Seed water status and root tip characteristics of two annual grasses on lichen-dominated biological soil crusts

Abstract

Biological soil crusts can affect seed germination and seedling establishment. We have investigated the effect of biological soil crusts on seed water status as a potential mechanism affecting seed germination. The seed water potential of two annual grasses, one exotic Bromus tectorum L. and another native Vulpia microstachys Nutt., were analyzed after placing the seeds on bare soil, on a crust that contains various lichens and mosses (mixed crust), or on a crust dominated by the crustose lichen Diploschistes muscorum (Scop.) R. Sant. (Diploschistes crust). Seed water potential and germination were similar on the bare soil and the mixed crust, except for the initial germination of V. microstachys, which was higher on the mixed crust than on the bare soil. For the two grasses studied, seed water potential was significantly higher on the bare soil and mixed crust than on the Diploschistes crust. These differences in water potential correlated with differences in germination, which was much lower on the lichen crust. Experiments were conducted under two watering regimens. Increasing the frequency of watering amplified the differences in seed water potential and germination between the Diploschistes crust and the other two surfaces. For a particular watering regimen, the bare soil, mixed crust, and Diploschistes crust received the same amount of water, but they reached significantly different water potentials. Throughout the experiments, the water potential of the soil and mixed crust remained above −0.6 MPa, while there was a marked decline in the water potential of the Diploschistes surface to about −4 MPa. To ascertain that water was the major factor limiting germination on the Diploschistes crust, we conducted germination tests in an environment with 100% relative humidity. Under these conditions, germination on the Diploschistes crust was similar to that on the bare soil. However, the seeds that germinated on the Diploschistes crust did not penetrate this surface and approximately 60% of their root tips became necrotic. Our results indicate that the presence of D. muscorum can inhibit seedling establishment by two mechanisms: a reduction in seed water absorption and an increase in root tip mortality.

Growth responses of five desert plants as influenced by biological soil crusts from a temperate desert, China

“…Most studies from many different climate zones show biocrusts either a positive or neutral effect (Li et al 2005;Deines et al 2007;Serpe et al 2008). For instance, in a cool desert, Harper and Pendleton (1993) found plants growing in biocrusts had four times greater biomass than those in uncrusted soils.…”

Effect of biological soil crusts on the germination of three plant species under laboratory conditions

“…Escudero et al (2007) and Serpe et al (2008) showed that BSC reduced seedling emergence when it was dominated by species like Diploschistes sp., because this lichen might seal the soil, thus reducing water availability during the germination period of some plants (Otsus and Zoel, 2004;Morgan, 2006). Contrastingly, the presence of both algal and moss crusts significantly enhanced the germination of Bassia dasyphylla (Fisch.…”

“…reduced plant emergence (Escudero et al, 2007;Serpe et al, 2008). This might be due to the sealing of the soil pores by these crusts that might reduce water availability and thus inhibit germination (Eldridge et al, 2010).…”

Fifty years of ‘Waging war on cheatgrass’: research advances, while meaningful control languishes

“…In addition to detrimentally affecting nitrogen budgets, the destruction removes what I term here the ' fi rst line of defence ' against cheatgrass proliferation (Kaltenecker et al 1999 ). Members of the crust, principally the crustose lichen Diploschistes muscorum and the moss Bryum argenteum , delay or largely thwart the establishment of cheatgrass (Deines et al 2007 ;Serpe et al 2006Serpe et al , 2008. For D. muscorum , key in its role is the physical barrier this cryptogam ' s thalli create to root penetration by seedlings.…”

“…It reserves its greatest kudos, however, for those who heed the warnings and take concrete steps to turn back disasters, such as the invasion of cheatgrass. mesic water status ( − 0.6 MPa) on bare soil (Serpe et al 2008 ). Admittedly, the biological soil crust in any community is not composed entirely of crustose lichens or B. argenteum , or both.…”