Clonal and non-clonal edaphic island plants have different persistence strategies
Except for plant height and BDMC, we assessed different traits for clonal and non-clonal species, mainly because i) collecting anatomical traits for clonal plants is challenging and destructive (the oldest part of the rhizome is necessary but often out-of-reach or decomposed), and ii) some traits may be measured only for one group, such as lateral spread for clonal plants (Klimešová et al., 2019). Yet, all the traits included in this study capture different dimensions associated with non-acquisitive functions shaping species persistence strategies. These are: 1) resource conservation represented by BDMC and storage tissue, 2) plant growth associated with plant height, lateral spread, radial growth, and vessel size, and 3) plant lifespan linked to plant age. Not all traits, however, proved to have the same responsiveness. BDMC emerged as the most responsive and consistent trait across species, especially for clonal plants – the only case where the considerable portion of the explained variability in the model was attributable to predictors only (and no effect of species identity was detected; Table 2). This trait is the belowground coarse organ parallel to LDMC and mainly linked to resource conservation function and carbohydrate storage. BDMC can provide insights also into plant ability to overwinter, store water, and multiply clonally – similarly to LDMC reflecting leaf longevity (de Bello et al., 2012; Pérez-Harguindeguy et al., 2013). The functional significance of BDMC and its relationship with other traits would deserve further investigation in different ecological contexts; BDMC may serve as an easy surrogate for other belowground traits and functions that are more laborious to gather data for.
By treating clonal and non-clonal species separately, we were able to detect similarities as well as differences within and among perennial species forming temperate dry grasslands. Clonal species, capable of both vegetative and sexual reproduction, exhibited consistently similar trait responses to variations in environmental conditions and insularity. In temperate grasslands, clonal species tend to prefer moist and nutrient-rich environments (Klimešová et al., 2016b, 2018). Therefore, clonal plants specialized to the dry, sandy, shallow-soil and nutrient-poor environments of isolated rocky outcrops may occupy one of the limits of their ecological niche in the temperate grassland biome. Clonal species may avoid local extinction by extending their longevity through low-cost resource economics (Klimešová et al., 2016a) linked to higher dry matter content of the belowground organ. We cannot, however, fully support this conclusion by direct age determination because for clonal plants, we lack direct measures. Yet, from demographical studies, we know that these species can largely exceed the lifespan of non-clonal plants (Janovský & Herben, 2020), and may persist in remnant populations (Jiménez-Alfaro et al., 2016; Marini et al., 2012; Saar et al., 2012).
A very different scenario emerged for non-clonal species instead. Half of the species (Carlina , Helianthemum, Lychnis, Scleranthus ) were highly responsive to variation in environmental and insularity conditions. Yet, only in few instances trait responses were consistent across species. Conversely, the other half of the species, especially Silene and Thymus , remained almost unaffected by marked variations in the edaphic status, climate or insularity. Also, trait responses (or lack thereof) did not mirror plant functional type either. For example, the chamaephytes Helianthemum andThymus or the forbs Carlina , Centaurea ,Knautia and Scleranthus were distinguished by well-differentiated strategies to successfully persist on the edaphic islands (Figure 2b). This may be due to differences in rooting depth and regenerative strategies (Rosbakh & Poschlod, 2021) and not to plant longevity (see also Doležal et al., 2021). Such a complex and species-specific set of responses may indicate that the focal non-clonal species are likely to be well-adapted to cope with (and not limited by) the distinct ecological and biogeographical conditions provided by the spatially-confined temperate dry grasslands. This inference seems further supported by the almost complete segregation of non-clonal species niches in the multifunctional space identified by non-acquisitive persistence-related traits (Figure 2).