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Groundwater-dependent ecosystems (GDEs) are threatened by over-extraction of groundwater for human needs across the world. A fundamental understanding of relationships between naturally occurring gradients in depth-to-groundwater (DGW) across landscapes and the ecological properties of vegetation assemblages is essential for effective management of the impacts of groundwater extraction. Little is known, however, about relationships between DGW and the ecology of mesic woodlands in GDEs. Here, we investigated relationships between a naturally occurring DGW gradient and plant species composition, richness and abundance in mesic Eucalyptuswoodlands of eastern Australia. Across 16 sites varying in DGW from 2.4 m to 43.7 m, we found that plant species composition varied significantly in relation to DGW, independently of a range of 14 physical and chemical attributes of the environment. Nine understorey species, representing only 7% of the pool of 131 plant species, were identified as contributing to up to 50% of variation in species composition among the study sites. We suggest this dominant pattern driver in the understorey is explained by differential abilities among understorey species in their ability either to tolerate extended dry conditions at deeper DGW sites during periods of low rainfall, or to withstand periodically waterlogged conditions at shallow sites. Plant species richness and total plant abundance (a measure of plant productivity) were not significantly and independently related to DGW or any of the other 14 environmental attributes. Our finding for a direct relationship between DGW and plant species composition provides important reference information on the ecological condition of these mesic woodlands in the absence of groundwater extraction. Such information is vital for setting ecological thresholds that ensure sustainable extraction of groundwater.

Groundwater-dependent ecosystems (GDEs) are threatened by over-extraction of groundwater for human needs across the world. A fundamental understanding of relationships between naturally occurring gradients in depth-to-groundwater (DGW) across landscapes and the ecological properties of vegetation assemblages is essential for effective management of the impacts of groundwater extraction. Little is known, however, about relationships between DGW and the ecology of mesic woodlands in GDEs. Here, we investigated relationships between a naturally occurring DGW gradient and plant species composition, richness and abundance in mesic Eucalyptuswoodlands of eastern Australia. Across 16 sites varying in DGW from 2.4 m to 43.7 m, we found that plant species composition varied significantly in relation to DGW, independently of a range of 14 physical and chemical attributes of the environment. Nine understorey species, representing only 7% of the pool of 131 plant species, were identified as contributing to up to 50% of variation in species composition among the study sites. We suggest this dominant pattern driver in the understorey is explained by differential abilities among understorey species in their ability either to tolerate extended dry conditions at deeper DGW sites during periods of low rainfall, or to withstand periodically waterlogged conditions at shallow sites. Plant species richness and total plant abundance (a measure of plant productivity) were not significantly and independently related to DGW or any of the other 14 environmental attributes. Our finding for a direct relationship between DGW and plant species composition provides important reference information on the ecological condition of these mesic woodlands in the absence of groundwater extraction. Such information is vital for setting ecological thresholds that ensure sustainable extraction of groundwater.

Phytotoxicity due to excessive boron (B) uptake by plants impedes routine agronomic utilisation of coal fly ash. We assessed 11 fly ashes (pH 3.14–10.77) having total B content (Bt) of 12–136mg/kg, of which 20–30% was hot water soluble (Bs) in the acidic ashes (pH <5) and 5–10% in the alkaline ashes, for their potential to supply B to plants and their risk associated with phytotoxicity. We found the Bs/Btto be negatively correlated (R2=0.63**, N=11) with ash pH. We conducted two pot trials in which canola was grown in soils amended with fly ash. In the first trial, an alkaline fly ash (Bt66mg/kg) was incorporated at 5 rates of up to 625Mg/ha into the top 50mm of 2 acidic soils in 0.30-m-long intact cores, and sown with canola. Boron concentration in leaves at flowering reached the phytotoxic threshold, and both plant growth and seed yield were reduced, only at 625Mg/ha. In the second trial, 4 fly ashes (pH 3.29–10.77, Bt12–127mg/kg) were incorporated at 4 rates of up to 108Mg/ha into the top 0.10m of 2 acidic soils in 1.0-m-long intact cores and then sown with canola. Ashes with highest Bt, when applied at 108Mg/ha, increased B concentration in the topsoil only. Of the 2 ashes with the highest Bt, only that which produced low soil pH and applied at 108Mg/ha increased B concentration in the shoot, but was still below phytotoxic threshold. The results suggest that B derived from these ashes may not cause phytotoxicity and excessive soil B accumulation if the ashes are applied at modest rates (<36Mg/ha) to the topsoil layers.

To explore the agronomic potential of an Australian coal fly ash, we conducted two glasshouse experiments in which we measured chlorophyll fluorescence, CO2assimilation (A), transpiration, stomatal conductance, biomass accumulation, seed yield, and elemental uptake for canola (Brassica napus) grown on soil amended with an alkaline fly ash. In Experiment 1, application of up to 25 Mg/ha of fly ash increased Aand plant weight early in the season before flowering and seed yield by up to 21%. However, at larger rates of ash application A, plant growth, chlorophyll concentration, and yield were all reduced. Increases in early vigor and seed yield were associated with enhanced uptake of phosphorus (P) by the plants treated with fly ash. Fly ash application did not influence accumulation of B, Cu, Mo, or Zn in the stems at any stage of plant growth or in the seed at harvest, except Mo concentration, which was elevated in the seed. Accumulation of these elements was mostly in the leaves, where concentrations of Cu and Mo increased with any amount of ash applied while that of B occurred only with ash applied at 625 Mg/ha. In Experiment 2, fly ash applied at 500 Mg/ha and mixed into the whole 30 cm soil core was detrimental to growth and yield of canola, compared with restricting mixing to 5 or 15 cm depth. In contrast, application of ash at 250 Mg/ha with increasing depth of mixing increased Aand seed yield. We concluded that fly ash applied at not more than 25 Mg/ha and mixed into the top 10 to 15 cm of soil is sufficient to obtain yield benefits.

Cost-benefit analysis of foliar construction and maintenance costs and of carbon assimilation of leaves of differing life-span were conducted using two evergreen, three semi-deciduous, and three deciduous tree species of savannas of north Australia. Rates of radiant-energy-saturated CO2assimilation (Pmax) and dark respiration were measured and leaves were analysed for total nitrogen, fat, and ash concentrations, and for heat of combustion. Specific leaf area, and leaf N and ash contents were significantly lower in longer-lived leaves (evergreen) than shorter-lived leaves (deciduous) species. Leaves of evergreen species also had significantly higher heat of combustion and lower crude fat content than leaves of deciduous species. On a leaf area basis, Pmaxwas highest in leaves of evergreen species, but on a leaf dry mass basis it was highest in leaves of deciduous species. Pmaxand total Kieldahl N content were linearly correlated across all eight species, and foliar N content was higher in leaves of deciduous than evergreen species. Leaf construction cost was significantly higher and maintenance costs were lower for leaves of evergreen than deciduous species. Maintenance and construction costs were linearly related to each other across all species. Leaves of evergreen species had a higher cost-benefit ratio compared to leaves of deciduous species but with longer lived leaves, the payback interval was longer in evergreen than deciduous species. These results support the hypotheses that longer lived leaves are more expensive to construct than short-lived leaves, and that a higher investment of N into short-lived leaves occurs which supports a higher Pmaxover a shorter payback interval.

Abstract This paper examines the effects of seedling size and age on fire tolerance of Allosyncarpia ternata(Myrtaceae), a dominant tree in patches of monsoon rainforest of the wet-dry tropics in the Northern Territory, Australia. We address the following questions: how large does a seedling have to be to tolerate fire; how old does it have to be to reach this fire-tolerant size; and how can land-management authorities best manage fire regimes to maintain Allosyncarpiaforest? In a field experiment, shadehouse-grown seedlings aged from 8 months to 5 years were subjected to low- and high-intensity fires in September 1994. Among 5-year-old seedlings, mortality was independent of fire intensity. However, mortality of young (8-month-old) seedlings was significantly higher in the high-intensity fire. Three-year-old seedlings behaved in an intermediate manner; their survivorship and growth were marginally favoured by low-intensity fire, rather than high-intensity fire or no fire at all, and were dependent on pre-treatment seedling height. Thus, the critical age that distinguishes fire-tolerant from fire-sensitive seedlings is somewhat more than 3 years for relatively short seedlings and somewhat less than 3 years for taller seedlings. In August 1993, a wildfire penetrated several hundred metres into Allosyncarpiaforest growing on a steep, rocky escarpment, where it caused severe damage to A. ternataseedlings. More than three-quarters of the = 3.5-year-old seedlings (including some that had suffered the total loss of above-ground parts) recovered during the following wet season and showed higher growth rates than their unburned neighbours. New growth was also promoted in those tall seedlings and saplings that had sustained only partial leaf scorch. In contrast, all 18-month-old seedlings were killed by the fire. Measurements of leaf-scorch height in burned Allosyncarpiaforest on the escarpment indicated a general uphill decrease in fire intensity, matching trends in increasing site rockiness and decreasing fuel density. An important implication for land management is that a fire-free interval of at least 3 years following a seed-fall event is required for a new generation of A. ternatagerminants to progress into the cohort of established seedlings.

AbstractSoil moisture was augmented experimentally during two successive dry seasons and the intervening wet season in a humid tropical savanna in Darwin, northern Australia. Leaf phenology was monitored in four common tree species Termmalia ferdinandianaand Planchonia careya(both deciduous species), and Eucalyptus miniataand Eucalyptus tetrodonta(both evergreen species). Irrigation produced consistently significant effects in only T. ferdinandiana. In this species leaf-flush was significantly earlier, canopy decline and leaf-fall were significantly later and the attainment of full canopy was earlier in irrigated compared with non-irrigated trees. Litterfall, and the seasonal patterns of contraction and expansion of stems (a measure of stem water status or storage) were not significantly affected by irrigation in any species. Leaf longevity in the deciduous species was 6–8 months; some eucalypt leaves lived for approximately 1 year, but none lived longer than 18 months. Irrigation had relatively little effect on leaf longevity. While variation in soil moisture is a potentially important cue to both leaf-fall and leaf-flush, stem water status and climatic factors such as vapour pressure deficit may also be important climatic cues to phenological behaviour.

A combination of micro-meteorological, soil physical and groundwater chemical methods enabled the water balance of a tropical eucalypt savanna ecosystem in Northern Australia to be estimated. Heat pulse and eddy correlation were used to determine overstory and total evapotranspiration, respectively. Measurements of soil water content, matric suction and water table variations were used to determine changes in soil moisture storage throughout the year. Groundwater dating with chlorofluorocarbons was used to estimate net groundwater recharge rates, and stream gauging was used to determine surface runoff. The wet season rainfall of 1585 mm is distributed as: evapotranspiration 810 mm, surface runoff (and shallow subsurface flow) into the river 410 mm, groundwater recharge 200 mm and increase in soil store 165 mm. Of the groundwater recharge, 160 mm enters the stream as baseflow in the wet season, 20 mm enters as baseflow in the dry season, and the balance (20 mm) is distributed to and used by minor vegetation types within the catchment or discharges to the sea. In the dry season, an evapotranspiration of 300 mm comprises 135 mm rainfall and 165 mm from the soil store. Because of the inherent errors of the different techniques, the water balance surplus (estimated at 20 mm) cannot be clearly distinguished from zero. It may also be as much as 140 mm. To our knowledge, this is the first time that such diverse methods have been combined to estimate all components of a catchment's water balance.

Gas exchange responses of mangosteen (Garcinia mangostana L.) leaves to photosynthetic photon flux density (PPFD), internal CO(2) concentration (C(i)), leaf-air vapor pressure deficit (VPD), leaf temperature (T(l)) and time of day were investigated in plants grown in three shade treatments. Maximal photosynthetic rate (P(n(max))) per unit leaf area at light saturation did not differ significantly among plants grown in the different shade treatments despite significant morphological differences. Light compensation point (9-15 micro mol m(-2) s(-1)) and quantum yield (0.022-0.023) did not differ significantly among treatments, whereas light saturation point was significantly higher for leaves grown in 20% shade than for leaves grown in 50 or 80% shade (951, 645 and 555 micro mol m(-2) s(-1), respectively). Shade treatments significantly affected assimilation responses to varying CO(2) concentrations. At CO(2) concentrations between 600 and 1000 micro mol mol(-1), leaves from the 20% shade treatment recorded higher P(n) (6.44 micro mol m(-2) s(-1)) than leaves from the 80% shade treatment (4.57 micro mol m(-2) s(-1)). Stomatal conductance (g(s)) decreased with increasing CO(2) concentrations. Vapor pressure deficits higher than 2.5 kPa significantly decreased P(n) and g(s), whereas P(n) remained steady over a 24-33 degrees C temperature range in leaves in 80% shade and over a 27-36 degrees C range in leaves in 20 and 50% shade. Highest carbon gain during a 12-hour photoperiod was observed for leaves grown in 50% shade. The results imply that mangosteen is a shade-tolerant, lower canopy tree adapted to humid tropical lowlands. Providing low VPD in the nursery may result in maximal growth. However leaves of seedlings grown in 50 or 20% shade tolerated high VPD and temperatures better than leaves of seedlings grown in 80% shade, indicating some adaptability to the seasonally wet and dry tropics of northern Australia.

Red spruce (Picea rubens Sarg.) seedlings growing outside in open-top chambers were sprayed twice weekly with artificial mists at either pH 2.5 or 5.6, for five months during the 1988 growing season. The mists contained one of the following: water, pH 5.6 (control); (NH(4))(2)SO(4), pH 5.6; NH(4)NO(3), pH 5.6; HNO(3), pH 2.5; H(2)SO(4), pH 2.5; or (NH(4))(2)SO(4) + NH(4)NO(3), pH 2.5. During January 1989, the light responses of assimilation and stomatal conductance were assessed in the laboratory following a 4-day equilibration at 12 degrees C. The aerial portions of the intact trees were then subjected to a mild (-10 degrees C) frost for three hours during the night and the rate of recovery of light-saturated assimilation (A(max)) was determined the following day using the same branches as were used for the assimilation studies before the frost treatment. The same trees were then subjected to a second frost of -18 degrees C for three hours during the following night and the recovery of A(max) of the same branches was measured the next day. All of the acid mist treatments increased A(max) and apparent quantum yield relative to the control treatment when measured before the frost treatments. Frosts of -10 and -18 degrees C resulted in a significant decline in A(max) of seedlings in all treatments except the control. Stomatal conductance increased with increasing irradiance in seedlings in the acid mist treatments that did not contain SO(4) (2-) ion. Stomatal conductance of seedlings in acid mist treatments containing SO(4) (2-) ion was insensitive to changes in irradiance over the range 50-1500 micro mol m(-2) s(-1). It is concluded that acid precipitation increased the sensitivity of the assimilation response to midwinter frosts that follow a brief warm period. The SO(4) (2-) ion appears to be significant in causing increased sensitivity to frost and in causing stomatal insensitivity to light flux density.

Pressure-volume curves, day and night transpiration rates, needle drying curves, and shoot water potentials were determined for 2-year-old red spruce trees that had been exposed for three months to a range of acid mists (pH 2.5 to pH 5.0) containing equimolar (NH(4))(2)SO(4) and HNO(3). No effect of acid mist was observed on cuticular resistance or on the rates of day and night transpiration, although trees exposed to acid mist exhibited symptoms of mild water stress. Significant decreases in maximum turgor, the relative water content (RWC) associated with zero turgor, and bulk volumetric elastic modulus occurred as the pH of the mist decreased from 5.0 to 2.5. At all RWC values, there was an increase in solute potential as mist pH decreased. Shoot water potential declined with a decrease in pH of the mist.

Seeds of Maranthes corymbosa Blume, a monsoon rain forest species of northern Australia, were sown under ambient or elevated CO2 concentrations in tropical Australia. Seedlings were grown under conditions of photon flux density, temperature and atmospheric vapour pressure deficit which followed ambient variations as closely as possible. Specific leaf area, chlorophyll, stomatal density, stomatal conductance and assimilation responses to photon flux density were measured after 30 weeks growth. Gas exchange characteristics were divided into morning and afternoon data sets and analysed separately. Stomatal density decreased and leaf area:dry weight ratio decreased in response to elevated CO2. In contrast there was no effect of elevated CO2 upon chlorophyll (total or ratio of a:b). Apparent quantum yield and rates of light saturated assimilation (Amax) increased in response to elevated CO2. There was a significant decline in apparent quantum yield for both treatments between morning and afternoon. Stomatal conductance (gs) declined in response to elevated CO2. There was no significant difference in gs between morning and afternoon for ambient grown trees, but gs declined significantly between morning and afternoon for elevated CO2 grown trees. Instantaneous transpiration efficiency (ITE) was higher for elevated CO2 grown trees compared with control trees. There was a significant increase in ITE between morning and afternoon data for ambient grown trees; in contrast a significant decline in ITE was observed for elevated CO2 grown trees between morning anf afternoon data sets. The slope of the regression between assimilation rate and stomatal conductance increased for plants grown under elevated CO2. These data are discussed and compared with the responses of plants adapting to different photon flux densities.

The interaction between CO2 IAA, ABA, and temperature in the control of stomatal behaviour, was investigated in the chill-resistant Pisum sativum and chill-hardened Phaseolus vulgaris. It was found that the ability of kBA to induce stomatai closure was dependent upon the presence of CO2 in both species, at both temperatures (22 �C, 5�C) Similarly, the ability of IAA to decrease stomatal resistance, was dependent upon the presence of CO2 in both species, at both temperatures. Chilling at 5�C in the light did not influence the response characteristics of stomata to CO2 ABA or IAA, in either species. These results are discussed in relation to a model of the interactions of these regulators of stomatal aperture.

Eamus, D., Thompson, W., Cairney, J. W. G. and Jennings, D. H. 1985. Internal structure and hydraulic conductivity of basidiomycete translocating organs.−J. exp. Bot. 36: 1110–1116. The presence in rhizomorphs of Armillaria mellea and cords of Phallus impudicus of wide diameter hyphae (5–20 {diaeresis}m), which run for considerable distances along these linear organs, has been demonstrated. The longitudinal hydraulic conductivity of these organs has been determined experimentally and similar values were obtained when the hydraulic conductivity was calculated theoretically on the basis that the vessel hyphae were the sole channel for water movement along these organs. The experimental data have been discussed in relation to other data for long-distance translocation in basidiomycete linear organs. It is concluded that the vessel hyphae are the main channels for turgor-driven translocation.

In the chilling sensitive (C.S.) species Phaseolus vulgaris it was found that at 22 �C ABA induced stomatal closure but this effect was dependent on the presence of CO2. In the absence of CO2 the effect of ABA was completely lost. In contrast to ABA, the effect of IAA at 22 �C was to increase stomatal opening as the IAA concentration increased from 10−2 to 10 mol m−3, and this effect was dependent upon the presence of CO2. However, at 5 �C the action of ABA was reversed and it was found to induce stomatal opening when fed via the transpiration stream in excised leaves. Similarly, the CO2 response characteristics were reversed at low temperatures as removal of CO2 from the atmosphere caused stomatal closure. However, the effect of IAA at 5 �C in the presence of CO2 and with or without ABA was to increase stomatal aperture with increasing IAA concentration. Significantly, ABA was found to have no effect upon aperture in the presence of CO2 when IAA was added. The interactive effects of ABA, IAA, CO2 and low temperature are discussed in relation to a model proposed by the authors.

Using thermocouple psychrometry, the water, solute and turgor potentials of hyphae of Phallus impudicus and Serpula lacrimans, cords of P. impudicus, Phanerochaete velutina and S. lacrimans and rhizomorphs of Armillaria mellea were determined. A comparison was made between laboratory- and field-grown cords of P. impudicus and P. velutina. Comparison was made also between the water relations of the hyphae at the growing front, and hyphae of the more distal, basal regions. Similarly, the growing regions of cords/rhizomorphs were compared with the older, non-extending basal regions of the same structures. In all cases gradients of water and turgor potentials were found from basal, older regions to younger, extending regions. These results are discussed in relation to the mechanism of translocation in fungi.

Leaf abscisic acid (ABA) levels of chilled P. vulgaris were measured after 18 h chilling at 5°C, at a saturation deficit of 1.24 g m−3 (SD), and after chilling in a water-saturated atmosphere. Changes were also followed during a chill hardening period of 4 d at 12°C, 2.1 g m−3 SD. It was found that hardening resulted in an almost 5. fold increase in ABA levels after 3 d at 12°C, and this decreased to approximately control levels on the fourth day. Subsequent chilling of hardened plants produced no change in ABA levels from that of control plants (22° C). In contrast, non-hardened plants chilled at 1.24 g m−3 SD had ABA levels almost 3 times the level of control plants. However, chilling in a water-saturated atmosphere resulted in a decrease in ABA levels. In addition, the response of leaf diffusion resistance (LDR) to exogenous ABA fed via the transpiration stream was measured at 5 ° C and 22° C in hardened and non-hardened plants. Use of tritium-labelled ABA was made to calculate the stomatal sensitivity to ABA. It was found that exogenous ABA caused an increased in LDR at 22°C in both hardened and non-hardened plants. However, the sensitivity of the hardened plants to ABA was greater in terms of rate of closure and amount of ABA required to close the stomata. At 5°C, however, ABA caused stomatal opening and the maintainance of open stomata in non-hardened plants. In hardened plants, ABA caused stomatal closure at 5°C. These results are discussed in relation to the locking-open response of chilled P. vulgaris stomata.

Seedlings of Maranthes corymbosa (Blume) and Eucalyptus tetrodonta (F. Muell) were grown with or without CO2 enrichment (700μmol CO2 mol−1 The response of stomatal conductance (g2) to leaf drying, exogenous absclslc acid and calcium ions was investigated in M. corymbosa. Reciprocal transfer experiments were also conducted whereby plants were grown in one treatment and then transferred to the other before g, was measured. Stomatal conductance in M. corymbosa was more sensitive (a greater percentage decline in g2 per unit percentage decline in leaf fresh weight) to leaf water status under conditions of CO2 enrichment compared to ambient conditions. However, the rate of reduction of g2 in response to exogenous abscisic acid was not influenced by CO2 treatment. In contrast, the rate of reduction of g2, in response to exogenous CaCl2 was decreased under conditions of CO2 enrichment. Reciprocal transfer experiments showed that expo sure to CO2 enrichment results in a short-term, reversible decline in g2, as a result of decreased stomatal aperture and a long-term, irreversible decline in g2 as a result of a decreased stomatal density. Seedlings of E. tetrodonta were used to investigate the response of g2 to light flux density, leaf-to-air vapour pressure difference (LAVPD), leaf internal CO2 concentration (C1 and temperature. Reciprocal transfer experiments were also conducted. CO2 enrichment did not influence the pattern or sensitivity of response of g to LAVPD and C in E. tetrodonta. In contrast, the slope of the response of g2, to temperature decreased for trees grown under elevated [CO2]a conditions and the equilibrium g2 attained at saturating light was also decreased for plants grown under elevated [CO2a. conditions.

Leaf diffusion resistance interpreted as stomatal resistance, leaf water potential (Ψw), solute potential (Ψs) and leaf turgor potential (Ψp) of the chilling sensitive species Phaseolus vulgaris were determined during chilling at 4 °C in the light. Both chill-hardened and non-hardened plants were used. For comparison, the chilling resistant species Pisum sativum was also used. The results for chilled P. sativum were similar to those obtained for chill-hardened P. vulgaris plants receiving a chilling treatment. In both cases a reduction in stomatal aperture and the maintenance of a positive leaf turgor were the responses to chilling. Leaves of chilled but non-hardened P. vulgaris plants were found to maintain open stomata throughout the chilling treatment despite a severe wilt developing after 7 h at 4 °C. This was in contrast to the chill-resistant P. sativum. which showed a rapid closing and subsequent re-opening of the stomata to a new reduced aperture. During the first 12 h of chilling Ψwof P. vulgaris leaves changed from −0.47 MPa to −1.24 MPa. On more prolonged chilling Ψw tended to return to pre-chilling values. In addition. Ψp decreased from 0.42 MPa to zero after only 9 h of chilling, and remained at this value for the remainder of the chilling period, Ψs, changed rapidly from −0.89 MPa to −1.35 MPa in the first 7.5 h, and after 9 h. Ψw and Ψs, were equal, i.e. zero Ψp. In contrast, the chilling resistant plant P. sativum maintained a positive Ψp throughout the chilling period, and there was little difference between values of Ψw, and Ψs in control and chilled leaves.

A pressure-volume analysis of aubergine (Solanum melongena) leaves following water stress was undertaken to determine a possible role of changes in cellular water relations in influencing stomatal conductance responses to water stress. A comparison of two methods of rehydrating the leaves was also undertaken. It was shown that the rehydration of excised leaves did not reveal osmoregulation, whilst rehydration of intact plants did reveal osmoregulation following water stress. An increase in the bulk volumetric elastic modulus and the bound water fraction also occurred in response to water stress. These results are discussed in relation to pressure-volume technique and stomatal conductance responses to drought.