Interactive effects of herbivory and sand burial on growth of a tropical dune plant, Ipomoea pes-caprae

1. This study examined the effects of insect herbivory, sand burial, and the interactive effects of these factors, on the growth of beach morning glory, Ipomoea pes-caprae, a common tropical dune plant. Levels of herbivory and sand burial were manipulated on individual shoots, and effects on stem growth, leaf production, and production of adventitious roots and axillary branches by nodes were examined.
2. Sand burial had a significant positive effect on the production of roots, but did not affect growth in stem length or leaf production.
3. Effects of herbivory were consistently negative, and persisted for 6 weeks after the herbivore damage was incurred. Stem growth rates and leaf production decreased and the production of bare nodes (with no roots or branches) and mortality of apical meristems increased.
4. Interactive effects of herbivory and sand burial influenced both leaf production and root production. In the case of root production, the effects of herbivory in decreasing the proportion of nodes that produced roots occurred only in the presence of burial. In contrast, burial masked the negative effects of herbivory on leaf production.     

Facilitation and sand burial affect plant survival during restoration of a tropical coastal sand dune degraded by tourist cars

Coastal sand dunes support various ecosystem services, including storm protection and tourism. Restoration programs are often critical to preserve this ecosystem due to its fragility and high degree of degradation. Dune restoration still suffers from a general lack of knowledge of the ecological processes controlling tropical dune communities. We investigated if facilitation can increase restoration success by assisting plant survival in a Brazilian coastal dune degraded by buggies at the Environmental Protection Area of Jenipabu, RN, Brazil. We performed two field experiments on dune crest sites degraded by buggies. The first experiment tested how the presence of established vegetation and coconut mesh, mimicking soil‐stabilizing effect of vegetation, facilitates seedling survival and establishment of the early successional dominant dune plant Canavalia maritima (Fabaceae). The second experiment tested if coconut mesh and initial irrigation would allow the establishment of C. maritima outside the vegetation, using both seeds and transplants. We found that the presence of established vegetation positively affected seedling survival. Application of mesh positively affected microclimatic conditions and slightly increased survival, but only for seeds. Initial irrigation only had a small effect on transplanted seedlings survival. Nevertheless, there was extreme seedling mortality in the experiment in particular from sand burial. We conclude that restoration of these dune crests is very difficult. Facilitation by vegetation can reduce plant mortality by sand burial and desiccation, but successful restoration is likely to require a major effort involving a very high number of seedlings or seeds.     

The growth responses of coastal dune species are determined by nutrient limitation and sand burial

Past work suggests that burial and low nutrient availability limit the growth and zonal distribution of coastal dune plants. Given the importance of these two factors, there is a surprising lack of field investigations of the interactions between burial and nutrient availability. This study aims to address this issue by measuring the growth responses of four coastal dune plant species to these two factors and their interaction. Species that naturally experience either high or low rates of burial were selected and a factorial burial by nutrient addition experiment was conducted. Growth characteristics were measured in order to determine which characteristics allow a species to respond to burial. Species that naturally experience high rates of burial (Arctotheca populifolia and Scaevola plumieri) displayed increased growth when buried, and this response was nutrient-limited. Stable-dune species had either small (Myrica cordifolia, N-fixer) or negligible responses to burial (Metalasia muricata), and were not nutrient-limited. This interspecific difference in response to burial and/or fertiliser is consistent with the idea that burial maintains the observed zonation of species on coastal dunes. Species that are unable to respond to burial are prevented from occupying the mobile dunes. Species able to cope with high rates of burial had high nitrogen-use efficiencies and low dry mass costs of production, explaining their ability to respond to burial under nutrient limitation. The interaction between burial and nutrient limitation is understudied but vital to understanding the zonation of coastal dune plant species.     

The role of mycorrhizal fungi in growth enhancement of dune plants following burial in sand

1. Burial in sand of Agropyron psammophilum and Panicum virgatum plants had a stimulating effect on carbon dioxide exchange rate, leaf area and biomass, irrespective of whether sand used for burial did or did not contain mycorrhizal fungi.
2. Plants of both A. psammophilum and P. virgatum species grown in mycorrhiza-containing sand and then buried with mycorrhiza-containing sand had the highest CO₂ exchange rate, leaf area and biomass.
3. The growth stimulation following a burial episode is probably a composite response of several factors. The major contribution of mycorrhizal fungi will possibly be the exploitation of resources in the burial deposit.     

Photosynthetic responses of plant communities to sand burial on the machair dune systems of the outer hebrides, Scotland

BACKGROUND AND AIMS: The effects of both short-term (2 weeks) and long-term (6 weeks) burial on the photosynthetic efficiency of four typical plant sub-communities of the machair sand dunes of the Outer Hebrides are described. Previous studies have examined the photosynthetic responses on individual species rather than the response at the community level. METHODS: Three replicate turves from four different sub-community types (foredune grassland, dune slack, three-year fallow and unploughed grassland) were subjected to short- and long-term burial treatments after acclimatisation in an unheated greenhouse for approximately 10 weeks. Three replicate control turves from each sub-community were left unburied. After treatment, photosynthetic rate was measured at 16-20 h and 40-44 h after re-exposure, using an infra-red gas analyser, with standardization by total leaf area for each turf. Effects of sub-community type, burial duration and time since re-exposure were analysed by 3-factor split-plot analysis of variance (ANOVA) with repeated measures for time since re-exposure in the subplots. KEY RESULTS: Buried turves were characterized by a low dark respiration rate, which may represent a maintenance response to burial. After removal of sand, each machair sub-community showed some capacity for an elastic photosynthetic response. There were no differences between the effects of short- and long-term burial on the photosynthetic efficiency of machair vegetation, although turves buried for 6 weeks generally attained photosynthetic rates approaching those of control rates sooner than turves buried for 2 weeks. Photosynthetic responses to burial varied between sub-communities, with the slack turves exhibiting the poorest capacity for recovery within the investigated 44-h period. CONCLUSIONS: In the machair environment, the ability to maintain photosynthetic equipment whilst buried, and the ability to bring about a relatively rapid reinstatement of photosynthetic mechanisms on emergence or exposure, is an important adaptation for survival. Survival is closely related to the ability of a plant to replenish carbohydrate reserves before the next burial event.     

Responses of dune mosses to experimental burial by sand under natural and greenhouse conditions

Sand movement is a predominant feature of mobile coastal and lake-shoreline sand dunes. Plants growing in these environments are able to withstand and survive periods of burial by sand. Although mosses are important dune stabilizers in temperate dunes, there are few studies focused on their response to burial by sand. In this study we examined the effects of burial by sand on 11 moss species that grow naturally on Lake Huron sand dunes and occur in a gradient of habitats from the foredunes along the shore to forested areas. Artificial burial treatments (sand depth of 0, 1, 3, 5 and 7 cm) were imposed under greenhouse and field conditions. We measured final plant cover and calculated the speed of emergence and an interpretive index (tolerance index) to compare burial responses among species by calculating a burial ratio which standardized the initial size of each species. In the greenhouse, Ceratodon purpureus and Ditrichum flexicaule recorded the highest mean speeds of emergence and Dicranum scoparium, Plagiothecium laetum, Dicranum flagellare and Brachythecium sp. 1 the lowest. In the field the trends were similar although the speed of emergence was much slower. Three types of response to burial were evident in plant cover: neutral, inhibition and stimulation. Although all eleven studied species were able to emerge from the different depths of burial, we observed that species colonizing areas with high sand mobility and deposition (C. purpureus and D. flexicaule) were the most tolerant and emerged from depths of up to 35 times their height. Species growing inland, at the base of trees (Dicranum scoparium, Brachythecium sp. 2, Plagiomnium cuspidatum and Dicranum flagellare) showed the least tolerance of burial.     

不同厚度沙埋下植物光合特性变化与补偿性生长的关系

在自然条件下通过对海岸沙地不同株型单叶蔓荆(Vitextrifolia var.simplicifolia Cham)在不同厚度沙埋处理下土壤温度、湿度,沙上叶片鲜重(FW)和干重(DW)、叶片净光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)的测定以揭示沙埋后植物的快速生长与光合作用的关系以及植物补偿性生长在其耐沙埋中的作用。结果表明,不同厚度沙埋下,土壤表层含水量最低和温度最高(40℃),随着沙埋厚度增加,土壤含水量显著增加,而土壤温度(28℃)降低。轻度和中度沙埋5 d和10 d,幼株和成株沙上叶片鲜重(FW)和干重(DW)增加,单叶蔓荆成株沙上顶部叶片FW分别较对照增加27%和29%;DW较对照增加23%和27%,并与对照差异显著(P0.05)。幼株和成株单叶蔓荆对照和不同厚度沙埋下沙上叶片Pn、Tr、Gs日变化曲线均呈现"双峰型",且植株上部叶片Pn、Tr、Gs高于下部叶片。但在轻度和中度沙埋处理下,幼株和成株单叶蔓荆叶片Pn、Tr、Gs增加并高于对照,成株在光合第一个高峰期顶部叶片Pn分别较对照高13%和24%,Tr分别较对照增加33%和72%,Gs较对照分别增加了55%和27%。研究表明,沙埋下植株快速生长和叶片物质积累加速与光合作用增高呈正相关。沙埋胁迫激活植株补偿生长是引起植物Pn增加,干物质积累的主要原因。而沙埋使叶片损失导致植物能量代谢失衡是激活补偿生长的内因,沙埋使植物下部处于低温潮湿环境是补偿生长的外因。沙埋胁迫下植物补偿生长在其维持能量和物质代谢平衡和适应沙埋中起重要作用,是单叶蔓荆适应沙埋的重要生理调控策略。     

Degradation of seed mucilage by soil microflora promotes early seedling growth of a desert sand dune plant

In contrast to the extensive understanding of seed mucilage biosynthesis, much less is known about how mucilage is biodegraded and what role it plays in the soil where seeds germinate. We studied seed mucilage biodegradation by a natural microbial community. High‐performance anion‐exchange chromatography (HPAEC) was used to determine monosaccharide composition in achene mucilage of Artemisia sphaerocephala. Mucilage degradation by the soil microbial community from natural habitats was examined by monosaccharide utilization tests using Biolog plates, chemical assays and phospholipid fatty acid (PLFA) analysis. Glucose (29.4%), mannose (20.3%) and arabinose (19.5%) were found to be the main components of achene mucilage. The mucilage was biodegraded to CO₂ and soluble sugars, and an increase in soil microbial biomass was observed during biodegradation. Fluorescence microscopy showed the presence of mucilage (or its derivatives) in seedling tissues after growth with fluorescein isothiocyanate (FITC)‐labelled mucilage. The biodegradation also promoted early seedling growth in barren sand dunes, which was associated with a large soil microbial community that supplies substances promoting seedling establishment. We conclude that biodegradation of seed mucilage can play an ecologically important role in the life cycles of plants especially in harsh desert environments to which A. sphaerocephala is well‐adapted.     

Effects of an invasive plant on a desert sand dune landscape

Given the abundance of non-native species invading wildland habitats, managers need to employ informed triage to focus control efforts on weeds with the greatest potential for negative impacts. Our objective here was to determine the level of threat Sahara mustard, Brassica tournefortii, represents to meeting regional goals for protecting biodiversity. Sahara mustard has spread throughout much of the Mojave and lower Sonoran Deserts. It has occurred in southern California’s Coachella Valley for nearly 80 years, punctuated by years of extremely high abundance following high rainfall. In those years the mustard has clear negative impacts on the native flora. Using mustard removal experiments we identified reductions in native plant reproduction, shifting composition increasingly toward Sahara mustard while decreasing the fraction of native species. High between-year variance in precipitation may be a key to maintaining biodiversity as the mustard is less abundant in drier years. Sahara mustard impacts to the native fauna were much less evident. Of the animal species evaluated, only the Coachella Valley fringe-toed lizard, Uma inornata, demonstrated a negative response to mustard abundance; however the impacts were short-lived, lasting no more than a year after the mustard’s dominance waned. Without control measures the long-term impacts to desert biodiversity may rest on the changing climate. Wetter conditions or increased periodicity of high rainfall years will favor Sahara mustard and result in reduced biodiversity, especially of native annual plants. Drier conditions will keep the mustard from becoming dominant but may have other negative consequences on the native flora and fauna.     

Effects of burial in sand on the growth and reproduction of Cakile edentula

Studies were conducted to examine the effects of sand burial on the growth and reproduction of Cakile edentula under controlled greenhouse conditions Sand burial enhanced both the vegetative growth and reproduction of plants Within one week after burial, plants showed a significant increase in the length of the internode just below the current sand surface This response was not mediated by the dark conditions imposed by sand burial About two weeks after burial, adventitious roots grew upwards into the deposited sand Plants buried in washed sand did not differ in their dry weight whereas those buried in unwashed sand were significantly taller, produced greater biomass and larger number of seeds per plant than control However, the mean mass per fruit and per seed were not altered The frequency distribution of fruit and seed was only slightly modified by the burial treatments     

Seasonal and diurnal leaf orientation,bifacial sunlight incidence,and leaf structure in the sand dune herb Hydrocotyle bonariensis

A conceptual model has been proposed whereby leaf orientation and resulting sunlight exposure dictate functional leaf structure. Specifically, the model states that this relationship is driven by the absolute amount and ratio of incident sunlight on adaxial and abaxial leaf surfaces. To test this model, the relationships between corresponding values of leaf orientation and incident sunlight on both leaf surfaces were measured for the sand dune herb Hydrocotyle bonariensis over a growth season, along with examination of leaf structure. For mature leaves, leaf angle from horizontal and azimuth angle significantly increased over the growing season, indicating diurnal midday avoidance and seasonal maximization of incident sunlight. Consequently, seasonal changes in leaf orientation resulted in an overall decrease in midday sunlight incidence on the adaxial surface and a slight shift in the daily occurrence of peak abaxial incidence. Adaxial surfaces received three to four times more sunlight than abaxial surfaces, and leaf cross-sections revealed relatively thick (564 μm) leaves with multiple adaxial palisade layers and stomata on both leaf surfaces, as predicted by the conceptual model and measured ratio of incident sunlight on adaxial and abaxial leaf surfaces. These data provide further evidence of the relationship between leaf orientation and resulting absolute levels of sunlight incidence on both leaf surfaces, as well as their ratio, and corresponding differences in internal and external leaf structure.     

Leaf temperature of desert sand dune plants: perspectives on the adaptability of leaf morphology

The leaf temperature of six annual and six perennial plant species was monitored during spring and summer on a sand dune ecosystem in the delta Mediterranean coast of Egypt. During winter, leaves of all tested perennial species attained temperatures higher than the air temperature at night and shortly after sunrise, with maximum leaf–air temperature differences reaching up to 8°C. The lowest differences were less than 1°C. Around noon, the leaves of several species attained temperatures lower than that of the air whereas others showed higher temperatures. The opposite was true during summer, when leaf temperatures were lower than air temperature. The maximum leaf–air temperature differences occurred after midnight towards sunrise and reached up to 10°C. The lowest differences were found around noon and were of less than 5°C. The annual plant species have more pronounced variations than perennials in their leaf temperatures during the night and for most of the day. The leaves were heated or cooled a few degrees above or below the air temperature. The results are discussed in relation to the morphological characters of the leaves. The variation in leaf temperature at different times of the day was significantly related to leaf morphology, specific leaf area, thickness, volume, leaf area index and the surrounding environment.     

Zonal plant distribution and edaphic and micrometeorological conditions on a coastal sand dune

Some edaphic and meteorological conditions were examined to detect environmental gradients from shoreline to inland at the Kado-ori coast, Ibaraki, Japan, in 1989. Zonal distribution patterns of coastal dune plant species, including three ubiquitous perennials,Calystegia soldanella, Carex kobomugi andIschaemum anthephoroides, were described in relation to the environmental gradients. Environmental gradients were found in water availability, evaporative demand and soil-water salinity. Water availability, evaluated by thickness of capillary water layer, increased from 10 cm at 20 m to 48 cm at 85 m from the shoreline, reflecting the percentage of fine sand. Evaporative demand, which was evaluated by the evaporation rate from a wet black filter paper, decreased with increasing distance from the shoreline. Soil-water salinity was lowest (15 mmol/L) at 85 m from the shoreline and highest (90 mmol/L) at 30m. On the coast,C. soldanella, a salt-tolerant perennial, was distributed mainly in the environmentally harsh area 40–60 m from the shoreline.Ischaemum anthephoroides andC. kobomugi, less salt-tolerant perennials, occurred mainly 70–80 m from the shoreline, where environmental conditions were more hospitable.     

种子萌发和幼苗生长对沙丘环境的适应机制

综述了植物沙生适应机制的研究及其进展.一些植物的种子在刚成熟时具有休眠特性.种子需要适度沙埋促进萌发并实现幼苗定居,但过度沙埋则会抑制种子萌发和出苗.在沙层深处,没有萌发的种子会进入休眠状态,形成土壤种子库.幼苗通过增加节数和延长节间来适应沙埋.沙埋深度超过植物的忍耐限度会抑制幼苗生长,甚至导致幼苗死亡.沙生植物必须适应其他环境因子,如盐风与土壤盐分、昆虫采食、土壤养分亏缺等,才能在沙丘上成功生长.沙蚀可导致幼苗根系暴露并干燥脱水.一些沙漠植物的幼苗在萌发后可忍耐一段时期的干燥,水分条件得到满足之后,幼苗能够恢复生长.     

沙埋对花棒种子萌发和幼苗生长的影响

为探讨花棒(Hedysarum scopariium)种子萌发和幼苗生长对沙埋的响应,并为固沙造林、水土保持提供理论基础,研究了6种沙埋深度(0、1、2、3、4和5cm)对花棒种子萌发和幼苗生长的影响.结果表明,埋深对花棒幼苗出土率、首次出苗时间、单株叶片数、幼苗生长高度以及生物量的分配均有极显著影响(P<0.001).种子出苗率在2 cm沙埋下达到最高(95.6%),在5cm沙埋下最低(43.4%);幼苗最大高度(11.6cm)、绝对株高(13.9cm)和最大地上生物量(26.7mg)均出现在2cm的埋深,幼苗最小高度(3.3cm)、最小根长(4.3cm)和最小地上生物量(5.3mg)出现在5cm的埋深;生物量分配随沙埋深度增大而更多地分配给地下部分.2cm的沙埋是花棒种子萌发和幼苗生长的最佳深度.     

Arbuscular mycorrhizal fungal communities change among three stages of primary sand dune succession but do not alter plant growth

Plant interactions with soil biota could have a significant impact on plant successional trajectory by benefiting plants in a particular successional stage over others. The influence of soil mutualists such as mycorrhizal fungi is thought to be an important feedback component, yet they have shown benefits to both early and late successional plants that could either retard or accelerate succession. Here we first determine if arbuscular mycorrhizal (AM) fungi differ among three stages of primary sand dune succession and then if they alter growth of plants from particular successional stages. We isolated AM fungal inoculum from early, intermediate or late stages of a primary dune succession and compared them using cloning and sequencing. We then grew eight plant species that dominate within each of these successional stages with each AM fungal inoculum. We measured fungal growth to assess potential AM functional differences and plant growth to determine if AM fungi positively or negatively affect plants. AM fungi isolated from early succession were more phylogenetically diverse relative to intermediate and late succession while late successional fungi consistently produced more soil hyphae and arbuscules. Despite these differences, inocula from different successional stages had similar effects on the growth of all plant species. Host plant biomass was not affected by mycorrhizal inoculation relative to un‐inoculated controls. Although mycorrhizal communities differ among primary dune successional stages and formed different fungal structures, these differences did not directly affect the growth of plants from different dune successional stages in our experiment and therefore may be less likely to directly contribute to plant succession in sand dunes.     

五种荒漠植物幼苗出土及生长对沙埋深度的响应

研究了红砂、泡泡刺、花棒、白刺和沙拐枣5种荒漠优势植物的幼苗出土和生长对沙埋的响应,判断了幼苗的生长特征能否预测植物的定植能力。进行了0、1、2、3、5cm和8cm等6个沙埋深度处理,每个处理5个重复。结果表明：每种植物的出苗率都随着沙埋深度的增加而降低,而且遵循着指数方程关系。红砂种子的最佳沙埋深度应为0-1cm,3cm已是出苗和存活的最大沙埋深度;泡泡刺、花棒和白刺种子的最佳深埋深度为0—3cm;沙拐枣在0—8cm各个深度都有出苗现象,且出苗率没有显著差异,但8cm深度的出苗率只有4％,最佳沙埋深度约为5cm。幼苗的生长高度受沙埋深度的影响显著,在同一时间,幼苗的最大生长高度并不在0cm表层,但红砂幼苗除外。泡泡刺、花棒和白刺在0—3cm的沙埋深度的幼苗生长高度大于5-8cm沙埋深度的生长高度,但沙拐枣幼苗在5cm深度的生长高度最大。5种荒漠植物幼苗的生物量受沙埋深度的影响不显著。在同一沙埋深度下,红砂的绝对高度生长率明显低于其余4种植物,沙拐枣的绝对高度生长率高于其余4种植物幼苗;5种植物的相对高度生长率对沙埋深度的响应并不敏感。绝对高度生长率与相对高度生长率并不能预示幼苗存活成功率。     

Clonal growth of Lithospermum caroliniense (Boraginaceae) in contrasting sand dune habitats

The occurrence of clonal growth of distylous Lithospermum caroliniense was investigated in a population in the Nebraska Sandhills, an area where sand dunes have been relatively stable for at least 1500-3000 yr, and compared to a population occurring at the Indiana Dunes, an area of active sand dune formation. Spatial autocorrelation analysis indicated the occurrence of significant clonal propagation of genetically based floral morphs at Arapaho Prairie, but not for the Indiana Dunes. Apparent clonal growth in the Sandhills population had no overall negative effect on pollen deposition or fecundity relative to the Indiana population, although in some large clones the proportion of compatible pollen grains on stigmas was lower. Clonal growth may have occurred in the Sandhills population because of the greater age and stability of the Nebraska Sandhills; infrequent establishment of seedlings permits detection of clonal growth using the spatial pattern of floral morphs. At the Indiana dunes, repeated cycles of dune formation provide conditions favoring establishment of seedlings, and sand dune succession results in disappearance of L. caroliniense before the development of clones.     

沙埋对醉马草种子萌发和幼苗生长的影响

为探讨醉马草(Achnatherum inebrians)种群繁殖和扩散机理,并为其防控和开发利用提供理论基础,研究了不同沙埋深度(0、1、2、3、4和5cm)对醉马草种子萌发和幼苗生长的影响。结果表明:埋深对醉马草幼苗出土率、首次出苗时间、幼苗生长高度以及生物量的分配均有极显著影响(P<0.001);种子萌发和幼苗出土率在2cm沙埋下达到最高(92%),在5cm沙埋下最低(58.7%);幼苗最大高度(10.8cm)出现在3cm的沙埋,最小高度(6.3和7.1cm)出现在0和5cm的埋深;埋深为2cm时,地上和地下生物量最大,埋深5cm时地上和地下生物量均最小;最大根长(约5cm)和最小根长(1cm)分别出现在2～3cm和5cm的埋深。2～3cm的埋深是醉马草种子萌发和幼苗生长的最佳深度。