The Nutrient Dynamics of the Suhu Coastal Casuarina Stands

Autor: Tsai-Huei Chen, 陳財輝
Rok vydání: 1999
Druh dokumentu: 學位論文 ; thesis
Popis: 87
Summary The objectives of this study were to investigate the soil properties, microbial biomass, nutrient accumulation, standing biomass, net primary production, and nutrient return by litterfall and precipitation of Casuarina stands in the Suhu coastal area, Yunlin County, southwestern Taiwan. The mechanism of nutrient dynamics of these stands, between the 3 and 9-yr-old stage, and the influence of the growth rate by nutrient cycling in each stand were also investigated. Acidity of the surface soil in the 9-yr-old stand was lower than in the 3-yr-old stands. This is because of the decomposition of the litterfall. However, soil in deeper layers influenced by salty ground water is more alkaline than surface soil. The C/N ratio of the soil in these 3 stands is less than 15, indicating that the decomposition rate of organic matter in the Casuarina stands is rapid. Microbial biomass N was mainly distributed in surface soil and decreased with increasing soil depth. It was abundant in the 9-yr-old stand, which was due to the large amount of organic material. Heterotrophic bacteria and nitrifying bacteria were also abundant in the 9-yr-old stand, indicating that vigorous nitrification was progressing. Branchlet biomass of the 9-yr-old stand was 7.4 ton/ha, and it increased with stand growth. The space distribution of Casuarina stands in 2 age classes was quite different; there were branchlet amounts at all tree height levels in the 3-yr-old stands, but there were branchlets below 6 m in height in the 9-yr-old stand. Biomass values of the 3-yr-old stands were 30.9 and 38.7 ton/ha, whereas that of the 9-yr-old stand was 119.3 ton/ha. The percentages of branchlet biomass to total biomass in the 3 stands were 10.5%, 12.4%, and 6.2%, which decreased with stand growth. There was obvious vigorous growth in the 3-yr-old stands, whereas the 9-yr-old stand was experiencing intense competition; the growth increment was offset by the wither amount, with the result that there was almost no additional increment in standing biomass or nutrient content. Dry and wet seasons were divided according to the monthly rainfall during June 1997 to May 1998 on the Suhu coast. In the dry season (October to May), average monthly rainfall was only 38.7 ㎜, while in the wet season (June to September), it was 489 ㎜. Acidity (pH) of stemflow and throughfall solutions decreased as total rainfall increased, and obviously lower pH values in stemflow solution indicated the leaching of greater amounts of hydrogen ions. Suspended solids and conductivity of these 2 solutions in the dry season were about 10-20 times greater than those in the wet season. Moreover, values of these 2 solutions were 5 to 16 times in the dry season and 4 to 11 times in the wet season each greater than that of rainfall collected outside of stands. Concentrations of ions of sodium, potassium, calcium, magnesium, ammonia, or from nitrate nitrogen, chloride, or sulphate acid were greater in the dry than wet season. These ion concentrations of stemflow solution were greater than those of the throughfall solution in the dry season, but opposite results were observed in the wet season. Most ion amounts were similar between the two ages of stands during the study period. Only sodium and chloride were significantly greater in the 9-yr-old stand than in the 3-yr-old stands, indicating that more salt blown from the sea had adhered to the larger surface area of older trees, while concentrations of other ions produced from both ages of stands were not much different. The amount of nutrient input from throughfall within a year was much greater than that from either stemflow or rainfall outside of stands. The average inputs of different ions through precipitation from the 3 stands were 128.4-231.5 kg/ha/yr for sodium, 27.7-39.9 kg for potassium, 25.2-49.4 kg for calcium, 20.9-40.9 kg for magnesium, 28.2-58.0 kg for ammonium-nitrogen, 33.6-67.2 kg for nitrate-nitrogen, 215.7-407.3 kg for chloride, and 57.8-113.1 kg/ha/yr for sulphate. These high nutrient inputs from precipitation are obviously important to Casuarina stands growing on coastal sandy soils. Annual amounts of litterfall in the 3 Casuarina plantations ranged from 8.4 to 11.5 ton/ha, which could be broken down into 87.5-93.6% branchlet litter, 4.6-6.2% branch litter, and 1.8-6.3% organic litter. High litterfall occurred in the months of April, May, and July, and the falling pattern of litter was the same as the spring falling type of evergreen deciduous forests. Seasonal variation in nitrogen and phosphorus concentrations of litterfall was the lowest during September to November, with bimodal peaks in about June or July and the following February. But the nutrient content curves for potassium, magnesium, and sodium of branch litter showed opposite patterns, with the highest values during November and December, and the lowest about April or May. Nutrient return amounts in the Casuarina stands were 123.5-198.0 for nitrogen, 5.0-8.3 for phosphorus, 19.8-44.2 for potassium, 64.5-85.1 for calcium, 54-10.6 for magnesium, and 17.6-33.0 kg ha-1 yr-1 for sodium. The amounts of nitrogen and sodium return by litterfall in the Suhu Casuarina stands were quite remarkable. The net primary productions of the 3-yr-old Casuarina stands were 20.2 and 37.5 ton/ha, but the 9-yr-old stand yielded only 6.5 ton/ha. Branchlet litter made up the highest proportion in the net primary production of each stand. Biomass increments were higher than the corresponding litterfall in the 3-yr-old stands, whereas the 9-yr-old stand showed the opposite. These data suggest that the 3-yr-old stands were still at a fast-growing stage, while growth in the 9-yr-old stand had slowed considerably, so that increments of the entire stand appeared to almost equal the wither amounts.
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