O'Neill School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana, 47405, USA.
Ecology. 2020 Dec;101(12):e03148. doi: 10.1002/ecy.3148. Epub 2020 Aug 25.
We experimentally increased salinities in a tidal freshwater marsh on the Altamaha River (Georgia, USA) by exposing the organic rich soils to 3.5 yr of continuous (press) and episodic (pulse) treatments with dilute seawater to simulate the effects of climate change such as sea level rise (press) and drought (pulse). We quantified changes in root production and decomposition, soil elevation, and soil C stocks in replicated (n = 6) 2.5 × 2.5 m field plots. Elevated salinity had no effect on root decomposition, but it caused a significant reduction in root production and belowground biomass that is needed to build and maintain soil elevation capital. The lack of carbon inputs from root production resulted in reduced belowground biomass of 1631 ± 308 vs. 2964 ± 204 g/m in control plots and an overall 2.8 ± 0.9 cm decline in soil surface elevation in the press plots in the first 3.5 yr, whereas the control (no brackish water additions) and the fresh (river water only) treatments gained 1.2 ± 0.4 and 1.7 ± 0.3 cm, respectively, in a 3.5-yr period. There was no change in elevation of pulse plots after 3.5 yr. Based on measurements of bulk density and soil C, the decline of 2.8 cm of surface elevation resulted in a loss of 0.77 ± 0.5 kg C/m in press plots. In contrast, the control and the fresh treatment plots gained 0.25 ± 0.04 and 0.36 ± 0.03 kg C/m, respectively, which represents a net change in C storage of more than 1 kg C/m. We conclude that, when continuously exposed to saltwater intrusion, the tidal freshwater marsh's net primary productivity, especially root production, and not decomposition, are the main drivers of soil organic matter (SOM) accumulation. Reduced productivity leads to loss of soil elevation and soil C, which has important implications for tidal freshwater marsh persistence in the face of rising sea level.
我们通过将富含有机质的土壤暴露于持续（压力）和间歇性（脉冲）的淡水咸水 3.5 年来模拟气候变化的影响，如海平面上升（压力）和干旱（脉冲），在奥塔马哈河（美国佐治亚州）的潮汐淡水沼泽中实验性地增加了盐度。我们在复制（n=6）2.5×2.5m 的野外试验田中量化了根产量和分解、土壤高程和土壤 C 储量的变化。升高的盐度对根分解没有影响，但导致根产量和地下生物量显著减少，而地下生物量是建立和维持土壤高程资本所必需的。根产量减少导致地下生物量减少，试验田中为 1631±308g/m，对照田中为 2964±204g/m，在头 3.5 年中，压块中的土壤表面高程总体下降了 2.8±0.9cm，而对照（未添加咸水）和新鲜（仅河水）处理分别在 3.5 年内增加了 1.2±0.4 和 1.7±0.3cm。在 3.5 年后，脉冲试验田中土壤高程没有变化。基于体密度和土壤 C 的测量，2.8cm 的表面高程下降导致压块中损失了 0.77±0.5kg C/m。相比之下，对照和新鲜处理的试验田分别增加了 0.25±0.04 和 0.36±0.03kg C/m，这代表了超过 1kg C/m 的 C 储存的净变化。我们得出结论，当潮汐淡水沼泽持续暴露于海水入侵时，净初级生产力，特别是根产量，而不是分解，是土壤有机物质（SOM）积累的主要驱动因素。生产力的降低导致土壤高程和土壤 C 的损失，这对潮汐淡水沼泽在海平面上升的情况下的持续存在具有重要意义。
