An experimental test of CSR theory using a globally calibrated ordination method

Can CSR theory, in conjunction with a recently proposed globally calibrated CSR ordination (“StrateFy”), using only three easily measured leaf traits (leaf area, specific leaf area and leaf dry matter content) predict the functional signature of herbaceous vegetation along experimentally manipulated gradients of soil fertility and disturbance? To determine this, we grew 37 herbaceous species in mixture for five years in 24 experimental mesocosms differing in factorial levels of soil resources (stress) and density-independent mortality (disturbance). We measured 16 different functional traits and then ordinated the resulting vegetation within the CSR triangle using StrateFy. We then calculated community-weighted mean (CWM) values of the competitor (CCWM), stress-tolerator (SCWM) and ruderal (RCWM) scores for each mesocosm. We found a significant increase in SCWM from low to high stress mesocosms, and an increase in RCWM from lowly to highly disturbed mesocosms. However, CCWM did not decline significantly as intensity of stress or disturbance increased, as predicted by CSR theory. This last result likely arose because our herbaceous species were relatively poor competitors in global comparisons and thus no strong competitors in our species pool were selectively favoured in low stress and low disturbed mesocosms. Variation in the 13 other traits, not used by StrateFy, largely argeed with the predictions of CSR theory. StrateFy worked surprisingly well in our experimental study except for the C-dimension. Despite loss of some precision, it has great potential applicability in future studies due to its simplicity and generality.

能否将 CSR 理论（CSR theory）与新近提出的全局校准型 CSR 排序方法“StrateFy”相结合，仅依托3种易于测定的叶片功能性状——叶面积（leaf area）、比叶面积（specific leaf area）与叶片干物质含量（leaf dry matter content），即可预测实验操控的土壤肥力与干扰梯度下草本植被的功能特征？
为解答该问题，我们设置了土壤资源（胁迫）与密度无关死亡率（干扰）的双因子水平梯度，在24个中宇宙实验单元（mesocosms）中混合栽培37种草本植物，并持续培养五年。我们测定了16种不同的功能性状，随后利用StrateFy将所得植被群落数据投射至CSR三角坐标系中；进而计算各中宇宙单元的竞争者（competitor, CCWM）、耐胁迫者（stress-tolerator, SCWM）与杂草种（ruderal, RCWM）的群落加权平均（community-weighted mean, CWM）得分。
研究结果显示：随胁迫程度升高，SCWM呈显著上升趋势；随干扰强度提升，RCWM亦显著升高。但与CSR理论的预测相悖，CCWM并未随胁迫或干扰强度的增加而显著下降。这一结果可能源于：相较于全球尺度的物种比对，本研究所用草本物种整体竞争力偏弱，因此在低胁迫、低干扰的中宇宙单元中，并未有优势竞争者被选择性富集。此外，StrateFy未纳入的其余13种功能性状的变化，大体符合CSR理论的预测。
尽管在竞争轴（C-dimension）上存在一定精度损失，但StrateFy凭借其简洁性与普适性，在本实验研究中表现超出预期，在未来相关研究中具备极高的应用潜力。