LCZO -- Soil Biogeochemistry -- Iron and carbon cycling -- El Verde Instrumented hillslope -- (2016-2016)

Soils from humid forests undergo spatial and temporal variations in moisture and oxygen (O2) in response to rainfall, and induce changes in iron (Fe) and carbon (C) biogeochemistry. We hypothesized that high rainfall periods stimulate Fe and C cycling, with the greatest effects in areas of high soil moisture. To test this, we measured Fe and C cycling across three catenas at valley, slope, and ridge positions every two days for a two-month period in a rainforest in Puerto Rico. Over 12 days without rain, soil moisture, FeII, rapidly reducible Fe oxides (FeIIIRR), and dissolved organic C (DOC) declined, but Eh and O2 increased; conversely, during a 10-day period of intense rain (290 mm), we observed the opposite trends. Mixed-effects models suggest precipitation predicted soil moisture, soil redox potential (Eh), and O2, which in turn influenced Fe reduction/oxidation, C dissolution, and mineralization processes. The approximate turnover time for HCl-extractable FeII was four days for both production and consumption, and may be driven by fluctuations in FeIIIRR, which ranged from 42% to 100% of citrate–ascorbate-extractable FeIII (short-range order (SRO)-FeIII) at a given site. Our results demonstrated that periods of high precipitation (hot moments) influenced Fe and C-cycling within day-to-week timescales, and were more pronounced in humid valleys (hot spots).

湿润森林的土壤在水分和氧气（O2）的空间及时间变化方面对降雨产生响应，进而导致铁（Fe）和碳（C）的生物地球化学性质发生变化。本研究假设高降雨期会刺激Fe和C的循环，其影响在土壤水分含量较高的区域尤为显著。为此，我们在波多黎各的一片雨林中，对山谷、斜坡和山脊三个不同位置的三个坡面，每隔两天测量一次Fe和C的循环，持续两个月。在连续12天无雨期间，土壤水分、FeII、快速还原性铁氧化物（FeIIIRR）和溶解有机碳（DOC）迅速下降，而氧化还原电位（Eh）和O2则相应增加；相反，在连续10天强降雨（290毫米）期间，我们观察到相反的趋势。混合效应模型表明，降水量可以预测土壤水分、土壤氧化还原电位（Eh）和O2，而这些因素又反过来影响Fe的还原/氧化、碳的溶解和矿化过程。HCl可提取的FeII的周转时间约为四天，无论是生产还是消耗，这可能与FeIIIRR的波动有关，其在特定地点的范围内从42%至100%不等，对应于草酸-抗坏血酸可提取的FeIII（短程有序（SRO）-FeIII）。我们的研究结果表明，高降水量（热点时刻）对Fe和C的循环在日到周的时间尺度上产生显著影响，且在湿润的山谷（热点区域）更为明显。