Abstract:

In nutrient-limited environments, apoplastic decomposition is a critical biogeochemical process for carbon (C) and nutrient cycling. Apoplastic decomposition and nutrient release processes are particularly important in arid and extremely arid regions, where deserts and dryads are the dominant ecosystem types. These processes play a crucial role in stabilizing soil, improving texture, and replenishing soil fertility due to the dearth of nutrients and organic matter in the soil. Plant nutrient uptake efficiency in such soil primarily relies on the decomposition of apoplastic material. In extremely arid desert regions like the Taklamakan Desert, apoplastic burial by quicksand is common, yet the complexities and characteristics of apoplastic decomposition under sand burial remain relatively unknown. To characterize the decomposition and nutrient dynamics of apomictic material in desert highway shelterbelt forest strips, we studied assimilated Haloxylon ammodendron and Calligonum arborescens assimilated branches, along with Tamarix ramosissima leaves, under surface exposure and sand burial treatments 510 days. Additionally, decomposition tests were conducted using the apoplast net bag method. The results showed that: (1) There were significant differences in mass loss between exposed and sand-buried treatments for the three plant species, with higher mass loss of apomictic material under sand burial. By the end of the decomposition test, the weight loss rates of Haloxylon ammodendron, Calligonum arborescens, and Tamarix ramosissima under the exposed treatment were 7%, 6.8%, and 18.1%, respectively, and those of pike, arborvitae, and multi-branched tamarisk under the sand-buried treatment were 23.7%, 9.7%, and 21.9%, respectively. (2) During the decomposition process, changes in apoplastic C, N, and P contents under the two treatments were inconsistent. The N and P contents of Haloxylon ammodendron and Calligonum arborescens assimilated branches showed a net enrichment, while the C content demonstrated net release. Similarly, the N and P contents of leaves of multi-branched Tamarix ramosissima displayed net enrichment and net release, respectively, while the C content had an enriched-released state. (3) Olson’s exponential decay model was employed to analyze the decomposition process and fit the mass residual rate of the apoplastic material. The decomposition coefficients’ k values for the apoplastic material of the three plants were ranked as follows: sand-buried treatment > bare treatment; (4) An analysis of the k values of the apoplastic material and the related factors showed that the initial N, P, C:N, and C:P contents of the apoplastic material had a significant effect on the rate of decomposition (P < 0.01). These results indicate that sand burial significantly influences the decomposition process of apomictic litter in desert highway protection forests within extremely arid zones.

Key words: extreme arid areas, litter decomposition, sand burial, mass residue rate