Climate change may have an impact on the productivity of conifer trees by influencing the morphology (size and surface characteristics) and function (capacity for gas exchange) of conifer needles. In order to test the responses of needles to climatic variables, Douglas fir (Pseudotsuga menziesii [Mirb.] Franco), saplings were grown in sunlit controlled environment chambers at ambient or elevated (+200 parts per million above ambient) CO2 and at ambient or elevated temperature (+4 degrees C above ambient). Needle characteristics, including length, width, area, stomatal density (stomata per mm2), percentage of stomatal occlusion, and the morphology of epicuticular wax, were evaluated. Needle function was evaluated as stomatal conductance to water vapor and transpiration. Needle length increased significantly with elevated temperature but not with elevated CO2. Neither elevated CO2 nor elevated temperature affected stomatal density or stomatal number in these hypostomatous needles. Epicuticular wax was less finely granular at elevated than at ambient temperature and was similar in appearance at elevated and ambient CO2. Stomatal conductance and transpiration increased with elevated temperature and associated increased vapor pressure deficit; however, neither conductance nor transpiration was affected by elevated CO2. These results indicate that simulated climate change influences Douglas fir needle structure and function.

The concept of a common mycorrhizal network implies that the arrangement of plants and mycorrhizal fungi in a community shares properties with other networks. A network is a system of nodes connected by links. Here we apply network theory to mycorrhizas to determine whether the architecture of a potential common mycorrhizal network is random or scale-free. We analyzed mycorrhizal data from an oak woodland from two perspectives: the phytocentric view using trees as nodes and fungi as links and the mycocentric view using fungi as nodes and trees as links. From the phytocentric perspective, the distribution of potential mycorrhizal links, as measured by the number of ectomycorrhizal morphotypes on trees of Quercus garryana, was random with a short tail, implying that all the individuals of this species are more or less equal in linking to fungi in a potential network. From the mycocentric perspective, however, the distribution of plant links to fungi was scale-free, suggesting that certain fungus species may act as hubs with frequent connections to the network. Parallels exist between social networks and mycorrhizas that suggest future lines of study on mycorrhizal networks.

Summary• Nitrogen transfer among plants in a California oak woodland was examined in a pulse-labeling study using 15 N. The study was designed to examine N movement among plants that were mycorrhizal with ectomycorrhizas (EM), arbuscular mycorrhizas (AM), or both.• Isotopically enriched N (K 15 NO 3 -) was applied to gray pine ( Pinus sabiniana ) foliage (donor) and traced to neighboring gray pine, blue oak ( Quercus douglasii ), buckbrush ( Ceanothus cuneatus ) and herbaceous annuals ( Cynosurus echinatus , Torilis arvensis and Trifolium hirtum ).• After 2 wk, needles of 15 N-treated pines and foliage from nearby annuals were similarly enriched, but little 15 N had appeared in nontreated (receiver) pine needles, oak leaves or buckbrush foliage. After 4 wk foliar and root samples from pine, oak, buckbrush and annuals were significantly 15 N-enriched, regardless of the type of mycorrhizal association.• The rate of transfer during the first and second 2-wk periods was similar, and suggests that 15 N could continue to be mobilized over longer times.

No abstract

Plants are teeming with microbial organisms including those that colonize internal tissues as well as those that adhere to external surfaces. In the rhizosphere, the plant-associated microbiome is intricately involved in plant health and serves as a reservoir of additional genes that plants can access when needed. Microbiome regulation of plant trait expression affects plant performance, which in turn influences various ecosystem functions, such as primary productivity and soil health. Understanding these plant- and microbe-driven interactions requires a study of the nature and effects of the plant microbiome. Conceptualizing the microbiome requires a synthesis of microbial ecology, physiology, and bioinformatics, integrated with insight into host biology and ecology. Microbiome structure and function analyses are recognized as essential components to understand the genetic and functional capacity of the host (previously assigned solely to the host) and include vital aspects of metabolism and physiology. Here, as a special section, we present a set of papers that address the complex interactions between plants and root microbiomes in the rhizosphere. This unseen majority spans scales; with its microorganisms numerically dominant in terrestrial ecosystems, the root microbiome is also involved in plant genetics through integral roles in plant trait expression that can effect community composition and ecosystem functions, such as soil health.

Cytochemical staining reactions in pollen grain walls of three species of Compositae, Ambrosia trifida, Artemisia pycnocephala and Gerbera jamesonii, were examined. The intine gives positive reactions for protein and for insoluble polysaccharides including pectic acid, callose and hemicellulose. The exine gives positive reactions for protein and for extractable lipids. In addition the structural material of the exine, sporopollenin, gives positive reactions for aliphatic double bonds and for closely packed anionic sites. Sporopollenin gives negative results to common cytochemical tests for lignin but reacts the same as lignin to metachromatic dyes. Some staining differences between exine-1 and exine-2 were noted.

With global warming and the possible decline of conifers, more habitat may be available to oaks, particularly at higher elevations and more northerly latitudes. Whether oaks expand into new habitats will depend on their ability to disperse and establish at the margins of existing woodlands. Because oaks have a symbiotic relationship with ectomycorrhizal fungi, range expansion requires dispersal of both symbionts: the acorns and the mycorrhizal inoculum. Little is known of this dual dispersal. Here we assess the availability of ectomycorrhizal inoculum as a function of the distance from mature oaks. We examined soil cores for ectomycorrhizal roots and rodent fecal pellets for fungal spores along transects away from mature trees of Quercus garryana Dougl. ex Hook., and planted acorns as bioprobes. We identified spores by microscopy, and mycorrhizas by DNA sequences of the ITS region. Mycorrhizas were present in soil cores 5 m from parent trees, but not beyond. Spores of hypogeous fungi were found in rodent fecal pellets at distances up to 35 m from mature trees. Hypogeous fungi formed ectomycorrhizas with first-year seedlings within the root zone of mature trees and with second-year seedlings beyond the root zone. These data indicate that for seedlings near mature trees, the source of fungal inoculum was the mycorrhizal network of mature trees, and for seedlings beyond that, rodents dispersed the inoculum. We conclude that rodent dispersal of fungal spores promotes seedling establishment away from mycorrhizal networks in Q. garryana.

Differences among flagellated and nonflagellated sperm in land plants are striking, but close examination reveals similarities in pattern of cytoskeleton and in nuclear structure. The microtubular cytoskeleton of flowering plant sperm consists of microtubule bundles arranged obliquely around the nucleus, terminating in cellular extensions. Microtubules are linked into bundles that branch and rejoin along the axis of the sperm cell, forming a cytoskeleton that determines cell shape but does not actively participate in cell movement. Generative cells and sperm share a pattern of microtubules not found in somatic cells. This pattern is initiated in the generative cell, one division before sperm formation, a situation parallel to spermatogenous cell development in vascular plants with flagellated sperm. Chromatin in flagellated and nonflagellated sperm is condensed by specialized histones.