Root growth dynamics linked to above-ground growth in walnut (Juglans regia)

Background and Aims Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature.Methods Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia ‘Chandler’) using minirhizotron techniques.Key Results Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production.Conclusions The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs.     

Preliminary analysis of drinking from seawater sources by free-ranging rhesus macaques (Macaca mulatta)

Rhesus macaques on Key Lois Island were observed drinking seawater that flowed into four holes they had excavated in the sand. Data were gathered to determine the salinity (TDS) and pH levels of the water and which animals were using the holes. Average TDS level (4,506.8 ± 1,750.8), but not pH (8.1 ± .30) level, of water from the holes differed from the surrounding seawater (TDS = 29,000, pH = 8.0). There were significant variations in TDS and pH levels of water between holes. A total of 249 drinking and 11 digging bouts were observed. Adult females drank and dug most often (46.9% of total bouts). Of the 260 total drinking and digging bouts, 76.1% (N = 198) were concentrated at one hole. This hole had the lowest average TDS level (3,714.2 ± 1,504.4) and one of the highest average pH levels (8.1 ± .29). Age/sex class differences in drinking bout frequencies may have been due to differential social status. We suggest that the holes were excavated to overcome a temporary shortage of provisioned water. © 1993 Wiley-Liss, Inc.     

Regional ecological risk assessment using a relative risk model: A case study of the Darwin Harbour,Darwin, Australia

There are many proposed and ongoing commercial, industrial, and residential developments within the Darwin Harbour catchment in Northern Australia, to accommodate the projected population growth over the next 20 years. Hence, it is necessary to ensure the balance between these developments and ecosystem conservation. We evaluated ecological risk for the Darwin Harbour using a relative risk model (RRM). The catchment was divided into 22 risk regions based on small catchment boundaries and their homogeneity. Through the RRM, we ranked and summed the stressors and habitats within regions. The interaction between stressors and habitats were modeled through exposure and effect filters. The ecological assessment endpoints were maintenance of the mangrove health and the maintenance of water quality. The risk regions—Myrmidon Creek, Blackmore River, Bleesers Creek, and Elizabeth River—showed the highest total relative risk for ecological assets. These risk regions had a high percentage cover of industrial, commercial, and residential areas; diffuse entry points; and climate change effects. Creek A, Sandy Creek, West Arm, and Pioneer Creek were the risk regions with lowest total relative risk scores. The RRM is a robust application that is suitable for a large geographic area where multiple stressors are of concern.     

Transpiration difference under high evaporative demand in chickpea (Cicer arietinum L.) may be explained by differences in the water transport pathway in the root cylinder

• Terminal drought substantially reduces chickpea yield. Reducing water use at vegetative stage by reducing transpiration under high vapor pressure deficit (VPD), i.e. under dry/hot conditions, contributes to drought adaptation. We hypothesized that this trait could relate to differences in a genotype's dependence on root water transport pathways and hydraulics.
• Transpiration rate responses in conservative and profligate chickpea genotypes were evaluated under increasing VPD in the presence/absence of apoplastic and cell‐to‐cell transport inhibitors.
• Conservative genotypes ICC 4958 and ICC 8058 restricted transpiration under high VPD compared to the profligate genotypes ICC 14799 and ICC 867. Profligate genotypes were more affected by aquaporin inhibition of the cell‐to‐cell pathway than conservative genotypes, as measured by the root hydraulic conductance and transpiration under high VPD. Aquaporin inhibitor treatment also led to a larger reduction in root hydraulic conductivity in profligate than in conservative genotypes. In contrast, blockage of the apoplastic pathway in roots decreased transpiration more in conservative than in profligate genotypes. Interestingly, conservative genotypes had high early vigour, whereas profligate genotypes had low early vigour.
• In conclusion, profligate genotypes depend more on the cell‐to‐cell pathway, which might explain their higher root hydraulic conductivity, whereas water‐saving by restricting transpiration led to higher dependence on the apoplastic pathway. This opens the possibility to screen for conservative or profligate chickpea phenotypes using inhibitors, itself opening to the search of the genetic basis of these differences.

     

Numerical Simulations and Long-Column Tests of LNAPL Displacement and Trapping by a Fluctuating Water Table

Long-column laboratory tests were performed to validate improvements to the MOFAT program for simulating LNAPL displacement and entrapment in response to a fluctuating water table. The long-column tests consisted of a fluctuating water table and its subsequent displacement and entrapment of an LNAPL. The modifications of MOFAT include a linear LNAPL trapping estimate and a new scaling technique for the inhibition portion of the fluctuation (water table rise). Improved prediction of the LNAPL trapping was obtained by assuming the amount of LNAPL that is trapped by a rising water table is proportional to the antecedent water content of the porous medium. The pressure-saturation relationship for the air-water drainage system was scaled to estimate the LNAPL-water and air-LNAPL drainage relationships. Scaled inhibition pressure-saturation relationships are improved by incorporating a correction for contact angle hysteresis and surface roughness. The incorporation of these changes into MOFAT led to noticable improvements in the numerical simulation of the experimental data.     

Microbial carbonate production in a starved basin: The crenistria Limestone of the upper Viséan German Kulm facies

The crenistria Limestone is a set of three autochthonous massive limestone beds occurring with great lithological persistence in the Kulm Facies (cd III , upper Viséan) of the eastern Rheinisches Schiefergebirge. Microfacies analysis reveals mainly minipeloidal fabrics and homogeneous micrite. Uncrushed, sediment-filled conchs of goniatites represent loci of sheltered preservation of primary carbonate textures. Calcified radiolarians are abundant, forming between 20 and 80% of total rock volume. The alleged algal genus Rectangulina is common in the crenistria Limestone. It is reinterpreted to represent the faeces of goniatites. For the first time the presence of in situ preserved sponges is reported. They can be recognized as delicate networks of microsparitic needles embedded in peloidal fabrics. Hexactinellids with primary spicule arrangements can be found embedded in homogeneous micrite. The carbonate forming the limestone beds was produced microbially during decomposition of soft tissue of the radiolarians and sponges. During the cd III , anoxia in the bottom waters of the Kulm Basin persisted for long periods due to stable density stratification of the water column under humid climatic conditions. Oxic conditions in the bottom waters during formation of the limestone are indicated by bioturbation, the presence of sponges and the high Mn-contents of the carbonate. The latter derived from reduction of Mn-oxides during microbial carbonate formation.     

The rate of development of water deficits affects Saxifraga cernua leaf respiration

We allowed plant water deficits to develop at two different rates following the cessation of watering in order to investigate the effects of water stress on cytochrome pathway and alternative pathway respiration in the leaves of the arctic herb Saxifraga cernua. Plants were pretreated by growth in either a commercial organic (CO) mixture or a vermiculite-perlite (VP) mixture, which allowed the complete development of water deficits in 19 and 8 days, respectively. The rate of water potential reduction was approximately 0.11 MPa day⁻¹ in the leaves of CO plants, compared to a reduction of 0.21 MPa day⁻¹ in leaves of VP plants. Osmotic adjustment occurred to a greater extent in leaves of CO plants and corresponded with an increase in ethanol-soluble sugars. In leaves of CO plants, cytochrome pathway activity gradually declined from that of control rates until day 11, and then declined more rapidly. In contrast, cytochrome pathway activity significantly increased in response to water deficits in leaves of VP plants. In leaves of both CO and VP plants, alternative pathway activity declined as water stress progressed. Relatively severe water deficits reduced alternative pathway capacity in leaves of both CO and VP plants. We also investigated the effect of previous exposure to water deficits on leaf respiration. In plants that had previously experienced three cycles of water stress, the increase in cytochrome pathway activity during the fourth water stress cycle was small compared to the increase observed in leaves of plants experiencing water stress for the first time. These results suggest that cytochrome pathway activity is differentially sensitive to the rate of development of plant water deficits and that respiratory responses to acute water stress are not necessarily similar to the responses to chronic water stress.     

Comparison of heart rate monitoring combined with indirect calorimetry and the doubly labelled water (2H218O) method for the measurement of energy expenditure in children

The aim of the present study was to compare data on 24-h energy expenditure (EE24h) in nine boys and ten girls (mean age 9.3 and 8.1 years, respectively) by heart rates (fc) combined with energy expenditure obtained from a 1-day stay in an indirect calorimeter (EEcal) and a 2-week period of normal living using the doubly labelled water method (EEdlw). Individual calibration curves were derived from fc and oxygen uptake measured during sleep (in the calorimeter), standing and walking on a treadmill. An estimation of energy expenditure based on 24-h fc monitoring (EEfc) was made during the stay in the calorimeter and on a normal school-day. Mean results showed an overestimation in EEfc compared to EEcal and EEdlw of 10.4% and 12.3% respectively, varying from 6.3% to 16.2%. These results confirmed earlier observations in adults that for a group the fc method overestimates EE24h by about 10%.     

Eutrophication as an impact category

State of the art and research needs for the impact category eutrophication are discussed. Eutrophication is a difficult impact category because it includes emissions to both air and water — both subject to different environmental mechanisms — as well as impacts occurring in different types of terrestrial and aquatic ecosystems. The possible fate processes are complex and include transportation between different ecosystems. In some recent approaches, transportation modelling of air emissions has been included. However, in general, the used characterisation methods do not integrate fate modelling, which is a limitation. The definition of the impact indicator needs further research, too. The inclusion of other nutrients than those typically considered should also be investigated.