Soil DOC release and aggregate disruption mediate rhizosphere priming effect on soil C decomposition

Elevated carbon dioxide in the atmosphere (eCO2) has been found to influence soil C by altering the belowground balance between the decomposition of existing soil organic matter (SOM) and the accumulation of plant-derived C inputs. Even small changes in this balance can have a potentially large effect on future climate. The relative availability of soil nutrients, particularly N and P, are crucial mediators of both decomposition and new C accumulation, but both these two processes are rarely assessed simultaneously. We asked if the effect of eCO2 on soil C decomposition was mediated by soil N and P availability, and if the effect of CO2 and soil N and P availability on soil C decomposition was dependent on C pools (existing SOM C, newly added C). We grew Eucalyptus grandis and a C3 grass (Microlaena stipoides) from seed in an experimentally manipulated atmosphere with altered &#948;13C signature of CO2, which allowed the separation of plant derived C, from the existing SOM C. Then we manipulated N and P relative abundance via nutrient additions. We evaluated how the existing SOM and the new plant-derived C pool, and their respiration responded to eCO2 conditions and nutrient treatments. SOM respiration significantly increased in the eucalypts when N was added but was not affected by CO2. In the grass the SOM respiration increased with eCO2 and added N and SOM respiration per unit of SOM-derived microbial was significantly higher in both the added P and added N+P nutrient treatments. The rhizosphere priming of SOM was suppressed in both the added P and added N+P nutrient treatments. The heterotrophic respiration of plant-derived C was contingent on nutrient availability rather than eCO2 and differed by species. The grass-derived respiration was significantly higher than the eucalypt and was higher in both added P and added N+P nutrient treatments. Thus, nutrient stoichiometry had similar effects on SOM and plant derived C, but e CO2 only affected SOM and only for the Eucalyptus. &#160;This study shows how species differences have large effects on rhizosphere C cycling responses to eCO2 and stoichiometric conditions.&#160;&#160; &#160;&#160;&#160;

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Regulation of priming effect by soil organic matter stability over a broad geographic scale

Nature Communications ◽

10.1038/s41467-019-13119-z ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 20

Author(s):

Leiyi Chen ◽

Li Liu ◽

Shuqi Qin ◽

Guibiao Yang ◽

Kai Fang ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Priming Effect ◽

Basal Respiration ◽

Soil Conditions ◽

The Tibetan Plateau ◽

Geographic Scale ◽

Soil C ◽

Chemical Structures ◽

C Dynamics

Abstract The modification of soil organic matter (SOM) decomposition by plant carbon (C) input (priming effect) represents a critical biogeochemical process that controls soil C dynamics. However, the patterns and drivers of the priming effect remain hidden, especially over broad geographic scales under various climate and soil conditions. By combining systematic field and laboratory analyses based on multiple analytical and statistical approaches, we explore the determinants of priming intensity along a 2200 km grassland transect on the Tibetan Plateau. Our results show that SOM stability characterized by chemical recalcitrance and physico-chemical protection explains more variance in the priming effect than plant, soil and microbial properties. High priming intensity (up to 137% of basal respiration) is associated with complex SOM chemical structures and low mineral-organic associations. The dependence of priming effect on SOM stabilization mechanisms should be considered in Earth System Models to accurately predict soil C dynamics under changing environments.

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