Characteristics Of Sap Flow And Transpiration Of Three Woody Plant Species (Caragana Korshinskii, Hippophae Rhamnoides, Larix Principi-rupprechtii) In The Area Of Liupan Mountain, South Ningxia, China

In order to understand the relationship between ecological water use of vegetations and water resources in arid and semi-arid area of northwest China. We had eastamated the water consumption of three main species planted for reduceing erosion and for water resources protection , Hippophae rhamnoides, Caragana Korshinskii and Larix principi-rupprechti , by sap flow technology in the gnvting season of year 2003 to 2004. Some sap flow characteristics , single tree and stand transpiration , forest structure soil water and microclimate factors were discussed in this papars, the main results were as follows:1. Hippophae rhamnoidesThe sap flow flux of Hippophae rhamnoides were measured by the stem heat balance method in the area of the resources conservation forest in Die- Die- Gou valley of Liupan Mountain, Guyuan, Ning Xia Province from July to September. The transpiration intensity based on leaf area was estimated from sap flow flux. And the water consumption by transpiration was acquired by scaling-up from singletree to stand based on the leaf area index (LAI). Diurnal changes of sap flow and transpiration put up a type of single peak curve. Sensors of Dynagage system had detected the nighttime sap flow was about of 17.78% of daytime sap flow, and that was about of 12.873-13.838% of whole day. Sap flow movement was chiefly effected by solar radiation, water vapor pressure deficit (VPD), air temperature and relative humidity. And the correlation order of microclimate factors with transpiration intensity were follow as : VPD > solar radiation > relative humidity>wind speed > soil temperature. LAI changes in the growing season was not significant effect on sap flow flux . But leaves transpiration intensity showed a negative correlation with LAI (P<0.0001) and appeared obviously slowdown trend from June to September. Some stomatal compensation occurred for LAI increasing in growing season, and the compensation might be enhanced in high LAI stand. Water consumption by transpiration in Hippophae rhamnoides plantation would increase with LAI going up of stand, once the water consumption by transpiration was over the 95% of annual precipitation normally the stand ages was 8~9ages, the growth of Hippophae rhamnoides begun to limited by the soil water deficit which lead to the internal regulation of population. The growth and transpiration would keep undulation in phase during the accommodate period.2. Caragana KorshinskiiIn July of 2003, daily sap flow of Caragana Korshinskii planted in 1986 weremeasured by Dynagage Systems, and the microclimate were monitoring by LI-1401 Agro-Meteorological Station in the stand of Caragana Korshinskii plantation located in Shang Huang experimental area of Guyuan . The regressive models of transpiration estimated from sap flow were established based on the filed observation data. Comparisons in water consumption between two stands were also discussed combining with soil water data. The results showed that there was more sap flow flux founded in bigger diameter branch than that of in smaller one. The difference of sap flow flux between braches in daytime is much more significant in the daytime than that of in the night. It was founded that there were a noon break phenomenon in the daily course of transpiration from 121 Oh to 1320h in the sunny day. Nighttime sap flow had been detected by Dynagage Systems, and the mean nighttime transpiration is about 5.84% of total daily transpiration. Transpiration of Caragana Korshinskii was well correlated with solar radiation, air temperature, vapor pressure deficit (VPD), relative humidity. The regressive equations between the transpiration and environmental factors were better fitted with observed data. Water loss by transpiration in stand level were increased from 6.59% to 43.7% of total evaportranspiration (Et) in the lower density plantation , and it increased from 14.88% to 78.00% in higher density plantation during the period of 1988 to 1999. It is found that the stand transpiration(Ep) exceeded half of total Et than stand evaporation (Eg) and play an important role in total water loss in higher density plantation after 1994(10 ages plantation). Only mean value of 12.56mm rainfall enter soil every year to compensate water consumption in the higher density plantation in the period of 12 years, comparing with mean value of 22.99mm rainfall in the lower density stand. The Et were not significant different although the above-ground biomass were great different in the two stands. In the lower density plantaion, Et always kept a positive correlation with water input (Pi) come from rainfall, however, Et had no clearly relationship with Pi and the Et had exceeded the Pi in drought years which leading to more deficit in soil water in the traditional-method-stand.2. Larix principi-rupprechtiiIn September of 2003 and the period of June to September of 2004, the sap flow of Larix principi-rupprechtii in a 20 year plantation, in Die Die Gou valley of Guyuan, Ningxia, were measured by sap flow sensor (SF-L, Ecomatik Inc.), The results showed that a middle day depression in transpiration of larch {Larix principi-rupprechtii) and diurnal curve of transpiration showed a double peak were founded in a clear day. Usually, the first peak appeared at 1030h to 1200h AM, and the second peak appeared at 1400h to 1530hPM.Compared sap flux density between the south and north side of stem of sample tree, we found sap flux measured in south side changed more acutely than that of north side of stem. There were three peaks with relative lower middle peak compared with two peaks in the north side of stem. Thus, formed a compensation phenomenon in sap flux with time course. The compensation usually happened in clear day, and it could not be found in the cloud day. The difference between sap flux density (Js) of south side and that of north side of stem in breast height was about 15.85% of Js in the north side. Js measured in the south side in the daytime was bigger than that in the north side, but the Js of south side was smaller than that of in north side of stem in the nighttime.Js of single trees had three types of seasonal variation in the larch stand. There were: higher Js in early season and lower Js in late season, Relative stable Js during the growth season, lower Js in early season and higher Js in late season. In spite of the difference Js seasonal changes pattern, the stand level Js was relative stable during the period from June to September.According to the correlation analysis between single tree transpiration and some growth parameters of larch, these parameters of decreasing orders in correlation with transpiration of single tree were: sapwood area (Sa), Section area of breast height (Sc), DBH(D), leaf area(La), project canopy area (Sp), canopy height(Hc) and tree height(H). Regressive models also established between transpiration of single tree and these parameters. Consider DBH was suitable scalars to scale the water consumption from single tree to stand depend on the results of the comparison in different scaling methods.Water loss from transpiration was about 61.575% of total evapotranspiration of the 20 years old larch stand. The water used by understory herbaceous vegetation play an important role on water balance of stand. The saturated stem water storage could provide nearly half water use for a tree transpiration during a clear day. In fact, the stem storing water used by tree for transpiration was only 6.33% of total transpiration during the daytime in a clear day. During the nighttime, stem increased volume by imbibing water from soil was about 28.46% of transpiration estimated by sap flow method.A multiplicative type function model for canopy stomatal conductance (Gs) for larch stand were calibrated based on the meteorological data and transpiration of stand during the June to September of 2004, both the simulated results of Gs and stand transpiration in fifteen minutes step were considerable good agreement with the observed data by the validation of the model based on the data in September of 2003.The range for soil water active layer (SWAR) caused by water consumption was quite different with land covers. In general, SWAR mainly were distributed in the topsoilin the early season. It could expand the range of the layer with the water consumption increasing. SWAR would reach its biggest depth in July during growing season. After then, SWAR would return to topsoil similar to that of happened in the early season. We found biggest SWAR for south slope grassland and east-north slope grassland was distributed from 0~60 cm depth occurred in July. SWAR in larch stands located in foot flat land of hill (larch stand 1) extended to 100cm soil depth in July, and biggest SWAR in north slope larch stand(larch stand 2) could reach to 100cm depth soil in early season. SWAR of Hippophae rhamnoides shrub stand also was biggest in July and reached 80cm to 100cm depth soil. The soil moisture in larch stand 1 were similar to that of Hippophae stand. Both the larch stand 1 and Hippophae stand, had not difference with south slope grassland, but higher than that of east-north slope grassland. The soil moisture in Larch stand 2 was lowest among all five plots. It was founded that the soil moisture above the 100cm depth was closely related with the high-moisture- layer exited in soil profile. It was not found any evidences for dry-layer existing in the profile.Evapotranspiration (ET) usually rapidly increased from May, and ET were quite difference in five plots in June. It would go up to the highest in July with little difference among the five plots. After then ET would drop to August. ET in September was little lower than that in August. It estimated the ET in the winter-spring season was about 23.02-29.98% of annual ET. we found ET in larch stand 1 was higher than that in larch stand 2 in rich rainfall year , and was lower than that in larch stand 2 in a relative drought year. The ET in larch stand and east-north slope grassland were more sensitive than that of in south slope grassland and shrub {Hippophae) stand to rainfall change. Based on ET in five plots from September of 2003 to October of 2004. Degrade order of ET in five plots was that : larch stand l>larch stand 2 >shrub stand >east-north slope grassland >south slope grassland. Although there were difference among these plots, there were no soil water over consumed by the vegetation depend on the field data.