Effects of elevated CO2 and nitrogen on nutrient uptake in ponderosa pine seedlings |
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Authors: | Johnson Dale W Ball Timothy Walker Roger F |
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Institution: | (1) Biological Sciences Center, Desert Research Institute Reno, 89506, NV, USA;(2) Environmental and Resource Science University of Nevada, 89512 Reno Reno, NV, USA;(3) Desert Research Institute Reno, 89506, NV, USA;(4) Department of Biochemistry, University of Nevada, 89512 Reno Reno, NV, USA;(5) Environmental and Resource Science University of Nevada, 89512 Reno Reno, NV, USA |
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Abstract: | This paper reports on the results of a controlled-environment study on the effects of CO2 (370, 525, and 700 mol mol-1) and N 0, 200, and 400 g N g soil-1 as (NH4)SO4] on ponderosa pine (Pinus ponderosa) seedlings. Based upon a review of the literature, we hypothesized that N limitations would not prevent a growth response to elevated CO2. The hypothesis was not supported under conditions of extreme N deficiency (no fertilizer added to a very poor soil), but was supported when N limitations were less severe but still suboptimal (lower rate of fertilization). The growth increases in N-fertilized seedlings occurred mainly between 36 and 58 weeks without any additional N uptake. Thus, it appeared that elevated CO2 allowed more efficient use of internal N reserves in the previously-fertilized seedlings, whereas internal N reserves in the unfertilized seedlings were insufficient to allow this response. Uptake rates of other nutrients were generally proportional to growth. Nitrogen treatment caused reductions in soil exchangeable K+, Ca2+, and Mg2+ (presumably because of nitrification and NO3
- leaching) but increases in extractable P (presumably due to stimulation of phosphatase activity).The results of this and other seedling studies show that elevated CO2 causes a reduction in tissue N concentration, even under N-rich conditions. The unique response of N is consistent with the hypothesis that the efficiency of Rubisco increases with elevated CO2. These results collectively have significant implications for the response of mature, N-deficient forests to evevated CO2. |
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Keywords: | CO2 global change growth nitrogen nutrition Pinus ponderosa soil nutrients |
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