The chemical and mineralogical content of the plants of the Lake Huleh Preserve, Israel

Abstract

The Lake Huleh Project has involved as complete a biological, chemical and mineralogical study as possible with the intent that a biological and chemical history could be constructed of this basin, long thought to be one of the centres of origin of agriculture. The primary object of this aspect of the project was to gain some understanding of the chemical and mineralogical composition of the plant communities occupying the nature preserve and contiguous areas and what effect these communities have had on the chemical composition of past and present lake basins. Lake Huleh, the first lake that the Jordan River used to form, was drained between 1951 and 1958. A small area of this lake was retained as a nature preserve. Twentynine pl^nt families are represented here by 57 genera containing 71 species. On analysis, these species were found to be composed of 46 elements and 11 minerals. This paper is confined to these findings. A comparison of the chemical composition of annual and perennial plants revealed that only Na, Si and Mn were significantly (beyond the 0.1% level) taken up by perennials, while annual plants contained more K, Mg, P and Cl. A further subdivision relating habitat and chemical composition showed that aquatic plants contained significantly more Na, K, Si, S, P, Cl, Mn and opal minerals than their terrestrial counterparts. Rubidium, Cs, Li, Ag, Be, Hg, Ge, Pb, Se, Bi, V, F, Br, I, Fe, Co and the oxalate minerals exhibit the same pattern, but do not have concentrations statistically significantly different from those of land plants. Land plants were composed of more Mg, Ca, sylvite (KC1), calcite, quartz and gypsum than water plants. In addition, concentrations of Cu, Sr, Ba, Zn, Cd, B, Al, Sc, Y, La, Ce, Sn, Ti, Zr, Hf, Cr, Mo, As and Ni, though not statistically significantly different from those in water plants, followed the pattern observed in land plants. One of the unexpected discoveries in this study was the variation of 29 elements within the leaves of the Cyperaceae, the Typhaceae and the Gramineae. Although only 10 of these elements exhibit variation that is statistically significant, the remaining 19 vary in a consistent fashion. The elements that concentrate in the margins of leaves of these families are Na, Ag, Be, Ca, Sr, Ba, B, Al, Ga, Si, Ge, Pb, Cl, Br, I, Mn and Fe, while those concentrated in the midsection are K, Rb, Cs and Li and those in the blade are Cu, Mg, Zn, Cr, Mo and P. It is proposed that the function of these distributions may lie in protection against inclement conditions and insect damage, while those elements that are structurally important may function to retain leaf shape or be instrumental in forming the shape itself. A comparison was made between elemental composition and taxonomic position. It was found that K, Rb, P, Bi and F decrease with evolutionary time; that is to say the Nymphaeaceae contain more of these elements than the Gramineae. On the other hand, Si and Ti concentrations increase with time, the Gramineae containing larger amounts of these elements than the water lilies. These relationships were found to be significant at levels varying from 5.0 to 0.1%. It is proposed that the structurally important Si and Ti may act as a defence mechanism in that high concentrations of either or both of these elements tend to make plants less palatable. Nutritionally important elements such as K and P may decline in concentration with time as plants through adaptation become more efficient in their use of essential elements. This kind of conservation may permit population expansion, thus ensuring the longevity, in the evolutionary sense, of the species. It is important to note that seven out of 46 elements are taken up in relation to their phylogenetic position. Elemental content of the plants is subdivided into geochemically coherent groups. Each group is compared with what is known of the particular association in similar species grown in other parts of the world. Pertinent ratios of elements in Huleh plants are contrasted with means of the same elements in land plants, Huleh soils, Huleh rocks and the earth’s crust. A comparison of the elemental composition of parasitic plants and their hosts is also presented. Cuscuta planiflora (Cuscutaceae) parasitizes the legume Alhagi mannifera (Fabaceae). Under normal circumstances, the former is an annual inhabiting swamps and the latter a perennial growing in waste places. Cynanchum acutum (Asclepiadaceae) parasitizes (usually is epiphytical) the grass Phragmites australis (Gramineae). Both plants are perennial in their life cycle; the former is an inhabitant of moist places and the latter is a swamp resident. C. planiflora has 28 elements more concentrated in its tissues than in those of its host and C. acutum has 31 more concentrated in the whole plant than in the leaves of the host plant. C. planiflora derives water and elemental nutrition through haustoria embedded in the stems of its host. Microscopic examination revealed that the vascular elements of host and parasite were close together. If a ratio is calculated between the elements in C. planiflora and A. manifera , when the concentration in the former is greater than in the latter, only Bi and Mo have ratios higher than 2. In the reverse instance, only P and As have ratios greater tha.n 2. It is suggested that these observations are characteristic of an efficient relationship between parasite and host. The picture presented by C. acutum-P. australis is quite different from that of C. planiflora-A. mannifera . In the case where C. acutum contains higher concentrations than its host, the following ratios have been observed: 1- 2, Rb, Li, Cu, Sr, Ba, Zn, Pb; 2-5, Na, K, Cs, Ag, Mg, Ca, P, S, F, Co; 5-18, Be, Hg, B, Si, Sn, Mo and Cl. In the reverse case, where the host contains higher concentrations than the parasite, the following ratios were noted: 1-2, As, V, Cr, Br, Al, Ga, La, Ce; 2-5, Fe, Mn, Y, Ti; 5-18, Ge. It is suggested that the lack of uniformity of the ratios between the two of parasite-host combinations is probably due to the fact that C. acutum is usually epiphytic on P. australis and becomes parasitic only under dire circumstances. The mineralogical composition of Huleh plants may be divided into groups containing sylvite, oxalates, carbonates, siliceous minerals and finally, sulphates. Most plants form some oxalates, some carbonates and siliceous minerals. Sylvite (KC1) was detected only in the Urticaceae, Chenopodiaceae, Asteraceae and Typhaceae. It is suggested that an overabundance of light, in excess of that required by a particular species, encourages sylvite formation. Magnesium oxalate dihydrate (α form) has no mineral name. Its distribution in Huleh plants was confined to the Nymphaeaceae, Ghenopodiaceae, Amaranthaceae and Polygonaceae. It is suggested that the older plant families are more likely to form this mineral than those more recently evolved. Gypsum was found to occur in the Urticaceae, the Tamaricaceae, Fabaceae, Asclepiadaceae, Cuscutaceae and Asteraceae. It was encountered in C. planifora- A. mannifera and C. acutum but was not detectable in P. australis . All data here described were analysed by linear and multiple correlation techniques. In addition, it was of interest to discover whether there was more chemical similarity between plants of different genera residing in the same area on the same soil than between plants of the same genera living in different regions. It became clear, with the aid of statistical methodology, that plants inhabiting some parts of the Huleh preserve reflect the chemistry of the soil more profoundly than their genetic differences, whereas in other parts the genetic factors were more pronounced.