Tornillo pecan orchard soil CO2 efflux spatial variation

Spatial variability in soil CO2 efflux across landscapes is an important feature of the \"Critical Zone\" within dryland ecosystems. In dryland critical zones, resources are often distributed in patches or resource islands. Although this is particularly true in natural settings, the significance of spatial variability in CO2 efflux and its patterns also extends to dryland agriculture. In both irrigated and unirrigated systems, human management practices can significantly impact both organic and inorganic carbon cycling processes, highlighting the importance of studying CO2 efflux in these systems. We examined the spatial patterns of soil CO2 efflux and quantified the magnitude and scale of spatial autocorrelation using geostatistical techniques in a flood-irrigated pecan orchard and a creosote bush shrubland. Moreover, we explored some of the associated factors that may drive spatial variability in soil CO2 efflux. Our results indicated that while CO2 efflux was autocorrelated at short distances, it was quite variable and difficult to predict at larger scales across the study sites. Furthermore, the level of spatial autocorrelation varied depending on water availability, with weaker patterns at intermediate water levels at the flood-irrigated site. We also found that CO2 efflux had shorter ranges of autocorrelation compared to tree diameter and electrical conductivity. Tree diameter, proximity to the nearest tree and electrical conductivity did show some association with soil CO2 efflux, but the correlations were weak. Overall, this research provides evidence that electrical conductivity, tree diameter and proximity to the nearest tree are weak predictors of spatial variability in soil CO2 efflux and that there are likely other unmeasured factors that control spatial variation in soil CO2 efflux at these sites.景观尺度下土壤CO₂排放的空间变异，是旱地生态系统内“关键带（Critical Zone）”的重要特征。在旱地关键带中，资源通常呈斑块状分布，即形成资源岛。尽管这一现象在自然生境中尤为显著，但CO₂排放空间变异及其格局的重要性同样延伸至旱地农业领域。在灌溉与非灌溉系统中，人类管理活动均可显著影响有机与无机碳循环过程，凸显了研究此类系统中CO₂排放的必要性。本研究以漫灌式碧根果（pecan）果园与石炭酸灌丛（creosote bush）为研究对象，借助地统计技术（geostatistical techniques）解析了土壤CO₂排放的空间格局，并量化了空间自相关（spatial autocorrelation）的强度与尺度。此外，本研究还探讨了可能驱动土壤CO₂排放空间变异的相关影响因子。研究结果显示，尽管CO₂排放于短距离范围内存在空间自相关，但在研究样地的更大尺度上，其变异程度较强且难以预测。进一步而言，空间自相关程度随水分可利用性变化：在漫灌样地中，中等水分条件下的空间自相关格局较弱。本研究同时发现，相较于树木胸径与电导率（electrical conductivity），土壤CO₂排放的空间自相关尺度更短。树木胸径、与邻近树木的距离以及电导率虽与土壤CO₂排放存在一定关联，但相关系数均较弱。综上，本研究证实：电导率、树木胸径以及与邻近树木的距离仅能较弱地预测土壤CO₂排放的空间变异，且此类样地中土壤CO₂排放的空间变异可能受其他未被测定的因子调控。