Eclesia Roxana P, Jobbagy Esteban G, Jackson Robert B, Biganzoli Fernando, Piñeiro Gervasio
Estación Experimental Agropecuaria INTA Cerro Azul, Misiones, Argentina.
IFEVA/Facultad de Agronomía, Universidad de Buenos Aires/CONICET, Buenos Aires, Argentina.
Glob Chang Biol. 2012 Oct;18(10):3237-3251. doi: 10.1111/j.1365-2486.2012.02761.x. Epub 2012 Jul 24.
The replacement of native vegetation by pastures or tree plantations is increasing worldwide. Contradictory effects of these land use transitions on the direction of changes in soil organic carbon (SOC) stocks, quality, and vertical distribution have been reported, which could be explained by the characteristics of the new or prior vegetation, time since vegetation replacement, and environmental conditions. We used a series of paired-field experiments and a literature synthesis to evaluate how these factors affect SOC contents in transitions between tree- and grass-dominated (grazed) ecosystems in South America. Both our field and literature approaches showed that SOC changes (0-20 cm of depth) were independent of the initial native vegetation (forest, grassland, or savanna) but strongly dependent on the characteristics of the new vegetation (tree plantations or pastures), its age, and precipitation. Pasture establishment increased SOC contents across all our precipitation gradient and C gains were greater as pastures aged. In contrast, tree plantations increased SOC stocks in arid sites but decreased them in humid ones. However, SOC losses in humid sites were counterbalanced by the effect of plantation age, as plantations increased their SOC stocks as plantations aged. A multiple regression model including age and precipitation explained more than 50% (p < 0.01) of SOC changes observed after sowing pastures or planting trees. The only clear shift observed in the vertical distribution of SOC occurred when pastures replaced native forests, with SOC gains in the surface soil but losses at greater depths. The changes in SOC stocks occurred mainly in the silt+clay soil size fraction (MAOM), while SOC stocks in labile (POM) fraction remained relatively constant. Our results can be considered in designing strategies to increase SOC storage and soil fertility and highlight the importance of precipitation, soil depth, and age in determining SOC changes across a range of environments and land-use transitions.
全球范围内，牧场或人工林取代原生植被的现象日益增多。据报道，这些土地利用转变对土壤有机碳（SOC）储量、质量和垂直分布变化方向具有相互矛盾的影响，这可以通过新植被或原有植被的特征、植被取代后的时间以及环境条件来解释。我们采用了一系列配对田间试验和文献综述，以评估这些因素如何影响南美洲树木和草地（放牧）主导生态系统之间转变过程中的SOC含量。我们的田间试验和文献研究方法均表明，SOC变化（0 - 20厘米深度）与初始原生植被（森林、草地或稀树草原）无关，但强烈依赖于新植被（人工林或牧场）的特征、其年龄和降水量。在我们所有的降水梯度上，建立牧场都会增加SOC含量，且随着牧场老化，碳增益更大。相比之下，人工林在干旱地区增加了SOC储量，但在湿润地区却减少了SOC储量。然而，湿润地区的SOC损失被人工林年龄的影响所抵消，因为随着人工林老化，其SOC储量会增加。一个包含年龄和降水量的多元回归模型解释了播种牧场或种植树木后观察到的SOC变化的50%以上（p < 0.01）。当牧场取代原生森林时，在SOC的垂直分布中观察到的唯一明显变化是表层土壤SOC增加而更深层土壤SOC减少。SOC储量的变化主要发生在粉砂+粘粒土壤粒径部分（MAOM），而不稳定（POM）部分的SOC储量保持相对稳定。我们的研究结果可用于设计增加SOC储量和土壤肥力的策略，并突出了降水量、土壤深度和年龄在确定一系列环境和土地利用转变中SOC变化的重要性。
