Linking water uptake with rooting patterns in grassland species

Abstract

Water availability strongly governs grassland primary productivity, yet this resource varies dramatically in time (seasonally) and space (with soil depth and topography). It has long been assumed that co-occurring species differ in their partitioning of water use by depth, but direct evidence is lacking. We report data from two growing seasons (2004-2005) in which we measured the isotopic signature of plant xylem water from seven species (including C(3) forbs and shrubs and C(4) grasses) growing along a topographic gradient at the Konza Prairie Biological Station. Plant xylem stable oxygen isotope ratio (delta(18)O) values were compared to soil water delta(18)O profiles, recent rainfall events, and groundwater. Species varied in both their temporal patterns of water use and their responses to seasonal droughts in both years. During wet periods, species differences in water use were minimal, with common dependency on recent rainfall events stored in the upper soil layers. However, during dry periods, most C(3) species used proportionally more water from deeper portions of the soil profile relative to the C(4) grasses. Plants in uplands used more shallow soil water compared to those in lowlands, with the greatest differences across the topographic gradient occurring during dry periods. While the documented vertical root distribution varies by species and growth form in this grassland, each of the species we measured appeared to compete for the same surface layer soil moisture when water was not limiting. Thus, our results suggest that variation in precipitation history and landscape positions are greater determinants of water-use patterns than would be expected based on absolute rooting depth.

Effects of Different Land-Use Systems on Soil Aggregates: A Case Study of the Loess Plateau (Northern China)

“…Root biomass plays a vital role in the decomposition of SOM and helps in the formation of soil aggregates [10,45,60]. Generally, the study observations showed that animal grazing, the regular use of farm machinery, and several anthropogenic activities were assumed to be the reasons for low root biomass production in the CAO, Clm, and Clw; similar findings were observed by many researchers in their studies [62][63][64]. …”

Positive feedbacks amplify rates of woody encroachment in mesic tallgrass prairie

“…However, these and other mechanisms have been found to have a minimal impact on encroachment of tallgrass prairie (Briggs et al 2005, McKinley andBlair 2008). Instead, the nature of feedbacks in tallgrass prairie may involve factors that structure mesic grasslands: pronounced belowground competition in the upper soil layers (Nippert and Knapp 2007a, b), frequent and intense fires (Knapp et al 1998, van Wilgen et al 2003, Briggs et al 2005, Bond 2008) and predominance of clonal reproduction (Benson andHartnett 2006, Dalgleish and.…”

Identifying the water sources consumed by bison: implications for large mammalian grazers worldwide

“…18 O, À37% for dD [Nippert and Knapp 2007]). At this point on the MWL, the isotopic composition of water from fecal samples deviated from the MWL (Fig.…”

“…Water was extracted from fecal samples using cryogenic vacuum distillation (Nippert and Knapp 2007) using an extraction line operated in the Stable Isotope Mass Spectrometry Laboratory at KSU. Water samples from bison, rainfall, and stream-water were analyzed for their stable isotopic composition using a Picarro WS-CRDS isotopic water analyzer using ChemCorrect software to identify possible interference or sample contamination.…”