Annual Seedlings Research Articles

Transcriptional Analysis of Masson Pine (Pinus massoniana) under High CO2 Stress.

To explore the molecular mechanism of the response of Masson pine (Pinus massoniana), the main coniferous tree in southern China, to high CO2 stress, transcriptome sequencing was carried out to analyze the genome-wide responses of annual seedlings under different durations (0 h, 6 h, 12 h and 24 h) of high CO2 stress. The results showed that a total of 3080/1908, 3110/2115 and 2684/1483 genes were up-/down-regulated after 6 h, 12 h and 24 h of treatment, respectively, compared with control check group (CK, 0 h). Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that most of these differentially expressed genes (DEGs) were enriched in energy metabolism, carbohydrate synthesis, cell wall precursor synthesis and hormone regulation pathways. For energy metabolism, the expression of most genes involved in photosynthesis (including the light reaction and Calvin cycle) was generally inhibited, while the expression of genes related glycolysis, the tricarboxylic acid (TCA) cycle and PPP pathway was up-regulated. In addition, the increase in the CO2 concentration induced the up-regulation of gene expression in the sucrose synthesis pathway. Among all starch synthesis genes, GBSS (granule-bound starch synthase) had the highest expression level. On the other hand, during the synthesis of hemicellulose and pectin (cell wall precursor substances), the expression levels of GMD (GDP-mannose 4,6-dehydratase), MGP (Mannose-1-phosphate guanylyl transferase) and RHM (Rhamnose biosynthetic enzyme) were the highest, suggesting that the synthesis of the raw materials hemicellulose and pectin in Masson pine under stress were mainly supplied by GDP-Man, GDP-Fuc and UDP-Rha. Finally, stress inhibited gene expression in the ABA (Abscisic Acid) synthesis pathway and induced gene expression in the GA (Gibberellin), SA (Salicylic acid), BR(Brassinolide) and MeJA (Methyl Jasmonate) pathways. Stomatal switches were regulated by hormonal interactions. This experiment elaborated on the response and molecular mechanism of Masson pine to CO2 stress and aided in screening carbon sequestration genes for the corresponding molecular research of Masson pine in the future.

Effects of Two Trichoderma Strains on Plant Growth, Rhizosphere Soil Nutrients, and Fungal Community of Pinus sylvestris var. mongolica Annual Seedlings

Trichoderma spp. are proposed as major plant growth-promoting fungi that widely exist in the natural environment. These strains have the abilities of rapid growth and reproduction and efficient transformation of soil nutrients. Moreover, they can change the plant rhizosphere soil environment and promote plant growth. Pinus sylvestris var. mongolica has the characteristics of strong drought resistance and fast growth and plays an important role in ecological construction and environmental restoration. The effects on the growth of annual seedlings, root structure, rhizosphere soil nutrients, enzyme activity, and fungal community structure of P. sylvestris var. mongolica were studied after inoculation with Trichoderma harzianum E15 and Trichoderma virens ZT05, separately. The results showed that after inoculation with T. harzianum E15 and T. virens ZT05, seedling biomass, root structure index, soil nutrients, and soil enzyme activity were significantly increased compared with the control (p < 0.05). There were significant differences in the effects of T. harzianum E15 and T. virens ZT05 inoculation on the growth and rhizosphere soil nutrient of P. sylvestris var. mongolica (p < 0.05). For the E15 treatment, the seedling height, ground diameter, and total biomass of seedlings were higher than that those of the ZT05 treatment, and the rhizosphere soil nutrient content and enzyme activity of the ZT05 treatment were higher than that of the E15 treatment. The results of alpha and beta diversity analyses showed that the fungi community structure of rhizosphere soil was significantly different (p < 0.05) among the three treatments (inoculated with T. harzianum E15, T. virens ZT05, and not inoculated with Trichoderma). Overall, Trichoderma inoculation was correlated with the change of rhizosphere soil nutrient content.

Population dynamics and overwintering of a biological control beetle, Agasicles hygrophila, on a nontarget plant Alternanthera sessilis, along a latitudinal gradient

Assessing the impact of temperature changes on insect population and overwintering on nontarget hosts is important for prediction of nontarget effects in weed biological control. Agasicles hygrophila is a beetle used for biological control of the invasive plant alligator weed, Alternanthera philoxeroides, with nontarget damage to a native plant, Alternanthera sessilis. In this study, we monitored plant growth and phenology along with beetle population and overwintering on these two hosts along a latitudinal gradient from subtropical to temperate climates (Guilin, Wuhan and Kaifeng) in China. We found only annual A. sessilis seedlings in temperate Kaifeng, but both annual seedlings and perennial ramets of A. sessilis were found in Guilin and Wuhan. However, in winter, living A. sessilis plants were found in only subtropical Guilin. Beetles at the Guilin site could successfully maintain their populations and overwinter on A. sessilis. Although the beetle could sustain its populations on A. sessilis at the other two higher-latitude sites during the growing season, it failed to overwinter on either species, indicating that the temperatures in different climate zones may directly and/or indirectly affect the development of insect biological control agents and their population sizes on nontarget hosts. Therefore, it is important to consider the shifting plant–insect interactions induced by climate when assessing potential nontarget effects of species introduced as biological control agents.

Invasion of Siberian Pine Populations in Mountain Tundra in the Northern Urals

A new method for determining the upper forest border (UFB) as the border of the “root-closed” stand and regrowth as its potential vanguard is proposed. The mass dispersal of Pinus sibirica populations by the nutcracker (Nucifraga caryocatactes) in the UFB ecotone in the Northern Urals (Pavdinskii Kamen’ and Tretii Bugor Mountain) from the middle-mountain taiga to the mountain forest tundra and tundra at a distance reaching 1 km is found. It is done based on the original reconstruction method of the dynamics of population number in P. sibirica annual seedlings and on an analysis of their relations with the dynamics of the seed bearing and population number of the nutcracker. The trustworthy consortive relations of the number of Pinus sibirica generations in the mountain forested tundra and tundra zones, with its seed bearing and nutcracker number in the previous year in the middle-mountain taiga zone, are found. A significant increase, 3.7 times, in the number of seedling generations during the last 49 years is found in connection with the increase in the summer air temperature in the subarctic to 2.0°C. A hypothesis of the formation of the united genetic metapopulation of P. sibirica in the forest–tundra mountain ecotone zone as a consequence of its seed ornitochory from the highly different populations is formulated. A forecast of the mosaic formation of the vanguard “thin forests” in 20–25 years and the root-closed curtains of the forest in 40–50 years in the mountain tundra of the Northern Urals at the current rate of the rise in temperature is made.

Effects of different concentrations of nitrogen and phosphorus on growth and active components of Salvia miltiorrhiza

With annual Salvia miltiorrhiza seedlings as experimental material, using "3414" optimal regression design recommended by the Ministry of Agriculture and regularly watered with nutrient solution, through the dynamic sampling of S. miltiorrhiza in different growing stages, and the growth index, dry weight of plant root and content of active components were measured. The potted experiments were applied to study the effects of different nitrogen and phosphorus ratios on the growth, dry matter accumulation and accumulation of active components of S. miltiorrhiza, in order to explore a compatible fertilization method of nitrogen and phosphorus ratio that are suitable for production and quality of S. miltiorrhiza. The results reported as follows：①High concentrations of nitrogen fertilizer was beneficial to dry matter accumulation of S. miltiorrhiza aerial parts, and low concentration of nitrogen fertilizer transferred the dry matter accumulation to underground, and N1P1 could make the transfer ahead of time;②Regression analysis showed that in the early growth stage (before early July), we could use the nitrogen and phosphorus as basic fertilizer at a concentration of 1.521,0.355 g•L⁻¹ respectively to promote the growth of S. miltiorrhiza and at a concentration of 2.281,0.710 g•L⁻¹ respectively to promote the dry matter accumulation of root (after mid-August);③Five kinds of active components of S. miltiorrhiza decreased with the increase of nitrogen concentration, and increased with the increase of the concentration of phosphate fertilizer. Nitrogenous fertilizer, phosphate fertilizer in N-P=2∶3 ratio was more suitable for the accumulation of salvianolic acids, in N-P=1∶2 ratio was more suitable for the accumulation of tanshinone.

Ionic homeostasis of Populus ×euramericanna 'Neva' influenced by irrigation with magne-tized brackish water.

The research aimed to study the characteristic of ionic homeostasis of annual seedlings of Populus ×euramericanna under irrigation with non-magnetized and magnetized 0 or 4.0 g·L-1 NaCl solution for 30 days in the growing season. The ion contents of K+, Na+, Ca2+ and Mg2+ in the lea-ves and roots were measured by atomic absorption spectrophotometry (AAS). The ion homeostasis coefficient (K) and the ion selective transport coefficient (SXi,Na) from root system to leaves were analyzed. Compared with the unsalted treatment, the ion contents of Na+ and Ca2+, SK,Na and SMg,Na increased in leaves and roots under NaCl stress, while the K+ and Mg2+ ion content, the ratio of K+/Na+ and SCa,Na decreased. Compared with the non-magnetized NaCl solution (NM), the magnetized NaCl solution (M) made leaves and roots maintain lower content of Na+ but higher content of K+ and the K+/Na+. Compared with the NM, the content of Ca2+ decreased while that of Mg2+ increased in the M. In M, K was higher than that in NM, and there was significant increase in the leaves than that in the roots. The ratios of SK,Na and SMg,Na in leaves and roots in M were higher than those in NM, while the ratio of SCa,Na was lower. The magnetized NaCl solution decreased Na+ content, increased K+, Ca2+ and Mg2+ content, and maintained higher K+/Na+, which was beneficial for the physiological metabolism of the whole plant. So, the magnetic effect could promote the re-establishment of ionic homeostasis by ions selective absorption and transportation under NaCl stress.

Перспективи використання мигдалю звичайного (Amygdalus communis L.) у лісостеповій зоні України

Перспективи використання мигдалю звичайного (Amygdalus communis L.) у лісостеповій зоні України

Descriptive Analysis of Introduction of Innovative Technologies in Forestry

The problem of innovative development of the most important area of forestry is reforestation. Established thatquestions the use of innovative technologies in reforestation and afforestation in Russia is still not well defined.One promising avenue is the use of planting material with closed root system (MCS). However, for thedevelopment and practical application of technological innovation requires financial support, due to the high costof produce seed with MCS. As evidence of the economic cost calculation done on the basis of compiledcash-flow sheets on growing seedlings with open and closed root systems and the establishment of forestplantations biennial seedlings ACS and PCL-year seedlings grown in containers with a volume of cells 150, 200,300 and 400 cm3 conditions and non-heated greenhouses. The authors revealed that the main factor of the cost ofseedlings with MCS is the costs for the maintenance of machines and mechanisms, i.e. organization costs ofpurchasing and maintaining expensive greenhouses. It is proved that the cost of producing the annual containerplanting material (MCS) and the subsequent development of forest plantations is not significantly different fromthe receipt of annual and biennial seedlings from bare-root in a greenhouse covered ground, but its practicalapplication in silviculture production gives a whole other opportunities related primarily from a significantreduction in terms of the cultivation of seed and seedlings of high adaptability. It is proved that the establishmentof forest cultures seedlings with MCS is only possible with the support of the state, i.e. through the mechanismof public-private partnerships.

Perspectives on screening winter-flood-tolerant woody species in the riparian protection forests of the three gorges reservoir.

The establishment of riparian protection forests in the Three Gorges Reservoir (TGR) is an ideal measure to cope with the eco-environmental problems of the water-level fluctuation zone (WLFZ). Thus, the information for screening winter-flood-tolerant woody plant species is useful for the recovery and re-establishment of the riparian protection forests in the TGR WLFZ. Therefore, we discussed the possibilities of constructing and popularizing riparian protection forests in the TGR WLFZ from several aspects, including the woody plant species distribution in the WLFZ, the survival rate analyses of suitable candidate woody species under controlled flooding conditions, the survival rate investigation of some woody plant species planted in the TGR WLFZ, and the physiological responses of some woody plant species during the recovery stage after winter floods. The results of woody species investigation showed that most woody plant species that existed as annual seedlings in the TGR WLFZ are not suitable candidates for the riparian protection forests. However, arbor species (e.g., Salix matsudana, Populus×canadensis, Morus alba, Pterocarya stenoptera, Taxodium ascendens, and Metasequoia glyptostroboides) and shrub species (e.g., Salix variegata, Distylium chinensis, Lycium chinense, Myricaria laxiflora, and Rosa multiflora) might be considered suitable candidates for the riparian protection forests in the TGR WLFZ by survival rate analyses under controlled winter flooding conditions, and survival rate investigations of woody plant species planted in the TGR WLFZ, respectively. Physiological analyses showed that P.×canadensis, M. alba, L. chinense, and S. variegata could develop specific self-repairing mechanisms to stimulate biomass accumulation and carbohydrate synthesis via the increases in chlorophyll pigments and photosynthesis during recovery after winter floods. Our results suggested these woody plant species could endure the winter flooding stress and recover well, and be used as candidate for the construction of riparian protection forests in the TGR WLFZ.

Growth Responses of Ornamental Annual Seedlings Under Different Wavelengths of Red Light Provided by Light-emitting Diodes

Light-emitting diodes (LEDs) are of increasing interest in controlled environment plant production because of their increasing energy efficiency, long lifetime, and colors can be combined to elicit desirable plant responses. Red light (600–700 nm) is considered the most efficient wavelength for photosynthesis, but little research has compared growth responses under different wavelengths of red. We grew seedlings of impatiens (Impatiens walleriana), petunia (Petunia ×hybrida), tomato (Solanum lycopersicum), and marigold (Tagetes patula) or salvia (Salvia splendens) at 20 °C under six sole-source LED lighting treatments. In the first experiment, a photosynthetic photon flux (PPF) of 160 μmol·m−2·s–1 was provided for 18 h·d−1 by 10% blue (B; peak = 446 nm) and 10% green (G; peak = 516 nm) lights, with the remaining percentages consisting of orange (O; peak = 596 nm)–red (R; peak = 634 nm)–hyper red (HR; peak = 664 nm) of 20–30–30, 0–80–0, 0–60–20, 0–40–40, 0–20–60, and 0–0–80, respectively. There were no consistent effects of lighting treatment across species on any of the growth characteristics measured including leaf area, plant height, or shoot fresh weight. In a second experiment, seedlings were grown under two light intensities (low, 125 μmol·m−2·s–1 and high, 250 μmol·m−2·s–1) consisting of 10% B and 10% G light and the following percentages of R–HR: 0–80, 40–40, 80–0. Shoot fresh weight was similar in all light treatments, whereas shoot dry weight was often greater under the higher light intensity, especially under the 40–40 treatments. Leaf chlorophyll concentration under 40–40low, 80–0low, or both was often greater than that in plants under the high light treatments, indicating that plants acclimated to the lower light intensity to better use photons available for photosynthesis. We conclude that O, R, and HR light have generally similar effects on plant growth at the intensities tested when background G and B lights are provided and thus, selection of red LEDs for horticultural applications could be based on other factors such as economics and durability.

Relations between Cold Resistance and Composition and Content of Fatty Acids in Leaves of <i>Toona sinensis</i> from Different Provenances

The annual seedlings of ten Toona Sinensis provenances were selected for the study of the relationship between cold resistance and fatty acid composition and content of leaves. The results indicated that the fatty acid composition was the same among different provenances. The main ones were Dodecanoic acid, Hexadecanoic acid, (Z,Z)-9,12-Octadecadienoic acid, (Z,Z,Z)-9,12,15-Octadecatrienoic acid, Octadecanoic acid and Eicosanoic acid. But there were evident differences in fatty acid content and index of unsaturated fatty acid (IUFA) among different provenances. The content of unsaturated fatty acid and the IUFA was smaller in southern provenances of Xiapu of Fujian, Qianxinan of Guizhou and Dongkou of Hunan than those of the other provenances from north .The fatty acid content and IUFA were higher in provenances whose cold resistance were stronger. And the results showed that the fatty acid content and IUFA had a positive correlation with cold resistance of Toona sinensis.

Effects of <I>Rhizoctonia solani</I> toxin on defensive enzyme activity and MDA content in <I>Panax ginseng</I>

The annual ginseng seedlings were treated with three concentrations of Rhizoctonia solani toxin. The activity of the superoxide dismutase(SOD), catalase(CAT), peroxidase(POD) and malondialdehyde(MDA) content was measured after 0, 1, 3, 6, 12, 24 h treatment respectively. The results showed that the effects of Rhizoctonia solani crude toxin on defensive enzyme activity in ginseng seedling firstly increased and then decreased while MDA level remained high and kept rising.

JUDGMENT INDEX AND INHERITANCE OF CHILLING REQUIREMENT TO BREAK DORMANCY IN STRAWBERRY

Strawberry cropping systems adapted to each district from the southern to northern parts of Japan were developed together with advancing of studies on ecotype characteristics of various cultivars and techniques of controlling flower induction and dormancy, resulting in many cropping systems. The cultivars adapted to forcing culture have shallow dormancy and those adapted to semi-forcing culture and open culture have deep dormancy. This experiment was carried out to determine a judgment index for the chilling requirement to break dormancy and to investigate the inheritance of dormancy in strawberry plants. Runner plants of 8 varieties with various chilling requirements to break dormancy were exposed to varying degrees of chilling under 5°C. Runnering was a more effective index than the sudden extension of petiole length. Moreover, the cessation of continuous flowering under the minimum temperature of 15°C with a 16h photoperiod was used to judge the chilling requirements to break dormancy because the coefficient of variation of runnering was smaller than that of the sudden extension of petiole length and the cessation of continuous flowering. Chilling requirements and the cumulative hours of chilling to break dormancy of the runner plants were longest, while that of the over-wintered seedlings was longer than that of the annual seedlings. Runner plants of the selfed seedlings and the crosses between seedlings of a shallow dormancy variety 'Nyoho' and deep dormancy varieties 'Aiko' and 'Pajaro' were used to investigated the inheritance of dormancy. The degrees of dormancy of the crossed seedlings were tend aside of parents with shallow dormancy. It seems that the selection of strawberry plants with deep dormancy needed the use of many seedlings.

Contrasting Responses of Intermountain West Grasses to Soil Nitrogen

The mechanisms responsible for soil-N-mediated species replacement of native perennial grasses by the invasive annual grasses cheatgrass (Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae [L.] Nevski) on rangelands are not completely understood. In addition, the contributions of distinct forms of inorganic N (i.e., NH 4 + and NO 3 -) to these shifts in species composition are currently unclear. Consequently, we conducted a greenhouse experiment to test 2 hypotheses: 1) that low N availability reduces growth (root and shoot) and N allocation of invasive annual seedlings more than native perennial species, and 2) that seedling growth and N allocation of invasive annual grasses is more responsive than native perennial grasses when supplied with NO 3 - relative to NH 4 +. We grew seedlings of 2 annual grasses and the native perennial grasses bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love), and 4 populations of squirreltail (Elymus elymoides [Raf.] Swezey; E. multisetus [J.G. Smith] M.E. Jones) in separate pots and exposed them to treatments differing in N form and availability for 17 weeks. Unexpectedly, root and shoot growth of annual grasses were equal or greater than native perennial grasses under low N availability. Annual grasses took up more NO 3 - and allocated more growth and N to shoots than the perennial grasses (P < 0.05). Perennial grasses had significantly greater root:shoot dry mass ratios than the invasive annual grasses across treatments (P < 0.05). Invasive annual and native perennial grasses both had greater (P < 0.05) shoot and root mass and allocated more N to these structures when supplied with NO 3 - relative to NH 4 +. The ecological implications of these growth and N allocation patterns in response to N availability and form provide important clues regarding the specific traits responsible for differences in competitive ability between invasive annual and native perennial grasses on semiarid rangelands.

Contrasting responses of Intermountain West grasses to soil nitrogen

The mechanisms responsible for soil-N-mediated species replacement of native perennial grasses by the invasive annual grasses cheatgrass (Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae [L.] Nevski) on rangelands are not completely understood. In addition, the contributions of distinct forms of inorganic N (i.e., NH4+ and NO3-) to these shifts in species composition are currently unclear. Consequently, we conducted a greenhouse experiment to test 2 hypotheses: 1) that low N availability reduces growth (root and shoot) and N allocation of invasive annual seedlings more than native perennial species, and 2) that seedling growth and N allocation of invasive annual grasses is more responsive than native perennial grasses when supplied with NO3- relative to NH4+. We grew seedlings of 2 annual grasses and the native perennial grasses bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love), and 4 populations of squirreltail (Elymus elymoides [Raf.] Swezey; E. multisetus [J.G. Smith] M.E. Jones) in separate pots and exposed them to treatments differing in N form and availability for 17 weeks. Unexpectedly, root and shoot growth of annual grasses were equal or greater than native perennial grasses under low N availability. Annual grasses took up more NO3- and allocated more growth and N to shoots than the perennial grasses (P 0.05). Perennial grasses had significantly greater root:shoot dry mass ratios than the invasive annual grasses across treatments (P 0.05). Invasive annual and native perennial grasses both had greater (P 0.05) shoot and root mass and allocated more N to these structures when supplied with NO3- relative to NH4+. The ecological implications of these growth and N allocation patterns in response to N availability and form provide important clues regarding the specific traits responsible for differences in competitive ability between invasive annual and native perennial grasses on semiarid rangelands.

Competition among seedlings of perennial grasses, subterranean clover, white clover, and annual ryegrass in replacement series mixtures

Seedlings of 3 perennial grasses, Danthonia linkii Kunthcv. Bunderra, D. richardsonii Cashmore cv. Taranna(wallaby grasses), and Phalaris aquatica L. cv. Sirosa,were each grown in replacement series mixtures with seedlings ofTrifolium repens L. (white clover),Trifolium subterraneum L. var. brachycalycinum (Katzn.et Morley) Zorahy &amp; Heller cv. Clare (subterraneanclover), and Lolium rigidum L. (annual ryegrass). Plantswere sown 5 cm apart in boxes (45 by 29 by 20 cm) at a density of 307plants/m2. Maximum likelihood estimates were usedto derive parameters of a non-linear competition model using the dry matterweights of perennial grasses and competitors at 3 harvests, approximately 168,216, and 271 days after sowing. Intra-plant competition was examined inmonocultures of each species, grown at plant spacings of 2, 5, and 8 cm apartwith plants harvested at the above times.Competition occurred in all perennial grass–competitor mixtures, exceptin those of each perennial grass with white clover and thephalaris–subterranean clover mixture (Harvest 1) and those withD. richardsonii and phalaris grown with white clover(Harvest 2). For D. richardsonii (Harvests 1 and 2) andD. linkii (Harvest 1 only) grown with white clover andthe phalaris–subterranean clover (Harvest 1), the two species in themixture were not competing. In the phalaris–white clover mixture, eachspecies was equally competitive (Harvests 1 and 2). These differences incompetition and aggressiveness reflected differences in individual plantweights in monocultures where there was an effect (P &lt; 0.05) of species ondry matter weight per box, but no significant effect of plant spacing.These data indicated that for successful establishment,D. richardsonii and D. linkiishould not be sown in swards with either subterranean clover or white clover,or where populations of annual ryegrass seedlings are likely to be high.Phalaris was more compatible with both white clover and subterranean clover,but aggressively competed with by annual ryegrass.

Coexistence and interference between a native perennial grass and non-native annual grasses in California.

Little is known about the potential for coexistence between native and non-native plants after large-scale biological invasions. Using the example of native perennial bunchgrasses and non-native annual grasses in California grasslands, we sought to determine the effects of interference from non-native grasses on the different life stages of the native perennial bunchgrass Nassella pulchra. Further, we asked whether N. pulchra interferes with non-native annual grasses, and whether competition for water is an important component of these interspecific interactions in this water-limited system. In a series of field and greenhouse experiments employing neighbor removals and additions of water, we found that seedling recruitment of N. pulchra was strongly seed-limited. In both field and greenhouse, natural recruitment of N. pulchra seedlings from grassland soil was extremely low. In field plots where we added seeds, addition of water to field plots increased density of N. pulchra seedlings by 88% and increased total aboveground N. pulchra seedling biomass by almost 90%, suggesting that water was the primary limiting resource. In the greenhouse, simulated drought early in the growing season had a greater negative effect on the biomass of annual seedlings than on the seedlings of N. pulchra. In the field, presence of annuals reduced growth and seed production of all sizes of N. pulchra, and these effects did not decrease as N. pulchra individuals increased in size. These negative effects appeared to be due to competition for water, because N. pulchra plants showed less negative pre-dawn leaf water potentials when annual neighbors were removed. Also, simply adding water caused the same increases in aboveground biomass and seed production of N. pulchra plants as removing all annual neighbors. We found no evidence that established N. pulchra plants were able to suppress non-native annual grasses. Removing large N. pulchra individuals did not affect peak biomass per unit area of annuals. We conclude that effects of interference from nonnative annuals are important through all life stages of thenative perennial N. pulchra. Our results suggest that persistence of native bunchgrasses may be enhanced by greater mortality of annual than perennial seedlings during drought, and possibly by reduced competition for water in wet years because of increased resource availability.

Seedbank and Emerged Annual Weed Populations in Cornfields (Zea mays) in Colorado

Fifty irrigated cornfields in five eastern Colorado counties were sampled for their seedbanks and annual weed seedlings and mature populations between 1988 and 1992. Fourteen annual broadleaf species and seven annual grass species were identified in the 50 seedbanks sampled after the fields were tilled in the fall. Redroot pigweed and a mixture of green and yellow foxtail were the weed species encountered most, occurring in 90 and 54% of the fields, respectively. The single-plant populations of broadleaf and grass species in June and September were similar to those observed in the seedbanks. The number of weed species as seeds in the seedbank, June seedlings, and September plants per field ranged from zero to five grass species and zero to eight broadleaf species.

Seed Germination After Short-Duration Light Exposure: Implications for the Photo-Control of Weeds

A soil disturbance treatment often results in more annual weed seedlings emerging when conducted in light than when conducted in darkness, suggesting that seed germination in some species can be induced by short-duration light exposure (SDLE). We tested 70 species, most of them agricultural weeds, for their response to SDLE. Seeds were wet and cold stratified in darkness for 18 weeks before being subjected to light (12 hours per day), darkness, or 5 s light exposure (PAR: 210 mol m -2 s -1 ) followed by darkness. Of the 44 species for which meaningful comparison was possible, germination was stimulated by SDLE in 24, while the other 20 showed no or inconsistent responses. Eight of 11 plant families contained species that responded to SDLE. Extreme light sensitivity was shown equally by summer annual, winter annual and perennial species. There was no tendency for small-seeded species to be more light sensitive than largeseeded ones. Most species were represented by seeds from three populations and in many cases, large differences in percentage germination were found. Statements about a species' germination biology based on studies of a single population must therefore be interpreted with caution. The results suggest that a large number of weed species could potentially be 'photocontrolled'. However, the large variations in dormancy level between populations and the relatively small reduction in germination percentage in many cases imply that the effects of a strategy to photo-control, e.g. harrowing in darkness, can be unpredictable and sometimes small.

Vegetation recovery patterns in early volcanic succession

Permanently plots were monitored from 1983 to the present on Mount Usu after the eruptions of 1977–78 which destroyed the pre-eruption vegetation by 1–3 m thick accumulations of ash and pumice in order to clarify the processes and mechanisms of succession. Until now, 163 species were recorded in the summit area. Most of these species were derived from vegetative reproduction throughout the volcanic deposits. Vegetative reproduction plays a major role on increases in cover. Although long-distance seed-dispersal species could immigrate to the crater basin, their cover increase was slow. Seedbank species only established in gullies where the original topsoil was exposed by erosion. Most annuais were supplied by the seedbank in the original topsoil and woody species originated via immigration, suggesting that the source greatly determines the species composition of establishing vegetation. Annual seedlings showed low survival, while overwintering perennial seedlings steadily established. Ground surface movements strongly restricted increases in plant cover and the distance from source vegetation was the principal determinant of plant density. Due to differences in disturbance intensity, successional rates were higher in the stable substrates outside gullies and lower on the exposed original topsoil in some gullies.