Breaking up is natural: plant litter degradation in the San Luis Valley

Abstract

Nutrient cycling of carbon (C) and nitrogen (N) is critical for maintaining ecosystem processes. In many ecosystems where water availability is not limiting, microbial degradation of plant litter is the dominant process driving nutrient turnover. However, in water-limited regions such as semi- arid systems, photodegradation is likely to become more important to the degradation of vegetation. We attempted to quantify photodegradation across different land uses within the semi-arid San Luis Valley of Colorado. In a 20-week field study, we measured plant litter mass and chemical composition over time under varying degrees of exposure to solar radiation. The study was conducted on managed and unmanaged agroecosystems at three locations, using the dominant vegetation type at each site. At each site litter bags were placed at three positions: above the surface (no contact with soil), on the soil surface (in contact with soil), and below the surface (buried in soil). This arrangement allowed us to assess the key degradation processes associated within each land use. Results showed that, regardless of litter chemistry or land use, litter samples exposed to solar radiation (above the soil) exhibited the greatest nitrogen and lignin mineralization. Unexpectedly, litter total, mass loss due to photodegradation was observed to be greater than that due to microbial degradation at only at one of the sites. Nutrient fluxes due to plant litter degradation associated with photodegradation varied from microbial degradation and can substantially alter ecosystem structure and function. Understanding these degradation processes is crucial for managing agricultural activities and maintaining overall soil health in semi-arid systems.