Limited impact of irrigation on the phenology of Brachychiton megaphyllus: a deciduous shrub that flowers while leafless during the tropical dry season

2015 ◽  
Vol 31 (5) ◽  
pp. 459-467 ◽  
Author(s):  
Patricia J. Bate ◽  
Donald C. Franklin
Keyword(s):  
Soil Moisture ◽  
Reproductive Activity ◽  
Dry Season ◽  
Reproductive Phenology ◽  
Wet Season ◽  
Canopy Development ◽  
Seasonally Dry ◽  
Dry Tropics ◽  
Tap Root ◽  
Leaf Flush

Abstract:A suite of woody plants inhabiting the seasonally dry tropics flower while leafless during the dry season, raising intriguing questions about the role of moisture limitation in shaping their phenology. Brachychiton megaphyllus is one such species, a shrub of open forests and savannas in northern Australia. We documented leaf and reproductive phenology of 14 shrubs, and irrigated a further 15, to determine if soil moisture affected leafiness and reproductive activity. Brachychiton megaphyllus showed first flower buds shortly after the cessation of wet-season rains, and budded and flowered throughout the dry season. In some plants, leaf flush occurred prior to the first rains. Rates of fruit set and maturity were very low. Irrigation did not significantly influence leaf shoot or subsequent canopy development. Contrary to expectation, irrigation decreased the production of buds and flowers though it had no impact on the production of fruit, a response for which we suggest a number of hypotheses. Phenological responses to irrigation may have been limited because B. megaphyllus responds primarily to cues other than soil moisture and is buffered against seasonal drought by a large tap root. This suggests mechanisms by which flowering while leafless may occur in a range of species.

Diet selection by cattle grazing Stylosanthes-grass pastures in the seasonally dry tropics: effect of year, season, stylo species and botanical composition

1996 ◽  
Vol 36 (7) ◽  
pp. 781 ◽  
Author(s):  
DB Coates
Keyword(s):  
Cattle Grazing ◽  
Diet Selection ◽  
Dry Season ◽  
Major Influence ◽  
Botanical Composition ◽  
Wet Season ◽  
Seasonally Dry ◽  
Dietary Preference ◽  
Dry Tropics ◽  
Opportunity For Selection

The dietary preference of cattle grazing Stylosanthes-based pastures in the seasonally dry tropics of North Queensland was studied using faecal carbon ratios (S13C) to determine grass-legume proportions. Estimates were made at monthly intervals for several years in 1 experiment to determine the effect of year, season and botanical composition on dietary stylo proportions. In another experiment, the effect of stylo cultivars (Verano and Seca) on dietary preference was monitored for 17 months. Where pastures provided ample opportunity for selection, cattle showed a strong preference for grass in the early wet season and in the late dry season. The proportion of stylo in the diet increased during the wet season and reached peak proportions (as high as 80%) in the late wet season or early dry season. Dietary stylo proportions decreased as pastures dried off and as the stylo shed leaf or became more stemmy. The length of the wet season and the amount and distribution of rainfall had a major influence on the seasonal pattern of diet selection. Stylo rarely fell below 20% in the diet. On an annual basis, stylo accounted for about 45% of the diet which was appreciably higher than the proportion of stylo in the pasture. Dietary stylo proportions were higher on Seca-based pasture than on Verano-based pasture. The avoidance of stylo in the early wet season was less pronounced with Seca compared with Verano. Later in the season Seca was the dominant dietary component for a much longer period than Verano. The effect of botanical composition on dietary grass-legume proportions varied between and within years. Correlations between grass-legume proportions in the pasture and in the diet were highest in the late dry season and early wet season when preference for grass was strongest. At the end of the wet season when cattle preferred stylo, dietary stylo was not related to pasture stylo content except in a drought year. Averaged over the full year, dietary stylo content was significantly correlated with pasture stylo content in all years and the correlation was highest in a drought year when there was a high level of utilisation and less opportunity for selection. A simple model relating dietary stylo to pasture stylo was developed and is discussed.

Gut fill in cattle: effect of pasture quality on fasting losses

1985 ◽  
Vol 40 (3) ◽  
pp. 455-463 ◽  
Author(s):  
A. V. Goodchild
Keyword(s):  
Live Weight ◽  
Growing Season ◽  
Dry Season ◽  
The Other ◽  
Wet Season ◽  
Seasonally Dry ◽  
Dry Tropics ◽  
Pasture Quality ◽  
Grazing Cattle ◽  
Gut Fill

ABSTRACTAn abrupt fall in live weight of grazing cattle occurs at the beginning of the growing season in the seasonally dry tropics. In an experiment with grazing crossbred bulls in central Tanzania designed to monitor changes in gut fill, 16 were slaughtered in the dry season and 14 in the early wet season. Bulls were measured and weighed before, and weighed after, a 20-h fast and then slaughtered. Gut fill was measured and empty body weight (EBW) calculated.During fasting, the ratio gut fill/EBW fell from 0·291 to 0·217 in the dry season and from 0·207 to 0·119 in the wet season. Heart girth/EBW1/3 was 0·2577 and 0·2567 m/kg1/3 in the dry and wet seasons respectively.It was concluded that live weight before or after fasting is seriously affected by season and can give biased predictions of EBW change. On the other hand, heart girth is little affected by season and can be used to monitor relative increases or decreases of EBW within animals.

scholarly journals Seasonal changes in water quality and macrophytes and the impact of cattle on tropical floodplain waterholes

2012 ◽  
Vol 63 (9) ◽  
pp. 788 ◽  
Author(s):  
N. E. Pettit ◽  
T. D. Jardine ◽  
S. K. Hamilton ◽  
V. Sinnamon ◽  
D. Valdez ◽  
...  
Keyword(s):  
Water Quality ◽  
Seasonal Changes ◽  
Aquatic Macrophyte ◽  
Plant Cover ◽  
Critical Role ◽  
Dry Season ◽  
Nutrient Concentrations ◽  
Wet Season ◽  
Dry Tropics ◽  
The Impact

The present study indicates the critical role of hydrologic connectivity in floodplain waterholes in the wet–dry tropics of northern Australia. These waterbodies provide dry-season refugia for plants and animals, are a hotspot of productivity, and are a critical part in the subsistence economy of many remote Aboriginal communities. We examined seasonal changes in water quality and aquatic plant cover of floodplain waterholes, and related changes to variation of waterhole depth and visitation by livestock. The waterholes showed declining water quality through the dry season, which was exacerbated by more frequent cattle usage as conditions became progressively drier, which also increased turbidity and nutrient concentrations. Aquatic macrophyte biomass was highest in the early dry season, and declined as the dry season progressed. Remaining macrophytes were flushed out by the first wet-season flows, although they quickly re-establish later during the wet season. Waterholes of greater depth were more resistant to the effects of cattle disturbance, and seasonal flushing of the waterholes with wet-season flooding homogenised the water quality and increased plant cover of previously disparate waterholes. Therefore, maintaining high levels of connectivity between the river and its floodplain is vital for the persistence of these waterholes.

Fate of urea-nitrogen from cattle urine in a pasture-crop sequence in a seasonally dry tropical environment

1985 ◽  
Vol 36 (6) ◽  
pp. 809 ◽  
Author(s):  
I Vallis ◽  
DCI Peake ◽  
RK Jones ◽  
RL McCown
Keyword(s):  
Soil Depth ◽  
Soil Surface ◽  
Dry Season ◽  
Wet Season ◽  
Mineral N ◽  
Seasonally Dry ◽  
15N Urea ◽  
Almost All ◽  
Crop Sequence

The fate of urea-N in cattle urine applied during the dry season (in August) to the pasture phase of a pasture-crop sequence at Katherine, N.T., was investigated. Cattle urine labelled with 15N-urea was applied to three sets of microplots to measure the following parameters: (a) amount and distribution of 15N remaining in the microplots during the remainder of the dry season with 0, 0.5, 1.0 and 5.0 t ha-1 of pasture residues present initially; (b) the effect of placing the urine 5 cm below the soil surface on the amount of 15N remaining during the dry season; (c) uptake of 15N by the pasture during the early part of the wet season (October to December) and uptake by sorghum sown directly into the killed pasture in January. Residual 15N in the surface soil (0-15 cm) after the sorghum crop was also measured. Of the applied 15N, 26% was lost after 1 day, 32% after 7 days and 46% after 63 days. Losses were not affected by the amount of pasture residues on the microplots when the urine was applied. Almost all of the I5N remaining in the microplots was in the 0-7.5-cm layer of soil, and 65-75% of this was mineral N. The dry-season losses of 15N were presumably through volatilization of ammonia, because leaching was absent and no loss of 15N occurred when the urine was placed 5 cm below the soil surface. Pasture growth killed at the end of December contained 6.2% of the applied 15N, the sorghum crop recovered only a further 2.1%, and after harvest of the sorghum crop the 0-15.0-cm layer of soil contained 23%. Thus about half of the 15N remaining in the soil-plant system to the 15.0 cm soil depth at the end of the dry season disappeared during the following wet season, either as a gaseous loss or by leaching deeper into the soil.

Seasonal diet preferences of chital deer in the northern Queensland dry tropics, Australia

2020 ◽  
Vol 42 (3) ◽  
pp. 211
Author(s):  
Kurt Watter ◽  
Greg Baxter ◽  
Michael Brennan ◽  
Tony Pople ◽  
Peter Murray
Keyword(s):  
Dry Season ◽  
Wet Season ◽  
Variable Environment ◽  
Dry Tropics ◽  
Plant Groups ◽  
Axis Axis ◽  
Plant Group ◽  
Diet Preference ◽  
Dry Seasons

Chital deer (Axis axis) were introduced to the Burdekin dry tropics of north Queensland, Australia, in the late 1800s. Here rainfall and plant growth are highly seasonal and a nutritional bottleneck for grazing animals occurs annually before the wet season. This study describes the seasonal changes in diet and diet preference of chital in this seasonally-variable environment. Rumen samples were taken from 162 deer from two sites over the wet and dry seasons of two consecutive years and sorted macroscopically for identification. Relative seasonal availability of plant groups was estimated using step point sampling of areas grazed by chital. Chital alter their diet seasonally according to availability and plant phenology. Chital utilised 42 plant genera including grasses, forbs, subshrubs, shrubs, trees and litter. Grass consumption ranged from 53% of biomass intake during the dry season to 95% during the wet season. The predominance of grass in the wet season diet exceeded relative availability, indicating a strong preference. Although grass contributed more than half of the dry season diet it was the least preferred plant group, given availability, and the least actively growing. Shrubs were the preferred plant type in the dry season, and least subject to seasonal senescence. Composition and quantity of seasonal pastures vary markedly in north Queensland, and chital alter their diet by consuming those plants most actively growing. The increased dry season intake of non-grass forage appears to be a strategy to limit the detriment resulting from the progressive deterioration in the quality of grass.

Agronomic studies on soybean (Glycine max (L.) Merrill) in the dry season of the tropics. III. Effect of artificial photoperiod extension on phenology, growth and seed yield

1991 ◽  
Vol 42 (7) ◽  
pp. 1109 ◽  
Author(s):  
JD Mayers ◽  
RJ Lawn ◽  
DE Byth
Keyword(s):  
Seed Yield ◽  
Dry Season ◽  
Yield Potential ◽  
Wet Season ◽  
Canopy Development ◽  
North West ◽  
Precocious Flowering ◽  
Natural Photoperiod ◽  
Artificial Photoperiod ◽  
Delayed Flowering

Soybean cultivars developed for the tropical wet season performed poorly when grown in the dry season in north-west Australia. The proposition that breeding for later flowering time might enhance yields was tested by using artificial photoperiod extension (14 h day-1 for 28 days post-emergence) to delay flowering of field plots of agronomically improved genotypes. Canopy development and interception of photosynthetically active radiation (PAR), dry matter (DM) accumulation, seed yield and seed composition were examined, and compared with that from plants grown under natural photoperiods. Photoperiod extension delayed flowering an average 24 days, and maturity by an average 14.5 days, the effect being greater in the earlier-flowering genotypes. Differences among genotypes and photoperiod treatments in above-ground DM at the beginning and end of flowering were almost entirely due to the consequences of differences in phenology for cumulative PAR interception. DM at maturity was a simple linear function of crop duration (r2 = 0.95**), while seed yield exhibited an optimum-type response with DM ( R2 = 0.79**). The net consequence was that photoperiod extension increased DM production by an average 2.23 t ha-1 and seed yield by an average 0.65 t ha-1. The analyses suggested that a crop duration of c. 143-146 days would be needed to maximize seed yield under the agronomic conditions of the study, whereas the longest duration among the agronomically improved genotypes under natural photoperiod conditions was 136 days. It was concluded that breeding to constrain precocious flowering under short day conditions would be a viable strategy to improve the yield potential of soybean in the dry season.

Flowering and fruiting phenologies of seasonal and aseasonal neotropical forests: the role of annual changes in irradiance

2007 ◽  
Vol 23 (2) ◽  
pp. 231-251 ◽  
Author(s):  
Jess K. Zimmerman ◽  
S. Joseph Wright ◽  
O. Calderón ◽  
M. Aponte Pagan ◽  
S. Paton
Keyword(s):  
Soil Moisture ◽  
Seasonal Variation ◽  
Solar Irradiance ◽  
Seasonal Changes ◽  
Light Availability ◽  
Barro Colorado Island ◽  
Wet Season ◽  
Neotropical Forests ◽  
Seasonally Dry ◽  
Solar Declination

The seasonality of both rainfall and solar irradiance might influence the evolution of flowering and fruiting in tropical forests. In seasonally dry forests, to the degree that soil moisture limits plant productivity, community-wide peaks in reproduction are expected during the rainy season, with seedfall and germination timed to allow seedlings to become well established while soil moisture is available. Where soil moisture is never seasonally limiting, seasonal changes in light availability caused by periods of cloudiness or seasonally low zenithal sun angles should favour reproduction during seasons when irradiance levels are high. To evaluate these predictions, we documented the timing of flower and fruit fall for 10 and 15 y at El Verde, Puerto Rico, and Barro Colorado Island (BCI), Panama. At El Verde, rainfall is abundant year-round and solar declination largely determines seasonal variation in irradiance. At BCI, rainfall is abundant throughout the 8-mo wet season while drought develops and average solar irradiance increases by 40–50% over the 4-mo dry season. Seasonal variation in the number of species flowering and fruiting at both sites was generally consistent with the hypothesis that seasonal variation in irradiance limits the evolution of reproductive phenologies. Community-level metrics provided no evidence for a similar role for moisture availability at BCI. Seasonal variation in irradiance also strongly influenced seed development times at both sites. Thus, community-wide phenologies reveal a strong signature of seasonal changes in irradiance, even in those forests that exhibit some degree of seasonality in rainfall.

Soil water balance and evapotranspiration of irrigated cotton

1967 ◽  
Vol 69 (1) ◽  
pp. 95-101 ◽  
Author(s):  
W. R. Stern
Keyword(s):  
Soil Moisture ◽  
Water Balance ◽  
Soil Water ◽  
Balance Equation ◽  
Dry Season ◽  
Soil Water Balance ◽  
Wet Season ◽  
Water Balance Equation ◽  
Soil Moisture Storage ◽  
Moisture Storage

In a series of five irrigated cotton sowings (T2, T7, T9, T11, T14) evapotranspiration (Et) was determined for the period between October 1961 and October 1962 by observing frequently the changes in soil moisture storage, calculating through drainage, and solving for evapotranspiration in the water balance equation. Thus a water balance was obtained for each sowing extending over the entire crop.The average evapotranspiration in wet season sowings was of the order of 6·5 mm day−1 and in dry season sowings of the order of 4·5 mm day−1. The highest evapotranspiration values ranged between 10 and 12 mm day−1 in T2, T7 and T9 and between 7 and 9·5 mm day−1 in T11 and T14.

scholarly journals Measurements of soil respiration and simple models dependent on moisture and temperature for an Amazonian southwest tropical forest

2009 ◽  
Vol 6 (3) ◽  
pp. 6147-6177 ◽  
Author(s):  
F. B. Zanchi ◽  
H. R. da Rocha ◽  
H. C. de Freitas ◽  
B. Kruijt ◽  
M. J. Waterloo ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Soil Respiration ◽  
Soil Temperature ◽  
Field Measurements ◽  
Dry Season ◽  
Wet Season ◽  
Hourly Data ◽  
Fresh Litter ◽  
Favorable Conditions

Abstract. Soil respiration plays a significant role in the carbon cycle of Amazonian tropical forests, although in situ measurements have only been poorly reported and the dependence of soil moisture and soil temperature also weakly understood. This work investigates the temporal variability of soil respiration using field measurements, which also included soil moisture, soil temperature and litterfall, from April 2003 to January 2004, in a southwest Brazilian tropical rainforest near Ji-Paraná, Rondônia. The experimental design deployed five automatic (static, semi-opened) soil chambers connected to an infra-red CO2 gas analyzer. The mean half-hourly soil respiration showed a large scattering from 0.6 to 18.9 μmol CO2 m−2 s−1 and the average was 8.0±3.4 μmol CO2 m−2 s−1. Soil respiration varied seasonally, being lower in the dry season and higher in the wet season, which generally responded positively to the variation of soil moisture and temperature year round. The peak was reached in the dry-to-wet season transition (September), this coincided with increasing sunlight, evapotranspiration and ecosystem productivity. Litterfall processes contributed to meet very favorable conditions for biomass decomposition in early wet season, especially the fresh litter on the forest floor accumulated during the dry season. We attempted to fit three models with the data: the exponential Q10 model, the Reichstein model, and the log-soil moisture model. The models do not contradict the scattering of observations, but poorly explain the variance of the half-hourly data, which is improved when the lag-time days averaging is longer. The observations suggested an optimum range of soil moisture, between 0.115

Soil respiration in the seasonally dry tropics near Townsville, North-Queensland

Soil Research ◽  
1990 ◽  
Vol 28 (5) ◽  
pp. 737 ◽  
Author(s):  
JA Holt ◽  
MJ Hodgen ◽  
D Lamb
Keyword(s):  
Soil Respiration ◽  
Root Respiration ◽  
Respiratory Activity ◽  
Major Effect ◽  
Wet Season ◽  
Untreated Soil ◽  
Seasonally Dry ◽  
Respiration Rates ◽  
Dry Tropics ◽  
Total Soil Respiration

The contribution of root respiration to total soil respiration has been examined in an Australian tropical semi-arid woodland. Respiration rates were estimated by measuring CO2 released from untreated soil and from soil where roots had been severed and were extensively decomposed. The amount of C released as CO2 by soil respiration was estimated to be 3800 kg ha-1 year-1, and by root respiration to be 1500 kg C ha-l year-1. Soil moisture was found to have a major effect on soil respiration, with temperature being less significant. Consequently, most respiratory activity in the soil was confined to the relatively short wet season, with respiration rates being much lower during the dry season.

Sign in / Sign up

Export Citation Format

Share Document