Bioavailability of Macro and Micronutrients Across Global Topsoils: Main Drivers and Global Change Impacts

Understanding the chemical composition of our planet\u27s crust was one of the biggest questions of the 20th century. More than 100 years later, we are still far from understanding the global patterns in the bioavailability and spatial coupling of elements in topsoils worldwide, despite their importance for the productivity and functioning of terrestrial ecosystems. Here, we measured the bioavailability and coupling of thirteen macro- and micronutrients and phytotoxic elements in topsoils (3–8 cm) from a range of terrestrial ecosystems across all continents (∼10,000 observations) and in response to global change manipulations (∼5,000 observations). For this, we incubated between 1 and 4 pairs of anionic and cationic exchange membranes per site for a mean period of 53 days. The most bioavailable elements (Ca, Mg, and K) were also amongst the most abundant in the crust. Patterns of bioavailability were biome-dependent and controlled by soil properties such as pH, organic matter content and texture, plant cover, and climate. However, global change simulations resulted in important alterations in the bioavailability of elements. Elements were highly coupled, and coupling was predictable by the atomic properties of elements, particularly mass, mass to charge ratio, and second ionization energy. Deviations from the predictable coupling-atomic mass relationship were attributed to global change and agriculture. Our work illustrates the tight links between the bioavailability and coupling of topsoil elements and environmental context, human activities, and atomic properties of elements, thus deeply enhancing our integrated understanding of the biogeochemical connections that underlie the productivity and functioning of terrestrial ecosystems in a changing world

Data from: Decreased root heterogeneity and increased root length following grassland invasion

1. Plant invasions can be promoted by environmental heterogeneity, but the opposite effect, the impact of plant invasion on heterogeneity, has received little attention. Grassland invasions might contribute to decreased spatial heterogeneity because invaders tend to be larger than native vegetation. Lowered heterogeneity may contribute to the low diversity of invaded communities, as well as to the persistence of invasive populations. 2. We compared the spatial heterogeneity of roots and resources in uninvaded native grassland and in stands invaded by a relatively large exotic grass (Agropyron cristatum), in four combinations of mowing and nitrogen (N) addition. We focused on roots because they account for the majority of primary production in grasslands. 3. The spatial heterogeneity of root length (m root / m2 rhizotron image) and root production was significantly lower beneath A. cristatum than uninvaded grassland. This result was consistent in all combinations of mowing and N addition. 4. Beneath the invader, root length was significantly greater, and the proportion of samples that contained roots was significantly higher. This suggests that the invader decreased spatial heterogeneity by more completely filling the soil volume with roots. 5. Resource heterogeneity varied significantly between vegetation types in just one out of four cases examined, suggesting that invader effects on resource heterogeneity were small relative to its effects on root heterogeneity. 6. These results suggest a novel mechanism promoting invader success and persistence: high root heterogeneity, lower root length, and empty soil volumes in native grassland may make it relatively vulnerable to invasion, while reduced heterogeneity and greater root length in invaded grasslands may sustain stable, low-diversity communities dominated by the invader. Lowered heterogeneity accompanying invasion may partly account for the wide-spread occurrence of low diversity, invader dominated grasslands in North America

Different Root and Shoot Responses to Mowing and Fertility in Native and Invaded Grassland

Grassland root responses to mowing and fertility are less well known than shoot responses, even though as much as 90% of productivity in semiarid grasslands occurs belowground. Thus, understanding root responses may aid the management of invasive grassland species such as Agropyron cristatum (L.) Gaerth (crested wheatgrass). We asked whether root responses reflect shoot responses to mowing and fertility in native grassland with and without a major component of crested wheatgrass. We subjected grasslands in northern Montana to 5 yr of mowing at two nitrogen (N) levels and followed root responses with minirhizotrons. Surprisingly, the roots of both native and invaded grasslands were unaffected by mowing and N addition, despite significant changes in shoot mass across both vegetation types. Root length was significantly greater beneath areas heavily occupied by crested wheatgrass (363 m · m-2 image ± 200, mean ± standard deviation [SD]) than areas comprising largely native grassland (168 m · m-2 image ± 128 SD). Also, no interactions occurred between year and any other factor, indicating that there were no changes in belowground responses over the 5 yr examined. In contrast, shoot mass was significantly reduced by mowing (not mowed, 612 g · m-2 ± 235 SD; mowed, 239 g · m-2 ± 81 SD) and was significantly increased by N addition (no added N, 380 g · m-2 ± 215 SD; added N, 488 g · m-2 ± 287 SD). In conclusion, 5 yr of mowing decreased shoot mass, but not root mass. On the other hand, 5 yr of N addition increased shoot mass, but not root mass. Given that most production and competition in grasslands occurs belowground, this suggests that mowing may not be a successful tool for reducing crested wheatgrass root length, regardless of soil fertility. © 2014 The Society for Range Management.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Bioavailability of macro and micronutrients across global topsoils:Main drivers and global change impacts

Understanding the chemical composition of our planet's crust was one of the biggest questions of the 20th century. More than 100 years later, we are still far from understanding the global patterns in the bioavailability and spatial coupling of elements in topsoils worldwide, despite their importance for the productivity and functioning of terrestrial ecosystems. Here, we measured the bioavailability and coupling of thirteen macro‐ and micronutrients and phytotoxic elements in topsoils (3–8 cm) from a range of terrestrial ecosystems across all continents (∼10,000 observations) and in response to global change manipulations (∼5,000 observations). For this, we incubated between 1 and 4 pairs of anionic and cationic exchange membranes per site for a mean period of 53 days. The most bioavailable elements (Ca, Mg, and K) were also amongst the most abundant in the crust. Patterns of bioavailability were biome‐dependent and controlled by soil properties such as pH, organic matter content and texture, plant cover, and climate. However, global change simulations resulted in important alterations in the bioavailability of elements. Elements were highly coupled, and coupling was predictable by the atomic properties of elements, particularly mass, mass to charge ratio, and second ionization energy. Deviations from the predictable coupling‐atomic mass relationship were attributed to global change and agriculture. Our work illustrates the tight links between the bioavailability and coupling of topsoil elements and environmental context, human activities, and atomic properties of elements, thus deeply enhancing our integrated understanding of the biogeochemical connections that underlie the productivity and functioning of terrestrial ecosystems in a changing world