Functional Differences in Soil Water Pools: a New Perspective on Plant Water Use in Water-Limited Ecosystems

Root architecture might account for contrasting establishment success of Pseudotsuga menziesii var. menziesii and Pinus sylvestris in Central Europe under dry conditions

“…Longer roots enable Pinus sylvestris seedlings to reach deeper water pools already during early establishment. Deep water pools are depleted more slowly (Ryel et al 2008) and enable plants with an extensive root system to outlast transient drought periods (Niinemets 2010). By contrast, 40-50-year-old Pseudotsuga menziesii have been shown to concentrate their root biomass in the top 10-40 cm of the forest soil (Curt et al 2001;Eis 1987), which, according to our results, seems to hold for seedlings as well (Fig.…”

“…Consequently, the morphology and plasticity of the root system are crucial parameters to assess a species' ability to successfully establish and compete under current and future climatic conditions. Like most pines species, Pinus sylvestris produces a taproot already during the earliest seedling stages (Wilcox 1968), reaching up to 40-cm soil depth within 6 months after germination (Moser et al 2015) and allowing it to acquire water from deeper soil layers that are less rapidly depleted during drought events (Ryel et al 2008). By contrast, little is known about the root architecture of Pseudotsuga menziesii seedlings during early establishment (but see Preisig et al 1979 for 5-8-year-old seedlings), while 10-80-year-old Pseudotsuga menziesii were shown to have a superficial root system (Mauer and Palatova 2012), which only slowly advances to deeper soil layers (Domec et al 2004).…”

Horizontal heterogeneity in the frequency of plant‐available water with woodland intercanopy–canopy vegetation patch type rivals that occuring vertically by soil depth

“…In particular, variability of soil water vertically with soil depth has been used to predict the ratio of woody to herbaceous vegetation across regional gradients (Walter, 1971(Walter, , 1973Coffin and Lauenroth, 1990;Sala et al, 1997;Breshears and Barnes, 1999;Caylor and Shugart, 2006). A larger amount of deeper soil moisture is generally viewed as being favourable for supporting a larger proportion of woody plant biomass, although there are many situations where this relationship is either insufficient to explain or does not apply to observed patterns (Scholes and Walker, 1993;Le Roux et al, 1995;House et al, 2003;Ryel et al, 2008). More recently, differences in the frequency of soil moisture availability related to shallow and deeper 'pools' have been highlighted as a potential driver of vegetation dynamics in drylands (Ryel et al, 2008).…”

“…A larger amount of deeper soil moisture is generally viewed as being favourable for supporting a larger proportion of woody plant biomass, although there are many situations where this relationship is either insufficient to explain or does not apply to observed patterns (Scholes and Walker, 1993;Le Roux et al, 1995;House et al, 2003;Ryel et al, 2008). More recently, differences in the frequency of soil moisture availability related to shallow and deeper 'pools' have been highlighted as a potential driver of vegetation dynamics in drylands (Ryel et al, 2008).…”

“…Accounting for this fundamental differentiation between when soil water is readily available from when it is not has been integral to several key concepts of soil-plant water relationships that include 'wilting point', 'non-limiting water range', 'least limiting water range', 'available water', 'plant-available soil water' and 'readily available water' (e.g. da Silva et al, 1994;Kramer and Boyer, 1995;Sadras and Milroy, 1996;Zou et al, 2000;Kirkham, 2005), as well as more generally proposed 'growth' versus 'maintenance' pools of soil moisture (Ryel et al, 2008). Indeed, the converse-how often plant-available water is lacking in a given period-may be a key determinant of the major vegetation change associated with drought-induced plant mortality (McDowell et al, 2008;Adams et al, 2009).…”