Nitrogen Fertilizer Levels Affect the Growth and Quality Parameters of Astragalus mongolica.

Owing to overexploitation, wild resources of Astragalus mongolica, a Chinese herbal plant that is widely distributed in the arid and semi-arid areas of Northern China, have gradually become exhausted, and therefore, commercial cultivation is increasingly important to meet the growing demand for astragalus and reduce the pressure on wild populations. Nitrogen level is an important factor that affects the yield and quality of A. mongolica. However, uniform standards for fertilization among production areas have not yet been determined. In this study, the effect of nitrogen fertilizer treatment on the yield and quality of A. mongolica in the Qinghai-Tibet Plateau was explored using a control treatment (no added nitrogen, N0) and five different nutrient levels: 37.5 kg/ha (N1), 75 kg/ha (N2), 112.5 kg/ha (N3), 150 kg/ha (N4), and 187.5 kg/ha (N5). According to grey relational analysis, the optimal nitrogen fertilizer treatment was the N4 level followed by the N5 and N2 levels. Nitrogen fertilizer significantly increased the root biomass, plant height, root length, and root diameter. However, nitrogen fertilization had no significant effect on the content of Astragaloside IV and mullein isoflavone glucoside. The content of ononin and calycosin continually accumulated throughout the growing period. The results showed that the ononin and calycosin content under N4 and N2 is higher than other levels and there is not significantly different between different nitrogen fertilizer levels about them. The content of formononetin decreased gradually with the progression of the growing season. The optimal nitrogen fertilizer treatment for A. mongolica is recommended to be 150 kg/ha and the content of active compounds and yield were observed to reach the maximum in October.

Effects of Elevated CO2 on the Swainsonine Chemotypes of Astragalus lentiginosus and Astragalus mollissimus.

Rapid changes in the Earth's atmosphere and climate associated with human activity can have significant impacts on agriculture including livestock production. CO2 concentration has risen from the industrial revolution to the current time, and is expected to continue to rise. Climatic changes alter physiological processes, growth, and development in numerous plant species, potentially changing concentrations of plant secondary compounds. These physiological changes may influence plant population density, growth, fitness, and toxin concentrations and thus influence the risk of toxic plants to grazing livestock. Locoweeds, swainsonine-containing Astragalus species, are one group of plants that may be influenced by climate change. We evaluated how two different swainsonine-containing Astragalus species responded to elevated CO2 concentrations. Measurements of biomass, crude protein, water soluble carbohydrates and swainsonine concentrations were measured in two chemotypes (positive and negative for swainsonine) of each species after growth at CO2 levels near present day and at projected future concentrations. Biomass and water soluble carbohydrate concentrations responded positively while crude protein concentrations responded negatively to elevated CO2 in the two species. Swainsonine concentrations were not strongly affected by elevated CO2 in the two species. In the different chemotypes, biomass responded negatively and crude protein concentrations responded positively in the swainsonine-positive plants compared to the swainsonine-negative plants. Ultimately, changes in CO2 and endophyte status will likely alter multiple physiological responses in toxic plants such as locoweed, but it is difficult to predict how these changes will impact plant herbivore interactions.

[Influence of Different Growing Years on Accumulation of Flavonoids and Saponins in Astragali Radix].

OBJECTIVE: To study the effects of different growing years on the accumulation of flavonoids and saponins in Astragali Radix, in order to offer evidence to determine the most appropriate harvest time. METHODS: HPLC method was developed for the determination of the contents of flavonoids and saponins. RESULTS: The contents of flavonoids and saponins in different growing years of Astragali Radix existed obvious differences, the longer growing, the content was relatively higher. CONCLUSION: With the increase of growing years, the contents of flavonoids and saponins are roughly rising year by year, the harvest time has a great influence on the accumulation of the compositions.

Responses of social and solitary bees to pulsed floral resources.

Pulsed food resources lead to mismatches between distribution of consumers and resources in space and time. Many studies have investigated how pollinators and floral resources covary in space, but few have looked at their covariance among years. I studied responses of two bee taxa, Bombus (a social genus) and Anthophora (a solitary genus), to variation in flowering by Astragalus scaphoides, a perennial herb that flowers in alternate years. First, I quantified the rate at which individual plants were visited by bees. Anthophora showed evidence of a demographic response to resource pulses--that is, more individuals were seen in the year after a high-flowering year--whereas Bombus did not. Second, I quantified pollinator behavior by following individual bees and recording the proportion of visits to A. scaphoides within single foraging bouts. The proportion of visits to A. scaphoides by both taxa increased with A. scaphoides's flowering density. Higher specialization in high-flowering years likely makes both taxa better pollinators in high-flowering years. If these taxa differ in effectiveness as pollinators, then these responses translate into variation in pollination services in space and time, specifically, more activity by Bombus in high-flowering years and more by Anthophora in years following high-flowering years. They also emphasize that pollinator activity depends in part on past-as well as current-floral resources.

Inoculation of Astragalus racemosus and Astragalus convallarius with selenium-hyperaccumulator rhizosphere fungi affects growth and selenium accumulation.

Little is known about how fungi affect plant selenium (Se) accumulation. Here we investigate the effects of two fungi on Se accumulation, translocation, and chemical speciation in the hyperaccumulator Astragalus racemosus and the non-accumulator Astragalus convallarius. The fungi, Alternaria astragali (A3) and Fusarium acuminatum (F30), were previously isolated from Astragalus hyperaccumulator rhizosphere. A3-inoculation enhanced growth of A. racemosus yet inhibited growth of A. convallarius. Selenium treatment negated these effects. F30 reduced shoot-to-root Se translocation in A. racemosus. X-ray microprobe analysis showed no differences in Se speciation between inoculation groups. The Astragalus species differed in Se localization and speciation. A. racemosus root-Se was distributed throughout the taproot and lateral root and was 90 % organic in the lateral root. The related element sulfur (S) was present as a mixture of organic and inorganic forms in the hyperaccumulator. Astragalus convallarius root-Se was concentrated in the extreme periphery of the taproot. In the lateral root, Se was exclusively in the vascular core and was only 49 % organic. These findings indicate differences in Se assimilation between the two species and differences between Se and S speciation in the hyperaccumulator. The finding that fungi can affect translocation may have applications in phytoremediation and biofortification.

[Status and analysis of Astragali Radix resource in China].

To explore the status of the resources of Astragali Radix, a survey on its germplasm resources was carried out. Some conclusions can be drawn for Astragali Radix: the major source is the cultivated Astragalus mongolicus. The new major cultivation areas for A. mongolicus and A. membranaceus are Shandong and Gansu province. The semi-wildly planting model in Shanxi province maintains the genuine trait of Astragali Radix, but its yield is limited, and now a combination model has been developed. The major problems for Astragali Radix are the selection of planting sites, the rot root and difficulty in collecting and processing. Several developmental proposals for Astragali Radix were put forward including rational distribution of planting areas, establishment of standard system, development and standardization of producing technologies.

Are dormant plants hedging their bets? Demographic consequences of prolonged dormancy in variable environments.

During the growing season, some individuals in perennial plant populations may remain alive belowground while others emerge. This phenomenon, known as prolonged dormancy, seems maladaptive, because prolonged dormancy delays growth and reproduction. However, prolonged dormancy may offer the benefit of safety while belowground, leading to the hypothesis that prolonged dormancy is a bet-hedging strategy. We evaluated this hypothesis using a 25-year demographic study of Astragalus scaphoides, an iteroparous perennial plant. First, we determined the relationship between prolonged dormancy and fitness using data from individuals in our population. This analysis showed that prolonged dormancy decreased arithmetic mean fitness and reduced variance in fitness. Geometric mean fitness was maximized at intermediate levels of prolonged dormancy. Empirical patterns of lifetime reproductive success confirm this relationship. We also compared fitness of plants in our population to hypothetical plants without prolonged dormancy, which generally revealed benefits of prolonged dormancy, even if plants could forgo prolonged dormancy without costs to other vital rates. Therefore, prolonged dormancy may indeed function as a bet-hedging strategy, but the benefits of remaining belowground outweigh the costs only for a subset of individuals. Bet hedging has been demonstrated in plants with simple life histories, such as annuals and monocarpic perennials; we present evidence that bet hedging may be important for plants with more complex life histories.

Floral ontogeny in Astragalus compactus (Leguminosae: Papilionoideae: Galegeae): variable occurrence of bracteoles and variable patterns of sepal initiation.

Comparative studies of floral ontogeny represent a growing field that promise to provide new insights on floral evolution. Floral ontogenetic information has been used successfully in Leguminosae for re-examining phylogenetic relationships at different levels. Using epi-illumination light microscopy, we present original ontogenetic data in Astragalus compactus, which was chosen because of its unusual arrangement of inflorescence and variable occurrence of bracteoles on flowers. Based on our results, uncommon ontogeny of the inflorescence led to the arrangement of flowers in four different positions. Variation was observed not only in the presence of bracteoles, but also in the order of sepal initiation in flowers of the same inflorescence. Surprisingly, besides the widely stated unidirectional pattern, bidirectional, sequential and an atypical unreported order were observed. High degree of overlapping between whorls and formation of two types of common primordia also were found. The variable occurrence of bracteoles suggests that the species is in an intermediate state towards fully lacking of bracteoles. We propose that the variability of the sequence of sepal initiation is possibly a consequence of the function of mechanical forces generated by surrounding leaves. Relationships between mechanical force and auxin signalling are discussed.

Interactions of selenium hyperaccumulators and nonaccumulators during cocultivation on seleniferous or nonseleniferous soil--the importance of having good neighbors.

• This study investigated how selenium (Se) affects relationships between Se hyperaccumulator and nonaccumulator species, particularly how plants influence their neighbors' Se accumulation and growth. • Hyperaccumulators Astragalus bisulcatus and Stanleya pinnata and nonaccumulators Astragalus drummondii and Stanleya elata were cocultivated on seleniferous or nonseleniferous soil, or on gravel supplied with different selenate concentrations. The plants were analyzed for growth, Se accumulation and Se speciation. Also, root exudates were analyzed for Se concentration. • The hyperaccumulators showed 2.5-fold better growth on seleniferous than on nonseleniferous soil, and up to fourfold better growth with increasing Se supply; the nonaccumulators showed the opposite results. Both hyperaccumulators and nonaccumulators could affect growth (up to threefold) and Se accumulation (up to sixfold) of neighboring plants. Nonaccumulators S. elata and A. drummondii accumulated predominantly (88-95%) organic C-Se-C; the remainder was selenate. S. elata accumulated relatively more C-Se-C and less selenate when growing adjacent to S. pinnata. Both hyperaccumulators released selenocompounds from their roots. A. bisulcatus exudate contained predominantly C-Se-C compounds; no speciation data could be obtained for S. pinnata. • Thus, plants can affect Se accumulation in neighbors, and soil Se affects competition and facilitation between plants. This helps to explain why hyperaccumulators are found predominantly on seleniferous soils.

Selenium hyperaccumulation by Astragalus (Fabaceae) does not inhibit root nodule symbiosis.

PREMISE OF STUDY: A survey of the root-nodule symbiosis in Astragalus and its interaction with selenium (Se) has not been conducted before. Such studies can provide insight into how edaphic conditions modify symbiotic interactions and influence partner coevolution. In this paper plant-organ Se concentration ([Se]) was investigated to assess potential Se exposure to endophytes. • METHODS: Selenium distribution and molecular speciation of root nodules from Se-hyperaccumulators Astragalus bisulcatus, A. praelongus, and A. racemosus was determined by Se K-edge x-ray absorption spectroscopy. A series of greenhouse experiments were conducted to characterize the response of root-nodule symbiosis in Se-hyperaccumulators and nonhyperaccumulators. • KEY RESULTS: Nodules in three Se-hyperaccumulators (Astragalus crotalariae, A. praelongus, and A. preussii) are reported for the first time. Leaves, flowers, and fruits from Se-hyperaccumulators were routinely above the hyperaccumulator threshold (1,000 µg Se g(-1) DW), but root samples rarely contained that amount, and nodules never exceeded 110 µg Se g(-1) DW. Nodules from A. bisulcatus, A. praelongus, and A. racemosus had Se throughout, with a majority stored in C-Se-C form. Finally, an evaluation of nodulation in Se-hyperaccumulators and nonhyperaccumulators indicated that there was no nodulation inhibition because of plant Se tolerance. Rather, we found that in Se-hyperaccumulators higher levels of Se treatment (up to 100 µM Se) corresponded with higher nodule counts, indicating a potential role for dinitrogen fixation in Se-hyperaccumulation. The effect was not found in nonhyperaccumulators. • CONCLUSIONS: As the evolution of Se hyperaccumulation in Astragalus developed, root-nodule symbiosis may have played an integral role.

Identification and characterization of selenate- and selenite-responsive genes in a Se-hyperaccumulator Astragalus racemosus.

Plants with capacity to accumulate high levels of selenium (Se) are desired for phytoremediation and biofortification. Plants of genus Astragalus accumulate and tolerate high levels of Se, but their slow growth, low biomass and non-edible properties limit their direct utilization. Genetic engineering may be an alternative way to produce edible or high biomass Se-accumulating plants. The first step towards this goal is to isolate genes that are responsible for Se accumulation and tolerance. Later, these genes can be introduced into other edible and high biomass plants. In the present study, we applied fluorescent differential display to analyze the transcript profile of Se-hyperaccumulator A. racemosus treated with 20 µM selenate (K(2)SeO(4)) for 2 weeks. Among 125 identified Se-responsive candidate genes, the expression levels of nine were induced or suppressed more than twofold by selenate treatment in two independent experiments while 14 showed such changes when treated with selenite (K(2)SeO(3)). Six of them were found to respond to both selenate and selenite treatments. A novel gene CEJ367 was found to be highly induced by both selenate (1,920-fold) and selenite (579-fold). Root- or shoot-preferential expression of nine genes was further investigated. These identified genes may allow us to create Se-enriched transgenic plants.

[Comparative study of wild and cultivated astragali radix in Daqingshan district in Wuchuan of Neimenggu].

OBJECTIVE: To make a comparative study on wild and cultivated Astragali Radix in Wuchuan, Neimenggu where is one of the geo-authentic producing areas of Astragalus membranaceus var. mongholicus. METHOD: This comparative study focus on shapes and properties, microscopic features of transverse section and powder of roots, qualitative evaluation of wild and cultivated Astragali Radix. RESULT: Wild Astragali Radix had a cylindrical main root, 2 or 3 root branches, dark brown color and many lenticels on the root bark. Cultivated Astragali Radix had a long cylindrical root, few root branches, yellowish white or light brown and fewer lenticels on the root bark. The differences of microscopic features were that the number of cork cells layers in wild Astragali Radix was bigger than that in cultivated Astragali Radix; stone cells were only observed in wild Astragali Radix; distinct annual rings in the xylem were only existed in cultivated Astragali Radix. The results of qualitative evaluation reveal that the contents of major active isoflavonoids and saponins in wild Astragali Radix are higher than those in cultivated Astragali Radix. CONCLUSION: There are some diagnostic differences in the main microscopic features of transverse section and powder between wild and cultivated Astragali Radix. The contents of major active isoflavonoids and saponins in wild Astragali Radix are higher than those in cultivated Astragali Radix. Our study provides important scientific evidence for reasonable and effective uses of wild and cultivated Astragali Radix in Wuchuan, and also provides a reliable basis for the quality control of Astragali Radix.

Flower and pod development, grain-setting characteristics and grain yield in Chinese milk vetch (Astragalus sinicus L.) in response to pre-anthesis foliar application of paclobutrazol.

The number of grains per unit land area is the most important grain yield component in Chinese milk vetch. Flower and pod survival seem to be critical determinants of grain number, which is related to the number of fertile flowers and pods during the anthesis period. Flower and pod growth are frequently considered the key determinants to establish grain number. The objective of this study was to explore the influences of paclobutrazol on flower and pod development, grain-setting characteristics and grain yield in Chinese milk vetch under different concentrations of foliar spray and try to explore the physiological regulatory mechanisms. Field experiments were carried out during the 2017-2018 and 2018-2019 growing seasons at the Dayuzhuang experimental field. The experiment involved the Chinese milk vetch cultivar "Xinzi No. 1" and six levels of foliar application of paclobutrazol, 0, 200, 300, 400, 500, and 600 mg L-1, in treatments CK, T1, T2, T3, T4, and T5, respectively. Foliar spray was applied once, at the squaring stage. In comparison with the CK treatment, all of the paclobutrazol treatments yielded, to various degrees, increased values of the number of inflorescences per unit area, number of pods per unit area, grain-setting rate of pods, and number of grains per pod in all six inflorescence layers, with the largest increases observed in the T3 treatment. In the T3 treatment compared with the CK treatment, from the first to sixth inflorescence layers, the number of inflorescences per unit area was increased by 34.07-58.97%, the number of pods per unit area was increased by 39.69-68.35%, the grain number per pod was increased by 44.31-53.69%, and the grain-setting rate of pods was increased by 1.84-4.89%. An analysis of yield composition revealed that the paclobutrazol spray treatment had little impact on the grain weight of Chinese milk vetch. The correlations between the concentration of paclobutrazol spray and the grain yield of Chinese milk vetch reached a significant level. Grain yield was highest at the paclobutrazol concentration of 373.10 mg/L. The inflorescence contents of gibberellic acid 3 (GA3), indole-3-acetic acid (IAA), and abscisic acid (ABA) were reduced, whereas that of cytokinin (CTK) was increased, by foliar application of paclobutrazol (400 mg L-1, T3 treatment) relative to CK treatment during the stages of flowers and pods developing into grains.

Combining the Anticancer and Immunomodulatory Effects of Astragalus and Shiitake as an Integrated Therapeutic Approach.

Astragalus root (Huang Qi) and Shiitake mushrooms (Lentinus edodes) are both considered medicinal foods and are frequently used in traditional Chinese medicine due to their anticancer and immunomodulating properties. Here, the scientific literatures describing evidence for the anticancer and immunogenic properties of Shiitake and Astragalus were reviewed. Based on our experimental data, the potential to develop medicinal food with combined bioactivities was assessed using Shiitake mushrooms grown over Astragalus beds in a proprietary manufacturing process, as a novel cancer prevention approach. Notably, our data suggest that this new manufacturing process can result in transfer and increased bioavailability of Astragalus polysaccharides with therapeutic potential into edible Shiitake. Further research efforts are required to validate the therapeutic potential of this new Hengshan Astragalus Shiitake medicinal food.

Disappearing plants: why they hide and how they return.

Prolonged dormancy is a life-history stage in which mature plants fail to resprout for one or more growing seasons and instead remain alive belowground. Prolonged dormancy is relatively common, but the proximate causes and consequences of this intriguing strategy have remained elusive. In this study we tested whether stored resources are associated with remaining belowground, and investigated the resource costs of remaining belowground during the growing season. We measured stored resources at the beginning and end of the growing season in Astragalus scaphoides, an herbaceous perennial in southwest Montana, USA. At the beginning of the growing season, dormant plants had lower concentrations of stored mobile carbon (nonstructural carbohydrates, NSC) than did emergent plants. Surprisingly, during the growing season, dormant plants gained as much NSC as photosynthetically active plants, an increase most likely due to remobilization of structural carbon. Thus, low levels of stored NSC were associated with remaining belowground, and remobilization of structural carbon may allow for dormant plants to emerge in later seasons. The dynamics of NSC in relation to dormancy highlights the ability of plants to change their own resource status somewhat independently of resource assimilation, as well as the importance of considering stored resources in understanding plant responses to the environment.

Seedling biomass partition and water use efficiency of switchgrass and milkvetch in monocultures and mixtures in response to various water availabilities.

Seedling biomass and allocation, transpiration water use efficiency (TWUE), and species competition between switchgrass (Panicum virgatum L.) and milkvetch (Astragalus adsurgens Pall.) were investigated in a pot-cultivated experiment under different levels of water availability. The experiment was conducted using a simple replacement design in which switchgrass and milkvetch were grown in growth chamber with ten seedlings per pot, in three combinations of the two species (0:10, 5:5 and 10:0). Five water treatments included sufficient water supply (HW), gradual soil drying from HW (DHW), moderate water stress (LW), gradual soil drying from LW (DLW), and re-establishment of LW conditions after 12 days of drying from LW (RLW). Water treatments were applied over a 15-day period. Biomass production and its partitioning, and TWUE were determined at the end of the experiment. Species competitive indices (competitive ratio (CR), aggressivity (A) and relative yield total (RYT)) were calculated from the biomass dry weight data for shoots, roots and total biomass. Water stress significantly reduced seedling biomass production but increased root:shoot ratios in both monocultures and mixtures. In the RLW treatment, only switchgrass monocultures displayed compensatory biomass production and TWUE, while both species demonstrated compensatory growth in the mixture. Switchgrass was the dominant species and much more aggressive than milkvetch in the LW treatment, while in the other four treatments milkvetch was the dominant species as measured by the positive value of aggressivity and higher values of CR. The total biomass RYT values of the two species were higher than 1.0, indicating some degree of resource complimentarity. In the two-species mixture, although the biomass production was lower than that of milkvetch in the monoculture, there was better TWUE, especially under low and fluctuating water availability.

[Ecological environment of cultivated Astragali radix and market specification of prepared slices].

Astragali Radix is derived from roots of Astragalus membranaceus var. mongholicus and A. membranaceus. The exhaustion of wild Astragali Radix has made cultivated Astragali Radix possess the commercial market of Astragali Radix. So the ecological environment of cultivated Astragali Radix should be investigated through field survey. Through investigation, we found that A. membranaceus var. mongholicus are cultivated in Hengshan mountain of Shanxi province, Longnan of Gansu province, south of Inner Mongolia and Qinghai provinces. A. membranaceus var. mongholicus is almost planted on the plain, except in Shanxi province it grows on the sunny side of the mountain. What is more, soil type, elevation, annual temperature and annual rainfall of these locations are different. So the ecological environments of cultivated location of Astragali Radix are different from each other. A. membranaceus is wild in Heilongjiang and northeast of Inner Mongolia, but the resource is drying up. It is also planted in few places of the provinces of Shanxi, Shandong, Hebei, Gansu, but cultivated scope of A. membranaceus is smaller than A. membranaceus var. mongholicus.. So A. membranaceus var. mongholicus possesses large part of Astragali Radix market. In market, there exists no unified specification fro slices of Astragali Radix, and specification of prepared slices will influence the contents of chemical components. Through investigation, different kind of prepared slices can be collected and compared, this provides evidences for quality control of prepared slices. Through investigation, five different specifications of prepared slices were found in market. The distributions of some specification of prepared slices are specified, like transverseprepared slices prepared from A. membranaceus only found in Heilongjiang province. Transverse prepared slices possess half part of prepared slice market, and can be used to identify original plant of Astragali Radix. So transverse prepared slices should be the unified specification of Astragali Radix.

De novo transcriptome characterisation of two auxin-related genes associated with plant growth habit in Astragalus adsurgens Pall.

Astragalus adsurgens Pall., a perennial legume native to China, is commonly used as a forage crop. And it has great value for sustainable development of grasslands in arid and semi arid regions. However, to date, little is known regarding the A. adsurgens genome, and no studies have determined whether it would be possible to improve the germplasm of A. adsurgens through genetic modification. In this study, we used an RNA-seq protocol to generate a de novo transcriptome including 151,516 unigenes of A. adsurgens. We compared the transcriptomes of A. adsurgens having different growth habits (prostrate/erect) and identified 14,133 single nucleotide polymorphism sites (SNP) in 8,139 unigenes. Differential expression gene (DEG) analysis suggested that 10,982 unigenes were up-regulated in the prostrate plant relative to the erect plant, while 10,607 unigenes were down-regulated. Of the 21,589 DEG, Unigene72782_All (LAX4) and CL12494.Contig3_All (TIR1), an auxin transporter gene and an auxin transport inhibitor gene, respectively, were predicted to influence the growth habit of A. adsurgens, which were verified by qRT-PCR in these phenotypes. These results suggest that auxin transport was more active in the prostrate plant than in the erect plant, resulting in asymmetric distribution of auxin that affects the growth habit of A. adsurgens. Overall, this study may provide a basis for future research on key genes in A. adsurgens and may deepen our understanding of the molecular mechanisms regulating plant growth habit.

How do plants know when other plants are flowering? Resource depletion, pollen limitation and mast-seeding in a perennial wildflower.

Mast-seeding is the synchronous and periodic reproduction by plant populations. This phenomenon has been widely studied from a community-level perspective, but we know extremely little about how plants are able to synchronize reproduction. Here, we present the first experimental test of proximate mechanisms of mast-seeding, by preventing reproduction in an iteroparous, mast-seeding wildflower. Through a series of experiments, we show that mobile carbohydrate stores (NSC) control alternate-year flowering by individual plants; seed set depletes NSC which prevents flowering the following year. Plants are synchronized by density-dependent pollen limitation; when plants flower asynchronously, they set fewer seeds, which prevents NSC depletion. Therefore, these individual plants flower in subsequent years and become synchronized. Because mast-seeding is a consequence of physiological controls of reproduction, differences in plant resource acquisition and allocation could dramatically change patterns of seed production, and changes in plant consumers and pollinators could change selection on physiological and developmental pathways.

[Effects of Chinese milk vetch intercropped with rape under straw mulching on soil aggregate and organic carbon character]. / 秸秆覆盖条件下紫云英间作油菜的土壤团聚体及有机碳特征.

There are severe soil erosion, shallow soil, reduction of soil organic matter, and poor soil and water conservation in purple soil areas in Southwest China, which become the main limiting factors for the sustainable development of agriculture. A series of buckets and field experiments in the field were employed to explore the soil aggregate and soil organic carbon in response to Chinese milk vetch intercropped with rape under straw mulching, aiming to improve soil aggregate structure and increase organic carbon content. Results showed that intercropped Chinese milk vetch increased soil micro-aggregate content in rape rhizosphere, and reduced soil aggregate mean mass diameter. The change of soil macro-aggregate in rape rhizosphere was mainly caused by the change of content of soil aggregate on 10-5 mm and 5-2 mm, while the soil micro-aggregate was mainly caused by soil aggregate on 0.25-0.053 mm. Intercropped Chinese milk vetch and straw mulching significantly increased soil organic carbon content after corn growing season, with increasing the content of soil organic carbon on 10-20 cm and 20-30 cm. Though intercropped Chinese milk vetch and straw mulching had less effect on soil total organic carbon in rape season, more and more significant effect on 0-10 cm, 10-20 cm, and 20-30 cm with rape growing, especially in stem elongation stage, flowering stage, and harvest stage. Our results showed that the characteristic of soil aggregate in rape rhizosphere could be changed by intercropped Chinese milk vetch, and that the content of soil organic carbon could be increased by Chinese milk vetch intercropped with rape under straw mul-ching.