C.J. Luque

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.

Nucleation and facilitation in salt pans in Mediterranean salt marshes

Arthrocnemum macrostachyum is a perennial species acting as a primary colonizer of salt pans in Mediterranean high salt marshes. Salicornia ramosissima, an annual, occurs in salt pans under Arthrocnemum canopies and in open areas. The aim of this study was to analyse, in wild populations and a transplant experiment, how S. ramosissima population dy- namics and growth are affected by A. macrostachyum. The environmental conditions within the patches of Arthrocnemum were less stressful than in the open areas, with lower radiation levels and salinity concentrations. In the inner areas of A. macrostachyum patches, density-dependent mortality proc- esses of S. ramosissima seedlings led to low densities of adult individuals with greater morphological development and re- productive success than in open areas. However, at the edges of Arthrocnemum patches facilitation of seedling survival favoured high densities. Environmental stress hindered devel- opment, decreased reproduction and premature death. These results are in agreement with the general theory of factors controlling vegetation distribution that biotic interactions domi- nate in low stress environments, while abiotic interactions dominate under harsher environmental conditions. A. macro- stachyum plays an essential role in the succession in these salt pans, facilitating seed production and stimulating nucleation processes in S. ramosissima.

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.

Causes and consequences of salt-marsh erosion in an Atlantic estuary in SW Spain

This study reports on the quantification of horizontal erosion by undermining of slopes in the atlantic mesotidal salt marshes of Odiel, SW Spain, and analyses its causes and consequences. Horizontal erosion has produced considerable losses of salt marsh area, including zones of mature salt marsh. Human pressure, such as from water-borne traffic or the exploitation of the slopes for the capture of bait, increases the natural erosion processes. The role of vegetation in protecting the slopes against erosion is studied. Channel banks covered with plants, many of which belong to species with long-living, above-ground creeping stems, were less eroded than those without vegetation cover. The enormous volume of sediments moved (ca. 7000m3 in one year) could contribute to the silting-up of the navigable channels of the estuary, so that continual dredging is necessary to allow access to shipping. These sediments are highly contaminated, and dredging exposes them more directly to the trophic network of the estuary. There is a considerable loss of natural resources. Finally, the integrated management of this coastal ecosystem is discussed.

Comparative Field Summer Stress of Three Tree Species Co-occurring in Mediterranean Coastal Dunes

Chlorophyll a fluorescence, water potential (Ψs), and root system of Juniperus oxycedrus ssp. macrocarpa, Juniperus phoenicea ssp. turbinata, and Pinus pinea were studied in Mediterranean coastal dunes of SW Spain during summer drought and after fall rains in 1999, the driest year in the 90s. A strong and reversible depression in the photochemical efficiency of photosystem 2 of the three species was recorded, which happened concomitantly with the diurnal increase and decrease in radiation. J. phoenicea, with superficial root system, was the most affected species by summer drought. It showed high rates of down-regulation of photosynthesis by photoinhibition and positive correlation between Ψs and Fv/Fp, with Ψs lower than -7 MPa. However, it tolerated this high stress, showing a fast recovery of its physiological state after fall rains. On the other hand, J. oxycedrus and P. pinea, both with deep root systems, kept their Ψs values up to -3 MPa, showing lower stress during summer drought. On the other hand, J. oxycedrus and J. phoenicea were more sensible to changes in edaphic water content than P. pinea. These specific responses to summer drought would be determined by their root distributions and stomatal control of transpiration, conditioning the efficiency in getting and using the available water resources. Ecophysiological responses indicate that these species are well-adapted to long periods of drought in Mediterranean climate areas, developing different strategies: J. phoenicea tolerates high stress with a fast recovery after fall rains, while J. oxycedrus and P. pinea are less affected by summer drought since their deep root systems would allow them to reach deep water resources.

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.