Prof. LIU Wenyao and his team at Xishuangbanna Tropical Botanical Garden (XTBG) of Chinese Academy of Sciences conducted a multifactor in situ manipulation experiment via the ¹⁵N labelling technique in three co-existing and common epiphytic bryophyte species in the Ailaoshan subtropical cloud forest in SW China.

The researchers aimed to determine whether epiphytic bryophytes can take up N from tree bark or bark surface, and to confirm the capacity of epiphytic bryophytes to absorb organic N and quantify its amount in the total N economy of the bryophytes. They further wanted to address the potential impact of increased N deposition on the N uptake dynamics. 

The ¹⁵N enrichment in the epiphytic bryophyte shoots suggested that the epiphytic bryophytes can acquire N from the bark and translocate it to their shoots via various pathways, e.g. passive diffusion, endophytic fungi, and bacteria. The contribution of organic N (glycine) ranged between 28.4% and 44.5% of the total N uptake, which was comparable with NH₄⁺, but significantly higher than NO₃⁻.

No significant differences were detected for the acquisition of different N forms between air deposition and bark injection for all three epiphytic bryophyte species, which demonstrated that those organisms did not shift their N preference from air to bark N sources. Increased N deposition increased the total amount of N absorbed by the epiphytic bryophytes, but did not alter the N preference over a short time. 

The study highlighted that organic N, as opposed to inorganic N, contributed remarkably to the N economy. High N loads may result in excessive N uptake, which may induce biochemical disorders in bryophytes. Thus, organic N and bark N sources become important when estimating the role of epiphytic bryophytes in N cycling and the impacts of N deposition on epiphytic bryophytes in cloud forests. 

The study entitled “Organic nitrogen uptake is a significant contributor to nitrogen economy of subtropical epiphytic bryophytes” has been published in Scientific Reports.