High Soil Surface Temperatures Research Articles

Using mulching to reduce soil surface temperature to facilitate grass production

Ecosystems in semi-arid and arid Southern Africa experience high temperatures which translate to extremely hot soil surface temperatures. High soil surface temperatures lead to a decrease in seed germination and consequently less plant cover in these areas. To facilitate maintenance of optimum plant cover, soil surface temperature should be moderated with appropriate mitigation techniques. Temperature variations in low (kg.0.5 m−3) and high density (1 kg m−3) brush packing treatments were compared to bare soil. We also measured the grass productivity (g.m−2) against the effect of temperature in the three treatments. iButtons® were used to log soil surface temperature every hour for seven months. Daily and nightly temperatures of the hottest months were compared amongst the three treatments. Mid-day temperatures, corresponding to peak heat stress were also compared between the three treatments. There was a significant difference (p < 0.01) in soil surface temperature between the three treatments. The high density treatment was the most buffered against temperature variation, when compared to the bare soil. Grass production was generally higher in the high density treatment. Productivity can be increased by mulching the soil with brush packing as this will improve soil surface conditions such as moderating abrupt changes in temperatures to assist plant growth.

Effect of Biochar on Soil Temperature under High Soil Surface Temperature in Coal Mined Arid and Semiarid Regions

High soil surface temperature and loosened soil are major limiting factors of plant productivity in arid and semi-arid coal mining areas of China. Moreover, the extensive and illegitimate burning of crop residues is causing environmental pollution; whereas, these residues could be converted to biochar to benefit soil quality. In this study, the effect of wheat straw biochar (WSB) at rates of 0% (control, CK), 1% (low, LB), 2% (medium, MB) and 4% (high, HB) on soil temperature at different depths (5, 10, 15, and 20 cm) and moisture levels (10 and 20%) was investigated under high soil surface temperature of 50 °C and air humidity of 40%. Our data suggested that soil bulk density was inversely, and soil moisture was directly corelated with soil thermal parameters. Moreover, the increasing rate of WSB addition linearly decreased the soil thermal properties. The maximum decrease in soil bulk density at both moisture levels (10% and 20%) was measured in HB treatment compared to respective CKs. The highest decrease in soil thermal conductivity (59.8% and 24.7%) was found under HB treatment in comparison to respective controls (CK10% and CK20% moisture). The soil volumetric heat capacity was also strongly corelated with soil moisture content (r = 0.91). The WSB treatments displayed differential responses to soil temperature. Under 10% soil moisture, temperature of LB, MB and HB treatments was higher as compared to CK at 5–20 cm depth, and MB treated soil had the smallest increase in temperature. At the 15-cm depth, the MB treatment decreased the temperature by 0.93 °C as compared to the CK20%. Therefore, the effect of WSB on soil temperature was influenced by soil moisture content, soil depth and WSB application rates. It suggested that MB treatment could be a useful farming practice for mitigating soil temperature fluctuation.

Keratinophilic fungi: Specialized fungal communities in a desert ecosystem identified using cultured-based and Illumina sequencing approaches

Soil fungi in desert ecosystems are adapted to harsh environmental conditions such as high soil surface temperatures and limited organic matter and water. Given limited carbon inputs from plant material, heterotrophic fungi likely use unconventional sources of carbon in these systems. A baiting method was used to culture keratinophilic fungi from biocrust and rhizosphere soils in an arid grassland in Utah, USA. Fungi were baited using llama and sheep wool, horsehair, and snakeskin on two media, and pure cultures were identified using ITS and LSU rRNA sequences. One hundred-eighteen fungal colonies were grown, representing a total of 32 Operational Taxonomic Units (OTUs) at 97 % similarity. Cultures were dominated by the phylum Ascomycota (88 %) followed by Mucoromycota (8.6 %) and Basidiomycota (3.4 %). The orders Pleosporales, Eurotiales, Hypocreales, and Sordariales were commonly isolated, with the dominant taxa Alternaria (27 %), Aspergillus (22 %), Fusarium (11 %), and Chaetomium (8%). Thirty percent of the fungi isolated have the capacity to degrade keratin in vitro using a keratin azure assay, with Penicillium showing the highest degradation followed by Geomyces, Alternaria, and Fusarium. Although keratin degraders can be infectious, dermatophytes associated with skin infections were not isolated in culture or detected in Illumina sequencing. Illumina sequencing was used to determine general patterns in seasonal variation and habitat preference of keratinophiles. Alternaria was the most abundant genus with >70 % of the sequences. The combination of Illumina data with culture-dependent approaches facilitated the characterization of a specialized community and confirmed the low abundance of dermatophytes in this arid site.

Limited prospects for future alpine treeline advance in the Canadian Rocky Mountains.

Treeline advance has occurred throughout the twentieth century in mountainous regions around the world; however, local variation and temporal lags in responses to climate warming indicate that the upper limits of some treelines are not necessarily in climatic equilibrium. These observations suggest that factors other than climate are constraining tree establishment beyond existing treelines. Using a seed addition experiment, we tested the effects of seed availability, predation and microsite limitation on the establishment of two subalpine tree species (Picea engelmannii and Abies lasiocarpa) across four treelines in the Canadian Rocky Mountains. The effect of vegetation removal on seedling growth was also determined, and microclimate conditions were monitored. Establishment limitations observed in the field were placed in context with the effects of soil properties observed in a parallel experiment. The seed addition experiment revealed reduced establishment with increasing elevation, suggesting that although establishment within the treeline ecotone is at least partially seed limited, other constraints are more important beyond the current treeline. The effects of herbivory and microsite availability significantly reduced seedling establishment but were less influential beyond the treeline. Microclimate monitoring revealed that establishment was negatively related to growing season temperatures and positively related to the duration of winter snow cover, counter to the conventional expectation that establishment is limited by low temperatures. Overall, it appears that seedling establishment beyond treeline is predominantly constrained by a combination of high soil surface temperatures during the growing season, reduced winter snowpack and unfavourable soil properties. Our study supports the assertion that seedling establishment in alpine treeline ecotones is simultaneously limited by various climatic and nonclimatic drivers. Together, these factors may limit future treeline advance in the Canadian Rocky Mountains and should be considered when assessing the potential for treeline advance in alpine systems elsewhere.

Social life and sanitary risks: evolutionary and current ecological conditions determine waste management in leaf-cutting ants.

Adequate waste management is vital for the success of social life, because waste accumulation increases sanitary risks in dense societies. We explored why different leaf-cutting ants (LCA) species locate their waste in internal nest chambers or external piles, including ecological context and accounting for phylogenetic relations. We propose that waste location depends on whether the environmental conditions enhance or reduce the risk of infection. We obtained the geographical range, habitat and refuse location of LCA from published literature, and experimentally determined whether pathogens on ant waste survived to the high soil temperatures typical of xeric habitats. The habitat of the LCA determined waste location after phylogenetic correction: species with external waste piles mainly occur in xeric environments, whereas those with internal waste chambers mainly inhabit more humid habitats. The ancestral reconstruction suggests that dumping waste externally is less derived than digging waste nest chambers. Empirical results showed that high soil surface temperatures reduce pathogen prevalence from LCA waste. We proposed that LCA living in environments unfavourable for pathogens (i.e. xeric habitats) avoid digging costs by dumping the refuse above ground. Conversely, in environments suitable for pathogens, LCA species prevent the spread of diseases by storing waste underground, presumably, a behaviour that contributed to the colonization of humid habitats. These results highlight the adaptation of organisms to the hygienic challenges of social living, and illustrate how sanitary behaviours can result from a combination of evolutionary history and current environmental conditions.

Soil moisture and soil-litter mixing effects on surface litter decomposition: A controlled environment assessment

Recent studies suggest the long-standing discrepancy between measured and modeled leaf litter decomposition in drylands is, in part, the result of a unique combination of abiotic drivers that include high soil surface temperature and radiant energy levels and soil-litter mixing. Temperature and radiant energy effects on litter decomposition have been widely documented. However, under field conditions in drylands where soil-litter mixing occurs and accelerates decomposition, the mechanisms involved with soil-litter mixing effects are ambiguous. Potential mechanisms may include some combination of enhanced microbial colonization of litter, physical abrasion of litter surfaces, and buffering of litter and its associated decomposers from high temperatures and low moisture conditions. Here, we tested how soil-litter mixing and soil moisture interact to influence rates of litter decomposition in a controlled environment. Foliar litter of two plant species (a grass [Eragrostis lehmanniana] and a shrub [Prosopis velutina]) was incubated for 32 weeks in a factorial combination of soil-litter mixing (none, light, and complete) and soil water content (2, 4, 12% water-filled porosity) treatments. Phospholipid fatty acids (PLFAs) were quantified one week into the experiment to evaluate initial microbial colonization. A complementary incubation experiment with simulated rainfall pulses tested the buffering effects of soil-litter mixing on decomposition.Under the laboratory conditions of our experiments, the influence of soil-litter mixing was minimal and primarily confined to changes in PLFAs during the initial stages of decomposition in the constant soil moisture experiment and the oscillating soil moisture conditions of the rainfall pulse experiment. Soil-litter mixing effects on CO2 production, total phospholipid concentrations, and bacterial to total PLFA ratios were observed within the first week, but responses were fairly weak and varied with litter type and soil moisture treatment. Across the entire 32-week incubation experiment, soil moisture had a significant positive effect on mass loss, but soil-litter mixing did not. The lack of strong soil-litter mixing effects on decomposition under the moderate and relatively constant environmental conditions of this study is in contrast to results from field studies and suggests the importance of soil-litter mixing may be magnified when the fluctuations and extremes in temperature, radiant energy and moisture regimes common dryland field settings are in play.

Nitrogen losses from urea, UAN and LAN when applied to four different soils

Nitrogen transformations and losses from three nitrogenous fertilizers, urea, urea ammonium nitrate (UAN) and limestone ammonium nitrate (LAN), when applied to four South African soils, were compared in a laboratory study. The highest losses on all these soils were experienced when urea was applied, followed by UAN solution and then LAN. It also appears that a relationship exists between N volatilization and the change in pH of the soil. The lower the buffer capacity or clay content of the soil, the greater the pH change and the nitrogen losses. In the case of LAN, the pH did not rise to above 7 in any of the four soils and no ammonia volatilization was detected. Explanations for the nitrogen losses are proposed and supported with chemical reactions. High soil surface temperatures may result in accelerated mass flow and ammonia volatilization. On the other hand, it was shown that nitrites or nitrous acid promoted denitrification, especially when LAN was applied.

Warming and the dependence of limber pine (Pinus flexilis) establishment on summer soil moisture within and above its current elevation range

Continued changes in climate are projected to alter the geographic distributions of plant species, in part by affecting where individuals can establish from seed. We tested the hypothesis that warming promotes uphill redistribution of subalpine tree populations by reducing cold limitation at high elevation and enhancing drought stress at low elevation. We seeded limber pine (Pinus flexilis) into plots with combinations of infrared heating and water addition treatments, at sites positioned in lower subalpine forest, the treeline ecotone, and alpine tundra. In 2010, first-year seedlings were assessed for physiological performance and survival over the snow-free growing season. Seedlings emerged in midsummer, about 5-8 weeks after snowmelt. Low temperature was not observed to limit seedling photosynthesis or respiration between emergence and October, and thus experimental warming did not appear to reduce cold limitation at high elevation. Instead, gas exchange and water potential from all sites indicated a prevailing effect of summer moisture stress on photosynthesis and carbon balance. Infrared heaters raised soil growing degree days (base 5 °C, p < 0.001) and August-September mean soil temperature (p < 0.001). Despite marked differences in vegetation cover and meteorological conditions across sites, volumetric soil moisture content (θ) at 5-10 cm below 0.16 and 0.08 m(3) m(-3) consistently corresponded with moderate and severe indications of drought stress in midday stem water potential, stomatal conductance, photosynthesis, and respiration. Seedling survival was greater in watered plots than in heated plots (p = 0.01), and negatively related to soil growing degree days and duration of exposure to θ < 0.08 m(3) m(-3) in a stepwise linear regression model (p < 0.0001). We concluded that seasonal moisture stress and high soil surface temperature imposed a strong limitation to limber pine seedling establishment across a broad elevation gradient, including at treeline, and that these limitations are likely to be enhanced by further climate warming.

Comparing measurements methods of carbon dioxide fluxes in a soil sequence under land use and cover change in North Eastern Spain

Carbon dioxide measurements from soil surface may indicate the potential for soil respiration and carbon consumption according to microbial biomass and root activity. These processes may be influenced by land use and cover change, and abandonment especially in the upper soil organic layer. Seven environments from cultivation to late abandonment, with the same soil type classified as Lithic Xerorthent, were tested to ascertain the respiration capacity according to the current use and cover, and to establish the ability to preserve and eventually increase the organic matter pools after abandonment. Given the importance of carbon dioxide measurements at soil surface, a comparison between the classic soda lime method (SL) and a rapid method based on infrared sensor analyzer (IR) was performed from autumn 2008 to autumn 2009 in the field. The field measurements of CO2 proved significant correlations between the values from the two techniques under the same natural conditions and along the period of observation. However, the values of CO2 measured by the soda lime method were always higher than those obtained by the infrared analyzer. This pattern was attributed to the difference in time of measurement, larger in the former method, and type of measurement technique. Despite that the trend of measured CO2 values was rather similar along the year. On average, the highest values of CO2 emission in the field were recorded in the warmest periods of the year and with soil surface moisture not lower than 3% independently on the method used. High soil surface temperature with soil moisture below 3% decreased drastically the CO2 production from the dry soil. The cultivated environments and soil under forests have resulted higher CO2 producers than abandoned soils depending on the age of abandonment, climatic conditions, and within abandonment perturbations. Those abandoned soils preserved by perturbations like wildfire showed a higher potential for accumulating organic carbon, as indicated by the lowest emission of CO2 with respect to SOC content, during the period of observation. Results demonstrated the reliability of the methods used to evaluate the soil carbon dioxide production capacity and allowed to classify through environments with increasing potential for carbon sequestration. The classification was rather similar by using both methods indicating a higher susceptibility to carbon loss in the following order: soil under Vines (V)>under Olives (O)>under Pine trees (PI)>under Cork Trees (S)>under Pasture (PR)>under Cistus scrub (MC)>under Erica scrub (MB) by using the SL method and V>O>PI>S>MC>MB>PR by using the IR method. Indications about the need of management of abandoned areas were also considered in order to recover the landscape heterogeneity.

Soil-living nematodes of a savanna community in Botswana: A preliminary report

A quantitative study was made of the soil-living nematodes in a natural savanna community located on the University of Botswana campus. Preliminary identifications produced 38 species in 33 genera, 14 families and seven orders. Nematode densities were measured beneath the grasses Panicum maximum, Schmidtia pappophoroides and Eragrostis sp., and were respectively 6,360,125, 2,388,250 and 2,039,375 m −2 in the top 100 mm of soil. These relatively high densities compared with those recorded in similar studies elsewhere in Africa probably reflect the high productivity of these grasses. P. maximum, in particular, is a very productive perennial which favors shaded, relatively moist environments. Unlike most soil habitats, the soil at 50–100 mm depth had as many nematodes as at 0–50 mm depth. Measurement of soil moisture content showed a greater percentage of soil moisture at 50–100 mm which, combined with high soil surface temperatures, may explain the relatively high densities at the greater depth. A search of the literature for other records of soil-living nematodes from Botswana located 12 formal and informal records which, combined with the species identified in the present study, produced a list of 82 species reported from Botswana.

Cnemodus hirtipesBlatchley andC. mavortius(Say) (Hemiptera: Lygaeoidea: Rhyparochromidae) in Fallen Pine Cones, with Consideration of the Biological Significance of Cone Occupancy

Nymphs of all instars and adults of a lygaeoid bug, the myodochine rhyparochromid Cnemodus mavortius (Say), were collected from fallen pine cones, mainly those of longleaf pine (Pinus palustris Mill.; Pinaceae), at 22 sites in the southeastern United States (Alabama, Georgia, North Carolina, South Carolina). Nymphs and adults of C. hirtipes Blatchley were found in fallen pine cones at eight sites in Florida. Nymphs (occasionally >20/cone; n = 5) of all instars, exuviae, and teneral nymphs and adults were observed in cones, suggesting more than incidental and ephemeral occupancy by species of Cnemodus. The bugs might use the labium to transport seeds of pine and other plants to the shelter of cones before they begin to feed, obtain nutrition from pine seeds that remain in fallen cones, or feed on seeds of grasses or other plants that lodge in cones. Fallen cones could be used for overwintering and oviposition but might be most important for allowing the bugs to minimize desiccation in xeric habitats characterized by high soil-surface temperatures, especially if nymphs cluster in cones. Other heteropteran species were infrequent inhabitants of fallen pine cones: the rhyparochromids Eremocoris setosus Blatchley (Florida, Georgia, South Carolina), Neopamera bilobata (Say) (Florida), and Ozophora trinotata Barber (Florida); and the largid Arhaphe carolina Herrich-Schaeffer (South Carolina). We also record C. mavortius from crowns of bunchgrasses in southern states (Georgia, North Carolina, Oklahoma, South Carolina, Texas) and C. hirtipes from bunchgrasses in Florida.

Nitrogen isotope composition of inorganic soil nitrogen and associated vegetation under a sea bird colony on the Hatana islands, Rotuma Group, Fiji

Concentration together with the stable isotope composition (δ15N) of both ammonium- and nitrate-nitrogen were conducted for sedentary soils under the piscivorous seabird colony developed on Quaternary basaltic ejecta from the Hatana islands, Fiji, south Pacific. Higher inorganic nitrogen content (up to 2,420 mg-N/kg dry soil) was observed for soils under dense forest vegetation, relative to a lower nitrogen content for soils under sparse grass vegetation (270 mg-N/kg dry soil), reflecting the difference in the mulching effects of vegetative cover for leaching of nitrogen by meteoric water. Active mineralization of uric acid in the bird excreta followed by partial loss due to volatilization of ammonia, nitrification and denitrification were indicated by unique δ15N values of the inorganic nitrogen as high as +50‰. This unique process was facilitated by high soil surface temperature (24 to 32°C) in combination with the humid tropical climate (annual rainfall: 3560 mm). Distinct isotopic composition of the foliar nitrogen (δ15N = +13.6 to +36.7‰) indicated acquisition of the inorganic nitrogen derived from bird excreta in soils.

Directional growth of a clonal bromeliad species in response to spatial habitat heterogeneity

Habitat selection by directional growth of plants has previously been investigated but field evidence for this phenomenon is extremely scarce. In this study we demonstrate directional clonal growth in Aechmea nudicaulis, a monocarpic, perennial bromeliad native to spatially heterogeneous sandy coastal plains (restinga) in Brazil. This habitat is characterized by a matrix of bare sand with interspersed vegetation islands. Due to very high soil surface temperatures and other stress factors such as drought, A. nudicauliscan only germinate inside vegetation islands. Nevertheless, this species is very common on bare sand. In this study we tested the hypothesis that clonal fragments occurring at the border and inside vegetation islands show habitat selection by growing preferentially towards the bare sand habitat (i.e. away from the center of vegetation islands).

Microhabitat availability and seedling recruitment ofLobelia urens: a rare plant species at its geographical limit

AbstractIn Britain,Lobelia urens(L.) (the heath lobelia) occurs in rough grassland, is rare and only found in southern England, where it is at the northern limit of its range. Emergence and survival ofL. urenswas investigated at six locations in two geographically distinct sites experiencing spring, autumn or no grazing in two consecutive years. Four factors were evaluated qualitatively, as a means of characterizing microhabitats for germination and survival: all permutations of higher plant cover, bryophytes, plant litter and surface depressions. The potential effect of adjacent plants on recruitment was also assessed using the nearest neighbour distance (NND). Grazing created depressions, removed plant litter and increased the proportion of sites with higher plant cover. It also resulted in a more open sward with higher NNDs. None of these changes stimulated recruitment. Instead, small increases in the frequency of some rare or very rare microhabitat types were vital in making grazed rough grassland more suitable for emergence. Reduced litter loads and a greater quantity of moss were two key responses. Overall, survival ofL. urenswas less than 1% and was particularly favoured by moss and an increase in NNDs. Shading from higher plants, with or without plant litter, decreased emergence, but the precise role of litter was complex and most probably related to its quantity. In an experimental seed bed, only empty depressions favoured emergence. The microhabitat relationships ofL. urenswere unusually consistent among locations and consecutive years.L. urensrequires high soil surface temperatures but also adequate water for large scale recruitment, and such conditions are encouraged by grazing. The particular problems of experimental design and statistical analysis of data from recruitment experiments are also discussed.

Tolerance to soil temperatures experienced during and after the passage of fire in seeds of Acacia karroo, A. tortilis and Chromolaena odorata: a laboratory study

The effects of high daily soil surface temperatures (50° and 70 °C) of various durations (1, 2, 3, 4 weeks), and temperatures experienced in the soil during fires (100°, 150°, 200 °C) of various durations (1, 3, 5 minutes) on seed viability, germination and early seedling growth of Acacia karroo , A . tortilis and Chromolaena odorata were determined in laboratory simulations'. Seed viability declined with increasing duration of exposure at 50 °C in A . tortilis and C. odorata , but oniy slightly in A , karroo , which was stimulated to germinate. At 70 °C seed viability declined with length of exposure in all species. Seeds of C. odorata did not survive any exposure to temperatures of 100 °C or above. The acacias survived temperatures of 100° and 150 °C, with a few A . karroo surviving 200 °C ( A . karroo to high soil temperatures experienced during and after the passage of fire may be a factor that contributes to its ability to encroach in disturbed areas. The sensitivity of C . odorata seeds to high temperatures may be useful in the control of this aggressive alien invasive plant.

Grasshopper (Orthoptera: Acrididae) Foraging on Grasshopper Feces: Observational and Rubidium-Labeling Studies

Many grasshoppers are omnivores that feed on a variety of plants as well as on animal tissue and animal excrement. We conducted behavioral observations and rubidium chloride (RbCl) labeling studies to assess whether grasshoppers also feed on grasshopper feces, thus providing the potential for horizontal disease transmission. We observed 10 species of Acrididae feeding on grasshopper fecal pellets in 3 southwestern Montana rangeland communities during the summers of 1992 and 1994. Adults of both sexes and nymphs as young as 1st instars fed on the grasshopper feces soon after we placed the feces on the soil surface. The feeders included several species that are common pests: Aulocara elliotti Thomas, Ageneotettix deorum (Scudder), and Melanoplus sanguinipes (F.). Although activity tended to decline over the 2-h sampling period, grasshoppers continued to feed on feces even when high soil surface temperatures required them to undertake behaviors that alleviate thermal stress. There was also circumstantial evidence that grasshoppers completely consumed some of the 0.1-g samples within 24 h. We observed elevated levels of rubidium in the tissues of A. elliotti and M. sanguinipes after we gave them access to feces labeled with Rb in field cages. We discuss the implications of these findings for grasshopper biological control and diet studies.

High temperature and drought stress effects on survival of Pinus ponderosa seedlings

We studied the effects of high temperature and drought on the survival, growth and water relations of seedlings of Pinus ponderosa (Dougl.) Lawson, one of few coniferous tree species that can successfully colonize drought-prone sites with high soil surface temperatures. Temperature profiles were measured with 0.07-mm thermocouples in a sparse ponderosa pine forest in northern Idaho. The soil surface and the adjacent 5 mm of air reached maximum temperatures exceeding 75 degrees C, well above the lethal temperature threshold for most plants. Air temperatures 50 mm above the soil surface (seedling needle height) rarely exceeded 45 degrees C. Pinus ponderosa seedlings that survived maintained basal stem temperatures as much as 15 degrees C lower than the surrounding air. The apparent threshold temperature at the seedling stem surface resulting in death was approximately 63 degrees C for less than 1 min. No correlation between seedling mortality and needle temperature was found, although some needles reached temperatures as high as 60 degrees C for periods of </= 1 min. Surviving seedlings had significantly higher stomatal conductance than seedlings that did not survive until fall. Transpiration rates, calculated from measured needle temperatures, stomatal conductance and evaporative demand, were high (up to 16.7 mmol m(-2) s(-1)), indicating that water transport through seedling stems may have acted as a heat transfer mechanism, cooling the stem below the lethal threshold temperature. Heat exchange calculations showed that rapid water flow through seedling stems can absorb sufficient energy to reduce stem temperature by 30 degrees C during peak sunlight hours.

Windbreak-crop interactions in the Sahel. 2. Growth response of millet in shelter

Plant growth behind a windbreak varies considerably with changing macroclimate, species and windbreak type. This variability can often be explained in terms of the microclimate in the lee of a windbreak. This paper describes an investigation into the modification of microclimate by a windbreak and the influence of the windbreak on growth of a millet crop in its lee in Niger, West Africa. Growth of millet ( Pennisetum typhoides) was reduced by shelter at the start of the season because of high soil surface temperatures, caused by reduced boundary-layer conductance, which caused a delay in germination and emergence. Towards the middle of the season, leaf temperatures were in general lower than at the start of the season, and higher temperatures in shelter increased the rate of leaf expansion and senescence above that in the unsheltered parts of the field. At the start of the season, air and leaf temperatures in shelter increased whereas ambient vapour pressures remained relatively constant. This led to higher vapour pressure deficits at the surface of the leaves ( D 1) in shelter than in the unsheltered crop. In the middle of the growing season, vapour pressures increased in shelter so as to reduce D 1 and this increased the solar radiation conversion coefficient, probably because of increases in stomatal conductance. There was more transpiration in shelter as a result of both larger leaf area index in the middle and at the end of the growing season and higher transpiration per unit leaf area relative to the unsheltered crop. Transpiration per unit leaf area was higher in shelter because of higher leaf temperatures and stomatal conductances than in the unsheltered crop.

Ecology and physiology of establishment of eucalypt seedlings from seed: A review

Summary This paper provides a comprehensive review of the ecological and physiological factors affecting the establishment of eucalypts from seed, with particular reference to native forests and woodlands in Australia. Water, temperature, light in some cases, seed harvesting, pathogens, allelopathy, overstorey density and seedbed all have the potential to affect germination and emergence of eucalypts, but probably the most generally important factors are seed harvesting, water and seedbed condition. Mortality of eucalypt seedlings has been attributed to water deficits, high soil-surface temperatures, pathogenic fungi, low light intensity, frost, freezing temperatures, snow, fire, grazing and high seedling density. Mortality is usually greater beneath an overstorey and on undisturbed seedbeds, and may be reduced by application of fertilisers. Probably the most widespread causes of mortality are water deficits, especially in the drier areas, pathogens and the unsuitable conditions of an undisturbed seedbed....

Effects of High Soil Surface Temperature on Seedling Survival in Pearl Millet

SummaryA field technique to screen pearl millet genotypes for their emergence and survival at high soil surface temperatures is described. Genetic variation in seedling emergence and survival is shown and it is argued that this variation is largely due to tolerance of high temperatures rather than tolerance of soil moisture deficit, although some interaction occurred. An index for ‘thermotolerance’ is defined and genotypes are ranked accordingly for this trait, which is shown to be highly heritable. The technique is repeatable and allows a large number of genotypes to be screened at the same time.