| Popis: |
Soil nitrogen forms and contents are of great importance in ecological studies. The storage methods of soil samples have great effects on the accuracy of determination of nitrogen contents. We aimed to select a reasonable storage method for soil samples with forest soil of Castanopsis faberi fore-st at Wanmulin Nature Reserve in Jian'ou City as an example. The contents of soil ammonium, nitrate, total nitrogen, soluble organic nitrogen, amino acid nitrogen and microbial biomass nitrogen were measured in soil samples under the storage conditions of different temperature (at 25, 4 and -20 ℃) and different times (0, 7 and 30 days). The nitrogen contents during the process of cultivating under the room temperature after being frozen were also measured. The results showed that the contents of all nitrogen forms except for amino acid nitrogen were increased in the soil samples that stored at the room temperature for seven days. There were no significant differences between the contents of all the tested nitrogen forms in the refrigerated or frozen samples and the fresh soil samples. The changes of nitrogen content in soil samples at refrigerated and frozen storage were more stable than those at room temperature storage. The low temperature storage could stimulate soil mineralization. Hence, after stored for 30 days, contents of all the tested nitrogen forms in the refri-gerated and frozen storage soil samples were significantly higher than those in the fresh samples except for the soluble organic nitrogen, whereas there was no significant difference between the refrigerated and frozen storage methods. Therefore, fresh samples should be promptly processed when taken back to the laboratory. If the samples needed to storage, it should not be stored more than half a month. If the samples need a longer storage time, it must be placed in lower temperature (at -40 or -80 ℃). Pre-incubation treatment was required when the low temperature storage soil sample was subjected to an experiment. In the process of pre-incubation, the contents of all the tested nitrogen form in soil samples gradually approached the level of fresh soil sample with the increases of incubation time except for that of nitrate which decreased firstly and then increased rapidly. After incubation for about one week, the nitrogen content of soil sample returned to the level that was close to that of the fresh soil. In combination with studies previously reported, soil samples collected from field and air dried samples needed a pre-incubation for 5-14 days, and the pre-incubation time for the cold storage sample should not be less than one week.土壤氮素形态及含量具有重要的生态学研究意义,而土壤样品的储存对土壤氮素含量的准确测定有很大影响.为了选择合理的土壤样品储存方法,本研究以福建省建瓯市万木林保护区罗浮栲林土壤为研究对象,测定在不同温度(25、4和-20 ℃)、不同储存时间(0、7和30 d)下土壤铵态氮、硝态氮、总氮、可溶性有机氮、氨基酸氮含量和微生物生物量氮,以及冷冻后常温培养过程中的氮素含量.结果表明: 在7 d的储存时间内,除氨基酸氮以外,常温培养样品下其余的氮素含量均有所增加;与新鲜样品相比,冷藏、冷冻样品的所有氮素含量之间均无显著性差异,且氮素含量变化较常温培养下更加稳定.因低温储存样品有刺激氮矿化的效果,在30 d储存时间内,与新鲜样品相比,除可溶性有机氮外,冷藏、冷冻样品的所有氮素含量均显著升高;两种冷储存方法之间无显著差异.因此,新鲜样品带回实验室后应及时处理;如需要冷储藏,时间不要超过半个月.如果需要较长的储存时间,则需将样品放置于更低的温度(-40或-80 ℃).在对储存土壤样品进行培养试验之前,需要进行预培养处理.在预培养过程中,除硝态氮含量呈现先下降再迅速升高的趋势外,其余氮素均随着培养时间逐渐趋近于新鲜土壤样品含量,在培养一周左右恢复到与新鲜土壤样品氮含量最为接近的状态.结合已有研究,对野外取样和风干样品需要5～14 d的预培养,冷储存样品预培养时间不应少于一周. |
