Effects of biological soil crusts on profile distribution of soil water,organic carbon and total nitrogen in Mu Us Sandland,China

Aims Biological soil crusts(BSCs)can affect soil properties including water dynamics and cycling of soil carbon and nitrogen in dryland ecosystems.Previous research has mostly focused on effects of BSCs on soil water distribution or carbon and nitrogen fixation in the surface soil layer.Thus,little is known about effects of BSCs on properties throughout the soil profile.In the current study,we assessed the effects of BSCs on the distribution of soil water content(SW),soil organic carbon content(SOC)and soil total nitrogen content(STN)throughout the soil profile as well as the influence of water conditions on the effects of BSCs.Methods In a field investigation in Mu Us Sandland,North China,soil samples were taken from plots with and without BSCs on 13 and 28 September 2006,respectively.On the two sampling dates,average soil gravimetric water content was 3.83%(61.29%)and 5.08%(60.89%),respectively,which were regarded as low and high water conditions.Soil samples were collected every 5 cm to a depth of 60 cm,and SW,SOC and STN were measured in the laboratory.Important Findings(i)BSCs affected profile distribution of SW,SOC and STN.In addition,water conditions within the plots significantly modified BSCs’effects on the profile distribution of SW,but marginally affected the effects on SOC and STN.(ii)Under high water conditions,SW in the surface soil layer(0–10 cm)was higher in soils with BSCs compared to those without BSCs,while the opposite was true in the deep soil layer(30–55 cm).(iii)Under low water conditions,SW was lower with BSCs compared with no BSCs in near-surface(5–20 cm)and deep(25–40 cm)soil layers.(iv)BSCs affected SOC and STN only in the surface soil layer(0–5 cm)and were modified by plot water conditions.

Variation in plant diversity and dominance across dune fixation stages in the Chinese steppe zone

Aims Our aim was to study how diversity and dominance of plant species and plant functional types(PFTs)change and covary across three dune fixation stages in the Chinese steppe zone.Methods In the Chinese steppe zone,we measured coverage,mean height and density of each plant species in three types of dunes(mobile,semi-fixed and fixed dunes)in four sites(Mu Us,Otindag,Hulunbeir and Horqin).Plant species were grouped into 24 PFTs according to their lifespan,photosynthetic pathway,reproductive mode and life form.Dominance of each plant species and PFT were determined,and species diversity and PFT diversity were quantified using Shannon–Wiener index.Important Findings PFT diversity was positively related to plant species diversity in each dune stage,but PFT diversity increased more with increasing plant species diversity in the mobile and semi-fixed dunes than in the fixed dunes.Dune fixation stage explained 87.2%of the variation in plant species diversity and 84.8%of the variation in PFT diversity.Dominant species and PFTs differed among the three dune fixation stages;the more fixed the dunes were,the more perennial,shrubby,clonal and C3 species co-dominated.Specifically,in mobile dunes annual C4 non-clonal herbs were the most dominant,and in semi-fixed and fixed dunes perennial C3 clonal shrubs were most dominant.