%0 Journal Article
%T Nitrogen and Carbon Cycling in a Grassland Community Ecosystem as Affected by Elevated Atmospheric CO2
%A H. A. Torbert
%A H. W. Polley
%A H. B. Johnson
%J International Journal of Agronomy
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/817343
%X Increasing global atmospheric carbon dioxide (CO2) concentration has led to concerns regarding its potential effects on terrestrial ecosystems and the long-term storage of carbon (C) and nitrogen (N) in soil. This study examined responses to elevated CO2 in a grass ecosystem invaded with a leguminous shrub Acacia farnesiana (L.) Willd (Huisache). Seedlings of Acacia along with grass species were grown for 13 months at CO2 concentrations of 385 (ambient), 690, and 980£¿¦Ìmol£¿mol£¿1. Elevated CO2 increased both C and N inputs from plant growth which would result in higher soil C from litter fall, root turnover, and excretions. Results from the incubation indicated an initial (20 days) decrease in N mineralization which resulted in no change in C mineralization. However, after 40 and 60 days, an increase in both C and N mineralization was observed. These increases would indicate that increases in soil C storage may not occur in grass ecosystems that are invaded with Acacia over the long term. 1. Introduction The rise of CO2 in the atmosphere is well documented [1]; what has not been documented are the sinks for this C, with an estimated unknown sink of £¿g£¿C£¿yr£¿1 arising from the global C balance [2]. Carbon dioxide is a prime chemical input to the metabolism of higher plants and has a major role in governing plant-water relations and water use efficiency. The increased growth of most plants under higher levels of CO2 [3¨C6] has prompted recent speculation on the ability of terrestrial ecosystems to sequester C [7]. However, the fate of C within ecosystems is affected by a biological chain of events which includes competition between plants. The ability of terrestrial ecosystems to sequester C will depend on the cycling of C among the various biomass and soil C pools and on the residence time of C in these pools. The rate of C mineralization during decomposition of residue derived from plants grown under elevated CO2 has not been resolved. It has been theorized that the commonly observed increase in plant C£¿:£¿N ratio under elevated CO2 could lead to slower residue decomposition resulting in increased soil C storage and reduction in available N for plant production [8]. However, slower decomposition of leaf litter due to elevated CO2 is not supported by the literature on litter quality [9]. Others have suggested that increased biomass might enhance microbial activity, resulting in a ¡°priming effect¡± thereby leading to no increase in C storage [10]. Alternatively, microbial preference for easily decomposable plant material produced under CO2-enriched conditions
%U http://www.hindawi.com/journals/ija/2012/817343/