Fine Root Dynamics and Longevity of Artemisia halodendron Reflect Plant Growth Strategy in Two Contrasting Habitats

Fine roots have important physiological and ecological functions, including sequestrating and releasing carbon (C) and other nutrients. The C and nutrients returned to the soil through fine roots is almost equivalent to foliar litter due to their fast turnover rate. Therefore, fine root dynamics represent a significant source of energy and nutrient flow in ecosystems.

The extraordinary spatial heterogeneity of soil water and nutrients in microtopography is one of the significant characteristics of arid environments. The differences in soil water and nutrient content among habitats influence plant growth strategies and biomass distribution. Previous studies have shown that some plants follow different propagation patterns to adapt to changes in soil availability in different habitats. However, little is known about changes in fine root production and longevity during the conversion of plants from one growth pattern to another.

Artemisia halodendron Turcz. ex Bess. is the pioneer sand-fixing shrub species in the Horqin Sand Land in Northern China. Previous studies on A. halodendron have reported significant differences in biomass, biomass allocation, community distribution pattern, reproduction allocation pattern, as well as morphological and physiological characteristics between the mobile and fixed sand dunes. Accordingly, changes in biomass and biomass allocation could have profound effects on fine root dynamics and longevity due to their sensitivity to ambient environmental changes. However, few studies have simultaneously assessed both aboveground growth and fine root dynamics, and their combined effects on the root longevity of A. halodendron that has adapted to two contrasting habitats (mobile and fixed sand dunes).

Therefore, the minirhizotron technique was applied to investigate the fine root dynamics and longevity of A. halodendron in the mobile and fixed sand dunes in Inner Mongolia. For over two years of study, the cumulative fine root length production and turnover were all significantly higher in the mobile than the fixed sand dunes at soil depths of 0–20, 20–40, and 40–60 cm. The annual fine root production (8.46mm cm^-2 y^-1) and annual fine root turnover (7.38mm cm^-2 y^-1) of shrubs in the mobile sand dunes are about 38 and 70 percent higher than those in the fixed sand dunes. The fine root lifespan is higher for those in the fixed (47 days) than in the mobile (33 days) sand dunes, consistent with the higher ratio of first- (distal) to second-order roots of the former. The root production and lifespan are consistent with the adaptive responses of A. halodendron in the two habitats. The differences in root dynamics and lifespan between the mobile and fixed sand dunes may significantly explain the changes in the C fixation rate with the restoration of desert soils.

Main findings of this study have been published on Journal of Arid Environments, 2012, 79: 1–7. The paper is also archived at http://www.sciencedirect.com/science/article/pii/S0140196311003442.