Factors Controlling Mass Loss and Nitrogen Dynamics of Plant Litter Decaying in Northern Streams
Abstract:In this paper we consider the influences of initial litter quality, exogenous nutrient supply, temperature and oxygen tension on decay rates and nutrient immobilization potentials of plant litter materials decomposing in northern streams. We review a new method of estimating nitrogen and phosphorus immobilization potentials in decaying litter. And we discuss the mechanisms responsible for nitrogen immobilization.
Initial litter quality is the dominant factor that influences decay rate. Materials rich in nitrogen and poor in lignin generally decay most rapidly. Addition of nitrogen and/or phosphorus to the water often result(s) in increased decay rate as does elevation of water temperature. While low oxygen tension retards the decay of lignin and related compounds, it is not clear that low oxygen tension slows the rate of decay of more labile compounds.
Initial litter quality is also the dominant factor that influences nitrogen immobilization potential. Materials poor in both nitrogen and lignin generally have the highest immobilization potentials. Addition of nitrogen to the water increases the immobilization potential of a litter material. Plant litter decomposing under anaerobic conditions immobilizes less nitrogen than the same litter decomposing under aerobic conditions. And, all other conditions being equal, temperature changes will influence nitrogen immobilization rate but not its maximum amount.
The amount of nitrogen directly associated with microbial biomass makes up only a small fraction of the total nitrogen mass in decomposing litter. Microbes appear to be important agents in the nitrogen immobilization process on decaying litter. The microbes produce exoenzymes which in turn cause the degradation of large molecules such as polyphenolics and lignins. Some of these degradation products, such as the “reactive phenolics,” recondense with nitrogen containing compounds. The degradation-recondensation cycle continues throughout litter decay, with the ultimate product being nitrogen-rich humic substances.
Document Type: Research Article
Publication date: November 1, 1984
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