TO CONSTRUCTING AN ADAPTIVE COVER MODEL

A mathematical model for optimizing the growth and development of plant cover is investigated. For constant environmental parameters (humidity, soil and plant temperature), a balanced optimal distribution of photosynthetic assimilates was found by the choice of growth functions and the ratio of leaf and root biomass in explicit general terms, maximizing its reproductive biomass at the end of 3 phases of growth and development of plant cover. The expressions obtained are meaningfully interpreted and can be considered as the basis for an adaptive model of plant productivity and moisture transfer in soil in a constant or slowly changing environment.

Allometry and Yield Stability of Cereals

Crop plants grow, and then, they allocate resources to different structures, including seeds and fruits, which represent yield in most crops. We define the yield stability of a genotype as its ability to reduce the effects of temporal variation in resources and conditions on yield production, and we argue that yield stability can be understood in terms of two processes: (1) crop survival and growth (biomass production): the ability of the crop plants to survive and produce biomass under the range of conditions to which it is exposed and (2) the pattern of allocation of this biomass to yield across this range of conditions. Plant breeders and crop physiologists have focused on (1), but much less attention has been paid to (2). We hypothesize that (2) is primarily the result of reproductive allometry: the quantitative relationship between vegetative and reproductive biomass. Ecological theory and the allometric models we present predict a tradeoff between (a) the ability of a genotype to produce yield over a wide variety of conditions and (b) its ability to produce very high yields under optimal or near-optimal conditions. We reanalyze the data from two recent studies, and the results are consistent with this hypothesis. Yield stability in crops corresponds to bet-hedging in evolutionary ecological theory. It is the most appropriate strategy for smallholder farmers in developing countries, a group that comprises most of the farmers in the world. Researchers and crop breeders need to rethink their objectives if they want to develop optimal varieties for these farmers.

Sex ratio and life history traits at reaching sexual maturity in the dioecious shrub Fuchsia parviflora: field and common garden experiments

Fuchsia parviflora is a dioecious shrub that depends on biotic pollination for reproduction. Previous studies suggest that the male plants produce more flowers, and male-biased sex ratios have been found in some natural populations. To assess whether the biased sex ratios found between genders in natural populations are present at the point at which plants reach sexual maturity, and to identify possible trade-offs between growth and reproduction, we performed a common garden experiment. Finally, to complement the information of the common garden experiment, we estimated the reproductive biomass allocation between genders in one natural population. Sex ratios at reaching sexual maturity in F. parviflora did not differ from 0.5, except in one population, which was the smallest seedling population. We found no differences between genders in terms of the probability of germination or flowering. When flowering began, female plants were taller than males and the tallest plants of both genders required more time to reach sexual maturity. Males produced significantly more flowers than females, and the number of flowers increased with plant height in both genders. Finally, in the natural population studied, the investment in reproductive biomass was seven-fold greater in female plants than in male plants. Our results showed no evidence of possible trade-offs between growth and reproduction. Despite the fact that female plants invest more in reproductive biomass, they were taller than the males after flowering, possibly at the expense of herbivory defence.

Effect of depth gradient and temperature on Zostera marina vegetative and reproductive phenology in the first year of the 1997–1998 El Niño

Does Zostera marina exhibit phenotypic plasticity, maximizing fitness in traits responding to environmental factors, i.e., depth and temperature? We compared the vegetative and sexual phenology and reproductive effort of Z. marina by analyzing vegetative and reproductive shoot density, biomass, and reproductive stages to determine structural features of vegetative and reproductive shoots from subtidal and intertidal environments in San Quintín Bay, Baja California, a year before and after the 1997–1998 El Niño/Southern Oscillation (ENSO). We found significant differences in vegetative and reproductive biomass between intertidal and subtidal environments driven by temperature differences between ENSO and non-ENSO years. Subtidal plants had lower density of long reproductive shoots and a shorter reproductive cycle. Seed release occurred from May to October in the subtidal environment, and from May to November in the intertidal environment. Maximal recorded values were 219.5 (±45.8) seeds per reproductive shoot in the subtidal environment and 151.3 (±21.5) in the intertidal environment. We observed higher sexual activity and lower vegetative biomass in the intertidal environment, the most stressful environment. Both vegetative and reproductive biomass were affected by the increase in temperature during ENSO, but vegetative and reproductive shoot densities were not affected.

Variation in regrowth ability in relation to land-use intensity in three common grassland herbs

Aims Plant populations in managed grasslands are subject to strong selection exerted by grazing, mowing and fertilization. Many previous studies showed that this can cause evolutionary changes in mean trait values, but little is known about the evolution of phenotypic plasticity in response to land use. In this study, we aimed to elucidate the relationships between phenotypic plasticity – specifically, regrowth ability after biomass removal – and the intensity of grassland management and levels of temporal variation therein. Methods We conducted an outdoor common garden experiment to test if plants from more intensively mown and grazed sites showed an increased ability to regrow after biomass removal. We used three common plant species from temperate European grasslands, with seed material from 58 – 68 populations along gradients of land-use intensity, ranging from extensive (only light grazing) to very intensive management (up to four cuts per year). Important findings In two out of three species, we found significant population differentiation in regrowth ability after clipping. While variation in regrowth ability was unrelated to the mean land-use intensity of populations of origin, we found a relationship with its temporal variation in P. lanceolata, where plants experiencing less variable environmental conditions over the last 11 years showed stronger regrowth in reproductive biomass after clipping. Therefore, while mean grazing and mowing intensity may not select for regrowth ability, the temporal stability of the environmental heterogeneity created by land use may have caused its evolution in some species.

The Fate of Bryophyte Sporophytes—Phenology and Vectors of Buxbaumia viridis in the Kalkalpen National Park, Austria

Knowledge about the epixylic moss Buxbaumia viridis has increased significantly due to the monitoring obligation under the Habitats Directive. However, there are still open questions about its dispersal, as the wind plays a limited role in forest ecosystems, and vectors have been suspected but not yet studied systematically for this species. Here, we present data on potential vectors of Buxbaumia viridis collected for the first time with the help of cameras, completed by monitoring the fate of sporophytes during their life cycle in the Limestone Alps National Park in Austria over a period of two years. Young, green sporophytes appeared mainly in autumn, with the highest number in October. Most of them survived winter and spring but did not exceed the age of 14 months. The sharpest decline in capsules occurred in summer when mature, and the lowest number of sporophytes appeared at the end of August. Most likely, mice seem to be responsible for this loss, as the photos from the wildlife cameras suggest, and should be considered both as predators and vectors. Birds should be considered as vectors, too. In summary, most of the reproductive biomass is sacrificed in favor of more effective dispersal, including over longer distances.

Secondary Production

Secondary production is the generation of new heterotrophic biomass and is analogous to net primary production of autotrophs. For an individual, secondary production is equivalent to the growth of new somatic or reproductive biomass over time. For a population, secondary production comprises the total formation of biomass, regardless of its fate, by all individuals within the population over a defined time interval. Some consider secondary production the ultimate measure of population ‘success’ because it incorporates aspects of survivorship, individual growth rate, biomass, development time, and reproduction. Secondary production is often associated with the subfield of ecosystem ecology because it is a flux with dimensions of mass or energy area-2 time-1. This flux is typically estimated with an ecological currency (e.g., joules, carbon, organic matter) that can be compared with other ecosystem processes such as primary production or decomposition. Secondary production estimates are thus useful for placing species, populations, and communities within a broader ecosystem context, and for facilitating the study of energy flows and ecological efficiencies in trophic interactions. The vast majority of secondary production estimates have come from freshwater and marine ecosystems, while there are very few studies in terrestrial ecosystems. In the aquatic studies, although early work was largely focused on fishes, most estimates are for benthic invertebrates; some studies have quantified production of zooplankton, bacteria, and fungi. Early studies of secondary production were focused on methodology and basic comparisons among populations or communities. More recent literature has expanded the application of secondary production toward broader ecological questions related to, for example, energy and chemical flows in food webs, species interaction strengths, and responses to anthropogenic stressors. This bibliography focuses on primary literature that highlights key historic, conceptual, theoretical, and applied papers related to secondary production. Papers highlighted herein are biased toward freshwaters and invertebrates because of their dominance in the literature, but key references that extend to other habitats and taxa are included.

Variation in regrowth ability in relation to land use intensity and predictability in three common grassland herbs

AimsPlant populations in managed grasslands are subject to strong selection exerted by grazing, mowing and fertilization. Many previous studies showed that this can cause evolutionary changes in mean trait values, but little is known about the evolution of adaptive plant phenotypic plasticity in response to grassland management. MethodsWe conducted an outdoor common garden experiment to test if plants from more intensively mown and grazed sites showed an increased ability to regrow after biomass removal. We worked with three common plant species from temperate European grasslands, with seed material from 58 – 68 populations along gradients of land-use intensity, ranging from extensive (only light grazing) to very intensive use (up to four cuts per year). Important findingsIn two species, we found strong population-level variation in regrowth ability of fitness-related traits in response to a clipping treatment, which could reflect adaptation to land-use intensity. While the regrowth ability was unrelated to the land-use intensity of populations of origin, we found a relationship with the predictability of grassland management in P. lanceolata where plants experiencing more stable environmental conditions over the last 11 years showed stronger regrowth in reproductive biomass after clipping. In summary, grazing and mowing intensity apparently did not select for regrowth ability, but in some species, predictable heterogeneous environmental conditions created by land use may have caused its evolution.

Impact of grazing intensities on reproduction patterns of elm trees (Ulmus pumila) in degraded sandy lands in China

The effect of grazing on patterns of reproduction in trees has been little reported. We explored the effects of grazing intensities on reproductive growth, allocation patterns, and duration in elm trees (Ulmus pumila L.) at the Horqin Sandy Land, a degraded area in northern China. Current-year shoots were selected from branches and harvested from individual elm trees subjected to one of four grazing intensities (heavy, moderate, light, and no grazing). Shoots, flower buds, flowers, seeds, leaf buds, and leaves were collected, dried, and weighed. Results showed that the biomass in heavy, moderate and light grazing treatments is significantly higher than in no grazing treatment (P < 0.05). The reproductive allocation of U. pumila in heavy grazing treatment was significantly higher from that in the no grazing treatment (P < 0.05). Additionally, we found that reproduction of U. pumila ended later in grazed plots, suggesting the duration of reproduction is extended with grazing disturbance. Our findings suggest that U. pumila may prolong it s duration of reproduction and alter its reproductive biomass in response to grazing. It is not clear whether these effects are related to damage to U. pumila trees by grazers or whether they are due to grazers affecting soil properties or plant competitors around U. pumila trees.

Phosphorus Application Improves the Cotton Yield by Enhancing Reproductive Organ Biomass and Nutrient Accumulation in Two Cotton Cultivars with Different Phosphorus Sensitivity

Phosphorus (P) plays a pivotal role in cotton by enhancing the reproductive growth and yield formation. Cotton cultivars vary greatly in response to P availability, especially under P-deficient conditions. So, we hypothesized that the increasing P level promotes the reproductive growth in cotton cultivars varying with P sensitivity. For this, two cotton cultivars, Lu-54 (sensitive to low P) and Yuzaomian-9110 (tolerant to low P), in response to three different P levels (P0: 0 (control), P1: 100, and P2: 200 kg P2O5 ha−1) were studied at 39, 52, 69, 83, and 99 days after transplanting during 2017 and 2018. The results revealed that the seed cotton yield was improved in P1 and P2 treatments by 23.9%–34.5% and 30.8%–52.3% in Lu-54, and 16.6%–25.6% and 20.6%–38.5% in Yuzaomian-9110 during 2017 and 2018, respectively. The accumulation of reproductive organ biomass was 21.0%–52.1% and 28.5%–56.8% higher in Lu-54 and 24.2%–56.8% and 34.8%–69.1% higher in Yuzaomian-9110 in P1 and P2 over the control, respectively. During the fast accumulation period, the average accumulation of N, P, K, and biomass across the years in P2 were recorded as 0.75, 0.6, 0.5, and 120.5 kg ha−1 d−1 in Lu-54, while they were 0.65, 0.5, 0.8, and 98.5 kg ha−1 d−1 in Yuzaomian-9110. Overall, a longer period, in terms of reproductive biomass accumulation, was recorded for Yuzaomian-9110 compared with Lu-54 in 2017 and vice versa across the 2018 growing season. The results suggested that increasing P rate improved yield, reproductive organ biomass, as well as nutrient accumulation in both cotton cultivars. However, low P-sensitive cultivar (Lu-54) was more responsive to P application compared with low P-tolerant cultivar.