Response on root regrowth potential to soil moisture in Sedum species during winter in Særheim, Norway

The impact of winter moisture on root metabolism and root integrity has potential consequences for the geographical distribution of drought-adapted succulent species and for their long-term performance on green roofs. The interacting effects of soil characteristics and precipitation frequency on root mortality under winter conditions and the potential to grow new roots in spring were evaluated for six Sedum species under controlled conditions.

To test for the impact of soil moisture during winter on root regrowth potential in six Sedum species, we used a combination of two substrates with differing water-holding capacity and four contrasting watering regimes. Specially, for the fine and coarse substrates, total pore volume was 42 and 46 %, respectively, and maximum water-holding capacity (i.e. field capacity) was 0.50 and 0.33 kg water per L, respectively. The four watering treatments involved overhead watering to runoff (approx. 10 mm): once every second week, once a week, three times per week and three times per week with 1 cm standing water in trays from January to March 2019.

It was found that winter soil moisture had no major impact on root mortality or root regrowth potential in spring. Root mortality was not affected by watering frequency and regrowth potential showed no directional response to increased watering frequency, although species-specific responses were involved. Root diameter did not differ between the substrates, but there were some differences between the species. Sedum rupestre had on average the thickest roots (0.17 mm), followed by S. acre, S. anglicum and S. sexangulare (0.15-0.16 mm), while S. album and S. hispanicum had the thinnest roots (0.12-0.13 mm). Moreover, effects of watering frequency on root mortality and regrowth potential were not influenced by soil water-holding capacity across species. We concluded that winter soil moisture had no negative effects on root performance within the range of treatments tested here.

Root response to transient waterlogging or moist but unsaturated soil may not be an important mechanism for determining the survival and distribution of temperate Sedum species during winter.