降水变化对科尔沁沙地樟子松人工林土壤氮矿化和淋溶的影响

为研究降水量减少对沙地森林土壤氮循环过程的影响，以科尔沁沙地15年生樟子松人工林为研究对象，野外模拟不同降水量（自然降水、减少30%和50%）对沙地樟子松人工林土壤无机氮（SIN）含量、氮矿化速率和淋溶动态的影响。研究结果发现，沙地樟子松人工林SIN主要以硝态氮形态存在，模拟降水减少降低土壤硝态氮含量（P<0.05）和硝态氮/SIN值（P<0.001），而增加土壤铵态氮含量（P<0.05）。与自然降水相比，降水减少降低土壤净硝化速率和净矿化速率（P=0.002），但不同降雨处理的土壤净氨化速率差异不显著（P=0.86）。科尔沁沙地樟子松人工林土壤以硝态氮淋溶为主，不同降雨处理土壤硝态氮淋溶量差异不显著（P=0.09），但模拟降水减少降低土壤铵态氮淋溶（P=0.04）。此外，沙地樟子松人工林SIN含量、净氮矿化速率和淋溶量具有明显月动态特征，与降雨月动态规律基本一致。降水处理和采样时间对SIN含量和净氮矿化速率具有显著交互作用，但土壤氮淋溶量的交互作用不显著。可见，降水变化能够显著影响科尔沁沙地樟子松人工林土壤氮有效性、氮矿化速率和淋溶等过程，未来干旱加剧可能降低科尔沁沙地樟子松人工林土壤氮的可利用性。

Effects of precipitation change on soil nitrogen mineralization and leaching under Mongolian pine plantation in the Horqin Sandy Lands

To evaluate the effects of decreased precipitation on soil N cycle, we investigated monthly dynamics of soil inorganic nitrogen (SIN), nitrogen mineralization rate and leaching in three precipitation treatments (ambient, precipitation reduce by 30% and 50%) under Mongolian pine plantation in the Horqin Sandy Land. Our results showed that soil nitrate was main form of SIN pool in Mongolian pine (Pinus sylvestris var. Mongolica) plantation, and stimulating precipitation reduce could lead to the declines of soil nitrate concentration (P<0.05) and nitrate/SIN ratio (P<0.001), but increase of soil ammonium concentration (P<0.05). Soil net nitrification rate and net mineralization rate decreased in precipitation reduce treatments compared with ambient precipitation (P=0.002), but there were no differences of soil net ammonification rate among three treatments (P=0.86). Soil inorganic N was mainly leached through soil nitrate in Mongolian pine plantation, and precipitation could significantly reduce soil ammonium leaching (P=0.04), but there was no difference of soil nitrate leaching (P=0.09). In addition, soil inorganic N concentration, net N mineralization rate and leaching had monthly dynamic characteristics, consistent with the monthly dynamic of precipitation in the Horqin Sandly Land. There were significant interactions between precipitation treatment and sampling time on SIN concentration and soil net nitrogen mineralization rate, but not for soil inorganic N leaching. Our study implies that the change of precipitation can alter soil N availability, mineralization rate and leaching, and in future precipitation reduce may decrease soil nitrogen availability under Mongolian pine plantation in the Horqin Sandy Land.