Salinity is one of the main abiotic factors in salt marshes. Studies rooted to analyzed salinity tolerance of halophytes may help to relate their physiological tolerances with distribution limits in the field. Climate change-induced sea level rise and higher temperatures may magnify salt stress. On the other hand, hybridization is a common process and it usually occurs as a result of the introduction of alien species that cohabit with native ones. But little is known about the tolerance of invasive hybrids to the abiotic matrix.
This study reports the responses to salinity of the European native Spartina maritima Curtis (Fernald.), the South American invasive Spartina densiflora Brongn. in Europe and their hybrids S. maritima x densiflora and Spartina densiflora x maritima. We hypothesized that the hybrid taxa would show higher tolerance to salinity than their parental species due to transgressive traits relate to the hybrid vigour.
We studied ecophysiological, anatomical, morphological and biochemistry responses to four salinity treatments from fresh water to hypersalinity (0.5, 10, 20 and 40 ppm) in glasshouse experiments (n = 5). We recorded leaf length, width and area, leaf water content, specific leaf area, stem length and diameter, growth rate, salt excretion, density of salt glandules and stomata, proline and pigments concentration, delayed fluorescence and chlorophyll a fast kinetic fluorescence, net photosynthesis rate and stomatal conductance.
S. densiflora showed a more plastic response than S. maritima to different salinity treatments, with its optimum closed to 10 ppm. Although the hybrid at low marsh Spartina maritima x densiflora and at high marsh Spartina densiflora x maritima had different gene pools inherited from their parents, both were more similar in their responses to salinity to the invasive parent S. densiflora. The traits that correlated with salinity were 9 in S. maritima, 21 in S. densiflora, 9 in S. maritima x densiflora and 16 in S. densiflora x maritima. The hybrids of S. maritima and S. densiflora showed 2 responses similar to both parental species (salt excretion and proline concentration), 8 responses similar to S. densiflora and only 2 were responses different than both parental species.
Phenotypic plasticity of functional traits to salinity indicates the potential of S. densiflora and its hybrids in European and North American marshes to maintain invasive growth in response to rising estuarine salinity with climate change taking advantage also of the rising frequency of torrential rains events that would decrease salinity in estuaries.