Abstract
Litter bag method was conducted to investigate the decomposition characteristics of rice straw (6000 kg ha−1) and its associated microbial community under different nitrogen (N) addition rates (0, 90, 180 and 270 kg N ha−1) under double-rice rotation. Generally, straw mass reduction and nutrient release of rice straw were faster in early stage of decomposition (0−14 days after decomposition), when easily-utilized carbohydrates and amines were the preferential substrates for involved decomposers. Straw-associated N-acetyl-glucosamidase and L-leucine aminopeptidase activities, which were higher under 180 and 270 kg N ha−1 addition, showed more activities in the early stage of decomposition. Gram-positive bacteria were the quantitatively predominant microorganisms, while fungi and actinomycetes played a key role in decomposing recalcitrant compounds in late decomposition stage. Straw residue at middle decomposition stage was associated with greater cbhI and GH48 abundance and was followed by stronger β-glucosidase, β-cellobiohydrolase and β-xylosidase activities. Although enzyme activities and cellulolytic gene abundances were enhanced by 180 and 270 kg N ha−1 application, microbial communities and metabolic capability associated with rice straw were grouped by sampling time rather than specific fertilizer treatments. Thus, we recommended 180 kg N ha−1 application should be the economical rate for the current 6000 kg ha−1 rice straw returning.
Highlights
Crop straw represents a major source of carbon (C) in agroecosystems[1]
A systematic study under double-rice rotation was conducted to determine the effects of N fertilizer rate on (1) rice straw decomposition rate, nutrient release pattern and representative enzyme activities involved in straw decomposition, (2) structure and metabolic activity of the rice straw-associated microbial community and (3) straw-associated cellulolytic fungi and actinobacteria (GH48) gene abundances
The management of crop residues has become an important aspect of sustaining long-term fertility in cropping systems
Summary
Crop straw represents a major source of carbon (C) in agroecosystems[1]. Its decomposition involves the mineralization and transformation of photosynthesis products into stable soil organic matter, which plays the main role in resource recycling and soil nutrient transformation[2]. Hydrolytic enzymes are responsible for the acquisition of C, nitrogen (N) and phosphorus (P) to support primary metabolism and oxidative enzymes degrade recalcitrant compounds such as lignin in metabolic acquisition of nutrients[9] These changes reflect the dynamically catabolic capabilities during straw decomposition process. Enzyme activities and microbial community structure that engaged in straw decomposition vary with various environmental factors such as temperature, soil moisture and nutrient availability. They arise under complex alteration of the aerobic and anaerobic environment during the rice-planting period[10]. The results were expected to provide scientific information to support decisions on optimizing fertilizer N rates with a straw returning strategy in double-rice cropping system
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