WKBT Soils and Floodplain Nutrients

We examined effects of flooding on supply rates of 14 nutrients in floodplain areas invaded by Phalaris arundinacea (reed canarygrass), areas restored to young successional forests (browsed by white-tailed deer and unbrowsed), and remnant mature forests in the Upper Mississippi River floodplain. Plant Root Simulator ion-exchange probes were deployed for four separate 28-day periods. The first deployment occurred during flooded conditions, while the three subsequent deployments were conducted during progressively drier periods. Time after flooding corresponded with increases in NO3--N, K+ and Zn+2, decreases in H2PO4--P, Fe+3, Mn+2, and B(OH)4-B, a decrease followed by an increase in NH4+-N, Ca+2, Mg+2 and Al+3, and an increase followed by a decrease for SO4-2-S. Plant community type had weak to no effects on nutrient supply rates compared to the stronger effects of flooding duration. Our results suggest that seasonal dynamics in floodplain nutrient availability are similarly driven by flood pulses in different community types. However, reed canarygrass invasion has potential to increase availability of some nutrients, while restoration of forest cover may promote recovery of nutrient availability to that observed in reference mature forests.

我们探究了洪水对上密西西比河河漫滩内三类区域的14种养分供给速率的影响：一是被虉草（Phalaris arundinacea，reed canarygrass）入侵的河漫滩区域；二是被恢复为年轻演替林的区域（该区域包含白尾鹿采食与未采食两种样地）；三是该河漫滩内的残存成熟林。本研究采用植物根系模拟器（Plant Root Simulator）离子交换探针，开展了4个独立的28天周期的布设实验。首个布设周期处于洪水淹没状态，后续三个周期则依次在逐渐干旱的时期进行。淹水后的时间跨度与多种养分的供给速率变化存在对应关系：硝态氮（NO3--N）、钾离子（K+）与锌离子（Zn+2）的供给速率呈上升趋势；磷酸二氢根磷（H2PO4--P）、铁离子（Fe+3）、锰离子（Mn+2）与硼酸根硼（B(OH)4-B）的供给速率呈下降趋势；铵态氮（NH4+-N）、钙离子（Ca+2）、镁离子（Mg+2）与铝离子（Al+3）的供给速率先降后升；而硫酸根硫（SO4-2-S）的供给速率则先升后降。相较于洪水持续时长所产生的显著影响，植物群落类型对养分供给速率的影响微弱，甚至无显著影响。本研究结果表明，不同植物群落类型下的河漫滩养分有效性季节动态，均受洪水脉冲效应的相似驱动。不过，虉草入侵可能提升部分养分的有效性；而森林植被恢复则可推动养分有效性恢复至参照成熟林的水平。