Decadal-scale shifts in soil hydraulic properties as induced by altered precipitation

Abstract

Soil hydraulic properties influence the partitioning of rainfall into infiltration versus runoff, determine plant-available water, and constrain evapotranspiration. Although rapid changes in soil hydraulic properties from direct human disturbance are well documented, climate change may also induce such shifts on decadal time scales. Using soils from a 25-year precipitation manipulation experiment, we found that a 35% increase in water inputs substantially reduced infiltration rates and modestly increased water retention. We posit that these shifts were catalyzed by greater pore blockage by plant roots and reduced shrink-swell cycles. Given that precipitation regimes are expected to change at accelerating rates globally, shifts in soil structure could occur over broad regions more rapidly than expected and thus alter water storage and movement in numerous terrestrial ecosystems.

Fig. 1. Characterization of experimental water regimes.

(A) Total annual rainfall at the Konza Prairie Biological Station (Control) and total rainfall plus water applied as part of the ITE (Irrigated). (B) Volumetric soil water content (daily means across six sets of sensors) in control and irrigated transects for an example year. (C) Distribution of soil water content at the experimental site for an 8-year period (2008–2015).

Fig. 2. Soil infiltration and porosity.

(A) Infiltration rates (mean ± SE across pairs of plot-level values) at the five pressure potentials evaluated. Pore diameters are those of the largest pores transmitting water at the pressure potentials indicated. Outcomes of statistical evaluations are presented in table S1. (B) Total porosity of soil blocks (mean ± SE across block pairs). Statistical evaluations are summarized in tables S2 and S3. Horizontal offsets have been added to the points in (A) to reduce overlap.

Fig. 3. Soil water retention properties.

(A) Water retention curves from interpolated data (mean ± SE across four samples per treatment group). Insets show the sizes of predominant effects as the difference in water content (Δθ_v) between (B) upland and lowland landscape positions and (C) irrigated and control water regimes, each calculated from the means in (A). Statistical evaluations are summarized in table S4.

Fig. 4. CWM root diameter through the course of the ITE.

Points depict means (±SE) across all plots within water regimes (n = 5 per regime in the first 2 years of the experiment but n = 12 subsequently). Statistical evaluations are summarized in table S5.

Fig. 5. Additional soil properties.

(A) Size distribution of aggregates and fine particles in Konza Prairie soil (means of data aggregated to the plot level). (B) Soil carbon and nitrogen content (mean ± SE across triplicate samples in each of eight plots). (C) Estimated distribution of soil crack widths through eight growing seasons (bootstrapped mean ± SE). Statistical evaluations for (A) and (B) are summarized in tables S6 and S3, respectively.