Sample storage-induced changes in the quantity and quality of soil labile organic carbon.

Shou-Qin Sun,Hui-Ying Cai,Jagtar S Bhatti,Scott X Chang

doi:10.1038/srep17496

Abstract

Effects of sample storage methods on the quantity and quality of labile soil organic carbon are not fully understood even though their effects on basic soil properties have been extensively studied. We studied the effects of air-drying and frozen storage on cold and hot water soluble organic carbon (WSOC). Cold- and hot-WSOC in air-dried and frozen-stored soils were linearly correlated with those in fresh soils, indicating that storage proportionally altered the extractability of soil organic carbon. Air-drying but not frozen storage increased the concentrations of cold-WSOC and carbohydrate in cold-WSOC, while both increased polyphenol concentrations. In contrast, only polyphenol concentration in hot-WSOC was increased by air-drying and frozen storage, suggesting that hot-WSOC was less affected by sample storage. The biodegradability of cold- but not hot-WSOC was increased by air-drying, while both air-drying and frozen storage increased humification index and changed specific UV absorbance of both cold- and hot-WSOC, indicating shifts in the quality of soil WSOC. Our results suggest that storage methods affect the quantity and quality of WSOC but not comparisons between samples, frozen storage is better than air-drying if samples have to be stored, and storage should be avoided whenever possible when studying the quantity and quality of both cold- and hot-WSOC.

Highlights

Soil water soluble organic carbon (WSOC) is the most labile organic C form with fast turnover rates[16,17] and has been extensively studied in recent years due to the important role it plays in C cycling
Even though there are few studies on the effects of air-drying on WSOC and in all these studies the WSOC was extracted by water at room temperature, no one has tested the effect of sample storage on WSOC extracted by hot water (70–80 °C, hot-WSOC), and no one has reported the impact of sample storage methods on the changes in the quality of cold- and hot-WSOC
The linear relationships for WSOC concentrations between the air-dried and fresh soils and that between the frozen-stored and fresh soils support our second hypothesis, while it differs with previous results where the difference in cold-WSOC concentration among soil samples was decreased by air-drying[21 ], as well as those reporting that the differences in cold-WSOC concentration between air-dried and fresh soils were proportionately greater for soils with higher total soil organic matter concentrations[20]

Summary

Introduction

Soil water soluble organic carbon (WSOC) is the most labile organic C form with fast turnover rates[16,17] and has been extensively studied in recent years due to the important role it plays in C cycling. The concentration and properties of both the cold- and hot-WSOC in various soil types in fresh, air-dried and frozen-stored soil samples were measured. Our objectives were to: 1) test whether air-drying and frozen storage would change the concentration and property of cold- and hot-WSOC in different soil samples; and 2) to explore the relationships between the concentrations of WSOC in fresh soil samples and those in air-dried and frozen-stored samples. We hypothesized that 1) frozen storage would not change while air-drying would increase the concentrations and change the properties of both cold- and hot-WSOC, and 2) there would be a linear relationship in WSOC concentrations between samples stored with different methods as storage methods will cause a systematic shift in the extractability of soil organic C

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Conclusion