[Various effects on the Abundance and Composition of Arbuscular Mycorrhizal Fungal Communities in Soils in Karst Shrub Ecosystems].

Slope position is a key factor used in the restoration of vegetation in degraded karst ecosystems, and arbuscular mycorrhizal fungi (AMF) play an important role in improving this plant growth. However, little information is available regarding the effects of slope position on arbuscular mycorrhizal fungi. To test whether these fungal communities are impacted by slope position, the abundance, and composition of soil, AMF communities along the slope position were analyzed through terminal restriction fragment length polymorphism (T-RFLP) and real-time fluorescence-based quantitative polymerase chain reaction (real-time PCR). The diversity, richness, and evenness of plant species were evaluated through field surveys and soil properties were also measured. The results show that content of carbon, nitrogen, and phosphorus in the soil are different along the slope, and the trends identified were that the upper slope position ≈ middle slope position > lower slope position. The trend for AMF abundance was identified as upper slope position ≈ middle slope position < lower slope position. The available phosphorus content in the soil correlated significantly with the AMF abundance. A redundancy analysis showed that the structure of soil, AMF, and plant community compositions differed along the slope. The plant evenness index was shown to significantly contribute to the distribution of the AMF community structure, while the total nitrogen and total organic carbon content of the soil had a significant effect on the plant community structure. These results indicate that the interaction effects of soil nutrients and plant community structures on the soil AMF community structures suggest micro-morphology should be taken into account when AMF is used to restore vegetation in karst regions.

[Effects of Lithology on the Abundance and Composition of Soil Nitrogen-fixing Bacteria and Arbuscular Mycorrhizal Fungal Communities in Karst Shrub Ecosystem].

Lithology is a key factor when used to restore vegetation in karst degraded ecosystems, and arbuscular mycorrhizal (AM) fungi and nitrogen-fixing bacteria play an important role in improving plant growth. However, little information is available regarding the effects of lithology on these two groups of microorganisms. To test whether these microbial communities are impacted by lithology, the abundance and composition of soil AM fungal and nitrogen-fixing bacteria communities were determined through terminal restriction fragment length polymorphism (T-RFLP) and real-time fluorescence-based quantitative PCR (real-time PCR). Three types of lithology (dolomite, limestone and dolomite-limestone) were selected in this study. The diversity, richness, and evenness of plant species were evaluated through field surveys and soil properties were measured. The results showed that the abundances of soil nitrogen-fixing bacteria and arbuscular mycorrhizal fungal communities were significantly influenced by lithology. The abundances of these two groups of microorganisms were the lowest in dolomite soil, inferior to dolomite-limestone soil, while highest in limestone soil. Similarly, the composition of soil nitrogen-fixing bacteria and AM fungi communities varied among lithology. A significant linear correlation was observed among soil organic carbon, available phosphorus, clay content and nitrogen-fixing bacterial abundance (P<0.05), and a significant linear correlation among total nitrogen, clay content and AM fungal abundance (P<0.05). Redundancy analysis showed that the composition of nitrogen-fixing bacterial community was closely linked to plant evenness, and the AM fungal community composition was closely linked to plant diversity (plant evenness, Shannon-wiener and richness). These results indicated that lithology influenced the abundances and compositions of soil nitrogen-fixing bacteria and arbuscular mycorrhizal (AM) fungal communities mainly through plant and soil properties.

Salinity tolerance of three competing rangeland plant species: Studies in hydroponic culture.

Halogeton (Halogeton glomeratus) is an invasive species that displaces Gardner's saltbush (Atriplex gardneri) on saline rangelands, whereas, forage kochia (Bassia prostrata) potentially can rehabilitate these ecosystems. Salinity tolerance has been hypothesized as the predominant factor affecting frequency of these species. This study compared relative salinity tolerance of these species, and tall wheatgrass (Thinopyrum ponticum) and alfalfa (Medicago sativa). Plants were evaluated in hydroponics, eliminating the confounding effects of drought, for 28 days at 0, 150, 200, 300, 400, 600, and 800 mmol/L NaCl. Survival, growth, and ion accumulation were determined. Alfalfa and tall wheatgrass shoot mass were reduced to 32% of the control at 150 mmol/L. Forage kochia survived to 600 mmol/L, but mass was reduced at all salinity levels. Halogeton and Gardner's saltbush increased or maintained shoot mass up to 400 mmol/L. Furthermore, both actively accumulated sodium in shoots, indicating that Na+ was the principle ion in osmotic adjustment, whereas, forage kochia exhibited passive (linear) Na+ accumulation as salinity increased. This study confirmed the halophytic nature of these three species, but, moreover, discovered that Gardner's saltbush was as saline tolerant as halogeton, whereas, forage kochia was less tolerant. Therefore, factors other than salinity tolerance drive these species' differential persistence in saline-desert ecosystems.

[Plant and soil nutrient characteristics in the karst shrub ecosystem of southwest Hunan, China]. / æ¹˜è¥¿å—å–€æ–¯ç‰¹åœ°åŒºçŒä¸›ç”Ÿæ€ç³»ç»Ÿæ¤ç‰©å’ŒåœŸå£¤å »åˆ†ç‰¹å¾.

This research was conducted in light (LRD), moderate (MRD, abandoned land) and intense (IRD) rocky desertification shrub ecosystems in Shaoyang, Hunan Province. We collected plant samples and soil at 3 layers (0-15, 15-30, 30-45 cm), and analyzed the distribution patterns of soil and plant nutrients and the relationships among them. Our results showed that the contents of soil organic carbon (SOC) and total N in different soil layers were various and decreased with soil depth, while the contents of total P, K, Ca and Mg had no obvious variation among the different soil layers. The contents of total N, P, Ca and Mg in soil were significantly different among the 3 rocky desertification shrub ecosystems, and the SOC, total N and total P in MRD were relatively higher than in the others. The rank of macroelement contents in soils for LRD and IRD was SOC>total K>total Ca>total Mg>total N>total P, while it was SOC>total K>total Ca>total N>total Mg>total P for MRD. The rank of macroelement contents in plants from the 3 rocky desertification shrub ecosystems was Ca>N>K>Mg>P, and the contents of N and P in plants were significantly positively correlated with the corresponding contents of total N and total P in soils. Soil nutrients were closely related to vegetation growth. According to the soil nutrient status of desertification plots of different grades, we should integrate the forest reservation with artificial afforestation and targeted fertilization methods for managing karst rocky desertification.