Data from: Facilitation consequences for reproduction of the benefactor cushion plant Laretia acaulis along an elevational gradient: costs or benefits?

Environmental stress may favour facilitative interactions among plants but whether these interactions are positive for the benefactor and how this depends on stress factors, remains to be determined. We studied the effect of beneficiary cover and biomass on reproduction of the benefactor cushion plant Laretia acaulis (Apiaceae) in the central Chilean Andes during three years. Study sites were situated along an elevational gradient at 2600, 2800, 3000 and 3150 m a.s.l. This range comprises a cold- and a drought-stress gradient, with moisture increasing and temperature decreasing with elevation. We studied the effect of natural gradients in beneficiary cover and of experimental cover removal on cushion flower and fruit production. Beneficiary cover had a negative effect on flower production but not on infructescence and fruit densities or fruit weights. A positive effect of beneficiaries on the fraction of flowers converted into fruits was detected for hermaphrodite cushions. The effect of beneficiary cover on flowering was independent of elevation or cushion gender, although these latter factors explained most of the variation. Removing the aboveground parts of the beneficiaries positively affected flowering at 2800 m a.s.l. but not at the other elevations. Our results suggest negative effects of facilitation on L. acaulis flowering, but these are neutralized in fruit production. Surprisingly, this conclusion holds along the entire elevational or stress gradient. This suggests that this system of facilitation is evolutionarily stable and not very sensitive to environmental change. It remains to be tested, however, whether facilitation affects fitness via growth and long-term survival in these slow-growing alpine cushions.环境胁迫或可推动植物间形成促进性相互作用，但此类相互作用是否对施益植物有利，以及其如何随胁迫因子发生变化，仍有待探明。本研究历时三年，针对智利中部安第斯山脉的施益垫状植物Laretia acaulis（伞形科Apiaceae），探究了受益植物盖度与生物量对其繁殖的影响。研究样地沿海拔梯度布设，海拔分别为2600、2800、3000与3150米，该区间涵盖冷胁迫与干旱胁迫双重梯度：随海拔升高，湿度逐渐升高而温度逐步降低。本研究同时考察了自然状态下受益植物盖度梯度，以及人为移除受益植物地上部分对垫状植物开花与结实的影响。结果显示，受益植物盖度对开花量存在负向影响，但对果序密度、果实密度及单果重无显著作用；对于雌雄同株的垫状植株，受益植物可正向提升花转果率。尽管海拔与垫状植物性别可解释大部分变异，但受益植物盖度对开花的影响并不随这两个因素变化。人为移除受益植物的地上部分，仅在海拔2800米处对垫状植物的开花产生正向影响，其余海拔梯度无此效应。本研究结果表明，促进作用对L. acaulis的开花存在负向效应，但该效应在结实过程中被抵消。令人意外的是，该结论在整个海拔或胁迫梯度上均成立，这表明该促进作用系统在进化上具有稳定性，且对环境变化的敏感性较低。不过，对于这类生长缓慢的高山垫状植物而言，促进作用是否会通过生长与长期存活影响其适合度，仍有待进一步验证。