carbon, nitrogen, and micronutrients
We designed a study to examine the long-term spatial and temporal patterns of mass loss, changes in nitrogen content and chemical composition during decomposition of roots in a desert watershed.
Because nitrogen availability has been hypothesized to affect decomposition rates of buried litter in deserts, we studied decomposition of roots along a transect on a desert watershed that had been fertilized with ammonium nitrate and compared these results with the decomposition of roots along a transect that had not been fertilized.
Soils were collected from LTER I transects and analyzed for various characteristics including particle size, cations, moisture content, total nitrogen and PO4-P.
Transects pass across different vegetation zones of the Jornada Basin.
In the spring of 1982, as part of the establishment of the Jornada Long-Term Ecological Research site in southern New Mexico, a 135 ha portion of a 1500 ha, internally drained, watershed was exclos
ed from grazing by domestic livestock. Prior to exclosure the watershed, as well as the rest of the Jornada basin, had been moderately to heavily grazed for the past 100 years. Concurrent with grazing, the vegetation had undergone a dramatic change from desert grassland, with an almost continuous cover of C4 perennial grasses, to isolated patches of the original grassland in a mosaic with desert shrub dominated plant communities (Buffington and Herbel, 1965).
The exclosure lies along a northeast facing piedmont slope at the base of a steep isolated mountain peak, and covers a variety of component landforms from the foot of the mountain to the basin floor. The northeast side of the exclosure is immediately upslope of the College Playa located near the NMSU College Ranch.
Three parallel transects (2.7 km in length) run from the middle of the College Playa up into the foot of Mt. Summerford. The Control transect is to the west, the Treatment transect on the east side of the Control transect, and the Alternate Control to the east of the Treatment transect. Each transect is 30 meters wide with a 45 meter buffer zone between each transect. The Treatment transect was treated annually until 1987 with NHNO3 in a concentration equal to 10g N/m2. The station markers at 30 meter intervals along each transect. Perpendicular to each transect and crossing at each station marker is the 30 meter plant line intercept transect. This extends 15 meters on either side of the station marker. The ends of the plant line intercept transect are marker by short rebar sticking up about 6 inches aboveground. The plant line intercept transects are thus perpendicular to the direction of major drainage flow.
The litter fall traps are in the creosotebush zone on the upper bajada betwen the College Playa and Mt. Summerford. LTER-I Control transect, between Station C61 and C62 LTER-I Treatment transect, between Station T60 and T62
Litter is collected monthly using a CarVac vacuum run off of a rechargeable 12v battery. There are 10 30 cm2 aluminum screen baskets elevated on 3/8" rebar situated under creosote shrubs on each transect. Dry weight of total creosote litterfall per basket is recorded as well as leaf, stem, and seed fractions.
In the Chihuahuan Desert of southern New Mexico, mesquite occurs in a variety of landscape populations where water may accumulate: at depth from channeling and concentration of water into low-lying
areas (playas and arroyos); in high infiltration soils which permit deep infiltration and limit evaporation (dunes); and, as scattered individuals expanding into former grasslands where rooting is limited to the depth of infiltration of incident rainfall. We hypothesized that Prosopis glandulosa growing in these systems would vary considerably in root distribution and maximum rooting depth. The creosote system was expected to be more shallow rooted, and unlike mesquite, the community has been well characterized. The objective of these studies was to examine nematode, microarthropod, micronutrient, and nutrient concentrations at deep and surface soils in the different mesquite communties.
Recent studies suggest that rhizosphere soil microarthropods may have a major role in determining soil nitrogen availability.
Desert soil microarthropods are consumers of soil bacteria, fungi, and nematodes, thus they accelerate mineralization processes by causing turnover in immobilized nitrogen. [It is] hypothesized that changing densities of soil microarthropods would result in changes in nitrogen availability. In order to test this hypothesis, Erionueron pulchellum rhizosphere soil samples were taken monthly from control plots, plots irrigated with 6mm/wk, plots soaked with chlordane (to remove microarthropods), and plots treated with chlordane that were irrigated with 6 mm/wk. These samples were analyzed for available inorganic nitrogen (NO3 and NH4), gravimetric soil moisture, plant shoot and root biomass, plant shoot and root total nitrogen, plant growth, microarthropod and nematode densities.
Soil samples collected 5/12 and 5/13/86 to survey N availability in a variety of grassland and mesquite habitats.
Objective is development of hypotheses about desertification processes that degrade grassland into mesquite dominated ecosystems.
Three parallel transects (2.7 km in length) run from the middle of the College Playa up into the foot of Mt. Summerford. The Control transect is to the west, the Treatment transect on the east side of the Control transect, and the Alternate Control to the east of the Treatment transect. Each transect is 30 meters wide with a 45 meter buffer zone between each transect. The Treatment transect was treated annually until 1987 with NHNO3 in a concentration equal to 10g N/m2. The station markers at 30 meter intervals along each transect.
NO3 + NO2-N and NH4-N levels of soil samples collected at each station along transect. Moisture content of soil samples is also included.
Data for Jornada LTERII termite bait weight loss. Toilet paper roll termite baits are placed on grids on each consumer plot.
Data include initial bait weights and bait weights after baits have been retrieved from the field once each year. Weight loss is calculated as a measure of termite foraging activity.
Soil nutrient distribution in NPP quads in the Mesquite, Grassland, Playa, Creosotebush, and Tarbush plant communities sampled at 3 spatial scales of grids.
Soils were sampled from the NPP (biomass plots). Each of the five vegetation types (mesquite, grassland, playa, creosote, tarbush) had three sites (with low, medium, and high production levels). At 14 of 15 sites a grid of 70 by 70 meters was set out. Within this 49 plots of 10 by 10 meters were placed and labeled (numbered) in serpentine design. At the 15th site, Playa College, 48 plots of 10 by 10 meters were laid out in three long rows of 16 plots per row. At all sites the soil sample of 0-10 cm depth was taken 1 meter from the NE marker bar at a diagonal (heading toward the SW marker). At one of each of the five vegetation types another set of 49 soils (#101-149) was taken from within one of the 10 by 10 meter plots. Using a 7 by 7 meter grid (bounded by the southern east-west boundary line and the western north-south boundary line[#149 is in the SW corner]) soils were sampled 1 meter apart using a serpentine design.
Location: Northern Chihuahuan Desert 37 kilometers N of Las Cruces, New Mexico on the NMSU College Ranch and the USDA Jornada Exp. Range.
Climate: Characterized by an abundance of sunshine, a wide range between day and night temperatures, low relative humidity, an evapotranspiration rate averaging 229 cm per year, and extremely variable precipitation. The average annual precipitation is 230 mm, with 52% occurring during the summer. Droughts are recurrent climatic phenomenon. Vegetation: We are studying 5 vegetation communities that are dominant on the Jornada and are hypothesized to differ in their degree of desertification: 1) remnant black grama (Bouteloua eriopoda) grasslands; 2) playas or low-lying areas with heavy soils ( which are periodically flooded) and dominated by tobosa (Hilaria mutica) and burrograss (Scleropogon brevifolius); 3) tarbush stands (Flourencia cernua); 4) mesquite dunes (Prosopis glandulosa); 5) creosotebush-dominated bajadas (Larrea tridentata). For each community type, three permanent plots representing a range of primary productivity have been established to examine patterns of NPP, soil moisture, plant nutrients as a function of climatic variation.