青藏高原东缘雪被覆盖和凋落物添加对土壤氮素动态的影响

Effects of snowpack and litter input on soil nitrogen dynamics in the eastern Tibetan Plateau

高山和高纬度地区,氮素是植物生命活动的主要限制元素之一。这类区域冬季往往被长时间的季节性雪被覆盖着。研究证实,寒冷而漫长的冬季雪被下土壤氮素在维持年际土壤氮循环中起着重要的作用,然而目前对气候变化极其敏感的青藏高原东缘雪下土壤物质转化过程的研究却很少。为了探索青藏高原东缘季节性雪被覆盖地区,冬季凋落物输入对土壤氮素转化过程的影响,2010年1—5月在青藏高原东缘(松潘卡卡沟地区)采用PVC原位培养管培养土壤,并对培养土壤进行不同的雪厚度(0、30、100 cm)处理和不同水平的凋落物添加(0、5、20 g鲜卑花叶片)处理,从实验开始后,每隔1个月采集各个处理的土壤,测定其无机氮(NH4+-N和NO3--N)含量,并计算净氮矿化率,以探讨冬季季节性雪被覆盖下不同碳供应水平对高山土壤氮转化过程的动态影响。研究发现,雪被覆盖能有效地绝缘大气和土壤,减少冻融交替的幅度和频次,并加速了土壤的净氮矿化。说明对于雪被覆盖的高山土壤而言冷季是氮素循环的关键时期。冬季一定厚度的积雪覆盖可通过调节整个土壤氮素的矿化水平,从而为来年春季高山植物的生长提供一个巨大的潜在氮库。添加大量凋落物显著增加了NO3--N含量,降低了NH4+-N含量,加速了土壤净氮矿化。暗示在具有高有机质含量的青藏高原东部地区,土壤微生物的生长和活性极有可能仍然受到低水平可利用碳的限制。

Nitrogen is one of the most limiting elements for plants in alpine and high latitude areas which are covered by snow in winter for a long period. The mineralization of soil nitrogen under snow cover is a major component in annual nitrogen circle of soil. However, little work has been done domestically. We use in situ PVC culture tubes to study the influence of snow cover and litter input on soil nitrogen mineralization on the eastern Tibetan Plateau （Kaka valley, Songpan, Sichuan） from January to May of 2010. Three snow depth levels （0, 30 and 100 era） and three litter addition levels （0, 5 and 20 g leaf of Sibiraea angustata） are used to test inorganic nitrogen （NH4＋-N and NO3--N） content under different temperature regime and carbon input levels. Snow cover can decrease the extent and frequency of freezing and thawing process and accelerate soil mineralization. The increased available nitrogen can help the growth of alpine plants in spring. Litter addition stimulates the increase of NO3＋-N content and decrease of NH4＋-N content, implying a carbon-limited growth and activity of soil microbes.