喀斯特地区适生树种复羽叶栾树幼苗对干旱胁迫下异质生境的生长和光合响应

Response of Growth and Photosynthesis of Koelreuteria bipinnata, an Adaptive Tree Species to Karst Regions, to the Heterogeneous Habitat Under Water Stress

干旱缺水和水分异质性是影响喀斯特地区植物生长、分布及繁殖的主要因素.采用盆栽控制实验,研究了喀斯特地区适生树种复羽叶栾树( Koelreuteria bipinnata Franch.)幼苗在两种水分条件(对照和轻度干旱)及两种生境下(同质和异质)的净光合速率( Pn )、蒸腾速率( Tr )、气孔导度( Cs )、水分利用效率( WUE )及生物量积累和分配.结果表明:不管在对照还是干旱条件下,复羽叶栾树幼苗的净光合速率( Pn )和水分利用效率( WUE )在异质生境下均高于同质生境,但气孔导度( Cs )和蒸腾速率( Tr )在异质和同质生境下差异无统计学意义.复羽叶栾树幼苗的总生物量、地上生物量以及根系生物量在异质生境与同质生境中差异无统计学意义,但根生物量比在对照条件下对异质生境的响应显著低于同质生境,而在干旱时,对异质生境的响应则显著高于同质生境.可见,复羽叶栾树通过提高水分利用效率和降低对根系资源的投资来提高净光合速率以适应异质生境,但并未提高异质生境中植物生物量的积累.

Drought and water heterogeneity are very important factors influencing the growth , distribution and reproduction of plants in karst regions. A pot experiment was made, in which the seedlings of goldenrain tree ( Koelreuteria bipinnata ) were grown under two water conditions (well watering and moderate drought) and two kinds of habitats (homogeneous and heterogeneous), and their net photosynthetic rate ( Pn ), transpiration rate ( Tr ), stomatal conductance ( Cs ), water use efficiency ( WUE ) and biomass accumulation and distribution were studied. The main results were as follows. Either under well watering or moderate drought conditions, net photosynthetic rate ( Pn ) and water use efficiency ( WUE ) of K.bipinnata seedlings were significantly higher in the heterogeneous habitat than in the homogeneous habitat. However, their stomatal conductance ( Cs ) and transpiration rate ( Tr ) were not affected by habitats. No significant difference existed between the two different habitats in total biomass, aboveground biomass and root biomass of the seedlings. Their root biomass ratio in the heterogeneous habitat was significantly lower than that in the homogeneous habitat under well watering condition;while under moderate drought condition, their root biomass ratio was significantly higher than that in the homogeneous habitat. It is concluded, therefore, that to adapt to the heterogeneous habitat under moderate drought, K.bipinnata seedlings improve their WUE and Pn at the cost of reducing the investment to root biomass.