Variability in amount and frequency of water supply affects roots but not growth of arid shrubs

Abstract

Rainfall and soil moisture variability have a strong effect on plant survival and seed germination in arid environments, yet very little is known about the effects on roots and growth of woody seedlings. Here we focused on the effects of variability in both amount and frequency of water supply on juvenile root and leaf functional traits and growth of seven Mediterranean shrub species occurring in arid SE Spain, Anthyllis cytisoides, Atriplex halimus, Ephedra fragilis, Genista umbellata, Lycium intricatum, Retama sphaerocarpa, and Salsola oppositifolia. In a 14-month greenhouse experiment we manipulated water supply expecting that reduced water amount and pulses of watering of different magnitude affected functional traits and seedling growth, even if the amount of water provided was the same. Different watering patterns altered soil drying dynamics, with reduced supply of water amount and frequent watering becoming the driest treatment. We found that roots of all species responded to alterations in water supply by changing biomass allocation patterns (i.e., higher root-to-shoot mass [R:S] ratio in droughted plants), and by altering fine roots diameter, measured in terms of specific root length. Indeed, differences in growth rate among species were significantly linked to fine roots diameter and biomass allocation, which relates to uptake capacity of roots. However, relative growth rate and leaf traits such as specific leaf area were insensitive, likely because prolonged droughts over longer periods of time seem necessary to constraint growth in all these arid shrubs.

Trade-Offs between Drought Survival and Rooting Strategy of Two South American Mediterranean Tree Species: Implications for Dryland Forests Restoration

“…Padilla et al [24] also suggests that a key role is higher specific root length to resist water stress. In our study, the deep-rooted species increased all root morphology variables under water shortage with the exception of thin root dry mass.…”

“…In our study, besides finding a greater proportion of fine or thin roots in the shallow-rooted species in relation to roots of the other diametric class, we found that with higher water availability the thin roots increased considerably, and, in fact, quadrupled. Although some studies confirm the positive relationship between fine root production and water availability [46], several recent studies have found an increase in the size and density of fine roots under drought conditions [24,25]. Herná ndez et al [61] suggest that fine roots improve root hydraulic conductance, and, consequently, improve water status and plant productivity under drought [22].…”

Effects of gradual soil drought stress on the growth, biomass partitioning, and chlorophyll fluorescence of Prunus mongolica seedlings

“…Most species deal with heterogeneous water supply by changing biomass allocation patterns (Padilla et al, 2009). Short-term water stress increased the total dry mass and the components of P. mongolica seedlings, whereas prolonged drought decreased the total dry mass and their components, altered the biomass allocation from the shoot to the root system, and, thus, increased the R:S ratio (Figures 2 and 3).…”

Water availability and species identity control shrub colonization in abandoned semiarid steppes

“…Ephedra fragilis withstands harsh environmental conditions, although its ability to grow fast and root depth is less than those of other semiarid shrubs as Salsola oppositifolia Desf., Retama sphaerocarpa (L.) Boiss. and Olea europaea L. (Padilla et al, 2009a;Pugnaire, 2007, 2009). …”