Francisco Javier J. Nieva

Gas Exchange and Chlorophyll Fluorescence of C3 and C4 Saltmarsh Species

Spartina maritima (Curtis) Fernald, Spartina densiflora Brong, Arthrocnemum perenne (Miller) Moss, and Arthrocnemum fruticosum (L.) Moq are very frequent halophytes on the coasts of SW Europe. The first two are perennial Gramineae with C4 metabolism; the last two are perennial Chenopodiaceae with C3 metabolism. Controlled garden experiments were carried out with the four species to compare their physiological response, i.e., water potential (Ψ), net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), and chlorophyll fluorescence of photosystem (PS) 2 under saline and non-saline conditions. S. maritima behaves as an osmoconformer species, the other three as osmoregulators. In the four species, PN, E, and gs improved following freshwater irrigation. The variations in PN might be related with biochemical changes (which appear not to affect PS2), but not with significant stomatal fluctuations, which are associated with a lower water use efficiency in the case of Arthrocnemum. The species were segregated into two groups (not depending on their C3 or C4 photosynthetic pathway), in relation with the topographic level of this species in natural conditions: the relative responses of PN in S. maritima and A. perenne were lower than those of S. densiflora and A. fruticosum. The salt-tolerance index supports such segregation. S. densiflora demonstrated the best competitive possibilities against salt-tolerant glycophytes, with its more flexible response in saline or brackish environments, which explains its spreading along the rivers draining into the estuaries of the SW Iberian Peninsula.

Short-term responses to salinity of an invasive cordgrass

Salinity is one of the main chemical factors in salt marshes. Studies focused on the analysis of salinity tolerance of salt marsh plants are very important, since they may help to relate their physiological tolerances with distribution limits in the field. Spartina densiflora is a South America cordgrass, which has started its invasion of the European coastline from the southwestern Iberian Peninsula. In this work, short-term responses in adult tussocks of S. densiflora from southwestern Spain are studied over a wide range of salinity in a greenhouse experiment. Our results point out that S. densiflora has a high tolerance to salinity, showing high growth and net photosynthesis rates from 0.5 to 20 ppt. S. densiflora showed at the lowest salinity (0.5 ppt) high levels of photoinhibition, compensated by higher levels of energy transmission between photosystems. Adaptative mechanisms, as those described previously, would allow it to live in fresh water environments. At the highest salinity (40 ppt), S. densiflora showed a high stress level, reflected in significant decreases in growth, net photosynthesis rate and photochemical efficiency of Photosystem II. These responses support S. densiflora invasion patterns in European estuaries, with low expansion rates along the coastline and faster colonization of brackish marshes and river banks.

Ecophysiology of tidal and non-tidal populations of the invading cordgrass Spartina densiflora: seasonal and diurnal patterns in a Mediterranean climate

Abstract The invasion of salt marshes by alien species poses interesting questions concerning the mechanisms that determine their distribution. Spartina densiflora is one of the species that is invading the Atlantic marshes of SW Iberian Peninsula, where it tolerates a broad range of environmental conditions and it competes with the indigenous vegetation. The high ecological versatility of S. densiflora provides a good tool to study the ecophysiological responses of marsh plants. This article aims to compare the ecophysiological responses of S. densiflora in populations from two contrasting habitats: tidal (middle marsh) and non-tidal (drainage intercepted marsh). The higher values in A (net photosynthesis rate), A / C i (apparent carboxylation efficiency), water use efficiency (intrinsic WUE) and F V / F P (potential photochemical efficiency) recorded at the non-tidal population, except in summertime, agree with previous studies that found better physiological state at lower salinity and higher redox potential. A clear reduction of A at higher irradiance was recorded in spring and summer in the tidal population, coinciding with the lowest ψ (leaf water potential) values. These results help to explain the high primary productivity recorded in S. densiflora populations at brackish marshes in Mediterranean areas. Different responses in gas exchange and chlorophyll fluorescence during summer were recorded for each population. The tidal population showed the maximum values of A in summer. In contrast, the non-tidal population suffered reductions in A , A / C i and F V / F P during summer, when salinity was higher. Thus, salinity limits carbon fixation in S. densiflora non-tidal populations during Mediterranean summer drought. In tidal populations, photosynthesis seems to be more influenced by anoxic conditions. High levels of photoinhibition and low A were recorded on the coldest and less cloudy day, which provoked permanent damages to the photosynthetic apparatus of S. densiflora . This may limit its winter production, as well as its invasion of marshes at higher latitudes in Europe. Finally, discussion about the possible effects of Global Climatic Change on S. densiflora invasion is undertaken.

Wetland Loss by Erosion in Odiel Marshes (SW Spain)

ABSTRACT Wetland loss in many estuaries around the world, has been attributed mainly to undermining and collapse of channel banks. This study aims to quantify bank erosion and vertical erosion/accretion rates on intertidal sediments in the Odiel tidal marshes (SW Spain). Bi-monthly erosion/accretion measurements were taken on eight channels over a four year period, using markers (iron stakes) located on intertidal areas and on eroding banks. The intensity of erosion divides the Odiel marshes into two zones. The northern zone has low erosion rates (horizontal erosion c. −20 cm year−1 and vertical erosion / accretion between 0 and −1 cm year−1), and coincides with low levels of human activities. The southern zone has higher erosion rates (horizontal erosion c. −25 cm year−1 and vertical erosion / accretion between 0 and −5 cm year−1) and exhibits higher levels of anthropogenic pressure. The highest horizontal and vertical erosion rates (c. −80 cm year−1) were recorded on navigation channels. Horizontal and vertical erosion showed a positive linear relationship (r2 = 0.66; P< 0.01), indicating that sediments mobilized by bank erosion are not deposited on adjacent intertidal areas. Erosion led to mature marsh habitat loss of c. 17000 m2 year−1 and a sediment mobilization of c. 16500 m3 year−1.

The effects of heavy metals on germination and seedling characteristics in two halophyte species in Mediterranean marshes

The influence of different concentrations (10-2000 μM) of heavy metals (Cu, Mn, Ni, Zn) was analysed in Atriplex halimus and Salicornia ramosissima germination pattern and seedling size. They are two halophyte species that grow in the Estuary of Huelva (Southwest Iberian Peninsula, Spain), one of the most heavy metal-polluted environments in the world. All of the metals tested affected the final germination percentage in A. halimus and only Ni reduced germination in S. ramosissima. The germination rate was unaffected in both species. The study of seedling development shows that S. ramosissima, an intertidal annual species, has a higher tolerance of metals than A. halimus, a bush that inhabits the upper part of the marshes. Taking into account the metal concentrations in the estuary and the effects of these on the seedling development of the species analysed, we conclude that metals might limit plant colonisation in some parts of the marshes.

Pollen production in halophytic species of the Chenopodiaceae in a Mediterranean marsh

Abstract The pollen production per anther has been analysed in ten species of Chenopodiaceae that grow in the salt marshes of the Marismas del Odiel Natural Park (Huelva, south-west Spain). The mean pollen production per anther is 5819, ranged from 580 in Salicornia ramosissima to 12 467 in Salsola vermiculata, and is related to the size of the anthers. In six of the species, pollen production per anther has been studied in two populations and a strong interaction between species and populations was found. Pollen production of central and lateral flowers has been compared in four species, showing that central flowers produce significantly more pollen than lateral ones. In Arthrocnemum macrostachyum, a comparison between the pollen production of upper and lower stamens was performed and no significant differences were found. The pollen/ovule (P/O) ratio has been estimated for each of the species studied for the monoecious species, using the previously calculated male flower/female flower ratio. The monoecious species have the highest P/O ratios, followed by those with hermaphrodite flowers and allogamous reproduction. The lowest P/O ratios were found in Salicornia ramosissima (681) and Suaeda albescens (6025), possibly due to them being autogamous, which is consistent with the annual cycle and ecology of the species. The biggest value was found in the monoecious species Halimione portulacoides (88 405). In the remainder of the species, the P/O ratio depends on the density of individuals of each species in the communities.