Ecophysiology of algae living in highly acidic environments

Highly acidic environments are inhabited by acidophilic as well as acidotolerant algae. Acidophilic algae are adapted to pH values as low as 0.05 and unable to grow at neutral pH. A prerequisite for thriving at low pH is the reduction of proton influx and an increase in proton pump efficiency. In addition, algae have to cope with a limited supply of carbon dioxide for photosynthesis because of the absence of a bicarbonate pool. Therefore, some algae grow mainly in near terrestrial situations to increase the CO₂-availability or actively move within the water body into areas with high CO₂. Beside these direct effects of acidity, high concentrations of heavy metals and precipitation of nutrients cause indirect effects on the algae in many acidic environments.     

Control of pH at the soil-root interface

A method to control the rhizosphere pH of plants under controlled nutritional conditions is suggested. An earlier developed method for plant growth in soilless culture according to the principle of regeneration and pH control by adjusting the percentage of total N supplied as NH₄-N in the maintenance solution was applied to control rhizosphere pH in connection with a recently developed plant-growing technique. Using this technique, thin soil layers (0.2 mm) at different proximity to a root mat can be sliced from a soil column and analyzed.Results show a high predictive values with respect to pH profiles in the soil and demonstrate that nutrition of the rape plants was kept equal when rhizosphere pH decreased by 1.2 units, and was kept constant or was increased by 0.4 units by varying the percentage of total N supplied as NH₄-N (15, 6 or 0) in the nutrient solutions via wicks and not via the soil column. The method thus offers new possibilities in rhizosphere studies, as control of pH in the rhizosphere of plants under equal nutritional conditions has been a problem for a long time.     

Nutrient loading of a forest soil

Summary During July 1988 rooted and non-rooted experimental chambers were established in a Norway spruce (Picea abies. Karst) stand in south Devon U.K. Replicates were supplemented with ammonium and nitrate. The leachates were analysed to monitor the release of mineral-N species and cations over the 17-week experimental period. Ammonium treatments leached 300% more calcium and magnesium than controls. The onset of nitrification resulted in a decrease in sodium losses from ammonium treatments reflecting a decrease in the exchanging capacity of the soil solution. These results are discussed in relation to mineral ion leaching in soils subjected to increesed N-loading, and the ability of soils to buffer these perturbations.     

Biochemical and genetic analysis of a Chlamydomonas reinhardtii mutant devoid of chloroplastic glutamine synthetase activity

A spontaneous double mutant of Chlamydomonas reinhardtii, designated ARF3, was resistant to L-methionine-S-sulfoximine (MSX), lacked chloroplastic glutamine synthetase (GS2) activity, and grew very poorly in all media tested. In segregants obtained after genetic crosses, the poor-growth phenotype was always linked to the lack of GS2 and to a diminished rate of consumption of ammonium, even under conditions where photorespiration was minimized. The ammonium permeases in mutant ARF3, however, were not altered. This indicates that, unlike in higher plants, GS2 contributes substantially to the primary assimilation of ammonia in this alga, and that its function cannot be replaced by the cytosolic glutamine synthetase. In genetic crosses, the MSX resistance and the lack of GS2 segregated independently, indicating that resistance was not due to an altered form of GS2. Received: 5 June 1998 / Accepted: 10 September 1998     

Effects of nitrogen supply and elevated carbon dioxide on construction cost in leaves of Pinus taeda (L.) seedlings

Seedlings of loblolly pine (Pinus taeda L.) were grown under varying conditions of soil nitrogen and atmospheric carbon dioxide availability to investigate the interactive effects of these resources on the energetic requirements for leaf growth. Increasing the ambient CO₂ partial pressure from 35 to 65 Pa increased seedling growth only when soil nitrogen was high. Biomass increased by 55% and photosynthesis increased by 13% after 100 days of CO₂ enrichment. Leaves from seedlings grown in high soil nitrogen were 7.0% more expensive on a g glucose g^–1 dry mass basis to produce than those grown in low nitrogen, while elevated CO₂ decreased leaf cost by 3.5%. Nitrogen and CO₂ availability had an interactive effect on leaf construction cost expressed on an area basis, reflecting source-sink interactions. When both resources were abundant, leaf construction cost on an area basis was relatively high (81.8±3.0 g glucose m^–2) compared to leaves from high nitrogen, low CO₂ seedlings (56.3±3.0 g glucose m^–2) and low nitrogen, low CO₂ seedlings (67.1±2.7 g glucose m^–2). Leaf construction cost appears to respond to alterations in the utilization of photoassimilates mediated by resource availability.     

Needle CO2 exchange, structure and defense traits in relation to needle age in Pinus heldreichii Christ – a relict of Tertiary flora

 Pinus heldreichii Christ is a long-lived, slow-growing Tertiary relict from the Balkans. In this study we evaluated the physiological characteristics of eight needle-age classes of P. heldreichii grown at the Arboretum of the Institute of Dendrology in Kórnik, Poland. At the end of the growing season, current-year foliage had the highest rates of mass-based light-saturated net photosynthesis (A_sat) of 33.5 nmol CO₂· g^–1· s^–1. A_sat decreased with needle age, but older needle classes retained from approximately 62 to 26% of the current needles’ rate. The relationship between leaf N and chlorophyll a concentration among all needle-age classes was highly significant (r = 0.96, P = 0.0006). The variation in A_sat of 1- to 7-year-old needles was linearly related to needle N concentration (r = 0.98, P = 0.0001). Needle dark respiration rates among these needle age classes ranged from 0.8 to 2.2 nmol · g^–1· s^–1 and decreased with needle age and nitrogen concentration. Total phenols and glucose concentrations increased linearly with needle age. A similar pattern was observed in acid buffering capacity and the pH of tissue homogenates. The water content ranged from 62% for the current needles to 51% for the 6-year-old needles. Greater investment in leaf structural tissue and increased chemical defense is associated with higher structural cost of older needles and may reduce their photosynthetic activity. Significant declines in water and nitrogen content with needle age and an increase in content of phenolics is most likely a defense adaptation of P. heldreichii related to the species’ long-lived leaves. Received: 8 January 1997 / Accepted: 4 March 1997     

Methodological approach for the assessment of environmental effects of agroforestry at the landscape scale

Silvoarable agroforestry, the deliberate combined use of trees and arable crops on the same area of land, has been proposed in order to improve the environmental performance of agricultural systems in Europe. Based on existing models and algorithms, we developed a method to predict the environmental effects of SAF at a farm and landscape scale. The method is comprised of an assessment of soil erosion, nitrogen leaching, carbon sequestration, and landscape diversity and allowed the comparison of the environmental performance of SAF with arable systems using these four indicators.The method was applied to three landscape test sites of 4 km × 4 km each in Spain, France, and The Netherlands, and compared different levels of agroforestry adoption on farmland of different potential productivity. Silvoarable agroforestry was predicted to reduce soil erosion by up to 70%, to reduce N leaching by 20–30%, to increase C sequestration over 60 years by up to 140 tonnes C ha⁻¹, and to increase landscape diversity up to four times. The method developed was executed with widely available landscape and farm structural data and can therefore be applied to other regions in order to obtain a broader assessment of the environmental performance of silvoarable agroforestry systems.     

The nature value of the ditch vegetation in peat areas in relation to farm management

Farmers can play an important role in enhancing the diversity of plant species in ditches, since they carry out most of the management. Little is known about the measures farmers can take to enhance aquatic biodiversity in ditches. Therefore, a field study was set up to determine how dredging, ditch cleaning, and nutrient supply in the adjacent fields affect the floristic values of the ditch vegetation in peat areas. A total of 240 ditches on 84 dairy farms were selected, to establish the effect of ditch cleaning, dredging, and nutrient supply. Generalised linear modelling was used to determine the most relevant factors, and to obtain quantitative relations between those factors and two indices of floristic value. Ditch management, field management, and water management were found to affect the floristic values of the ditch vegetation. Increasing the water depth proved to be the most cost-effective measure. Further improvements can be obtained by choosing certain machines or specific management periods, or reducing the N supply. The effect of the P supply is not yet sufficiently clear. The water boards can enhance floristic values by raising the ditch water table and by lowering the Cl^– concentration in the ditches.     

Boat harbour design can exacerbate hull fouling

Abstract Hull fouling is a major cost for owners of small vessels and an important pathway for the spread of non‐indigenous aquatic species. The extent of fouling depends on a hull's susceptibility to recruitment by aquatic organisms and the local availability of competent planktonic propagules (‘propagule pressure’). Management strategies have typically been concerned with increasing resistance of the hull to recruitment through the use of toxic paints. Here we tested the hypothesis that fouling is influenced by the design of the harbour in which the boat is moored. We compared recruitment of sessile invertebrates to available surfaces in two types of recreational boat harbours: marinas that were partially enclosed by a permanent breakwall, and marinas that lacked breakwalls. Recruitment in the marinas was compared to coastal reference sites that were not used for mooring. At each location, recruitment tiles were deployed for 4 weeks on four separate occasions over a period of 2 years. Measurements of current velocities and spatial patterns of water flow at each location showed that permanent breakwalls created complex patterns of circulation that retained water within the marina basin for up to 12 h d^?1. Despite large regional and temporal variability in fouling over time, most organisms recruited in greatest numbers to surfaces in partially enclosed marinas, and were often several orders of magnitude more abundant in the enclosed marinas than in unenclosed marinas or coastal reference locations. Harbour design has an important influence on the rate at which fouling organisms recruit to available surfaces within marinas. Entrainment of water in enclosed marinas may limit the dispersal of planktonic propagules by advective currents but effectively increases propagule pressure to available surfaces, including resident boat hulls. This is likely to accelerate the development of hull‐fouling assemblages and increase the chances of transport of non‐indigenous species that establish populations in the harbour basin.