Abstract: An experiment was conducted with the two provenances of Eucalyptus camaldulensis (tolerant = SL2 and sensitive= SL4) selected from the previous studies to scrutinize the ionic content and growth under saline environments using gravel technique. It was observed that plant height, shoot and root fresh and dry weight and stem diameter decreased with the increase in salinity levels in both the provenances upto 2% NaCI, However reduction was more clear in salt sensitive provenance of Eucalyptus camaldulensis. The chemical analysis for different ion showed that Na+ increased in shoot and root in both the provenances of Eucalyptus. However root contain more Na+ in both provenances under all salt treatments. The other ions such as K+, Ca++ decreased with the application of salinity. The reduction was more pronounced in sensitive provenance. In case of P reduction was observed with salinity but it was not up to the deficient mark. The N contents severely decreased with salinity in shoot and root of both the provenances, however N contents are less in salt sensitive provenance under all treatment in shoot as well as root.
Introduction
Salinization of soil creates extremely unfavourable conditions for plant growth. Accumulation of salts increases the osmotic potential of soil solution which in turn affects water movement and restricts its uptake by plants. Thus delayed germination, limited seedling survival and stunted plant growth are common in saline soils. Pakistan is situated in arid and semi arid regions of the world where evaporation is greater than precipitation. The magnitude of problem is therefore, huge in Pakistan and about 6.3 million hectares (mha) are salt-affected and is mainly located in the heart of its agriculturally the most important and productive belt, i.e the Indus plain (Khan, 1993).
The development of economical and efficient methods to combat with these problems is of paramount importance in order to feed the exponentially increasing population of the country. This can be achieved either through hydrological engineering approaches along with the use of chemical ammendments or biological reclamation of salt-affected soil i.e., saline agriculture. However, certain limitations especially insufficient supply of canal water, poor quality of ground water, huge initial investment, i.e Rs, 11,000 per hectare (Qureshi et al., 1993 ) and poor drainage restricts the liberal use of hydrological approach while under these circumstances alternative approach of utilization of salt affected soil is "Saline Agriculture", to deal with this problem under Pakistani situation. It is both cost effective and sustainable.
In Pakistan out of the total salt-affected soils, approximately half are waste lands and are extremely saline and saline sodic in nature. These are mostly unfit for agricultural crops. It is the urgent need to use such waste land for cultivation to fulfil the food, fuel and industrial raw material requirements of even growing population of Pakistan.
However Eucalyptus has been identified as a tolerant tree species to salinity and waterlogging and has more than 85% survival rate under saline soil conditions (ECe of 10 to 15 dS m‾1) (Sandhu and Qureshi, 1986). The agronomical studies about Eucalyptus are well documented in literature (Marcar, 1993; Shah et al., 1992; Hafeez, 1993; Qureshi et al., 1993; Akilan et al., 1997). However, the information about mechanism of salt tolerance are still investigating and scanty. The present study was, therefore, planed to determine morpho-physiological studies of Eucalyptus grown under saline condition.
Materials and Methods
Nursery of Eucalyptus camaldulensis was raised in sand from seeds, when the seedlings were of one month old, transferred in to plastic bags containing silt and 25% sand (mixed). Three month old seedlings were used for gravel culture experiment conducted in plastic pots in the net house of NIAB, Faisalabad. A plastic pot having hole at the bottom with diameter and length of 22×20 cm filled with washed sterilized marble gravels and this pot was placed in another plastic pot with diameter and length of 25×23 cm having no hole which is used to,collect drained solution from the first pots filled with gravel. The pots were filled with Y2 strength Hoagland's solution and three month old seedlings of Eucalyptus camaldulensis of tolerant provenance "SL2" (seed collected from University of Agriculture, Faisalabad) and sensitive provenance "SL4" (seed collected from Biosaline Research Station-I, Lahore) were transplanted and allowed to grow and acclimatise for 15 days. Five salinity treatment (Control, 0.5, 1.0, 1.5 and 2.0% NaCI) were created with NaCI, each treatment have 5 replications. For the appropriate growth the pH of solution was checked daily and if it was found above 7.5 then it maintained upto 6.5 by adding few drops of concentrated H2SO4.
| Fig. 1: | Effect of salinity on plant Neigh (a) stem diameter (b) fresh weight of plant shoot dry weight (d) fresh root weight (e) dry weight of root (f) of tw provenances of Eucalyptus camaldulensis |
The solution was changed after one week and plants were allowed to grow for a month. After one month the plants were harvested and their shoot length, root length, shoot and root fresh and dry weight were recorded. The dried material of shoot and root was used to determine ionic content. The data was subjected to analysis of variance and treatment and provenance means were compared by using DMR test (Steel and Torrie, 1980).
Results
The results showed that plant height significantly reduced by the application of salinity in both type of provenances, however reduction was more pronounced in salt sensitive provenance (SL4) at 2% NaCl. Similarly shoot length also decreased by increasing the salt concentration. The minimum root length was recorded in highest salinity level (2% NaCI) in both provenances, however the reduction in tolerant provenances was less as compared to non tolerant. The dry weight, fresh weight of shoot and root were also influenced by salinity (Fig. 1c-f). The maximum fresh and dry weight were recorded under normal conditions which reduced by increasing salt concentration. The reduction in salt tolerant provenance under highest salinity level was less than 50% while it was more than 70% in sensitive provenance of Eucalyptus camaldulensis. Same is the case with plant stem diameter (Fig. 1b).
The ionic content like 10 and Ca++ decreased by increasing salinity while Na+ increased in both the provenances under all salt treatment. The Na+ content was much higher in salt sensitive provenance, while K+ and Ca++ were greater in salt tolerant provenance in both root and shoot. The effect of salinity on phosphorous was not much pronounced because the contents in both provinces were beyond the deficiency level (Fig. 2i, j). In other word no effect of salinity was observed in case of P uptake. N content decreased in both root and shoot in all provenances due to salinity (Fig. 2g, h). The reduction was more clear in sensitive provenance. The minimum N content were observed at highest salinity level in both the provenances.
Discussion
Although Eucalyptus is a salt tolerant tree plant however, in the present study the two provenances tolerant and sensitive upto 2% NaCI were screened (unpublished data) and used in the present study to compare for their growth and ionic content mechanism.
| Fig. 2: | Effect of salinity on ion contents in shoot and root in two provenances of Eucalyptus camaldulensis: Na+ in shoot (a) Na in root (b) K in shoot (c) K in root (d) Ca in shoot (e) Ca in root (f) N in shoot (g) N in root (h) P in shoot |
The data on growth showed reduction due to salinity in both the provenances. However reduction was more clear in case of salt sensitive provenance (Fig. 1a). Many reports (Ashraf et al., 1999; Qureshi et al., 2000) indicated reduction in growth due to salinity, even in halophytic plants. The reduction in growth may be due to reduction in cell turgor Potential which is necessary for cell enlargement and elongation (Ashraf and Khan, 1994) which may be the reason in the present study for reduction in plant growth (Qureshi et al., 2000). Present study confirms that tolerant provenance have longer root than non tolerant, which is a sign of osmotic adjustment with environmental conditions (Khan et al., 1992).
The data on ions content showed that Na+ content increased in both root and shoot of all the provenances (Fig. 2a, b). There are many reports (Khan and Ashraf, 1988; Khan et al., 1995) showed that high Na+ content create toxicity which Ultimately retards plant growth. The present study confirms these findings. The reduction in K+ (Fig. 2c, d) and Ca++ (Fig. 2e, f) may be due to antagonistic effect of Na+ in uptaking the K+ and Ca++. The results showed that Ca++ and K+were higher in salt tolerant provenance of Eucalyptus. K+ play key role in the osmotic adjustment of plant which is necessary to maintain the turgor potential (Khan et al., 1992), Similarly. Ca++ has major role in the cell membrane stability and the plant having higher cell membrane stability were more stress tolerant than others (Ashraf et al., 1992).
N contents reduced in the plants growing under saline condition (Ashraf and Khan, 1993) present study also confirms it. The literature (Khan et al., 1990; Ashraf and Khan, 1993) showed that under saline condition different enzymes like Nitrate reductase, Nitrite reductase and Arnmonia-lyase activities decreased due to salt stress which effect the N metabolism of the plant and reduced the N contents. The reduction in N content in the present study may be due to above mentioned reasons.
Many reports (Khan and Ashraf, 1988; Khan et al., 1995) showed that salinity did not affect the P contents however in the present study it decreased but not up to the deficient. mark which showed that plant had enough P for their survival and metabolic activities.