Spring Ephemeral Plant Research Articles

Dynamic transcriptome analysis provides molecular insights into underground floral differentiation in Adonis Amurensis Regel & Radde

Understanding flower developmental processes is a prerequisite for improving flowering ‘plants’ production. Adonis amurensis is a fascinating spring ephemeral plant that develops its flower organs underground. Nevertheless, knowledge of the molecular mechanisms driving this particular process is scarce. Herein, we examined transcriptional changes during underground flower differentiation in A. amurensis and unveiled key differently regulated genes and pathways. High-throughput RNA sequencing of meristems at different flower developmental stages, including flower primordium (FP), sepal stage (SE), perianth primordium (PE), stamen stage (ST), and pistil stage (PI), identified 303,234 unigenes that showed 44.79% similarity with sequences in Aquilegia coerulea. Correlations, principal component, and differentially expressed genes (DEGs) analyses revealed that few molecular changes occurred during the transition from PE to ST. Many DEGs exhibited stage-specific regulations. Transcription factor (TF) and phytohormone family genes are critical regulators of the floral differentiation process in A. amurensis. The most differentially regulated TFs were MADS, FAR1, MYBs, AP2/ERF, B3, C2H2, and LOBs. We filtered out 186 candidate genes for future functional studies, including 18 flowering/circadian-related, 32 phytohormone-related, and TF family genes. Our findings deepen our understanding of the underground flower differentiation process and offer critical resources to dissect its regulatory network in A. amurensis. These findings establish a foundational platform for researchers dedicated to exploring the unique phenotypic characteristics of this specific flowering modality and delving into the intricate molecular mechanisms underpinning its regulation and expression.

Potential distribution of the spring ephemeral plant Adonis amurensis in Northeast China under future climate change

AbstractAdonis amurensis Regel et Radde is an early spring plant in northeastern China that has great ornamental value because it blooms before other plants have sprouted. It has not been used to its full potential due to environmental restrictions on its growth. It will be extremely important for its application to comprehend the possible habitat of A. amurensis and the critical environmental factors controlling its distribution under current and future climatic scenarios. In this work, two climate change scenarios of 2041–2060 and 2081–2100 were utilized to predict the suitable habitat of A. amurensis. The results showed that the suitable habitat was mainly distributed along the Changbai Mountains, with a total area of 303,090 km2, and the potential and high‐potential habitat area were 141,218 and 161,872 km2, respectively. In the future climate scenarios, the suitable habitat of A. amurensis was still distributed along the Changbai Mountains, but the area was reduced. In ssp126 and ssp585 scenarios of 2041–2060 and 2081–2100, the area was reduced by 7.13% and 22.34% and 18.66% and 8.09%, respectively. The reduced suitable habitat was mainly located in central Heilongjiang (southeastern Xiao Xing'an Ling), central Jilin, and northeastern Liaoning. The suitable habitat was significantly influenced by precipitation, mainly affected by annual precipitation, followed by precipitation seasonality, soil surface pH, and slope. The results of this study can serve as empirical support for the artificial cultivation, ecological restoration, and long‐term use of A. amurensis.

Multiple reproductive strategies of a spring ephemeral plant, Fritillaria maximowiczii, enable its adaptation to harsh environments

AbstractSpring ephemeral plants that experience harsh environments have developed specific reproductive characteristics. These characteristics are of great importance to the survival and reproduction of these species, particularly for rare and endangered plants. Fritillaria is a genus consisting of spring ephemeral plants with significant medicinal and ornamental value whose wild resources are highly threatened and whose reproductive characteristics and adaptative evolutionary mechanisms are still not well understood. Fritillaria maximowiczii is positioned at the most basal clade on the Fritillaria phylogenetic tree, whose reproductive characteristics remain obscure. In this study, we report the flowering dynamics, pollination biology and breeding system of F. maximowiczii. The flowering process of F. maximowiczii can be divided into seven stages. Based on the pollen/ovule ratio, the outcrossing index and a field pollination experiment on a natural population, F. maximowiczii showed high levels of outcrossing and self‐compatibility. Three types of pollinators were observed: two kinds of bumblebees, and spiders. Diverse herkogamy and dichogamy may have considerably improved its reproductive success rate. Furthermore, a special reproductive mode not previously reported in wild populations of Fritillaria, apomixis, was strongly suspected based on a high fruit setting rate (36.84%). Our study suggests F. maximowiczii has developed multiple reproductive strategies to adapt to harsh environments and ensure population reproduction, and the diverse reproductive mechanisms may be related to its primitive phylogenetic position in the genus. This study not only broadens our understanding of mechanisms of ecological adaptation in spring ephemeral plants but also provides key data for the conservation of Fritillaria.

The ecological roles of seed mucilage on germination of Lepidium perfoliatum, a desert herb with typical myxospermy in Xinjiang

Myxospermy is considered as an adaptation to unideal habitats, which is characterized as a gelatinous layer of mucilage around the seed upon contact with water. Studies on the ecological roles of seed mucilage should provide valuable information on seed germination strategy. In the present study, the germination properties of Lepidium perfoliatum L., an early spring ephemeral plant with typical myxospermy in desert of northwestern China, were investigated with the intact seeds and demucilaged seeds under different conditions. Results revealed that, firstly, the seed mucilage was essential for intact seeds to germinate quickly and efficiently under abundant or excess water condition, while had no effect on relief of seed germination at low water potential or other stressful conditions; secondly, the presence of mucilage layer stimulated intact seed germination under relatively higher temperature, appropriate light, permeable soil matrix, which helps seed germinate efficiently under favorable conditions; thirdly, the existence of mucilage may limit air diffusion into seed and subsequently reduce germination, which might be a strategy to ensure a proportion of seeds staying in soil seed bank to wait for next favourable conditions. Our results suggest that the seed mucilage of L. perfoliatum applies multiple ecological roles in protection of seed germination to avoid unfavourable conditions, which should be an adaptation strategy for population survival and succession in a harsh desert environment.

Mapping Spring Ephemeral Plants in Northern Xinjiang, China

Spring ephemeral plants (SEP) are a particular component of flora that take full advantage of water resources and temperature conditions to rapidly complete their life cycle in about two months. In China, they are mainly distributed in northern Xinjiang. They play important roles in dune stability and are precious food for the livestock and wild animals in the early spring. Northern Xinjiang is under dramatic climate changes and land-use/land-cover changes, which can affect the growth of SEP in this region. To explore how the distribution of SEP have varied under these changes, Moderate-Resolution Imaging Spectrodiometer (MODIS) Enhanced Vegetation Index (EVI) time series of two years (2000 and 2014) were applied to detect SEP in each period. The TIMESAT software was used to extract the seasonality information from the EVI data. The results show that SEP in northern Xinjiang are mainly located in the south of the Gurbantunggut desert and along the Ili Valley and piedmont hills of the mountains. In 2000, its total area was 3.83 × 104 km2, accounting for 10% of the entire region. By 2014, the total area was about 2.74 × 104 km2, with a decrease of 28.5% relative to 2000. Land-use/land-cover datasets can be used to determine whether changes in SEP over time are caused by human activities or natural factors. Combing the SEP maps with the synchronous land-use/land-cover datasets indicates that the decrease is mainly caused by natural factors, which are possibly related with the temperature and precipitation changes in this region. Human activities only contributed 4% to the decrease, with most SEP areas being replaced by croplands. The observed SEP dynamics and changes pertain only to the years with below-average precipitation.

Elusive Parnassius mnemosyne (Linnaeus, 1758) larvae: habitat selection, sex determination and sex ratio (Lepidoptera: Papilionidae)

The charismatic and regionally declining Parnassius mnemosyne (Linnaeus, 1758) is notable for surpluses of males in mark-recapture studies, as well as for poor detectability of its larvae, which develop on spring ephemeral plants, Corydalis spp. In order to study whether the bias towards male exists already in larval stage, we searched for the larvae at three localities in the Czech Republic and attempted to sex the larvae using two alternative methods: (i) by identification of the female specific sex chromatin formed by multiple copies of the W chromosome in polyploid somatic nuclei of the Malpighian tubule cells and (ii) by dissection of ovaries and testes. Finding the larvae in the field was extremely difficult, and 38 person-days of fieldwork yielded only 78 larvae. Consistent with the literature, they dwelled under sparse canopy of oak dominated mature woodlands or on woodland margins. Sexing by genitalia dissection worked well (N = 22) and revealed a prevalence of females (16 vs. 6). In contrast, the identification of sex chromatin was not possible as sex chromatin was absent (N = 56). Further cytogenetic analysis confirmed the haploid number of chromosomes n = 29, which is by one smaller than in the congeneric Parnassius apollo (Linnaeus, 1758). This reduction of chromosome number is probably the result of a fusion of sex chromosomes with a pair of autosomes, a situation not uncommon in Lepidoptera. The female-biased larval sex ratio, contrasting with male biases found so often in adults, is based on just 22 genitally dissected larvae, and may be biased by faster growth rate of males.

The complete chloroplast genome of the spring ephemeral plant Alyssum desertorum and its implications for the phylogenetic position of the tribe Alysseae within the Brassicaceae

Alyssum desertorum (Alysseae, Brassicaceae) is an annual spring ephemeral plant whose life cycle is only 2–3 months. It typically has high photosynthetic capacity and a high growth rate. However, little was known about the chloroplast (cp) genome structure of this species. Furthermore, the phylogenetic position of the tribe Alysseae relative to other tribes in the Brassicaceae has not been established and there appear to be inconsistences between different DNA markers. This study is the first report on a cp genome of the genus Alyssum and discusses the phylogenetic relationships of the tribe Alysseae relative to other tribes in the family. The complete cp genome of A. desertorum was 151 677 bp in size and is thus the smallest cp genome of Brassicaceae sequenced to date. The genome includes a large single‐copy region of 81 551 bp, a small single‐copy region of 17 804 bp, and two inverted repeats of 26 161 bp each. The genome contains 132 genes, including 86 protein‐coding genes (PCGs), 38 tRNA genes and 8 rRNA genes. A total of 16 genes contained introns, including 10 PCGs and 6 tRNA genes; the ycf3 and clpP genes contained two introns, and the remaining genes each contained one. Compared to the cp genomes of 21 other Brassicaceae species, the cp genome of Alyssum desertorum was the smallest, as due to variation in gene content and gene length, such as a lack of the rps16 gene and the deletion of some coding genes. Additionally, deletions of introns and intergenic spacers were observed, but their total length was not significantly shorter than those of other taxa. Phylogenetic analysis at the tribal level based on a cp genome dataset revealed that the tribe Alysseae is an early‐diverging lineage that is sister to other species within subclade B of clade II.

Thaw circles around tree trunks provide spring ephemeral plants with a big head start on the growing season

Thaw circles around tree trunks provide spring ephemeral plants with a big head start on the growing season

The showy invasive plant Ranunculus ficaria facilitates pollinator activity, pollen deposition, but not always seed production for two native spring ephemeral plants

Showy invasive plants can reduce pollinator visitation to native plants, resulting in a reduction of seed-set in insect-pollinated species. Seed set in native plants may also be reduced due to the presence of foreign pollen. Alternatively, additional floral resources provided by invasive plants may increase pollinator activity, and facilitate pollination of native species. Ranunculus ficaria is a perennial herb invading deciduous forests of the eastern United States. It produces many showy flowers that may influence pollinator activity in heavily invaded habitats. We compared pollinator visitation rates, stigma pollen loads, and seed production of two sympatrically flowering, entomophilous native species (Claytonia virginica and Cardamine concatenata) between habitats invaded by R. ficaria and uninvaded habitats. We found significantly higher pollinator activity (visits to plots) in invaded plots. We also found significantly higher per flower visitation rates to C. virginica in invaded plots. Claytonia virginica stigmas from invaded habitats had more conspecific pollen resulting in more seeds per capsule in invaded areas. There was more conspecific pollen on C. concatenata stigmas in invaded compared to uninvaded habitats, but there were significantly more seeds per silique in uninvaded habitats. Our results indicated that this invasive species increases pollinator activity and conspecific pollen deposition on sympatrically flowering native ephemerals, but may have differential effects on native seed production. Management options should consider the facilitative effects of this species on pollination services, as well as the possible negative competitive effects.

Effects of Commercial Harvesting on Population Characteristics and Rhizome Yield of Anemone altaica

Effects of Commercial Harvesting on Population Characteristics and Rhizome Yield of Anemone altaica. Commercial harvesting constitutes a direct threat to numerous non–timber forest products (NTFPs), but its ecological effects have not been well documented. Anemone altaica Fisch. ex C. A. Mey, a spring ephemeral plant found in temperate forests of Eurasia, is a traditional Chinese herb. Owing to medicinal value, its rhizomes have been harvested for commercial purposes in northwestern China for many years. This paper addresses the ecological effects of commercial harvesting on A. altaica populations under different harvest intensities. The results show that size–selective harvesting of rhizomes can increase population densities by asexual propagation. Currently, two– to three–year–old individuals derived from asexual propagation are the main targets of commercial harvesting. The increased demand in recent years has resulted in earlier and more intensive harvesting activities largely impacting the natural recovery of the harvested populations. For sustainable use of this traditional medicinal species, we recommend that a periodic harvest strategy of three to four years be adopted.

Floral characters and breeding systems in the dimorphic annual plant Diptychocarpus strictus (Cruciferae)

Diptychocarpus strictus is an early spring ephemeral plant mainly distributed in Junggar Basin of China. It is one of the few species of Cruciferae that has heterocarpy on the same raceme. The upper and lower flowers in a raceme develop into two kinds of siliques that differ in morphology and in manner of dehiscence. This paper deals primarily with the floral syndromes and breeding system of D. strictus. The results can be summarized as follows. (1) This species has two floral morphs, purple-flowered and white-flowered, and the color of flowers is stably inherited. The ratio of the two morphs within a population is close to 1:1. (2) There are significant differences between the two morphs in anther length of the longer stamens in the upper part flowers of a raceme and in length of petal and style of the lower flowers in a raceme (P0.01). Additionally, there are significant differences between the two morphs in length of outer sepals, petals, filaments of longer stamens, ovary, and style between upper and lower flowers in a raceme (P0.01). The data of morphological characters of the upper flowers in a raceme are larger than those of the lower flowers. (3) Number of pollen grains per flower in upper and lower flowers of a raceme in purple-flowered and white-flowered morphs are 7589.07±976.64 and 5428.93±900.45 and 7044.73±557.37 and 5138.60±813.48, respectively; number of ovules per ovary, 31.83±3.36 and 25.03±3.72 and 32.03±3.43 and 25.70±2.61, respectively; and P/O ratios, 241.31±41.85 and 222.33± 52.51 and 222.19±27.80 and 201.84±37.52, respectively. Number of pollen grains per anther is greater in the shorter stamens than they are in the longer stamens of the same flower (P0.01). Abortion rate of pollen is very low, and it differs between longer and shorter stamens (P0.05). (4) In the same raceme of the two morphs, the upper flowers have more pollen grains, higher P/O ratios, and more ovules than the lower flowers (P0.01). Also, there are significant differences between the two morphs in number of pollen grains per anther in the longer stamens of the upper flowers in a raceme (P0.01). (5) Pollen longevity and stigma receptivity barely overlap; the period of highest pollen vigor is just the same as the peak of stigma receptivity. Dynamic curves of pollen viability of the longer and the shorter stamens in the two morphs are similar. At the beginning of anther dehiscence, the pollen vigor of both longer and shorter stamens is 90%. (6) Few pollinators were present during flowering, and self-pollen could germinate normally on the stigma. In the two morphs, fruit-set was 88.2%and 85.7%, respectively, in no emasculation and bagging treatments, and 95.0% and 90.0%, respectively, under conditions of natural pollination, indicating that D. strictus is a facultative selfer.

Arbuscular mycorrhizal status of spring ephemerals in the desert ecosystem of Junggar Basin, China

A survey was made of the arbuscular mycorrhizal (AM) status of 73 spring ephemeral plant species that grow in the desert ecosystem of Junggar Basin, northwest China. The proportion of AM colonization ranged from 7 to 73% with a mean value of 30%. A total of 65 plant species studied were AM with coils/arbuscules or vesicles and the remaining eight species were possibly AM with no coils/arbuscules or vesicles but with fungal mycelia in the root cortex. AM fungal spores were isolated from rhizosphere samples of all 73 plant species and identified. The mean spore density was 22 per 20 ml of air-dried soil, ranging from 0 to 120. Colonization and spore density of perennials were slightly higher than of annuals and varied among different plant families. A total of 603 AM fungal spore (or sporocarp) specimens were isolated belonging to six genera, Acaulospora, Archaeopora, Entrophospora, Glomus, Paraglomus, and Scutellospora; Glomus was the dominant genus. We conclude that spring ephemerals may be highly dependent on AM associations for survival in the very infertile and arid soils of this desert ecosystem.

Field and allozyme studies investigating optimal mating success in two sympatric spring-ephemeral plants, Trillium erectum and T. grandiflorum.

A combination of field experiments and allozyme studies was used to test whether two spring-ephemeral plants growing in eastern North America, Trillium erectum and T. grandiflorum (Liliaceae), exhibited an optimal outcrossing distance for fruit and seed production. Furthermore, the spatial genetic structure of the Trillium populations was examined in light of the outcrossing results. In field experiments, recipient plants were pollinated with either self pollen or with pollen from donors growing 1 m, 10 m, 100 m, and 1500 m away. These distances represented crosses between individuals growing within the same population (1 m, 10 m, and 100 m crosses) and between individuals growing in different populations (1500 m crosses). Self-pollinated T. erectum and T. grandiflorum produced 71% and 89% fewer seeds, respectively, than all other outcrossing treatments. However, there were no significant differences among outcrossing treatments for fruit or seed production. As neither T. erectum nor T. grandiflorum exhibited an optimal outcrossing distance for fruit or seed production, it was predicted that populations of the two would not demonstrate strong spatial genetic structure or isolation by distance. The allozyme results only partially supported the patterns revealed in the outcrossing treatments. Populations of T. erectum and T. grandiflorum showed moderate spatial genetic differentiation based on F-statistics, and only T. grandiflorum exhibited significant isolation by distance based on spatial autocorrelation analyses. The lack of optimal outcrossing distances and the patterns of allozyme variation in T. erectum and T. grandiflorum populations may be attributed to a number of factors, including active seed dispersal by ants, rare long-distance gene-flow events, post-pollination and post-fertilization selection, and/or the severity of inbreeding depression.

Why are annual plants rarely spring ephemerals?

The period of active growth for spring ephemeral plants coincides with the period of high light, water and nutrient availability between snow melt and canopy closure in the understorey of deciduous forests in eastern North America. However, low temperatures prevail during this period and might restrict the performance of these plants. Remarkably, this peculiar phenology is extremely rare among annual plants. To understand better the role of light and water availability and of temperature in the phenology of spring ephemeral plants, we investigated the effects of two temperature regimes (low: 16/7 °C and high: 21/14 °C), three water availability levels (saturated, control and drought), and three photosynthetically active photon flux densities: low (85–100 μmol m−2 s−1); intermediate (182–196 μmol m−2 s−1); high (437–454 μmol m−2 s−1) on the growth and reproduction of the annual Floerkea proserpinacoides. Total biomass, total leaf area and flower and seed production increased with increasing temperature, water availability and light intensity. Total leaf area and total biomass were reduced in plants that were stressed under drought. However, at high temperatures, this reduction was less pronounced when droughted plants were partially shaded. At low temperatures, plants began to senesce after approximately 9 wk, whereas at higher temperatures, signs of senescence appeared after only 7 wk of growth. Despite shorter longevity, total biomass was approximately 1.5 times higher in the control water treatment at higher than at lower temperatures as a result of greater above‐ground growth, and plants allocated a significantly greater proportion of mass gain to seed production. Although F. proserpinacoides can tolerate low temperatures such as those typical of early spring, higher temperatures such as those of late spring/early summer are more favorable for growth and reproduction as long as water and light are not limiting. Spring ephemeral annuals might be rare because low temperatures reduce growth rate and extend the life cycle. An annual plant might not have time to reproduce before resource availability deteriorates with canopy closure unless reproduction begins early in the life cycle of the species.

Spring ephemeral herbs and nitrogen cycling in a northern hardwood forest: an experimental test of the vernal dam hypothesis

In the late 1970s R.N. Muller and F.H. Bormann posited their "vernal dam" hypothesis, stating that spring-ephemeral herbs in deciduous forests serve as a temporary sink for N when overstory trees are dormant, and then release this N later, in the summer, when the trees are active. This hypothesis has gained wide acceptance, yet two of its critical assumptions have never been experimentally tested: (1) that N taken up by spring ephemerals would otherwise be lost from the ecosystem, and (2) that N from senesced ephemeral tissues contributes to increased rates of summertime N mineralization. To test these assumptions, I quantified patterns of N cycling and loss from a set of paired plots, half of which served as controls and from half of which all spring-ephemeral plants were removed. There were no significant differences in NO3- leaching between plots with and without spring ephemeral vegetation. These results are consistent with the relatively low rates of N uptake by the dominant spring ephemeral, Allium tricoccum, and its apparent preference for NH4+, which is far less mobile in soil than NO3-. In addition, based on sequential sampling, I found that soil microorganisms took up 8 times as much N during the spring than did spring-ephemeral herbs (microbial uptake=3.19 vs. plant uptake=0.41 g N m-2), suggesting that microbial immobilization of N is the dominant sink for N during this season. Removal of spring ephemeral vegetation also had no effect on summertime rates of net N mineralization. Furthermore, the addition of spring ephemeral litter to soil+forest floor microcosms did not significantly increase rates of N mineralization in a laboratory incubation. Instead, this experiment demonstrated the overwhelming influence of forest floor litter in controlling the release of mineral N from these soils. Overall, neither assumption of the vernal dam hypothesis holds true in this ecosystem, where patterns of N cycling and loss appear to be dominated by microbial decomposition of forest floor material and soil organic matter.

Under-saturated distribution of Floerkea proserpinacoides Willd. (Limnanthaceae) at the northern limit of its distribution

Habitat availability and dispersal ability are commonly the major factors controlling the distribution of habitat specialists. However, these species often have an “under-saturated” distribution, i.e., their habitat is more frequent than their populations. Floerkea proserpinacoides is an annual spring ephemeral plant of the deciduous forest of eastern North America. It is considered rare in most of its range. In Québec (Canada), where the species reaches the northern limit of its distribution, F. proserpinacoides is mostly restricted to rich, low woods on islands of the St. Lawrence River. To elucidate the factors responsible for this peculiar distribution, we determined the dispersal ability of F. proserpinacoides nutlets and attempted to establish new populations at apparently suitable, but unoccupied sites within the species range in Québec. Primary dispersal is barochorous and nutlets have no accessory structures to assist in dispersal. Secondary dispersal is also limited, and nutlets typically move distances < 50 cm from their original point of fall. Yet, nutlets are buoyant and hydrochory is a possible means of long-distance dispersal. When nutlets were introduced at apparently suitable but unoccupied sites, the seeds could germinate and the individuals completed their life cycle. However, nutlets from different populations did not have the same success. The under-saturated distribution of F. proserpinacoides in Québec is not related to a lack of suitable habitat. Instead, long-distance dispersal events may be too infrequent to allow the occupation of all potential sites, or conditions may be too variable among years on certain sites to allow for population persistence.

Effects of inflorescence size on visits from pollinators and seed set of Corydalis ambigua (Papaveraceae).

Female reproductive success (seed set) of a spring ephemeral plant, Corydalis ambigua Cham. et schlecht (Papaveraceae) was investigated in relation to inflorescence size and foraging behavior (frequency and duration of visitations) by pollinators (namely, overwintered queens of Bombus hypocrita sapporensis) by detailed daily observations of a natural population. Pollination experiments indicated that C. ambigua is self-incompatible and that seed set was significantly affected by the behavior of the pollinating queens. Plants with larger inflorescences were visited more often than those with fewer flowers. Fecundity also increased with increasing size of inflorescences. Visitation time (duration of foraging) rather than the frequency of visitations (number of visits) was critical for higher fecundity. Seed production was strongly enhanced by a few long visits (of more than 60 s), and seemed to be independent of large numbers of short visits (of less than 60 s). Hence, plants with larger inflorescences, which provide a conspicuous signal to pollinators and offer greater rewards in terms of nectar, received longer visits by B. hypocrita sapporensis queens and those plants exhibited higher fecundity.

Robber‐like pollinators: overwintered queen bumblebees foraging on Corydalis ambigua

ABSTRACT. The behaviour of nectar‐collecting Bombus hypocrita sapporensis Cockerell queens was observed on a population of a spring ephemeral plant Corydalis ambigua Cham, et Schlecht. Daily patterns of activity and behaviour changed with the progress of flowering. Activity peaked shortly before sunset early in the flowering season but approximately at noon towards the end of flowering. In the peak flowering period the queens tended to visit nearby plants and to change direction often, whereas early or late in the flowering period they flew further between visits and were less likely to change direction. Each plant was visited 0 to 24 times (mean 9.4 ±SD 5.2) by the queens during the whole flowering season. The queens collected nectar, rarely through the front of the flowers but mostly through the spurs perforated by themselves or predecessors. At the beginning of the flowering season the illegitimate foragers often visited the front of the flowers before moving to the spurs; later, most queens quickly learned to land directly on the spurs. Even the 59.7% of plants that were visited only by illegitimate foragers set seeds. Close observation confirmed that the illegitimate foragers opened the inner petals enclosing anthers and stigma frequently when visiting the front of the flowers before robbing, or occasionally when walking about on the flowers or collecting nectar through the perforated spurs.

Carbon and Nitrogen Dynamics During the Decomposition of Litter and Roots of a Chihuahuan Desert Annual, Lepidium Lasiocarpum

Carbon and nitrogen dynamics were analyzed during the decomposition of litter and roots of the desert ephemeral pepperweed (Lepidium lasiocarpum). We treated litter bags with the insecticide chlordane and the fungicides benomyl and captan to eliminate or restrict groups of soil biota. The mass losses of buried litter (51, 39, and 25% for untreated, insecticide—treated, and fungicide—insecticide—treated material, respectively) were higher than those of the respective root treatments (35, 18, and 15%) at 96 d. The mass loss of untreated material was correlated with numbers of detritivorous—fungivorous microarthropods, and only a small percentage of this loss was as CO2: 27 and 42% for litter and roots, respectively. In the absence of microarthropods a higher percentage of mass—loss carbon could be accounted for as CO2: 33 and 76% for litter and roots, respectively, indicating that mass loss was due primarily to litter removal by microarthropod activity and not to mineralization. Litter removal by microarthropods was less dependent on abiotic constraints such as soil moisture (r = 0.65, P &lt; .001) than was mass loss when microarthropods were absent (r = 0.79, P &lt; .001). In the absence of microarthropods, mass loss was more closely coupled with biomass of grazers, such as nematodes, which require free water for activity (r = 0.99, P &lt; .0001). Unlike mass loss, carbon mineralization was highest in untreated roots, suggesting a stimulation of microbial activity by microarthropods, while in untreated litter no stimulation was observed when compared to insecticide treatments. This difference was primarily a function of fungivorous microarthropod density, with overgrazing occurring in the untreated litter. Nitrogen budgets indicated the importance of microarthropods in the turnover of root nitrogen. In the presence of microarthropods 132% of the initial root nitrogen could be accounted for after 96 d, while in the absence of microarthropods 270% could be accounted for. This net immobilization of nitrogen was primarily in the soil organic fraction around the roots and was associated with fungal development. Data from this study re—emphasize the importance of microarthropods as regulators of decomposition in deserts and suggest that predation by nematodes or protozoa on bacteria and fungi contributes to rate regulation. Nitrogen flux data suggest that when spring ephemeral plant production is high, decomposition of ephemeral roots with attendant nitrogen immobilization can reduce the nitrogen available to creosotebush, Larrea tridentata, thus reducing shrub production. Higher taxa of soil biota, i.e., nematodes and microarthropods, may thus be important regulators of nitrogen fluxes and of mass loss in decomposition.