José Herrera

Novel Root Fungal Consortium Associated with a Dominant Desert Grass

ABSTRACT The broad distribution and high colonization rates of plant roots by a variety of endophytic fungi suggest that these symbionts have an important role in the function of ecosystems. Semiarid and arid lands cover more than one-third of the terrestrial ecosystems on Earth. However, a limited number of studies have been conducted to characterize root-associated fungal communities in semiarid grasslands. We conducted a study of the fungal community associated with the roots of a dominant grass, Bouteloua gracilis, at the Sevilleta National Wildlife Refuge in New Mexico. Internal transcribed spacer ribosomal DNA sequences from roots collected in May 2005, October 2005, and January 2006 were amplified using fungal-specific primers, and a total of 630 sequences were obtained, 69% of which were novel (less than 97% similarity with respect to sequences in the NCBI database). B. gracilis roots were colonized by at least 10 different orders, including endophytic, coprophilous, mycorrhizal, saprophytic, and plant pathogenic fungi. A total of 51 operational taxonomic units (OTUs) were found, and diversity estimators did not show saturation. Despite the high diversity found within B. gracilis roots, the root-associated fungal community is dominated by a novel group of dark septate fungi (DSF) within the order Pleosporales. Microscopic analysis confirmed that B. gracilis roots are highly colonized by DSF. Other common orders colonizing the roots included Sordariales, Xylariales, and Agaricales. By contributing to drought tolerance and nutrient acquisition, DSF may be integral to the function of arid ecosystems.

Diversity and distribution of soil fungal communities in a semiarid grassland

The fungal loop model of semiarid ecosystems integrates microtopographic structures and pulse dynamics with key microbial processes. However limited data exist about the composition and structure of fungal communities in these ecosystems. The goal of this study was to characterize diversity and structure of soil fungal communities in a semiarid grassland. The effect of long-term nitrogen fertilization on fungi also was evaluated. Samples of rhizosphere (soil surrounding plant roots) and biological soil crust (BSC) were collected in central New Mexico, USA. DNA was amplified from the samples with fungal specific primers. Twelve clone libraries were generated with a total of 307 (78 operational taxonomic units, OTUs) and 324 sequences (67 OTUs) for BSC and rhizosphere respectively. Approximately 40% of soil OTUs were considered novel (less than 97% identity when compared to other sequences in NCBI using BLAST). The dominant organisms were dark-septate (melanized fungi) ascomycetes belonging to Pleosporales. Effects of N enrichment on fungi were not evident at the community level; however the abundance of unique sequences, sampling intensity and temporal variations may be uncovering the effect of N in composition and diversity of fungal communities. The fungal communities of rhizosphere soil and BSC overlapped substantially in composition, with a Jaccard abundance similarity index of 0.75. Further analyses are required to explore possible functions of the dominant species colonizing zones of semiarid grassland soils.

Effect of long-term nitrogen fertilization on mycorrhizal fungi associated with a dominant grass in a semiarid grassland

We studied the diversity of arbuscular mycorrhizal fungi (AMF) in semiarid grassland and the effect of long-term nitrogen (N) fertilization on this fungal community. Root samples of Bouteloua gracilis were collected at the Sevilleta National Wildlife Refuge (New Mexico, USA) from control and N-amended plots that have been fertilized since 1995. Small subunit rDNA was amplified using AMF specific primers NS31 and AM1. The diversity of AMF was low in comparison with other ecosystems, only seven operational taxonomic units (OTU) were found in B. gracilis and all belong to the genus Glomus. The dominant OTU was closely related to the ubiquitous G. intraradices/G. fasciculatum group. N-amended plots showed a reduction in the abundance of the dominant OTU and an increase in AMF diversity. The greater AMF diversity in roots from N-amended plots may have been the result of displacement of the dominant OTU, which facilitated detection of uncommon AMF. The long-term implications of AMF responses to N enrichment for plant carbon allocation and plant community structure remain unclear.

Shifting fungal endophyte communities colonize Bouteloua gracilis: effect of host tissue and geographical distribution.

Communities of root-associated fungi (RAF) commonly have been studied under the auspices of arbuscular mycorrhizal fungi (AMF) or ectomycorrhizal fungi. However many studies now indicate that other groups of endophytic RAF, including dark septate endophytes (DSE) are more abundant in some plants and environments. The common forage grass, Bouteloua gracilis, was used as a model to examine whether RAF also colonize different organs within the same plant and to compare RAF communities from sites across North America, spanning the latitudinal range of B. gracilis (from Canada to Mexico). We compared the RAF communities of organs within individual plants at one site and within plant roots among six sites. With the possible exception of one group related to genus Paraphaeosphaeria there was little evidence that RAF colonized vertically beyond the crowns. Furthermore, although there was some variation in the constitution of rare members of the RAF communities, several taxonomically related groups dominated the RAF community at all sites. These dominant taxa included members in the Pleosporales (related to the DSE, Paraphaeosphaeria spp.), Agaricales (related to Moniliophthora spp., or Campanella spp.) and Hypocreales (related to Fusarium spp.). AMF were notable by their near absence. Similar phylotypes from the dominant groups clustered around adjacent sites so that similarity of the RAF communities was negatively correlated to site inter-distance and the RAF communities appeared to group by country. These results increase the possibility that at least some of these common and widely distributed core members of the RAF community form important, intimate and long lasting relationships with grasses.

Molecular characterization of coprophilous fungal communities reveals sequences related to root-associated fungal endophytes.

This paper reports the use of molecular methods to characterize the coprophilous fungal communities (CFC) that inhabit the dung of four species of mammalian herbivores at two sites, Sevilleta National Wildlife Refuge (SNWR) in New Mexico and Wind Cave National Park (WCNP) in South Dakota. Results reveal that CFC from domesticated cattle (Bos taurus) at SNWR, and bison (Bison bison) and black-tailed prairie dogs (Cynomys ludovicianus) at WCNP were diverse but dominated primarily by members within eight taxonomic orders, including the rarely cultured and anaerobic order Neocallimastigales. In addition, 7.7% (138 of 1,788) of the sequences obtained from all dung samples were at least 97% similar to root-associated fungal (RAF) sequences previously described from blue grama (Bouteloua gracilis), a common forage grass found throughout North America and growing at both study sites. In contrast, 95.8% (295 of 308) of the sequences and four of the total seven operational taxonomic units obtained from pronghorn antelope (Antilocapra americana) dung belonged to the Pleosporalean order. We hypothesize that some herbivore vectors disperse non-systemic (non-clavicipitaceous) fungal endophytes. These dispersal events, it is argued, are most likely to occur via herbivores that occasionally forage and masticate root tissue, especially in arid regions where aboveground vegetation is sparse. The results of this study suggest that some (possibly many) members of the RAF community can expand their ecological role to include colonizing dung.

Precipitation increases the abundance of some groups of root‐associated fungal endophytes in a semiarid grassland

Diverse communities of Root-Associated Fungal (RAF) species, including Dark Septate Endophytes (DSE), inhabit grasses in semiarid soils. These aridlands are often distinguished by large but variable precipitation events (monsoons). We sought to compare the composition and fungal load of the RAF community inhabiting the roots of Sporobolus cryptandrus, a dominant forage grass, exposed to variable precipitation events. We used a rainfall manipulation experiment at the Sevilleta National Wildlife Refuge (SNWR) to examine the abundance and composition of the RAF communities using molecular and microscopic techniques. Molecular data reveals that the RAF communities are dominated by Ascomycetes and few sequences were related to Arbuscular Mycorrhizal Fungi (AMF). The most dominant group (Paraphaeosphaeria spp.) clearly increased in abundance in response to water amendments and the addition of similar volumes of water appeared to increase similarity among the RAF communities, irrespective of size and distribution of precipitation events. Microscopic examinations of the roots also revealed an increased fungal load when exposed to elevated moisture, irrespective of rainfall frequency. We suggest that the increase in these cosmopolitan and abundant groups of Ascomycete fungi, in part, represents a common but complicated strategy of water translocation in a variety of soil types, similar to that proposed and shown in the arbuscular mycorrhizal fungi (AMF). Additional work should examine whether many (or most) members of the Ascomycete RAF also can facultatively broker water in the larger biological network in the soil.

Assessment of fungal growth on sodium polyborate-treated cellulose insulation

Cellulose insulation has rapidly gained a large market share among general contractors and homeowners. Recent interest regarding health effects of high concentrations of fungi within indoor environments (building-related illnesses or sick building syndrome) has promoted concern about susceptibility of building materials, including wood products (in general) and cellulose insulation (specifically), to fungal attack. This study reports an assessment of fungal growth on cellulose insulation made from recycled paper and treated with varying concentrations of sodium polyborate within half-scale wall units exposed to variable and high ambient temperatures and relative humidities throughout the summer. Boron-treated and untreated (control) cellulose insulation within the wall units were challenged with a suspension containing high concentrations of spores of five fungal species commonly found in indoor environments. Our results suggest that cellulose insulation treated with sodium polyborate (a) precludes the growth of the five common fungal species; (b) harbors fewer fungal species before and after being challenged with the fungal spore suspension; and (c) is likely having a cytotoxic or sporocidal effect on many, if not all, fungal species. These results suggest that cellulose insulation treated with sodium polyborate, when properly applied and installed, precludes fungal growth for at least 124 days at high temperatures and relative humidities.

STACKING OF SEEDS CHANGES SPOILAGE DYNAMICS OF FOOD CACHES OF THE BANNER-TAILED KANGAROO RAT (DIPODOMYS SPECTABILIS)

Abstract We report a previously undescribed seed-storing behavior of banner-tailed kangaroo rats (Dipodomys spectabilis) that reduces losses to microbes. D. spectabilis cuts upper stems of the grass Sporobolus cryptandrus into 3- to 5-cm sections that we refer to as seed stems. Seeds within these seed stems remain attached to their rachis and are protected by an enveloping leaf. Most seed stems are bundled together tightly in packs of about 50 to several hundred individual stems and jammed vertically into cul-de-sacs excavated in the walls of their burrows. This behavior reduces rate of infection of seeds by fungi and also may reduce number of seeds pilfered by arthropods. Furthermore, compared with seeds of S. cryptandrus housed in middle sections of seed stems, those housed in the ends had a higher rate of infection. Simulated seed stems of wheat straw containing seeds of white millet (Panicum miliaceum) had a lower rate of infection and fewer species of fungi than seeds only protected by wire mesh. Seeds closer to the top of the simulated seed stems were more likely to be infected and had more species of fungi. Community structure and dynamics of microfungi also appeared affected by the protective layering of seed stems. We suggest that D. spectabilis manages the structure, and perhaps dynamics, of communities of microbes within their food caches by modifying position, location, or organization of food items.