[Response of understory species distribution of Robinia pseudoacacia plantation to environmental factors in loess hilly region, China.] / é»„åœŸä¸˜é™µåŒºåˆºæ§ç¾¤è½æž—ä¸‹ç‰©ç§åˆ†å¸ƒå¯¹çŽ¯å¢ƒå› å­çš„å“åº”.

We explored the distribution characteristics and influencing factors of understory species in Robinia pseudoacacia plantation in Wuqi, Ansai, Mizhi, Yichuan and other places, in combination with niche breadth, soil, altitude and other environmental factors. We analyzed the response mechanism of species distribution to environmental factor to provide a scientific basis for the mana-gement of R. pseudoacacia plantation in loess hilly region. The results showed that the broadly distributed understory species in R. pseudoacacia plantation were Setaria viridis, Heteropappus altaicus, Artemisia scoparia, Poa sphondylodes, Artemisia leucophylla, Ixeris sonchifolia, and Incarvillea sinensis. With the increasing rehabilitationage, the dominant understory species distribution followed the order: Artemisia capillaries → P. sphondylodes → A. scoparia → others (Rubia cordifolia, Rosa rubus and so on) → A. leucophylla → S. viridis. Results from principal component analysis showed that soil total phosphorus (25.6%), altitude (20.3%) and soil total nitrogen (19.3%) were the key factors influencing understory species distribution in R. pseudoacacia plantation. Soil organic carbon content, soil total nitrogen content, soil total phosphorus content, soil water content and the number of understory species distribution in R. pseudoacacia plantation were generally positively correlated with the degree of correlation varying across different species. There was no correlation between the slope aspect and the understory species distribution in R. pseudoacacia plantation. In conclusion, topography and soil factors played important roles in driving understory species distribution. The steeper the slope, the higher the altitude, the fewer understory species in R. pseudoacacia plantation. Understory species distribution was mainly affected by soil total phosphorus content and altitude. The understory species distribution reflected the differences of soil nutrient status, which had a certain guiding role in the management of R. pseudoacacia plantation.

[Stoichiometric characteristics of Artemisia sacrorum communities under different site conditions and their correlation with soil nutrients]. / ä¸åŒç«‹åœ°é“æ†è’¿åŒ–å­¦è®¡é‡ç‰¹å¾åŠå ¶ä¸ŽåœŸå£¤å »åˆ†çš„å ³ç³».

We explored the stoichiometric characteristic of Artemisia sacrorum communities and its correlation with soil characters by considering the aspect and slope position, and variation of soil nutrient in Yangqingchuan catchment of Wuqi. Our results showed that total carbon, total nitrogen, total phosphorus contents and C:N ratio in A. sacrorum (both shoot and root) in the top of hillock>sunny slope>semi-shady slope>shady slope. The C:P ratio in shoot and the N:P ratio in root decreased consistently. The N:P ratio in shoot and the C:P ratio in root decreased first and then increased. While the total nitrogen and total phosphorus in shoot, and the organic carbon in root increased first and then decreased with the decreases of slope position, the C:N ratio and N:P ratio in shoot decreased first and then increased. The stoichiometric characteristic of A. sacrorum communities was positively correlated with the soil stoichiometric characteristics. However, the C:N ratio, C:P ratio and N:P ratio of A. sacrorum and the total phosphorus of root were negatively correlated to corresponding soil indices. The correlation between shoot nutrition and soil was greater than that between soil and root nutrition. In conclusion, middle position of shady slope was optimal for the growth of A. sacrorum. The stoichiometric characteristics of plants were significantly correlated with soil nutrient condition. Aspect and slope position had a significant effect on the stoichiometric cha-racteristics of A. sacrorum community and soil. Proper A. sacrorum community could help restore soil nutrition.

[Response of volatiles of Artemisiae Argyi Folium to climatic factors].

Combined headspace solid-phase microextraction with gas chromatography-mass spectrometry (HS-SPME-GC-MS), this paper studied the volatiles of Artemisiae Argyi Folium that respectively collected from Kongdong, Huanglong, Ankang, Qichun and Tongbai，and then explored the influence of climatic factors on the main components of the volatiles. The results showed that 54, 52, 57, 47 and 55 compounds were respectively identified from the leaves from five regions, mainly consist of monoterpenes, sesquiterpenoids and their oxygen-containing derivatives, a few aldehydes, alkanes and benzenes. It is different that the volatiles of Artemisiae Argyi Folium that collected in different habitats, neither composition nor content. There are total 18 kinds of compounds that exist in all five leaves. Eucalyptol, camphor, terpinen-4-ol, eugenol and caryophyllene could be considered to be the main conponents because of their efficacy or toxicity and relatively high content. Grey correlation analysis shows that the annual lowest temperature and annual sunshine duration have a great influence on the content of eucalyptol and camphor; the effect of annual precipitation and annual accumulated temperature on the content of terpinen-4-ol and caryophyllene was relatively significant; while the annual sunshine duration and the annual highest temperature are the main influencing factors for eugenol. The research suggests that long-day and extreme temperature may be more conductive to the accumulation of volatiles. According to the laws of effect of climatic factors on volatiles, we can optimize the cultivation conditions and select suitable locality to improve the quality of Artemisiae Argyi Folium.

[Niche of main populations and environmental interpretation in grassland of Loess Plateau hilly region, China]. / é»„åœŸä¸˜é™µåŒºè‰åœ°ä¸»è¦ç§ç¾¤ç”Ÿæ€ä½åŠå ¶çŽ¯å¢ƒè§£é‡Š.

Focused on different rehabilitation ages grassland in Wuqi County in loess hilly region, the present study aimed to explore niche characteristics of populations and their influence factors. The results showed that the dominant species were Artemisia sacrorum, A. leucophylla, A. scoparia, Lespedeza daurica and Poa sphondylodes, and the dominant species varied along with the rehabilitation age. The niche breadth of dominant populations increased with increasing rehabilitation age from 5 to 10 years, indicating enhanced adaptability to the environment. The niche breadth indices of the populations decreased from 10 to 20 years, and then increased from 20 to 25 years. After 25 years, the niche breadth of the grassland narrowed gradually, indicating weakened adaptability. The niche breadth indices of most populations peaked at 10 and 25 years, respectively. There was no li-near relationship between synthetic dominance index and niche breadth in different grass communities. With the increasing rehabilitation age, the niche overlap indices were highest at 15 years with a single hump pattern, indicating that the interspecific competition increased to the highest at 15 years and then decreased. It was shown that attitude, soil water content (SWC) and soil organic matter content (SOM) were the main factors affecting the niche breadth, while soil total nitrogen content (STN), attitude and SWC were the main factors affecting the niche overlap. There was no linear relationship between niche breadth and niche overlap of tested species in different rehabilitation ages due to resource spatial heterogeneity and growth stages of grass species. These findings indicated that with the increasing rehabilitation age, the population adaptability to the environment are generally enhanced and the resource competition among populations increases and then decreases. It was concluded that attitude, SWC and STN were the key environmental factors that affect population adaptability and interspecific relationship in natural grassland of loess hilly region.

[Variation in leaf functional traits of different-aged Robinia pseudoacacia communities and relationships with soil nutrients]. / ä¸åŒæž—é¾„åˆºæ§å¶åŠŸèƒ½æ€§çŠ¶å·®å¼‚åŠå ¶ä¸ŽåœŸå£¤å »åˆ†çš„å ³ç³».

On the basis of various leaf functional traits of different-aged Robinia pseudoacacia communities, as well as the relationships between the traits and soil nutrients, the adaptation strategy of R. pseudoacacia in relation to soil conditions was analyzed in Ansai County, the Loess Plateau, China. The results showed that specific leaf area, leaf area, leaf water content, leaf total nitrogen content and leaf organic carbon content first increased and then decreased with the increasing stand age. The peak values of specific leaf area (279.18 cm2·g-1), leaf area (12.33 cm2), leaf water content (0.09%), leaf total nitrogen content (33.01 g·kg-1) and leaf organic carbon content (523.08 g·kg-1) were obtained at 30 years old. With the increasing stand age, leaf tissue density, leaf total phosphorus content, leaf thickness and stomata density increased, and stomata length and stomata width decreased. Leaf area, specific leaf area, leaf total phosphorus content, leaf water content, leaf thicknessand stomata density were the main indexes based on principal component analysis (PCA), for R. pseudoacacia leaf functional traits responding to the increased stand age. The indexes were correlated with each other, indicating that R. pseudoacacia was capable of changing leaf morphological structure to adapt to environmental changes. Soil total nitrogen content was the main factor influencing leaf area, leaf water content, specific leaf area and stomata length, while soil organic carbon content mainly affected stomata width, leaf tissue density, leaf thickness, leaf total phosphorus content, leaf total nitrogen content and stomata density. Therefore, soil total nitrogen and organic carbon content were main factors that affected leaf functional traits of R. pseu-doacacia in different stand ages. Soil nutrients in R. pseudoacacia communities were improved with the increasing stand age, which eventually affected leaf functional traits. The flexibility of leaf functional traits indicated that R. pseudoacacia communities had great potential to adapt to environmental change in Loess Plateau hilly region.

[Effects of drying and re-watering on the photosynthesis and active oxygen metabolism of Periploca sepium seedlings].

Taking two-year-old Periploca sepium seedlings as test materials, an experiment with controlled soil water contents was conducted to study the effects of repeated drying and re-watering on the leaf photosynthetic characteristics and the lipid peroxidation and antioxidant system in young leaves, mature leaves, old leaves, new stems, and fine roots. The seedlings were subjected to three cycles of drying and re-watering, with regular irrigation to maintain the soil water content at around 80% of field capacity as the control (CK). Under drying, the leaf relative water content (RWC) and net photosynthesis rate (Pn) decreased significantly, while the leaf photosynthetic pigments content increased. When the seedlings were re-watered, their leaf RWC recovered to the CK level, showing a strong repair capacity after drying. Both the leaf chlorophyll content and the Pn after repeated drying and re-watering presented a higher level than those of the CK, indicating a compensatory effect appeared and an appropriate drought stress being able to induce the adaptability of P. sepium to drought stress. Stomatal closure was the main factor limiting P. sepium photosynthesis under drought stress, while non-stomatal limitation only worked at noon. Under drying, the superoxide anion radical (O2-*) production rate in young leaves, new stems, and fine roots increased while the malondialdehyde (MDA) contents decreased, suggesting that these young tissues were not suffered from the oxidative stress. The activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in different organs had different variation trends, with those in fine roots changed actively, suggesting the important role of fine roots in the acclimation of P. sepium to drought environment. It was the cooperation and coordination among plant organs that made P. sepium more adaptive to the repeated drying and wetting conditions in drought-prone regions.