Nutrient gain from wet and dry atmospheric deposition and rainfall acidity in southern California chaparral.

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.

Temperature effect on growth rates of Eriophorum vaginatum roots.

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.

Seasonal root growth in the arctic tussock tundra.

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.

Root studies in the Chilean matorral.

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.

Seasonal changes of fine root density in the Southern Californian chaparral.

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.

Root systems of chaparral shrubs.

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.