Research Article

Comparative Effect of Drought on Eucalyptus camaldulensis and Tamarix aphylla at Early Stages of Growth

Muhammad Safdar Hussain1*, Muhammad Farrakh Nawaz2, Muhammad Ayyoub Tanvir2 and Noor-E-Hira1

1School of Forest Resources and Conservation, Institute of Food and Agricultural Sciences, University of Florida, USA; 2Department of Forestry and Range Management, Faculty Agriculture, University of Agriculture, Faisalabad, Pakistan.

Received | June 09, 2019; Accepted | April 02, 2020; Published | April 28, 2020

*Correspondence | Muhammad Safdar Hussain, School of Forest Resources and Conservation, Institute of Food and Agricultural Sciences, University of Florida, USA; Email: [email protected]

Citation | Hussain, M.S., M.F. Nawaz, M.A. Tanvir and N. Hira. 2020. Comparative effect of drought on Eucalyptus camaldulensis and Tamarix aphylla at early stages of growth. Sarhad Journal of Agriculture, 36(2): 559-566.

DOI | http://dx.doi.org/10.17582/journal.sja/2020/36.2.559.566

Keywords | Agroforestry, Drought tolerance, Sustainable development, E. Camaldulensis, T. aphylla, Water stress

Introduction

Plant stress refers to any unfavorable condition or substance that affects a plant’s metabolism, reproduction, root development, or growth. (Gaspar et al., 2002). There are various kinds of stresses like salt, drought, heat, cold and heavy metals stress. Among these drought stresses is one of the most threatening factors causes changes in the physiological, morphological, biochemical, and molecular mechanisms of the plants. It has been studied that drought stress is a very important limiting factor that affects both elongation and expansion of growth at the initial phase of plant growth and establishment (Anjum et al., 2003a; Bhatt and Srinivasa, 2005; Kusaka et al., 2005; Shao et al., 2008). Water stress is an important factor that needs to be addressed because the growth and productivity of plants are negatively affected by water shortage (Zlatev and Lidon, 2012).

Regular accessibility of water is necessary to cope demands of human beings in present as well as for the future, unfortunately, due to climatic changes, its scarcity is increasing gradually (Rosegrant and Cline, 2003). Weather changes are another factor, owing to which water availability is becoming low resulting in erratic conditions. This situation ultimately has long- lasting effects on the growth and productivity of plants (Harb et al., 2010). Water scarcity in soil affects on apical and lateral growth of plants and reduces biomass formation (Yordanov et al., 2000); (Zlatev and Lidon, 2012). Therefore, the yield losses of crops have reached up to 50% because of drought stress (Bray, 2000; Wang et al., 2003).

Pakistan is a thickly populated country and the population of Pakistan is 207.774 million with an average annual growth rate of 2.4% over the period of 1998–2017 (Pakistan Bureau of Statistics, 2018). So, current and predicted population pressure for wood and its products on its (Pakistan) rare forest resources (4.2 mha) is enormous (Rahim and Hasnain, 2010). Unfortunately, forests cover is very low (about 0.001 ha) per capita in Pakistan, while in the rest of the world it is about 1.00 ha per capita (Hosonuma et al., 2012). Furthermore, forests of Pakistan are gradually decreasing because of deforestation and human-induced activities (Khan et al., 1990).

Establishing new forests (Irrigated Plantations) in Pakistan is a big challenge due to water shortage. Pakistan has suffered severe drought conditions since 1998, which reduced wheat production and income of a farmer in the southern area of Sindh province (Faruqui, 2004). About 7.8 million ha of land in Pakistan is affected by water shortage which can be used for tree plantations by introducing drought-resistant species (Irshad et al., 2011).

Because of the severe water shortage in Pakistan, the land under forest cover can be increased by introducing only agroforestry systems. While these systems can be successfully established by introducing drought-resistant tree species (Nawaz et al., 2018). Agroforestry is the only hope which can reduce the pressure on existing forest cover and fulfill the wood demands of the community in Pakistan (Bartholome and Belward, 2005; Nawaz et al., 2016). The agroforestry practices not only cope with wood deficiency but also provides ecosystem services, improve degraded soils and mitigate microclimate of the area (Paul et al., 2017).

Growing drought-tolerant trees play a vital role in the agroforestry system to fulfill the deficiency of water (Bauer et al., 2013), because they adopt different mechanisms against drought stress, like osmotic adjustment, accumulation of solutes in cells and different morphological adoptions (Brock, 1994). The Eucalyptus camaldulensis is considered high water-consuming tree but throughout world it is one of the most important trees due to high growth rate, environmental adaptability and superior pulp properties (Stape et al., 2004). Being evergreen species, it absorbs more water at deeper depth as compared to other tree species (Baker et al., 2002). While Tamarix aphylla has adaptability against drought and salt stress due to its xerophytic and halophytic nature, respectively (Brock, 1994). Tamarix aphylla is native species of the Middle East, the Arabian Peninsula, and Pakistan. Tamarix aphylla is a drought-tolerant plant which can survive on less water availability in soil by adopting many physiological and morphological changes (El-Ghani, 2000).

Plants respond and adapt to and survive under drought stress by the induction of various morphological, biochemical and physiological responses. Plant drought tolerance involves changes at whole-plant, tissue, physiological and molecular levels. Manifestation of a single or a combination of inherent changes determines the ability of the plant to sustain itself under limited moisture supply (Farooq et al., 2009).

Focusing on water scarcity in Pakistan especially under arid and semi-arid climate there is a dire need to compare water use efficiency of the introduced and native species and discover the truth about Eucalyptus camaldulensis whether it can grow under water shortage or not as compare Tamarix aphylla for sustainable Agroforestry practices in Pakistan. Therefore, this study was designed to compare above-mentioned tree species through a pot experiment.

Materials and Methods

Soil analysis

Prior to experiment random soil samples were taken at 0-15 cm depth from the study area to analyze the chemical and physical properties of soil used in pots. Samples were dried, ground, sieved, prepared and analyzed for electrical conductivity (dS 1), pH, field capacity (%), saturation percentage (%) and organic matter by using the standard method of soil analysis in soil and water testing laboratory (Table 1).

Table 1: Physico-chemical properties of soil used in pots.

Parameters	Nursery soil
EC dSm-1	1.00 ± 0.04
pH	8.2 ± 0.1
Sand (%)	59 ± 1
Silt (%)	22 ± 0.5
Clay (%)	19 ± 0.5

 

Plant materials and experimental design

The experiment was carried out at the research zone of the department of Forestry UAF. Two common tree species Eucalyptus camaldulensis (drought-sensitive) and Tamarix aphylla (drought-tolerant) were used under this study. Both species were grown in plastic bags (filled with clay and sand) with seeds and cutting respectively for the period of three (3) months, then transplanted into pots (filled with 4383.5g) sandy loam soil.

One month after transplanting, fifteen (15) plants per species were shifted to a green net house in order to protect from rainwater. Each specie was subjected to three treatments 100%, 75% and 50% field capacity in other words (control, 25% and 50% drought stress). Five replicates per treatment were used under complete randomized design (CRD) due to homogeneous experimental materials. After establishing plants in pots completely, water was given according to treatments (902 ml for 100%, 676 ml for 75% a and 451 ml for, 50% field capacity). Due to hot weather, water was given after an interval of 3 days by measuring each pot firstly then the required amount of water was given to each treatment. After completing 6 weeks of treatment, plants were harvested manually including roots and brought into laboratory for measurements and data analysis.

Data collection

Average monthly metrological data were collected from the Metrological Station that is permanently installed at just a few meters away from the experimental site. The summary of climatic conditions during experimental period (February 2014 to June 2014) is given in (Table 2)

Table 2: Average monthly temperature and rainfall range during February 2014 to June 2014.

Month	Temperature			R.H.	Rain fall	Pan evaporation
	MAX	MIN	Avg.
	Avg. ºC	Avg. ºC	ºC	%	Total (mm)	Avg. (mm)
February	20.0	08.9	14.4	65.0	14.3	01.7
March	24.7	13.6	19.2	60.1	41.7	03.0
April	32.2	18.6	25.4	52.2	28.2	05.3
May	38.7	24.9	31.8	27.5	17.0	07.6
June	40.9	28.1	34.5	33.5	07.1	08.4

 

Data for, morphological parameters, such as fresh and dry weight (g), root and shoot height (cm), and diameter (mm) of plants was taken). Root and shoot lengths (cm) were measured with measuring tape, and collar diameter (mm) was recorded by digital Vernier caliper. Fresh weight (g) was taken immediately after harvesting while dry weight (g) was taken after drying in an oven for 72 hours.

Relative water contents in plants leaves were calculated before harvesting the plants. To calculate (RWC), fresh leaves (0.5 g) of each plant were taken and dipped in distilled water, after four hours, leaves were taken out, and the surface water was removed with the help of tissue paper and then weighed to get the turgid weight (TW g). After getting TW, leaf samples were dried at 65 °C in the oven until the complete drying, after 72 hours the samples were again weighed, and the relative water contents were calculated by using formula (Jensen et al., 2019).

RWC= [(FW-DW)/ (TW-DW)]

Here FW is showing the fresh weight of the leaf in (g), TW is turgid weight in (g) measured after floating the leaf, and DW is the dry weight in (g) found by drying the leaf samples.

The percent growth reduction of each treatment was calculated by using following equation. First, % growth of each treatment was calculated, the growth of 100% field capacity (control) was kept 100%, after calculating % growth for both T1 and T2 treatments, the values were deducted from 100 (control) value. The resulted values are % growth reduction.

% Growth = Control/T1(100)

% Reduction= 100 - % growth

Statistical analysis

One-way analysis of variance (ANOVA) was used to test the effect of treatment using Stata SE 15. The difference among treatment was analyzes by using Tukey HSD test at P ≤ 0.05.

Results and Discussion

Effects of water stress on morphological characteristics of Eucalyptus camaldulensis and Tamrix aphylla

Results shows that a significant difference (LSD at P<0.05=6.64) occurred between treatment for plant height as showed in Figure 1a which shows that Eucalyptus camaldulensis and Tamrix aphylla gained up to 38.16 cm and 34.8 cm height, respectively at control conditions while at 25% (75% FC) drought, height of shoot was (31.96 cm and 31.22 cm) for Eucalyptus camaldulensis and Tamarix aphylla, respectively. The extreme drought (50%) caused maximum growth reduction in Eucalyptus camaldulensis and minimum in and Tamarix aphylla (17.14 cm, 24.94 cm respectively). The percent reduction (16.1% and 10%) in shoot length of Eucalyptus camaldulensis and Tamarix aphylla was found at 25% drought stress respectively while at 50% drought stress, shoot length was reduced (55% and 28%) respectively in both species.

Results in Figure 1b shows a significant difference (LSD at P<0.05=0.4980) between treatments for root length. It was found at well-watered, Eucalyptus camaldulensis gained 59.8 cm with increasing of water stress root length increased more up to 71.1 cm, at high drought stress root length started to decline and was measured 48.1 cm at 50% drought conditions. In the case of Tamarix aphylla the root length also significantly increased at 25% drought but decreased at 50% drought stress. Figure 1b shows that the root length of Tamarix aphylla was found 43.1 cm, 50.4 cm and 38.8 cm at control, 25 %, and 50% drought, respectively. The percent change in root length of Eucalyptus camaldulensis was found 18% higher at 25% drought as compared to well the water condition, while at 50% drought 20% reduction in root length was measured. In Tamarix aphylla percent increase and reduction in root length were 16.93% and 10% at 25% and 50% drought accordingly.

Effects of water stress on the biomass of Eucalyptus camaldulensis and Tamrix aphylla

Drought stress at different levels influenced significantly (LSD at P<0.05=8.790) the root shoot fresh weight (Biomass). Under well-watered conditions, Eucalyptus camaldulensis produced maximum biomass of 17.8 g, while 13.0 g and 8.03 g were found at 25% and 50% drought, respectively. In the case of Tamarix aphylla, it produced 16.1g fresh weight under well-watered conditions, while 14.1g and 11.4g biomasses were produced at 25% and 50% water stress. The percent comparison of both species shows that Eucalyptus camaldulensis reduced more fresh weight as compared to Tamarix aphylla. The percent loss in fresh weight of Eucalyptus camaldulensis at 25% and 50% drought stress was 27% and 55%, respectively while percent reduction in fresh weight of Tamarix aphylla was 13% and 31% at 25% and 50% drought respectively.

A significant reduction (LSD at P<0.05=6.40) in dry weight of both species was found. Under well-watered conditions, the total dry weight 10.8g was recorded in Eucalyptus camaldulensis while 8.9g and 5.03g dry weights were found at 25% and 50% water stress respectively. In the case of Tamarix aphylla, 12.17g dry weight under well-watered conditions, while 7.28g and 6.21g dry weights were recorded at 25% and 50% water stress respectively. The percent comparison of both species showed that Eucalyptus camaldulensis reduced more dry weight as compare to Tamarix aphylla. The percent loss in dry weight of Eucalyptus camaldulensis and Tamarix aphylla was recorded as 17%, 53% and 40%, 49% at 25% and 50% water stress, respectively. The water deficit soil inhibited the plant growth due to which the growth of root elongation and fresh weight decreased.

No significant differences were found in the diameters of both species at the early stages of growth therefore the diameters at different water regime for Eucalyptus camaldulensis were found 5mm, 4.8 mm and 2.5 mm at control, 25%, and 50% drought respectively. While diameters of Tamarix aphylla at different water level was recorded 6 mm, 5.5 mm and 4 mm at well-watered, 25%, and 50% drought, respectively.

Xerophytic plants effort to preserve high relative water content than that of sensitive ones by the osmotic adjustment which decrease their water potential in this way they absorb more water. Tamarix aphylla which is relatively drought-tolerant showed higher relative water content at drought conditions than Eucalyptus camaldulensis which is more sensitive to drought stress.

A study was conducted to estimate the water use efficiency of both discussed species, the results showed that Eucalyptus camaldulensis utilized more water as compared to Tamarix aphylla. Planting of Eucalyptus camaldulensis on marginal (waterlogged) lands can convert them into productive lands (Afzal, 2018). Similar results were observed by (Cheng and Cheng, 2015) who stated when the irrigation interval increased, the plant height significantly decreased. Our results showed contrast with (Haworth et al., 2017) who stated that significant differences were not observed in the mean height of Arundo donax. It was questioned why root increased its length against drought stress, the answer found in previous studies was that when roots tips face stress their tips contained less water contents while the process of osmotic adjustments starts which increased level of soluble sugars and proline contents, therefore these sugars increase water content in root tips (Ji et al., 2014).

Similar results were reported by (McDonald and Davies, 1996) which indicate that enhanced biomass partitioning to roots may result from a drought-induced reduction in the sink strength of the above-ground plant tissues, making more assimilates available for root growth. Another research reported greater increases in the root length of Eucalyptus camaldulensis in the water-stress regime than in the well-watered regime (59% and 16%) respectively. whereas root growth ceased completely after week 5 in water-stressed (Silva et al., 2004). It was studied that cottonwood and willow forests flourish where groundwater is 3 m or less deep, yet Tamarix aphylla woodlands can survive where groundwater is 7 m deep or more(Stromberg and Chew, 2002). When drought stress occurs, it affects the yield and production by affecting the weight and number of branches (Nawaz et al., 2013).

According to one study, plant height, shoot weight, leaves area and plant biomass showed a decline in response of less-water conditions (Sirousmehr et al., 2014). Another study showed that leaf area index and plant dry matter significantly decreased when plants faced drought stress, while stem length showed less effect as compared to other root traits (Aranjuelo et al., 2010). Our results are also similar with (Allen et al., 2010) who discovered that the water deficit in soil inhibited the plant growth due to which the growth of root elongation and fresh weight decreased.

Our results correlate with (Elhadi et al., 2013) who indicated that no significant differences in tree collar diameter (mm) were observed among all irrigation frequencies at the early stages of growth. It was concluded by (Stoyanov, 2005) that drought-tolerant bean cultivars maintained high relative water content under limited water availability. According to (Ramoliya and Pandey, 2003) high relative water content of leaves indicated to be an adaptation under xerophytic habitat.

Conclusions and Recommendations

In this study, overall % growth at well-watered was found better for Eucalyptus camaldulensis, as it is fast growing and water loving tree, however, under drought conditions, growth of Tamarix aphylla was found better than Eucalyptus camaldulensis as amarix aphylla is drought resistant plant. The percentage reduction in growth parameters was minimum in Tamarix aphylla as compared to Eucalyptus camaldulensis at high drought stress at their early stages of growth that decides the adaptability of a tree species in arid conditions. At high stress the growth parameter and biomass were started to more decline especially in Eucalyptus camaldulensis as compared to even wilting of plants.

Pakistan is facing water shortage therefore, it is recommended that less water consuming, and drought-tolerant species should be recommended, so, Tamarix aphylla is a better specie for agroforestry practices under the semi-arid climate of Pakistan due to drought tolerance ability. However, research work is necessary to study (genetically and physiologically) to various tree species, especially Eucalyptus camaldulensis that is fast-growing but more water demanding to bring modification in it that can make it more drought-tolerant plant, so that the deficiency of water can be minimized to produce more forests in Pakistan.

Acknowledgements

We acknowledge to Endowment Fund Secretariat, University of Agriculture Faisalabad for sponsoring this research project through grant number TT-09/12.

Novelty Statement

Planting of eucalyptus in Pakistan especially in areas having low water availability is under miss conceptions. It is the need of hours to compare its water use efficiency and resistance against drought. Therefore, this study was designed to compare its performance against water stress with a tree that is drought resistant, so that its recommendations for agroforestry could be made successful.

Author’s Contributions

MSH performed research trial and preparations of the first manuscript draft, MFN supervised the study, gave the idea and designed the study. MAT provided help in data analysis, manuscript improvement and corrections. NEH played a vital role in editing, data entry and in manuscript revisions. All authors read and approved the final manuscript.

Conflict of interest

There is no conflict of interests regarding the publication of this article.

References

Afzal, S., M.F. Nawaz, M.T. Siddiqui and Z. Aslam. 2018. Comparative study on water use efficiency between introduced species (Eucalyptus camaldulensis) and indigenous species (Tamarix aphylla) on marginal sandy lands of Noorpur Thal. Pak. J. Agric. Sci. 55(1): 127-135. https://doi.org/10.21162/PAKJAS/18.6626

Allen, C.D., A.K. Macalady, H. Chenchouni, D. Bachelet, N. McDowell, M. Vennetier and E.T. Hogg. 2010. A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. For. Ecol. Manage. 259(4): 660-684. https://doi.org/10.1016/j.foreco.2009.09.001

Anjum, F., M. Yaseen, E. Rasul, A. Wahid and S. Anjum. 2003a. Water stress in barley (Hordeum vulgare L.). I. Effect on morphological characters. Pakistan J. Agric. Sci., 40: 43–44.

Aranjuelo, I., G. Molero, G. Erice, J. C. Avice and S. Nogués. 2010. Plant physiology and proteomics reveals the leaf response to drought in alfalfa (Medicago sativa L.). J. Exp. Bot. 62(1): 111-123. https://doi.org/10.1093/jxb/erq249

Baker, T.R., K. Affum-Baffoe, D.F.R.P. Burslem and M.D. Swaine. 2002. Phenological differences in tree water use and the timing of tropical forest inventories: conclusions from patterns of dry season diameter change. For. Ecol. Manage. 171: 261-274. https://doi.org/10.1016/S0378-1127(01)00787-3

Bartholome, E. and A.S. Belward. 2005. A new approach to global land cover mapping from Earth observation data. Int. J. Remote Sens. 26 (9): 1959-1977. https://doi.org/10.1080/01431160412331291297

Bauer, H., P. Ache, S. Lautner, J. Fromm, W. Hartung, K.A. Al-Rasheid and N. Lachmann. 2013. The stomatal response to reduced relative humidity requires guard cell-autonomous ABA synthesis. Curr. Biol. 23(1): 53-57. https://doi.org/10.1016/j.cub.2012.11.022

Bhatt, R.M. and N.K.S. Rao. 2005. Influence of pod load response of okra to water stress. Indian J. Plant Physiol., 10: 54–59.

Bray, E.A., 2000. Response to abiotic stress. Biochem. Mol. Biol. Plant. pp. 1158-1203.

Brock, J.H., 1994. Tamarix spp.(salt cedar), an invasive exotic woody plant in arid and semi-arid riparian habitats of western USA. Eco. Manage. Invasive Riverside. Plant. 4: 28-44.

Cheng, F. and Z. Cheng. 2015. Research progress on the use of plant allelopathy in agriculture and the physiological and ecological mechanisms of allelopathy. Front. Plant Sci. 6: 1020. https://doi.org/10.3389/fpls.2015.01020

El-Ghani, M.M.A., 2000. Vegetation composition of Egyptian inland saltmarshes. Bot. Bull. Acad. Sinica. pp. 41.

Elhadi, M.A., K.A. Ibrahim and T.A. Magid. 2013. Effect of Different Watering Regimes on Growth Performance of Five Tropical Trees in the Nursery. Environ. Nat. Resour. 1: 14-18.

Farooq, M., A. Wahid, N. Kobayashi, D.B.S.M.A. Fujita and S.M.A. Basra. 2009. Plant drought stress: effects, mechanisms and management. In Sustainable agriculture Springer, Dordrecht. pp. 153-188. https://doi.org/10.1007/978-90-481-2666-8_12

Faruqui, N.I., 2004. Responding to the water crisis in Pakistan. Int. J. Water Resour. Dev. 20(2): 177-192. https://doi.org/10.1080/0790062042000206138

Gaspar, T., T. Franck, B. Bisbis, C. Kevers, L. Jouve, J.F. Hausman and J. Dommes. 2002. Concepts in plant stress physiology. Application to plant tissue cultures. J. Plant Growth. Regul. 37(3): 263-285. https://doi.org/10.1023/A:1020835304842

Harb, A., A. Krishnan, M.M. Ambavaram and A. Pereira. 2010. Molecular and physiological analysis of drought stress in Arabidopsis reveals early responses leading to acclimation in plant growth. J. Plant Physiol. 154(3): 1254-1271. https://doi.org/10.1104/pp.110.161752

Haworth, M., M. Centritto, A. Giovannelli, G. Marino, N. Proietti, D. Capitani and F. Loreto. 2017. Xylem morphology determines the drought response of two Arundo donax ecotypes from contrasting habitats. Glob. Change Biol. Bioenergy. 9(1): 119-131. https://doi.org/10.1111/gcbb.12322

Hosonuma, N., M. Herold, V. De-Sy, R.S. De Fries, M. Brockhaus, L. Verchot and E. Romijn. 2012. An assessment of deforestation and forest degradation drivers in developing countries. Environ. Res. Lett. 7(4): 044009. http://www.pbs.gov.pk/content/block-wise-provisional-summary-results-6th-population-housing-census-2017-january-03-2018 https://doi.org/10.1088/1748-9326/7/4/044009

Irshad, M., A. Khan, M. Inoue, M. Ashraf and H. Sher. 2011. Identifying factors affecting agroforestry system in Swat, Pakistan. Afr. J. Agric. Res. 6(11): 2586-2593.

Jensen, S.M., J. Svensgaard. and C. Ritz. 2020. Estimation of the harvest index and the relative water content–Two examples of composite variables in agronomy. Eur. J. Agron. 112: 125962.

Ji, H., L. Liu, K. Li, Q. Xie, Z. Wang, X. Zhao and X. Li. 2014. PEG-mediated osmotic stress induces premature differentiation of the root apical meristem and outgrowth of lateral roots in wheat. J. Environ. Exp. Biol. 65(17): 4863-4872. https://doi.org/10.1093/jxb/eru255

Khan, A., G. Morgan and A. Sofranko. 1990. Farmer’s utilization of information sources: a study of the farmers in NWFP. J. Rural Dev. Adm. 22(1): 38-58.

Kusaka, M., M. Ohta and T. Fujimura. 2005. Contribution of inorganic components to osmotic adjustment and leaf folding for drought tolerance in pearl millet. Physiol. Plant. 125: 474–489. https://doi.org/10.1111/j.1399-3054.2005.00578.x

McDonald, A. and W. Davies. 1996. Keeping in touch: responses of the whole plant to deficits. Adv. Bot. Res. 22: 229. https://doi.org/10.1016/S0065-2296(08)60059-2

Nawaz, A., M. Farooq, S.A. Cheema and A. Wahid. 2013a. Differential response of wheat cultivars to terminal heat stress. Int. J. Agric. Biol. 15(6): 1354–1358.

Nawaz, M., M. Yousaf, G. Yasin, S. Gul, I. Ahmed, M. Abdullah, S. Afzal. 2018. agroforestry status and its role to sequester atmospheric co2 under semi-arid climatic conditions in Pakistan. Appl. Ecol. Environ. Res. 16(1): 645-661. https://doi.org/10.15666/aeer/1601_645661

Nawaz, M., S. Gul, T. Farooq, M. Siddiqui, M. Asif, I. Ahmad and N. Niazi. 2016. Assessing the actual status and farmer’s attitude towards agroforestry in Chiniot, Pakistan. Int. J. Biol. 10: 465-469.

Pakistan Bureau of Statistics 2018. Pakistan bureau of statistics block wise provisional summary results of 6th population and housing census-2017 (2018)

Paul, C., M. Weber and T. Knoke. 2017. Agroforestry versus farm mosaic systems–Comparing land-use efficiency, economic returns and risks under climate change effects. Sci. Total Environ. 587: 22-35. https://doi.org/10.1016/j.scitotenv.2017.02.037

Rahim, S.M.A. and S. Hasnain. 2010. Agroforestry trends in Punjab, Pakistan. Afr. J. Environ. Sci. Tech. 4(10): 639-650.

Ramoliya, P. and A. Pandey. 2003. Effect of salinization of soil on emergence, growth and survival of seedlings of Cordia rothii. For. Ecol. Manage. 176(1-3): 185-194. https://doi.org/10.1016/S0378-1127(02)00271-2

Rosegrant, M.W. and S.A. Cline. 2003. Global food security: Challenges and policies. Sci. 302(5652):1917-1919. https://doi.org/10.1126/science.1092958

Shao, H.B., L.Y. Chu, M.A. Shao, C.A. Jaleel and M. Hong-Mei. 2008. Higher plant antioxidants and redox signaling under environmental stresses. Comp. Rend. Biol., 331: 433–441. https://doi.org/10.1016/j.crvi.2008.03.011

Silva, F.C.E., A. Shvaleva, J. Maroco, M. Almeida, M. Chaves and J. Pereira. 2004. Responses to water stress in two Eucalyptus globulus clones differing in drought tolerance. Tree Physiol. 24(10):1165-1172. https://doi.org/10.1093/treephys/24.10.1165

Sirousmehr, A., J. Arbabi and M.R. Asgharipour. 2014. Effect of drought stress levels and organic manures on yield, essential oil content and some morphological characteristics of sweet basil (Ocimumbasilicum). Adv. Environ. Bio. pp. 1322-1328.

Stape, J.L., D. Binkley and M.G. Ryan. 2004. Eucalyptus production and the supply, use and efficiency of use of water, light and nitrogen across a geographic gradient in Brazil. For. Ecol. Manage., 193(1-2): 17-31. https://doi.org/10.1016/j.foreco.2004.01.020

Stoyanov, Z., 2005. Effect of water stress on leaf water relations of young bean. J. Cent. Eur. Agric., 6: 5-14. https://doi.org/10.1007/s00425-003-1105-5

Stromberg, J.C. and M.K. Chew. 2002. Foreign visitors in riparian corridors of the American Southwest: Is xenophytophobia justified. Invasive exotic species in the Sonoran region. University of Arizona Press and Arizona-Sonora Desert Museum, Tucson. pp. 195-219.

Wang, W., B. Vinocur and A. Altman. 2003. Plant responses to drought, salinity and extreme temperatures: towards genetic engineering for stress tolerance. Planta. 218(1): 1-14.

Yordanov, I., V. Velikova and T. Tsonev. 2000. Plant responses to drought, acclimation, and stress tolerance. Photosynthetica. 38(2): 171-186. https://doi.org/10.1023/A:1007201411474

Zlatev, Z. and F.C. Lidon. 2012. An overview on drought induced changes in plant growth, water relationsand photosynthesis. Emir. J. Food. Agric. pp. 57-72. https://doi.org/10.9755/ejfa.v24i1.10599

Zlatev, Z.S., 2005. Effects of water stress on leaf water relations of young bean plants. J. Cent. Eur. Agric. 6(1): 5-14.