Seasonality effect on the allelopathy of cerrado species

The Brazilian cerrado presents strong climate seasonality. During the dry season, plants may be exposed to stressful situations, such as a soil surface water deficit, that stimulate their chemical defenses. However, the seasonality effect on the production of allelopathic compounds of cerrado plant species is poorly understood. In this study, the phytotoxic activities of common native cerrado plants were evaluated during rainy and dry seasons. Crude leaves extracts (10% concentration: weight/volume, with dry leaves and distilled water) from eleven species were tested on lettuce and sesame germination. The negative effects on germination percentages, rates and informational entropies of the target species were higher when submitted to plant extracts from the dry season, where the germination rate was the most sensible parameter. The higher sensibility of lettuce and the germination rate parameter showed this difference. Only two exceptions had higher effects for rainy season extracts; one species showed higher negative effects on germination informational entropy of lettuce and another species on the germination rate of sesame. Thus, increases in the allelopathic activity were seen in the majority of the studied cerrado plant species during the dry season. These distinct responses to stressful situations in a complex environment such as the Brazilian cerrado may support the establishment and survival of some species.

Download Full-text

Survival of Colletotrichum gloeosporioides on Stylosanthes scabra cv. Fitzroy during the dry season

Australian Journal of Agricultural Research ◽

10.1071/ar9950959 ◽

1995 ◽

Vol 46 (5) ◽

pp. 959 ◽

Cited By ~ 4

Author(s):

RM Boland ◽

S Chakraborty ◽

JAG Irwin

Keyword(s):

Colletotrichum Gloeosporioides ◽

Soil Surface ◽

Dry Season ◽

Wet Season ◽

Intermittent Light ◽

Light Rain ◽

Large Numbers ◽

Assessment Period ◽

Dry Seasons ◽

Stylosanthes Scabra

Infected stems of the tropical pasture legume Stylosanthes scabra cv. Fitzroy were assessed over two consecutive dry seasons to determine if Colletotrichum gloeosporioides survived as conidia on lesions formed during the previous wet season or as hyphae within infected tissue. In the second season, infected stem pieces placed on the soil surface (debris) and in a 15�C incubator at the beginning of the dry season were assessed in addition to the material from living plants. Infective conidia were present in sufficient numbers to be detected in all but the initial sample in each season, and C. gloeosporioides could be isolated from lesions on plant tissue throughout both dry seasons. Conidium density on live stems was variable in the first season, where no rain fell until the onset of the wet season in mid-November. Conidia were present in similar densities on stems throughout the second dry season, when intermittent light rain fell during the assessment period. The mean density of conidia was significantly higher on live stems than on debris or stems stored at 15�C. Large numbers of conidia were produced on stem pieces from living plants and debris after incubation under conditions conducive to sporulation. Conidia were, therefore, present or could be rapidly produced to initiate an epidemic once favourable conditions for dispersal and infection occurred.

Download Full-text

Seed dormancy in four Tibetan Plateau Vicia species and characterization of physiological changes in response of seeds to environmental factors

Seed Science Research ◽

10.1017/s0960258513000019 ◽

2013 ◽

Vol 23 (2) ◽

pp. 133-140 ◽

Cited By ~ 14

Author(s):

Xiaowen Hu ◽

Tingshan Li ◽

Juan Wang ◽

Yanrong Wang ◽

Carol C. Baskin ◽

...

Keyword(s):

Tibetan Plateau ◽

Seed Dormancy ◽

Germination Rate ◽

Soil Surface ◽

The Tibetan Plateau ◽

Physical Dormancy ◽

High Germination ◽

One Year ◽

Hydrotime Model ◽

Aba Biosynthesis

AbstractAlthough seed dormancy of temperate legumes is well understood, less is known about it in species that grow in subalpine/alpine areas. This study investigated dormancy and germination of four Vicia species from the Tibetan Plateau. Fresh seeds of V. sativa were permeable to water, whereas those of V. angustifolia, V. amoena and V. unijuga had physical dormancy (PY). One year of dry storage increased the proportion of impermeable seeds in V. angustifolia, but showed no effect on seed coat permeability in V. amoena or V. unijuga. Seeds of all four species also had non-deep physiological dormancy (PD), which was especially apparent in the two annuals at a high germination temperature (20°C). After 1 year of storage, PD had been lost. The hydrotime model showed that fresh seeds obtained a significantly higher median water potential [Ψb(50)] than stored seeds, implying that PD prevents germination in winter for seeds dispersed without PY when water availability is limited. After 6 months on the soil surface in the field, a high proportion of permeable seeds remained ungerminated, further suggesting that PD plays a key role in preventing germination after dispersal. Addition of fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, evened-out the differences in germination between fresh and stored seeds, which points to the key role of ABA biosynthesis in maintaining dormancy. Further, fresh seeds were more sensitive to exogenous ABA than stored seeds, indicating that storage decreased embryo sensitivity to ABA. On the other hand, the gibberellic acid GA3 increased germination rate, which implies that embryo sensitivity to GA is also involved in seed dormancy regulation. This study showed that PY, PD or their combination (PY+PD) plays a key role in timing germination after dispersal, and that different intensities of dormancy occur among these four Vicia species from the Tibetan Plateau.

Download Full-text

Facilitation Effects of Haloxylon salicornicum Shrubs on Associated Understory Annuals, and a Modified “Stress-Gradient” Hypothesis for Droughty Times

Plants ◽

10.3390/plants9121726 ◽

2020 ◽

Vol 9 (12) ◽

pp. 1726

Author(s):

Nasr H. Gomaa ◽

Ahmad K. Hegazy ◽

Arafat Abdel Hamed Abdel Latef

Keyword(s):

Species Richness ◽

Water Availability ◽

Stress Gradient ◽

Growing Season ◽

Annual Species ◽

Negative Effects ◽

Growing Seasons ◽

Dry Seasons ◽

The Impact ◽

Haloxylon Salicornicum

Perennial shrub-annual plant interactions play key roles in desert regions influencing the structure and dynamics of plant communities there. In the present study, carried out in northwestern Saudi Arabia, we examined the effect of Haloxylon salicornicum shrubs on their associated understory annual species across four consecutive growing seasons, along with a record of the seasonal rainfall patterns. We measured density and species richness of all the annual species in permanent quadrats located beneath individual shrubs, as well as in the spaces between shrubs. During wet growing season H. salicornicum shrubs significantly enhanced the density and species richness of sub-canopy species, whereas in the relatively dry seasons they exerted negative effects on the associated species. In all growing seasons, the presence of shrubs was associated with enhanced soil properties, including increased organic carbon content, silt + clay, and levels of nutrients (N, P and K). Shrubs improved soil moisture content beneath their canopies in the wet growing season, while in the dry seasons they had negative effects on water availability. Differences in effects of H. salicornicum on understory plants between growing seasons seem due to the temporal changes in the impact of shrubs on water availability. Our results suggest the facilitative effects of shrubs on sub-canopy annuals in arid ecosystems may switch to negative effects with increasing drought stress. We discuss the study in light of recent refinements of the well-known “stress-gradient hypothesis”.

Download Full-text

Factors affecting Cyperus difformis seed germination and seedling emergence

Planta Daninha ◽

10.1590/s0100-83582013000400008 ◽

2013 ◽

Vol 31 (4) ◽

pp. 823-832 ◽

Cited By ~ 7

Author(s):

A. Derakhshan ◽

J. Gherekhloo

Keyword(s):

Seed Germination ◽

Integrated Management ◽

Germination Rate ◽

Seedling Emergence ◽

Management Strategies ◽

Soil Surface ◽

Weed Species ◽

Factors Affecting ◽

Cyperus Difformis ◽

Emergence Patterns

Specific knowledge about the dormancy, germination, and emergence patterns of weed species aids the development of integrated management strategies. Laboratory studies were conducted to determine the effect of several environmental factors on seed germination and seedling emergence of Cyperus difformis. Germination of freshly harvested seeds was inhibited by darkness; however, when seeds were subsequently transferred to complete light they germinated readily. Our results showed that 2 wk of cold stratification overcome the light requirement for germination. Seeds of C. difformis were able to germinate over a broad range of temperatures (25/15, 30/20, 35/25, and 40/30 ºC day/night). The response of germination rate to temperature was described as a non-linear function. Based on model outputs, the base, the optimum and the ceiling temperatures were estimated as 14.81, 37.72 and 45 ºC, respectively. A temperature of 120 ºC for a 5 min was required to inhibit 50% of maximum germination. The osmotic potential and salinity required for 50% inhibition of maximum germination were -0.47 MPa and 135.57 mM, respectively. High percentage of seed germination (89%) was observed at pH=6 and decreased to 12% at alkaline medium (pH 9) pH. Seeds sown on the soil surface gave the greatest percentage of seedling emergence, and no seedlings emerged from seeds buried in soil at depths of 1 cm.

Download Full-text

Chitosan coating on bean and maize seeds: release of agrochemical fungicide and post-storage condition

Journal of Seed Science ◽

10.1590/2317-1545v43254286 ◽

2021 ◽

Vol 43 ◽

Author(s):

Nancy Araceli Godínez-Garrido ◽

Juan Gabriel Ramírez-Pimentel ◽

Jorge Covarrubias-Prieto ◽

Francisco Cervantes-Ortiz ◽

Artemio Pérez-López ◽

...

Keyword(s):

Seed Germination ◽

Defense Mechanisms ◽

Germination Rate ◽

Storage Condition ◽

Germination Percentage ◽

Negative Effects ◽

Retention Capacity ◽

Chitosan Coating ◽

Maize Seeds ◽

Germination Speed

Abstract: Chitosan is a biopolymer obtained from deacetylation of chitin; it has multiple applications in agriculture as an antifungal, soil conditioner, inducer of defense mechanisms, fruits postharvest coating, leaves and seeds, among others. The objective in this research was to evaluate the effect of chitosan coatings mixed with fungicide (dithiocarbamate) on the germination and germination speed of bean and maize seeds in storage and to determine the retention capacity of the fungicide in the coated seeds under different times of imbibition. Two coating treatments at concentrations of 0.1 and 0.5% chitosan in water, two coatings treatments at 0.1 and 0.5% chitosan supplemented with 0.5% fungicide and a coating without chitosan using only 0.5% fungicide in water were used in bean and maize seed; and as control seeds imbibed in distilled water were used; after treatments, germination percentage and germination speed were determined, also fungicide release were determined at 0, 1, 2 and 6 h of imbibition, and the effect of storage time on germination and germination speed was determined at 30, 60, 90, 120, 150 and 180 days of storage at 4 °C and 45% relative humidity. The fungicide release effect was determined by inhibiting Fusarium oxysporum conidia germination. There were no negative effects of coatings on seed germination after storage. The treatment that provided both greater retention of the fungicidal agent and released it gradually, was 0.5% chitosan mixed with fungicide concentration. Chitosan coating seeds mixed with fungicide do not cause negative changes in seed germination or germination rate.

Download Full-text

Rising ecosystem water demand exacerbates the lengthening of tropical dry seasons

10.21203/rs.3.rs-218770/v1 ◽

2021 ◽

Author(s):

Hao Xu ◽

Xu Lian ◽

Ingrid Slette ◽

Hui Yang ◽

Yuan Zhang ◽

...

Keyword(s):

Water Demand ◽

Potential Evapotranspiration ◽

Central Africa ◽

Dry Season ◽

Land Area ◽

Key Factor ◽

Dry Seasons ◽

The Tropics ◽

Factor Governing

Abstract The timing and length of the dry season is a key factor governing ecosystem productivity and the carbon cycle of the tropics. Mounting evidence has suggested a lengthening of the dry season with ongoing climate change. However, this conclusion is largely based on changes in precipitation (P) compared to its long-term average (P ̅) and lacks consideration of the simultaneous changes in ecosystem water demand (measured by potential evapotranspiration, Ep, or actual evapotranspiration, E). Using several long-term (1979-2018) observational datasets, we compared changes in tropical dry season length (DSL) and timing (dry season arrival, DSA, and dry season end, DSE) among three common metrics used to define the dry season: P < P ̅, P < Ep, and P < E. We found that all three definitions show that dry seasons have lengthened in much of the tropics since 1979. Among the three definitions, P < E estimates the largest fraction (49.0%) of tropical land area likely experiencing longer dry seasons, followed by P < Ep (41.4%) and P < P ̅ (34.4%). The largest differences in multi-year mean DSL (> 120 days) among the three definitions occurred in the most arid and the most humid regions of the tropics. All definitions and datasets consistently showed longer dry seasons in southern Amazon (due to delayed DSE) and central Africa (due to both earlier DSA and delayed DSE). However, definitions that account for changing water demand estimated longer DSL extension over those two regions. These results indicate that warming-enhanced evapotranspiration exacerbates dry season lengthening and ecosystem water deficit. Thus, it is necessity to account for the evolving water demand of tropical ecosystems when characterizing changes in seasonal dry periods and ecosystem water deficits in an increasingly warmer and drier climate.

Download Full-text

Growth of Brahman cross heifers to 2 years of age in the dry tropics

Animal Production Science ◽

10.1071/an17305 ◽

2019 ◽

Vol 59 (1) ◽

pp. 148

Author(s):

Geoffry Fordyce ◽

Kerri Chandra

Keyword(s):

Body Condition ◽

Body Condition Score ◽

Dry Season ◽

Protein Supplementation ◽

Negative Effects ◽

Northern Forest ◽

Forest Region ◽

Supplementation Period ◽

Condition Score ◽

Height Gain

Growth of 1368 Brahman cross heifers from 6 year cohorts was monitored over the 2 years post-weaning in Australia’s northern forest, a low-animal-growth dry tropical environment. Heifers weighing 47–266 kg at weaning were managed in groups weighing <100 kg, 100–149 kg, 150–199 kg, and >199 kg during the post-weaning dry season. Weaner heifers were allocated to receive 300 g/day of a protein meal during the dry season or to basic nutritional management to sustain health. Heifers in three cohorts were allocated to first mating at 1 or 2 years of age, in four cohorts to vaccination against androstenedione, and in a small proportion of two cohorts to ovariectomy post-weaning. Growth was highly variable between seasons and years; average cohort liveweight by the start of 2-year-old mating was 256–319 kg. Heifer groups not receiving protein supplementation gained –16 to 21 kg (2 kg average) during 6-month dry seasons, and 49–131 kg (101 kg average) during wet seasons to reach an average of two-thirds of mature liveweight (445 kg) and 95% of mature hip height (1350 mm) by the start of mating at 2 years. Average body condition score (1–5) fluctuated by 1–2 units between seasons. Hip height gain continued, irrespective of season, commencing at ~0.60 mm/day at 6 months of age, and decelerating by ~0.00075 mm/day through to 2.5 years of age. Standard errors of predicted means across analyses were ~0.015 for average daily weight gains, 0.4 mm for average monthly height gain and 0.06 score units for average seasonal body condition score change. Post-weaning dry-season supplementation increased gains in liveweight, height and body condition score by an average of 0.1 kg/day, 0.1 mm/day and 0.5 units, respectively, during the supplementation period. Periods of poor nutrition or high nutritional demand secondary to reproduction suppressed daily gains in liveweight and hip height, at which times body condition score was also reduced. Subsequent to this, partial to full compensation occurred for all measures. Ovariectomy had negative effects on growth. Androstenedione vaccination had no effect on growth. The main conclusion is that heifer growth in Australia’s dry tropical northern forest region is highly variable between seasons and years, thus limiting significant proportions of some cohorts from reaching target weights for mating at 2 years of age, even after compensatory growth.

Download Full-text

Dormancy break in seeds of "quina" (Strychnos pseudoquina A. St.-Hil.)

Revista Brasileira de Plantas Medicinais ◽

10.1590/s1516-05722011000400017 ◽

2011 ◽

Vol 13 (4) ◽

pp. 507-511 ◽

Cited By ~ 1

Author(s):

J.M. Vasconcelos ◽

M.A. Rodrigues ◽

S.C. Vasconcelos Filho ◽

J.F. Sales ◽

F.G. Silva ◽

...

Keyword(s):

Sulfuric Acid ◽

Medicinal Plant ◽

Gibberellic Acid ◽

Plant Species ◽

Germination Percentage ◽

Boiling Water ◽

Medicinal Plant Species ◽

Distilled Water ◽

Brazilian Cerrado ◽

Germination Speed

"Quina" (Strychnos pseudoquina A. St. Hil) is a medicinal plant species from the Brazilian Cerrado. As its seeds show dormancy, they were subjected to the treatments pre-cooling at 5ºC during 7 days, pre-heating at 40ºC during 7 days, pre-soaking in sulfuric acid PA during 5 and 15 min, pre-soaking in boiling water during 5 and 15 min, pre-soaking in 100 and 200 ppm gibberellic acid during 48 h, pre-soaking in distilled water during 24 and 48 h, and mechanical scarification to break dormancy. Counts were daily conducted from the 2nd day after the experiment implementation until the germination stabilization at the 65th day. The germination speed index (GSI) and the germination percentage were evaluated. Germination rates above 96% were reached in seeds pre-soaked in water during 48 h and substrate moistened with water or KNO3.

Download Full-text

Effects of an accidental dry-season fire on the reproductive phenology of two Neotropical savanna shrubs

Brazilian Journal of Biology ◽

10.1590/1519-6984.174660 ◽

2017 ◽

Vol 78 (3) ◽

pp. 564-573 ◽

Cited By ~ 5

Author(s):

P. Dodonov ◽

C. B. Zanelli ◽

D. M. Silva-Matos

Keyword(s):

Seed Bank ◽

Woody Plant ◽

Fire Effects ◽

Plant Ecology ◽

Dry Season ◽

Reproductive Phenology ◽

Negative Effects ◽

Floral Buds ◽

Savanna Vegetation ◽

Eastern Brazil

Abstract Fire is a recurrent disturbance in savanna vegetation and savanna species are adapted to it. Even so, fire may affect various aspects of plant ecology, including phenology. We studied the effects of a spatially heterogeneous fire on the reproductive phenology of two dominant woody plant species, Miconia albicans (Melastomataceae) and Schefflera vinosa (Araliaceae), in a savanna area in South-eastern Brazil. The study site was partially burnt by a dry-season accidental fire in August 2006, and we monitored the phenolology of 30 burnt and 30 unburnt individuals of each species between September 2007 and September 2008. We used restricted randomizations to assess phenological differences between the burnt and unburnt individuals. Fire had negative effects on the phenology of M. albicans, with a smaller production of reproductive structures in general and of floral buds, total fruits, and ripe fruits in burnt plants. All unburnt but only 16% of the burnt M. albicans plants produced ripe fruits during the study. Fire effects on S. vinosa were smaller, but there was a greater production of floral buds and fruits (but not ripe fruits) by burnt plants; approximately 90% of the individuals of S. vinosa produced ripe fruits during the study, regardless of having been burnt or not. The differences between the two species may be related to S. vinosa’s faster growth and absence from the seed bank at the study site, whereas M. albicans grows more slowly and is dominant in the seed bank.

Download Full-text

Fruiting phenology and consumption by birds in Ficus calyptroceras (Miq.) Miq. (Moraceae)

Brazilian Journal of Biology ◽

10.1590/s1519-69842002000200018 ◽

2002 ◽

Vol 62 (2) ◽

pp. 339-346 ◽

Cited By ~ 24

Author(s):

J. RAGUSA-NETTO

Keyword(s):

Food Resource ◽

Bird Species ◽

Dry Season ◽

Dry Forest ◽

Wet Season ◽

Frugivorous Birds ◽

Fruiting Phenology ◽

Dry Seasons ◽

Seed Dispersers ◽

Wet And Dry Seasons

Figs are a remarkable food resource to frugivores, mainly in periods of general fruit scarcity. Ficus calyptroceras Miq. (Moraceae) is the only fig species in a type of dry forest in western Brazil. In this study I examined the fruiting pattern as well as fig consumption by birds in F. calyptroceras. Although rainfall was highly seasonal, fruiting was aseasonal, since the monthly proportion of fruiting trees ranged from 4% to 14% (N = 50 trees). I recorded 22 bird species feeding on figs. In the wet season 20 bird species ate figs, while in the dry season 13 did. Parrots were the most important consumers. This group removed 72% and 40% of the figs consumed in the wet and dry seasons, respectively. No bird species increases fig consumption from dry to wet season. However, a group of bird species assumed as seed dispersers largely increases fig consumption from wet to dry season, suggesting the importance of this resource in the period of fruit scarcity. The results of this study points out the remarkable role that F. calyptroceras plays to frugivorous birds, in such a dry forest, since its fruits were widely consumed and were available all year round.

Download Full-text