Abstract
It is unclear whether exogenous nutrients and carbon (C) additions alter substrate immobilization to deposited nitrogen (N) during decomposition. In this study, we used laboratory microcosm experiments and 15N isotope tracer techniques with five different treatments including N addition, N+non-N nutrients addition, N+C addition, N+non-N nutrients+C addition and control, to investigate the coupling effects of non-N nutrients, C addition and N deposition on forest floor decomposition in subtropical China. The results indicated that N deposition inhibited soil organic matter and litter decomposition by 66% and 38%, respectively. Soil immobilized 15N following N addition was lowest among treatments. Litter 15N immobilized following N addition was significantly higher and lower than that of combined treatments during the early and late decomposition stage, respectively. Both soil and litter extractable mineral N were lower in combined treatments than in N addition treatment. Since soil N immobilization and litter N release were respectively enhanced and inhibited with elevated non-N nutrient and C resources, it can be speculated that the N leaching due to N deposition decreases with increasing nutrient and C resources. This study should advance our understanding of how forests responds the elevated N deposition.
Highlights
It is unclear whether exogenous nutrients and carbon (C) additions alter substrate immobilization to deposited nitrogen (N) during decomposition
CO2 emission rates following [N+ both] treatment were significantly lower than those following [N+carbon] treatment during both soil and litter decomposition, no significant difference was observed during the late stage of litter decomposition (Table 1)
It should be noted that this effect of enhanced N immobilization might be uncertain in field situation, because organic substrate decomposition-induced N immobilization can be influenced by plant growth[39]. This is the first experimental investigation of the mechanism by which non-N nutrient and carbon resources alter the effect of N deposition on soil organic matter and litter decomposition in subtropical Chinese fir forest plantation
Summary
It is unclear whether exogenous nutrients and carbon (C) additions alter substrate immobilization to deposited nitrogen (N) during decomposition. The results indicated that N deposition inhibited soil organic matter and litter decomposition by 66% and 38%, respectively. Litter 15N immobilized following N addition was significantly higher and lower than that of combined treatments during the early and late decomposition stage, respectively. The global increase in N deposition is expected to alter soil organic matter and litter decomposition and to affect forest ecosystem C storage and nutrient status[6,7]. Nitrogen deposition has been found to increase, decrease or have no effect on decomposition[8], while soil and litter responses to N deposition often differ[9]. The effect of the mixed addition of C, N and P on C and N dynamics differed from the effects of the individual element treatments for litters of both species
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