Data_Sheet_1_Afforestation With Different Tree Species Causes a Divergent Evolution of Soil Profiles and Properties.PDF

Land-use change and specifically a change in the type of vegetation cover affects soil morphology, chemistry, biology, and nutrient regimes. Numerous studies have documented that in land-use conversions from agricultural land to forest, or from plantations to restored natural savanna most soil attributes and functions undergo changes. The purpose of the present study was to evaluate the changes brought about by afforestation of degraded croplands and to understand the impact of forest vegetation on soil evolution in a semiarid region where soils originally co-evolved with a savanna biotope. We used long-term experiments (>40 years) of five tree species: Pinus halepensis (PH), Pinus halepensis inoculated with ecto-mycorrhiza at planting (PM), Pinus pinea (PP), Eucalyptus spp. (E), and Gleditsia triacanthos (G) and compared these to an agricultural soil (A) at the same site near Santa Rosa, La Pampa in the semiarid center of Argentina. Soil profiles were described, and samples taken for chemical and physical analyses of soil properties [organic matter (OM), pH, cation exchange capacity (CEC) and exchangeable cations, particle size distribution (texture), aggregate stability (MWD), bulk density (BD), porosity (TP), and water holding capacity (WHC)]. We found a strong effect of tree species on soil profile morphology, even taxonomy, and on all studied variables. PM and G had highest OM, CEC, neutral pH, higher TP, WHC, while PH, PP, and E had acid pH, lower base saturation, OM, TP, and WHC. The effect of tree species on the soil profile was noticeable a depth of about 40 cm, comprising the A and AC, but not the C horizons. The results showed that to obtain reasonable results of OM sequestration under forest systems, tree species should be chosen to include legumes to improve C/N stoichiometry for C fixation, or inoculation with mycorrhiza to promote microbial transformation of forest litter.

土地利用变化，尤其是植被覆盖类型的转变，会对土壤形态、化学特性、生物学属性及养分状况产生影响。已有大量研究证实，在农田转为林地，或是人工林转为恢复型天然稀树草原（savanna）的土地利用转换过程中，多数土壤属性与功能均会发生改变。本研究旨在评估退化农田造林所引发的土壤变化，并阐明在半干旱区域中，森林植被对土壤演化的影响——该区域的土壤原本与稀树草原生境（savanna biotope）协同演化。研究采用了5个树种的长期定位试验（时长超40年）：阿勒颇松（Pinus halepensis, PH）、种植时接种外生菌根（ecto-mycorrhiza）的阿勒颇松（Pinus halepensis inoculated with ecto-mycorrhiza at planting, PM）、意大利石松（Pinus pinea, PP）、桉属植物（Eucalyptus spp., E）以及美洲皂荚（Gleditsia triacanthos, G），并以阿根廷拉潘帕省半干旱中部圣罗莎附近同点位的农田土壤（A）作为对照。研究人员对土壤剖面进行了描述，并采集土壤样品以分析其理化性质，包括有机质（organic matter, OM）、pH值、阳离子交换量（cation exchange capacity, CEC）与交换性阳离子、粒径分布（质地）、团聚体稳定性（mean weight diameter, MWD）、容重（bulk density, BD）、总孔隙度（total porosity, TP）以及持水量（water holding capacity, WHC）。研究发现，树种对土壤剖面形态、甚至土壤分类，以及所有被测变量均存在显著影响。其中，PM与G组的有机质、阳离子交换量、中性pH值、总孔隙度及持水量均处于较高水平；而PH、PP与E组则呈现酸性pH、较低的盐基饱和度、有机质含量、总孔隙度与持水量。树种对土壤剖面的影响在约40cm深度范围内（包含A层与AC层）较为显著，但未影响C层。研究结果表明，若要在森林生态系统中实现有效的有机质固存（OM sequestration），应优先选择豆科树种以优化碳氮化学计量比（C/N stoichiometry），助力碳固定；或是接种菌根（mycorrhiza），以促进森林凋落物的微生物转化过程。