Physiological and Anatomical Responses to Water Deficits in the Cam Epiphyte Tillandsia ionantha (Bromeliaceae)

Abstract

Although physiological responses to drought have been examined in several species of epiphytic bromeliads, few have included a comprehensive methodological approach to the study of the carbon and water relations of a single species undergoing drought stress. Thus, physiological and anatomical responses to an imposed drought treatment were examined in the atmospheric Crassulacean acid metabolism (CAM) epiphyte Tillandsia ionantha. From 0 through 20 d without water, nocturnal malic acid accumulation and C0 2 uptake rates did not change despite a 17% reduction in relative water content. In addition, water potentials averaged -0.40 MPa and, unlike leaf water content, did not decline. The avoidance of further declines in leaf water content was attributed to the restriction of stomatal opening to the night (a characteristic feature of CAM), to low stomatal densities and small stomatal pores, and to a thick boundary layer resulting from a dense foliar trichome cover. The maintenance of high physiological activity during the first 20 d of the drought treatment was most likely a result of the high water potentials in the chlorenchyma, which were attributed, in part, to water movement from the water-storage parenchyma (= "hydrenchyma") to the chlorenchyma. Nocturnal malic acid accumulation and the rate of net C0 2 exchange declined in a linear fashion from 30 to 60 d without water, as did leaf water potential and osmotic potential. During this time, C0 2 recycling increased from ca. 20% to nearly 75%. Though declining throughout this later stage of the drought treatment, metabolic activity remained relatively high, possibly as a result of the observed osmotic adjustment as well as a potentially high cell wall elasticity.

Drought and extreme temperature tolerance for Tillandsia dasyliriifolia , an epiphytic bromeliad from the northern coastal dune scrubland in Yucatan, Mexico

“…For example, after 50 days of drought the metabolizing region of Tillandsia ionantha Planch. leaf not shows a strong desiccation, allowing a positive assimilation of CO 2 ; consequence of water movement from the hydrenchyma to the chlorenchyma (Nowak and Martin, 1997). Moreover, the presence of hydrenchyma in Tillandsia usneoides allowed an increase of 700 % in tissue water content after a rain and a reduction of 300 % after a severe drought (Penfound and Deiler, 1947).…”

On the Controls of Leaf-Water Oxygen Isotope Ratios in the Atmospheric Crassulacean Acid Metabolism Epiphyte Tillandsia usneoides

“…In general, the measured water potential of atmospheric epiphytes, T. usneoides included, has rarely been observed below 21 MPa (Martin, 1994). In one experiment with Tillandsia ionantha, total plant water potential did not drop below 20.75 MPa after 60 d of imposed drought (Nowak and Martin, 1997). Considering that the water potential of air at h = 0.99 is 21.4 MPa (and 22.8 MPa at h = 0.98, both at 20°C), it is hard to imagine a scenario in which water adsorbed onto trichomes that are in equilibrium with subsaturated air could move against the water potential gradient into the living cells of T. usneoides, and the work of Martin and Schmitt (1989) and the plant tissue is covered with liquid water, the trichomes become appressed against the cuticle and channel the absorption of liquid water into the underlying living cells (Benzing et al, 1976).…”

CAM Photosynthesis in Bromeliads and Agaves: What Can We Learn from These Plants?

“…One possibility is that these were well-hydrated greenhouse plants, so the rates of CO 2 recycling would be low when compared to CO 2 assimilated during night. In another study, Nowak and Martin [94] analyzed the CAM responses of Tillandsia ionantha under drought for 60 days. From the 30 th day on, the CO 2 uptake started to drop until the 60 th day.…”