Accounting for land use changes beyond the farm-level in sustainability assessments: The impact of cocoa production

Impact assessments are used to raise evidence and guide the implementation of sustainability strategies in commodity value chains. Due to methodological and data difficulties, most assessments of agricultural commodities capture the impacts occurring at the farm-level but often dismiss or oversimplify the impacts caused by land use dynamics at larger geographic scale. In this study we analyzed the impacts of two cocoa production systems, full-sun and agroforestry, at the farm-level and beyond the farm-level. We used life cycle assessment to calculate the impacts at the farm-level and a combination of land use modelling with spatial analysis to calculate the impacts beyond the farm-level. We applied this to three different future cocoa production scenarios. The impacts at the farm-level showed that, due to lower yields, cocoa agroforestry performs worse than cocoa full-sun for most impact indicators. However, the impacts beyond the farm-level showed that promoting cocoa agroforestry in the landscape can bring the largest gains in carbon and biodiversity. A scenario analysis of the impacts at the landscape-level showed large nuances depending on the cocoa farming system adopted, market dynamics, and nature conservation policies. The analysis indicated that increasing cocoa demand does not necessarily result in negative impacts for carbon stocks and biodiversity, if sustainable land management and sustainable intensification are adopted. Landscape-level impacts can be larger than farm-level impacts or show completely opposite direction, which highlights the need to complement farm-level assessments with assessments accounting for land use dynamics beyond the farm-level.

Differences in Root Nitrogen Uptake Between Tropical Lowland Rainforests and Oil Palm Plantations

Conversion of lowland tropical rainforests to intensely fertilized agricultural land-use systems such as oil palm (Elaeis guineensis) plantations leads to changes in nitrogen (N) cycling. Although soil microbial-driven N dynamics has been largely studied, the role of the plant as a major component in N uptake has rarely been considered. We address this gap by comparing the root N contents and uptake in lowland rainforests with that in oil palm plantations on Sumatra, Indonesia. To this aim, we applied ¹⁵N-labeled ammonium to intact soil, measured the ¹⁵N recovery in soil and roots, and calculated the root relative N uptake efficiency for 10 days after label application. We found that root N contents were by one third higher in the rainforest than oil palm plantations. However, ¹⁵N uptake efficiency was similar in the two systems. This finding suggests that lower N contents in oil palm roots were likely caused by plant internal utilization of the absorbed N (e.g., N export to fruit bunches) than by lower ability to take up N from the soil. ¹⁵N recovery in roots was primarily driven by the amount of root biomass, which was higher in oil palm plantation than rainforest. The oil palms unveiled a high capacity to acquire N, offering the possibility of enhancing sustainable plantation management by reducing N fertilizer application.

Effects on Carbon Sources and Sinks from Conversion of Over-Mature Forest to Major Secondary Forests and Korean Pine Plantation in Northeast China

The effects of replacing over-mature forest with secondary forests and plantations are significant for terrestrial ecosystem carbon (C) dynamics. However, the carbon balance and recovery time of this replacement process remain unclear. This study measured the fluxes of CH4 and CO2 in soils and the annual net C sequestration (ANCS) from seven ecosystems with different vegetation types (over-mature forest (OMF), Korean pine plantation (KPP), hardwood forest (HWF), Betula platyphylla forest (BPF), Populous davidiana forest (PDF), mixed deciduous forest (MDF), and Mongolian oak forest (MOF)) using the static chamber-gas chromatography method and the relative growth equation method. We examined the effects of environmental factors (e.g., air and soil temperature, soil volumetric water content (SVWC), soil pH, nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), and soil organic carbon (SOC)) on CH4 and CO2 fluxes at the Maoershan Ecosystem Research Station in Northeast China. The carbon source or sink of OMF, KPP, and five secondary forests (HWF, BPF, PDF, MDF, and MOF) were then evaluated based on net ecosystem C balance. The results revealed that the mean annual CH4 fluxes varied between −0.046 and −0.077 mg m−2 h−1. The mean annual absorption of CH4 in the secondary forests and OMF were respectively 1.09–1.67 times and 1.11 times higher than that of KPP (0.046 mg m−2 h−1, p < 0.05). The mean annual CO2 fluxes varied between 140.425 and 250.023 mg m−2 h−1. The CO2 fluxes in the secondary forests and KPP soils were respectively 1.33–1.78 times and 1.16 times higher than that of OMF (140.425 mg m−2 h−1, p < 0.05). The CH4 and CO2 fluxes were mainly influenced by air and soil temperature, SVWC, soil pH, NO3−-N, NH4+-N, and SOC in Northeast China. The ANCS of vegetation (3.41 ± 0.27 − 6.26 ± 0.75 t C ha−1 y−1) varied widely among different forest types: KPP had the largest ANCS (6.26 ± 0.75 t C ha−1 y−1, which was higher than secondary forests and OMF by 1.20–1.84 times and 1.46 times, respectively, p > 0.05). Carbon sources and sinks were significantly different among the seven types of vegetation: OMF and KPP were observed to be the greatest C sinks, and secondary forests were shown to be the weakest carbon sinks or net C sources in the study region.

Activity and abundance of methane-oxidizing bacteria in secondary forest and manioc plantations of Amazonian Dark Earth and their adjacent soils

The oxidation of atmospheric CH₄ in upland soils is mostly mediated by uncultivated groups of microorganisms that have been identified solely by molecular markers, such as the sequence of the pmoA gene encoding the β-subunit of the particulate methane monooxygenase enzyme. The objective of this work was to compare the activity and diversity of methanotrophs in Amazonian Dark Earth soil (ADE, Hortic Anthrosol) and their adjacent non-anthropic soil. Secondly, the effect of land use in the form of manioc cultivation was examined by comparing secondary forest and plantation soils. CH₄ oxidation potentials were measured and the structure of the methanotroph communities assessed by quantitative PCR (qPCR) and amplicon pyrosequencing of pmoA genes. The oxidation potentials at low CH₄ concentrations (10 ppm of volume) were relatively high in all the secondary forest sites of both ADE and adjacent soils. CH₄ oxidation by the ADE soil only recently converted to a manioc plantation was also relatively high. In contrast, both the adjacent soils used for manioc cultivation and the ADE soil with a long history of agriculture displayed lower CH₄ uptake rates. Amplicon pyrosequencing of pmoA genes indicated that USCα, Methylocystis and the tropical upland soil cluster (TUSC) were the dominant groups depending on the site. By qPCR analysis it was found that USCα pmoA genes, which are believed to belong to atmospheric CH₄ oxidizers, were more abundant in ADE than adjacent soil. USCα pmoA genes were abundant in both forested and cultivated ADE soil, but were below the qPCR detection limit in manioc plantations of adjacent soil. The results indicate that ADE soils can harbor high abundances of atmospheric CH₄ oxidizers and are potential CH₄ sinks, but as in other upland soils this activity can be inhibited by the conversion of forest to agricultural plantations.

Atmospheric Ionic Deposition in Tropical Sites of Central Sulawesi Determined by Ion Exchange Resin Collectors and Bulk Water Collector

In the light of global change, the necessity to monitor atmospheric depositions that have relevant effects on ecosystems is ever increasing particularly for tropical sites. For this study, atmospheric ionic depositions were measured on tropical Central Sulawesi at remote sites with both a conventional bulk water collector system (BWS collector) and with a passive ion exchange resin collector system (IER collector). The principle of IER collector to fix all ionic depositions, i.e. anions and cations, has certain advantages referring to (1) post-deposition transformation processes, (2) low ionic concentrations and (3) low rainfall and associated particulate inputs, e.g. dust or sand. The ionic concentrations to be measured for BWS collectors may easily fall below detection limits under low deposition conditions which are common for tropical sites of low land use intensity. Additionally, BWS collections are not as independent from the amount of rain fallen as are IER collections. For this study, the significant differences between both collectors found for nearly all measured elements were partly correlated to the rainfall pattern, i.e. for calcium, magnesium, potassium and sodium. However, the significant differences were, in most cases, not highly relevant. More relevant differences between the systems were found for aluminium and nitrate (434-484 %). Almost five times higher values for nitrate clarified the advantage of the IER system particularly for low deposition rate which is one particularity of atmospheric ionic deposition in tropical sites of extensive land use. The monthly resolution of the IER data offers new insights into the temporal distribution of annual ionic depositions. Here, it did not follow the tropical rain pattern of a drier season within generally wet conditions.