Reproductive Tillers Research Articles

Impacts of grazing and mowing on reproductive behaviors of Stipa grandis and Stipa krylovii in a semi-arid area

Disturbance can affect biomass allocation of plants, but can it influence plant reproductive behavior? To address this issue, we performed field plant community investigations and explored the reproductive behaviors of Stipa grandis and Stipa krylovii in response to grazing and mowing treatments at Maodeng pasture of Xilinguole League of Inner Mongolia, China during 2007–2009. The results showed that, with a similar niche width for the two plant species under mowing and grazing treatments, mowing significantly increased the ratio of ramet to genet number of S. krylovii and the carbon to nitrogen ratio of S. grandis, and grazing significantly decreased the ratio of vegetative to reproductive tiller biomass of S. grandis and increased the ratio of vegetative to reproductive tiller number of S. krylovii. Regression analysis showed that the significantly positive effect of root to shoot biomass ratio was stronger on the ratio of vegetative to reproductive tiller number of S. grandis than on that of S. krylovii. These results indicated that grazing and mowing influenced the reproductive manner and the process of sexual reproduction of S. grandis and S. krylovii.

Shifts of Sexual Reproductive and Vegetative Growth Allocation in <i>Stipa grandis</i> along a Climate Gradient in Inner Mongolia Steppe

Trade-off between vegetative growth and reproduction is an important plant adaptive strategy to environmental variability. The study investigated the Stipa grandis resource allocation and the relationship between its sexual reproduction and climate factors among three sites located along a typical environmental gradient in the Inner Mongolian Plateau. The results show that different climatic characteristics among three habitats cause the growth differentiation of S. grandis. S. grandis exhibits a prominent change on the resource allocation patterns. The number of reproductive tillers and panicles biomass allocation are significantly increased along the gradient of water availability and temperature whereas the number of vegetative tillers and root biomass allocation are reduced. The rate of the percentage increase is prominently reduced although the foliage allocation increased. It suggests that under the environments with drought and high temperature, S. grandis allocates more resources to sexual reproduction but reduces the investment in vegetative growth and asexual reproduction. Moreover, the amount of precipitation in April and May are significantly correlated with the sexual reproductive allocation of S. grandis.

Combining Glyphosate With Burning or Mowing Improves Control of Yellow Bluestem (Bothriochloa ischaemum)

The invasive yellow bluestem (Bothriochloa ischaemum [L.] Keng) threatens native biodiversity, and its control is of interest to land managers involved in restoration of invaded grasslands. We used single, double, and triple applications of glyphosate (2.125kg ai · ha‒1 · application‒1) over the course of one growing season in combinations at different timings (early, middle, late season) with and without a mechanical treatment of mowing or burning to determine the most effective control method. One year after treatment, burning and mowing prior to a mid-season single or double early, middle, and/or late season herbicide application resulted in a similar level of control of yellow bluestem relative to a triple herbicide application, all of which had greater control relative to herbicide treatment alone. Reproductive tiller density and visual obstruction increased 2yr after treatment with two herbicide treatments applied either early and middle season or early and late season, but it was prevented with burning and mowing prior to herbicide application. With the exception of three herbicide applications, combining burning or mowing with herbicide applications provided more effective control of yellow bluestem than any individual herbicide applications. Burning or mowing likely improves glyphosate effectiveness by altering the invasive grass structure so that plants are clear of standing dead and have shorter, active regrowth to enhance herbicide effectiveness. During restoration projects requiring control of invasive yellow bluestem, an effective management option is a combination of mechanical and chemical control.

Climate warming and precipitation redistribution modify tree–grass interactions and tree species establishment in a warm‐temperate savanna

Savanna tree-grass interactions may be particularly sensitive to climate change. Establishment of two tree canopy dominants, post oak (Quercus stellata) and eastern redcedar (Juniperus virginiana), grown with the dominant C4 perennial grass (Schizachyrium scoparium) in southern oak savanna of the United States were evaluated under four climatic scenarios for 6years. Tree-grass interactions were examined with and without warming (+1.5°C) in combination with a long-term mean rainfall treatment and a modified rainfall regime that redistributed 40% of summer rainfall to spring and fall, intensifying summer drought. The aim was to determine: (1) the relative growth response of these species, (2) potential shifts in the balance of tree-grass interactions, and (3) the trajectory of juniper encroachment into savannas, under these anticipated climatic conditions. Precipitation redistribution reduced relative growth rate (RGR) of trees grown with grass. Warming increased growth of J. virginiana and strongly reduced Q. stellata survival. Tiller numbers of S. scoparium plants were unaffected by warming, but the number of reproductive tillers was increasingly suppressed by intensified drought each year. Growth rates of J. virginiana and Q. stellata were suppressed by grass presence early, but in subsequent years were higher when grown with grass. Quercus stellata had overall reduced RGR, but enhanced survival when grown with grass, while survival of J. virginiana remained near 100% in all treatments. Once trees surpassed a threshold height of 1.1m, both tiller number and survival of S. scoparium plants were drastically reduced by the presence of J. virginiana, but not Q. stellata. Juniperus virginiana was the only savanna dominant in which neither survival nor final aboveground mass were adversely affected by the climate scenario of warming and intensified summer drought. These responses indicate that climate warming and altered precipitation patterns will further accelerate juniper encroachment and woody thickening in a warm-temperate oak savanna.

Study of Silicon Effects on Plant Growth and Resistance to Stem Borer in Rice

This research was conducted to evaluate silicon (Si) effects on the morphological characteristics and resistance to rice stem borer under greenhouse conditions at Sari Agricultural Sciences and Natural Resources University in 2009. The experiment was conducted as factorial in a complete randomized design (two factors) with three replications. The factors included four levels of silicon (Si) (Si0 = 0, Si1 = 5, Si2 = 10, Si3 = 20 g Si kg−1 soil) and three rice cultivars (Parto, Line 34, and Neda). The results showed Si fertilizer had a significant effect on percentage of white head, length of leaf, width of leaf, diameter of stem, and percentage of reproductive tiller. Also, increased stem Si increased the resistance to striped stem borer in the rice cultivars studied. The greatest resistance to striped stem borer was observed with the application of 20 g Si kg−1 soil. The application of Si at the rate of 20 g Si kg−1 soil significantly reduced the percentage of white head from 18.10% (without Si) to 0.11% (with 20 g Si kg−1 soil) in Parto cultivar.

Seed yield variation in plains rough fescue (Festuca hallii (Vasey) Piper) populations and its relation with phenotypic characteristics and environmental factors

AbstractPlains rough fescue (Festuca hallii (Vasey) Piper) is a dominant grass in the endangered Fescue Prairie of North America. Infrequent and unpredictable seed production presents a challenge for the use of this species in restoration and rangeland seeding. The objective of this study was to compare seed yield of different plains rough fescue populations and to determine the dependence of seed yield on phenotypic characteristics. Effect of weather conditions during the floral induction and initiation period of different years of the study was also compared. In 2007, a completely randomized field plot experiment was established from eleven populations of plains rough fescue at Swift Current, SK, Canada. In 2007, 2010 and 2011, individual plant seed yield, reproductive tillers, above‐ground biomass, plant height and crown diameter were measured, and plant vigour was scored. All measured variables differed significantly (P ≤ 0·05) among populations. Four populations were identified as having higher seed yield potential. Plants in these four populations also had characteristics of good plant vigour, taller stems, more reproductive tillers and greater biomass. Seed yield increased linearly with increasing plant height, crown diameter, above‐ground biomass and number of reproductive tillers (r2 ranged 0·17–0·67, P < 0·001), but number of reproductive tillers (r2 = 0·53–0·67, P < 0·001) was a better predictor for selection of lines with higher seed yield. Although seed yield varied among years, populations with higher seed yield tended to produce greater amounts of seed over the period of the study.

Tiller organization within the tussock grass Schizachyrium scoparium: a field assessment of competition–cooperation tradeoffs

Tussock grasses are characterized by a compact spatial arrangement of tillers that contributes to intense intratussock competition. This investigation was designed to directly assess the magnitude of competition among autonomous subunits of tillers within individual tussocks (i.e., integrated physiological units) to further define the mechanisms of tiller organization within this successful growth form. Experimentally constructed tussocks of Schizachyrium scoparium (Michx. Nash) were grown in the field in central Texas, USA, for 2 years with 1, 4, 8, or 12 autonomous subunits to span the range observed in naturally occurring local populations. Increasing numbers of subunits per tussock did not affect tiller density or the mean mass of individual vegetative or reproductive tillers, but it did intensify intratussock competition as evidenced by a large reduction in total tiller mass and number per subunit. This pattern of tiller organization is indicative of a division of labor within the tussock that is manifested as a tradeoff between competition among autonomous subunits and cooperation among tillers within these physiologically integrated subunits. We conclude that an increasing number of autonomous subunits associated with tussock basal expansion contributes to coarse-scale resource preemption and competitive ability, while resource sharing among tillers within subunits supports new tiller establishment and growth within this highly competitive microenvironment.

Characterization of tillers in deferred Piata palisade grass with different initial heights and nitrogen levels

This experiment was conducted to estimate the effects of nitrogen fertilization associated with the initial height of the Piata palisade grass on the number and structural characteristics of individual tillers after the deferment period. An area with Brachiaria brizantha cv. Piata measuring approximately 288 m2 was used. Combinations of levels of nitrogen fertilization (0, 75 and 150 kg/ha of nitrogen) and initial heights of the sward (low - 20 cm, medium - 30 cm and high - 40 cm) were evaluated. The experimental design was of completely randomized blocks in subdivided plots with three replications. The number of vegetative tillers, the stem length of the vegetative, reproductive and dead tillers, and the number of dead leaves of the reproductive and the dead tillers linearly increased with the elevation in the nitrogen level. The deferred Piata palisade grass with low initial height showed lower number of dead basal tillers, shorter length of stems and leaf blades in reproductive tillers and lower number of live and dead leaves in vegetative tillers in relation to the one managed with height considered medium and high. Nitrogen fertilization, in association with low initial height, provides the optimization of forage of Piata palisade grass in deferment conditions.

Taxonomic placement of Epichloë poae sp. nov. and horizontal dissemination to seedlings via conidia

A new Epichloe species distributed in Africa, Europe, North America and South America on host genera Bromus, Festuca, Lolium and Poa is described. Stromata, characteristic of the genus, frequently occurred on the reproductive tillers of Poa secunda subsp. juncifolia, but neither perithecia nor mature asci were observed. Conidiogenous cells and conidial characteristics were in the range of Epichloe typhina. Regions of the genes encoding β-tubulin (tub2) and translation elongation factor 1-α (tef1) were amplified and sequenced. Phylogenetic analyses of these sequences grouped the Poa secunda subsp. juncifolia endophyte into one group within a non-hybrid Epichloe species complex. On the basis of morphology, host range and evolutionary history we propose that this endophyte represents a new species of Epichloe. The name Epichloe poae is proposed for this endophyte. The infectivity of the conidia produced on plants was evaluated. In the first experiment, using conidia of Epichloe poae from leaves and endophyte-free seeds of Poa secunda subsp. juncifolia we show that when germinating seeds and developing seedlings of the plant were exposed to conidia, 28–57 % of seedlings became infected by the endophyte. The non-inoculated control plants showed no colonization by the endophyte. In the following spring after vernalization, colonized plants on flowering culms produced stromata with conidia. In the second experiment, using stromal conidia and the same procedure, 19–42 % of seedlings of Poa secunda subsp. juncifolia became colonized by the endophyte. Our results demonstrate that Epichloe poae may spread to uninfected grass hosts by conidia frequently formed on the surfaces of plant leaves as well as by conidia formed on stromata.

Steer and Plant Responses to Chemical Suppression of Seedhead Emergence in Toxic Endophyte‐Infected Tall Fescue

ABSTRACTChaparral herbicide has been shown to suppress seedhead emergence in tall fescue [Lolium arundinaceum (Schreb.) Darbysh] and potentially mitigate the effects of fescue toxicosis. A two‐year grazing experiment evaluated steers grazed on endophyte‐infected fescue–Kentucky bluegrass (Poa pratensis L.) pastures either treated or untreated with Chaparral herbicide to determine if seedhead suppression alleviates fescue toxicosis and increases average daily gain (ADG). Treatments were assigned to six, 3.0‐ha fescue‐bluegrass pastures in a randomized complete block design with three replications. Pastures were grazed with 48 steers (2.7 steers ha−1) from 9 Apr. to 1 July 2009 and 6 Apr. to 7 July 2010. Reproductive tiller densities in treated pastures were low in both years (<7 m−2) in comparison with untreated pastures (113 and 69 tillers m−2 in 2009 and 2010, respectively). Ergovaline and ergovalinine concentrations were three‐ to sixfold greater in seeds than in leaf blades and sheaths of vegetative and reproductive tillers. Crude protein, water soluble carbohydrates, and in vitro digestible dry matter concentrations of tillers declined over time at a greater rate in untreated than in treated pastures. Steers on treated pastures had greater (P < 0.01) ADG, lower (P < 0.10) rectal temperatures, and greater (P < 0.01) serum prolactin concentrations. Results indicated that Chaparral herbicide can suppress reproductive development of fescue to increase ADG and reduce the severity of toxicosis.

荒漠植物白刺属4个物种的生殖分配比较

The reproductive characteristics of four plant species of the genus Nitraria L.in Ulan Buh Desert,Nitraria tangutorum Bobr.,N.sibirica Pall.,N.roborowskii Kom.,N.sphaerocarpa Maxim.,were studied.The reproductive allocation characteristics of reproductive tillers were studied based on measurements of the reproductive modules during blooming.The results showed significant quantitative differences exist in some reproductive modules of the four species,such as ramet height,reproductive tiller length,reproductive tiller diameter,number of flowers per tiller,dry weight of cymes,and dry weight of branches and leaves.Of the four plant species,N.sphaerocarpa was the smallest based on the above measured characters.N.sibirica allocated 44.51% of its mass to reproduction while the other three species allocated less than 20%.Statistical analyses were performed on the reproductive characteristics of four plant species.A significant linear correlation was found between reproductive tiller length and ramet height(P0.05).The correlation coefficients were 0.8207,0.7408,0.8401,and 0.9144 for N.tangutorum,N.sibirica,N.roborowskii,and N.sphaerocarpa,respectively.The statistical significant test level of the curve fitness was 0.0067,0.0224,0.0046 and 0.0006 for N.tangutorum,N.sibirica,N.roborowskii,and N.sphaerocarpa,respectively.Also,the cymous dry weight was significantly correlated to ramet height.Specifically the absolute biomass allocated to the reproductive organs from the total biomass of the reproductive tillers increased as ramet height increased.The correlation coefficients of the two indices for N.tangutorum,N.sibirica,N.roborowskii,N.sphaerocarpa were 0.9283,0.6631,0.8350,and 0.8324,respectively.The fitted curves of the two indices for N.tangutorum and N.roborowskii followed a linear relationship,whereas that of N.sibirica followed a power law,and that of N.sphaerocarpa was quadratic.Third,the reproductive allocation of the four plant species decreased as the biomass of the reproductive tillers increased which represented the size of the plant.The fitted curves of the two indices for N.sibirica and N.roborowskii were linear,and those for N.tangutorum and N.sphaerocarpa were inverse.Plant size had a significantly negative correlation with the reproductive allocation.The characteristics of the reproductive allocation of four plant species of genus Nitraria reflect their strategies for the resource utilization and the trade-off with the clonal propagation and ecological adaptation to the environment.

Tillering and forage accumulation in Marandu grass under different grazing intensities

Studies of plant responses to defoliation are important to develop pasture management strategies. The objective of this study was to evaluate the population density of basal, aerial and reproductive tillers, tiller appearance and mortality rates, forage accumulation and sward structure in Marandu grass pastures under different grazing intensities. The experimental period was from January to June 2006, divided in three seasons: summer, autumn and winter. The pastures were continuously grazed using variable stocking rates. The grazing intensities corresponded to 15, 30 and 45 cm of sward height. The experiment was arranged in a complete randomized block design with three treatments and two replicates. The sward heights were measured twice a week. The response variables were: forage accumulation, forage mass and its morphological components; and population densities of basal (TPDb), aerial (TPDa) and reproductive (TPDr) tillers. The highest TPDb (P > 0.05) was recorded for the shortest sward pasture, and the highest TPDr (P<0.05) for the tallest sward pasture. Swards showed a tiller size/density compensation mechanism and, consequently, the forage accumulation was similar (P > 0.05) among the grazing intensities. Pasture with a sward height of 35 cm had 94% of sun light interception. The highest variations in forage accumulation and sward structure were more influenced by seasonal differences than by grazing intensities. Pastures of Marandu grass showed large flexibility in grazing management, which allowed it to be maintained at sward heights between 15 and 35 cm.

A new Epichloë species with interspecific hybrid origins from Poa pratensis ssp. pratensis in Liyang, China

We describe a new Epichloë species found in symbiosis with Poa pratensis ssp. pratensis in Liyang, China. Stromata characteristic of Epichloë spp. were present on some of the reproductive tillers of individual host grasses. Only three of the 98 stromata observed on field plants became orange and produced perithecia. Phylogenetic analyses based on sequences of tubB and tefA indicated that this Epichloë sp. was an interspecific hybrid related to both E. yangzii and members in the E. typhina complex clade (ETC). Allele-1 of tefA and tubB grouped in the E. bromicola/E. yangzii clade; allele-2 of these two genes clustered in a distinct subclade in the ETC. This is the first report of an Epichloë species that has interspecific hybrid origins. We propose the name Epichloë liyangensis Z. Wang, Y. Kang et H. Miao, sp. nov. for this species.

Preliminary study on the adaptation of wild Guinea grass (Panicum maximum) to different agro-climatic regions in Hambanthota District

Guinea grass (Panicum maximum Jacq.) was introduced to Sri Lanka in the 1820s for forage and has become naturalised in most ecological zones, ecosystems and habitats. This is generally called “Wild Guinea Grass” and has become common and valuable forage especially in the Southern area. Two main varieties are found: a coarse, broad leaved, hairy, stemmy, robust grass up to 3 meters high, known locally as Guinea-“A” and a finer, narrower leaved, leafy grass with smaller culms of 1-2 meters known as Guinea-“B”. Naturally, it now overruns road and railway sides, natural forests, crop plantations, natural grasslands and scrubland at low and mid elevations. Therefore, the objectives of this study were to compare the morphological and proximate properties of wild Guinea grass grown in Katuwana (IL1b) and Sooriyawewa (DL5) respectively intermediate and drought regions in Hambanthota District where it was used as sole cattle feed especially during drought periods. Random samples of Guinea grass were collected from three representative places of each from Katuwana and Sooriyawewa areas. Morphological parameters such as plant height, number of tillers, number of reproductive tillers, leaf width, leaf length, stem diameter, panicle length, panicle width, spikelet width (from base) and, root depth were investigated in the field itself. Proximate analysis was done for both post and pre blooming stages of P. maximum. It was revealed that height of P. maximum plants in Sooriyawewa area (231.33a ±16.0cm) were shorter than (P>0.05) that of Katuwana area (172.3b ± 17.5cm), may be attributed with the prolonged drought stress. Similarly, as water stress enhanced the tillering habit, numbers of tillers and reproductive tillers per plant were (27.67a ± 4.04 and 8.33 a ± 2.52 respectively) greater in (P>0.05) Sooriyawewa area as compared with Katuwana (7.333b ± 1.155 and 1.667b ± 0.577 respectively). When compared the inflorescence characters panicle length showed significantly higher value for Katuwana area (65.00a ± 12.00cm) as compared to Sooriyawewa (42.00b ± 5.00cm) while the panicle length and spikelet width (from base) were also slightly higher in Katuwana area. Dry matter (DM) content of Guinea samples was slightly higher in Sooriyawewa in both pre and post blooming stages. Furthermore, in crude protein (CP) content was also slightly higher in pre blooming stage in drought area (10.094% ± 0.624) than intermediate climate (8.54% ± 2.50) but it is opposite in post blooming stage as 5.429% ± 0.839 in drought area and 6.52% ± 1.75 in intermediate climatic area. The results revealed that drought stress could effect on phenotypical characters of wild Guinea grass therefore, yield could be affected but not the quality by means of dry matter and crude protein contents. However, further investigations should be carried out to find out whether those characters are genetically heritable or not.

Direct Evidence of Endophyte (Neotyphodium coenophialum) Genotype Effect on Growth and Vertical Transmission of Endophyte in Tall Fescue (Schedonorus phoenix Scop.) Under Water Stress

Tall fescue (Schedonorus phoenix Scop.) is resistant to abiotic and biotic stresses through a symbiotic relationship with Neotyphodium coenophialum. However, this endophyte has been considered detrimental since it produces toxic alkaloids to animals. It is vital to understand mutuality between these two to maximize positive impact of the endophyte on agri-ecosystem. Little research has been conducted on endophyte transmission mechanism in planta. To provide basic information related to endophyte transmission, an experiment was conducted to examine the effect of endophyte genotype and water stress on endophyte transmission by imposing soil moisture deficits at different stages of panicle development. There was water stress effect on endophyte frequency but not on concentration, whereas endophyte genotype significantly influenced endophyte concentration in pseudostem of tall fescue at boot stage. Reproductive tillers showed greater endophyte frequency and concentration. Endophyte frequency in florets or seeds depended on position within panicle. There was no drought effect on endophyte concentration, but showed the effect of endophyte genotype on endophyte concentration in florets and seeds. Overall endophyte concentration in seeds was higher. From this study, we may conclude that although water stress reduced endophyte frequency in vegetative tiller, water stress does not have effect on endophyte transmission, suggesting that drought is not an important factor controlling the endophyte transmission from plant to seed. Endophyte genotype and seed position in a panicle affected endophyte transmission, indicating that these two factors are involved in endophyte transmission and may determine seed transmission of endophyte in tall fescue.

Competition between Native Hawaiian Plants and the Invasive Grass Megathyrsus maximus: Implications of Functional Diversity for Ecological Restoration

Biodiversity loss is a global crisis, due primarily to habitat destruction and widespread nonnative invasions. Invasive grasses are particularly problematic in many tropical ecosystems, where they possess traits that promote their persistence and can drastically alter native plant communities. We explored the ecophysiological basis for restoring native Hawaiian dryland ecosystems currently dominated by the nonnative invasive grass Megathyrsus maximus (guinea grass) in a garden experiment. Three native species—Myoporum sandwicense (naio; canopy tree), Dodonaea viscosa (aalii; shrub), and Plumbago zeylanica (iliee; groundcover)—were grown with M. maximus at three levels of native functional diversity (one, two, or three species) while holding overall plant density constant. We tested which individual and functional combinations of native species were more productive and best suppressed M. maximus growth and reproduction. Megathyrsus maximus had 39–94% higher maximum photosynthetic rates (Amax) than native species and increasing native functional diversity did not affect M. maximus Amax. Aboveground, belowground, and total biomass of M. maximus varied with functional diversity, although intraspecific competition reduced growth as much as interspecific competition. Reproductive tiller production by M. maximus decreased significantly when planted with any of the native species and with increasing native functional diversity. These results indicate that high native functional diversity in an ecological restoration setting may aid in the control of a dominant invasive grass and the reintroduction of diverse native species. Recommendations for restoring degraded nonnative grasslands in Hawaii and throughout the tropics include selection of native species that are ecophysiologically competitive and have high functional diversity.

Número e peso de perfilhos no pasto de capim-braquiária sob lotação contínua

The experiment was conducted to study the relationship between the number and weight of tiller categories in Brachiaria decumbens cv. Basilisk pasture managed under continuous stocking with cattle. The pasture was managed with an average height of about 25 cm. Plants of four different heights (10, 20, 30 and 40 cm) were evaluated by means of the randomized block design with two replications. The number of vegetative tillers, both live and total, reduced linearly according to the plant height. The number of reproductive tillers increased linearly according to pasture plant height (from 8 to 84 tillers m-2 when comparing plants 10 to 40 cm high). Vegetative and reproductive tiller weight increased linearly according to pasture plant height. Vegetative tiller weight (0.316 g average) was lower than the reproductive tiller weight (0.401 g average). A linear and negative relationship was found between the number and weight of the vegetative tillers, whereas a linear and positive one was found for the reproductive tillers. There are fewer vegetative tillers, and a greater number of reproductive and dead tillers in places with tall plants. At the places with high B. decumbens plants, tillers are heavier.

Produção de sementes de quatro ecótipos de Paspalum nativos do Rio Grande do Sul

O objetivo neste trabalho foi estudar os componentes da produção e da produção de sementes de duas espécies de Paspalum. Foram avaliados dois ecótipos de Paspalum notatum (André da Rocha; e Bagual) e dois de Paspalum urvillei (André da Rocha; e Eldorado do Sul). O delineamento experimental foi completamente casualizado, num esquema fatorial (ecótipos x dias após o plantio), com cinco repetições aninhadas dentro dos dias após o plantio. Cada espécie foi analisada separadamente para determinação dos componentes da produção e produção de sementes, realizada por amostragens semanais entre 7/11/2006 e 31/3/2007. Foram avaliadas as seguintes variáveis: número de perfilhos vegetativos; número de perfilhos reprodutivos/m²; porcentagem de perfilhos férteis; número de racemos/m²; peso de mil sementes; número de sementes/ inflorescência; número de sementes/racemo; e rendimento de sementes/área. A produção de sementes de Paspalum é prejudicada pelo longo período de florescimento e pela capacidade de retenção das sementes na inflorescência. A produção de sementes difere entre ecótipos, uma vez que os valores médios foram de 47,17 kg/ha (Paspalum notatum André da Rocha), 61,01 kg/ha (Paspalum notatum Bagual), 30,60 kg/ha (Paspalum urvillei André da Rocha) e 47,95 kg/ha (Paspalum urvillei Eldorado do Sul). A produção de sementes dessas espécies é altamente influenciada pelo número de perfilhos reprodutivos, pela porcentagem de perfilhos férteis e pelo peso de mil sementes.

Effects of grazing management system on plant community structure and functioning in a semiarid steppe: scaling from species to community

Under the aim of searching for a more sustainable grazing management system, a mixed management system (grazing and haymaking alternate annually) was proposed and tested against traditional management system (used consistently either for grazing or haymaking) in the semiarid grassland of Inner Mongolia with a field manipulation experiment. The responses of aboveground biomass to the two grazing management systems were examined across different levels of organization (i.e., species, plant functional group, and community) and in five consecutive years from 2005 to 2009. The effects of the two systems on seed production potential of four dominant species (Leymus chinensis, Stipa grandis, Agropyron cristatum, Cleistogenes squarrosa) were also investigated. Our results demonstrate that, in the traditional system, aboveground biomass production across all the levels of organization was reduced by grazing. In mixed system, however, no significantly negative relationship between the biomass response and stocking rate was detected at all organization levels. Precipitation fluctuation had strong influence on biomass responses, and compared to the traditional system the slope of the biomass-precipitation relationship tends to be higher in the mixed system. This effect might be attributed to the more positive response of L. chinensis and A. cristatum to increase in precipitation. In the traditional system, both the ratio and the density of reproductive tillers of the grazing subplots were significantly reduced compared to the haymaking or ungrazed control plots. In the mixed system, there was no significant difference between the haymaking subplots and the ungrazed control plots, regardless of the grazing pressures imposed on the haymaking subplots in the previous growing season. Our findings suggest that the mixed system mitigates the sheep grazing-induced species shift and it tends to be more responsive to increasing precipitation as compared to the traditional system. Therefore, replacement of the traditional grazing strategy with the mixed system could provide an important contribution to sustainable land-use of the Inner Mongolia grasslands.

CARACTERÍSTICAS ESTRUTURAIS DE PERFILHOS VEGETATIVOS E REPRODUTIVOS EM PASTOS DIFERIDOS DE CAPIM-BRAQUIÁRIA

The aim of this work was to compare the structural characteristics of vegetative and reproductive tillers on Brachiaria decumbens cv. Basilisk pastures diferred for 73, 95 and 116 days. Randomized block design in a split plot scheme with three replications was used. The stockpiling period did not influence (P>0.10) the number of vegetative tillers (VT) but increased (P<0.10) the number of reproductive tillers (RT) (from 16 to 117 tillers/m2). On pastures diferred for up to 95 days, RT were heavier (P<0.05) than VT. Contrarily to VT, the relation between the number and weight of reproductive tillers was positive (P<0.10). A linear increase (P<0.01 and P<0.10) for tiller pseudostem length in relation to the diferring periods of the pasture was found. The number of living leaves (NLL) per tiller was not increased (P>0.10) by the deferring period. The RT revealed (P<0.05) a higher pseudostem length, higher number of dead leaves (NDL) and lower NLL when compared to VT. RT showed (P<0.05) higher percentages of stem and dead leaf as well as a lower percentage of living leaf (P<0.05) than VT. VT showed a better morphological composition than RT. The deferring period alters the structural characteristics and worsens the morphological composition of tillers on deferred Brachiaria decumbens cv. Basilisk pastures.KEYWORDS: Brachiaria decumbens, leaf number, morphological composition, tiller number, tiller weight.