Seeds germination time courses of <i>E</i>. <i>poaeoides</i> (a), <i>A</i>. <i>capillaris</i> (b) and <i>S</i>. <i>glareosa</i> (c) in different cyanobacterial crust treatments.

<p>E.p. indicate <i>E</i>. <i>poaeoides</i> monoculture, E.P. + S.g. indicate <i>E</i>. <i>poaeoides</i> mixed cultivation with <i>S</i>. <i>glareosa</i>; A.c. indicate <i>A</i>. <i>capillaris</i> monoculture, A.c. + S.g.—indicate <i>A</i>. <i>capillaris</i> mixed cultivation with <i>S</i>. <i>glareosa</i>; S.g. + E.P. indicate <i>S</i>. <i>glareosa</i> mixed cultivation with <i>E</i>. <i>poaeoides</i>, S.g. + A.c. indicate <i>S</i>. <i>glareosa</i> mixed cultivation with <i>capillaries</i> and S.g. indicate <i>S</i>. <i>glareosa</i> monoculture.</p

The time to 50% cumulative germination (T50) of exotic and native plants in different treatments.

<p>The time to 50% cumulative germination (T50) of exotic and native plants in different treatments.</p

Results of a two-way ANOVA of cumulative percent germination and shoot biomass of <i>S</i>. <i>glareosa</i> in different experiment treatments.

<p>Results of a two-way ANOVA of cumulative percent germination and shoot biomass of <i>S</i>. <i>glareosa</i> in different experiment treatments.</p

Seed cumulative percent germination <i>E</i>. <i>poaeoides</i> (a), <i>A</i>. <i>capillaris</i> (b) and <i>S</i>. <i>glareosa</i> (c) in different cyanobacterial crust treatments.

<p>Values with different lower case letters show significant differences of cumulative percent germination among different experimental treatments at 0.05 levels.</p

Individual biomass of <i>E</i>. <i>poaeoides</i> (a), <i>A</i>. <i>capillaris</i> (b) and <i>S</i>. <i>glareosa</i> (c) comparison between monoculture and mixed cultivation.

<p>Values with different lower letters show significant differences of individual biomass among different experimental treatments at 0.05 levels. Individual biomass denoted average value of all plant biomass in a pot.</p

Diel hysteresis between soil respiration and soil temperature in a biological soil crust covered desert ecosystem

<div><p>Soil respiration induced by biological soil crusts (BSCs) is an important process in the carbon (C) cycle in arid and semi-arid ecosystems, where vascular plants are restricted by the harsh environment, particularly the limited soil moisture. However, the interaction between temperature and soil respiration remains uncertain because of the number of factors that control soil respiration, including temperature and soil moisture, especially in BSC-dominated areas. In this study, the soil respiration in moss-dominated crusts and lichen-dominated crusts was continuously measured using an automated soil respiration system over a one-year period from November 2015 to October 2016 in the Shapotou region of the Tengger Desert, northern China. The results indicated that over daily cycles, the half-hourly soil respiration rates in both types of BSC-covered areas were commonly related to the soil temperature. The observed diel hysteresis between the half-hourly soil respiration rates and soil temperature in the BSC-covered areas was limited by nonlinearity loops with semielliptical shapes, and soil temperature often peaked later than the half-hourly soil respiration rates in the BSC-covered areas. The average lag times between the half-hourly soil respiration rates and soil temperature for both types of BSC-covered areas were two hours over the diel cycles, and they were negatively and linearly related to the volumetric soil water content. Our results highlight the diel hysteresis phenomenon that occurs between soil respiration rates and soil temperatures in BSC-covered areas and the negative response of this phenomenon to soil moisture, which may influence total C budget evaluations. Therefore, the interactive effects of soil temperature and moisture on soil respiration in BSC-covered areas should be considered in global carbon cycle models of desert ecosystems.</p></div

Mean monthly diel cycles of soil respiration (solid points) and soil temperature at a depth of 5 cm (open points) in the lichen-dominated crusts.

<p>Each point is the monthly mean for a particular time of day.</p

Analysis of the mean monthly diel cycles of soil respiration and soil temperature at a depth of 5 cm in the BSC-covered areas, including the correlation coefficients before synchronization and lag times in the diel cycles.

<p>The Pearson correlation coefficients and <i>p</i> values are given.</p

Diel hysteresis between soil respiration and soil temperature in a biological soil crust covered desert ecosystem - Fig 1

<p><b>Daily mean soil temperature at a depth of 5 cm (A), volumetric soil water content at a depth of 5 cm (B), and soil respiration (C) in the BSC-covered areas during the experimental periods from November 2015 to October 2016 in the Shapotou region of the Tengger Desert, northern China.</b> Error bars of the soil temperature are omitted for clarity (n = 48).</p

Physical and chemical characteristics of the BSC-dominated soils at a depth of 0–5 cm.

<p>Physical and chemical characteristics of the BSC-dominated soils at a depth of 0–5 cm.</p