Rock Fragment Content in Soils Shift Root Foraging Behavior in Xerophytic Species

Aims Root traits associated with resource foraging, including fine-root branching intensity, root hair and mycorrhiza, may change in soils with various physical structure indicated by rock fragment content (RFC), while how these traits covariate at the level of individual root branching order is largely unknown.Methods We subjected two xerophytic species, Artemisia vestita (subshrub) and Bauhinia brachycarpa (shrub), to increasing RFC gradients (0%, 25%, 50% and 75%, v v-1) in an arid environment and measured fine-root traits related to resource foraging.Results Root hair density and mycorrhizal colonization of both species decreased with increasing root order, but increased in 3rd- and 4th-order roots at high RFCs (50% or 75%). The two species tend to produce more root hairs than mycorrhizas under the high RFCs. For both species, root hair density and mycorrhizal colonization intensity were negatively correlated with root length and root diameter. Rockiness reduced root branching intensity in both species comparing with rock-free soil. At the same level of RFC, A. vestita had thicker roots and lower branching intensity than B. brachycarpa, and tended to produce more root hairs.Conclusion Our results suggest the high RFC soil conditions stimulated greater foraging functions in higher root orders. We found evidence for a greater investment in root hairs and mycorrhizal symbioses as opposed to building an extensive root system in rocky soils. The subshrub and shrub species took different approaches to foraging in the rocky soil through distinctive trait syndromes of fine-root components.

Effects of rock fragments on the water infiltration and hydraulic conductivity in the soils of the desert steppes of Inner Mongolia, China

Soils that contain rock fragments (particles > 2 mm in diameter) are distributed all over the world. The presence of these small rock fragments can have a great impact on soil water retention properties, as well as on the soil-water infiltration and vegetation restoration in semi-arid regions. To quantitatively describe the transport of water in stony soils, repacked soil cores were used to determine the infiltration rates for different rock fragment contents (0%, 10%, 20%, 30%, and 40%) and rock fragment sizes (2–5, 5–8, 8–11, and 2–11 mm). The results showed that both the content and size of the rock fragments and their interaction significantly affected the infiltration process. The infiltration rates over time and the saturated hydraulic conductivity (K_s) decreased with an increasing rock fragment content to an observed minimum value for a 40% rock fragment content. The soil-water infiltration processes were accurately described by the Kostiakov model. The measured and calculated K_s values decreased with an increasing rock fragment content, which was in accordance with the published data and in accordance with the K_s obtained by five empirical methods. The variations in the measured K_s were likely due to the variations in the soil properties caused by the soil sample repacking. The results of this study may improve the understanding of the effects of the rock fragment content and size on the infiltration processes in arid and semi-arid desert steppes.

Aggregate stability of cultivated vineyard soils with high rock fragment content in the Mosel area, Germany

<p>Within the European project Diverfarming (Horizon 2020, no 728003), which investigates crop diversification and low-input farming across Europe, we study the aggregate stability variability of soils with high rock fragment content on steep sloping vineyards in the upper Saar valley of the Mosel area (Wawern, Rhineland-Palatinate, Germany).</p><p>In the framework of the case study researched by Trier University and their partners, aromatic herbs (Oregano and Thyme) are planted in rows underneath the grapevines to minimize soil erosion, suppress unwanted weeds and to be harvested for further use. Additionally, this cultivation affects different soil characteristics such as aggregate stability.</p><p>We analyse the aggregate stability using and comparing three different methods:</p><ul><li>wet sieving which is executed in two different ways – slaked and rewetted treatment,</li> <li>percolation method and</li> <li>single drop technique.</li> </ul><p>Aim of the study is to understand the effect of soil treatments underneath the grapevines, and to identify the method(s) being able to quantify the differences best.</p><p>Regarding the different methods, first results indicate that the quantified aggregate stabilities of each method are comparable. With this, we could identify differences between uncultivated rows (control areas), and the rows intercropped with aromatic herbs. In the latter ones, the aggregate stability underneath the grapevines is affected positively. Furthermore, there is a clear difference between slaked and rewetted treatment within the wet sieving method, where less stable aggregates are isolated.</p><p>The results indicate that the accomplished management (vine intercropped with Oregano and Thyme) improves the aggregate stability and therefore it improves the soil quality in general.</p>

Pore size distribution and pore functional characteristics of soils as affected by rock fragments in the hilly regions of the Sichuan Basin, China

Soil pore size distribution and pore functional characteristics are the most important for soil physical properties, water retention, and transmission. Furthermore, considerable amounts of rock fragments are present in hilly region soils. In this study, we discuss the pore size distribution and pore functional characteristics of soils as affected by rock fragments in the hilly regions of Sichuan Basin, China. The soil water characteristic curve was measured to calculate the soil total porosity and the ratio of equivalent pores in each diameter class. The results suggest that the soil total porosity decreases with increasing rock fragments size. The proportion of transmission pores increased gradually with increasing rock fragment content, whereas the fractions of storage pores and residual-bonding pores decrease gradually. Furthermore, the ratio of effective soil porosity to total porosity is higher than that of ineffective porosity to total porosity with increasing rock fragment content. In summary, increasing the rock fragment content can notably increase the proportion of soil transmission pores, thereby increasing soil aeration and water permeability. However, a high rock fragment content is not conducive to maintaining the water needed for normal plant growth.