Light and Heavy Fractions of Soil Organic Matter in Response to Climate Warming and Increased Precipitation in a Temperate Steppe

Bing Song,Shuli Niu,Haijun Yang,Zhe Zhang,Shiqiang Wan,Linghao Li,Jack Anthony Gilbert

doi:10.1371/journal.pone.0033217

Abstract

Soil is one of the most important carbon (C) and nitrogen (N) pools and plays a crucial role in ecosystem C and N cycling. Climate change profoundly affects soil C and N storage via changing C and N inputs and outputs. However, the influences of climate warming and changing precipitation regime on labile and recalcitrant fractions of soil organic C and N remain unclear. Here, we investigated soil labile and recalcitrant C and N under 6 years' treatments of experimental warming and increased precipitation in a temperate steppe in Northern China. We measured soil light fraction C (LFC) and N (LFN), microbial biomass C (MBC) and N (MBN), dissolved organic C (DOC) and heavy fraction C (HFC) and N (HFN). The results showed that increased precipitation significantly stimulated soil LFC and LFN by 16.1% and 18.5%, respectively, and increased LFC∶HFC ratio and LFN∶HFN ratio, suggesting that increased precipitation transferred more soil organic carbon into the quick-decayed carbon pool. Experimental warming reduced soil labile C (LFC, MBC, and DOC). In contrast, soil heavy fraction C and N, and total C and N were not significantly impacted by increased precipitation or warming. Soil labile C significantly correlated with gross ecosystem productivity, ecosystem respiration and soil respiration, but not with soil moisture and temperature, suggesting that biotic processes rather than abiotic factors determine variations in soil labile C. Our results indicate that certain soil carbon fraction is sensitive to climate change in the temperate steppe, which may in turn impact ecosystem carbon fluxes in response and feedback to climate change.

Highlights

As atmospheric CO2 concentrations are rising, global temperature has increased and will continue to increase in the future [1]
The overall warming effects were marginally significant on light fraction C (LFC) (p = 0.07, Table 1) but insignificant on LFN (p = 0.16, Table 1)
LFC changed from 3.0360.32 g C kg21 dry soil in the control plots to 2.6660.20 g C kg21 dry soil in the warmed plots with ambient precipitation

Summary

Introduction

As atmospheric CO2 concentrations are rising, global temperature has increased and will continue to increase in the future [1]. Global soils contain 1500 Pg (1Pg = 1015 g) of organic carbon in the top soil layer to the depth of 1 m, which is more than the amounts of C in the atmosphere and vegetation combined [4,5]. Even slight change in the amount of soil C may dramatically influence atmospheric CO2 concentration [6]. The stocks of soil C result from the balance between carbon inputs and outputs. Any factors impacting carbon inputs (net primary productivity) and outputs (dominated by soil respiration) could change the quantity of organic carbon in soils [7]

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Conclusion