Impact of living mulch on soil C:N:P stoichiometry in orchards across China: A meta-analysis examining climatic, edaphic, and biotic dependency

The use of living mulch in orchards is a widely accepted management strategy for improving soil quality and enhancing tree productivity. Although the effects of living mulch on soil organic carbon (C) and nutrients have been previously investigated, changes in the stoichiometric ratios of C, soil total nitrogen (N), and soil total phosphorous (P) under different climatic, edaphic, and biotic conditions are currently unknown. These factors are important indicators of elemental balance associated with ecological interactions. In order to examine the effects of living mulch in orchards on soil C:N:P stoichiometry under different conditions, a meta-analysis was undertaken. The results showed that in general, living mulch significantly (P < 0.05) increased C:P and N:P ratio, while the impact on C:N ratio was not significant, a result that was related to the coupled increase of C and N. Phosphorous limitation occurred shortly after the addition of living mulch; after four years this effect receded. In contrast, an increase in C occurred simultaneously with N increase at all stages. Specifically, the treatment effect was context-dependent. The living mulch did not change soil stoichiometry in orchards with old trees (> 10 years), an occurrence which may be related to changes in the amount of fungi. Grass life history also had a significant influence on the treatment effect on soil stoichiometry, while N-fixing characteristics did not. The treatment effect was significant in areas with moderate mean annual temperature and mean annual precipitation, which might be related to the litter ratio of grass and trees. Effects on stoichiometric ratios were significant in the top soil layer (0-20 cm), in contrast to the deep soil layers. Therefore, grass species and management practices, such as fertilization, should be selected according to the specific soil and climatic conditions of the management area.