Resilience or degradation of Patagonian wetland soils: Soil structure and organic matter under contrasting land-use intensities.

How land-use intensity (LUI) affects soil structure-dependent functions and organic matter (OM) quality in Patagonian wetland soils (Vegas) of southern Chile is an intriguing question. These wetland soils, which store large amounts OM and regulate water and nutrient fluxes, are increasingly exposed to  intensification. While degradation of peatlands under drainage and conversion to agricultural activities is well documented, the long-term effects of contrasting LUI under intensification of livestock systems and peat extraction in southern Patagonia remain poorly understood. Research was conducted along a west–east climatic and aridity gradient in the Magallanes Region Chile. Four pairs of Vegas with contrasting LUI, low-and-high-intensity use of livestock and peat extraction sites were selected, spanning Histosols and Gleysols, including sedge meadows and Sphagnum peatlands. At each site, environmental conditions, vegetation inventory, and livestock management (stocking rate and density) were characterized. Soil structure-dependent functions were quantified from undisturbed cores collected at the surface horizon (5 cm) and the last horizon (~ 70 cm) before the appearance of glacial material or the water table. The water retention and shrinkage curves were measured, and from this, the bulk density (BD), air capacity (AC), plant available water (PAW), coefficient of linear extensibility (COLE), air permeability (Ka) were derived. The saturated hydraulic conductivity (ks), and anisotropy of air and water flows were quantified. The total and dissolved organic carbon and nitrogen (TC, TOC, IC, DOC, TN, TIN and TON), stable isotopes (¹³C, ¹⁵N), and ATR-FTIR spectroscopy. Most Vegas showed high OC (3,69-44%) with very high porosity (>80%), high shrinkage capacity, and strong deformation due to soil drying (COLE> 0.09), particularly in Histosols. and ks decrease with depth, especially in Sphagnum peatlands due to the OM decomposition and pore-size reduction. A soil structural shrinkage phase normally is presence, being often a residual and zero-shrinkage phases absent under low LIU.  Anisotropy in fluid conduction was sporadic and more pronounced in the Gleysolic sites. OM quality varied strongly in the top and depth soils across sites. Sphagnum peatlands had the highest C:N ratios and high FTIR signatures of recalcitrant organic compounds, whereas sedge-dominated Vegas showed more similar spectral patterns. Depth profile declines in C:N and shifts in ¹³C and ¹⁵N abundances showing progressive OM decomposition and N enrichment. Unexpectedly, we found that high LUI did not deteriorate the structure-dependent functions. In several cases, more intensive but better managed systems displayed higher porosity, greater ks and Ka, and well-developed structural shrinkage phases. However, peat extraction in Sphagnum systems clearly damaged structural integrity. Results indicate that LUI effects are context dependent and that both low-intensity and over grazing for livestock production can be detrimental. A high LUI did not result in a marked deterioration of structure dependent soil functions, instead, it revealed a continuum of responses across the study sites. Recovery in structure-dependent soil functions were primarily associated with increased organic matter content, accompanied by a relative enhancement in organic matter quality. This implies that low land use intensity can be just as harmful without proper utilization and controlled use of natural resources.