[Effects of biological crusts on soil organic carbon in sandlands under a precipitation gradient]. / 不同降水条件下生物结皮覆盖对沙地土壤有机碳的影响.

Biological crusts (Biocrusts) are important surface active coverings in arid and semi-arid regions, which affect the content of soil organic carbon (SOC), SOC labile fractions and stability of SOC through photosynthetic carbon fixation. At present, studies on the variation characteristics of SOC, SOC labile fractions and the stability of SOC in biocrusts are rather limited. In this study, two types of typical biocrusts (moss crusts and algae crusts) were selected along a precipitation gradient from northwest to southeast in the Mu Us Sandland (straight line distance 188 km) by measuring soil organic carbon (SOC), soil microbial biomass carbon (MBC), water soluble carbon (DOC), particulate carbon (POC), easily oxidizable carbon (ROC). We aimed to explore the effects of biocrusts on the stability of SOC and carbon decomposition across the precipitation gradient. Results showed that:1) Two types of biocrusts significantly increased the contents of SOC, MBC, DOC, POC, ROC and stability of SOC. Moss crusts increased SOC contents by 1.6 to 2.6 times as that of algae crusts. 2) The lowest SOC contents of the two types of biocrusts were 6.43 g·kg-1 and 14.50 g·kg-1 respectively, which showed an increasing trend with increasing precipitation along the gradient. 3) With the increases of precipitation, the decomposition time of moss litters gradually decreased. The decomposition coefficient of moss litters during the study period (From July to Feb-ruary of the next year) ranged from 0.010 to 0.014, which was significantly lower than that of vascular plants. The carbon release of moss litters from northwest to southeast was 8.09, 10.89, 12.88 g·kg-1, respectively. 4) Results of canonical correspondence analysis showed that water vapor partial pressure, actual evapotranspiration, annual average temperature, subsurface short-wave radiation, potential evapotranspiration and vapor pressure difference were the key climate factors affecting the content of SOC and its active components. Silt content was the main soil factor affecting the content of SOC and its active components.

New field wind manipulation methodology reveals adaptive responses of steppe plants to increased and reduced wind speed.

BACKGROUND: Wind strongly impacts plant growth, leaf traits, biomass allocation, and stem mechanical properties. However, whether there are common whole-plant wind responses among different plant species is still unclear. We tested this null hypothesis by exposing four eudicot steppe species to three different wind treatments in a field experiment: reduced wind velocity using windbreaks, ambient wind velocity, and enhanced wind velocity through a novel methodology using wind-funneling baffles. RESULTS: Across the four species, wind generally decreased plant height, projected crown area, and stepwise bifurcation ratio, and increased root length and stem base diameter. In contrast, the response patterns of shoot traits, especially mechanical properties, to wind velocity were idiosyncratic among species. There was no significant difference in total biomass among different treatments; this might be because the negative effects on heat dissipation and photosynthesis of low wind speed during hot periods, could counteract positive effects during favorable cooler periods. CONCLUSIONS: There are common wind response patterns in plant-size-related traits across different steppe species, while the response patterns in shoot traits vary among species. This indicates the species-specific ways by which plants balance growth and mechanical support facing wind stress. Our new field wind manipulation methodology was effective in altering wind speed with the intended magnitude. Especially, our field wind-funneling baffle system showed a great potential for use in future field wind velocity enhancement. Further experiments are needed to reveal how negative and positive effects play out on whole-plant performance in response to different wind regimes, which is important as ongoing global climatic changes involve big changes in wind regimes.