Abstract:

Maowusu sandland is classical one of arid and semi-arid sandland in China.Water is the most limited factor there.The distribution pattern and productivity of terrestrial ecosystem are greatly affected with the future global severer change,especially global precipitation change.It is investigated for the response of physiological ecology of A.ordosica seedlings,a dominant shrub in Maowusu sandland,to the global precipitation change by artificially controlling four water supply gradients.The results show that the diurnal changes of photosynthetic rate,transpiration rate,stomatal conductance,intercellular CO₂ concentration,leaf temperature,solar energy utilization efficiency,and water utilization efficiency of A.ordosica seedlings show significantly different under different water supply treatments.The seedlings have low stomatal conductance and transpiration rate by shutting stomata so as to lower losing water by transpiration,mainly due to severe water stress in the deficit water supply,but high stomatal conductance,intercellular CO₂ concentration,transpiration rate and low leaf temperature by opening stomata so as to increase photosynthesis in full water supply.So the seedlings show different physiological ecological adaptation strategies under different water supply.The fluorescence efficienc increases with the increase of water supply,which explains on mechanism why photosynthesis increases with the increase of water supply treatments.The analyses of backward eliminated variable indicate that the number of main factors which restrict photosynthetic rate of seedlings decrease with the increase of water supply.PAR and leaf temperature are most restricted factor in full water supply,and transpiration rate,intercellular/air CO₂ concentration margin and PAR in middle water supply,but transpiration rate,stomatal conductance,intercellular/air CO₂ concentration margin,leaf/air temperature and air temperature in deficient water supply.

Key words: Simulated precipitation, Maowusu sandland, A.ordosica seedlings, Physiological ecology process, Fluorescence efficiency