Root carboxylate release is common in phosphorus-limited forest ecosystems in China: using leaf manganese concentration as a proxy

Certain plant species release root carboxylates in response to phosphorus (P) limitation; however, the prevalence of root exudate release in species in P-limited forest ecosystems remains unexplored due to challenges in field assessment.

Manganese (Mn) accumulation in mature leaves can indicate the presence of root carboxylate exudates in rhizosphere soil. To account for environmental factors such as soil pH, a negative reference species that does not release carboxylates is used for comparison. In this study, we assessed multiple forest stands across soil types and different levels of P availability in northern (Gansu) and southern (Guangxi) China. Leaf and soil samples were collected from 188 plant families representing various life forms, and leaf Mn concentration ([Mn]) was analyzed as a proxy for root carboxylate exudation patterns, using Dryopteridaceae as a negative reference.

The results supported our hypotheses that leaf [Mn] was higher in P-limited forests of southern China compared to P-richer forests of northern China, even though the soil [Mn] was higher in the forests of northern China. Additionally, we observed a higher prevalence of species with high leaf [Mn] across various plant families in Guangxi (82%) than in Gansu (42%).

Our findings suggest a potential common strategy among plants in Guangxi forests, where root exudates are released in response to P limitation, possibly due to ineffective mycorrhizal symbiosis for nutrient acquisition. The diverse forest systems in China exhibit varying soil P availability, leading to the evolution of plant species with distinct P-acquisition strategies.