Transfer characteristics of nutrient elements through hydrological process of a Pinus tabulaeformis stand in the West Mountain of Beijing
Tóm tắt
Forest precipitation chemistry is a major issue in forest hydrology and forest ecology. Chemical contents in precipitation change significantly when different kinds of external chemical materials are added, removed, translocated and transformed to or in the forest ecosystem along with precipitation. The chemistry of precipitation was monitored and analyzed in a 31-year-old Pinus tabulaeformis forest in the West Mountain of Beijing. Movement patterns of nutrient elements in hydrological processes can be discovered by studying this monitored data. Also, the information is useful for diagnosing the function of ecosystems and evaluating the impact of the environment on the ecosystem. Samples of rainfall, throughfall and stemflow were collected on the site. In the lab, Ca2+ and Mg2+ were analyzed by flame atomic absorption and K+ and Na+ by flame emission. NH4
+-N was analyzed by indophenol blue colorimetry and NO3
−-N was analyzed by phenoldisulfonic acid colorimetry. The results showed that: 1) The concentration gradient of nutrient elements clearly changed except for Na+. The nutrients in stemflow were significantly higher than those of throughfall and rainfall as the precipitation passed through the P. tabulaeformis forest. The monthly patterns showed distinct differentiation. There are indications that a large amount of nutrients was leached from the canopy, which is a critical function of intra-ecosystem nutrient cycling to improve the efficiency of nutrient use. 2) The concentrations of NO3
−-N and K+ changed more than those of the other nutrient elements. The concentration of NO3
−-N in throughfall and stemflow was 4.4 times and 9.9 times higher than those in rainfall, respectively. The concentration of K+ in throughfall and stemflow was 4.1 times and 8.1 times higher than those in rainfall, respectively. 3) The leaching of nutrient elements from the stand was an important aspect of nutrient return to the P. tabulaeformis forest, which returned a total amount of nutrient of 54.1 kg/hm2, with the contribution of Ca2+ and K+ much greater than that of other elements. Also, K+ was the most active element in leaching intensity. 4) Nutrient input through precipitation was the main source in the West Mountain of Beijing and the amount of nutrient added was 66.4 kg/hm2, of which Ca2+ and N contributed much more than the other nutrient elements. When precipitation passes through the P. tabulaeformis forest, 121 kg/hm2 of nutrient is added to the forest floor. Ca2+ recorded the greatest nutrient increase, with 61.2 kg/hm2, followed by N (NH4
+-N and NO3
−-N), K+ and Mg2+, with 31.3 and 16.5, and 8.11 kg/hm2, respectively. The least was Na+, 3.34 kg/hm2.
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