Does light exposure make plant litter more degradable?

Abstract

Many field experiments have indicated that litter decomposition in semi-arid areas may be partly or fully controlled by photodegradation. We devised a study to test our hypothesis that light exposure makes plant litter more degradable. Dry, senescent, aboveground plant litter from Miscanthus x giganteus was exposed to light including ultraviolet (UV) radiation for various lengths of time from 0 to 289 days. Weight loss was measured after exposure and appeared to be modest and did not increase with time of exposure. The litter of the longest and shortest exposure time as well as controls were then incubated with soil and moisture for 35 days and CO 2 and N 2 O production were measured. The longest exposed litter degraded much faster than any other treatment during incubation with moisture, about twice as fast as the unexposed control. The shortest exposed however, degraded only slightly faster than the unexposed control. This suggests that increasing litter degradability is a more important mechanism for photodegradation than direct light-induced mass loss. N 2 O production from decomposition of the exposed litter was high in the beginning, suggesting that nitrogen may be released quickly. The mechanism is probably that light exposure leaves the nitrogen in plant litter easily available to microbial utilisation upon wetting. Such a mechanism might play an important role for nutrient cycling in semi-arid areas.

Photodegradation alleviates the lignin bottleneck for carbon turnover in terrestrial ecosystems

“…We show that, in litter of a broad range of plant species, photodegradation can directly reduce lignin concentration (Fig. 3 A and B), which adds generality to the results of previous studies (19,20,43). In addition, an important implication of the present experiments is that the degradation of litter lignin caused by sunlight exposure may increase the digestibility of labile carbon compounds locked in lignin linkages within the cell wall matrix (Fig.…”

Photodegradation for Nutrient Management in the Dry Tropics

“…These environments are characterized by high radiation levels coinciding with low vegetation cover for at least part of the year, meaning that the degrading litter on the soil surface will be exposed to high radiation. The mechanism for how photodegradation happens is still imperfectly known, but our earlier experiment indicates that photodegradation may work by increasing subsequent microbial decomposition rate in the wet season [10]. Substantial photo-exposure appears to be necessary, as the effect was not found when plant litter was exposed to lower amounts of radiation [10][11][12].…”

“…The mechanism for how photodegradation happens is still imperfectly known, but our earlier experiment indicates that photodegradation may work by increasing subsequent microbial decomposition rate in the wet season [10]. Substantial photo-exposure appears to be necessary, as the effect was not found when plant litter was exposed to lower amounts of radiation [10][11][12]. The mechanism for how photo-exposure affects litter mass loss is insufficiently known, but recent work suggests that it particularly affects the degradation of lignin, the plant compound most resistant to microbial degradation [13].…”

“…The mechanism for how photo-exposure affects litter mass loss is insufficiently known, but recent work suggests that it particularly affects the degradation of lignin, the plant compound most resistant to microbial degradation [13]. The effect of photoexposure on nitrogen mineralization has been less studied, but there is some evidence that this may increase rate of nitrogen as well as carbon release from the litter substantially [5,10]. In particular, the evidence suggests that photoexpose can make at least some of the nitrogen in plant litter mineralize very quickly [10].…”

“…The effect of photoexposure on nitrogen mineralization has been less studied, but there is some evidence that this may increase rate of nitrogen as well as carbon release from the litter substantially [5,10]. In particular, the evidence suggests that photoexpose can make at least some of the nitrogen in plant litter mineralize very quickly [10]. It is possible that this is related to degradation of lignin as lignin is an important compound in the plant cell wall, and degradation of this wall could make more easily degradable and nitrogen rich cell components leak out.…”