Studies On The Water Eco-physiology Of The Main Aforestation Trees In Maowusu Sandland

Maowusu sandland is the typical semi-arid area in china, the selection of anti-drought trees and technology of the afforestion in this area is becoming more and more important in the forestry development. Therefore this dissertation is investigate the effect of the Climatic Factors on Growth of Pinus sylvestris var.mongolica and Pinus tabulaeformis in the Maowusu sand land ; the water characteristics and gas exchange of Pinus sylvestris var.mongolica and Pinus tabulaeformis mixed land and Salix psammophyila and S.microstachya mixed land. The target of the researches is to meet the need in tree species selection that with drought-tolerance and lower water consumption, higher survival rates, and afforestation and reconstruction of forest vegetation in the arid and semiarid areas of Northern China.The dominant climatic factors which influenced the growth of Pinus sylvestris var.mongolica were annual rainfall of the previous year, ≥10℃ accumulated temperature, and annual evaporation; The dominant climatic factors which influenced the growth of Pinus tabulaeformis were annual rainfall of the previous and current years. Pinus sylvestris var.mongolica in this area grew better than Pinus tabulaeformis, which show stronger drought resistance ,So climatic factors of this area was more suitable to the growth of Pinus sylvestris var.mongolica .In growing season, the maximum and the average value of the net photosynthesis of the Pinus sylvestris var.mongolica is larger than that of the Pinus tabulaeformis.The average of the water utility efficiency of Pinus sylvestris var.mongolica is 3.62CO₂.mmol^-1H₂O,and the Pinus tabulaeformis is the 3.33μmolCO₂.mmol^-1H₂O, the former is always larger than the later. The factors that influenced the Pinus sylvestris var.mongolica photosynthesis are PAR,Gs and Ci,which influned the Pinus tabulaeformis are PAR and Gs.As is shown from the whole period (4 months),the maxium and average value of the net photosynthesis and transpiration of the Salix psammophyila,S.microstachy a, Hippoplhae rhamnoides L,Salix matsudana,in. June,July and August are larger tha n in May .In these 4 species, the sort order of the net photosynthesis is Hippoplha e rhamnoides L>S.microstachya>Salix psammophyila>Salix matsudana, which the mo unts is 30.3μmol.m^-2.s^-1,29μmol.m^-2.s^-1,26.8μmol.m^-2.s^-1,20.19μmol.m^-2.s^-1.The order of the transpiration is Hippoplhae rhamnoides L>S.microstachya>Salix psammophyila>Salix matsudana,. which the mounts is 15.4mmol.m^-2.s^-1,12.9mmol.m^-2.s^-1,11mmol.m^-2.s^-1, 9.96mmol.m^-2.s^-1. In the growing season,the efficiency curve of the water utility of t he 4 speceis showed the decline trend.The order is Salix psammophyila>S.microstac hya>Hippoplhae rhamnoides L>Salix matsudana,which the mounts is 2.83μmolCO₂.m mol^-1H₂O,2.79μmolCO₂mmol^-1H₂O,2.70μmolCO₂.mmol^-1H₂O,2.67μmolCO₂.mmol^-1H₂O respectively,and the main factors influenced photosynthesis is PAR and Gs.