Yu Kailiang, D'Odorico Paolo, Li Wei, He Yongli
Department of Environmental Sciences, University of Virginia, Charlottesville, VA, 22904, USA.
State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A and F University, Yangling, 712100, China.
Oecologia. 2017 Jun;184(2):351-361. doi: 10.1007/s00442-017-3868-6. Epub 2017 Apr 11.
Abiotic drivers of environmental stress have been found to induce CAM expression (nocturnal carboxylation) in facultative CAM species such as Mesembryanthemum crystallinum. The role played by biotic factors such as competition with non-CAM species in affecting CAM expression, however, remains largely understudied. This research investigated the effects of salt and water conditions on the competition between M. crystallinum and the C grass Bromus mollis with which it is found to coexist in California's coastal grasslands. We also investigated the extent to which CAM expression in M. crystallinum was affected by the intensity of the competition with B. mollis. We found that M. crystallinum had a competitive advantage over B. mollis in drought and saline conditions, while B. mollis exerted strong competitive effects on M. crystallinum in access to light and soil nutrients in high water conditions. This strong competitive effect even outweighed the favorable effects of salt or water additions in increasing the biomass and productivity of M. crystallinum in mixture. Regardless of salt conditions, M. crystallinum did not switch to CAM photosynthesis in response to this strong competitive effect from B. mollis. Disturbance (i.e., grass cutting) reduced the competitive pressure by B. mollis and allowed for CAM expression in M. crystallinum when it was grown mixed with B. mollis. We suggest that moderate competition with other functional groups can enhance CAM expression in M. crystallinum, thereby affecting its plasticity and ability to cope with biological stress.
已发现环境胁迫的非生物驱动因素会诱导兼性景天酸代谢（CAM）植物如冰花（Mesembryanthemum crystallinum）中CAM途径的表达（夜间羧化作用）。然而，诸如与非CAM植物竞争等生物因素在影响CAM途径表达方面所起的作用，在很大程度上仍未得到充分研究。本研究调查了盐分和水分条件对冰花与软雀麦（Bromus mollis）（一种C3禾本科植物）之间竞争的影响，这两种植物共存于加利福尼亚州的沿海草原。我们还研究了冰花中CAM途径的表达受与软雀麦竞争强度影响的程度。我们发现，在干旱和盐碱条件下，冰花比软雀麦具有竞争优势，而在水分充足的条件下，软雀麦在获取光照和土壤养分方面对冰花具有强烈的竞争作用。这种强烈的竞争作用甚至超过了添加盐分或水分对混种时冰花生物量和生产力增加的有利影响。无论盐分条件如何，冰花都不会因软雀麦的这种强烈竞争作用而转变为CAM光合作用。干扰（即割草）降低了软雀麦的竞争压力，并使与软雀麦混种的冰花能够表达CAM途径。我们认为，与其他功能组的适度竞争可以增强冰花中CAM途径的表达，从而影响其可塑性和应对生物胁迫的能力。
