Atmospheric CO₂, soil nitrogen and turnover of fine roots

Abstract

SUMMARYIn most natural ecosystems a significant portion of carbon fixed through photosynthesis is allocated to the production and maintenance of fine roots, the ephemeral portion of the root system that absorbs growth-limiting moisture and nutrients. In turn, senescence of fine roots can be the greatest source of C input to forest soils. Consequently, important questions in ecology entail the extent to which increasing atmospheric CO^ may alter the allocation of carbon to, and demography of, fine roots. Using microvideo and image analysis technology, we demonstrate that elevated atmospheric CO^ increases the rates of both fine root production and mortality. Rates of root mortality also increased substantially as soil nitrogen availability increased, regardless of COg concentration. Nitrogen greatly infiuenced the proportional allocation of carbon to leaves vs. fine roots. The amount of available nitrogen in the soil appears to be the most important factor regulating fine root demography in Populus trees.

Effects of nitrogen and water limitation and elevated atmospheric CO2 on ectomycorrhiza of longleaf pine

“…The positive correlations between below-ground starch concentration and percentage or number of ectomycorrhizas observed in this study reflect overall sink/source trends of the host, while the negative correlation between mycorrhiza and steady-state soluble carbohydrate concentration might reflect changes in demand and use by the fungal symbiont (Hacskaylo, 1973). Understanding sink/source relationships, particularly quantifying the flux of C between above-and below-ground plant tissues, might give a greater understanding of mechanisms regulating mycorrhizal response in elevated-COg environments (Zak et al, 1993;Pregitzer et al, 1995).…”

“…Under ambient CO2 levels, mycorrhizal infection can cause plants to assimilate more COg and to allocate a greater proportion of this assimilate to their root systems (Reid, Kidd & Ekwebelam, 1983). Extra C from elevated atmospheric COg can also enter the rhizosphere via root turnover and exudation Pregitzer et al, 1995). The possibility of additional C entering rhizospheres of plants growing under atmospheric COg enrichment has prompted researchers to hypothesize increased colonization by mycorrhizal fungi (Lamborg, Hardy & Paul, 1983) Effects of COg enrichment on colonization of plant roots by mycorrhizal fungi have received limited attention and results have been variable.…”

Tissue chemistry and carbon allocation in seedlings of Pinus palustris subjected to elevated atmospheric CO2 and water stress

“…Because changes in plant tissue chemistry will affect decomposition rates (Meentemeyer 1978, Ryan et al 1990, Cotrufo and Ineson 1996, O'Neill and Norby 1996), elevated CO 2 could impact C turnover and storage in soils (Prior et al 1997c, Torbert et al 1997. Pregitzer et al (1995) suggested that increased rates of root turnover may occur in response to elevated CO2, and if coupled with increased C:N, could lead to increased belowground C storage.…”

Mycorrhizal fungi have a potential role in soil carbon storage under elevated CO2 and nitrogen deposition

“…Nitrogen content also decreased in P. involutus. Finally, we note that elevated CO # can increase fine-root mortality (Pregitzer et al, 1995), which might be followed by a decrease in the life span of relatively long-lived ECM root tips and rhizomorphs.…”

“…Nitrogen concentrations of hyphae from one P. involutus isolate were reported to increase with higher N availability in a culture experiment (Wallander et al, 1999), with possible shifts in decomposition rate. Additionally, root turnover can increase with N fertilization (Pregitzer et al, 1995 ;Majdi & Nylund, 1996), and this response could produce a corresponding decrease in the life span of ECM structures such as mycorrhizal root tips and rhizomorphs.…”