マメ科の1種, Tephrosia apollineaの根系の適乾燥応
Nihon Seitai Gakkaishi
STUDY OF ROOT SYSTEM OF TEPHROSIA APOLLINEA AND ITS SURVIVAL VALUE UNDER ARID CONDITIONS
1979. Study ofroot system of Jephrosia apoltinea and its survival value under arid conditions" Jap. J. Ecol. 29, 71Ephrosia apoUinea (DEL.) LiNK is a perennial hcrb of sandy plains and at Jaipur it dominates the vegetation stands throughout the year. The root system is well developed and penetrates to a depth of 3 m or more. This deep roet system helps in absorption of moisture from the deeper soil layers. Fufther, the roots also stere the moisture in the cortex which
... lps the plant in continuing its growth and reproduction at a time when soil moisture is highly deficient. Introductien The survival and growth ofplants under extreme-Iy dry conditions as obtained in the arid and semiarid region of the world have been of considerable interest to plant physiologists and ecologists sincc long, The literature on the subiect has been reviewed by STocKER (1960), OppENHmMER (1960), KozLowsKi (1968). In many studies it has been shown that an extensive root system enables the plant to grow under arid conditions as the deep rooting provides it an aocess to easy and permanent water supply (WEAvER, 1919; ALBERTsoN, 1937 and KozLowsKT, l968) More recently BATANouNy and WAHA'B (1973) have shown that in Leptadenia avrotechnica the root system occupies a large volume of the soil which allows access to soil mojsture sufi ficient for the plant for a period of upto four years without replenishment by rainfa11. The present commuhication gives some data on the expanse of the root system of 71!phrosia apoUinea (DEL.) LiNK, a plant of arid and semi-arid regions. It also discusses its significapce in the survival of this plant underthearidconditions. Material and Methods 71!phrosia apollinea (Family Leguminosae) is a perennial herb ofsandy plains, attaining a height of 45 to 50 cm. At Jaipur (260 19' N, Lat, and 75e 48' E. Long.) it dominates the vegetation stands throughout the year. The pheno!ogy of the species has been described in detail by BHARDwAJ (1976). The root system of several plants of different ages were exeavated to study their extent. Further, the roet system of plants were taken out at different times of the year, particularly during the dry period. Soil moisture content at every 50 cm depth was determined by drying the soil in hot air oyen at 105eC. Root moisture content was also determined and correlated with soil moisture. 11he root system The root systems of three plants ef throe difTerent ages-1, 2 and 3 years, are shown in Fig. 1. It is seen that the Toot elongation continues year after year. The maximum excavated length of the root system was 2,93 m with a horizontal spread of 1 1O cm (55 cm radius from its mai.n branch). Lateral branches up to 1.6 m long were noted. Secondary fine branches are more abundant between 1O-20 cm zone. The oldest tap root had a rnaximum diameter of6 mm near the soil level and it gradually tapered down to O,2 mm at the tip. The total soil volume exploited by the 3 years old root system is 2.7 8 m3. Similar]y a one year old root system occupies a soil volume of about O.6 m3. It is nQteworthy that in some areas, the density is suMciently high (7 plants/m2) and therefbre, the root systems of many plants would oocupy the same volume, The EcologicalSociety of Japan Vol. 29, No. 3 gg H ig de ma \k tTE t t Fig. 1. Root system of one (1), two (2) and three (3) years old plants. VVbter relations of the roots Th¢ data on soil moisture content at different depths during the year (Fig. 2) show that suMcient moisture is available in the soil particularly in the deeper strata, during the driest part of the year and may be available to the plant for absorption. How-. ever, soil moisture is greatly depleted till the rains rqplenish it. --A study of root moisture content at various strata during the same period (Fig. 3 ) revea!s a few interesting facts. The root moisture at greater depth (1.5-2.5 m) is relatively higher than would be expected for the woody roots. The reots are gradually depleted of their moisture during the summer (when new branohes sprout and fiowering also occurs) but stillretain 50-75 % moisture of that during late winter (February). As soon as rainfa11 occurs, the root moisture content again rises steeply. This shows that roots store and retain water in their tissues during the rains and winter season and utilize it to some extent during summer.