Abstract

Water relation and growth parameters of drought stressed seedlings of Chir pine (Pinus roxburghii Sarg.) were studied over a one year period. The seedlings were subjected to three drought cycles of 9, 18, 27 days and one control level (watered every alternate day) in a polyhouse. Pre-dawn (5.30-6.30 AM) and Mid-day water potential was estimated using a pressure chamber. The bench drying method was followed for developing P-V curves for estimating components of water potential. Osmotic adjustment was estimated as the difference between the osmotic potential at zero and full turgor of seedlings kept at control and those given 27 days drought. Across drought cycles the pre- dawn water potential ranged between -0.59 MPa and -2.12 MPa and the mid-day water potentials were always lower than pre-dawn water potentials. The Osmotic adjustment was – 1.17 MPa at full turgor and -2.0 MPa at zero turgor. The seedlings growth was positively related to soil moisture and water potential. The daily change in water potential (difference between pre-dawn and mid-day water potential) declined with increasing drought and was nominal (less than -0.2 MPa) in seedlings subjected to 18 and 27 days drought cycle. Needle characteristics were severely affected by water stress. In Pinus roxburghii Sarg seedlings osmotic adjustment may be an important adaptive mechanism that assists it to invade and grow on dry inhospitable sites.

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