Spatial heterogeneity of fine root biomass and soil carbon in a California oak savanna illuminates plant functional strategy across periods of high and low resource supply

Abstract

We sampled isolated trees and tree clusters from a blue oak, Quercus douglasii, savanna to determine the spatial heterogeneity of fine root biomass and soil carbon across the landscape as a function of tree size and configuration. We aimed to understand how fine root structure enables sustained ecosystem metabolism through a summer of limited moisture and high heat and facilitates resource acquisition during the short period of high resource supply. An additional goal was to provide a basis for upscaling root biomass and soil carbon to the landscape scale. We sampled trees of different size and tree clusters via a stratified sampling scheme that accounted for spatial heterogeneity in root biomass and soil carbon with lateral distance from the tree bole, or cluster centre, and soil depth. We upscaled these estimates using site‐specific information from a lidar survey. We found that fine roots and soil carbon are spatially heterogeneous in their landscape distribution and greatly increase with tree size. We also found that Q. douglasii possesses a dimorphic fine root architecture, uniquely suited to the region's climatic constraints and exhibits morphological plasticity among trees of different size and physical setting. Copyright © 2014 John Wiley & Sons, Ltd.

Oak Transpiration Drawn From the Weathered Bedrock Vadose Zone in the Summer Dry Season

“…For example, Miller et al (2010) proposed that Q. douglasii in the western foothills of the Sierra Nevada, CA, obtains 80% of its water from groundwater in June, July, and August based on hydrometric data. This is consistent with reported rooting patterns: Mediterranean oaks are noted for their dimorphic root structure (David et al, 2013;Koteen et al, 2015), in which a dense shallow root system is underlain by vertically oriented sinker or taproots that can extend to great depth (Canadell & Zedler, 1995;Canadell et al, 1996;Matsuda & McBride, 1986). These taproots are particularly common where the oaks inhabit easily penetrated substrates with accessible water like fine alluvium (e.g., Mendes et al, 2016).…”

On the inter‐ and intra‐annual variability of ecosystem evapotranspiration and water use efficiency of an oak savanna and annual grassland subjected to booms and busts in rainfall

“…Annual grasses and oak savanna adopt two different strategies to exist and survive in this Mediterranean type climate with rainless and hot summers. Their success can be explained in part by the adage by Ian Cowan (Cowan, 2002): The annual grasses possess relatively shallow roots (Koteen et al, 2015), so they do not tap groundwater. Consequently, they must grow as fast as possible when water is available, then die and cast their seeds and their fate into the wind, hoping for a resumption of rain the next autumn.…”

Bacterial diversity is positively correlated with soil heterogeneity

“…), and this accumulation can vary spatially based on plant age and distance between the drip line and tree trunk (Moody and Jones , Koteen et al. ). In particular, soils under oaks (Gallardo ) and coastal sage scrub (Dickens et al.…”

“…Woody species have heterogeneous distributions of deep roots and vertical stratification of soil resources that reflect the differences in root architecture between plant species (Moody and Jones , Koteen et al. ). We therefore expected that invasive annual grasses would reduce soil heterogeneity both horizontally and vertically and as a result would lead to lower microbial alpha‐ and beta‐diversity.…”