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Decades of grazing studies have identified a number of key plant and soil processes affected by large herbivores and how those grazer effects vary among different grassland types. However, there remains little mechanistic understanding about how the effects of grazers on plants and soils may be biogeochemically linked in regulating grassland processes., Here we measured monthly plant and soil variables, including soil moisture, soil nitrogen (N) availability, plant biomass, shoot N concentration and plant production, in grazed and ungrazed (fenced) grasslands during the 2012-2014 growing seasons. Measurements were used to assess direct and indirect biogeochemical pathways by which grazers influenced net above-ground plant production ( NAP) in dry and mesic grasslands in Yellowstone National Park ( YNP)., Herbivores only had direct effects on plant variables at the dry grassland compared to direct and indirect effects on both plant and soil variables at the mesic grassland. By enhancing leaf N content at both grasslands, grazers shifted the resource controlling NAP from N in ungrazed grassland to moisture, and potentially phosphorus and/or other soil nutrients, in grazed grassland., Synthesis. These results indicate the mechanistic linkage between top-down (herbivore) and bottom-up (soil resource) control of grassland production. Changing the resources that limit net above-ground plant production ( NAP) likely has a profound impact on how grazed vs. ungrazed Yellowstone National Park ( YNP) grasslands respond to environmental (e.g., climate, atmospheric N deposition) variability. Because grazing enhances leaf N among many types of grasslands, increasing the sensitivity of plant production to the availability of moisture and nutrients other than N may be a general response of grasslands to grazing. [ABSTRACT FROM AUTHOR]

Plant ecological knowledge accumulated over the past 150 years has enormous implications for agriculture, but most of these implications have not been appreciated by ecologists or agronomists. Here, I present several of the most salient examples., Agriculturalists refer to 'improvements', but plant ecologists know that 'trade-offs' represent a better conceptual framework for agricultural production. There is much evidence for trade-offs between yield and resource use efficiency, and between individual fitness and population yield. I argue that there is also a 'limiting trade-off' between short-term yield and sustainability, and it is important to take this into consideration if we are serious about increasing sustainability., At the local level, agricultural sustainability is about maintaining or improving soil fertility, but this is not a priority in most agricultural systems world-wide. Increased biomass density (both living and dead) in the field is the key to increasing sustainability while maintaining high yields, and I present a vision of 'High Biomass Cropping Systems'., Classical and current research in plant community ecology tells us that rotation of crops with different nutritional needs, pests, diseases and weeds can make a major contribution to sustainability. The very limited crop rotations practised in most modern plant production systems are a clear indication that farming practices are usually based on short-term economic and regulatory factors, without much if any consideration for sustainability., Synthesis. The modern scientific method tells us how we should test hypotheses, but it says nothing about how hypotheses are generated. We need to address the agricultural research agenda if it is to serve the interests of farmers, consumers and society as a whole, rather than narrow but powerful economic interests. [ABSTRACT FROM AUTHOR]

1. While great effort has been made in documenting the processes that drive plant-induced susceptibility after herbivore attack and it is widely accepted that herbivores can facilitate plant diseases, the relative importance of this interaction in controlling plant growth in natural systems remains largely unexplored. 2. In south-western Atlantic salt marshes, we investigated the importance of disease after herbivory by examining: (i) whether or not a herbivorous crab facilitates disease (i.e. fungus infection) in marsh plants ( Spartina alterniflora and S. densiflora) when clipping off small portions of leaves and (ii) the separate and interactive effects of crab grazing but fungal infection in controlling marsh plant growth. 3. Our results show that crab grazing facilitates fungal infection in Spartina leaves. A factorial field experiment shows that both direct crab herbivory and fungal infection strongly suppress plant production (by more than 50%). 4. Synthesis. These experimental results demonstrate that fungal infection following herbivory attack can decrease salt marsh plant production and that increased disease susceptibility can be a fundamental factor in controlling plant production in natural ecosystems, even in cases where herbivores do not directly inoculate the pathogen but only damage plant tissue. [ABSTRACT FROM AUTHOR]

1. Plant species affect ecosystem carbon uptake via biomass production and carbon release via decomposition processes. Differences in their responses to climate change and effects on ecosystem carbon cycling processes may thus feedback to the atmospheric carbon balance and the climate at a global scale. Hierarchical species classifications based on plant growth forms are widely used in cold, northern biomes to generalize and predict these differences. This review investigates the usefulness of broad (vascular, non-vascular), intermediate (woody, non-woody) and narrow (evergreen shrubs, deciduous shrubs, graminoids, forbs) plant growth-form-based groups in these biomes for predicting plant responses to climate change and effects on the main processes of the full carbon cycle by looking at the similarity of species within growth-form groups and the consistency of differences among groups under changing environmental conditions. 2. Production responses to climate change differ between broad growth-form groups, but their opposite responses do not imply that the responses of non-vascular plants are consistently negative. Within vascular growth forms, production responses to climate change are not always similar among species under identical conditions, and average differences among narrow vascular growth forms are usually small. Moreover, differences in production responses among growth forms strongly depend upon the duration of the study, the region and the ecosystem type. 3. Species within narrow growth forms show a high similarity for a range of leaf litter chemistry variables and differences among narrow growth forms are often large and consistent. However, differences in leaf litter decomposability are large between broad growth-form groups, but small and environment-dependent among important narrow vascular growth forms. Litter feedback effects to plant production vary among narrow vascular growth forms, but the differences strongly depend on the study duration. Data on the climate dependence of growth-form differences regarding this aspect of the carbon cycle are currently lacking. 4. Synthesis: Overall, the usefulness of growth-form-based groups clearly differs between carbon cycling processes. Different aggregation levels are therefore needed for different processes. For most processes there is evidence that the differences among growth forms depend on environmental conditions, which hampers their use for generalizations and modelling. Future studies should therefore explicitly test for differences among growth-form groups and aim to unravel the dependence of growth-form differences on environmental conditions. [ABSTRACT FROM AUTHOR]

Summary 1 The influence of botanical composition on annual phytomass production of a semi-arid grassland in response to precipitation was tested with a 19-year experiment. Three compositional states reflecting good, medium and poor rangeland condition, whose basal cover increased from poor through to good, were created in 1978. 2 Multiple regression models were developed for assessing whether phytomass was influenced by precipitation, composition, phytomass of the previous year, basal cover, abundance of individual species, or diversity. Composition and precipitation accounted for 66% of the variation in phytomass, but a separate model of basal cover by precipitation was equally successful. The linear effect of rainfall on phytomass was enhanced as composition improved from poor (0.076 g m-2 mm-1 ) through medium (0.197 g m-2 mm-1 ) to good (0.277 g m-2 mm-1 ). Phytomass increased for low precipitation if it had been high the preceding year. Phytomass was more variable over time with deteriorating condition. 3 Species’ complementarity ensured greater and more stable production. Setaria sphacelata , Eragrostis chloromelas and Digitaria eriantha increased phytomass on the good or medium condition grasslands during drier years, whereas Themeda triandra had this effect during wetter years. 4 Precipitation-use efficiency (PUE) was influenced mostly by composition and a linear and quadratic effect of precipitation (63% of variance). Optimum PUE of 0.308, 0.203 and 0.096 g m-2 mm-1 for the good, medium and poor condition grasslands, respectively, occurred at intermediate amounts (±680 mm) of precipitation. PUE was increased if phytomass had been high the previous year. 5 Species’ complementarity of PUE in response to precipitation was evident for all compositional states. Ten, mostly uncommon, species and their interaction with precipitation explained an extra... [ABSTRACT FROM AUTHOR]