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Ecosystem engineer species influence their community and ecosystem by creating or altering the physical structure of habitats. The function of ecosystem engineers is variable and can depend on both abiotic and biotic factors. Here we make use of a primary successional system to evaluate the direct and interactive effects of climate change (precipitation) and fungal endophyte symbiosis on population traits and ecosystem function of the ecosystem engineering grass species, Ammophila breviligulata. We manipulated endophyte presence in A. breviligulata in combination with rain-out shelters and rainfall additions in a factorial field experiment established in 2010 on Lake Michigan sand dunes. We monitored plant traits, survival, growth, and sexual reproduction of A. breviligulata from 2010-2013, and quantified ecosystem engineering as the sand accumulation rate. Presence of the endophyte in A. breviligulata increased vegetative growth by up to 19%, and reduced sexual reproduction by up to 46% across all precipitation treatments. Precipitation was a less significant factor than endophyte colonization for A. breviligulata growth. Reduced precipitation increased average leaf number per tiller but had no other effects on plant traits. Changes in A. breviligulata traits corresponded to increases in sand accumulation in plots with the endophyte as well as in plots with reduced precipitation. Sand accumulation is a key ecosystem function in these primary successional habitats, and so microbial symbiosis in this ecosystem engineer could lead to direct effects on the value of these dune habitats for humans.

Vegetation at the aquatic-terrestrial interface can alter landscape features through its growth and interactions with sediment and fluids. Even similar species may impart different effects due to variation in their interactions and feedbacks with the environment. Consequently, replacement of one engineering species by another can cause significant change in the physical environment. Here we investigate the species-specific ecological mechanisms influencing the geomorphology of U.S. Pacific Northwest coastal dunes. Over the last century, this system changed from open, shifting sand dunes with sparse vegetation (including native beach grass, Elymus mollis), to densely vegetated continuous foredune ridges resulting from the introduction and subsequent invasions of two nonnative grass species (Ammophila arenaria and Ammophila breviligulata), each of which is associated with different dune shapes and sediment supply rates along the coast. Here we propose a biophysical feedback responsible for differences in dune shape, and we investigate two, non-mutually exclusive ecological mechanisms for these differences: (1) species differ in their ability to capture sand and (2) species differ in their growth habit in response to sand deposition. To investigate sand capture, we used a moveable bed wind tunnel experiment and found that increasing tiller density increased sand capture efficiency and that, under different experimental densities, the native grass had higher sand capture efficiency compared to the Ammophila congeners. However, the greater densities of nonnative grasses under field conditions suggest that they have greater potential to capture more sand overall. We used a mesocosm experiment to look at plant growth responses to sand deposition and found that, in response to increasing sand supply rates, A. arenaria produced higher-density vertical tillers (characteristic of higher sand capture efficiency), while A. breviligulata and E. mollis responded with lower-density lateral tiller growth (characteristic of lower sand capture efficiency). Combined, these experiments provide evidence for a species-specific effect on coastal dune shape. Understanding how dominant ecosystem engineers, especially nonnative ones, differ in their interactions with abiotic factors is necessary to better parameterize coastal vulnerability models and inform management practices related to both coastal protection ecosystem services and ecosystem restoration.

The beach vole (Microtus breweri), found only on Muskeget Island, Massachusetts, consumes different parts of its main food plant, beach grass (Ammophila breviligulata), at different times of the year. Blades are consumed in spring and summer, roots in the late summer and fall, and stems from the late fall through the winter into early spring. This feeding behavior, assessed by food choice experiments, was highly correlated with the fiber, water, and phosphorous content of the plant part. We confirm also the general observation that overall nutritional content (N, P, Mg, Ca) of the blades is high in the spring and early summer when the blades are preferred. This is the period of breeding, and hence maximum nutritional stress.

The coast of North Carolina is discontinuously paralleled by a series of narrow, usually elongate islands. These lowlying sandy "banks" may support a sclerophyllous forest in which live oak (Quercus virginiana L.) predominates and which includes numerous characteristic species -of southern affinity. Descriptions of the general nature of the vegtation are available in several papers: Johnson ('00), Kearney ('00), Coker ('05), Lewis ('18), Wells ('39). Because of the full exposure to almost constant wind from the ocean, a slight disturbance of the vegetative cover may result in extensive "blow outs" of the unconsolidated soil. Once initiated, the shifting of the sand may not be checked naturally for years. Man's activities have contributed materially to the destruction of cover. Grazing has been particularly serious, for it has indirectly transformed several of the banks into almost barren seas of shifting sand. Today, grazing has been largely discontinued and, on government controlled areas particularly, much time and effort have been expended in attempts to stabilize the shifting dunes. Miles of brush barriers have been constructed and thousands of acres have been planted with grasses. The success of these attempts cannot yet be evaluated. One of the most effective native sandbinding grasses is sea oats ( Uniola paniculata L.) which is found in abundance on these coastal dune areas. The importance of this species and its associates as natural stabilizers prompted an investigation of the environmental factors governing their distribution. A portion of Bogue Bank near old Fort Macon at the entrance to Beaufort harbor, North Carolina, was chosen for intensive study. The area has been relatively undisturbed in recent years and illustrates all degrees of stability and vegetational development. The exposed position of the bank subjects it to the full sweep of the ocean wind and the pounding surf. The ocean side of the bank is bordered by a sand beach of varying width which terminates at a low (5-15 ft.) foredune. Behind this is an extensive depression sometimes covered with small dunes in all stages of development and stability, sometimes blown out to a depth very near the water table. This area may be only 150 feet wide but is often 600 feet or more in width, and it terminates inland at a relatively high rear dune which may be 40 feet high. The rear dune forms a

At four constant thermoperiods (65°, 75°, 85° and 95°F) and three alternating diurnal thermoperiods (65° —75°, 65° —95°F), good germination (above 70%) was obtained with seed of Ammophila breviligulata Fern., Panicum amarulum Hitch. and Chase., and Spartina patens (Ait.) Muhl. without cold treatment under certain temperature conditions. None of the constant temperature treatments yielded good germination. All attempts to obtain good germination with Uniola paniculata L. without cold treatment were unsuccessful. Various periods of cold treatment had no effect upon subsequent germination in the 65° —95°F alternating diurnal thermoperiod in A. brevilligulata and S. patens. In P. amarulum cold treatment for 15 days was sufficient to ensure good germination. Cold treatment for 30 days was adequate for good germination in U. paniculata, but 15 days was not always sufficient. When cold treatment for 30 days at 43°F preceded germination in the seven temperature conditions, germination was increased in all species. Maximum tolerance limits for A. breviligulata and U. paniculata to NaCl lie between 1.0% and 1.5%. The upper limit of NaCl concentration for germination of P. amarulum is between 1.5% and 2.0% and for S. patens about 4.0%. Germination response to salinity was primarily an inverse linear relationship for A. breviligulata, P. amarulum, and U. paniculata, but a curvilinear relationship in S. patens. In this species germination was successful at 2.0% NaCl. Germination inhibition in A. breviligulata, P. amarulum, and S. patens was apparently primarily an osmotic effect. Based on germination response, S. patens is the most salt tolerant, followed by P. amarulum which is more than U. paniculata. A. breviligulata is the most salt sensitive.

Tolerance to salt in the substratum was determined in seedlings of four perennial dune grasses: Ammophila breviligulata Fern., Panicum amarulum Hitch. & Chase., Spartina patens (Ait.) Muhl., and Uniola paniculata L. An inverse linear relationship existed between growth and increased salinity in A. breviligulata, S. patens, and U. paniculata. Panicum ama- rulum seedlings demonstrated a curvilinear response to; salinity. Seedlings of A. breviligulata and U. paniculata grew moderately well in salinities up to 1.0% NaCl, those of P. amarulum achieved even better growth in this salinity range, and some seedlings of S. patens survived the entire 28-day experimental period at 4.0% NaCl. Seedlings of S. patens collected from the field were more salt tolerant than those grown from seed collected from the field and germinated in the laboratory. In the other species the performance of field- and laboratory- grown seedlings did not differ. Based on seedling growth response, the order of decreasing salt tolerance for the four species is S. patens, P. amarulum, U. paniculata, and A. breviligu- lata. This pattern correlates well with performance in nature. ance to burial, sand-blasting, salt spray, drought, and flooding. Although mature plants of these grasses grow together in the dune system, seedlings of sev- eral different species occupy fairly distinct areas or microhabitats. Seedlings of all species are exposed to approximately equal intensities of most environ- mental factors with the exception of flooding with sea water, which is related to elevation. Substrate salinity can damage and kill plants when flooding by salt tides is not accompanied by rainfall in hot, dry weather. Thus, substrate salinity can act as a major selective force determining seedling establishment and survival in areas subject to flooding. The present study was designed to determine substrate salt toler- ance among seedlings of four perennial grasses, Am- mophila breviligulata Fern., Panicum amarulum Hitch. & Chase., Spartina patens (Ait.) Muhl., and Unio~a paniculata L., to see whether this response could be correlated with habitat conditions of seed- ling populations in nature.