Title: Fog as a source of nitrogen for redwood trees: evidence from fluxes and stable isotopes

Abstract

A defining feature of the redwood forest in coastal California is the presence of fog in the summer months, a time when there is typically little rainfall. Our goal was to determine the role of summer fog in canopy transformation of nitrogen, nitrogen uptake by trees and photosynthesis within a coastal redwood forest ecosystem. We measured horizontal and vertical inputs of nitrogen, the isotopic composition of nitrogen in a variety of atmospheric sources (summer fog, winter rain and throughfall throughout the year), nitrogen pools (soil solution) and plant tissue (roots and foliage), as well as rates of photosynthesis and nitrogen uptake by trees. Throughfall nitrogen fluxes were greater at the forest edge compared to the interior both within the canopy (sampled 10m above-ground) and onto the forest floor (sampled 1m above-ground; P<0.05). Similarly, soil solution $$\mathrm{NO^{-}_{3}}$$ and total inorganic nitrogen were greater at the forest edge compared to the interior (P=0.0014 and 0.009, respectively). Whereas natural abundance δ¹⁵NO₃ values were not significantly different between winter rain (measured as bulk precipitation) and summer fog water (average δ¹⁵N=-1.2±0.68 0/00), δ¹⁵NH₄ values were significantly greater in fog water (11.4±2.7 0/00) compared to rain (1.2±0.9 0/00). We found no difference in δ¹⁵N in roots from forest edge trees compared to interior trees. In contrast, nitrogen concentrations and δ¹⁵N in foliage from forest edge trees were significantly greater compared to interior trees (P<0.0001), suggesting that the leaves of forest edge trees may be obtaining a greater proportion of their nitrogen from fog compared to those of the interior trees. Natural abundance ¹³C of leaf sugars and rates of photosynthesis were significantly higher at the forest edge compared to the interior during the fog season (P<0.05), but not different between locations in the rain season (P>0.05). Nitrification in the forest floor, rather than the canopy, is the primary source of $$\mathrm{NO^{-}_{3}}$$ in these soils throughout the year. Synthesis. Finally, summer fog provides nitrogen directly and indirectly to redwood trees, especially those at the forest edge, and affects the physiologic function of redwood trees. Summer fog provides nitrogen directly and indirectly to redwood trees, especially those at the forest edge, and affects the physiologic function of redwood trees.

Authors:

Templer, Pamela H. ^[1]; Weathers, Kathleen C. ^[2]; Ewing, Holly A. ^[3]; Dawson, Todd E. ^[4]; Mambelli, Stefania ^[4]; Lindsey, Amanda M. ^[2]; Webb, Jeramy ^[1]; Boukili, Vanessa K. ^[4]; Firestone, Mary K. ^[4]

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+ Show Author Affiliations

1. Boston Univ., Boston, MA (United States)
2. Cary Inst. of Ecosystem Studies, Millbrook, NY (United States)
3. Bates College, Lewiston, ME (United States)
4. Univ. of California, Berkeley, CA (United States)

Publication Date:

2015-10-20

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1579711

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Ecology

Additional Journal Information:

Journal Volume: 103; Journal Issue: 6; Journal ID: ISSN 0022-0477

Publisher:

Wiley

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; ammonium; ecophysiology; natural abundance stable isotopes; nitrate; nitrogen budget; plant uptake of nitrogen