Table 1.
Environmental and soil characteristics of the upper and lower sites on Rattlesnake Mountain, Washington, USA.
Environmental data include long-term mean annual temperature (MAT) and precipitation (MAP) based on both older [63] and recent (unpublished weather station data) sources; this climatic regime has been broadly stable for the last 3000–5000 years [64]. Soil values are 0–5 cm means±s.d. of the ‘native’ cores sampled from upper and lower sites (N = 24). Bulk density, carbon and nitrogen, particulate organic matter (POM) C, and POM N all differed significantly (P<0.001) between the lower and upper sites. Soil cores were taken from areas of the two sites dominated by Poa spp.
Fig 1.
Daily air temperature cycle (a) and density plot (showing normalized distribution of data) of core soil moisture status (b), by incubation chamber, over the 100-day incubation. The two chambers mimicked the lower and upper sites, respectively, on Rattlesnake Mountain.
Fig 2.
Soil respiration (F) as a function of temperature, by core origin and location over the 17-year transplant experiment.
Cores originally from the lower site (panels a, b) respired less than those originally from the upper site (c, d). Values for respiration at 20°C (F20, mg C kg soil-1 day-1) and Q10 are also given with SEs, based on combined data from both incubation treatments. Curves and shaded error regions are the Q10-style models with parameters given in each panel.
Table 2.
Summary of the linear model of soil core respiration.
Terms include parameter estimate based on type III sum of squares, standard error (SE), t-value, and P-values. Effects include core location (1994–2012 experiment, Upper or Lower), core source (pre-1994 location, Upper or Lower site; cf. Table 1), core type (Native or Transplant), water content (WC, percent, gravimetric), relative air temperature (Trel, i.e. normalized against each incubation chamber’s mean temperature), and chamber (simulating conditions for the Upper or Lower site). A colon denotes an interaction between the main effects above. For example, the “LocationUpper” value means that cores that spent 17 years at the upper site exhibited a flux rate 0.311 log(mg C kg-1 soil day-1) lower than cores transplanted to the lower site, after all other factors are considered. The dependent model variable F has units of mg C kg-1 soil day-1 and was log-transformed prior to modeling. The model had an overall Akaike’s Information Criterion of 1809 and Schwarz's Bayesian criterion of 1861.
Table 3.
Activities of β-glucosidase and N-acetyl-β-D-glucosaminidase in soils from the Rattlesnake Mountain transplant experiment.
Soil codes are lower site native (LN), lower control (LC), lower-to-upper transplant (LU), upper native (UN), upper control (UC), and upper-to-lower transplant (UL). Significant differences (labeled as “a”, “b”, etc.) between soils within depths (based on Turkey’s HSD) were only detected in the 0–5 cm depths; values followed by the same letter are not significantly different. Units are μmol MUB g-1 soil h-1 for both enzymes.
Fig 3.
Non-metric multidimensional scaling plot of Morisita-Horn indices (showing dissimilarity in bacterial community structure) for the incubated soils.
Red markers indicate soils whose pre-1994 location was the lower site (cf. Table 1), and green markers the upper site. Squares are native soils, triangles are within-site transplant controls, and open circles are the reciprocally transplanted soils. Thus the red open circles represent the soils transplanted from the lower to the upper site, and the green open circles represent the soils transplanted from the upper to the lower site. Soils were incubated in environmental chambers simulating (a) lower or (b) upper site conditions.