PS 67-37 - Distinct effects of N and P addition on soil enzyme activities and C distribution in aggregates: Implications for soil C stocks

Friday, August 11, 2017
Exhibit Hall, Oregon Convention Center
Junsheng Huang1,2,3, Wenjing Chen1, Kaibin Qi1, Xueyong Pang1, Robert L. Sinsabaugh3, Bing Yang1 and Weikai Bao1, (1)Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, China, (2)University of Chinese Academy of Sciences, (3)Department of Biology, University of New Mexico, Albuquerque, NM

The increasing nitrogen (N) deposition has greatly enhanced N input to terrestrial ecosystems and even resulted in an imbalance of N and phosphorus (P) availability. N and P are primary nutrients affecting carbon (C) cycling in terrestrial ecosystems, but the effects of N and P availability on soil C pool, the largest C pool in terrestrial ecosystems, are not well studied, especially the underlying mechanisms. Bulk soil C pool consists of heterogeneously functional pools, which can be affected by N and/or P differentially. To better evaluate the effects of N and P on soil C pool, there is a need to identify the soil fractions that are affected and the extent to which they are affected. We investigated dynamics of soil enzyme activities and C in bulk soil and three aggregate fractions, i.e. macroaggregates (5000-250 μm; MaA), microaggregates (250-53 μm) and silt and clay (<53 μm; S&C), following two growing seasons of N addition (0, 5 and 20 g N m-2 yr-1) without and with P addition (15 g P m-2 yr-1) in a subalpine spruce plantation.


We found distinct effects of N and P on enzyme activities and C content across bulk soil and aggregate fractions. The activities of two lignolysis enzymes (catalase and polyphenol oxidase) in bulk soil increased after N and P addition, while β-glucosidase activity was suppressed by N in S&C but increased by P in MaA and P addition increased catalase activity of S&C, consistent with the common decomposition sequence that polysaccharides and lignin deplete in particle and mineral fractions, respectively. Bulk soil C content showed no response to nutrient treatments, whereas C distribution in aggregates was affected, with increased relative C content of S&C in N-only addition plots and increased and decreased relative C content of MaA and finer aggregates (<250 μm), respectively, after P addition. We attributed the distinct effects of N and P on C distribution in aggregates to differential responses of aggregates, in addition to the effect of increased fine root biomass induced by P. Furthermore, our results indicate N addition has the potential to increase soil C storage while P would cause soil C losses, and the dynamics of soil C and enzyme activities in aggregates are better predictors of long-term soil C sequestration than those in bulk soil.