Search

The deciduous tropical dry forest at Chamela (Jalisco, Mexico) occurs in a seasonal climate with eight rainless (November through June) and four wet months (700 mm annual precipitation). The forest reaches a mean height of 10 m. Tree density in the research area was 4700 trees per ha with a basal area at breast height of 23 m2 per ha. The above-and below-ground biomass of trees, shrubs, and lianas was 73.6 Mg ha−1 and 31 Mg ha−1, respectively. A root:shoot biomass ratio of 0.42 was calculated. Nearly two thirds of all roots occur in the 0–20 cm soil layer and 29% of all roots have a diameter of less than 5 mm.

The effect of varying independently nutrient solution temperature (5, 15, 25°C) and air temperature (10, 20, 30°C) on hydroponically grown Ceanothus greggii (Rhamnaceae) seedlings was studied. Increasing both air and solution temperatures caused higher root and shoot biomass and larger root and leaf areas. Root/shoot biomass ratio increased with increasing solution temperature and decreased with increasing air temperature. The surface area of individual leaves decreased with higher air temperatures but did not change with solution temperatures.

The purpose of the experiment was to see whether a change in nutrient availability resulting from perturbations might alter rates of development of the major plant growth forms of an arctic tussock tundra slope. Slow release fertilizer pellets (NPK) were spread in June and July 1985 on the frost surface under an 8-20 cm thick layer of thawed tundra in the northern foothills of the Brooks Range, Alaska. Initiation day of main phenological events, their duration and their intensity (% plants reaching a phenophase in a plot) were recorded during the 1985, 1986 and 1987 growing season. Variations in initiation day of phenophases were mainly due to environmental variations among years and to a lesser degree to fertilization; only timing of vegetative bud break of evergreen shrubs was significantly affected by fertilization, and occurred earlier than in the control. Flowering intensity varied significantly from one year to an other but was not significantly stimulated by fertilization.

Very limited information regarding fine-root growth and production of tropical dry forests is available. Fine roots and small roots are defined as rootlets with diameters < 1 mm and 1.1 to 5 mm, respectively. Live and dead fine-and small-root mass fluctuations were studied over one year by means of soil core analyses in the deciduous dry forest of Chamela, Mexico, at 19° 30′, 2 km inland from the Pacific Ocean. By means of systematically varying the distance of soil core extraction points from tree stems, it was shown that random core collection is justified. A difference between fine-root biomass on south and north facing slopes was documented, although this difference was significant only during the rainy season. The live/dead ratio of fine roots was highest during the rainy period. The annual fine-root production for 1989 was estimated at 4.23 Mg ha-1 by summing significant fine-root biomass changes between sampling dates. This value is higher than most of the comparable data from other ecosystems.

Quercus coccifera L., the characteristic scrub oak of the garrigue, covers more than 100,000 ha in southern France alone. Precipitation in this area averages 900 mm/year and summer rains are not rare. A total belowground biomass of 7.2 kg/m2, including rhizomes and lignotubers, was harvested. Roots were concentrated in the uppermost 50 cm of the soil. It was hypothesized that low winter temperatures inhibit active fine-root growth. This hypothesis was tested by means of fine-root extractions of soil samples from 0–50 cm depth from November 1987 to June 1988. Although the fine-root analysis could not be extended into late summer and fall, the data supported the hypothesis. Ratios of live/dead fine roots reached their minimum at 0.2–0.3 from December to April. They increased to 1.0–1.2 during late spring and early summer. Initiation of fine-root growth in early April was synchronous with bud break. Starch contents of roots, rhizomes, and lignotubers fluctuated from 4.3% in January to 8.3% in April. The starch stored in belowground organs of Q. coccifera in a closed canopy stand amounted to about 500 g/m2 in April. This amount declined to 400 g with bud burst and fine-root growth initiation.

Nitrogen (N) deficiencies in tundra ecosystems could be caused, in part, by the kinetics of root N uptake. The objectives of this study were to quantify NH4 uptake by field-grown excised roots of Eriophorum vaginatum I. under controlled NH4 concentrations (0-250 μmol I-1) and temperatures (5-20°C) and to evaluate this laboratory derived model as a means of estimating field NH4 uptake. There was no consistent temperature effect on root NH4 uptake which suggests a relative in-sensitivity of E. vaginatum roots to short-term temperature fluctuations. The Michaelis-Menten equation parameters for NH4 uptake were Vmax= 22.1 μmol h-1 g-1 and Km= 191 μmol I-1. Using field NH4 concentrations, field E. vaginatum root biomass data, and the Michaelis-Menten equation, an estimate was made of NH4 uptake over a 42 day period; this estimate of NH4 uptake accounted for 28% of the net incorporation of N into leaves and roots which is a reasonable estimate for E. vaginatum which relies primarily on N retranslocation for supplying new leaves and roots. Major uncertainties in field N uptake rates, model parameterization, and site characterization preclude an accurate model validation and indicate research areas most in need of future study.

Eriophorum vaginatum tillers were collected at Eagle Creek, Alaska and cultivated in aerated solutions under controlled environmental conditions. The nutrient solutions contained traces, 1.05 and 21 mg l−1 N (nitrate) and traces, 0.15 and 3.10 mg l−1 P (phosphate), pH was maintained at 5.5. The high N, 21 mg l−1, and P, 3.18 mg l−1, nutrient solution produced significant biomass increases. Functional leaf areas were significantly enhanced by high N and P doses in the solutions. Root surface areas varied considerably between treatments; however, significant differences were not found. The mean root surface area of a tiller reached 126 cm2 (range 35–290 cm2), whereas the functional leaf area was 6.8 cm2 (range 3.3–20.3 cm2). Tillers growing in the highest N + P solutions produced twice the number of daughter tillers as tillers growing in solutions with trace amounts of N and P.

Ceanothus greggii var. perplexans is a common shrub in the southern California chaparral. Clusters of nodules found under the canopy of this species are modified roots which contain a nitrogen-fixing endophyte, Frankia ceanothi (Actinomycetales), within the cortex. The nodule density per m2 obtained from root system excavations is much lower than that reported for different Ceanothus species in northern California. Field observations indicate that soil moisture is an important factor in nodule formation. Anatomical studies with the scanning electron microscope and acetylene reduction assays support the hypothesis that the vesicles, spherical swellings of hyphal endings (1.2-3.0 ,tm in diam), are indeed the sites of N2 fixation. No bacteria-like bodies were found. The acetylene reduction rates of C. greggii endophytes were of the same order of magnitude as those reported for other members of the genus Frankia. It is estimated that 100 grams of nitrogen are fixed per year per hectare for a specific area in the southern Californian chaparral where C. greggii comprises 1/3 of the ground cover. This amount appears to be large enough to replace the nitrogen that is lost annually by drainage and runoff from winter rain storms.

A B S T R A C T The sclerophyllous evergreen shrub vegetation of southern California and central Chile is characterized by several examples of morphologically similar species. For each one out of a group of four Californian shrub species, four morphologically analogous sclerophyllous evergreens from Chile were chosen. In monthly intervals two-year branchlets from these eight species were collected and their cambium aetivity was evaluated by means of a histological analysis. Similar shrub species from Chile and California show a surprisingly strong coincidence in their seasonal fluctuations of cambium activity regardless of their systematic position. This observation is interpreted to mean that convergence has taken place.

Nitrogen fixation in excised root nodules of 2-year-old, postfireCeanothus tomentosus andC. leucodermis seedlings was measured over an 8-month period using the acetylene reduction method. High levels of NO3−N and NH4−N present in postfire soils were limited to the upper 10 cm and did not inhibit nodulation in these deeper-rooting seedlings. Decreases in acetylene reduction activity occurred with decreased soil moisture and increased soil temperature. Nitrogen gains from these two Ceanothus shrub seedlings totalled 1.6 kg N ha−1 yr−1.

Root and leaf growth of the arctic sedge Eriophorum vaginatum L. were studied from early spring (June 7) to early fall (August 7) in the foothills of the Brooks Range in northern Alaska. The observations were designed to test the hypothesis that root and leaf growth occur at similar rates. The results confirmed this hypothesis. The root/leaf biomass ratio remained constant over the growing season. Thus, root biomass can be estimated based on harvested leaf biomass. It was also shown that root and leaf surface areas can be calculated from the respective biomass values. However, changes in the specific weights of leaves and roots over the growing season would affect the accuracy of root biomass or root surface area predictions.

The Arctic Tundra Simulator (ARTUS) is a computer—based simulation model of Eriophorum vaginatum tussock tundra ecosystems found in north central Alaska. ARTUS simulates the annual patterns of heat and water balance, carbon fixation, plant growth, and nitrogen and phosphorus cycling. ARTUS runs in 1—d time steps for a growing season from 1 May to 17 September and is intended to run for several years. The abiotic section of ARTUS encodes the seasonal input of the environmental driving variables and calculates the resultant thermal and water regimes to define the heat and water environments for the tussock tundra system. The primary driving variables are daily total solar radiation, air temperature, precipitation, surface albedo, wind, and sky conditions. The soil compartment contains three organic horizons, which are recognized by their state of physical and chemical decomposition, and one mineral horizon. Six vascular plant species and four moss species are simulated. The model has seven compartments for each vascular plant species: total nonstructural carbohydrates, total nitrogen, total phosphorus, leaves grown in the current season, leaves grown in previous years, conducting and storage stems plus roots, and absorbing roots. In ARTUS the functional unit of the plant is the shoot system or ramet. Each shoot system consists of leaves, stems, fine roots (which do not have secondary growth and have a limited life—span), and larger roots, which have secondary growth and an extended life—span. Although plant processes are based on individual shoots, the ARTUS model as a whole is based on a square metre of ground. Values per square metre are calculated from the values per shoot by multiplying by the shoot density of each species. The model was validated by comparing calculated and measured peak season biomasses and nutrient contents, and the seasonal progression of environmental processes, biomass, carbohydrate contents, and nutrient contents. ARTUS successfully simulated the seasonality of the physical environment, but simulated thaw depths were deeper than those measured at all sites. The simulated value for total vascular plant production was 77% of the measured value. The simulated values for ecosystem respiration for Eagle Creek were within the range of measured values. Simulations with ARTUS indicated different patterns of growth and different storage—carbohydrate levels in deciduous shrubs, evergreen shrubs, and graminoids. The simulated seasonal course of net primary production of vascular plants and mosses was similar to the pattern measured at Eagle Creek. Sensitivity analysis using ARTUS indicated that the tussock tundra is more sensitive to external environmental factors, such as increased temperature, than to internal ecosystem variables. The development of ARTUS was limited by the unavailability of data on whole—plant carbon balance including root and stem respiration. More data are also needed on decomposition processes and nitrogen and phosphorus cycling. Adequate climatological data for northern Alaska are needed for extensive validations of the model. While caution should be used in basing managerial decisions on model simulations, ARTUS can be used to identify and quantify the magnitude and direction of plant responses to changes in state variables in the model.

In December 1981 a 2 ha site of 54-yr southern California chaparral was burned. A frequent species on this site wasAdenostoma sparsifolium. This shrub regenerates after fire with stump sprouting. The total fine root (diam.

The effect of a fertilizer dose of 20 g nitrogen (N), 16 g phosphorus (P), and 20 g N + 16 g P m-2 on fine root growth and shoot development of four common shrubs was tested in the Chilean matorral, a typical mediterranean-type shrub vegetation. The fine root density (root diameter ~< 2 mm) was highest in late spring and lowest in late summer. The mean fine root length for the 6 mo research period reached 2 km m-2 in Lithraea caustica in the unfertilized controls and 7 km m-2 with N fertilization. Colliguaya odorifera responded similarly. In Cryptocarya alba, fertilizer reduced total fine root length. The fine roots of Trevoa trinervis, a N2-fixing shrub, did not respond to N addition, but enhanced fine root growth with P was observed. The effect of P and N + P on the other shrubs was erratic. In general, fertilizer application shifted the time of the peak of fine root biomass production from spring toward summer. Shoot response to fertilizer became visible only in the second growing season. Nitrogen enha...

The quantity of growing root tips per unit of soil volume was analyzed in a central Alaskan tussock tundra site. By June 10, the aboveground fraction of the vegetation had initiated the flush of spring growth and flowering while less than 5 active root tips cm-3 were found. By June 25 this value had increased to 30 root tips cm-3. Similar values in July were followed by a complete cessation of root growth after the first week of August. By then, leaf senescence had also become visible. In the spring, low root temperatures were responsible for the time lag between shoot growth initiation and the beginning of root growth. In early August, root growth stopped in spite of adequate soil temperatures and accumulated carbohydrate for root growth. It is proposed that use of reserve carbohydrate for root growth in August would compromise the flush of spring growth in the following year.

The effect of differential root and shoot temperatures on biomass production of the arctic sedges Eriophorum vaginatum and Carex bigelowii was analyzed under controlled environmental conditions. Both species showed active growth at 2 °C root and shoot temperatures although warmer conditions substantially enhanced biomass production. In E. vaginatum, under the optimal 12 °C root and 12 °C shoot temperature regime, about six times more biomass was produced than under the 2 °C conditions. The corresponding temperatures for C. bigelowii were 12 °C root and 22 °C air, although the data did not preclude a higher temperature optimum for this species. The results support the hypothesis that in arctic sedges the root/shoot biomass ratios are small with low root temperatures, i.e., a relatively large fraction of the photosynthate is allocated to leaf production under cold conditions.

The amount and distribution of organic matter was measured in different categories in six montane tundra vegetation types in a snow accumulation area and in tussock and intertussock areas in Eriophorum vaginatum tussock tundra in central Alaska. In root properties, the tussock and intertussock areas were more similar to the fellfield zone than to the vegetation zones below the snow accumulation area. Root density apparently increased as soil nutrients decreased, but this increase may be caused by higher soil moisture and higher root relative water content. The tussock tundra has accumulated more dead soil organic matter than any of the montane zones.

Seasonal patterns of leaf area increment and shoot elongation of six Chilean matorral shrub species were analyzed. The leaf area of individual shoots was measured weekly. The leaf area growth rates during the flushing period varied from 0.6 cm2/wk for Satureja gilliesii to 28.9 cm2/wk for Lithraea caustica. The six species had characteristic temporal growth patterns. Satureja gilliesii initiated growth shortly after the first winter rains in June while L. caustica, the last species to become vegetatively active, showed first leaf growth in November (late spring). Shoot elongation rates ranged from 0.06 cm/day for Colliguaya odorifera to 0.17 cm/day for the two summer-deciduous species, S. gilliesii and Trevoa trinervis. The species with low growth rates have long growth periods, and species with high growth rates have short but intensive flushing periods.

The objective was to measure the competition for nitrogen among vascular plants, mosses, and soil microbes along a continuum of nitrogen availability, induced by carbon and nitrogen amendments, in a tussock tundra ecosystem.15N was used as a tracer. Vascular plants showed an increasing15N recovery with increasing time and with increasing nitrogen availability; the latter suggests that nitrogen was limiting vascular plant growth. Green mosses took up15N initially, but showed no significant trends with either treatment or time. There was a higher15N recovery in the soil insoluble compartment for the carbon-amended treatment than in the nitrogen-amended treatments; this suggested that carbon as an energy source limited microbial activity. After two months, the relative15N recovery fell in the order: soil microbes (≈79%)>vascular plants (≈16%) >green mosses (≈2%).

Fine-root density in a mature cacao plantation in Bahia/Brazil was monitored at weekly intervals from October, 1980 until March, 1981. About 40 g m−2 of fine roots (diameter

Slow release fertilizer pellets (NPK) were spread in June and July 1985, on the frost surface under an 8–20 cm thick layer of thawed tundra in the northern foothills of the Brooks Range, Alaska. The fertilizer was applied at a rate of 3.8 kg N, 1.2 kg P2O5, and 2.4 kg K to two, 10 × 0.75 m tussock bands. These bands were placed parallel to the contour lines in the middle of a uniform 10° slope. The purpose of the experiment was to test the hypothesis that fertilizer moves at a measurable rate downslope, affecting the vegetation in its course. The results support this hypothesis. One year after fertilizer application, plants collected 2 to 6 m downslope from the fertilizer band had significantly larger leaves and significantly higher nitrogen and phosphorus concentrations than those upslope from fertilizer application. It is concluded that nutrient-releasing tundra perturbations affect the downslope tundra vegetation.

A B S T R A C T The annual rhythm of cambial activity is compared in Proustia cuneifolia and Acacia caven, two typical shrubs of the "matorral" in the semiarid region of central Chile. Proustia, a drought deciduous shrub, shows a typical desert cambial rhythm, highly sensitive to rainfall. The growth activity of this species is limited to the periods of adequate moisture. Acacia is an evergreen whose cambial activity is observed almost throughout the year; it is not synchronous with rainfall. Adaptation in this species seems to consist in developing long roots able to tap underground water. These results indicate that both shrubs, although growing together, have different adaptive strategies to the same xerophytic conditions. THE STUDY of the adaptations of plants to the

KUMMEROW, JOCHEN. (U. Chile, Santiago.) Endogenous fluctuations of germination capacity in Dactylis glomerata. Amer. Jour. Bot. 50(9): 915-920. Illus. 1963.-Dactylis glomerata caryopses, 'New Zealand' strain, furnished by the Ministerio de Agricultura of Chile, were enclosed in test tubes, carefully sealed with a Bunsen flame, and stored under constant conditions. Their germination capacity was periodically determined. In 1958/1959, a 2-peak annual germination curve was obtained. The germination increase was related with a diminution of the water content of the caryopses. The same material was seeded in 8 different zones of the Chilean Central Valley between 28?34' and 40?35' S. lat. The same germination procedures were practiced with the caryopses harvested in these 8 parcels. In the 1960/1962 period, 1-peak germination curves were found. We did not find the same relation between water content and germination as found in 1958/ 1959. There exists a certain relation between the velocity of germination and caryopsis origin. The velocity of germination decreases from north to south.

Ionic concentration and annual deposition of NO -3 -N, NH +4 -N, Ca2+, and Mg2+ from bulk precipitation and dry atmospheric deposition were studied for one year in southern California. Data were collected from an inland chaparral site at 1,300 m elevation, 75 km from the coast. The annual depositions of NO -3 -N and NH +4 -N amounted to 96.3 and 56.0 mg m-2 ground area yr-1, respectively. The corresponding values for calcium and magnesium ions were 207.4 and 57.4 mg m-2 yr-1. The average pH of rainwater was 3.74 (range 3.37 to 4.75), thus documenting acid rain for an inland site in California, distant from urban sources of air contamination. An estimate of nitrogen gains and losses indicated that the time between recurrent chaparral fires should be about 60 years in order to maintain a balanced nitrogen budget.

Fine root extractions from soil cores of a south facing slope in the Southern Californian chaparral were used to study the dynamics of feeder root growth in a summer-dry area. The studies were concentrated on the root systems of Adenostoma fasciculatum, Arctostaphylos glauca, Ceanothus greggii, and Rhus ovata. The total fine root biomass of Adenostoma fasciculatum increased from 0.6 g dm-3 in early spring to 3.6 g dm-3 in late summer. Considering the specific soil conditions at this site and earlier gained information on fine root distribution with depth, the value of 3.6 g dm-3 converts to 1.58 kg m-2 of ground shaded by the shrub canopy. The observed seasonal biomass increase is mainly due to the accumulation of dead root material in the soil when low soil moisture contents presumably inhibited decomposition processes. The total length of living fine roots also increased during the season, e.g. from 0.8 m dm-3 to more than 5 m dm-3 (0.35 km m-2 to 2.2 km m-2) in A. fasciculatum. Unusual summer rains in the research year stimulated vigorous fine root growth at a time when the normally low soil moisture would prohibit further fine root growth. The average fine root diameters and total lengths of fine roots beneath one square meter of ground surface allowed an estimate of root area indices (RAI) analogous to the leaf area indices (LAI). The data provide evidence for a significant fine root turnover in the chaparral.

The roots of matorral shrubs were excavated from an 18 m2 site of a mixed matorral stand located on a 27° NE facing slope at 1000 m elevation 40 km NNW from Santiago de Chile. The climate in this area is similar to that of the Southern Californian chaparral. The main species present were Lithraea caustica, Cryptocarya alba, Colliguaya odorifera, Mutisia retusa, and Satureja gilliesii. After harvesting the above ground biomass, the soil was washed out in 20 cm layers down to a depth of 60 cm. The roots were harvested according to their position in the site, separated into species and root size classes. Soil analysis indicated a fertile and deep reaching, clayish soil. L. caustica was a deep rooting species with many thick roots growing deeper than 60 cm. This species had a massive burl of 67 kg dry weight in the excavation site. Cryptocarya was less deep rooting, and C. odorifera had a shallow root system. It is thought that the root: shoot biomass ratios of 4.9 and 1.4 for L. caustica and C. alba respectively are indicative of the forest character of this site in the past. This forest would have been destroyed by continuous charcoal manufacture. The bulk of the fine roots was found in the 20-40 cm soil layer. The average distance between fine roots was calculated as 1.9 cm. The results were compared with an earlier excavation in the Californian chaparral.

Root systems of chaparral shrubs were excavated from a 70 m2 plot of a mixed chaparral stand located on a north-facing slope in San Diego County (32°54' N; 900 m above sea level). The main shrub species present were Adenostoma fasciculatum, Arctostaphylos pungens, Ceanothus greggii, Erigonum fasciculatum, and Haplopappus pinifolius. Shrubs were wired into their positions, and the soil was washed out beneath them down to a depth of approximately 60 cm, where impenetrable granite impeded further washing and root growth was severely restricted. Spacing and interweaving of root systems were recorded by an in-scale drawing. The roots were harvested in accordance to their depths, separated into diameter size classes for each species, and their dry weights measured. Roots of shrubs were largely confined to the upper soil levels. The roots of Eriogonum fasciculatum were concentrated in the upper soil layer. Roots of Adenostoma fasciculatum tended to be more superficial than those from Ceanothus greggii. It is hypothesized that the shallow soil at the excavation site impeded a clear depth zonation of the different root systems. The average dry weight root:shoot ratio was 0.6, ranging for the individual shrubs from 0.8 to 0.4. The root area always exceeded the shoot area, with the corresponding ratios ranging from 6 for Arctostaphylos pungens to 40 for Haplopappus pinifolius. The fine root density of 64 g dry weight per m2 under the canopy was significantly higher than in the unshaded area. However, the corresponding value of 45 g dry weight per m2 for the open ground is still high enough to make the establishment of other shrubs difficult.

In the foothills of the Philip Smith Mountains, Brooks Range, Alaska, tussock tundra occurs on rolling hills and in valleys that were shaped by Pleistocene glaciations. During the 1986 and 1987 summer seasons, Sphagnum growth and production were determined in "water tracks" on tundra slopes that acted to channel water flow to the valley bottom stream and in "intertrack tundra" areas that were relatively homogeneous with respect to downslope drainage. Measurements were made under ambient environmental conditions and on mosses receiving supplemental irrigation in each area. Growth rate for Sphagnum spp. (cm shoot length increase/day) was low and relatively constant in intertrack tundra and highest but quite variable in water tracks. A strong negative correlation was found between Sphagnum spp. growth rate and solar irradiance in the shady environment below Salix canopies in the water tracks. Estimates of net annual dry weight (DW) production for Sphagnum spp. ranged from 0.10 g DW dm-2 yr-1 in intertrack tundra vegetation to 1.64 g DW dm-2 yr-1 in well-shaded water tracks. Experimental water additions had little effect on growth and production in intertrack tundra and well-developed water tracks, but significantly increased growth in a weakly-developed water track community. Low production over large areas of tundra slopes may occur due to presence of slow growing species resistant to dessication in intertrack tundra as opposed to rapidly growing less compact species within the limited extent of water tracks. We hypothesize that species capable of rapid growth occur also in weakly-developed water tracks, and that these are water-limited more often than plants occurring in well-developed water track situations. Where experienced, high light intensity may additionally limit growth due to photoinhibition.

Individual shoots of the shrubs Ledum palustre L., Vaccinium uliginosum L., and Betula nana L. were severed from their parent plants beneath the moss surface in an Alaskan tussock tundra. These shoots remained one year in their original position in peat moss cushions without further disturbance. After this period fine root dry weight, fine root surface area, leaf dry weight, and leaf area of these shoots were measured and compared with equivalent values from unsevered control shoots. Dry weight ratios of fine roots/leaves were similar in cut and control shoots, with the exception of B. nana. The fine root surface/leaf area ratios showed significant differences between control and cut shoots except in L. palustre. Without tedious rootlet extractions it should be possible to estimate fine root surface area from leaf area of L. palustre.

The ever increasing urge for intensive and highly productive agriculture demands from biological research the answers to numerous new or scarcely investigated questions. Besides the more spectacular problems of genetic research, the use of foliar fertilizers, the intensive application of herbicides and insecticides, etc., there are many other unresolved problems. The work on such problems may not provoke another “green revolution” but may help our understanding of the physiology of development, a field of considerable practical importance.

Vast territories in the Mediterranean Basin, in southern California, South Africa, southwestern Australia and central Chile are characterized by a physiognomically uniform vegetation. In general terms the predominant vegetation of these regions is termed “xerophytic” according to the concept of Schouv (1822), who so designated plants of dry habitats. Later this concept has been narrowed and precisely defined. Thoday (1933) proposed that the term “xerophyte” should not carry any particular functional or structural implication, but should be used for plants of dry areas, irrespective of their modes of adaptation to such habitats. Walter and Kreeb (1970) state that xerophytes are those plants growing in arid zones and on dry habitats without access to ground water. The aboveground organs of these plants remain alive through the entire year with the exception of the foliage of deciduous species. Excluded from this group are the water accumulating species, the succulents. Nevertheless, the remaining group of xerophytes is still extraordinarily heterogeneous and has been further subdivided. Walter and Kreeb (1970) distinguish the poikilohydrous, malakophyllous, sclerophyllous, aphyllous, and stenohydrous xerophytes.

The summer dry, winter wet climates (Mediterranean) of the world are located in five disjunct areas which generally lie on the west sides of continents between latitudes of 30° to 40° (Fig. 1). All of these areas have vegetations dominated by evergreen sclerophyllous shrubs and trees, and with annuals and herbaceous perennials as additional important vegetation components (Specht, 1969; Mooney and Dunn, 1970; di Castri and Mooney, 1973).

Root growth rates of the sedge Eriophorum vaginatum L. were studied under controlled environmental conditions. The air temperature was maintained constant at 15°C while the root temperatures varied in 5°C intervals between 2° and 37° C (12° C excluded). Root growth rates of 1.2 mm d-1 at 2°, 20.4 mm d-1 at 32° C and 10.1 mm d-1 at 37° C were recorded. A Q10 of 3.2 was calculated for the temperature range from 7° to 27° C. Root growth rates at temperatures above 17° C declined after one week of growth. The degree of decline was proportional to the applied root temperature. Depletion of available nonstructural carbohydrate was the probable cause for this decline.