Interactions of arbuscular mycorrhizal fungi, critical loads of nitrogen deposition, and shifts from native to invasive species in a southern California shrubland

Anthropogenic nitrogen (N) deposition and invasive species are causing declines in global biodiversity, and both factors impact the diversity and functioning of arbuscular mycorrhizal (AM) fungi. Shifts in arbuscular mycorrhizal fungal (AMF) communities can generate feedback to native plants and affect their success, as was observed in California’s coastal sage scrub, which is a Mediterranean-type shrubland threatened by invasive grasses. As vegetation-type conversion from native shrubland to exotic annual grassland increased along a gradient of increasing N deposition, the richness of native plant species and of spore morphotypes decreased. Rapid declines in all plant and fungal values occurred at the critical load (CL) of 10–11 kg N·ha−1·year−1, indicating that AM fungi respond to the same environmental signals as the plants, and can be used to assess CL. Shrub root colonization also decreased along the N gradient, but colonization of the invasive grass was dominated by a fine AMF endophyte that was unresponsive to elevated N. A greenhouse experiment to assess AMF functioning showed that the native shrub Artemisia californica Less. had a negative growth response to an inoculum from high-N but not low-N soils, whereas the invasive grass Bromus rubens L. had a positive response to both inocula. Differential functioning of AM fungi under N deposition may in part explain vegetation-type conversion and the decline of this native shrubland

Deliberate clinical inertia: Using meta-cognition to improve decision-making

Deliberate clinical inertia is the art of doing nothing as a positive response. To be able to apply this concept, individual clinicians need to specifically focus on their clinical decision-making. The skill of solving problems and making optimal clinical decisions requires more attention in medical training and should play a more prominent part of the medical curriculum. This paper provides suggestions on how this may be achieved. Strategies to mitigate common biases are outlined, with an emphasis on reversing a 'more is better' culture towards more temperate, critical thinking. To incorporate such an approach in medical curricula and in clinical practice, institutional endorsement and support is required

Mycorrhizal community dynamics following nitrogen fertilization: A cross-site test in five grasslands. Ecol. Monogr

Abstract. Arbuscular mycorrhizal fungi (AMF) are considered both ecologically and physiologically important to many plant communities. As a result, any alteration in AMF community structure following soil nitrogen (N) enrichment may impact plant community function and contribute to widespread changes in grassland productivity. We evaluated the responses of AMF communities to N fertilization (!100 kg NÁha ) in five perennial grasslands within the Long-Term Ecological Research network to generate a broader understanding of the drivers contributing to AMF species richness and diversity with increasing soil N fertility, and subsequent effects to host-plant communities. AMF spore and hyphal community data at three mesic sites (Cedar Creek, Kellogg Biological Station, Konza Prairie) and two semiarid sites (Sevilleta, Shortgrass Steppe) were collected over two consecutive years and used to test four hypotheses about AMF responses to N fertilization. Under ambient soil N, plant annual net primary productivity and soil phosphorus (P) were strongly related to climatic differences in AMF communities (semiarid vs. mesic). Following N fertilization, the drivers of AMF community structure were soil N availability, N:P supply ratio, and host-plant photosynthetic strategy (C 3 vs. C 4 ) but not climate. In P-rich soils (low N:P), N fertilization reduced AMF productivity, species richness, and diversity and intensified AMF community convergence due to the loss of rare AMF species and the increased abundance of Glomus species. In P-limited soils (high N:P), AMF productivity, species richness, and diversity increased with N fertilization; the most responsive AMF taxa were Acaulospora, Scutellospora, and Gigaspora. Soil N or N:P 3 host-plant (C 3 , C 4 ) interactions further modified these responses: AMF hyphae (primarily Gigasporaceae) associated with C 3 plants increased in abundance with N fertilization, whereas C 4 plants hosted nitrophilous Glomus species. Such responses were independent of the duration or quantity of N fertilization, or the time since cessation of N fertilization. This synthesis provides a new understanding of AMF community patterns and processes, and it identifies three key drivers (soil N, N:P, host plant) of AMF community structure that may be tested in other communities

Nitrogen enrichment alters mycorrhizal allocation at five mesic to semiarid grasslands.

Abstract. Arbuscular mycorrhizal (AM) fungi are integral components of grasslands because most plants are associated with interconnected networks of AM hyphae. Mycorrhizae generally facilitate plant uptake of nutrients from the soil. However, mycorrhizal associations are known to vary in their mutualistic function, and there is currently no metric that links AM functioning with fungal colonization of roots. Mycorrhizal structures differ in their physiological and ecological functioning, so changes in AM allocation to intraradical (inside roots) and extraradical (in soil) structures may signal shifts in mycorrhizal function. We hypothesize that the functional equilibrium model applies to AM fungi and that fertilization should reduce allocation to arbuscules, coils, and extraradical hyphae, the fungal structures that are directly involved in nutrient acquisition and transfer to plants. This study compared AM responses to experimental N enrichment at five grasslands distributed across North America. Samples were collected from replicated N-enriched (and some P-enriched) and control plots throughout the growing season for three years. Intraradical AM structures were measured in over 1400 root samples, extraradical hyphal density was measured in over 590 soil samples, and spore biovolume was analyzed in over 400 soil samples. There were significant site ϫ N interactions for spore biovolume, extraradical hyphae, intraradical hyphae, and vesicles. Nitrogen enrichment strongly decreased AM structures at Cedar Creek, the site with the lowest soil N:P, and it increased AM structures at Konza Prairie, the site with the highest soil N:P. As predicted by the functional equilibrium model, in soils with sufficient P, relative allocation to arbuscules, coils, and extraradical hyphae was generally reduced by N enrichment. Allocation to spores and hyphae was most sensitive to fertilization. At the mesic sites, this response was associated with a shift in the relative abundance of Gigasporaceae within AM fungal communities. This study demonstrates that N enrichment impacts mycorrhizal allocation across a wide range of grassland ecosystems. Such changes are important because they suggest an alteration in mycorrhizal functioning that, in turn, may impact plant community composition and ecosystem function

Reading tea leaves worldwide: Decoupled drivers of initial litter decomposition mass-loss rate and stabilization

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large-scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass-loss rates and stabilization factors of plant-derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy-to-degrade components accumulate during early-stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass-loss rates and stabilization, notably in colder locations. Using TBI improved mass-loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early-stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models

Reading tea leaves worldwide: decoupled drivers of initial litter decomposition mass‐loss rate and stabilization

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large‐scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass‐loss rates and stabilization factors of plant‐derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy‐to‐degrade components accumulate during early‐stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass‐loss rates and stabilization, notably in colder locations. Using TBI improved mass‐loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early‐stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models

Don't just do something, stand there! The value and art of deliberate clinical inertia

It can be difficult to avoid unnecessary investigations and treatments, which are a form of low-value care. Yet every intervention in medicine has potential harms, which may outweigh the potential benefits. Deliberate clinical inertia is the art of doing nothing as a positive response. This paper provides suggestions on how to incorporate deliberate clinical inertia into our daily clinical practice, and gives an overview of current initiatives such as ‘Choosing Wisely’ and the ‘Right Care Alliance’. The decision to ‘do nothing’ can be complex due to competing factors, and barriers to implementation are highlighted. Several strategies to promote deliberate clinical inertia are outlined, with an emphasis on shared decision-making. Preventing medical harm must become one of the pillars of modern health care and the art of not intervening, that is, deliberate clinical inertia, can be a novel patient-centred quality indicator to promote harm reduction.</p

Efflux of hydraulically lifted water from mycorrhizal fungal hyphae during imposed drought

Apart from improving plant and soil water status during drought, it has been suggested that hydraulic lift (HL) could enhance plant nutrient capture through the flow of mineral nutrients directly from the soil to plant roots, or by maintaining the functioning of mycorrhizal fungi. We evaluated the extent to which the diel cycle of water availability created by HL covaries with the efflux of HL water from the tips of extramatrical (external) mycorrhizal hyphae, and the possible effects on biogeochemical processes. Phenotypic mycorrhizal fungal variables, such as total and live hyphal lengths, were positively correlated with HL efflux from hyphae, soil water potential (dawn), and plant response variables (foliar 15N). The efflux of HL water from hyphae was also correlated with bacterial abundance and soil enzyme activity (P), and the moistening of soil organic matter. Such findings indicate that the efflux of HL water from the external mycorrhizal mycelia may be a complementary explanation for plant nutrient acquisition and survival during drought