Soil Aggregation and Organic Carbon Dynamics in Poplar Plantations

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.

Changes in Soil Arthropod Abundance and Community Structure across a Poplar Plantation Chronosequence in Reclaimed Coastal Saline Soil

“…Soil fauna populations appeared to be lower when the uptake of water and nutrients were greatest during the stem exclusion stage, leaving fewer resources available for soil fauna [28,59]. In our study system, the available nitrogen tended to be higher in the 10-year-old stands than in the other stands (Table 1), and published data have demonstrated that microbial biomass carbon exhibited the same trend [16]. There was also a strong relationship between the total abundance and soil properties [17], but we lacked the litter data required to analyze the correlation between the litter quantity and soil arthropod activities.…”

“…Stand development following afforestation can reduce the soil pH through the accumulation of biomass [14,15]. There are wide variations in condition during different stand development phases, such as canopy closure, humidity, and other abiotic and biotic factors [16][17][18], which directly or indirectly impact soil arthropod activity [19][20][21][22].Soil arthropod communities are highly dynamic in forests [23], and following their establishment, they are modified by stand development. In European subalpine spruce forests, the abundance of Collembola was higher in young fertile stands, while that of Oribatida was more abundant in mature stands with increased litter input [24,25].…”

“…Stand development following afforestation can reduce the soil pH through the accumulation of biomass [14,15]. There are wide variations in condition during different stand development phases, such as canopy closure, humidity, and other abiotic and biotic factors [16][17][18], which directly or indirectly impact soil arthropod activity [19][20][21][22].…”

The Case for Digging Deeper: Soil Organic Carbon Storage, Dynamics, and Controls in Our Changing World

“…Physical protection takes place in the fine pores of soil microaggregates (0.053 mm < diameter (Ø) < 0.25 mm) in which anoxic conditions prevail or which are inaccessible to, or spatially separated from, microbial decomposers [20,21]. Microaggregates are often formed and stabilized within macroaggregates (Ø > 0.25 mm), the formation of which is fostered primarily by roots [21,22]. Microorganisms, particularly root-associated microorganisms, and organic matter also play key roles in fostering aggregate formation [21][22][23].…”

“…Microaggregates are often formed and stabilized within macroaggregates (Ø > 0.25 mm), the formation of which is fostered primarily by roots [21,22]. Microorganisms, particularly root-associated microorganisms, and organic matter also play key roles in fostering aggregate formation [21][22][23]. The sorption of dissolved organic C (DOC) compounds to minerals occurs in large part with the clay fraction [24,25].…”