Abstract
Many vital ecosystem processes take place in the soils and are greatly affected by the increasing active nitrogen (N) deposition observed globally. Nitrogen deposition generally affects ecosystem processes through the changes in soil biochemical properties such as soil nutrient availability, microbial properties and enzyme activities. In order to evaluate the soil biochemical responses to elevated atmospheric N deposition in bamboo forest ecosystems, a two-year field N addition experiment in a hybrid bamboo (Bambusa pervariabilis × Dendrocalamopsis daii) plantation was conducted. Four levels of N treatment were applied: (1) control (CK, without N added), (2) low-nitrogen (LN, 50 kg N ha−1 year−1), (3) medium-nitrogen (MN, 150 kg N ha−1 year−1), and (4) high-nitrogen (HN, 300 kg N ha−1 year−1). Results indicated that N addition significantly increased the concentrations of NH4 +, NO3 −, microbial biomass carbon, microbial biomass N, the rates of nitrification and denitrification; significantly decreased soil pH and the concentration of available phosphorus, and had no effect on the total organic carbon and total N concentration in the 0–20 cm soil depth. Nitrogen addition significantly stimulated activities of hydrolytic enzyme that acquiring N (urease) and phosphorus (acid phosphatase) and depressed the oxidative enzymes (phenol oxidase, peroxidase and catalase) activities. Results suggest that (1) this bamboo forest ecosystem is moving towards being limited by P or co-limited by P under elevated N deposition, (2) the expected progressive increases in N deposition may have a potential important effect on forest litter decomposition due to the interaction of inorganic N and oxidative enzyme activities, in such bamboo forests under high levels of ambient N deposition.
Highlights
Anthropogenic nitrogen (N) deposition, primarily from food and energy production [1], has increased three- to five-fold over the last century [2], and presently adds more than 200 Tg yr21 of N to terrestrial and ocean ecosystems [1]
Carbon sequestration in forests depends on the balance between C fixation through plant growth and C loss through decomposition of soil organic matter (SOM) and plant litter
The litterfall from April to June accounted for 68% of annual total litterfall
Summary
Anthropogenic nitrogen (N) deposition, primarily from food and energy production [1], has increased three- to five-fold over the last century [2], and presently adds more than 200 Tg yr of N to terrestrial and ocean ecosystems [1]. Studies have shown that the increased N deposition substantially affected a range of essential processes relevant to the carbon (C) cycle in terrestrial ecosystems [4,5]. Carbon sequestration in forests depends on the balance between C fixation through plant growth and C loss through decomposition of soil organic matter (SOM) and plant litter. The effects of N deposition on SOM and plant litter decomposition are highly controversial [9,10,11,12,13] due to the variability of forest properties and environmental factors. Soil extracellular enzymes (SEE) produced by microbes and plant roots were direct executors in the decomposition of litter and soil organic matter (SOM) [14]
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