Photodegradation of plant litter in the Sonoran Desert varies by litter type and age

Thomas Day, René Guénon, Christopher T. Ruhland

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

Predicting litter decay rates in arid systems has proved elusive and sunlight (photodegradation) is a potentially important but poorly understood driver of litter decay in these systems. We placed three litter types (Cynodon dactylon, Larrea tridentata leaves, and L.tridentata twigs) in envelopes whose tops either transmitted all solar radiation, filtered UV-B, filtered all UV, or filtered all UV and visible solar radiation, on the soil surface of the Sonoran Desert and assessed mass loss over 14 months. Regardless of treatment, final mass loss was greatest in C.dactylon litter and least in L.tridentata twig litter, consistent with initial litter characteristics of presumed litter quality; C.dactylon had the lowest lignin concentration and lignin:N, and the highest cellulose:lignin and area:mass. Compared to litter in sunlight, excluding solar UV, or UV-B, slowed mass loss of all 3 litter types, and UV-B appeared more effective than UV-A in photodegradation. The relative contribution of UV photodegradation to mass loss increased with litter age. After 14 months, litter exposed to solar UV lost 1.2 (C.dactylon), 1.3 (L.tridentata twigs) and 1.4 (L.tridentata leaves) times as much mass as litter not exposed to UV radiation. The relative contribution of UV photodegradation to mass loss increased with the initial C:N ratio of litter, but was not related to initial lignin concentration or optical properties (i.e. UV and visible absorbance and transmittance) of litter. Within all litter type by treatment combinations, there was a strong positive correlation between litter mass loss and ash concentration. In some cases, a discontinuity in this relationship was detected, suggesting a threshold ash concentration, above which further mass loss was negligible. We expected these thresholds to be most prevalent in sunlight, because soil films could prevent sunlight from reaching litter and thereby minimize photodegradation. Contrary to expectations, thresholds were more common in shade or UV filter treatments, suggesting that reductions in photodegradation attributable to soil films were not typically responsible. The effect of shading, which likely enhanced microbial degradation via higher relative humidity due to lower temperatures, depended on litter type and time. Compared to litter in sunlight, mass loss of shaded litter was greater over the initial 3 months in all litter types, illustrating that microbial degradation in shade was greater than photodegradation in sunlight. These differences in mass loss between shaded and sunlit litter increased over the 14 month experiment in L.tridentata twigs, declined in L.tridentata leaves, and disappeared within 6 months in C.dactylon, illustrating that the timing of this shift in the dominance of photodegradation versus microbial degradation was highly dependent on litter type. In a second experiment, we reduced microclimate differences among sun and shade treatments, pre-sterilized litter to reduce microbial degradation, and examined the mass loss of young and old and L.tridentata leaf litter after 53 days outdoors. Consistent with our first experiment, mass loss attributable to photodegradation was greater in old than young litter. Unsterilized litter exposed to sunlight (UV and visible) lost 1.3 (young) and 1.5 (old) times as much mass as shaded litter. Pre-sterilized litter exposed to sunlight lost 11.4 (young litter) and 45.9 (old litter) times as much mass as shaded litter. These large differences in pre-sterilized litter were the result of the very small mass loss of shaded litter (≤0.2%), together with modest losses of sunlit litter (<5%). Taken together, our findings suggest that as litter aged, microbial degradation became a weaker driver of mass loss, while photodegradation became stronger.

Original languageEnglish (US)
Pages (from-to)109-122
Number of pages14
JournalSoil Biology and Biochemistry
Volume89
DOIs
StatePublished - Oct 1 2015

Fingerprint

Sonoran Desert
Photolysis
photolysis
photodegradation
plant litter
Sunlight
litter
desert
solar radiation
Lignin
biodegradation
Soil
ultraviolet radiation
lignin
shade
Larrea
Cynodon
Radiation
Microclimate
films (materials)

Keywords

  • Cynodon dactylon
  • Larrea tridentata
  • Litter decomposition
  • Photodegradation
  • Soil-litter mixing
  • UV radiation

ASJC Scopus subject areas

  • Soil Science
  • Microbiology

Cite this

Photodegradation of plant litter in the Sonoran Desert varies by litter type and age. / Day, Thomas; Guénon, René; Ruhland, Christopher T.

In: Soil Biology and Biochemistry, Vol. 89, 01.10.2015, p. 109-122.

Research output: Contribution to journalArticle

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