Tree effects on litter mass loss at different soil depths in a young temperate alley cropping system revealed with tea bag method

Litter decomposition is poorly investigated in young temperate alley cropping (AC) systems but may be an integrative indicator to explore the early effect of trees on overall biological activity throughout soil profile. We evaluated the effect of four-year-old trees on recalcitrant-rooibos and labile-green tea mass loss at different soil depths at the Ramecourt AC experimental site.

In May 2021, tea bags were inserted within aluminum ingrowth bags and incubated at three depths 1.5 m from a reference tree for 6 months. The tea mass loss variability was analyzed according to factors: type of tea, type of system (AC, sole-crop control or CC and forest plantation control or FC), soil incubation depth, tree species and was correlated with fine roots and soil parameters.

At 30 cm depth, the mass loss was significantly lower for rooibos than green tea regardless of the type of system, whereas at 50 cm and 100 cm depth, this difference was observed only in AC and FC. We observed a lower rooibos mass loss in AC than in CC at 100 cm depth. At 30 cm depth, soil mineral nitrogen content explained 23% of the rooibos tea mass loss variability whereas, soil organic matter content and fine root biomass within tea bags accounted for 50% of green tea mass loss variability.

We highlighted the ability of AC to slow recalcitrant litter decomposition in depth, however further works are needed to elucidate the processes leading to retarded decomposition.