Solar park microclimate and vegetation management effects on grassland carbon cycling

Increasing energy demands and the drive towards low carbon (C) energy sources has prompted a rapid increase in ground-mounted solar parks across the world. This represents a significant global land use change with implications for the hosting ecosystems that are poorly understood. In order to investigate the effects of a typical solar park on the microclimate and ecosystem processes, we measured soil and air microclimate, vegetation and greenhouse gas emissions for twelve months under photovoltaic (PV) arrays, in gaps between PV arrays and in control areas at a UK solar park sited on species-rich grassland. Our results show that the PV arrays caused seasonal and diurnal variation in air and soil microclimate. Specifically, during the summer we observed cooling, of up to 5.2 °C, and drying under the PV arrays compared with gap and control areas. In contrast, during the winter gap areas were up to 1.7 °C cooler compared with under the PV arrays and control areas. Further, the diurnal variation in both temperature and humidity during the summer was reduced under the PV arrays. We found microclimate and vegetation management explained differences in the above ground plant biomass and species diversity, with both lower under the PV arrays. Photosynthesis and net ecosystem exchange in spring and winter were also lower under the PV arrays, explained by microclimate, soil and vegetation metrics. These data are a starting point to develop understanding of the effects of solar parks in other climates, and provide evidence to support the optimisation of solar park design and management to maximise the delivery of ecosystem services from this growing land use

Biogeographic differences in soil biota promote invasive grass response to nutrient addition relative to co-occurring species despite lack of belowground enemy release

Multiple plant species invasions and increases in nutrient availability are pervasive drivers of global environmental change that often co-occur. Many plant invasion studies, however, focus on single-species or single-mechanism invasions, risking an oversimplifcation of a multifaceted process. Here, we test how biogeographic diferences in soil biota, such as belowground enemy release, interact with increases in nutrient availability to infuence invasive plant growth. We conducted a greenhouse experiment using three co-occurring invasive grasses and one native grass. We grew species in live and sterilized soil from the invader’s native (United Kingdom) and introduced (New Zealand) ranges with a nutrient addition treatment. We found no evidence for belowground enemy release. However, species’ responses to nutrients varied, and this depended on soil origin and sterilization. In live soil from the introduced range, the invasive species Lolium perenne L. responded more positively to nutrient addition than co-occurring invasive and native species. In contrast, in live soil from the native range and in sterilized soils, there were no diferences in species’ responses to nutrients. This suggests that the presence of soil biota from the introduced range allowed L. perenne to capture additional nutrients better than co-occurring species. Considering the globally widespread nature of anthropogenic nutrient additions to ecosystems, this efect could be contributing to a global homogenization of fora and the associated losses in native species diversity

Can digital image classification be used as a standardised method for surveying peatland vegetation cover?

The ability to carry out systematic, accurate and repeatable vegetation surveys is an essential part of long-term scientific studies into ecosystem biodiversity and functioning. However, current widely used traditional survey techniques such as destructive harvests, pin frame quadrats and visual cover estimates can be very time consuming and are prone to subjective variations. We investigated the use of digital image techniques as an alternative way of recording vegetation cover to plant functional type level on a peatland ecosystem. Using an established plant manipulation experimental site at Moor House NNR (an Environmental Change Network site), we compared visual cover estimates of peatland vegetation with cover estimates using digital image classification methods, from 0.5 m × 0.5 m field plots. Our results show that digital image classification of photographs taken with a standard digital camera can be used successfully to estimate dwarf-shrub and graminoid vegetation cover at a comparable level to field visual cover estimates, although the methods were less effective for lower plants such as mosses and lichens. Our study illustrates the novel application of digital image techniques to provide a new way of measuring and monitoring peatland vegetation to the plant functional group level, which is less vulnerable to surveyor bias than are visual field surveys. Furthermore, as such digital techniques are highly repeatable, we suggest that they have potential for use in long-term monitoring studies, at both plot and landscape scales

Vascular plants promote ancient peatland carbon loss with climate warming

Northern peatlands have accumulated one third of the Earth's soil carbon stock since the last Ice Age. Rapid warming across northern biomes threatens to accelerate rates of peatland ecosystem respiration. Despite compensatory increases in net primary production, greater ecosystem respiration could signal the release of ancient, century- to millennia-old carbon from the peatland organic matter stock. Warming has already been shown to promote ancient peatland carbon release, but, despite the key role of vegetation in carbon dynamics, little is known about how plants influence the source of peatland ecosystem respiration. Here, we address this issue using in situ 14C measurements of ecosystem respiration on an established peatland warming and vegetation manipulation experiment. Results show that warming of approximately 1 °C promotes respiration of ancient peatland carbon (up to 2100 years old) when dwarf-shrubs or graminoids are present, an effect not observed when only bryophytes are present. We demonstrate that warming likely promotes ancient peatland carbon release via its control over organic inputs from vascular plants. Our findings suggest that dwarf-shrubs and graminoids prime microbial decomposition of previously ‘locked-up’ organic matter from potentially deep in the peat profile, facilitating liberation of ancient carbon as CO2. Furthermore, such plant-induced peat respiration could contribute up to 40% of ecosystem CO2 emissions. If consistent across other sub-arctic and arctic ecosystems, this represents a considerable fraction of ecosystem respiration that is currently not acknowledged by global carbon cycle models. Ultimately, greater contribution of ancient carbon to ecosystem respiration may signal the loss of a previously stable peatland carbon pool, creating potential feedbacks to future climate change

Belowground competition drives invasive plant impact on native species regardless of nitrogen availability

Plant invasions and eutrophication are pervasive drivers of global change that cause biodiversity loss. Yet, how invasive plant impacts on native species, and the mechanisms underpinning these impacts, vary in relation to increasing nitrogen (N) availability remains unclear. Competition is often invoked as a likely mechanism, but the relative importance of the above and belowground components of this is poorly understood, particularly under differing levels of N availability. To help resolve these issues, we quantified the impact of a globally invasive grass species, Agrostis capillaris, on two co-occurring native New Zealand grasses, and vice versa. We explicitly separated above- and belowground interactions amongst these species experimentally and incorporated an N addition treatment. We found that competition with the invader had large negative impacts on native species growth (biomass decreased by half), resource capture (total N content decreased by up to 75%) and even nutrient stoichiometry (native species tissue C:N ratios increased). Surprisingly, these impacts were driven directly and indirectly by belowground competition, regardless of N availability. Higher root biomass likely enhanced the invasive grass’s competitive superiority belowground, indicating that root traits may be useful tools for understanding invasive plant impacts. Our study shows that belowground competition can be more important in driving invasive plant impacts than aboveground competition in both low and high fertility ecosystems, including those experiencing N enrichment due to global change. This can help to improve predictions of how two key drivers of global change, plant species invasions and eutrophication, impact native species diversity

Direct isotopic evidence of biogenic methane production and efflux from beneath a temperate glacier

The base of glaciers and ice sheets provide environments suitable for the production of methane. High pressure conditions beneath the impermeable ‘cap’ of overlying ice promote entrapment of methane reserves that can be released to the atmosphere during ice thinning and meltwater evacuation. However, contemporary glaciers and ice sheets are rarely accounted for as methane contributors through field measurements. Here, we present direct field-based evidence of methane production and release from beneath the Icelandic glacier Sólheimajökull, where geothermal activity creates sub-oxic conditions suited to methane production and preservation along the meltwater flow path. Methane production at the glacier bed (48 tonnes per day, or 39 mM CH4 m-2 day-1), and evasion to the atmosphere from the proglacial stream (41 tonnes per day, or 32 M CH4 m-2 day-1) indicates considerable production and release to the atmosphere during the summer melt season. Isotopic signatures (-60.2 ‰ to -7.6 ‰ for δ13CCH4 and -324.3 ‰ to +161.1 ‰ for DCH4), support a biogenic signature within waters emerging from the subglacial environment. Temperate glacial methane production and release may thus be a significant and hitherto unresolved contributor of a potent greenhouse gas to the atmosphere

Fungal diversity regulates plant-soil feedbacks in temperate grassland

Feedbacks between plants and soil microbial communities play an important role in vegetation dynamics, but the underlying mechanisms remain unresolved. Here, we show that the diversity of putative pathogenic, mycorrhizal, and saprotrophic fungi is a primary regulator of plant-soil feedbacks across a broad range of temperate grassland plant species. We show that plant species with resource-acquisitive traits, such as high shoot nitrogen concentrations and thin roots, attract diverse communities of putative fungal pathogens and specialist saprotrophs, and a lower diversity of mycorrhizal fungi, resulting in strong plant growth suppression on soil occupied by the same species. Moreover, soil properties modulate feedbacks with fertile soils, promoting antagonistic relationships between soil fungi and plants. This study advances our capacity to predict plant-soil feedbacks and vegetation dynamics by revealing fundamental links between soil properties, plant resource acquisition strategies, and the diversity of fungal guilds in soil

Does agri-environmental management enhance biodiversity and multiple ecosystem services?: A farm-scale experiment

Agri-environmental management has been promoted as an approach to enhance delivery of multiple ecosystem services. Most agri-environment agreements include several actions that the farmer agrees to put in place. But, most studies have only considered how individual agri-environmental actions affect particular ecosystem services. Thus, there is little understanding of how the range of agri-environmental actions available to a farmer might be deployed on any individual farm to enhance multiple services. To address this knowledge gap, we carried out an experimental study in which we deployed a set of agri-environmental actions on a commercial farm in southern England. Agri-environmental actions comprised wildflower margins and fallow areas in arable fields, creating and enhancing grassland with wildflowers, and digging ponds. Alongside biodiversity responses, we measured effects on a number of ecosystem services: pollination, pest control, crop and forage yield, water quality, climate regulation and cultural services. Wildflower margins enhanced invertebrates, pest control and crop yield, and aesthetic appeal. A greater number of pollinators was linked to enhanced oilseed rape yield. But these margins and the fallows did not prevent run-off of nutrients and sediment into waterways, and showed limited carbon sequestration or reduction of greenhouse gas emissions. Newly-dug ponds captured large amounts of sediment and provided aesthetic appeal. Grasslands had higher soil carbon content and microbial biomass, lower N20 emissions, and net sequestration of carbon compared to arable land. Enhancement of grassland plant diversity increased forage quality and aesthetic appeal. Visitors and residents valued a range of agri-environmental features and biodiversity across the farm. Our findings suggest one cannot necessarily expect any particular agri-environmental action will enhance all of a hoped-for set of ecosystem services in any particular setting. A bet-hedging strategy would be for farmers to apply a suite of options to deliver a range of ecosystem service benefits, rather than assuming that one or two options will work as catch-all solutions

Factors influencing early secondary succession and ecosystem carbon stocks in Brazilian Atlantic Forest

Ecologically relevant restoration of secondary Atlantic forest on abandoned land offers a potential means to recover biodiversity and improve crucial ecosystem services, including carbon sequestration. Early secondary successional trajectories are determined by a range of environmental factors that influence plant community development. Context-specific understanding of forest vegetation communities, their dynamics, and underlying drivers is needed for future restoration strategies. In this study we examined relationships between soil (chemical and physical) and environmental (landscape and topographical) characteristics, plant community attributes, and carbon stocks during early secondary succession. Data were collected at two sites undergoing early secondary succession in seasonally-dry Atlantic Forest (Rio de Janeiro State, Brazil). Both sites were previously used for pasture and abandoned at similar times, but showed differing vegetation communities. We found tree biomass and diversity and ecosystem carbon storage to be strongly positively related to the amount of surrounding forest, less steep slopes and clay soils, and negatively to the abundance of the shrub Leandra aurea. Soil carbon pools significantly increased with aboveground tree biomass. The only factor significantly affecting the metric of overall successional development (combining tree biomass and diversity) was total surrounding forest cover. Our findings suggest recovery of secondary forest and below- and aboveground carbon storage is limited by the amount of adjacent forest, some soil properties and dense shrub establishment down-regulating the succession process. Overall we offer evidence of potential to improve recovery of Atlantic forest with ecologically relevant seeding/planting programmes and selective shrub removal that could benefit ecosystem carbon storage

Interactive biotic and abiotic regulators of soil carbon cycling:evidence from controlled climate experiments on peatland and boreal soils

Partially decomposed plant and animal remains have been accumulating in organic soils (i.e. >40% C content) for millennia, making them the largest terrestrial carbon store. There is growing concern that, in a warming world, soil biotic processing will accelerate and release greenhouse gases that further exacerbate climate change. However, the magnitude of this response remains uncertain as the constraints are abiotic, biotic and interactive. Here, we examined the influence of resource quality and biological activity on the temperature sensitivity of soil respiration under different soil moisture regimes. Organic soils were sampled from 13 boreal and peatland ecosystems located in the United Kingdom, Ireland, Spain, Finland and Sweden, representing a natural resource quality range of C, N and P. They were incubated at four temperatures (4, 10, 15 and 20 °C) at either 60% or 100% water holding capacity (WHC). Our results showed that chemical and biological properties play an important role in determining soil respiration responses to temperature and moisture changes. High soil C : P and C : N ratios were symptomatic of slow C turnover and long-term C accumulation. In boreal soils, low bacterial to fungal ratios were related to greater temperature sensitivity of respiration, which was amplified in drier conditions. This contrasted with peatland soils which were dominated by bacterial communities and enchytraeid grazing, resulting in a more rapid C turnover under warmer and wetter conditions. The unexpected acceleration of C mineralization under high moisture contents was possibly linked to the primarily role of fermented organic matter, instead of oxygen, in mediating microbial decomposition. We conclude that to improve C model simulations of soil respiration, a better resolution of the interactions occurring between climate, resource quality and the decomposer community will be required