Clay Natalie A, Donoso David A, Kaspari Michael
Department of Biology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK, 73019, USA,
Oecologia. 2015 Feb;177(2):571-9. doi: 10.1007/s00442-014-3183-4. Epub 2014 Dec 18.
Nutrient pulses can profoundly impact ecosystem processes and urine is a frequently deposited source of N and K, and Na. Na is unimportant to plants, but its addition can increase decomposition and change invertebrate community structure in Na-poor tropical forests. Here we used synthetic urine to separate the effects of Na from urine's other nutrients and contrasted their roles in promoting decomposition and detritivore recruitment in both a Na-poor inland Ecuadorian and Na-rich coastal Panamanian tropical forest. After 2 days, invertebrate communities did not vary among +Na, H2O, Urine+Na, and Urine-Na treatments. But after 2 weeks, Ecuador wood, but not cellulose, decomposition was twofold higher on Urine+Na and +Na plots compared to H2O and Urine-Na plots accompanied by >20-fold increases in termite abundance on these plots. Panama, in contrast, showed no effect of Na on decomposition. In both forests, plots fertilized with urine had nearly twofold decrease in detritivores after 2 weeks that was likely a shock effect from ammonification. Moreover, the non-Na nutrients in urine did not enhance decomposition at this time scale. On control plots, Panama had higher decomposition rates for both cellulose and wood than Ecuador, but the addition of Na in Ecuador alleviated these differences. These results support the hypothesis that in Na-poor tropical forests, urine can enhance wood decomposition and generate an important source of heterogeneity in the abundance and activity of brown food webs.
营养脉冲会对生态系统过程产生深远影响，尿液是氮、钾和钠的常见沉积来源。钠对植物不重要，但在钠含量低的热带森林中，添加钠可增加分解作用并改变无脊椎动物群落结构。在此，我们使用合成尿液来分离钠与尿液中其他营养物质的作用，并对比它们在促进厄瓜多尔内陆钠含量低的热带森林和巴拿马沿海钠含量高的热带森林中分解作用及碎屑食性动物招募方面的作用。两天后，添加钠、水、尿液加钠和尿液减钠处理之间的无脊椎动物群落没有差异。但两周后，与水和尿液减钠处理的地块相比，尿液加钠和添加钠处理的地块上，厄瓜多尔木材（而非纤维素）的分解速度提高了两倍，这些地块上白蚁数量增加了20倍以上。相比之下，巴拿马的分解作用未受钠的影响。在这两种森林中，用尿液施肥的地块在两周后碎屑食性动物数量减少了近两倍，这可能是氨化作用产生的冲击效应。此外，在这个时间尺度上，尿液中的非钠营养物质并未增强分解作用。在对照地块上，巴拿马纤维素和木材的分解速率均高于厄瓜多尔，但在厄瓜多尔添加钠缓解了这些差异。这些结果支持了以下假设：在钠含量低的热带森林中，尿液可增强木材分解，并在棕色食物网的丰度和活动中产生重要的异质性来源。
