[Population spatial patterns of grassland plant communities in different slope aspects in the loess hilly area, China.] / é»„åœŸä¸˜é™µæ²Ÿå£‘åŒºä¸åŒå¡å‘æ’‚è’è‰åœ°æ¤ç‰©ç¾¤è½ç§ç¾¤ç©ºé—´æ ¼å±€.

We investigated the species composition and diversity of four grassland communities with different slope aspects in the loess hilly area of China. The power law was used to analyze spatial heterogeneity of the community and spatial pattern of the population. The results showed that Artemisia sacrorum was the dominant species and occurred in each site. Other species had different status and contributed differently to the spatial pattern of communities. Moreover, the spatial patterns of communities responded differently to various slope aspects, with the degree of aggregation ranked as sunny > half-sunny > half-shady > shady. The spatial heterogeneity index of community was positively correlated with the Simpson diversity index, but was negatively correlated with Margalef richness, Shannon diversity and Pielou evenness. The relative spatial heterogeneity index of the dominant species (A. sacrorum), sub-dominant species (Lespedeza dahurica and Stipa bungeana), and a few associated species (Artemisia scoparia, Melica scabrosa) were larger than that of the community, which resulted in cluster distribution. However, the relative spatial heterogeneity index of most associated species (Phragmites communis, Sonchus arvensis, and Bothriochloa flaccidum) showed the similar trends with the distribution of the community. In contrast, the relative spatial heterogeneity index of Cephalanoplos segetum, Gueldenstaedtia multiflora and Artemisia giraldii was lower than that of the community. These differences reduced the aggregation degree of the community. In summary, the aggregation degree of community was determined by dominant species, sub-dominant species and occasional species. Specifically, the dominant species, sub-dominant species and some associated species could promote the aggregation of the community, but occasional species would reduce the cluster distribution.

[Relationship Between the Vegetation Community and Soil Nutrient and Enzyme Activity During the Restoration of Abandoned Land in the Loess Hilly Region].

The trends of and relationships among the plant community, soil nutrients, and four soil enzymes were investigated after being abandoned for 10, 15, 20, 30, and 45 years to reveal the soil properties during the restoration in the Loess Hilly Region. The results indicate the following ranking of dominant plant community species:Artemisia scoparia→Lespedeza dahurica+Artemisia sacrorum→Artemisia giraldii+irons Artemisia annua→Bothriochloa flaccidum+Artemisia selengensis. The ranking reflects an increase along the chronosequence of abandoned land. Moreover, the ratio of the total species of Compositae, Poaceae, and Leguminosae decreases from 66.67% to 50% and then increases up to 75%. The SOC, TN, TP, AN, AP, and four enzyme activity types (ALP, CAT, UE, and SC) increase but respond differently to restoration, while the stoichiometric ratio fluctuates. In contrast to the number of plant families, genus, species, and plant diversity, Compositae, Poaceae, and Leguminosae have major effects on the soil nutrient and enzyme activity, which explains the total variation of 72.8%, 69.1%, and 66.0%, respectively. The effects of these three families on the soil enzymes are greater than that on soil nutrients. Poaceae and Leguminosae have a positive effect on the nutrient and enzyme activity, while the family Compositae has a negative effect. Overall, the changes of dominant species of grassland communities during restoration significantly affect the soil enzyme and thereby are responsible for the soil nutrient dynamics.