RESUMO
In the areas with seasonal drought, water is the key factor affecting plant growth and development. Based on long-term continuous observation data, it is of great significance to explore plant water use patterns for vegetation construction in areas with seasonal drought. Taking Platycladus orientalis in Beijing mountainous area as the research object, stable hydrogen and oxygen isotope technique was applied to measure the isotopic composition of water from the soil, plant branches, and precipitation from 2012 to 2017. The relative contribution of soil water from different soil layers to P. orientalis was quantified by the MixSIAR model. The results showed that soil water in the deep layer (40-100 cm) was more stable than that in the shallow layer (0-40 cm). The variation of soil water content and water isotope values in the shallow layer were more obvious due to the effects of evaporation and precipitation. P. orientalis mainly absorbed stable deep soil water, with a relative contribution rate of 55.7%. In the dry season, with the decreases of soil water content, the absorption depth of plants to soil water gradually shifted to the shallow layer. Under conditions of moist, natural condition, mild drought and moderate drought, the relative contribution rates of deep soil water were 59.8%, 57.9%, 54.6%, 52.7%, respectively. To maintain higher transpiration in the wet season, P. orientalis relied more on deep soil water under mild and moderate drought conditions than in the dry season. Under the conditions of moist, natural condition, mild drought and moderate drought, the relative contribution rates of deep soil water were 58.9%, 57.6%, 56.4%, and 57.1%, respectively. The adaptive characteristic of P. orientalis, which adjusts the depth of root water absorption according to soil moisture condition, is of great significance for tree species selection in ecological afforestation and long-term management planning in areas with seasonal drought.
Assuntos
Secas , Árvores , Pequim , Estações do Ano , Solo , ÁguaRESUMO
The stable hydrogen and oxygen isotopes are environmental isotopes, which widely exist in various kinds of water. Their relative abundance variation in water can indicate the water circulation and mechanism of water use in plant. This research selected two major kinds of greening tree species, evergreen coniferous Platycladus orientalis and deciduous broad-leaved Quercus variabilis, in Beijing mountainous area, and the water movement process in soil-plant-atmosphere continuum was investigated by the variation characteristics analysis of stable hydrogen and oxygen isotope compositions in precipitation, soil water, groundwater, plant stem water and leaf water. The results showed that the meteoric water line equation of the study area was δD=7.17δ18O+1.45 (R2=0.93), and the soil evaporation line equation was δD=3.85δ18O+1.45 (R2=0.76). A certain degree of evaporation fractionation existed in the processes of rainfall infiltration into soil water. In different seasons, the δD and δ18O values of precipitation, soil water and spring water had different variation regularity. In rainy season, the mean δD and δ18O values were in order of precipitation> spring water>soil water, with the precipitation and soil water supplied spring water together; in dry season, the order was precipitation > soil water > spring water, and the precipitation and spring water both contributed to soil water. The δD and δ18O fitting line equations of stem water of P. orienta-lis and Q. variabilis were respectively δD=5.03δ18O-30.78 and δD=3.0δ18O-48.92. The uptake water of Q. variabilis was more enriched than that of P. orientalis, and the depth of Q. variabilis water uptake in soil profile was shallower than P. orientalis. The leaf water isotopic variation of Q. varia-bilis was more sensitive to atmospheric environment, with the kinetic isotopic fractionation of Q. variabilis being more enriched than that of P. orientalis, but they had the same response to variation of environmental condition.
Assuntos
Hidrogênio , Solo , Pequim , China , Isótopos de OxigênioRESUMO
Complicated high-resolution spectral structures are often observed for molecules doped in solid molecular hydrogen. The structures can result from miscellaneous effects and are often interpreted differently in references. The spectrum of the ν(3) band of CO(2) in solid para-H(2) presents a model system which exhibits rich spectral structures. With the help of the potential energy simulation of the CO(2) molecule doped in para-hydrogen matrix, and extensive experiments with different CO(2) isotopologues and different ortho-hydrogen concentrations in the matrix, the spectral features observed in p-H(2) matrix are assigned to the CO(2)···(o-H(2))(n) clusters and also to energy level splitting that is due to different alignments of the doped CO(2) molecules in the matrix. The assignments are further supported by the dynamics analysis and also by the spectrum recorded with sample codoped with O(2) which serves as catalyst transferring o-H(2) to p-H(2) in the matrix at 4 K temperature. The observed spectral features of CO(2)/pH(2) can potentially be used as an alternative readout of the temperature and orthohydrogen concentration in the solid para-hydrogen.
RESUMO
A midinfrared laser spectrometer is built up based on the difference frequency generation (DFG) of a Nd:YAG (yttrium aluminum garnet) laser and a tunable Ti:sapphire (Ti:Sa) laser. Tuning the Ti:Sa laser and operating properly with the periodically poled lithium niobate crystal, the DFG emission is tunable in the spectral range of 2.3-5.0 microm. The 1064 nm Nd:YAG laser frequency is stabilized to the 10(-6) cm(-1) level on a Doppler-broadened I(2) absorption line at 532 nm. As a result, the DFG emission frequency is stabilized within 1x10(-4) cm(-1). The measurement of an absorption line of CH(4) near 3 mum demonstrates that the DFG spectrometer is very suitable for the molecular absorption line profile studies in the midinfrared region.
