Abstract
Efforts to monitor terrestrial decomposition dynamics at broad spatial scales are hampered by the lack of a cost-effective and scalable means to track the decomposition process. Recent advances in remote sensing have enabled the simulation of litter spectra throughout decomposition for grasses in general, yet unique decomposition pathways are hypothesized to create subtly different litter spectral signatures with unique ecosystem functional significance. The objectives of this study were to improve spectra–decomposition linkages and thereby enable the more comprehensive monitoring of ecosystem processes such as nutrient and carbon cycles. Using close-range hyperspectral imaging, litter spectra and multiple decomposition metrics were concurrently monitored in four classes of naturally decayed litter under four decomposition treatments. The first principal component accounted for approximately 94% of spectral variation in the close-range imagery and was attributed to the progression of decomposition. Decomposition-induced spectral changes were moderately correlated with the leaf carbon to nitrogen ratio (R2 = 0.52) and sodium hydroxide extractables (R2 = 0.45) but had no correlation with carbon dioxide flux. Temperature and humidity strongly influenced the decomposition process but did not influence spectral variability or the patterns of surface decomposition. The outcome of the study is that litter spectra are linked to important metrics of decomposition and thus remote sensing could be utilized to assess decomposition dynamics and the implications for nutrient recycling at broad spatial scales. A secondary study outcome is the need to resolve methodological challenges related to inducing unique decomposition pathways in a lab environment. Improving decomposition treatments that mimic real-world conditions of temperature, humidity, insolation, and the decomposer community will enable an improved understanding of the impacts of climatic change, which are expected to strongly affect microbially mediated decomposition.
Highlights
While this study indicates that decomposition spectral signatures have minimal variability and straightforward evolution, these results are strongly dependent on the conditions of the decomposition treatment
As microbial and photodegradation are concurrent processes, incorporating UV radiation into the methodological design is essential for understanding the diversity of decaying leaf spectra. These results suggest that field studies manipulating the environmental conditions to encourage unique decomposition pathways may be required
The hypothesis that litter spectral signatures were dependent on the decomposition treatment and that litter spectra had linkages to important metrics relevant for ecosystem processing of carbon and nutrients was partially validated
Summary
Linking the reflectance spectra of living leaves to variations in their biochemical and biophysical attributes has proven useful in monitoring ecosystem functions—for instance, assessing carbon dioxide (CO2 ) sinks [1] through quantifying chlorophyll content [2] and light stress [3]. Despite biomass decomposition being a fundamental process in the life cycles of plants, coupling the spectral evolution of litter (in this study, defined as dead leaves of grasses undergoing decomposition) to ecosystem processes remains a major task [4]. Decomposition controls nutrient availability in the soil, regulating primary production, there is a paucity of studies investigating the spatial–temporal dynamics of litter-borne carbon and nutrient fluxes.
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