SHORT COMMUNICATION Changes in leaf water use after removal of leaf lower surface hairs on Mallotus macrostachyus (Euphorbiaceae) in a tropical secondary forest in Malaysia Tanaka Kenzo Æ Reiji Yoneda Æ Mohamad Alias Azani Æ Nik Muhamad Majid Received: 20 August 2007 / Accepted: 25 December 2007 / Published online: 2 February 2008 Ó The Japanese Forest Society and Springer 2008 Abstract Leaf hairs may assist in maintaining high leaf water use efficiency in tropical secondary forest tree species. We compared leaf temperature, transpiration, photosynthesis and water use efficiency between hairy and depilated leaves in Mallotus macrostachyus (Euphorbia- ceae), to determine the role of leaf hair in leaf water use efficiency (WUE) in tropical degraded secondary forest in Malaysia. Measurements were made on five mature indi- viduals growing in sun-exposed conditions and five in shaded conditions. The hair dry weight per unit leaf area was significantly greater in sun leaves than in shade leaves. The transpiration rate (Tr max ) of depilated leaves in sun- exposed conditions was slightly higher than in hairy leaves in both morning and afternoon measurements. In contrast, Tr max in the shade leaves was almost identical in hairy and depilated leaves. Leaf stomatal conductance (g s ) in the morning showed almost the same value among leaf types and light conditions. In the afternoon, g s slightly decreased from the morning values in both sun and shade conditions. In the morning, the leaf water use efficiency (A max /Tr max ) in both conditions did not differ significantly between hairy and depilated leaves. However, in the afternoon, WUE in the depilated leaves was significantly lower than in hairy leaves in sun-exposed conditions. These observations suggest that leaf hairs in M. macrostachyus contribute to the high leaf water use efficiency in drought conditions, such as high vapor pressure deficit experienced at midday in degraded tropical secondary forests. Keywords Boundary layer Á Leaf trichomes Á Photosynthesis Á Transpiration Á Water use efficiency Introduction Leaf hairs occur in various plant species in many shapes and arrangements (Esau 1953; Johnson 1975). Leaf hairs have several physiological and ecological roles, including UV protection (Karabourniotis et al. 1992; Ripley et al. 1999; Gregoriou et al. 2007), reduction of boundary layer conductance and leaf transpiration rate (Wuenscher 1970; Parkhurst 1976; Schreuder et al. 2001), reduction of the leaf temperature (Ehleringer and Bjorkman 1978; Ehle- ringer and Mooney 1978), and reduction of solar radiation received (Gausman and Cardenas 1969; Ehleringer et al. 1976). These roles are important in stressful environments, such as coastal dunes and arid land, in reducing the effects of strong sunlight, high temperatures and drought (Johnson 1975). In fact, leaf hair density is higher in the dry season than in the wet season (Smith and Nobel 1977; Aronne and Micco 2001), and is significantly correlated with both temperature and radiation in single species of temperate trees (Pe ´rez-Estrada et al. 2000). The tropical rainforest environment is humid all year round, and many tree species grow in low water stress conditions, especially in the inner forest (Whitmore 1998; Kenzo et al. 2007b). Dense leaf hair is uncommon in tropical rainforest tree species (Richards 1952; Bongers and Popma 1990; Turner 2001); of 250 tropical rainforest tree species in Venezuela, only 15 had a dense covering of hairs (Roth 1984). The open grass land and large canopy T. Kenzo (&) Á R. Yoneda Bureau of International Partnership, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan e-mail: mona@affrc.go.jp M. A. Azani Á N. M. Majid Faculty of Forestry, Universiti Putra Malaysia (UPM), Serdang, Malaysia 123 J For Res (2008) 13:137–142 DOI 10.1007/s10310-008-0062-z