South Patagonian peat bogs are little studied sources of methane (CH 4 ). Since CH 4 fluxes can vary greatly on a small scale of meters, high-quality maps are needed to accurately quantify CH 4 fluxes from bogs. We used high-resolution color infrared (CIR) images captured by an Unmanned Aerial System (UAS) to investigate potential uncertainties in total ecosystem CH 4 fluxes introduced by the classification of the surface area. An object-based approach was used to classify vegetation both on species and microform level. We achieved an overall Kappa Index of Agreement (KIA) of 0.90 for the species-and 0.83 for the microform-level classification, respectively. CH 4 fluxes were determined by closed chamber measurements on four predominant microforms of the studied bog. Both classification approaches were employed to up-scale CH 4 closed chamber measurements in a total area of around 1.8 hectares. Including proportions of the surface area where no chamber measurements were conducted, we estimated a potential uncertainty in ecosystem CH 4 fluxes introduced by the classification of the surface area. This potential uncertainty ranged from 14.2 mg¨m´2¨day´1 to 26.8 mg¨m´2¨day´1. Our results show that a simple classification with only few classes potentially leads to pronounced bias in total ecosystem CH 4 fluxes when plot-scale fluxes are up-scaled.

Abstract. Peatlands are significant global methane (CH4) sources, but processes governing CH4 dynamics have been predominantly studied in the Northern Hemisphere. Southern hemispheric and tropical bogs can be dominated by cushion-forming vascular plants (e.g. Astelia pumila, Donatia fascicularis). These cushion bogs are found in many (mostly southern) parts of the world but could also serve as extreme examples for densely rooted northern hemispheric bogs dominated by rushes and sedges. We report highly variable summer CH4 emissions from different microforms in a Patagonian cushion bog as determined by chamber measurements. Driving biogeochemical processes were identified from pore water profiles and carbon isotopic signatures. Intensive root activity throughout a rhizosphere stretching over 2 m in depth accompanied by molecular oxygen release created aerobic microsites in water-saturated peat, leading to a thorough CH4 oxidation (< 0.003 mmol L−1 pore water CH4, enriched in δ13C-CH4 by up to 10 ‰) and negligible emissions (0.09±0.16 mmol CH4 m−2 d−1) from Astelia lawns. In sparsely or even non-rooted peat below adjacent pools pore water profile patterns similar to those obtained under Astelia lawns, which emitted very small amounts of CH4 (0.23±0.25 mmol m−2 d−1), were found. Below the A. pumila rhizosphere pore water concentrations increased sharply to 0.40±0.25 mmol CH4 L−1 and CH4 was predominantly produced by hydrogenotrophic methanogenesis. A few Sphagnum lawns and – surprisingly – one lawn dominated by cushion-forming D. fascicularis were found to be local CH4 emission hotspots with up to 1.52±1.10 mmol CH4 m−2 d−1 presumably as root density and molecular oxygen release dropped below a certain threshold. The spatial distribution of root characteristics supposedly causing such a pronounced CH4 emission pattern was evaluated on a conceptual level aiming to exemplify scenarios in densely rooted bogs. We conclude that presence of cushion vegetation as a proxy for negligible CH4 emissions from cushion bogs needs to be interpreted with caution. Nevertheless, overall ecosystem CH4 emissions at our study site were probably minute compared to bog ecosystems worldwide and widely decoupled from environmental controls due to intensive root activity of A. pumila, for example.

Natural peatlands contribute significantly to global carbon sequestration and storage of biomass, most of which derives from Sphagnum peat mosses. Atmospheric CO2 levels have increased dramatically during the twentieth century, from 280 to > 400 ppm, which has affected plant carbon dynamics. Net carbon assimilation is strongly reduced by photorespiration, a process that depends on the CO2 to O2 ratio. Here we investigate the response of the photorespiration to photosynthesis ratio in Sphagnum mosses to recent CO2 increases by comparing deuterium isotopomers of historical and contemporary Sphagnum tissues collected from 36 peat cores from five continents. Rising CO2 levels generally suppressed photorespiration relative to photosynthesis but the magnitude of suppression depended on the current water table depth. By estimating the changes in water table depth, temperature, and precipitation during the twentieth century, we excluded potential effects of these climate parameters on the observed isotopomer responses. Further, we showed that the photorespiration to photosynthesis ratio varied between Sphagnum subgenera, indicating differences in their photosynthetic capacity. The global suppression of photorespiration in Sphagnum suggests an increased net primary production potential in response to the ongoing rise in atmospheric CO2, in particular for mire structures with intermediate water table depths.

Rangeland rehabilitation has multiple, sometimes conflicting goals, such as the reestablishment of the predisturbance vegetation, soil protection, and forage production. The rehabilitation techniques should be also cost-effective and practicable. Given the difficulties and high costs of restoring Succulent Karoo rangelands and the continuously high grazing pressure in the communal lands, tradeoffs should be accepted in the achievement of these goals. We tested the capability of paddock manure redistribution to reverse degradation trends in a heavily grazed Succulent Karoo rangeland in South Africa. Over 3 years, the effects of the manure application were compared with areas planted with mature shrubs as a benchmark for a predisturbance vegetation structure and with four popular rehabilitation techniques: (1) livestock exclusion; (2) brushpacking (coverage of dead shrubs); (3) mineral fertilizing; and (4) microcatchment construction. Manure was, besides planting, the only treatment that resulted in a significant increase in drought-resistant vegetation cover, but it compromised the dominance of native vegetation. In the manure plots, a pasture-like vegetation of non-native forage plants (which germinated mainly from seeds in the dung), developed (foremost Atriplex semibaccata). Manure application counteracted erosion as effectively as the planted shrubs and brushpacks. Expected negative side effects such as a decrease in plant species richness or salinization of topsoil were not detected. We also checked the potential of topsoil salinization by the halophytic A. semibaccata and found it to be low. For sites where a decrease in grazing pressure is unrealistic under current land tenure, redistribution of manure should be further explored to mitigate acute symptoms of degradation.

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Peatlands are significant global methane (CH&lt;sub&gt;4&lt;/sub&gt;) sources, but processes governing CH&lt;sub&gt;4&lt;/sub&gt; dynamics have been predominantly studied on the northern hemisphere. Southern hemispheric and tropical bogs can be dominated by cushion-forming vascular plants (e.g. &lt;i&gt;Astelia pumila&lt;/i&gt;, &lt;i&gt;Donatia fascicularis&lt;/i&gt;). These cushion bogs are found in many (mostly southern) parts of the world but could also serve as extreme examples for densely rooted northern hemispheric bogs dominated by rushes and sedges. We report highly variable summer CH&lt;sub&gt;4&lt;/sub&gt; emissions from different microforms in a Patagonian cushion bog as determined by chamber measurements. Driving biogeochemical processes were identified from pore water profiles and carbon isotopic signatures. An intensive root activity within a rhizosphere stretching over 2&amp;#8201;m depth accompanied by molecular oxygen release created aerobic microsites in water-saturated peat leading to a thorough CH&lt;sub&gt;4&lt;/sub&gt; oxidation (&lt;&amp;#8201;0.003&amp;#8201;mmol&amp;#8201;L&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; pore water CH&lt;sub&gt;4&lt;/sub&gt;, enriched &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4&lt;/sub&gt; by up to 10&amp;#8201;&amp;#8240;) and negligible emissions (0.09&amp;#8201;&amp;#177;&amp;#8201;0.16&amp;#8201;mmol&amp;#8201;CH&lt;sub&gt;4&lt;/sub&gt;&amp;#8201;m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt;&amp;#8201;d&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;) from &lt;i&gt;Astelia&lt;/i&gt; lawns. Root activity even suppressed CH&lt;sub&gt;4&lt;/sub&gt; emissions from non-rooted peat below adjacent pools (0.23&amp;#8201;&amp;#177;&amp;#8201;0.25&amp;#8201;mmol&amp;#8201;CH&lt;sub&gt;4&lt;/sub&gt;&amp;#8201;m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt;&amp;#8201;d&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;), in which we found similar pore water profile patterns as obtained under &lt;i&gt;Astelia&lt;/i&gt; lawns. Below the rhizosphere pore water concentrations increased sharply to 0.40&amp;#8201;&amp;#177;&amp;#8201;0.25&amp;#8201;mmol&amp;#8201;CH&lt;sub&gt;4&lt;/sub&gt;&amp;#8201;L&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; and CH&lt;sub&gt;4&lt;/sub&gt; was predominantly produced by hydrogenotrophic methanogenesis. Few &lt;i&gt;Sphagnum&lt;/i&gt; lawns and &amp;#8211; surprisingly &amp;#8211; one lawn dominated by cushion-forming &lt;i&gt;D. fascicularis&lt;/i&gt; were found to be local CH&lt;sub&gt;4&lt;/sub&gt; emission hot spots with up to 1.52&amp;#8201;&amp;#177;&amp;#8201;1.10&amp;#8201;mmol&amp;#8201;CH&lt;sub&gt;4&lt;/sub&gt; &amp;#8201;m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt;&amp;#8201;d&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; presumably as root density and molecular oxygen release dropped below a certain threshold. The spatial distribution of root characteristics supposedly causing such pronounced CH&lt;sub&gt;4&lt;/sub&gt; emission pattern was evaluated on a conceptual level that aimed to reflect extreme examples of general scenarios in densely rooted bogs. We conclude that presence of cushion vegetation as a proxy for negligible CH&lt;sub&gt;4&lt;/sub&gt; emissions from cushion bogs needs to be interpreted with caution. Nevertheless, overall ecosystem CH&lt;sub&gt;4&lt;/sub&gt; emissions at our study site were probably minute compared to bog ecosystems worldwide and widely decoupled from environmental controls due intensive root activity of e.g. &lt;i&gt;A. pumila&lt;/i&gt;.&lt;/p&gt;