Roots Of Herbaceous Plants Research Articles

Internal axial light conduction in the stems and roots of herbaceous plants

In order to reveal any roles played by stems and roots of herbaceous plants in responding to the surrounding light environment, the optical properties of the stem and root tissues of 18 herbaceous species were investigated. It was found that light was able to penetrate through to the interior of the stem and was then conducted towards the roots. Light conduction was carried out within the internodes and across the nodes of the stem, and then in the roots from the tap root to lateral roots. Light conduction in both the stem and root occurred in the vascular tissue, usually with fibres and vessels serving as the most efficient axial light conductors. The pith and cortex in many cases were also involved in axial light conduction. Investigation of the spectral properties of the conducted light made it clear that only the spectral region between 710 nm and 940 nm (i.e. far-red and near infra-red light) was the most efficiently conducted in both the stem and the root. It was also found that there were light gradients in the axial direction of the stem or root, and the light intensity generally exhibited a linear attenuation in accord with the distance of conduction. These results revealed that tissues of the stem and root are bathed in an internal light environment enriched in far-red light, which may be involved in phytochrome-mediated metabolic activities. Thus, it appears that light signals from above-ground directly contribute to the regulation of the growth and development of underground roots via an internal light-conducting system from the stem to the roots.

Herbivore abundance is independent of weather? A 20‐year study of a galling aphid Baizongia pistaciae (Homoptera: Aphidoidea)

AbstractThe gall abundance of Baizongia pistaciae (L.) (Pemphiginae: Fordini) on marked Pistacia palaestina trees (Anacardiaceae) was monitored for 20 years at two natural sites in Israel (Carmel, in the center of the host distribution, and Beit Guvrin, near its southern limit), and in the botanical gardens of Tel Aviv University. Gall abundance varied between zero and 500 galls/tree and fluctuated from year to year. The analysis aimed at a diagnosis of the underlying causes of the temporal changes in gall abundance. Weather variables were expected to synchronize gall abundance on most trees on the same site. There was little indication of synchrony among trees in most years. Correlations of mean gall abundance with weather variables were low (<0.4, explaining <16% of the variation) and almost none were significant. The temporal pattern of gall abundance was analyzed for every tree separately (the “autecological” paradigm). There was no convincing evidence of self‐regulation (density‐dependence) in gall abundance on any tree, although the rate of change in abundance tended to decrease with increasing density on some trees. At one site (Carmel), significantly more abundance peaks (1 SD above the mean) occurred in “wet” years (precipitation above average) than in “dry” years. This pattern was not observed at the other sites. The biannual fluctuations in abundance, observed in the first 10 years of the study, were far less clear when the 20‐year sequence was analyzed. If the causative mechanism is tree stress – as assumed previously – then the biannual pattern may not be expected except in years of favorable conditions, when gall abundance is high enough to drain the tree of resources and cause a lower gall abundance the following year. The life cycle of galling aphids is very complex. A clone enclosed in a gall on a tree alternates with a subterranean population on the roots of herbaceous plants, with two migratory phases in between. Moreover, a sequence of parthenogenetic generations is interrupted by a single event of sexual reproduction. In B. pistaciae, this cycle takes two years to complete. Regulating mechanisms of gall abundance at the different stages may work in different directions, canceling each other out. I suggest that direct effects of weather on the aphids at any stage of their complex life cycle may be obscured when the net result (gall abundance) is studied. Weather effects may be detectable only when it is extremely favorable or unfavorable for the aphids (or the host plant).

Decomposition of fine roots of Pinus kesiya and turnover of organic matter, N and P of coarse and fine pine roots and herbaceous roots and rhizomes in subtropical pine forest stands of different ages

Organic matter accumulation, N and P concentrations of fine (<2 mm diameter) and coarse (2–10 mm) roots of Pinus kesiya and fine roots and rhizomes of ground vegetation, and decomposition of P. kesiya fine roots (<2 mm diameter) were studied in 6-, 15- and 23-year-old P. kesiya forest stands at Shillong, the capital of Meghalaya, India. The mean annual dry weight of P. kesiya fine roots did not vary significantly between the stands, but the coarse root mass increased significantly from the 6- to 23-year-old stand. However, herbaceous fine roots and rhizomes showed a reverse trend. Live roots (biomass) showed a higher N and P concentration than the necromass (dead root mass). Nutrient concentrations were greater in the fine roots compared to coarse roots. N and P accumulation was maximum in the 6-year-old stand and minimum in the 15-year-old stand. P. kesiya fine roots decomposed in a three-phased manner in all the stands. The first phase, lasting about 30 days, was characterised by a slow rate of weight loss. This was followed by a rapid phase of weight loss up to 90 days, with an average weight loss of 7.7 mg day–1, and the third phase showed a slow decay pattern (1.2 mg day–1). The weight loss pattern showed a strong seasonal trend; a faster rate of decay in the warm-humid period and a slow rate of decay in the dry-cold period. Nitrogen and P concentration in the decomposing root litter showed a marked decrease and/or increase during decomposition. The study reveals that in the 6-year-old pine stand the roots of herbaceous plants play a more significant role in maintaining the organic matter, N and P status of the soil, while in the older stands pine roots assumed greater significance.

The response of roots of herbaceous plant species to heavy metals

Current knowledge on the uptake, translocation and distribution of heavy metals in plants is summarized, with emphasis on the roots of herbaceous plants and their reactions to this kind of stress. Results from investigations at several contaminated sites in the Eastern Alps of Europe (predominantly mine spoil) on heavy metal accumulation and exclusion characteristics of plants are presented. General resistance strategies of plants are discussed indicating some possible misunderstandings in the usage of resistance terminology. Finally, some neglected questions on topics in the ‘mainstream’ of experimental work on heavy metals and plants are considered.

EVOLUTIONARY REDUCTION OF COMPLEX LIFE CYCLES: LOSS OF HOST-ALTERNATION IN PEMPHIGUS (HOMOPTERA: APHIDIDAE).

In a Utah canyon, the aphid, Pemphigus betae, exhibits two life cycles: a cycle involving host-alternation between cottonwood trees and roots of herbaceous plants and a secondarily reduced cycle, in which the cottonwood generations are eliminated so that wingless forms live year round on roots. Relative frequencies of the two life-cycle types vary along a 30-km stretch of the canyon, with the reduced cycle predominating at upper sites. Factors underlying this life-cycle variation were examined with common-garden and transfer experiments. Results showed 1) a facultative increase in production of alternating forms in response to crowding in root colonies, 2) a genetic component to both within- and between-site variation in tendency to produce alternating morphs, and 3) site-specific environmental effects on level of investment in the reduced versus alternating life cycles. Thus, the variation in frequency of life-cycle reduction in this aphid is dependent on a complex of interdependent factors. These include adaptive phenotypic plasticity, microgeographically variable cues affecting mechanisms of morph determination, and genetically based variation in tendency to show reduction versus alternation. Genetic variation between sites corresponds to microgeographic variation in success of life-cycle phases. Where cottonwood hosts are absent (lower elevations) or where the cottonwood phase has low survival (upper elevations), clones tend to produce fewer migrating morphs, as compared to clones from middle elevations, where the cottonwood phase is relatively favorable. Such independence between conditions in alternate phases is a general feature of complex life cycles and can generate strong site-specific selection for permanent life-cycle reduction. Such life-cycle shifts have sometimes been followed by extensive radiations in aphids and other groups.

Vascular differentiation in the pear root

Abstract does not appear. First page follows. Introduction The present paper deals with the development of the root of Pyrus communis L., with special attention to the vascular tissues. Though considerable information is available on root structure of herbaceous plants (Hayward, 1938); (Esau, 1940),3 only one rather complete account of tissue differentiation in a root of a woody species appears to exist in modern botanical literature (Hayward and Long, 1942). The need for such accounts in the teaching of plant anatomy, especially in agricultural institutions, is obvious. The present problem was selected also because of the writer’s interest in the differentiation of the phloem tissue in different organs of seed plants. Since many studies have been made on the phloem of roots of herbaceous plants (review by Esau, 1943), it seemed timely to add some data on the ontogeny of this tissue in a woody root. Materials and Methods The root material used in preparing the permanent slides and the photomicrographs was obtained from trees grown in a culture solution by the Plant Nutrition division at Berkeley. The material was killed in a formalin-acetic-alcohol fixing fluid and imbedded in paraffin after ordinary dehydration and clearing in mixtures of ethyl alcohol and xylene. The roots grown in the culture solution were compared with soil grown roots from young trees 5 to 6 inches high grown from seeds of the Winter Nelis variety. The latter roots were examined in free-hand sections.