Monday, November 28, 2011

Have the World's best wine regions benefited from a previously unrecognized source of nitrogen?

Recently published research on sedimentary bedrock (Morford, Houlton, and Dahlgren, Increased forest ecosystem carbon and nitrogen storage from nitrogen rich bedrock, Nature, 9/1/2011, pp. 78-81) leads me to posit that some of the major wine growing regions of the world have been the unknowing beneficiaries of a heretofore unheralded source of nitrogen and that this has benefited them in their production of high quality wines.  Before expounding further on this hypothesis, I will provide some background.

As shown in the table below, nitrogen is an essential element in the growth of grape vines and an imbalance in its levels can lead to problems in the vineyard and/or in the winery.

Nitrogen and grape vines (Compiled from Grande Passione -- Soil minerals vs wine quality)

According to Schwarcz and Schoeninger (Stable Isotope Analysis in Human Nutrition, Yearbook of Physical Anthropology 34, pp. 293-321), almost 100% of exchangeable nitrogen is found in the atmosphere or dissolved in the world's oceans and is transferred from these environments into the biological system through the processes illustrated in the figure below.  The commonly held view is that grape vine plants receive their nitrogen through the terrestrial nitrogen cycle but the Morford study calls this into question.


Nitrogen, as is the case for all plant nutrients, is sourced from the soil by the plant.  According to Christopher Bargman (Geology and wine in South Africa, Geoscientist 15(4), April 2005), soil is the major influence on the growth of the vine plant as it provides: (i) a supply of water; (ii) anchorage in the ground; and (iii) a source of nutrition. The classic soil profile is shown below.

Now back to the Morford, Houlton, and Dahlgren study.  According to the authors, sedimentary rocks contain considerably more fixed nitrogen than all of the fixed nitrogen in the biosphere due to the capture of "... organic matter in marine and freshwater sediments, where it is incorporated into rock as organic N or as ammonium in silicate materials."  Greater amounts of this rock-based N is contained in sedimentary rock (consolidated rock deposited in layers) than is contained in metamorphic ( a rock formed from preexisting solid rocks by mineralogical, structural, and chemical changes, in response to extreme changes in temperature, pressure, and shearing stress -- and igneous rocks (formed when molten minerals cool from a liquid into a solid).  Even though it has been known to geologists that this fixed N is secreted in bedrock, "... it is generally believed that rock N is not sufficiently important to alter the terrestrial N cycle."  The results of this study has shown otherwise.

The authors studied the nitrogen content of soils and forest foliage in forests that were underlain by both sedimentary and igneous bedrock and found the following: (i) the nitrogen content in soils and foliage that grow above sedimentary bedrock is 50% higher than soils and foliage that grow over igneous bedrock; (ii) nitrogen isotope values for rock, soils, and plants are indistinguishable among each other when located above a nitrogen-rich sedimentary bedrock but that is not the case for the same elements overlaying an igneous bedrock; and (iii) "forest responses to geological N inputs are manifested as higher foliar biomass production ..."

The authors conclude that "Our results raise the possibility that rock weathering may be a significant source of N to terrestrial ecosystems..." underlain by terrestrial bedrock.

I compiled the following table of wine regions that may and may not have benefited from the phenomenon described by the authors.  The table shows that some of the world's foremost wine regions are underlain by sedimentary bedrock and may have benefited from that "siteing.".

Additional study will be required to determine the benefits and disadvantages associated with subterranean nitrogen, the implications, and what, if anything, should be done to maximize its effects and minimize its disadvantages.  The information provided herein could be of benefit in making decisions regarding vineyard locations or vineyard retention in the case of a vine-uprooting program.

1 comment: