Abstract
The interaction between plant, soil and microorganism plays a crucial role in sustainable development of terrestrial ecosystem function and diversity. However, little information is known about how plant growth, soil organic carbon (C) fractions and microorganism respond to exogenous C addition in soils with low organic C content. Three levels of 13C-glucose (equal to 0, 100% and 500% of initial microbial biomass C) were added to non-sterilized (corresponding to treatment abbreviation of CK, Glu-1, Glu-2, respectively) and sterilized soils (corresponding to treatment abbreviation of SS, SS+Glu-1, SS+Glu-2, respectively) planted with apple rootstock (Malus baccata (L.) Borkh.) seedings. The objectives of this study were to analyse the dynamics of soil organic C (SOC) fractions and soil bacterial community diversity with glucose levels and soil sterilization, and to explore the morphology of roots and nitrogen (N) metabolism by plant after glucose addition to sterilized/non-sterilized soils. Results showed that the contents of labile organic C fractions were significantly varied (P<0.05) with the levels of glucose addition and soil sterilization. SS+Glu-2 and Glu-2 treatments increased the contents of labile organic C fractions, on average, by 48.47% and 35.33% compared with no glucose addition, respectively. About 21.42% and 16.17% of glucose-C remained in sterilized and non-sterilized soils, respectively at the end of experiment (day 45). Regardless of soil sterilized or not, the glucose addition increased the richness and diversity indices of soil bacterial community compared with no-glucose addition. The glucose addition optimized root zone conditions, and enhanced root vitality, morphology and biomass. Both SS+Glu-2 and Glu-2 treatments significantly enhanced (P<0.05) the contents of nitrate (NO3-N) and nitrite (NO2-N), but sharply decreased (P<0.05) the ammonium (NH4+-N) content compared with no glucose addition. Also, these two treatments significantly (P<0.05) increased the enzymic activities and gene transcript levels involved in root N metabolism, which demonstrated that the high level of glucose addition promoted N assimilation and transformation into free amino acids by root. Overall, the addition of exogenous C to not only promotes its fixation and bacterial community diversity in C-poor soils, but also improves root morphology and N absorption by plant.
Highlights
IntroductionThe slight change in soil organic C (SOC) can have a remarkable effect on global C budget and cycle
Soil is the largest carbon (C) pool in terrestrial ecosystems
Non-sterilized soil with high level of glucose addition decreased the content of total soil organic C (SOC), on average, by 3.7%, while that with low level of glucose addition and without glucose addition increased the content of total SOC by 5.4%~7.5% during the whole sampling time
Summary
The slight change in soil organic C (SOC) can have a remarkable effect on global C budget and cycle. SOC is the main component of soil organic matter, which has the advantages of supplying nutrients for crops, increasing crop yields, and improving soil fertility and quality, etc [1,2]. Exploring the mechanism of SOC dynamics is essential for sustainable development of agricultural and environment. The change in total SOC is hard to be monitored in short term due to its high background levels and the heterogeneous properties of soil [3]. Labile organic C (LOC) fractions in soil as sensitive indicators are used to describe the dynamics of SOC storage. Understanding the characteristics of LOC fractions is an important to assessing SOC dynamics in agricultural ecosystems
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