Driven by the research in global climatic changes, the effect of N precipitation on the carbon cycling and carbon budget in terrestrial ecosystem has become a central issue to research workers. The effect is dependent on the direction and extent of responses of C input, such as primary production and output, such as litter decomposition. Existed work indicated N precipitation promotes plant growth and forest primary production. However, the effect of simulated N precipitation and increased in N availability is uncertain. The existed work is focused on litter decomposition on the forest floor but overlooked the below-ground process- fine roots decomposition. It is known that the soil carbon pool essentially comes from the input by fine roots death and decomposition.
Dr SUN Tao in IAE, in the work cooperated with Prof WANG Zhengwen and Prof LV Xiaotao, explored the effect of long-term N addition to fine root (diameter<0.5 mm) decomposition of 5 temperate tree species and related mechanisms in a five- year- long experiment. It was found that the Asymptote Model reasonably described the long-term mass loss rate. N addition enhanced the activity of enzymes for cellulose decomposition, accelerated the decomposition in the early In the later phase, N addition inhibited the activity of enzymes related to lignin oxidation and thus inhibited the decomposition rate of fine roots, irrespective to the original lignin content in fine roots. The results indicate that long-term N precipitation may increase or decrease the litter decomposition rate and the inhibition effect has nothing to do with the primary lignin content in the litter.
The work was founded by NNSFC No 31270494 and published in Soil Biology & Biochemistry, 2016, 93: 50-59.
Full text URL: Effects of long-term nitrogen deposition on fine root decomposition and its extracellular enzyme activities in temperate forests.
Key words: Decomposition; Fine roots; Litter quality; Microbial enzymes; Nitrogen; Temperate forests
Abstract: Resolving the effects of nitrogen (N) on decomposition is ecologically critical for predicting the ecosystem consequences of increased anthropogenic N deposition. Although root litter is the dominant soil carbon and nutrient input in many forest ecosystems, studies have rarely examined how the process of root decomposition is affected by N availability. In a field experiment, we studied the effects of N addition on fine root (< 0.5 mm diameter) decomposition using five substrates ranging in initial gravimetric lignin concentrations (from 10.8% to 34.1%) over five years, and made a simultaneous characterization of effects of N on the enzymatic activity of the decomposer community in three temperate forests. Across substrates, asymptotic decomposition models best described the decomposition. The effects of N addition shifted over the course of fine root decomposition, regardless of initial lignin concentrations, with N speeding up the initial rate of decomposition, but ultimately resulting in a larger, slowly decomposing litter fraction (A). Such contrasting effects of N addition on initial and later stages of decomposition were closely linked to the dynamics of its extracellular enzyme activity. Our results emphasized the need for studies of N effects on litter decomposition that encompass the later stages of decomposition. This study suggested that atmospheric N addition may have contrasting effects on the dynamics of different carbon pools in forest soils, and such contrasting effects of N should be widely considered in biogeochemical models.
Publication Name: Tao Sun, Lili Dong, Zhengwen Wang, Xiaotao Lü, Zijun Mao
E-mail: sunt@iae.ac.cn
