Studies On Water Consumption Characteristics Of Main Plantation Tree Species And Technoloy Of Drought Resistance For Afforestation In Northern China

In this paper, the water consumption of main plantation tree species in Northern Chinaunder different growth seasons and water supply was studied by using the method ofsimulated drought in greenhouse. Through analyzed the relationships between waterconsumption and soil moisture, leaf water potential of seedlings, the water consumptionpatterns of seedlings in normal water supply and drought stress conditions were observed.Moreover, it was also studied that effect of stand density on soil moisture, applicationeffects of new drought-resistant afforestaion technology in lack adequate water areas, andinfluence of leaf anatomical structure on its transpiration of seedlings. Target of theresearches is to meet the need in choice of tree species with drought-tolerance and lowerwater consumption, higher survival rates, and afforestation and reconstruction of forestvegetation in the arid and semiarid areas of Northern China.The results of studies on water consumption of seedlings in normal water supplyshowed that the daily variations in quantities and rates of water consumption (WCQ andWCR) of seedlings were clearly. The daily highest quantity and rate of water consumptionof seedlings was in 10:00~14:00. Moreover, the WCQs were half of that in whole day, andthe average hourly WCQs of coniferous species in that time were occupied about 10.5% ofthe quantities of the whole day and 12% of daytime. And that of broadleaf tree specieswere occupied 13% and 15% respectively. The daytime WCQ of seedlings was occupiedabout 85% to 90% of the quantities of whole day. The WCR of seedlings in summer was 2to 4 times as much as in spring and autumn. The highest hourly WCR of coniferous specieswas 1.48 times as much as their average hourly WCR in daytime and 1.5 to 1.8 timeshigher than their average hourly WCR in all-day. The highest hourly WCR of broadleaftree species were 1.77 and 3 times as much as that in daytime and whole day, respectively.The results of research on the leaf anatomical structure demonstrated showed that theconiferous species had strong keratose stratum and their stomata were caved in epidermis,therefore, their ability which controlled water loss were higher than that of broadleaf treespecies and their WCRs were less obviously than that of the latter. The WCRs of higherwater consumption of broadleaf tree species, like as Populus tomentosa, Hippopaerhamnoides, Lycium barbarum, Caragana korshinskii, were 11 to 20 times as much as thatof Pinus tabulaeformis and Platycladus orientalis. And the WCRs of tree species withdrought tolerance, such as Cotinus coggygria, Rhus typhina, Ailanthus altissima and Acertruncatum, were 3 to 9 times higher than that of P. tabulaeformis and P. orientalis. TheWCQ of trees is relevant to their WCR and leaf area, accordingly, it is very important toselect tree species, which has lower water consumption and drought tolerance, and setreasonable stand density in recovery and reconstruction of forest vegetation.When the seedlings were subjected to drought stress, their daily variations of WCRand WCQ became unclearly. The time when the daily highest WCR appeared was movedup. The average hourly WCQs of seedlings in 10:00~14:00 were occupied about 10% to12% of that of whole day and about 8% to 11% of that of daytime. The WCQ and WCR ofseedlings decreased when the seedlings were in drought stress, and, of which decreasedsharply and were reduced over 50% in slight drought stress. The WCQ of most seedlingsdecreased by about 20% to 30%, some seedlings by about 10%, of that in norm al watersupply condition when the seedlings were in medium drought stress. When the seedlingswere subjected to serious drought stress, the WCQs of all tree species were few and wereoccupied less than 10% of that in normal water supply. The WCQ proportion betweendaytime and whole day was trend to decrease in drought stress.The water consumption of tree increased with increasing stand density, thus, the soilmoisture decreased correspondingly. The bare soil had strong evaporation and its watercontent was lower than woodland. Woodland and cover technique can reduce effectivelythe soil surface evaporation. Therefore, the reasonable spatial structure and stand density inafforestation would be beneficial to increase and maintain soil moisture.By application of new drought-resistant afforestation technology in lack adequatewater areas, higher water content of the soil round the tree root system can be kept,essential water supply for tree and preserved the survival of seedlings can be guaranteed,and the afforestation survival rate is increased obviously. Application of drought-resistanttechnology must be according to tree species and regions, which the patterns and quantitiesof water need is different. Application and spread of new drought-resistant afforestationtechnology are rather fit to the regions where it is difficult to rise the survival of seedlingsby general afforestation. The cost of new drought-resistant technology in afforestation willbe lower than that of general afforestation.