School of Forestry and Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, Arizona 86011, USA.
Ecology. 2010 Feb;91(2):474-84. doi: 10.1890/09-0243.1.
The Walker and Syers model of phosphorus (P) transformations during pedogenesis is widely accepted for the development of humid ecosystems, but long-term P dynamics of more arid ecosystems remain poorly understood. We tested the Walker and Syers model in semiarid piñon-juniper woodlands by measuring soil P fractions under tree canopies and in intercanopy spaces along a well-constrained, approximately 3000 ka (1 ka = 1000 years) volcanic substrate age gradient in northern Arizona, USA. The various pools of soil P behaved largely as predicted; total soil P and primary mineral P declined consistently with substrate age, labile inorganic P increased early in soil development and then declined at later stages, and organic phosphorus increased consistently across the chronosequence. Within each site, soils under tree canopies tended to have higher concentrations of labile and intermediately available P fractions compared to intercanopy soils. However, the degree of spatial heterogeneity conferred by tree islands was moderated by the stage of soil development. In contrast, tree islands had no influence on within-site distribution of more recalcitrant soil P pools, which appear to be controlled solely by the stage of pedogenesis. Coincident with declines in total P, primary mineral P, and labile inorganic P, we found that phosphatase enzyme activity increased with substrate age; a result consistent with greater ecosystem-level P demand on older, more highly weathered substrates. Our results suggest that, compared to humid climates, reduced inputs of water, energy, and acidity to semiarid ecosystems slow the rate of change in P fractions during pedogenesis, but the overall pattern remains consistent with the Walker and Syers model. Furthermore, our data imply that pedogenic change may be an important factor controlling the spatial distribution of labile P pools in semiarid ecosystems. Taken together, these data should both broaden and unify terrestrial ecosystem development theory.
沃克和赛耶斯（Walker and Syers）的磷（P）转化模型在成土过程中被广泛应用于湿润生态系统的发展，但对更干旱生态系统的长期磷动态仍知之甚少。我们通过测量美国亚利桑那州北部一个受良好控制的、约 3000 年（1ka=1000 年）火山基岩年龄梯度上树冠下和树冠间土壤 P 分数，在半干旱的派尤特松-杜松林地测试了沃克和赛耶斯模型。土壤 P 的各种库大部分按预期表现；总土壤 P 和原生矿物 P 随着基岩年龄的增加而持续下降，易解无机 P 在土壤发育早期增加，然后在后期下降，有机磷在整个时间序列中持续增加。在每个地点内，树冠下的土壤通常比树冠间的土壤具有更高浓度的易解和中等有效性的 P 分数。然而，树冠岛屿带来的空间异质性程度受到土壤发育阶段的调节。相比之下，树冠岛屿对更难分解的土壤 P 库的场内分布没有影响，这些库似乎仅由成土阶段控制。与总 P、原生矿物 P 和易解无机 P 的下降相一致，我们发现磷酸酶酶活性随着基岩年龄的增加而增加；这一结果与较老、风化程度较高的基岩上对生态系统水平 P 需求增加的结果一致。我们的结果表明，与湿润气候相比，水、能量和酸度输入减少到半干旱生态系统中，减缓了成土过程中 P 分数的变化速度，但总体模式仍与沃克和赛耶斯模型一致。此外，我们的数据表明，成土变化可能是控制半干旱生态系统中易解 P 库空间分布的一个重要因素。总的来说，这些数据应该拓宽和统一陆地生态系统发展理论。
