Plant clonal traits, coexistence and turnover in East Ladakh, Trans-Himalaya

To what extent does plant clonality contribute to the assemblage of species in communities? Two apparently contrasting, and largely untested, hypotheses envisage the potential role of plant clonal traits in community assembly: (i) environmental filters constrain coexisting species to have functionally similar traits (i.e. trait convergence); (ii) niche differentiation selects for functionally dissimilar species (i.e. trait divergence) allowing them to exploit different spatial and temporal niches. These hypotheses are assessed using a large dataset of 369 plots (100 m2) covering altitudes between 4100 and 5800 m a.s.l. and including the major vegetation types found in Ladakh, NW Himalaya. Patterns of clonal traits, coexistence and turnover were assessed using a functional diversity partitioning framework in the context of different null models. Functional diversity was expressed both for morphologically delimited clonal growth forms (17 categorical growth forms) and for functionally delimited clonal characters (combining 16 different traits differentiating the 17 growth forms). PERMANOVA revealed that both α (within-plots) and β (between-plots) functional diversity varied across environmental conditions and vegetation types highlighting a filtering effect on clonal traits. Alpha diversity, however, was more stable across habitats than β diversity. Despite the significant turnover of clonal traits across habitats, most of the diversity of clonal traits was found within plots, with a higher trait divergence than expected by chance, which suggests that niche differences determine species coexistence. While both trait convergence and trait divergence were detected, convergence was stronger when using null models that shuffled all species in the regional pool across plots and functional diversity expressed in terms of different clonal growth forms. Divergence, in contrast, was detected mostly when using null models that shuffled species cover across species co-occurring in given plots and considering functional diversity in terms of clonal traits. By detecting both trait convergence and trait divergence this study supports both initial hypotheses and brings new evidence on the relevance of clonal traits as a function of species that both inhabit different environments and coexist.