Interactive Effects of Atmospheric CO 2 and Soil-N Availability on Fine Roots of Populus tremuloides

Abstract

Abstract. The objective of this experiment was to understand how atmospheric carbon dioxide (CO 2 ) and soil-nitrogen (N) availability influence Populus tremuloides fine-root growth and morphology. Soil-N availability may limit the growth response of forests to elevated CO 2 and interact with atmospheric CO 2 to alter litter quality and ecosystem carbon (C) and N cycling. We established a CO 2 ϫ N factorial field experiment and grew six genotypes of P. tremuloides for 2.5 growing seasons in 20 large open-top chamber/rootbox experimental units at the University of Michigan Biological Station in northern lower Michigan (USA). In this paper we describe an integrated examination of how atmospheric CO 2 and soil-N availability influence fine-root morphology, growth, mortality, and biomass. We also studied the relationship between root biomass and total soil respiration.Over 80% of the absorbing root length of P. tremuloides was accounted for by roots Ͻ0.4 mm in diameter, and specific root length (100-250 m/g) was much greater than reports for other temperate and boreal deciduous trees. Elevated atmospheric CO 2 increased the diameter and length of individual roots. In contrast, soil N had no effect on root morphology. Fine-root length production and mortality, measured with minirhizotrons, was controlled by the interaction between atmospheric CO 2 and soil N. Rates of root production and mortality were significantly greater at elevated CO 2 when trees grew in high-N soil, but there were no CO 2 effects at low soil N. Fine-root biomass increased 137-194% in high-N compared to low-N soil, and elevated atmospheric CO 2 increased fine-root biomass (52%) in high soil N, but differences in low soil N were not significant. Across all treatments, dynamic estimates of net fine-root production were highly correlated with fine-root biomass (soil cores; r ϭ 0.975). Mean rates of soil respiration were more than double in high-N compared to low-N soil, and elevated atmospheric CO 2 , when compared to ambient atmospheric CO 2 , increased mean rates of soil respiration 19% in 1995 and 25% in 1996. Across all treatments, total root biomass was linearly related to mean rates of soil respiration (r 2 ϭ 0.96).Our results indicate that atmospheric CO 2 and soil-N availability strongly interact to influence P. tremuloides fine-root morphology, growth, and C turnover. Aspen-dominated ecosystems of the future are likely to have greater productivity fueled by greater nutrient uptake due to greater root length production. Further, it appears that elevated atmospheric CO 2 will result in greater C inputs to soil through greater rates of fine-root production and turnover, especially in high-fertility soils. Increased C inputs to soil result in greater rates of soil respiration. At this time, it is not clear what effects increased rates of root turnover will have on C storage in the soil.

Spatial and temporal patterns of root distribution in developing stands of four woody crop species grown with drip irrigation and fertilization

“…6). Previous reports also show a positive response of RLD or root biomass to fertilization (Johnson 1990;Kubiske et al 1998;Majdi 2001;Pregitzer et al 2000). However, the influence of resources on root system expansion was small in comparison to the effect of temporal, spatial or genetic factors (Tables 4 and 5), and the magnitude of the response to resource availability was dependent upon the level of other factors (Figs.…”

Responses of tree fine roots to temperature

“…When high soil temperatures are associated with conditions of drought, there is no de facto reason to expect root growth to increase as soil temperatures rise. An increase in soil N availability can also cause an increase in the rate of root length extension King et al, 1999 ;Pregitzer et al, 2000). Because N mineralization increases as soils warm (MacDonald et al, 1995 ;Piatek & Allen, 1999), it is important to remember that root growth might be responding to multiple soil factors that covary as soil temperatures increase.…”

“…Most of the extant root length in any perennial plant is dominated by short lateral roots (Weaver, 1958 ;Pregitzer et al, 1997Pregitzer et al, , 2000. Presumably, main root axes persist for much longer than lateral roots, which grow and die in response to changing soil environmental conditions (Pregitzer et al, 1997).…”

Effects of Soil Rhizosphere Aeration on the Root Growth and Water Absorption of Tomato

“…Soil rhizosphere aeration status is an important aspect of soil quality and soil ecology, which has been paid to less attention to [1][2][3]. The condition of root growth is directly related to plant growth and development, whereas root environment and root respiration are important factors for the normal growth of the roots.…”

“…Therefore, researchers are paying increasing attention to the provision of suitable environments (i.e., adequate water vapor) for the healthy growth of crops. Soil-root system is the most important aspect [1][2][3][4]. Excessive soil moisture and compaction can greatly inhibit the healthy growth of crops [4][5][6].…”