Brushing effects on the growth and mechanical properties ofCorispermum mongolicumvary with water regime

Abstract

High water availability and mechanical stress can induce opposite responses in plants. In arid areas of Northern China the occurrence of high wind and high water availability tend to be negatively correlated. Since turgor pressure is a determinant of the mechanical stability of annuals, it is hypothesised that the effects of mechanical perturbation (MP) on annuals may depend on soil water availability. To test this proposal, we conducted an experiment in which a pioneering annual Corispermum mongolicum was subjected to two levels of MP and water supply, and then determined its growth and mechanical traits. Brushing had no effect on plant height and total biomass, but stimulated leaf and branch production. Water supply affected plant height, basal diameter, total biomass and stem rigidity, but not leaf and branch number, root/shoot ratio or flexibility. With high water availability, brushing stimulated the production of stiffer stems (thicker and with a higher Young's modulus) and more roots relative to shoot mass, but with low water availability MP induced the opposite response. This shows that both the degree and direction of plant responses to MP depend on the presence of other factors. We discuss how the interactive effects of MP and water availability on growth and mechanical properties may help C. mongolicum to establish in windy and arid environments.

Mechanical shaking and soil water affect the growth of Psammochloa villosa in the Mu Us Sandland

“…The results support the hypothesis that increased water availability can ameliorate the negative effects of MP on perennial grasses. These results are similar to those in the annual herb C. mongolicum (Wang et al, 2009), but different from those in the perennial semi-shrub H. laeve (Wang et al, 2008). Lignification or turgor pressure may play roles in explaining the different responses of different species (Wang et al, 2008(Wang et al, , 2009).…”

“…These results are similar to those in the annual herb C. mongolicum (Wang et al, 2009), but different from those in the perennial semi-shrub H. laeve (Wang et al, 2008). Lignification or turgor pressure may play roles in explaining the different responses of different species (Wang et al, 2008(Wang et al, , 2009). We note that in the future work, the degree of lignification and changes in turgor pressure should be measured, which will help improve our understanding of their roles in the complex responses.…”

“…MP significantly decreased the total biomass of P. villosa, which is consistent with some similar studies on the growth effects of wind or mechanical stress (Anten et al, 2010;Niklas, 1998;Retuerto and Woodward, 1993;Wang et al, 2008), but is inconsistent with other studies (Anten et al, 2005;Wang et al, 2009). This negative effect of MP may be linked to the reduced leaf expansion (Retuerto and Woodward, 1993), combination of the retarded expansion of new leaves and the temporary reduction in stomata aperture (Mitchell, 1996), and/or reduced photosynthesis (Anten et al, 2005;Ennos, 1997).…”

“…In our recent studies, the MP effects on the semi-shrub Hedysarum laeve did not show dependence on soil water availability (Wang et al, 2008) but the MP effects on the annual herb Corispermum mongolicum showed strong dependence on soil water availability (Wang et al, 2009). For woody and semi-shrub plants, the degree of lignification is the critical trait for their mechanical properties; in contrast, for herbaceous plants, turgor pressure can contribute significantly to them, especially in soft, non-or low-lignified tissues and organs due to primary growth (Niklas, 1989(Niklas, , 1991.…”

“…In many semiarid ecosystems like the Mu Us Sandland, wind speeds tend to be high and the vegetation is sparse, thereby allowing plants tend to be exposed to high levels of MP (Wang et al, 2008(Wang et al, , 2009). On the other hand, in these areas soil water availability is usually low, especially in the spring (Zhang, 1994).…”