Tuesday, March 14, 2017

Tuesday, March 14th,  2017

Nitrogen Deficiency Hypothesis revisited (assay #3)

The nitrogen deficiency hypothesis* gets some highly tentative support from my work this week (March 4-11 2017).  “Not yet shown to be a dumb idea” - that’s how I’d put it.  These results may justify followup work:  more samples in a good experimental design, rigorous sample prep, laboratory assays by someone who really knows what they are doing.

[*The hypothesis:  by 200 years, a fir/hemlock/cedar forest needs a new nitrogen source, with early succession nitrogen fixation exhausted.   Lobaria oregena is reported to perform this role in the Andrews Experimental Forest; salmon (abetted by flooding and predation) in BC and Alaska.  References on request.   Without lobaria - which is reported to be sensitive to pollution - and in the absence of salmon predation (no bears), the old-growth forest at Seward Park may be experiencing a deficiency of available nitrogen.  Perhaps this is most dire at Ground Zero.  Perhaps this weakened the sword ferns.  Perhaps an opportunistic pest (phytophthora,  thrips) gained a foothold.  Lots of as-yet unsupported conjecture from me here.]

This time around, my third round of sampling, I:
  1. divided each vertical 6-inch soil core into four segments each ~1.5 inches in length
  2. dried the samples for a week indoors at room temperature
  3. pulverized the dry soil, creating fine soil particles
  4. used two positive controls: freshly purchased potting soil, with and without nitrogen fertilizer added


The color-code:

   
Potted soil samples (unfertilized on left, fertilized on right):



Three field samples:

1) 50’ east of the Jobox in second growth forest, across the upper loop road (south) from the sqebeqsed trail entrance, between two large red alder trees, at successive 1.5 inch depths, surface to depth.  I see faint red in sample 1 (perhaps), in sample2, maybe also in sample 4.





2) Ground Zero, central site #1. I see faint red in sample 1, none in sample 2-4. 






3) Ground Zero, slightly west of center, site #2.  I see no red here at all.