Priming refers to microbial decomposition accelerated by resources supplied in available forms. Most previous priming studies have investigated single C additions, but they are not very representative for litterfall and root exudation in many terrestrial ecosystems.

   Dr. Qiao Na and Dr.Douglas Schaefer of Xishuangbanna Tropical Botanical Garden (XTBG), in cooperation with colleagues from Institute of Geographic Sciences and Natural Resources Research (IGSNRR) and Germany Göttingen University, conducted a study in the Ailao Mountains Nature Reserve (24°32′ N, 101°01′ E, 2476 m asl) and Xishuangbanna Tropical Rainforest Ecosystem Station (21°54′ N, 101°16′ E, 560 m asl) in Yunnan Province. Their study was aimed to clarify whether single vs. more frequent glucose inputs produce different priming effects.

   The researchers evaluated effects of ¹³C-labeled glucose added to soil in three temporal patterns: single, repeated, and continuous on dynamics of CO₂ and priming of SOC decomposition using soils with very different carbon contents. They hypothesized: 1) greater SOC priming would occur in the tropical soil; 2) continuous additions would result in stronger priming than a single addition of the same total amount of glucose; 3) the net C balances between primed C and retention of added glucose-C could be negative in both forest soils.

   To test those hypotheses, they conducted 170-day incubations of tropical (Xishuangbanna) and subtropical (Ailaoshan) forest soils.

   The researchers found that single additions of glucose overestimated priming effects in those subtropical and tropical soils and thus did not adequately reflect natural ecosystem C inputs. Continuous C inputs resulted in a greater C increase in the soil than single additions, further emphasizing the importance of labile organic carbon (LOC) addition patterns. Those patterns aside, responses of the very different soils to glucose additions were remarkably similar in terms of glucose release, priming, and net-C balance. They presented evidence that LOC additions might generally increase net C balances in soils.

The study entitled “Labile carbon retention compensates for CO2 released by priming in forest soils” has been published online in Global Change Biology.