Haloxylon ammodendron, with its tolerance of drought, high temperature, and salt alkali conditions, is one of the main sand-fixing plant species in the oasis-desert transition zone in China. This study used the TDP30(...Haloxylon ammodendron, with its tolerance of drought, high temperature, and salt alkali conditions, is one of the main sand-fixing plant species in the oasis-desert transition zone in China. This study used the TDP30(where TDP is the thermal dissipation probe) to measure hourly and daily variations in the stem sap flow velocity of H. ammodendron at three age-classes(10, 15, and 20 years old,which were denoted as H10, H15, and H20, respectively) in the Minqin oasis-desert transition zone,China, from May through October 2020. By simultaneously monitoring temperature, relative humidity,photosynthetically active radiation, wind speed, net radiation, rainfall, and soil moisture in this region, we comprehensively investigated the stem sap flow velocity of different-aged H. ammodendron plants(H10,H15, and H20) and revealed its response to physical factors. The results showed that, on sunny days, the hourly variation curves of the stem sap flow velocity of H. ammodendron plants at the three age-classes were mainly unimodal. In addition, the stem sap flow velocity of H. ammodendron plants decreased significantly from September to October, which also delayed its peak time of hourly variation. On rainy days, the stem sap flow velocity of H. ammodendron plants was multimodal and significantly lower than that on sunny days.Average daily water consumption of H. ammodendron plants at H10, H15, and H20 was 1.98, 2.82, and 1.91kg/d, respectively. Temperature was the key factor affecting the stem sap flow velocity of H. ammodendron at all age-classes. Net radiation was the critical factor influencing the stem sap flow velocity of H.ammodendron at H10 and H15;however, for that at H20, it was vapor pressure deficit. The stem sap flow velocity of H. ammodendron was highly significantly correlated with soil moisture at the soil depths of 50and 100 cm, and the correlation was strengthened with increasing stand age. Altogether, our results revealed the dynamic changes of the stem sap flow velocity in different-aged H. ammodendron forest stands and its response mechanism to local physical factors, which provided a theoretical basis for the construction of new protective forests as well as the restoration and protection of existing ones in this region and other similar arid regions in the world.展开更多
Many studies have focused on soil nutrient heterogeneity and islands of fertility in arid ecosystems. However, few have been conducted on an oasis-desert transitional zone where there is a vegetation pattern changing ...Many studies have focused on soil nutrient heterogeneity and islands of fertility in arid ecosystems. However, few have been conducted on an oasis-desert transitional zone where there is a vegetation pattern changing from shrubs to annual herbs. The goal of the present study was to understand vegetation and soil nutrient heterogenity along an oasis-desert transitional zone in northwestern China. Three replicated sampling belts were selected at 200 m intervals along the transitional zone. Twenty-one quadrats （10 x 10m） at 50m intervals were located along each sampling belt. The vegetation cover was estimated through the quadrats, where both the soil under the canopy and the open soil were sampled simultaneously. The dominated shrub was Haloxylon ammodendron in the areas close to the oasis and Nitraria tangutorum dominated the areas close to the desert. In general, along the transitional zone the vegetation cover decreased within 660 m, increased above 660 m and decreased again above 1 020 m （close to the desert）. The soil nutrients （organic matter, total N, NO3^- and NH4^＋） showed significant differences along the zone. The soil nutrients except the soil NH4^＋ under the canopy were higher than those in open soil, confirming ＂islands of fertility＂ or nutrient enrichment. Only a slight downward trend of the level of ＂islands of fertility＂ for soil organic matter appeared in the area within 900 m. Soil organic matter both under canopy and in interspace showed a positive correlation with the total vegetation cover, however, there was no significant correlation between the other soil nutrients and the total vegetation cover. We also analyzed the relationship between the shrubs and annuals and the soil nutrients along the zone. Similarly, there was no significant correlation between them, except soil organic matter with the annuals. The results implied that annual plants played an important role in soil nutrient enrichment in arid ecosystem.展开更多
基金supported by the National Natural Science Foundation of China Subsidization Project (32260425, 31860238)the Natural Science Foundation of Gansu Province, China (32060246, 21JR7RA733)。
文摘Haloxylon ammodendron, with its tolerance of drought, high temperature, and salt alkali conditions, is one of the main sand-fixing plant species in the oasis-desert transition zone in China. This study used the TDP30(where TDP is the thermal dissipation probe) to measure hourly and daily variations in the stem sap flow velocity of H. ammodendron at three age-classes(10, 15, and 20 years old,which were denoted as H10, H15, and H20, respectively) in the Minqin oasis-desert transition zone,China, from May through October 2020. By simultaneously monitoring temperature, relative humidity,photosynthetically active radiation, wind speed, net radiation, rainfall, and soil moisture in this region, we comprehensively investigated the stem sap flow velocity of different-aged H. ammodendron plants(H10,H15, and H20) and revealed its response to physical factors. The results showed that, on sunny days, the hourly variation curves of the stem sap flow velocity of H. ammodendron plants at the three age-classes were mainly unimodal. In addition, the stem sap flow velocity of H. ammodendron plants decreased significantly from September to October, which also delayed its peak time of hourly variation. On rainy days, the stem sap flow velocity of H. ammodendron plants was multimodal and significantly lower than that on sunny days.Average daily water consumption of H. ammodendron plants at H10, H15, and H20 was 1.98, 2.82, and 1.91kg/d, respectively. Temperature was the key factor affecting the stem sap flow velocity of H. ammodendron at all age-classes. Net radiation was the critical factor influencing the stem sap flow velocity of H.ammodendron at H10 and H15;however, for that at H20, it was vapor pressure deficit. The stem sap flow velocity of H. ammodendron was highly significantly correlated with soil moisture at the soil depths of 50and 100 cm, and the correlation was strengthened with increasing stand age. Altogether, our results revealed the dynamic changes of the stem sap flow velocity in different-aged H. ammodendron forest stands and its response mechanism to local physical factors, which provided a theoretical basis for the construction of new protective forests as well as the restoration and protection of existing ones in this region and other similar arid regions in the world.
基金Supported by the National Natural Science Foundation of China(90102015,30170161 and 30670385)Cooperation Project of International in China and Greece(05-46).
文摘Many studies have focused on soil nutrient heterogeneity and islands of fertility in arid ecosystems. However, few have been conducted on an oasis-desert transitional zone where there is a vegetation pattern changing from shrubs to annual herbs. The goal of the present study was to understand vegetation and soil nutrient heterogenity along an oasis-desert transitional zone in northwestern China. Three replicated sampling belts were selected at 200 m intervals along the transitional zone. Twenty-one quadrats （10 x 10m） at 50m intervals were located along each sampling belt. The vegetation cover was estimated through the quadrats, where both the soil under the canopy and the open soil were sampled simultaneously. The dominated shrub was Haloxylon ammodendron in the areas close to the oasis and Nitraria tangutorum dominated the areas close to the desert. In general, along the transitional zone the vegetation cover decreased within 660 m, increased above 660 m and decreased again above 1 020 m （close to the desert）. The soil nutrients （organic matter, total N, NO3^- and NH4^＋） showed significant differences along the zone. The soil nutrients except the soil NH4^＋ under the canopy were higher than those in open soil, confirming ＂islands of fertility＂ or nutrient enrichment. Only a slight downward trend of the level of ＂islands of fertility＂ for soil organic matter appeared in the area within 900 m. Soil organic matter both under canopy and in interspace showed a positive correlation with the total vegetation cover, however, there was no significant correlation between the other soil nutrients and the total vegetation cover. We also analyzed the relationship between the shrubs and annuals and the soil nutrients along the zone. Similarly, there was no significant correlation between them, except soil organic matter with the annuals. The results implied that annual plants played an important role in soil nutrient enrichment in arid ecosystem.
