Rock Outcrops Redistribute Organic Carbon and Nutrients to Nearby Soil Patches in Three Karst Ecosystems in SW China

<div><p>Emergent rock outcrops are common in terrestrial ecosystems. However, little research has been conducted regarding their surface function in redistributing organic carbon and nutrient fluxes to soils nearby. Water that fell on and ran off 10 individual rock outcrops was collected in three 100 × 100 m plots within a rock desertification ecosystem, an anthropogenic forest ecosystem, and a secondary forest ecosystem between June 2013 and June 2014 in Shilin, SW China. The concentrations of total organic carbon (TOC), total nitrogen (N), total phosphorus (P), and potassium (K) in the water samples were determined during three seasons, and the total amounts received by and flowing out from the outcrops were calculated. In all three ecosystems, TOC and N, P, and K were found throughout the year in both the water received by and delivered to nearby soil patches. Their concentrations and amounts were generally greater in forested ecosystems than in the rock desertification ecosystem. When rock outcrops constituted a high percentage (≥ 30%) of the ground surface, the annual export of rock outcrop runoff contributed a large amount of organic carbon and N, P, and K nutrients to soil patches nearby by comparison to the amount soil patches received via atmospheric deposition. These contributions may increase the spatial heterogeneity of soil fertility within patches, as rock outcrops of different sizes, morphologies, and emergence ratios may surround each soil patch.</p></div

Organic carbon and nutrient concentrations (mean ± standard error) in input water.

<p>RDE, AFE, SFE are as defined in the text. Different lowercase letters indicate significant differences between two systems (<i>P</i><0.05); different uppercase letters indicate significant differences between two seasons (<i>P</i><0.05) in the same ecosystem.</p

The comparison of probiotics during the period of experiment.

<p>a, <i>Bifidobacteria</i>; b, <i>Lactobacilli</i>. Data with asterisk were significantly different (<i>p</i><0.05).</p

Cd content in blood, liver, kidney and colon of mice during the period of experiment.

<p>Data were mean±SD.</p

General features of the sampled outcrops and the tree canopy coverage.

<p>General features of the sampled outcrops and the tree canopy coverage.</p

Summary of collection time, volume, number, and chemical analyses for samples.

<p>Summary of collection time, volume, number, and chemical analyses for samples.</p

Estimated ratios of TOC and nutrients received annually from rock runoff water to those received from atmospheric deposition by soil patches with different outcrop to soil area ratios (R/S) in the three ecosystems.

<p>Estimated ratios of TOC and nutrients received annually from rock runoff water to those received from atmospheric deposition by soil patches with different outcrop to soil area ratios (R/S) in the three ecosystems.</p

Comparison of the diameter of the colony between control and Cd treatments during the period of incubation.

<p>Comparison of the diameter of the colony between control and Cd treatments during the period of incubation.</p

(a) Collection systems for rock runoff water; (b) collection systems for input water falling on rock surface; (c) determination of rock projected area, and (d) sampling of epiliths.

<p>(a) Collection systems for rock runoff water; (b) collection systems for input water falling on rock surface; (c) determination of rock projected area, and (d) sampling of epiliths.</p

Ratios of the annual input of total organic carbon (TOC) and nutrients per m² of rock projected area (<i>INP</i>) to those of the epiliths pool (<i>POOL</i>), ratios of annual runoff exportation of TOC, and nutrients per m² of rock projected area (<i>EXP</i>) to those of the annual input (<i>INP</i>) for the three ecosystems.

<p>Ratios of the annual input of total organic carbon (TOC) and nutrients per m² of rock projected area (<i>INP</i>) to those of the epiliths pool (<i>POOL</i>), ratios of annual runoff exportation of TOC, and nutrients per m² of rock projected area (<i>EXP</i>) to those of the annual input (<i>INP</i>) for the three ecosystems.</p