Abstract
To investigate the dynamics and relative drivers of cellulose degradation during litter decomposition, a field experiment was conducted in three individual ecosystems (i.e., forest floor, stream, and riparian zone) of an alpine forest meta-ecosystem on the eastern Tibetan Plateau. Four litter species (i.e., willow: Salix paraplesia, azalea: Rhododendron lapponicum, cypress: Sabina saltuaria, and larch: Larix mastersiana) that had varying initial litter chemical traits were placed separately in litterbags and then incubated on the soil surface of forest floor plots or in the water of the stream and riparian zone plots. Litterbags were retrieved five times each year during the two-year experiment, with nine replicates each time for each treatment. The results suggested that foliar litter lost 32.2%–89.2% of the initial dry mass depending on litter species and ecosystem type after two-year’s incubation. The cellulose lost 60.1%–96.8% of the initial mass with degradation rate in the order of stream > riparian zone > forest floor. Substantial cellulose degradation occurred at the very beginning (i.e., in the first pre-freezing period) of litter decomposition. Litter initial concentrations of phosphorus (P) and lignin were found to be the dominant chemical traits controlling cellulose degradation regardless of ecosystems type. The local-scale environmental factors such as temperature, pH, and nutrient availability were important moderators of cellulose degradation rate. Although the effects of common litter chemical traits (e.g., P and lignin concentrations) on cellulose degradation across different individual ecosystems were identified, local-scale environmental factors such as temperature and nutrient availability were found to be of great importance for cellulose degradation. These results indicated that local-scale environmental factors should be considered apart from litter quality for generating a reliable predictive framework for the drivers of cellulose degradation and further on litter decomposition at a global scale.
Highlights
Litter decomposition is a key ecological process in forest ecosystems, in cold biomes where large amounts of plant litter accumulate [1]
Intensive research on the subject of cellulose degradation has been carried out for decades [2], our current understandings on this process are mainly derived from terrestrial ecosystems such as forest floors [5,6,7], and little information is available on the dynamics of cellulose during litter decomposition in aquatic ecosystems, where the environmental factors substantially vary from those in terrestrial ecosystems
Litter decomposition is traditionally thought to be hierarchically controlled by three main factors in the order of climate > litter quality > decomposer [8,9], but recent studies found that litter quality, which is usually expressed as litter species, can explain a much higher percent of variation in litter decomposition at both local and global scales [10,11]
Summary
Litter decomposition is a key ecological process in forest ecosystems, in cold biomes where large amounts of plant litter accumulate [1]. Forests 2016, 7, 176 plant-synthesized biopolymer and typically constitutes 20%–30% of the C sequestered in plant litter [4] In this respect, the understanding of cellulose degradation during litter decomposition in forest ecosystem is essential for future predictive power of litter decomposition models and terrestrial C cycles. Litter decomposition in terrestrial and aquatic ecosystems can share some common driving factors such as ambient nutrient availability, decomposer community, and litter quality [11,15,16], several fundamental differences of environmental conditions in aquatic ecosystems can preclude a generalization for litter decomposition patterns These include the buffered temperature ranges, unlimited water availability, and limiting oxygen levels in aquatic ecosystems [17]
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