Effects of competition on induction of crassulacean acid metabolism in a facultative CAM plant

Abstract

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.

The competitive advantage of a constitutive CAM species over a C4 grass species under drought and CO2 enrichment

“…Previous studies showed that high drought resistance accounted for the competitive advantage of a model facultative CAM species ( M. crystallinum ) over its co‐occurring grass species ( B. mollis ) found in California grasslands under global change scenarios (Yu et al. , b). This study investigated whether water stress and concurrent CO 2 enrichment—which are known to affect the interactions between C 3 and C 4 plants (Smith et al.…”

“…Yu et al. (, b) experimentally found that a model facultative CAM species ( Mesembryanthemum crystallinum ) had a competitive advantage over a co‐occurring grass ( Bromus mollis ) in California under global change scenarios of increased drought, soil salinity, and nitrogen deposition. An empirical evaluation of the response of constitutive CAM plants and their competitive relationships with other functional groups (i.e., C 4 plants) to CO 2 enrichment and changing climate, however, is still missing (Poorter and Navas ).…”

Response of a facultative CAM plant and its competitive relationship with a grass to changes in rainfall regime

“…2d). In fact, B. mollis is not drought tolerant (Yu et al 2017b(Yu et al , 2017c) and appeared to be severely damaged by early extreme droughts, thus restricting the ability of B. mollis to recover and benefit from later rainfall events (Walter et al 2011). This Bmemory^of early droughts was not significant for M. crystallinum which as facultative CAM plants have higher plant water contents and are more drought (Lüttge 2004;Borland et al 2009;Yu et al 2017bYu et al , 2017c.…”

“…Studies of CAM plants are engendering scientific interest, particularly in recent years, because of their ability to adapt to drought through photosynthetic plasticity which may allow them to increase their dominance in a future (drier and warmer) climate (Drennan and Nobel 2000;Lüttge 2004;Borland et al 2009;Yu et al 2017bYu et al , 2017c. This study investigates the response of a model facultative CAM species (Mesembryanthemum crystallinum, occasional crop species) and its competitive relationship with a C 3 grass (Bromus mollis) to changes in rainfall regime (i.e., intra-seasonal rainfall variability and rainfall seasonality).…”

The effect of nitrogen availability and water conditions on competition between a facultative CAM plant and an invasive grass

“…These key global change drivers (i.e., altered water and nutrient conditions) have been found to greatly affect ecological processes such as interspecific interactions in ecosystems where C 3 and/or C 4 plants dominate (Niu, Liu, & Wan, ; Van der Waal et al., ). It remains unclear, however, how water and nutrient conditions affect plants with crassulacean acid metabolism (CAM) and their competitive relationship with other functional types (but see Yu & D'Odorico, , ; Yu, D'Odorico, Li, & He, ).…”