13C abundance, water-soluble and microbial biomass carbon as potential indicators of soil organic carbon dynamics in subtropical forests at different successional stages and subject to different nitrogen loads

Abstract

Chronic atmospheric nitrogen deposition affects the cycling of carbon (C) and nitrogen (N) in forest ecosystems, and thereby alters the stable C isotopic abundance of plant and soil. Three successional stages, disturbed, rehabilitated and mature forests were studied for their responses to different nitrogen input levels. N-addition manipulative experiments were conducted at low, medium and high N levels. To study the responses of C cycling to N addition, the C concentration and 13 C natural abundances for leaf, litter and soil were measured. Labile organic carbon fractions in mineral soils were measured to quantify the dynamics of soil organic C (SOC). Results showed that three-year continuous N addition did not significantly increase foliar C and N concentration, but decreased C/N ratio and enriched 13 C in N-rich forests. In addition, N addition significantly decreased microbial biomass C, and increased water soluble organic C in surface soils of N-rich forests. This study suggests that N addition enhances the water consumption per unit C assimilation of dominant plant species, restricts SOC turnover in N-poor forests at early and medium successional stages (thus favored SOC sequestration), and vice versa for N-rich mature forests.

Effects of nitrogen deposition on soil organic carbon fractions in the subtropical forest ecosystems of S China

“…Those studies reveal that elevated N deposition modifies C dynamics in these forests by modulating the soil microbial enzymatic activity (Waldrop et al, 2004) and litter biochemical characteristics (Gallo et al, 2005). Preliminary results from subtropical forests show that N addition influences SOC by decreasing the microbial biomass C and increasing water-soluble organic C in the surface soils (Fang et al, 2009). Reduction in respiration after N addition in the broadleaf forests have also been reported for these forests (Mo et al, 2008).…”

“…Readily oxidizable organic C (ROC) has relatively high turnover, and is responsive to management practices (Datta et al, 2010). Soil microbial biomass C (MBC) can indirectly indicate soil microbial activity (Fang et al, 2009). Examining the changes in these labile C fractions is a more sensitive tool to measure the changes in SOC dynamics in response to environmental changes, but the long-term C storage is critically dependent on the stable SOC fractions (Neff et al, 2002).…”

Short-term effects of nutrient management regimes on biochemical and microbial properties in soils under rainfed ginger (Zingiber officinale Rosc.)

“…This is most likely due to N fertilizer (urea) used in split doses (at 45 and 90 DAP). A fertilization treatment effect upon soil microbial biomass is not new (Rifai et al, 2010) and lower levels of soil microbial biomass that are attributable to inorganic N fertilization have been reported by many (Fang et al, 2009;Wallenstein et al, 2006;Wang et al, 2008). Wallenstein et al (2006) reported that chemical N addition lowered C MIC by an average of 40-59% and that C MIC had negative relationships with total N inputs in both mineral soils and organic soils.…”

Nitrogen fertilization changes the molecular composition of soil organic matter in a subtropical plantation forest

“…These processes directly increase SOC storage in subtropical plantation forests (Fan et al., ). On the other hand, atmospheric N deposition inputs can increase vegetation productivity and root biomass (Kou, Guo, Yang, Gao, & Li, ) and alter the chemical properties of foliage and litter in subtropical plantation forests (e.g., the C/N ratio)(Fang et al., ). The changes in substrate availability can affect the composition and function of the microbial community mediating C turnover (Xiao et al., ), indirectly affecting the cumulative rate and stability of organic matter in soils (Cheng, Fang, & Yu, ).…”