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INTERACTIVE EFFECTS OF ATMOSPHERIC CO 2 AND SOIL‐N AVAILABILITY ON FINE ROOTS OF POPULUS TREMULOIDES
Author(s) -
Pregitzer Kurt S.,
Zak Donald R.,
Maziasz Jennifer,
DeForest Jared,
Curtis Peter S.,
Lussenhop John
Publication year - 2000
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/1051-0761(2000)010[0018:ieoaca]2.0.co;2
Subject(s) - soil carbon , biomass (ecology) , deciduous , soil respiration , carbon dioxide in earth's atmosphere , taiga , environmental science , carbon dioxide , growing season , agronomy , ecosystem , terrestrial ecosystem , plant litter , soil water , botany , ecology , biology , soil science
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 × N factorial field experiment and grew six genotypes of P. tremuloides for 2.5 growing seasons in 20 large open‐top chamber/root‐box 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 <0.4 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 = 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 = 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.