PDF《中国科学院研究生院 硕士学位论文》

24 个月的研究.同时,我 们进行一系列的试验处理控制土壤碳的输入, 以探讨土壤地上地下碳的输入与土 壤氮矿化之间的关系.这些处理有:a.利用树皮环割处理(环割)控制光合作用产 物向地下的输入;

b.利用去除地面凋落物处理(去凋)控制地上碳输入;

c.利用切断 树根处理(切根)控制根系分泌物和根凋落物.我们的研究结果如下: 1. 土壤有效氮含量季节变化为 22.96-68.20mgN・kg-1 ,其中铵态氮的含量 (10.89-47.85mgN・kg-1 )大于硝态氮含量(1.48-31.74mgN・kg-1 ),NH4-N 占总有效氮 的42%-94%,是有效氮的主体;

有效氮总量干湿季节变化均极显著,NH4-N 在 湿季末最高,干季末最低,NO3-N 湿季初最高,湿季末最低. 2. 只有干季初的有效氮出现消耗大于积累,而其它培养期均是积累大于消 耗.该地区一年的净有效氮矿化总量为 159.23kgN・hm-2 (土壤层 0-15cm). 3. 净矿化速率、净氨化速率、净硝化速率的干湿季节变化均不显著,原因在 于土壤重量含水量全年维持在一个很高的水平(1.16±0.13kg・kg-1 ),并且土壤内部 环境的干湿季节变化平缓,且这种变化滞后于大气的降雨量变化. 4. 环割处理一年内增加了有效氮含量,而随着时间的推移,这种影响逐渐消 失,但环割处理会显著增加铵态氮的含量.而对于土壤净矿化速率,环割处理只 对净硝化速率有显著的减小效应,而对总净矿化速率以及净氨化速率均没有影 响.据此我们认为,植物的光合作用以及光合作用向根部运输的光合产物是影响 土壤中铵态氮含量的重要因素,也和土壤净硝化速率有密切关系,但与土壤总有 效氮含量以及总净矿化速率没有显著影响. 5. 去凋处理会显著增加有效氮含量,而对净氮矿化速率没有影响.这说明: 土壤地上碳输入与有效氮含量之间有密切联系,而与净氮矿化速率没有直接联 系. 6. 切根处理会显著减少有效氮含量,而对净氮矿化速率没有影响.这说明: 根系分泌的有机物和根凋落物强烈控制着土壤有效氮含量, 而不对净氮矿化速率 云南哀牢山中山湿性常绿阔叶林土壤氮矿化研究 iv 产生影响,同时,减少根系分泌的有机物和根凋落物向土壤的输入,将显著降低 土壤有效氮含量. 7.我们的结论是:土壤地上地下碳输入是影响土壤有效氮库储量的重要因 素,但与土壤氮净矿化速率没有直接联系. 关键词:土壤有效氮 氮矿化 环割 切根 去凋 摘要 v Abstract We made a continuous investigation of soil N availability and N mineralization from Oct.

2003 to Oct.

2005 in a mountane moist evergreen broad-leaved forest in Ailao Mountains by using close-top tube incubation method. And, in order to reveal the relation between soil carbon input and nitrogen mineralization, we executed some treatments to the trees investigated including girdling, litter exclusion and trenching. a).girdling to control products of photosynthesis. b).litter exclusion to control aboveground carbon input. c).trenching to control root exudates and root litter. The results were as follows: 1. The soil available nitrogen concentrations varied from 22.96 to 68.20 mgN・kg-1 and nitrate ranged from 1.48 to 31.74, ammonia whose variation is from 10.89 to 47.85 and it showed a dominant part (42%-94%) in gross available nitrogen of this ecosystem. Gross available nitrogen varied significantly between dry and wet season. Ammonia climbed to the top at the end wet season and declined to the bottom at the end dry season, while it was different for nitrate, highest at the beginning wet season and lowest at the end wet season. 2. Nitrogen mineralization showed a net accumulation in all over the year except the short beginning dry season. Annual amount of net nitrogen mineralization was 159.23kgN・hm-2 (for 0-15cm soil layer). 3. Not only net nitrogen mineralization rate, but also ammonification and nitrification did not show a significant variation between dry and wet season, this should attribute to the smooth change of the inner soil humid and temperature. For example, the soil moisture held a very high level among the year (1.16±0.13kg・kg-1 ). Furthermore, the soil inner change lag behind of the air environment. 4. Girdling increased the ammount of available nitrogen in the first year, but it disappeared in the second year, and it also increased the ammonia amount 云南哀牢山中山湿性常绿阔叶林土壤氮矿化研究 vi significantly all over the experimental period. As for nitrogen net mineralization rate, girdling minished the net nitrification rate significantly, but showed no effect on net ammonification rate and gross net mineralization rate. So we made a conclusion that photosynthesis and products of photosynthesis was critical to ammonia and net nitrification rate, but it had no relation with nitrite and ammonification rate. 5. Litter exclusion significantly increased available nitrogen concentration, but showed no effect on net mineralization rate including nitrification and ammonification. It indicated that soil aboveground carbon input had a close relation with available nitrogen concentration but litter relation with net mineralization rate. 6. Trenching exclusion minished available nitrogen concentration significantly, while it showed no effect both on nitrification rate and ammonification rate. So, we concluded that root exudates and root litter was critical to soil available nitrogen amount, but it had no direct relation to soil nitrogen net mineralization. Meanwhile, the available nitrogen amount decreased significantly if root exudates and root litter were limited. 7. We drawed a conclusion that both aboveground and belowground soil carbon input were critical to soil available nitrogen concentration, but they showed no relation with soil nitrogen net mineralization rate. Key words: soil available nitrogen, nitrogen mineralization, girdling, litter exclusion, trenching.