The nutrient release rate accounts for the effect of organic matter type on soil microbial carbon use efficiency of a Pinus tabulaeformis forest in northern China

Abstract

Microbial carbon use efficiency (CUE) greatly controls the magnitude of soil organic carbon turnover. This study was conducted to estimate the CUE with the additions of different organic matter (OM) to the top soil of a Pinus tabulaeformis forest and explore the variations of CUE and ecoenzyme activity with the quality of the added OM. Five types of OM, i.e., P. tabulaeformis leaves, Quercus wutaishanica leaves, maize straw, biochar, and wood, were separately crushed by a machine and then manually mixed in the top 20 cm of soil in a plot at 5 × 5 m in June 2014. Concurrently, 20 g of each OM larger than 1 cm was put in a nylon bag of 10 × 15 cm and placed above the plot ground to monitor the OM decomposition. The soil samples were taken and analyzed for the physicochemical properties, the extracellular enzyme activity, and soil microbial biomass, and the OM decomposition rate was also measured in August 2017. The OM in the litter bag absorbed nitrogen from the soil particle during the decomposition period, and the nitrogen release rates of wood debris and maize straw were significantly lower at − 625.01% and − 276.98%. The carbon targeting enzyme, i.e., α-1,4-glucosidase (AG), was also influenced by the OM addition and changed from 5.39 nmol h−1 g−1 with the Q. wutaishanica leaf addition to 14.82 nmol h−1 g−1 with the wood debris addition. Significant differences were simultaneously detected in the soil microbial biomass carbon content among different OM additions. These changes in soil biophysical properties contributed to much of the variation in CUEC:N. The CUEC:N meaning the microbial carbon assimilation at the cost of nitrogen was highest at 0.221 for wood debris addition. The addition of OM differing in quality could influence the soil resource content, exo-enzyme activity, and soil microbial biomass through its nutrient release rate. The CUEC:N could act as an integrative proxy of soil biophysical properties because it also correlated with the soil nutrient content, ecoenzymatic stoichiometry and the OM nutrient release rate. The high CUEC:N value indicated a big carbon stabilization in soils with wood debris addition.