Soil C and N availability determine the priming effect: microbial N mining and stoichiometric decomposition theories

Abstract

The increasing input of anthropogenically derived nitrogen (N) to ecosystems raises a crucial question: how does available N modify the decomposer community and thus affects the mineralization of soil organic matter (SOM). Moreover, N input modifies the priming effect (PE), that is, the effect of fresh organics on the microbial decomposition of SOM. We studied the interactive effects of C and N on SOM mineralization (by natural (13) C labelling adding C4 -sucrose or C4 -maize straw to C3 -soil) in relation to microbial growth kinetics and to the activities of five hydrolytic enzymes. This encompasses the groups of parameters governing two mechanisms of priming effects - microbial N mining and stoichiometric decomposition theories. In sole C treatments, positive PE was accompanied by a decrease in specific microbial growth rates, confirming a greater contribution of K-strategists to the decomposition of native SOM. Sucrose addition with N significantly accelerated mineralization of native SOM, whereas mineral N added with plant residues accelerated decomposition of plant residues. This supports the microbial mining theory in terms of N limitation. Sucrose addition with N was accompanied by accelerated microbial growth, increased activities of β-glucosidase and cellobiohydrolase, and decreased activities of xylanase and leucine amino peptidase. This indicated an increased contribution of r-strategists to the PE and to decomposition of cellulose but the decreased hemicellulolytic and proteolytic activities. Thus, the acceleration of the C cycle was primed by exogenous organic C and was controlled by N. This confirms the stoichiometric decomposition theory. Both K- and r-strategists were beneficial for priming effects, with an increasing contribution of K-selected species under N limitation. Thus, the priming phenomenon described in 'microbial N mining' theory can be ascribed to K-strategists. In contrast, 'stoichiometric decomposition' theory, that is, accelerated OM mineralization due to balanced microbial growth, is explained by domination of r-strategists.

Microbial community structure mediates response of soil C decomposition to litter addition and warming

“…Despite extensive work on the subject, the degree to which C chemistry alone drives the decomposition of litter and soil in response to elevated temperatures is frequently debated (Giardina and Ryan, 2000;Bol et al, 2003;Fierer et al, 2005;Knorr et al, 2005;Bauer et al, 2008;Conant et al, 2008;Craine et al, 2010;Hopkins et al, 2012;Suseela et al, 2013;Lefevre et al, 2014), as is the response of soil-C to N addition (Melillo et al, 2002;Neff et al, 2002;Auyeung et al, 2013). Part of this confusion may lie in the impact and influence of microbial community structure and function, as it has been shown as a potential driver of soil C turnover in response to N (Billings and Ziegler, 2008;Chen et al, 2014;Kaiser et al, 2014), warming (Bardgett et al, 2008;Balser and Wixon, 2009;Yuste et al, 2011;Zhou et al, 2012;Nie et al, 2013;Ziegler et al, 2013;Hopkins et al, 2014;Wei et al, 2014), and the interactive effects of N and warming (Cusack et al, 2010;Li et al, 2013).…”

Species and Genotype Effects of Bioenergy Crops on Root Production, Carbon and Nitrogen in Temperate Agricultural Soil

“…As TN did not change significantly over time, the SOC/TN ratio increased, particularly in the top 0.2 m under Sinensis. This may reflect the high C/N ratio of the source material: the C/N ratio of Miscanthus roots can exceed 40 (data not presented) suggesting that microbial N mining may control the decomposition of organic C, thereby increasing potential C sequestration rates, and the maintenance of poor TN contents in this N-limited system [41].…”

Assessment of the Influence of Oil Palm and Rubber Plantations in Tropical Peat Swamp Soils Using Microbial Diversity and Activity Analysis

“…Enzyme activities, such as β-glucosidase, cellobiohydrolase, chitinase and acid phosphatase are involved in C, N and P cycling and catalyze organic matter decomposition and nutrient mineralization. These key soil enzymes have been used extensively in soil research as their activities have been shown to be sensitive to land-use change [23]- [25]. The availability of soil nutrient to plants is important for ensuring agricultural sustainability.…”