Abstract
Fine-root decomposition contributes a substantial amount of nitrogen that sustains both plant productivity and soil metabolism, given the high turnover rates and short root life spans of fine roots. Fine-root decomposition and soil carbon and nitrogen cycling were investigated in a 1-year field litterbag study on lower-order roots (1–2 and 3–4) of Pinus massoniana to understand the mechanisms of heterogeneity in decomposition rates and further provide a scientific basis for short-time research on fine-root decomposition and nutrient cycling. Lower-order roots had slower decay rates compared with higher-order roots (5–6). A significantly negative correlation was observed between the decay constant mass remaining and initial N concentrations as well as acid unhydrolyzable residues. Results also showed that in lower-order roots (orders 1–2 and 3–4) with a lower C:N ratio, root residual N was released and then immobilized, whereas in higher-order roots (order 5–6) with a higher C:N ratio, root residual N was immobilized and then released in the initial stage. In the later stage, N immobilization occurred in lower-order roots and N release in higher-order roots, with the C:N ratio gradually decreasing to about 40 in three branching-order classes and then increasing. Our results suggest that lower-order roots decompose more slowly than higher-order roots, which may result from the combined effects of high initial N concentration and poor C quality in lower-order roots. During the decomposition of P. massoniana, N release or N immobilization occurred at the critical C:N ratio.
Highlights
In terrestrial ecosystems, fine-root decomposition plays an important role in nutrient cycling and soil C sequestration [1,2,3,4]
Recent studies have suggested that input of organic matter during fine-root decomposition promotes greater changes in stable soil organic matter (SOM) and nutrients in the surrounding soil environment compared with SOM input in aboveground ecosystems [3,6]
Talbot et al [39] reported on decomposition in the model plant Arabidopsis thaliana, and the results indicated that initial N concentration positively affected N loss owing to the high-N substrates more sufficiently meeting microbial demand than low-N substrates
Summary
Fine-root decomposition plays an important role in nutrient cycling and soil C sequestration [1,2,3,4]. Fine roots account for about half of the net primary productivity in forest ecosystems [5]. Recent studies have suggested that input of organic matter during fine-root decomposition promotes greater changes in stable soil organic matter (SOM) and nutrients in the surrounding soil environment compared with SOM input in aboveground ecosystems [3,6]. Most previously reported belowground assessments have focused on traditional fine-root. Forests 2020, 11, 14 decomposition (≤2 mm in diameter) instead of examining the rapid turnover of the smallest distal roots [7]. Very fine roots are physiologically more active than larger ones
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