Causal hypotheses accounting for correlations between decomposition rates of different mass fractions of leaf litter

Pruned litter decomposition primes fluorine bioavailability in soils planted with different tea varieties

Tea (Camellia sinensis L.) plant is fluoride (F) hyperaccumulator. The decomposition of pruned litter in tea plantations releases a large amount of F back into the soil. However, the effect of pruned litter return on soil F bioavailability has remained unclear. We investigated the decomposition dynamics of pruned litter from four tea varieties (Chuannong Huangyazao, Chuancha No. 3, Chuanmu No. 217 and C. sinensis 'Fuding Dabaicha') and its effect on soil F bioavailability. The decomposition of pruned litter occurred in two distinct periods, with an early period of rapid decomposition during the first 120 days, releasing 26-33 % of F, followed by a late period of slow decomposition during 120-360 days, releasing 2-9 % of F. The decomposition of pruned litter enhanced soil F bioavailability by increasing the concentrations of soil water-soluble F (WS-F), exchangeable F (EX-F), and organic matter-bound F (OR-F). The increase in WS-F, EX-F, and OR-F concentrations was higher than the amount of F released from pruned litter, suggesting that the increases in soil F availability did not solely originate from the release of F from pruned litter. The findings reveal the pathway of pruned litter decomposition priming soil F bioavailability through both the direct release of F and transformation from other fractions. Furthermore, the traits (C, N, lignin, and cellulose) of pruned litter from different tea varieties were the dominant factors controlling F release and soil F bioavailability. Compared with other tea varieties, the pruned litter of Chuanmu No. 217 with low lignin and cellulose content promoted higher mass loss and F release, resulting in the highest soil F bioavailability. These findings provide new insights into the mechanisms underlying the accumulation of bioavailable F in soil. These insights offer valuable support for devising effective management strategies for the incorporation of pruned litter into soil.

The response of litter decomposition to extreme drought modified by plant species, plant part, and soil depth in a temperate grassland

Plant litter decomposition is a key ecosystem process in carbon and nutrient cycling, and is heavily affected by changing climate. While the direct effects of drought on decomposition are widely studied, in order to better predict the overall drought effect, indirect effects associated with various drought-induced changes in ecosystems should also be quantified. We studied the effect of an extreme (5-month) experimental drought on decomposition, and if this effect varies with two dominant perennial grasses, plant parts (leaves vs. roots), and soil depths (0-5 cm vs. 10-15 cm) in a semi-arid temperate grassland. After 12 months, the average litter mass loss was 43.5% in the control plots, while only 25.7% in the drought plots. Overall, mass loss was greater for leaves (44.3%) compared to roots (24.9%), and for Festuca vaginata (38.6%) compared to Stipa borysthenica (30.5%). This variation was consistent with the observed differences in nitrogen and lignin content between plant parts and species. Mass loss was greater for deep soil (42.8%) than for shallow soil (26.4%). Collectively, these differences in decomposition between the two species, plant parts, and soil depths were similar in magnitude to direct drought effect. Drought induces multiple changes in ecosystems, and our results highlight that these changes may in turn modify decomposition. We conclude that for a reliable estimate of decomposition rates in an altered climate, not only direct but also indirect climatic effects should be considered, such as those arising from changing species dominance, root-to-shoot ratio, and rooting depth.