Growth and C allocation of Populus tremuloides genotypes in response to atmospheric CO₂ and soil N availability

Abstract

We grew cuttings of two early (mid Oct.) and two late (early Nov.) leaf-fall Populus tremuloides Michx. genotypes (referred to as genotype pairs) for c. 150 d in open-top chambers to understand how twice-ambient (elevated) CO # and soil N availability would affect growth and C allocation. For the study, we selected genotypes differing in leaf area duration to find out if late-season photosynthesis influenced C allocation to roots. Both elevated CO # and high soil N availability significantly increased estimated whole-tree photosynthesis, but they did so in different ways. Elevated CO # stimulated leaf-level photosynthesis rates, whereas high soil N availability resulted in greater total plant leaf area. The early leaf-fall genotype pair had significantly higher photosynthesis rates per unit leaf area than the late leaf-fall genotype pair and elevated CO # enhanced this difference. The early leaf-fall genotype pair had less leaf area than the late leaf-fall genotype pair, and their rate of leaf area development decreased earlier in the season. Across both genotype pairs, high soil N availability significantly increased fine root length production and mortality by increasing both the amount of root length present, and by decreasing the life span of individual roots. Elevated CO # resulted in significantly increased fine root production and mortality in high N but not low N soil and did not affect fine root life span. The early leaf-fall genotype pair had significantly greater fine root length production than the late leaf-fall genotype pair across all CO # and N treatments. These differences in belowground C allocations are consistent with the hypothesis that belowground C and N cycling is strongly influenced by soil N availability and will increase under elevated atmospheric CO # . In addition, this study reinforces the need for better understanding of the variation in tree responses to elevated CO # , within and among species.

CO2 and N-fertilization effects on fine-root length, production, and mortality: a 4-year ponderosa pine study

“…A number of other studies on trees have found that CO 2 -induced increases in fine-root standing crop were limited at lower levels of N availability (Curtis and Wang 1998;Kubiske et al 1998;Pregitzer et al 2000;Prior et al 1997;Zak et al 2000), presumably reflecting resource limitations for increased growth. Conversely, Dyckmans and Flessa (2002) and Liu et al (2002) reported that C allocation to beech and spruce roots increased in response to CO 2 enrichment only at low levels of N. Dyckmans and Flessa (2002) concluded this showed a tendency for the plant to increase soil N uptake to match the elevated C supply as predicted by tree models (Lacointe 2000).…”

“…Belowground, N availability has been observed to curtail CO 2 -induced increases in root standing crop, production, and/or mortality in both trees (Curtis and Wang 1998;Kubiske et al 1998;Pregitzer et al 2000;Prior et al 1997;Zak et al 2000) and grasses (Kettunen et al 2005;Li et al 2004;Loiseau and Soussana 1999).…”

Soil carbon dioxide partial pressure and dissolved inorganic carbonate chemistry under elevated carbon dioxide and ozone

“…While these increases in fine root standing stock represent increased levels of R A , they also facilitate increases in R H . For the 1999 data, King et al (2001) reported a 139% increase in dead-root stock under elevated CO 2 , and the authors have concluded that elevated atmospheric CO 2 increases fine root turnover (Kubiske et al 1998;Pregitzer et al 1995Pregitzer et al , 2000. As most microbial communities are C limited , this enhanced addition of organic matter through organic acids, root turnover, and increased microbial metabolism likely increased R H as well .…”

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.…”