title: Photosynthetic thermotolerance of woody savanna species in China is correlated with leaf life span.
abstract: OBJECTIVE
  Photosynthetic thermotolerance (PT) is important for plant survival in tropical and sub-tropical savannas. However, little is known about thermotolerance of tropical and sub-tropical wild plants and its association with leaf phenology and persistence. Longer-lived leaves of savanna plants may experience a higher risk of heat stress. Foliar Ca is related to cell integrity of leaves under stresses. In this study it is hypothesized that (1) species with leaf flushing in the hot-dry season have greater PT than those with leaf flushing in the rainy season; and (2) PT correlates positively with leaf life span, leaf mass per unit area (LMA) and foliar Ca concentration ([Ca]) across woody savanna species.
  
  
  METHODS
  The temperature-dependent increase in minimum fluorescence was measured to assess PT, together with leaf dynamics, LMA and [Ca] for a total of 24 woody species differing in leaf flushing time in a valley-type savanna in south-west China.
  
  
  RESULTS
  The PT of the woody savanna species with leaf flushing in the hot-dry season was greater than that of those with leaf flushing in the rainy season. Thermotolerance was positively associated with leaf life span and [Ca] for all species irrespective of the time of flushing. The associations of PT with leaf life span and [Ca] were evolutionarily correlated. Thermotolerance was, however, independent of LMA.
  
  
  CONCLUSIONS
  Chinese savanna woody species are adapted to hot-dry habitats. However, the current maximum leaf temperature during extreme heat stress (44·3 °C) is close to the critical temperature of photosystem II (45·2 °C); future global warming may increase the risk of heat damage to the photosynthetic apparatus of Chinese savanna species.
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan, China.
authors.forename: Jiao-Lin
authors.initials: JL
authors.lastname: Zhang
authors.forename: L
authors.initials: L
authors.lastname: Poorter
authors.forename: Guang-You
authors.initials: GY
authors.lastname: Hao
authors.forename: Kun-Fang
authors.initials: KF
authors.lastname: Cao
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D002681:China; D002734:Chlorophyll / Q000378:metabolism; D006358:Hot Temperature; D010641:Phenotype; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology*; D011891:Rain; D012621:Seasons; D013997:Time Factors; D014197:Trees / Q000502:physiology*
chemical_list: D002734:Chlorophyll; D002118:Calcium