Effects of fertilizer type and rate on partitioning of soil organic matter into pools of different stability

Deutsche Forschungsgemeinschaft (Graduiertenkolleg 1397/1

Higher subsoil carbon storage in species-rich than species-poor temperate forests

Forest soils contribute ca. 70% to the global soil organic carbon (SOC) pool and thus are an important element of the global carbon cycle. Forests also harbour a large part of the global terrestrial biodiversity. It is not clear, however, whether tree species diversity affects SOC. By measuring the carbon concentration of different soil particle size fractions separately, we were able to distinguish between effects of fine particle content and tree species composition on the SOC pool in oldgrowth broadleaved forest plots along a tree diversity gradient (1, 3and 5species). Variation in clay content explained part of the observed SOC increase from monospecific to mixed forests, but we show that the carbon concentration per unit clay or fine silt in the subsoil was by 30–35% higher in mixed than monospecific stands indicating a significant species identity or species diversity effect on C stabilization. Underlying causes may be differences in fine root biomass and turnover, in leaf litter decomposition rate among the tree species, and/or speciesspecific rhizosphere effects on soil. Our findings may have important implications for forestry offering management options through preference of mixed stands that could increase forest SOC pools and mitigate climate warming.Open-Access-Publikationsfonds 201

Carbon stocks, litterfall and pruning residues in monoculture and agroforestry cacao production systems

Agroforestry systems (AFS) can serve to decrease ecosystem carbon (C) losses caused by deforestation and inadequate soil management. Because of their shade tolerance, cacao plants are suitable to be grown in AFS, since they can be combined with other kinds of trees and shrubs. The potential for C sequestration in cacao farming systems depends on various factors, such as management practices, stand structure and plantation age. We compared conventionally and organically managed cacao monoculture systems (MCS) and AFS in Sara Ana (Bolivia) with respect to C stocks in plant biomass and to amounts of litterfall and pruning residues. The total aboveground C stocks of the AFS (26 Mg C ha−1) considerably exceeded those of the MCS (~7 Mg C ha−1), although the biomass of cacao trees was greater in the MCS compared to the AFS. Due to higher tree density, annual litterfall in the AFS (2.2 Mg C ha−1 year−1) substantially exceeded that in the MCS (1.2 Mg C ha−1 year−1). The amounts of C in pruning residues (2.6 Mg C ha−1 year−1 in MCS to 4.3 Mg C ha−1 year−1 in AFS) was more than twice those in the litterfall. Annual nitrogen (N) inputs to the soil through pruning residues of cacao and N-fixing trees were up to 10 times higher than the N inputs through external fertiliser application. We conclude that appropriate management of cacao AFS, involving the pruning of leguminous trees, will lead to increases in biomass, litter quantity and quality as well as soil C and N stocks. Thus, we recommend stimulating the expansion of well-managed AFS to improve soil fertility and enhance C sequestration in soils

Inaccessible Andean sites reveal human-induced weathering in grazed soils

Human activity affects properties and development of ecosystems across the globe, to such a degree that it is now challenging to get baseline values for undisturbed ecosystems. This is especially true for soil development, which is potentially affected by land-use history and holds a legacy of past human interventions. Therefore, it is still largely unknown for most ecozones how soil would have developed ‘naturally’. Here, we show undisturbed soil development, i.e. the processes of weathering and accumulation of soil organic matter (SOM), by comparing pristine with grazed sites in the high Andes (4500 m) of southern Peru. We located study plots on a large ledge (0.2 km2) that is only accessible with mountaineering equipment. Plots with pristine vegetation were compared to rangeland plots that were presumably under relatively constant grazing management for at least four millennia. Vegetation change, induced by grazing management, led to lower vegetation cover of the soil, thereby increasing soil surface temperatures and soil acidification. Both factors increased weathering in rangeland soils. Formation of pedogenic oxides with high surface area explained preservation of SOM, with positive feedback to acidification. Higher contents of pyrophosphate extractable Fe and Al oxides indicated the importance of organo-mineral associations for SOM stabilization on rangeland sites, which are likely responsible for a higher degree of humification. This higher degree of humification induced melanization (darker colour) of the rangeland soils which, together with sparse vegetation cover, also feeds back to soil temperature. With this work, we present a conceptual framework of positive feedback links between human-induced vegetation change, soil development and accumulation of SOM, which is only possible due to the unique baseline values of a pristine ecosystem. Using ‘inaccessibility’ as a tool to quantify human impact in future interdisciplinary studies may push research forward on evaluating anthropogenic impact on Earth’s ecosystems

Diversity and composition of herbaceous angiosperms along gradients of elevation and forest-use intensity.

Terrestrial herbs are important elements of tropical forests; however, there is a lack of research on their diversity patterns and how they respond to different intensities of forest-use. The aim of this study was to analyze the diversity of herbaceous angiosperms along gradients of elevation (50 m to 3500 m) and forest-use intensity on the eastern slopes of the Cofre de Perote, Veracruz, Mexico. We recorded the occurrence of all herbaceous angiosperm species within 120 plots of 20 m x 20 m each. The plots were located at eight study locations separated by ~500 m in elevation and within three different habitats that differ in forest-use intensity: old-growth, degraded, and secondary forest. We analyzed species richness and floristic composition of herb communities among different elevations and habitats. Of the 264 plant species recorded, 31 are endemic to Mexico. Both α- and γ-diversity display a hump-shaped relation to elevation peaking at 2500 m and 3000 m, respectively. The relative contribution of between-habitat β-diversity to γ-diversity also showed a unimodal hump whereas within-habitat β-diversity declined with elevation. Forest-use intensity did not affect α-diversity, but β-diversity was high between old-growth and secondary forests. Overall, γ-diversity peaked at 2500 m (72 species), driven mainly by high within- and among-habitat β-diversity. We infer that this belt is highly sensitive to anthropogenic disturbance and forest-use intensification. At 3100 m, high γ-diversity (50 species) was driven by high α- and within-habitat β-diversity. There, losing a specific forest area might be compensated if similar assemblages occur in nearby areas. The high β-diversity and endemism suggest that mixes of different habitats are needed to sustain high γ-richness of terrestrial herbs along this elevational gradient

Relict high-Andean ecosystems challenge our concepts of naturalness and human impact

What would current ecosystems be like without the impact of mankind? This question, which is critical for ecosystem management, has long remained unanswered due to a lack of present-day data from truly undisturbed ecosystems. Using mountaineering techniques, we accessed pristine relict ecosystems in the Peruvian Andes to provide this baseline data and compared it with the surrounding accessible and disturbed landscape. We show that natural ecosystems and human impact in the high Andes are radically different from preconceived ideas. Vegetation of these ‘lost worlds’ was dominated by plant species previously unknown to science that have become extinct in nearby human-affected ecosystems. Furthermore, natural vegetation had greater plant biomass with potentially as much as ten times more forest, but lower plant diversity. Contrary to our expectations, soils showed relatively little degradation when compared within a vegetation type, but differed mainly between forest and grassland ecosystems. At the landscape level, a presumed large-scale forest reduction resulted in a nowadays more acidic soilscape with higher carbon storage, partly ameliorating carbon loss through deforestation. Human impact in the high Andes, thus, had mixed effects on biodiversity, while soils and carbon stocks would have been mainly indirectly affected through a suggested large-scale vegetation change.Fil: Sylvester, Steven P.. Universitat Zurich; Suiza. Philipps-Universität Marburg; AlemaniaFil: Heitkamp, Felix. Universität Göttingen; AlemaniaFil: Sylvester, Mitsy D. P. V.. Universitat Zurich; Suiza. Universidad Nacional del San Antonio Abad del Cusco; PerúFil: Jungkunst, Hermann F.. Universität Koblenz-Landau; AlemaniaFil: Sipman, Harrie J. M.. Freie Universität Berlin; AlemaniaFil: Toivonen, Johanna M.. University of Turku; FinlandiaFil: Gonzales Inca, Carlos A.. University of Turku; FinlandiaFil: Ospina Gonzalez, Juan Camilo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Kessler, Michael. Universitat Zurich; Suiz

Land-use induced soil carbon stabilization at the expense of rock derived nutrients: insights from pristine Andean soils

Soils contain significantly more carbon than the atmosphere, hence we should understand how best to stabilize it. Unfortunately, the role of human interventions on soil organic carbon (SOC) persistence in the Anthropocene remains vague, lacking adequate sites that allow unbiased direct comparisons of pristine and human influenced soils. Here we present data from a unique study system in the High Andes that guarantees pristineness of the reference sites by physical inaccessibility through vertical cliffs. By comparing the isotopic signatures of SOC, mineral related carbon stabilization, and soil nutrient status across grazed versus pristine soils, we provide counterintuitive evidence that thousands of years of pastoralism increased soil C persistence. Mineral associated organic carbon (MAOC) was significantly higher in pastures. Land use increased poorly crystalline minerals (PCM's), of which aluminum correlated best with MAOC. On the other hand, human's acceleration of weathering led to acidification and higher losses of cations. This highlights a dilemma of lower soil quality but higher persistence of SOC due to millennia of pastoralism. The dynamics of soil genesis in the Anthropocene needs better understanding, but if human-induced weathering proves generally to promote soil carbon persistence it will need to be included in climate-soil feedback projections.ISSN:2045-232

Schematic representation of the sampling design.

<p>We measured α-diversity in plots of 20 m x 20 m given as a mean of five plots. Five plots represent one habitat. We defined habitat as a homogenous type of forest-use intensity within one location. A location is representative of an elevational belt and harbors three different habitats (old-growth OG, degraded DE, and secondary SE). We measured two different β-diversities based on pairs of plots. Within-habitat β-diversity represents the compositional heterogeneity of a habitat. It is measured as the 1-Sørensen index based on multiple pairwise comparisons of the five plots within each habitat of a specific location. Between-habit β-diversity represents the compositional heterogeneity between different forest-use intensity. Measurement is similar to within-habitat β-diversity, but multiple pairwise comparisons based on the plots between habitats of a specific location. We defined γ-diversity as the total number of the local species pool across all 15 plots within a location, i.e. three habitats with five plots each.</p

Parameter estimates from generalized linear models.

<p>The parameters link herb α-diversity, the proportion of endemics and β-diversity to environmental explanatory variables, along an elevational gradient at central Veracruz, Mexico. Estimates are on the standardized scale ± standard error. We marked significant estimates with an asterisk (* < = 0.05, ** < = 0.01 and *** < 0.001). Empty cells indicate terms not included in the best model for a given response variable.</p