Fast Spectrophotometric Method as Alternative for CuO Oxidation to Assess Lignin in Soils with Different Tree Cover

Tiziana Danise,Michele Innangi,Georg Guggenberger,Elena Curcio,Antonietta Fioretto

doi:10.3390/f11121262

Tiziana Danise, Michele Innangi + Show 3 more

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https://doi.org/10.3390/f11121262

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Abstract

Given the ongoing climate change, estimating the amount of less degradable plant compounds that can be stored in the soil, such as lignin, is a topic of primary importance. There are few methods applicable to soils for the determination of lignin, such as the copper oxide (CuO) oxidation method (CuOL). Acetyl bromide spectrophotometric lignin (ABSL) could be a valid alternative providing information that is less detailed compared to CuOL, but it offers data on the bulk amount of lignin and may offer a valid, fast, and cheap alternative to the CuO method. The aim of this work was to compare ABSL with the CuO method on several soils receiving plant residues from different trees. Mineral soil samples from 0 to 10 cm depth were obtained from a former agricultural site in northern Italy (Brusciana, Tuscany), where different tree plantations were established 22 years ago. The plantations were white poplar and common walnut, which were also intercropped with other species such as hazelnut, Italian alder, and autumn olive. Soil samples under these plantations were also compared to soil under an adjacent agricultural field. In general, the amount of lignin in the afforested stands was approximately double than in the agricultural field as determined by either method. The two methods returned a largely different scale of values due to their different mechanisms of action. The acid-to-aldehyde ratio of syringyl structural units highlights that forest plantation provides a plant input material that is more slowly oxidatively degraded compared to arable soil. A linear mixed model proved that ABSL performed well in relation to CuOL, especially when considering the random variation in the model given by the plantation field design. In conclusion, ABSL can be considered a valid proxy of soil C pool derived from structural plant component, although further analyses are needed.

Highlights

There is a growing consensus that human activities in the last two centuries have induced dramatic and unprecedented changes in the global chemical and physical environment
The biodegradation of water-soluble leaf fractions is characterized by a preferential metabolization of carbohydrates [29], leaving the residual material relatively enriched in lignin-derived compounds that, in turn, contributes to the formation of a continuum of organic fragments that are continuously processed by the decomposer community toward smaller molecular size in forested soils [30]
Danise et al (2018) [19] analyzed the lignin fractions is characterized by a preferential metabolization of carbohydrates [29], leaving the residual material relatively enriched in lignin-derived compounds that, in turn, contributes to the formation of a continuum of organic fragments that are continuously processed by the decomposer community toward smaller molecular size in forested soils [30]

Summary

Introduction

There is a growing consensus that human activities in the last two centuries have induced dramatic and unprecedented changes in the global chemical and physical environment Such climatic and environmental changes are predicted to exert strong effects on the ecosystem functioning, which in turn, are reflected at an infrastructural [1] and economic level [2]. Through their C-sink role, forests contribute to regulating the atmospheric CO2 concentration level [6] and, by storing C, can mitigate global warming [7] All actions such as afforestation, reforestation, as well as restoration of cultivated, abandoned, and marginal agricultural lands, can potentially reverse or reduce the process of C loss and increase ecosystem C storage [8], representing a valid tool to mitigate climate change. It is a priority to apply management to induce the increase in C sink in the soil, and to quickly and reliably quantify the C pool that is less prone to biological degradation and can be stored in the soil

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