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Direct and Indirect Facilitation of Plants with Crassulacean Acid Metabolism (CAM)

机译：直接和间接促进草甘蓝酸代谢（CAM）的植物

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Plants with crassulacean acid metabolism (CAM) are increasing their cover in many dryland regions around the world. Their increased dominance has been related to climate warming and atmospheric CO2 fertilization, while the effects of interspecies interactions and the role of CAM plant facilitation by trees and grasses remain poorly understood. Woody plants are known for their ability to directly facilitate CAM plants through amelioration of the abiotic environment. Mechanisms of indirect facilitation of trees on CAM plants in tree-grass-CAM associations, however, have received less attention. It is also unclear whether grasses might facilitate CAM plants in mixed tree-grass-CAM communities. For instance, the inclusion of grasses in tree-CAM associations could enhance hydraulic lift and facilitate CAM plants in their access to shallow soil moisture at the expenses of deep-rooted trees. If this effect outweighs the competitive effects of grasses on CAM plants, grasses could overall facilitate CAM plants through hydraulic lift. Here we develop a process-based ecohydrological model to investigate the direct and indirect facilitation in tree-CAM-grass associations; the model quantifies transpiration of CAM plants when isolated as well as in associations with trees and/or grasses. It is found that woody plants having a high root overlap with CAM plants indirectly facilitate CAM plants by significantly reducing grass transpiration in shaded conditions. For situations of a low-to-moderate root overlap, facilitation may occur both directly and indirectly. Conversely, grasses are unable to indirectly facilitate CAM plants through the mechanism of hydraulic lift because the competitive effects of grasses on CAM plants outweigh the facilitation induced by hydraulic lift.
机译：在世界上许多干旱地区，具有十字花兰酸代谢（CAM）的植物的覆盖率正在增加。它们的优势地位增加与气候变暖和大气中的CO2施肥有关，而种间相互作用的影响以及树木和草类对CAM植物的促进作用仍然知之甚少。木本植物以改善非生物环境直接促进CAM植物的能力而闻名。然而，在树-草-CAM协会中，间接促进CAM植物上的树木的机制受到的关注较少。还不清楚草是否会促进混合草木CAM群落中的CAM植物。例如，将草类纳入树木CAM协会可以提高水力提升并促进CAM植物以根深蒂固的树木为代价获取浅层土壤水分。如果此效果胜过草对CAM植物的竞争作用，则草可以通过液压提升总体上促进CAM植物的生长。在这里，我们建立了一个基于过程的生态水文模型，以研究树-CAM-草协会中的直接和间接促进。该模型量化了孤立时以及与树木和/或草相关的CAM植物的蒸腾作用。发现具有高根与CAM植物重叠的木本植物通过在阴影条件下显着减少草蒸腾作用而间接地促进了CAM植物。对于根部重叠程度低到中等的情况，促进可能会直接或间接发生。相反，草无法通过水力提升机制间接地促进CAM植物生长，因为草对CAM植物的竞争效应超过了水力提升所带来的促进作用。

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