkB gene-containing bacteria and their family lineages increased substantially during the first 15 days incubation in all habitats. Furthermore, several bacterial genera were exclusively present in the ravine habitat, whereas some were only in the leeward and windward habitats. Despite the heterogeneity of microbial proliferation, difference in biomass and n-alkane degradation among the three habitats, most of the n-alkane-associated biomarkers remained the same. Therefore, we concluded that the microbial effects on n-alkane degradation during the early phase in plant leaves had little influence on the results of most n-alkane biomarkers.

Keywords: Litterbag experiment; Next-generation sequencing; Plant biomarkers; alkB gene; n-Alkane.