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P.W. Masinde, H. Stützel, S.G. Agong, and A. Fricke

Plant growth and osmotic adjustment of spiderplant were investigated in a glasshouse and under field conditions. Two fast-growing genotypes (P-landrace and P-commercial) and a slow-growing landrace (G-landrace) were grown under soil water deficit and watered conditions. The fraction of transpirable soil water (FTSW) was used as an indicator of water availability in pots. In the greenhouse, transpiration was determined by changes in daily pot weights and the ratio of transpiration of plants in soil water deficit to watered treatments expressed as normalized transpiration ratio (NTR). Water use in the field experiment was determined by gravimetric methods. The fast-growing genotypes had a higher rate of soil drying due to a higher rate of leaf area development. They were also more sensitive to soil water deficit with NTR beginning to decline at FTSW of 0.55-0.77 as compared to 0.29 for the slow-growing landrace. Also, the fast growing genotypes had FTSW thresholds for the stem elongation rate of 0.35-0.55 as compared to 0.20 for the slow growing landrace. The rate of leaf development declined when 40% to 60% of available water in the soil was removed, regardless of genotype. Leaf area of plants under field conditions decreased when the soil moisture was <60% field capacity. Under severe soil water deficit stress in pots, plants partitioned more biomass to roots than above ground; however, biomass partitioning between leaves and stems was not influenced by soil water deficit. Spiderplant showed limited osmotic adjustment (OA) in the range of 0.10-0.33 MPa at the highest soil water deficit (FTSW = 0). Thus, spiderplant is mainly a drought avoiding species. To achieve maximum growth, it is necessary to keep FTSW above 0.6.

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Sarah E. Cathey, Jason K. Kruse, Thomas R. Sinclair, and Michael D. Dukes

stomatal conductance and photosynthesis rates (reviewed by Sadras and Milroy, 1996 ). Studies across a range of agronomic species have shown that the normalized transpiration ratio (NTR), which compares drying vs. well-watered plants, declines with a two