Hutchins Benjamin T, Engel Annette Summers, Nowlin Weston H, Schwartz Benjamin F
Ecology. 2016 Jun;97(6):1530-42. doi: 10.1890/15-1129.1.
The prevailing paradigm in subterranean ecology is that below-ground food webs are simple, limited to one or two trophic levels, and composed of generalist species because of spatio-temporally patchy food resources and pervasive energy limitation. This paradigm is based on relatively few studies of easily accessible, air-filled caves. However, in some subterranean ecosystems, chemolithoautotrophy can subsidize or replace surface-based allochthonous inputs of photosynthetically derived organic matter (OM) as a basal food resource and promote niche specialization and evolution of higher trophic levels. Consequently, the current subterranean trophic paradigm fails to account for variation in resources, trophic specialization, and food chain length in some subterranean ecosystems. We reevaluated the subterranean food web paradigm by examining spatial variation in the isotopic composition of basal food resources and consumers, food web structure, stygobiont species diversity, and chromophoric organic matter (CDOM), across a geochemical gradient in a large and complex groundwater system, the Edwards Aquifer in Central Texas (USA). Mean δ13C values of stygobiont communities become increasingly more negative along the gradient of photosynthetic OM sources near the aquifer recharge zone to chemolithoautotrophic OM sources closer to the freshwater-saline water interface (FWSWI) between oxygenated freshwater and anoxic, sulfide-rich saline water. Stygobiont community species richness declined with increasing distance from the FWSWI. Bayesian mixing models were used to estimate the relative importance of photosynthetic OM and chemolithoautorophic OM for stygobiont communities at three biogeochemically distinct sites. The contribution of chemolithoautotrophic OM to consumers at these sites ranged between 25% and 69% of total OM utilized and comprised as much as 88% of the diet for one species. In addition, the food web adjacent to the FWSWI had greater trophic diversity when compared to the other two sites. Our results suggest that diverse OM sources and in situ, chemolithoautotrophic OM production can support complex groundwater food webs and increase species richness. Chemolithoautotrophy has been fundamental for the long-term maintenance of species diversity, trophic complexity, and community stability in this subterranean ecosystem, especially during periods of decreased photosynthetic production and groundwater recharge that have occurred over geologic time scales.
地下生态学中流行的范式认为，地下食物网很简单，仅限于一两个营养级，并且由于食物资源在时空上的零散分布和普遍存在的能量限制，其由广食性物种组成。这一范式基于对易于进入的充气洞穴的相对较少的研究。然而，在一些地下生态系统中，化能无机自养可以作为基础食物资源补贴或替代基于地表的光合衍生有机物质（OM）的异地输入，并促进生态位特化和更高营养级的进化。因此，当前的地下营养范式未能解释一些地下生态系统中资源、营养特化和食物链长度的变化。我们通过研究美国德克萨斯州中部一个大型复杂地下水系统——爱德华兹含水层中，基础食物资源和消费者的同位素组成、食物网结构、穴居生物物种多样性以及发色有机物质（CDOM）的空间变化，重新评估了地下食物网范式。穴居生物群落的平均δ13C值沿着从含水层补给区附近的光合OM源到靠近含氧淡水与缺氧、富含硫化物的盐水之间的淡水 - 盐水界面（FWSWI）的化能无机自养OM源的梯度，变得越来越负。穴居生物群落物种丰富度随着离FWSWI距离的增加而下降。贝叶斯混合模型用于估计光合OM和化能无机自养OM对三个生物地球化学特征不同的地点的穴居生物群落的相对重要性。在这些地点，化能无机自养OM对消费者的贡献占总利用OM的25%至69%，并且占一个物种饮食的比例高达88%。此外，与其他两个地点相比，FWSWI附近的食物网具有更高的营养多样性。我们的研究结果表明，多样的OM源和原位化能无机自养OM生产可以支持复杂的地下水食物网并增加物种丰富度。化能无机自养对于这个地下生态系统中物种多样性、营养复杂性和群落稳定性的长期维持至关重要，特别是在地质时间尺度上发生的光合生产和地下水补给减少的时期。
