PLANT MICROBE INTERACTIONS Could the Canopy Structure of Bryophytes Serve as an Indicator of Microbial Biodiversity? A Test for Testate Amoebae and Microcrustaceans from a Subtropical Cloud Forest in Dominican Republic D. Acosta-Mercado & N. Cancel-Morales & J. D. Chinea & C. J. Santos-Flores & I. Sastre De Jesús Received: 31 March 2011 / Accepted: 29 December 2011 / Published online: 2 February 2012 # Springer Science+Business Media, LLC 2012 Abstract The mechanisms that ultimately regulate the di- versity of microbial eukaryotic communities in bryophyte ecosystems remain a contentious topic in microbial ecology. Although there is robust consensus that abiotic factors, such as water chemistry of the bryophyte and pH, explain a significant proportion of protist and microcrustacean diver- sity, there is no systematic assessment of the role of bryo- phyte habitat complexity on such prominent microbial groups. Water-holding capacity is correlated with bryophyte morphology and canopy structure. Similarly, canopy struc- ture explains biodiversity dynamics of the macrobiota sug- gesting that canopy structure may also be a potential parameter for understanding microbial diversity. Canopy roughness of the dominant bryophyte species within the Bahoruco Cloud Forest, Cachote, Dominican Republic, con- comitant with their associated diversity of testate amoebae and microcrustaceans was estimated to determine whether canopy structure could be added to the list of factors explaining microbial biodiversity in bryophytes. We hypoth- esized that smooth (with high moisture content) canopies will have higher species richness, density, and biomass of testate amoebae and higher richness and density of micro- crustaceans than rough (desiccation-prone) canopies. For testate amoebae, we found 83 morphospecies with relative low abundances. Species richness and density differed among bryophytes with different bryophyte canopy struc- tures and based on non-metric multidimensional scaling, canopy roughness explained 25% of the variation in species composition although not as predicted. Acroporium pungens (low roughness, LR) had the lowest species richness (2± 0.61 SD per gram dry weight bryophyte), and density (2.1± 0.61 SD individual per gram of dry weight bryophyte); whereas Thuidium urceolatum (high roughness) had the highest richness (24±10.82 SD) and density (94±64.30 SD). The fact that the bryophyte with the highest roughness had the highest levels of diversity for testate amoebae sug- gests that moisture levels at the level of the bryophyte canopy may not represent a biodiversity driver in a cloud forest with high relative humidity; however, high roughness could generate a dynamic and fluctuating moisture environ- ment with concomitant alternating microbial communities. A total of 26 microcrustacean morphospecies were found across 11 bryophytes; however, no bryophyte canopy effect was detected on their richness and density. Microcrustacean mean density was low ranging from less than one individual per 50 cm 2 of bryophyte in Leucobryum (LR) to a maximum of 6±3.37 SD individuals/50 cm 2 in Monoclea (LR). This lack of pattern suggests that possible explanatory variables may be related to larger scale processes than those examined in this study. Introduction Understanding the factors that ultimately regulate the com- munity assembly of microbial eukaryotes in ecosystems remains a contentious topic in microbial ecology. Although there is robust consensus that abiotic factors, such as water chemistry and pH, explain a significant por- tion of protist [1–3] and microcrustacean [4] community composition, there are few systematic assessments of the D. Acosta-Mercado (*) : N. Cancel-Morales : J. D. Chinea : C. J. Santos-Flores : I. Sastre De Jesús Department of Biology, University of Puerto Rico, Mayagüez Campus, Mayagüez, PR 00682, USA e-mail: dimaris.acosta@upr.edu Microb Ecol (2012) 64:200–213 DOI 10.1007/s00248-011-0004-8