Effects of climate warming on Sphagnum photosynthesis in peatlands depend on peat moisture and species‐specific anatomical traits

Abstract

Climate change will influence plant photosynthesis by altering patterns of temperature and precipitation, including their variability and seasonality. Both effects may be important for peatlands as the carbon (C) sink potential of these ecosystems depends on the balance between plant C uptake through photosynthesis and microbial decomposition. Here, we show that the effect of climate warming on Sphagnum community photosynthesis toggles from positive to negative as the peatland goes from rainy to dry periods during summer. More particularly, we show that mechanisms of compensation among the dominant Sphagnum species (Sphagnum fallax and Sphagnum medium) stabilize the average photosynthesis and productivity of the Sphagnum community during summer despite rising temperatures and frequent droughts. While warming had a negligible effect on S. medium photosynthetic capacity (Amax) during rainy periods, Amax of S. fallax increased by 40%. On the opposite, warming exacerbated the negative effects of droughts on S. fallax with an even sharper decrease of its Amax while S. medium Amax remained unchanged. S. medium showed a remarkable resistance to droughts due to anatomical traits favouring its water holding capacity. Our results show that different phenotypic plasticity among dominant Sphagnum species allow the community to cope with rising temperatures and repeated droughts, maintaining similar photosynthesis and productivity over summer in warmed and control conditions. These results are important because they provide information on how soil water content may modulate the effects of climate warming on Sphagnum productivity in boreal peatlands. It further confirms the transitory nature of warming‐induced photosynthesis benefits in boreal systems and highlights the vulnerability of the ecosystem to excess warming and drying.

Modelling the habitat preference of two key <i>Sphagnum</i> species in a poor fen as controlled by capitulum water retention

“…Although this was derived from a simplified system with only the two species, it highlighted the potential of rapid turnover of Sphagnum species: the hummock-lawn difference of water table in simulation was comparable to the expected water-table drawdown in fens under the warming climate (Whittington and Price, 2006;Gong et al, 2013b). Because of the large interspecific differences of traits such as photosynthetic potential, hydraulic properties and litter chemistry (Laiho 2006;Straková et al, 2011;Jassey & Signarbieux, 2019), change…”

“…On the other hand, experimental work has addressed the species-specific responses of net photosynthesis to changes in capitulum water content (Hájek and Beckett, 2008;Schipperges and Rydin, 2009) and light intensity (Rice et al, 2008;Laine et al, 2011;Bengtsson et al, 2016). Net photosynthesis and hydrological processes are linked via capitulum water retention, which controls the response of capitulum water content to water potential changes (Jassey & Signarbieux, 2019). However, these mechanisms have not been integrated with ecosystem processes in modelling.…”

Morphological and biochemical responses ofSphagnummosses to environmental changes

“…Sphagnum species indeed show a high interspecific variability in their inhered anatomical and biochemical traits (Bengtsson et al, 2020b(Bengtsson et al, , 2018(Bengtsson et al, , 2016Chiapusio et al, 2018;Dorrepaal et al, 2005;Gong et al, 2019). While Sphagnum anatomical traits are more and more used to explain how Sphagnum species adapt to environmental conditions (Bengtsson et al, 2020b;Jassey and Signarbieux, 2019) , our knowledge on Sphagnum biochemical traits, how they vary among species and phylogeny, how they relate to anatomical traits and how they respond to local and global changes remain limited.…”

“…anatomical tissues) and the internal regulation of plant cell physiology (Ferrer et al, 2008;Tissier et al, 2014). Furthermore, environmental transitory or constant environmental stress can cause an array of morpho-anatomical and physiological changes in Sphagnum mosses, which may affect Sphagnum growth and may lead to drastic changes in peatland functioning (Bengtsson et al, 2020b;Jassey and Signarbieux, 2019). In addition, environmental stress often leads to accelerated production of toxic metabolic by-products in plants, i.e.…”

“…We characterized the stress-avoiding adaptations to climate variation of each Sphagnum species using a suite of five anatomical traits, quantified following (Jassey and Signarbieux, 2019): volume of the capitulum (top layer), water-holding capacity of the capitulum and stem (0-1 cm) , number of hyaline cells in tissues (i.e. dead cells storing water), and surface of hyaline cells (length x width), width of chlorocystes (bordering hyaline cells).…”