Developments in Agricultural Soil Quality and Health: Reflections by the Research Committee on Soil Organic Matter Management

The North Central Education and Research Activity Committee (NCERA-59) was formed in 1952 to address how soil organic matter formation and management practices affect soil structure and productivity. It is in this capacity that we comment on the science supporting soil quality and associated soil health assessment for agricultural lands with the goal of hastening progress in this important field. Even though the suite of soil quality indicators being applied by U.S. soil health efforts closely mirrors the “minimum data set” we developed and recommended in the mid-1990s, we question whether the methods or means for their selection and development are sufficient to meet current and emerging soil health challenges. The rush to enshrine a standard suite of dated measures may be incompatible with longer-term goals. Legitimate study of soil health considers soil change accrued over years to decades that influence on- and off-site function. Tailoring of methods to local conditions is needed to effectively apply and interpret indicators for different soil resource regions and land uses. Adherence to a set suite of methods selected by subjective criteria should be avoided, particularly when we do not yet have adequate data or agreed upon interpretive frameworks for many so-called “Tier 1” biological indicators used in soil health assessment. While pooling data collected by producer-groups is one of the most exciting new trends in soil health, standardizing methods to meet broad inventory goals could compromise indicator use for site or application-specific problem solving. Changes in our nation’s research landscape are shifting responsibility for soil stewardship from national and state government backed entities to public-private partnerships. As a result, it is critical to ensure that the data needed to assess soil health are generated by reproducible methods selected through a transparent process, and that data are readily available for public and private sector use. Appropriate methods for engagement need to be applied by public-private research partnerships as they establish and expand coordinated research enterprises that can deliver fact-based interpretation of soil quality indicators within the type of normative soil health framework conceived by USDA over 20 years ago. We look to existing examples as we consider how to put soil health information into the hands of practitioners in a manner that protects soils’ services

Developments in Agricultural Soil Quality and Health: Reflections by the Research Committee on Soil Organic Matter Management

The North Central Education and Research Activity Committee (NCERA-59) was formed in 1952 to address how soil organic matter formation and management practices affect soil structure and productivity. It is in this capacity that we comment on the science supporting soil quality and associated soil health assessment for agricultural lands with the goal of hastening progress in this important field. Even though the suite of soil quality indicators being applied by U.S. soil health efforts closely mirrors the “minimum data set” we developed and recommended in the mid-1990s, we question whether the methods or means for their selection and development are sufficient to meet current and emerging soil health challenges. The rush to enshrine a standard suite of dated measures may be incompatible with longer-term goals. Legitimate study of soil health considers soil change accrued over years to decades that influence on- and off-site function. Tailoring of methods to local conditions is needed to effectively apply and interpret indicators for different soil resource regions and land uses. Adherence to a set suite of methods selected by subjective criteria should be avoided, particularly when we do not yet have adequate data or agreed upon interpretive frameworks for many so-called “Tier 1” biological indicators used in soil health assessment. While pooling data collected by producer-groups is one of the most exciting new trends in soil health, standardizing methods to meet broad inventory goals could compromise indicator use for site or application-specific problem solving. Changes in our nation’s research landscape are shifting responsibility for soil stewardship from national and state government backed entities to public-private partnerships. As a result, it is critical to ensure that the data needed to assess soil health are generated by reproducible methods selected through a transparent process, and that data are readily available for public and private sector use. Appropriate methods for engagement need to be applied by public-private research partnerships as they establish and expand coordinated research enterprises that can deliver fact-based interpretation of soil quality indicators within the type of normative soil health framework conceived by USDA over 20 years ago. We look to existing examples as we consider how to put soil health information into the hands of practitioners in a manner that protects soils’ services

Designing forest biodiversity experiments : general considerations illustrated by a new large experiment in subtropical China

Funded by German Research Foundation. Grant Number: DFG FOR 891/1 and 2 National Natural Science Foundation of China. Grant Numbers: NSFC 30710103907, 30930005, 31170457 , 31210103910 Swiss National Science Foundation (SNSF) Sino-German Centre for Research Promotion in BeijingPeer reviewedPublisher PD

Designing forest biodiversity experiments: general considerations illustrated by a new large experiment in subtropical China


 Biodiversity-ecosystem functioning (BEF) experiments address ecosystem-level consequences of species loss by comparing communities of high species richness with communities from which species have been gradually eliminated. BEF experiments originally started with microcosms in the laboratory and with grassland ecosystems. A new frontier in experimental BEF research is manipulating tree diversity in forest ecosystems, compelling researchers to think big and comprehensively.
 We present and discuss some of the major issues to be considered in the design of BEF experiments with trees and illustrate these with a new forest biodiversity experiment established in subtropical China (Xingangshan, Jiangxi Province) in 2009/2010. Using a pool of 40 tree species, extinction scenarios were simulated with tree richness levels of 1, 2, 4, 8 and 16 species on a total of 566 plots of 25.8 × 25.8 m each.
 The goal of this experiment is to estimate effects of tree and shrub species richness on carbon storage and soil erosion; therefore, the experiment was established on sloped terrain. The following important design choices were made: (i) establishing many small rather than fewer larger plots, (ii) using high planting density and random mixing of species rather than lower planting density and patchwise mixing of species, (iii) establishing a map of the initial 'ecoscape' to characterize site heterogeneity before the onset of biodiversity effects and (iv) manipulating tree species richness not only in random but also in trait-oriented extinction scenarios.
 Data management and analysis are particularly challenging in BEF experiments with their hierarchical designs nesting individuals within-species populations within plots within-species compositions. Statistical analysis best proceeds by partitioning these random terms into fixed-term contrasts, for example, species composition into contrasts for species richness and the presence of particular functional groups, which can then be tested against the remaining random variation among compositions.
 We conclude that forest BEF experiments provide exciting and timely research options. They especially require careful thinking to allow multiple disciplines to measure and analyse data jointly and effectively. Achieving specific research goals and synergy with previous experiments involves trade-offs between different designs and requires manifold design decisions.&#13

Seasonal Plant Nitrogen Use and Soil N pools in Intermediate Wheatgrass (<i>Thinopyrum intermedium</i>)

Intermediate wheatgrass (Thinopyrum intermedium; IWG) is a perennial grass under development as a grain and forage crop. Although IWG is known for its ability to take up nitrate and improve water quality, seasonal nitrogen (N) demand and uptake by IWG is not well known. We measured IWG shoot, root, and grain production, tissue N concentration, and soil mineral N at multiple plant growth stages in 1- and 2-year-old IWG stands fertilized with various rates of N: (1) 80 kg N ha−1 applied at spring regrowth (spring), (2) 40–40 kg N ha−1 applied at spring regrowth and anthesis (split), and (3) an unfertilized control. We also calculated nitrogen use efficiency and biomass N yield. Soil mineral N, N-mineralization rates, and plant N concentration increased with fertilization, and lodging increased with spring fertilization, while root physiological N use efficiency (PNUE) declined with fertilization. Seasonally, shoot and root N concentration declined at physiological maturity, while shoot PNUE was highest at maturity, suggesting either that surplus N was allocated to grain or that more biomass was being produced per unit N taken up. In the 1-year-old stand, during fall regrowth, soil mineral N levels were among the lowest; however, the total soil N was highest compared with other sampling times, suggesting a large influx of organic N between physiological maturity and fall regrowth. Based on our results, IWG is well suited to use nitrogen inputs and avoid excess N leaching into groundwater, but it is also clear that IWG has strong seasonal N allocation patterns that should be taken into consideration with N recommendations and best practices

Changes in enzyme activities and in the functional diversity of actinomycetes due to long term agricultural management

Long-term agricultural management alters soil organic matter, nutrient status, and potentially the decomposer community. We measured the abundance and activity of cellulose, chitin, and protease degrading bacteria, and total soil extra-cellular enzyme activity for cellulose (&#x3b2;-glucosidase), chitinase (N-acetyl-glucosaminidase), xylosidase, and phosphatase activity. By combining these methods, we could determine how bacterial decomposer abundance and function were altered by long-term management, and how the bacterial decomposer community relates to overall soil enzyme activity. We also measured microbial total fungal and bacterial biomass, soil organic carbon pools, and extractable nitrogen for supplementary comparisons. Soil samples were taken in June of 2010 from the Bad Lauchst&#xe4;dt field station&#x2019;s Static Fertilization Experiment, under treatment for 108 years. Treatments include mineral (NPK) fertilizer (none or added at 140, 60, and 230 kg ha-1 yr-1) and manure addition (none, 20 T ha-1 2yr-1, and 30 T ha-1 2yr-1) in a full factorial experiment. We found that total cellulase activity and the abundance of cellulase degrading bacteria were higher in plots with manure addition. We observed the same pattern for total phosphatase activity, total chitinase activity, and the abundance of chitin degrading bacteria, although the trend was not statistically significant for total chitinase activity. These results suggest that long-term management does alter decomposition and that total soil enzyme activity reflects the abundance of decomposer bacteria

Leaf litter diversity alters microbial activity, microbial abundances, and nutrient cycling in a subtropical forest ecosystem

Human activities affect both tree species composition and diversity in forested ecosystems. This in turn alters the species diversity of plant litter and litter quality, which may have cascading effects on soil microbial communities and their functions for decomposition and nutrient cycling. We tested microbial responses to litter species diversity in a leaf litter decomposition experiment including monocultures, 2-, and 4-species mixtures in the subtropical climate zone of southeastern China. Soil microbial community composition was assessed by lipid analysis, and microbial functions were measured using extracellular enzyme activity and gross rates of nitrogen mineralization. We observed a positive relationship between litter species diversity and abundances of mycorrhizal fungi and actinomycetes. Alternatively, enzyme activities involved in carbon and phosphorus acquisition, and enzyme indices of relative carbon limitation, were higher only in the 4-species mixtures. This suggests that the minimum basal substrate level for enzyme production was reached, or that limitation was higher, at the highest diversity level only. Responses to litter diversity also changed over time, where phosphatase responses to litter diversity were strongest early in decomposition and the indices of carbon limitation relative to other nutrients showed stronger responses later in decomposition. Enzyme activities were related to lipid biomarker data and the mass of litter remaining at the third time point, but relationships between enzyme activity and the mass of litter remaining were not consistent across other time points. We conclude that litter species richness will likely only reduce microbial functions at key intervals of diversity loss while microbial growth is more sensitive to incremental diversity loss, with no clear relationships between them or to ecosystem functions. The observed litter diversity effects on soil microbial biomass and enzyme activity indicate interactions of aboveground and belowground communities, and together with environmental conditions they are important for maintaining ecosystem functions

Soil microbial responses to warming and increased precipitation and their implications for ecosystem C cycling

A better understanding of soil microbial ecology is critical to gaining an understanding of terrestrial carbon (C) cycle-climate change feedbacks. However, current knowledge limits our ability to predict microbial community dynamics in the face of multiple global change drivers and their implications for respiratory loss of soil carbon. Whether microorganisms will acclimate to climate warming and ameliorate predicted respiratory C losses is still debated. It also remains unclear how precipitation, another important climate change driver, will interact with warming to affect microorganisms and their regulation of respiratory C loss. We explore the dynamics of microorganisms and their contributions to respiratory C loss using a 4-year (2006-2009) field experiment in a semi-arid grassland with increased temperature and precipitation in a full factorial design. We found no response of mass-specific (per unit microbial biomass C) heterotrophic respiration to warming, suggesting that respiratory C loss is directly from microbial growth rather than total physiological respiratory responses to warming. Increased precipitation did stimulate both microbial biomass and mass-specific respiration, both of which make large contributions to respiratory loss of soil carbon. Taken together, these results suggest that, in semi-arid grasslands, soil moisture and related substrate availability may inhibit physiological respiratory responses to warming (where soil moisture was significantly lower), while they are not inhibited under elevated precipitation. Although we found no total physiological response to warming, warming increased bacterial C utilization (measured by BIOLOG EcoPlates) and increased bacterial oxidation of carbohydrates and phenols. Non-metric multidimensional scaling analysis as well as ANOVA testing showed that warming or increased precipitation did not change microbial community structure, which could suggest that microbial communities in semi-arid grasslands are already adapted to fluctuating climatic conditions. In summary, our results support the idea that microbial responses to climate change are multifaceted and, even with no large shifts in community structure, microbial mediation of soil carbon loss could still occur under future climate scenarios

Fire affects the taxonomic and functional composition of soil microbial communities, with cascading effects on grassland ecosystem functioning

Fire is a crucial event regulating the structure and functioning of many ecosystems.Yet few studies have focused on how fire affects taxonomic and functional diversi‐ties of soil microbial communities, along with changes in plant communities and soil carbon (C) and nitrogen (N) dynamics. Here, we analyze these effects in a grasslandecosystem 9 months after an experimental fire at the Jasper Ridge Global ChangeExperiment site in California, USA. Fire altered soil microbial communities con ‐siderably, with community assembly process analysis showing that environmentalselection pressure was higher in burned sites. However, a small subset of highly connected taxa was able to withstand the disturbance. In addition, fire decreasedthe relative abundances of most functional genes associated with C degradationand N cycling, implicating a slowdown of microbial processes linked to soil C and N dynamics. In contrast, fire stimulated above‐ and belowground plant growth, likely enhancing plant–microbe competition for soil inorganic N, which was reduced by a factor of about 2. To synthesize those findings, we performed structural equationmodeling, which showed that plants but not microbial communities were responsi‐ble for significantly higher soil respiration rates in burned sites. Together, our resultsdemonstrate that fire ‘reboots’ the grassland ecosystem by differentially regulating plant and soil microbial communities, leading to significant changes in soil C and N dynamics