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Cultivation of perennial crops can be an option to sequester carbon in agricultural soils. To determine the carbon budget of a perennial cropping system under the boreal climate, we studied carbon dioxide (CO2) and methane (CH4) exchange of timothy and meadow fescue mixture (TIM) on a boreal mineral soil. Based on the mean annual net ecosystem CO2 exchange (NEE), TIM was a sink for both CO2 (-1000 g CO2 m-2) and CH4 (-140 mg CH4 m-2). In comparison, soil without vegetation (BARE) was a source of CO2 (1300 g CO2 m-2). Based on the literature review, the net CO2 uptake of TIM was similar to the perennial cropping systems in northern Finland but higher than that of the annual cropping systems in this region. Our multi-year study shows that the perennial cultivation system based on TIM is an environmentally sustainable land-use option to mitigate agricultural CO2 emissions in regions with short growing seasons. [ABSTRACT FROM AUTHOR]

Abstract: With the aim of addressing the broader issues of land use, climate change and energy crisis, eddy covariance measurements of energy and CO2 exchange from a bioenergy crop (reed canary grass, Phalaris arundinaceae, L.) cultivated on a drained organic soil (a cutover peatland) in eastern Finland were initiated in the spring of 2004. Based on the climatically diverse dataset from the 2004 to 2010 period, the objectives of the work presented here are to characterize the interannual variability in water vapor exchange and to understand the linkage between energy and CO2 exchange from this perennial crop during two extreme growing seasons. Correcting the measured soil heat flux by accounting for the change in heat storage above the heat flux plates helped close the energy balance at this site. Interannual variability in ecosystem processes of energy and CO2 exchange were attributed primarily to marked differences in the amount and distribution of seasonal precipitation. Differences in the phonological development of the crop during seasons with contrasting climatic conditions were reflected in the normalized difference vegetation index (NDVI) estimated from the radiation instruments installed on the tower. Wet years were characterized by an even distribution of seasonal precipitation, low to moderate air and soil temperatures, lower solar and net radiation intensities (owing to reduced number of bright sunshine hours and therefore, higher amount of diffuse sky radiation), moderate to saturated soil moisture conditions and lower vapor pressure deficit. These climatic conditions resulted in high bulk surface conductance (g s ), high evapotranspiration (ET) and low sensible heat flux with a peak seasonal Bowen ratio (β =0.1). These conditions were favourable for a high uptake of atmospheric CO2. Dry years, on the contrary, were marked by long dry spells during important phases of crop growth, climatic and soil moisture stress leading to high evaporative demand, low g s values, reduced evapotranspiration and high sensible heat flux (β =0.3–0.4). On a seasonal basis, the ET losses during a dry year were 13% lower compared to those during a wet year. The corresponding reduction in gross ecosystem productivity (GEP), however, was to the extent of 21%. Owing to the ability of this perennial crop to sequester large amounts of atmospheric carbon into its above- and below-ground biomass, the water use efficiency (defined as the slope of the linear regression of monthly values of GEP against ET) of this cultivation system was found to be 9.1g CO2 per kg of H2O lost as ET. The results stemming from this work further support our earlier conclusions that this bioenergy system is a suitable land use option on drained and abandoned cutover peatlands with a high potential for offsetting CO2 load to the atmosphere. [Copyright &y& Elsevier]

Abstract: We tested here a plant-soil system to separate recent, plant-derived and native, soil-derived carbon in soil respiration. The approach uses a perennial crop cultivated on an organic soil where upper soil layers have been removed as a result of peat extraction. There, the 14C signal from native organic matter is highly depleted compared to that in vegetation established at the site after peat extraction ceased. Radiocarbon was analyzed in carbon dioxide respired from soil over one growing season, and a two-pool isotope mixing model was applied to calculate the relative contribution of old vs. new carbon sources. The analysis showed that the approach is reliable for source partitioning with isotopes. After six years of cultivation, old peat decomposition contributed less to total soil respiration than respiration of recent plant material (30% vs. 70% on average, respectively), but the relative proportions were highly variable over the growing season. The approach offers a new possibility to follow the fate of old, native soil organic matter in highly organic soils. [Copyright &y& Elsevier]

Stress-induced changes to plant biochemistry and physiology can influence plant nutritional quality and subsequent interactions with herbivorous pests. However, the effects of stress combinations are unpredictable and differ to the effects of individual stressors. Here we studied the effects of exposure to the phytotoxic air-pollutant ozone (O 3 ), feeding by larvae of the large cabbage white butterfly (Pieris brassicae), and a combination of the two stresses, on the emission of volatile organic compounds (VOCs) by black mustard plants (Brassica nigra) under field and laboratory conditions. Field-grown B. nigra plants were also measured for carbon-nitrogen (C-N) content, net photosynthetic activity (Pn), stomatal conductance (gs) and biomass. The effects of O 3 on interactions between plants and a herbivorous pest were addressed by monitoring the abundance of wild diamondback moth larvae (Plutella xylostella) and feeding-damage to B. nigra plants in an O 3 -free air concentration enrichment (O 3 -FACE) field site. Herbivore-feeding induced the emission of VOCs that were not emitted by undamaged plants, both under field and laboratory conditions. The combination of O 3 and herbivore-feeding stresses resulted in enhanced emission rates of several VOCs from field-grown plants. Short-term O 3 exposure (of 10 days) and P. brassicae-feeding did not affect C-N content, but chronic O 3 exposure (of 34 and 47 days) and P. brassicae-feeding exacerbated suppression of Pn. Ozone exposure also caused visible injury and decreased the plant biomass. Field-grown B. nigra under elevated O 3 were infested with fewer P. xylostella larvae and received significantly less feeding damage. Our results suggest that plants growing in a moderately polluted environment may be of reduced quality and less attractive to foraging herbivores., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)