title: Two strategies by epiphytic orchids for maintaining water balance: thick cuticles in leaves and water storage in pseudobulbs.
abstract: Epiphytes are an important component of tropical and subtropical flora, and serve vital ecological functions in forest hydrology and nutrient fluxes. However, they often encounter water deficits because there is no direct contact between their roots and the soil. The strategies employed by epiphytes for maintaining water balance in relatively water-limited habitats are not completely understood. In the present study, we investigated the anatomical traits, water loss rates, and physiology of leaves and pseudobulbs of four Dendrobium species with different pseudobulb morphologies to understand the roles of leaf and pseudobulb in maintaining water balance of epiphytic orchids. Our results showed that two species (D. chrysotoxum and D. officinale), with lower rates of water loss, have thicker leaves and upper cuticles, but lower epidermal thickness and leaf dry mass per area. In contrast, the other two species (D. chrysanthum and D. crystallinum) with thinner cuticles and higher rates of water loss, have less tissue density and greater saturated water contents in their pseudobulbs. Therefore, our results indicate that these latter two species may resist drought by storing water in the pseudobulbs to compensate for their thin cuticles and rapid water loss through the leaves. Under the same laboratory conditions, excised pseudobulbs with attached leaves had lower rates of water loss when compared with samples comprising only excised leaves. This implies that epiphytic orchids utilize two different strategies for sustaining water balance: thick cuticles to conserve water in leaves and water storage in pseudobulbs. Our results also show that Dendrobium species with thin cuticles tend to have pseudobulbs with high water storage capacity that compensates for their faster rates of water loss. These outcomes contribute to our understanding of the adaptive water-use strategies in Dendrobium species, which is beneficial for the conservation and cultivation of epiphytic orchids.
authors.affiliation: Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, China Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China sbzhang@mail.kib.ac.cn.
authors.forename: Shi-Jian
authors.initials: SJ
authors.lastname: Yang
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China National Plateau Wetlands Research Centre, Kunming, Yunnan 650224, China sbzhang@mail.kib.ac.cn.
authors.forename: Mei
authors.initials: M
authors.lastname: Sun
authors.affiliation: Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, China.
authors.forename: Qiu-Yun
authors.initials: QY
authors.lastname: Yang
authors.affiliation: Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, China Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China.
authors.forename: Ren-Yi
authors.initials: RY
authors.lastname: Ma
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China.
authors.forename: Jiao-Lin
authors.initials: JL
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, China sbzhang@mail.kib.ac.cn.
authors.forename: Shi-Bao
authors.initials: SB
authors.lastname: Zhang
keywords: Cuticles; Dendrobium; pseudobulb; relative water content; water conservation; water loss