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Plant community biodiversity can be maintained, at least partially, by shifts in species interactions between facilitation and competition for resources as environmental conditions change. These interactions also drive ecosystem functioning, including productivity, and can promote over‐yielding‐ an ecosystem service prioritized in agro‐ecosystems, such as pastures, that occurs when multiple species together are more productive than the component species alone. Importantly, species interactions that can result in over‐yielding may shift in response to rising CO2 concentrations and changes in resource availability, and the consequences these shifts have on production is uncertain especially in the context of tropical mixed‐species grasslands.We examined the relative performance of two species pairs of tropical pasture grasses and legumes growing in monoculture and mixtures in a glasshouse experiment manipulating CO2. We investigated how over‐yielding can arise from nitrogen (N) niche partitioning and biotic facilitation using stable isotopes to differentiate soil N from biological N fixation (BNF) within N acquisition into above‐ground biomass for these two‐species mixtures.We found that N niche partitioning in species‐level use of soil N versus BNF drove species interactions in mixtures. Importantly partitioning and overyielding were generally reduced under elevated CO2. However, this finding was mixture‐dependent based on biomass of dominant species in mixtures and the strength of selection effects for the dominant species.This study demonstrates that rising atmospheric CO2 may alter niche partitioning between co‐occurring species, with negative implications for the over‐yielding benefits predicted for legume‐grass mixtures in working landscapes with tropical species. Furthermore, these changes in inter‐species interactions may have consequences for grassland composition that are not yet considered in larger‐scale projections for impacts of climate change and species distributions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Copyright of Functional Ecology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Biological nitrogen fixation (BNF) provides a globally important input of nitrogen (N); its quantification is critical but technically challenging. Leaf reflectance spectroscopy offers a more rapid approach than traditional techniques to measure plant N concentration ([N]) and isotopes (δ15N). Here we present a novel method for rapidly and inexpensively quantifying BNF using optical spectroscopy. We measured plant [N], δ15N, and the amount of N derived from atmospheric fixation (Ndfa) following the standard traditional methodology using isotope ratio mass spectrometry (IRMS) from tissues grown under controlled conditions and taken from field experiments. Using the same tissues, we predicted the same three parameters using optical spectroscopy. By comparing the optical spectroscopy-derived results with traditional measurements (i.e. IRMS), the amount of Ndfa predicted by optical spectroscopy was highly comparable to IRMS-based quantification, with R 2 being 0.90 (slope=0.90) and 0.94 (slope=1.02) (root mean square error for predicting legume δ15N was 0.38 and 0.43) for legumes grown in glasshouse and field, respectively. This novel application of optical spectroscopy facilitates BNF studies because it is rapid, scalable, low cost, and complementary to existing technologies. Moreover, the proposed method successfully captures the dynamic response of BNF to climate changes such as warming and drought. [ABSTRACT FROM AUTHOR]

Northern peatlands represent a long-term net sink for atmospheric C[O.sub.2], but these ecosystems can shift from net carbon (C) sinks to sources based on changing climate and environmental conditions. In particular, changes in water availability associated with climate control peatland vegetation and carbon uptake processes. We examined the influence of changing hydrology on plant species abundance and ecosystem primary production in an Alaskan fen by manipulating the water table in field treatments to mimic either sustained flooding (raised water table) or drought (lowered water table) conditions for 6 years. We found that water table treatments altered plant species abundance by increasing sedge and grass cover in the raised water table treatment and reducing moss cover while increasing vascular green area in the lowered water table treatment. Gross primary productivity was lower in the lowered treatment than in the other plots, although there were no differences in total biomass or vascular net primary productivity among the treatments. Overall, our results indicate that vegetation abundance was more sensitive to variation in water table than total biomass and vascular biomass accrual. Finally, in our experimental peatland, drought had stronger consequences for change in vegetation abundance and ecosystem function than sustained flooding. Key words: primary productivity, peatland, hydrologic manipulation, drying, flooding. A long terme les tourbieres nordiques constituent un puits net pour le C[O.sub.2] atmospherique mais ces ecosystemes peuvent passer d'un puits a une source nette de carbone (C) a cause du changement climatique et des conditions environnementales. Plus particulierement, les modifications de la disponibilite en eau associees a l'effet du climat influencent la vegetation des tourbieres et les processus d'absorption de C. Nous avons etudie l'influence de la modification du regime hydrique sur l'abondance des especes vegetales et la production primaire de l'ecosysteme dans une tourbiere basse en Alaska. Le regime hydrique a ete modifie en manipulant la nappe phreatique avec des traitements sur le terrain visant a reproduire les conditions d'une inondation (elevation de la nappe phreatique) ou d'une secheresse (abaissement de la nappe phreatique) qui ont persiste pendant 6 ans. Nous avons observe que les modifications de la nappe phreatique ont influence l'abondance des especes vegetales : la couverture de carex et de graminees a augmente alors que la couverture de mousses a diminue ou la nappe phreatique avait ete elevee tandis que la superficie occupee par les plantes vasculaires a augmente ou la nappe phreatique avait ete abaissee. La production primaire brute etait plus faible ou la nappe phreatique avait ete abaissee que dans les autres parcelles mais il n'y avait pas de differences entre les traitements quant a la biomasse totale ou la productivite primaire nette des plantes vasculaires. Globalement, nos resultats indiquent que l'abondance de la vegetation est plus sensible a la variation de la nappe phreatique que la biomasse totale et l'accroissement de la biomasse des plantes vasculaires. Finalement, dans notre tourbiere experimentale la secheresse a davantage contribue a modifier l'abondance de la vegetation et la fonction de l'ecosysteme que l'inondation persistante. [Traduit par la Redaction] Mots-cles: productivite primaire, tourbiere, manipulation hydrologique, secheresse, inondation., Introduction Carbon (C) sequestration in the biosphere plays a substantial role in offsetting increases of atmospheric C from anthropogenic sources (Esser et al. 2011). Despite a small global land area, [...]

Symbiotic fungi mediate important energy and nutrient transfers in terrestrial ecosystems. Environmental change can lead to shifts in communities of symbiotic fungi, but the consequences of these shifts for nutrient dynamics among symbiotic partners are poorly understood. Here, we assessed variation in carbon (C), nitrogen (N) and phosphorus (P) in tissues of arbuscular mycorrhizal (AM) fungi and a host plant (Medicago sativa) in response to experimental warming and drought. We linked compositional shifts in AM fungal communities in roots and soil to variation in hyphal chemistry by using high‐throughput DNA sequencing and joint species distribution modelling. Compared to plants, AM hyphae was 43% lower in (C) and 24% lower in (N) but more than nine times higher in (P), with significantly lower C:N, C:P and N:P ratios. Warming and drought resulted in increases in (P) and reduced C:P and N:P ratios in all tissues, indicating fungal P accumulation was exacerbated by climate‐associated stress. Warming and drought modified the composition of AM fungal communities, and many of the AM fungal genera that were linked to shifts in mycelial chemistry were also negatively impacted by climate variation. Our study offers a unified framework to link climate change, fungal community composition, and community‐level functional traits. Thus, our study provides insight into how environmental change can alter ecosystem functions via the promotion or reduction of fungal taxa with different stoichiometric characteristics and responses. see also the Perspective by Pierre‐Luc Chagnon [ABSTRACT FROM AUTHOR]

Under warmer and drier future conditions, global livestock and dairy production are threatened by impacts on the productivity and nutritional quality of pastures. However, morphological and nutritional adjustments within plants in response to warming and drought vary among species and less is known how these relate to production and forage quality. To investigate this, we grew two common pasture species, tall fescue (Festuca arundinacea: grass) and lucerne (Medicago sativa: legume), in a climate‐controlled facility, under different temperatures (ambient and elevated) and watering regimes (well‐watered and droughted). We found that drought had a strong negative impact on biomass production, morphology and nutritional quality while warming only significantly affected both species when response metrics were considered in concert, although to a lesser degree than the drought. Furthermore, interactions between warming and drought were only seen for lucerne, with a reduction in biomass and an increase in dead material and dry matter. In tall fescue, drought had bigger impacts on nutritional composition than morphological traits, while in lucerne, drought affected all morphological traits and most of the nutritional parameters. These findings suggest that in future climate scenarios, drought may be a stronger driver of changes in the morphology and nutritional composition of pasture grasses and legumes, compared to modest levels of warming. [ABSTRACT FROM AUTHOR]

Plant species show a broad spectrum of plasticity in their covarying root traits in response to soil water limitation ranging from no change to shifts towards traits that enhance water and nutrient acquisition. Knowledge of root trait correlations and associated trait plasticity under drought is crucial to sustaining grassland production, including rangelands and pastures, under future, drier climates.Here, we investigated below‐ground responses to drought in four C3 and three C4 grasses and whether these explain above‐ground responses during extreme cool‐season drought and post‐drought recovery in a well‐replicated field experiment. We hypothesised that (a) C3 and C4 functional groups differ in their below‐ground trait responses to drought: C3 species shift their traits in line with a drought avoidance strategy and C4 species shift towards drought tolerance strategies; (b) post‐drought recovery is associated with below‐ground carbon reserves in both functional groups.Root traits in the C3 functional group differed from C4 by having higher values for specific root length, nitrogen and soluble sugar concentrations, while C4 root traits were associated with higher mean diameter, tissue density and starch concentrations. Drought‐induced plasticity in root traits in both functional groups was evidenced by increased values for specific root length, soluble sugars and nitrogen concentrations, and reduced values for tissue density, which we interpret as a drought avoidance strategy. Increasing root soluble sugars in C3 and C4 grasses and lower root tissue density in C4 species under drought were associated with greater above‐ground productivity. Above‐ground biomass recovery post‐drought was predicted by root and crown soluble sugar concentrations and root longevity across both plant functional groups.These findings highlight the importance of understanding links between root trait plasticity and plant productivity during and following drought for predicting plant species' responses to changes in a future climate. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Given the frequent overlap between biological plant invasion and ecological restoration efforts it is important to investigate their interactions to sustain desirable plant communities and modify long-term legacies both above- and below-ground. To address this relationship, we used natural reference, invaded and created vernal pools in the Central Valley of California to examine potential changes in direct and indirect plant effects on soils associated with biological invasion and active restoration ecosystem disturbances. Our results showed that through a shift in vegetation composition and changes in the plant community tissue chemistry, invasion by non-native plant species has the potential to transform plant inputs to soils in vernal pool systems. In particular, we found that while invasive plant litter decomposition was driven by seasonal and interannual variability, associated with changes in precipitation, the overall decomposition rates for invasive litter was drastically lower than native species. This shift has important implications for long-term alterations in plant-based inputs to soils in an amplifying feedback to nutrient cycling. Moreover, these results were independent of historic active restoration efforts. Despite the consistent shift in plant litter decomposition rates and community composition, we did not detect associated shifts in below-ground function associated with invasion by non-native plants. Instead, soil C:N ratios and microbial biomass did not differ between invaded and naturally occurring reference pools but were reduced in the manipulated created pools independent of invasion levels. Our results suggest that while there is an observed invasive amplifying feedback above-ground this trajectory is not represented below-ground, and restoration legacies dominated 10 years after practices were applied. Restoration practices that limit invasive plant feedbacks and account for soil legacy recovery, therefore offer the best solution for disturbed ephemeral ecosystems. [ABSTRACT FROM AUTHOR]

Northern peatlands represent a long-term net sink for atmospheric CO2, but these ecosystems can shift from net carbon (C) sinks to sources based on changing climate and environmental conditions. In particular, changes in water availability associated with climate control peatland vegetation and carbon uptake processes. We examined the influence of changing hydrology on plant species abundance and ecosystem primary production in an Alaskan fen by manipulating the water table in field treatments to mimic either sustained flooding (raised water table) or drought (lowered water table) conditions for 6 years. We found that water table treatments altered plant species abundance by increasing sedge and grass cover in the raised water table treatment and reducing moss cover while increasing vascular green area in the lowered water table treatment. Gross primary productivity was lower in the lowered treatment than in the other plots, although there were no differences in total biomass or vascular net primary productivity among the treatments. Overall, our results indicate that vegetation abundance was more sensitive to variation in water table than total biomass and vascular biomass accrual. Finally, in our experimental peatland, drought had stronger consequences for change in vegetation abundance and ecosystem function than sustained flooding. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The increasing prevalence of drought events in grasslands and shrublands worldwide potentially has impacts on soil organic carbon (SOC). We leveraged the International Drought Experiment to study how SOC, including particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) concentrations, responds to extreme drought treatments (1-in-100-year) for 1 to 5 years at 19 sites worldwide. In more mesic areas (aridity index > 0.65), SOC and POC concentrations decreased by 7.9% (±3.9) and 15.9% (±6.2) with drought, respectively, but there were no impacts on MAOC concentrations. However, drought had no impact on SOC, POC, or MAOC concentrations in drylands (aridity index < 0.65). The response of SOC to drought varied along an aridity gradient, concomitant with interannual precipitation variability and standing SOC concentration gradients. These findings highlight the differing response magnitudes of POC and MAOC concentrations to drought and the key regulating role of aridity. [ABSTRACT FROM AUTHOR]

This paper reviews information about field observations of vegetation productivity in Australia’s rangeland systems and identifies the need to establish a national initiative to collect net primary productivity (NPP) and biomass data for rangeland pastures. Productivity data are needed for vegetation and carbon model parameterisation, calibration and validation. Several methods can be used to estimate pasture productivity at various spatial and temporal scales, ranging from in situ measurements to satellite-based approaches and biogeochemical modelling. However, there is a barrier to implementing national vegetation and carbon modelling schemes because of the lack of digitised and readily available data derived from field observations, not because of the lack of modelling expertise. Our main goal in this paper is to explore the potential for consolidation of existing NPP and biomass databases for Australian rangelands. A protocol structure was proposed to establish a productivity database for Australia. The TERN (Terrestrial Ecosystems Research Network) national field data network for rangeland pasture productivity monitoring and modelling team could potentially coordinate the database. Government agencies and national and international research institutions could use the outputs from productivity models to inform greenhouse gas emissions and in measuring mitigation activities relevant for reporting against the United Nations’ Sustainable Development Goals and other international obligations. Other applications include monitoring fire danger, tracking ecological restoration and protection, and estimating fodder availability. Australian researchers have the tools needed to succeed in creating such a national database and a robust community of practice to curate it, enhance it and benefit from its availability. [ABSTRACT FROM AUTHOR]

The increasing prevalence of drought events in grasslands and shrublands worldwide potentially has impacts on soil organic carbon (SOC). We leveraged the International Drought Experiment to study how SOC, including particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) concentrations, responds to extreme drought treatments (1-in-100-year) for 1 to 5 years at 19 sites worldwide. In more mesic areas (aridity index > 0.65), SOC and POC concentrations decreased by 7.9% (±3.9) and 15.9% (±6.2) with drought, respectively, but there were no impacts on MAOC concentrations. However, drought had no impact on SOC, POC, or MAOC concentrations in drylands (aridity index < 0.65). The response of SOC to drought varied along an aridity gradient, concomitant with interannual precipitation variability and standing SOC concentration gradients. These findings highlight the differing response magnitudes of POC and MAOC concentrations to drought and the key regulating role of aridity.