Greater differentiation in nitrogen sources is essential for co-occurring epiphytes under low-nitrogen canopy conditions

Abstract

Acquiring enough nitrogen (N) to support their life processes in nutrient-poor canopies is a crucial challenge for epiphytes. When different epiphytes coexist in the same environment, they may use different strategies to acquire N. In this study, we employed stable isotope analysis to explore N acquisition and differentiation among co-occurring epiphytes in a subtropical forest in Southwest China. We found that functional group was the most important factor influencing N and 15N natural abundance (δ15N) of epiphytes, and that different epiphyte groups used different N acquisition, uptake, and utilization pathways. Our analysis of the enrichment factors suggested that biological nitrogen fixation, phorophytes, canopy soil and ground soil could participate in N acquisition of epiphyte groups to varying degrees. However, epiphytes were more affected by precipitation and other canopy N sources than soil. Our structural equation models (SEMs) further showed that the potential N sources of plants and substrates affected throughfall and stemflow, thereby influenced N acquisition and preference of N forms in epiphytes. Overall, our findings indicate that there is differentiation in N sources among co-occurring epiphytes.