DIFFERENTIAL RESPONSE OF THE EDAPHIC ECOTYPES IN CYNODON DACTYLON (L)

Transcription

1 DIFFERENTIAL RESPONSE OF THE EDAPHIC ECOTYPES IN CYNODON DACTYLON (L) PERS. TO SOIL CALCIUM BY P. S. RAMAKRISHNAN* AND VIJAY K. SINGH Department of Botany, Panjab University, -^, India {Received 24 April 1965) SUMMARY This paper describes the differential response to calcium of the three edaphic ecotypes of Cynodon dactylon (L) Pers. growing, respectively, on non-calcareous, moderately calcareous, and highly calcareous soils. A close correlation was discernible for the three populations with the habitats they occupy in nature. The population from a highly calcareous soil showed a better yield in calcareous soils than in non-calcareous soils, though in highly calcareous soils it tended to decrease. The reverse was found to be the case for the population from non-calcareous soils; the population from moderately calcareous soil showed an intermediate behaviour. ly different responses were found between the three populations with regard to mineral uptake in both calcareous and non-calcareous soils. Although calcium uptake was higher in the case of plants from non-calcareous soils compared to those from calcareous soils in experiments using calcareous and non-calcareous soils, in extremely calcareous soil the reverse was found to be the case. The ash content and the uptake of calcium, potassium and magnesium, in general, increased with increase in soil calcium level. However, the calcium uptake of the populations from moderately calcareous or non-calcareous soils and the magnesium uptake of the latter decreased in highly calcareous soils. It is concluded from the present studies that there are at least three 'edaphic ecotypes' within this species, each markedly different from the other in its physiologic-ecological attributes and that the basis for the differentiation is chiefly due to their response to soil calcium. INTRODUCTION Three edaphic ecotypes were recognized within the 'red ecotype' (Ramakrishnan, 1961(7, h) of Euphorbia thymifolia growing in soils with different levels of soil calcium (Ramakrishnan, 19650, b) and also within Tridax procumbens (Ramakrishnan and Jain, 19650, b, c). It was shown from these studies that the edaphic ecotypes in these two species show differential response to soil calcium with regard to seed germination, growth performance and mineral uptake. The present paper deals with the differential response to calcium within the species Cynodon dactylon (L). Pers., a pasture grass which forms extensive meadows in the plains of India. Preliminary observations of the populations at revealed that this species occurs in three distinct soils of different origin: (i) the Gangetic alluvium at ; (ii) the conglomerate (about 15 km from ); and (iii) the highly calcareous soil derived from the limestone rocks at (about 25 km from ). Hence, a detailed study of the growth yield and mineral uptake of these three populations of C. dactylon was undertaken. * Present address: Department of Botany, University of Western Ontario, London, Ontario, Canada.

2 Edaphic ecotypes in Cynodon dactylon METHODS Leaf samples from fully mature plants were collected for chemical analysis from ten sites in each of the habitats of, and. Culture experiments were done by transplanting small pieces of the shoot (ramets) of uniform size, with four leaves, on to a neutral substratum at the Botanical Garden at or into culture pots. Culture experiments were conducted from August to November 1964, and the leaf samples of the three populations were analysed at the end of the experiment (after 4 months growth). Two grams of dried and powdered leaf sample were used for chemical analysis. Total plant ash, calcium, potassium and magnesium were determined by dry ashing the leaf sample and following the procedure given by Piper (1944). Phosphorus was determined colorimetrically using the chlorostannous-reduced molybdophosphoric blue method. The level of minerals found in the leaf samples was taken as an indicator of the amount taken up by the plant. RESULTS ioi Soil The soils of the three habitats were markedly different from each other. The data presented in Table i show significant s between the three habitats at the o. i % level of probability for ph, exchangeable calcium and carbonates. Differences have also been noted at 5% level between exchangeable potassium, magnesium and phosphate. Table i. Soil analysis of the three habitats {mean values + standard error) ph 8.08 ± ± ± Total ± ± ± Exchangeable bases (m-equiv. Calcium Potassium ± ±2.74 ± ± ± /\ /o) Magnesium ± ± ± Carbonates (%) ± Exchangeable phosphate (mg/ioo g) ± ± ± soil is highly alkaline compared to the and soils. The soils of the latter two habitats are also alkaline but tend more towards neutrality. soil was found to be extremely rich in exchangeable calcium compared to soil. soil was moderately well supplied with calcium. soil was found to be rich in exchangeable magnesium compared to the soils of the other two habitats. soil was found to have a better supply of exchangeable phosphate compared to and soils. No significant was found for exchangeable phosphate between the habitats of and. Mineral uptake in natural habitats The three populations showed markedly different levels of minerals in the leaf tissue. Signiffcant s were obtained at 0.1% level of probability for calcium and potassium uptake and at the i % level for ash content and magnesium uptake. The population showed a consistently higher level of ash, calcium, potassium and magnesium

3 IO2 P. S. RAMAKRISHNAN AND VIJAY K. SINGH in the leaf tissue than the population. The population was more or less intermediate between the other two except in the case of magnesium content, which showed the lowest level. No significant s were found with regard to phosphorus in the leaf tissue (Table 2), Table 2. Mineral content of leaves for the three populations of Cynodon dactylon in their natural habitats {mean values + standard error) Ash (%) ± ± Calcium 2-33 ± ± ± Potassium (7o) ± ± ± MagnesiuiT1 rhospho (7o) (mg/g ±0-433 ± ±0,618 ± ±0.910 ± Growth and mineral uptake on a neutral substratu?n In order to discover if the s in mineral uptake were genetically determined, and also to find out if there were any inherent s in the growth yield of the shoot, ramets of the three populations of Cynodon dactylon were transplanted to a non-calcareous neutral substratum in the Botanical Garden at. The experiment was designed in a randomized block manner and was replicated three times. The soil of the neutral substratum analysed before starting the experiment showed 12 m-equiv. % of exchangeable calcium. The plants were harvested after 3 months of growth. The results (Table 3) showed significant s between the three populations in growth yield and mineral uptake. The population showed the best growth and a higher content of calcium, potassium, magnesium, phosphorus and ash than the other populations. The population was intermediate between the and populations in all respects except potassium and phosphorus contents, when it gave the lowest values. Table 3. Groivth and mineral uptake {mean values) of the three populations of Cynodon dactylon grown on a neutral substratum Dry weight of Ash Calcium Potassium Magnesium Phosphorus shoot (g) (%) (%) (%) (%) (mg/g) 35, , , ,15 1,99 3,27 2, , Growth and mineral uptake from soils with different levels of calcium The data presented in Table i showed that the soils of the three habitats have markedly different levels of calcium and that the three populations show marked s in growth and mineral uptake, both on a neutral substratum and in nature. Experiments were therefore designed to study the behaviour of the three populations in noncalcareous and calcareous soils.

4 Edaphic ecotypes in Cynodon dactylon 103 Three sets of five culture pots were filled with garden soil. One pot of each set was kept as a control and the soil of the other four of each set was treated with powdered limestone brought from so that the soil had 2, 5, 8 and 12"^ CaCOj respectively. The analytical data of the control and the treated soils in culture pots at the end of the experiment are given in Table 4. Table 4. Analysis of the soil in culture pots zvith different calcium levels 3 added to soil in pots Control 2% 5% 8% 12.% ph Carbonates (%) o Exchangeable calcium (m-equiv. %) Growth yield. Dry weight yields of the shoots given in Table 5 show significant s between the three populations at the 0.1 level of probability, between the treatments at the i (, level and for their interaction at the 5/^, level. The population showed a consistently higher dry weight in both calcareous and non-calcareous soils than the population, while the population was intermediate. Further, it was found that the s between the three populations were more pronounced at lower levels of calcium in the soil than in highly calcareous soils. The and populations showed an increase in growth yield up to 5 o CaCOj in the soil, but at higher levels they showed a decrease. The population showed an increase in dry weight yield up to 2% CaCOj in the soil, but at the 5,, level it showed a slight decrease, and at higher levels it showed a marked decrease. Table 5. Fffect of soil calcium on the dry weight yield {g) of the three populations of Cynodon dactylon {mean values) Control % CaCOa added 5/O to soil in pots no,' /o % Some significant s were found at the 5 ^ level of probability for dry weight yield of root between the three populations. These s between the three populations are recognizable only in the comparatively non-calcareous soils, and above 5% CaCOj in the soil no significant s were noticed. In the case of the population, the dry weight yield of the root increased gradually up to 5% CaCOj in the soil and then decreased. The population showed an increase of dry weight yield of the root at 2% CaCOj in the soil but it decreased at higher levels. The population showed more or less the same dry weight yield of the root in the various treatments (Table 6) Table 6. Effect of soil calcium on dry weight yield of the root {g) of the three populations of Cynodon dactylon {mean values) Control CaCO3 added to soil in pots 2% 5% 8% 12%

5 IO4 P. S. RAMAKRISHNAN AND VIJAY K. SINGH Up to 5% CaCOj in the soil, the population showed a high value for the root/shoot ratio and the population gave the least value, the population being intermediate. However, in highly calcareous soils, the population gave higher values than the other two and this time the population was intermediate. The and populations showed an abrupt increase in the values for root/ shoot ratio at 2"o CaCOj in the soil compared to the controls, and at higher levels of CaCOj they decreased to more or less constant values. The population gave more or less the same root/shoot ratio in both calcareous and non-calcareous soils (Table 7)- Table 7. Effect of soil calciitm on root/shoot ratio {mean values) of the three populations of Cynodon dactylon Control o CaCOj added - 0, 0.I9I to soil in pots 00/ O/o % Mineral uptake. The leaf samples of the three populations, growing under various calcium levels in the soil, were analysed in order to determine s in the uptake of various mineral nutrients. The results presented here are each based on the mean of two determinations. s have been found between the three populations at the i % level of probability, between the treatments at the 0.1% level and also for their interaction at the 0.1 o level. The ash content of the population was consistently higher than the population in the control soil and the treated soils, except at 12% CaCOj in the soil when the reverse was true. The population was intermediate between the other two. In the case of the population, at i2/o CaCOj in the soil the ash content was much higher than in the control and other treated soils. The and populations showed more or less the same level of ash content in the various treatments (Table 8). Table 8. Effect of soil calcium on ash content { ^) of the three of Cynodon dactylon {mean values) populations Control CaCOj added to soil in pots 2% 5% 8% 12% diff'erences between the and populations were found in calcium uptake from soils containing more than 5,, CaCOj. At lower levels of calcium in the soil, no significant s were found between the populations. The population was intermediate in calcium uptake between the other populations. In general, calcium uptake was higher for the population than the population, except in the soil with 12% CaCOj where the population showed a much higher uptake than the others. The uptake of calcium for the population showed a gradual increase up to 8% CaCOj in the soil and at 12% there was a marked increase. For the population, the uptake increased gradually up to 8% CaCOj in the soil and at

6 Edaphic ecotypes in Cynodon dactylon % there was a sudden fall. The population showed a similar behaviour to the population (Table 9). Table 9. Fffect of soil calcium on calcium content (%) of the three populations of Cynodon dactylon {mean values) Control ooo % CaCO 3 added 5% to soil in pots 00/ O/O % Data presented in Table 10 show significant s for potassium uptake between the populations at the 1 % level of probability, between the various treatments at the 0.1% level and for their interaction at the 0.1% level. The uptake of potassium in the case of the population was consistently higher than in the case of the other two populations. The population had the least amount of potassium in the leaf tissue whilst the population was intermediate between the other two. The and populations showed an increase in potassium uptake with increase in soil calcium. The population showed more or less the same level of potassium uptake in all treatments except in the soil with 12% CaCOj where it showed a sudden increase. Potassium uptake gradually increased, in the case of the population, up to 8 o CaC03 in the soil and at 12% it increased abruptly. Table 10. Fffect of soil calcium onpotassiitm content {%) of the three populations of Cynodon dactylon {mean valttes) Control % I -915 I CaCOj added 5% to soil in pots 2.OS % O.I2O The population showed a significantly higher uptake of magnesium than the other two. The population consistently showed a lower level, while the population was intermediate between the other two. The population showed a greater increase in uptake of this mineral in calcareous than in non-calcareous soils. Uptake of magnesium in the case of the population increased gradually with increase in soil calcium up to 8% CaCOj but at 12% it decreased (Table 11). Table 11. Fffect of soil calcium on magnesium content (%) of the three populations of Cynodon dactylon {mean values) Control % CaCOj added 5% to soil in pots 8% %

7 io6 P. S. RAMAKRISHNAN AND VIJAY K. SINGH No significant s were found in phosphorus uptake between the three populations, the various treatments and their interaction (Table 12). Table 12. Effect of soil calcium on phosphorus content {mgjg) of the three popidations of Cynodon dactylon {mean values) Control CaCOj added to soil in pots 2% 5% 8% i2 /o (P = o-os) i-i i.4» O DISCUSSION Very little data has as yet been published on the differential response between natural populations within a plant species to edaphic factors. Results are presented here for Cynodon dactylon, and similar studies have been published for populations of Euphorbia thymifolia (Ramakrishnan, i()6ia, b, 19650, b) and Tridax procumbens (Ramakrishnan and Jain, 19650, b, c) thriving at, and. These results, together with those obtained for populations occurring on and off serpentine soils by Kruckeberg (1951, 1954), Walker, Walker and Ashworth (1955) and McMillan (1956), and for populations of Eestuca ovina by Snaydon and Bradshaw (1961), all suggest that such ecotypic differentiation within a species is more frequent than the present lack of information indicates. In nature, the three populations of Cynodon dactylon occupy very diverse habitats with markedly different levels of exchangeable calcium. These populations show a varying capacity to accumulate different minerals in the leaf tissue and these s are maintained even when the three populations are cultivated on a neutral substratum. ly enough, the population of this species showed much greater uptake of various nutrients compared with the population, the population being intermediate between the other two. This is of interest since the population grows in a comparatively non-calcareous soil with a low supply of exchangeable bases compared to the other two populations. This is therefore in contrast to the 'red ecotype' (Ramakrishnan, 1961a, b) oi Euphorbia thymifolia (Ramakrishnan, 1965^) where the population showed better capacity to accumulate various minerals than the and populations, the latter showing the least capacity for tiiineral accumulation. A close correlation was discernible for the three populations of Cynodon dactylon with their natural habitats. The population, which occupied a highly calcareous soil, showed better growth yield in calcareous soils than in non-calcareous soils, though in extremely calcareous soils the growth yield tended to decrease. The population showed better growth in comparatively non-calcareous soils than in calcareous soils, while the population showed an intermediate behaviour. In general, the population showed better growth in both calcareous and non-calcareous soils than the population. s were noted for dry weight yield of the root between the three populations only in non-calcareous soils. The population gave significantly low values for root production compared to the other two populations. It was interesting to note that in calcareous soils the root production was more or less the same for all the three populations. Further, it was seen that in the case of the population, the root production improved in calcareous soils whilst in the case of the

8 Edaphic ecotypes in Cynodon dactylon 107 population it was more or less the same in both calcareous and non-calcareous soils, and again, the population showed an intermediate behaviour. s were found between the three populations with regard to mineral uptake in both non-calcareous and calcareous soils. In general, the plant ash content and the uptake of calcium, potassium and magnesium were found to be significantly higher in the population compared with that of ; the population was intermediate between the other two. Though calcium uptake was higher in plants compared to those of in both non-calcareous and calcareous soils, in the highly calcareous range with 12% CaCOs the reverse was found to be the case (see Table 9). The uptake of calcium, potassium and magnesium, in general, increased with increase in soil calcium level. However, the calcium uptake of the and populations and the magnesium uptake of the population decreased in the highly calcareous soil with 12% CaC03. The uptake of phosphorus by the three populations of C. dactylon was not significantly different nor was the uptake of this element influenced by different calcium levels in the soil. By contrast, it may be pointed out here that the three populations at, and of Euphorbia thymifolia (Ramakrishnan, 1965^) and Tridax procttmbens (Ramakrishnan and Jain, 1965c) showed highly significant s in phosphorus uptake in both calcareous and non-calcareous soils. The differential ability of the three populations to produce roots, especially the poor development of roots of the population in the non-calcareous control soil (Tables 6 and 7), suggest that the low calcium level may be the controlling factor for such behaviour, though the actual cause for root stunting is not yet clearly known. Snaydon and Bradshaw (1961) suggest that the induction of heavy metal toxicity at the lowest calcium levels may be one of the factors for poor development of roots. However, the direct effect of calcium itself on root growth is not ruled out. The results presented in this paper indicate clearly that the s between the three populations are as marked as those that may be found for different species with completely different edaphic tolerance ranges. Though the population thrived on a highly calcareous soil, its uptake of calcium both in nature as well as under cultural conditions is significantly lower than that of the population which grows naturally in a comparatively non-calcareous soil. Further, the uptake of various minerals by the populations of Cynodon dactylon at, and is characteristically different whatever treatment they are subjected to, ranging from low calcium to very high calcium levels in the soil. The explanation is to be sought in the selective absorption of ions leading to a nutrient composition characteristic of the populations within the species. However, as pointed out by Godall and Gregory (1947), under extreme deficiency or very high levels in the soil, marked s may sometimes be noticed in the mineral nutrient composition in the tissues as has been found, for example, in calcium uptake at 12% CaCOj in the soil (see Table 9) for the and populations, the latter showing lower uptake of this mineral than the former. The present studies clearly point to the occurrence of at least three 'edaphic ecotypes' within the species C. dactylon, each markedly different from the other in their physiologico-ecological attributes, and that the s are chiefly due to their differential response to soil calcium. Further, it appears from the present investigations and similar studies reported for Euphorbia thymifolia (Ramakrishnan, 1965a, b) and Tridax procumbens (Ramakrishnan and Jain, 1965a, b, c) that the ecotypic differentiation may be very frequently encountered in species which are common to all the three different

9 io8 P. S. RAMAKRISHNAN AND VIJAY K. SINGH habitats of Gangetic alluvium, conglomerate and the soil derived from limestone rocks at. ACKNOWLEDGMENT We are thankful to Professor P. N. Mehra, Head of the Department of Botany, Panjab University, for laboratory facilities. REFERENCES GoDALL, D. W. & GREGORY, F. G. (1947). Chemical composition of plants as an index of their nutritional status. Tech. Commun. imp. Bur. Hort. Plantn Crops, 17. KRUCKEBERG, A. R. (1951). Intraspecific variability in response of certain native plant species to serpentine soil. ^»;. J. Bo?., 38, 208. KRUCKEBERG, A. R. (1954). The ecology of serpentine soils. III. Plant species in relation to serpentine soils. Ecology, 35, 267. MCMILLAN, C. (1956). The edaphic restriction of Cupressus and Pinus in the coast ranges of Central California. Ecol. Monogr., 26, 177. PIPER, C. S. (1944). Soil and Plant Analysis. Interscience, New York. RAMAKRISHNAN, P. S. (19610). Calcicole and calcifuge problem in Euphorbia thymifoua Linn. J. Indianbot. Soc, 40, 66. RAMAKRISHNAN, P. S. (19616). Studies in the ecological life history of Euphorbia thymifoua Linn. Proc. natn. lust. Sci. India, 27B, 347. RAMAKRISHNAN, P. S. (1965a). Studies on edaphic ecotypes in Euphorbia thymifoua L. I. Seed germination. y. Ecol., 53, 157. RAMAKRISHNAN, P. S. (19656). Studies on edaphic ecotypes in Euphorbia thymifoha L. IL Growth performance, mineral uptake and inter-ecotypic competition. J. Ecol., 53, 705. R,«IAKRISHNAN, P. S. & JAIN, R. S. {ii)()$a). Germinability of the seeds of the edaphic ecotypes in Tridax procumbens L. Trop. Ecol., 6, (In press). RAMAKRISHNAN, P. S. & JAIN, R. S. (19656). Differential response to calcium and growth yield of the edaphic ecotypes in Tridax procumbens L. J. Indian bot. Soc, 43, (In press). RAMAKRISHNAN, P. S. & JAIN, R. S. (1965c). Mineral uptake by the edaphic ecotypes in Tridax procumbens L. Proc natn. Inst. Sci. India, 31B, (In press). SNAYDON, R. W. & BR.ADSH.\W, A. D. (1961). Differential response to calcium within the species Festuca ovina L. New Phytol., 60, 219. WALKER, R. B., WALKER, H. M. & ASHWORTH, P. R. (1955). Calcium-magnesium nutrition with special reference to serpentine soils. PL Physiol., Lancaster, 30, 214.

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