Seasonal variation in photosynthesis in six woody species with different leaf phenology in a valley savanna in southwestern China

Abstract

During 2003During -2005, we examined the effect of seasonal drought on water status, gas exchange, d 13 C, chlorophyll fluorescence and spectral reflectance in six woody species in a valley savanna near the Yuanjiang River (the upper Red River) in southwestern China. Three different phenological types of these woody species were compared, i.e., an evergreen species, Cyclobalanopsis helferiana, two winter-deciduous (WD) species, Buchanania latifolia and Symplocos racemosa, and three droughtdeciduous (DD) species, Terminthia paniculata, Wendlandia tinctoria and Woodfordia fruticosa. We aimed to test the following three hypotheses: (1) the evergreen and WD species employ a drought avoidance strategy, whereas DD species employ a drought tolerance strategy; (2) the evergreen and WD species have a more economical water use strategy than the DD species and (3) the evergreen and WD species have a stronger photoprotection capacity through thermal dissipation than the DD species. At the end of a prolonged drought, the predawn leaf water potential (W pd ) in C. helferiana and S. racemosa dropped to ca. À0.8 MPa, whereas the W pd in B. latifolia remained close to zero and DD species were leafless. In the rainy seasons, maximal photosynthetic rates of the evergreen (18.4 lmol m À2 s À1 ) and W. fruticosa (18.0 lmol m À2 s À1 ) were higher than those of the other four species (12.2À13.8 lmol m À2 s À1 ). The evergreen and WD species responded to drought by closing stomata and thus maintained a constant relative water content (RWC), which is a typical drought avoidance strategy; however, it is at the expense of carbon gain. DD species maintained a high photosynthetic capacity with a decrease in both stomatal conductance and RWC until the driest period, and then shifted from the drought tolerance strategy to the avoidance mechanism by shoot dieback. There was no significant difference in the means of d 13 C across the phenological groups. The evergreen and WD species had stronger heat dissipation than the DD species in dry seasons. All species increased leaf spectral reflectance, probably because of degradation of chlorophyll as indicated by the leaf reflectance index, which should reduce light harvesting. All species showed a strong increase in the ratio of red to green spectral reflectance of leaves during dry seasons, indicating the accumulation of anthocyanin, which may contribute to screening sunlight and scavenging reactive oxygen species. Different responses to drought of savanna woody species with different leaf phenologies may facilitate the partitioning of resource use and hence their co-existence.

Canopy temperature variability in a tropical rainforest, subtropical evergreen forest, and savanna forest in Southwest China

“…For gc of the sample tree species at the SAF site, we used the gc values from the literature (Zhang et al 2007) for the same site.…”

Plant drought tolerance assessment for re-vegetation in heterogeneous karst landscapes of southwestern China

“…The frequent temporary water deficit caused by the fluctuation of soil water is considered one of the major limiting factors in survival, growth and distribution of plant species and the competition among species in the karst vegetation. A large number of studies on morphological and physiological adaptive responses of the karst plants to water deficit have been focused on woody species or species grown under controlled environments (Chen et al, 2009;Deng et al, 2006;Liu et al, 2010Liu et al, , 2011aWei et al, 2007;Wu et al, 2009;Zhang et al, 2007;Zhu et al, 2009). Only few comparative field studies have been reported for the purpose of 'site-species matching', which can provide valuable suggestions on selecting species candidates for specific restoration sites.…”

Exploitation of patchy soil water resources by the clonal vine Ficus tikoua in karst habitats of southwestern China

“…For example, soil water content ranges from 2.2 to 15.0% by weight from one microhabitat to another (Zhang et al 2006). Previous studies on morphological and physiological adaptations of karst plants to water stress have focused mainly on the responses of plants to homogeneous water conditions (Zhang et al 2007;Chen et al 2009;Wu et al 2009;Zhu et al 2009). The responses of karst plants to heterogeneous water resources have yet to be studied.…”