Roles of weathered bedrock and soil in seasonal water relations of Pinus Jeffreyi and Arctostaphylos patula

Abstract

In the southern Sierra Nevada, California, relatively thin soils overlie granitic bedrock that is weathered to depths of several metres. The weathered granitic bedrock is porous and has a plant-available water capacity of 0.124 m3·m–3, compared with 0.196 m3·m–3 for the overlying soil. Roots confined within bedrock joint fractures access this rock-held water, especially during late summer when overlying soils are dry. We sought to determine seasonal soil and bedrock water changes in a Jeffrey pine (Pinus jeffreyi Grev & Balf.) plantation and to examine concurrent effects on the water relations of Jeffrey pine and greenleaf manzanita (Arctostaphylos patula Greene). In 1996, plant-available water in the 75 cm thick soil was depleted by late June, with soil water potential (ψsoil) <–2.2 MPa, but below 75 cm, bedrock water potential (ψbedrock) was still > –2.2 MPa. Thus, the bedrock, not the soil, supplied water to plants for the remainder of the dry season. Higher values of, and smaller fluctuations in, seasonal predawn pressure potential (ψpredawn) for Jeffrey pine indicated that it is deeply rooted, whereas active roots of greenleaf manzanita were interpreted to be mostly within the upper 100 cm. The extra rooting volume supplied by weathered bedrock is especially important to pine relative to manzanita.

Soil-Plant-Microbial Relations in Hydrothermally Altered Soils of Northern California

“…The greatest difference in the understory vegetation was the abundance of manzanita in the lower pH, less fertile acid-sulfate soils at both Maidu and Lassen and its absence in the unaltered soils. This finding agrees with other research noting the tolerance of manzanita to lower soil moisture and pH conditions (Hubbert et al, 2001;Rose et al, 2003). Pinus sp.…”

Reviews and syntheses: on the roles trees play in building and plumbing the critical zone

“…However, where soils are shallow, the underlying substrate may contain roots, sometimes to many meters in depth, especially in upland areas (Hellmers et al, 1955;Scholl, 1976;Stone and Kalisz, 1991;Anderson et al, 1995;Canadell and Zedler, 1995;Jackson et al, 1999;Hubbert et al, 2001a;EgertonWarburton et al, 2003;Rose et al, 2003;Witty et al, 2003;Bornyasz et al, 2005;Graham et al, 2010;Roering et al, 2010;Estrada-Medina et al, 2013). Both fine, absorptive roots and larger framework roots have been found at tens of meters in depth beneath the land surface (Canadell et al, 1996;Jackson et al, 1999).…”

“…In those environments, trees must grow deep roots to harvest water in fractured or porous bedrock material (Lewis and Burgy, 1964;Zwieniecki and Newton, 1995;Hubbert et al, 2001a;Egerton-Warburton et al, 2003;Rose et al, 2003;Witty et al, 2003;Bornyasz et al, 2005;Schenk, 2008;Graham et al, 2010;Schwinning, 2010). In contrast, in temperate regions with higher rainfall (e.g., Gaines et al, 2016), trees have been observed to access water from predominantly the upper soil even though their roots can still reach depths of several meters.…”

“…In contrast, in temperate regions with higher rainfall (e.g., Gaines et al, 2016), trees have been observed to access water from predominantly the upper soil even though their roots can still reach depths of several meters. In general, however, the extent of deep root penetration has not been systematically explored since most researchers have focused only on shallow depths (Maeght et al, 2013) and only a few lithologies: e.g., granite (Hubbert et al, 2001a;Witty et al, 2003;Bornyasz et al, 2005;Graham et al, 2010;Poot et al, 2012); shale (Hasenmueller et al, 2017); or limestone (Hasselquist et al, 2010;Estrada-Medina et al, 2013). For example, Hasenmueller et al (2017) identified fine roots that penetrate meters into bedrock in a temperate humid forest where trees generally are not water limited.…”

Beyond Mutualism: Complex Mycorrhizal Interactions

“…Roots and mycorrhizal fungi extend even into granite and calcareous bedrock. In some cases, these roots are in bedrock, whereas in others, the roots search out perched water pockets (e.g., Hubbert et al 2001;Querejeta et al 2007b;Estrada-Medina et al 2013). Mycorrhizal fungal hyphae track these roots through fractures in the rock and then extend from root tips penetrating the granite (EgertonWarburton et al 2003;Bornyasz et al 2005).…”