Soil Aggregation and Organic Carbon Dynamics in Poplar Plantations

Zhiwei Ge,Rongwei Zhu,Sili Peng,Han Chen,Honghua Ruan,Shuiyuan Fang

doi:10.3390/f9090508

Abstract

Soil resident water-stable macroaggregates (diameter (Ø) > 0.25 mm) play a critical role in organic carbon conservation and fertility. However, limited studies have investigated the direct effects of stand development on soil aggregation and its associated mechanisms. Here, we examined the dynamics of soil organic carbon, water-stable macroaggregates, litterfall production, fine-root (Ø < 1 mm) biomass, and soil microbial biomass carbon with stand development in poplar plantations (Populus deltoides L. ‘35’) in Eastern Coastal China, using an age sequence (i.e., five, nine, and 16 years since plantation establishment). We found that the quantity of water-stable macroaggregates and organic carbon content in topsoil (0–10 cm depth) increased significantly with stand age. With increasing stand age, annual aboveground litterfall production did not differ, while fine-root biomass sampled in June, August, and October increased. Further, microbial biomass carbon in the soil increased in June but decreased when sampled in October. Ridge regression analysis revealed that the weighted percentage of small (0.25 mm ≤ Ø < 2 mm) increased with soil microbial biomass carbon, while that of large aggregates (Ø ≥ 2 mm) increased with fine-root biomass as well as microbial biomass carbon. Our results reveal that soil microbial biomass carbon plays a critical role in the formation of both small and large aggregates, while fine roots enhance the formation of large aggregates.

Highlights

Soil aggregation, a primary determinant of soil fertility and productivity, results from the rearrangement of soil particles, flocculation and cementation, which is facilitated by organic inorganic compounds [1,2,3].Soil aggregates are formed in varying size classes, which are commonly classified as microaggregates (diameter (Ø) ≤ 0.25 mm) and macroaggregates (Ø > 0.25 mm) [4]
Our results revealed that the quantity of soil organic carbon (SOC), weight percentages, and mean weight diameter (MWD) of both small and large soil aggregates increased with stand age in poplar plantations that were reclaimed from the ocean via the construction of coastal levees in Eastern China
Based on a chronosequence of seven to 201 years since fire, Yuan et al [54] showed that fine-root biomass peaked in 94-year-old stands, while fine-root production peaked in 11-year-old stands. These results indicated that the associations between the SOC and fine roots were dependent on both age spans of chronosequences, and the correlation of fine-root biomass or production, and SOC

Summary

Introduction

A primary determinant of soil fertility and productivity, results from the rearrangement of soil particles, flocculation and cementation, which is facilitated by organic inorganic compounds ( long-chain polysaccharides and proteins, ionic bridging, and carbonates) [1,2,3]. Soil aggregates are formed in varying size classes, which are commonly classified as microaggregates (diameter (Ø) ≤ 0.25 mm) and macroaggregates (Ø > 0.25 mm) [4]. The weight percentage of water-stable macroaggregates (WSM) might serve as indicators of soil quality by virtue of their large surface areas and strong chemical bonds [5,6]. Stand development following afforestation may improve the physical and chemical properties of damaged and young soils [11,12]. The loss of soil carbon and Forests 2018, 9, 508; doi:10.3390/f9090508 www.mdpi.com/journal/forests

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