No abstract

No abstract

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.

Type and rate of fertilizers influence the level of soil organic carbon (C org ) and total nitrogen (N t ) markedly, but the effect on partitioning of C and N into different pools is open to question. Objectives were to investigate the impact of fertilizer type and rate on labile, intermediate and passive C and N pools in a sandy Cambisol at Darmstadt, Germany, after 27 years of different fertilization treatments. The six treatments were: straw incorporation plus application of mineral fertilizer (MSI) and application of farmyard manure (FYM) each at high (140-150 kg N ha −1 year −1 ), medium (100 kg N ha −1 year −1 ) and low (50-60 kg N ha −1 year −1 ) rates. Soil microbial biomass C (C mic ) and N (N mic ) and C and net N mineralization (266 days incubation at 10°C and 50% waterfilled pore space) were determined. Soils (0-25 cm) of MSI treatments had significantly (p≤0.05) lower C mic stocks (308-361 kg ha −1 ) than soils of FYM treatments (404-520 kg ha −1 ). Differences in N mic stocks were less pronounced. After 266 days, mineralized C (1130-1820 kg ha −1 ) and N (90-125 kg ha −1 ) had significantly increased with fertilizer rate. The application of an exponential two-pool model showed that very labile pools (turnover times: 17 and 9 days for C and N, respectively) were small (1.3-1.8% of C org and 0.5-1.0% of N t ) and not influenced by type or rate of fertilizer. Stocks of the modeled labile C and N pools (turnover times: 462 and 153 days for C and N, respectively) were not influenced by the type of fertilizer but depended significantly on the application rate and ranged from 7 to 13% of C org and from 4 to 5% of N t . In contrast, the size of the calculated intermediate C pool was greater for the FYM treatments, and depended significantly on the interaction of fertilizer type and rate. The intermediate N pool was unaffected by fertilizer type or rate. Passive C and N pools, as experimentally revealed by oxidation with disodium peroxodisulfate (Na 2 S 2 O 8 ), were independent of the treatments. Overall, labile and intermediate pools were affected differently by the fertilizer type and the application rate.