permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15091762&dopt=Citation>

1: Environ Pollut. 1994;83(1-2):155-89.         Related Articles, Links
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    Plant responses to atmospheric CO2 enrichment with emphasis on roots and 
the rhizosphere.

    Rogers HH, Runion GB, Krupa SV.

    National Soil Dynamics Laboratory, ARS-USDA, PO Box 3439, Auburn, Alabama 
36831, USA.

    Empirical records provide incontestable evidence of global changes: foremost among these changes is the rising 
concentration of CO(2) in the earth's atmosphere. Plant growth is nearly always stimulated by elevation of CO(2). 
Photosynthesis increases, more plant biomass accumulates per unit of water consumed, and economic yield is enhanced. The 
profitable use of supplemental CO(2) over years of greenhouse practice points to the value of CO(2) for plant 
production. Plant responses to CO(2) are known to interact with other environmental factors, e.g. light, temperature, 
soil water, and humidity. Important stresses including drought, temperature, salinity, and air pollution have been shown 
to be ameliorated when CO(2) levels are elevated. In the agricultural context, the growing season has been shortened for 
some crops with the application of more CO(2); less water use has generally, but not always, been observed and is under 
further study; experimental studies have shown that economic yield for most crops increases by about 33% for a doubling 
of ambient CO(2) concentration. However, there are some reports of negligible or negative effects. Plant species respond 
differently to CO(2) enrichment, therefore, clearly competitive shifts within natural communities could occur. Though of 
less importance in managed agro-ecosystems, competition between crops and weeds could also be altered. Tissue 
composition can vary as CO(2) increases (e.g. higher C: N ratios) leading to changes in herbivory, but tests of crop 
products (consumed by man) from elevated CO(2) experiments have generally not revealed significant differences in their 
quality. However, any CO(2)-induced change in plant chemical or structural make-up could lead to alterations in the 
plant's interaction with any number of environmental factors-physicochemical or biological. Host-pathogen relationships, 
defense against physical stressors, and the capacity to overcome resource shortages could be impacted by rises in CO(2). 
Root biomass is known to increase but, with few exceptions, detailed studies of root growth and function are lacking. 
Potential enhancement of root growth could translate into greater rhizodeposition, which, in turn, could lead to shifts 
in the rhizosphere itself. Some of the direct effects of CO(2) on vegetation have been reasonably well-studied, but for 
others work has been inadequate. Among these neglected areas are plant roots and the rhizosphere. Therefore, experiments 
on root and rhizosphere response in plants grown in CO(2)-enriched atmospheres will be reviewed and, where possible, 
collectively integrated. To this will be added data which have recently been collected by us. Having looked at the 
available data base, we will offer a series of hypotheses which we consider as priority targets for future research.

    PMID: 15091762 [PubMed]