Sex Differences in Desiccation Tolerance Varies by Colony in the Mesic Liverwort Plagiochila porelloides

Abstract

Water scarcity, a common stress factor, negatively impacts plant performance. Strategies to cope with it, such as desiccation tolerance, are becoming increasingly important to investigate. However, phenomena, such as intraspecific variation in stress responses have not received much attention. Knowledge of this variability and the environmental drivers can be leveraged to further investigate the mechanisms of desiccation tolerance. Here we tested for variation in desiccation tolerance in Plagiochila porelloides among colonies and sexes within the same riparian zone. Field-collected dehardened plants were subjected to a desiccation event, under controlled conditions and then rehydrated. Plant water status, photosynthetic rates, net carbon gain, and efficiency of photosystem II (PSII) were assayed to evaluate tissue desiccation, basic metabolic processes and plant recovery. To establish a linkage between plant response and environmental factors, field light conditions were measured. We detected intraspecific variation, where a more exposed colony (high percentage of open sky, large temporal range of light quantity, and high red/far-red ratio) showed sex differences in desiccation tolerance and recovery. Overall, PSII recovery occurred by 72 h after rehydration, with a positive carbon gain occurring by day 30. This within species variation suggests plastic or genetic effects, and likely association with light conditions.

Keywords: desiccation tolerance; ecophysiology; environmental association; maximum quantum yield; net carbon assimilation; sex difference.

Figure 1

Plagiochila porelloides morphology visually changes with hydration status–dorsal view. (A) full hydrated condition, with no liquid water added; (B) partly desiccated condition; (C) completely dry condition, exhibiting highly contorted leaves.

Figure 2

Colony 3 received more light than colony 1 and 2. From late May to the middle of July, Plagiochila porelloides colony C3 was estimated to receive more light than the two other P. porelloides colonies (PPFD below 9 mol m⁻² d⁻¹). Otherwise, colony C3 received similar or lower PPFD than the other two colonies. PPFD was estimated every 5 days from May to September using hemispherical canopy photographs and analyzed with WinSCANOPY. Above the canopy is the estimated PPFD above the canopy which was the same for all three colonies. C1, C2, and C3 are colonies 1, 2 and 3.

Figure 3

Desiccation tolerance in Plagiochila porelloides differs by sex and varies across colonies. Percent recovery of photosystem II assayed by chlorophyll fluorescence over 216 h after the drying event. (A) Overall sex difference in recovery for all three colonies combined; (B,C) Colony 1 and 2 respectively, showed no sex differences in recovery, although colony 2 was approaching a tendency of females having higher recovery (p = 0.1113). (D) Colony 3 showed higher recovery in females relative to males. Data are untransformed percent recovery. The bars indicate standard errors.

Figure 4

By 14 h in the desiccation chamber Plagiochila porelloides plants reached a desiccated state. (A) Relative humidity (RH) inside desiccation chamber during the assay showing RH stabilized in 40% after 10 h (600 min); (B) Water plant status showing water content loss during the desiccation assay at 40% RH. The bars indicate standard errors.

Figure 5

Non-desiccated Plagiochila porelloides plants have higher net carbon gain than plants rehydrated for three hours and 72 h but not for one month (M). Net carbon assimilation was evaluated through photosynthetic assays in three treatment groups (G1—seven sets of non-desiccated plants, G2—three sets of desiccated plants, measured three hours after rehydration, and G3—three sets of desiccated plants measured three days (72 h) after rehydration. G2 and G3 were again measured one month after rehydration. The bars indicate standard errors.