Soil biogeochemical responses to multiple co-occurring forms of human-induced environmental change

Multiple forms of human-induced environmental change are impacting arid ecosystems. Climate change is increasing temperatures and altering precipitation patterns, and many rapidly-growing urban centers are in arid locations. Nitrogen deposition from air pollution accompanies urban activities in many of these locations. These forms of environmental stressors will certainly impact soil communities and the biogeochemical processes for which they are responsible. However, most studies investigate these multiple environmental change factors independently or sometimes in pairs, but rarely all together as co-occurring forms of change. We examined how the simultaneous manipulation of increasing temperatures, altered precipitation patterns (both pulse size and frequency), nitrogen deposition, and urbanization influenced soil respiration and mineral N pools in the Sonoran Desert. In a laboratory microcosm, we incubated soils collected from an urban vs. exurban site, from plots receiving ~20 yrs of experimental N fertilization vs. control plots. The microcosm soils were incubated at ambient vs. +2 degree C temperatures under a factorial precipitation treatment of decreased frequency and increased pulse size. We measured the response of soil respiration rates and inorganic N pools to these co-occurring forms of environmental change.多种人为驱动的环境变化正持续干扰干旱生态系统。气候变化导致气温升高、降水格局发生改变，而诸多快速扩张的城市中心均坐落于干旱区域。此类区域的城市活动往往伴随来自大气污染的氮沉降。上述各类环境胁迫因子势必会对土壤群落及其所介导的生物地球化学过程产生显著影响。然而，现有绝大多数研究仅单独或成对探究这些多环境变化因子，极少将其作为协同发生的变化形式开展综合研究。本研究以索诺兰沙漠（Sonoran Desert）为研究对象，探究增温、降水格局改变（涵盖降水脉冲强度与频率）、氮沉降以及城市化的协同作用如何影响土壤呼吸与矿质氮库（mineral N pools）。本研究借助实验室微宇宙（laboratory microcosm）开展培养实验：采集城市与远郊样地的土壤，以及接受约20年模拟氮添加处理的样地与对照样地的土壤；将微宇宙中的土壤分别置于环境温度与升温2℃的条件下，并设置降水频率降低、脉冲强度升高的因子试验处理。最终测定了土壤呼吸速率与无机氮库对这些协同发生的环境变化的响应。