The purpose of this project is to test the hypothesis that the smallest 50% of precipitation events during the monsoon season affect microbial functioning and grassland productivity in mixed grasslands of B.eriopoda and B. gracilis at the SNWR. At the SNWR, the summer monsoon season accounts for 60% of total annual precipitation and drives the majority of vegetation productivity during the year; the largest 25% of precipitation events account for the majority of this precipitation. I predict that important ecological variables such as nutrient and soil moisture availability are disproportionately influenced by smaller events. The proposed project will help tease apart the importance of precipitation event classes on nutrient availability and grassland aboveground net primary production (ANPP). This research will also provide a basis for understanding how increased aridity in the U.S. southwest due to increasing global surface temperature and altered precipitation could affect grassland communities at the SNWR.
We will implement 10 open plots (control) and 10 precipitation exclosure plots(treatment; 20 total plots) at a mixed blue and black grama grassland site at the SNWR. In this experiment, treatment plots will only receive the largest 50% of precipitation events. This will maintain statistically similar total precipitation between control and treatment plots because the smallest 50% of events have an insignificant effect on total seasonal precipitation. How these small events are linked to microbial activity and vegetation productivity is still very much unknown. I predict that soil microbial activity and nutrient availability will differ between control and treatment plots and will result in differing vegetation ANPP between them. These effects may become more distinct as time progresses, which is the reason for conducting this research for a series of monsoon seasons.
Existing precipitation exclosures (2.45 m x 2.45 m) will be employed at the mixed grassland site. We will implement 20 total plots (10 control, 10 treatment; approx. 500 m2 total area). Temporary site infrastructure will include 10 precipitation exclosures, a water tank (1100 gal.) and soil moisture probes. This infrastructure currently exists at the mixed grassland site and will be adopted from Michell Thomey's project entitled, "Soil moisture extremes and soil water dynamics across a semiarid grassland ecotone."
Precipitation is the only independent variable in this experiment. Using precipitation exclosures, I will remove all ambient precipitation from treatment plots from DOY 182-273. Ambient daily precipitation thatexceeds the estimated 50% threshold will be delivered to the plots within 24 hours of an event. Delivered precipitation will be adjusted for atmospheric demand differences.
Dependent variables in this experiment are vegetation ANPP, soil nitrogen content, soil enzymatic activityand soil moisture content. Vegetation biomass will be collected from the sites on DOY 181 and 274. Soil enzymatic activity will be determined approximately 4 times per monsoon season using plot soil samples. Soil nitrogen content will be measured under vegetation using nitrogen probes. Volumetric soil moisture content [m3 m-3] will be measured continuously using soil moisture probes (30 cm depth).
Biological soil crusts (BSCs) are complex assemblages of fungi, lichens, bacteria, mosses and green algae that stabilize surface soils and manage and traffic photosynthate, nutrients and water to diverse microbial and producer communities in arid environments worldwide. In Sevilleta grasslands, BSCs occupy much of the open space between clumps of vegetation and vary substantially in terms of structure.
BSCs have important biological and physical roles. They have been termed ‘mantles of fertility’ because of their general importance in biogeochemical cycling and net primary production in arid ecosystems. It has been proposed that BSCs play a role in the rapid movement of N, C and water from open areas to plants (see below). BSCs stabilize soils, and physical and chemical disturbances of BSCs lead to topsoil loss and dust storms. BSCs are therefore critical components in efforts to understand implications of both climate change and physical disturbance. Related to this, it has been suggested that BSC diversity can be used to inform conservation policies.
BSCs have been the subject of several previous Sevilleta LTER studies. Green et al. showed that stable-isotope carbon and nitrogen could be transferred bi-directionally between BSCs and adjacent plants. This led Collins et al. to propose that fungal hyphae provide connections between plant roots and BSCs that allow for transport between the two, a proposal known as the “fungal loop hypothesis.” Porras-Alfaro et al. have surveyed the diversity of fungi in BSCs from Sevilleta grasslands using molecular methods. We have also shown that thermophilic fungi are common in BSCs (unpublished results), a result that is not unexpected given the high summer temperatures attained in Sevilleta surface soils. Yet, many questions remain regarding the organisms present in BSCs, their biological roles and how long it takes for BSCs to re-establish after disturbance. Long-term, we are interested in the types of fungi present in BSCs and in how fungi function in transporting nutrients between BSCs and adjacent plants. We are also interested in the extent to which specific fungi provide structure to BSCs and in how they help protect from stress agents such as desiccation. We are interested in the extent to which fungi might help BSCs tolerate high summer soil temperatures, which often reach ≥ 60C. We therefore have a special interest in thermophilic fungi present in the BSCs. To date, little has been done to actually culture fungi from Sevilleta BSCs, hence the need for the current study.
In summary, BSCs are one of the most important features of aridland ecosystems and form a critical interface between physical and biological domains. Understanding the roles of BSCs in protecting soil structure, and in the cycling of carbon, water and nitrogen, is fundamental to aridland ecology. The work proposed here continues efforts to characterize the specific fungi associated with Sevilleta BSCs. It is a modest but important step toward addressing the long-term goals mentioned above.
For each sampling site and sampling period a small amount of surface crust (approx. one teaspoon per sample) was taken from each of 10 locations at approximately 1 meter intervals across a transect. Samples were transported back to the laboratory in plastic bags.
On rare occasions, a larger sample of 0.5 liter volume or less may have been removed at one or two sampling stations.
Data was collected at: LTER PJ site (N 34 23’ 08.7” W 106 31’ 27.0”), a sand dune above the railroad tracks near the Sevilleta wetlands (N34 18' 06.5" W106 51' 14.1"), gypsum outcroppings (N34 12' 40.5" W106 45' 35.5"), grasslands near the Sev LTER warming and monsoon sites (N34 21' 34.3" W106 41' 29.4" and N34 20' 38.1" W106 43' 34.5"), and the Rio Grande Bosque (N34 19'45" W106 51'40").
Plant phenology or life-history pattern changes seasonally as plants grow, mature, flower, and produce fruit and seeds. Plant phenology follows seasonal patterns, yet annual variation may occur due to annual differences in the timing of rainfall and ambient temperature shifts. Foliage growth and fruit and seed production are important aspects of plant population dynamics and food resource availability for animals.
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