Search

Afforestation and agroforestry both sequester atmospheric carbon (C) and store C in the soil. However, the response of soil nutrients and soil organic carbon (SOC) to these practices has not been fully examined, especially in deep soil layers. We therefore investigated the effects of afforestation and agroforestry on the nutrient contents and organic carbon (OC) stocks within a 100‐cm depth in eastern China. The soil nutrient contents and stoichiometry as well as the SOC contents and stocks exhibited different vertical patterns and varied among the five planting systems. The total nitrogen (TN), total phosphorus (TP), and SOC contents decreased dramatically at a 20‐cm depth, and the total potassium (TK) content exhibited a different pattern. Compared with adjacent croplands and nurseries, the forest plantation and agroforestry systems had higher SOC stocks, ranging from 42.9 to 111.6 t·hm⁻² in the whole soil profile. The SOC distribution among the depth gradient varied among planting systems, and the topsoil SOC stocks played crucial roles in total SOC storage within a depth of 100 cm in the cropland and nursery systems. The soil pH and bulk density (BD) were negatively correlated with the SOC content, and a significant positive linear relationship occurred between the TN and SOC contents and between the TP and SOC contents. We recommend that combinations of nitrogen (N) and phosphorus (P) fertilizers would benefit SOC storage and improve stabilization in agroforestry and plantation systems.

The objective of this study was to investigate the changes in soil microbial biomass C, microbial metabolic activity, functional diversity, and metabolic diversity pattern during the restoration process of a pine (Pinus tabulaeformis) plantation. In this study, a chronosequence approach was adopted. Three sites of pine plantations along a restoration chronosequence (12 years old (PF12), 25 years old (PF25), 35 years old (PF35)), and their paired reference sites of natural shrub community (Shrub1, Shrub2, and Shrub3) were selected. Soil microbial biomass C increased and microbial quotient declined with pine plantation age. Microbial metabolic activity, as measured by average well color development (using Biolog GN(2) plates), exhibited a decline along the restoration chronosequence with values ranked as PF12 > PF35 > PF25 in topsoil and PF12 > PF25 > PF35 in subsoil. Functional diversity, as estimated by substrate diversity and substrate richness, exhibited a pattern similar to the metabolic activity. Principal component analysis indicated that metabolic diversity followed recognized patterns along the restoration chronosequence with PF12 significantly different from PF25 and PF35. There was an apparent reduction of microbial metabolic activity and functional diversity during pine plantation restoration, which can be explained by a general decline in soil nutrient availability, particularly C availability, and soil pH associated with the establishment of a coniferous species.

The magnitude of soil CO(2) emission varying significantly among different vegetation types for plants could alter the microclimatic environment of soil. In a Pinus tabulaeformis plantation and an adjacent Quercus aliena var. acuteserrata shrub, which are located in a dry-hot valley region of Minjiang River in the Southwest of China, the daily soil CO(2) emission dynamics was measured in August 2004 and in May, July, and October 2005. The results showed that the soil CO(2) emission in the oak shrub was significantly higher than the pine plantation in each measurement period. Additionally, soil organic matter, microbial biomass carbon, and the leaf litter decomposition rate in the two vegetations differed significantly from each other. The variation of soil organic matter and microbial biomass carbon partially contributed to the evident difference in Soil CO(2) emission. Moreover, the correlations between Soil CO(2) emission, soil temperature, and soil water content were evaluated in this study. The soil temperature positively controlled Soil CO(2) emission in the pine plantation and the oak shrub, while the soil water content negatively influenced Soil CO(2) emission in the two vegetation types. However, the soil temperature and soil water content played varied roles in the different vegetation types. By the means of stepwise regression, the soil temperature more significantly influenced the dynamics of soil CO(2) emission for the plantation than the soil water content; oppositely, the soil water content was the more significant controlling factor for the shrub. Based on the exponent model between the Soil CO(2) emission and soil temperature, the Q(10) values were estimated, which was 1.7 in the pine plantation and 3.0 in the oak shrub. The former was lower than the global average level of 2.0, whereas the latter was higher than the global average level.