Monitoring transformation of two tropical lignocellulosics and their lignins after residence in Benin soils

Thermally assisted Hydrolysis and Methylation (THM), and 2D-heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy were used to monitor the transformation of ramial chipped wood (RCW) from Gmelina arborea and Sarcocephalus latifolius, together with their organosolv lignins, following soil incubation in Benin (West Africa). Mesh litterbags containing RCW were buried in soils (10 cm depth) and were retrieved after 0, 6, 12 and 18 months of field incubation. Chemical analysis showed that total carbohydrate content decreased, while total lignin content increased as RCW decomposition progressed. Ash and mineral content of RCW increased significantly after 18 months of decomposition in soil. Significant N-enrichment of the RCW was determined following 18 months incubation in soils, reaching 2.6 and 1.9 times the initial N-content for G. arborea and S. latifolius. Results of THM showed that the S + G sum, corresponding to lignins, increased with RCW residence time in the soils, in contrast to the response of compounds derived from carbohydrates, the sum of which decreased. Remarkably, lignin interunit linkages, most notably β-O-4′ aryl ethers, β-β′ resinol, β-5′ phenylcoumaran and p-PCA p-coumarate, survived after 18 months in the soil, despite their gradual decrease over the duration of the experiment.

Don’t drink it, bury it: comparing decomposition rates with the tea bag index is possible without prior leaching

Purpose The standardized ‘Tea Bag Index’ enables comparisons of litter decomposition rates, a key component of carbon cycling, across ecosystems. However, tea ‘litter’ may leach more than other plant litter, skewing comparisons of decomposition rates between sites with differing moisture conditions. Therefore, some researchers leach tea bags before field incubation. This decreases comparability between studies, and it is unclear if this modification is necessary. Methods We submerged green and rooibos tea bags in water, and measured their leaching losses over time (2 min – 72 h). We also compared leaching of tea to leaf and root litter from other plant species, and finally, compared mass loss of pre-leached and standard tea bags in a fully factorial incubation experiment differing in soil moisture (wet and dry) and soil types (sand and peat). Results Both green and rooibos tea leached strongly, levelling-off at about 40% and 20% mass loss, respectively. Mass loss from leaching was highest in green tea followed by leaves of other plants, then rooibos tea, and finally roots of other plants. When incubated for 4 weeks, both teas showed lower mass loss when they had been pre-leached compared to standard tea bags. However, these differences between standard and pre-leached tea bags were similar in moist vs. dry soils, both in peat and in sand. Conclusions Thus, despite large leaching losses, we conclude that leaching tea bags before field or lab incubation is not necessary to compare decomposition rates between systems, ranging from as much as 5% to 25% soil moisture.

Fungal diversity, woody debris, and wood decomposition in managed and unmanaged Patagonian Nothofagus pumilio forests

Fungal diversity, woody debris, and wood decomposition were assessed in Nothofagus pumilio forests with and without forest management. A plot in a managed forest (MF) and a plot in an unmanaged control forest (C) were established in three sites in Chubut, Argentina. On each plot, forest structure, volume of woody debris, temperature, and humidity were recorded. Basidiomata of aphyllophoroid fungi were recorded in the fall and spring for 2 years. A decomposition assay with branches and twigs in two decay classes (DC) was established, and mass loss was measured after 3 and 2 years of field incubation respectively. To evaluate fungal diversity and mass loss within MF and C, generalized linear mixed-effects models (GLMM) were performed. Neither richness nor abundance differed between treatments, and community composition was similar. Only branches in DC2 showed greater mass loss in MF than in C. The volume of CWD was greater in MF and had a positive effect on fungal richness. A few aphyllophoroid species showed significant differences in abundance between treatments. Forest management in the conditions evaluated did not generate evident changes in fungal diversity, nor in wood decomposition. However, the differences observed in mass loss of DC2 could indicate that there were some factors operating in the past, that are no longer seen in the present, which may have accelerated decomposition. This highlights the need for studies evaluating changes in canopy cover, microclimate and fungal community, including potential key species, over a period starting just after the forest management.

Bleaching of leaf litter accelerates the decomposition of recalcitrant components and mobilization of nitrogen in a subtropical forest

Selective removal of lignin and other recalcitrant compounds, collectively registered as acid-unhyrolyzable residue (AUR), results in bleaching of leaf litter, but the importance of bleaching in decomposition processes on forest soil has not been fully evaluated. The aims of this study were to elucidate the occurrence of bleached area in decomposing leaf litter and to compare chemical composition between bleached and nonbleached portions in a subtropical forest in Japan. Field incubation of leaf litter was performed over an 18-month period with the litterbag method. The decomposition processes during the first 9 month were characterized by the relatively rapid mass loss and increase of bleached area, whereas the mass loss was slowed down and the bleached area decreased thereafter. Mass loss of leaf tissues was faster and AUR content was lower in bleached than in nonbleached portions, indicating the acceleration of mass loss in bleached leaf tissues by the selective decomposition of recalcitrant compounds. The decrease in carbonyl-C in the bleached portions was associated with the increase of extractable nitrogen. The results suggest that the bleaching plays a dominant role in the transformation and turnover of organic compounds and nitrogen in decomposing leaf litter.

Response of bermudagrass to enhanced-efficiency fertilizers, application strategies and release under tropical conditions

Nitrogen fertilization is an important input for crop yield; however, it can result in detrimental environmental effects due to low use efficiency of regular N sources. This study evaluated the effects of N fertilizers and application strategies (single vs. split application) on bermudagrass (Cynodon spp.) responses and release pattern and rate in controlled and field incubations. The bermudagrass study was arranged in a two-way factorial scheme of 6 N fertilizers, urea, Polymer Coated Urea (PCU), PCU-6 (6 months), PCU-4 (4 months), PCU-2 (2 months) and urea + urease inhibitor (U-NBPT) applied as a single (400 kg N ha-1 yr-1) or two split applications of 200 kg N ha-1 (400 kg N ha-1 yr-1). The controlled experiment was a two-way factorial of PCU-6, PCU-4, PCU-2 and 15, 45 and 90% water hold capacity (WHC), sampling period of 170 days, the field incubation used the same sources sampled up to 220 days. Enhanced-efficiency fertilizers (EEF) increased herbage accumulation (HA) by 1.3 Mg ha-1 compared to untreated urea, on average. Nitrogen use efficiency (NUE) was greater for EEFs (44%) than urea (36%). Results showed that increased soil moisture inferred positive responses in release pattern and a minimum of 45% WHC was necessary for optimum release. Fertilizers at field conditions resulted in an earlier release than expected, ~20 days.

Evaluating Litter Yield and Decomposition for Re-Vegetated Mangroves in a Subtropical Mudflat

Field monitoring and incubation experiments were conducted to evaluate the litter yield and examine the decomposition of the litter of three representative mangrove species frequently used for mangrove re-vegetation in a subtropical mudflat on the South China coast. The results show that the litter yield of the investigated mangrove species varied significantly from season to season. The annual litter production was in the following decreasing order: Heritiera littoralis > Thespesia populnea > Kandelia obovata. Initially, rapid decomposition of easily degradable components of the litter materials resulted in a marked weight loss of the mangrove litter. There was a good linear relationship between the length of field incubation time and the litter decomposition rate for both the branch and the leaf portion of the three investigated mangrove species. Approximately 50% or more of the added mangrove litter could be decomposed within one year and the decomposed litter could be incorporated into the underlying soils and consequently affect the soil carbon dynamics. An annual soil carbon increase from 2.37 to 4.64 g/kg in the top 5 cm of the soil was recorded for the investigated mangrove species.

Apatite Stimulates the Deposition of Glomalin-Related Soil Protein in a Lowbush Blueberry Commercial Field

Many wind-sensitive and unproductive soils could benefit from increased glomalin-related soil protein (GRSP), an operationally defined soil protein pool known to improve soil quality and nutrient storage. We expect at least part of this GRSP fraction to originate from fungal biomass. Although P-rich minerals such as apatite are known to increase C allocation from plants to mycorrhizal fungi, there are no studies directly linking apatite with GRSP. We investigated the effect of apatite on GRSP deposition rates in a cultivated field of wild lowbush blueberry (Vaccinium angustifolium Aiton; Vaccinium myrtilloides Michx.) in the Saguenay‒Lac-Saint-Jean region of Quebec (Canada). A field incubation technique (145 days) using sterilized porous sand bags (50 µm pores) was used to measure in situ easily extractable GRSP (EE-GRSP) deposition rates from bags with (n = 10) and without (n = 10) apatite. Half of the bags (n = 10) were also soaked in Proline® 480 SC (Bayer CropScience, Calgary, Alberta, Canada) (Prothioconazole) to determine if EE-GRSP deposition rates were affected by this commonly applied fungicide. Our results indicated that adding apatite into sand bags significantly increased (+70%) EE-GRSP deposition rates, whereas soaking the bags in fungicide had no significant effect. Although the direct linkage between GRSP and lowbush blueberry plants remains to be detailed, our study reports for the first time GRSP concentrations from lowbush blueberry soils. Implications of these findings are discussed.