Drought And Salinity Resistant Physiology And Water Consumption Characteristics Of Main Plantation Tree Species In High-cold Region Of Loess Plateau

With main plantation tree species in high-cold region of Loess Plateau:Hippophea rhamnoides Linn., Atraphaxis bracteata A. Los., Shepherdia argentea (Pursh) Nutt., Betula platyphylla Suk., Larix principis-rupprechtii Mayr. and Picea crassifolia Kom. as test materials, this paper comprehensively studied the physiological responses of plant growth, leaf water relations and photosynthetic characteristics to draught and salt stress, as well as the laws of water consumption of these tree species. The aim of this paper was to deeply analyzed the drought and salinity resistant physiology and water consumption characteristics of the four main plantation tree species in order to pave the way for screening and cultivation of adverse-resistant plants during vegetation recovery period in different site conditions and also to provide a scientific theoretical foundation for the ecological environment construction and returning farmland to forests or grassland project. By means of research, main conclusions are elicited as follows:(1) Drought resistant characters of the four main plantation tree species in high-cold region of Loess PlateauDrought stress significantly decreased stem height, leaf area per plant, biomass yield of H. rhamnoides, B. platyphylla and S. argentea seedlings and the decrement was greater under higher drought stress. Overall, the growth and biomass yield of B. platyphylla seedlings were most sensitive to drought stress, and next was A. bracteata, H. rhamnoides and S. argentea seedlings could well perform under drought stress.Drought-induced inhibition of photosynthesis in the leaves of H. rhamnoides and S. argentea seedlings was attributed to stomatal limitations under W1 (> 22.7%), W2 (15.1%-22.7%) and W3 (7.6%-15.1%) treatments, and attributed to non-stomatal factors under W4 (< 7.6%) treatment. The decrease of photosynthesis in the leaves of A. bracteata seedlings was caused by stomatal limitations under W1 and W2 treatments, and caused by non-stomatal factors under W3 and W4 treatments. In contrast, non-stomatal limitations became a leading factor in the decline of photosynthesis in the leaves of B. platyphylla seedlings from W2 to W4 treatments.(2) Discrimination results of drought tolerant mechanism of the four tree speciesIn the wilting experiment, the largest decline of soil relative water content of B. platyphylla seedlings was found and serious wilting symptoms occurred on 30 d when soil relative water content dropped to 5.75%. H. rhamnoides seedlings had the highest enduring capability to drought stress compared to other three tree species and wilting symptoms were obtained on 45 d when soil relative water content dropped to 3.85%. Meanwhile, A. bracteata and S. argentea seedlings could endure drought stress for 40 days. According to soil water depleted index, and the magnitude of drought tolerance in decreasing order was H. rhamnoides> S. argentea> A. bracteata> B. platyphylla.Relationships between leaf water potential of the seedlings and soil water content and soil water potential were studied in detail. For the optimum effect, this relationship can be expressed by regression equation:y= a+blx for leaf water potential and soil water content and regression equation:y= axb for leaf water potential and soil water potential. Mechanism and types of drought tolerance of tree species can be recognized using the existing models and the discrimination results of drought tolerant mechanism of the four tree species are the same, i.e. drought tolerance by dehydration tolerance at low tissue water potential.(3) Salt resistant physiology of the four main plantation tree species in high-cold region of Loess PlateauSignificant salt-induced suppression of leaf photosynthetic capacity of A. bracteata and S. argentea seedlings appeared only at the highest salinity level (600 mmol·L-1 NaCl solution), whereas rapid decline of photosynthesis of H. rhamnoides and B. platyphylla seedlings was found even at the lowest salinity level (200 mmol·L-1 NaCl solution). Compared with the control, the content of chlorophyll a (Chla), chlorophyll b (Chlb), chlorophyll (Chi) and carotenoid (Car) decreased significantly under salt stress. Salinity also induced an excessive accumulation of Na+ and a severe inhibition of K+ and Ca2+ in the leaves of plants, consequently leading to ionic imbalance. On the whole, the magnitude of salinity tolerance in decreasing order was S. argentea> A. bracteata> H. rhamnoides> B. platyphylla.This experiment was performed for 30 d under native condition in the open air and our results showed that, morphological symptoms of salt injury in H. rhamnoides seedlings occurred on the 10th day, and all seedlings were dead on the 20th day under 600 mmol-L-1 NaCl solution. As for B. platyphylla seedlings, all seedlings were dead on the 23th day under 400 mmol·L-1 NaCl concentration and on the 18th day under 400 mmol·L-1 NaCl. In contrast, S. argentea and A. bracteata seedlings could survive at the highest salinity level (600 mmol·L-1 NaCl solution) for above 30 days without obvious change of leaf characters, indicating that the two species are highly tolerant to salinity.Sanility-induced inhibition of photosynthesis in the leaves was mainly attributed to the stomatal efficient closure predetermined by a low water potential in leaves (i.e. stomatal limitations) in short term, and was mainly due to non-stomatal limitations in long run, including disorder of physiological metabolic of leaves, suppression of chloroplast capacity to fix CO2 caused by severe cellular dehydration, photosynthetic capacity decline caused by degradation of the photosynthetic pigment, ionic imbalance and toxicity, and so on. Moreover, the higher NaCl concentration, the earlier time changing from stomatal limitations into non-stomatal limitations.(4) Water consumption characteristics of the four main plantation tree species in high-cold region of Loess PlateauSap flow fluctuations of H. rhamnoides, L. principis-rupprechtii and P. crassifolia were measured continuously with Granier's thermal dissipation probe (TDP). It was obtained that sap flow velocity of L. principis-rupprechtii and P. crassifolia had circadian rhythmicity during growing season. Sap flow flux of these three species had the same change rule as sap flow velocity but there were remarkable differences in value of sap flow flux among species because of the breast height. Total water consumption of the tree species during growing season was 449.46 kg for P. crassifolia No.1,3708.65 kg for P. crassifolia No.2,663.33 kg for L. principis-rupprechtii and 75.94 kg for H. rhamnoides, respectively.Correlation analysis between meteorological factors and sap flow velocity of different plants indicated that sap flow velocity was closely related to the fluctuation of meteorological factors. Sap flow velocity had an obviously positive correlation with solar radiation, air temperature and wind speed, but it had a highly negative correlation with relative humidity, indicating that sap flow velocity of tree species was comprehensively impacted by meteorological factors.