Contingency in the direction and mechanics of soil organic matter responses to increased rainfall

Asmeret Asefaw Berhe, K. Blake Suttle, Sarah D. Burton, Jillian F. Banfield

Research output: Contribution to journalArticleResearchpeer-review

52 Citations (Scopus)

Abstract

Background and Aims: Rainfall is expected to show greater and more variable changes in response to anticipated rising of earth surface temperatures than most other climatic variables, and will be a major driver of ecosystem change. Methods: We studied the effects of predicted changes in California's rainy season for storage and stabilization mechanisms of soil organic matter (SOM). In a controlled and replicated experiment, we amended rainfall over large plots of natural grassland in accordance with alternative scenarios of future climate change. Results: We found that increases in annual rainfall have important consequences for soil carbon (C) storage, but that the strength and even direction of these effects depend critically on seasonal timing. Additional rainfall during the winter rainy season led to C loss from soil while additions after the typical rainy season increased soil C content. Analysis of MIneral-Organic Matter (OM) associations reveals a potentially powerful mechanism underlying this difference: increased winter rainfall greatly diminished the role of Fe and Al oxides in SOM stabilization. Dithionite extractable crystalline Fe oxides explained more than 35% of the variability in C storage under ambient control and extended spring rainfall conditions, compared to less than 0. 01% under increased winter rainfall. Likewise, poorly crystalline Fe and Al oxides explained more than 25 and 40% of the variability in C storage in the control and extended spring rainfall treatments, respectively, but less than 5% in the increased winter rainfall treatment. Conclusions: Increases in annual precipitation identical in amount but at three-month offsets produced opposite effects on soil C storage. Such clear differences in the amount and chemical composition of SOM, and in the vertical distribution of oxides in the soil profile in response to treatment timing carry important implications for the C sequestration trajectory of this ecosystem.

Original languageEnglish
Pages (from-to)371-383
Number of pages13
JournalPlant and Soil
Volume358
Issue number1-2
DOIs
Publication statusPublished - Sept 2012
Externally publishedYes

Keywords

  • Changes in rainfall
  • Mechanisms of SOM stabilization
  • MIneral-Organic Matter (OM) associations
  • Soil carbon

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