ß-diversity in temperate grasslands is driven by stronger environmental filtering of plant species with large genomes.

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS) has long been hypothesized to potentially affect species' capacity to tolerate environmental stress and might therefore help drive community assembly. However, its role in driving ß-diversity (i.e., spatial variability in species composition) remains unclear. We measured GS for 161 plant species and community composition across 52 sites spanning a 3200-km transect in the temperate grasslands of China. By correlating the turnover of species composition with environmental dissimilarity, we found that resource filtering (i.e., environmental dissimilarity that includes precipitation, and soil nitrogen and phosphorus concentrations) affected ß-diversity patterns of large-GS species more than small-GS species. By contrast, geographical distance explained more variation of ß-diversity for small-GS than for large-GS species. In a 10-year experiment manipulating levels of water, nitrogen, and phosphorus, adding resources increased plant biomass in species with large GS, suggesting that large-GS species are more sensitive to the changes in resource availability. These findings highlight the role of GS in driving community assembly and predicting species responses to global change.

[Effects of fertilization and water addition on soil acid neutralizing capacity in an old-field grassland]. / æ–½è‚¥å’Œå¢žæ°´å¯¹å¼ƒè€•è‰åœ°åœŸå£¤é ¸ä¸­å’Œå®¹é‡çš„å½±å“.

Increasing nitrogen (N) deposition results in soil acidification in grasslands. Acid buffering capacity of soil is a critical index evaluating soil acidification, the response of which to N input is regulated by precipitation and concentration of other limiting elements. To explore the responses of soil acidification to N, phosphorus (P), and water inputs, we conducted a 13-year field experiment in an old-field grassland and calculated the acid buffering capacity (ABC) and acid neutralizing capacity (ANC) at the reference of pH=5.0 (ANCpH5.0) and 4.0 (ANCpH4.0), using quadratic curve fitting model. The results showed that, without water addition, single N addition or combined with P addition significantly decreased soil pH, ANCpH5.0 and ANCpH4.0, whereas single P addition had no significant effect on soil pH, ANCpH5.0 or ANCpH4.0. With water addition, the addition of N or combined with P decreased soil pH, ANCpH5.0 and ANCpH4.0, whereas P addition decreased soil pH, increased ANCpH4.0, without effect on ANCpH5.0. In contrast with treatments without water addition, water addition had positive effects on soil pH, ANCpH5.0 and ANCpH4.0. For soils with different initial soil pH values, it was better to select ANC rather than ABC as an index to evaluate soil anti-acidification capacity.

[Effects of long-term fertilization and water addition on soil properties and plant community characteristics in a semiarid grassland.] / 长期施肥和增水对半干旱草地土壤性质和植物性状的影响.

We summarized the effects of fertilization and water addition on some soil properties and plant community characteristics in a long-term field experiment established in 2005 in a degraded grassland in Duolun, Inner Mongolia, China. The results showed that nitrogen (N) addition resulted in surface soil acidification and decreased acid buffering capacity, increased the availability of carbon (C), N, phosphorus (P), sulfur (S) and DTPA-extractable iron (Fe), manganese (Mn), and copper (Cu) contents, depleted the sum of base cations calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na), decreased the diversity of soil microbial community. Nitrogen addition enhanced the uptake of N, P, S, K, Mn, Cu and Zn by plants, while inhibited plant Fe uptake, but with no effect on the uptake of Ca or Mg. Nitrogen addition increased aboveground net primary productivity (ANPP) but declined plant species diversity and community stability. Phosphorus addition alone increased total P and Olsen-P contents and fungal abundance in the surface soil, and improved N, P and S uptake by leaves, but had no significant influence on other soil basic chemical properties, ANPP, and plant species diversity. Water addition could improve the resistance of plant community, but its contribution to ANPP was limited by soil N availa-bility. Water addition could buffer soil acidification and the decline of microbial and plant diversity induced by N addition. Under the treatments of N and water addition or P and water addition, the diversity and function of soil microorganisms were affected by plant community structure and function. Long-term controlled field experiments were useful for understanding ecosystem structure and functions of grasslands. However, to uncover the underlying mechanisms in grassland ecosystem ecology, single-site experiments should be incorporated with multiple-site controlled field experiments in different regions. More attentions should be paid to the linkage of above- and below-ground ecological processes.

[Effects of nitrogen and water addition on soil bacterial diversity and community structure in temperate grasslands in northern China].

In this study, we measured the responses of soil bacterial diversity and community structure to nitrogen (N) and water addition in the typical temperate grassland in northern China. Results showed that N addition significantly reduced microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) under regular precipitation treatment. Similar declined trends of MBC and MBN caused by N addition were also found under increased precipitation condition. Nevertheless, water addition alleviated the inhibition by N addition. N addition exerted no significant effects. on bacterial α-diversity indices, including richness, Shannon diversity and evenness index under regular precipitation condition. Precipitation increment tended to increase bacterial α-diversity, and the diversity indices of each N gradient under regular precipitation were much lower than that of the corresponding N addition rate under increased precipitation. Correlation analysis showed that soil moisture, nitrate (NO3(-)-N) and ammonium (NH4+-N) were significantly negatively correlated with bacterial evenness index, and MBC and MBN had a significant positive correlation with bacterial richness and evenness. Non-metric multidimensional scaling (NMDS) ordination illustrated that the bacterial communities were significantly separated by N addition rates, under both water ambient and water addition treatments. Redundancy analysis (RDA) revealed that soil MBC, MBN, pH and NH4+-N were the key environmental factors for shaping bacterial communities.

Abundance and community structure of ammonia-oxidizing Archaea and Bacteria in response to fertilization and mowing in a temperate steppe in Inner Mongolia.

Based on a 6-year field trial in a temperate steppe in Inner Mongolia, we investigated the effects of nitrogen (N) and phosphorus (P) fertilization and mowing on the abundance and community compositions of ammonia-oxidizing Bacteria (AOB) and Archaea (AOA) upon early (May) and peak (August) plant growth using quantitative PCR (qPCR), terminal-restriction fragment length polymorphism (T-RFLP), cloning and sequencing. The results showed that N fertilization changed AOB community composition and increased AOB abundance in both May and August, but significantly decreased AOA abundance in May. By contrast, P fertilization significantly influenced AOB abundance only in August. Mowing significantly decreased AOA abundance and had little effect on AOA community compositions in May, while significantly influencing AOB abundance in both May and August, Moreover, AOA and AOB community structures showed obvious seasonal variations between May and August. Phylogenetic analysis showed that all AOA sequences fell into the Nitrososphaera cluster, and the AOB community was dominated by Nitrosospira Cluster 3. The results suggest that fertilization and mowing play important roles in affecting the abundance and community compositions of AOA and AOB.

[Variation in soil Mn fractions as affected by long-term manure amendment using atomic absorption spectrophotometer in a typical grassland of inner Mongolia].

The effect of sheep manure amendment on soil manganese fractions was conducted in a 11 year experiment at inner Mongolia grassland, using sequential extraction procedure in modified Community Bureau of Reference, and determined by atomic absorption spectrophotometer. Five treatments with dry sheep manure addition rate 0, 50, 250, 750, and 1500 g x m(-2) x yr(-1), respectively, were carried out in this experiment. Results showed that the recovery rate for total Mn was 91.4%-105.9%, as the percentage recovered from the summation of the improved BCR results with aqua regia extractable contents, and it was 97.2%-102.9% from certified soil reference materials. Plant available exchangeable Mn could be enhanced by 47.89%, but reducible and total Mn contents decreased significantly under heavy application of manure at depth of 0-5 cm. The effect of manure amendment on Mn fractions was greater in 0-5 cm than in 5-10 cm soil layer. The results are benefit to micronutrient fractions determination and nutrient management in grassland soils.