[Elevational Pattern and Control Factors of Soil Microbial Carbon Use Efficiency in the Daiyun Mountain].

Microbial carbon use efficiency (CUE) refers to the C transformation to microbial biomass from C uptake. The study of soil microbial CUE is very important for understanding the soil C cycle. Here, CUE, Cgrowth, and Crespiration were measured using the 18O-H2O-DNA labeling method at six elevational sites (980-1765 m) in Daiyun Mountain, a subtropical montane forest, to understand the variation characteristics and influencing mechanisms. The results showed that:CUE varied from 0.1 to 0.4 and increased linearly with elevation; CUE was positively correlated with Cgrowth, Crespiration, and qgrowth but negatively correlated with qCO2, indicating that CUE increased with elevation by increasing microbial growth and inhibiting respiration; and temperature was the first controlling factor for the elevation variation in microbial CUE in the subtropical forest ecosystem.

Habitat-specific environmental factors regulate spatial variability of soil bacterial communities in biocrusts across northern China's drylands.

Biocrusts are common biotic components in dryland ecosystems worldwide, they contain diverse soil organisms and effectively enhance soil stability and perform a series of key ecological functions. However, the geographical pattern of microbial communities in biocrusts is rarely assessed, despite it is closely related to the spatial variation of ecosystem functions in drylands. We assessed soil bacterial communities in biocrusts across four ecosystems (Gobi, desert, desert steppe and grassland) in a precipitation gradient (16-566 mm yr-1) in northern China. Bacterial OTU number and phylogenetic diversity did not linearly increase with decreasing aridity, they were significantly lower in Gobi and similar among desert, desert steppe and grassland. Soil bacterial community composition in Gobi and desert were different than those in desert steppe and grassland, and they were similar between Gobi and desert, this suggests the key role of habitat in structuring soil bacterial communities. The geographic pattern of soil bacterial communities was strongly influenced by both geographic distance and environmental factors. The first explanatory factor for the geographic variation of bacterial community dissimilarity differed among four ecosystems, being aridity in Gobi and desert, precipitation in desert steppe, and soil inorganic nitrogen in grassland. The geographic pattern of the bacterial functional group profile showed a similar pattern with community composition across four ecosystems, and the groups of containing mobile elements and gram negative bacteria were more abundant in drier habitats of Gobi and desert. Our results reveal the non-linear changes in diversity, composition and functional group of soil bacterial communities in biocrusts across the precipitation gradient from hyper-arid to semi-humid regions, and suggest that the geographic distance and habitat-specific environmental factors determine the distribution of soil bacterial communities in different ecosystems.

[Effects of exogenous nitrogen addition on litter decomposition and nutrient release in a temperate desert]. / å¤–æºæ°®æ·»åŠ å¯¹æ¸©å¸¦è’æ¼ åœ°è¡¨å‡‹è½ç‰©åˆ†è§£åŠå »åˆ†é‡Šæ”¾çš„å½±å“.

A litterbag decomposition experiment was carried out in southern Gurbantunggut Desert, with four nitrogen treatments: N0(0 g N·m-2·a-1), N5(5 g N·m-2·a-1), N10(10 g N·m-2·a-1) and N20(20 g N·m-2·a-1). The aims were to examine the effects of exogenous nitrogen addition on decomposition rate and nutrient release of Tamarix ramosissima, Salicornia europaea and their mixture. Results showed that decomposition rates were significantly different among litter types. After 345 days, the decomposition rates of T. ramosissima, S. europaea and their mixture under different treatments were 0.64-0.70, 0.84-0.99 and 0.71-0.81 kg·kg-1·a-1, respectively. Both mono- and mixed-litters exhibited nutrient release during decomposition process, with the release rates being 60.6%-67.4%, 56.7%-62.6%, 57.4%-62.3%, 46.8%-63.0% for N, and 51.9%-77.9%, 59.9%-74.7%, 53.0%-79.9%, 52.3%-76.4% for P, respectively for the N0, N5, N10 and N20 treatments. Nitrogen addition did not affect litter decomposition rate. The dynamics of N and P during decomposition of different litter types showed different responses to nitrogen addition. Nitrogen addition inhibited N and P releases of S. europaea litter and P release of the mixed litter, but did not affect the nutrient release of T. ramosissima. The results suggested that nitrogen input would not promote litter decomposition in temperate desert ecosystems, but might retard the nutrient returning to soil system.

[Influence of different concentration Ni and Cu on the photosynthesis and chlorophyll fluorescence characteristics of Peganum harmala].

A pot experiment was conducted to study the influence of different concentration (0, 50, 100, 200, and 400 mg kg(-1)) Ni and Cu on the growth, photosynthesis, and chlorophyll fluorescence characteristics of Peganum harmala seedlings. With increasing concentration Ni in the medium, the seedlings growth parameters, photosynthetic pigment content, net photosynthetic rate (P(n)), stomatal conductance (G(s)), transpiration rate (T(r)), maximal photochemical efficiency of PS II (F(v)/F(m)), quantum efficiency of electric transport of PS II (phi (PS II)), and coefficient of photochemical quenching (q(P)) of P. harmala decreased significantly, while the intercellular CO2 concentration (C(i)) and the coefficient of non-photochemical quenching (q(N)) were in adverse. The decrease of P(n) under Ni stress was mainly caused by non-stomatal limitation. At 50 mg kg(-1) Cu, the growth parameters, photosynthetic pigment content, P(n), G(s), T(r), C(i), F(v)/F(m), phi(PS II), and q(P) reached their peak values; at 100 mg kg(-1) Cu, the growth parameters, chlorophyll a and b contents, P(n), G(s), T(r), C(i), and F(v)/F(m) were still slightly higher than the control; while with the further increasing Cu concentration in the medium, all the test indices except q(N) tended to decrease. The decrease of P(n) under Cu stress was mainly caused by stomatal limitation.

[Effects of elevated temperature and CO2 on desert algal crust photosynthesis].

Taking the 26- and 51-year-old artificial vegetation areas and the natural vegetation area in Shapotou region of southeast Tengger Desert as study sites, this paper measured the net photosynthetic rate (Pn) of algal crusts, and analyzed its relationships with crust water content (> 100%, 40%-60%, and <20%), atmospheric CO2 concentration (360 and 700 mg x L(-1)), and air temperature (13 degrees C, 24 degrees C, and 28 degrees C). The Pn of the crusts in the 26- and 51-year-old artificial vegetation areas and natural vegetation area was 3.4, 4.4, and 3.2 micromol x m(-2) x s(-1), respectively, and the Pn in 51-year-old artificial vegetation area was significantly higher than that in the other two areas. Crust water content had significant effects on the Pn, which was significantly higher at medium water content (40%-60%) than at low (<20%) and high (>100%) water content. When the CO2 concentration doubled (700 mg x L(-1)), the Pn increased by 1.8-3.3 times at medium and high crust water content but had less change at low crust water content, compared with that under ambient CO2 concentration (360 mg x L(-1)). At medium and high crust water content, the Pn at 24 degrees C and 28 degrees C was 27%-66% higher than that at 13 degrees C (P < 0.05), but at low crust water content, no significant difference was observed at the three temperatures.

[Soil moisture dynamics of artificial Caragana microphylla shrubs at different topographical sites in Horqin sandy land].

Based on the investigation data of vegetation and soil moisture regime of Caragana microphylla shrubs widely distributed in Horqin sandy land, the spatiotemporal variations of soil moisture regime and soil water storage of artificial sand-fixing C. microphylla shrubs at different topographical sites in the sandy land were studied, and the evapotranspiration was measured by water balance method. The results showed that the soil moisture content of the shrubs was the highest in the lowland of dunes, followed by in the middle, and in the crest of the dunes, and increased with increasing depth. No water stress occurred during the growth season of the shrubs. Soil moisture content of the shrubs was highly related to precipitation event, and the relationship of soil moisture content with precipitation was higher in deep soil layer (50-180 cm) than in shallow soil layer (0-50 cm). The variation coefficient of soil moisture content was also higher in deep layer than in shallow layer. Soil water storage was increasing in the whole growth season of the shrubs, which meant that the accumulation of soil water occurred in this area. The evapotranspiriation of the shrubs occupied above 64% of the precipitation.

[Effects of moss crust on soil seed bank at southeast edge of Tengger Desert].

An investigation was made on the soil seed bank at southeast edge of Tengger Desert with moss crust under natural and artificial vegetations. The results showed that the density of soil seed bank increased with the development of moss crust, which was 3.4 times higher under natural vegetation than under 24 years old artificial vegetation. In the seed bank, a total of 12 species belonging to 6 families were identified, among which, annuals occupied more than 70%. No perennial seeds were found under artificial vegetation, but under natural vegetation, 20% of the seeds were of perennials. As for semi-shrub seeds, they occupied 20% and 10% under artificial and natural, vegetation, respectively. Under artificial vegetation, the species richness index of soil seed bank was relatively lower, being about a half of that under natural vegetation. The species diversity index of the seed bank had a slight decrease with the development of moss crust under artificial vegetation, but increased to the maximum (0. 693) under natural vegetation. The species similarity index was 1 among the seed banks under artificial vegetations, and 0.4 between those under artificial and natural vegetation. The development of moss crust increased the roughness of surface soil and improved soil environment significantly, which could have positive effects on seed entrapment and plant establishment.