Plant sex influences on riparian communities and ecosystems

Over the past several decades, we have increased our understanding of the influences of plant genetics on associated communities and ecosystem functions. These influences have been shown at both broad spatial scales and across many plant families, creating an active subdiscipline of ecology research focused on genes-to-ecosystems connections. One complex aspect of plant genetics is the distinction between males and females in dioecious plants. The genetic determinants of plant sex are poorly understood for most plants, but the influences of plant sex on morphological, physiological, and chemical plant traits are well-studied. We argue that these plant traits, controlled by plant sex, may have wide-reaching influences on both terrestrial and aquatic communities and ecosystem processes, particularly for riparian plants. Here we systematically review the influences of plant sex on plant traits, influences of plant traits on terrestrial community members, and how interactions between plant traits and terrestrial community members can influence terrestrial ecosystem functions in riparian forests. We then extend these influences into adjacent aquatic ecosystem functions and aquatic communities to explore how plant sex might influence linked terrestrial-aquatic systems as well as the physical structure of riparian systems. This review highlights data gaps in empirical studies exploring the direct influences of plant sex on communities and ecosystems but draws inference from community and ecosystem genetics. Overall, this review highlights how variation by plant sex has implications for climate change adaptations in riparian habitats, the evolution and range shifts of riparian species and the methods used for conserving and restoring riparian systems.

Distribution of the Riparian Salix Communities in and around Romanian Carpathians

Salix riparian communities are particularly diverse and of extraordinary ecological importance. This study will analyze the diversity of Salix riparian communities (S. alba, S. fragilis, S. purpurea and S. triandra), their distribution, ecological importance, and conservation. There were 444 records for S. alba, 417 for S. fragilis, 457 for S. purpurea, and 375 for S. triandra, both from the literature and herbaria. Thus, it can be seen that the distribution of the four Salix species studied is very widespread throughout the territory where this study was carried out. According to EIVE (Ecological Indicator Values of Europe) but also to the national list values for niche positions and niche widths, they were noted to be very close for all ecological indicators: M (soil moisture), L (light), and T (temperature), but not for the ecological indicator of soil nitrogen (N) availability or R (soil reaction). Obviously, those riparian Salix communities are important for the functions they indicate, primarily for climate change mitigation, but also for regulating water flow, improving water quality, and providing habitats for wildlife. Conservation and management of these important ecosystems are necessary to maintain their biodiversity, and ecological services and strategies that can be used to protect and manage these communities are outlined.

The influence of weevil herbivory on leaf litter chemistry in dioecious willows

Leaf litter inputs can influence the structure and function of both terrestrial and adjacent aquatic ecosystems. Dioecy and herbivory are two factors that together have received little attention, yet have the potential to affect the quantity, quality, and timing of riparian litterfall, litter chemistry, and litter decomposition processes. Here, we explore litter chemistry differences for the dioecious Sitka willow (Salix sitchensis Sanson ex. Bong), which is establishing on primary successional habitats at Mount St. Helens (WA, USA) and is heavily infested with a stem-boring weevil (Cryptorhynchus lapathi). Weevil-attacked branches produced summer senesced litter that had significantly higher %N, lower C:N ratios, and lower condensed tannins than litter from branches that were unattacked by the weevil and senesced naturally in the autumn. Weevils more often attack female willows; however, these common litter chemicals did not significantly differ between males and females within the weevil-attacked and -unattacked groups. High-resolution mass spectrometry was used to isolate compounds in litter from 10 Sitka willow individuals with approximately 1500-1600 individual compounds isolated from each sample. There were differences between weevil-attacked litter and green leaf samples, but at this level, there was no clustering of male and female samples. However, further exploration of the isolated compounds determined a suite of compounds present only in either males or females. These findings suggest some variation in more complex litter chemistry between the sexes, and that significant differences in weevil-attacked litter chemistry, coupled with the shift in seasonality of litter inputs to streams, could significantly affect in-stream ecological processes, such as decomposition and detritivore activity.

Chromosome-scale assemblies of the male and female Populus euphratica genomes reveal the molecular basis of sex determination and sexual dimorphism

Reference-quality genomes of both sexes are essential for studying sex determination and sex-chromosome evolution, as their gene contents and expression profiles differ. Here, we present independent chromosome-level genome assemblies for the female (XX) and male (XY) genomes of desert poplar (Populus euphratica), resolving a 22.7-Mb X and 24.8-Mb Y chromosome. We also identified a relatively complete 761-kb sex-linked region (SLR) in the peritelomeric region on chromosome 14 (Y). Within the SLR, recombination around the partial repeats for the feminizing factor ARR17 (ARABIDOPSIS RESPONSE REGULATOR 17) was potentially suppressed by flanking palindromic arms and the dense accumulation of retrotransposons. The inverted small segments S1 and S2 of ARR17 exhibited relaxed selective pressure and triggered sex determination by generating 24-nt small interfering RNAs that induce male-specific hyper-methylation at the promoter of the autosomal targeted ARR17. We also detected two male-specific fusion genes encoding proteins with NB-ARC domains at the breakpoint region of an inversion in the SLR that may be responsible for the observed sexual dimorphism in immune responses. Our results show that the SLR appears to follow proposed evolutionary dynamics for sex chromosomes and advance our understanding of sex determination and the evolution of sex chromosomes in Populus.

Reference-quality genomes of both sexes of the dioecious tree species, Populus euphratica, provide further insight into the evolution of Populus sex chromosomes and highlight male-specific fusion genes that may contribute to sexual dimorphism.

Climatic Change Can Influence Species Diversity Patterns and Potential Habitats of Salicaceae Plants in China

Salicaceae is a family of temperate woody plants in the Northern Hemisphere that are highly valued, both ecologically and economically. China contains the highest species diversity of these plants. Despite their widespread human use, how the species diversity patterns of Salicaceae plants formed remains mostly unknown, and these may be significantly affected by global climate warming. Using past, present, and future environmental data and 2673 georeferenced specimen records, we first simulated the dynamic changes in suitable habitats and population structures of Salicaceae. Based on this, we next identified those areas at high risk of habitat loss and population declines under different climate change scenarios/years. We also mapped the patterns of species diversity by constructing niche models for 215 Salicaceae species, and assessed the driving factors affecting their current diversity patterns. The niche models showed Salicaceae family underwent extensive population expansion during the Last Inter Glacial period but retreated to lower latitudes during and since the period of the Last Glacial Maximum. Looking ahead, as climate warming intensifies, suitable habitats will shift to higher latitudes and those at lower latitudes will become less abundant. Finally, the western regions of China harbor the greatest endemism and species diversity of Salicaceae, which are significantly influenced by annual precipitation and mean temperature, ultraviolet-B (UV-B) radiation, and the anomaly of precipitation seasonality. From these results, we infer water–energy dynamic equilibrium and historical climate change are both the main factors likely regulating contemporary species diversity and distribution patterns. Nevertheless, this work also suggests that other, possibly interacting, factors (ambient energy, disturbance history, soil condition) influence the large-scale pattern of Salicaceae species diversity in China, making a simple explanation for it unlikely. Because Southwest China likely served as a refuge for Salicaceae species during the Last Glacial Maximum, it is a current hotspot for endemisms. Under predicted climate change, Salicaceae plants may well face higher risks to their persistence in southwest China, so efforts to support their in-situ conservation there are urgently needed.

Community and species-specific responses of plant traits to 23 years of experimental warming across subarctic tundra plant communities

To improve understanding of how global warming may affect competitive interactions among plants, information on the responses of plant functional traits across species to long-term warming is needed. Here we report the effect of 23 years of experimental warming on plant traits across four different alpine subarctic plant communities: tussock tundra, Dryas heath, dry heath and wet meadow. Open-top chambers (OTCs) were used to passively warm the vegetation by 1.5-3 °C. Changes in leaf width, leaf length and plant height of 22 vascular plant species were measured. Long-term warming significantly affected all plant traits. Overall, plant species were taller, with longer and wider leaves, compared with control plots, indicating an increase in biomass in warmed plots, with 13 species having significant increases in at least one trait and only three species having negative responses. The response varied among species and plant community in which the species was sampled, indicating community-warming interactions. Thus, plant trait responses are both species- and community-specific. Importantly, we show that there is likely to be great variation between plant species in their ability to maintain positive growth responses over the longer term, which might cause shifts in their relative competitive ability.

Climate change perils for dioecious plant species

Climate change, particularly increased aridity, poses a significant threat to plants and the biotic communities they support. Dioecious species may be especially vulnerable to climate change given that they often exhibit spatial segregation of the sexes, reinforced by physiological and morphological specialization of each sex to different microhabitats. In dimorphic species, the overexpression of a trait by one gender versus the other may become suppressed in future climates. Data suggest that males will generally be less sensitive to increased aridity than co-occurring females and, consequently, extreme male-biased sex ratios are possible in a significant number of populations. The effects of male-biased sex ratios are likely to cascade to dependent community members, especially those that are specialized on one sex.

Alternative Growth and Defensive Strategies Reveal Potential and Gender Specific Trade-Offs in Dioecious Plants Salix paraplesia to Nutrient Availability

Population sex ratios of many dioecious plants in nature are biased. This may be attributed to sexually different resource demands and adaptive capacity. In male-biasedPopulus, males often display stronger physiological adaptation than females. Interestingly, Populus and Salix, belonging to Salicaceae, display an opposite biased sex ratio, especially in nutrient-poor environmental conditions. Do female willows have a greater tolerance to nutrient deficiency than males? In this study, we investigated the growth and defensive strategies of Salix paraplesia cuttings, which were grown with high and low soil fertility for about 140 days over one growing season. Results suggest that different strategies for biomass allocation may result in sexually different defense capacities and trade-offs between growth and defense. Females are likely to adopt radical strategies, overdrawing on available resources to satisfy both growth and defense, which seems to be more like a gamble compared with males. It is also suggested that females may have an extra mechanism to compensate for the investment in growth under nutrient-poor conditions. In summary, the results may help focus restoration efforts on sex selection such that a moderate increase in female willow quantity could increase the resistance and resilience of willow populations to early sporadic desertification.

Complex carbon cycle responses to multi-level warming and supplemental summer rain in the high Arctic

The Arctic has experienced rapid warming and, although there are uncertainties, increases in precipitation are projected to accompany future warming. Climate changes are expected to affect magnitudes of gross ecosystem photosynthesis (GEP), ecosystem respiration (ER) and the net ecosystem exchange of CO2 (NEE). Furthermore, ecosystem responses to climate change are likely to be characterized by nonlinearities, thresholds and interactions among system components and the driving variables. These complex interactions increase the difficulty of predicting responses to climate change and necessitate the use of manipulative experiments. In 2003, we established a long-term, multi-level and multi-factor climate change experiment in a polar semidesert in northwest Greenland. Two levels of heating (30 and 60 W m(-2) ) were applied and the higher level was combined with supplemental summer rain. We made plot-level measurements of CO2 exchange, plant community composition, foliar nitrogen concentrations, leaf δ(13) C and NDVI to examine responses to our treatments at ecosystem- and leaf-levels. We confronted simple models of GEP and ER with our data to test hypotheses regarding key drivers of CO2 exchange and to estimate growing season CO2 -C budgets. Low-level warming increased the magnitude of the ecosystem C sink. Meanwhile, high-level warming made the ecosystem a source of C to the atmosphere. When high-level warming was combined with increased summer rain, the ecosystem became a C sink of magnitude similar to that observed under low-level warming. Competition among our ER models revealed the importance of soil moisture as a driving variable, likely through its effects on microbial activity and nutrient cycling. Measurements of community composition and proxies for leaf-level physiology suggest GEP responses largely reflect changes in leaf area of Salix arctica, rather than changes in leaf-level physiology. Our findings indicate that the sign and magnitude of the future High Arctic C budget may depend upon changes in summer rain.

Gender differences in Salix myrsinifolia at the pre-reproductive stage are little affected by simulated climatic change

Females of dioecious species are known often to prioritize defense, while males grow faster. As climatic change is known to influence both growth and defense in plants, it would be important to know whether it affects the sexes of dioecious species differently. This could have impacts on future sex ratios in nature. We grew four clones of each sex of Salix myrsinifolia in greenhouse chambers under ambient conditions, enhanced temperature, enhanced CO2 or enhanced temperature  +  enhanced CO2 . The females had the greatest growth and also the highest levels of phenolic compounds in twigs, while in leaves some compounds were higher in males, some in females. Enhanced CO2 increased growth equally in both sexes, while growth was not affected by elevated temperature. Phenolic compounds in twigs were, however, lowered under elevated temperature. The gender differences were not strongly affected by the simulated climatic changes, but the effects seen on some highly concentrated compounds may be important. We interpret the intensive growth at pre-reproductive phase as a strategy in females to get an initial advantage before later periods with fewer resources available for growth.

Sex-related differences in morphological, physiological, and ultrastructural responses of Populus cathayana to chilling

Low temperature is one of the abiotic factors limiting plant growth and productivity. Yet, knowledge about sex-related responses to low temperature is very limited. In our study, the effects of low, non-freezing temperature on morphological, physiological, and ultrastructural traits of leaves in Populus cathayana Rehd. males and females were investigated. The results showed that 4 °C temperature caused a chilling stress, and females suffered from greater negative effects than did males. At the early growth stage of development, chilling (4 °C) significantly inhibited plant growth, decreased net photosynthesis rate (P(n)), stomatal conductance (g(s)), transpiration (E), and chlorophyll pigments (Chl), and increased intercellular CO(2) concentration (C(i)), chlorophyll a/b (Chl a/b), proline, soluble sugar and H(2)O(2) contents, and ascorbate peroxidase (APX) activity in both sexes, whereas peroxidase (POD) and glutathione reductase (GR) activities decreased and thiobarbituric acid reactive substance (TBARS) content increased only in females. Chilling stress also caused chloroplast changes and an accumulation of numerous plastoglobules and small vesicles in both sexes. However, disintegrated chloroplasts and numerous tilted grana stacks were only found in chilling-stressed females. Under chilling stress, males showed higher Chl and soluble sugar contents, and higher superoxide dismutase (SOD), POD, and GR activities than did females. In addition, males exhibited a better chloroplast structure and more intact plasma membranes than did females under chilling stress. These results suggest that sexually different responses to chilling are significant and males possess a better self-protection mechanism than do females in P. cathayana.

Changes in antioxidant enzyme activities and isozyme profiles in leaves of male and female Populus cathayana infected with Melampsora larici-populina

Populus cathayana Rehd., a dioecious tree species, is widely distributed in the northern, central and southwestern regions of China. In poplars, Melampsora larici-populina Kleb. is mainly responsible for rust disease, which is considered to be the world's most important disease of poplars. Yet, little is known about sex-related responses to rust disease in poplars. The purpose of this work was to determine whether sexually different responses occur in the antioxidant system of poplars after infection by rust disease. Three-month-old male and female P. cathayana individuals were inoculated with M. larici-populina in a greenhouse. After 12 days of incubation, we investigated the changes in physiology, biochemistry, enzyme activities and isozyme profiles. It was discovered that (i) leaf rust disease inhibited photosynthesis, caused oxidative stress and cellular membrane damage and changed antioxidant enzyme activities and isozyme profiles in poplar leaves; (ii) male poplars suffered from lower infection levels and less negative effects of leaf rust disease than did females; (iii) males showed higher antioxidant activities and less H(2)O(2) accumulation than did females after being infected by leaf rust. Thus, our results indicate that leaf rust disease is more severe in female poplars, and they suffer from greater negative effects than do males. This is the first report about sexually different responses of poplars in the antioxidant reactions to rust disease. It offers some useful information about the effect of leaf rust on dioecious plants, especially on dioecious woody plants.

Sex-specific responses of Populus cathayana to drought and elevated temperatures

Dioecious plant species represent an important component of terrestrial ecosystems. Yet, little is known about sex-specific responses to drought and elevated temperatures. Populus cathayana Rehd, which is a dioecious, deciduous tree species, widely distributed in the northern, central and southwestern regions of China, was employed as a model species in our study. In closed-top chamber experiments, sex-specific morphological, physiological and biochemical responses of P. cathayana to drought and different elevated temperatures were investigated. Compared with the controls, drought significantly decreased the growth and the net photosynthesis rate (A), and increased the intrinsic water use efficiency (WUE(i)), carbon isotope composition (delta13C), and the malondialdehyde (MDA) and abscisic acid (ABA) contents in droughted plants. In contrast, elevated temperatures significantly promoted the growth and the A, but decreased the WUE(i), delta13C, MDA and ABA contents in well-watered individuals. When compared with males, elevated temperatures induced well-watered females to express a greater increase in the height growth (HG), basal diameter (BD), leaf area (LA), total number of leaves (TNL), dry matter accumulation (DMA) and specific leaf area (SLA), and a lower decrease in the A value, transpiration (E), stomatal conductance (g(s)), MDA and ABA contents, while elevated temperatures induced drought-stressed females to exhibit lower values of HG, BD, LA, TNL, DMA, A, E, g(s) and the intercellular CO2 concentration (C(i)), and higher levels of SLA, WUE(i), delta13C, MDA and ABA contents. Our results indicated that the female individuals of P. cathayana are more responsive and suffer from greater negative effects than do males when grown under environments with increased drought stress and elevated temperature.

Variation in leaf physiology of Salix arctica within and across ecosystems in the High Arctic: test of a dual isotope (Δ13C and Δ18O) conceptual model

Leaf carbon isotope discrimination (Delta(13)C) varies with the balance between net photosynthesis (A) and stomatal conductance (g ( s )). Inferences that can be made with Delta(13)C are limited, as changes could reflect variation in A and/or g ( s ). Investigators have suggested that leaf delta(18)O enrichment above source water (Delta(18)O) may enable differentiation between sources of variation in Delta(13)C, as leaf Delta(18)O varies with transpiration rate (E), which is closely correlated with g ( s ) when leaves experience similar leaf to air vapor pressure differences. We examined leaf gas exchange of Salix arctica at eight sites with similar air temperatures and relative humidities but divergent soil temperatures and soil water contents near Pituffik, Greenland (76 degrees N, 38 degrees W). We found negative correlations at the site level between g ( s ) and Delta(18)O in bulk leaf tissue (r (2) = 0.62, slope = -17.9 per thousand/mol H(2)O m(-2) s(-1), P = 0.02) and leaf alpha-cellulose (r (2) = 0.83, slope = -11.5 per thousand mol H(2)O m(-2) s(-1), P < 0.01), consistent with the notion that leaf water enrichment declines with increasing E. We also found negative correlations at the site-level between intrinsic water-use efficiency (iWUE) and Delta(13)C in bulk leaf tissue (r (2) = 0.65, slope = -0.08 per thousand/mumol CO(2) /mol H(2)O, P = 0.02) and leaf alpha-cellulose (r (2) = 0.50, slope = -0.05 per thousand/[mumol CO(2) /mol H(2)O], P = 0.05). When increasing Delta(13)C was driven by increasing g ( s ) alone, we found negative slopes between Delta(13)C and Delta(18)O for bulk leaf tissue (-0.664) and leaf alpha-cellulose (-1.135). When both g ( s ) and A (max) increased, we found steeper negative slopes between Delta(13)C and Delta(18)O for bulk leaf tissue (-2.307) and leaf alpha-cellulose (-1.296). Our results suggest that the dual isotope approach is capable of revealing the qualitative contributions of g ( s ) and A (max) to Delta(13)C at the site level. In our study, bulk leaf tissue was a better medium than leaf alpha-cellulose for application of the dual isotope approach.

Leaf photosynthetic characteristics and net primary production of the polar willow (Salix polaris) in a high arctic polar semi-desert, Ny-Ålesund, Svalbard

Photosynthetic characteristics and their leaf-age dependence were examined to estimate ecophysiological effects on net primary production (NPP) of a polar willow (Salix polaris), a dominant dwarf shrub species in a polar semi-desert area of Ny-Ålesund, Svalbard. Leaves of S. polaris emerged just after snowmelt in early July in 2000; flowers were initiated within 1 week, and fruits in late July. Light-saturated rate of photosynthesis and stomatal conductance to water vapor increased rapidly to their maximum values within 1 week after leaf emergence and then decreased gradually. Depending on the leaf age, photosynthetic rates saturated at photosynthetically active photon flux density (PPFD) of 200–400 µmol·m–2·s–1, which is the light level usually available in the natural habitat. Optimum leaf temperature of photosynthesis ranged from 10 to 18°C, while air temperature in the habitat ranged from 8 to 20°C. These light and temperature responses of photosynthesis of S. polaris would be suitable for efficient carbon gain in the natural habitat characterized by highly variable light and temperature conditions. Using the photosynthetic and respiratory characteristics, biomass distribution, and meteorological data, NPP of S. polaris in the current year was estimated to be 26.1 g C·m–2. A model simulation of rising temperature conditions predicted a reduction of NPP because of a large increase in respiration. It was suggested that temperature condition and leaf phenological aspects strongly influence the carbon fixation by plants in the high arctic area studied.Key words: arctic semi-desert, climate change, net ecosystem production (NEP), net primary production (NPP), Salix polaris, photosynthesis.