Environmental and Plant-Derived Controls on the Seasonality and Partitioning of Soil Respiration in an American Sycamore (Platanus occidentalis) Bioenergy Plantation Grown at Different Planting Densities
Academic Article
Overview
Research
Identity
Additional Document Info
Other
View All
Overview
abstract
Bioenergy is one of the most considered alternatives to fossil fuels. Short-rotation woody crops (SRWCs) as bioenergy sources are capable of alleviating energy constraints and sequestering atmospheric CO2. However, studies investigating soil carbon (C) dynamics at SWRC plantations are scarce. We studied American sycamore (Platanus occidentalis) as a model tree species for SRWC at different planting densities ((1) 0.5 2.0 m (10,000 treesha1 or tph), (2) 1.0 2.0 m (5000 tph), and (3) 2.0 2.0 m (2500 tph)) to examine seasonal variation in total soil respiration (Rtotal), partitioned into heterotrophic (Rh) and autotrophic (Ra) respiration, and we evaluated climatic and biological controls on soil respiration. Rtotal and Rh exhibited larger seasonal variation than Ra (p < 0.05). During the nongrowing seasons, the average Rtotal was 0.60 0.21 gCm2day1 in winter and 1.41 0.73 gCm2day1 in fall. During the growing season, Rtotal was 27 times higher in spring (3.49 1.44 gCm2day1) and summer (4.01 1.17 gCm2day1) than winter. Average Rtotal was 2.30 0.63 gCm2day1 in 2500 tph, 2.43 0.64 gCm2day1 in 5000 tph, and 2.41 0.75 gCm2day1 in 10,000 tph treatments. Average Rh was 1.72 0.40 gCm2day1 in 2500 tph, 1.57 0.39 gCm2day1 in 5000 tph, and 1.93 0.64 gCm2day1 in 10,000 tph, whereas Ra had the lowest rates, with 0.59 0.53 gCm2day1 in 2500 tph, 0.86 0.51 gCm2d1 in 5000 tph, and 0.48 0.34 gCm2day1 in 10,000 tph treatments. Rh had a greater contribution to Rtotal (63%80%) compared to Ra (20%37%). Soil temperature was highly correlated to Rtotal (R2 = 0.92) and Rh (R2 = 0.77), while the correlation to Ra was weak (R2 = 0.21). Rtotal, Rh, and Ra significantly declined with soil water content extremes (e.g., <20% or >50%). Total root biomass in winter (469 127 gCm2) was smaller than in summer (616 161 gCm2), and the relationship of total root biomass to Rtotal, Rh, and Ra was only significant during the growing seasons (R2 = 0.12 to 0.50). The litterfall in 5000 tph (121 16 g DWm2) did not differ (p > 0.05) from the 2500 tph (108 16 g DWm2) or 10,000 tph (132 16 g DWm2) treatments. In no circumstances were Rtotal, Rh, and Ra significantly correlated with litterfall amount across planting densities and seasons (p > 0.05). Overall, our results show that Rtotal in American sycamore SRWC is dominated by the heterotrophic component (Rh), is strongly correlated to soil environmental conditions, and can be minimized by planting at a certain tree density (5000 tph).
