On a global scale, the fluxes of nitrogen (N), phosphorus (P) and sulfur (S) have increased due to human intervention. There are many hypotheses about which nutrient may affect the response of epiphytic bryophytes to N enrichment, but the relative importance among these covariant nutrients remains poorly understood. 

Prof. LIU Wenyao and his team of Xishuangbanna Tropical Botanical Garden (XTBG) carried out a manipulative experiment in a subtropical montane cloud forest in the Ailao Mountains National Nature Reserve (23° 36′–24° 56′ N 100° 44′–101° 30′ E). They hypothesized that N fertilization had adverse impacts on physiological performance of epiphytic bryophytes, whereas the combined fertilization with P and S would mitigate the physiological stresses induced by excessive N. 

The researchers investigated the physiological responses of two ecologically related but taxonomically distinct bryophytes (Homaliodendron flabellatum (Sm.) Fleisch. and Plagiochila assamica Steph.) to nutrient addition. They wanted to test whether the combined additions of P and S with N could mitigate the adverse physiological responses in two epiphytic bryophytes. They further wanted to see which physiological parameters were the more reliable indicators of increased artificial fertilization.

Their field experiment suggested that enhanced atmospheric depositions imposed detrimental impacts on physiological performance of two epiphytic bryophytes, whereas the metabolic burden imposed by excessive N cannot be completely alleviated by P and S addition. In general, foliar N was not a robust indicator of N deposition in bryophytes concerning the saturation uptake and the species-specific response of N concentration to application regimes. Moreover, none of the species showed a pronounced relationship between N:P ratio and N and P addition, indicating that N:P ratio was not yet an ideal candidate for bioindication programs of atmospheric deposition.  

The researchr results confirmed that one can not assess the type of nutrient limitation simply by calculating the N:P ratio for bryophytes and applying the critical values developed from vascular plants to bryophytes. 

The study entitled “Physiological Responses of Two Epiphytic Bryophytes to Nitrogen, Phosphorus and Sulfur Addition in a Subtropical Montane Cloud Forest” has been published in PLoS ONE.