Transgressivity in Key Functional Traits Rather Than Phenotypic Plasticity Promotes Stress Tolerance in A Hybrid Cordgrass

Hybridization might promote offspring fitness via a greater tolerance to environmental stressors due to heterosis and higher levels of phenotypic plasticity. Thus, analyzing the phenotypic expression of hybrids provides an opportunity to elucidate further plant responses to environmental stress. In the case of coastal salt marshes, sea level rise subjects hybrids, and their parents, to longer tidal submergence and higher salinity. We analyzed the phenotypic expression patterns in the hybrid Spartina densiflora x foliosa relative to its parental species, native S. foliosa, and invasive S. densiflora, from the San Francisco Estuary when exposed to contrasting salinities and inundations in a mesocosm experiment. 37% of the recorded traits displayed no variability among parents and hybrids, 3% showed an additive inheritance, 37% showed mid-parent heterosis, 18% showed best-parent heterosis, and 5% presented worst-parent heterosis. Transgressivity, rather than phenotypic plasticity, in key functional traits of the hybrid, such as tiller height, conveyed greater stress tolerance to the hybrid when compared to the tolerance of its parents. As parental trait variability increased, phenotypic transgressivity of the hybrid increased and it was more important in response to inundation than salinity. Increases in salinity and inundation associated with sea level rise will amplify the superiority of the hybrid over its parental species. These results provide evidence of transgressive traits as an underlying source of adaptive variation that can facilitate plant invasions. The adaptive evolutionary process of hybridization is thought to support an increased invasiveness of plant species and their rapid evolution

Low leaf N and P resorption contributes to nutrient limitation in two desert shrubs

Both water and nutrients are limiting in arid environments, and desert plants have adapted to these limitations through numerous developmental and physiological mechanisms. In the Mono Basin, California, USA, co-dominant Sarcobatus vermiculatus and Chrysothamnus nauseosus ssp. consimilis are differentially N and P limited. We hypothesized that low leaf N resorption contributes to N-limitation in Sarcobatus and that low leaf P resorption contributes to P-limitation in Chrysothamnus. As predicted, Sarcobatus resorbed proportionally 1.7-fold less N than Chrysothamnus, but reduced leaf P in senescent leaves to lower levels than Chrysothamnus (8.0–10.8-fold lower based on leaf area or mass, respectively), consistent with N, but not P limitations in Sarcobatus. Again, as predicted, Chrysothamnus resorbed proportionally 2.0-fold less P than Sarcobatus yet reduced leaf N in senescent leaves to lower levels than Sarcobatus (1.8–1.3-fold lower based on leaf area or mass, respectively), consistent with P, but not N limitations in Chrysothamnus. Leaf N and P pools were approximately 50% of aboveground pools in both species during the growing season, suggesting leaf resorption can contribute significantly to whole plant nutrient retention. This was consistent with changes in leaf N vs. P concentration as plants grew from seedlings to adults. Our results support the conclusion that N-limitation in Sarcobatus and P-limitation in Chrysothamnus are in part caused by physiological (or other) constraints that prevent more efficient resorption of N or P, respectively. For these species, differential nutrient resorption may be a key physiological component contributing to their coexistence in this saline, low resource habitat

Invasion by Aegilops triuncialis (Barb Goatgrass) Slows Carbon and Nutrient Cycling in a Serpentine Grassland

Invasive plant species alter plant community composition and ecosystem function. In the United States, California native grasslands have been displaced almost completely by invasive annual grasses, with serpentine grasslands being one of the few remaining refugia for California grasslands. This study examined how the invasive annual grass, Aegilops triuncialis, has altered decomposition processes in a serpentine annual grassland. Our objectives were to (1) assess howA. triuncialis alters primary productivity and litter tissue chemistry, (2) determine whether A. triuncialis litter is more recalcitrant to decomposition than native litter, and (3) evaluate whether differences in the soil microbial community in A. triuncialis-invaded and native-dominated areas result in different decomposition rates of invasive and/or native plant litter. In invaded plant patches, A. triuncialis was approximately 50% of the total plant cover, in contrast to native plant patches in which A. triuncialis was not detected and native plants comprised over 90% of the total plant cover. End-of-season aboveground biomass was 2-fold higher in A. triuncialis dominated plots compared to native plots; however, there was no significant difference in belowground biomass. Both above- and below-ground plant litter from A. triuncialis plots had significantly higher lignin:N and C:N ratios and lower total N, P, and K than litter from native plant plots. Aboveground litter from native plots decomposed more rapidly than litter from A. triuncialis plots, although there was no difference in decomposition of belowground tissues. Soil microbial community composition associated with different soil patch types had no effect on decomposition rates. These data suggest that plant invasion impacts decomposition and nutrient cycling through changes in plant community tissue chemistry and biomass production

Functional trait values, not trait plasticity, drive the invasiveness of Rosa sp. in response to light availability

PREMISE OF THE STUDY : Functional trait plasticity in resource capture traits has been suggested as an underlying mechanism promoting invasive species establishment and spread. Earlier studies on this mechanism treat invasiveness as a discrete characteristic (i.e., invasive vs. noninvasive) and do not consider the potential impacts of evolutionary history. In the present study, we used a continuous measure of invasiveness and a phylogenetic framework to quantify the relationship between functional trait expression, plasticity, and invasiveness in Rosa

Global temporal patterns in plant nutrient resorption plasticity

Aim Leaf nutrient resorption is a key nutrient conservation trait, which also influences nutrient cycling rates and pools. Most global biogeochemical models assume that resorption is non‐varying at a temporal scale. However, this trait can differ substantially within populations among years. We assessed the commonality of attaining proficient resorption, the factors associated with proficient resorption, as well as the variability of this trait and the factors controlling trait variability

Impacts of drought on plant water relations and nitrogen nutrition in dryland perennial grasses

Background and aims Extensive worldwide dryland degradation calls for identification of functional traits critical to dryland plant performance and restoration outcomes. Most trait examination has focused on drought tolerance, although most dryland systems are water and nutrient co-limited. We studied how drought impacts both plant water relations and nitrogen (N) nutrition. Methods We grew a suite of grasses common to the Intermountain West under both well-watered and drought conditions in the greenhouse. These grasses represented three congener pairs (Agropyron, Elymus, Festuca) differing in their habitat of origin (“wetter” or “drier”). We measured growth, water relations, N resorption efficiency and proficiency and photosynthetic N use efficiency in response to drought. Results Drought decreased growth and physiological function in the suite of grasses studied, including a negative impact on plant N resorption efficiency and proficiency. This effect on resorption increased over the course of the growing season. Evolutionary history constrained species responses to treatment, with genera varying in the magnitude of their response to drought conditions. Surprisingly, habitat of origin influenced few trait responses. Conclusions Drought impacted plant N conservation, although these responses also were constrained by evolutionary history. Future plant development programs should consider drought tolerance not only from the perspective of water relations but also plant mineral nutrition, taking into account the role of phylogeny

TRAIT CONVERGENCE AND PLASTICITY AMONG NATIVE AND INVASIVE SPECIES IN RESOURCE-POOR ENVIRONMENTS

Premise of study: Functional trait comparisons provide a framework with which to assess invasion and invasion resistance. However, recent studies have found evidence for both trait convergence and divergence among coexisting dominant native and invasive species. Few studies have assessed how multiple stresses constrain trait values and plasticity, and no study has included direct measurements of nutrient conservation traits, which are critical to plants growing in low-resource environments. Methods: We evaluated how nutrient and water stresses affect growth and allocation, water potential and gas exchange, and nitrogen (N) allocation and use traits among a suite of six codominant species from the Intermountain West to determine trait values and plasticity. In the greenhouse, we grew our species under a full factorial combination of high and low N and water availability. We measured relative growth rate (RGR) and its components, total biomass, biomass allocation, midday water potential, photosynthetic rate, water-use effi ciency (WUE), green leaf N, senesced leaf N, total N pools, N productivity, and photosynthetic N use effi ciency. Key results: Overall, soil water availability constrained plant responses to N availability and was the major driver of plant trait variation in our analysis. Drought decreased plant biomass and RGR, limited N conservation, and led to increased WUE. For most traits, native and nonnative species were similarly plastic. Conclusions: Our data suggest native and invasive biomass dominants may converge on functionally similar traits and demonstrate comparable ability to respond to changes in resource availability

Variation in nutrient resorption by desert shrubs

Plant nutrient resorption prior to leaf senescence is an important nutrient conservation mechanism for aridland plant species. However, little is known regarding the phylogenetic and environmental factors influencing this trait. Our objective was to compare nitrogen (N) and phosphorous (P) resorption in a suite of species in the Asteraceae and Chenopodiaceae and assess the impact of soil salinity on nitrogen resorption. Although asters and chenopods did not differ in N resorption proficiency, chenopods were more proficient than asters at resorbing P. Plant responses to salinity gradients were species-specific and likely related to different salt-tolerances of the species. During the three year study, precipitation varied 6.4- and 9.9-fold from the long term averages at our two desert sites; despite these differences, annual variation in nutrient resorption was not linked to annual precipitation. More detailed studies are required to understand the influence of salinity and precipitation on resorption. Understanding controls on this trait may give insight into how species will respond to anthropogenic soil salinization and desertification

Geologic composition influences distribution of microbiotic crusts in the Mojave and Colorado Deserts at the regional scale

Abiotic and biotic factors influencing distribution of microbiotic crusts within hot deserts, such as the Mojave and Colorado Deserts, are poorly known. Our objective was to examine microbiotic crust distribution with reference to soil and parent material characteristics as well as plant functional groups in wilderness areas of Joshua Tree National Park (JTNP). A total of 75 sites were visually assessed for crust abundance and plant community composition; soil physical and chemical factors also were measured. Microbiotic crusts of JTNP, in particular lichen and moss crusts, were not as well-developed or as widely distributed as in other arid regions of North America. Algal crusts were most prevalent, lichen crusts were sparse, and crusts containing mosses were rare, with average percent land surface absolute (and relative) cover for these three cover categories being 11.4% (17.4%), 1.7% (2.7%), and 0.02% (0.02%), respectively. Previously reported individual drivers of crust development, such as pH, electrical conductivity (EC), and soil texture, did not appear to strongly influence crust development in this study of the Mojave and Colorado Deserts. Proximity to granitic bedrock and grusy granitic soils associated with it were the key determinants of microbiotic crust distribution in the wilderness areas of JTNP. In particular, crusts were best developed in grusy granitic soils. Overall, our study emphasized the importance of geology in driving crust distribution and its potential value as a predictor of where crusts may occur in the hot deserts of North America

Functional Traits Explain Variation in Chaparral Shrub Sensitivity to Altered Water and Nutrient Availability

Worldwide drylands are threatened by changes in resource availability associated with global environmental change. Functional traits may help predict which species will be most responsive to these alterations in nutrient and water availability. Current functional trait work focuses on tissue construction and nutrient concentrations, but plant performance in low resource environments also may be strongly influenced by traits related to nutrient budgets and allocation. Our overall objective was to compare trait responses in a suite of serpentine and nonserpentine congener pairs from the California chaparral, a biodiverse region facing nutrient deposition and future changes in precipitation. In a common garden greenhouse environment, we grew small plants of Arctostaphylos manzanita, A. viscida, Ceanothus cuneatus, C. jepsonii, Quercus berberidifolia, and Q. durata in contrasting soil nutrient and moisture treatments. We measured a suite of traits representing physiological, growth, and mineral nutrient responses to these treatments. Overall, plant growth rate and leaf-level phosphorus use efficiency were greatest in the low water, high nutrient treatment, and lowest in the high water, low nutrient treatment. Variation in growth rate and plasticity among species and treatments was primarily associated with differences in mineral nutrition-based traits as opposed to differences in biomass allocation or specific leaf area. Namely, faster growing species and species with greater plasticity allocated more nitrogen and phosphorous to leaves and demonstrated greater photosynthetic phosphorus use efficiency. Overall, nonserpentine species had greater plasticity and biomass response to resource addition than serpentine species, and congener pairs responded to these resource additions more similarly to each other than species across congener pairs. This study extends our general understanding of how functional traits may influence species responses to environmental change and highlights the need to integrate mineral nutrition-based traits, including allocation of nutrient pools and nutrient use efficiency into this larger trait framework. Ultimately, this insight can help identify, in part, why coexisting species may vary in sensitivity to anthropogenic driven changes in soil resource availability