| Proline contents, chlorophyll a and b contents, carotenoids contents, water relations, leaf water potential, photosynthetic light response, gas exchange, stomatal conductance, growth and biomass allocation were assessed in one-year-old seedlings of Quercus liaotungensis, Fraxinus rhynchophylla, Spiraea pubescens and Lepsedeza bicolor which were subjected to soil drying(s). The results are as follows.(1) Proline contents were related to leaf age and species. Proline contents were higher in old leaves than young leaves, suggesting that old leaves may have more drought resistance. The degree of drought-induced increase was greater in roots than in stems and leaves, implying that roots may be more sensitive to soil drying. Twelve hours after re-watering, porline contents were decreased. After re-watering, compared with Spiraea pubescens and Lepsedeza bicolor, proline contents were lower in Quercus liaotungensis, Fraxinus rhynchophylla.(2) Soil drying decreased pigments contents on leaf-area basis, but increased on fresh-leaf-weight basis. However, the ratios of chl a/ch b and carotenoids/chls were dropped due to drought, independently of sampling unit. Chlorophyll contents were less in young and old leaves than in mature leaves, while carotenoids were increased with leaf age. The ratio of chla /chl b were decreased with leaf age in Quercus liaotungensis, Fraxinus rhynchophylla and Lepsedeza bicolor. Soil drying had more effect on the ratios of chla/b and carotenoids/chls in old leaves than in young and mature leaves.(3) Soil drying increased the bound water (9)and modulus of bulk elasticity (s), but decreased the ratio of weight at full turgor: dry weight(TW:DW), osmotic potential at turgor loss point (ψtlp) and relative water content at turgor loss point (RWCtlp). Osmotic potential at full turgor (ψsat) was markedly reduced due to soil drying in seedlings of Quercus liaotungensis and Fraxinus rhynchophylla, while there was no significant decline in ψsat of Spiraea pubescens and Lespedeza bicolor seedlings, indicating that osmotic adjustment occurred in the former but not in the latter.(4)The time when the leaf water potential reached the lowest during the day was earlier in seedlings of Quercus liaotungensis and Fraxinus rhynchophylla subjected to soil drying than in the control. Spiraea pubescens and Lespedeza bicolor seedlings did not show recovery in leaf water potential after noon in the end of soil drying.(5) Non-significant difference was detected in the maximum net photosynthetic rateof leaf (Pnmax) in seedlings of Quercus liaotungensis, Fraxinus rhynchophylla and Spiraea pubescens. Pnmax, light saturation point (LSP) and apparent quantum yield ( ) were dropped due to soil drying, whereas light compensation point (LCP) and leaf respiration (R) were increased.(6) Net photosynthetic rate (Pn), mesophyll conductance (gm) and transpiration rate (E) were decreased due to soil drying, while there was no decline in intercellular concentration, suggesting that the decline in Pn was likely attributable to the rise in mesophyll resistance. Before the presence of wilting symptoms, the water use efficiency rose with soil drying but was significantly decreased when wilting symptoms appeared.(7) Under soil drying conditions, total leaf area, leaf number was reduced but specific leaf weight (SLW) and the ratio of root to shoot were increased. The total dry weight was lowest in Spiraea pubescens, followed by Quercus liaotungensis, and highest in Lespedeza bicolor, followed by Fraxinus rhynchophylla. Soil drying caused more decrease in stem height of Spiraea pubescens and Lespedeza bicolor than that of Quercus liaotungensis and Fraxinus. The increase in the ratio of root to shoot was more in Spiraea pubescens and Lespedeza bicolor than in Quercus liaotungensis and Fraxinus, which shows that biomass allocation preferred to roots not to stems or leaves under drought conditions.(8) The drought resistance for these four species was ranked as follows: Quercus liaotungensis > Fraxinus rhynchophylla...
|
PDF Full Text Request