Effects of soil water on photosynthetic characteristics and leaf traits of Cyclobalanopsis glauca seedlings growing under nutrient-rich and -poor soil

Cyclobalanopsis glauca is a dominant species in mid-subtropical forest, and usually plays an important role in forest ecosystems. However, it often suffers redundant precipitation or water stress, which often concurs with high temperature, nutrient depletion and strong irradiance. The study presented in the paper hypothesized that soil water exerted strong influence on leaf gas exchange and traits. The objective of this study was to clarify the effect of soil water changes on photosynthetic characteristics and leaf traits and their relationships of C. glauca seedlings growing on nutrient-rich and nutrient-poor soil at three water levels. The study measured the specific leaf area (SLA), nitrogen content, chlorophyll concentrations and photosynthetic light response curve. Its results showed that there were no differences in leaf size, leaf dry weight, SLA, leaf dry matter content, Leaf nitrogen concentration and Leaf chlorophyll between the two soil nutrient treatments, while these parameters differed significantly among different water levels for either of the treatments. There were large variations in leaf photosynthetic parameters and leaf traits among the different water treatments, indicating different response patterns of C. glauca   seedling and its adaptation to the different soil water conditions. There were no significant differences in light-saturated photosynthetic rate (AmaxAmax) and apparent quantum yield (Ø) between the nutrient-rich and nutrient-poor soils, which indicated that the C. glauca   seedlings could maintain similar capacities in different soils that differed in nutrient condition. As to the relation between the photosynthesis and leaf traits, the AmaxAmax and PNUE were positively correlated with the SLA, respectively, but the SLA   had significant negative relationship with the leaf N (P<0.01P<0.01) in nutrient-rich soil. In contrast, both AmaxAmax and PNUE were significantly negatively correlated with the SLA  , respectively (P<0.01P<0.01); and the SLA   was not significantly positively correlated with the leaf nitrogen concentration of the nutrient-poor soil (P>0.05P>0.05). The specific leaf areas (SLA  ), nitrogen and chlorophyll concentrations as well as other photosynthetic features were influenced in a coordinative manner by the soil water. The relation among the AmaxAmax, PNUE   and the NmassNmass, SLA could be described as a binomial equation and a liner negative regression for the nutrient-rich and nutrient-poor soil, respectively. In conclusion, soil water was more constraining factor than the soil nutrient to the photosynthesis of C. glauca seedlings, nutrient-rich soil could offset some negative influence resulting from soil water deficit on LSP and LCP. Factors affecting the variations of photosynthetic characteristics and leaf traits of C. glauca seedlings differed between the nutrient-rich and nutrient-poor soils.