Biomass production physiology and soil carbon dynamics in short-rotation-grown Populus deltoides and P. deltoides x P. nigra hybrids

Fast-growing woody species grown in dense, short-rotation plantations on land previously in agriculture offer potential economic benefits in products such as engineered construction material, boiler fuel, non-food-based biofuel feed stocks and other carbon (C)-based products and credits. However, information on the effects on major C pools of short-rotation culture is relatively sparse. In this study, Populus deltoides and P. deltoides x P. nigra hybrid clones were grown for 5 years at 1 m x 1 m spacing in plantations on a former pasture of high native fertility in the Missouri River floodplain in the lower Midwest U.S.A. Above and below-ground biomass production, leaf area-based production efficiency, photosynthetic attributes and soil C dynamics were studied. Populus clones yielded up to 70 Mg ha(-1) over 5 years, results that compare favorably to poplar culture in other regions. P. deltoides clones yielded almost twice as much as hybrids (66.3 vs. 36.9 Mg ha(-1)) despite more rapid early growth by the latter. Superior yields of P. deltoides clones were associated with greater (32-120%) production efficiency (total biomass yield per unit of time-integrated leaf area) and greater (17-42%) photosynthetic capacity, but not with differential allocation patterns of C above and below ground. Soil C losses were observed over 5 years, mostly from the top 12.5 cm of soil. Soil C loss in this study was associated with conversion from organic matter input-rich pasture culture, and subsequent rotations might not be accompanied by losses of the magnitude observed in the first. Net C sequestration in measured carbon stocks ranged from 11.4 to 33.5 Mg ha(-1) in the two plantations. (C) 2008 Elsevier B.V. All rights reserved.